HK1227966B - Compression-release engine brake system for lost motion rocker arm assembly and method of operation thereof - Google Patents

Description

Compression-release engine braking system for a lost motion rocker arm assembly and method of operating the same

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to Provisional Application No. 61/908,272 filed November 25, 2013 by V. Meneely and R. Price and Provisional Application No. 62/001,392 filed May 21, 2014 by V. Meneely and R. Price, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates generally to compression-release engine braking systems and, more particularly, to a compression-release engine braking system and method including a freewheeling engine brake rocker arm assembly that incorporates structure for implementing a valve reset function.

Background Art

The compression release engine braking system (or retarder) for diesel engines was designed and developed in North America in the early 1960s. Many variations have been made which have improved retarding performance, reduced cost, reduced engine loads, and reduced engine valve train loads.

Conventionally, an engine brake compression-release retarder transforms a power-producing diesel generator into an energy-absorbing air compressor. The air in the cylinder is compressed during the compression stroke and released near top dead center (TDC) just before the expansion stroke to reduce cylinder pressure and prevent it from pushing the piston downward during the expansion stroke. In a so-called exhaust brake system, work is performed on the air during the exhaust stroke, when the piston moves upward and pressure in the exhaust manifold increases due to turbocharger restriction or exhaust restriction.

Opening the exhaust valve near TDC to vent cylinder pressure can be accomplished in many different ways. Some of the most common methods are additional housings that hydraulically transfer intake or exhaust cam motion from an adjacent cylinder, or fuel injector motion from the same cylinder, to provide a method of timing the exhaust valve to open near TDC on the compression stroke, thereby optimizing the release of compressed air in the cylinder.

Other engine braking systems have rocker brakes that use an exhaust rocker arm (or lever) to open the exhaust valve near TDC compression stroke. The term used to identify this type of rocker brake is the lost motion concept. This concept adds an additional low-lift profile to the exhaust cam lobe, which opens the exhaust valve near TDC compression stroke while removing excess exhaust valve lash from the valve train.

Rocker arm brake systems utilizing the lost motion principle have been known for many years. A problem with conventional rocker arm brake systems is the increased exhaust/intake valve overlap, which reduces braking performance. Furthermore, opening a single valve increases the exhaust/intake overlap, and opening the exhaust crossbar during the initial normal exhaust lift is unbalanced and can cause damage to the engine's top. The increased overlap allows exhaust gas to flow from the exhaust manifold back into the engine through the inlet valves and into the inlet manifold. In other words, the increased valve overlap causes undesirable exhaust manifold air mass flow into the engine's intake system, thereby reducing exhaust stroke work and reducing braking performance.

We disclose a system that opens the exhaust valves as late as possible, opens them as wide as possible, and empties the cylinders quickly to provide high-performance engine braking. Many engine parameters can limit optimal valve opening. These limitations include valvetrain loads, engine design limitations, emissions regulations, and other considerations.

Summary of the Invention

According to a first aspect of the present invention, a compression-release braking system is configured to operate at least one exhaust valve of an internal combustion engine. The compression-release braking system of the present invention operates in a brake-on mode during compression-release engine braking operation and in a brake-off mode during positive power operation. When performing compression-release engine braking operation, the compression-release braking system maintains the at least one exhaust valve open during a portion of the engine's compression stroke. The compression-release braking system includes an exhaust rocker assembly for operating the at least one exhaust valve. The exhaust rocker assembly includes an exhaust rocker arm mounted about a rocker shaft and selectively pivotable to open the at least one exhaust valve. The compression-release braking system also includes an actuating piston movable between a retracted position and an extended position and slidably positioned within an actuating piston bore formed in the exhaust rocker arm. The actuating piston is operatively coupled to the at least one exhaust valve when in its extended position. The actuating piston defines an actuating piston chamber within the actuating piston bore between the actuating piston bore and the actuating piston. The compression-release braking system also includes a supply conduit formed within the exhaust rocker arm. The supply conduit is configured to supply pressurized hydraulic fluid to the actuating piston chamber when a spacing exists between the actuating piston and the at least one exhaust valve to displace the actuating piston to the extended position. The compression-release brake system also includes an exhaust valve reset device mounted to the exhaust rocker arm. The exhaust valve reset device includes a reset check valve located between the supply conduit and the actuating piston chamber, thereby hydraulically locking the actuating piston chamber by closing the reset check valve when the pressure of the hydraulic fluid in the actuating piston chamber exceeds the pressure of the hydraulic fluid in the supply conduit. The reset check valve is biased open by the pressure of the hydraulic fluid in the actuating piston chamber during a brake-on mode.

According to a second aspect of the present invention, a method for operating a compression-release brake system in a brake-on mode is provided for operating at least one exhaust valve of an internal combustion engine during a compression-release engine braking operation. The compression-release brake system maintains the at least one exhaust valve open during a compression stroke of the engine while the compression-release engine braking operation is being performed. The compression-release brake system includes an exhaust rocker assembly for operating the at least one exhaust valve. The exhaust rocker assembly includes an exhaust rocker arm mounted about a rocker shaft and selectively pivotable to open the at least one exhaust valve. The compression-release brake system also includes an actuating piston movable between a retracted position and an extended position and slidably positioned within an actuating piston bore formed in the exhaust rocker arm. The actuating piston is operatively coupled to the at least one exhaust valve when in its extended position. The actuating piston defines an actuating piston chamber within the actuating piston bore between the actuating piston bore and the actuating piston. The compression-release brake system also includes a supply conduit formed within the exhaust rocker arm. The supply conduit is configured to supply pressurized hydraulic fluid to the actuating piston chamber when a gap exists between the actuating piston and the at least one exhaust valve to displace the actuating piston to the extended position. The compression-release brake system also includes an exhaust valve reset device mounted to the exhaust rocker arm. The exhaust valve reset device includes a reset check valve located between the supply conduit and the actuating piston chamber, thereby hydraulically locking the actuating piston chamber by closing the reset check valve when the pressure of the hydraulic fluid in the actuating piston chamber exceeds the pressure of the hydraulic fluid in the supply conduit. The reset check valve is biased by the pressure of the hydraulic fluid in the actuating piston chamber during a brake-on mode. The reset check valve is biased closed by the pressure of the hydraulic fluid in the actuating piston chamber during a portion of the brake-on mode.

The method includes the steps of mechanically biasing the reset check valve closed during a first portion of the valve brake lift of the at least one exhaust valve during a compression stroke of the internal combustion engine; hydraulically biasing the reset check valve closed during a second portion of the valve brake lift of the at least one exhaust valve during a compression stroke; and resetting the at least one exhaust valve during an expansion stroke of the engine by opening the reset check valve and releasing hydraulic fluid from the actuating piston chamber to close the at least one exhaust valve.

The compression release braking system of the present invention is low cost and can be integrated into the overall engine design. In addition, the present invention provides a compression release braking system that is lightweight, does not mechanically and thermally overload the engine system, has quiet operation, and produces optimal retarding power over the entire engine speed range in which engine braking is used.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part of the specification. Together with the general description given above and the detailed description of exemplary embodiments and methods given below, they serve to explain the principles of the invention. In the drawings:

1 is a perspective view of a valve system assembly including a rocker arm compression-release engine braking system according to a first exemplary embodiment of the present invention;

2 is a partial perspective view of an exhaust camshaft and an exhaust rocker arm assembly according to a first exemplary embodiment of the present invention;

3 is a perspective view of an exhaust rocker arm according to a first exemplary embodiment of the present invention, wherein some parts are shown with dotted lines;

4 is a partial perspective view of a rocker arm compression-release engine brake system according to a first exemplary embodiment of the present invention; wherein some parts are shown with dotted lines;

5A is a partial cross-sectional view of a rocker arm compression-release engine braking system in a brake-on mode according to a first exemplary embodiment of the present invention;

5B is a partial cross-sectional view of a rocker arm compression-release engine braking system in a brake-off mode according to a first exemplary embodiment of the present invention;

5C is a partial cross-sectional view of a rocker arm compression-release engine braking system in a brake-off mode according to an alternative exemplary embodiment of the present invention;

FIG5D is an enlarged partial cross-sectional view of the reset device of the rocker arm compression-release engine braking system of FIG5C;

6A is a perspective view of an exhaust valve beam according to a first exemplary embodiment of the present invention;

6B is a cross-sectional view of a single valve actuating pin according to a first exemplary embodiment of the present invention;

7 is a perspective view of an actuating piston according to a first exemplary embodiment of the present invention;

8 is a perspective view of a sleeve body according to a first exemplary embodiment of the present invention;

9A is a cross-sectional view of the exhaust valve resetting device in a brake opening mode according to the first exemplary embodiment of the present invention;

9B is a cross-sectional view of the exhaust valve resetting device in the brake closing mode according to the first exemplary embodiment of the present invention;

10 is a perspective view of a valve system assembly including a rocker arm compression-release engine braking system according to an alternative to the first exemplary embodiment of the present invention;

FIG. 11A illustrates pressurized hydraulic fluid supplied to a rocker arm compression-release engine braking system according to an exemplary embodiment of the present invention, with some portions shown by dashed lines;

11B is an alternative view of pressurized hydraulic fluid supplied to a rocker arm compression-release engine braking system according to an exemplary embodiment of the present invention, with portions shown by dashed lines;

FIG11C is a perspective view of a rocker arm base supporting a rocker shaft;

FIG11D is a schematic diagram of a brake-open supply channel;

12 is a graph of intake and exhaust valve lift versus crank angle under positive power operation and during engine braking operation of a rocker arm compression-release engine braking system according to an exemplary embodiment of the present invention;

13 is a perspective view of a valve system including a rocker arm compression-release engine braking system according to a second exemplary embodiment of the present invention;

14 is a cross-sectional view of a rocker arm compression-release engine braking system in a brake-on mode according to a second exemplary embodiment of the present invention;

15A is an alternative perspective view of a valve system including a rocker arm compression-release engine braking system according to a second exemplary embodiment of the present invention;

FIG15B is a cross-sectional view of the rocker arm compression-release engine braking system of FIG15A in a brake-off mode;

16 is a cross-sectional view of a valve system assembly including a rocker arm compression-release engine braking system in a brake-off mode according to a third exemplary embodiment of the present invention;

17A is a cross-sectional view of a rocker arm compression-release engine braking system in a brake-off mode according to a third exemplary embodiment of the present invention;

17B is a cross-sectional view of a rocker arm compression-release engine braking system in a brake-on mode according to a third exemplary embodiment of the present invention;

18A is a cross-sectional view of an exhaust valve resetting device in a brake closing mode according to a third exemplary embodiment of the present invention;

18B is a cross-sectional view of the exhaust valve resetting device in a brake opening mode according to the third exemplary embodiment of the present invention;

19 is a cross-sectional view of a valve system assembly including a rocker arm compression-release engine braking system in a brake-on mode according to a fourth exemplary embodiment of the present invention; and

20 is an enlarged front view of a portion of the compression-release engine braking system shown in cycle 20 of FIG. 19 .

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments and methods of the present invention as illustrated in the accompanying drawings, wherein like reference numerals designate like or corresponding parts throughout the several views. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods.

This description of the exemplary embodiments is not intended to be read in conjunction with the accompanying drawings, which are considered a part of the entire written specification. In the description, relative terms, such as "horizontal", "vertical", "front", "rear", "up", "down", "top", "bottom" and their derivatives (e.g., "horizontally", "downward", "upward", etc.) should be interpreted as referring to the orientations described later or shown in the drawings under discussion and relative to the vehicle body. These relative terms are given for convenience of description and are not generally intended to require a specific orientation. Terms referring to attachment, coupling, etc., such as "connect" and "interconnect", refer to relationships in which structures are fixed or attached to each other directly or indirectly through intermediate structures and movable or rigid attachments or relationships, unless otherwise expressly described. The term "operatively connected" is such an attachment, coupling or connection that permits the related structures to operate as intended by the relationship. In addition, "one" as used in the claims means "at least one".

In summary, the embodiments disclosed herein utilize a reset mechanism carried by or integrated into the engine rocker arm that actuates one of the two exhaust valves. The exhaust valve reset device prevents opening of an unbalanced exhaust valve beam and additionally minimizes exhaust/intake valve overlap near the start of the intake stroke. Actuating one of the two exhaust valves reduces valvetrain load and provides the ability to delay exhaust valve opening, thereby increasing loading for better braking performance. Reduced valve overlap increases exhaust manifold backpressure by reducing the exhaust manifold air mass flowing back into the intake manifold. Increased exhaust stroke pressure causes the engine brake to generate additional engine work during the exhaust stroke. Increased valve overlap causes undesirable exhaust manifold air mass to flow into the engine intake system, thereby reducing exhaust stroke work and degrading braking performance.

During braking, the reset check valve in the reset mechanism is hydraulically locked due to the increased cylinder pressure during the compression stroke. As cylinder pressure drops after top dead center in the compression stroke, the hydraulic pressure applied to the reset check valve begins to decrease accordingly. Eventually, the hydraulic pressure drops enough that the biasing force on the reset check valve overcomes the hydraulic pressure, and the reset check valve opens, allowing engine oil to flow, thereby resetting the exhaust valves and allowing both exhaust valves to move during the exhaust cycle.

Figures 1-12 illustrate a first exemplary embodiment of a valvetrain assembly for an internal combustion engine, generally designated by reference numeral 10. Valvetrain assembly 10 includes a rocker arm compression-release engine braking system 12 for an internal combustion (IC) engine according to a first exemplary embodiment of the present invention. Preferably, the IC engine is a four-stroke diesel engine comprising a cylinder block having a plurality of cylinders. However, for simplicity, Figure 1 illustrates valvetrain assembly 10 for only one cylinder. Each cylinder is provided with a piston that reciprocates therein. Each cylinder is also provided with at least one intake valve and at least one exhaust valve, each valve being provided with a return spring and a valve system for lifting and closing the intake and exhaust valves. The IC engine is capable of performing both positive power operation (normal engine cycle) and engine braking operation (engine compression-release braking cycle). Compression-release braking system 12 operates in a compression-braking mode, or brake-on mode, during engine compression-braking operation, and a compression-braking deactivated mode, or brake-off mode, during positive power operation. A switch in the vehicle cabin is typically used to switch between the various modes and control fuel flow to the cylinders depending on the mode.

The rocker arm compression-release engine braking system 12 according to an exemplary embodiment of the present invention is a freewheeling engine braking system, as best shown in FIG2 , which includes an exhaust cam 2 having a normal (conventional) engine exhaust cam profile 6, an engine brake lift profile 7 for compression-release engine braking events during engine braking operation, and a preload lift profile 8. For ease of explanation, the cam lift profiles 7 and 8 are stylized. The normal engine power mode (i.e., a normal engine cycle) includes sufficient clearance in the exhaust valve system to eliminate the additional cam lift profiles 7 and 8 during normal positive power engine operation.

A rocker arm compression-release engine brake system 12 according to a first exemplary embodiment of the present invention includes a conventional intake rocker assembly (not shown) for operating two intake valves 1 and a lost motion exhaust rocker assembly 16 for operating the exhaust valves. The exhaust rocker assembly 16 according to the first exemplary embodiment of the present invention is a lost motion assembly provided with automatic hydraulic adjustment and reset functionality. The exhaust rocker assembly 16 includes an exhaust rocker arm 22 pivotally mounted about a rocker shaft 20 and configured to open the first and second exhaust valves ₃₁ and ₃₂ , respectively, via an exhaust valve crossbar 24. The rocker shaft 20 is supported by a rocker arm support member (or rocker arm base) 25 and extends through a rocker arm eyelet 33 formed in the exhaust rocker arm 22 (as best shown in Figures 1, 3, and 5B). The rocker arm base 25, in turn, is mounted to a base support member 27.

As best shown in FIG3 , the exhaust rocker arm 22 has two ends: a driving (first distal) end 22 a that controls the engine exhaust valves ₃₁ and ₃₂ , and a driven (second distal) end 22 b that is adapted to contact the exhaust cam 2, which is mounted to the rotating exhaust camshaft 4 (best shown in FIG2 ). The exhaust cam 2 is provided with an exhaust lift profile 6, an engine brake lift profile 7, and a preload lift profile 8.

The driven end 22b of the exhaust rocker arm 22 includes an exhaust cam lobe follower 21, as best shown in FIG2. The exhaust cam lobe follower 21 is adapted to contact the exhaust lift profile 6, the engine brake lift profile 7, and the preload lift profile 8 of the exhaust cam 2.

In addition, the exhaust rocker arm 22 also includes a rocker arm adjusting screw assembly 68 (best shown in Figures 1, 3, and 4) that is adjustably mounted (such as via threads) in a generally cylindrical threaded screw bore 23a in the driving end 22a of the exhaust rocker arm 22. As best shown in Figures 1, 3, and 4, the rocker arm adjusting screw 68 is used to engage the exhaust valve crossbar 24 to open the exhaust valves ₃₁ and _32. The rocker arm adjusting screw 68 includes an adjusting screw 70 that is adjustably mounted (such as via threads) in the generally cylindrical threaded screw bore 23a in the driving end 22a of the exhaust rocker arm 22, and a contact (so-called "elephant") foot 72 that is rotatably mounted on one end of the adjusting screw 70 adjacent the exhaust valve crossbar 24.

Adjusting screw 70 is provided with a hexagonal socket 71 accessible from above exhaust rocker arm 22. This socket is used to set a predetermined valve lash (or clearance) δ between contact foot 72 of adjusting screw 68 and exhaust valve crossbar 24 when exhaust rocker roller follower 21 contacts lower base circle 5 on exhaust cam 2, i.e., when exhaust cam 2 is not acting on (pressing) exhaust rocker arm 22. The predetermined valve lash δ is set to provide normal exhaust valve motion during positive power operation, and the clearance is used to increase the valvetrain components at engine operating temperatures. During engine braking operation, all lash (except the predetermined lash δ) is removed from the valvetrain, and the brake cam profile determines the timing of opening, profile, and lift of the exhaust valve.

The idle engine brake rocker arm assembly 16 is part of a rocker arm compression-release engine brake system 12 for an internal combustion (IC) engine. Pressurized hydraulic fluid, such as engine oil, is supplied to the exhaust rocker arm 22 under high pressure through a high-pressure hydraulic circuit, as best shown in Figures 1-3, to remove valve system lash (except for a predetermined valve lash δ). As best shown in Figure 4, the high-pressure hydraulic circuit includes a continuous supply line (or passage) 26, a high-pressure line 28, and a brake release supply line 30. The brake release supply line 30 is controlled by a solenoid valve (not shown), which is selectively operated to supply pressurized hydraulic fluid to the brake release line 30.

The exhaust rocker arm 22 also includes a generally cylindrical actuation piston bore 64 (best shown in Figures 3 and 4) formed in the drive end 22a of the exhaust rocker arm 22 for receiving the actuation piston 62 (best shown in Figures 5A and 5B) therein. The actuation piston 62 is movable between retracted and extended positions relative to the actuation piston bore 64 and is adapted to contact a top end surface 76a of a single valve actuation pin 76 (best shown in Figures 5A, 5B, and 6B). The single valve actuation pin 76 is slidably movable relative to the exhaust valve crossbar 24 through an opening 25 (best shown in Figure 6A) in the exhaust valve crossbar 24.

The actuating piston 62 defines an actuating (or resetting) piston chamber 65 (best shown in Figures 5A and 5B) within the actuating piston bore 64 in the exhaust rocker arm 22. The actuating piston 62, shown in detail in Figure 7, includes a hemispherical bottom surface 63a for engaging the single-valve actuating pin 76 and a rearward extension 63b for contacting the closed end of the actuating piston bore 64, thereby limiting rearward movement of the actuating piston 62 within the actuating piston bore 64 and preventing the actuating piston 62 from covering the hole in the actuating piston bore 64 that fluidly connects the actuating piston chamber 65 with the high-pressure line 28. In the extended position, the rearward extension 63b of the actuating piston 62 is separated from the closed end of the actuating piston bore 64 by a piston clearance _k1 (shown in Figures 5C and 14), such as 0.15".

Furthermore, the hemispherical bottom surface 63a of the actuating piston 62 of the exhaust rocker arm 22 (which faces the exhaust valve crossbar 24) is adapted to contact the top end surface 76a of the single-valve actuating pin 76. A bottom end surface 76b of the single-valve actuating pin 76, axially opposite the first surface 76a thereof, engages the proximal end of the first exhaust valve _31. The exhaust single-valve actuating pin 76 allows the actuating piston 62 to press against the first exhaust valve ₃₁ during compression-release engine braking operation (i.e., in the brake-on mode) to open the first exhaust valve ₃₁ (opening only one of the two exhaust valves 3). In other words, the single-valve actuating pin 76 is reciprocable relative to the exhaust valve crossbar 24, thereby enabling the first exhaust valve ₃₁ to move relative to the second exhaust valve ₃₂ and the exhaust valve crossbar 24. Thus, during a compression-release engine braking event of an engine compression braking operation, the beam surface 76c of the single valve actuation pin 76 (best shown in FIG. 6B ) is separated from the exhaust valve beam 24 by an actuation pin gap k ₂ (best shown in FIG. 5C and 14 ), such as 0.05″.

The rocker arm compression-release brake system 12 also includes an exhaust valve reset device 32 located in the exhaust rocker arm 22. The reset device 32, according to a first exemplary embodiment of the present invention (shown in detail in Figures 8-9B ), is in the form of a generally cylindrical hollow sleeve and includes a generally cylindrical sleeve body 34 having an annular supply groove 36 fluidly connected to the continuous supply line 26, an annular brake groove 38 fluidly connected to the brake-release supply line 30, and an annular piston groove 40 fluidly connected to the high-pressure line 28. As best shown in Figures 1, 4, 5A, and 5B, the cylindrical sleeve body 34 of the reset device 32 is located outboard of the adjusting screw assembly 68 at the driven (second distal) end 22b of the exhaust rocker arm 22. Alternatively, as shown in Figure 10 , the sleeve of the reset device 32 is located inboard of the adjusting screw assembly 68. The exhaust valve crossbar ₂₄₁ has a crossbar extension ₂₄₁₂ for trigger contact. 10 , when the reset trigger 50 is in the extended position, the elongated distal end 52 of the reset trigger 50 contacts the crossbar extension 24 ₁₂ of the exhaust valve crossbar 24 _1. Thus, the sleeve of the reset device 32 can be located inside and outside the rocker shaft or parallel to the rocker shaft and have a fixed cam profile relative to the rocker support.

Each of the supply groove 36, brake activation groove 38, and piston groove 40 is formed on the outer cylindrical surface of the sleeve body 34 and is axially spaced apart from one another. Furthermore, the supply groove 36 is provided with at least one continuous supply port 37 extending through the sleeve body 34, the brake activation groove 38 is provided with at least one brake activation supply port 39 extending through the sleeve body 34, and the piston groove 40 is provided with at least one piston supply port 41 extending through the sleeve body 34. The cylindrical sleeve body 34 is immovably positioned within the generally cylindrical reset bore 23b in the exhaust rocker arm 22. Thus, the high-pressure conduit 28 fluidly connects the actuating piston bore 64 with the piston groove 40 of the sleeve body 34 of the reset device 32. The internal cavity 42 within the cylindrical sleeve body 34 is enclosed between the upper and lower sleeve plugs 35a, 35b. In other words, the annular grooves 36, 38, and 40 are fluidically connected to the internal cavity 42 of the sleeve body 34 via one or more ports (or bores) 37, 39, and 41. As best shown in Figures 4-5B, the sleeve body 34 is axially spaced apart from the exhaust valve crossbar 24.

As best shown in Figures 9A and 9B, the reset device 32 also includes a ball valve member 44 and a ball check valve spring 46 positioned between the ball valve member 44 and the upper sleeve plug 35a. The ball valve member 44 is biased against the ball check valve seat 45 by the biasing spring force of the ball check valve spring 46, thereby closing a communication port 48 in the sleeve body 34 that fluidly connects the continuous supply port 37 of the sleeve body 34 with the piston supply port 41. The ball valve member 44, the ball check valve seat 45, and the ball check valve spring 46 define a reset check valve 43, which is normally biased closed by the ball check valve spring 46. The reset check valve 43 is positioned between the continuous supply line 26 and the actuating piston chamber 65 and provides selective fluid communication between the continuous supply line 26 and the high-pressure line 28. It should be understood that any suitable type of check valve is within the scope of the present invention.

The exhaust valve reset device 32 also includes a reset trigger 50 axially slidable within the sleeve body 34. The reset trigger 50 has an elongated distal end 52 that extends at least partially from the sleeve body 34 through an aperture 35c in the lower sleeve plug 35b. The reset trigger 50 is movable relative to the sleeve body 34 between an extended position, shown in Figures 5A and 9A, and a retracted position, shown in Figures 5B and 9B. The reset trigger 50 is normally biased to the retracted position by a trigger return spring 56 positioned between the proximal end of the reset trigger 50 (axially opposite the distal end 52) and the lower sleeve plug 35b. Furthermore, the reset trigger 50 is configured to raise an upset pin 58, which, under the resilient bias of the trigger return spring 56, contacts, lifts, and supports the ball valve member 44 away from the spherical check valve seat 45 during all non-engine braking operations. The upper end of the expansion pin 58 is positioned adjacent to the ball valve member 44, while the lower end of the expansion pin 58 engages the reset trigger 50 via a spring retainer 55 and a reset pressure spring 57 located within the reset trigger 50 between its distal end 52 and the spring retainer 55. Specifically, when the reset trigger 50 is in its retracted position (best shown in FIG. 5A ), the expansion pin 58 lifts and supports the ball valve member 44, causing it to open (i.e., away from the ball check valve seat 45). On the other hand, in the extended position of the reset trigger 50 (shown in FIG. 5B ), the ball valve member 44 returns to the closed position and is supported against the ball check valve seat 45 by the biasing force of the ball check valve spring 46, thereby closing the communication port 48 in the sleeve body 34 and thereby disconnecting the fluid connection between the continuous supply port 37 of the sleeve body 34 and the piston supply port 41. As further shown in FIG. 5A , when the reset trigger 50 is in its extended position, the elongated distal end 52 of the reset trigger 50 contacts the exhaust valve crossbar 24. Furthermore, when the reset trigger 50 is in the extended position, the reset trigger 50 engages the lower sleeve plug 35b, which limits outward axial movement of the reset trigger 50 in a direction toward the exhaust valve crossbar 24. However, when the reset trigger 50 is in its retracted position, the elongated distal end 52 of the reset trigger 50 is axially spaced apart from the exhaust valve crossbar 24, as best shown in FIG5B .

The trigger return spring 56 biases the reset trigger 50 upward against the counterbored stop 35d in the sleeve body 34. The compression spring 57, which is used only in the engine brake on mode, has a greater spring force than the conical ball check valve spring 46, enabling the expansion pin 58 to retain the ball check valve 44 off the ball check valve seat 45, thereby allowing oil from the continuous supply line 26 to flow unrestricted into and out of the actuating piston chamber 65 to eliminate actuating piston clearance during positive power engine operation, thereby eliminating valve train noise.

As best shown in Figures 9A and 9B , the expansion pin 58 extends through a guide pin sleeve 60 that supports and guides the reciprocating linear motion of the expansion pin 58. As further shown in Figures 9A and 9B , the inner cavity 42 of the sleeve body 34 is divided by the guide pin sleeve 60 into a check valve chamber 42 ₁ and a reset chamber 42 ₂ . According to the first exemplary embodiment of the present invention, the reset chamber 42 ₂ is in fluid communication with the brake release oil supply line 30 via the brake release groove 38 and the brake release supply port 39. In turn, the reset check valve 43 selectively provides fluid communication between the continuous supply line 26 and the high-pressure line 28 (i.e., between the continuous supply line 26 and the actuating piston chamber 65).

FIG5C illustrates an alternative embodiment of a rocker arm compression-release engine brake system _122. The rocker arm compression-release engine brake system ₁₂₂ is generally similar in structure and function to the compression-release engine brake system 12 according to the first exemplary embodiment, with the exception of the reset device _322. The alternative reset device ₃₂₂ is generally similar in structure to the reset device 32 according to the first exemplary embodiment. The difference between the two reset devices is that, unlike the reset device 32 according to the first exemplary embodiment, the alternative reset device ₃₂₂ does not include the cylindrical sleeve body 34 of the reset device 32 positioned within the cylindrical reset aperture 23b in the exhaust rocker arm 22. Instead, the reset device ₃₂₂ is machined directly into the rocker arm ₂₂₂ , as shown in FIG5C. In other words, the cylindrical reset aperture 23b in the exhaust rocker arm ₂₂₂ is machined to mimic the sleeve body 34 of the reset device 32. The alternative reset device ₃₂₂ is generally similar in operation to the reset device 32 according to the first exemplary embodiment.

As shown in FIG5D , the reset trigger 50 of the reset device ₃₂₂ has an annular inner stop portion 50a facing the cup-shaped spring retainer _552. In turn, the spring retainer ₅₅₂ has an annular stop portion 5521 facing the inner stop portion 50a of the reset trigger _50. The stop portion 50a of the reset trigger 50 and the stop portion ₅₅₂₁ of the spring retainer 552 define a reset failsafe mechanism that is used to prevent failure of the pressure spring 57 within the reset trigger ₅₀ , which would result in the single engine-stop exhaust valve ₃₁ not being reset prior to normal exhaust movement, leading to an unbalanced exhaust valve beam and possible engine damage.

Specifically, the stop portion ₅₅₂₁ of the spring retainer ₅₅₂ defines a mechanical stop that is activated by an additional upward stroke of the reset trigger 50 exceeding its normal maximum stroke. This additional stroke of the reset trigger 50 would occur if the compression spring 57 fails and does not force the ball check valve 44 off its valve seat 45, and the individual engine brake exhaust valve ₃₁ is not reset before the normal exhaust valve is lifted by the balancing beam. The additional stroke of the elephant foot ₇₂₂ pressing against the center of the exhaust valve beam ₂₄₂ causes a small imbalance in the exhaust valve beam ₂₄₂ until the additional trigger stroke caused by the rocker rotation during normal exhaust valve movement forces the stop portion ₅₅₂₁ of the spring retainer ₅₅₂ to contact the internal stop portion 50a of the reset trigger 50. Then, during the beginning of the exhaust valve stroke, the reset trigger 50 mechanically forces the ball check valve 44 off the valve seat 45 of the reset check valve 43 via the expansion pin 58. This mechanical forcing of the ball check valve 44 off its seat 45 during the beginning of the normal exhaust lift profile continues until the engine brake is operated.

The rocker shaft 20 according to an exemplary embodiment of the present invention, shown in Figures 11A and 11B, includes a generally cylindrical accumulator bore 20a and a rocker shaft accumulator 77 therein. The rocker shaft accumulator 77 includes a generally cylindrical accumulator piston 78 slidably movable within the accumulator bore 20a, an accumulator ball check valve 92, and an accumulator chamber 94 defined between the accumulator piston 78 and the accumulator ball check valve 92. The accumulator piston 78 is spring-loaded by an accumulator spring 79, thereby being biased toward the accumulator ball check valve 92. The accumulator ball check valve 92 is positioned to only allow hydraulic fluid to enter the accumulator chamber 94 and prevent hydraulic fluid from flowing from the accumulator chamber 94 through the accumulator ball check valve 92. In other words, the accumulator ball check valve 92 prevents oil from flowing back into the oil supply. The accumulator ball check valve 92 is biased in its closed position by a ball check valve spring.The rocker shaft accumulator 77 stores the returning hydraulic fluid under pressure to subsequently refill the actuating piston chamber 65 during the next engine exhaust cam motion.

As further shown in Figures 11A-11D, pressurized hydraulic fluid is supplied through a hydraulic fluid supply passage 93 formed in one or more rocker arm supports 25 (preferably, in a hold-down bolt of the rocker arm support 25). The hydraulic fluid supply passage 93 is fluidically connected to the accumulator eyelet 20a. The rocker shaft 20 also includes a connection passage 97 that is fluidically connected to the accumulator chamber 94 via a connection port 96. The connection passage 97 is provided with at least one supply port 95 that is fluidically connected to the continuous supply conduit 26 in the exhaust rocker arm 22.

In operation, pressurized hydraulic fluid is supplied to the accumulator chamber 94 through the supply passage 93 and the accumulator ball check valve 92. The pressurized hydraulic fluid then flows from the accumulator chamber 94 to the continuous supply conduit 26 of the exhaust rocker arm 22 through the connecting port 96, the connecting passage 97, and the supply port 95. During an engine brake reset operation, the pressurized hydraulic fluid is dumped back into the rocker shaft accumulator chamber 94. The accumulator ball check valve 92 prevents the hydraulic fluid from flowing back into the hydraulic fluid supply passage 93.

The rocker arm compression-release brake system 12 also includes an on-off solenoid valve 98, shown in Figures 11B and 11D , that selectively provides pressurized hydraulic fluid to the brake-release supply line 30 of the rocker arm compression-release brake system 12. As best shown in Figures 11B and 11C , brake-release pressurized hydraulic fluid is selectively supplied to the brake-release supply line 30 by operating the on-off solenoid valve 98, which is mounted on one of the rocker arm bases 25, and a brake-release supply oil passage 99 formed in the exhaust rocker arm 22 and fluidly connected to the brake-release supply line 30. As further shown in Figure 11D , pressurized hydraulic fluid, such as engine oil, is supplied from the tank 80 to the on-off solenoid valve 98 via the fluid pump 83 through the brake-release supply passage 82a and is returned (or dumped) back into the tank 80 through the brake-close dump passage 82b.

The engine's positive power operation is as follows. During positive power operation, when the engine brake is not activated, the hydraulic fluid continuous supply line 26 provides a continuous flow of hydraulic fluid, such as engine oil, to the check valve chamber ₄₂₁ via the continuous supply groove 36 and the continuous supply port 37. Furthermore, during positive power operation, the reset trigger 50 is in a retracted position due to the biasing force of the trigger return spring 56. In this position, the ball valve member 44 is lifted off the ball check valve seat 45 by the reset trigger 50 (to the open position of the reset check valve 43). Specifically, the reset trigger 50 is lifted by the resilient biasing action of the trigger return spring 56 and the expansion pin 58. During all non-engine braking operations, the expansion pin 58 contacts, lifts, and supports the ball valve member 44 off the ball check valve seat 45. When the reset check valve 43 is open, pressurized hydraulic fluid flows from the check valve chamber ₄₂₁ through the piston supply port 41, through the check valve 43, and into the high-pressure line 28. The pressurized hydraulic fluid then flows into the actuator piston bore 64 through the high-pressure line 28. The pressurized hydraulic fluid fills the actuator piston chamber 65, thereby eliminating valve system clearances (except for the predetermined valve clearance δ), such as the actuator piston clearance, i.e., the clearance between the actuator piston 62 and the single-valve actuator pin 76. The increase in the volume of the hydraulic fluid in the actuator piston chamber 65 also allows the exhaust rocker roller follower 21 to maintain contact with the exhaust camshaft brake lift profile 7 and, together with the additional displacement of the actuator piston 62, eliminates the brake lift and provides a normal exhaust valve profile for the exhaust stroke, labeled as exhaust valve lift profile 85 in FIG. 12 , i.e., brake-closed valve lift.

In engine brake off mode, with valve system lash eliminated (except for the predetermined valve lash δ), the exhaust rocker arm 22 then advances from the lower base circle 5 on the exhaust cam 2 to the engine brake lift profile 7. When the engine brake lift profile 7 acts on the driven end 22b of the exhaust rocker arm 22 and pivotally rotates the exhaust rocker arm 22, the distal end of the actuating piston 62 presses against the single-valve actuating pin 76, which in turn presses only the exhaust valve stem of the exhaust valve _31. Subsequently, the actuating piston 62 is forced upward, thereby reducing the volume of the actuating piston chamber 65 without opening the exhaust valve _31. This causes the pressure in the actuating piston chamber 65, generated by the force of the exhaust valve spring ₉₁ (shown in FIG. 19 ), inertial forces, and cylinder pressure, to increase. This upward travel (movement) of the actuating piston 62 causes hydraulic fluid to be displaced from the actuating piston chamber 65 back to the continuous supply line 26 through the open one-way valve 43. A certain amount of hydraulic fluid below the actuating piston chamber 65 flows back to the accumulator chamber 94 in the rocker shaft 20 through the continuous supply line 26. In addition, due to the predetermined valve clearance δ, the adjusting screw 68 is not pressed onto the exhaust valve bridge 24. Therefore, during positive power operation of the engine, the exhaust valves ₃₁ and ₃₂ remain closed throughout the compression stroke.

During the exhaust stroke of positive power operation, when the exhaust cam profile 6 acts on the driven end 22b of the exhaust rocker arm 22 and pivotally rotates the exhaust rocker arm 22, the single-valve actuation pin 76 presses against the actuation piston 62. Subsequently, the actuation piston 62 is forced upward, thereby reducing the volume of the actuation piston chamber 65. This causes the pressure in the actuation piston chamber 65, generated by the force of the exhaust valve spring ₉₁ (shown in FIG. 19 ) of the exhaust valve ₃₁ , inertial forces, and cylinder pressure, to increase. Similarly, this upward travel (movement) of the actuation piston 62 causes hydraulic fluid to be displaced from the actuation piston chamber 65 back to the continuous feed line 26 through the open one-way valve 43. A certain amount of hydraulic fluid below the actuation piston chamber 65 flows back to the accumulator chamber 94 through the continuous feed line 26. Then, when the predetermined valve lash δ is canceled and the rocker arm adjusting screw 68 is pressed against the exhaust valve bridge 24, the exhaust valve bridge 24 presses and opens the exhaust valves ₃₁ and ₃₂ , as shown as an exhaust valve lift profile 85 in FIG12 during a normal engine exhaust stroke. Specifically, when the rocker arm adjusting screw 68 presses the exhaust valve bridge 24, the exhaust valve bridge 24 presses the second exhaust valve ₃₂ , which is directly located on the bridge surface 76c of the single valve actuating pin 76, which in turn presses and opens the first exhaust valve ₃₁ .

When the engine brake is not activated (brake-off mode) and the exhaust cam is on lower base circle 5, the actuator piston 62 extends into the actuator piston bore 64 in the exhaust rocker arm 22 to eliminate all valvetrain lash (except for the predetermined valve lash δ). The engine brake profile 7 of the exhaust cam 2 cannot open the exhaust valve ₃₁ for compression brake release because the reset check valve 43 is held open by the expansion pin 58. Hydraulic fluid flows out of the actuator piston cavity 65 and into the rocker shaft accumulator 77 located in the rocker shaft 20 (as shown in Figures 11A and 11B). This additional hydraulic fluid eliminates all valvetrain lash in the valvetrain assembly. Removing this lash with hydraulic fluid eliminates valvetrain noise and potential valvetrain damage.

In the brake-on mode, solenoid valve 98 is energized, allowing the supply of pressurized hydraulic fluid for brake-on to the brake-on supply line 30. Pressurized hydraulic fluid from the brake-on supply line 30 enters the reset chamber 422 in the sleeve body 34 of the exhaust valve reset device _32. The pressurized hydraulic fluid in the reset chamber ₄₂₂ overcomes the biasing force of the trigger return spring 56 and moves the reset trigger 50 to the extended position. In this position, as best shown in Figures 5A and 9A, the elongated distal end 52 of the reset trigger 50 engages the exhaust valve crossbar 24. Furthermore, in the extended position of the reset trigger 50 (shown in Figures 5A and 9A), the ball valve member 44 returns to the closed position and is seated against the ball check valve seat 45 by the biasing force of the ball check valve spring 46, thereby closing the communication port 48 in the sleeve body 34 and disconnecting the fluid connection between the continuous supply port 37 of the sleeve body 34 and the piston supply port 41. Pressurized hydraulic fluid now fills the actuation piston chamber 65 and removes all exhaust valve system lash by passing through the continuous feed line 26 and the high pressure line 28 and into the check valve chamber ₄₂₁ through the reset check valve 43 by overcoming the biasing force of the ball check valve spring 46 when the hydraulic pressure in the continuous feed line 26 is higher than the hydraulic pressure in the actuation piston chamber 65. However, if the hydraulic pressure in the continuous feed line 26 is lower than the hydraulic pressure in the actuation piston chamber 65, hydraulic fluid is inhibited in the high pressure hydraulic circuit and the engine braking cam profile and the engine braking cycle are activated.

The engine brake operation will be described below.

The rocker shaft 20, which supplies pressurized hydraulic fluid, is designed with two passages 97 and 99 to supply pressurized hydraulic fluid to the continuous supply line 26 and the brake release supply line 30 of the engine brake rocker arm assembly 16, respectively. The brake release supply line 30 is controlled by a solenoid valve 98, which supplies pressurized hydraulic fluid to the brake release line 30, which displaces the reset trigger 50 downward, allowing the reset check valve 43 to be seated (i.e., in the closed position) and acting as a one-way valve to lock the hydraulic fluid in the high-pressure line 28 and the actuation piston chamber 65. The hydraulic pressure within the actuation piston chamber 65 ensures that all lash (except for a predetermined valve lash δ) is removed from the valve system components and that the exhaust rocker roller follower 21 of the exhaust rocker arm 22 remains in contact with the exhaust cam 2.

To initiate the engine brake on mode, solenoid valve 98 is energized, causing oil to flow through brake on supply line 30 to reset chamber 42 ₂ , thereby biasing reset trigger 50 and providing clearance between ball valve member 44 and expansion pin 58, allowing ball check valve spring 46 to bias ball valve member 44 against ball check valve seat 45. Pressurized engine oil is supplied through reset check valve 43 and high pressure line 28 to rocker arm continuous supply port 37 and into actuation piston chamber 65, removing all valvetrain clearance between the single valve actuation pin 76 and actuation piston 62, as well as between cam follower 21 and the lobe of exhaust cam 2.

With all valve system clearances (except for a predetermined valve clearance δ) eliminated and hydraulic fluid locked in the actuating piston chamber 65, the roller follower 21 advances from the lower base circle 5 on the exhaust cam 2 to the engine brake lift profile 7, opening only the exhaust valve ₃₁ via the single-valve actuating pin 76 just before top dead center (TDC) of the compression stroke to exhaust the highly compressed air in the cylinder generated by the compression stroke. When the engine brake lift profile 7 acts on the driven end 22b of the exhaust rocker arm 22 and pivotally rotates the exhaust rocker arm 22, the distal end of the actuating piston 62 presses the single-valve actuating pin 76, which in turn presses only the exhaust valve stem of the first exhaust valve ₃₁ . During a compression-release engine braking event of an engine compression braking operation, when the actuating piston 62 presses the single-valve actuating pin 76 to open the exhaust valve ₃₁ just before TDC of the compression stroke, the fluid pressure in the actuating piston chamber 65 becomes higher than the fluid pressure in the one-way valve chamber ₄₂₁ , thereby forcing the ball valve member 44 of the one-way valve 43 to seat on the spherical one-way valve seat 45, thereby hydraulically locking the engine oil (hydraulic fluid) in the actuating piston chamber 65.

With all valve system lash removed (except for the predetermined valve lash δ) and hydraulically locked, during a compression-release engine braking event, the brake lift profile 7 of the exhaust cam member 2 only opens the exhaust valve ₃₁ just before TDC of the compression stroke, as shown in portion ₈₈₁ of the exhaust valve lift profile 85 in FIG12 . Due to the predetermined valve lash δ, the adjusting screw 68 does not press the exhaust valve bridge 24. Therefore, the second exhaust valve ₃₂ remains closed throughout the compression-release engine braking event of the entire engine compression braking operation.

During opening of the single exhaust valve ₃₁ using the single valve actuator pin 76, cylinder pressure increases and quickly reaches peak cylinder pressure just before TDC compression, and then rapidly decreases just after TDC compression ends. Due to the release of compression near TDC and the downward movement of the engine piston in the cylinder, the cylinder pressure rapidly decreases and the pressure in the actuator piston chamber 65 also decreases rapidly, causing the lower pressure to bias the ball valve member 44 against the ball check valve seat 45.

During a compression-release engine braking event, during the power stroke, the resetting process of the exhaust valve ₃₁ is achieved by causing the elongated distal end 52 of the reset trigger 50 to contact the top surface 24a of the exhaust valve crossbar 24, which acts as a pre-set stop member because the exhaust valve crossbar 24 cannot move relative to the rocker shaft 20 during the compression-release braking operation due to the predetermined valve clearance δ.

With the elongated distal end 52 of the reset trigger 50 contacting the exhaust valve crossbar 24, when the driving end 22a of the exhaust rocker arm 22 rotates downward due to the action of the brake lift profile 7 of the exhaust cam member 2, the exhaust valve crossbar 24 forces the reset trigger 50, which is biased downward by the fluid pressure of the brake opening supply line 30, upward relative to the sleeve body 34 toward the reset check valve 43 (against the biasing force of the pressurized hydraulic fluid in the reset chamber ₄₂₂ ). Consequently, the reset pressure spring 57 is compressed, and the expansion pin 58 contacts the ball valve member 44 in the seated position. The compressed reset pressure spring 57 exerts an upward force on the ball valve member 44, and the hydraulic pressure in the actuating piston chamber 65 biases the ball valve member 44 to the seated position. When the biasing force of the reset pressure spring 57 exceeds the force generated by the pressure drop in the actuating piston chamber 65, the ball valve member 44 is forced to leave its valve seat 45, thereby causing the ball valve member 44 of the one-way valve 43 to leave its seat (i.e., move the ball valve member 44 to the open position) by resisting the biasing force of the spherical one-way valve spring 46 through the expansion pin 58.

In other words, resetting occurs when the reset trigger 50 is forced upward by rotating the exhaust rocker arm 22, which causes the reset pressure spring 57 to be compressed and apply a large force to the ball valve member 44 of the check valve 43, which force initially fails to move the ball off its valve seat 45 until the cylinder pressure and the pressure in the actuating piston chamber 65 decrease to a point where the reset pressure spring 57 will force the ball valve member 44 off its valve seat 45. This occurs at the end of the expansion stroke 89 when cylinder pressure is low.

Opening the one-way valve 43 causes a portion of the hydraulic fluid to be released from the actuation piston chamber 65, i.e., allows the pressurized hydraulic fluid in the actuation piston chamber 65 to return to the continuous supply line 26 in the exhaust rocker arm 22. This causes the actuation piston 62 and the single-valve actuation pin 76 to move upward, thereby allowing the single exhaust valve ₃₁ to be reset and the first exhaust valve ₃₁ to return to its valve seat.

During engine braking operation in an engine without an exhaust valve reset device 32, with all valvetrain lash removed (except for the predetermined valve lash δ), the normal exhaust valve lift profile 14 will increase lift 15 and duration, as shown in FIG12 . The increased exhaust valve lift 15 requires increased piston/valve clearance to eliminate potential exhaust valve and engine piston contact at top dead center (TDC) exhaust/intake without a valve reset device. With valve lash δ removed, the increased exhaust valve lift 15 will increase intake and exhaust valve overlap 17 at TDC, as shown in FIG12 . The extended valve overlap 17 allows high-pressure exhaust gas in the exhaust manifold to flow into the engine cylinders and then into the intake manifold. This can cause inlet noise, damage intake air components, and reduce engine braking deceleration power. For these reasons, an exhaust valve reset device is required for engine brake rocker arm lost motion systems. Portion 87 of the exhaust valve lift profile 14 illustrates the optimal loading event (shown in FIG12 ) caused by the action of the preload lift profile 8 of the exhaust cam member 2. FIG. 12 also shows a normal intake valve lift profile 84 .

During engine braking operation of an engine with the exhaust valve reset device 32 (shown at 88 in FIG. 12 ), the reset trigger 50 is positioned to begin releasing hydraulic oil in the actuation piston chamber 65 back into the high-pressure line 28 and the rocker shaft accumulator 77 at approximately 50% of the compression-release engine braking event (shown at 88 ₂ in FIG. 12 ). Consequently, the first exhaust valve 3 ₁ is closed, thereby resetting the first exhaust valve 3 ₁ to the closed position, as shown by portion 88 ₃ of the exhaust valve brake lift profile 88 in FIG. 12 . This restores the normal positive power exhaust valve lift profile ( 85 in FIG. 12 ), eliminating the extended exhaust valve lift and extended overlap at TDC, as shown at 90 in FIG. Exhaust valves 3 ₁ and 3 ₂ are now opened by the exhaust cam lift 6 and by the rocker arm adjustment screw 68 contacting the exhaust crossbar 24 .

As shown in FIG12 , the exhaust/intake valve overlap 90 at TDC during operation of the compression-release engine braking system 12 with the exhaust valve reset device 32 is significantly less than the intake and exhaust valve overlap 17 during operation of a compression-release engine braking system without the exhaust valve reset device 32 according to the present invention. In other words, due to the release of pressurized hydraulic fluid from the actuation piston chamber 65, the exhaust valves ₃₁ and ₃₂ will return to a normal positive power exhaust valve lift profile 85, eliminating the increased exhaust valve lift ( 15 in FIG12 ) and increased overlap ( 17 in FIG12 ). Therefore, resetting the exhaust valves ₃₁ and ₃₂ to the closed position (i.e., releasing pressurized hydraulic fluid from the actuation piston chamber 65 during a compression-release engine braking event) eliminates the increased intake/exhaust valve overlap, which results in reduced exhaust manifold backpressure and reduced engine braking deceleration power.

Makeup hydraulic fluid for resetting the hydraulic fluid is supplied from the rocker shaft accumulator 77, which, according to an exemplary embodiment of the present invention, is located in the rocker shaft 20. Alternatively, the rocker shaft accumulator 77 may be located in the rocker shaft support. This accumulated hydraulic fluid is stored in the rocker shaft accumulator 77, close by and at a higher pressure, to assist in filling the actuating piston chamber 65 and the high-pressure line 28 for the next preload lift profile 8 or engine brake exhaust lift profile 7. The preload lift profile 8 of the exhaust cam lobe 2 approaches the opening of the first exhaust valve ₃₁ at the end of the intake stroke. This adds a high-pressure air charge and additional charge from the exhaust manifold to the cylinder at the beginning of the exhaust stroke, performing more work on the air during the compression stroke and potentially the exhaust stroke, and, due to the high exhaust manifold backpressure, may result in reduced engine brake exhaust sound levels.

Therefore, the lost motion rocker arm compression release engine braking system according to the first exemplary embodiment of the present invention opens only one of the two exhaust valves during an engine compression release event and resets the exhaust valve prior to normal exhaust stroke valve movement. In the first exemplary embodiment of the present invention, the engine compression release single exhaust valve lift opening is approximately 0.100 inches and lift begins just before reaching TDC of the compression stroke.

Modern diesel generators are typically equipped with an exhaust valve crossbar and two exhaust valves. It is desirable that the reset device according to the present invention closes the single brake exhaust valve before opening both exhaust valves during the normal exhaust stroke, thereby preventing the exhaust valve crossbar from being in an unbalanced condition. An unbalanced condition is when the single valve actuation pin has not yet returned the single brake exhaust valve to its seated position, resulting in unbalanced forces acting on the crossbar during normal exhaust valve opening.

The reset device 32 according to the first exemplary embodiment of the present invention is positioned farther from the center of rotation of the exhaust rocker arm 22 (or rocker arm shaft 20) than the center of the exhaust valve crossbar 24 and the adjusting screw 68 to provide maximum trigger movement, thereby allowing the reset trigger 50 to move upward in the sleeve body 34, which removes the gap between the ball valve member 44 and the expansion pin 58 and provides compression of the reset pressure spring 57. The compression releases the cylinder pressure, causing the reset check valve 43, which has been biased closed by the high-pressure hydraulic circuit pressure. During the beginning of the expansion stroke, the cylinder pressure quickly decreases to a value at which the compressed reset pressure spring 57 can lift the ball valve member 44 off its valve seat 45.

When the ball valve member 44 is forced off its valve seat 45, the hydraulic fluid in the actuating piston chamber 65 is released, thereby resetting the single engine brake exhaust valve _31. The resetting function occurs before the normal exhaust stroke, so that both exhaust valves ₃₁ and ₃₂ are seated and the exhaust valve crossbar 24 can now be opened by the exhaust rocker arm 22, wherein the exhaust crossbar 24 is in a balanced condition.

Current commercially available freewheeling rocker brakes lack a reset mechanism and are implemented by incorporating reinforced crossbar guide pins to address the issue of unbalanced crossbar loads. This prior art approach is more expensive and offers lower deceleration performance due to increased intake/exhaust valve overlap. Increased intake/exhaust valve overlap results in a loss of exhaust manifold air mass and pressure in the return and inlet cylinders. This loss of exhaust manifold pressure degrades engine braking deceleration performance.

The single-valve rocker arm lost motion compression-release engine brake system with a reset mechanism according to the present invention reduces the cost of conventional engine brake systems or dedicated cam actuators. The rocker arm compression-release engine brake system of the present invention provides better performance than exhaust cam actuated brakes or injector actuated brakes. The performance of the single-valve rocker arm lost motion compression-release engine brake system of the present invention is close to that of dedicated cam engine brakes in most environments. Compared to other engine brake configurations, the single-valve rocker arm lost motion compression-release engine brake system with a reset mechanism offers advantages in terms of weight, development cost, requirement for fundamental changes to existing engines, engine height, and per-engine manufacturing cost.

13-15B illustrate a second exemplary embodiment of a valvetrain assembly for an internal combustion engine, generally designated by the reference numeral 110. Components identical to those of the first exemplary embodiment of the present invention are designated by the same reference numerals. Components functionally identical to those of the first exemplary embodiment of the present invention depicted in FIGs. 1-12 are designated by the same reference numerals, some of which have been incremented by 100, and sometimes are not described in detail because the reader will readily recognize the similarities between corresponding parts of the two embodiments.

The valvetrain assembly 110 includes a rocker arm compression release engine braking system 112 according to a second exemplary embodiment of the present invention for an internal combustion (IC) engine. Preferably, the IC engine is a four-stroke diesel generator.

As shown in FIG13 , a rocker arm compression-release engine brake system 112 according to a second exemplary embodiment of the present invention includes a conventional intake rocker assembly 115 for operating two intake valves 1 and an idler exhaust rocker assembly 116 for operating the exhaust valves 1. The compression-release brake system 112 according to the second exemplary embodiment of the present invention includes a push rod 9 that actuates the exhaust rocker assembly 116 and is driven by the exhaust cam 2, as shown in FIG13 .

An exhaust rocker assembly 116 according to a second exemplary embodiment of the present invention is a lost motion assembly equipped with automatic hydraulic adjustment and reset functionality. The exhaust rocker assembly 116 includes an exhaust rocker arm 122 pivotally mounted about a rocker shaft 20 and configured to open the first and second exhaust valves ₃₁ and ₃₂ , respectively, via an exhaust valve crossbar 24. The rocker shaft 20 is supported by a rocker arm support (or rocker arm base) 25 and extends through a rocker arm eyelet 133 (shown in FIGS. 13-15B ) formed in the exhaust rocker arm 122.

The rocker arm compression-release brake system 112 also includes an exhaust valve reset device 132 located in the exhaust rocker arm 122. The exhaust valve reset device 132 according to the second exemplary embodiment of the present invention is generally identical in structure and function to the exhaust valve reset device 32 according to the first exemplary embodiment of the present invention (detailed in Figures 8-9B ) and takes the form of a generally cylindrical sleeve. The sleeve body 134 is provided with an annular supply groove 136 fluidly connected to the continuous supply line 26, an annular brake release groove 38 fluidly connected to the brake release supply line 30, and an annular piston groove 140 fluidly connected to the high-pressure line 28. The cylindrical sleeve body 134 is threadably and adjustably positioned within the generally cylindrical reset aperture in the exhaust rocker arm 122. Furthermore, the sleeve body 134 is provided with a contact foot 72 rotatably mounted to the distal end of the sleeve body 134 proximate the exhaust valve crossbar 24. As shown in FIGS. 14 and 15B , the reset trigger 150 extends from the sleeve body 134 and the contact foot 72 through an opening in the contact foot 72 .

As best shown in FIG14 , each of the supply groove 136, the brake opening groove 138, and the piston groove 140 is formed on the outer cylindrical surface of the sleeve body 134 and is axially spaced apart from one another. The cylindrical sleeve body 134 is positioned within a generally cylindrical reset aperture in the exhaust rocker arm 122, thereby setting a predetermined valve lash (or clearance) δ between the contact foot 72 and the exhaust valve bridge 24 when the exhaust rocker roller follower contacts the lower base circle 5 on the exhaust cam 2, i.e., when the exhaust cam 2 is not acting on (pressing) the exhaust rocker arm 122. The predetermined valve lash δ (e.g., 0.05") is set to provide normal exhaust valve motion during positive power operation, and the clearance is used to allow for the increase in valvetrain components at engine operating temperatures. During engine braking operation, all lash (except the predetermined valve lash δ) is removed from the valvetrain, and the brake cam profile determines the timing of opening, profile, and lift of the exhaust valve.

Alternatively, the outer cylindrical surface 149 (generally designated 132') of the sleeve body 134' of the alternative embodiment of the exhaust valve resetting device is threaded in whole or in part, as best shown in Figures 15A and 15B. Each of the supply groove 136, the detent release groove 138, and the piston groove 140 is formed on the threaded outer cylindrical surface 149 of the sleeve body 134' and is axially spaced apart from one another. The threaded cylindrical sleeve body 134' is adjustably positioned within the generally cylindrical threaded resetting aperture 123a in the exhaust rocker arm 122 to set a predetermined valve lash (or gap) δ between the contact foot 72 and the exhaust valve crossbar 24 when the exhaust rocker roller follower contacts the lower base circle 5 on the exhaust cam 2, i.e., when the exhaust cam 2 is not acting on (pressing) the exhaust rocker arm 122.

Upper sleeve plug 135a is immovably restrained (i.e., fixed) to sleeve body 134' and is provided with a hexagonal socket 171, accessible from above exhaust rocker arm 122, for setting a predetermined valve lash δ. A locking nut 151 is disposed on threaded, cylindrical adjustment sleeve body 134'. The predetermined valve lash δ is set to provide normal exhaust valve movement during positive power operation, with the clearance provided for increased clearance of valve train components at engine operating temperatures. During engine braking operation, all clearances (except the predetermined valve lash δ) are removed from the valve train, and the brake cam profile determines the timing of opening, profile, and lift of the exhaust valve. In other words, reset device 132 combines the functions of a rocker arm adjusting screw assembly, a check valve, and a reset device. This arrangement of the exhaust valve reset device is particularly beneficial for internal combustion engines with overhead camshafts.

16-18B illustrate a third exemplary embodiment of a valvetrain assembly for an internal combustion (IC) engine, generally designated by the reference numeral 310. Components identical to those of the first exemplary embodiment of the present invention are designated by the same reference numerals. Components having the same function as those of the first exemplary embodiment of the present invention depicted in FIGs. 1-12 are designated by the same reference numerals, some of which have been incremented by 300, and some of which are not described in detail because the reader will readily recognize the similarities between corresponding parts of the two embodiments.

The valvetrain assembly 310 includes a rocker arm compression-release engine brake system 312. Preferably, the internal combustion engine is a four-stroke diesel engine including a cylinder block with multiple cylinders. The rocker arm compression-release engine brake system 312 includes a conventional intake rocker assembly (not shown) for operating the two intake valves 1 and a freewheeling exhaust rocker assembly 316 for operating the first and second exhaust valves ₃₁ and _32. The exhaust rocker assembly 316, according to the third exemplary embodiment of the present invention, is a freewheeling assembly equipped with automatic hydraulic adjustment and reset functions. The exhaust rocker assembly 316 includes an exhaust rocker arm 322, which is pivotally mounted about a rocker shaft 20 and is used to open the first and second exhaust valves ₃₁ and ₃₂ , respectively, via the exhaust valve crossbar 24. The rocker shaft 20 is supported by a rocker arm support (or rocker arm base) and extends through a rocker arm eyelet 333 (shown in FIG. 16 ) formed in the exhaust rocker arm 322.

The rocker arm compression-release brake system 312 also includes an exhaust valve reset device 332 positioned in the exhaust rocker arm 322 in a direction generally parallel to the exhaust valves ₃₁ and _32. As best shown in Figures 18A and 18B, the exhaust valve reset device (or spool sleeve) 332 according to the third exemplary embodiment of the present invention takes the form of a compression-release spool sleeve assembly and includes a generally cylindrical sleeve body 334 having a continuous hydraulic fluid pressure supply port 337 fluidically connected to the continuous hydraulic fluid pressure supply line 26 and a piston supply port 341 fluidically connected to the actuating piston chamber 65 via the high-pressure line 28. The continuous pressure supply port 337 and the piston supply port 341 are axially spaced apart from each other. The cylindrical sleeve body 334 is immovably positioned within a generally cylindrical reset aperture in the exhaust rocker arm 322. In a third exemplary embodiment of the present invention, a cylindrical sleeve body 334 is threadably and adjustably positioned within a generally cylindrical reset bore in the exhaust rocker arm 322. This means that the reset device 332 is adjustable for a predetermined valve lash δ. Furthermore, the sleeve body 334 is provided with a contact (or ball) foot 372, which is rotatably mounted to a sliding ball foot 374, which in turn is mounted to the distal end of the sleeve body 334 proximate the exhaust valve crossbar 24. In other words, the reset device 332 according to the third embodiment of the present invention combines the functionality of a rocker arm adjusting screw assembly and an exhaust valve reset device.

The reset device 332 also includes a generally cylindrical reset spool 340 axially slidably located within the cylindrical sleeve body 334. The reset spool 340 is movable within and relative to the sleeve body 334 between a retracted position shown in Figures 17A and 18A and an extended position shown in Figures 17B and 18B.

As further shown in Figures 18A and 18B, the reset spool 340 has an internal cavity divided by a separating wall 360 into a one-way valve cavity ₃₄₂₁ and a reset cavity _3422. The one-way valve cavity ₃₄₂₁ within the reset spool 340 is enclosed between the upper sleeve plug 335 and the separating wall 360. The reset spool 340 also has a first annular spool recess 350 formed between the inner circumferential surface 335 of the sleeve body 334 and the outer circumferential surface 347 of the reset spool 340. The first annular recess 351 defines a lower spool cavity and is in direct fluid communication with the continuous pressure supply port 337 in the sleeve body 334. The lower spool cavity 351 is then in fluid communication with the one-way valve cavity ₃₄₂₁ via at least one first communication port 353 in the reset spool 340. Depending on the axial position of the reset spool 340, the lower spool cavity 351 is selectively fluidically connected to the piston supply port 341. For example, in the retracted position of the reset spool 340 shown in Figure 18A, the lower spool chamber 351 is fluidly connected to the piston supply port 341, while in the extended position of the reset spool 340 shown in Figure 18B, the lower spool chamber 351 is fluidly disconnected from the piston supply port 341.

The reset spool 340 also forms a second annular spool recess 354 located between the inner circumferential surface 335 of the sleeve body 334 and the outer circumferential surface 347 of the reset spool 340. The second annular recess 354 defines an upper spool chamber and is in fluid communication with the one-way valve chamber ₃₄₂₁ via at least one second communication port 355 in the reset spool 340. As best shown in Figures 18A and 18B, the lower spool chamber 351 is fluidically separated from the upper spool chamber 354 by an annular flange 358 that is in sliding contact with the inner circumferential surface 335 of the sleeve body 334. In other words, the at least one second communication port 355 is axially separated from the at least one first communication port 353. Depending on the axial position of the reset spool 340, the second communication port 355 selectively fluidly connects the one-way valve chamber ₃₄₂₁ with the piston supply port 341.

Reset device 332 also includes a ball valve member 344 and a ball check valve spring 346 positioned between ball valve member 344 and upper sleeve plug 335. Ball valve member 344 is biased against ball check valve seat 345 by the biasing spring force of ball check valve spring 346, thereby closing a communication port 348 in reset spool 340 that fluidly connects continuous pressure supply port 337 of sleeve body 334 with check valve chamber ₃₄₂₁ of reset spool 340. Ball valve member 344, ball check valve seat 345, and ball check valve spring 346 define reset check valve 343. Check valve 343 provides selective fluid communication between continuous supply conduit 26 and high-pressure conduit 28 (i.e., between continuous supply conduit 26 and actuating piston chamber 65) via second communication port 355. It should be understood that any suitable type of check valve is within the scope of the present invention.

The continuous pressure supply port 337 and the piston supply port 341 are formed on the outer peripheral cylindrical surface of the sleeve body 334 and are axially spaced apart from each other. The threaded cylindrical sleeve body 334 is adjustably seated within a generally cylindrical reset bore in the exhaust rocker arm 322.

The exhaust valve reset device 332 also includes a reset trigger 350 slidably positioned axially within the reset cavity ₃₄₂ of the reset spool 340. The reset trigger 350 has a hemispherical distal end 352 that extends at least partially from the sleeve body 334. The reset trigger 350 is movable relative to the sleeve body 334 between a retracted position (as shown in Figures 17A and 18A) and an extended position (as shown in Figures 17B and 18B). The reset spool 340 is typically biased to the retracted position by a trigger return spring 356 located within the sleeve body 334 and outside the reset spool 340. The reset trigger 350 is also typically biased to the extended position within the reset spool 340 by a reset pressure spring 357 located within the sleeve body ₃₃₄ and within the reset cavity 342 of the reset spool 340. The reset trigger 350 is used to lift the reset spool 340 under the resilient bias of the reset pressure spring 357 to reset the brake operation.

The valve system assembly 310 according to the third exemplary embodiment of the present invention further includes a compression-release actuator 376 for selectively moving the reset spool 340 between a retracted position shown in Figures 17A and 18A and an extended position shown in Figures 17B and 18B. The compression-release actuator 376 shown in Figures 17A and 17B is in the form of a fluid (e.g., pneumatic or hydraulic) actuator. Alternatively, the compression-release actuator 376 may be in the form of an electromagnetic actuator. The fluid compression-release actuator 376 includes a housing 378 that is immovable relative to the rocker shaft 20 and a brake-release piston 380 that reciprocates within the housing 378. The brake-release piston 380 defines an actuating (or brake-release) piston chamber 381 within the housing 378 (best shown in Figures 17A and 17B). The housing 378 includes a fluid port 382 that opens into the actuating piston chamber 381 and is connected to a source of pressurized fluid (air or liquid), such as a brake-release supply line. The cover 378 is provided with a piston stroke limiting pin 384 that limits the upward and downward limited movement of the brake opening piston 380. Specifically, the brake opening piston 380 is provided with an axially extending groove 385 in which the piston stroke limiting pin 384 is received.

The compression-release brake system 312 operates in a compression-braking mode or brake-on mode (during engine compression-braking operation) and a compression-braking-deactivated mode or brake-off mode (during positive power operation).

During operation of an engine including a rocker arm compression-release engine brake system 312 with a reset device 332 according to the third exemplary embodiment of the present invention, during brake-off mode, the compression-release actuator 376 is deactivated and the brake-on piston 380 is in a compressed position, axially separating the compression-on piston 380 from the reset spool 340 of the reset device 332, as shown in Figures 16 and 17A. Consequently, the reset spool 340 is biased by the trigger return spring 356 to a retracted position, best shown in Figure 18A. In this position, the reset trigger 350 does not extend from the elephant foot 372. During brake-off mode, pressurized hydraulic fluid, such as engine oil, is continuously supplied to the continuous pressure supply port 337, providing a repetitive flow of engine oil through the lower spool chamber 351 to the piston supply port 341. This continuous oil flow eliminates mechanical lash in the valve train (beyond a predetermined valve lash δ) during positive power engine operation, eliminating valve train noise and maintaining continuous contact between the exhaust cam profile and the roller follower.

Thus, during brake off mode, pressurized fluid is continuously supplied from continuous supply conduit 26 to actuating piston chamber 65 through lower spool chamber 351 and piston supply port 341 of reset device 332 and high pressure passage 28 as shown in Figures 16, 17A and 18A.

The engine brake operates during the brake-on mode as follows.

To activate the engine brake, compression-release actuator 376 is activated and brake-on piston 380 moves to the extended position, as shown in FIG17B . Subsequently, brake-on piston 380 forces reset spool 340 downward, sealing piston supply port 341 from lower spool chamber 351. Actuator piston chamber 65 continues to fill with pressurized hydraulic fluid from continuous pressure supply port 337 via one-way valve 343, one-way valve chamber 342 ₁ , at least one second communication port 355 in reset spool 340, upper spool chamber 354, and piston supply port 341. Simultaneously, when brake-on actuator piston 62 is fully extended downward, one-way valve 343 hydraulically locks actuator piston chamber 65. Once on lower base circle 5 of exhaust cam 2, exhaust rocker arm 322 will begin to open single exhaust valve ₃₁ , releasing compressed air from the engine cylinder. At approximately 0.050 inches of exhaust valve lift, the hemispherical distal end 352 of the reset trigger 350 contacts the exhaust cross member 24 , causing the reset pressure spring 357 to generate an increased biasing force on the reset spool 340 to move upward.

During the engine compression stroke, the biasing force of the brake-opening piston 380 of the compression-release actuator 376 and the hydraulic pressure in the upper spool chamber 354 bias the biasing spool 340 in its extended position. On the other hand, the reset pressure spring 357 and the trigger return spring 356 bias the reset spool 340 in the retracted position. As cylinder pressure continues to increase, the hydraulic pressure in the upper spool chamber 354 also increases, generating a greater biasing force to maintain the reset spool 340 in the downward, extended position and continue to lock the hydraulic fluid in the actuation piston chamber 65 above the single-valve actuation piston 62.

When the engine stroke changes from the compression stroke to the expansion stroke, the cylinder pressure drops rapidly to approximately atmospheric pressure. When the pressure in the piston supply port 341 and the upper spool chamber 354 drops to approximately 250 psi, any significant hydraulic bias on the reset spool 340 is eliminated, causing the upward bias of the reset pressure spring 357 to exceed the downward bias of the compression release actuator 376. As a result, the reset spool 340 turns upward to open the piston supply port 341 to the lower spool chamber 351, thereby unlocking the actuating piston 62, i.e., allowing hydraulic fluid from the actuating piston chamber 65 to flow back to the continuous oil supply line 126 through the continuous pressure supply port 337. This oil flow through the continuous pressure supply port 337 allows the single exhaust valve ₃₁ to unseat and complete the single valve reset function. The reset pressure spring 357 has a spring rate that generates a force large enough to overcome the approximately 100 pounds of force from the valve spring ₉₁ of the brake exhaust valve ₃₁ , which creates a pressure differential across the reset ball valve member 444 of the reset check valve 443 at the end of the expansion stroke to reset the single exhaust valve ₃₁ .

19 and 20 illustrate a fourth exemplary embodiment of a valvetrain assembly for an internal combustion (IC) engine, generally designated by the reference numeral 410. Components identical to those of the first exemplary embodiment of the present invention are designated by the same reference numerals. Components having the same function as those of the first exemplary embodiment of the present invention depicted in FIGs. 16-18B are designated by the same reference numerals, some of which have been incremented by 100, and are sometimes not described in detail because the reader will readily recognize the similarities between corresponding parts of the two embodiments.

The valvetrain assembly 410 includes a rocker arm compression-release engine brake system 412. Preferably, the internal combustion engine is a four-stroke diesel engine including a cylinder block with multiple cylinders. The rocker arm compression-release engine brake system 412 includes a conventional intake rocker assembly (not shown) for operating the two intake valves 1 and a freewheeling exhaust rocker assembly 416 for operating the first (or brake) and second exhaust valves ₃₁ and _32. The exhaust rocker assembly 416, according to the fourth exemplary embodiment of the present invention, is a freewheeling assembly equipped with automatic hydraulic adjustment and reset functions. The exhaust rocker assembly 416 includes an exhaust rocker arm 422, which is pivotally mounted about a rocker shaft 20 and is used to open the first and second exhaust valves ₃₁ and ₃₂ , respectively, via the exhaust valve crossbar 24. The rocker shaft 20 is supported by a rocker arm support (or rocker arm base) and extends through a rocker arm eyelet 433 (shown in FIG. 19 ) formed in the exhaust rocker arm 422.

An internal combustion engine incorporating a compression-release brake system 412 according to a fourth exemplary embodiment of the present invention includes a pushrod (shown in FIG. 13 ) actuating an exhaust rocker assembly 416 and driven by an exhaust cam 2 (shown in FIG. 13 ). An exhaust rocker arm 422 has a driving (first distal) end 422 a for operatively engaging the engine exhaust valves ₃₁ and ₃₂ to control the engine exhaust valves ₃₁ and ₃₂ , and a driven (second distal) end 22 b located adjacent the pushrod.

The rocker arm brake system 412 also includes a generally cylindrical actuating piston bore 464 formed in the exhaust rocker arm 422 for slidably receiving an actuating piston 462 (best shown in FIG. 20 ) therein. The actuating piston 462 is movable between retracted and extended positions relative to the reset piston bore 464 in a direction generally parallel to the exhaust valves ₃₁ and ₃₂ and is configured to contact a top end surface 76a of a single-valve actuating pin 76 (best shown in FIG. 20 ). The single-valve actuating pin 76 is slidably movable relative to the exhaust valve crossbar 24. The actuating piston 462 defines a reset piston chamber 465 within the reset piston bore 464 in the exhaust rocker arm 422 (best shown in FIG. 20 ). During compression-release engine braking operation (i.e., in brake-on mode), the exhaust single-valve actuating pin 76 allows the actuating piston 462 to press against the first exhaust valve ₃₁ to open the first exhaust valve ₃₁ . In other words, the single valve actuating pin 76 can reciprocate relative to the exhaust valve bridge 24 , thereby allowing the first exhaust valve ₃₁ to move relative to the second exhaust valve ₃₂ and the exhaust valve bridge 24 .

The rocker brake system 412 also includes an exhaust valve reset device 432 located in the exhaust rocker arm 422. As shown in Figures 19 and 20, the exhaust valve reset device 432 includes a reset check valve located in the actuating piston 462. In an exemplary embodiment of the present invention, the reset check valve is in the form of a ball check valve 443, which is normally biased open. It should be understood that any suitable type of check valve other than a ball check valve is within the scope of the present invention. The reset check valve 443 includes a ball valve member 444, a ball check valve seat 445 and a biasing (or reset) spring 446, which biases the reset ball valve member 444 upward to the open position of the reset check valve 443.

The ball valve member 444 is biased open, i.e., urged away from the ball check valve seat 445 by the biasing spring force of the reset spring 446, thereby opening the communication port 448 in the actuating piston 462, which fluidically connects the reset piston chamber 465 with the communication conduit 453 formed through the actuating piston 462. In turn, the communication conduit 453 in the actuating piston 462 is directly fluidically connected to the continuous supply conduit 426. In other words, when the reset check valve 443 is open, the continuous supply conduit 426 is fluidically connected to the reset piston chamber 465.

The exhaust valve reset device 432 of the rocker arm brake system 412 also includes a rocker check valve 450, also located in the exhaust rocker arm 422. In the exemplary embodiment of the present invention, the rocker check valve 450 is in the form of a ball check valve that is normally biased closed. It should be understood that any suitable type of check valve other than a ball check valve is within the scope of the present invention. The rocker check valve 450 is located in a check valve bore 434 formed in the exhaust rocker arm 422, generally perpendicular to the rocker arm bore 433 that receives the rocker shaft 20. The bore 434 is sealed by a plug 435. The rocker check valve 450 includes a ball valve member 440 located in the check valve bore 434 and a ball check valve spring 442 that biases the ball valve member 440 into its closed position. In other words, the ball valve member 440 is supported on the ball check valve seat by the biasing spring force of the ball check valve spring 442, thereby closing the communication opening 452 through the rocker check valve 450, and the communication opening 452 connects the continuous supply pipeline 426 and the reset piston chamber 465 fluidly through the reset pipeline 428.

The rocker arm brake system 412 according to the fourth exemplary embodiment of the present invention also includes a compression-release actuator 476 for selectively controlling the exhaust valve reset device 432. The compression-release actuator 476 shown in Figures 19 and 20 is in the form of a fluid (e.g., pneumatic or hydraulic) actuator. Alternatively, the compression-release actuator 476 may be in the form of an electromagnetic actuator. The fluid compression-release actuator 476 includes a housing 478 that is immovable relative to the rocker shaft 20 and a brake-activating piston 480 that reciprocates within the housing 478. The brake-activating piston 480 defines a brake-activating piston chamber 481 within the housing 478 (best shown in Figure 20). The housing 478 includes a brake-activating fluid supply port 482 that opens into the brake-activating piston chamber 481 and is connected to a source of pressurized fluid (air or liquid). The housing 478 is provided with a piston stroke limiter pin 484. The piston stroke limiter pin 484 is an adjustable positive stop that limits the upward and downward linear movement of the brake-activating piston 480. Specifically, the brake opening piston 480 is provided with an axially extending slot 485 that receives a piston stroke limiting pin 484 therein.

The rocker arm brake system 412 according to the fourth exemplary embodiment of the present invention further includes a reset pin 458 extending between the brake opening piston 480 and the brake ball valve member 444 of the reset check valve 443 .

In addition, the exhaust rocker arm 422 includes a rocker arm adjusting screw assembly 468 (best shown in FIG. 1 ) adjustably mounted in the driven end 422 b of the exhaust rocker arm 422 such that the adjusting screw assembly 468 is located in the exhaust valve actuation system on the camshaft side of the engine and is operatively coupled to the pushrods. The adjusting screw assembly 468 defines an adjustable linkage between the exhaust rocker arm 422 and the pushrods in the exhaust valve actuation system.

19, a rocker arm adjusting screw assembly 468 is used to engage a pushrod to open exhaust valves ₃₁ and _32. The adjusting screw assembly 468 includes an adjusting screw 470 adjustably mounted (such as threaded) in the driven end 422b of the exhaust rocker arm 422.

The screw assembly 468 includes an adjusting screw 470 having a spherical end 471 for being received in a socket (not shown) coupled to the top end of the pushrod. The adjusting screw 470 is adjustably mounted, such as by threads, in the driven end 422b of the exhaust rocker arm 422 and is secured in place by a locking nut 473.

The compression-release braking system 412 operates in a compression-braking mode or brake-on mode (during engine compression-braking operation) and a compression-braking-deactivated mode or brake-off mode (during positive power operation).

The engine brake operates as follows during brake-on mode.

To activate the engine brake, the compression-release actuator 476 is activated and pressurized fluid enters the brake-opening piston chamber 481 through the brake-opening fluid supply port 482. Pneumatic or hydraulic fluid, such as engine oil, is supplied to the brake-opening piston chamber 481, forcing the brake-opening piston 480 downward. The brake-opening piston 480 then moves to its extended position, thereby engaging and moving the piston stroke limit pin 484 downward, shown in FIG19 . The brake-opening fluid supply port 482 is adjusted to maintain a constant supply pressure to maintain a continuous force of approximately 16 pounds to bias the brake-opening piston 480 downward to close the ball valve member 444. Alternatively, the brake-opening piston 480 of the compression-release actuator 476 can be activated by an electric solenoid or electromagnet. The downward linear movement of the brake-opening piston 480 biases the reset pin 458 downward and closes the reset check valve 443. When the brake opening piston 480 closes the reset check valve 443 via the reset pin 458, the actuating piston 462 does not retract into the reset piston bore 464 because the hydraulic fluid is locked in the reset piston bore 464 by the closed reset check valve 443 and the rocker check valve 450.

Operation of the compression-release engine brake system 412 according to the fourth exemplary embodiment requires only opening one of the two exhaust valves ₃₁ and ₃₂ , thereby not exceeding the maximum valvetrain load specification of the valvetrain. Opening the brake exhaust valve ₃₁ includes approximately 0.100 inches of single-valve brake lift. For initial valve opening, approximately 50% of the typical 0.100-inch lift of the brake exhaust valve ₃₁ , the compression-release engine brake system 412 requires the brake opening piston 480 to apply a generally downward biasing force to the ball valve member 444 of the reset check valve 443 via the reset pin 458, thereby sealing (i.e., closing) the reset check valve 443. In other words, the ball valve member 444 is mechanically biased closed during the initial 0.050 inches of the single-valve brake lift.

When the exhaust brake valve ₃₁ is at approximately 50% (or 0.050 inches) of its full engine brake lift, the brake opening piston 480 engages the adjustable piston stroke limit pin (or rigid stop) 484. From this point on, downward linear movement of the brake opening piston 480 is arrested. Subsequently, as the exhaust rocker arm 422 continues to move downward toward the exhaust cross member 24, the brake opening piston 480 ceases to push the brake pin 458 downward.

During the second half of the brake exhaust valve ₃₁ 's movement, cylinder pressure, and thus the valve force against the actuating piston 462, continues to increase. The increased hydraulic pressure now firmly seats the reset ball valve member 444 against its valve seat 445, eliminating the need to contact the reset pin 458 for the last (or second) 50% of movement. In other words, as the exhaust rocker arm 422 continues to open the brake exhaust valve ₃₁ , the downward biasing force of the reset pin 458 on the ball valve member 444 is eliminated when the brake exhaust valve ₃₁ is approximately 50% open due to the brake opening piston 480 contacting the adjustable rigid stop 484. During the compression stroke, cylinder pressure continues to increase, thereby biasing the brake exhaust valve ₃₁ upward and increasing the oil pressure in the reset piston chamber 465. Consequently, a downward biasing force is provided on the reset ball valve member 444. The high pressure in the reset piston chamber 465 creates a high pressure differential across the reset ball valve member 444 to continue biasing the reset ball valve member 444 into position, i.e., to the closed position of the reset check valve 443. In other words, the pressure in the actuating piston chamber 465 hydraulically biases the reset check valve 443 closed during the second and final half of the single valve brake lift (i.e., 0.050 inches of lift).

As described above, the reset spring 446 is located inside the actuating piston 462, and the initial force of the reset spring 446, approximately 13 lbf, is used to bias the reset ball valve member 444 upward to the open position that resets the check valve 443. During the expansion stroke 89, the cylinder pressure _89P will decrease rapidly due to the release of air from the cylinder during the engine braking compression release event near the TDC compression stroke.

The mass of cylinder air released into the engine exhaust manifold through the opening of the brake exhaust valve ₃₁ results in a very low cylinder pressure near the end of the expansion stroke. Since the brake exhaust valve ₃₁ remains open at approximately 0.100 inches of lift, the valve spring ₉₁ of the brake exhaust valve ₃₁ generates an upward biasing force of approximately 100 pounds-force (lbf) against the actuating piston 462.

Towards the end of the expansion stroke 89, as cylinder pressure approaches atmospheric pressure and the additional small biasing force from the valve spring ₉₁ of the brake exhaust valve ₃₁ , the higher biasing force from the reset spring 446 lifts the reset ball valve member 444 off its valve seat 445, causing hydraulic fluid to return from the reset piston chamber 465 to the continuous supply line 426 and the hydraulic fluid supply passage 93, such as an engine oil source. The return flow of hydraulic fluid allows the valve spring ₉₁ of the brake exhaust valve ₃₁ to force the actuating piston 462 upward, causing the reset pin 458 and the brake opening piston 480 to come into contact.

The spring bias of the valve spring ₉₁ of the brake exhaust valve ₃₁ is approximately 100 lbf, generating a pressure of approximately 220 psi in the reset piston chamber 465, forcing the hydraulic fluid back into the hydraulic fluid supply passage 93, allowing the actuating piston 462 to move upward. When the brake exhaust valve ₃₁ approaches 0.050 inches from the seated position, the reset pin 458 contacts the brake opening piston 480, and the reset ball valve member 444 is seated, i.e., the reset check valve 443 is closed.

The biasing force of the valve spring ₉₁ of the brake exhaust valve ₃₁ , which is approximately 100 lbf, exceeds the downward biasing force of the brake opening piston 480, which is approximately 12 pounds, forcing the brake opening piston 480 upward and approximately 0.050 inches above the adjustable rigid stop 484. This causes the actuating piston 462 and the single-valve actuating pin 76 to move upward, thereby allowing the single exhaust valve ₃₁ to be reset and returning the first exhaust valve ₃₁ to its valve seat. In other words, resetting the single exhaust brake valve ₃₁ is achieved by sensing the reduced cylinder pressure during the expansion stroke and the corresponding hydraulic pressure in the actuating piston chamber 465, causing the ball check valve 444 to unseat and release hydraulic fluid from the actuating piston chamber 465, thereby closing or resetting the single exhaust valve ₃₁ and eliminating the unbalanced exhaust crossbar before normal exhaust valve lift.

Hydraulic fluid supply passage 93 may add any needed make-up oil to reset piston chamber 465 through rocker check valve 450 .

The rocker check valve 450 is fluidly connected to the continuous supply line 426 for supplying hydraulic fluid to the reset piston chamber 465. The rocker check valve 450 needs to fill the reset piston chamber 465 before the compression brake stroke begins. During the opening ₉₁₁ and closing ₉₁₂ exhaust lift profiles, the operation of the brake opening piston 480 biases the reset check valve 443 into position within approximately 0.050 inches of the brake exhaust valve ₃₁ .

During refilling of the actuating piston chamber 465, the passage 453 only adds supply oil until the brake piston 480 and reset pin 458 bias the reset ball valve member 444 of the reset check valve 443 before the start of the last 0.050" of the single-valve brake lift (or lost motion). Because the reset ball valve member 444 is designed to seal the reset check valve 443 during the first 0.050" of a single brake lift, it cannot add supplemental reset supply oil during the last 0.050" of a single brake lift. For this reason, the rocker check valve 450 is required.

During a compression-release engine braking event, during the first 0.050 inches of the opening portion ₈₈₁ of the exhaust cam lift profile 88, the brake opening piston 480 (via the reset pin 458) biases the reset check valve 443 closed, thereby preventing the continuous supply line 426 from adding any supplemental oil at normal supply pressure. The conical biasing spring 442 of the rocker check valve 450, having a low biasing force, provides supplemental oil from the continuous supply line 426 to fill the reset piston cavity 465 and remove all exhaust valve system lash prior to the next compression-release engine braking event 88 (as shown in FIG. 12 ).

During the expansion stroke 89, hydraulic fluid flows from the reset piston chamber 465 back into the continuous supply line 426, allowing the brake exhaust valve ₃₁ to be seated (displaced) to its closed position. With the brake exhaust valve ₃₁ seated (or closed), the normal exhaust cycle opens with both exhaust valves ₃₁ and ₃₂ closed, which eliminates the unbalanced exhaust valve beam 24 opening formed by the closed outer exhaust valve ₃₂ and the partially open brake exhaust valve ₃₁ .

During engine compression operation, peak cylinder pressures in the engine cylinders can reach as high as 1000 psi, resulting in a pressure of approximately 4000 psi in the reset piston cavity 465. Reset pin 458 includes an elongated (e.g., cylindrical) portion (or stop portion) 458a integrally formed therewith (i.e., immovably or fixedly) thereto, located between the distal ends of reset pin 458 and within reset piston cavity 465. Stop portion 458a of reset pin 458 is configured to control an upper stop of reset pin 458 within reset piston cavity 465 and to control the upper biasing force generated by the hydraulic pressure within reset piston cavity 465. The cross-sectional area (or diameter) of stop portion 458a is greater than the cross-sectional area (or diameter) of reset pin 458 outside cylindrical portion 458. This area difference of reset pin 458 is designed to minimize the inner surface area of reset pin 458 within reset piston cavity 465, thereby reducing or eliminating undesirable biasing of reset ball valve member 444 during seating and unseating functions. Furthermore, an upper pin stop surface 458 b of the stop portion 458 a faces and is configured to selectively engage a reset stop surface 459 of the exhaust rocker arm 422 to limit upward movement of the reset pin 458 .

The engine operates as follows during brake off mode.

In operation of an engine including the rocker arm compression release engine brake system 412 with the reset device 432 according to the fourth exemplary embodiment of the present invention, during brake-off mode, the compression-release actuator 476 is deactivated and the brake-on piston 480 is in a compressed position. Consequently, the reset check valve 443 is biased open by the reset spring 446.

In this position, biasing pin 458 does not bias reset check valve 443 closed. In the brake-off mode, pressurized hydraulic fluid, such as engine oil, is continuously supplied to reset piston chamber 465 from continuous supply line 426 through communication line 453, communication port 448, and the open reset check valve 443. Furthermore, the open reset check valve 443 allows pressurized hydraulic fluid to flow into and out of reset piston chamber 465 through communication line 453 and communication port 448 to continuous supply line 426. This continuous oil flow removes mechanical lash (beyond a predetermined valve lash δ, FIG. 20 ) from the valvetrain during positive power engine operation, eliminating valvetrain noise and maintaining constant contact between the exhaust cam profile and the roller follower.

When the source of brake fluid supplied to the brake piston chamber 481 through the brake opening fluid supply port 482 is turned off, the reset spring 446 and the hydraulic fluid pressure acting on the lower pin stop surface 458c of the stop portion 458a bias the reset pin 458 upward to the reset stop surface 459 of the exhaust rocker arm 422, thereby biasing the reset ball valve member 444 upward to its open position to allow unrestricted fluid flow in the reset piston chamber 465 to allow engine oil to flow freely into and out of the reset piston chamber 465 from the continuous supply line 426 to remove all exhaust valve system clearances, thereby reducing valve system shock and mechanical noise during positive power engine operation.

During the compression stroke 86, the addition of pressurized hydraulic fluid to the reset piston chamber 465 via the continuous feed line 426 removes all valve system lash, causing the reset piston 462 to engage the brake exhaust valve _31. Near the end of the compression stroke 86, the engine brake lift profile 7 of the exhaust cam 2 rotates the exhaust rocker arm 422. As the exhaust rocker arm 422 pivots toward the brake exhaust valve ₃₁ , the reset piston 462 is unable to overcome the resilient bias of the valve spring ₉₁ of the brake exhaust valve ₃₁ and is displaced into the reset piston bore 464, allowing pressurized hydraulic fluid to flow from the reset piston chamber 465 into the continuous feed line 426 through the open reset check valve 443, which is biased away from its valve seat 445 by the reset spring 446.

After completing the exhaust lift profile 88 (shown in Figure 12), pressurized hydraulic fluid flows from the continuous supply line 426 back to the reset piston chamber 465 through the open reset check valve 443, which is biased away from its valve seat 445 by the reset spring 446, to bias the reset piston 462 downward toward the brake exhaust valve ₃₁ and remove the valve system clearance.

The exhaust rocker arm 422 is then ready to continue the normal exhaust cam lift profile 85 on the exhaust cam profile (or upper base circle) 6 of the exhaust cam 2. With the reset spring 446 continuing to support the reset ball valve member 444 away from its valve seat 445, thereby allowing unrestricted flow of engine oil in the reset piston chamber 465, valve system lash is eliminated during positive power operation of the engine.

Therefore, incorporating a hydraulic lash adjuster and exhaust valve reset mechanism on a freewheeling rocker arm brake offers the advantages of adjusting brake valve lash at initial installation and between maintenance intervals, as well as providing automatic valvetrain adjustment to accommodate any valvetrain wear and reduce valvetrain mechanical noise levels. Furthermore, the rocker arm compression-release engine brake system according to the present invention is lighter than conventional compression-release engine brake systems, providing a lower valve cover height and reduced cost.

According to the provisions of the patent law, the foregoing description of the exemplary embodiments of the present invention is provided for the purpose of illustration. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed. In accordance with the above teachings, various modifications or changes may be made. The embodiments disclosed above are selected to best illustrate the principles of the present invention, and thus their practical application enables those of ordinary skill in the art to best utilize the present invention in various embodiments and with various modifications suitable for specific intended uses, as long as the principles described herein are followed. Therefore, the present invention described above may be modified without departing from the purpose and scope of the present invention. In addition, the scope of the present invention is defined by the appended claims.

Claims (29)

1. A compression release braking system for realizing compression release engine braking operation associated with an internal combustion engine, the internal combustion engine including an engine cylinder associated with a four-stroke piston cycle including a compression stroke and an expansion stroke, and provided with at least one intake valve, at least one exhaust valve, and at least one exhaust valve return spring, the exhaust valve return spring applying a closing force on the exhaust valve to push the exhaust valve into a seated state, the compression release braking system comprising: Idle exhaust rocker assembly, which includes a rocker arm; An actuating piston, slidably received by a rocker arm to define a portion of a piston chamber within the rocker arm, and movable between a retracted position and a extended position, the actuating piston being configured to be operatively connected to an exhaust valve to allow the exhaust valve to disengage from its seated position; and A reset device, which is received by a rocker arm and includes: A reset check valve movable between an open position and a closed position, wherein in the open position the communication port is open to allow the piston chamber to be in fluid communication with the supply line through the communication port, and in the closed position the communication port between the piston chamber and the supply line is closed; A reset pressure spring, operatively connected to the reset check valve, allows a bias force to be applied to the reset check valve to push it toward the open position; and A trigger, operatively connected to a reset check valve and a reset pressure spring, and movable between a retracted position and an extended position; The compression-release braking system is configured such that, when operating in the brake-on mode, the reset device is operatively connected to the actuating piston so that, after the at least one exhaust valve is dislodged and when the hydraulic pressure in the piston chamber decreases, the bias force of the reset pressure spring compressed by the trigger moves the reset check valve to the open position, thereby releasing a portion of the hydraulic fluid in the piston chamber through the communication port, such that the closing force of the exhaust valve reset spring at the end of the expansion stroke resets the at least one exhaust valve to the in-position state. 2. The compression release braking system according to claim 1 further includes an actuator operatively connected to the reset device to move the trigger to the trigger extension position. 3. The compression release braking system of claim 1, wherein the compression release braking system is configured such that when installed on an internal combustion engine and operated in a brake-on mode: The idling exhaust rocker assembly is operatively connected to the reset device so that during the compression stroke, the relative movement between the pivoting rocker arm and the stop member of the idling exhaust rocker assembly moves the trigger toward the trigger retracted position, causing the trigger to compress the reset pressure spring and keep the reset check valve in the closed position. The idle exhaust rocker assembly is operatively connected to the actuating piston to apply sufficient force to the exhaust valve during the compression stroke to disengage the exhaust valve. 4. The compression release braking system according to claim 3, wherein: The internal combustion engine cylinders are equipped with the exhaust valve and at least one additional exhaust valve; and In brake-start mode, the additional exhaust valve remains closed throughout the entire compression and expansion strokes. 5. The compression release braking system according to claim 3 further includes a single-valve actuation pin, which operatively connects the actuation piston to the exhaust valve, wherein: The engine cylinders of the internal combustion engine are connected to the exhaust valve and at least one additional exhaust valve, and In the brake-start mode, the stop member includes a valve beam with an opening through which the single-valve actuation pin can slide relative to the valve beam, allowing the actuating piston to apply sufficient force to the exhaust valve via the single-valve actuation pin to disengage the exhaust valve during the compression stroke while the additional exhaust valve remains in place. 6. The compression release braking system according to claim 1, wherein the reset check valve comprises a ball-type check valve. 7. The compression release braking system according to claim 1, wherein the reset pressure spring is arranged within the trigger. 8. The compression release braking system of claim 1, wherein the reset device includes a trigger reset spring configured to bias the trigger toward the trigger retracted position. 9. The compression release braking system of claim 1, wherein the reset device further comprises an expansion pin operatively connected to the trigger and the reset check valve, and configured to hold the reset check valve in the open position during a brake-off mode for positive power operation of the internal combustion engine. 10. The compression release braking system of claim 1, wherein the reset device further comprises a sleeve body mounted to the rocker arm and spaced apart from the actuating piston. 11. The compression release braking system according to claim 1, wherein: The reset device also includes a one-way valve spring configured to push the reset check valve toward the closed position, the one-way valve spring applying a one-way valve spring bias force to the reset check valve in the opposite direction to the bias force of the reset pressure spring. 12. The compression release braking system according to claim 2, wherein: The reset device further includes a reset cavity; and The actuator includes a solenoid valve that can be selectively controlled to supply pressurized fluid to the reset chamber to move the trigger to the trigger extension position. 13. The compression release braking system according to claim 2, wherein: The reset device further includes a reset chamber and a trigger reset spring, which applies a reset spring bias force to bias the trigger toward the trigger retracted position; and The actuator includes a solenoid valve that can be selectively controlled to supply pressurized fluid to the reset chamber beyond the reset spring bias, thereby moving the trigger to the trigger extension position. 14. The compression release braking system according to claim 2, wherein: The starter is operatively connected to the reset device to deactivate the compression release braking system to a brake-off mode for positive power operation of the internal combustion engine; and The reset device is configured to keep the reset check valve in the open position throughout the entire brake-off mode. 15. The compression release braking system according to claim 3, further comprising: An adjusting screw assembly includes an adjusting screw that is adjustable relative to a rocker arm to set a predetermined valve clearance between the end of the adjusting screw assembly and a stop member. 16. The compression release braking system of claim 3, further comprising an adjusting screw assembly and a single-valve actuation pin operatively connecting the actuation piston to the exhaust valve, wherein: The engine cylinders of the internal combustion engine are connected to the exhaust valve and at least one additional exhaust valve; The stop member includes a valve crossbeam with an opening, through which the single-valve actuating pin can slide relative to the valve crossbeam, allowing the actuating piston to apply sufficient force to the exhaust valve via the single-valve actuating pin in the brake-opening mode, to disengage the exhaust valve during the compression stroke while the additional exhaust valve remains in place; and In the brake-off mode for positive power operation of an internal combustion engine, the adjusting screw assembly is configured to move the valve beam downwards, thereby opening both the exhaust valve and the additional exhaust valve. 17. The compression release braking system of claim 1, wherein the rocker arm includes an internal hydraulic fluid circuit comprising the supply conduit, a check valve chamber accommodating the reset check valve, and an additional conduit connecting the check valve chamber to the piston chamber. 18. The compression release braking system according to claim 17, wherein the rocker arm further comprises: A continuous supply line configured to supply hydraulic fluid to the check valve chamber. 19. The compression release braking system of claim 18, wherein the idling exhaust rocker assembly further includes a rocker shaft including an energy storage chamber connected to the continuous supply conduit and configured to deliver hydraulic fluid to the check valve chamber during the compression stroke in the braking open mode, and to receive hydraulic fluid from the check valve chamber near the end of the expansion stroke in the braking open mode. 20. The compression release braking system of claim 1, wherein the idling exhaust rocker arm assembly is configured to drive and actuate the rocker arm via an exhaust cam. 21. The compression release braking system according to claim 1, wherein: The reset device includes a sleeve body with external threads; and The rocker arm has an opening with an internal thread that threadably and adjustably engages with the external thread of the sleeve body. 22. The compression release braking system of claim 3, wherein the stop member includes an exhaust valve crossbeam, wherein the reset device is adjustable relative to the rocker arm to set a predetermined valve clearance between the end of the reset device and the exhaust valve crossbeam. 23. The compression release braking system of claim 1, wherein the reset device further includes a contact foot defining an end of the reset device. 24. The compression release braking system according to claim 3, further comprising a single-valve actuation pin that operatively connects the actuation piston to the exhaust valve, wherein: The engine cylinders of the internal combustion engine are connected to the exhaust valve and at least one additional exhaust valve; The stop member includes a valve crossbeam with an opening, through which the single-valve actuating pin can slide relative to the valve crossbeam, allowing the actuating piston to apply sufficient force to the exhaust valve via the single-valve actuating pin in the brake-opening mode, to disengage the exhaust valve during the compression stroke while the additional exhaust valve remains in place; and In the brake-off mode for positive power operation of an internal combustion engine, the reset device is configured to move the valve beam downward and thereby open both the exhaust valve and the additional exhaust valve. 25. A compression release braking system selectively used to realize compression release engine braking operation associated with an internal combustion engine, the internal combustion engine including an engine cylinder associated with a four-stroke piston cycle including a compression stroke and an expansion stroke, and provided with at least one intake valve, at least one exhaust valve, and at least one exhaust valve return spring, the exhaust valve return spring applying a closing force on the exhaust valve to push the exhaust valve into a seated state, the compression release braking system comprising: Idle exhaust rocker assembly, which includes a rocker arm; An actuating piston, which is slidably received by a rocker arm to define a portion of a piston chamber within the rocker arm, and is movable between a retracted position and a extended position, the actuating piston being configured to be operatively connected to an exhaust valve to allow the exhaust valve to disengage from its seated position. A reset device, which is received by a rocker arm and includes: A reset check valve, disposed in an actuating piston and movable between an open and a closed position, wherein in the open position the communication port is open to allow fluid communication between the piston chamber and the supply line, and in the closed position the communication port between the piston chamber and the supply line is closed; and A reset pressure spring, operatively connected to the reset check valve, allows a bias force to be applied to the reset check valve to push it toward the open position; and An actuator, which is operatively connected to the reset device, causes the reset check valve to move to the closed position; The compression release braking system is configured such that, when operating in the brake open mode, the reset device is operatively connected to the actuating piston so as to return the exhaust valve to its in-position state at the end of the expansion stroke in the brake open mode. 26. The compression release braking system according to claim 25, wherein: The internal combustion engine cylinders are equipped with the exhaust valve and at least one additional exhaust valve; and The additional exhaust valve is configured to remain closed throughout the entire compression and expansion strokes in brake-activated mode. 27. The compression release braking system according to claim 25, further comprising: An additional connection port, arranged in the exhaust rocker arm, connects the supply pipe and the piston chamber; and A rocker check valve, configured to open and close the additional communication port. 28. A compression release braking system for realizing compression release engine braking operation associated with an internal combustion engine, the internal combustion engine including an engine cylinder associated with a four-stroke piston cycle including a compression stroke and an expansion stroke, and provided with at least one intake valve, at least one exhaust valve, and at least one exhaust valve return spring, the exhaust valve return spring applying a closing force on the exhaust valve to push the exhaust valve into a seated state, the compression release braking system comprising: Idle exhaust rocker assembly, which includes a rocker arm; An actuating piston, slidably received by a rocker arm to define a portion of a piston chamber within the rocker arm, and movable between a retracted position and a extended position, the actuating piston being configured to be operatively connected to an exhaust valve to allow the exhaust valve to disengage from its seated position; and The reset device, which is received by the rocker arm, The compression release braking system is configured such that when installed on an internal combustion engine and operated in the brake open mode, the reset device is operatively connected to the actuating piston to allow the exhaust valve to return to its in-place position at the end of the expansion stroke in the brake open mode. 29. The compression release braking system of claim 28, further comprising a reset pressure spring, wherein the compression release braking system is configured such that when mounted on an internal combustion engine and operated in a brake-on mode: The idling exhaust rocker assembly is operatively connected to the reset device to cause the reset pressure spring to apply an increased bias force to the reset device during the compression stroke, and The reset device is operatively connected to the actuating piston so that, in the brake-opening mode, when the hydraulic pressure in the piston chamber decreases during the expansion stroke, the biasing force of the reset pressure spring causes the reset device to move to the open position. In the open position, a portion of the hydraulic fluid in the piston chamber is released by the reset device, so that the closing force of the exhaust valve return spring at the end of the expansion stroke resets the exhaust valve to the in-place position.