JP2001280160A - Compression pressure release type brake for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen engine braking force and a set width of a maximum cylinder internal pressure, in a compressed pressure release type brake for an engine. SOLUTION: In the compressed pressure opening type brake for the engine, which is provided with an exhaust brake valve interposed in an exhaust passage of the engine and an exhaust valve communicated with the exhaust passage in a cylinder in synchronism with engine rotation, which is capable of closing the exhaust brake valve when the brake is operated, opening the exhaust valve other than an intake stroke, and temporarily closing the exhaust valve in a compressing stroke, a maximum lift amount L of the exhaust valve is set lower than that in an after zone at a front zone from a valve closing zone in the compressing stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a compression pressure release type brake of an engine.

[0002]

2. Description of the Related Art As an auxiliary brake provided in a vehicle such as a heavy truck, an exhaust brake valve provided in the middle of an exhaust pipe of an engine is closed when a brake is operated, and the exhaust valve is opened other than in the intake stroke. Some engines are equipped with an engine compression pressure release type brake (Japanese Patent Laid-Open No.
JP-A-259523, JP-A-6-193412,
reference).

Conventionally, as a compression pressure release type brake of this type of engine, the present applicant has disclosed Japanese Patent Laid-Open No. 2000-212.
No. 6 has already been filed by temporarily closing the exhaust valve during the compression stroke during braking.
The air in the cylinder is prevented from flowing into the exhaust passage, and the maximum cylinder pressure is increased in a low speed range to secure the engine braking force.

[0004]

However, in the case of such a conventional device, the exhaust valve is temporarily closed during the compression stroke when the brake is actuated, but the exhaust gas is exhausted before and after the valve closing interval in the compression stroke. Since the maximum lift amounts of the valves were substantially equal, there was a problem that the setting range of the engine braking force and the maximum cylinder pressure was limited.

The present invention has been made in view of the above problems, and an object of the present invention is to widen a set range of an engine braking force and a maximum in-cylinder pressure in a compression pressure release type brake of an engine.

[0006]

According to a first aspect of the present invention, there is provided a brake having an exhaust brake valve disposed in an exhaust passage of an engine, and an exhaust valve for communicating the inside of the cylinder with the exhaust passage in synchronization with engine rotation. The present invention is applied to a compression pressure release type brake of an engine in which an exhaust brake valve is closed during operation and the exhaust valve is opened other than in the intake stroke, and the exhaust valve is temporarily closed in a compression stroke.

The maximum lift amount of the exhaust valve is made different before and after the valve closing section in the compression stroke during the braking operation.

According to a second aspect, in the first aspect, the maximum lift amount of the exhaust valve is set to be lower in a section before the valve closing section in the compression stroke than in a section after the valve closing section.

In a third aspect based on the first aspect, the maximum lift amount of the exhaust valve is set to be higher in a section before the valve closing section in the compression stroke than in a section after the valve closing section.

[0010]

According to the first aspect of the present invention, when the compression pressure release type brake is operated, the exhaust valve is closed in the intake stroke and opened in each of the other strokes. The compressor acts as a compressor, increasing the pressure in the cylinder, causing the engine to perform negative work and increasing the engine braking force.

When the brake is operated, the exhaust pressure is low in a low-speed range where the engine speed is low, and the exhaust valve is operated during the brake operation in response to the fact that the pressure in the cylinder rises above the exhaust pressure early in the compression stroke. By temporarily closing the valve in the compression stroke, the air in the cylinder is prevented from flowing into the exhaust passage.

By making the maximum lift amount of the exhaust valve different before and after the valve closing section in the compression stroke, the set range of the engine braking force and the maximum in-cylinder pressure can be widened.

In the second invention, by setting the maximum lift amount of the exhaust valve so as to be lower in a section before the valve closing section in the compression stroke than in a section after the valve closing section, in the high-speed region where the exhaust pressure increases, this compression is performed. In the section before the valve closing section in the stroke, the amount of exhaust gas flowing backward from the exhaust passage into the cylinder is suppressed, so that the maximum cylinder pressure is prevented from becoming too high even in a high speed range, and the engine braking force is suppressed. further,
It is possible to prevent the maximum pressure in the cylinder from becoming too high in the high-speed range, prevent an excessive load from being applied to the valve operating system, secure the durability thereof, and reduce the weight of the valve operating system.

In the third aspect of the present invention, the maximum lift amount of the exhaust valve is set so as to be higher in a section before the valve closing section in the compression stroke than in a section after the valve closing section in the compression stroke. As a result, the amount of exhaust gas flowing backward from the exhaust passage into the cylinder increases, and the engine braking force can be increased.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, FIGS. 1 and 2 show a specific configuration of an engine to which the present invention can be applied, which has already been filed by the present applicant as Japanese Patent Application Laid-Open No. 2000-2126.

In FIG. 1, reference numeral 1 denotes an exhaust valve of an engine;
Is a cam that rotates in synchronization with the crankshaft. Push rod 4 via lifter 3 with rotation of cam 2
The rocker arm 5 swings with the reciprocating movement of the push rod 4 to open and close the exhaust valve 1.

In a four-stroke diesel engine, intake air is drawn into a cylinder from an intake passage as an intake valve (not shown) is opened, and the intake air is compressed by a piston.
In FIG. 3, a chain line indicates a lift characteristic of the intake valve. In the figure, the crank angle θ is 0 ° at the piston bottom dead center in the compression stroke. That is, when the crank angle θ is 0 °, the piston is at the bottom dead center and shifts from the suction stroke to the compression stroke. When θ = 180 °, the piston is at the top dead center, and shifts from the compression stroke to the expansion stroke. At this time, fuel is injected from the injector into the cylinder, and the fuel is ignited and burned to lower the piston. θ = 360 °
At this time, the piston is at the bottom dead center, and shifts from the expansion stroke to the exhaust stroke. In the exhaust stroke in which the piston rises, the exhaust valve is open, and exhaust is discharged to the exhaust passage 9. θ = 54
At 0 °, the piston is at top dead center, and shifts from the exhaust stroke to the intake stroke, and these strokes are repeated continuously.

In order to increase the engine braking force, an exhaust brake valve is interposed in the exhaust passage of the engine, and the engine is provided with a compression pressure release type brake for opening the exhaust valve 1 other than during the intake stroke. 2, the rocker arm 5 is swingably supported via a journal portion 6a of the rocker shaft 6. Journal part 6a
Are formed eccentrically by a predetermined amount with respect to the center axis of the rocker shaft 6. When the rocker shaft 6 is rotated by the actuator 8 via the lever 7, the rocker arm 5 pushes down the exhaust valve 1 as the journal portion 6a moves down as shown by the broken line in FIG. As a result, the lift amount of the exhaust valve 1 becomes larger when the compression pressure release type brake is activated than when it is not activated, and the exhaust valve 1 is opened slightly apart from a valve seat (not shown) also in the compression stroke and the expansion stroke.

In FIG. 3, the solid line indicates the lift characteristic of the exhaust valve 1 when the compression pressure release type brake is not operated, and the broken line in FIG. 3 indicates the lift characteristic of the exhaust valve 1 when the compression pressure release type brake is operated. I have. When the compression pressure release type brake is operated, the exhaust valve 1 closes during the suction stroke,
By opening the valve in each of the other strokes, the engine functions as a compressor for increasing the pressure in the exhaust passage, and increasing the pressure in the cylinder causes the engine to perform negative work, thereby increasing the engine braking force.

When the compression pressure release type brake is operated, the exhaust valve 1 is temporarily closed during the compression stroke. The profile of the cam 2 is shown in FIG.
A ridge 2a that protrudes with respect to the base circle portion 2b in an angle region where the lifter 3 slides in the exhaust stroke, a first valley portion 2c that is depressed with respect to the base circle in an angle region where the lifter 3 slides in the suction stroke, and compression. A second valley portion 2d that is depressed with respect to the base circle in an angle range where the lifter 3 slides in the stroke.

When the compression pressure release type brake is operated, the exhaust pressure is low in a low speed region where the engine speed is low, and the pressure in the cylinder rises above the exhaust pressure at an early stage of the compression stroke. , The air in the cylinder is prevented from flowing into the exhaust passage. As a result, even in the low speed range, the maximum cylinder pressure is increased to increase the negative work of the engine, and the generated engine braking force can be sufficiently ensured.

Similarly, in the high-speed range where the engine speed is high during the braking operation, the exhaust pressure is high, and the timing at which the pressure in the cylinder rises above the exhaust pressure in the compression stroke is delayed, but the exhaust valve 1 is temporarily moved during the compression stroke. , It is possible to prevent a large amount of air from flowing back from the exhaust passage into the cylinder, and to prevent the maximum cylinder pressure from becoming too high even in a high-speed range.

However, in the case of such a conventional apparatus, although the exhaust valve 1 is temporarily closed during the compression stroke when the brake is operated, the maximum lift amount of the exhaust valve in the section before and after the valve closing section in this compression stroke is sandwiched. Have been substantially equal, there has been a problem that the setting range of the engine braking force and the maximum cylinder pressure is limited.

For example, in order to increase the engine braking force, it is necessary to delay the valve closing interval in the compression stroke. However, the limit on the profile of the cam 2 limits the range from 130 to 140 ° from the piston bottom dead center.

In order to reduce the engine braking force, it is necessary to advance the valve closing section in the compression stroke. However, the limit on the profile of the cam 2 limits the range of 80 to 90 ° from the piston bottom dead center. Was.

In response to this, the present invention temporarily closes the exhaust valve 1 in the compression stroke during the operation of the compression pressure release type brake, and sets the maximum value of the exhaust valve in a section before and after the valve closing section in the compression stroke. The gist of the present invention is to increase the setting range of the engine braking force and the maximum cylinder pressure by making the lift amount different.

Hereinafter, a specific example of the compression pressure release type brake will be described.

In FIG. 4, the valve lift characteristic indicated by a dashed line is that of the conventional apparatus, and the valve lift characteristic indicated by a solid line is that of the present embodiment. In this embodiment, the exhaust valve 1 is temporarily closed between 105 and 120 ° from the piston bottom dead center in the compression stroke, and the maximum lift amount of the exhaust valve is set in a section after the valve closing section in the compression stroke. L is 1.6m
m, and the maximum lift amount L of the exhaust valve in the section before the valve closing section in the compression stroke is set to about 1.0 mm.

As described above, the maximum lift amount L of the exhaust valve is reduced by about 0.6 mm in the section before the valve closing section in the compression stroke and in the section after the valve closing section in the compression stroke. In the section before the valve closing section in the stroke, the amount of exhaust gas flowing backward from the exhaust passage into the cylinder is suppressed, so that the maximum cylinder pressure is prevented from becoming too high even in a high speed range, and the engine braking force is suppressed.

Further, by delaying the valve closing section in the compression stroke by about 10 ° as compared with the conventional device, the engine braking force in a low speed range is secured.

FIG. 5 shows how the engine braking force and the cylinder pressure change according to the engine speed. The characteristics indicated by dashed lines are those of the conventional device, and the characteristics indicated by solid lines are those of the present embodiment. In the present embodiment, the engine braking force in the low speed range is increased as compared with the conventional device, and the engine braking force and the cylinder pressure in the high speed range are reduced. As a result, an excessive load is prevented from being applied to the valve trains such as the exhaust valve 1, the rocker arm 5, the push rod 4, the cam 2, and the durability thereof is secured, and the valve trains are lightened.

As another embodiment, the maximum lift amount L of the exhaust valve may be higher in a section before the valve closing section in the compression stroke than in a section after the valve closing section.

In this case, in the section before the valve closing section in the compression stroke, the amount of exhaust flowing back into the cylinder from the exhaust passage increases, and the engine braking force can be increased.

It is apparent that the present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the technical idea.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a valve train to which the present invention can be applied.

FIG. 2 is a view showing the operation of a valve train.

FIG. 3 is a valve lift characteristic diagram.

FIG. 4 is a valve lift characteristic diagram showing the embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the relationship between the engine braking force and the cylinder pressure with respect to the engine speed.

FIG. 6 is a valve lift characteristic diagram showing another embodiment.

[Explanation of symbols]

 Reference Signs List 1 exhaust valve 2 cam 5 rocker arm 6 rocker shaft 8 actuator

Continued on the front page F term (reference) 3G065 AA01 AA09 CA00 CA24 DA02 DA04 EA05 EA11 EA12 GA29 KA04 3G092 AA02 AA06 AA11 DA02 DA06 DA15 DC13 DG06 DG07 EA12 FA13 FA34 GA13 GA17 GA18 HF25Z

Claims (3)

[Claims] 1. An exhaust brake valve interposed in an exhaust passage of an engine, and an exhaust valve for communicating the inside of a cylinder with the exhaust passage in synchronization with engine rotation, wherein the exhaust brake valve is closed when a brake is operated. Let
In a compression pressure release type brake for an engine in which the exhaust valve is opened other than in the intake stroke and the exhaust valve is temporarily closed in the compression stroke, a section before and after a valve closing section in the compression stroke when the brake is operated. A compression pressure release type brake for an engine, wherein the maximum lift amount of the exhaust valve is made different. 2. The compression pressure release of the engine according to claim 1, wherein the maximum lift amount of the exhaust valve is set to be lower in a section before the valve closing section in the compression stroke than in a section after the valve closing section. Expression brake. 3. The compression pressure release of the engine according to claim 1, wherein the maximum lift amount of the exhaust valve is set to be higher in a section before the valve closing section in the compression stroke than in a section after the valve closing section. Expression brake.