GB2340881A

GB2340881A - I.c. engine with outwardly-opening poppet valves held closed by cylinder pressure

Info

Publication number: GB2340881A
Application number: GB9818108A
Authority: GB
Inventors: Benzion Olsfanger
Original assignee: KLAFF SHARON DIANNE
Current assignee: KLAFF SHARON DIANNE
Priority date: 1998-08-19
Filing date: 1998-08-19
Publication date: 2000-03-01
Anticipated expiration: 2018-08-19
Also published as: GB9818108D0; GB2340881B

Abstract

An internal combustion engine having poppet valves (2) associated with inlet and outlet ports (1) and positioned externally of the cylinder (6a), each poppet valve having a piston (5) fixed thereto which is slidable in a chamber (5c) on movement of the valve between open and closed positions. Ducting (8-10) connects the cylinder (6a) to each chamber (5c) for supplying, in use, pressurised gas from the cylinder to the chamber (5c) to provide a closing force acting on the piston (5) when the valve is in its closed position. The engine may be a four-stroke opposed piston engine (figs.1-3) in which one piston (63) reciprocates at twice the frequency of the other (62).

Description

2340881 An Internal Combustion Engine This invention relates to an

internal combustion engine and in particular, but not exclusively, to an opposed piston internal combustion engine. The invention also relates to a method of preventing inadvertent opening of an outwardly opening engine poppet valve.

Opposed piston engines have been known for many years. One design of such known opposed piston engines is disclosed in both US-A-4,010,611 and FR-A2,505,930 and comprises a pair of opposed pistons which reciprocate within a common cylinder at frequencies one'of which is twice that of the other one. The chamber defined by the cylinder and the opposed pistons varies in volume during the operating cycle of the engine and each piston reciprocates within a common part of the cylinder during each cycle. Combustion fluid is supplied to the chamber via a valved inlet port in the cylinder for subsequent compression, ignition and expansion. The compressed, ignited and expanded gas is exhausted from the chamber via a valved outlet port in the cylinder. The design of the valved inlet and outlet ports is important for the operation of the engine as conventional poppet valves opening into the cylinder cannot be employed since they would interfere with the reciprocating opposed pistons. However, in neither US-A-4,010611 nor FR-A- 2,505,930 is the question of inlet/outlet port design discussed in detail.

In GB-A-2,212,857 there is disclosed an internal combustion engine having a cylinder provided with inlet and outlet ports and poppet valves associated therewith. Each poppet valve is positioned externally of the cylinder and has a stem terminating in a valve head. The poppet valve is urged by a valve spring acting in a first direction'along the valve stem towards the valve head into a port-closing position. To open the port, it is necessary to move the 2 poppet valve in a second direction opposite to said first direction in opposition to the spring force. However, to ensure that the poppet valve remains in a port-closing position for the required period of an operating cycle, it is necessary to ensure that the valve spring is large and this complicates the design and operation of the engine.

Another known poppet valve assembly for opening and closing the inlet and outlet ports of a cylinder is disclosed in GB-A-2,264,535. This known specification is concerned with the provision of a mechanical stop mechanism for preventing a poppet valve from inadvertently moving out of a port closing position during an engine operating cycle.

The present invention seeks to provide an improved method of preventing inadvertent outward opening of a poppet valve during an engine operating cycle.

According to one aspect of the present invention an internal combustion engine comprising a cylinder having an inlet port for supplying combustion fluid to -the cylinder for subsequent compression, ignition and expansion therein and an outlet port for exhausting compressed, ignited and expanded gas from the cylinder, a separate poppet valve associated with each of said inlet and outlet ports and positioned externally of the cylinder, each poppet valve being movable between open and closed positions and including a valve spring providing a spring force acting in a first direction, and valve actuating means for moving during the engine cycle each poppet valve from said closed position to said open position in a second direction opposite to said first direction and in opposition to said spring force, is characterised in that a separate piston is fixed to each valve for reciprocating movement in a cylindrical chamber on movement of the valve between its open and closed positions, in that a separate port means opens into each cylindrical chamber and is closed by the associated piston when the valve is in its open position and 1 s open for communication with the cylindrical chamber when - 3 the valve is in its closed position, and in that duct means connect the cylinder with each port means, whereby in use pressurised gas from the cylinder is supplied via the duct means to each cylindrical chamber when the associated valve is in its closed position for providing a force acting on the piston to resist movement of the valve in the second direction out of its closed position.

Whilst a valve is in its closed position, gases at high temperature and pressure are fed from the cylinder to the cylindrical chamber associated with the valve to hold the valve in the closed position. The operation of the valve actuating means to open a valve, relieves the high pressure in the cylinder, and the associated cylindrical chamber, so that opening of the valve is not resisted.

is Preferably each valve comprises a valve stem, to which the piston is fixed, slidably received in a valve guide.

Preferably each valve and its associated piston are made of lightweight material, e.g. lightweight gamma- aluminide material, to reduce acceleration and deceleration force stresses.

Suitably the duct means comprises pipe means connecting each port with the cylinders, each pipe means passing through cooling means, e.g. a water cooling duct.

According to another aspect of the present invention there is provided a method of preventing inadvertent opening of an outwardly opening poppet valve when the latter is in a closed position closing a port opening into a combustion chamber of the engine, the method comprising supplying pressurised gas from the combustion ' chamber to assist in keeping the poppet valve in said closed position.

4 An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of part of an internal combustion engine according to the invention in the form of an opposed piston engine; Figures 2 and 3 illustrate in more detail the cylinder and pistons of the opposed piston engine shown in Figure 2; Figure 4 illustrate the slow-speed crank positions for the slow speed piston of the opposed piston engine shown in Figures 1 to 3; Figure 5 is a sectioned side-view of a poppet valve assembly for a cylinder of an internal combustion engine according to the invention of the opposed piston type; Figure 6 is a partly sectioned plan taken on the line VI-VI of Figure 5; Figure 7 is a partly sectioned view taken on the line VII-VII of Figure 5; and Figure 8 is a enlarged view of a detail of the poppet valve assembly shown in Figure 5.

Figures 1 to 4 illustrate an embodiment of an internal combustion engine according to the present invention in the form of a variable four-stroke opposed piston engine. Figure 1 shows the ends 62a and 63a of a pair of opposed pistons 62 and 63 movable towards and away from each other in a cylinder 6a defined by a cylinder wall 6. Piston 63 reciprocates within the cylinder at twice the frequency of piston 62. The piston. ends 62a and 63a are shaped or angled and the volume enclosed between the piston ends and the cylinder wall 6 constitutes the open chamber which varies in volume during the operating cycle of the engine as the pistons 62 and 63 reciprocate within the cylinder. The wedge shaped portion 64 of the open chamber is preferred since it creates, in use, turbulence at the end of the compression stroke, and provides a comparatively cool pocket for the last portion of the charge to burn. This permits the use of a higher compression ratio without knock.

Figures 2 and 3 illustrates in more detail the construction of the engine and illustrates different piston positions I, II, III, IV, (III), (II), (I), VII, VIII, IX and X over one slow speed engine revolution and one variable four-stroke thermodynamic cycle. The cylinder wall 6 has an inlet port li and an outlet port lo formed therein which are openable and closable by an inlet poppet valve 2i and an outlet poppet valve 2o, respectively. The poppet valves 2i and 2o seat on valve seats 4i and 4o, respectively, in the closed positions of the poppet valves. A spark plug 61 is mounted in the wall 6. However if the engine comprises a compression-ignition engine instead of a spark ignition engine, the spark plug would be replaced by a fuel injector. The wedge-shaped chamber 64 makes possible the insertion of the spark plug 61 which, of course, would not be feasible if the piston ends were not shaped or angled. The movements of the pistons 62 and 63 within the cylinder 6a during an operating cycle are described below.

The inlet port li is located at a minimum distance Z from the end of piston 63 in the full line position (position I) of the pistons 62 and 63. In position I, the pistons 62 and 63 are located at their positions of minimum clearance corresponding to slow speed crank angle Oc (see Figure 4) and the distance between them is the closeclearance distance 65 of Figure 1. Poppet valve 2i is already partially open as described hereafter, but the port 1i is masked by the piston 63. In position I, the outlet valve 2o is in its closed position and the clearance volume is filled with residual exhaust gas. Position I is, of 6 course, transient, both pistons 62 and 63 moving towards the right in the suction stroke and 63 drawing away from 62.

In position II, piston 63 begins to uncover port li, t he residual gases having expanded sub-atmospherically, which is beneficial for the induction of the fresh charge.

In position III, the inlet port 1, is completely uncovered and the inlet valve 2i is completely or almost completely open.

In position IV, at the end of the suction stroke, piston 63 is in its inner dead-centre position relative to the centre of the high-speed crankshaft, whilst piston 62 is in its outer dead-centre position relative to the centre of the low-speed crankshaft and the piston end is located at the end of the inlet port li.

Both pistons 62 and 63 begin to reverse their motions a nd during the compression stroke they occupy, in reverse order, positions (III), (II) and (1) corresponding to positions III, II and I.

Figure 4 shows the corresponding slow-speed crank positions over one slow-speed crank revolution. The corresponding slow- speed crank positions in Figure 4 during suction are 1, 11, 111, IV and during compression the corresponding crank position are (III), (II) and (I) as shown in dotted lines. At crank position V the inlet valve 2i closes. At crank positions I and (1) the angle is Oc as shown. Between positions (II) and (I), ignition occurs and - the valves 2i and 2o are shielded by the pistons from the high combustion temperatures and pressures.

Figure 3 shows pistons 62 and 63 in positions (I), VII and VIII during expansion. Piston 62 moves towards the left from position (1) drawing away from piston 63. Piston 63 moves initially to the left and follows piston 62 until it reaches position VII when it is in its outer dead-centre 1 - 7 position relative to the centre of the high-speed crankshaft and then it reverses its motion. During its motion from position (I) to position VII and back to position (I), the piston 63 shields the valve 2i and partially shields valve 2o. From position VII, pistons 62 and 63 move in opposite directions until they reach position VIII, when piston 62 is at its inner dead- centre position relative to the centre of the low-speed crank shaft and piston 63 is at its inner dead-centre position relative to the centre of the high- speed crankshaft, this completing the expansion stroke. At slow-speed crank position VIII, the outlet valve 2o begins to open. At position VIII pistons 62 and 63 reverse their respective motions and approach each other in the exhaust stroke. When they reach position IX piston 63 has masked inlet port li and inlet valve 2i begins to open at slowspeed crank position IV. Piston posi.tion X is identical to piston position VII. At position X piston 62 moves to the right whilst piston 63 is at its outer dead-centre position relative to the centre of the high-speed crankshaft. Piston 26 63 reverses its motion and commences to move to the right with piston 62 closing in on piston 63 until the position of close clearance I is again reached, this completing the exhaust stroke and one thermodynamic cycle. At position I the outlet valve closes and the next thermodynamic cycle commences.

In use of the internal combustion engine described above, high gas pressure occurs within the cylinder 6a during the period of the engine cycle when the gas contained in the cylinder is compressed, ignited and expanded. The present invention is primarily concerned with designing the poppet valves to prevent this gas pressure from prematurely lifting the poppet valves out of their port-closing positions.

outwardly opening poppet valve assemblies, in particular for opposed piston engines, have been described in GB-A-2,212, 857 and GB-A-2,264,535. These prior art specifications addressed the problem of preventing - 8 inadvertent outward opening of the poppet valves in different ways. In GB-A-2,212,857 it was suggested that the valve spring needed to be stif f to prevent inadvertent valve opening and in GB-A-2,264,535 a - mechanical stop was 5 disclosed to prevent the poppet valve inadvertently opening. The poppet valve assembly disclosed below with reference to Figures 5 to 8 describes a further more elegant solution for preventing inadvertent poppet valve opening. Poppet valves for closing inlet and outlet ports li and lo are basically of the same construction but are opened and closed at different times. In the following description, the same reference numerals will be used to describe those parts which correspond to parts described with reference to Figures 1 to 3 but without the use of the "inlet" and "outlet" designators "ill and 'loll, respectively.

Figures 5-8 show an opposed piston engine of the kind described above with reference to Figures 1 to 4 and which includes a number of cylinders 6a defined by cylinder walls 6 and a "cylinder head" or first housing part 40 integrally formed with the cylinder walls 6 defining a valve chamber 3, having a gas port 34, the chamber 3 enabling the passage of gas under suction pressure into or out of the cylinders 6a through cylinder ports 1. Cooling channels 7 for cooling fluid, e.g. water, are formed in the housing part 40.

Further cooling channels 32, 33 are shown in Figure 7.

A number of second housing parts 19 are detachably attached to the first housing part 40 for the mounting of poppet valves 2 (only one of which is shown in Figure 7) externally of the cylinders 6a to enable opening and closing of the ports 1. As shown in Figure 5, this detachable attachment of the housing parts 19 and 40 is conveniently provided by bolts 15 and lock washers 14. Only one of these poppet valves 2 will be described in detail.

Each poppet valve 2 comprises an elongate valve stem 2a received for reciprocation in a detachable valve guide 12 and a valve head 2b at one end of the valve stem 2a. A 9 piston 5 is fixed on the valve stem 2a for sliding movement within a cylindrical opening Sa formed in the cylinder head 40. A cylindrical chamber Sc is formed in the cylindrical opening 5a between the valve guide 12 and the piston 5. The poppet valve is movable between a port-closing position (shown in full lines in Figure 5) and an open position (shown in Figure 7 and in dashed lines in Figure 5). In the port-closing position of the valve 2, the valve head 2a rests on the valve seat 4 which surrounds the port 1 and which is hardened and machined. The valve guide 12 has an axial bore in which is positioned a bush 13 for axially slidably receiving the valve stem 2a.

The end of the valve stem 2a remote from the valve head 2b is tapered and threaded and carries a valve spring retainer 16 which is retained on the valve stem by means of a nut 18 and lock washer 17. Between the end of the second housing part 15 and the valve spring retainer 16 there is an axial space in which a pre- compressed valve spring 20 (shown in its valve-open position in Figure 5) is positioned. This valve spring 20 acts on the retainer.16 and exerts a spring force directed in a first axial direction for urging the poppet valve 2 towards its port-closing position.

An opening is formed in a wall of the housing part 19 through which opening there extends a bifurcated limb 22b of a, rocker arm 22. As shown in Figure 6, the legs of the bifurcated limb 22b are positioned on either side of the valve stem 2a and are arranged beneath the valve spring retainer 16. The rocker arm 22 forms part of valve gear for operating the poppet valve 2. On pivoting the rocker arm 22 about the axis of its rocker shaft 32, the bifurcated limb can be arranged to press against the underside of the retainer 16 and to lift the valve 2 in a second axial direction opposite to the first axial direction in opposition to the spring force exerted by the valve spring 20 thereby lifting the valve head 2b clear of the valve seat 4 and opening the port 1. During valve opening a valve inertia force acts towards the valve head 2b during acceleration and away from the valve head during deceleration. During valve closing the valve inertia force acts away from the valve head 2b during acceleration and towards the valve head during deceleration. Separation of the valve from the spring retainer 16 when the inertia force acts towards the valve head is inhibited by the nut fastening. During valve closing the valve spring force is transmitted via the spring retainer 16 to the tips of the bifurcated limb 22b of the rocker arm and thence via the valve gear, which is described hereafter, to a cam 31. When the valve is in the closed position, tappet clearance ensures that the valve spring force is transmitted via the spring retainer 16 to the poppet valve 2 and thence to the valve seat 4. The rocker shaft 32 is supported by brackets on the housing part 19 as shown in Figure 6. Reference numeral 23 is a rocker arm bush and reference numeral 24 designates wearing washers.

The rocker arm 22 has another limb 22a disposed at approximately 900 to the limb 22b. The free end of the limb 20. 22b contacts one end of an elongate cam follower 25 slidably received in an open-ended elongate chamber 29 at the upper end of the housing part 19. The opposite end of the cam follower 25 contacts the cam 31 mounted on a cam shaft 30 driven by means (not shown). The cam follower 25 consists of three different diameter circular cylindrical portions, the small diameter portion being at the end which contacts the free end of the limb 22a and the large diameter portion being at the end which contacts the cam 31. The intermediate diameter portion has a sleeve 27 thereon and is surrounded by a partly compressed helical spring 28 which has one end pressing against the large diameter portion of the cam follower 25 and its other end pressing against an annular shoulder of the open-ended chamber 29. The spring 28 thus ensures that the cam follower is urged into contact 35with the cam 31 at all times. In use the rotating cam 31 presses on the cam follower 25 to turn the rocker arm 22 to open the poppet valve 2 and the compressed spring 20 presses on the spring retainer 16 to close it.

In order to prevent inadvertent opening of the valve during the operating cycle of the engine, ducting in the form of straight pipes 8 and 10 and an elbow pipe 9 connect the combustion chamber 64 of the cylinder 6a with the cylindrical chamber Sc. The pipe 8 passes through the cylinder wall 6 and through the cooling channel 7 and the pipe 10 connects with a port 50 which opens into the side of the cylindrical chamber 5c. The port 50 is positioned so that it is open when the valve 2 is in its closed position but is closed by the cylindrical wall of the piston 5 when the valve 2 is in its open position (see Figure 8).

In use, when the valve 2 is closed, a small quantity of high pressure and high temperature gas is bled from the combustion chamber 64 and is supplied via the pipes 8-10 to the cylindrical chamber 5c defined between the valve guide 12 and the end of the piston 5. The pressure of the gas in the chamber 5c acts to press downwardly on the piston 5 to resist inadvertent opening of the valve 2. When the valve opens under the control of the cam 31, the piston moves upwards to the position shown in dashed lines in Figure 8 and closes the port 50 thereby blocking the inflow of gases from the combustion chamber 64 through the pipes 8-10. Of course as soon as the valve 2 begins to open, gas from the combustion chamber 64 can exit the port 1 and pressure within the cylindrical chamber 5c will be relieved.

An opening 11 is conveniently formed in the housing part 40 to enable the pipe 10 to be fitted. The pipe 8 is suitably fitted via the engine cylinder 6a. The pipes 8 and 10 should be tight fits, preferably received in machined holes. Ideally the valve 2 and piston 5 should be made of lightweight material, e.g. gamma-aluminide material, in order to reduce acceleration and deceleration stress forces in use. The valve guide 12 acts as a "shield', defining one end of the cylindrical chamber Sc and should be made of a suitable material. Seals (not shown) may be provided to seal the valve stem 2a with the bush 13 in the axial bore of the valve guide 12.

12 Ducting is of course required for both inlet and outlet poppet valves of an engine according to the present invention.

The stiffness of the valve spring 20 and the amount 6f spring precompression are reduced by the provision of the pipes 8-10. The cylinder fluid pressure tending to lift the valve is at a maximum at or near the commencement of gas expansion and drops rapidly, over a comparatively small portion of the expansion stroke and its duration period, down to much lower values. The gas bled from the combustion chamber 64 and fed to chamber 5c through the pipes 8-10 counteracts the lifting force when the latter is at its maximum - i.e. in the valve-closed position. The valve 20 assists in supplying the closing force to maintain the valve 2 in its closed position and also provides a restoring force to urge the valve 20 towards its closed position when the valve is moved out of its closed position.

Although the present invention finds specific application in opposed piston engines, it will be appreciated that the invention can be applied to other types of internal combustion engines having poppet valves openable outwardly of the working cylinder(s) of the engine.

Claims

1. An internal combustion engine comprising a cylinder having an inlet port for supplying combustion fluid to the cylinder for subsequent compression, ignition and expansion therein and an outlet port for exhausting compressed, ignited and expanded gas from the cylinder, a separate poppet valve associated with each of said inlet and outlet ports and positioned externally of the cylinder, each poppet valve being movable between open and closed positions and including a valve spring providing a spring force acting in a first direction for urging the valve into said closed position, and valve actuating means for moving during the engine cycle each poppet valve from said closed position to said open position in a second direction opposite to said first direction and in opposition to said spring force, characterised in that a separate piston is fixed to each valve for reciprocating movement in a cylindrical chamber on movement of the valve between its open and closed positions, in that a separate port means opens into each cylindrical chamber and is closed by the associated piston when the valve is in its open position and is open for communication with the cylindrical chamber when the valve is in its closed position, and in that duct means connect the cylinder with each port means, whereby in use pressurised gas from the cylinder is supplied via the duct means to each cylindrical chamber when the associated valve is in its closed position for providing a force acting on the piston to resist movement of the valve in the second direction out of its closed position.

2. An engine according to c ' laim 1, in which each valve comprises a valve stem, to which the piston is fixed, slidably received in a valve guide.

3. An engine according to claim 1 or 2, in which each valve and its associated piston are made of lightweight material, e.g. lightweight gamma-aluminide material, to reduce acceleration and deceleration force stresses.

14 -

4. An engine according to any one of the preceding claims, in which the duct means comprises pipe means connecting each port with the cylinders, each pipe means passing through cooling means, e.g. a water cooling duct.

5. A method of preventing inadvertent opening of an outwardly opening poppet valve when the latter is in a closed position closing a port opening into a combustion chamber of the engine, comprising supplying pressurised gas from the combustion chamber to assist in keeping the poppet valve in said closed position.

6. A method according to claim 5, wherein the poppet valve includes a valve stem on which a piston is mounted, the piston being slidable in a cylindrical chamber, and wherein the said pressurised gas is supplied to said cylindrical chamber when the poppet valve is in its closed position.

7. An internal combustion engine substantially as herein described with reference to, and as illustrated in, Figures 1 to 8 of the accompanying drawings.

1 Amendments to the claims have been filed as follows CLAIMS 1. An internal combustion engine comprising a cylinder having an inlet port for supplying combustion fluid to the cylinder for subsequent compression, ignition and expansion therein and an outlet port for exhausting compressed, ignited and expanded gas from the cylinder, a separate poppet valve associated with each of said inlet and outlet ports and positioned externally of the cylinder, each poppet valve being movable between open and closed positions and including a valve spring providing a spring force acting in a first direction for urging the valve into said closed position, and valve actuating means for moving during the engine cycle each poppet valve from said closed position to said open position in a second direction opposite to said first direction and in opposition to said spring force, characterised in that a separate piston is fixed to each valve f or reciprocating movement in a cylindrical chamber on movement of the valve between its open and closed positions, in that a separate port means opens into each cylindrical chamber and is closed by the associated piston when the valve is in its open position and is open for communication with the cylindrical chamber when the valve is in its closed position, and in that duct means connect the cylinder with each port means, whereby in use pressurised gas from the cylinder is supplied via the duct means to each cylindrical chamber when the associated valve is in its closed position for providing a force acting on the piston to resist movement of the valve in the second direction out of its closed position.

5. A method of preventing inadvertent opening of an outwardly opening poppet valve when the latter is urged by spring means into a closed position closing a port opening into a combustion chamber of the engine, comprising supplying pressurised gas from the combustion chamber to assist the spring means in keeping the poppet valve in said closed position.