GB2184783A - Poppet valve gear - Google Patents

Abstract

A valve arrangement comprising a reciprocable valve (4) which is biased into a closed position by a spring (3) disposed between two spring seats (1 and 2) whose separation in the direction of movement of valve (4) is variable. Respective levers (8, 10 and 9, 11) are operatively coupled to the seats (1 and 2) and are simultaneously operated by a cam disc (25) to move the valve to its open position whilst maintaining the separation between the seats (1 and 2) during at least an initial portion of the opening movement.

Description

SPECIFICATION Delayed Tension Valves This invention relates to the operation of reciprocating valves of the type commonly used in internal combustion engines. This type of valve is generally known as a "Poppet Valve", and is used in combination with a cam device. The resultant arrangement is employed in order to allow the internal combustion engine to "breath" i.e. in most four-stroke engines, it is normal to employ one intake valve and one outlet or exhaust valve per cylinder.

In order to better define the opening and/or closing characteristics of the reciprocating valve, there have been many different approaches made, ranging from the normal push-rod/rocker/valvespring types, to the more exotic desmodromic designs. However, the desire to reach perfect operating characteristics has always been tempered by the cost of manufacture and the reliable performance. The mechanical desmodromic approaches, although able to offer a more ideal opening/closing envelope, are costly to manufacture and noisy in operation.

Ideally, each valve (outlet or inlet) should be made capable of reaching its designed lift elevation instantaneously, remain open for the whole of its designed period, and close instantaneously.

However, in practice, it is very difficult to achieve anything like this requirement as a steeply profiled cam is both noisy and prone to excessive wear.

Furthermore, the weight of the valve/spring combination prohibits truly rapid acceleration as this would place under strain upon various components involved.

The present invention aims to provide an improved valve arrangement and, to this end, there is provided a valve arrangement in which a reciprocable valve member is biased into a closed position by resilient means extending between two abutment members whose separation in the direction of movement of the valve member is variable, and actuating means are provided for moving one of the abutment members to which the valve member is operatively coupled to displace the valve from its closed position toward an open position and for moving the other abutment member to maintain the separation of the abutment members during at least an initial portion of the movement of the valve member.

An advantage of the present invention is that the opening of the valve and the tensioning of the return spring or fluid etc, is no longer confined to a single action, i.e., in opening the valve and compressing the return spring, large loads are created and a very narrow time factor is involved, with the onus of compromise too heavily upon the successful operation of the necessary components which result in restraints being included in the basic initial design of almost every internal combustion engine.

The present invention retains the use of basic well-known valve gear components together with a small amount of desmodromic thinking. The result is a semi-desmodromic device which retains the simplicity of the normal gear-train but imbues it with the meticulous and exacting performance capabilities of the best desmodromic types.

The present invention enables the use of steeply graduated, flat-peak cams without the hitherto inherent mechanical problems normally associated with this approach.

For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 shows the basic principles of the invention applied to a single poppet valve; Figure 2 is a plan view of cam disc as shown in Figure 1; Figure 3 shows an embodiment of the invention incorporating electromagnetic actuation; Figure 4 shows a variation on the actuating means of Figure 1; Figure 5 shows a diagrammatic section of the cam disc of Figure 1; Figure 6 shows an end elevation view of an embodiment of the invention incorporating an overhead cam system.

Figure 7 is a side elevation view of Figure 6; Figure 8 shows the change in cam/follower contact angle in Figure 6; Figure 9 is a variation of Figure 8; Figure 10 shows a composite layout of a disc/ overhead embodiment of the invention; Figure 11 is a view of the cam profile of Figure 10; Figure 12 shows an overhead/cam disk layout; Figure 13 is a variation on Figure 12; Figure 14 shows an end inside/outside cam arrangement; Figure 15 shows a shaft device for accelerating the opening of a poppet valve.

Referring now to the Figures, Figure 1 is a hypothetical layout depicting a single poppet valve 4 of the overhead type, in that it is situated directly above the cylinder 28. The inlet, or outlet duct 27 is situated between the valve 4 and the manifold 29.

The cylinder-head 26 is shown to be water-cooled.

However, it should be clearly understood that this valve can be used in any type of internal combustion engine type. The valves may be placed at any angle relative to the piston crown and may be side valves, or any other layout design.

Instead of the usual single rocker-arm, Figure 1 features a double-rocker assembly with two rocker arms 8, 10 and 9, 11 being pivoted, at approximately mid point in either case on fulcrum axles 14 and 15 with shoulders 16, 17. In this embodiment, parallel movement of the rocker arms 8, 10 and 9, 11 can be effected. The length of each arm, either side of the fulcrum axles 14 and 15 is hypothetical and any desirable length can be included according to requirements. Displacement of the rocker arms is achieved by a cam disc arrangement 25 of which Figure 2 is a diagrammatic plan view and of which Figure 5 is a peripheral contour drawing. The crosssection of the cam-disc 25 depicted in Figure 1 is that shown as being cross-section X-X in Figure 5.

The cam-disc 25 is free-running upon a fixed vertical axle 20 and a means of causing its rotation is schematically indicated by a gear-tooth or sprocket member 23. However, the disc may be rotated by any suitable means, i.e. belt, chain, electric motor, hydraulic system, air pressure system etc.

The upper rocker 8, 10 is positioned with one end thereof against the upper surface of the cam disc 25, while the opposite end is fashioned so as to form a valve-cap 6 and valve-spring seat or abutment 1.

This is shown as a rigid unitary construction, however, a flexible or pivoting design could be substituted and a composite structure could be included. Furthermore, the valve is attached to the seat/cap 1,6 in the accepted manner as used in present valve arrangements.

The valve 4 is mounted in a valve-guide 5. If it is assumed that valve 4 is an intake-valve, then it will be seen that Figure 5 has been broken-up into the four-stroke cycle pattern in the following way: "a"/ "b" is the "firing" stroke; "b"/"c" is the "exhaust" stroke, "c"P'd" is the intake-stroke and "d"/"a" is the compression-stroke. The upper surface of the disc rises sharply between sections "b"P'c" and "c"/ "d" which corresponds with the opening flank of a normal lobe-type cam. However, it rises very steeply and terminates in a plateau, sustained for almost the entire length of the intake-stroke "c"/"d". The plateau, of sustained peak, ends with an abrupt downward slope, or ramp between sections "c"/"d" and "d"/"a". This second ramp corresponds with the closing section of a normal lobe-type cam.

The rocker arm 8, is placed against the upper surface of the cam disc 25 and provided with a cam follower 12. The rotation of cam-disc 25 will cause the rocker 8, to be actuated by the follower 12 coming into contact with the ramp between "b"/"c" and "c"/"d". This will cause lever 10 to rise, and lever 8 to fall. As lever 8 ig attached to valve-cap 6 and valve 4, together with spring-seat 1, then it is clear that the action of the cam-disc 25 will cause the valve to open (i.e. accelerate downwards), the spring to compress against spring-seat or abutment 2 and the action to reverse upon the plateau terminating contact at the point of the closing-ramp reaching the follower 12.However, this would be a similar action to any other valve opening/closing sequence apartfrom the steepness of the two actuating ramps.

This sequence of events, as described above, assumes that seat 2 is, as in normal valve arrangements, of rigid design. However, in the present invention, it will be seen that seat 2 is mounted upon, or attached to, rocker arm 9, 11.

Therefore, spring 3 is held between two movable seats 1 and 2. The spring 3 is no longer a set tension component; (it can be of any strength and harmonic sensitivity) but the variable separation between seats 1 and 2 enables the available tension to be placed on the spring at any point of the cycle. For example if the seat 2 was able to move downwards at precisely the same speed and, if possible, in parallel with the seat 1, then there would be no tension created at the spring 3. However, the valve would have been opened. It is assumed that spring 3 is under some sufficient tension between 1 and 2 so as to ensure that the cam followers 12 and 13 adhere to the surface contouring of the disc 25. If the underside cam track of disc 25 were without feature, then rocker arm 9, 11 would remain rigid.However, Figure 5 indicates that at or around point "bc"/"cd" there is a parallel rise in the surface profile to that of the ramp featured on the upper surface. This will means that followers 12 and 13 will described the same trajectory, or trace, thereby moving rockers 8, 10 and 9, 11 in the same direction and at the same rate.

In Figure 4 the cam-disc 25 has been replaced by a double disc construction. This provides the possibility of further control and variation, in that the cam-disc 25a may be driven with, or independently of, cam-disc 25b.

Figures 3 and 4 offer an alternative method of effecting the initial opening function of the valve by making use of electro-magnetic and even electrostatic actuation. In the present invention, with the spring loadings being removed from the opening sequence, the energy required to open the valve in an electromagnetic system would drop considerably, thereby allowing a realistic system to be contemplated. Furthermore, as a solenoid is capable of holding a given position, once achieved, with a modest energy requirement, it would be reasonable to consider using such a device to open the valve/spring combination to its desired elevation. Once this is achieved, the solenoid would then hold its position, meanwhile allowing a mechanical cam to apply the delayed tension to the return spring.Once the desired opening period, or interval, has been accomplished, the energy being supplied to the solenoid could be either completely cut-off or reduced, thus allowing the return spring to exert its energy upon the unrestricted valve assembly, and close the valve in the normal way.

However, if a pulse of energy were again applied to the solenoid, just before the valve reached its seat 4a, then the result would be to decelerate the assembly. (Any hold, or intermittent pause, or brake situations and/or positions could be contemplated).

Figure 3 shows a solenoid 30 being used in conjunction with a single side cam-disc 25, the camtrack being featured on the underside of the disc.

The centre axle 20 of Figure 1 is replaced by a hollow post 19 in which the solenoid drive pin 31 is received in a free-running condition. The post 19 could be a separate item or as shown, part of the basic cylinder-head structure 26. Rocker arm 8, 10 has a follower 12 which engages pivotally the tip of the pin 31, thereby ensuring that any travel created in pin 31 by the solenoid 30 will be transferred directly to rocker-arm 8, 10.

As the cam disc 25 is rotated in a continuous fashion, as previously described, on reaching the position "bc"P'cd", any electrical input to the solenoid 30 will cause pin 31 to travel upwards and away from the solenoid 30. This will cause the rocker arms to respond in exactly the same way as previously described in respect of Figure 1 but without the need to provide an upper cam face. The lower contour of Figure 5 will then provide a means of placing the spring 3 under tension pressure for as long as the solenoid 30 is provided with electricity.

Therefore, the sustained peak situation is no longer the result of a mechanical cam profile coming into contact with a follower. The duration of the open condition of the valve and tye degree of opening are now, in this example, a function of the electrical input to the solenoid and the duration of said input.

With this system, a new approach to valve timing is possible, in that, it is possible to use a microprocessor, for example in conjunction with the ignition distribution network, in order to determine the actuation of a particular valve, together with the duration of the dwell (sustained peak), elevation (extent of the valve's travel), and any deceleration or semi-closed situation.

The complete flexibility of such a device, as herein described, can be further contemplatd in respect of the intake valve. For example, if it is supposed that Figure 3 depicts an inlet valve assembly then, if the opening puise is supplied to the solenoid 30 at point "bc"P'cd", the lower profile G of Figure 5 will continue to apply spring tension from the point immediately after the opening-action (regardless of the amount of travel initiated). Once the valve is open, it can remain so for as long as the solenoid is supplied with electrical energy sufficient to hold the valve against the spring tension. This could, therefore, provide the valve with a means of overlapping the following stroke by any degree desirable.

Figures 6 and 7 show two views of an overhead camshaft arrangement, embodying the delayed tension principle of the present invention. This embodiment is similar in operating function to the layout described in Figure 1, however, the callipertype rockers have been replaced by a direct valve tappet 12 and a tension cage 32, both receiving their actuation from a multi-lobed camshaft 34. In this embodiment, it is possible to show something of the versatility of the invention. The overhead camshaft is a well established format and the provision of two basic cam profiles, in replacement for the single such device, is a straight-forward development. The layout depicted by Figures 6 and 7 emphasises the overall simplicity of the realisation.The profiles of cams 25d and 25c indicate a similar arrangement to that depicted in respect of the cam-disc 25 of Figures 1 and 2, in that the lift ramp of the opening/ sustaining cam 25d corresponds to a negative profile on cam 25c, i.e. the falling section on cam 25c is shown as being a mirror profile of the rising section of cam 25d. This means that as the cam shaft 34 rotates as indicated, the lift ramp on 25d causes the follower 12 to open the valve 4 and follower 13a, attached to the cage device 32, also moves in the same direction and at the same rate of acceleration.

This results in the cage 32, the top spring-seat 1, the valve 4, the spring 3, and the lower spring-seat 2 moving together without applying any compressive pressure to spring 3. However, if the evaluation of the lift ramp exceeds the length of the negative ramp, spring 3 could be made to come under compression before the peak has been reached, thereby retaining the valve well within its critical escape velocity. As spring-seat 2 is attached to cage 32, it is clear that the same delayed tensioning of the spring-seat 3 is effected, in much the same way as described in Figure 1. Therefore, it is clear that a camshaft (such as shaft 34) could be used in combination with the callipers type arrangement of Figures 1 and 2. Furthermore, the cam-disc, as depicted in Figures 1 and 2 can be used to service more than one valve.

Figures 8 and 9 indicate the change in cam/ follower contact angle as the cam ramp or lobe is followed. The increase in elevation causes the follower to assume a quite different radial pitch. The indicated rocker arm pivot assembly 14, 16 provides an at rest datum position of 1 D. As the ramp takes effect, the datum position moves up through datum points (2D/3D/4D/5D) etc., the follower 12 face to cam face angle increasing as the graduation takes place.

The increments indicated would be smooth, i.e., a sliding encompassment rather than a stepped motion. This changing in cam-track/follower pitch would enable a fuller contact area to be maintained and further possibilities to reduce the sudden change in elevation. Furthermore, Figure 9 indicates the peripheral facing inwards situation.

Figure 10 is a composite design, or layout, of a disc/overhead type of arrangement. A gear driver 23 is connected to a feed-shaft 20 which is coupled to a cam-disc 25. This in turn, comes into contact with two sets of followers, i.e., as the design includes an equal actuation from each side of the cam-disc at the same time. There are two sets of cam profiles included (see Figure 11) this means that the disc, in four-strome operation, would revolve at one quarter engine speed, rather than one half as is usual.

Therefore, when the cam-disc 25 is caused to rotate, the reaction of the cam-disc followers will cause 6a, 6 to activate seat 1 and 32 to activate seat 2. The same compressive cycle can, therefore, be presumed as in previous embodiment and variations as already described can be assumed for this layout also.

Figure 12 is also an overhead/cam-disc layout.

However, in this embodiment the spring 3 and the two seats 1 and 2 are part of the split disc construction, i.e. the seat/cap 1,6 is in point of fact, the upper of a disc arrangement as depicted in Figure 4 and seat/cap 2,23 is the lower of the pair.

However, this component also provides the drive gear 23 in composite form. As the disc assembly rotates, the oscillatory action of the two disc sections 23, 1 follow the same cyclic compression sequence as in the other variation of this principle.

However, valve 4 is attached, in free-running but constant communication, with seat 1 by way of a bearing iocated collar 37. It will be appreciated, therefore, that the valve will be prevented (by means not shown) from rotating and is confined to reciprocation only.

Figure 13 is a direct variation of Figure 4, in that, it is twin disc arrangement, However, top disc 25a has been omitted and the black arrow T indicates that any desirable means, as previously described for example, solenoid etc, may be considered for providing the top half of the device. The base section is included as for Figure 4. Further combinations of spring elements can be included and it is intended that the whole device rotates with the exception of the valve 4. However, if the spring 3 and seats 1 and 2 are intended to remain stationary, then it is necessary to include two slip type seats within the ones indicated and a device or arrangement to prevent rotation. In this embodiment, section 25b/2a/2b/2/7 reciprocates as a result of rotational involvement with fixed followers 13,13b.

Figure 14 is an inside/outside cam arrangement, suitable for use in a similar device as depicted by Figures 6 and 7. However, the outer section 39 contains the opening ramp and plateau section, and the inner section 38 includes the usual negative opening fall, together with the spring compression ramp. The followers 12 and 13 are as previously described. Rotation is as indicated by the skeletal arrow R, and the operating direction (the movement derived from the followers 12 and 13) is indicated by the solid black arrow.

Figure 15 is a shaft device for accelerating the opening of the valve without direct action of a rotating cam, i.e., the leading edge, or ramp, is replaced by a captive bolt arrangement which drives the valve into its open position by way of linear force. The shaft 45 is provided with a cross-bored cylinder 47, in which a drive spring 48 is situated and abuts a valve spring adjustment cap 44 secured into the bore. This is a similar type of spring to those described throughout. Ashieid or retaining annulus 46 is provided in order to ensure that the spring 48 is kept compressed, after being so rendered by compression ramp 42. As the shaft rotates, the spring 48 is held in compression until it reached the break in the retention wall directly above valve 4.

This allows the spring 48 to expand and drive captive piston 41 downwards and outwards, thus pushing valve 4 clear of the plateau section 39.

Therefore, the valve 4 is accelerated to an elevation equal to the sustaining peak 39 and once there, retained in the open position.

Although the above description has been given with reference to use of the invention in internal combustion engines it is envisaged that the invention is suitable for use in any situation wherein the repeated opening and closing of a valve is required.

Claims (11)

1. A valve arrangement in which a reciprocable valve member is biased into a closed position by resilient means extending between two abutment members whose separation in the direction of movement of the valve member is variable, and actuating means are provided for moving one of the abutment members to which the valve member is operatively coupled to displace the valve from its closed position towards an open position and for moving the other abutment member to maintain the separation of the abutment members during at least an initial portion of the movement of the valve member.

2. A valve arrangement according to claim 1, in which the actuating means includes a respective pivotal lever connected to each of the abutment members.

3. Avalve arrangement according to claim 2, in which the actuating means includes a face cam rotatable about an axis parallel to the direction of movement of the valve member and having at least one cam face engaged by one of the pivotal actuating levers.

4. A valve arrangement according to claim 3, in which the face cam has two cam faces engaged respectively by the pivotal actuating levers.

5. A valve arrangement according to claim 3, in which the other of the pivotal actuating levers is coupled to a solenoid operating device.

6. A valve arrangement according to claim 2, in which the actuating means includes a pair of face cams rotatable about a common axis parallel to the direction of movement of the valve member and each having a cam face engaged by a respective one of the pivotal actuating levers.

7. A valve arrangement according to claim 1, in which the actuating means includes a cam assembly rotatable about an axis normal to the direction of movement of the valve member and having respective cam profiles engaged by cam followers carried by the abutment members.

8. A valve arrangement according to claim 1 in which the actuating means comprises a cam rotable concentrically about the valve member and coupled to a drive gear for rotating the cam, having at least one cam face engaged by one of the abutment members.

9. A valve arrangement according to claim 8, in which the cam has two cam faces engaged respectively by the abutment members.

10. A valve arrangement according to claim 8, in which the other abutment member is actuated by means other than the said cam.

11. Any novel feature or combination of features disclosed herein.