EP0172197A4

EP0172197A4 - Poppet valve drive.

Info

Publication number: EP0172197A4
Application number: EP19850900956
Authority: EP
Inventors: Reginald John Hardy
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-02-20
Filing date: 1985-02-19
Publication date: 1986-07-24
Also published as: EP0172197A1; WO1985003737A1; JPS61501580A

Abstract

A valve lifting apparatus for an internal combustion engine which utilizes a shuttle (6) which is oscillated by a cranked cam (13). The valve (7) is resiliently mounted in the shuttle (6). Adjustment spiral or stepped ramp cams (21) and (24) allow variation in valve timing and valve lift. Variation can be made while the engine is running to change from a slow running to high speed engine.

Description

POPPET VALVE DRIVE

This invention relates to improvements in the manner of operation of poppett valves used in internal combustion engines and similar machines.

It is well known to use poppett valves to allow 5. entry and exit of gases to and from a cylinder of an internal combustion engine and conventionally such valves are operated by means of a cam acting directly on the stem of the valve or acting through a rocker on the stem of the valve. Conventionally such valves are spring 10. loaded so that the cam pushes the valve open and when the cam pressure is removed the spring shuts the valve.

A problem with this form of valve operation is however that at high engine speeds when the valve may open up to 50 times per second what is termed "valve

15. bounce" occurs and the valve does not shut properly.

It is therefore desirable to have a method of valve operation which has positive valve closing and such systems are known as desmodronic valves. In such valves a further cam drives an arm which lifts the valve but in such systems 20. tolerances must be such that the valve is firmly shut but not pushed any further s.hut which can cause stress in the stem of the valve.

Another problem with valves as used at the present is valve timing. The presently employed static valve

25. timing of, for instance, an engine designed for maximum high revolutions per minute and maximum energy development has a valve open cycle of long duration and a high lift. Such an engine is wasteful of fuel and has as what may be termed a "rough" operation at low revolutions per

30. minute. Conversely an engine which has a valve timing and lift cycle of short duration and low lift respectively is smooth and powerful at low engine -revolutions but is wasteful of fuel and poor producer of energy at high engine speeds.

It would therefore be desirable if a system could 5- be devised by which variable valve timing and valve lift could be achieved so that a valve setting desirable for a particular range of engine revolutions may be used.

A further problem with valves which are returned by means of springs is that the spring must necessarily

10. be powerful to shut the valve relatively quickly but at this return spring has to return all the valve opening apparatus to its closed position at great speed it necessarily is a very strong spring and subjects the valve seat and valve to great shock and strain loading.

15. At high engine revolutions this spring return system tends to "float" causing a drop in engine energy developmen and frequently mechanical malfunction if contact of the valve head and the piston crown occurs.

It is therefore further desirable if a valve system 20. can be designed which will jnot cause such shock loads upon closing the valve but will at the same time close the valve quickly and maintain it closed during the expansi and compression strokes of the internal combustion engine.

It is therefore an object of this invention to overcom 25. one or more of the above problems.

In one form therefore, the invention is said to reside in a valve lifting apparatus of an internal combusti engine, the valve lifting apparatus including a cranked camshaft and a shuttle assembly in a guide, a stem of a valve being mounted in the shuttle assembly and the cranke portion of the camshaft being received in the shuttle assembly, whereby rotation of the camshaft causes a positive reciprocation of the shuttle assembly in the guide and hence 5. moves the valve in and out of sealing engagement with a valv seat.

It will be seen therefore that the crank moves the valve into and out of engagement with the valve seat and hence positive closing of the valve will occur.

10. In one preferred embodiment, the valve stem may be resiliently mounted in the shuttle assembly such that a strong shock, load is not placed on the valve seat as the valve shuts against the valve seat.

In a further preferred form of the invention, there 15. may be provided variable length spacer means between the cranked portion of the cam shaft and the head of the valve stem within the shuttle assembly thereby enabling varation in valve lift from the valve seat and variation of valve timing.

20. In a preferred embodiment the variable length spacer means may be infinitely variable by means of a continuous spiral ramp cam.

In an alternative further embodiment the variable length spacer means may be variable by means of a series 25. of steps on a stepped spiral ramp cam.

In a preferred embodiment the resilient mounting of the valve stem in the shuttle may be by means of a spring acting between the valve stem and the shuttle. Change in length of the variable length spacer means may be provided by an arm extending from the ramp cam to outside the shuttle and being actuated by an actuation means.

In a preferred embodiment the variable length spacer means may comprise a first and second spiral stepped ramp cams each having four steps acting against each other, the first cam being mounted in the shuttle to be prevented from rotation with respect thereto and the

10. second cam being adapted to be rotated in relation to the first cam whereby movement up and down the steps varies the valve timing and valve lifting.

The actuation means may include a shaft extending past the shuttle assembly and the arm extending into ₁₅ a recess in the shaft such that longitudinal movement of the shaft may cause the variation in length of the spacer means.

Alternatively, arms may extend from both ramp cams in opposite directions to outside the shuttle so that two ₂₀ actuating shafts may be used.

In a further form the invention may be said to reside in an internal combustion engine including inlet valves and exhaust valves, the valves being actuated by valve lifting apparatus as defined in any one of the embodiments 25. discussed above.

The cam lobe provided on the cranked portion of the camshaft as discussed above has the effect that as the cam shaft rotates the tip of the lobe on the crank portion will describe a circle of slightly greater diameter 30. than that of the outer surface of the cranked camshaft. This extra lobe on the camshaft will allow a difference in valve timing and valve lifting by the following means. A variation to the amount of lift of the valve off its seat is achieved by means of increasing or decreasing the value of a dimension between the actuating cam lobe and the valve stem end. This variation is achieved by the inclusion between the cam face and the valve end _5> of two opposed stepped face plate members or ramp cams, one of which can be rotated relative to the other in a helical or spiral manner thus achieving a. variation of the dimension between the cam face and a valve end as one of the rotating step members climbs up or down 0. the steps of its opposite fixed member.

The variable movement of the helical stepped face members or ramp cams may be achieved whilst the variable cam assembly is in motion by means of a tang or arm on the rotating member protruding outside the shuttle cage 5_^ and located on a selection control device or actuation shaft which is controlled by remote action by the engine operator or engine condition and speed sensing devices.

Such devices could be in the form of an engine governi apparatus.

20 The postioning of the stepped face plate members or ramp cams in relation to.one another, at any setting may be maintained by means of corresponding nib and notch built into the faces of each step on said members to provide a series of detents on each step.

-c A pre-loaded compression may be maintained between the faces of the the two stepped face members by a com¬ pression type helical coil spring exerting a constant expansion force between the lower internal body of the shuttle and the base of the lower face cam member thus

,₀ compressing the two members together at all times and maintaining a constant offering of the cam follower surface to the actuating eccentric cam face.

It will be seen that by means of these variable dimension members the degree of lift of the valve may

5. be changed by increasing the dimension between the cam face and the head of the valve stem so in fact the cam will in effect contact the head of the valve earlier in its cycle of the rotation hence making the valve open earlier and at the same time lift the valve further-.

10. Similarly, when the valve is closing it will be held open for a longer period of time as the cam will take longer to disengage from the valve head but it will be realised that because the absolute dimension between the valve seat and the valve closing cam surface has

25_, not been changed then the valve will close the same distanc and will not have excess force on it as it closes.

It is envisaged that in one preferred embodiment four main settings of the dimension between the cam and valve head may be used for various valve settings but 20. the invention is not limited to these and may incorporate any one or more of these settings.

Broadly the settings may be a high performance setting, a normal performance setting, an idling and slow running setting and an engine retardation setting. These may 25_# be termed A, B, C and D respectively. All of the phases

A, B, C and D may be directly attributable to the combinati of the features unique in the cranked and lobed cam in conjunction with the opposing stepped face and plate members situated within the valve holding shutter assembly.

30_# It should be noted that setting D as an engine retardation setting can only be used as a supplement ?.

to any or all of settings A, B and C. An engine would not run merely on setting D.

Looking in more detail at the various settings, setting A is the setting in which the valve is open to 5. its maximum position and for as long as possible and this setting will allow for higher engine speed to be obtained before critical valve operating speeds are reached and it will as a consequence to this allow for greater volumetric efficiency at these higher engine speeds and 10. greater power development.

The second phase B setting is designed to promote greater efficiency in the medium to slow speed running, having a setting such as would be normally used in a family sedan type car engine.

15. The third phase setting C is that which would be used in a very slow speed engine such as a standing diesel engine or the like and also this is a setting designed for engine idling speeds. This setting may have a negative valve overlap timing in order to promote longer burning

20. stroke and a shorter induction stroke thus promoting complete burning of the reduced quantity of induction gases consequently reducing emitted after-burn pollutants normally found in high performance engines operating at lower speeds than their most efficient speed range.

25. The fourth phase D setting is one in which the valve timing has an extremely retarded valve opening sequence and conversely an advanced closing sequence, thus inducing a partial second compression phase near the end of the exhaust stroke. This second compression cycle with the

30. following late opening of the inlet valve exerts a braking 3.

or deceleration cycle to the engine which is particularly suitable for large diesel transport vehicle engines and the like.

This then generally defines the present invention but to more clearly assist with understanding of the invention, reference will now be made to the accompanying drawings which show preferred embodiments of the drawings.

Generally, FIG. 1 shows a cross-sectional view of a valve assembly according to this invention looking

10. along the length of the cam shaft.

FIG. 2 shows a cross-section 2-2 in FIG. 1, showing particularly the method of variation of valve timing.

FIG. 3 shows a further view of the shuttle assembly, looking at right angles to the length of the camshaft 15. as seen in FIG. 1.

FIG. 4 shows a schematic view of a stepped ramp cam according to this invention.

FIG. 5 shows a same schematic view of a stepped ramp cam according to this-^"invention in its widest open 20. position.

FIG. 6 shows one embodiment of a stepped ramp cam according to this invention.

FIG. 7 shows a continuous spiral ramp cam according to this invention.

25. FIG. 8 shows a range of exhaust and inlet cycles obtainable by the preferred embodiment of this invention an FIG. 9 shows an alternative embodiment of spiral ramp cams having actuating arms extending from each cam.

Now looking more closely at the drawings, FIG. 1 shows a shuttle assembly generally 1 mounted in an engine 5. block 2 within a guide 3 and including a nib 4 extending from the shuttle assembly 1 and running in a track 5 in the head 2.

The shuttle assembly 1 consists of a generally cylindrical outer casing 6. Extending from the lower

10. end of the cylindrical casing 6 is a valve stem 7 extending through a valve guide 8 into an inlet or exhaust port 9 to a valve head 10 sitting on a valve seat 11. The valve stem 7 is resiliently mounted to the lower end of the casing 6 by means of spring 12, the complete functio

15. of which will be described later.

A cranked cam shaft 13 extends through an aperture not shown, in the walls of the cylindrical casing and an upper cam follow 14 bears against the upper face of the cam shaft. A lower cam follower 15 bears against 20. the lower side of the cam 13. A lobe 16 is provided on the cam 13 extending in the same direction as the direction of the crank from the main axis of the cam shaft as can be seen more clearly in FIG. 3.

Above the cam follower 14 a nut 17 and a lock nut 25. 18 internally threaded into the casing 6 and a locking cotter pin 19 is provided to ensure that the lock nut 18 will not move.

The lower cam follower 15 is mounted by means of a circlip 20 into an upper stepped ramp cam to provide 30. a wear face for this cam and the upper stepped ramp cam 21 is prevented from rotation within the shuttle by means of a nib 22 extending into a notch 23 in the cylindrical casing 6. A lower stepped ramp cam 24 is rotatable with respect to the upper stepped ramp cam 21 by means of 5. an arm 25 extending from the lower stepped ramp cam and extending through an aperture 26 in the cylindrical casing to a tang 27 received in a slot _28 in an actuation member - 29.

The head 30 of the valve stem 7 bears directly onto 10. the centre of the lower stepped ramp cam 24 and hence with rotation of the^' crank 13 the whole shuttle assembly 1 and hence the valve stem 7 moves but by movement of the actuation member 29 so that the stepped ramp cam member moves to a different position, the amount of opening 15. of the valve will be varied as the distance between the head of the valve 30 and the face of the cam 13 determines the amount of valve opening and the valve timing. It is to be noted that in fact it does not alter th.e actual distance the valve closes because this is determined by the position 20. of the upper cam follower 14 which bears upon the upper fac of the cam and determines the closing position of the cam.

The head of the valve. €tern 7 includes a spring cap 31 and collets 32 of known construction, to provide a spring receiving surface for the spring 12 which acts 25_# between the valve stem 7 and the casing 6. This spring reduces shock loading on the valve head 10 as the valve is opened and shut.

Spring 33 acts between the lower end of the casing and a distance piece 34 which bears against the lower 30. stepped ramp cam and hence the spring 33 maintains the two ramped cams pressed against each other and hence pressed against the lower face of the cam 13. Now looking at FIG. 2, it will be seen that the actuating arm member 29 can move the tang and hence arm and stepped ramp cam 24 into positions denoted A, B, C and D which give variable timing and valve opening as 5. will be discussed below.

FIG. 3 shows a view of the shuttle assembly 1 in an engine block 2 at substantially right angles to the view shown in FIG. 1 without a cut away view of the shuttle assembly 1. It can be seen in this view that the stepped

10. portion 13 of the cam shaft 35 has a lobe 16 extending therefrom and this lobe 16 bears against lower cam follower 15. The upper and lower stepped ramp cams 21 and 24 are shown generally in section but it can be seen that the arm 25 extends from the centre of the lower stepped

15. ramp cam 24.

It will be seen in this view that the valve head 10 has extended a distance generally shown by the arrows 36 but that if the stepped ramp cams were at the full length of their adjustment then the opening would be the 20. amount as shown by the arrows 37 as shown by the dotted face 38 of the valve head.

.« FIG. 4 and FIG. 5 show the extremes of position of the stepped ramp cams according to this invention.

In FIG. 4 the tallest portion A of each step are 25. furthest apart and hence the distance 39 between the upper and lower surfaces of the cams is least whereas in FIG. 5 where the steps A are adjacent to each other the distance 40 is greater by the amount distance 41.

This distance 41 is equivalent to the difference 30. in distance 36 and 37 of the valve opening as shown in FIG. 3. FIG. 6 shows a view of one of the stepped ramp cams of this invention and it will be seen that on each stepped ramp cams two sets of steps are provided so that balance may be maintained. In this view the upper cam is shown 5. with the locating nib 23 extending from one side. A series of slight ramps 42 is provided between each step

A, B, C and D on the ramped cams to enable stepping between the various levels.

FIG. 7 shows an alternative form of ramp cam where 10. a continuous spiral surface 45 is provided on each cam surface so that an infinitely variable amount of valve opening can be obtained between the maximum and minimum levels.

This view FIG. 7 shows the upper and lower cams 15. opposed to each other but spaced apart for- clarity purposes and it will be seen that the upper cam 7 has the nib 23 to prevent it rotating whereas the lower cam 24 has arm 25 extending from it to tang 27 so that it may be actuated by the actuation member 29 as seen in FIG. 2 20. to vary the spacing between the upper and lower surfaces of the ramp cam pair.

FIG. 9 shows an alternative embodiment of spiral ramp cams in which arms 50 and 51 extend from upper and lower ram cams 52 and 53 respectively. These cams are of the spiral 25. kind with spiral ramps 54 but the stepped ramp cams may also be used with two arms.

FIG. 8 shows the variation in exhaust and inlet valve opening for the series of cycles A, B, C and D for a preferred embodiment of the invention, but it is 30. to be realised that the invention is not restricted to these particular values but may be used for any particular value dependent upon the type of engine. It will be seen that in cycle A as shown on FIG. 8, rotatio of the engine is shown generally by the arrow 46 and it wil be seen that the inlet opens 45 degrees before top dead centre and closes 68 degrees after bottom dead centre while 5. the exhaust opens 68 degrees before bottom dead centre and closes 45 degrees after top dead centre. The considerable overlap provided by this means enables efficient scavenging of gases at very high engine revolutions per minute and efficient charging of the cylinder upon inlet.

20. Cycle B provides a more conventional engine setting for engines running at normal speeds with the inlet opening 26 degrees before top dead centre and closing 50 degrees after bottom dead centre while exhaust opens 50 degrees before bottom dead centre and closes 26 degrees after

15. top dead centre.

Cycle C provides an efficient cycle for low speed diesel engines, slow running of normal petrol engines and idling running for such engines. In this embodiment the inlet does not open until 4 degrees after top dead 20. centre and closes 24 degrees after bottom dead centre. The exhaust opens 24 degrees before bottom dead centre and closes 4 degrees before* top dead centre.

In the cycle D which is a braking or retardation cycle particularly useful for large diesel engines the

25. inlet does not open until 30 degrees after top dead centre and closes 3 degrees before bottom dead centre so that minimal charging occurs and the exhaust does not open until 3 degrees after bottom dead centre and closes 30 degrees before top dead centre so that a further compressio 0_ occurs in the 30 degrees between exhaust closing and top dead centre which provides an engine braking effect. The inclusion of the wear plate cam surface and the ramp members are for wear compensation and precise valve timing adjustment by having a replaceable hardened steel cam follower interplaced between the cam face and variable 5. stepped cam members. This steel cam follower additionally may be designed to be incremental in depth dimension by a .mean value plus or minus increments of multiples of one thousandth of an inch for instance thus allowing for accurat adjustment of dimensions between the end of the valve -stem 10. • and the face of the cam facilitating wear compensation and engine building specification compliance.

Claims

i s

1. A valve lifting apparatus of an internal combustion engine, the valve lifting apparatus including a cranked cam shaft and a shuttle assembly in a guide, a stem of the valve being mounted in the shuttle assembly and the

5. cranked portion of the cam shaft being received in the shuttle assembly whereby rotation of the cam shaft causes a positive reciprocation of the shuttle assembly in the guide and hence moves the valve in and out of sealing engagement with a valve seat.

2. A valve lifting apparatus as in claim 1 wherein the valve stem is resiliently mounted in the shuttle assembly.

3. A valve lifting apparatus as in claim 1 or claim 2 wherein the cranked cam shaft further includes a cam extending from the apex of the cranked portion of the camshaft.

4. A valve lifting apparatus as in any one preceding claim, further including variable length spacer means between the cam shaft and the head of the valve stem within the shuttle assembly thereby enabling variation

5. in valve lift from the valve seat and variation of valve timing.

5. A valve assembly as in claim 4 wherein the variable length spacer means is variable by means of a series of steps on a stepped spiral ramp cam.

6. A valve lifting apparatus as in claim 4 wherein the variable length spacer means is infinitely variable by means of a continual spiral ramped cam. 7- A valve lifting apparatus as in any one of claims 2 to 6 wherein the resilieήtly mounting of the valve stem in the shuttle is by means of a spring acting therebetween.

8. A valve lifting apparatus as in any one of claims 4 to 7 wherein change in length of the variable length spacer means is provided by an arm extending from the ramp cam to outside the shuttle assembly and actuated

5. by an actuation means.

9. A valve lifting apparatus as in claim 8 wherein the actuation means includes a shaft extending past the shuttle assembly and the arm extending into a recess in the shaft such that longitudinal movement of the shaft 5 causes the variation in length of the spacer means.

10. A valve lifting assembly as in claim 4 wherein the variable length spacer means comprises first and second spiral stepped ramp cams each having four steps and acting against each other, the first cam being mounted in the

5 shuttle to be prevented from rotation with respect thereto and the second cam being adapted to be rotated in relation to the first cam whereby movement up and down the steps varies the valve timing and^* the degree of valve lift.

11. A valve lifting apparatus as in claim 10 wherein means to actuate each of the spiral stepped ramp cams comprise arm extending from respective cams to outside the shuttle to be acted upon by actuation means.

12. An internal combustion engine including inlet valves and exhaust valves, the valves being actuated by a valve lifting apparatus as in any one of claims 1 to 11. 13. An internal combustion engine having valve lifting apparatus as hereinbefore described with reference to the drawings.

14. Valve lifting apparatus substantially as hereinbefore defined with reference to and as illustrated by the drawing