GB2478559A - Timing mechanism to provide variable valve timing in an internal combustion engine - Google Patents

Abstract

A timing mechanism to control valves to provide variable valve timing (VVT), variable valve actuation (VVA) and variable valve duration (VVD) is disclosed. The VVT mechanism comprising care means 1, 2, a cam follower 4, 5 arranged to engage the cam means 1, 2 and a linkage 7 connected at one end to the cam follower through a pin/bearing 23, 24 which may slide in an arc about the care axis and at the other end to a rocker arm 6 to actuate a valve of the engine such that movement of the pin means along the arcuate locus advances or retards the valve timing. A VVA mechanism which comprises a further rocker arm(s) that is slidingly moveable on an arcuate locus that increase/decrease the amplitude of the actuation is also disclosed. Also disclosed is a VVD mechanism comprising of a double pair of cam followers engaging cam means of which one pair of cam followers is rotatable about the care linkage. Differential inputs in form of pinion gears meshed with racks along the cam follower linkage are used to adjust the pin position.

Description

DESCRIPTION

INTERNALCOMBUSTION ENGINE VALVE CONTROL

This invention relates to internal combustion engines. In particular, this invention relates to valve control mechanisms for crankless internal combustion engines.

In a conventional internal combustion engine it is necessary to vary the valve timing to optimise engine efficiency at different engine speeds and loads. To reduce pumping losses and provide for an Atkinson Cycle' effect it is also necessary for valve timing overlap' where both inlet and exhaust valves are open during the engine cycle. For camshafts using a mainly sinusoidal valve actuation this is often referred to as phase adjustment' or Variable Valve Duration (VVD). Current systems of VVT (Variable Valve Timing) and VVD use complex systems which effectively delay/extend the rotation of a camshaft. Ideally the valve actuation is not a sinusoidal function but a step function only limited by the acceleration of the valve, not by the camshaft profile and valve spring arrangement traditionally used. For Atkinson Cycle engines ((PCT/GB2009/050858) the optimum Atkinson Ratio (induction stroke/power stroke) would also be dependant on engine speed and load conditions. This invention provides for a more efficient system where WT/VVD is used to give additional Atkinson effect' from a median Atkinson ratio base point rather than effecting the Atkinson Cycle from a position where the power stroke is equal to the induction stroke. In conventional engines the fixed geometry of the connecting rod and crankshaft, the ignition and exhaust strokes are of equal lengths and the compression ratio is effectively fixed.

Maximum efficiency is obtainable only where the exhaust stroke is shorter than the power stroke, and where the compression ratio can be tuned to a particular fuel type. However where the intake is longer than the power stroke the engine becomes self-supercharged.

Varying the valve timing by an engine cycle would enable an Atkinson cycle engine to run as a supercharged engine where the compression ratio can be tuned.

Prior art has established that variable compression ratio can improve the efficiency particularly for lean burn', homogenous charge compression ignition (HCCI) direct injection and flexible fuel engines. Internal combustion engines exist which can vary the compression ratio, valve timing, valve duration and actuation. However, these engines are costly to produce due to the complex nature of the internal mechanisms and external electro mechanic, mechatronic and hydraulic/pneumatic systems required.

In conventional fuel injection engines mass air flow is controlled using a butterfly or throttle' on the inlet manifold for high flow rates and an idling air control valve' for low flow rates. Both of these functions could be accommodated using Variable Valve Actuation using valves designed to control flow rate at the cylinder head.

This invention aims to provide a solution to one or more of the above problems and/or to provide an alternative to using conventional camshafts to control valves in internal combustion engines.

According tothefirstaspectofthe invention there is provided an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a connecting rod extending from the piston for converting reciprocating movement of the piston into rotational movement of an output shaft, and at least one valve for controlling the ingress and/or egress of a fluid into the cylinder, the valve being actuated by a linkage carrying a pair of cam followers cooperating with the surfaces of primary and secondary valve cam means which rotate with the output shaft. The surface of the primary valve cam means comprises a generally circular portion and a pair of protrusions, and the surface of the secondary valve cam means comprises a generally circular portion and a pair of indentations, a first one of the cam followers cooperating with the surface of the primary valve cam means and a second one of the cam followers cooperating with the surface of the secondary valve cam means, which protrusions and indentations cause the valve to open or close respectively as the cam followers roll there over, characterised by a stepped transition between the generally circular portion and the protrusion and/or indention of the valve cams.

Preferably, the transition from the generally circular portion to the protrusion or indention takes place within less than a few degrees of rotation of the valve cam, limited only by the maximum acceleration of the valve and piston clearance.

Additionally or alternatively to the foregoing, it is often desirable for an engine to have VVT which enables the injection of fuel into the cylinder to be advanced or retarded with respect to top-dead-centre (TDC) of the engine cycle, or the expulsion of combustion products to be advanced or retarded with respect to bottom-dead-centre (BDC) of the engine cycle. When the valve timing is advanced, the valves are opened or closed shortly before they would ordinarily do so, and conversely, when retarded, they open or close shortly after they would normally do so. There is provided a timing mechanism for an internal combustion engine, said internal combustion engine comprising an output shaft, and the timing mechanism comprising: a cam means mounted on, and rotatable with, the shaft; a cam follower arranged to engage the cam means; a linkage connected at one end to the cam follower through a pin/bearing sliding arcuate about the cam axis and such that movement of the pin means along the arcuate locus advances or retards the timing of the engine. The other end of the linkage is connected to a rocker arm; said rocker arm being connected to a further rocker arm(s) and being adapted to actuate an induction, idle or exhaust valve of the engine; wherein; the pivot means is slidingly moveable on an arcuate locus that increases or decreases the amplitude of the movement (VVA). A valve actuation can be linked to a single rocker system for VVT alone, or VVA alone, or connected using two rockers as described to provide both VVT and VVA. In VVA operation the valves have an additional function of continuously varying the flow rate. The main inlet valve(s) control the high mass flow rate to the engine and effectively replace the butterfly or throttle' valve on the inlet manifold air intake. A separate rocker is required to control the low mass flow rate valve to allow the engine to idle with varying idle speed engine loads. Flow rate control is by a varying the restriction of flow according to the valve position. The cam means may be rotatable in unison with the engines output shaft, or may be geared to rotate at half the speed of the output shaft to allow use in a conventionally cranked engine. Furthermore, the present invention is compatible with other engine regimes, e.g. a six-stroke cycle engine, in which case the cam means would be geared to rotate at one-third of the engine's output shaft speed.

According to the second aspect of the invention there is provided an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a connecting rod extending from the piston for converting reciprocating movement of the piston into rotational movement of an output shaft, and at least one valve for controlling the ingress and/or egress of a fluid into the cylinder, the valve being actuated by a linkage carrying a double pair of cam followers cooperating with the surfaces of primary and secondary valve cam means which rotate with the output shaft. One pair of cam followers is rotatable about the cam linkage with one cam follower offset by an angle equal to the primary cam protrusion angle. The indentation angle is twice the protrusion angle on the secondary valve cam. When indentation cam followers are in line the protrusion followers are set at protrusion angle and the linkage follows for the full indentation angle (maximum valve duration) as the cams rotate; when the indentation followers are set at the protrusion angle the protrusion followers are inline and the linkage follows for the protrusion angle (minimum valve duration). Continuous variable valve duration (VVD) adjustment is provided for angles between the protrusion angle and the indentation angle of the primary and secondary valve cam means.

According to a third aspect of the invention there is provided an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a connecting rod extending from the piston for converting reciprocating movement of the piston into rotational movement of an output shaft, and at least one valve for controlling the ingress and/or egress of a fluid into the cylinder, the valve being actuated by a linkage connected to a mechanical differential. One input to the differential is reversed. The inputs are gears connected to racks along a linkage carrying a pair of cam followers cooperating with the surfaces of primary and secondary valve cam means which rotate with the output shaft. The output of the differential mechanism remains fixed as the cam followers and linkage rotate about the shaft, the output only moves as the cam followers engage the protrusions/indentations on the cams. Thus the valve timing can be set for any angle, eg.

For the Atkinson Cycle engine described in PCT/GB2009/050858 changing the valve timing by 90 degrees allows the engine to run self-supercharged.

In the present invention the rocker arms, and hence the valves, are actuated directly by the timing cam means, as compared to a known VVT system in which they are actuated indirectly, for example using a cam belt or a hydraulic system. Because the engine timing is dictated by the angle of the rollers about the cams and the valve actuation dictated by the position of a pivot point on the arcuate locus it is possible to vary the valve timing, the valve actuation and valve duration in infinitely small increments.

The arcuate locus along which the pivot means is moveable may be defined by an arcuate slot or track in or on which the pivot means is slideably moveable. In a preferred embodiment of the invention the pivot means is rotated along an arcuate rack using rack and pinion gear. In such a case there is a direct relationship between the amount of rotation of the pinion gear and the amount of valve actuation. The linkage may comprise a substantially rigid rod. The linkage is preferably constrained to reciprocate axially along a straight locus that intersects the axis of the engine's output shaft. The linkage may be retained in linear bushes located on opposite sides of the engine's output shaft.

The cam follower may comprise a roller or ball bearing that is arranged to engage an edge of the cam means. A plurality of cam followers may be provided. In a preferred embodiment of the invention the cam follower comprises a pair of rollers or ball bearings arranged to engage diametrically opposite portions of the edge of the cam means. Such an arrangement enables the linkage to operate desmodromically so that the engines valves are opened and closed directly, rather than being operated against a biasing means, such as a spring. Such an arrangement can give rise to more precise control of the valves and removes the necessity for the timing mechanism to work against the force of spring.

Preferred embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic side and end view of an embodiment of VVA double rocker mechanism for a single valve shown partially open and fully open; Figure 2 is a schematic side and end view of an embodiment of VVA double rocker mechanism for a single valve shown closed; Figure 3 is a schematic end view of the WI mechanism at zero and full advance/retard; Figure 4 is a schematic sectional side view of the cylinder head inlet, exhaust and idle valve arrangement identifying inlet, exhaust and idle valve actuation control shafts; Figure 5 is a schematic top view showing of the cylinder head inlet, exhaust and idle valve arrangement identifying inlet, exhaust and idle valve actuation control gears; Figure 6 is a schematic end view of a cylinder head; Figure 7 is a exploded sectional diagram of the idle valve; Figure 8 is a schematic view of the engine with WT, VVA and VVD; Figure 9 is a component schematic of the cam linkage for WT and VVD; Figure 10 is a component schematic of the cam control for WI and WD; Figure 11 a schematic side view of the VVT VVD mechanism; Figure 12 is a schematic end view of the VVT VVD mechanism; Figure 13 is a component schematic view using planetary gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle; Figure 14 is a partial schematic side view using planetary gears for the differential providing large angle WI for Atkinson/Supercharged engine cycle; Figure 1 5 is a schematic end view using planetary gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle; Figure 1 6 is a schematic side view using planetary gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle; Figure 17 is a component schematic view using spur gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle; Figure 18 is a partial schematic side view using spur gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle; Figure 19 is a schematic end view using spur gears for the differential providing large angle WI for Atkinson/Supercharged engine cycle; Figure 20 is a schematic side view using spur gears for the differential providing large angle WI for Atkinson/Supercharged engine cycle; Figure 21 is a schematic end view using spur gears for the differential providing large angle VVT for Atkinson/Supercharged engine cycle at 90 degrees valve timing; Figure 22 is a partial component schematic of the cam control for large angle Atkinson/Supercharged for VVI; Figure 23 is partial component schematic of the cam control for large angle Atkinson/Supercharged for VVD; Figure 24 is a schematic side view of the cam linkage for large angle Atkinson/Supercharged WI mechanism with WD in Atkinson cycle configuration; Figure 25 is a schematic end view of the cam linkage for large angle Atkinson/Supercharged WI mechanism with WD in Atkinson cycle configuration; Figure 26 is a schematic end view of the cam linkage for large angle Atkinson/Supercharged VVI mechanism with WD in supercharged cycle configuration in valve open position; Figure 27 is a schematic side view of the cam linkage for large angle Atkinson/Supercharged WI mechanism with WD in Atkinson cycle configuration in valve closed position.

For ease of understanding, features common to all embodiments of the invention described herein are identified using identical reference numerals and in general refer to the engine described in patent PCT/GB2009/050858.

Figures 1 and 2 shows a primary 1 and a secondary valve cam 2 rigidly connected to the output shaft 3. For a conventional 4 stroke engine the valve cam would be connected to a separate shaft or half shaft'. The outer edge of the primary valve cam 1 cooperates with a pair of valve cam followers 4 and 5, which are connected to a valve actuation adjustment lever 6 via a rigid linkage 7. A valve actuation lever 8 is connected to the valve adjustment lever 6 with a slidable baIl 9 and tracked socket 10 which extends from the centre axis of the valve adjustment lever 6. The pivot mount 11 of valve adjustment lever 6 is fixed; the pivot mount 12 of the valve actuation lever 8 is slidable on a track 13 arcuate with valve 14.

A rack 15 arcuate with valve 14 and pinion gear 16 control the position of baIl 9 in track 10 and hence the amplitude of the valve actuation as lever 8 operates the valve 14.

The outer edge primary valve cam 1 is generally circular, but has a pair of diametrically opposed protrusions 17. The outer edge secondary valve cam 2 is also generally circular, but comprises a pair of diametrically opposed recesses 18. In operation, a first one of the cam followers 4 cooperates with the outer edge of the primary valve cam 1 and a second one of the cam followers cooperates with the outer edge of the secondary valve cam 2. As the valve cams 1, 2 rotate, the linkage 7, which is guided by the bushes 19, moves in a desmodromic fashion and hence operates adjustment lever 6 hence can actuate valve actuator lever 8 and through linkage 20 the valve 14 according to the position of valve actuation lever pivot 12. Valve shown open in Figure 1 and closed in Figure 2.

The protrusions 17 and recesses 18 are stepped from the generally circular outer edge of the valve cams 1, 2 by step profile 21. The profile of the step portions is determined by the maximum acceleration the valve mechanism can accommodate; ideally would be so steep so that virtually instantaneous actuation of the valve 14 is possible. Moreover, since there are two valve cam followers 4, 5, one of which is responsible for opening the valve 14 and the other of which is responsible for closing the valve 14, there is no need for the valve to be biased open or closed using springs. It will be appreciated that the valve timing can be adjusted by the careful selection of valve cam edge profile, and that the valve opening and closing times can be chosen by the careful selection of step portion 21 gradients: steeper gradients giving rise to shorter opening times and vice-versa. It thus becomes possible to precisely design the valve opening and closing characteristics of the engine, which can give rise to greater engine efficiencies and/or powers.

In Figure 3 it can be seen that the timing rod 7 moves longitudinally guided by bushes/seals 19 and connected to rocker arm 6 with slidable pin means 22 or alternatively using linkage 20 as shown in Figures 1 and 2. The other end is held by a pin 23 free to slide in an arcuate slot 24 whose curvature is part-circular and centred on the engines output shaft 3 connected to a roller cage assembly. Rollers 4, 5 are held in a roller cage assembly consisting carrier plates 25, 26 and spacers 27, 28. The roller carrying plates 25, 26 are located on opposite sides of the timing cams 1, 2 which are positioned close to, or in mating contact with one another, on the output shaft 3 of the engine. The first roller 4 is rotatably mounted on the first carrier plate 25 and the second roller 5 is rotatably mounted on the second roller carrying plate 26. The lower ends of the roller carrying plates 25, 26 are connected to one another at a position below the timing cams 1, 2 by a second spacer block 28. Extending outwardlyfrom the spacer 28 is an extension rod 29 which is coaxial with an extension rod 30 extending from spacer 27. The roller cage assembly is rotationally constrained by a timing mechanism which is free to rotate about the output shaft 3 on bearing 31. The timing mechanism comprises an annular plate 32 which has pair of radially extending support arms 33, 34 which carry support blocks 35, 36 having bushes 37, 38 through which the extension rods 29, 30 slidingly pass. Attached to one support arm (33 shown) is a rack 39 arcuate to output shaft 3 and pinion gear 40 for control of the timing.

In use, as the engine's output shaft 3 rotates, the timing rod 7 reciprocates with the roller cage assembly, causing the rocker arms 6, 8 to oscillate thereby opening and closing the valve(s) 14. The phase and duration of the opening and closing of the valve(s) 14 is determined by the timing cams' 1, 2 edge profiles and their rotational position relative to the engine's output shaft 3. Preferably the above described mechanism is provided for inlet valves(s) and for exhaust valve(s).

Figure 4, 5 sectional side view and top view show the timing rod 7 further connected to an additional idle valve actuation adjustment rocker 41 connected to idle valve rocker 42 connected to idling control valve 43 via linkage 44. Idle valve actuation rocker 42 is connected to the idle valve adjustment rocker 41 with a slidable ball 45 and tracked socket 46 which extends from the centre axis of the idle valve adjustment lever 41. The pivot mount 46 of idle valve adjustment lever 41 is fixed; the pivot mount 47 of the idle valve actuation lever 42 is slideable on a track 48 arcuate with idle valve 43. A rack 49 arcuate with idle valve 43 and pinion gear 50 control the position of ball 45 in track 48 and hence the amplitude of the idle valve actuation as rocker 42 operates the idle valve 43.

By turning control shaft 40 for inlet valve (similarly control shaft 51 for exhaust valve) the phase of the engine's timing can be adjusted. As extensions 33, 34 rotate in the same direction as the direction of rotation of the output shaft 3, then the valves will be actuated ahead of time, i.e. the timing is advanced. Conversely, rotation in the opposite direction to the direction of rotation of the output shaft 3, then the valve timing lags behind that of the piston, i.e. the timing is retarded. For when the actuator is servo-controlled, the servo is controlled using an engine management computer.

As can be best seen in Figure 7, the dual purpose for inlet variable valve actuation is to provide sealing on valve seat 52 and to control flow rate. The tapered section 53 increases the orifice area as the valve is opened. Ideally the main inlet valve and idling valve tapers 53, 54 are designed to provide a gradual decrease in flow restriction to emulate the function of the butterfly valve or throttle' valve and idling air control valve in a conventional engine.

In Figures 5, 8 separate valve actuation mechanisms are provided for two induction valves and two exhaust valves. Variable valve actuation is shown here for the exhaust valves as may be required for example when the engine is switched form Atkinson cycle to supercharged cycle.

Referring to Figures 9-12, the valve open time is determined by the protrusion angle 8x. For the protrusion cam 1 the angle is effectively lengthened by adding further cam follower 55 at angle Oy from the centre axis of the cam followers 4, 5 and the effective protrusion angle becomes ex+ey to a maximum 28x where ex=ey. Therefore the indentation cam 2 angle is 2ex and can be effectively shortened by adding a further cam follower 56 at angle ex-ey from the centre axis of the cam followers 4, 5. When angle ey=ex, i.e. both indentation cam followers 5 and 56 are in line, the effective indentation angle is 2ex-(ex-eY)=2ex. As angle 8y is increased, the effective indentation angle decreases until 8x=O and the valve duration is effectively 8x thus effecting variable valve duration control between protrusion angle 8x to 28x. Figure 10 shows the valve duration roller cage assembly rotatable about the valve timing roller cage assembly about bearing 58. The valve duration roller cage assembly has extension rod 59 guided by bush 60 and is rotationally constrained by a valve duration control mechanism which is free to rotate about the output shaft 3 on bearing 61. Attached to support arm 62 is a rack 63 arcuate to output shaft 3 and pinion gear 64 for control of the valve duration.

In operation to vary the valve timing both valve timing control shaft 40 and valve duration control shaft 64 are actuated simultaneously by equal amounts. To vary the valve duration only, the valve duration control shaft 64 alone is actuated.

Figures 13-23 are mechanisms which allow engines as described in PCT/GB2009/050858 to be switchable between Atkinson and Supercharged cycles by rotating the valve timing cams through ninety degrees relative to the output shaft. This changeover would also require adjusting the timing of the injectors to inject during the phase-changed stroke of the engine and in a petrol engine would entail swapping the timing of the injectors and sparking plugs.

Referring to Figures 13-16 roller 4 follows the indention cam 2 and roller 5 follows a protrusion cam 1. As the output shaft 3 rotates, the roller carrier linkages 25, 26 move linearly about the axis of output shaft 3. One side of the indentation carrier linkage 25 has rack 65 that meshes with pinion 66; the other side of the protrusion carrier linkage 26 has rack 67 that meshes with pinion 68. The pinions 66, 68 are held in position by the valve timing mechanism 69 on bearings 70, 71. As carrier linkages 25, 26 move down (Figure 13) pinion 66 rotates counter clockwise and pinion 68 rotates clockwise and vice versa. Pinions 66, 68 also mesh with the input gears 72, 73 to a differential mechanism 74. One of the inputs is reversed by gears 75 which are mounted to the engine frame represented in the drawings by cross hatching. The output of the differential mechanism 74 is connected to linkage rod 7 to actuate the valve(s). In operation, as the valve timing mechanism 69 is rotated about output shaft 3 pinion gear bearings 70, 71 rotate bearing pinion gears 66, 68, said gears remain fixed about their own axis by the racks 65, 67 on the cam follower linkage 25, 26 and thus rotate gears 72, 73 in unison. Gears 75 reverse the rotation on one input so that gear 76 rotates the same but in the opposite direction to gears 72, 73, pinions 66, 68 and the valve timing mechanism 69. Since the inputs to the differential 74 are now equal and opposite in direction, the output remains fixed and there is no valve actuation. The mechanism therefore can permit full 360 degree rotation in valve timing. As the roller carrier linkage moves according to the protrusions/indentations on the cams, pinions 66, 68 rotate in opposite directions by an equal amount. Input gear 76 now rotates with the same direction as input gear 72 and the output of the differential rotates in unison with the input gears. Linear movement of the roller cam linkage is transferred to valve actuation for any angle of valve timing.

Figures 17-21 show an alternate design for the differential mechanism using spur gears 77 and single input gear 78. In Figure 19 the timing is at zero degrees with the valve in open position and Figure 21 shows the timing rotated by 90 degrees and the valve is in closed position.

In Figures 22, 27 show the valve control mechanism with VVT, VVA and VVD to allow an Atkinson Cycle to be switched to a Supercharged Cycle by rotating the valve timing by 90 degrees. Pinion gear 40 rotates rack 77 and pinion 64 rotates on rack 78 to vary the valve timing. Pinion 64 or pinion 40 rotating independently on racks 77, 78 vary the valve duration.

Figure 25, 27 show the extended racks arcuate with output shaft 3 for varying the valve timing by 120 degrees and valve duration by 20 degrees (equivalent to 480 degrees and 80 degrees on a conventional crankshaft). The hashed lines in figure 23, 27 represent the positions for maximum valve duration. Figure 24 and Figure 25 are a side and end view of a complete VVT, VVA, VVD, switchable Atkinson Cycle or supercharged Cycle valve control mechanism. Figure 26 shows the timing mechanism in supercharged cycle with valves open and Figure 27 with valves closed.

Claims (13)

1. CLAIMS1. A timing mechanism for an internal combustion engine, said internal combustion engine comprising an output shaft, and the timing mechanism comprising: a cam means mounted on, and rotatable in unison with, the shaft; a cam follower arranged to engage the cam means; a linkage connected at one end to the cam follower through a pin/bearing sliding arcuate about the cam axis and at the other end to a rocker arm; said rocker arm being pivotally connected to a pivot means and being adapted to actuate an induction or exhaust valve of the engine such that movement of the pin means along the arcuate locus advances or retards the timing of the engine.
2. 2. A timing mechanism as claimed in 1 wherein the linkage at the rocker and pin allow the rod to be constrained by bushes.
3. 3. A timing mechanism as claimed in any of claims 1, 2 wherein the arcuate locus is defined by an arcuate slot or track in or on which the pin means is slideable.
4. 4. A timing mechanism according to any of claims 1, 2 and 3 wherein the linkage comprises a substantially rigid rod.
5. 5. A timing mechanism as claimed in any of claims 1 to 4, wherein the cam follower comprises a roller or ball bearing arranged to engage an edge of the cam means.
6. 6. A timing mechanism as claimed in claim 5, wherein the cam follower comprises a pair of rollers or ball bearings arranged to engage diametrically opposite portions of the edge of the cam means.
7. 7. A timing mechanism as claimed in claim 1, where said rocker arm being connected to a further rocker arm(s) and being adapted to actuate an induction, idle or exhaust valve of the engine; wherein; the pivot means of said further rocker arm(s) is slid ingly moveable on an arcuate locus that increases or decreases the amplitude of the movement (Variable Valve Actuation, VVA) the pivot means is adapted to allow pivoting and rotation of the rocker arm.
8. 8. An actuation mechanism as claimed in 7 wherein the arcuate locus is defined by an arcuate slot or track in or on which the pivot means is slideable.
9. 9. An actuation mechanism as claimed in 7, 8 for variable actuation of an idle valve, said valve having profiled taper for low mass flow rate control.
10. 10. An actuation mechanism as claimed in any of claims 7 to 9 for variable actuation of inlet valve(s), said valve(s) having profiled taper for mass flow rate control.
11. 11. A timing mechanism as claimed in claim 1, where said cam follower comprises of a double pair of cam followers cooperating with the surfaces of primary and secondary valve cam means which rotate with the output shaft. One pair of cam followers is rotatable about the cam linkage with one cam follower offset by an angle equal to the primary cam indentation angle. The indentation angle is twice the protrusion angle on the secondary valve cam. Continuous variable valve duration (VVD) adjustment is provided for angles between the protrusion angle and the indentation angle of the primary and secondary valve cam means.
12. 12. A timing mechanism as claimed in claim 1, where the valve being actuated by a linkage is connected to output of a mechanical differential. The differential inputs are gears connected to racks along a linkage carrying a pair of cam followers cooperating with the surfaces of primary and secondary valve cam means which rotate with the output shaft.One input to the differential is reversed. The output only moves as the cam followers engage the protrusions/indentations on the cams. Thus the valve timing can be set for large angles to enable switchable engine cycles.
13. 13. A variable valve timing, variable valve actuation and variable valve duration mechanisms according to any of claims 1 to 12 substantially as hereinbefore described, with reference to, and as illustrated in the accompanying drawings.