This invention proposes a means of providing variable timing, lift and deactivation of a poppet valve system.

In the broadest aspect as set out in Claim 1, the invention is a poppet valve actuation system in which the poppet valve is operated, via a cam follower, by a cam which is mounted on a shaft supported in bearings and which is joined by 2 pivoted links to a connecting rod, driven by a crankshaft, the first link, termed the"cam link", being rotatably connected at one end of the link to the cam, whilst the other end of the first link connects rotatably to one end of the second link, termed the"control link", this second link being rotatably connected, along its length, to the small end of the said connecting rod, the other end of this second link, termed the"free"end, being connected to an actuator that may selectively apply a displacement to this free end of the second link, such that the second link's angularity relative to the first link and therefore the angular displacement of the cam can be adjustably controlled by the said displacement of the free end of the second link causing rotation about the connection of the second link with the small-end of the said connecting rod, the big end of which being free to rotate on the said crankshaft, the said crankshaft being driven in appropriate phase with the main engine crankshaft.

Other aspects of the invention are outlined in the further subordinate claims.

Background explanations and specific embodiments of the invention are now described by way of example with reference to the accompanying drawings in which: Fig. 1 is an end elevation of one embodiment of the invention, with the poppet valve closed.

Fig. 2 is an end elevation of one embodiment of the invention, with the poppet valve open.

Fig. 3 is an end elevation of one embodiment of the invention in the valve de- activation mode position, with the crank at the same position as Fig. 2.

Fig. 4 is an end elevation of one embodiment of the invention in the valve de- activation mode position, and the crank at the same position as Fig. 1.

Fig. 5 is a plan view of one embodiment of the invention.

Fig. 6 is a control system diagram.

Fig. 7a, 7b and 7c is a schematic of the actuation of the control link to follow a linear path. Fig. 7a is a side view, Fig. 7b is an end view of one embodiment of the linear path actuator, and Fig. 7c is an end view of the linear path adjuster rack.

Fig. 8 is actuation of the control link in a path of varying curvature.

Fig. 9 is an end elevation of another embodiment of the invention, with the poppet valve closed.

Fig. 10 is an end elevation of another embodiment of the invention, actuating 2 poppet valves.

Fig. 11 is side elevation of the variable valve actuation system and another embodiment of a control system.

Figs. 12a 12b are side elevations of the control system elements shown in Fig. l l.

Fig. 13 is an isometric view of the embodiment shown in Figure 11.

Fig. 14 is an isometric view another actuator arrangement, using ball screws.

Fig. 15 is a sectional view of an eccentric adjuster for valve clearance control.

With reference to Fig. l, poppet valve 17 is actuated by a bucket tappet 16, or any other typical valve actuation system, which is in contact with a cam 1, having supporting journals 200, which is made to oscillate via a pair of rigid links 4 and 6, joined to a connecting rod 9 via a pivoting joint 7 between the link 6 and the connecting rod small-end 8, the connecting rod big-end 10 being driven by a crankshaft 13 which is driven from the main engine crankshaft, or via an electric motor. Link 4, the"cam link", is joined rotatably at one end to the cam 1 via a connection 2, and is rotatably connected to the second link 6 at its other end via connection 5. Link 6 is referred to as the"control"link because the position of its other end 15, which is nominally fixed relative to the engine structure, may be adjusted by controllably moving the end 15, in one embodiment, by a crank arm 19, actuated by an actuator shaft 22. In this embodiment, an actuating device, such as an electric motor of the stepper motor type, would position the arm at a particular angle, rotating the end 15 of link 6 along the arc 18, such that link 6 rotates about the small end 8 of the connecting rod 9, the big end of which being free to rotate around the crank eccentric 12, resulting in arcuate movement of the joint 5, and effectively changing the phase angle between the crankshaft 13 and the position of the cam 1.

The rotation of link end 15 also modulates the maximum angular oscillatory motion of the cam 1 which varies the valve lift depending on the cam profile. For the crankshaft position shown in Fig. 1, the valve is in its seated position with the control link is adjustably positioned at A to permit a high angular oscillation of the cam.

In this particular embodiment, the crank arm is shown rigidly connected to the actuator shaft 22, and this connection can be achieved in one embodiment by force fitting the crank arm 19, onto a shaft 22, or by having a monolithic arrangement of crank arm and shaft, as would be achieved with a casting. The crankshaft 13, which is supported in bearings, is shown in this embodiment of Fig. 1, with an eccentric 12 to operate the connecting rod 9.

The rotational speed of the valve actuating crankshaft may either be equal to that of the main engine crankshaft in order to provide 2-stroke engine operation, or the rotational speed of the valve actuating crankshaft may be half that of the main engine crankshaft in order to provide 4-stroke engine operation, or may be selectively set to any desired fraction or multiple of the main crankshaft speed in to provide whatever number of strokes are required for operation of the engine cycle. In one embodiment, this is achieved by driving the valve actuating crankshaft via a variable speed electric motor.

In another embodiment, there may be a phase change actuator of the vane or helical spline type, or epicyclic gear train, between the main engine crankshaft and the valve actuation crankshaft so that the timing of the valve events can be further influenced.

With reference to Fig. 2, the crankshaft 13 has rotated 180° so that the valve 17 is opened with the control link pivoting about point A. After full valve lift has been achieved, further rotation of the crankshaft 13 in the same direction will cause the reverse direction of motion of the links 4 and 6 and the cam 1, so that the crankshaft 13 effectively oscillates the links and cam in order to generate the valve motion.

With reference to Fig. 3, the end 15 of the control 6 link has been adjusted to another fixed point B by the actuator crank arm 19, and the crankshaft 13 is shown in the same position as Fig. 2. It will be noticed that this crankshaft position now generates substantially zero valve lift, whereas the same crankshaft position, with the link rod pivoting about point A in Fig. 2 generates maximum lift.

With reference to Fig. 4, the end 15 of the control 6 link has been adjusted to a fixed point B, as in Fig. 3, by the actuator crank arm 19, and the crankshaft 13 is shown in the same position as Fig. l. It will be noticed that the crankshaft 13 and cam 1 positions are similar to that of Fig. l, inspite of the differing positions, A and B, of the end 15 of the control rod 6 between Figs. l & 4. Although not obvious from the Figs. l and 4, the"overcentre"motion, denoted by G, of links 4 & 6 relative to axis between the centre 2a of the cam link 4 and the centre 8a conrod smallend, induces a secondary oscillation of the cam profile 1, ie the cam profile oscillates twice for every revolution of the valvetrain crankshaft 13. There are a range of positions of end location 15 of the control link 6 which will result in this secondary motion of the cam profile ; this can be significant for increasing the functionality of the valvetrain for certain performance and emission aspects. In particular, this secondary cam motion is induced if the actuator end of the control link is moved to a position relative to the cam link, such that always is an acute included angle between the cam link and the control link, as viewed from the actuating crankshaft side of the cam and control links.

With reference to Figs. 1 and 4, at intermediate positions between A and B of the end 15 of the control link 6, the maximum valve lift, duration and phase relative to the crankshaft can be varied depending on the locus of the path between A and B which may be a circular arc, straight line or a path of varying curvature.

With reference to Fig. 5, this shows cam bosses 2a and 2b forming a fork, which receives the blade end of cam link 4, the joint being secured by pin 3, whilst the second end of cam link 4 has a similar blade connection, via pin 5, with the forked ends 36a and 36b of link 6. In another embodiment the"blade"part of the connection between cam 1 and link 4 may be formed on the cam, and the"fork"part of the connection made part of the link 4. In another embodiment, the connection point between the cam 1 and the link 4 may be situated in any other region of the cam 4.

The connection of link 6 with the small end 8 of the connecting rod is made with the pin 14 via side members 46a and 46b of the control link 6, these side members having bores for connection to the small end of the said valve actuating connecting rod. In another embodiment the cross-section of the control link 6 is U-shaped. In another embodiment the cross-section of the cam link 4 is U-shaped. In Fig. 5, the journals 13a and 13b of the crankshaft 13 which has an axial centreline 13c are partially shown.

The cam 1, having supporting journals 200a and 200b, and cam link 4 may be joined by a pin 3 which has interference with at least one of the interconnecting bores of the cam and cam link. The cam link 4 and control link 6 may be joined by a pin 5 which has interference with at least one of the interconnecting bores of the cam link and control link. The control link 6 and connecting rod 9 may be joined by a pin 14 which has interference with at least one of the interconnecting bores of the control link 6 and connecting rod 9.

The actuator shaft, with arm 19 shown forked for connection to link 6, is supported on journals 22a and 22b. The crankshaft may be of monolithic construction, the crank throw being formed in one embodiment by a cylindrical solid of revolution which is eccentric to the main axis of the crankshaft which is indented on one side so that the connecting rod can be passed along the crankshaft for assembly. The said actuating crankshaft may be supported on journals by bearings which may receive lubricating oil. The monolithic crankshaft may be of cast iron, or forged steel material, suitably hardened at the appropriate bearing surfaces, such as the journals, eccentrics and axial thrust faces. In another embodiment, the crankshaft may be of built-up construction, the crank throw being formed by a cylindrical solid of revolution which is force fitted eccentrically to a main hollow shaft, the main journals also being solids of revolution that are force fitted to the hollow main shaft. In one embodiment of the built-up shaft, the solids of revolution that are used for the main journals and crank throws are of sintered material, such as sintered iron, and may be finish sintered. The actuator shaft, which may be supported by more than one journal bearing, may be of monolithic construction, the crank throw being formed in one embodiment by a cylindrical solid of revolution which is eccentric to the main axis of the actuator shaft.

The monolithic actuator shaft may be of cast iron, or forged steel material, suitably hardened at the appropriate bearing surfaces. In another embodiment, the actuator shaft may be of built-up construction, the crank throw being formed by a cylindrical solid of revolution which is force fitted eccentrically to a main hollow shaft, which may be steel, the main journals being co-axial solids of revolution that are force fitted to the hollow main shaft, which may be of steel. In one embodiment of the built-up shaft, the solids of revolution that are used for the main journals and crank throws are of sintered material, such as sintered iron, and may be finish sintered. The valve actuating crankshaft, its supporting bearings and actuator shaft may receive oil from the engine lubricating system, and may distribute this oil to connecting members via internal drillings in the shafts and members. Specifically, the crankshaft may pass oil to the connecting rod for lubrication of the big-end and small-end, and the actuator rod may pass oil into the crank arm 19. The various connections, such as the pin joints of the cam, the cam link to control link, the control link to actuator arm, the control link to connecting rod small end, may receive oil by splash lubrication or from directed oil jets located in the engine, or from the oil passages in the links that are connected to the crankshaft or actuator shaft. The cam may also receive lubricating oil. In one embodiment, the connecting rod may be of monolithic construction, being of sintered metal material, forged aluminium, forged steel, cast-iron, or of metal matrix composite, for example aluminium reinforced with alumina fibres.

The valve actuating crankshaft 13 may be located in the cylinder block, in the cylinder head, in a carrier attached to the cylinder block, in a carrier attached to the cylinder head, or the said valve actuating crankshaft may be located between the cylinder head and the cylinder block or may be located between the cylinder head and the cam carrier.

In another embodiment the supporting bearings of said valve actuating crankshaft are located on the same split line as the supporting bearings of the valve actuating cam.

The connecting means between the cam, cam link, control link, connecting rod small end and actuator control may either be solid or hollow pins, fixed to one of the links, with a clearance in the bush on the other connecting link, or one, or more, or all of the connecting means may use the pins, fixed to one of the links, and in contact with rolling element bearings on the other link.

With reference to Fig. 6, the linear position of the poppet valve 17 may be monitored by an inductive displacement or Hall effect sensor 51 located near the valve stem 111, and the sensor signal supplied to an electronic computer controller 53. Similarly, the angular position of the actuator crank arm 19 may be monitored by an inductive displacement sensor, a potentiometer, or Hall effect sensor 52 located near to a disc attached to the actuator shaft, and the sensor signal supplied to an electronic computer controller 53. These signals are used, in combination with other engine sensor signals, such as main crankshaft speed sensor output 55, engine load condition sensor output 56, engine coolant temperature sensor output 57, engine exhaust gas recirculation content sensor output 58, to send control signals to the electric motor 54 controlling the angular position of the actuating shaft and crank arm 19. These control signals may control the actuating shaft in open loop, feedback or feedforward modes, or combinations of open loop and feedback modes so that the position of the valve 17 may be continuously identified and adjusted according to engine demand.

One particular use of the feedback control is to adjust valvetrain positions to compensate for any tolerance or wear effects. One particular embodiment of this control strategy is to adjust the position of the actuator crank arm 19 so that the valve displacement, velocity or acceleration, as deduced from the valve position sensor 51, or alternatively measurables, such as a mass airflow signal, or a manifold depression signal, optionally used in combination with time signals and crank position signals in the electronic controller 53, can be regulated to match target values contained in the electronic memory of the electronic controller. This particular strategy may be particularly important for valve trains using end pivoted levers having valve/cam lift ratios approaching unity, where hydraulic lash adjusters are not effective and the feedback adjustment of the valve motion, as just described, can effectively provide similar compensations as hydraulic lash adjusters.

Fig. 7 shows an embodiment in which the end 15 of the control link 6, partially shown, moves in a linear path between positions A and B shown in Figs. 1 and 3. In this embodiment, the control shaft 71 runs along the length of the engine to which the links 6 of the various valve lines are rotatably connected. The shaft 71 is supported at various positions along its length by guides 75 which run in caps 72. At one or more positions, the control shaft is provided with a collar 73 in which a thread is formed to transfer motion from a threaded actuation shaft 74 which is operated by an actuation device such as a stepper motor. In another embodiment, the control shaft 71 can be connected to an hydraulic actuator in an hydraulic control system which includes a spool valve and a differential lever so that for a given input displacement signal to the differential lever, the hydraulic actuator positions the control shaft which is then effectively locked in position by the fluid contained in the actuator until a further input displacement occurs.

Fig. 8 shows an embodiment in which the control shaft 71 moves in a path of varying curvature between positions A and B shown in Figs. 1 and 3. The exact locus of movement of the control link end depends on application requirements. The proposed variable valve actuation system can vary both valve opening period and lift, independently or simultaneously. More specifically, the valve periods can be varied at constant lift, or the valve periods can be varied at variable lift. In the embodiment of Fig. 8, the control shaft 71 runs along the length of the engine to which the control links of the various valve operation lines are rotatably connected. The control shaft has a spigot 76 on one or both ends to which a slider 77 and sleeve 78 are rotatably connected. The said slider is slideably connected to a slotted arm 79 rigidly fixed to actuator shaft 22 which is rotated by an actuation device to position the said slotted arm. At any angular position of the slotted arm 79 the slider 77 is positioned radially by the sleeve 78 which is slideably located in a cam track 80 in a stationary cam plate 81. In another embodiment, the camplate 81 can be rotated, relative to the control arm 79, through prescribed angles to provide greater directional control of the control shaft spigot 76; this rotational movement can be continuous to dynamically control the position of the end of the control link, or occasional, to compensate for systematic drifts and offsets. In another embodiment, the outer surface of the said sleeve is profiled to reduce the contact stress between the said sleeve and the said cam track.

This control actuator may be used on individual variable valve actuation systems, or may be used for a pair of valves, or for a group of valves.

In the embodiments of Figs 1-8, the said valve actuating crankshaft may be located in the cylinder head, or the cylinder block, or in a carrier attached to the cylinder head, or in a carrier attached to the cylinder block or may be located between the cylinder head and the cylinder block, or located between the cylinder head and the cam carrier.

In another embodiment of the invention, the supporting bearings of said valve actuating crankshaft may be located on the same split line as the supporting bearings of the valve actuating cam.

With reference to Figure 9, the cam 1 may have a primary profile la, used substantially as described with reference to Figs. 1-8, and a secondary profile lb, which may be on one or other side of the primary profile la, and in some embodiments cam 1 may also have a third profile. The additional profiles may be selectively engaged by appropriate location of the end point 15 of the control link 6.

These additional profiles may be engaged so that only one of these profiles is experienced during an engine cycle, or 2 profiles are experienced per cycle, or all 3 profiles are experienced in each engine cycle, by controlling the end position 15 of the control link 6.

The embodiments of Figs. 1-9 may be applied to a single or multiple poppet valves of an internal combustion engine. In one embodiment, one or more additional cams are coaxially mounted with, and attached to, the primary cam of the invention to operate one or more additional valves.

In a further embodiment of the invention, the mechanisms outlined in Figs 1-9 may be applied to a poppet valve via a lever system instead of via a bucket tappet. The lever system may be an end pivoted lever system, ie where the lever is supported to the base engine at one end of the lever, or may be a centre pivoted lever system. The cam may actuate the lever via a sliding contact or a rolling contact. The pivot point of the lever may be a fixed post connection to the engine, or the pivot may be a hydraulic tappet or the pivot may be a shaft which may be a continuous shaft for some or all the levers which actuate the valves. In the case of the centre pivoted lever system, the lever may incorporate a hydraulic tappet.

With reference to Fig. 10, this embodiment uses a centre pivoted lever, or rocker, 201 which makes contact with cam 1 of the variable valve timing mechanism via rolling element bearing 202, or a fixed contact pad, and the rocker actuates a pair of valves 17a and 17b via a bridge piece 204. Static valve clearances can be optionally adjusted via the screw thread 205 and locking nut 206. In this embodiment, the plane of the valves 17a and 17b may differ to that of the valve actuating and control mechanisms.

The jointed arrangement of the cam 1, cam link 4, control link 6, conrod 9 and actuator 19 allows the cam contact point to be disposed below the contact point with the rocker rolling element (202 in Fig. 10), whilst the other linking elements can be disposed with some degree of flexibility relative to the axis XOX'. Specifically, the crankshaft 13 can be located either above or below the axis XOX'and likewise the control actuator can be located above or below axis XOX'. It is also possible to have either the valve actuating crankshaft located below axis XOX', with parts of the linkage mechanism above axis XOX', or in another arrangement both the actuating crankshaft and the control actuator are below axis XOX'. Further packaging flexibility may be afforded by using a lever which is cranked so that arm OX'with the rolling element contact of the rocker is at an angle to the arm XO, with the screw adjuster, of the rocker.

With reference to Fig. l l, the end point 19a of the control link 6 is located off centred to a first cylindrical body 20, which itself is housed off centred, and with clearance, to the cylindrical hole 21b of a second body 21 which is free to rotate in a fixed housing about the major axis of its external surface 21e. The first cylindrical body 21 may be rotated by various means, such as an electric motor, in particular a stepper motor, whilst the second body 21 may also rotated by various means, such as an electric motor, in particular a stepper motor. The position of the control point 19a may thus be varied in 2 orthogonal directions by appropriate rotations of the cylindrical bodies 20 and 21.

With reference to Fig. 12a, the cylindrical pin 21 is rigidly attached to the substantially cylindrical body 20, which has a clearance volume 22 to accommodate the end of the control link. The cylindrical pin 21 is offset by an amount Y from the major axis ZOZ of the substantially cylindrical body 20, and the substantially cylindrical body 20 fits with clearance to the cylindrical body 2 la of Fig. 12b.

With reference to Fig. 12b, the cylindrical body 21a has a substantially cylindrical cavity 21f, the major axis of which is offset by an amount F from the major axis ROR of the cylindrical body 21a, the cylindrical body 21a being rotatably contained in a housing 30 with clearance 31, the housing being rigidly fixed relative to the actuating crankshaft 13 of Fig. 11.

With reference to Fig. 13, this shows the two substantially cylindrical bodies 20 and 21 of Figs. 11 & 12, connected to the end 15 of the control link 6, which in turn connects to the eccentric 13 via the connecting rod 10, and to the cam link 4. With the eccentric assembly, ie eccentrics 20 and 21 contained rigidly in the housing (not shown in this figure), independent and simultaneous rotation of the eccentrics 20 and 21 will cause the end point 15 of the control link 6 to move in a plane containing 2 orthogonal directions, and this in turn will control the oscillating angle of the cam 1.

With reference to Fig. 14, the end point 15 of the control link 8 of the variable valve actuation system is contained in a ball joint which connects via stirrup 19, and threaded screw drive 18, to the threaded shaft of an electric motor 16, the same ball joint also connecting the control link end point 15 to another stirrup 21, and threaded screw drive 22, to the threaded shaft 20 of an electric motor 23. Each stirrup and threaded connection is termed a"ball screw drive". By suitable location of each motor, the pair of motors and ball screw drives enable the control rod end 15 to be moved in 2 orthogonal directions in one plane. In one embodiment, the electric motors are parallel to each other but substantially orthogonal to the plane of variable valve actuation mechanism, whilst in another embodiment axes of the 2 motors may be at right angles to each other.

With reference to Fig. 15, the oscillating cam 1 is fitted with means for adjusting the clearance of the cam relative to the tappet or follower that is in contact with the valve tip, for conditions of zero lift. This is frequently referred to as"valve clearance". In one embodiment of the invention, the means for adjusting the clearance, relative to the tappet or follower, comprise a rotatable member 3 that is mounted between an inner bore 4 in the cam and the shaft 2 supporting the cam, the rotatable member being off centred from the centre of the shaft, and this rotatable member being adjustable in angular position relative to the cam. The rotatable member may be an eccentric which can be locked to a particular angular position relative to the cam by various means. In one embodiment, the locking means is a high friction thread between the inside bore of the cam and the outside surface of the rotatable member; this high friction thread may be deformable. In another embodiment, the means of locking comprises at least one locknut engaging with a thread which is on the rotatable member.

In a further embodiment of the invention, cam 1 (of Figs 1-7,9-10) may contain an additional, retractable and slideable cam lobe which can be selectably latched in 2 positions substantially perpendicular to the main axis of the camshaft so that the slideable cam lobe can be withdrawn and latched within the outer profile of cam 1 so that cam 1 controls the valve lift, as well as the slideable cam being latched in a second position to provide the controlling valve lift. This enables additional valve opening periods to be achieved, as for instance may be required with the exhaust In a further embodiment of Figs. 1-10, some of the inlet valves may be controlled with one set of the valve actuation mechanism, whilst the other inlet valves are operated with another set of the valve actuating mechanism, thus allowing the 2 sets to have independent modes of operation and control. The same arrangement can also be applied to the exhaust valves.