Abstract:
A mechanism for actuating an engine poppet valve includes two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the stem of the valve, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. In the invention, an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, and a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem. The latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams. Such valve actuating mechanisms are known per se and are described for example in U.S. Pat. No. 6,854,434, GB Pat. Appln. No. 0519876.7, and U.S. patent application Ser. No. 11/284,725. 
       BACKGROUND OF THE INVENTION 
       [0002]    In addition to controlling engine valves to vary such parameters as phase, valve lift and event duration, cylinder deactivation is becoming increasingly common on large displacement gasoline engines, where significant fuel economy improvements can result from running an eight cylinder engine on four cylinders during light load operation. Deactivating one of a pair of intake valves on a diesel engine in order to control in-cylinder swirl levels is also an interesting concept for future research. 
       OBJECT OF THE INVENTION 
       [0003]    The present invention therefore seeks to provide a system for controlling valve lift and duration which is additionally capable of deactivating one or more valves per cylinder. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with the present invention, there is provided an internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams, characterised in that an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed. 
         [0005]    In the invention, two cams are used to actuate one or more valves via a summation system, and the valve lift characteristic can be changed by phasing one of the cam lobes relative to the other. Such systems can be arranged such that valve lift will only occur when both cam lobes are on lift and the valve will be closed if either of the cam profiles is on its base circle radius. It follows that there will be some clearance in the system during some portion of the camshaft cycle when both cams are close to their base circle radii, and it is this clearance that provides the opportunity for a valve deactivation system to operate. 
         [0006]    Many valve deactivation and cam switching devices are known from the prior art that are designed to operate when the valve is closed (e.g. U.S. Pat. No. 6,196,175 US 2002/0014217 U.S. Pat. No. 6,135,074) but in conventional systems where there is little or no clearance when the valves are closed the switching of the valve deactivation system has to be carefully controlled in order to prevent the switching process from taking place when the valve begins to lift. This would be likely to cause overloading of the locking components and damage to the system. In order to avoid this, the switching of the systems applied to each cylinder of the engine is often controlled independently to make sure each cylinder switches fully whilst the valve is closed. 
         [0007]    Unlike conventional valve train systems, the summation rocker system design requires the rocker system to move whilst the valve is closed and the system is not heavily loaded. This allows a number of different implementations of the present invention, in which use is made of this additional rocker motion to effect the switching of the rocker system to a deactivated mode of operation. This allows the timing of the switch to be controlled such that it will always occur whilst the valve is closed and also offers the opportunity for the deactivation system to be integrated into the design of the rocker system rather than being a totally separate system. 
         [0008]    The different embodiments of the invention, which will be described below, offer the following advantages as compared with prior art systems, namely:
       Additional valve train flexibility for advanced combustion strategies,   Valve deactivation occurs only whilst the valve is closed,   Valve deactivation and lift control systems can be integrated instead of being separate, and   The invention can be implemented in different ways to suit a wide variety of engine architectures.       
 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
           [0014]      FIGS. 1A and 1B  are perspective views of two different types of known summation valve trains, 
           [0015]      FIG. 2  is a graph showing the principle of operation of a summation valve train, 
           [0016]      FIGS. 3A ,  3 B and  3 C are a section, end view and perspective view, respectively, of a first embodiment of the invention in which a valve deactivation system is located in the position of a lash adjuster, 
           [0017]      FIGS. 4A ,  4 B and  4 C are similar views showing a modification of the valve deactivation system of  FIG. 3 , 
           [0018]      FIGS. 5A and 5B  show side and perspective views of another embodiment of the invention, 
           [0019]      FIGS. 6A ,  6 B and  6 C show isometric, side and exploded views of the deactivation system incorporated in the valve train of  FIG. 5 , 
           [0020]      FIGS. 7A and 7B  are isometric and side views, respectively, of a further embodiment of the invention using mechanical valve deactivation, 
           [0021]      FIGS. 8A ,  8 B,  8 C and  8 D are respectively a section, an end view, a perspective view and an exploded view of a rocker in  FIGS. 7A and 7B , 
           [0022]      FIGS. 9A to 9F  show end views and views from below of the rocker of  FIGS. 7 and 8  in different positions, 
           [0023]      FIGS. 10A and 10B  show a side view and a perspective view, respectively, of an embodiment of the invention in which a single rocker is used to actuate two valves through a bridge piece, 
           [0024]      FIGS. 11A to 11E  are a side view, section, plan view from above, perspective view and an exploded view of one of the rockers in  FIG. 10 , 
           [0025]      FIG. 12  shows the valves and bridge piece operated by the rocker in  FIG. 11 , 
           [0026]      FIGS. 13A and 13B  are assembled and exploded perspective views of a further embodiment of the invention, 
           [0027]      FIGS. 14A to 14C  are an exploded view from the opposite end and details of modifications of the embodiment shown in  FIG. 13 , 
           [0028]      FIGS. 15A and 15B  are assembled and exploded perspective views of a further embodiment of the invention, 
           [0029]      FIGS. 16A ,  16 B and  16 C are a perspective, plan and exploded view, respectively, of three-part rocker in  FIGS. 15A and 15B , 
           [0030]      FIGS. 17  A to C are different sections through the rocker of  FIG. 16 , 
           [0031]      FIGS. 17D and 17E  are sections similar to the sections of  FIGS. 17A and 17B  but showing the locking pins in a different position, 
           [0032]      FIGS. 18A ,  18 B and  18 C are a perspective view, a section and an exploded perspective view, respectively, of a rocker of a further embodiment of the invention, 
           [0033]      FIGS. 19A and 19B  show a valve train using the rocker of  FIG. 18  in the deactivated and activated positions, respectively, 
           [0034]      FIG. 19C  shows a front view of the valve train of  FIGS. 19A and 19B , 
           [0035]      FIG. 20  is a perspective view of the valve train of  FIG. 19 , 
           [0036]      FIG. 21A  is a side view of a cam follower embodying the invention, 
           [0037]      FIG. 21B  is a section through the cam follower of  FIG. 21A  along the section line A-A in  FIG. 21A , 
           [0038]      FIGS. 21C to 21E  are sections along the line B-B of  FIG. 21B  showing different states of the cam follower, and 
           [0039]      FIGS. 22A ,  22 B,  22 C and  22 D are a side view, a partially cut away perspective view, a section and an exploded view, respectively, of a further cam follower embodying the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    The drawings in this specification are derived from complete technical engineering drawings which show different practical implementations of the invention in more detail than is necessary for an understanding of the invention. The function of many of the components will be self-evident to the person skilled in the art and the description of the drawings will therefore be confined mainly to an explanation of the way in which valve deactivation is achieved. 
         [0041]    Two different types of summation valve train have been considered for the application of valve deactivation systems as shown in  FIGS. 1A and 1B , respectively. The valve train of  FIG. 1A  is for use in overhead valve engines where the camshaft is located in the cylinder block whilst the valve train of  FIG. 1B  is for engines with an overhead camshaft. In each of these valve trains, each valve  10  is acted upon by valve-opening rocker  12 , the angular position of which is defined by a first cam profile, and the valve-opening rocker  12  is itself carried by a pivot on a supporting rocker  14  which is moved by a second cam profile. 
         [0042]    In the valve train of  FIG. 1A , two cams mounted on the same or different camshafts have cam followers  16  and  18  which transmit the movement of the two cams to the rockers  12  and  14  by way of push rods  20  and  22 , respectively. In the valve train of  FIG. 1B , the cams are mounted on a common assembled camshaft  30 . A roller follower  32  transmits the motion of one cam to the rocker  14  which is pivoted about a fixed shaft  34  and carries the pivot shaft  36  of the valve opening rockers  12 , each of the latter having a roller follower  38  in contact with a respective cam of the assembled camshaft  30 . 
         [0043]      FIG. 2  shows the way in which the two cam profiles  40  and  42  are added together in order to produce the valve lift  44 . For some of the time when the valve is closed, neither cam profile is at its maximum lift, and this results in clearance being present in the valve train. An additional control spring is normally integrated into the system in order to dictate whether this clearance will occur between the valve tip and its rocker or between one of the cam followers and its associated cam lobe (see GB Patent Appln. No. 0426352.1 and U.S. Ser. No. 11/284,725). 
         [0044]    By varying the phase of the cams acting on the two rockers relative to one another, it is possible to vary the overlap period and hence the event duration. The phase of the valve event can be varied by altering the phase of both cams relative to the crankshaft. 
         [0045]    The rocker system is not stationary during the clearance phase of the motion, but moves from its valve closing position back to its valve opening position. The proposed designs utilise the clearance in the system and the movement of the rocker system in the clearance phase to effect the valve deactivation. 
         [0046]    A number of different locations can be selected for integrating a valve deactivation systems into the summation valve trains shown in  FIGS. 1A and 1B . In essence it is only necessary to interrupt either one of the paths transmitting motion, be it directly or indirectly, from one of the cams to the valve, to cause the valve to remain closed at all times. In the case of the OHC design shown in  FIG. 1B , where a pair of valves is being actuated, the valve deactivation could be applied to one valve or to both valves as required. 
         [0047]    In the first embodiment of the invention, shown in  FIGS. 3A ,  3 B and  3 C, valve deactivation is effected by preventing transmission of force at the interface between the valve stem and the valve-opening rocker  12 . 
         [0048]    The rocker design shown in  FIG. 3  is intended as a direct replacement for the valve opening rockers  12  for either of the valve trains shown in  FIGS. 1A and 1B . 
         [0049]    The deactivation system is integrated into a clearance adjuster  50 , which is mounted in the end of the rocker  12  and acts on the valve tip. The adjuster  50  comprises a hollow plunger  52  that can slide into the end of the rocker  12  and is biased into contact with the valve stem (not shown in  FIG. 3 ) by means of a spring  54 . The opposite end of the spring  54  acts on a ball  56  that can itself slide within an inner sleeve  55  located inside the plunger  52 . The ball  56  which can itself be urged out of the inner sleeve  55  by application of hydraulic pressure serves as part of a latching system which prevents the plunger  52  from being retracted into the end of the rocker  12 . 
         [0050]      FIG. 3  shows the system in its locked position where the rocker will lift the valve. The lift is transmitted to the valve via the plunger  52 , which is prevented from sliding into its bore in the rocker by the ring of balls  58  connecting it to an inner sleeve  55  which is in turn located by the clearance adjusting screw  60 . The balls  58  are prevented from sliding inwards by the large central ball  56 , which is held against an end stop by a spring and the contact forces of the smaller balls. 
         [0051]    The valve is deactivated by applying oil pressure to a drilling in the rocker, which acts to force the central ball downwards against the action of the spring  54 . The central ball  56  can only move when there is clearance between the rocker and the valve tip because it has to force the small balls away from the centre in order to pass through. The movement of the small balls pushes the plunger out of the rocker slightly due to the angle of the face on which they locate and this can only happen when the plunger is unloaded. The spring  54  also acts to move the plunger axially to a position where the small balls  58  can move freely. 
         [0052]    When the rocker next contacts the valve, the plunger  52  will push the small balls inwards and retract freely into the rocker  12 . If the oil pressure is removed, the large ball will move back against its stop under the action of the spring  54  the next time the system is in clearance. The contact of the small balls  58  on the larger ball  56  ensures that there are only two stable equilibrium positions, with the large ball being held against its upper stop, or against its retaining clip. 
         [0053]    The latching system is an over-centre arrangement which cannot operate when the rocker is in contact with the valve tip, hence the switch between valve lifting and valve deactivation modes can only occur during the clearance part of the valve train cycle. 
         [0054]    The system is also of a bi-stable design in that if the rocker is brought into contact with the valve whilst the system is in the process of switching, the contact forces the system into one or other of its stable positions. This avoids any extremely high forces being applied to the components of the latch. 
         [0055]    This design can be applied to one or both valves of a pair, depending on whether single valve deactivation or cylinder deactivation are required. It would also be possible to switch a pair of valves independently if two separate switched oil feeds were provided—one for each rocker. Although it has been drawn for an OHC application, this design could be simply applied to a pushrod valve train system to achieve valve deactivation. In all cases a control spring is still required to maintain contact between both cam profiles and their respective followers. 
         [0056]    An alternative design for the mechanism of  FIG. 3  is shown in  FIG. 4  in which the large central ball  56  is replaced by a sliding sleeve  66  that holds a ring of balls  58 ′ in engagement with the sliding plunger  52 ′ to lock it into position. The sleeve  66  is moved upwards as viewed hydraulically to release the latch and it moved into the illustrated latching position by a spring  64 . The surface of the sleeve  66  that contacts the balls  58 ′ is profiled in order to give the system a bi-stable characteristic as described above. In other respects, the device will operate in a similar manner to the design in  FIG. 3 . 
         [0057]    The embodiment of  FIGS. 5 and 6  is similar to the embodiments of  FIGS. 3 and 4  in that it provides a method for disconnecting the valve tip from the valve-opening rocker such that the opening rocker motion is no longer transmitted to the valve. However the deactivation system is operated mechanically, rather than by an oil pressure signal. 
         [0058]    A first method for achieving this objective is shown in  FIGS. 5A and 5B  where control shafts  70  may be rotated in order to determine which valves are deactivated at any particular time. When a lever  72  on a rocker  12  is moved towards the valve by rotating the control shaft  70 , the valve is deactivated. Having different profiled sections on the control shaft to act on each rocker will allow different combinations of valves to be deactivated. 
         [0059]      FIG. 6  illustrates how the valve deactivation system operates in more detail. A ball-ended clearance adjuster  74  is threaded into a sliding cylinder  76  that has an interrupted external key  78  on both sides and runs in a corresponding slot in the rocker body. In the locked position (as drawn in  FIGS. 6A and 6B ), a latching plate  82  is located between the lower part of the key  78  on the sliding cylinder  76  and the underside of the body of the rocker  12 , preventing the sliding cylinder  76  from moving and hence lifting the valve. 
         [0060]    When the latching lever  72  is moved towards the valve, springs  80  between itself and the latching plate  82  become loaded, and the latching plate  82  will rotate on its pivot as soon as the system is in the clearance portion of the motion. As the system moves back towards the beginning of the valve lift, the lower section of the key  78  on the sliding cylinder  76  moves past the latching plate  82  and simply slides up into the rocker  12  rather than lifting the valve. A further spring  84  acts on the top of the sliding cylinder in order to maintain contact with the valve tip. 
         [0061]    If the lever  72  is moved just as valve lift is about to commence, the latch plate  82  may not move quickly enough the avoid contact with the key on the sliding cylinder. In this case, the latch plate  82  will be forced back to its seated position in contact with the underside of the rocker body against the action of the two springs, and no damage to the moving parts will occur. 
         [0062]    There will clearly be some movement of the latching lever  72  relative to the control shaft  70  during the operating cycle of the rocker, but this does not cause a problem as it is the position of the lever in the valve seated position that determines whether or not the valve will be deactivated. 
         [0063]    An alternative mechanical valve deactivating system is shown in  FIGS. 7 and 8 . As with the previous design, the valve can be deactivated by allowing a sliding plunger  94  to move into the rocker instead of transmitting the rocker motion to the valve. 
         [0064]    Each rocker is fitted with a lever  96 , the position of which determines whether the valve lift will be deactivated. Positioning of the lever  96  close to the pivot point of the rocker  12  minimises its movement relative to the static parts of the cylinder head and a number of fairly simple methods for moving the levers are feasible. One such method is shown in, and will be described below by reference to,  FIG. 10 . 
         [0065]    The different views in  FIG. 8  show the design of the valve-lifting rocker in more detail. The valve lift is enabled and deactivated via a sliding plate  98  that pivots about a pin  92  mounted in the rocker body. The plate  98  slides against the underside of the rocker body, and has a bore  100  through which the ball-ended plunger  94  for lifting the valve is able to pass. When the bore  100  in the plate  98  is aligned with the plunger bore in the rocker, the plunger is free to slide and the valve will be deactivated. Rotating the plate through a small angle about the pin  92  allows it to engage in a recess  102  machined into the plunger  94 , and this will lock the plunger  94  in position to transmit the rocker motion to the valve. 
         [0066]    An interlock system is provided to ensure that any change from valve activation to valve de-activation may only occur during the clearance phase of the rocker motion. This is achieved by a pin  104  that is fitted to the plunger  94  and passes through a slot  106  in the rocker body, into a profiled slot  108  in the sliding plate  98 . 
         [0067]    The plunger  94  is loaded by a spring  110 , so that as clearance appears in the rocker system, the plunger will move out of its bore and the pin  104  will move to the bottom of the ‘V’ profile of the slot  108 , rotating the plate to a ‘central’ position between the locked and unlocked positions. As the system approaches the point of valve lift, the clearance reduces and the pin travels up one or other side of the ‘V’, moving the plate into one of its extreme positions. 
         [0068]    The movement of the plate  98  is determined by a torque spring  112  that acts on the pivot pin  92  of the plate  98  and reacts against the control lever  96 . Moving the control lever therefore determines the direction in which the plate is preloaded by the torque spring  112 , and this in turn determines whether the interlock pin  104  will move up the short or the long side of the ‘V’ slot. 
         [0069]      FIGS. 9A to 9F  show the operation of the interlock system as the system moves from the valve lift position ( FIG. 9A ) through the clearance position ( FIG. 9C ) and into the valve-deactivated position ( FIGS. 9E ). The corresponding views of the underside of the rocker as seen in  FIGS. 9B ,  9 D and  9 F, respectively, show how the plate engages with the plunger to transmit the rocker motion to the valve. 
         [0070]    A similar deactivation system can be applied to an engine using bridge pieces to transmit the lift of a single rocker to a pair of valves. The bridge piece design is particularly popular for engines using ‘twisted’ or ‘diamond pattern’ valve arrangements (as shown in  FIG. 10 ) where different rocker geometry would be necessary to actuate the valves of each pair individually. 
         [0071]      FIGS. 10 to 12  show how the deactivation method described by reference to  FIGS. 7 to 9  can be used to switch from two-valve operation via a bridge piece to single valve operation. This is achieved by deactivating a plunger  124  that acts on the centre of the bridge  130  and actuating a single valve via an insert  132  that passes through the bridge piece  130  (see  FIG. 12 ). The valve lift of the single valve will be less than that of the pair of valves because it is closer to the pivot point of the rocker  12  than the centre of the bridge  130 . 
         [0072]      FIG. 10  also shows how the control levers  96  on the rockers may be actuated by a simple plate  140  mounted to the cylinder head cover that is free to slide parallel to the camshaft axis. The plate  140  engages the control levers  96  of the rockers via slots, such that changing the position of the plate  140  will cause all of the levers  96  to rotate. The plate is engaged with an eccentric  142  at one end such that rotating the eccentric will cause the plate  140  to move. 
         [0073]    The design of the valve-lifting rocker may be described more easily with reference to the different views of  FIG. 11 . The rocker  12  is fitted with two spherical pads  150 ,  152 . The first pad  150  acts on the centre of the bridge piece  130 , whilst the second pad  152  acts on the separate insert  132  in the bridge piece  130  that opens a single valve  10 B. The first pad  150  is part of the sliding plunger  124  that may be disconnected from the rocker  12  by the valve deactivation system, whilst the second pad  152  is fixed and may be threaded into the rocker  12  for adjustment purposes. 
         [0074]      FIG. 11  shows the design of the deactivation system for the plunger  124  that acts on the centre of the bridge piece  130 . A moving plate  160  engages with a step on the plunger  124  in order to prevent it from sliding in the rocker, and the plate  160  is provided with an interlock arrangement to ensure that it may only be in one of its two end positions at the point of valve lift. In principle this system operates in an identical manner to that described by reference to  FIGS. 7 to 9 . 
         [0075]      FIG. 12  shows the arrangement of the bridge piece  130  and the insert  132 , which allows a single valve  10 B to be operated through the bridge. Any of the previously described embodiments may be adapted to work with a bridge piece of this type as outlined above. 
         [0076]    All the embodiments described above have operated on the principle of decoupling the valve actuating rocker from the valve stem, that it is say allowing the rocker to oscillate without transmitting its movement to the valve. There are however other ways of integrating a valve deactivation system into a summation valve train such as by decoupling the rockers from one another, decoupling the rockers from the cams or push rods or by forming one of the rocker of two parts that can be selectively locked to one another. 
         [0077]    The embodiment of  FIGS. 13 and 14  deactivates the valve lift by isolating a pivot  200  of the valve-lifting rocker  12  from the movement of the supporting rocker  14 . 
         [0078]      FIGS. 13 and 14  illustrate how this may be achieved on an OHV engine by mounting the valve-opening rocker  12  on a separate eccentric sleeve  200 . The eccentric sleeve  200  is mounted for rotation about a fixed pivot shaft  202 , which also supports the second ‘supporting’ rocker  14 . A latching system  210  is integrated with the eccentric  200  in order to connect the eccentric for rotation with the second rocker  14  and removing this connection acts to deactivate the valve lift. 
         [0079]    The latching system  210  is designed to transmit rotation in only one direction. This is achieved by forming an end surface  214  of a latch pin  212  (see  FIGS. 14B and 14C ) with a ramp which terminates in an abrupt step, thereby acting in a manner analogous to a pawl and ratchet. During the valve lift the latch pin is forced against the driving step on the second rocker (see  FIG. 14A ) causing the eccentric to rotate with the rocker. During the clearance portion of the valve train cycle whilst the valve is closed, the second rocker is still in motion and this causes the latch pin to move away from the driving step on the closing rocker. The contact face  214  of the latch pin  212  and the second rocker  14  are profiled such that the relative motion forces the latch pin into its bore in the eccentric against the action of a spring  216 . As the system approaches the valve opening position, the latch pin  212  moves back into its engaged position under the action of the spring  216 . 
         [0080]    Valve deactivation is achieved by holding the latch pin  212  in its disengaged position so that it is unable to re-engage under the action of the spring  216 . Two different methods for doing this are illustrated in  FIGS. 14B and 14C  which show the design of the eccentric  200 .  FIG. 14B  illustrates a locking ball  220  that will prevent the latch pin from returning when it is supplied with oil pressure whilst  FIG. 14C  shows a mechanical system  230 , shown as being a ball catch, that will always trap the pin  212  in its withdrawn position unless an external force is applied to the end of the pin to re-engage it. This could be achieved with a spring-loaded mechanical system. 
         [0081]    A similar arrangement is possible for the OHC design where the supporting rocker  314  may be divided into a number of sections ( 314   a,    314   b  and  314   c ) as shown in  FIGS. 15A and 15B . In this way either one or both of the valves may be deactivated by disconnecting the respective linkages  314   a,    314   c  from the central section of the support rocker  314   b.    
         [0082]    A number of possibilities exist for locking the outer linkages such that they rotate with the centre section of the location rocker, including a latch pin design as described above. Alternatively a different connection system may be used as will be described below by reference to  FIGS. 16 and 17 . 
         [0083]    As shown in the exploded view of  FIG. 16C  locking may be achieved via a stepped pin  312 . The step of the pin  312  engages with a corresponding step on the central section  314   b  of the support rocker  314  during the valve lift, and the two parts move out of contact during the clearance portion of the motion. The stepped pin  312  can be pushed into a disengaged position by supplying oil pressure to a small hydraulic piston located in a bore in the central section  314   b  of the rocker. 
         [0084]    The locking arrangement can be seen more clearly in  FIG. 17 , where  FIG. 17C  shows the oil drilling  316  used to deactivate the lift and  FIGS. 17A &amp; 17B  and  FIGS. 17D and 17E  show the different positions of the locking pins  312 .  FIGS. 17A and 17B  show the system in its disengaged position whilst the  FIGS. 17C and 17D  show the system in its engaged position where the two pistons  318  are pushed fully into the central section  314   b  of the rocker and the locking pins  312  are engaged with the drive step on the central section  314   b  of the rocker. 
         [0085]    The stepped locking pins  312  need to be retained in a suitable angular alignment in order to engage properly, so each is provided with a slot  320  into which is engaged a ball  322  to limit the angular rotation of the pin  312  (see  FIG. 16C ). A spring  324  behind the pin is designed to act as combined compression and torque spring so that it acts to urge the locking pin  312  out of its bore and to hold it against the end of its angular rotation range. 
         [0086]    It can be seen from  FIG. 17B  that the disengaged pin  312  is designed to move into a position where its flat contact surface is not aligned with that of the centre section  314  of the rocker. This ensures that the pin  312  can only engage when there is some clearance in the system and this prevents the pin starting to engage right at the point of valve lift commencing and causing damage to the parts of the system. Once engaged, the pin will automatically be rotated to the correct position against the action of its spring as the clearance in the system reduces. 
         [0087]    The embodiment of  FIG. 18  deactivates the valve by disconnecting the motion of the cam follower from the rocker system and offers the opportunity for integrating the deactivation system with a control spring for positioning the rocker system during the clearance phase of the cycle. 
         [0088]      FIG. 18  shows the design for an OHC application, where the valve-operating rocker  412  has been divided in to two sections  412   a  and  412   b  that are connected by a pivot shaft  414 . The cam follower  416  is mounted into the lower section  412   b  of the rocker and is able to move relative to the main section  412   a  of the rocker against the action of a control spring  418  that is installed in the main section  412   a  of the rocker. During the clearance portion of the motion cycle, the cam follower  416  will be held in contact with the cam and the clearance adjuster  420  will be held in contact with the valve by the control spring  418 . As the system moves back towards the start of the valve lift cycle, a latch pin  422  may be engaged to transmit the motion of the lower section  412   b  to the main section  412   a  of the rocker in order to lift the valve. If the pin  422  is held out of contact with an abutment  424  on the main section of the rocker, the section  412   b  will continue to move independently of the main section  412   a  of the rocker, thereby deactivating the valve lift. 
         [0089]      FIGS. 19A to 19C  illustrate how a simple spring may be integrated with the rocker assembly to hold the pin  422  out of engagement with the abutment  424 . Valve lift is activated by forcing the pin  422  downwards into the path of the abutment  424  via a strip of spring steel  450  installed into the engine cover. The position of the steel strip  450  is determined by its contact with a control shaft  452  mounted in the cover. The control shaft  452  has a number of profiled sections that each contact the steel strips  450  associated with the different rockers. When the steel strip is contacted by the high portion of the profile, the latch pin  422  is forced to engage and valve lift is produced, but when the steel strip  450  contacts the low portion of the profile, the latch pin  422  will disengage and the valve will be deactivated. 
         [0090]    The operation of the valves is controlled by the rotation of the control shaft  452 , but it is not necessary for all of the valves to be deactivated at the same time. By producing the control shaft  452 , as shown in  FIG. 20 , with a number of different profiles, it is possible to provide a variety of different control shaft positions that will deactivate different combinations of valves. 
         [0091]    The principle of integrating a control spring with the valve deactivation system can also be applied to an OHV system by integrating the control spring and the deactivation system into the cam follower assembly.  FIG. 21A to 21E  shows how this may be achieved using an over-centre locking system similar to that previously described by reference  FIG. 3 . 
         [0092]      FIG. 21B  shows the cam follower  16  in its fully extended position with the large central ball  510  in its upper position to force a ring of smaller balls  512  outwards into a recess in the main body of the cam follower. A hole is provided on the left side of the follower to feed the deactivation oil supply into this recess and force the central ball  510  into its lower position. A second oil drilling is provided on the right hand side to allow lubricating oil into the cam follower. 
         [0093]      FIGS. 21C to 21E  show the arrangement of the balls in the three different positions of the follower.  FIG. 21C  shows the follower fully extended in order to control the rocker system,  FIG. 21D  shows the follower in its locked position where the ring of locking balls  512  are engaged with the lower face of the cut-out in the follower bore, and the  FIG. 21E  shows the follower in its fully compressed state (valve deactivated) where the central ball  510  has been moved into its lower position by oil pressure and the ring of smaller balls  512  have moved inwards in order to pass the edge of the recess. 
         [0094]    An alternative design for integrating a deactivation system into a cam follower is shown in  FIG. 22 . The valve deactivation in this case is achieved via a pair of splined components  610 ,  612  that may either be aligned so that the inner spline will slide into the outer spline, deactivating the valve lift, or misaligned so that the end of the inner spline will contact the top face of the outer spline, transmitting the cam lift to the rocker system. 
         [0095]    The internally splined component  612  has a helical groove  614  machined into its outer diameter, which is engaged by a ball  616  that is permanently fitted to the body of the cam follower. Oil can be supplied to the cavity below the internally splined component in order to move it to a higher position and this also causes it to rotate because of the helical groove  614 . When the lower splined component  612  is held in this upper position, the upper spline can pass through it without making contact. When the lower splined component  612  is in its lower position, the two sets of splines are misaligned and so the upper spline cannot enter the lower spline. 
         [0096]    The lower splined component  612  can only move to its upper position when the valve train is in the clearance portion of the cycle and the cam follower is fully extended. If it should be in the process of movement when it comes into contact with the upper spline, it will simply be forced back into its bore and take up the locked position. 
         [0097]    A pair of slots in the bore of the follower locates the upper spline  610  and allows it a small range of angular travel. It is preloaded against one side of these slots by a torque spring  618  that is located beneath it in a housing  620 , which also engages into the slots in the follower bore. This allows the upper splined component  610  to rotate with the lower spline when the pair are engaged and the lower spline is forced back into its bore under the action of the cam lift.