Abstract:
An internal combustion engine is described having a valve mechanism that comprises two cams ( 120,122 ) mounted coaxially and a summation lever ( 124 ) having cam followers ( 126, 127 ) in contact with both cams so as to move in proportion to the instantaneous sum of the lifts of the respective cams. A control spring ( 128 ) is provided to maintain contact between one cam profile and its respective follower(s), and a valve actuator ( 114 ) opens the engine valve ( 110 ) in dependence upon the movement of the summation lever, thereby enabling so as to enable the valve timing, valve lift and valve event duration to be adjusted by varying the phases of the two cams. In the invention, the summation lever is constructed in two parts ( 124   a,    124   b ) that can be selectively locked and unlocked to allow the valve lift to be deactivated and the motion of both parts is controlled by the control spring ( 128 ) when the two parts of the summation lever are unlocked from one another.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an internal combustion engine having a valve actuating mechanism that comprises two cams mounted coaxially, a summation lever having at least one cam follower in contact with each respective cam and movable in proportion to the instantaneous sum of the lifts of the two cams, a control spring acting to maintain one cam in contact with each follower associated therewith, and a valve actuating rocker serving to open an engine valve in dependence upon the movement of the summation lever, the timing, lift and duration of each valve event being adjustable by varying the phases of the two cams. 
       BACKGROUND OF THE INVENTION 
       [0002]    An internal combustion engine as set out above is described in the Applicants&#39; earlier GB Patent Application No. 0708967.5. In the accompanying drawings,  FIG. 1   a  is a perspective view of a valve actuating mechanism as described in the latter patent application and  FIG. 1   b  is a section through the same mechanism. A poppet valve  10  is urged towards its closed position against its valve seat in the engine cylinder head by a valve spring  12 . A downwards force to open the valve  10  is applied by an actuating rocker  14  of which the opposite end is pivoted on an adjustable articulated link  16 . Valve actuation is effected by a camshaft driven in synchronism with the engine crankshaft which carries two cams  20  and  22  that can be phase shifted in relation to one another. The cam  20  is formed from two identical parts that straddle the other cam  22 . A summation lever  24 , which is pivotably carried by the actuating rocker  14  has roller followers  26 ,  27  at its opposite ends one of which is maintained in contact with a respective one of the two cams  20  and  22  by a control spring  28 . The control spring  28  is required in a cam summation system of this type in order to control the motion of the summation lever  24  and to maintain contact between the actuating rocker  14  and the valve tip whilst the valve is closed. It can be seen from  FIG. 1   b  that the control spring  28  acts in a downward direction to force the adjacent cam follower  26  away from its cam lobe  22 , and this forces the two followers  27  on the opposite side of the summation lever into contact with their respective cam lobes  20 . 
         [0003]    The present invention seeks to provide an improvement of the valve actuating mechanism described above which additionally enables the valve  10  to be deactivated. 
         [0004]    It has been previously proposed in WO03/016684 to provide valve deactivation in a valve train employing a summation lever by forming the summation lever in two parts that may be selectively locked to one another.  FIGS. 2   a ,  2   b  and  2   c  of the accompanying drawings correspond respectively to  FIGS. 11 ,  12  and  13  of WO03/016684. The two parts  24   a  and  24   b  of the summation lever are pivotable relative to one another about a pivot pin  30  and can be locked to one another by a locking pin  32 . In the locked position shown in  FIGS. 2   a  and  2   c  the summation lever moves as one piece and opens the valve  10  under the action of the two cams  20  and  22 . However, when the locking pin  32  is released, as shown in  FIG. 2   b , the two parts  24   a  and  24   b  are merely articulated relative to another by the action of the two cams  20  and  22  and the valve remains closed. 
         [0005]    It is well accepted that a valve deactivation system requires a lost motion spring to control the position of the valve train system and maintain contact between each cam lobe and its follower during the cam lift event when it is being operated with the valve deactivated. However, WO03/016684 is silent on how such a spring is incorporated in the valve deactivation system. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention, there is provided an internal combustion engine having a valve mechanism that comprises two cams mounted coaxially, a summation lever having cam followers in contact with both cams, the summation lever being moveable in proportion to the instantaneous sum of the lifts of the respective cams, a control spring to maintain contact between one cam profile and its respective follower(s), and a valve actuator serving to open the engine valve in dependence upon the movement of the summation lever, so as to enable the valve timing, valve lift and valve event duration to be adjusted by varying the phases of the two cams, wherein the summation lever is constructed in two parts that can be selectively locked and unlocked to allow the valve lift to be deactivated and the motion of both parts is controlled by the control spring when the two parts of the summation lever are unlocked from one another. 
         [0007]    The invention employs a two part summation lever design, which allows the followers for the two different cam profiles to move independently from one another. It also provides a latch mechanism for locking the two parts together. The key feature of the design is that it allows the control spring to act as a lost motion spring whilst the valve lift is deactivated, as well as controlling the movement of the summation lever to ensure that its cam follower(s) maintain contact with one of the cam profiles at all times. By combining the functions of the lost-motion spring required by a deactivation system and the control spring required by a cam summation system, the invention enables valve deactivation to be achieved with a minimum of additional complexity. 
         [0008]    Incorporating a valve deactivation system into the summation lever is advantageous in that it allows the mass of the moving components to be minimised whilst the valve is deactivated. The disadvantage of using the summation lever is that it is difficult to find space for a sufficiently strong lost motion spring, and if such a spring were to be integrated with the actuating rocker, it would significantly add to the valve train mass during normal operation when the valve lift is activated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:— 
           [0010]      FIGS. 1   a  and  1   b  show a known cam summation system as described above, 
           [0011]      FIGS. 2   a ,  2   b  and  2   c  show a known two part summation lever as described above, 
           [0012]      FIG. 3   a  is an exploded view of the summation lever of a first embodiment of the invention, 
           [0013]      FIG. 3   b  is a perspective assembled view similar to  FIG. 1   a  of the first embodiment of the invention, 
           [0014]      FIG. 3   c  is an end view of the first embodiment, 
           [0015]      FIG. 4   a  is a side view of the first embodiment with the valve closed, 
           [0016]      FIG. 4   b  is a section through the first embodiment (taken on the line A-A in  FIG. 3   c ) with valve closed, 
           [0017]      FIG. 4   c  is a side view of the first embodiment with the valve open, 
           [0018]      FIG. 4   d  is a section through the first embodiment (taken on the line A-A in  FIG. 3   c ) with valve open, 
           [0019]      FIGS. 5   a  and  5   b  are a side view and a section of the first embodiment with the cam off lift and the valve deactivated, 
           [0020]      FIGS. 5   c  and  5   d  are a side view and a section of the first embodiment with the cam on lift and the valve deactivated, 
           [0021]      FIGS. 6   a  and  6   b  are views similar to  FIGS. 3   a  and  3   b  showing an embodiment operating in the same way as the first embodiment but fitted with a lever for operating the latch mechanism, 
           [0022]      FIGS. 7   a  to  7   d  are side views and sections showing the second embodiment of the invention under different conditions, 
           [0023]      FIGS. 8   a  and  8   b  are details of  FIGS. 7   c  and  7   d  drawn to an enlarged scale, 
           [0024]      FIGS. 9   a  and  9   b  show exploded and assembled perspective view of a third embodiment of the invention, 
           [0025]      FIGS. 10   a ,  10   b  and  10   c  are an end view, a side view and a section explaining the latch mechanism employed by the third embodiment of the invention, 
           [0026]      FIGS. 11   a  to  11   d  are views of a fourth embodiment of the invention using a latch mechanism similar to that of the third embodiment but a different operating mechanism for the latch pin, 
           [0027]      FIGS. 12   a  to  12   e  are different views of a fifth embodiment of the invention in which the latch mechanism for selectively locking the two parts of the summation lever to one another is built into the axle of the single roller follower, 
           [0028]      FIGS. 13   a  to  13   d  are side and end views in different positions of an embodiment having a hydraulically actuated latch mechanism, 
           [0029]      FIGS. 14   a  and  14   b  are a perspective and a side view of the embodiment of  FIG. 13 , and 
           [0030]      FIG. 14   c  is a section on the line D-D in  FIG. 14   b.    
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    To avoid unnecessary repetition, components serving the same function will be given similar reference numerals throughout the description of the different illustrated embodiments, but components of this first embodiment will be in the 100&#39;s series, those of the second embodiment in the 200&#39;s series and so on. 
         [0032]      FIGS. 3 ,  4  and  5  show a first embodiment of the invention which demonstrates how the invention may be applied to the valve train of  FIG. 1 . The summation lever is constructed in two parts  124   a  and  124   b , that can move relative to one another. The first part  124   a  is supported by the valve actuating rocker  114  by means of a pivot  160  and carries a pair of cam followers  127  that contact the cam profiles  120 . The second part  124   b  of the summation lever is connected to the first  124   a  by a pivot pin  130  received in holes  130   a  in the first part  124   a  and a hole  130   b  in the second part. The second part  124   b  carries a single cam follower roller  126 , which is rotatable about an axle pin  129  and contacts the second cam profile  122 . The second part  124   b  of the summation lever is also connected by a pin  128   a  received in holes in the second part  124   b  to the control spring  128  which controls the motion of the summation lever while the valve is closed. 
         [0033]    The summation lever assembly also contains a latch mechanism for selectively preventing relative movement between the two parts of the summation lever. The latch mechanism is composed of a nose  150  on the second part  124   b  of the summation lever and a recess  152  in a latch pin  132  mounted in holes  132   a  in the first part  124   a  of the summation lever. By rotating the latch pin  132  to engage or disengage it from the nose  150 , the two parts  124   a  and  124   b  of the summation lever can either be locked together or allowed to move independently. 
         [0034]    When the latch mechanism is engaged and the two parts of the summation lever are unable to move relative to each other, the valve lift will occur in the normal manner, as shown in the views of  FIGS. 4   a  to  4   d.    
         [0035]    When the latch pin  132  is rotated, the two parts  124   a  and  124   b  of the summation lever are able to move relative to each other so that, when both the cams  120  and  122  are on lift, the single cam follower  126  moves independently to the pair of followers  127  causing the control spring  128  to compress instead of the valve spring, the valve  110  therefore remaining closed. The action of the control spring  128  ensures that both sets of cam followers remain in contact with their respective profiles  120 ,  122  throughout the lift event—thus performing the function of a lost motion spring. The operation of the system with the latch mechanism disengaged is illustrated in  FIGS. 5   a  to  5   d . The important point to notice in  FIGS. 5   b  and  5   d  is that the nose  150  of the second part  124   b  of the summation lever has been allowed to move past the latch pin  132  by rotating the latter. 
         [0036]    All of the remaining embodiments of the invention now to be described share the same fundamental principle of operation of using a two-part summation lever and utilising the summation lever control spring to act as a lost-motion spring whilst the valve lift is deactivated. It can be appreciated however that there are a wide variety of possible methods for selectively connecting and disconnecting the two parts of the summation lever. 
         [0037]    As described above, the embodiment of  FIGS. 3 to 5  uses a rotating latch pin  132  but no means have been shown for rotating the latch pin  132  to switch between valve activation modes. It is important that any changeover between operating modes should take place only while the valve is closed. 
         [0038]    A suitable operating mechanism for rotating the latch pin of the embodiment shown in  FIGS. 3 to 5  is shown in  FIGS. 6 to 8 . The previously described components have all been allocated the same reference numerals, but in the 200 series, and only the operating mechanism used to rotate the latch pin  232  need now be described. 
         [0039]    The latch operating mechanism comprises a deactivation lever  262  that is used to rotate the pivot  260  connecting the first part  224   a  of the summation lever to the valve actuating rocker  214 . As best seen from the sectional views of  FIGS. 8   a  and  8   b , the pivot pin  260  has a recess  261  defining an eccentric that is engaged by a small rod  263  guided for sliding movement in the actuating rocker  214  and urged into the recess  261  by means a U-shaped spring clip  267 . The opposite end of the rod  263  engages a shoulder on the opposite side of the latch pin  232  from the recess  252 . If the pivot pin  260  is rotated counter-clockwise as viewed in  FIG. 8   a , the rod  263  is retracted away from the latch pin  232 . The latch pin  232  is biased by the spring  268  counter-clockwise as viewed causing the nose  250  to engage in the recess  252  thereby locking the two parts of the summation lever for movement with one another. If however the pivot pin  260  is rotated clockwise by the deactivation lever  262  into the position shown in  FIGS. 8   a  and  8   b , then when the summation lever  224  attempts to rotate clockwise about the pivot pin  260 , as occurs between valve events, the rod  263  engages the shoulder on the latch pin  232  causing it to rotate clockwise, as shown by  FIGS. 8   a  and  8   b . This allows the nose  250  of the second part  224   b  of the summation lever to move past the latch pin  232  and articulates the summation lever so as to prevent the valve from opening. 
         [0040]    The spring  268  used to bias the latch pin  232  is also used to bias the deactivation lever  262 . The deactivation lever  262  is retained on the end of the pivot pin  260  by a fastener  272  and is coupled for rotation with it by a spring biased lost motion coupling consisting of a narrow key  264  on the deactivation lever  262  engaged in a wider recess  266  in the pivot pin  260 , the biasing spring of the pivot pin  260  being designated  265  in  FIG. 6   a.    
         [0041]    When the valve lift is activated, the surface of a curved pad on the deactivation lever  262  is concentric with the pivot axis of the actuating rocker  214  and hence the surface maintains the same position throughout the valve lift cycle. The spring  268  acts on the lever  262  such that it will return to this position in the absence of any control input. 
         [0042]    In order to deactivate the valve lift, the lever  262  may be depressed by a solenoid actuator, or by a hydraulic or mechanical actuator to the position shown in the  FIG. 7   b . This will not immediately move the pivot pin  260  but will move the key  264  to a new position. The key acts as a stop limiting the rotation of the pivot pin  260  by the spring  265 . When the cams reach a suitable position for valve deactivation to take place, the pivot pin  260  will be rotated to its new position by the spring  265 . 
         [0043]    The position of the lever pad will again be constant throughout the camshaft cycle because the valve lift is deactivated and the valve actuator does not rotate about its pivot. 
         [0044]    The embodiment of  FIGS. 6 to 8  thus uses the motion of the summation lever in between valve events to ensure that the transition between valve activation and deactivation will always occur just after the valve has closed, regardless of when the motion of the deactivation lever takes place. 
         [0045]    It can be appreciated that a number of different methods exist for selectively disconnecting the two parts of the summation lever.  FIGS. 9 and 10  show an alternative embodiment which, in place of a rotating latch pin, uses a sliding latch pin  383  engageable in a pair of notches  385  in the second part  324   b  of the summation lever. 
         [0046]    As with the previous embodiment, the system is mechanically operated by moving one of two deactivation levers  381  (only one is shown in  FIG. 9   a ) pivotable about the pivot pin  315  of the actuating rocker  314 . Each deactivation lever  381  has a projecting spigot  382  that engages between two arms of a torque spring  384  that is itself also free to rotate about the pivot pin  315 . The ends of the latch pin  383  are straddled by the free ends of the arms of the torque springs  384 . The springs  384  act as biased lost motion mechanisms connecting the deactivation levers  381  to the ends of the latch pin  383 . The levers  381  tension the springs  384  and these in turn act to move the latch pin  383  at the first occasion when it is in line with the notches  385  and free to be moved by the force of the springs  384 . In  FIGS. 10   b  and  10   c  the latch pin  383  is shown in the engaged position from which it can be released to deactivate the associated valve by rotating the levers  381  counter clockwise. 
         [0047]    The embodiment of  FIG. 11  uses a similar latching pin  483  to the third embodiment described above, but the deactivation lever  481  forms part of an interlock mechanism such that it can only move at one point in the valve lift cycle. In this case, forked members  487  straddling the ends of the pin  483  are secured for rotation with the deactivation levers  481 . The pivot shaft  460  connecting the valve actuator  414  to the summation lever  424   a  is fixed for rotation with the summation lever  424   a  and has a profiled cut-out  491  in one end that engages with an interlock pin  489  on the deactivating lever  481 .  FIG. 11   a  shows the interlock pin positioned outside the cut-out  491  in the pivot shaft such that the valve lift is activated. FIG.  11   d  on the other hand shows the interlock pin  489  engaged in the cut-out  491  in the pivot shaft  460  such that the valve lift is deactivated. 
         [0048]    The profile of the cut-out  491  in the pivot shaft  460  prevents the interlock pin  489  from moving freely between these two positions, and it may only do so when the valve has just closed and the summation lever  424   a  is rotated to its furthest anti-clockwise position as shown in  FIGS. 11   b  and  11   c . Once the summation lever moves away from this position, the deactivation lever is locked in position until after the next valve lift event. 
         [0049]    In addition to the deactivation capability, it would be possible to use the two-part summation lever design to adjust the clearance in the system by a small amount. For example, the latching pins  383  and  483  could be a graded component and this would allow the activated position of the second parts  324   b  and  424   b  to be adjusted relative to the main parts  324   a  and  424   a  of the summation lever. 
         [0050]    There are further alternative latch designs that may be considered, one example being shown in  FIG. 12 . In this embodiment, the single roller follower  526  has a hollow axle in which there is received a spring biased latch pin  532 . An actuator  533  in the form of a push button is mounted on the first part  524   a  of the summation lever and is used to push in the locking pin  532 . In the position shown in the section of  FIG. 12   d , with the button  533  depressed, the latching mechanism locks the two parts of the summation lever to one another through the engagement of the locking pin  532  in a hole in one of the cheeks of the first part  524   a  of the summation lever and through engagement of the deactivation button  533  in the second part  524   b  of the summation lever. In  FIG. 12   e  the latch is released and the valve is deactivated because the button  533  is retracted and the locking pin  532  does not project beyond the axle of the roller follower  526 . 
         [0051]      FIGS. 13 and 14  show how the latch may be designed to operate hydraulically and also depict how the concept may be applied to a pair of valves rather than a single valve. 
         [0052]    The latching of the two summation lever parts  624   a  and  624   b  is achieved by a retractable pin  632  (see  FIG. 13   c ) contained in the first part  624   a  of the summation lever that can be engaged into a receiving hole or slot in the second part  624   b  of the summation lever to lock the two parts together. The latching pin  632  has a return spring to disengage it from the second part of the summation lever, but the application of oil pressure to the pin will overcome the spring and connect the two parts of the summation lever so that valve lift is enabled. It can be appreciated that a latch could also be designed such that the return spring caused the two parts to be locked together and the application of oil pressure would deactivate the valve lift. 
         [0053]    Oil is supplied to the latch pin  632  via the pivot shaft  660  connecting the summation lever  624   a  to the valve actuator  614 , and this pivot shaft  660  also contains a spool  601  to control the timing of the latching and unlatching events, as shown in  FIG. 14   c.    
         [0054]    Oil under pressure is fed into the pivot shaft  660  from one of the valve actuators  614  and acts to move the spool  601  and compress its return spring  602 . The spool  601  may only move if there is a vent in the cavity containing the spool return spring, otherwise the position of the spool  601  is maintained via a hydraulic lock. The venting of the cavity is achieved via a drilled hole in the pivot shaft  660  and a corresponding hole in the second valve actuator  614  (see  FIG. 13   a ). These two drillings only line up when the summation lever is rotated to one extreme of its motion, when the valve event has just finished. This means that the spool  601  will not move just prior to valve opening and will ensure that the latch will change state when there are no forces acting on the latch pin  632 . 
         [0055]    When the spool  601  moves to compress its return spring  602 , the oil pressure is connected to the drilling through the centre of the pivot shaft (see  FIG. 13   c ) and acts to engage the latch pin  632 . When the oil pressure is removed, the spool  601  will move back under the action of the return spring  602  and the central drilling in the pivot shaft is connected to the vent hole at the end of the next valve event. 
         [0056]    The preferred embodiments of the invention described above offer the following advantages:— 
         [0057]    Valve deactivation can be achieved with only a small additional mass. 
         [0058]    No additional lost motion spring is required, allowing the system mass and packaging space to be minimised. 
         [0059]    The timing of the mechanical switching event can be synchronised with the motion of the actuating rocker system so that it always occurs at the correct point in the lift cycle regardless of the timing of the control input.