Abstract:
A switching mechanism capable of switching between a two-stroke and a four-stroke operation of an engine as desired, wherein the switching mechanism is switchable between engagement with a first cam lobe for four-stroke operation and a second cam lobe for two-stroke operation, the four-stroke operation maximizing fuel and emissions efficiency and the two-stroke operation maximizing power.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a switching mechanism and more particularly to a switching mechanism capable of switching between a two-stroke and a four-stroke operation of an engine as desired, wherein the switching mechanism is switchable between engagement with a first cam lobe for four-stroke operation and a second cam lobe for two-stroke operation. 
   BACKGROUND OF THE INVENTION 
   Conventional internal combustion engines operate according to thermodynamic principles following either a two-stroke cycle or a four-stroke cycle which are commonly classified as a two-stroke engine or a four-stroke engine, respectively. Both types of engines can operate using a range of fuels including gasoline, diesel, alcohol and gaseous fuels. The fuel is typically introduced into the engine using a range of devices including carburetors and fuel injectors, for example. The fuel-air mixture can be ignited by a range of methods including spark ignition and compression ignition. Each engine cycle type has different merits and shortcomings with varying power density, fuel consumption, exhaust emissions, noise, vibration, engine size, weight, cost, etc. 
   For ordinary driving conditions, a typical vehicle is powered by an engine that is sized for the maximum performance requirement of the vehicle. For example, a passenger vehicle passing another vehicle on a hill may for a brief period utilize the maximum power of the engine. At virtually all other times, from low speed city driving to highway cruising, the power demand is a fraction of the available power. Over-dimensioned engines with large displacements are therefore constructed to meet only occasional power demands. 
   The situation for large displacement working vehicles is even more dramatic. Freight hauling tractor-trailers, delivery trucks, and other vehicles are designed with engines to accommodate full loads. When traveling empty, the power requirement is substantially diminished. Similarly, marine engines often must shift from high speed or power operation to low speed where the engine operates in idle for long periods of time. Unused displacement or over displacement results in over-sized, large engines with a multiplicity of cylinders, having a weight and complexity resulting in an unnecessary consumption of fuel and excess pollution. 
   Existing internal combustion engines are usually limited in their operation to two-stroke or four-stroke cycles. The engines have a fixed fuel distribution system, optimized for a limited range of operation. With fixed compression ratios and limited means of optimizing performance for all ranges of power, torque, and engine speed, fuel consumption is typically characterized by a specific fuel consumption curve with one point of minimum fuel consumption. 
   Although certain improvements to engine design have addressed these problems, for example, the use of a turbocharger for high performance operation, satisfaction of power demand is at the expense of optimized fuel consumption. 
   Existing internal combustion engines have used switchable cam followers to actuate valves from multiple cam profiles to provide for variations in valve lash between one cam profile to the next. In a conventional system where a rocker arm or a cam follower operate with only a single cam profile, common practice is the use of a hydraulic valve adjuster that is pressurized by lubrication oil and held in a filled position using an internal check valve. These hydraulic valve adjusters have been placed in the block, in the head or in the rocker arm or cam follower itself and are very universal in their application. It is, however, inadequate in valve trains where multiple cam profiles actuate the valves through the use of rocker arms or cam followers that by some means switch from one profile to another. 
   It would be desirable produce a switching mechanism for switching an engine from two-stroke to four-stroke operation wherein fuel efficiency, emissions efficiency, and power are maximized. 
   SUMMARY OF THE INVENTION 
   Consistent and consonant with the present invention, a switching mechanism for switching an engine from two-stroke to four-stroke operation wherein fuel efficiency, emissions efficiency, and power are maximized, has surprisingly been discovered. 
   The switching mechanism for switching an engine from one stroke type to another stroke type comprises:
         a first pair of pins, a first end of each of the first pair of pins in communication with a pressure fluid and a second end of each of the first pair of pins urged by a spring; and   a switching mechanism adapted to transform a rotary motion of a cam shaft to a linear motion of a valve, the switching mechanism housing the first pair of pins and being adapted to engage a two-stroke cam surface and a four-stroke cam surface of the cam shaft, whereby a change in pressure of the pressure fluid causes a movement of at least one of the first pair of pins to stop the transformation of motion from one of the two-stroke cam surface and the four-stroke cam surface to the valve.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic left side elevational view of a mechanism for switching an engine from one stroke type to another stroke type including an engine valve, rocker, and cam shaft assembly in accordance with the present invention; 
       FIG. 2  is a schematic top view of the assembly shown in  FIG. 1 ; 
       FIG. 3  is a schematic sectional view of the assembly shown in  FIG. 1  taken along line  3 — 3 ; 
       FIG. 4  is a schematic front elevational view of a second embodiment in accordance with the present invention showing a mechanism for switching an engine from one stroke type to another stroke type including a switching tappet in section and a cam shaft; 
       FIG. 5  is a schematic sectional view of the switching tappet and the cam shaft of  FIG. 4  taken along line  5 — 5 ; 
       FIG. 6  is a schematic front elevational view of the switching tappet and the cam shaft of  FIG. 4  showing a locking pin in a position to cause transfer of motion from a four-stroke cam only and with the tappet in a base circle position; 
       FIG. 7  is a schematic front elevational view of the switching tappet and the cam shaft of  FIGS. 4 and 6  showing the locking pin in a position to cause transfer of motion from a four-stroke cam only and with the tappet in a full lift position; 
       FIG. 8  is a schematic front elevational view of the switching tappet and the cam shaft of  FIG. 4  showing a locking pin in a position to cause transfer of motion from two-stroke cams only and with the tappet in a base circle position; 
       FIG. 9  is a schematic front elevational view of the switching tappet and the cam shaft of  FIGS. 4 and 8  showing the locking pin in a position to cause transfer of motion from the two-stroke cams only and with the tappet in a full lift position; 
       FIG. 10  is a schematic front elevational view of the switching tappet and the cam shaft of  FIG. 4  showing a mechanical type lash adjustment; 
       FIG. 11  is a schematic front elevational view of the switching tappet and the cam shaft of  FIG. 4  showing a hydraulic type lash adjustment; 
       FIG. 12  is a schematic side sectional view of a third embodiment in accordance with the present invention showing a mechanism for switching an engine from one stroke type to another stroke type including a cam follower and rocker arm assembly; and 
       FIG. 13  is a schematic sectional view of the assembly of  FIG. 12  taken along line  13 — 13 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , there is shown generally at  10  a schematic left side elevational view of a mechanism for switching an engine from one stroke type to another stroke type or an engine valve actuating assembly in accordance with the present invention. An engine valve  12  has one end thereof seated in a cylinder block  14 . The other end of the valve  12  abuts a rocker arm  16  of a rocker assembly  18 . An aperture  20  formed in the rocker assembly  18  receives a hollow rocker shaft  22  therein. The number of the valves  12  provided varies depending upon the number of cylinders provided in an automobile engine (not shown). 
   As clearly illustrated in  FIG. 2 , a pair of spaced apart follower arms  24 ,  26  extend outwardly from the rocker assembly  18  in a direction away from the valve  12 . The follower arms  24 ,  26  have a linking member  27  disposed therebetween. A follower roller  28 ,  30  is respectively disposed on a distal end of each of the follower arms  24 ,  26 . The follower roller  28  is operably engaged with a four-stroke cam surface  32  and the follower roller  30  is operably engaged with a two-stroke cam surface  34 . The four-stroke cam surface  32  and the two-stroke cam surface  34  are disposed on an outer surface of a cam shaft  36 . 
     FIG. 3  shows a schematic sectional view of the engine valve actuating assembly  10  shown in  FIG. 1  taken along line  3 — 3 . The rocker shaft  22  has a radial bore  38  formed therein. The radial bore  38  provides communication between the hollow portion of the rocker shaft  22  and a pressure fluid chamber  40  formed in the linking member  27  of the rocker assembly  18 . A first locking pin  42  and a second locking pin  44  are disposed in opposing ends of the pressure fluid chamber  40 . A third pin  43  is disposed adjacent the first locking pin  42  on a side opposite the second locking pin  44 . A fourth pin  45  is disposed adjacent the second locking pin  44  on a side towards the first locking pin  42 . A first return spring  46  with at least a portion thereof disposed in a bore formed in the follower arm  24  urges the third pin  43  and the first locking pin  42  towards the middle portion of the pressure fluid chamber  40  or towards the second locking pin  44 . A second return spring  48  with at least a portion thereof disposed in a bore formed in the follower arm  26  urges the second locking pin  44  and the fourth pin  45  towards the middle portion of the pressure fluid chamber  40  or towards the first locking pin  42 . 
   In operation, the engine is typically operated in a standard mode, one of the four-stroke and the two-stroke mode. For illustrative purposes, standard operation will be considered four-stroke operation. Operation of the valve  12  is controlled by the rocker assembly  18 . As the cam shaft  36  rotates, a lobe  33  of the four-stroke cam surface  32  is caused to rotate through 360 degrees. As the lobe  33  of the four-stroke cam surface  32  passes under the follower roller  28 , the rocker assembly  18  is caused to pivot about the rocker shaft  22 . Thus, the distal end of the rocker arm  16  is caused to move downwardly causing the valve  12  to open. As the lobe  33  of the four-stroke cam surface  32  moves beyond the follower roller  28 , the rocker arm  16  is caused to move upwardly and the valve  12  is caused to close. Operation of the valve  12  by the lobes  35  of the two-stroke cam surface  34  is the same as that described for the lobe  33  of the four-stroke cam surface  32 . 
   The engine, which has a combustion system suitable for both two-stroke and four-stroke operation, can be changed from one operating mode to another by changing from the operation of the valve  12  from once per revolution of the cam shaft  36  or crank to twice per revolution of the cam shaft  36 . This is accomplished by switching the engine valve  12  from following the four-stroke cam surface  32  to following the two-stroke cam surface  34 . The first locking pin  42  operates to lock and engage the follower arm  24  for four-stroke mode. The second locking pin  44  operates to lock and engage the follower arm  26  for two-stroke mode. The third pin  43  ensures proper alignment of the first locking pin  42  to engage the follower arm  24  for the four-stoke mode. The fourth pin  45  ensures proper alignment of the second locking pin  44  to engage the follower arm  26  for the two-stroke mode. In the embodiment shown, when one of the first locking pin  42  and the second locking pin  44  is engaged with the respective follower arm  24 ,  26 , the other of the first locking pin  42  and the second locking pin  44  is disengaged from the respective follower arm  24 ,  26 . 
   Engagement and disengagement of the first locking pin  42  and the second locking pin  44  is accomplished by a hydraulic pressure applied which is controlled by a solenoid valve based on a signal from an engine management system. A pressure fluid such as engine oil, for example, is supplied to the hollow portion of the rocker shaft  22 . The pressure fluid enters the radial bore  38  and the pressure fluid chamber  40  and urges the first locking pin  42  and the third pin  43  to move against the force of the first return spring  46  and the second locking pin  44  and the fourth pin  45  to move against the force of the second return spring  48 . In the embodiment shown, when it is desired to operate in the four-stroke mode, the pressure fluid causes the first locking pin  42  to move in a direction against the force of the first return spring  46  to engage the follower arm  24 . The second locking pin  44  is likewise caused to move in a direction against the force of the second return spring  48  to disengage the follower arm  26 . The split between the second locking pin  44  and the fourth pin  45  facilitates the disengagement of the follower arm  26 . When it is desired to operate in the two-stroke mode, a flow or pressure of the pressure fluid is reduced and the force of the second return spring  48  causes the second locking pin  44  to move to the position shown in  FIG. 3  and engage the follower arm  26 . The first locking pin  42  and the third pin  43  are likewise caused to move to the position shown in  FIG. 3 , thus disengaging the follower arm  24 . The split between the first locking pin  42  and the third pin  43  facilitates the disengagement of the follower arm  24 . 
   Referring now to  FIGS. 4 and 5 , there is shown generally at  50  a schematic front elevational view of a mechanism for switching an engine from one stroke type to another stroke type or switching tappet assembly which represents a second embodiment of the present invention. The tappet assembly  50  is disposed between a cam shaft  52  and a valve stem  54 . The tappet assembly  50  includes an inner tappet  56  and an outer tappet  58 . A valve plunger  60  is disposed between the inner tappet  56  and the outer tappet  58 , and is substantially concentric therewith. The inner tappet  56  abuts a four-stroke cam surface  62  of the cam shaft  52  and the outer tappet  58  abuts a pair of two-stroke cam surfaces  64 . It is understood that the inner tappet  56  could abut a two-stroke cam surface and the outer tappet  58  could abut four-stroke cam surfaces without departing from the scope and spirit of the invention. An inner tappet stop ring  66  militates against separation of the inner tappet  56  from the valve plunger  60 . An outer tappet stop  68  formed on the opposite end of the outer tappet  58  from the inner tappet stop ring  66  militates against separation of the valve plunger  60  from the outer tappet  58 . 
   The inner tappet  56  is maintained in contact with the four-stroke cam surface  62  by an inner tappet return spring  70 . One end of an outer tappet return spring  72  urges the outer tappet  58  to maintain contact with the two-stroke cam surfaces  64  of the cam shaft  52 . The other end of the outer tappet return spring  72  abuts a spring retainer  74 . 
   Lateral holes  76  are formed in opposing sides of the inner tappet  56  and are aligned with a hole  78  formed in the valve plunger  60  and a hole  80  formed in the outer tappet  58 . Locking pin return springs  82  are disposed in the holes  76  of the inner tappet  56 . One end of each of the locking pin return springs  82  is received in a locking pin plunger  84 . A locking pin  86  is disposed on a side of the locking pin plunger  84  opposite the locking pin return springs  82  and is slidingly received in the holes  76 ,  78 ,  80 . A pair of locking pin retainers  88  prevent each of the locking pins  86  from sliding free of the outer tappet  58 . Each of the locking pin retainers  88  has a central aperture  90  formed therein and is in communication with a pressure fluid source (not shown). A lubrication and lash adjustment aperture  92  is also formed in the outer tappet  58  and the valve plunger  60 . As clearly shown in  FIG. 5 , an antirotation pin  94  is disposed in a wall of the valve plunger  60  and abuts the inner tappet  56  and the outer tappet  58 . 
   In operation, the engine is typically operated in a standard mode, one of the four-stroke and the two-stroke mode. For illustrative purposes, standard operation will be considered four-stroke operation. Actuation of the valve stem  54  is controlled by the tappet assembly  50 . As the cam shaft  52  rotates, a lobe  96  of the four-stroke cam surface  62  is caused to rotate through 360 degrees. As the lobe  96  of the four-stroke cam surface  62  rotates into the inner tappet  56 , the inner tappet  56  is caused to move downwardly, thus causing the valve stem  54  to move downwardly and open a valve (not shown). As the lobe  96  of the four-stroke cam surface  62  moves beyond the inner tappet  56 , the inner tappet  56  is caused to move upwardly, thus causing the valve stem  54  to move upwardly and close the valve. Downward movement of the valve stem  54  by a pair of lobes  98  of the two-stroke cam surface  64  is caused by the lobes  98  causing the outer tappet  58  to move downwardly, similar to that described for the lobe  96  of the four-stroke cam surface  62 . The outer tappet return spring  72  causes the tappet assembly  50  to maintain contact with the lobes  96 ,  98  of the cam shaft  52  and return to the position shown in  FIG. 4  when the lobes  96 ,  98  have passed the respective inner tappet  56  and outer tappet  58 . 
   The engine, which has a combustion system suitable for both two-stroke and four-stroke operation, can be changed from one operating mode to another by changing from the actuation of the valve stem  54  from once per revolution of the cam shaft  52  or crank to twice per revolution of the cam shaft  52 . This is accomplished by switching the tappet assembly  50  from following the four-stroke cam surface  62  to following the two-stroke cam surface  64 . In the embodiment shown, the locking pins  86  operate to unlock and disengage the valve plunger  60  from the outer tappet  58  for four-stroke mode. Conversely, the locking pins  86  operate to lock and engage the valve plunger  60  to the outer tappet  58  for two-stroke mode. 
   Engagement and disengagement of the locking pins  86  is accomplished by a hydraulic pressure applied to the locking pins  86  by a solenoid valve under the control of an engine management system. A pressure fluid such as engine oil, for example from the pressure fluid source, is supplied through the apertures  90  to the locking pins  86 . The pressure fluid causes the locking pins  86  to move inwardly and disengage the valve plunger  60  from the outer tappet  58  for four-stroke mode. The pressure fluid enters the radial bore apertures  90  and urges the locking pins  86  against the force of the locking pin return springs  82 . Thus, when it is desired to operate in the four-stroke mode, the pressure fluid causes the locking pins  86  to move inwardly from the position shown in  FIG. 4  and disengage the valve plunger  60  from the outer tappet  58 . Therefore, when the outer tappet  58  is urged downwardly by the lobes  98  of the two-stroke cam surface  64 , the outer tappet  58  slides freely on the outer portion of the valve plunger  60  and does not cause actuation of the valve stem  54 . In the embodiment shown, when it is desired to operate in the two-stroke mode, a flow or pressure of the pressure fluid is reduced and the force of the locking pin return springs  82  cause the locking pins  86  to move to the position shown in  FIG. 4  and engage the valve plunger  60  to the outer tappet  58 . Therefore, when the outer tappet  58  is urged downwardly by the lobes  98  of the two-stroke cam surface  64 , the outer tappet  58  and the valve plunger  60  both are caused to move downwardly and cause actuation of the valve stem  54 . As can be clearly understood, the locking pins  86  are designed so that they can only engage either the inner tappet  56  to the valve plunger  60  or the outer tappet  58  to the valve plunger  60  at one time. It should be noted that the outer tappet  58  is caused to move with the inner tappet  56  and the plunger  60  when disengaged due to the outer tappet stop  68 . Additionally, the locking pins  86  are formed with chamfers for the purpose of driving the locking pins  86  to a fully locked position should the controlled switching motion be too slow or insufficient to accomplish safe locking. 
     FIGS. 6 ,  7 ,  8 , and  9  illustrate the position of the tappet assembly  50  during operation.  FIG. 6  shows the tappet assembly  50  at a base position during four-stroke mode and  FIG. 7  shows the tappet assembly  50  at a full lift position during four-stroke mode.  FIG. 8  shows the tappet assembly  50  at a base position during two-stroke mode and  FIG. 7  shows the tappet assembly  50  at a full lift position during two-stroke mode. 
     FIGS. 10 and 11  show the tappet assembly  50  of  FIGS. 4 and 5  including examples of two different lash adjustment types.  FIG. 10  uses a lash shim  100  to manually make up for the clearance or play between the tappet assembly  50  and the valve stem  54 .  FIG. 11  uses a hydraulic check ball and spring type lash adjustment assembly  102  to make up for the clearance or play between the tappet assembly  50  and the valve stem  54 . It is understood that other lash types could be used without departing from the scope and spirit of the invention. 
   A third embodiment of the invention is illustrated in  FIGS. 12 and 13 . In  FIG. 12 , there is shown generally at  110  a schematic side sectional view of a mechanism for switching an engine from one stroke type to another stroke type or a cam follower and rocker arm assembly. A valve stem  112  abuts an end of a rocker arm assembly  114 . A piston  116  is disposed in a hydraulic lash adjustment cavity  118  formed within the rocker arm assembly  114 . The piston  116  is urged into engagement with the valve stem  112  by a spring  120 . Fluid communication between the hydraulic lash adjustment cavity  118  and a shuttle pin cavity  122  is provided by a first conduit  124 . An exhaust orifice  126  provides fluid communication between the shuttle pin cavity  122  and the atmosphere. A second conduit  128  provides fluid communication between the hydraulic lash adjustment cavity  118  and a first axially extending oil supply conduit  130 , which is in communication with a first oil supply (not shown). As illustrated, the first oil supply conduit  130  is formed in a rocker shaft  132  and includes an annular array of radially extending passages. Other routes of supply to the second conduit  128  and the hydraulic lash adjustment cavity  118  can be used as desired. A check valve  134  is disposed in the second conduit  128 . 
   Referring now to  FIG. 13 , there is shown a schematic sectional view of the cam follower and rocker arm assembly  110  of  FIG. 12  taken along line  13 — 13 . A second axially extending oil supply conduit  136  having an annular array of radially extending passages is formed in the rocker shaft  132  and is in communication with a second oil supply (not shown). A third conduit  138  provides fluid communication between the second oil supply conduit  136  and the shuttle pin cavity  122 . A shuttle pin piston  140  is reciprocatively disposed in one end of the shuttle pin cavity  122  adjacent the third conduit  138 . A first end of a shuttle pin  142  abuts the shuttle pin piston  140 . A second end of the shuttle pin  142  abuts a shuttle pin return piston  144 . The shuttle pin  142  has a circumferrential groove  146  formed thereon at a point between the first end and the second end thereof. A shuttle pin return spring  148  urges the shuttle pin return piston  144 , the shuttle pin  142 , and the shuttle pin piston  140  in a direction towards the end of the shuttle pin cavity  122  communicating with the third conduit  138 . A four-stroke follower arm  150  and a two-stroke follower arm  152  respectively abut four-stroke and two-stroke cam surfaces of a cam shaft (not shown). The four-stroke follower arm  150  and the two-stroke follower arm  152  are adapted to operate independently of one another, as described in the operation of the cam follower and rocker arm assembly  110 . 
   In operation, the cam follower and rocker arm assembly  110  facilitates a selection of either a four-stroke or a two-stroke operation of an internal combustion engine (not shown) by switching between engagement of the four-stroke follower arm  150  and the two-stroke follower arm  152 . The cam follower and rocker arm assembly  110  also allows compliance with manufacturing tolerance variation by incorporating a hydraulic lash adjustment device, which includes the piston  116  and the spring  120 , that is deactivated while switching between the four-stroke follower arm  150  and the two-stroke follower arm  152 . In both  FIG. 12  and  FIG. 13 , the shuttle pin  142  is shown in a deactivated position with the shuttle pin  142  urged towards engagement of the four-stroke follower arm  150  by the shuttle pin return spring  148 . 
   Under normal operating conditions, as illustrated, the internal combustion engine is running in the four-stroke mode which is determined by the engagement of the four-stroke follower arm  150  by the shuttle pin  142 . The shuttle pin  142  and shuttle pin piston  140  are held in this position by due to the urging of the shuttle pin return spring  148 . Thus, the actuation of the valve stem  112  will be controlled by the four-stroke follower arm  150 . Pressurized oil is supplied to the hydraulic lash adjustment cavity  118  through the first oil supply conduit  130 , via the second conduit  128 . Control of the supply of pressurized oil can be accomplished using any conventional control method such as an on-board vehicle computer and control valve system, for example. The check valve  134  militates against backflow of the oil through the second conduit  128  to prevent depressurization of the hydraulic lash adjustment cavity  118  during operation. 
   When it is desired or required to switch to the two-stroke operation mode, pressurized oil is supplied to the shuttle pin cavity  122  through the second oil supplying conduit  136 , via the third conduit  138 . Control of the supply of pressurized oil can be accomplished using any conventional control method such as an on-board vehicle computer and control valve system, for example. The pressurized oil introduced to the shuttle pin cavity  122  urges the shuttle pin piston  140 , the shuttle pin  142 , and the shuttle pin return piston  144  against the force of the shuttle pin return spring  148  causing them to move against the force of the shuttle pin return spring  148 . At a point in the travel of the shuttle pin  142 , the groove  146  aligns with and communicates with the first conduit  124  and the exhaust orifice  126 . This alignment, in essence allowing the shuttle pin  142  to act as a spool valve, allows depressurization of the hydraulic lash adjustment cavity  118  and deactivates the hydraulic lash adjustment device. Upon full travel of the shuttle pin piston  140 , the shuttle pin  142 , and the shuttle pin return piston  144 , the four-stroke follower arm  150  is disengaged by the shuttle pin  142  and the two-stroke follower arm  152  is engaged by the shuttle pin  142 . Communication between the groove  146 , the first conduit  124 , and the exhaust orifice  126  is also interrupted, thus allowing re-pressurization of the hydraulic lash adjustment cavity  118  to re-activate the hydraulic lash adjustment device to resume the function of taking up or compensating for clearances between the valve stem  112  and the rocker arm assembly  114 . 
   To return to the four-stroke mode, the reverse of the above is accomplished. The oil supply to the shuttle pin cavity  122  is interrupted and vented, thus relieving the pressure and allowing the shuttle pin return spring  148  to cause the shuttle pin return piston  144 , the shuttle pin  142 , and the shuttle pin piston  140  to move in the shuttle pin cavity  122  in the direction of the force of the shuttle pin return spring  148 . The groove  146  again aligns with and communicates with the first conduit  124  and the exhaust orifice  126  to allow depressurization of the hydraulic lash adjustment cavity  118  and deactivate the hydraulic lash adjustment device. Upon full travel of the shuttle pin return piston  144 , the shuttle pin  142 , and the shuttle pin piston  140 , the four-stroke follower arm  150  is re-engaged by the shuttle pin  142  and the two-stroke follower arm  152  is disengaged by the shuttle pin  142 . Communication between the groove  146 , the first conduit  124 , and the exhaust orifice  126  is also interrupted, thus allowing re-pressurization of the hydraulic lash adjustment cavity  118  to re-activate the hydraulic lash adjustment device. 
   From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.