TITLE

MODULATED COMBINED LUBRICATION AND CONTROL PRESSURE SYSTEM FOR TWO-STROKE/FOUR-STROKE SWITCHING

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of the co-pending U.S. patent application serial no. 10/802,487 filed March 17, 2004, to be issued as U.S. Pat. No. 7,036,465 on May 2, 2006.

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 operation 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. 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 devices including carburetors and fuel injectors, for example. The fuel-air mixture can be ignited by different 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-sized engines with large displacements are therefore installed to meet only occasional high 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 high 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 during much of the operating time.

Existing internal combustion engines are usually limited in their operation to two- stroke or four-stroke operation. 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 maximum 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 operates 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.

In one two-stroke/four-stroke switching valvetrain (shown in U.S. Patent Application Publication 2005/0205019), the valve rocker shaft is provided with two lengthwise drillings, one to provide lubrication to all the rockers running on the shaft, and a second separate passage connecting to the rocker switching mechanism to provide control pressure to the hydraulic piston which locks and unlocks the rocker pairs. While

this configuration functions well (with lubrication and control functions separate) the shaft with two small drillings is expensive and difficult to manufacture.

In addition, the response of the locking mechanism is slowed by the requirement to raise the pressure from some low level up to the spring preload threshold where the piston and locking pin may begin to move. While other switching valve trains have overcome this difficulty by raising the lower pressure to just under the spring threshold

(see U.S. Patent 4,917,057) this passive arrangement has unsymmetrical response since the raising of the pressure over the threshold is rapid, but the lowering (with the higher back pressure) is slowed. In addition, the passive system cannot be controlled to vary lubrication or control pressure to suit the operating condition.

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

The present invention relates generally to a two-stroke/four-stroke switching valvetrain for an engine where cylinders must be switched individually at known timing. A rocker shaft has a single internal oil passage formed along its length, typically blocked off to form a separate chamber for each cylinder's valvetrain. An actuator driving a 3- port spool valve is provided at each cylinder which feeds oil into the rocker shaft chamber. This actuator typically is a linear solenoid with position control by pulsewidth modulating current to it, but it may also be a servo motor or stepper motor which moves the valve spool. The three ports are control oil out (center port), oil pressure feed (one end port) and oil pressure dump (opposite end port). The ports are arranged so that the control pressure port can be either partially or fully connected to either the oil feed port or the oil dump port in response to control input to the actuator.

In this way the valve can be modulated to provide a flow orifice which creates control pressure just below the motion threshold, both to provide rocker lubrication and to minimize the slew rate of changing control pressure to actuate the locking mechanism. Full available system pressure will be applied (supply port fully connected to control port) to make the switching as rapid as possible when required.

Since the lower lubrication pressure would be a detriment when it is desired to unlock the rockers (depressurizing the control chamber) a further level of control input is provided to the actuator which fully connects the control pressure port to an atmospheric pressure dump port which returns oil to the sump. The momentary loss of lubrication pressure should not be detrimental (since the switching can happen only when the rocker is unloaded and stationary), but with some loss of performance, this pressure too can be regulated to a level which provides lube during the dumping event. Once the switching event is over, the command to the actuator will be returned to the level which is appropriate for lubrication, and in preparation for the next switching event. A pressure transducer may be connected to the control port to enable closed loop control of all the levels of pressure (4 .stroke/lube, 2 stroke/lube, dump/no lube) by the engine management system. This would allow adjustment of the lube pressure (for speed, load, engine temperature, closeness to the switching threshold). The holding pressure (maintaining the 2 stroke mode) can be adjusted to minimize oil or electrical power, or to lower the pressure threshold of switching back to the 4 stroke state to improve speed. The dump pressure can be regulated to provide adequate lubrication. The pressure transducer can also provide timing information about the switching event to the engine management system to coordinate other critical parameters. It may also be used to confirm that switching is successfully taking place for on-board diagnostics. The timing sequence of a 4 stroke to two stroke and return event is shown in the figures.

The invention is a 2 stroke/4 stroke switching system wherein a rocker shaft has a single longitudinal bore extending there through blocked off to form a separate chamber for the valvetrain of each cylinder. An actuator for each cylinder drives a hydraulic piston slidably disposed in a three-port spool valve that is supplied oil from the bore in the rocker shaft. The three ports are "control oil out" (center port), "oil pressure feed" (one end port) and "oil pressure dump" (opposite end port). The control port can be either partially or fully connected to either the feed port or the dump port in response to control input to the actuator. The valve is modulated just below the motion threshold to provide rocker lubrication and to minimize the slew rate of changing control pressure to actuate the locking mechanism. Full pressure is used when unlocking the rockers by fully connecting the feed port with the control port.

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.

DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of 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;

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 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 showing a mechanism for switching an engine from one stroke type to another stroke type including a cam follower and rocker arm assembly; Fig. 13 is a schematic sectional view of the assembly of Fig. 12 taken along line

13-13;

Fig. 14 is a schematic fragmentary sectional view of a fourth embodiment showing a mechanism for switching an engine, from one stroke type to another stroke type including a cam follower and rocker arm assembly; Fig. 15 is an elevation view of a solenoid actuator with a spool valve in cross section and positioned for four-stroke operation of the mechanism shown in Fig. 14 in accordance with the present invention;

Fig. 16 shows the spool valve of Fig. 15 positioned for two-stroke operation;

Fig. 17 shows the spool valve of Fig. 15 in transition between two-stroke operation and four stroke operation; and

Figs. 18a through 18d are plots of the voltage applied to the solenoid actuator of Fig. 15, the control pressure, the spool position and the locking piston position according to the present invention.

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 lpbe 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 tluid 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 5 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

10 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.

15 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

20 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

25 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.

30 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

5 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

10 102 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

15 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 0 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 5 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 0 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 circumferential 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.

A fourth embodiment includes a switching mechanism for a two-stroke/four- 5 stroke switching valvetrain for an engine where cylinders must be switched individually at known timing. The switching mechanism is shown in Fig. 14 wherein a rocker assembly 160 receives a hollow rocker shaft 162 therein. A pair of spaced apart follower arms 164, 166 extend outwardly from the rocker assembly 160 in a direction away from a valve rocker arm 168. The follower arms 164, 166 have a linking member 170 disposed

10 therebetween. As explained above, the follower arm 164 can engage with a four-stroke cam surface (not shown) and the follower arm 166 can engage with a two-stroke cam surface (not shown).

A control pressure chamber 172 is formed in the arms 164, 166 and the linking member 170. A hydraulic piston 174 is positioned in a portion of the chamber 172

15 formed in the follower arm 164. A hollow locking pin 176 is positioned in a portion of the chamber 172 formed in the linking member 170 and abuts the piston 174. A spring cup 178 is positioned in a portion of the chamber 172 formed in the follower arm 166 and abuts the locking pin 176. A return spring 180 has one end received in the cup 178 and an opposite end abutting an end wall 182 of the chamber 172 in the follower arm

20 166. An aperture 184 is formed in the end wall 182 and an aperture 186 is formed in the cup 178 such that a surface of the piston 174 abutting the pin 176 is in fluid communication with the aperture 184 through the interior of the pin 176, the aperture 186 and the portion of the chamber 172 retaining the cup 178 and the spring 180.

To enable this operation, and with reference to Figs. 14-18, a rocker shaft 162

25 includes a single internal oil passage 188 formed along its length, typically blocked off to form a separate chamber for each cylinder's valvetrain. An actuator 190 driving a 3-port spool valve 192 is provided at each cylinder which feeds oil into the rocker shaft chamber 172. This actuator 190 typically is a linear solenoid with position control by pulsewidth modulating current to it, but it may also be a servo motor or stepper motor

30 which moves the valve spool. The three ports are control oil out (center port) 194, oil pressure feed (one end port) 196 and oil pressure dump (opposite end port) 198. The ports are arranged so that the control pressure port 194 can be either partially or fully

connected to either the oil feed port 196 or the oil dump port 198 in response to control input to the actuator 190.

In this way the valve can be modulated to provide a flow orifice which creates control pressure just below the motion threshold, both to provide rocker lubrication and to minimize the slew rate of changing control pressure to actuate the locking mechanism.

Full available system pressure will be applied (supply port 196 fully connected to control port 194) to make the switching as rapid as possible when required.

Since the lower lubrication pressure would be a detriment when it is desired to unlock the rockers (depressurizing the control chamber) a further level of control input is provided to the actuator 190 which fully connects the control pressure port 194 to an atmospheric pressure dump port 198 which returns oil to the sump. The momentary loss of lubrication pressure should not be detrimental (since the switching can happen only when the rocker is unloaded and stationary), but with some loss of performance, this pressure too can be regulated to a level which provides lube during the dumping event. Once the switching event is over, the command to the actuator will be returned to the level which is appropriate for lubrication, and in preparation for the next switching event.

A pressure transducer may be connected to the control port to enable closed loop control of all the levels of pressure (4 stroke/lube, 2 stroke/lube, dump/no lube) by the engine management system. This would allow adjustment of the lube pressure (for speed, load, engine temperature, closeness to the switching threshold). The holding pressure (maintaining the 2 stroke mode) can be adjusted to minimize oil or electrical power, or to lower the pressure threshold of switching back to the 4 stroke state to improve speed. The dump pressure can be regulated to provide adequate lubrication. The pressure transducer can also provide timing information about the switching event to the engine management system to coordinate other critical parameters. It may also be used to confirm that switching is successfully taking place for on-board diagnostics.

The timing sequence of a 4 stroke to two stroke and return event is illustrated in Figs. 18a-d where the operating state of 4 stroke, lube typically corresponds to the valve spool 192 location shown in Fig. 15; the operating state of 2 stroke, lube typically corresponds to the valve spool 192 location shown in Fig. 16; and the operating state of switching between 2 stroke and 4 stroke lube typically corresponds to the valve spool 192 location shown in Fig. 17.

Note that the arrangement of the ports in the order shown in the figures is critical, since the control pressure cannot be allowed to pass through full pressure on the path from dump to lube pressure, since this would just undo the switch which has just been completed. In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.