Rocker Arm Engine Brake System

Abstract

A rocker arm engine brake system for an internal combustion engine in which a rocker arm is movable by a cam operating off the cam shaft to open the exhaust valve of a cylinder at the usual time in the piston cycle; and when it is desired to retard the speed of the engine, a lash piston in the rocker arm is hydraulically extensible at the will of the operator to take up the usual lash between the rocker arm and the exhaust valve so as to enable an auxiliary cam operating off the cam shaft to effectively cooperate with the rocker arm to open the exhaust valve at a time toward the end of a compression stroke of the piston so as to dissipate the energy of gases of compression from acting upon the piston. Separate passages in the rocker arm shaft are utilized for providing fluid for operating the lash piston and for general lubrication. The passages are interconnected by bleed holes. Selective control of the hydraulic system is obtained by means of a solenoid operable valve.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the art of rocker arm engine brake devices incorporated in an internal combustion engine, the devices being of a type wherein the exhaust valve of a piston cylinder is caused to be cammed open not only during the usual time in the piston cycle, but also at a time near the end of a compression stroke so as to relieve the cylinder of compressed gases and, as a consequence, dissipate the energy which would otherwise be applied to the piston.

2. Description of Prior Art

Devices of the general nature are known from U.S. Pat. Nos. 3,367,312 and 3,332,405. In these devices, the usual cam operating off the cam shaft acts through a rocker arm to open the exhaust valve at the usual time in the engine's cycle. To cause the exhaust valve to open toward the end of the compression stroke when it is desired to retard the speed of the engine, a lash piston is hydraulically operable in the rocker arm at the will of the operator to take up the ususal lash existing between the rocker arm and the exhaust valve so as to enable an auxiliary cam operating off the cam shaft to act through the rocker arm to open the exhaust valve.

The objective of the present invention is to provide a device of this lash piston type having an improved hydraulic system for operating the lash piston.

A feature of this improved system lies in the manner in which the rocker arm shaft is utilized for supplying crankcase oil for general lubricating purposes and for also supplying crankcase oil for operating the lash piston.

Another feature of this improved system lies in the structured arrangement of the passages for the hydraulic feed whereby undesirable air bubbles are relieved from the system.

Other features and advantages of the system will appear from the detailed description of the invention.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided in an internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, pedestal means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, an hydraulic circuit for feeding pressurized fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit, wherein the shaft is formed with a pair of longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawing:

FIG. 1 is a top plan view of a section of a rocker arm shaft of an internal combustion diesel engine in which the invention is embodied;

FIG. 2 is a section on line 2--2 of FIG. 1 directed to the solenoid valve control unit incorporated in a supporting pedestal of the rocker arm shaft;

FIG. 3 is an enlarged fragmentary portion of FIG. 2 showing the moved position of the solenoid valve following enerization of the solenoid;

FIG. 4 is a section taken on line 4--4 of FIG. 1 showing the relation of an exhaust rocker arm to the exhaust valves of one of the cylinders of the engine;

FIG. 5 is an enlarged detail showing the follower end of the push rod of FIG. 4 in association with a cam element carried by the engine's cam shaft;

FIG. 6 is an enlarged detail of the rocker arm shown in FIG. 4 with portions cut away;

FIG. 7 is a section taken on line 7--7 of FIG. 6 illustrating the normal position of the combined shuttle and check valve unit;

FIG. 8 is an enlarged detail illustrating the moved condition of the combined shuttle and check valve unit shown in FIG. 7;

FIG. 9 is a view corresponding to that of FIG. 6 of a modified embodiment but illustrating the arrangement in the hydraulic system of the shuttle and check valves as separate elements;

FIG. 10 is a section on line 10--10 of FIG. 9 illustrating the arrangement of the shuttle and check valves; and

FIG. 11 is a view corresponding to that of FIG. 4 but showing an embodiment in which the rocker arm arm overlies a single exhaust valve.

DESCRIPTION OF A PREFERRED EMBODIMENT (FIGS. 1-8)

Reference is directed to the several FIGURES of the accompanying drawing, and now especially to FIGS. 1-8, wherein the invention is illustrated as incorporated in an internal combustion diesel engine in association with one of its cylinders 10 (FIG. 4). The piston 11 operating in the cylinder is of the four-stroke cycle type. Only so much of the engine needed for an understanding of the invention is described. Accordingly, no description is made of the usual fuel injector and air intake mechanism associated with the cylinder.

The cylinder is served by a pair of exhaust valves 12 which are normally held closed, as in FIG. 4, by the usual valve springs 13. An exhaust valve actuating bridge 14 spanning the stems 15 of both valves is actuable by an overhead rocker arm 16 to force the valves to open condition. The bridge is slidably supported upon a stud 17, anchored in the cylinder head 18 in such manner as to allow axial sliding movement of the bridge relative to the valves.

The rocker arm is pivoted between its ends upon a stationary rocker arm shaft 21 which is supported by pedestal means 22 (FIG. 1) bolted atop the cylinder head. One end of the rocker arm is located above the central area of the bridge 14 and an opposite end overlies a push rod 24. The rocker arm is pivotable by the push rod relative to the bridge upon cooperation of a rotating cam element 25 (FIG. 5) with the push rod. The push rod is provided with a boot or follower 26 which rides the periphery of the cam element. The cam element is carried by the usual cam shaft 27. The latter is drivably connected in conventional manner to the usual crankshaft of the engine.

The cam element 25 has a main cam rise or lobe 28 on its periphery which is cooperable with the push rod at the usual time in the piston cycle to open the exhaust valves. There is also provided on the periphery of the cam element in angular space relation to the rise 28 an auxiliary or second cam rise 29 of smaller or lesser radial extent than that of the main rise 28. It is cooperable with the push rod to pivot the rocker arm relative to the bridge 14 at a time near the end of the compression stroke of the piston. The auxiliary cam rise is obtained by undercutting the base circle of the cam element as indicated by the broken line 30. The timing of the cooperation of the respective cam rises with the push rod is determined by the angular position given to the cam rises relative to each other and by the angular disposition of the cam element 25 upon the cam shaft 27.

Normally, the cooperation of the auxiliary cam rise with the push rod is ineffective to cause movement of the bridge to open the exhaust valves because of the usual slight lash or loss motion existing between the rocker arm and the bridge. When it is desired to convert the engine from normal power operation to braking operation, it is intended that the lash in the rocker arm be taken up so that the exhaust valves will be caused to open through the action of the auxiliary cam rise 29 at or near the end of the compression stroke so as to relieve the cylinder of the driving energy of compressed gases. To accomplish this, a lash piston 31 (FIGS. 4, 6, 7) is provided in a bore 32 of the rocker arm 16. It is arranged to be operable upon demand of the operator to move outwardly of the rocker arm into pressed relation with the valve bridge so as to take up the lash in the rocker arm.

The lash piston is located in the rocker arm above the central area of the valve bridge. It is normally held seated against the bottom of its bore by the biasing force of a return spring 33. The spring is of U-form (FIG. 7), having a bridge piece 34 fastened to the underside of an ear 36 of the rocker arm, and having a pair of parallel spring legs 35. One of the legs extends across a flat at one side of an externally projecting portion of the piston, and the other leg extends across a similar flat at the opposite side of the piston. The spring legs exert a biasing force upon overhead shoulders 37, defined by the flats of the piston, which force normally seats the piston in its bore. The spring legs also cooperate with the flats to prevent turning of the piston in its bore.

The lash piston is hydraulically movable at the election of the operator outwardly of the rocker arm against the bias of the return spring 33 to take up the lash between the rocker arm and the bridge. The hydraulic system, whereby oil is fed from the engine's crankcase to operate the lash piston, and whereby the spent oil is subsequently returned to the crankcase when the braking operation is terminated, represents an advantageous feature of the invention.

The hydraulic system includes a solenoid control valve unit 38 (FIGS. 1-3), shown here as mounted in the pedestal 22. It may, however, be mounted in any convenient location suitable for the purposes intended; for example, on an end of the rocker arm shaft, or outside of the engine. The unit is operable by means of a switch, schematically indicated at 39. The latter may be located in the instrument panel for manual operation, or may be associated with a foot pedal or other convenient means of operation. The valve unit includes a solenoid spool valve 40 which has a normal position, as in FIG. 2, blocking operating oil flow from the crankcase to the lash piston.

When the control unit 38 is energized, the solenoid valve 40 is moved downwardly against the force of a return spring 41 to an "on" condition, as in FIG. 3, for conducting hydraulic operating fluid to the lash piston. This allows oil drawn by a pump 42 from the engine's crankcase 43 to be forced at a predetermined high pressure over a supply line 44 into the valve chamber and through side ports 45 to a passage 46. The latter passage leads through the wall of the rocker arm shaft 21 into a conduit 48 extending axially through the shaft.

Conduit 48 has been provided by inserting a spring partition strip 49 axially into the usual center hole of the rocker arm shaft so as to divide the hole into a pair of longitudinally extending conduits 48 and 51. Conduit 48 is utilized for conducting oil to operate the lash piston; whereas conduit 51 is used for conducting a supply of oil for lubricating purposes. Conduit 51 is connected by an individual supply passage 52 with the crankcase. Oil is pumped from the crankcase in usual manner through passage 52 into conduit 51. The oil flowing in conduit 51 passes through various bleed holes in the rocker arm shaft, one being shown at 53 (FIG. 6), to lubricate the rocker arm and the push rod. Conduits 48 and 51 are sealed at opposite ends from one another.

Pressurized oil entering conduit 48 flows out of a port 54 (FIGS. 6-8) in the wall of the rocker arm shaft to a passage 55 in the rocker arm connecting at 56 to one end of a shuttle valve chamber 57 in the rocker arm. An opposite open end of the valve chamber is covered by a drain plate 58 having a groove defining a relief port 59 exiting at the uppermost area of the rocker arm, as best seen in FIG. 6. A port 61 intermediately of the ends of the valve chamber leads to an area at the back or upper end of the bore 32 of the lash piston.

A combined shuttle valve and check valve unit 62 operable in the valve chamber 57 controls flow of pressure oil to force the lash piston 31 downward and outwardly of the rocker arm against the valve bridge 14 to take up the existing lash in the rocker arm. It also controls subsequent relief of such oil to the drain port 59 so as to enable the lash piston to be returned by its spring 33 to normal condition, as in FIG. 6, seated at the back of its bore 32.

A shuttle valve member 63 of the combined valve unit has a cylindrical body provided with an axial bore in which a seat 64 for a ball check valve 65 is fitted. A return spring 66 normally holds the check valve seated so as to block communication of an inlet passage 67 through the check valve with side ports 68 opening through the mid-area of the body of the shuttle valve. The shuttle valve has a normal position, under the bias of a return spring 69 (as in FIG. 7) wherein its side ports are blocked by the wall of the valve chamber from communicating with the port 61 leading to the area at the back of the lash piston. The shuttle valve has an opposite or moved position (as in FIG. 8) in which its side ports 68 register with port 61, and in which the latter is blocked by a rear body portion of the shuttle valve from communicating with the relief port 59 in plate 58. A bushing 71 fitted in the shuttle valve chamber serves as a stop to limit the moved position of the shuttle valve.

Pressurized oil flowing in passage 55 from the rocker arm shaft to the end 56 of the shuttle valve chamber 57 moves the valve against the bias of its return spring 69 to register its side ports 68 with the port 61, as in FIG. 8. With this action, the pressurized oil passes through the seat of the ball check valve 65 to the back of the lash piston 31 and forces the latter down against the valve bridge 14. The oil pressure acting upon the lash piston is adequate to move the piston against the force of its return spring 33 sufficiently to take up the existing lash, but is inadequate to cause the valve bridge to open the exhaust valves.

As long as the solenoid valve unit 38 is energized to maintain the oil pressure against the lash portion, the latter retains its displaced condition and is hydraulically locked by means of the one-way check valve 65 from returning to its normal condition. Each time the rocker arm is subsequently pivoted by the auxiliary cam rise 29, as well as by the main cam rise 28, it acts through the extended lash piston, pressing against the valve bridge to open the exhaust valves. As the engine cycles, the exhaust valves will be opened at the usual time in the cycle through the camming action of the main cam rise 28 with the push rod and will also be opened near the end of the compression stroke through the camming action of the auxiliary cam rise 29 with the push rod.

When it is desired to convert the engine from braking operation back to normal power operation, the solenoid control valve unit 38 is deenergized by the operator. The solenoid spring 41 then returns the solenoid valve to its normal or "off" position (FIG. 2), in which position the inlet ports 44 of the unit are blocked from the valve ports 45 and the latter communicate around the lower end of the solenoid valve with a drain port 70. Upon deenerigization of the solenoid valve unit, the pressure of oil filling the passageways 46, 48 and 55 between the solenoid valve outlets 45 and the area 56 at the back of the shuttle valve chamber is relieved as the oil spills over through the solenoid ports 45 to the drain port 70. Oil issuing from the latter drops to the cylinder head or deck 18 and finds its way in conventional manner back to the crankcase 43.

Also, as the pressure behind the shuttle valve is relaxed following deenergization of valve 38, spring 69 returns the shuttle valve to its normal position, as in FIG. 7. This serves to communicate the lash piston feed port 61 with the drain 59. Oil at the rear of the lash piston is then forced to spill out of the drain 59 as spring 33 returns the lash piston to its normally retracted condition (FIG. 6). Oil spilling from the drain 59 drips downward onto the cylinder head to find its way back to the crankcase in conventional manner.

A desirable advantage of the hydraulic system lies in its capacity to purge itself of air and air bubbles, especially in the passage 61 between the shuttle valve 63 and the bore 32 of the lash piston. It is to be noted in this respect that, when the oil pressure in the passages 46, 48, 55 between the solenoid valve 38 and the chamber 57 of the shuttle valve unit is relaxed, the check valve 65 is caused to close by its spring 66 and the pressure of oil at the rear of the lash piston is relieved through the drain port 59. The latter port is located at the upper most area of the rocker arm at a level above that of the bore 32 of the lash piston and above the level of the horizontally disposed shuttle valve chamber 57, as best seen in FIG. 6. Accordingly, the hydraulic circuit area between the shuttle valve and the bore 32 of the lash piston remains at all times filled with oil. If any air bubbles should find their way to the circuit area beyond the check valve 65, they will rise upwardly through the oil to escape through the drain port 59. Air bubbles are undesirable in the circuit area beyond the check valve when the lash piston has been hydraulically extended since they are subject to compression and may cause the piston to be correspondingly retracted into its bore when the rocker arm is actuated by the auxiliary cam rise. This retraction or spongy action of the lash piston could result in a failure of the rocker arm to adequately open the exhaust valves.

A further advantage of the hydraulic system is that no undesirable pumping action of the lash piston takes place relative to its bore 31 after the braking operation has been terminated. This is because the piston is held retracted and seated at the bottom of its bore by the return spring 33 and is, accordingly, solidly backed each time it is pressed by the rocker arm against the valve bridge during power operation of the engine. Nor is there any pumping action of the lash piston during the braking operation since it is hydraulically locked outwardly in its extended condition.

Air is also constantly being urged or driven from the conduit 48 during the time that the solenoid unit is deenergized. Conduit 48 is being constantly primed and flushed during this period with oil bleeding into it from conduit 51 through bleed holes 50 in the partition strip 49, one being shown in FIG. 6. Oil pumped from the crankcase is constantly being circulated through conduit 51 for lubricating purposes. This constant entry of oil from conduit 51 to conduit 48 to the circuit between the solenoid valve and the shuttle valve causes a continuous spill of oil through the drain 70 of the solenoid valve unit that tends to prevent any air from possibly accumulating in the circuit. It is also to be noted (FIG. 2) that the side ports 45 of the solenoid valve unit incline upwardly from the passage 46 that opens through the wall of the rocker shaft into conduit 48. Accordingly, ports 45 are at a level above port 46 so that the conduit 48 is never fully drained of its oil, and oil therein always remains at a level above its entry port 46. This construction further inhibits the possibility of air entering the hydraulic circuit.

It is to be noted that in lieu of utilizing the flexible strip 49 in conjunction with the usual center hole in the rocker arm shaft to provide the passages 48 and 51, a rocker arm shaft may be designed for this purpose having a pair of separate longitudinal extending holes therein interconnected with one another by bleed holes.

SECOND EMBODIMENT (FIGS. 9, 10)

In the embodiment described above, the shuttle and check valves 63, 65 are shown in FIGS. 7 and 8 as combined into a unit or one-piece arrangement. In the embodiment shown in FIGS. 9 and 10, the shuttle valve 63a and the check valve 65a, 64a are shown as two separate elements. In this second embodiment, a passage 72 connects conduit 48 with a passage 73. The check valve unit 65a, 64a is located in a branch 74 of passage 73, and it normally blocks passage 73 from a passage 75 connected with a passage 76 leading to the back of the bore 32a of the lash piston 31a. The shuttle valve 63a is a solid member or slug slidable in a second branch 77 of the passage 73. This second branch 77 normally communicates the back of the piston bore 32a from passages 76 and 78 with a drain passage 79. In the operation of this embodiment, when pressurized crankcase oil is fed to passage 72 from conduit 48, it flows to passage 73 and simultaneously shifts the shuttle valve 63a to block passages 76, 78 from the drain; and opens the check valve 65a to flow of pressurized oil to passage 76 to displace the lash piston. When pressure of oil in passage 73 is subsequently relaxed upon discontinuance of flow to conduit 48, the check valve 65a is closed by its spring; and the shuttle valve 63a is reshifted by its spring to communicate the back of the lash piston with the drain passage 79. The drain passage exits at a level above passage 76, as at 80.

It is understood that a separate rocker arm assembly, as described above in the foregoing embodiments, could be associated with the exhaust valves of each cylinder of the engine; and that all of the exhaust valve rocker arms pivoted upon the rocker arm shaft 21 could be controlled by but one solenoid control valve unit since the conduit 48 in the rocker arm shaft would be common to and serve the several rocker arms pivoted upon the shaft, and the conduit 51 would be common to the several rocker arms for lubricating purposes.

FIG. 11 EMBODIMENT

While the rocker arm assembly has been shown as acting through a bridge to operate a pair of exhaust valves, it is understood that where (as in FIG. 11) a cylinder 10b is served by a single exhaust valve 12b, the bridge would be eliminated and the lash piston 31b would directly overlie the stem 15b of the single exhaust valve.

Claims

1. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, an hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit, wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes, the control valve means having a closed normal position blocking feeding of hydraulic fluid into the first conduit and allowing relief of hydraulic fluid from the first conduit to a relief port, and having an open operated position allowing feed of hydraulic fluid into the first conduit and blocking escape of hydraulic fluid from the first conduit to the relief port, wherein a one-way check valve is disposed in the rocker arm in the passage means between the bore of the lash piston and the control valve means permitting flow in the passage means to the bore, and wherein a relief passage connects the passage means between the check valve and the bore

2. An internal combustion engine as in claim 1, wherein a shuttle valve normally blocks flow of fluid beyond the check valve to the bore of the lash piston and communicates the bore of the lash piston with the drain

3. An internal combustion engine as in claim 2, wherein the drain port is at a level above that of the bore of the lash piston and the passage

4. An internal combustion engine as in claim 2, wherein the shuttle valve has a moved position in the passage means communicating the bore of the lash piston with flow through the check valve, and blocking communication

5. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, a hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit, wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, there being a check valve in the passage means between the bore and the control valve means and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes, the control valve means having a closed normal position blocking feeding of hydraulic fluid into the first conduit and allowing relief of hydraulic fluid from the first conduit to a relief port, and having an open operated position allowing feed of hydraulic fluid into the first conduit and blocking escape of hydraulic fluid from the first conduit to the relief port, wherein the control valve means is connected upstream of the check valve with a supply line leading through a pump to the oil crankcase of the engine, and wherein the relief port is connected with the first conduit by a passage having a level corresponding to a level about

6. An internal combustion engine as in claim 5, wherein the flow of oil fluid in the second conduit is continuous, a partition strip separates the first conduit from the second, and bleed holes are provided in the partition strip communicating oil fluid from the second conduit to the first conduit whereby the first conduit in the normal condition of the control valve is being continuously flushed by bleed oil from the second

7. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, a hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit, wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes, the control valve means having a closed normal position blocking feeding of hydraulic fluid into the first conduit and allowing relief of hydraulic fluid from the first conduit to a relief port, and having an open operated position allowing feed of hydraulic fluid into the first conduit and blocking escape of hydraulic fluid from the first conduit to the relief port, and wherein a unit comprising a one-way check valve member combined with a shuttle valve member is positioned in the rocker arm in the passage means between the control valve means and the bore of the lash piston, the unit having a normal position upon a relaxed fluid pressure condition existing in the passage means upstream of the unit, in which normal position the bore of the lash piston is in communication with a drain port and is blocked by the shuttle valve member from communication with the check

8. An internal combustion engine as in claim 7, wherein the unit has a moved condition under pressure of hydraulic fluid admitted to the passage means, in which moved condition the shuttle valve member blocks communication of the bore of the lash piston with the drain port and provides communication of said bore with the check valve member, the check valve member being movable under said hydraulic pressure so as to allow

9. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, a hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit, wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes; wherein a one way check valve is disposed in the rocker arm in the passage means between the bore of the lash piston and the control valve means permitting flow in the passage means to the bore; and wherein a relief passage connects the

10. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, an hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit; wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, there being a check valve in the passage means between the bore and the control valve means and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes; wherein the control valve means is connected upstream of the check valve with a supply line leading through a pump to the oil crankcase of the engine; wherein the control valve means has a normal condition blocking flow from the supply line to the first conduit and communicating the said conduit with a relief port; and wherein the relief port is connected with the first conduit by a passage having a level corresponding

11. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, an hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit; wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase, the conduits being interconnected by bleed holes; and wherein a unit comprising a one way check valve member combined with a shuttle valve member is positioned in the rocker arm in the passage means between the control valve means and the bore of the lash piston, the unit having a normal position upon a relaxed fluid pressure condition existing in the passage means upstream of the unit, in which normal position the bore of the lash piston is in communication with a drain port and is blocked by the shuttle valve member from communication with the check valve member.

12. An internal combustion engine including a piston cylinder served by an exhaust valve, a rocker arm pivotable about a rocker arm shaft against the valve to force the valve to open condition, means supporting the shaft upon the engine, rotating cam means having periodic cooperation with the rocker arm to pivot it relative to the valve but disabled because of loss motion existing between the rocker arm and the valve from pivoting the rocker arm sufficiently to force the valve to open condition, and selectively operable means for taking up the loss motion so as to remove said disability of the cam means, the selectively operable means comprising a lash piston in a bore of the rocker arm having a retracted condition in which said loss motion exists and having a projected condition in which the loss motion is taken up, an hydraulic circuit for feeding hydraulic fluid to the bore to project the lash piston, and selectively operable control valve means in the circuit for controlling flow of said fluid in the circuit; wherein the shaft is formed with a pair of separate longitudinally extending conduits, a first one of the conduits being part of said circuit and connecting the control valve means with passage means in the rocker arm leading to the bore of the lash piston, and the second one of the conduits having lateral lube ports through the wall of the shaft and connected for receiving oil feed from the engine's crankcase; wherein a one way check valve is disposed in the rocker arm in the passage means between the bore of the lash piston and the control valve means permitting flow in the passage means to the bore; and wherein a relief passage connects the passage means between the check valve and

13. An internal combustion engine as in claim 12, wherein a shuttle valve normally blocks flow of fluid beyond the check valve to the bore of the lash piston and communicates the bore of the lash piston with the drain

14. An internal combustion engine as in claim 13, wherein the drain port is at a level above that of the bore of the lash piston and the passage

15. An internal combustion engine as in claim 12, wherein a unit comprising a one way check valve member combined with a shuttle valve member is positioned in the rocker arm in the passage means between the control valve means and the bore of the lash piston, the unit having a normal position upon a relaxed fluid pressure condition existing in the passage means upstream of the unit, in which normal position the bore of the lash piston is in communication with a drain port and is blocked by the shuttle

16. An internal combustion engine as in claim 15, wherein the unit has a moved condition under pressure of hydraulic fluid admitted to the passage means, in which moved condition the shuttle valve member blocks communication of the bore of the lash piston with the drain port and provides communication of said bore with the check valve member, the check valve member being movable under said hydraulic pressure so as to allow fluid flow to the said bore.