Rocker arm assembly for engine braking

An exhaust valve rocker arm assembly operable in a combustion engine mode and an engine braking mode can include a rocker shaft and a rocker arm. The rocker shaft can define a pressurized oil supply conduit. The rocker arm can receive the rocker shaft and is configured to rotate around the rocker shaft. The rocker arm can have an oil supply passage defined therein. A valve bridge can engage a first exhaust valve and a second exhaust valve. In the engine braking mode, pressurized oil is communicated through the pressurized oil supply conduit, through the rocker arm oil supply passage and against an actuator such that a first plunger acts on the valve bridge during rotation of the rocker arm to a first angle opening the first valve a predetermined distance while the second valve remains closed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application under 35 U.S.C. § 371 of International Application No. PCT/EP2014/052876, filed on Feb. 14, 2014. The International Application was published in English on Aug. 20, 2015, as WO 2015/120897 A1 under PCT Article 21(2).

FIELD

The present disclosure relates generally to a rocker arm assembly for use in a valve train assembly and more particularly to a rocker arm assembly that provides a compression brake function.

BACKGROUND

Compression engine brakes can be used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A compression engine braking system is arranged, when activated, to provide an additional opening of an engine cylinder's exhaust valve when the piston in that cylinder is near a top-dead-center position of its compression stroke so that compressed air can be released through the exhaust valve. This causes the engine to function as a power consuming air compressor which slows the vehicle.

In a typical valve train assembly used with a compression engine brake, the exhaust valve is actuated by a rocker arm which engages the exhaust valve by means of a valve bridge. The rocker arm rocks in response to a cam on a rotating cam shaft and presses down on the valve bridge which itself presses down on the exhaust valve to open it. A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash or gap that develops between the components in the valve train assembly.

SUMMARY

An aspect of the invention provides an exhaust valve rocker arm assembly operable in a combustion engine mode and an engine braking mode, the exhaust valve rocker arm assembly comprising: a rocker shaft that defines a pressurized oil supply conduit; a rocker arm configured to receive the rocker shaft and configured to rotate around the rocker shaft, the rocker arm including an oil supply passage defined in the rocker arm; a valve bridge configured to engage a first exhaust valve at a spherical elephant foot and a second exhaust valve at a cylindrical elephant foot; a hydraulic lash adjuster assembly, disposed on the rocker arm, including a first plunger body movable between a first position and a second position, wherein, in the first position, the first plunger body is configured to extend rigidly and cooperatively engage with the valve bridge; and a check valve, disposed on the rocker arm, including an actuator configured to selectively release pressure in the hydraulic lash adjuster. The assembly is configured such that, in the engine braking mode, pressurized oil is communicated through the pressurized oil supply conduit, through the rocker arm oil supply passage and against the actuator such that the first plunger body occupies the first position and acts on the valve bridge during rotation of the rocker arm to a first angle opening the first exhaust valve a predetermined distance while the second exhaust valve remains closed.

DETAILED DESCRIPTION

An exhaust valve rocker arm assembly operable in a combustion engine mode and an engine braking mode can include a rocker shaft and a rocker arm. The rocker shaft can define a pressurized oil supply conduit. The rocker arm can receive the rocker shaft and is configured to rotate around the rocker shaft. The rocker arm can have an oil supply passage defined therein. A valve bridge can engage a first exhaust valve and a second exhaust valve. A hydraulic lash adjuster assembly can be disposed on the rocker arm having a first plunger body movable between a first position and a second position. In the first position, the first plunger body extends rigidly for cooperative engagement with the valve bridge. A check valve can be disposed on the rocker arm and have an actuator that selectively releases pressure in the hydraulic lash adjuster. In the engine braking mode, pressurized oil is communicated through the pressurized oil supply conduit, through the rocker arm oil supply passage and against the actuator such that the first plunger occupies the first position and acts on the valve bridge during rotation of the rocker arm to a first angle opening the first valve a predetermined distance while the second valve remains closed.

According to additional features, the hydraulic lash adjuster assembly is at least partially received by a first bore defined on the rocker arm. The hydraulic lash adjuster assembly further comprises a second plunger body that is at least partially received by the first plunger body. The second plunger body can define a valve seat. The check valve can be disposed between the first and second plunger bodies. The check valve can further comprise a check ball that selectively seats against the valve seat on the second plunger body.

According to other features, the actuator can further comprise a needle having a longitudinal pin portion and a disk portion. In the engine braking mode, pressurized oil acts against the disk portion moving the longitudinal pin portion a distance away from the check ball. The disk portion of the actuator can be received in a second bore defined in the rocker arm. The first and second bores can be collinear.

According to still other features, rotation of the rocker arm to a second predetermined angle disconnects the oil supply passage from the pressurized oil supply conduit. The rocker shaft can further define a vent channel. Rotation of the rocker arm to a third predetermined angle connects the oil supply passage to a vent channel releasing the oil pressure from the actuator. A spigot can be disposed on the rocker arm. In the engine braking mode, subsequent to the opening of the first valve the predetermined distance, further rotation of the rocker arm causes the spigot to move the valve bridge and open the second valve while further opening the first valve. The spigot can be configured to slidably translate along a passage defined in the rocker arm prior to moving the valve bridge.

An exhaust valve rocker arm assembly operable in a combustion engine mode and an engine braking mode according to additional features can include a rocker shaft that defines a pressurized oil supply conduit. A rocker arm can receive the rocker shaft and be configured to rotate around the rocker shaft. The rocker arm can have an oil supply passage defined therein. A valve bridge can engage a first exhaust valve and a second exhaust valve. A first plunger body can be movable between a first position and a second position. In the first position, the first plunger body extends rigidly for cooperative engagement with the valve bridge. An actuator can selectively release pressure acting against the first plunger body. In the engine braking mode, pressurized oil can be communicated through the pressurized oil supply conduit, through the rocker arm oil supply passage and against the actuator such that the first plunger occupies the first position and acts on the valve bridge during rotation of the rocker arm to a first angle opening the first valve a predetermined distance while the second valve remains closed.

According to other features, rotation of the rocker arm to a second predetermined angle disconnects the oil supply passage from the pressurized oil supply circuit. The rocker shaft can further define a vent channel. Rotation of the rocker arm to a third predetermined angle connects the oil supply passage to a vent channel releasing the oil pressure from the actuator. A spigot can be disposed on the rocker arm. In the engine braking mode, subsequent to the opening of the first valve the predetermined distance, further rotation of the rocker arm causes the spigot to move the valve bridge and open the second valve while further opening the first valve. A second plunger body can be at least partially received by the first plunger body. The second plunger body can define a valve seat. A check valve can be disposed between the first and second plunger bodies. The check valve can further include a check ball that selectively seats against the valve seat on the second plunger body.

According to additional features, the actuator can further comprise a needle having a longitudinal pin portion and a disk portion. In the engine braking mode, pressurized oil acts against the disk portion moving the longitudinal pin portion a distance away from the check ball. The disk portion of the actuator can be received in a second bore defined in the rocker arm. The first and second bores can be collinear.

An exhaust valve rocker arm assembly operable in a combustion engine mode and an engine braking mode according to another example of the present disclosure includes a rocker shaft that defines a pressurized oil supply conduit and a vent channel. A rocker arm can receive the rocker shaft and be configured to rotate around the rocker shaft. The rocker arm can have an oil supply passage defined therein. A valve bridge can engage a first exhaust valve and a second exhaust valve. A first plunger body can be movable between a first position and a second position. In the first position the first plunger body extends rigidly for cooperative engagement with the valve bridge. A check valve can be disposed on the rocker arm and have an actuator that selectively releases pressure acting on the first plunger body. In the engine braking mode the rocker arm is configured to rotate (i) a first predetermined angle wherein pressurized oil is communicated through the pressurized oil supply conduit, through the rocker arm oil supply passage and against the actuator. The first plunger occupies the first position and acts on the valve bridge opening the first valve a predetermined distance while the second valve remains closed. The rocker arm continues to rotate (ii) a second predetermined angle wherein the rocker arm oil supply passage disconnects from the pressurized oil conduit and (iii) a third predetermined angle wherein the rocker arm oil supply passage connects with the vent channel releasing oil pressure from the actuator.

In other features, the exhaust valve rocker assembly further comprises a spigot disposed on the rocker arm. In the engine braking mode, subsequent to the opening of the first valve the predetermined distance, further rotation of the rocker arm causes the spigot to move the valve bridge and open the second valve while further opening the first valve.

With initial reference toFIG. 1, a partial valve train assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference10. The partial valve train assembly10utilizes engine braking and is shown configured for use in a three-cylinder bank portion of a six-cylinder engine. It will be appreciated however that the present teachings are not so limited. In this regard, the present disclosure may be used in any valve train assembly that utilizes engine braking.

The partial valve train assembly10can include a rocker assembly housing12that supports a rocker arm assembly20having a series of intake valve rocker arm assemblies28and a series of exhaust valve rocker arm assemblies30. A rocker shaft34is received by the rocker housing30. As will be described in detail herein, the rocker shaft34cooperates with the rocker arm assembly20and more specifically to the exhaust valve rocker arm assemblies30to communicate oil to the exhaust valve rocker arm assemblies30during engine braking.

With further reference now toFIGS. 2 and 3, an exhaust valve rocker arm assembly30will be further described. The exhaust valve rocker arm assembly30can generally include a rocker arm40, a valve bridge42, a spigot assembly44and a hydraulic lash adjuster (HLA) assembly46. The valve bridge42engages a first and second exhaust valve50and52(FIG. 3) associated with a cylinder of an engine. The first and second exhaust valves50and52have a corresponding elephant foot or E-foot50aand52a. The E-feet50aand52aallow the valve bridge42to move without creating any side load on the corresponding valve stem50and52. The E-foot50ais spherical. The E-foot52ais cylindrical. A pushrod54(FIG. 3) moves upward and downward based on a lift profile of a cam shaft. Upward movement of the pushrod54, as indicated by arrow200, pushes an arm56fixed to the rocker arm40and in turn causes the rocker arm40to rotate counter-clockwise around the rocker shaft34in the direction of arrow202.

The HLA assembly46can comprise a plunger assembly60including a first plunger body62and a second plunger body64. The second plunger body64can be partially received by the first plunger body62. The plunger assembly60is received by a first bore66defined in the rocker arm40. The first plunger body64can have a first closed end68that defines a first spigot70which is received in a first socket72that acts against the valve bridge42. The second plunger body64has an opening that defines a valve seat76(FIG. 4). A check ball assembly80can be positioned between the first and second plunger bodies62and64. The check ball assembly80can include a first biasing member82, a cage84, a second biasing member86and a check ball90. A snap ring92nests in a radial groove provided in the first bore66of the rocker arm40. The snap ring92retains the first plunger body62in the first bore66.

An actuator or needle100is received in a second bore104of the rocker arm40. The needle100acts as an actuator that selectively releases pressure in the HLA assembly46. The needle100includes a longitudinal pin portion110and an upper disk portion112. A first cap116is fixed to the rocker arm40at the second bore104and captures a biasing member120therein. The biasing member120acts between the first cap116and the upper disk portion112of the needle100. In the example shown, the biasing member120biases the needle100downwardly as viewed inFIG. 3.

The spigot assembly44will be described in greater detail. The spigot assembly44can generally include a second spigot130having a distal end that is received by a second socket132and a proximal end that extends into a third bore136defined in the rocker arm40. A collar138can extend from an intermediate portion of the second spigot130. The second spigot130can extend through a passage139formed through the rocker arm40. A second cap140is fixed to the rocker arm40at the third bore136and captures a biasing member144therein. The biasing member144acts between the second cap140and a snap ring148fixed to the proximal end of the second spigot130. As will be described, the second spigot130remains in contact with the rocker arm40and is permitted to translate along its axis within the passage139.

With reference now toFIGS. 4 and 9-11, an oil circuit150of the rocker arm assembly20will now be described. The rocker shaft34can define a central pressurized oil supply conduit152, a vent oil passage or conduit154, a lubrication conduit156and a lash adjuster oil conduit180. The vent oil conduit154can have a vent lobe157extending generally parallel to an axis of the rocker shaft34and transverse to the vent oil conduit154. A connecting passage158with oil flowing in the direction of arrow204(FIG. 11) can connect the central pressurized oil supply conduit152with an oil supply passage160defined in the rocker arm40. As discussed herein, the pressurized oil supply conduit152, the connecting passage158and the oil supply passage160cooperate to supply pressurized oil to the second bore104to urge the upper disk portion112of the needle100upward. As the rocker arm40rotates around the rocker shaft34in the direction of arrow202, the vent lobe157will align with the oil supply conduit causing oil to be vented away from the second bore104through the vent oil conduit. When the pressure drops in the second bore104, the second spring120will urge the needle100downward such that the longitudinal pin110will act against the ball90and move the ball away from the valve seat76. Oil is then permitted to flow through the valve seat76and out of the HLA assembly46through the lash adjuster oil conduit180(FIG. 10).

As will become appreciated herein, the exhaust rocker arm assembly30can operate in a default combustion engine mode with engine braking off (FIG. 3) and an engine braking mode (FIGS. 4-6). When the exhaust rocker arm assembly30is operating in the default combustion engine mode (FIG. 3), an oil control valve152is closed (not energized). As a result, the oil supply passage160defined in the rocker arm40has low pressure such as around 0.3 bar. Other pressures may be used. With low pressure, the biasing member120will force the needle100in a downward direction causing the longitudinal pin portion110to urge the ball90away from the valve seat76. The check ball assembly80is therefore open causing the HLA assembly46to become “soft” and not influencing a downward force upon the valve bridge42. In the default combustion engine mode (FIG. 3), rotation of the rocker arm40in the counter-clockwise direction shown by arrow202will continue causing the collar138on the second spigot130to engage the rocker arm40. Continued rotation of the rocker arm40will cause both the first and the second valves50and52to open together.

With specific reference now toFIG. 4, operation of the exhaust valve rocker arm assembly30in the engine braking mode will be described. In braking mode, oil pressure is increased in oil supply passage160in the direction of arrow206causing the needle100to move upward in the direction of arrow208against the bias of the biasing member120. As a result, the longitudinal pin portion110is moved away from the check ball90. The HLA assembly46acts as a no-return valve with the first plunger body62rigidly extending toward the valve bridge42.

Turning now toFIG. 5, the rocker arm40has rotated further counter-clockwise around the rocker shaft34in the direction of arrow202. In the example shown, the rocker arm40has rotated 2.72 degrees. Because the HLA assembly46is rigid, the first spigot70will force the first socket72against the valve bridge42causing the first valve50to move off a first valve seat170in the direction of arrow210. In this example, the first valve50moves off the first valve seat170a distance of 2.85 mm. It will be appreciated that other distances (and degrees of rotation of the rocker arm40) are contemplated. Notably, the second valve52remains closed against a second valve seat172. The collar138on the second spigot130, while traveling toward the rocker arm40in the direction of arrow212, has not yet reached the rocker arm40. The second spigot130remains in contact (through the second socket132) with the rocker arm40.

With reference now toFIG. 6, the rocker arm40has rotated further counter-clockwise around the rocker shaft34in the direction of arrow202. In the example shown, the rocker arm40has rotated 4.41 degrees. Again, the HLA assembly46remains rigid and the first spigot70continues to force the first socket72against the valve bridge42causing the first valve50to move further off the first valve seat170in the direction of arrow210. In this example, the first valve50moves off the first valve seat170a distance of 4.09 mm. It will be appreciated that other distances (and degrees of rotation of the rocker arm40) are contemplated. At this point the collar138has moved further in the direction of arrow212and made contact with the rocker arm40and both the first and second valves50and52will be opened concurrently.

Turning now toFIG. 7, the rocker arm40has rotated further counter-clockwise around the rocker shaft34in the direction of arrow202. In the example shown, the rocker arm40has rotated 8.82 degrees. Again, the HLA assembly46remains rigid. Regardless, the second spigot130urges the bridge42downward to open the first and second valves50and52off their respective valve seats170and172, in the direction of arrows210and214, respectively. In this example, the first and second valves50and52are moved off their valve seats170and172a distance of 9.1 mm. It will be appreciated that other distances (and degrees of rotation of the rocker arm40) are contemplated.

With reference now toFIG. 8, the rocker arm40has rotated further counter-clockwise around the rocker shaft34in the direction of arrow202. In the example shown, the rocker arm40has rotated 12.9 degrees. At this point, the rocker arm40has rotated 12.9 degrees and the first and second valves50and52are at maximum lift off their valve seats170and172, in the direction of arrows210and214, respectively. In the example shown the first and second valves50and52are displaced 15.2 mm off their respective valve seats170and172. As shown, the oil supply passage160in the rocker arm40is fully disconnected from the connecting passage158of the central pressurized oil supply conduit152and is now connected to the vent oil conduit154by way of the vent lobe157. In this position, the supply of pressurized oil is interrupted and the oil pressure will drop in the oil supply passage160. As a result, the biasing member120urges the needle100downward such that the longitudinal pin portion110pushes the check ball90off the valve seat76, opening the HLA assembly46. Once the check ball90is open, the HLA assembly46becomes “soft” again and during valve closing will not exercise any force on the first valve50that could otherwise prevent its closing. Once the pushrod54occupies a position consistent with the base circle on the cam (not shown), the above process will continuously repeat until combustion mode is selected.