Variable valve actuation system for type II valverain using lost motion and reset

A rocker arm assembly for a Type II valvetrain arranged for cooperation with a cylinder head includes a roller finger follower (RFF) and a lost motion with reset (LMR) hydraulic assembly. The RFF has a first end and a second end. The first end cooperates with a valve. The LMR hydraulic assembly has a hydraulic control element and a plunger. The LMR hydraulic assembly moves the plunger between a rigid position and a non-rigid position. The LMR hydraulic assembly is configured at the second end of the RFF.

FIELD

The present disclosure relates generally to a rocker arm assembly for use in a valve train assembly and more particularly to a hydraulic lash adjuster configuration having controlled collapsing used as a reset function configured on a Type II valvetrain.

BACKGROUND

Decompression 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 decompression 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.

SUMMARY

A rocker arm assembly for a Type II valvetrain arranged for cooperation with a cylinder head includes a roller finger follower (RFF) and a lost motion with reset (LMR) hydraulic assembly. The RFF has a first end and a second end. The first end cooperates with a valve. The LMR hydraulic assembly has a hydraulic control element and a plunger. The LMR hydraulic assembly moves the plunger between a rigid position and a non-rigid position. The LMR hydraulic assembly is configured at the second end of the RFF.

The rocker arm assembly can further comprise an accumulator. The hydraulic control element selectively passes oil to the accumulator. The hydraulic control element further includes a spool valve that connects oil volume to a vented dump. A reset pin contacts the RFF and controls the spool valve to connect oil volume to the vented dump. A biasing member biases the RFF toward a cam.

According to additional features, the rocker arm assembly can further include a roller bearing that is positioned generally intermediate the first end of the RFF and the second end of the RFF. A hydraulic lash adjuster (HLA) can be positioned at the first end to accommodate lash between the RFF and a valve. The rocker arm assembly provides variable valve assembly functions including engine brake, early exhaust valve opening (EEVO) and late intake valve closing (LIVC). The LMR hydraulic assembly is accommodated in the cylinder head. The LMR hydraulic assembly is in the form of an LMR capsule.

A rocker arm assembly for a Type II valvetrain arranged for cooperation with a cylinder head according to another example of the present disclosure includes a roller finger follower (RFF) and a lost motion with reset (LMR) hydraulic assembly. The RFF has a first end and a second end. The first end cooperates with a valve. The LMR hydraulic assembly has a plunger assembly and a shuttle assembly. The plunger assembly has a plunger that selectively translates within a plunger chamber between an extended rigid position based upon the plunger chamber being pressurized with oil and a retracted non-rigid position based upon the plunger chamber being depressurized. The plunger, through the RFF, moves the engine valve toward an open position. The shuttle assembly moves between a first position and a second position based upon oil communicated into the LMR hydraulic assembly from an oil supply channel. The shuttle assembly has a shuttle valve that selectively moves between a closed position and an open position. In the open position, oil flows into the plunger chamber. The rocker arm assembly sequentially moves along a first valve lift profile, a reset valve lift profile and a valve closing profile. In the first valve lift profile, pressurized oil is communicated from the oil supply channel. The shuttle assembly moves into the second position causing the shuttle valve to be opened, the pressure chamber to be pressurized and the plunger to move to the extended rigid position. In the reset valve lift profile, pressurized oil is not communicated from the oil supply channel. The shuttle assembly moves into the first position.

According to additional features, the rocker arm assembly further includes a reset pin that extends from the cylinder head that is moved by the RFF. The reset pin has a connecting channel that selectively aligns with one of an oil supply channel and an oil dump channel at an onset of the reset valve lift profile. Both of the oil supply channel and the oil dump channel defined in the cylinder head. The LMR hydraulic assembly is received in a receiving bore of the cylinder head. A biasing member biases the RFF toward a cam.

The rocker arm assembly can further include a roller bearing positioned generally intermediate the first end of the RFF and the second end of the RFF. A hydraulic lash adjuster (HLA) can be positioned at the first end to accommodate lash between the RFF and a valve. The rocker arm assembly can further provide variable valve assembly functions including engine brake, early exhaust valve opening (EEVO) and late intake valve closing (LIVC). The LMR hydraulic assembly can be in the form of an LMR capsule. The rocker arm assembly can further comprise an accumulator. The hydraulic control element can selectively pass oil to the accumulator.

DETAILED DESCRIPTION

With initial reference toFIG. 1, a plot according to prior art is shown where standard exhaust lift is identified and an added motion engine brake lift is further identified. A typical system to provide this valve motion uses separate, independent actuation systems for the standard exhaust lift and brake events.

With reference toFIGS. 2 and 3, a first exhaust profile10and a second exhaust profile12are shown. The first exhaust profile10is associated with engine brake lift. The second exhaust profile12is associated with standard exhaust valve lift. According to the present disclosure, while in brake mode, after brake gas recirculation (BGR) and compression release (CR), at a certain point, identified at reset20(FIG. 3), a hydraulic capsule will collapse for an amount of lift loss (reset) and the exhaust valve would complete the remainder of the lift as a standard lift. In this regard, the resulting profile will follow the first exhaust profile10until the reset20where the profile will transition to the second exhaust profile12.

With additional reference now toFIG. 4, the present disclosure uses the lost motion with reset principle to create a modular variable valve actuation (VVA) system for a Type II valvetrain. In particular, the present application provides a VVA system for a Diesel engine with a Type II dual overhead cam valvetrain using a lost motion with reset principle to provide VVA functions such as engine brake, early exhaust valve opening (EEVO) and late intake valve closing (LIVC). The system can also incorporate a hydraulic lash adjuster (HLA). In a Type II valvetrain, an overhead cam lobe40drives a rocker arm44. A first end of the rocker arm44pivots over a fixed pivot or an HLA48, while a second end of the rocker arm44actuates a valve50. In a fixed pivot configuration, the end pivot may be a ball and socket configuration or a rocker shaft.

With reference now toFIG. 5, a rocker arm assembly according to one example of the present disclosure is shown and generally identified at reference numeral60. The rocker arm assembly60includes a roller finger follower (RFF)62that may include an HLA66. A roller bearing70can be positioned generally intermediate a first end72of the RFF62and a second end74of the RFF62. The roller bearing70can cooperate with an overhead cam lobe (see40,FIG. 5) to transfer motion of the cam to motion of the RFF62. The HLA66can be positioned generally at the first end72to accommodate lash between the RFF62and a valve80. The HLA66can be located elsewhere in the rocker arm assembly60. The second end74of the RFF62can rest on a lost motion with reset (LMR) hydraulic assembly84.

The LMR hydraulic assembly84can be accommodated at a cylinder head86. Explained further, the LMR hydraulic assembly84can be incorporated into or fixed to the cylinder head86. While the following discussion and related illustrations include an LMR hydraulic assembly84in the form of a capsule, the components such as the hydraulic piston, spool valve and accumulator could be individually or collectively separated throughout the cylinder head86rather than packaged in a single capsule. The LMR hydraulic assembly84includes a hydraulic control element90and a plunger92with a pivot end. The hydraulic control element90can control whether the plunger92is hydraulically solid (rigid), or allows the plunger92to pass oil to an accumulator100in a non-rigid (limp) position. A reset pin102having a connecting passage104can contact the RFF62and control a spool valve (or control plunger)110that connects oil volume (control oil feed)112to a vented dump114. Other configurations are contemplated for providing the timing function. For example, any timing element, such as an electronic timing element, that switches the control element90from supply to dump is contemplated. A biasing member116can bias the reset pin102to a position fluidly connected to the control oil feed112. A biasing member118can bias the RFF62toward the cam (or a set mechanical lash) and valve contact point. The biasing member118can absorb lost motion when the plunger92is non-rigid.

Turning now toFIGS. 6 and 7, additional features will be described. A rocker arm configuration can include an exhaust rocker arm assembly150and an intake rocker arm assembly152. The exhaust rocker arm assembly150cooperates with exhaust valves154,156. The intake rocker arm assembly cooperates with intake valves164,166. It will be appreciated that the present teachings may be similarly applicable to other rocker arm configurations. The exhaust rocker arm assembly150can include a LMR hydraulic assembly84afor EEVO on a first RFF62aand a LMR hydraulic assembly84bfor engine brake on a second RFF62b. The hydraulic assembly84atherefore can be used in a configuration for early exhaust valve opening and the LMR hydraulic assembly84bcan be used in a configuration for engine brake. Any combination of capsule configurations may be used. It is further appreciated that one or both of the LMR hydraulic assemblies84aand84bcan be arranged in the cylinder head86as described above.

On the intake rocker arm assembly152, a similar configuration can be incorporated. A LMR hydraulic assembly84cis provided on a third RFF62cfor LIVC. Very similar hardware can be incorporated on the intake side to achieve further benefit of intake valve closing. In this regard, the same capsule assembly84therefore can be incorporated in configurations for engine braking (early exhaust valve opening) as well as late intake valve closing. The capsule assembly84can provide hydraulic lash adjustment as well as controlled collapsing used as a reset function. It is further appreciated that the LMR hydraulic assembly84ccan be arranged in the cylinder head86as described above. The function can be used on both of the exhaust valves for compression brake and on an intake valve for intake valve closing. On the intake rocker arm assembly152, the lift profile will initially follow a high lift plot170and transition to a low lift plot172subsequent to a reset event174. The reset event174can occur very close to the maximum lift.

With continued reference toFIG. 5and additional reference now toFIGS. 8-13, additional features and operation of the LMR hydraulic assembly84will be described. The cylinder head86defines the oil supply channel112, the oil dump or relief channel114, an LMR hydraulic assembly84receiving bore202and an HLA oil feed204. As will explained herein, the oil supply channel112is caused to supply oil to the LMR hydraulic assembly84during a first operating condition while the relief channel114is caused to drain oil from the LMR hydraulic assembly84based on a position of the reset pin102.

LMR hydraulic assembly84includes a capsule housing212received in the receiving bore202of the cylinder head86. The capsule housing212defines a plunger chamber214, a shuttle chamber216and a connecting port218that connects the plunger chamber214and the shuttle chamber216. The capsule assembly210generally includes a plunger assembly220and a shuttle assembly224. The plunger assembly220includes a plunger228, a plunger biasing member230, a guide rod232and an elephant foot234. The plunger228is slidably received in the plunger chamber214and biased outwardly by the plunger biasing member230. As will become appreciated the plunger228is caused to be urged outwardly in a rigid position upon accumulation of oil within the plunger chamber214.

The shuttle assembly224can generally include an outer body240, an inner body242, a ball244, a ball biasing member246, a shuttle biasing member250, a pin252and a cap or closure member256. The outer and inner body240and242are collectively referred to herein as a shuttle body260. The shuttle body260can define an upstream shuttle port262and a downstream shuttle port264. The shuttle body260, ball244and ball biasing member246can collectively provide a shuttle valve270that selectively allows fluid communication in an open position (with the shuttle assembly224translated leftward as viewed in the drawings) between the connecting port218, upstream shuttle port262and downstream shuttle port264.

With reference toFIG. 7, possible valve lift profiles on the exhaust side and intake side for a valve train incorporating rocker arm configurations according to the present disclosure are shown compared to a standard exhaust and intake lift profiles. In the example shown inFIG. 7, the x-axis represents degrees of camshaft rotation and the y-axis represents valve lift. The actual values are merely exemplary. In a standard exhaust lift profile the exhaust valves154and156open at2A and close at5A. In standard intake valve lift, one or both intake valves164and166open at point6and close at point10.

According to one configuration of the present disclosure, the first RFF62acan be configured for de-compression engine brake. In general, the exhaust valve154opens at point1, goes through exhaust gas recirculation, almost closes, goes through compression release and at point4, goes through a reset function. Subsequent to the reset function, the exhaust valve154follows a standard exhaust valve closing profile and closes at point5. The second RFF62bcan be configured for early exhaust valve opening. In general, the exhaust valve156opens at point3, goes through a reset function at point4and follows a standard exhaust valve closing profile and closes at point5.

In addition, the intake rocker arm assembly152can be configured for early intake valve closing where one or both of the intake valves164and166are opened at point6, following opening flank travels close to maximum lift where at point7, goes through a reset function and closes at point8. Similarly, the intake rocker arm assembly152can be configured for late intake valve closing wherein one or both of the intake valves164and166are opened at point6and follow the late intake valve closing cam lift until closing at point9. It will be appreciated that in some examples a bridge can cause both intake valves164and166to move concurrently. In other arrangements, dedicated intake rocker arms may be provided to independently operate the first and second intake valves164and166. Other configurations are contemplated. In the example described one oil control valve can be incorporated for delivering oil to the intake valve rocker arm assembly152.

Turning now toFIGS. 3 and 7-13, operation of the exhaust rocker arm assembly150having the reset function in engine brake and drive mode will be described. In drive mode (identified by “FIG. 8” inFIG. 3), the shuttle assembly224generally occupies a first position (translated rightward as viewed inFIG. 8) biased by the shuttle biasing member250. In engine brake mode (identified by “FIG. 9” inFIG. 3), the shuttle assembly224translates leftward and occupies a second position. In engine brake mode, pressurized oil is communicated through the oil supply channel112, causing the shuttle assembly224to translate leftward and the shuttle valve270to open causing oil to fill the plunger chamber214and the plunger228to move to an extended rigid position.

In drive mode with lost motion (identified by “FIG. 10” inFIG. 3), the shuttle assembly224occupies the first position and the plunger chamber214is not pressurized. Therefore, the plunger228is permitted to translate against the bias of the plunger biasing member230.

The reset function will now be described. When the RFF62acontinues rotation around the rocker shaft, the reset pin102is contacted by the RFF62aand is caused to move its connecting passage104from alignment with the oil supply channel112to alignment with the oil dump channel114(identified by “FIG. 11” inFIG. 3) causing oil to be drained away from the capsule assembly210. The shuttle assembly224is caused to translate rightward, (identified by “FIG. 13” inFIG. 3), from the bias of the shuttle biasing member250. The plunger228is then free to move to a retracted position (plunger chamber214is no longer pressurized). In this regard, the lift profile transitions from the solid line to the dashed line (FIG. 3). Upon completion of the reset function, (identified by “FIG. 12” inFIG. 3), the shuttle assembly224remains biased rightward by the shuttle biasing member250and the valve lift can follow a standard exhaust lift profile. For rocker arms configured for engine brake and early exhaust valve opening, the oil control valve would be upstream of the capsule assembly210controlling oil flow into the capsule assembly210. For early and late intake valve closing, the oil control valve would be downstream controlling oil flow from the capsule.

The foregoing description of the examples has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.