FIELD

[0001] The present disclosure relates generally to valvetrain systems and, more particularly, to a Type II valvetrain variable valve actuation (VVA) system for providing secondary valve lift such as engine braking.

BACKGROUND

[0002] Various systems have been developed for altering the valve-lift characteristics for internal combustion engines. Such systems, commonly known as variable valve timing (VVT) or variable valve actuation (VVA), improve fuel economy, reduce emissions and improve drive comfort over a range of speeds.

[0003] Discrete variable valve lift can be obtained through the use of switching rocker arm technology. Switching roller finger followers or switching rocker arms allow for control of valve actuation by alternating between latched and unlatched states, usually involving an inner arm and an outer arm. In some circumstances, these arms engage different cam lobes, such as low-lift lobes, high-lift lobes, and no-lift lobes. Mechanisms are required for switching rocker arm modes in a manner suited for operation of internal combustion engines. [0004] In engine braking, engine valve lift is modified for producing a valve event particularly for converting an internal combustion engine into an air compressor temporarily. By allowing compressed air to be released, energy absorbed by the engine to compress the gas during the compression stroke is not returned to the engine piston during the subsequent expansion or power stroke, but dissipated through the exhaust and radiator systems of the engine. The net result is an effective braking of the engine.

[0005] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

[0006] According to various aspects of the present disclosure, a hydraulic system for a rocker arm assembly having an exhaust rocker arm configured to selectively open an engine valve is provided. In one example, the system includes a carrier assembly configured to couple to a cylinder head of an engine, a brake plunger assembly disposed in the carrier assembly and configured to be actuated by a braking lobe of a camshaft, and a slave plunger assembly disposed in the carrier assembly and configured to be selectively hydraulically coupled to the brake plunger assembly. When the brake plunger assembly and the slave plunger assembly are hydraulically coupled, the brake plunger assembly is configured to impart movement via hydraulic fluid and the slave plunger assembly to actuate the exhaust rocker arm and open the engine valve to perform an engine braking operation. [0007] In addition to the foregoing, the described assembly may include one or more of the following features: a spool valve fluidly coupled between the brake plunger assembly and the slave plunger assembly, the spool valve selectively movable between (i) a sealed position that hydraulically couples the brake plunger assembly and the slave plunger assembly into a pressurized activated position, and (ii) an unsealed position that vents the brake plunger assembly and the slave plunger assembly into a depressurized, deactivated position that does not perform the engine brake operation.

[0008] In addition to the foregoing, the described assembly may include one or more of the following features: wherein the brake plunger assembly includes a plunger slidingly disposed within a cavity defined by a housing; a biasing mechanism configured to bias the plunger out of the cavity toward the camshaft; wherein the slave plunger assembly includes a plunger slidingly disposed within a cavity defined by a housing; and a biasing mechanism configured to bias the plunger into the cavity away from the exhaust rocker arm.

[0009] According to various aspects of the present disclosure, a hydraulic system for a rocker arm assembly of an engine is provided. In one example, the system includes an exhaust rocker arm having a first end and a second end, the first end configured to cooperate with an engine valve, a carrier assembly configured to couple to a cylinder head of the engine, a brake plunger assembly disposed in the carrier assembly and configured to be actuated by a braking lobe of a camshaft, and a slave plunger assembly disposed in the carrier assembly and configured to be selectively hydraulically coupled to the brake plunger assembly. When the brake plunger assembly and the slave plunger assembly are hydraulically coupled, the brake plunger assembly is configured to impart movement via hydraulic fluid and the slave plunger assembly to actuate the exhaust rocker arm and open the engine valve to perform an engine braking operation.

[0010] In addition to the foregoing, the described assembly may include one or more of the following features: a spool valve fluidly coupled between the brake plunger assembly and the slave plunger assembly, the spool valve selectively movable between (i) a sealed position that hydraulically couples the brake plunger assembly and the slave plunger assembly into a pressurized activated position, and (ii) an unsealed position that vents the brake plunger assembly and the slave plunger assembly into a depressurized, deactivated position that does not perform the engine brake operation.

[0011] In addition to the foregoing, the described assembly may include one or more of the following features: wherein the brake plunger assembly includes a plunger slidingly disposed within a cavity defined by a housing; a biasing mechanism configured to bias the plunger out of the cavity toward the camshaft; wherein the slave plunger assembly includes a plunger slidingly disposed within a cavity defined by a housing; a biasing mechanism configured to bias the plunger into the cavity away from the exhaust rocker arm; wherein the exhaust rocker arm is a roller finger follower; and a camshaft having a first lobe configured to engage the exhaust rocker arm to perform a drive mode operation, and the braking lobe configured to engage the brake plunger assembly to perform the engine braking operation.

[0012] In addition to the foregoing, the described assembly may include one or more of the following features: wherein the exhaust rocker arm second end is operably coupled to a deactivating pivot configured to selectively move between an activated position acting as a rigid body, and a deactivated position for absorbing downward motion of the exhaust rocker arm, wherein the deactivating pivot includes an outer body, a plunger slidingly disposed within the outer body, a latching mechanism, and a ball pivot, wherein the exhaust rocker arm second end is configured to pivot about the ball pivot. [0013] According to various aspects of the present disclosure, a method is provided for operating a hydraulic system for a rocker arm assembly of an engine. The hydraulic system including a carrier assembly configured to couple to a cylinder head of the engine, a brake plunger assembly disposed in the carrier assembly and configured to be actuated by a braking lobe of a camshaft, and a slave plunger assembly disposed in the carrier assembly and configured to be selectively hydraulically coupled to the brake plunger assembly. In one example, the method includes operating in a normal drive mode including hydraulically depressurizing the hydraulic system so the brake plunger assembly does not impart movement to the slave plunger assembly. In the normal drive mode the camshaft rotates normal lift lobes into contact with an exhaust rocker arm to open the engine valve. The method further includes operating in a brake mode including pressurizing the hydraulic system such that the camshaft rotates the brake lift lobe into contact with brake plunger assembly to impart movement to the slave plunger assembly to thereby contact the exhaust rocker arm and open the engine valve to perform an engine brake operation.

[0014] In addition to the foregoing, the described method may include one or more of the following features: wherein pressurizing the hydraulic system comprises supplying high pressure fluid to a volume between the brake plunger assembly and the slave plunger assembly; wherein supplying the high pressure fluid comprises supplying high pressure fluid to the volume via a spool valve; wherein operating in the brake mode includes contacting, with the brake lift lobe, a brake plunger of the brake plunger assembly, and transferring motion of the brake plunger to a slave plunger of the slave plunger assembly via the high pressure fluid in the volume between the brake plunger assembly and the slave plunger assembly.

In addition to the foregoing, the described method may include one or more of the following features: wherein the exhaust rocker arm includes a first end and a second end, and the method further includes operating a deactivating pivot in an activated position acting as a rigid body such that when the normal lift lobes contact the exhaust rocker arm, the second end pivots about the deactivating pivot and the first end transfers motion to the engine valve, selectively operating the deactivating pivot in a deactivated position for absorbing downward motion of the exhaust rocker arm, providing the deactivating pivot with a hydraulic lash adjuster (HLA), and loading the HLA during the brake mode to prevent pump up.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a sectional view of an example Type II valvetrain arrangement having a rocker arm assembly in accordance with the present disclosure;

[0016] FIG. 2 is a top sectional view of the valvetrain arrangement shown in FIG. 1 in accordance with the present disclosure; and

[0017] FIG. 3 is a cross-sectional view of an example spool valve that may be utilized with the valvetrain arrangement shown in FIGS. 1 and 2.

DETAILED DESCRIPTION

[0018] The present disclosure is directed to a variable valve actuation (VVA) system for adding secondary valve motion such as engine brake to an engine valve using a master/slave piston hydraulic system for a valvetrain such as a Type II (end pivot) valvetrain.

[0019] With reference to FIGS. 1 and 2, a Type II valvetrain arrangement 10 is shown positioned on a cylinder block 12. It will be appreciated, however, the present disclosure is not limited to a Type II arrangement and it is within the scope of the present disclosure for the various features described herein to be used in other valve train arrangements. In this regard, the features described herein associated with the valvetrain arrangement 10 can be suitable to a wide variety of applications. In the example embodiment, the valvetrain arrangement 10 is supported in a carrier 14 and each cylinder can include an intake valve rocker arm assembly 16 and an exhaust valve rocker arm assembly 18. The intake valve rocker arm assembly 16 is configured to control motion of intake valves of an associated engine.

[0020] In the example embodiment, the exhaust valve rocker arm assembly 18 incorporates integrated engine brake functionality and is configured to control opening of an exhaust valve 20 of the engine. In general, the exhaust valve rocker arm assembly 18 is configured to control exhaust valve motion in a combustion engine drive mode and an engine brake mode, as will be described herein in more detail.

[0021] With continued reference to FIGS. 1 and 2, the exhaust valve rocker arm assembly 18 will be described in more detail. In one example, the exhaust valve rocker arm assembly 18 can generally include an exhaust rocker arm 22, a pivot 24, and a hydraulic system 26 (FIG. 2). In general, an overhead camshaft 30 with valve actuating lobes selectively drive the rocker arm 22 to selectively actuate the exhaust valve 20, as will be described herein in more detail. By way of example only, the exhaust valve rocker arm assembly 18 is configured for operation with a three lobed camshaft 30 having first and second normal-lift lobes 32, 34 and a brake-lift lobe 36.

[0022] As shown in FIG. 1 , in the example embodiment, the exhaust rocker arm 22 generally includes a first end 40, an opposite second end 42, and outer arms 44 (only one shown). The first end 40 of the exhaust rocker arm 22 is configured to pivot over pivot 24, while the second end 42 is configured to selectively engage and actuate exhaust valve 20. The second end 42 also includes a contact member or surface 46 that can be operatively associated with the hydraulic system 26. Each of the outer arms 44 can include a roller 48 for cooperating with the first and second normal-lift lobes 32, 34 of the camshaft 30. As such, in the illustrated example, rocker arm 22 is a dual roller finger follower (RFF). Although described as having two rollers 48, it will be appreciated that exhaust rocker arm 22 may include any number of rollers (e.g., one or three) for cooperating with corresponding cam lobes. Alternatively, rocker arm 22 may include a contact surface or sliding pad (i.e. , no roller) for cooperating with corresponding cam lobes. In other examples, rocker arm 22 may be a switching roller finger follower (SRFF).

[0023] In the example embodiment, pivot 24 is a deactivating pivot with a hydraulic lash adjuster (HLA) configured to stay loaded and prevent pump up (e.g., during a brake mode). However, it will be appreciated that other types of pivots are contemplated such as, for example, fixed pivot or hydraulic lash adjuster. In a fixed pivot configuration, the end pivot may be a ball and socket configuration or a rocker shaft. Additionally, the systems described herein may include an alternative or additional HLA such as, for example, an HLA in a pivot (type II or III valvetrain), at a cam location (type V valvetrain), or a valve end (type III or V valvetrain). [0024] In the example embodiment, the hydraulic system 26 is integrated into the carrier 14 and generally includes a brake plunger assembly 50, a spool valve 52, a slave plunger assembly 54, and an oil control valve (OCV) 56. As shown in FIG. 2, the brake plunger assembly 50 includes a plunger 58 slidingly disposed within a cavity 60 defined within a housing 62. The brake plunger 58 is biased toward brake lift lobe 36 by a biasing mechanism 64 (e.g., a spring) and is selectively actuated (forced into housing 62) by the brake lift lobe 36. The cavity 60 is fluidly coupled to the spool valve 54 via a fluid passage 66.

[0025] With additional reference to FIG. 3, in the example embodiment, the spool valve 52 includes a check valve 68 (e.g., check ball) configured to selectively fluidly couple the fluid passage 66 with a second fluid passage 70 that is connected to the slave plunger assembly 54. The OCV 56 is configured to selectively supply a hydraulic fluid (e.g., pressurized oil) to an inlet port 72 to move the spool valve 52 to a sealed or closed position and provide the hydraulic fluid to the fluid passages 66, 70, thereby pressurizing the brake plunger assembly 50 and the slave plunger assembly 54. Shutting off the supply of pressurized hydraulic fluid moves the spool valve 52 to an unsealed or open position that vents the fluid passages 66, 70 and thus depressurizes the brake plunger assembly 50 and the slave plunger assembly 54.

[0026] In the example embodiment, as shown in FIG. 1 , the slave plunger assembly 54 includes a plunger 74 slidingly disposed within a cavity 76 defined within a housing 78. The plunger 74 includes a first end 80 and an opposite second end 82 that is configured to selectively engage the rocker arm second end 42 (e.g., contact surface 46) and/or the exhaust valve 20 to selectively open the exhaust valve 20, for example, to perform an engine brake operation. The plunger second end 82 is biased into the cavity 76 away from the rocker arm second end 42 and/or the exhaust valve 20 by a biasing mechanism 84 (e.g., a spring) supported at least partially by a seat or clip 86. The cavity 76 is fluidly coupled to the spool valve 54 via fluid passage 70.

[0027] With continued reference to FIGS. 1 -3, one example operation of the valvetrain arrangement 10 will now be described In a normal drive mode, the spool valve 52 is deactivated (no oil supplied) and as the camshaft 30 rotates the normal lift lobes 32, 34 into contact with the rollers 48 of the exhaust rocker arm 22, the first end 40 pivots about pivot 24 and the second end 42 moves downward to open the exhaust valve 20. As the camshaft 30 rotates the brake lift lobe 36 into contact with the brake plunger assembly 50, which is unpressurized due to no oil supply from OCV 56, the biasing mechanism 64 absorbs the inward movement of the brake plunger 58. In the deactivated state, because the spool valve 52 vents the fluid connection between the brake and slave plungers 58, 74, the motion of the plunger 58 is not translated to the slave plunger 74. Thus, slave plunger 74 does not act on rocker arm 22 or exhaust valve 20.

[0028] In the brake mode, a supply of high pressure fluid from OCV 56 enters inlet port 72, lifts check valve 68 into the sealed position, and fills (pressurizes) the volume between the brake plunger assembly 50 and the slave plunger assembly 54. Similar to above, as the camshaft 30 rotates the normal lift lobes 32, 34 into contact with the rollers 48 of the exhaust rocker arm 22, the first end 40 pivots about pivot 24 and the second end 42 moves downward to open the exhaust valve 20. As the camshaft 30 rotates the brake lift lobe 36 into contact with brake plunger 58, the plunger 58 is forced into cavity 60. However, because the brake and slave plungers 58, 74 are pressurized, the motion of plunger 58 is translated to the slave plunger 74, which is forced out of cavity 76 to impart the movement to open the exhaust valve 20 and thereby perform an engine brake operation. Advantageously, by imparting movement through the exhaust rocker arm 22, the HLA in the pivot 24 remains loaded and is configured to prevent pump up.

[0029] With additional reference to FIG. 1 , in the example implementation, pivot

24 is a deactivation pivot generally including an outer body 1 10, a plunger 1 12, a latching mechanism 1 14, and a ball pivot 116. However, it will be appreciated that pivot 24 may have various configurations.

[0030] Outer body 1 10 includes an oil communication groove 1 18 in fluid communication with a plurality of oil ports 120 via a plurality of oil channels 122. Plunger 1 12 is disposed at least partially within outer body 1 10 and is configured to selectively slide within the outer body 1 10 when deactivation pivot 24 is in an unlatched position (not shown). Ball pivot 1 16 is received within the plunger 1 12, and one or more biasing mechanisms 124 (e.g., a spring) can be disposed between the plunger 1 12 and a cap 126 to absorb downward motion of exhaust rocker arm first end 40 when deactivation pivot 24 is in the unlatched position. The biasing mechanism 124 can be configured to bias the plunger 1 12 outward from outer body 110 and absorb motion of the exhaust rocker arm 22 when the deactivation pivot 24 is in the deactivation mode, thereby providing a lost motion feature.

[0031] In the example implementation, the latching mechanism 1 14 is configured to selectively move between the latched position (FIG. 1 ) and the unlatched position (not shown). In the latched position, plunger 1 12 is prevented from movement relative to the outer body 1 10. In the unlatched position, plunger 112 is movable within and relative to the outer body 1 10.

[0032] When in the activated or latched position (FIG. 1 ), the deactivation pivot 24 acts as a rigid, unitary body and exhaust rocker arm first end 40 pivots about ball pivot 1 16 and imparts downward motion to the exhaust valve 20. In contrast, when the deactivation pivot 24 is in the deactivated or unlatched position, downward movement of exhaust rocker arm first end 40 causes the plunger 1 12 to slide downward within outer body 1 10. The biasing mechanism 124 subsequently absorbs the downward motion of exhaust rocker arm first end 40 such that exhaust rocker arm second end 42 does not transfer downward motion to the exhaust valve 20.

[0033] As shown in FIG. 2, latching mechanism 1 14 includes a pair of opposed pins 130 having a biasing mechanism (e.g., a spring) 132 arranged therebetween. The biasing mechanism 132 is configured to bias pins 130 away from each other and outward toward outer body 1 10. As such, when oil is not supplied to oil ports 120, biasing mechanism 132 biases pins 130 outward such that a shoulder 134 of each pin 130 is disposed adjacent a shoulder 136 of outer body 1 10. In this way, downward movement of plunger 1 12 is prevented by pin shoulder 134 abutting against outer body shoulder 136.

[0034] However, when a signal is received to transition deactivation pivot 24 to the unlatched position, an OCV provides a supply of oil to oil ports 120. The force of the supplied oil against pins 130 overcomes the biasing force of biasing mechanism 132, and the pins 130 move toward each other. As such, pin shoulders 134 are moved out of engagement with outer body shoulders 136, thereby enabling upward movement of plunger 1 12 within outer body 1 10 where biasing mechanisms 124 subsequently absorb the downward motion of exhaust rocker arm first end 40 and prevent transfer of motion to the exhaust valve 20. Although a particular latching mechanism 1 14 configuration is shown in FIG. 2, it will be appreciated that the latching mechanism 1 14 can have various configurations that enable valvetrain arrangement 10 to function as described herein. For example, in one alternative configuration, latching mechanism 114 can include an electromagnetic actuator (not shown) configured to receive a controller signal to selectively retract and deploy a latching device (e.g., pins 130) to enable and disable the deactivation function, thereby obviating a hydraulic system and OCV.

[0035] Described herein are systems and methods for adding secondary valve motion such as engine brake to a VVA system. In one example, the system includes a cam shaft with lobes for main lift and a lobe for a secondary valve lift, at least one finger follower type valve actuation with a fixed pivot. The pivot may include a hydraulic lash adjuster (HLA) assembly or deactivating element. Alternatively, the finger follower can include an HLA assembly. A carrier is mounted above the engine valves and includes a hydraulic system, which includes a master piston that interacts with the lobe for secondary valve lift, and a slave piston which interacts with the finger follower or engine valve directly to open the valve when the mater piston is compressed.

[0036] A spool valve is provided with a check valve that is selectively movable from a position where the connection between the master and slave pistons is vented, and a position where the connection is sealed. A hydraulic supply through an OCV switches the spool and seals and fills the volume between the master and slave pistons with oil. When the OCV is turned on, oil flows to the spool valve lifting it into a sealing position. This supply oil pressure will pressurize the master and slave pistons. Once pressurized, the cam lobe will provide input motion to the master piston. This motion will then be translated to the engine valve through the hydraulic connection and slave piston. When the OCV is turned off, the oil supply is vented.

[0037] 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.