HYDRAULIC ASSISTED ENGINE BRAKE MECHANISM FOR VALVE TRAIN

Abstract

An exhaust valve rocker arm assembly operable in a drive mode and an engine braking mode includes a rocker shaft, a rocker arm, a hydraulic lash adjuster assembly, an accumulator assembly and a locking pin. The rocker shaft has an oil gallery defined thereon. The rocker arm receives the rocker shaft and is configured to rotate around the rocker shaft. The rocker arm has an oil feed channel that is fluidly connected to the oil gallery. The rocker arm further defines an engine brake relief hold and an accumulator relief hole. The accumulator assembly is disposed in the rocker arm and is fluidly coupled to the hydraulic lash adjuster through an engine brake relief hole. The locking pin assembly is disposed in the rocker am and is selectively movable by a high pressure fluid from a closed position to an open position.

Description

FIELD

The present disclosure relates generally to engine braking and, more particularly, to hydraulic assisted engine braking.

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.

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

An exhaust valve rocker arm assembly operable in a drive mode and an engine braking mode includes a rocker shaft, a rocker arm, a hydraulic lash adjuster assembly, an accumulator assembly and a locking pin. The rocker shaft has an oil gallery defined thereon. The rocker arm receives the rocker shaft and is configured to rotate around the rocker shaft. The rocker arm has an oil feed channel that is fluidly connected to the oil gallery. The rocker arm further defines an engine brake relief hold and an accumulator relief hole. The hydraulic lash adjuster assembly is disposed on the rocker arm and has a plunger assembly including first and second plunger bodies. The first plunger body is movable between a first positon and a second position. In the first position, the first plunger body extends rigidly outwardly. The accumulator assembly is disposed in the rocker arm and is fluidly coupled to the hydraulic lash adjuster through an engine brake relief hole. The locking pin assembly is disposed in the rocker am and is selectively movable by a high pressure fluid from a closed position to an open position. In the open position, fluid flows from the accumulator relief hole causing the plunger assembly to be collapsible wherein the first plunger body is movable to the second position.

According to additional features, the accumulator assembly further comprises an accumulator piston and an accumulator biasing member. The rocker arm can define an accumulator chamber that receives the accumulator assembly. The lock pin assembly can comprise a lock pin and a lock pin biasing member. The rocker arm defines a lock pin receiving body that receives the lock pin biasing member.

In other features, during the drive mode, high pressure oil from the oil gallery is supplied through the rocker arm oil feed to the locking pin causing the locking pin to translate to an open position and the accumulator relief hole to open. In the drive mode, the plunger assembly is collapsible. During an exhaust lift, the plunger assembly compresses until the first plunger moves past a plunger engine brake relief hole in the first plunger and an engine brake relief hole in the rocker arm. In the brake mode, low pressure oil from the oil gallery is supplied through the rocker arm oil feed allowing the locking pin to move to a closed position and the accumulator relief hole to close. In the braking mode, the plunger assembly is rigid.

According to still other features, an angular position of the oil gallery on the rocker shaft is placed such that an oil supply on the rocker arm selectively locates with one of a high pressure oil source and a low pressure oil source. The locking pin can move to the open position causing the accumulator assembly to become compressible and providing lost motion in the plunger assembly upon the oil supply on the rocker arm aligning with the high pressure oil source. The locking pin can move to the closed position causing the accumulator assembly to become rigid upon the oil supply on the rocker arm aligning with the low pressure oil source.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1A is a front perspective view of an engine braking rocker arm constructed in accordance to one example of the present disclosure;

FIG. 1B is a sectional view taken along line 1B-1B of FIG. 1A and showing a lock pin in a closed position thereby blocking an accumulator relief hole during an engine brake event;

FIG. 1C is a sectional view taken along line 1C-1C of FIG. 1A;

FIG. 1D is a sectional view taken along line 1D-1D of FIG. 1A;

FIG. 2A is a partial front perspective view of the engine braking rocker arm of FIG. 1A;

FIG. 2B is a sectional view taken along line 2B-2B of FIG. 2A;

FIG. 2C is a plot illustrating valve lift versus cam degrees for an exemplary engine braking event carried out by the engine braking rocker arm of FIG. 1A;

FIG. 3A is a sectional view taken along line 3A-3A of FIG. 2A and shown with the lock pin in an open position thereby opening the accumulator relief hole during drive mode;

FIG. 3B is a sectional view taken along line 3B-3B of FIG. 2A and shown with the lock pin in the open position;

FIG. 4A is a sectional view of the engine braking rocker arm of FIG. 1A and shown with the lock pin in a closed position;

FIG. 4B is a sectional view of the engine braking rocker arm of FIG. 1A and shown with the lock in in the closed position;

FIG. 5A is a sectional view of the engine braking rocker arm of FIG. 1A shown with the locking pin just before reset;

FIG. 5B is a sectional view of the engine braking rocker arm of FIG. 5A just after reset;

FIG. 6A is a schematic view of an oil supply on the rocker arm aligned with a low pressure source on an oil gallery of a rocker shaft; and

FIG. 6B is a schematic view of the oil supply on the rocker arm aligned with a high pressure source on the oil gallery of the rocker shaft.

DETAILED DESCRIPTION

With reference to the FIGS., an engine braking rocker arm assembly is shown and generally indicated at reference numeral 10. In the example embodiment, the engine braking rocker arm assembly 10 provides an engine braking operation with the help of a hydraulic lash adjuster (HLA) 12, an accumulator assembly 16, and lock pin assembly 20. The engine braking rocker arm assembly 10 also provides a reset function which makes the maximum lift the same as the drive mode.

Engine braking is typically utilized to effectively slow down a vehicle on a downhill grade by opening the exhaust valve during the compression stroke. The function of an engine braking capsule is to absorb the lift from the cam in an engine braking off mode. The engine braking rocker arm assembly 10 described herein is configured to achieve lift absorption using the HLA 12, the accumulator assembly 16 and the lock pin assembly 20 in connection with a hydraulic circuit 26.

With particular reference to FIGS. 1A-1D, the rocker arm assembly 10 will be further described. The rocker arm assembly 10 generally includes a rocker arm 30 that defines a shaft receiving bore 32 and that is configured to receive and rotate around a rocker shaft 34 (FIG. 6A). The rocker arm 30 further defines an accumulator chamber 38 that receives an accumulator piston 40 and accumulator biasing member 42 of the accumulator assembly 16. The rocker arm 30 defines a relief hole 46 that is configured to drain oil from the accumulator chamber 38 depending upon a position of the lock pin assembly 20 as will become appreciated herein. The rocker arm 30 defines an oil feed channel 48 the delivers high pressure oil to the lock pin assembly 20. The rocker arm 30 defines a lock pin receiving body 50 that receives a lock pin 52 and lock pin biasing member 54 of the lock pin assembly 20. The rocker arm 30 further defines an HLA receiving bore 58 (FIG. 1C).

With reference now to FIGS. 1C and 1D, the HLA 12 will be further described. It will be appreciated that the HLA 12 may be configured differently within the scope of the present disclosure. The HLA 12 generally includes a capsule or plunger assembly 60 including a first plunger body 62 and a second plunger body 64. The second plunger body 64 can be partially received by the first plunger body 62. The plunger assembly 60 is received by the HLA receiving bore 58. The first plunger body 62 can have a closed end 68 that defines a spigot 70 which is received in a first socket 72 that ultimately acts against a valve stem. A check ball assembly 80 can be positioned between the first and second plunger bodies 62 and 64. The check ball assembly 80 can include a first biasing member 82, a cage 84, and a check ball 90. A snap ring 92 nests in a radial groove provided in the bore 58 of the rocker arm 30. The snap ring 92 retains the first plunger body 62 in the bore 58.

The engine braking rocker arm assembly 10 is operable between a drive mode (FIGS. 3A, 3B) and an engine brake mode (FIGS. 4A and 4B). In the drive mode, high pressure oil is supplied through the rocker arm oil feed 48 to the pin 52. This pushes the pin 52 backward and opens an oil path to the accumulator relief hole 46. During the BGR event, since the accumulator relief hole 46 is open, the engine brake capsule 60 is spongy and is able to absorb the BGR lift. During the exhaust lift, the capsule 60 is compressed until the second (internal) plunger 64 moves past a plunger engine brake relief hole 94 in the first plunger 62 and an engine brake relief hole 95 in the rocker arm 30. After the engine brake relief hole 94 is sealed, the entire cam lift is transferred.

In the engine brake mode, low pressure oil is supplied through the rocker arm oil feed 48 from low pressure cavity 94 (FIG. 6A) on the rocker shaft 34 to the pin 52. This keeps the pin 52 in position and keeps the accumulator relief hole 46 closed. During the BGR event, since the accumulator relief hole 46 is closed, the engine brake capsule 60 is rigid and transfers the BGR/CR lift. During the exhaust lift, the oil feed to the pin 52 can be positioned such that after the required rotation, the oil pin feed 48 connects to a high pressure cavity 96 (FIG. 6B) on the rocker shaft 34, thereby providing a reset function.

During the reset event, an oil gallery 100 is provided in the rocker shaft 34 connecting the main oil gallery (see FIGS. 6A and 6B). The angular position of the oil gallery 100 on the rocker shaft 34 is placed such that it connects with an oil supply 110 on the rocker arm 30 at the instant when reset is required. After it connects, the high pressure oil opens the lock pin 52 making the accumulator assembly 16 soft (compressible) thereby providing the required lost motion in the capsule 60. FIG. 5A shows the locking pin 52 before reset. FIG. 5B shows the locking pin 52 after reset. Once the rocker arm 30 moves back (FIG. 6A), it is disconnected from the high pressure oil 96 and the lock pin 52 subsequently closes again and capsule 60 becomes rigid. The rocker arm assembly 10 also works for reverse working pressures such as, for example, engine brake actuation with high pressure, low pressure in drive mode. In the illustrated example, rocker arm assembly 10 utilizes high pressure actuation in drive mode and low pressure in the engine brake mode.

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.

Claims

1. An exhaust valve rocker arm assembly operable in a drive mode and an engine braking mode, the exhaust valve rocker arm assembly comprising: a rocker shaft having an oil gallery defined thereon;a rocker arm that receives the rocker shaft and that is configured to rotate around the rocker shaft, the rocker arm having an oil feed channel that is fluidly connected to the oil gallery, the rocker arm further defining an engine brake relief hole and an accumulator relief hole;a hydraulic lash adjuster assembly disposed on the rocker arm, the hydraulic lash adjuster having a plunger assembly including first and second plunger bodies, wherein first plunger body is movable between a first position and a second position, wherein in the first position, the first plunger body extends rigidly outwardly;an accumulator assembly disposed in the rocker arm and fluidly coupled to the hydraulic lash adjuster assembly through an engine brake relief hole; anda locking pin assembly disposed in the rocker arm and that is selectively movable by a high pressure fluid from a closed position to an open position, wherein in the open position, fluid flows from the accumulator relief hole causing the plunger assembly to be collapsible wherein the first plunger body is movable to the second position.

2. The exhaust valve rocker arm assembly of claim 1 wherein the accumulator assembly further comprises an accumulator piston and an accumulator biasing member.

3. The exhaust valve rocker arm assembly of claim 2 wherein the rocker arm defines an accumulator chamber that receives the accumulator assembly.

4. The exhaust valve rocker arm assembly of claim 1 wherein the lock pin assembly comprises a lock pin and a lock pin biasing member.

5. The exhaust valve rocker arm assembly of claim 4 wherein the rocker arm defines a lock pin receiving body that receives the lock pin biasing member.

6. The exhaust valve rocker arm assembly of claim 1 wherein in the drive mode, high pressure oil from the oil gallery is supplied through the rocker arm oil feed to the locking pin causing the locking pin to translate to an open position and the accumulator relief hole to open.

7. The exhaust valve rocker arm assembly of claim 6 wherein in the drive mode the plunger assembly is collapsible.

8. The exhaust valve rocker arm assembly of claim 7 wherein during an exhaust lift, the plunger assembly compresses until the first plunger moves past a plunger engine brake relief hole in the first plunger and an engine brake relief hole in the rocker arm.

9. The exhaust valve rocker arm assembly of claim 8 wherein in the brake mode, low pressure oil from the oil gallery is supplied through the rocker arm oil feed allowing the locking pin to move to a closed position and the accumulator relief hole to close.

10. The exhaust valve rocker arm assembly of claim 9 wherein in the braking mode the plunger assembly is rigid.

11. The exhaust valve rocker arm assembly of claim 10 wherein an angular position of the oil gallery on the rocker shaft is placed such that an oil supply on the rocker arm selectively locates with one of a high pressure oil source and a low pressure oil source.

12. The exhaust valve rocker arm assembly of claim 11 wherein the locking pin moves to the open position causing the accumulator assembly to become compressible and providing lost motion in the plunger assembly upon the oil supply on the rocker arm aligning with the high pressure oil source.

13. The exhaust valve rocker arm assembly of claim 11 wherein the locking pin moves to the closed position causing the accumulator assembly to become rigid upon the oil supply on the rocker arm aligning with the low pressure oil source.