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.

What is claimed is: 
     
         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; and   a 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.