GB1373327A - Rocker arm engine brake system - Google Patents

Abstract

1373327 I C engine valve gear JACOBS MFG CO 6 June 1973 [11 July 1972] 26974/73 Heading F1B Engine braking is achieved by opening the exhaust valve of an I.C. engine when the piston is near the TDC position. A device for effecting this additional opening of the valve comprises a valve-opening rocker arm pivoted on a pedestalsupported rocker shaft, a rotatable cam which operates the rocker arm but is ineffective to open the valve because of the clearance between the rocker arm and valve stem, a piston mounted in a bore in the rocker arm and movable by hydraulic fluid-pressure to a projected position in which the clearance is taken up, the fluid circuit including a control valve and one of two separate conduits extending longitudinally through the rocker shaft, the other of the conduits receiving oil from the crank-case and the conduits being inter-connected by bleed holes in a partition wall common to the conduits. Rocker arm 16 mounted on rocker shaft 21 operates two exhaust valves 12 through bridge piece 14. Rocker arm 16 is oscillated by push rod 24 and cam 25 which has a main lobe 28 which opens the valves during the exhaust stroke and an auxiliary lobe 29 which opens the valves near the top of the compression stroke. For the lobe 29 to be effective, piston 31 is projected by admitting hydraulic fluid to the space behind the piston. Fluid is fed to each rocker arm by a conduit 48 formed by dividing a bore through the rocker shaft into two conduits by a partition 49. Fluid is supplied to conduit 48 by pump 2, through a solenoid-operated valve . unit 38. When the valve unit is energized, fluid flows through ports 45 to conduit 48. When the valve is de-energized, ports 45 connect conduit 48 to a drain 70. The fluid circuit also includes a fluid-operated shuttle valve 63 combined with a check valve 65. Shuttle valve 63, Fig. 7 is moved by fluid from conduit 48 to align a cross-bore im the shuttle with a passage 61, so that fluid flows past the check-valve 65 to move piston 31. The check-valve forms an hydraulic lock preventing return movement of the piston. When pressure in conduit 48 is relieved, the shuttle is moved by spring 69 to allow fluid behind the piston to vent through duct 59. To prevent air bubbles accummulating in duct 48, it is connected by bleed holes in partition 49 to the second conduit 51 which supplies lubricating oil to the valve gear and is therefore always filled with oil from the crank-case.