Camless valve actuator for compression braking and normal engine operations

Abstract

An actuator for opening a poppet exhaust valve, which is closed by a spring and opens in normal operation against a relatively low pressure and which opens for compression braking against a relatively high pressure, is motivated in either event by the same hydraulic pressure. The actuator has a unitary central valve and piston element, which is coaxially directed toward the exhaust valve stem and has an area providing, when subjected to the pressure, a force sufficient to open the exhaust valve for normal operation but insufficient to open the exhaust valve during compression braking. The element extends through a relatively larger diameter annular piston which is slidably fitted about the element and within a bore receiving the annular piston. In normal operation, the element provides enough force to move from an unactuated position and open the exhaust valve, and initial movement of the element closes off passages in the element that admit the pressure to the piston which thus does not move. During compression braking, the force developed by the central element cannot move the element and the exhaust valve so that these passages admit pressure to the piston which provides sufficient force to move with the central element and open the exhaust valve. In either event, when the hydraulic pressure is subsequently reduced, the spring closes the exhaust valve and returns the actuator to its unactuated position. The actuator may be constructed to provide a smaller valve opening for braking than for normal operation.