Valve area scheduling in a double acting piston for a

Abstract

A hydraulically-actuated fuel injector includes an injector body that defines a high pressure inlet, a low pressure drain, an upper actuation fluid cavity, a lower actuation fluid cavity, and a nozzle outlet. A piston is positioned in the injector body and moveable between a retracted position and an advanced position. A control valve is attached in the injector body and includes a spool valve member that is moveable between a first position and a second position. When the spool valve member is in its first position, the piston is biased toward its retracted position since the upper actuation fluid cavity is open to the low pressure drain, but the lower actuation fluid cavity is open to the high pressure inlet. During an injection event, the spool valve member is moved to its second position where the upper actuation fluid cavity is open to the high pressure inlet, but the lower actuation fluid cavity is open to the low pressure drain. At the end of an injection event, the spool valve member is moved through an intermediate position in which both the upper and lower actuation fluid cavities are exposed to the high pressure inlet. This causes the piston to abruptly cease its downward pumping stroke, resulting in a quicker drop in fuel pressure, a faster closure of the needle check valve, and hence a more abrupt end to the injection event.