Z orifice feature for mechanically actuated fuel injector

Abstract

A mechanically actuated electronically controlled fuel injector (MEUI) includes a first electrical actuator that controls the position of a spill valve, and a second electrical actuator to control pressure on a closing hydraulic surface associated with a directly operated nozzle check valve. The fuel injector is actuated via rotation of a cam to move a plunger to displace fuel from a fuel pumping chamber either to a spill passage, or at high pressure out of a nozzle outlet of the fuel injector for an injection event. The minimum controllable fuel injection quantity, especially as it relates to small closely coupled post injections following a large main injection, is accomplished by the inclusion of a Z orifice passage that maintains a fluid connection between a needle control chamber and the nozzle supply passage. The inclusion of the Z orifice passage slows the rate at which pressure drops in the needle control chamber to commence an injection event, but also hastens the rate at which pressure builds in the needle control chamber to end an injection event. The result is a smaller post injection quantity and, if desired, a longer, shorter or same dwell time between injection events.