Unit fuel injector with injection chamber spill valve

摘要

A unit fuel injector assembly (88) periodically injects fuel of a variable quantity on a cycle to cycle basis as a function of the pressure of fuel supplied to the injector from a source of fuel and at a variable time during each cycle as a function of the pressure of the timing fluid supplied to the injector from a source of timing fluid. A reciprocating plunger assembly (146) is received within the injector body (106) and includes an upper plunger section (148), a lower plunger section (150) and an intermediate plunger section (152) in order to define a variable volume timing chamber (138), a variable volume injection chamber (162) and a variable volume compensation chamber (176). Biasing means including an upper compression spring (180) and lower compression spring (182) are arranged in the compensation chamber (176) to independently bias the lower plunger section (150) and the imtermediate plunger section (152) in opposite directions to tend to collapse the timing chamber (138) and injection chamber (162). Provision is made for causing both the timing chamber (138) and injection chamber (162) to be spilled at the end of each injection event. A spill valve (204) for spilling fuel from the injection chamber (162) is located at a lower end portion of the injection chamber (162), is spring biased to a closed position and is openable by an end face of the injection plunger (150) coming into contact with a contact piece (210) of a spill valve (204) at the end of an injection stroke.