Electromagnetic unit fuel injector

Claim 1

An electromagnetic unit fuel injector (1) for injecting fuel into the combustion chamber of an engine, the electromagnetic unit fuel injector comprising an injector body (10) including a bushing (11) with a pump plunger (12) reciprocable therein between a suction stroke and a pump stroke and defining with the bushing a pump chamber (16) open at one end, a supply/drain passage (30,48,50) in the injector body with one end thereof in flow communication with the pump chamber and its opposite end being connectable to a source of fuel at a predetermined supply pressure, flow through the supply/drain passage being controlled by a control valve (32); a solenoid (31) for controlling actuation of the control valve; a fuel injection nozzle assembly attached to the injector body, and including a spray tip (21), a discharge passage (70) effecting flow communication between the pump chamber and the spray tip, and an injection valve (80) which is pressure actuated, operatively positioned in the fuel injection nozzle assembly to control flow discharge from the spray tip; characterised in that the injector body (10) includes a spill port (90) therein having one end thereof in flow communication with the supply/drain passage and having its other end defining an annular groove (88) in the bushing (11) at a predetermined axial location, and in that the pump plunger (12) includes a spill passage (85) in flow communication at one end with the pump chamber and at its other end axially located so as to come into flow communication with the annular groove after a predetermined pump stroke of the pump plunger (12) whereby the spill passage and the spill port will be operative to assist the control valve to effect the rapid spill of injection pressure at a predetermined injector output and/or engine operating speed above which fuel can no longer be effectively added to the combustion process in the combustion chamber.