Lubrication oil controlled unit injector

Abstract

A unit fuel injector adapted for periodic injection of fuel into a combustion chamber of an engine at variable times from cycle to cycle under the control of the engine lubrication fluid is provided, comprising an injector body containing an injector cavity and a discharge orifice communicating with one end of the injector cavity to discharge fuel into the combustion chamber, a lubrication fluid timing circuit and a fuel metering circuit separate from the lubrication fluid timing circuit. A lubrication fluid link positioned in the lubrication fluid timing circuit within the injector cavity has a variable effective length which is varied by the operation of a control valve positioned within the lubrication timing circuit to vary the timing of injection. The control valve is operated to control the flow of lubrication fluid in the lubrication fluid timing circuit to control both the timing of injection and the metering of fuel on a cycle by cycle basis. The control valve is operable to be placed in a first position in which lubrication fluid may flow through the lubrication fluid timing circuit into the timing chamber and fuel flow from the fuel metering circuit into the metering chamber is shut off and a second position in which lubrication fluid flow into the timing chamber is shut off. Lubrication fluid is maintained at a higher pressure than the fuel pressure when the control valve is in the first position to stop the movement of a metering plunger to define the metered quantity of fuel thereby avoiding the need for a bias spring. By using lubrication fluid as timing fluid in a timing circuit separate from the fuel metering circuit, the amount of fuel required by the injector and the amount of heated fuel returned to the fuel supply tank is minimized.