Servo-controlled fuel injector with leakage limiting device

Abstract

A servo-controlled fuel injector is provided which includes a leakage limiting valve device for limiting the quantity of high pressure fuel available for leakage into the combustion chamber in the event the closed nozzle valve element fails to sealingly engage its seat between injection events. The servo-controlled fuel injector includes a control volume positioned adjacent an outer end of the nozzle valve element, a control volume charge circuit for supplying fuel to the control volume, a drain circuit for draining fuel from the control volume to a low pressure drain and an injection control valve positioned along the drain circuit for controlling the flow through the drain circuit so as to cause reciprocal movement of the nozzle valve element. The leakage limiting valve is integrated into the fuel injector body and positioned along a fuel transfer passage to block the flow of high pressure fuel to a nozzle cavity between injection events. The leakage limiting valve may be a cylindrical valve element positioned between the nozzle valve element and the injection control valve. Alternatively, the leakage limiting valve may be in the form of an annular valve sleeve slidably mounted on one end of the nozzle valve element so as to position the control volume immediately adjacent the injection control valve thereby minimizing the trapped volume and thus the valve response time.