Electromagnetic unit fuel injector

In an electromagnetic unit fuel injector of the type including a housing means having a pump cylinder means therein;

• an externally actuated plunger reciprocable in said cylinder means to define therewith a pump chamber;
• said housing means including a valve body having a spray outlet at one end thereof for the discharge of fuel;
• an injection valve movable in said valve body to control flow through said spray outlet;
• an inlet passage means in flow communication with said pump chamber and being connectable at its other end to a source of fuel;
• a pressure modulated servo chamber means in said housing means, a spring means and a servo piston means operatively connected to said injection valve with said servo piston means being positioned so as to be acted on by the pressure of fuel in said servo chamber;
• a discharge passage means in said housing means connecting said pump chamber to said spray outlet and to said servo chamber and having a throttle orifice controlling fuel flow to said servo chamber, said housing means further including a drain passage means in flow communication at one end with said servo chamber and at its opposite end with a source of fuel at a predetermined pressure, said drain passage means including drain chamber means and a pressure equalizing chamber means in axially spaced apart relationship to each other with a guide bore extending therebetween and with a conical valve seat encircling said guide bore at the drain chamber end thereof;
• a pressure sensitive control valve operatively positioned in said housing means, said control valve having a stem slidably received in said guide bore and a head loosely received in said drain chamber with a valve seating surface for movement relative to said valve seat and defining therewith when unseated therefrom a drain orifice, said stem including a reduced diameter stem portion next adjacent to said valve seating surface of said head whereby to define with said guide bore an annulus chamber as part of said drain passage means;
• a pull type solenoid means operatively supported in said housing means, said solenoid means including an armature means operatively associated with said control valve;
• a valve return spring operatively associated with said control valve to normally bias said valve seating surface of said head thereof into seating engagement with said valve seat;
• and, a fuel passage means connectable at one end to a source of fuel at a suitable supply pressure and at its other end being in operative flow communication with said pump chamber;
• the improvement wherein said control valve is in the form of a poppet valve and wherein said stepped bore includes an enlarged internal diameter portion next adjacent to said valve seat whereby the pressure of fuel in said annulus cavity can act against said head in a valve opening direction and wherein the force of said valve return spring is preselected so that said control valve is also operative as a pressure relief valve.