Piston and barrel assembly with stepped top and hydraulically-actuated fuel injector utilizing same

The present invention relates generally to hydraulically driven piston and barrel assemblies, and more particularly hydraulically-actuated fuel injectors utilizing stepped piston and barrel assemblies. A hydraulically actuated fuel injector has an injector body including a barrel and defining a nozzle chamber, a needle control chamber, and a nozzle outlet that opens to the nozzle chamber. The injector body further includes an actuation fluid inlet and an actuation fluid drain. A barrel defines an actuation fluid cavity and a piston bore, which includes an upper bore and a lower bore. Fuel is hydraulically pressurized in the nozzle chamber. A piston with a stepped top slides in the piston bore and moves in between a retracted position and an advanced position. A needle valve member in the nozzle chamber moves between an open position and a closed position. The needle valve member includes a closing hydraulic surface exposed to pressure in the needle control chamber. A needle control valve including an actuator is attached to the injector body and moves between an off position in which the needle control chamber is opened to a source of high pressure fluid and an on position in which the needle control chamber is opened to a low pressure passage. An actuation fluid control valve opens and closes the actuation fluid cavity.