Hydraulically-actuated fuel injector with direct control needle valve

A fuel injection system comprising:

• a plurality of hydraulically actuated fuel injectors with direct control needle valves, each injector having a needle valve with a closing hydraulic surface exposed to pressure in a needle control chamber and at least one control valve that alternately opens said needle control chamber to a source of high pressure fluid or a low pressure passage, and each injector also having an actuation fluid cavity, an actuation fluid inlet, an actuation fluid drain and a fuel supply passage and said at least one control valve including an actuation fluid control valve mounted in said injector body and moveable between a first position in which said actuation fluid cavity is open to said actuation fluid inlet and a second position in which said actuation fluid cavity is open to said actuation fluid drain;
• a source of fuel connected to said fuel supply passage of each said injector;
• a source of high pressure actuation fluid connected to said actuation fluid inlet;
• a low pressure reservoir connected to said actuation fluid drain;
• and
• a computer in communication with and capable of controlling each of said at least one control valve.

A method of fuel injection comprising the steps of:

• providing a hydraulically actuated fuel injector having a nozzle outlet that pens to a nozzle chamber in which a needle valve reciprocates, and said needle valve having a closing hydraulic surface exposed to pressure in a needle control chamber, and said injector also having at least one control valve that alternately opens said needle control chamber to a source of high pressure fluid or a low pressure passage, and said at least one control valve including an actuation fluid control valve that alternately opens an actuation fluid cavity to an actuation fluid inlet or an actuation fluid drain;
• hydraulically pressurizing fuel in said nozzle chamber to an injection pressure at least in part by moving said actuation fluid control valve to open said actuation fluid cavity to said actuation fluid inlet;
• moving said needle valve to an opened position to open said nozzle outlet to said nozzle chamber at least in part by opening said needle control chamber to said low pressure passage with said at least one control valve;
• and
• moving said needle valve to a closed position to close said nozzle outlet to said nozzle chamber at least in part by opening said needle control chamber to said source of high pressure fluid with said at least one control valve.