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 hydraulic means for pressurizing fuel that includes a an actuation fluid control valve with a solenoid, a needle valve member with a closing hydraulic surface exposed to pressure in a needle control chamber and a needle control valve with said solenoid 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 inlet, an actuation fluid drain and a fuel supply passage;
• 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 said needle control valve and said actuation fluid control valve.

A method of fuel injection comprising the steps of:

• providing a hydraulically actuated fuel injector having a nozzle chamber open to a nozzle outlet, a needle valve member and a single two-way solenoid that is part of a needle control valve and an actuation fluid control valve, and said needle control valve having an off position and an on position, and said actuation fluid control valve having an open position and a closed position;
• energizing said solenoid for an amount of time sufficient to move said actuation fluid control valve from said closed position to said open position and move said needle control valve from said off position to said on position;
• hydraulically pressurizing fuel in said nozzle chamber to an injection pressure;
• moving said needle valve member to open said nozzle outlet;
• and
• de-energizing said solenoid to move said needle control valve from said on position to said off position.