Patent ID: 6928986

Claim:
A fuel injector, comprising: an injector body defining a nozzle outlet and a high-pressure fuel chamber; a needle valve member mounted in the injector body and having an opening hydraulic surface substantially surrounded by a high pressure fuel line which is in fluid communication with the high-pressure fuel chamber, the needle valve member being movable between an open position and a closed position with respect to the nozzle outlet; a piezoelectric actuator being activated between an off position and an on position for positioning a control valve into one of an open position and a closed position; a control piston having a closing hydraulic surface, the control piston being positioned in mechanical communication with the needle valve member; a piston control chamber positioned between the control valve and the closing hydraulic surface of the control piston, the piston control chamber being in fluid communication with the control valve and the high-pressure fuel chamber via throttles; wherein a high-pressure fuel condition is maintained in the piston control chamber by fuel supplied directly from the high-pressure fuel chamber and independent of any actuation of the control valve, the high-pressure fuel condition results in a downward force acting on the closing hydraulic surface of the control piston, a pressure loss fuel condition is generated within the piston control chamber by activation of the piezoelectric actuator which moves the control valve to the open position for releasing fuel, and a force on the opening hydraulic surface of the needle valve member is greater than the downward force on the closing hydraulic surface of the control piston, in the pressure loss fuel condition, thereby opening the needle valve member for producing an injection event.