Patent ID: 7644878

Claim:
An injector for injecting high-pressure fuel supplied by a fuel supply source, the injector comprising: a nozzle hole through which high-pressure fuel is injected; a needle that opens or closes the nozzle hole; an actuator that extends or contracts in an axial direction of the needle; a piston that is displaced in the axial direction according to the extension or contraction of the actuator; an outer sleeve holding the piston slidably on an outer circumferential side of the piston and defining a pressure chamber of high-pressure fuel, wherein: the pressure chamber is expanded or shrunk according to the displacement of the piston; fuel pressure in the pressure chamber is applied to the needle in a valve opening direction in which the needle opens the nozzle hole; and the fuel pressure in the pressure chamber is increased upon the extension of the actuator, so that the needle opens the nozzle hole and thereby high-pressure fuel is injected through the nozzle hole; an inner sleeve slidably fitted around an outer circumferential side of the needle and received in the pressure chamber; an urging means for urging the inner sleeve in the axial direction, and for increasing or decreasing urging force of the urging means applied to the inner sleeve according to the displacement of the piston; an engagement surface, which the inner sleeve urged by the urging means annularly engages or disengages from; and a fuel chamber into which high-pressure fuel is supplied by the fuel supply source, wherein a gap between the fuel chamber and the pressure chamber is closed or opened when the inner sleeve engages or disengages from the engagement surface, respectively.