Patent ID: 7644874

Claim:
An injector comprising: a needle that is slidable in a valve opening direction and a valve closing direction to respectively open and close an injection hole, which is located at a distal end side of the injector, wherein the needle includes a first shaft portion and a second shaft portion, which are separately supported in an axially slidably manner, and the second shaft portion is located on a distal end side of the first shaft portion and has an outer diameter smaller than that of the first shaft portion; a sleeve that slidably supports the first shaft portion; a body that loosely receives the sleeve therein; an actuator that axially expands and contracts to drive the needle; a piston that is axially moved forward and backward in response to expansion and contraction, respectively, of the actuator; and a control chamber, in which a fuel pressure is increased and decreased in response to forward movement and backward movement, respectively, of the piston, wherein: the control chamber applies the fuel pressure to the first shaft portion in the valve opening direction of the needle; when the actuator is expanded, the piston is moved forward to increase the fuel pressure in the control chamber, so that the needle is lifted away from the injection hole to open the injection hole; and when the sleeve is urged toward the distal end side and is thereby seated against an internal surface of the body, the control chamber is defined by an inner peripheral surface of the sleeve, the internal surface of the body, an outer peripheral surface of the second shaft portion of the needle and a distal end surface of the first shaft portion, wherein: the sleeve is a first sleeve; and the injector further comprises a second sleeve, which slidably receives the piston, and a flange, which is located on a distal end side of the piston and defines a pressure chamber in cooperation with the piston and the second sleeve; a fuel pressure of the pressure chamber is increased and decreased in response to the forward movement and the backward movement, respectively, of the piston; the second sleeve and the flange are located on a rear end side of the first sleeve and are loosely received in the body; the control chamber is communicated with the pressure chamber through a communication passage, so that the fuel pressure of the control chamber is increased and decreased in response to the forward movement and the backward movement, respectively, of the piston; and the communication passage between the control chamber and the pressure chamber penetrates through the flange and the first sleeve and is separated from an outer peripheral chamber that is defined between an inner peripheral surface of the body and outer peripheral surfaces of the flange and of the first sleeve.