Patent ID: 7644875

Claim:
An injector comprising: a piezoelectric actuator that causes displacement when voltage is applied thereto; a pressurizing piston that is driven by the piezoelectric actuator to move in an axial direction; a pressure chamber that stores a pressurization fluid inside such that pressure of the pressurization fluid changes according to the movement of the pressurizing piston; a valve body that is formed with a guide hole in the axial direction and with an injection hole at a tip end portion of the guide hole, the valve body being structured such that an axial rear end face thereof on a side opposite from the injection hole side defines a wall face defining the pressure chamber; a needle that is slidably held in the guide hole and that opens and closes the injection hole, the needle having a middle shaft section protruding from the rear end face in a direction opposite from the injection hole side and a needle pressure receiving face, which has an external diameter larger than that of the middle shaft section and receives internal pressure of the pressure chamber in the axial direction such that the internal pressure of the pressure chamber acting on the needle pressure receiving face functions as a valve opening force for biasing the needle in a valve opening direction; an inner sleeve that is located inside the pressure chamber and that is formed in the shape of a cylindrical body slidably fitted with an outer periphery of the middle shaft section; and a spring that biases the inner sleeve toward the rear end face, wherein the inner sleeve has an inner periphery sliding face of the cylindrical body for inhibiting the pressurization fluid in the pressure chamber from flowing out toward the injection hole side through a sliding gap between an outer peripheral face of the middle shaft section and the inner sleeve and an axial end portion for inhibiting the pressurization fluid in the pressure chamber from flowing out toward the injection hole side through a portion of the inner sleeve closely pressed against the rear end face by the spring.