Abstract:
The present invention provides a wide range injection timing, small dispersion, good response and simple structure. In order to obtain this, in a fuel injection device for a diesel engine comprising a cylindrical body ( ), an upper plunger ( ) inserted thereto and capable of sliding in a vertical direction in response to a cam, an intermediate plunger forming a pressure chamber ( ) with respect to the upper plunger, a lower plunger ( ) brought into contact with the intermediate plunger, and an injection chamber ( ) provided in a lower end portion of the body plunger, in which a fuel in the injection chamber is injected by the lower plunger being subject to a force from the upper plunger, the improvement comprises a passage, having a large cross-sectional area, formed in the body for supplying a pressurized oil to the pressure chamber, the intermediate plunger ( ) being vertically movable in response to an oil pressure so as to make it possible to change a volume of the pressure chamber, and a timing spring ( ) having an end being brought into via contact with the intermediate plunger and the other end being brought into contact with the lower plunger and vertically moving the intermediate plunger in response to the pressure.