Abstract: A servo piston is driven to compress fuel in a pressure chamber which communicates with a needle valve which is spring biased to block communication between the pressure chamber and a fuel injection nozzle. When the fuel pressure exceeds a value equivalent to the preload of the spring, the pressurized fuel moves the needle valve off its seat so that fuel from the pressure chamber is injected into an engine through the injection nozzle. Further movement of the servo piston unblocks a port to allow fuel at supply pressure to act on the needle valve in the same direction as the spring to sharply seat the needle valve and cleanly terminate fuel injection. Further movement of the servo piston uncovers another port so that the pressure chamber is depressurized through connection with the supply and the needle valve is firmly held on its seat.

Abstract: An air vortex chamber is provided downstream of the valve seat portion of a fuel injection valve body such that the fuel injecting from the valve seat portion collides with the inner wall of the vortex chamber in a plane coincident with a plurality of tangential air passages which introduce air into the vortex chamber and create the vortex action.