Patent ID: 7290530

Claim:
In a fuel injection system having an injection valve, a line supplying fuel at high pressure to the injection valve in operation, a control valve which controls the pressure in a control chamber of the injection valve that communicates with the aforementioned line, the control valve including movable valve part actuatable by an actuator via a hydraulic coupler that has two pistons, cooperating with a booster chamber of the coupler, the seat of the movable valve part has an inside cross-sectional area f 3 , and the pistons having guidance gaps through which the booster chamber is filled with fuel that is under pressure, the improvement wherein the pistons are located parallel to one another with one inside the other; the booster chamber being located on the ends of the pistons toward the actuator, a filling chamber provided in the interior of the outer piston, the filling chamber communicating with the aforementioned line; and rod means mechanically coupling a cross-sectional area f 4 of the one piston to the actuator, the rod means having a cross-sectional area f 5 ; the other piston, having a piston area f 2 and actuating the control valve via a rod having a cross-sectional area that is smaller than f 2 ; the direction of the closing motion of the movable valve part matching the direction of fuel flowing out of the control chamber, so that the control valve is at least partially force-balanced because of the pressure acting on the further piston in the booster chamber.