1. Field of the Invention
The invention relates to an injector for injecting fuel into combustion chambers.
2. Description of the Prior Art
German Patent Disclosure DE 103 53 169 A1 describes a common-rail injector having a control valve for blocking and opening a fuel outflow course from a control chamber. For actuating the control valve, a piezoelectric actuator is provided, which acts in an adjusting fashion in the axial direction on a valve piston via a boosting piston. By means of the control valve, embodied as a 3/2-way valve, the fuel pressure inside a control chamber can be varied, and the control chamber is supplied with fuel from a high-pressure fuel reservoir via a pressure conduit having both an inlet throttle restriction and an additional conduit. By varying the fuel pressure inside the control chamber, a nozzle needle is adjusted between an open position and a closed position, and in its open position, the nozzle needle opens up the fuel flow into the combustion chamber of an internal combustion engine. Since the known control valve is not pressure-compensated in the axial direction, high adjusting forces are needed for opening the control valve.
From European Patent Disclosure EP 1 612 403 A1, a common-rail injector with a control valve that is pressure-compensated in the axial direction is known. The known control valve has, as its adjustable valve element, an axially displaceable sleeve that is subjected solely in the radial direction to fuel pressure from a high-pressure region. Because of the use of a pressure-compensated control valve, only slight adjusting forces are needed for opening the control valve, so that the adjusting task in the known injector is performed by an electromagnetic drive mechanism. If the control valve known from EP 1 612 403 A1 were adopted for the injector known from DE 103 53 169 A1, then the entire configuration of the injector would have to be changed. In particular, in the piezoelectric-actuator-driven injector, the low-pressure chamber would have to be shifted substantially farther in the direction toward the control chamber.