1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
One fuel injection system of the type with which this invention is concerned is known from European Patent Disclosure EP 0 987 431 A2. For each cylinder of the engine, this fuel injection system has one high-pressure fuel pump and one fuel injection valve communicating with it. The high-pressure fuel pump has a pump piston, which defines a pump work chamber and is driven in a reciprocating motion by the engine. The fuel injection valve has a pressure chamber communicating with the pump work chamber and also has an injection valve member, by which at least one injection opening is controlled and which is movable by the pressure prevailing in the pressure chamber in the opening direction, counter to a closing force, to uncover the at least one injection opening. A first electrically actuated control valve is provided, by which a connection of the pump work chamber to a relief chamber is controlled. A second electrically actuated control valve is also provided, by which a connection of a control pressure chamber to a relief chamber is controlled. The control pressure chamber communicates with the pump work chamber via a throttle restriction. The control pressure chamber is defined by a control piston, which is braced on the injection valve member and is urged in the closing direction of the injection valve member by the pressure prevailing in the control pressure chamber. For a fuel injection, the first control valve is closed and the second control valve is opened, so that high pressure cannot build up in the control pressure chamber, and the fuel injection valve can open. With the second control valve open, however, fuel flows out of the pump work chamber via the control pressure chamber, so that of the fuel quantity pumped by the pump piston, the fuel quantity that is available for injection is reduced, and the pressure available for the injection is also reduced. As a consequence, the efficiency of the fuel injection system is not optimal.