The unit pump system is a modular, time-controlled single-pump injection system. Each engine cylinder is supplied by a separate module consisting of a high-pressure plug-in pump with integrated, fast-switching solenoid valve and nozzle holder assembly. The unit pump is integrated in the diesel engine block and powered directly by an injection cam on the engine camshaft via a roller plunger.
If the solenoid valve is open, the pump cylinder can be filled during the suction stroke of the pump piston and return flow is possible during the delivery stroke. If the solenoid valve is energized and therefore closed, a pressure in the high-pressure range builds up between the pump piston and injection nozzle during the delivery stroke of the pump piston. If the nozzle opening pressure is exceeded, fuel is injected into the engine's combustion chamber. Closure of the solenoid valve determines the start of the injection process, while opening of the valve determines the injection quantity.