In internal combustion engines, fuel is transported by means of a fuel pump from a tank in preparation for a subsequent high-pressure pump. The high-pressure pump is normally driven by the internal combustion engine and transports the fuel into a fuel pressure accumulator (fuel rail). The high-pressure pump itself is not regulated and conveys the fuel which is made available at its inlet connection into the fuel pressure accumulator.
In order to provide a defined fuel quantity to the high-pressure pump, provision is made for a volume flow control valve between the fuel pump and the high-pressure pump, said volume flow control valve being controlled by a control unit. The fuel through-flow through the volume flow control valve is adjusted depending on a current which flows in a valve coil of the volume flow control valve. The pressure in the fuel pressure accumulator can be adjusted via the fuel volume which is provided to the high-pressure pump.
The volume flow control valve normally has a leakage flow in the zero-flow state. This can result in an unwanted fuel pressure increase in the fuel pressure accumulator when the injection volumes are very small or, for example, no fuel is injected in the case of an overrun cut-off.
As a result of the construction, preventing the leakage flow in the zero-flow state of the volume flow control valve can only be achieved at considerable cost and is moreover undesirable in specific cases, if emergency operation of the internal combustion engine occurs in the event of a failure of the volume flow control valve or the control unit.
A regulator valve is normally provided at the fuel pressure accumulator, by means of which regulator valve the pressure in the fuel pressure accumulator can be adjusted depending on a control current. The regulator valve is actively controlled by the control current, such that the pressure in the fuel pressure accumulator is adjusted depending on the control current and depending on a fuel flow through the regulator valve. The fuel flow must exceed a threshold value so that the regulator valve can be operated in a linear range. This additional fuel flow through the regulator valve must be conveyed by the high-pressure pump, in order that the regulator valve can be operated in the linear range. When the high-pressure pump is dimensioned, it is therefore necessary to ensure that the high-pressure pump supplies the regulator valve with a minimum through-flow and moreover provides the volume that is required to build up the pressure or to maintain the fuel pressure in the fuel pressure accumulator.