An injection system of an internal combustion engine usually supplies a plurality of injectors of an internal combustion engine with fuel from a fuel tank. By way of example, the construction of the injection system is explained using a common rail injection system of a diesel engine. However, other injection systems and other fuels can also be used.
In a common rail injection system, fuel is sucked out of the fuel tank with the aid of a fuel delivery pump. The fuel delivery pump increases the fuel pressure to approximately from 2 to 5 bar and is connected to a high pressure pump. The fuel is guided from the high pressure pump via a fuel distributor rail (common rail) to the plurality of injectors. The fuel pressure between the high pressure pump and the plurality of injectors is over 1500 bar and is generally called the high pressure region of the injection system. Excess fuel is fed from the plurality of injectors via a return line to the fuel tank again.
The components which are present in the high pressure region, such as the fuel lines and the fuel distributor rail, are designed for operation at a defined fuel pressure. If this defined fuel pressure is exceeded, partial or complete destruction or damage of the components in the high pressure region can occur. In order to prevent the partial or complete destruction or damage, the high pressure region is equipped with a pressure relief device. The pressure relief device in the high pressure region allows the defined fuel pressure in the injection system to be lowered to the defined fuel pressure if a pressure limiting value is exceeded.
EP 0 678 668 B1 has disclosed a fuel injection device for internal combustion engines having a pressure relief device. The pressure relief device comprises a pressure limiting valve which additionally has a return line with a rupture disk inserted in the latter. If a maximum pressure is exceeded, the rupture disk releases an enlarged outflow cross section in the return line. As a result, the pressure limiting valve is protected from excessively high pressure loading.
During operation, the pressure limiting valve is actuated if a pressure drop cannot be achieved via regulation of the high pressure pump. As a result of the actuation, fuel flows out of the injection system through the pressure limiting valve into the return line. When the pressure has dropped again, the pressure limiting valve is closed. If the pressure exceeds a pressure limiting value during opening of the pressure relief valve, the rupture disk is destroyed and an enlarged outflow cross section is released in the return line. In this way, the pressure is lowered again to the defined fuel pressure. As soon as the rupture disk has been destroyed, the enlarged outflow cross section of the return line is used during every actuation of the pressure relief valve, however.
One disadvantage of this system is that the defined pressure can continue to be exceeded after the destruction of the rupture disk. As a result, this can lead to the damage of the components and to the impairment of the injection system.
Furthermore, it is disadvantageous that more rapid pressure changes occur in the fuel injection system on account of the enlarged outflow cross section, which requires precise control of the pressure limiting valve.