1.  Field of the Invention
The invention is based on a high-pressure fuel pump for a fuel injection system of an internal combustion engine, and more particularly to such a pump having a pump housing in which a drive shaft is supported by a first bearing and a second bearing; having at least one pump element disposed radially relative to the drive shaft; having a fuel feed line, with a prefeed pump that pumps fuel into the fuel feed line; having a fuel return line; having a metering unit for regulating the pump capacity of the pump element or elements; and having a pressure regulating valve. 
2.  Description of the Prior Art
In these high-pressure fuel pumps known from the prior art, the pressure regulating valve serves to regulate the pressure in the low-pressure circuit of the high-pressure fuel pump.  The pump capacity of the prefeed pump is typically split into three partial flows.  A first partial flow flows through the metering unit to the intake side of the pump element or elements.  The second partial flow as a rule flows through the pump housing via a lubricating throttle restriction and serves there to cool and lubricate the pump.  From the pump housing, the second partial flow reaches the fuel return line of the fuel injection system.  A third partial flow flows through the pressure regulating valve, which may also be embodied as an overflow valve, and likewise reaches the fuel return line. 
With increasing injection pressures, the mechanical and thermal loads on both the drive shaft and the bearing of the drive shaft in the pump housing also increase.  Conventional high-pressure fuel pumps are not capable of withstanding these increasing loads. 
The object of the invention is to furnish a high-pressure fuel pump for a fuel injection system that makes do with the same installation space as conventional high-pressure fuel pumps and nevertheless is superior with regard to thermal and mechanical bearing capacity, to the high-pressure fuel pumps known from the prior art.  Moreover, the high-pressure fuel pump of the invention should be simple in construction and capable of being produced economically. 
In a high-pressure fuel pump for a fuel injection system of an internal combustion engine, having a pump housing, having a drive shaft with the drive shaft supported in the pump housing by a first bearing and a second bearing, having at least one pump element disposed radially relative to the drive shaft, having a fuel feed line, where a prefeed pump pumps fuel into the fuel feed line, having a fuel return line, having a metering unit for regulating the pump capacity of the pump element or elements, and having a pressure regulating valve, this object is attained in that the pressure regulating valve is disposed in the fuel return line.