While the high-pressure pump used in common rail fuel injection systems seems to be a relatively simple piece of hardware, it can be an extremely challenging component to design. Some challenges faced by pump designers include:
1. Maintaining high reliability with increasing pressure trends and often under poor lubricating conditions while keeping cost increases to a minimum.
2. Achieving high fuel injection system efficiency under a variety of operating conditions. This not only minimizes energy consumption but also controls fuel temperature.
3.Accurate control of rail pressure under all conditions. When coupled to the need to maximize pump efficiency, this can become a very challenging task. The amount of fuel supplied to the pump must be carefully controlled.
Common rail fuel systems use a positive displacement piston pump to pressurize fuel to the common rail pressure.
Radial Pumps. An example of a radial piston design is illustrated in below first figure. In this pump, three plungers are arranged symmetrically around a single cam, resembling three in-line pumps at 120° phasing.
The illustrated design evolved from a pump produced by Rexroth for the passenger car common rail system commercialized by Bosch in 1997.
While three plungers are found to be particularly advantageous as the load on the camshaft is substantially constant throughout the full 360° rotation of the cam, two and one piston versions are also available. A similar design is available from all major fuel injection system manufacturers.
Bosch CP 3.2 radial piston high pressure common rail pump
This design is normally fuel lubricated and relies entirely on the fuel having good lubricity to ensure that the pump’s durability targets are met. However, oil lubricated radial piston pumps, such as the Bosch CP3.4 used in some heavy-duty applications, are also available.
Below figure shows some of the main components located on the pump illustrated in the first figure.
Major components of Bosch CP 3.2 high pressure common rail pump
