Mini_DV6 rail pressure control

Rail pressure control, general.

The following components belong to the common rail system and influence the rail pressure control:

• High-pressure pump (CP1H)
  
• Flow regulating valve (integrated in the high-pressure pump)
  
• Rail-pressure sensor / common rail sensor
  
• High-pressure accumulator (common rail)
  
• High-pressure lines
  
• One injector per cylinder
  

The aim of the rail pressure control is to supply each of the cylinders with the optimal volume of fuel required to drive the vehicle in its current state and with its current driving characteristics.

The fuel supply consists of all components that are involved in supplying diesel fuel from the fuel tank into the common rail system with the final aim of combustion, as well as the software-based control of this supply (see functional description of fuel supply.

Component information:

The high pressure pump constantly generates the system pressure held in the fuel rail. The right pressure in the rail on the present engine - in contrast to the BMW diesel engines - can only be created via the flow regulating valve at the end of the high-pressure pump. No additional rail-pressure regulating valve exists (”pressure regulation according to the single-controller concept”).

Rail-pressure monitoring and fuel limitation

The rail pressure is monitored during engine start and engine operation by way of setpoint/actual value comparison. The rail-pressure sensor / common rail sensor delivers the actual value to the DDE. The set point is calculated by the DDE depending on the operating status. If the DDE detects a diskrepancy between the specified and actual level that is outside the permissible limits, a fault is stored in the fault memory. The flow regulating valve is integrated in the high-pressure pump. It limits the volume of fuel the pump delivers depending on the requirement. The flow regulating valve is activated via a PWM signal. Power is supplied via terminal 87.

An impermissible deviation of the rail pressure from the setpoint can be caused by the following:

• External leaks at components in the common rail system
  
• The flow regulating valve is faulty
  
• Leaks elsewhere in common rail system, e.g.
  
  • ... in the high pressure pump (e.g. worn piston)
    
  • ... on flow regulating valve (diverting too little or too much fuel into the return line)
    
  • ... at the four solenoid-valve fuel injectors (too much volume in the return flow)
    
• External influences such as defective fuel supply, clogged fuel return system, air in fuel system