GF07.16-P-3012P CDI High Pressure Circuit, Function
GF07.16-P-3012P CDI High Pressure Circuit, Function
The high pressure pump delivers fuel depending on the coolant temperature, position of the accelerator pedal, the engine speed and the fuel temperature into the left rail and from there simultaneously into the right rail. The fuel passes from the respective rail over the high pressure lines to the fuel injectors. The fuel injectors spray fuel selectively for each cylinder in a fine atomized form.
The CDI control unit (N3/9) calculates the injection quantity selectively for each cylinder according a performance map for the respective operating condition. The injection quantity is dependent upon the fuel pressure in the rail and the actuation time of fuel injectors.
The fuel pressure in the rail is controlled via the pressure regulator valve and quantity control valve. The effectively applied fuel pressure in the rail is detected by the rail pressure sensor, passed on permanently to the CDI control unit and limited to a maximum of 1600 bar by the pressure regulator valve.
The fuel temperature is detected by the fuel temperature sensor and permanently passed on to the CDI control unit.
Regulation except OM 642.920, OM 642.940 and OM 642.950 with code (494) USA version, except OM 642.920 with code (498) Japan version, except OM 642.920 in model 211.024
At a fuel temperature < 20 °C and up to 30 seconds after engine start, the feed to the high-pressure pump is not controlled by the quantity control valve. The heated fuel returns to the tank via the quantity control valve and the return line. For a fuel temperature > 90 °C the CDI control unit activates the tank protection function to protect the fuel tank and the high-pressure pump. This function reduces the injection quantity and rail pressure. The rail pressure is controlled in this time by the quantity control valve.
Regulation with OM 642.920, OM 642.940 and OM 642.950 with code (494) USA version, in OM 642.920 with code (498) Japan version, in OM 642.920 in model 211.024
Regulation of the rail pressure takes place according to the 2-regulator concept.
2-regulator concept
- The 2-regulator concept combines the known standard regulating circuits, that is rail pressure regulation by the pressure regulator valve and rail pressure regulation by the quantity control valve
- The 2-regulator concept controls and checks regulation on the basis of specified values for the system
Aims:
- 1-regulator pressure regulation via the quantity control valve or the pressure regulator valve is possible
- 2-regulator operation with pressure regulation is possible over the pressure regulator valve and throttling of the high-pressure pump over the quantity control valve
- Changing of regulating mode in running mode is supported
- The change between rail pressure regulation via the quantity control valve, via the pressure regulator valve and via 2- regulator operation takes place with the smallest possible disturbances to the rail pressure
Rail pressure regulation is subdivided into 3 regulator modes:
Pressure regulator valve regulation
The rail pressure is regulated via the pressure regulator valve for a starting procedure and regulated for heating the fuel. The quantity control valve is controlled opened. Pressure regulator valve regulation takes place under the following conditions:
- Up to 30 s after the engine start in idle
- Up to a fuel temperature of 20 °C
- For OM 942.940 and OM 642.950 up to a 500 rpm higher idle speed or for an injection quantity < 16 mm3
- For OM 642.920 up to a 300 rpm higher idle speed or for an injection quantity < 30 mm3
2-regulator concept regulation
The rail pressure is jointly regulated in idle and in overrun mode by the pressure regulator valve and quantity control valve.
Quantity control valve regulation
The rail pressure is regulated by the quantity control valve under the following conditions:
- From 30 s after engine start
- For OM 942.940 and OM 642.950 from a 500 rpm higher idle speed or for an injection quantity > 16 mm3
- For OM 642.920 from a 300 rpm higher idle speed or for an injection quantity > 30 mm3
The pressure regulator valve is controlled closed.
- For 2-regulator concept regulation and for quantity control valve regulation the fuel is heated less strongly than for pressure regulator valve regulation.
- After switching off the engine there is a residual pressure of about 50 to 80 bar in the high-pressure control circuit. The high-pressure system may only be opened after completely relieving the pressure on safety grounds.