Denso-Common Rail System – Principle of high pressure generation
A Pump plunger 1
B Pump plunger 2
C To fuel rail
1 Inlet valve
2 Outlet valve
3 Eccentric cam
4 Eccentric cam ring
5 Fuel metering valve
6 Drive shaft
The rotary movement of the drive shaft is converted to a reciprocating movement by the eccentric cam. The eccentric cam ring transfers the reciprocating movement to the pump plungers.
The pump plungers are offset by 180 degrees. This means, that during a reciprocating movement, pump plunger 1 performs exactly the opposite movement to pump plunger 2.
The eccentric cam produces an “upward” stroke:
• Pump plunger 1 moves in the direction of TDC, thus compressing the fuel and delivering it to the fuel rail via the outlet valve. The inlet valve is pressed into its seat by the delivery pressure.
• Pump plunger 2 is moved by the tension spring force in the direction of BDC. Due to the high pressure in the fuel rail, the outlet valve is pressed into its seat. The pump internal pressure opens the inlet valve and fuel flows into the high pressure chamber.
The eccentric cam produces a “downward” stroke:
• The process is the reverse to that previously described.
Calibrating the high-pressure pump (fuel metering valve)
After replacing the high pressure pump and/or the PCM the fuel metering valve of the high pressure pump must be calibrated with the aid of WDS.