Bosch-Common Rail System – High pressure generation
1 High pressure to fuel rail
2 Outlet valve
4 Fuel feed
5 Drive shaft
6 Eccentric cam
7 High-pressure chamber
8 Pump plunger
9 Inlet valve
The high-pressure pump is driven via the drive shaft. An eccentric element is fixed to the drive shaft and moves the three plungers up and down according to the cam lobes of the eccentric element.
Fuel pressure from the transfer pump is applied to the inlet valve. If the transfer pressure exceeds the internal pressure of the high pressure chamber (pump plunger in TDC position), the inlet valve opens.
Fuel is now forced into the high-pressure chamber, which moves the pump plunger downwards (intake stroke).
If the BDC position of the pump plunger is exceeded, the inlet valve closes due to the increasing pressure in the high-pressure chamber. The fuel in the high-pressure chamber can no longer escape.
As soon as the pressure in the high-pressure chamber exceeds the pressure in the fuel rail, the outlet valve opens and the fuel is forced into the fuel rail via the high-pressure connection (delivery stroke).
The pump plunger delivers fuel until TDC is reached.
The pressure then drops so that the outlet valve closes.
As the pressure on the remaining fuel is reduced, the pump plunger moves downward.
If the pressure in the high-pressure chamber falls below the transfer pressure, the inlet valve reopens and the process starts again.