The high-pressure pump is the interface between the high-pressure component and the low-pressure component of the fuel system.
Its task is always to provide sufficiently compressed fuel in all operating ranges.
This also includes making available a fuel reserve which is necessary for a rapid pressure increase in the high-pressure rail.
Illustration L0008378 shows the high-pressure pump and its installation position on the removed Y 25 DT engine.
| 1 | Pressure regulating valve | 4 | Fuel return line |
|---|---|---|---|
| 2 | High pressure pump | 5 | High-pressure line from high-pressure pump to the high-pressure rail |
| 3 | Fuel feed line |
The high-pressure pump continuously creates the system pressure of 1350 bar for the high-pressure rail.
- The high-pressure pump is driven by the engine directly by the crankshaft via a chain.
- It is lubricated using the fuel.
- The pressure regulating valve is located directly on the high-pressure pump.
| 1 | Pump drive shaft with tapered mount for drive gear | 5 | Fuel return connection |
|---|---|---|---|
| 2 | Pump piston cover | 6 | Fuel feed connection |
| 3 | Connection for high-pressure line to high-pressure rail | 7 | Attachment flange on engine block |
| 4 | Pressure regulating valve |
The fuel is compressed using three pump pistons arranged radially within the high-pressure pump.
These pistons are arranged 120° offset with respect to one another.
| 1 | Feed | 4 | Pump piston |
|---|---|---|---|
| 2 | Outlet valve | 5 | Eccentric cams |
| 3 | Intake valve | 6 | Drive shaft |
The auxiliary fuel pump delivers fuel to the safety valve via the fuel filter with water separator.
The fuel is conducted through the throttle orifice of the safety valve and into the high-pressure pump.
The drive shaft with its eccentric cams controls the three pump pistons according to the cam shape.
If the delivery pressure (8 bar) exceeds the opening pressure of the safety valve (0.5 – 1.5 bar), the auxiliary fuel pump can force fuel through the inlet valve of the high-pressure pump and into the respective pump element chamber in which the pump piston is moving downwards (intake stroke).
If the BDC of the pump piston is exceeded, then the inlet valve closes and the fuel in the pump element chamber can no longer escape.
It can then be compressed to above than the delivery pressure of the auxiliary fuel pump.
The pressure that builds up opens the outlet valve as soon as the pressure in the high-pressure rail (1350 bar) has been reached; the compressed fuel enters the high-pressure circuit.
The pump piston delivers fuel until the TDC is reached (delivery stroke).
Then the pressure drops, closing the outlet valve. The remaining fuel decompresses, the pump piston moves downwards.