P07.02-A013-79
Example illustration of engine 256 |
1 | Fuel high-pressure pump | 2 | Quantity control valve |
Overview
This document contains information on:
General
Location
Function
General
The high-pressure fuel pump delivers the fuel for high-pressure fuel injection.
The high-pressure fuel pump is driven mechanically in the case of gasoline and diesel engines. As a result, the delivery rate of the high-pressure fuel pump is rpm-dependent.
The high-pressure fuel pump is mechanically driven by the following devices:
Roller tappet via intake or exhaust camshaft
Toothed belt
Timing chain
High-pressure fuel pump (general and sectional views) |
1 | Fuel high-pressure pump |
2 | Quantity control valve |
3 | Low pressure connection fitting |
4 | High pressure connection fitting |
5 | Pressure limiting valve |
6 | Low pressure pulsation damper |
7 | Float needle |
8 | Pump element |
9 | Cup tappet |
10 | O-ring |
11 | High pressure outlet valve |
A | Area with high pressure |
B | Area with low pressure |
P07.02-A025-75
Function
Spark-ignition engine function
During the upward motion of the pump element, the fuel volume in the pump cylinder is pressurized. When system pressure is achieved, the high-pressure exhaust valve opens and fuel is delivered via the high pressure lines to the rails. A pressure limiting valve protects the high pressure fuel pump from any excess pressure buildup.
The fuel quantity which reaches the pump element is regulated such that the high pressure fuel pump only delivers the fuel that is required by the engine. In this way, the high fuel pressure is regulated up to approx. 200 bar depending on the operating status of the engine.
The fuel system high pressure pump is cooled and lubricated by the fuel. Consequently, the fuel delivered is not able to mix with lubricant.
Diesel engine high-pressure fuel pump |
1 | Fuel high-pressure pump |
2 | Quantity control valve |
P07.02-A010-76
View of diesel engine high-pressure fuel circuit |
1 | Fuel high-pressure pump |
2 | Quantity control valve |
12 | Fuel temperature sensor |
P07.16-A050-76
Diesel engine function
The function comprises the following partial functions:
Low-pressure side function
Function: high-pressure side
Low-pressure side function
The fuel delivered by the electric fuel pump arrives at the high-pressure fuel pump flange, on which the fuel temperature sensor is located, and is routed there to the quantity control valve and to the fuel overpressure valve.
The quantity control valve controls the volume of fuel fed through the annular passage to the two pump elements of the high-pressure fuel pump (fuel feed to the high-pressure elements).
Fuel is led from the fuel feed directly into the pump drive over a cooling and lubricating throttle for cooling and lubrication of the pump drive.
The mechanical fuel overpressure valve integrated in the high-pressure fuel pump regulates the fuel pressure applied to the quantity control valve to approx. 5 bar.
The excess fuel is led back over the pump drive into the fuel tank.
Any air carried along by the fuel is fed via the fuel overpressure valve and the cooling and lubricating throttle to the return flow of the high-pressure fuel pump.
Function: high-pressure side
With its cam plate, the eccentric shaft moves the piston back and forth against the piston spring.
The high-pressure side function consists of the following subfunctions:
Filling the piston
Generation of high pressure
Filling the piston
The piston is moved down as a result of the piston spring. The fuel supplied by the fuel pump flows through the annular passage and fuel feed, and pushes against the valve spring to pass through the valve into the cylinder.
A ball valve prevents the fuel from flowing back into the fuel tank from the high-pressure channel.
Generation of high pressure
The piston is moved upward by the upward movement of the eccentric shaft. This compresses the fuel. The valve closes the delivery volume against the fuel feed. If the fuel pressure in the cylinder exceeds the pressure in the high-pressure fuel circuit, the ball valve opens and the fuel is delivered into the high-pressure fuel circuit.