P47.00-2270-79
Example illustration of low-pressure and high-pressure fuel circuit |
1 | Fuel distributor | 6 | Fuel system high pressure pump | |
2 | Fuel pressure sensor | 7 | Quantity control valve | |
3 | Fuel injectors | A | Low-pressure line | |
4 | Fuel tank | B | High-pressure fuel line | |
5 | Fuel feed module |
Overview
This document contains information on:
General
Function requirements
Function
General
The fuel supply system (low-pressure fuel circuit) provides fuel from the fuel tank for mixture formation under all operating conditions.
Function requirements
Engine management ON (circuit 87M)
Ignition ON (circuit 15)
Function
Low-pressure fuel circuit, function
The fuel supply for mixture formation is provided via the low-pressure fuel circuit.
The low-pressure fuel circuit essentially consists of the following components:
Fuel tank
Fuel feed module
Fuel temperature sensor
Fuel pressure and temperature sensor
Fuel pump control unit
Fuel filter module (for diesel engines)
Fuel preheating control unit (for diesel engines)
The fuel is delivered from the fuel tank to the high-pressure fuel pump by the fuel delivery module with integrated fuel pump.
In spark-ignition engines, a fuel filter is integrated in the fuel delivery module to hold back impurities. There is a check valve at the feed point of the fuel filter which prevents reduction of the fuel pressure when the fuel pump is switched off.
In diesel engines, the fuel filter is in the fuel filter module between the fuel delivery module and the high-pressure fuel pump. In diesel engines, the fuel filter module has the following tasks:
Holding back impurities in the fuel
Separating condensation
Fuel preheating system
Depending on the fuel requirements, the fuel pressure is variably regulated to approx. 4.0 to 6.7 bar by the pressure limiting valve. The quantity control valve regulates the feed quantity in line with demand. This avoids excessive heating of the fuel. The fuel temperature can be kept low as a result.
Function sequence for fuel low-pressure circuit
The fuel pump is switched on as soon as the signal "fuel pump ON" is received by the fuel system control unit.
The fuel system control unit ascertains the fuel pressure through a voltage signal from the fuel pressure sensor and compares the actual pressure with the specified pressure. The fuel pump is actuated by the fuel system control unit via a pulse width modulated signal. In this way, the fuel specified pressure and the delivery rate are adapted to the current fuel requirements.
In order to determine the fuel specified pressure, the combustion engine control unit evaluates the actual fuel pressure and the load requirements. The evaluated information is passed on to the fuel system control unit.
The fuel temperature is constantly recorded and transmitted to the combustion engine control unit.
Function schematics | |||
Function schematic for fuel supply system | Engine 608 in model 118, 177, 247 | ||
Engine 654 in model 118, 167, 177, 247Engine 654 in model 213, 238, 257 as of model year 2021Engine 656 in model 167, 223 | |||
Engine 139 in model 118, 177Engine 256 in model 213, 238 as of model year 2021Engine 256, 264 in model 167Engine 260, 282 in model 118, 177, 247Engine 264 in model 213, 238, 257 as of model year 2021 | |||
Engine 176, 177 in model 167, 223 | |||
Engine 279 in model 223 | |||
Engine 256 in model 223 | |||
Engine 176 in model 223 | |||
Control units | |||
Fuel system control unit, basic function | Engine all (CAR) | ||
Detailed information | |||
Fuel supply system, detailed information | Engine 608, 654, 656 | ||
Engine 176, 254, 256, 260, 264 | |||
Components | |||
Fuel tank, basic function | Engine all (CAR) |