Function requirements for charging - general
Circuit 87M ON (Engine management ON)
Engine running.
The CDI control unit (N3/40) detects engine running by evaluating the signals of the crankshaft Hall sensor (B70). The CDI control unit directly reads in the signals of the crankshaft Hall sensor.
Forced induction, general
The forced induction improves the cylinder charging efficiency. The engine torque and the engine output are increased. The flow energy of the exhaust gases is used to drive the exhaust gas turbocharger. The ATL suctions in fresh air through the air filter on the compactor inlet and feeds it through the compressor outlet into the charge air pipe upstream of the charge air cooler.
The high number of revolutions of the compressor wheel and the resulting high flow volume compacts and heats the air. This charge air flows via the charge air pipe to the charge air cooler. The charge air cooler cools down the charge air and feeds it through another charge air pipe to the charge air distributor.
Charging is regulated by the boost pressure control. The boost pressure is regulated by the CDI control unit depending on the signals from the following sensors:
Atmospheric pressure sensor in CDI control unit
Hot film mass air flow sensor (B2/5)
Boost pressure sensor (B5/2)
Low-pressure turbocharger boost pressure sensor (B5/4)
Coolant temperature sensor (B11/16)
Charge air temperature sensor (B17/8)
Temperature sensor upstream of exhaust gas turbocharger (B16/24)
Diesel particulate filter differential pressure sensor (B28/26)
Low-pressure exhaust gas recirculation differential pressure sensor (B28/91)
Exhaust pressure sensor (B60)
Crankshaft Hall sensor (B70)
The CDI control unit actuates the boost pressure regulator (Y77/1) to regulate the boost pressure, depending on the following sensor signals:
atmospheric pressure, via the atmospheric pressure sensor in the CDI control unit
Coolant temperature, via the coolant temperature sensor (B11/16)
Engine speed, via the crankshaft Hall sensor (B70)
Boost pressure, via the low-pressure turbocharger boost pressure sensor (B5/4) and boost pressure sensor (B5/2)
Exhaust pressure, over the exhaust pressure sensor (B60)
Intake air mass, via the hot film mass air flow sensor (B2/5)
Soot content of the diesel particulate filter (DPF) via the diesel particulate filter differential pressure sensor (B28/26)
The injection quantity is determined via the injection period of fuel injectors (Y76) and the fuel pressure in the rail. The fuel pressure in the rail is recorded by the high pressure fuel pressure sensor (B4/6).
The CDI control unit actuates the following components for the adaptation of the injection quantity:
Pressure regulating valve (Y74)
Fuel injectors (Y76)
Quantity control valve (Y94)
Function sequence for charging
After evaluation of the input signal, the CDI control unit regulates the position of the boost pressure positioner according to a characteristics map. According to the actuation, the boost pressure positioner adjusts the position of the guide vanes. The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine. The guide vanes thus match the gas pressure present at the turbine to the required boost pressure.
The turbine speed of the exhaust gas turbocharger is used to determine the amount of pre-compressed air and thus the boost pressure. The boost pressure is constantly being monitored by the boost pressure sensor and passed on to the CDI control unit.
To protect the ATL from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the ATL and the exhaust pressure through the exhaust pressure sensor. The boost pressure is reduced if there is any risk of thermal or mechanical overload.
Referenced documents
- gf0716d9994tsd Overview of system components for Common Rail Direct Injection (CDI)