Function requirements for charging - general
Circuit 87M ON (Engine management ON)
Engine runs
Forced induction, general
The cylinder charging efficiency is improved as a result of forced induction. As a result, the engine torque and power output are boosted.
During forced induction, the flow energy of the exhaust gases is used to drive the ATL.
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 rpm of the compressor impeller and the resultant high volumetric flow rate compacts the air in the charge air pipe.
The compacting heats the charge air, which now flows through the charge air pipe to the charge air cooler. This cools off the charge air and feeds it through the charge air pipe to the cylinder head.
Turbocharging is regulated by the boost pressure control. The boost pressure is regulated by the CDI control unit (N3/36) depending on the following values and associated components:
Charge air pressure and temperature sensor (B5/14)
Pressure sensor downstream of air filter (B5/17)
Coolant temperature sensor (B11/15)
Exhaust temperature sensor upstream of ATL (B17/7)
Crankshaft Hall sensor (B704), for the engine speed
Injection quantity is determined over the injection period of the cylinder fuel injector 1 to cylinder fuel injector 4 (Y76/29 to 32) and the fuel pressure in the rail. The fuel pressure in the rail is recorded by the high pressure fuel pressure sensor (B4/11).
Exhaust pressure sensor (B515), for the exhaust pressure in the exhaust system
Atmospheric pressure sensor (integrated in CDI control unit), for recording the atmospheric pressure
Function sequence for boost pressure control
The boost pressure control occurs electropneumatically over the boost pressure control pressure transducer (Y77/11).
The pressure transducer boost pressure control is actuated on a characteristics map and load-dependent basis by the CDI control unit for boost pressure control.
For this purpose, the CDI control unit evaluates the following sensor signals:
Coolant temperature sensor
Charge air pressure and temperature sensor
Pressure sensor downstream of air filter
Exhaust temperature sensor upstream of ATL
Exhaust pressure sensor
High pressure fuel pressure sensor
Crankshaft Hall sensor
Atmospheric pressure sensor
In wide open throttle operation, maximum boost pressure builds up.
Over the control linkage the position of the guide vanes in the ATL are adjusted.
The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine wheel.
The guide vanes thus adapt the gas pressure present at the turbine wheel to the required boost pressure.
The ATL rpm is used to determine the quantity of pre-compressed air and thus the boost pressure.
The boost pressure is constantly being monitored by the charge air pressure and temperature sensor downstream of air filter and passed on to the CDI control unit.
As a protection against overload the ATL, the exhaust temperature and the exhaust pressure is monitored by the CDI control unit.
The boost pressure is reduced if there is any risk of thermal or mechanical overload.
Referenced documents
- gf0716s9997tra Overview of system components for common rail diesel injection (CDI)