Function requirements for charging - general
Circuit 87M ON (Engine management ON)
Engine running.
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 rotational speed 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.
Charging is regulated by the boost pressure control. The boost pressure is regulated by the CDI control unit (N3/9) depending on the following values and associated components:
Charge air pressure and temperature sensor (B4/32)
Coolant temperature sensor (B11/4)
Temperature sensor upstream of ATL (B19/11)
Pressure sensor downstream of throttle valve (EU6/7) (with code 927 (Emissions standard B28))
Crankshaft position sensor (L5), engine speed
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 detected by the rail pressure sensor (B4/6).
Exhaust pressure sensor (B60), 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 (Y77/1).
The boost pressure regulator is actuated dependent on the characteristics map and the load by the CDI control unit for the purposes of boost pressure control.
For this purpose, the CDI control unit evaluates the following sensor signals:
Coolant temperature sensor
Charge air pressure and temperature sensor
Exhaust pressure sensor
Fuel pressure sensor
Crankshaft position sensor
In wide open throttle operation, maximum boost pressure builds up.
The position of the guide vanes in the ATL are altered via the control linkage of the boost pressure regulator.
The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine wheel.
The guide vanes thus match 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 and passed on to the CDI control unit.
To protect the ATL from overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the ATL and the exhaust pressure via the exhaust pressure sensor.
The boost pressure is reduced if there is any risk of thermal or mechanical overload.
Referenced documents
- gf0716p9997ora Overview of system components for common rail diesel injection (CDI)