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 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 charge air distributor.
Turbocharging 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:
Boost pressure sensor (B5/1)
Coolant temperature sensor (B11/4)
Charge air temperature sensor (B17/8)
Pressure sensor downstream of air filter (B28/5)
Temperature sensor upstream of ATL (B19/11)
Crankshaft Hall sensor (B70), for 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, for measuring the atmospheric pressure
Function sequence for charging
After evaluating the input signals, the CDI control unit actuates the boost pressure regulator (Y77/1) by means of a pulse width modulated signal, dependent on the boost pressure characteristics map. The position of the guide vanes in the turbocharger 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. The guide vanes thus match the gas pressure present at the turbine 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 boost pressure sensor and passed on to the CDI control unit.
To protect the turbocharger from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the turbocharger and the exhaust back pressure through the exhaust back pressure sensor.
The boost pressure is reduced if there is any risk of thermal or mechanical overload.
Referenced documents
- gf0716p9997olb Overview of system components for common rail diesel injection (CDI)