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 charge-air distributor.
Turbocharging is regulated by the boost pressure control. The boost pressure is regulated by the CDI control unit depending on the following values and associated assembly parts:
atmospheric pressure sensor, for acquisition of the atmospheric pressure
Charge air temperature sensor (B17/8)
Temperature sensor upstream of ATL (B19/11)
Injection quantity is determined over the injection period of the cylinder 1 to cylinder 4 fuel injectors (Y76/1 to Y76/4) and the fuel pressure in the rail. The fuel pressure in the rail is recorded by the high pressure fuel pressure sensor (B4/6).
Boost pressure positioner (Y77/1)
The CDI control unit actuates the boost pressure positioner dependent on the following sensor signals:
Coolant temperature, over the coolant temperature sensor (B11/4)
atmospheric pressure, via the atmospheric pressure sensor in the CDI control unit
Engine speed, via the crankshaft Hall sensor (B70)
Boost pressure, via the boost pressure sensor (B5/1)
Exhaust pressure, over the exhaust pressure sensor (B60)
Intake air mass, over the hot film mass air flow sensor (B2/5)
DPF differential pressure sensor (B28/8), soot content of the diesel particulate filter (DPF)
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 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 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
- gf0716p9997ore Overview of system components for common rail diesel injection (CDI)