View of charge air cooling |
1 | Charge air cooler |
2 | Exhaust gas recirculation cooler (water-cooled) |
M16/6 | Throttle valve actuator |
Y27/7 | Low pressure exhaust gas recirculation actuator |
Y27/8 | High pressure exhaust gas recirculation actuator |
A | Charge air (uncooled) |
B | Charge air (cooled) |
C | Exhaust downstream of diesel particulate filter |
D | Cooled exhaust |
P09.41-2749-76
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 turbocharger.
The turbocharger 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 (N3/9) depending on the following values and associated components:
Charge air pressure and temperature sensor (B4/32)
Hot film mass air flow sensor (B2/5)
Intake air temperature sensor (B2/5b1)
Coolant temperature sensor (B11/4)
Temperature sensor upstream of turbocharger (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 recorded by the high pressure fuel pressure sensor (B4/6).
Exhaust pressure sensor (B60), for the exhaust pressure in the exhaust system
Atmospheric pressure sensor integrated in the CDI control unit, for detection of the atmospheric pressure
Function sequence for boost pressure control
The boost pressure control occurs electropneumatically via the boost pressure control pressure transducer (Y31/5).
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
High pressure fuel pressure sensor
Crankshaft Hall sensor
In wide open throttle operation, maximum boost pressure builds up.
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 wheel.
The guide vanes thus adapt the gas pressure present at the turbine wheel to the required boost pressure.
The turbocharger 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 turbocharger from overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the turbocharger 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
- gf0716p9997orb Overview of system components for common rail diesel injection (CDI)