Charging, function

Function requirements for charging - general

 Circuit 87M ON (engine timing ON)

 Circuit 61 ON

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. Forced induction is performed by 2 inline exhaust gas turbochargers of different size which function together in different ways depending on the operating range.

The boost pressure is regulated while taking account of the respective load condition of the engine dependent on a characteristics map over the boost pressure control flap pressure transducer (Y93/1) and the wastegate pressure transducer (Y77/7).

The CDI control unit (N3/28) actuates the pressure transducer with a pulse width modulation (PWM) signal dependent on the following sensor signals:

– coolant temperature, over the coolant temperature sensor (B11/17)

– atmospheric pressure, via the atmospheric pressure sensor in the CDI control unit

– intake air pressure, over the intake manifold pressure sensor (B28/17)

– engine speed, via the crankshaft sensor (L5/10)

– boost pressure, via the low-pressure turbocharger boost pressure sensor (B5/9) and the boost pressure sensor (B5/6)

– exhaust pressure, via the exhaust back pressure sensor (B60/3)

– intake air mass, via the hot film mass air flow sensor (B2/12)

– DPF differential pressure sensor (B28/18), soot content of the diesel particulate filter (DPF)

Function sequence for charging

The function sequence is described in the following steps:

 Function sequence for boost pressure with wide open throttle operation up to 1200 rpm

 Function sequence for boost pressure with wide open throttle operation as of 1200 rpm

 Function sequence for boost pressure with wide open throttle operation as of 2800 rpm

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Function sequence for boost pressure control with wide open throttle operation up to 1200 rpm

Up to an engine speed of 1200 rpm in wide open throttle operation, the boost pressure control flap is closed and the entire flow of exhaust gas flows via the turbine wheel of the high-pressure turbocharger to the turbine wheel of the low-pressure turbocharger and then to the exhaust system. The largest part of the exhaust gas energy acts on the turbine wheel of the high-pressure turbocharger which thereby generates the main part of the necessary boost pressure.

The remaining exhaust gas energy acts on the turbine wheel of the low-pressure turbocharger which drives the compressor wheel via the supercharger shaft. The low-pressure turbocharger does not therefore act as a hydrodynamic retarder. The wastegate and charge air check valve are closed.

D09.40-0106-76

Function sequence for boost pressure control with wide open throttle operation as of 1200 rpm

As of an engine speed of 1200 rpm in wide open throttle operation, the boost pressure control flap is opened depending on the required boost pressure. The larger part of the exhaust flow continues to flow via the turbine wheel of the high-pressure turbocharger to the turbine wheel of the low-pressure turbocharger and then to the exhaust system.

The largest part of the generated boost pressure is provided by the high-pressure turbocharger. The spring-loaded charge air check valve is continuously opened due to the increasing boost pressure.

The low-pressure turbocharger is continuously activated and precompresses the drawn-in clean air.

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Function sequence for boost pressure control with wide open throttle operation as of 2800 rpm

From an engine rpm of 2800 rpm the boost pressure control flap is opened. The low-pressure turbocharger thus generates the necessary boost pressure.

Part of the exhaust flow drives the turbine wheel of the high-pressure turbocharger.

The generated boost pressure is controlled via the wastegate.

The CDI control unit uses the boost pressure sensor to monitor the boost pressure actually generated. The low-pressure turbocharger boost pressure sensor detects the boost pressure downstream of the low-pressure turbocharger. By comparing the boost pressure actually generated with the boost pressure stored in the performance map and the boost pressure downstream of the low-pressure turbocharger, it is possible to detect faults at the high-pressure and low-pressure turbocharger.