Turbocharging, function

P09.00-2090-06

1 Turbocharger

2 Charge air cooler

3 Exhaust gas recirculation actuator with mixed air housing

4 Charge air distribution pipe

B5/1 Charge pressure sensor

B17/8 Charge air temperature sensor

M44 Charge air fan motor

A suctioned in fresh air

B hot charge air

C cooled charge air

General

The cylinder charging efficiency is improved as a result of charging. As a result the engine torque and power output are boosted.

When charging, the flow energy of the exhaust gases are used to drive the turbocharger.

The turbocharger draws in fresh air at the compressor inlet and passes this via the compressor outlet and the charge air pipe to the charge air cooler.

The high speed of the compressor turbine wheel and the resultant high volume flow compresses the air in the charge air pipe. The charge air cooler then cools the charge air warmed by compression and passes it on to the mixed air housing. It then passes from the mixed air housing to the charge air manifold and thus the individual intake ports.

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The boost pressure is detected by the boost pressure sensor and the charge air temperature by the charge air temperature sensor and sent in the form of voltage signals to the CDI control unit (N3/9).

At a too high Charge air temperature the CDI control unit sends a request signal to the SAM control unit (N10/10) which causes the charge air fan motor (M44) to be energized. The function of the charge air cooler is also supported by the charge air fan motor.

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Boost pressure control

Boost pressure control takes place pneumatically based in overpressure control. The exhaust flow for the turbine wheel drive is diverted for the purpose of boost pressure control through a boost pressure control flap (bypass flap) via a bypass. The vacuum cell is connected in this case via a hose directly to the compressor impeller housing. The current boost pressure operates permanently on a membrane in the vacuum cell which in turn is connected with the control rod.

According to engine load the exhaust flow is passed via the vacuum cell and the control rod past the bypass flap and the bypass duct on the turbine wheel.

The more exhaust gases are passed by the less the turbine wheel is driven. Thus the boost pressure is limited and the respective engine load is adapted.

 Acceleration of the turbine wheel requires a minimum amount of exhaust which is only available from a engine speed of 1800 rpm. Below this rpm the turbocharger remains ineffective.