Turbocharging, function

P09.00-2091-76

1 Air filter box

2 Intake air duct

3 Intake air resonator

4 Charge air cooler

5 Turbocharger

6 Charge air line

7 Charge air distribution pipe

B5/1 Charge pressure sensor

B28 Intake manifold pressure sensor

M16/6 Throttle valve actuator

M44 Charge air fan motor

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A Suctioned in fresh air

B Hot charge air

C Cooled charge air

D Exhaust gases

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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 is 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 manifold to the charge air cooler.

The high speed of the compressor turbine wheel and the resultant high volume flow compresses the air.

The charge air cooler then cools the charge air warmed by the compression and passes it on to the throttle valve actuator. It passes from the throttle valve actuator to the charge air manifold and thus the individual intake ports.

The boost pressure is detected by the charge pressure sensor and the air temperature by the intake manifold pressure sensor and sent in the form of voltage signals to the ME-SFI [ME] control unit (N3/10).

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Charging includes the following subfunctions

 Charge pressure control

 Charge air cooling

Charge pressure control

The boost pressure control is performed pneumatically. Using a boost pressure control valve (wastegate) part of the exhaust flow is passed by the turbine wheel (bypass), whereby the maximum boost pressure is limited. The vacuum cell actuates the boost pressure control valve via a control rod. Via the pressure regulator valve (Y74) the vacuum cell is supplied with vacuum from the intake air line. For boost pressure control, the pressure regulator valve is actuated by the ME-SFI [ME] control unit. As long as the pressure regulator valve is not actuated the vacuum cell closes by means of the spring force of the boost pressure control valve. In this way the bypass is closed and the whole amount of the exhaust drives the turbine wheel. As the exhaust gas quantity increases, the turbine speed increases and thus the boost pressure.

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If the pressure regulator valve is actuated is passes on the applied vacuum on to the vacuum cell. This actuates the control rod which opens the boost pressure control valve. If the bypass is opened, part of the exhaust gas volume can bypass the turbine wheel. Thus the speed of the turbine wheel is reduced and therefore the boost pressure.

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

Charge air cooling

The suctioned in fresh air is warmed by the temperature of the turbocharger and compacting.

Nevertheless, in order to achieve optimum cylinder charge the heated charge air is led directly to the turbocharger through a charge air cooler in order to cool it again. The function of the charge air cooler is supported depending on temperature by the charge air fan motor.

Below the charge air cooler there is an air duct which picks up fresh outside air under the vehicle and leads its to the charge air cooler. On the under side of the charge air cooler the air flows out of the air duct and is suctioned here by the charge air fan motor through the charge air cooler cooling fins.