Charging, function

P09.00-2104-76

Build-up of the charging

12 Intake manifold

50 Turbocharger

50/1 Boost pressure control flap

50/2 Boost pressure control flap vacuum cell

50/3 Noise damper

110/1 Air cleaner housing

110/2 Suction pipe

110/3 Charge air manifold to charge air cooler

110/4 Charge air cooler

110/5 Charge air manifold to throttle valve actuator

B17/8 Charge air temperature sensor

B28/6 Pressure sensor upstream of throttle valve

B28/7 Pressure sensor downstream of throttle valve

B28/15 Pressure sensor upstream of compressor impeller

M16/6 Throttle valve actuator

Y31/5 Boost pressure control pressure transducer

Y101 Divert air switchover valve

A Exhaust

B Intake air

C Charge air (uncooled)

D Charge air (cooled)

Function requirements for charging - general

 Circuit 87 M ON (engine timing ON)

 Engine running

Forced induction, general

Cylinder filling efficiency is improved by forced induction. This raises the engine torque and engine power.

The fuel quantity corresponding to the increased air mass is metered by the ME-SFI [ME] control unit (N3/10).

When charging, 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 compressor inlet and feeds it through the compressor outlet into the charge air pipe upstream of 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 maximum boost pressure is 0.7 bar.

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The noise damper on the compressor outlet dampens the charge pressure fluctuations and thus the associated flow noises which occur for rapid changes in engine speed .

The compressed charge air flows via the charge air pipe upstream of the charge air cooler to the charge air cooler. This finally cools the air which was heated by the compression and leads it over the charge air pipe to the intake manifold.

Function sequence for forced induction

The function sequence is divided into the following subfunctions:

 Function sequence for boost pressure control

 Function sequence for bypass air

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Function sequence for boost pressure control

The boost pressure is controlled electro-pneumatically via the boost pressure control pressure transducer (Y31/5).

The pressure transducer which actuated dependent on the characteristics map and the load by the ME-SFI [ME] control unit for the purposes of boost pressure control.

Do this the ME-SFI [ME] control unit evaluates the following sensors and functions of the engine timing:

- Charge air temperature sensor (B17/8)

- Pressure sensor upstream of the throttle valve (B28/6), boost pressure

- Pressure sensor downstream of the throttle valve (B28/7), intake manifold pressure

- Pressure sensor upstream of the compressor impeller (B28/15), intake pressure

- Accelerator pedal module (B37), load request made by driver

- Crankshaft Hall sensor (B70), engine speed

- Knock control, transmission overload protection, overheating protection

In full-load range, the maximum boost pressure is built up.

In order to reduce the boost pressure the exhaust flow for driving the charger turbine is diverted through the opening of the boost pressure control flap, via a bypass (wastegate).

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The boost pressure control pressure transducer actuates the boost pressure control flap vacuum cell using boost pressure from the charge air manifold to do this. The vacuum cell then opens the boost pressure control flap over a linkage which closes the bypass.

The boost pressure control valve enables the exhaust gas stream to bypass the turbine wheel (bypass), and the boost pressure is thus controlled and the speed of the turbine wheel limited.

In this way the boost pressure can be adapted from a maximum of 0.7 bar to the current load demand on the engine.

To monitor the current boost pressure, the pressure sensor upstream of the throttle valve sends the corresponding voltage signal to the ME-SFI [ME] control unit.

The pressure sensor upstream of the compressor impeller, which is located in the suction line upstream of the exhaust gas turbocharger, serves to the ME-SFI [ME] control unit in monitoring the charging.

The charge air temperature is detected in the intake manifold by the charge air temperature sensor and sent to the ME-SFI [ME] control unit in the form of a voltage signal.

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Function sequence for bypass air

The exhaust gas turbocharger turns back a little after beginning deceleration due to the inertia of the shaft, compressor and turbine wheel.

In the case of rapid closing of the throttle valve actuator (M16/6) a charge pressure shaft therefore runs back to the exhaust gas turbocharger. This charge pressure shaft would create a condition with a low delivery volume and high pressure conditions at the compressor wheel which leads to the charger pumps (shorter howling and less mechanical stress). Opening the bypass air switchover valve prevents this through rapid depressurization in the intake duct.

If the ME-SFI [ME] control unit identifies the transition from load to deceleration operation, the switchover valve deceleration switchover is actuated.

The bypass air switchover valve reacts by opening the bypass which bypasses the compressor impeller, through which the boost pressure is reduced.

In charge mode the bypass air switchover valve is closed by an integral spring.