Turbocharging, function

P09.00-2026-76

View of engine from front left

50 Compressor

50/1 Pressure damper (charge air)

110/1 Suction pipe

110/2 Charge air cooler

110/6 Charge air line

122 Suction damper (intake air)

B2/5 Hot film mass air flow sensor

M16/6 Throttle valve actuator

M16/7 Air recirculation flap actuator

Function requirements for forced induction - general

- "Tml. 87 M" ON (engine control ON)

- Engine running

Forced induction, general

The compressor makes it possible to raise engine torque, particularly in the lower rpm range.

The intake air is compressed in the compressor and then cooled down in the charge air cooler. The degree of cylinder filling is increased by the compacted intake air (charge air). This raises the engine torque and engine power.

The ME-SFI control unit (N3/10) regulates the boost pressure through the air recirculation flap actuator. To do this, it reads the information from the following sensors and signals:

- Hot film MAF sensor, engine load

- Intake air temperature sensor (B17), charge air temperature

- Pressure sensor (B28), intake manifold air pressure

- Accelerator pedal sensor (B37), load request by driver

- Crankshaft position sensor (L5), crankshaft rotational speed

- Air recirculation flap actuator, air recirculation flap position

The boost pressure control also depends on the safety functions of the engine control (for example, knock control and overheating/knock protection).

Forced induction function sequence

For the boost pressure control, the ME-SFI control unit opens the air recirculation flap according to a performance map, which causes the charge air to pass through the air recirculation line back to the compressor (charge air pressure falls).

The pressure sensor detects the charge air pressure in the intake manifold and sends it as a voltage signal to the ME-SFI control unit.

After being cooled in the charge air cooler, the charge air temperature is detected by the intake air temperature sensor, which sends it as a voltage signal to the ME-SFI control unit.

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Charging increases the intake air mass detected by the hot film MAF sensor. The ME-SFI control unit then lengthens the injection time of the fuel injection valves (Y62) accordingly.

P09.50-2046-82

Maximum boost pressure of air flow

50 Compressor

50/1 Pressure damper (charge air)

50/2 Recirculated air line

110/1 Suction pipe

110/2 Charge air cooler

110/6 Charge air line

122 Suction damper (intake air)

M16/7 Air recirculation flap actuator

a Recirculated air flap closed

When the air recirculation flap is closed, the maximum boost pressure is made available to the engine.

In full-load operation, maximum boost pressure builds up.

P09.50-2045-82

Flow controlled boost pressure

50 Compressor

50/1 Pressure damper (charge air)

50/2 Recirculated air line

110/1 Suction pipe

110/2 Charge air cooler

110/6 Charge air line

122 Suction damper (intake air)

M16/7 Air recirculation flap actuator

b Recirculated air flap open

If the recirculated air flap is opened, the boost pressure air is guided back via the recirculated air line to the compressor.

The air recirculation flap can be adjusted continuously from 0 to 90° and can regulate the boost pressure over the recirculated air line.

Recirculated air flap actuator, emergency mode

If one of the actual value potentiometers (M16/7r1, M16/7r2) fails, the other actual value potentiometer is used.

If the actuator motor (M16/7m1) fails, or both actual value potentiometer fail, the air recirculation flap is opened by the integrated return spring, thus preventing the buildup of boost pressure (engine power falls).