Forced induction, function

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Shown: electric motor 471.9, code (M5Z) Engine version Euro VI

1 Turbocharger

2 Charge air manifold

3 Turbine wheel

4 Vacuum cell

5 Compressor impeller

6 Shaft

Y636 Charge pressure positioner

A Intake air from air filter

B Charge air to charge air cooler

C Charge air from charge air cooler

D Exhaust

7 Valve

8 Bypass opening

B610 Rpm sensor for turbine wheel
(only for code (M5Z) Engine version Euro VI)

General

Charging on the engines from the model series OM 470 and OM 471 takes place through a turbocharger (1).

Through compression of the suctioned in air in the turbocharger (1) a larger air mass is brought into the combustion chamber.

The following advantages result through this:

 An increase in the engine power and the torque

 Reduction of fuel consumption in comparison to not supercharged diesel engines of the same power output

 Reduction of the pollutant emission

Function

The turbocharger (1) consists of a turbine and a compressor which are fitted to a joint shaft (6).

The exhaust (D) flows over the turbine wheel (3) and causes this to rotate. This rotational movement is transferred to the compressor impeller (5) over the shaft (6).

Through the compressor impeller (5) the intake air is compacted by the air filter (A) and passes over a charge air pipe to the charge air cooler.

In the charge air cooler the compacted air is cooled whereby the air density of the fresh gas filling and thus the output of the engine is increased.

The charge air then passes from the charge air cooler (C) via the charge air manifold (2) into the individual cylinders.

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Boost pressure control and turbocharger protection function, shown engine 471.9, code (M5Z) Engine version Euro VI

A4 Engine management control unit (MCM)

B608 Charge air pressure and temperature sensor in charge air pipe

B610 Rpm sensor for turbine wheel
(only for code (M5Z) Engine version Euro VI)

B611 Temperature sensor downstream of air filter (only for code (M5Z) Engine version Euro VI)

Y636 Charge pressure positioner

Boost pressure control (via wastegate)

The engine management (MCM) control unit (A4) determines the current boost pressure via the charge air pressure and temperature sensor in the charge air pipe (B608).

If the engine management (MCM) control unit (A4) recognizes that the current boost pressure is too high, it limits the boost pressure in that it actuates the boost pressure regulator (Y636) with an appropriate pulse width modulated signal. The engine management (MCM) control unit (A4) can use the duty cycle of this signal to influence the pressure (up to 2.8 bar) which should be applied to the vacuum cell (4). The valve (7) is opened over a linkage according to this pressure, so that more or less exhaust (D) is passed over the bypass opening (8) on the turbine wheel (3) depending on how far it is opened.

Since only part of the exhaust (D) hits the turbine wheel (3) the acceleration is not so strong anymore and the boost pressure drops.

Turbocharger protection function

For vehicles with code (M5Z) Engine version Euro VI the rotor speed of the turbocharger (1) as well as the temperature of the intake air are monitored by the air filter (A) on the compressor inlet to protect the turbocharger.

This occurs with the aid of the turbine wheel rpm sensor (B610) and the temperature sensor downstream of air filter (B611).

Since these sensors for vehicles with code (M5R) Engine version EEV and vehicles with code (M5Y) Engine version Euro VI are not installed, the engine management (MCM) control unit (A4) orients itself on the ambient temperature and on the altitude the vehicle is at. The latter is determined using the installed atmospheric pressure sensor.

Dependent on the determined values and values stored in the characteristics maps for the turbocharger protection function the engine management (MCM) control unit (A4) adapts the injection which leads to a lowering of the combustion temperature.

One indirect effect of actuation of the boost pressure regulator (Y636) can be reduction of the rotor speed of the turbocharger.