Turbocharging, function

P09.40-2063-06

5/1 Charge air cooler, left cylinder bank

5/2 Charge air cooler, right cylinder bank

12 Intake manifold

110/1 Suction line, air filter housing

110/6 Boost pressure pipe

110/7 Hose section with hose clamps

110/8 Y-connection

121/1 Air filter, left cylinder bank

121/2 Air filter, right cylinder bank

110 A Left turbocharger

110b Right turbocharger

M16/6 Throttle valve actuator

B Exhaust

D Clean air (downstream of air filter)

E Charge air

For exhaust-gas turbocharging the flow kinetic energy of the exhaust gases coming out of each cylinder bank is used to drive the turbocharger (110a, 110b). The turbochargers take in clean air downstream of the air filters. The compressed air (E) is cooled in the charge air cooler (5/1, 5/2).

Downstream of the charge air coolers, the combined charge air (E) from the right and left turbochargers flows to the intake manifold (12) via the throttle valve actuator (M16/6).

There is a coolant cooled turbocharger (biturbo) installed in every cylinder bank. An optimal response characteristic and a resulting high boost pressure are achieved even at low rpm speeds by installing the turbochargers immediately on the exhaust manifolds. Short exhaust gas paths guarantee fast warm up and thus a high efficiency of the three way catalytic converters.

The turbochargers start to produce boost pressure at approx. 1500 rpm. The maximum boost pressure is reached at approx. 2000 rpm. Injection quantity and ignition timing are controlled by the ME-SFI [ME] control unit (N3/10) as needed for the present load condition.

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The boost pressure is measured through the signal of the pressure sensor upstream of the throttle valve actuator (B28/6), the load is measured through the signal of the pressure sensor downstream of the throttle valve actuator (B28/7).

Boost pressure control of both turbochargers is performed by means of the boost pressure control pressure transducer (Y31/5) and the pressure regulator valves (wastgate valves) operated by the vacuum cells in the turbine housings.

Additionally, fast control operations and load adjustments below the basic charge pressure are performed via the throttle valve actuator.

The maximum boost pressure at sea level is:

 For engine 275.950/951/953/954 approx. 0.9 bar

 For engine 285.950 about 1.3 bar

 For engine 275.980/981/982, 285.980 (AMG) about 1.5 bar.

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The cooled air downstream of the charge air coolers has a higher density. Through this, the cylinder charge and hence the engine output are increased. Furthermore the tendency to knock is reduced. The maximum boost pressure is released only when the charge air temperature is less than 70°C. The charge air temperature sensor (B17/8) is mounted at the intake manifold.

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If the charge air temperature becomes too high, the reason for this could be air bubbles in the low temperature cooling circuit.

During a load change, e.g. when changing into deceleration mode, a deceleration air valve opens at each compressor housing. Through this the boost pressure is quickly reduced and charger noises are prevented.

A pressure sensor downstream of air filter for the left or right cylinder bank (B28/4, B28/5) is located in the air filter housing after every air filter in order to recognize the pressure drop over the air filter.

In order to limit the maximum charger rpm the pressure conditions downstream and upstream of the turbocharger is calculated (based on pressure values for the pressure sensor downstream of air filter and pressure sensor upstream of throttle valve actuator (B28/6)) and regulated dependent on the performance map by the boost pressure control.

In higher altitudes the maximum boost pressure is limited.