Charging, function - GF09.00-P-2000OMA

ENGINE 651.9 (except 651.913) in MODEL 204.0/2 

ENGINE 651.9 (except 651.925) in MODEL 212.0 (except 212.098), 212.2 (except 212.298) 

ENGINE 651.9 in MODEL 204.3, 204.9 up to 5/31/12, 207.3/4, 218 

Function requirements for charging - general 

• Circuit 87M ON (engine timing ON)
• Engine running

Forced induction, general 

The cylinder charging efficiency is improved as a result of forced induction. As a result, the engine torque and power output are boosted. For forced induction, the flow energy of the exhaust gases is used to drive both turbochargers.

Forced induction is performed by 2 inline exhaust gas turbochargers of different size which function together in different ways depending on the operating range.

The boost pressure is regulated by the CDI control unit (N3/9) depending on the following values and associated components:

• Charge air temperature sensor (B17/8)
• Temperature sensor upstream of turbocharger (B19/11)
• The injection quantity which is determined via the injection time of fuel injectors (Y76) and the fuel pressure in the rail. The fuel pressure in the rail is detected by the rail pressure sensor (B4/6).
• Atmospheric pressure sensor, for measuring the atmospheric pressure
• Boost pressure control flap pressure transducer (Y93)
• Boost pressure control pressure transducer (Y31/5)
• Charge air bypass flap switchover valve (Y132) (up to 05/10)

The CDI control unit actuates the pressure transducer by means of a pulse width modulated signal (PWM signal) and up to 05/10 the charge air switchover valve bypass flap by means of a simple voltage signal depending on the following sensor signals:

• Intake air mass, via the hot film mass air flow sensor (B2/5)
• Intake air temperature, via the intake air temperature sensor (B2/5b1)
• Boost pressure, via the low-pressure turbocharger boost pressure sensor (B5/4) and the boost pressure sensor (B5/1)
• Coolant temperature, over the coolant temperature sensor (B11/4) (model 204, 207, 212) or coolant temperature sensor (B11/4) (model 218)
• Intake air pressure, via the pressure sensor downstream of the air filter (B28/5)
• DPF differential pressure sensor (B28/8) with code (474) particulate filter, soot content of the diesel particulate filter (DPF)
• Charge air cooler temperature sensor (B17/11) (with code (494) USA version) (as of 01.09.2013) Bosch
• Exhaust pressure, via the exhaust pressure sensor (B60)
• Engine rpm, over the crankshaft Hall sensor (B70) (with code (B03) ECO start/stop function)
• Engine speed, over the crankshaft position sensor (L5) (except code (B03) ECO start/stop function)
• Atmospheric pressure, via the atmospheric pressure sensor in the CDI control unit

Function sequence for charging 

The function sequence is described in the following steps:

• Function sequence for boost pressure with wide open throttle operation up to 1200 rpm 
• Function sequence for boost pressure with wide open throttle operation from 1200 up to 2800 rpm 
• Function sequence for boost pressure with wide open throttle operation from 2800 rpm 

Function sequence for boost pressure control with wide open throttle operation up to 1200 rpm 

Up to an engine speed of 1200 rpm in wide open throttle operation, the boost pressure control flap is closed and the entire exhaust flow flows via the turbine wheel of the high-pressure turbocharger to the turbine wheel of the low-pressure turbocharger and then to the exhaust system.

The largest part of the exhaust gas energy acts on the turbine wheel of the high-pressure turbocharger which thereby generates the main part of the necessary boost pressure.

The remaining exhaust gas energy acts on the turbine wheel of the low-pressure turbocharger which drives the turbine wheel via the supercharger shaft. The low-pressure turbocharger does not therefore act as a hydrodynamic retarder. The wastegate actuated by the boost pressure control pressure transducer and the charge air bypass flap are closed.

Schematic representation showing wide open throttle operation boost pressure control up to 1200 rpm 

Fig 1: Wide Open Throttle Operation Boost Pressure Control Schematic - Up To 1200 RPM

Courtesy of MERCEDES-BENZ USA

Function sequence for boost pressure control with wide open throttle operation as of 1200 rpm to 2800 rpm 

As of an engine speed of 1200 rpm in wide open throttle operation, the boost pressure control flap is opened depending on the required boost pressure.

The larger part of the exhaust flow continues to flow via the turbine wheel of the high-pressure turbocharger to the turbine wheel of the low-pressure turbocharger and then to the exhaust system.

The largest part of the generated boost pressure is provided by the high-pressure turbocharger.

The low-pressure turbocharger is continuously activated and precompresses the drawn-in clean air.

As of an engine speed of approx. 2800 rpm, the boost pressure control flap is fully open.

The wastegate actuated by the boost pressure control pressure transducer and the charge air bypass flap continue to be closed.

Function presentation for boost pressure control with wide open throttle operation as of 1200 rpm to 2800 rpm 

Fig 2: Wide Open Throttle Operation Boost Pressure Control Schematic - As Of 1200 RPM To 2800 RPM

Courtesy of MERCEDES-BENZ USA

Function sequence for boost pressure control with wide open throttle operation as of 2800 rpm 

As of an engine speed of 2800 rpm, the charge air bypass flap and boost pressure control flap are opened. The largest part of the charge air generated by the low-pressure turbocharger flows in front of the compressor housing of the high-pressure turbocharger via the charge air pipes to the charge air cooler and the charge air distributor. The low-pressure turbocharger thus generates the necessary boost pressure. Part of the exhaust flow drives the turbine wheel of the high-pressure turbocharger. The boost pressure generated is regulated by the wastegate actuated by the boost pressure control pressure transducer.

The CDI control unit uses the boost pressure sensor to monitor the boost pressure actually generated. The low-pressure turbocharger boost pressure sensor detects the boost pressure downstream of the low-pressure turbocharger. By comparing the boost pressure actually generated with the boost pressure stored in the characteristics map and the boost pressure downstream of the low-pressure turbocharger, it is possible to detect faults at the high-pressure and low-pressure turbocharger.

Schematic representation showing wide open throttle operation boost pressure control as of 2800 rpm 

Fig 3: Wide Open Throttle Operation Boost Pressure Control Schematic - As Of 2800 RPM

Courtesy of MERCEDES-BENZ USA

For vehicles as of 06/10 a modified turbocharger with a pressure-dependent self-regulating compressor bypass is used. The spring-loaded check valve takes on the work of the charge air bypass flap switchover valve with an associated vacuum aneroid capsule which takes the high-pressure turbocharger out of the delivery flow at high loads via the charge air bypass flap.

Shown: turbocharger as of 06/10 compressor bypass closed 

Fig 4: Turbocharger Compressor Bypass Check Valve & Return Spring

Courtesy of MERCEDES-BENZ USA

Shown: turbocharger as of 06/10 compressor bypass closed 

Fig 5: Turbocharger Compressor Bypass Check Valve

Courtesy of MERCEDES-BENZ USA