Boost pressure control, function - GF09.40-P-3000M

ENGINE 275.950 in MODEL 215, 220

ENGINE 275.951 in MODEL 230 up to Model Year 8

ENGINE 275.953 in MODEL 216, 221 up to Model Year 8

ENGINE 275.954 in MODEL 230 up to Model Year 8

ENGINE 275.980 in MODEL 215, 220

ENGINE 275.981 in MODEL 230 up to Model Year 8

ENGINE 275.982 in MODEL 216, 221 up to Model Year 8

ENGINE 285.950 in MODEL 240

ENGINE 285.980 in MODEL 240

Fig 1: Boost Pressure Control Communication Diagram

Courtesy of MERCEDES-BENZ USA

The ME-SFI [ME] control unit actuates the boost pressure control pressure transducer for the boost pressure control by means of pulse width modulation with a duty cycle of 5 to 95% and with a frequency of 30 Hz. According to the duty cycle, the boost pressure operates fully or partially in the vacuum cells of the turbocharger.

The boost pressure control valves (wastegate valves) are actuated via vacuum cells and control rods. For limitation of the boost pressure, the boost pressure control valves open and part of the exhaust is guided past the turbine wheel.

The boost pressure is calculated based on the pressure conditions downstream and upstream of the turbochargers (based on the pressure values of the pressure sensor downstream of air filter and pressure sensor upstream of throttle valve actuator).

The boost pressure control is performed in line with the performance map.

Identification of the load (dependent on throttle valve angle) is performed through the signal of the pressure sensor downstream of throttle valve actuator.

Boost pressure control shown on a turbocharger Duty cycle (t _i ) on boost pressure control pressure transducer <5 %

Fig 2: Boost Pressure Control Pressure Transducer <5 %

Courtesy of MERCEDES-BENZ USA

Without actuation, the entire boost pressure in the vacuum cell is used. The boost pressure control valve opens at approx. 300 mbar boost pressure (mechanical basic boost pressure). The boost pressure does not increase further and power shortage is the consequence.

Boost pressure control shown on a turbocharger Duty cycle (t _i ) on boost pressure control pressure transducer >5%

Fig 3: Boost Pressure Control Pressure Transducer >5%

Courtesy of MERCEDES-BENZ USA

The vacuum cell is vented to the atmosphere so that no boost pressure can act anymore in the vacuum cell. In unpressurized condition, a spring holds the boost pressure control valve closed in the vacuum cell. The whole exhaust gas drives the turbine wheel and the maximum boost pressure is generated.

If the hose lines between the vacuum cells, pressure transducer and charge air cooler on the right cylinder bank are leaky the fault "Boost pressure too high" is stored in the ME-SFI [ME] control unit.

The input parameters for the boost pressure control are:

Pressure values of pressure sensor downstream of air filter
Pressure values from pressure sensor upstream of throttle valve actuator
Charge air temperature, signal from charge air temperature sensor
Load recognition from pressure sensor downstream of throttle valve actuator
Ambient pressure (altitude correction), signal from pressure sensor in ME-SFI [ME] control unit
Engine speed
Coolant temperature
Engaged drive mode
Engine oil temperature
Pressure drop in air filter, detection by pressure sensor downstream of air filter
Exhaust gas temperature (from model calculation/performance map)
Knock control active (maximum boost pressure only possible with RON 98)
Catalytic converter damaging misfire recognized/not recognized

The function of the boost pressure control can only be evaluated if the message "Boost pressure control adapted" is read out using the DAS. After replacing the ME-SFI [ME] control unit or a turbocharger is a long drive under certain operating conditions is required to perform the adaptation.

The maximum boost pressure is only released via the signal from the charge air temperature sensor, if the charge air temperature is less than < 70°C.

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

In order to protect the exhaust gas turbochargers from overspeed when in altitude mode and in case of soiled air filters, the maximum boost pressure is limited pressure conditions upstream/downstream of the turbochargers.

Further to the boost pressure control it is possible under certain conditions (e.g. for an excessively high boost pressure due to leaky lines to the vacuum cell) for load limiting to take place through closing of the throttle valve.

	ME-SFI control unit, location/task/design/function		GF07.61-P-5000M
	Boost pressure control pressure transducer, location/task/design/function		GF07.17-P-3160M
	Pressure sensor upstream of throttle valve actuator, location/task/function		GF07.04-P-5048M
	Pressure sensor downstream of throttle valve actuator, location/task/function		GF07.04-P-5049M
	Charge air temperature sensor, location/task/function		GF07.04-P-5038M
	Turbocharger, location/task/function		GF09.40-P-3100M
	Pressure sensor downstream of air filter, location/task/function		GF07.04-P-5041M
	ME-SFI pneumatic diagrams		PP07.61-P-5000M