Charging, Function - GF09.00-P-2000MRD
Engine 274.9 in model 213, 238
up to model year 2021
Function requirements, general
- Engine runs
The ME-SFI [ME] control unit (N3/10) detects engine running by evaluating the signals of the crankshaft Hall sensor (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.
Forced induction, general
The cylinder charging efficiency is improved as a result of forced induction. The engine torque and the engine performance are therefore increased. The fuel quantity corresponding to the increased air mass is metered by the ME control unit.
During forced induction, the flow energy of the exhaust gases is used to drive the ATL. The exhaust gas turbocharger intakes fresh air via the air filter at the compressor inlet and supplies this via the compressor outlet to the charge air pipe. The high rotational speed of the compressor wheel and the resulting high flow volume compresses and heats the air in the charge air pipe. The maximum boost pressure here is approx. 0.7 to 1.5 bar depending on the engine variant involved.
The charge air flows via the charge air pipe to the charge air cooler where it is cooled down to temperatures of approx. 30°C. The charge air is then routed to the charge-air distributor where it is supplied to the cylinders for combustion.
Design of charging system
The charging is divided into the following subfunctions:
- Charge pressure control
- Overrun mode bypass air
- Charge air cooling
Charge pressure control
The boost pressure control occurs electropneumatically over the boost pressure control pressure transducer (Y77/1). The vacuum is generated by the mechanical vacuum pump attached to the engine. The pressure transducer is actuated dependent on the characteristics map and the load by the ME-SFI [ME] control unit for the purposes of boost pressure control. To do this the ME-SFI [ME] control unit evaluates signals from the following sensors and functions of the engine management:
- Charge air temperature
Charge air temperature sensor upstream of throttle valve
Charge air temperature sensor downstream of throttle valve
- Intake pressure
Pressure sensor downstream of air filter
- Boost pressure
Pressure sensor upstream of throttle valve
- Engine load
Pressure sensor downstream of throttle valve
- Load request from driver
Accelerator pedal sensor (B37)
- Engine speed
Crankshaft Hall sensor (B70)
- Knock control, transmission overload protection, overheating protection
In full-load operation, the max. boost pressure is built up in a mechanically dependent manner. To reduce the boost pressure, the exhaust flow for the drive of the turbine wheel is diverted via a bypass by opening the boost pressure control flap.
To do this, the boost pressure control pressure transducer actuates the boost pressure control flap vacuum cells with vacuum from the vacuum pump. The vacuum cell then opens the boost pressure control flap over a linkage which closes the bypass. Part of the exhaust flow is directed through the bypass past the turbine wheel, whereby the boost pressure is regulated and the turbine speed limited. In this way the boost pressure can be adapted to the current load demand on the engine.
To monitor the current pressure and temperature conditions in the charge air duct from the exhaust gas turbocharger to the charge-air distributor, the ME-SFI [ME] control unit evaluates the signals from the pressure and temperature sensors and adjusts the boost pressure to the engine-related requirements.
Overrun mode bypass air
The exhaust gas turbocharger continues turning in overrun mode due to the inertia of the shaft, compressor and turbine wheels. In the case of rapid closing of the throttle valve, a charge pressure wave therefore runs back to the compressor impeller. This charge pressure wave would create a condition with a low delivery volume and high pressure conditions at the compressor impeller, which causes charger pumping (brief howling and mechanical stress). Opening of the bypass air switchover valve (Y101) prevents this by rapidly reducing the pressure via a bypass duct in the intake side of the ATL.
Schematic display of ATL with divert air switchover valve
In load operation of the engine, the bypass is kept closed by means of a diaphragm under boost pressure.
If the engine is switched off, the diaphragm is pressed into the seat by a spring integrated into the deceleration air switchover valve. If the ME-SFI [ME] control unit detects the closing of the throttle valve and thus overrun mode via actual value potentiometer 1 (M16/6r1) and actual value potentiometer 2 (M16/6r2), it actuates the overrun mode bypass air switchover valve. The diaphragm is pulled open against the spring force and boost pressure and opens the bypass duct to the intake side. The excess boost pressure is thereby relieved.
If the engine changes from deceleration mode to load operation, the bypass air switchover valve is no longer actuated. The spring presses the diaphragm in the direction of the seat. There the diaphragm is pulled into the seat by the prevailing boost pressure and thus closes the bypass duct again.
Sectional view of deceleration air switchover valve
Charge air cooling
The liquid-cooled charge air cooler is connected to the low-temperature circuit with the low-temperature cooler and the low-temperature circuit circulation pump 1 (M43/6). If the charge air temperature is greater than 35°C, the powertrain control unit (N127) actuates the low-temperature circuit circulation pump 1 via the drivetrain LIN (LIN C3). If the charge air temperature drops below 25°C, the low-temperature circuit circulation pump 1 is switched off again.
The charge air temperature is detected in the charge air cooler by the charge air temperature sensor upstream of throttle valve and sent to the ME-SFI [ME] control unit using a voltage signal.
In the low-temperature circuit the temperature control of the charge air cooler takes place over the low-temperature circuit switchover valve (Y73/1). This regulates the volumetric flow rate in the low-temperature circuit as required. The low-temperature circuit switchover valve is actuated by the powertrain control unit via the drivetrain LIN. The low-temperature circuit switchover valve also transmits its position via the drivetrain LIN to the powertrain control unit.
The temperature in the low-temperature circuit is detected over the low-temperature circuit temperature sensor (B10/13).
View of low-temperature circuit (shown on model 213)
| Electrical function schematic for charging | PE09.00-P-2050-97DBD | ||
| Overview of system components for gasoline injection and ignition system with direct injection | Engine 274.9 in model 213 (except 213.050/053/153), 238 up to model year 2021 | GF07.70-P-9998MRD | |
| Engine 274.9 in model 213.050/053/153 up to model year 2021 | GF07.70-P-9998MRP |