Charging, Function - GF09.00-P-2000MNL
Engine 176.9, 177.9 in model 217
Engine 176.9, 177.9 in model 222
Engine 177.9 in model 290
up to model year 2021
Function requirements for charging - general
- Circuit 87 M (engine management ON)
- Engine runs
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. The fuel quantity corresponding to the increased air mass is metered by the ME-SFI control unit (N3/10).
With forced induction, the flow energy of the exhaust gases is used to drive the ATL. The ATLs draw in fresh air via the air filters at the compressor inlets and lead it via the compressor outlets in the charge air pipes upstream to the charge air coolers.
Due to the high rotational speed of the compressor impellers and the resulting high volume flow rates, the intake air becomes compressed in the charge air pipes. The compressed charge air flows via the charge air pipes to the charge air coolers. These subsequently cool the air which was heated by the compression and lead it via the charge air distributor to the cylinders.
Charging set up (shown on engine 177.9)
Forced induction function sequence
The function sequence is divided into the following subfunctions:
- Function sequence for boost pressure control
- Function sequence for bypass air
Function sequence for boost 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 control unit evaluates the following sensor signals and functions of the engine management:
- Left charge air temperature sensor and right charge air temperature sensor (B17/15), charge air temperature
- Pressure sensors downstream of air filter, left and right cylinder bank (B28/4, B28/5), intake air pressure
- Pressure sensors upstream of throttle valve on the left and right, boost pressure
- Pressure sensor downstream of left throttle valve and pressure sensor downstream of right throttle valve (B28/23), engine load
- Accelerator pedal sensor (B37), load request made by driver
- Crankshaft Hall sensor (B70), engine speed
- Knock control, transmission overload protection, overheating protection
In wide open throttle operation, maximum boost pressure builds up. To reduce the boost pressure, the exhaust flows that drive the ATL are each redirected through bypasses by opening the boost pressure control flaps. To do this the boost pressure control pressure transducer actuates the boost pressure control flap vacuum units with vacuum from the vacuum pump. The vacuum units react by closing the boost pressure control flap linkages over a rod, which close the bypasses.
If there is no vacuum at the vacuum cells, the boost pressure control flaps and thus also the bypasses are opened. The boost pressure control flaps therefore allow the exhaust flow to bypass the turbine wheels (bypass), thus controlling the boost pressure and limiting the turbine speed. In this way the boost pressure can be adapted to the current load demand on the engine.
Boost pressure buildup is not possible if there is a leakage in the line between the vacuum pump and the vacuum cells.
To monitor the current boost pressure, the pressure sensors upstream of the left and right throttle valve send the corresponding voltage signal to the ME-SFI control unit.
The charge air temperature is detected in the charge air cooler by the left and right charge air temperature sensors and sent to the ME-SFI control unit in the form of a voltage signal.
The boost pressure control function can only be assessed if the "boost pressure control adapted" message is displayed with the Xentry Diagnostics. If the ME-SFI control unit or one of the ATLs is replaced, a longer driving distance is required in certain operating conditions, in order to allow the ME-SFI control unit to perform the adaptation. If the hose lines are leaky between the vacuum cells, boost pressure control pressure transducer and charge air cooler, a "boost pressure too high" fault is stored in the ME-SFI [ME] control unit. Quick load requirements below the basic charge pressure are controlled via the throttle valve actuator.
Function sequence for bypass air
The ATLs continue turning for a period of time after the start of deceleration mode due to the inertia of the shaft, compressor and turbine wheel.
Through rapid closing of the throttle valve back pressures and unfavorable vibrations occur in the air column downstream of the ATLs. This vibrations would create a condition with a low delivery volume and high pressure conditions at the compressor impellers, which causes charger pumping (brief howling and mechanical stress). If the ME-SFI [ME] control unit recognizes closing of the throttle valves over the actual value potentiometer 1 left and right (M16/60r1 and M16/61r1) and actual value potentiometer 2 left and right (M16/60r2 and M16/61r2) and therefore decel mode, the bypass air switchover valves on the left and right are actuated.
These are located on the charge air coolers and each open a bypass from the charge pressure side downstream of the ATL to the suction side downstream of the air filters. The excess boost pressure and the respective air volumes are rapidly reduced in this way and thus prevent braking of the compressor impeller on the ATL.
If the engine changes from deceleration mode to load operation, the bypass air switchover valve is no longer actuated.
Shown: engine 177.9 from the front
| Electrical function schematic for charging | Engine 177.9 in model 290 up to model year 2021 | PE09.00-P-2050-97XBA | |
| Engine 176.9, 177.9 in model 217 Engine 176.9, 177.9 in model 222 |
PE09.00-P-2050-97SEL | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNL |