Charging, Function - GF09.00-P-2000MMX
ENGINE 276.8 in MODEL 166
as of model year 2016
ENGINE 276.8 in MODEL 292
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. This raises the engine torque and engine power output. The fuel quantity corresponding to the increased air mass is metered by the ME-SFI [ME] control unit (N3/10).
With forced induction, the flow energy of the exhaust gases is used to drive the ATL.
The ATLs draw fresh air through the air filters into the compressor inlets, from where it passes through the compressor outlets in the charge air pipes to the charge air cooler.
Due to the high rotational speed of the compressor impellers and the resulting high volumetric flow rates, the intake air becomes compressed in the charge air pipes.
The compressed charge air flows via the charge air pipes upstream of the charge air cooler to the charge air cooler. This then cools the charge air heated up by the compression and routes it to the charge air distributor.
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 charge air cooling
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 [ME] control unit evaluates the following sensor signals and functions of the engine management:
- Charge air temperature sensor (B17/8), charge air temperature
- Pressure sensor downstream of air filter, left cylinder bank (B28/4), intake pressure
- Pressure sensor downstream of air filter, right cylinder bank (B28/5), intake pressure
- Pressure sensor upstream of throttle valve (B28/6), boost pressure upstream of throttle valve
- Pressure sensor downstream of throttle valve (B28/7), boost pressure downstream of throttle valve
- Accelerator pedal sensor (B37), load request made by driver
- Crankshaft Hall sensor (B70), engine rpm
- 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 cell with vacuum from the vacuum pump. The vacuum cells 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 then 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 compressor impellers (bypass), whereby the boost pressure is then regulated and compressor speed limited.
In this way the boost pressure can be adapted to the current load demand on the engine.
If there is leakage in the line between the vacuum pump and the vacuum cells then no build up of boost pressure is possible.
To monitor the current boost pressure, the pressure sensor upstream of the throttle valve sends the corresponding voltage signal to the ME-SFI [ME] control unit. The pressure sensors downstream of the air filter serve to allow the ME-SFI [ME] control unit to monitor the charging. The charge air temperature is detected in the charge air cooler by the charge air temperature sensor and sent to the ME-SFI [ME] 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 [ME] 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 [ME] 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.
Shown: the flow pattern of the intake air
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.
In the case of rapid closing of the throttle valve, a charge pressure wave therefore runs back to the exhaust gas ATLs. 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 the bypass air switchover valves prevents this through rapid depressurization through a bypass in the intake side of the ATL. 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 bypass air switchover valves.
Schematic display of ATL with left divert air switchover valve
If the ME-SFI [ME] control unit detects through the actual value potentiometer 1 and 2 (M16/6r1, M16/6r2) that the throttle valve has closed, and therefore the deceleration mode, then the bypass air switchover valves are actuated. 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.
View of right ATL with sectional view of right divert air switchover valve
Function sequence for charge air cooling
Charge air cooling - general
The charge air cooling maintains a charge air temperature of < 60°C at 20°C ambient temperature. The cooled air downstream of the charge air cooler has higher density. This increases the cylinder charge, and therefore engine performance. The tendency to knock is also reduced and also the tendency to generate nitrogen oxide (NOx) is reduced by low exhaust temperatures.
Both cylinder banks are fitted with a common coolant-cooled charge air cooler. The 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).
Charge air cooling (except model 166 063)
If the charge air temperature is > 35°C, the ME-SFI [ME] control unit actuates the low-temperature circuit circulation pump 1 over the ATL relay (F58kO). If the charge air temperature falls 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 and sent to the ME-SFI [ME] control unit using a voltage signal.
Shown on low-temperature circuit (except on model 166.063)
Charge air cooling (on model 166 063)
If the charge air temperature is > 35°C, cooling output is requested by the ME-SFI [ME] control unit from the powertrain control unit (N127). This actuates circulation pump 1 of the low-temperature circuit via the drivetrain LIN (LIN C3). If the charge air temperature falls below 25°C, the low-temperature circuit circulation pump 1 is switched off again.
The low-temperature circuit temperature sensor (B10/13) records the coolant temperature in the low-temperature circuit and transmits it to the powertrain control unit via a voltage signal.
The charge air temperature is detected in the charge air cooler by the charge air temperature sensor and sent to the ME-SFI [ME] control unit using a voltage signal.
View of low-temperature circuit (on model 166.063)
| Electrical function schematic for charging | PE09.00-P-2050-97NBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | ENGINE 276.8 in MODEL 166 (except 166.063) as of model year 2016 ENGINE 276.8 in MODEL 292 |
GF07.70-P-9998MMX | |
| ENGINE 276.8 in MODEL 166.063 as of model year 2016 | GF07.70-P-9998MMM |