Charging, function - GF09.00-P-2000MMR
ENGINE 157.9, 278.9 in MODEL 166 up to model year 2016
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.
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 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 boost pressure control is actuated on a characteristics map and load-dependent basis by the ME-SFI [ME] control unit for boost pressure control. To do this the ME-SFI [ME] control unit evaluates the following sensors and functions of the engine management:
- Charge air temperature sensor (B17/8)
- Pressure sensor downstream of left cylinder bank air filter (B28/4)
- Pressure sensor downstream of right cylinder bank air filter (B28/5)
- Pressure sensor upstream of throttle valve (B28/6), boost pressure
- Pressure sensor downstream of throttle valve (B28/7), boost pressure
- Accelerator pedal sensor (B37), load request made by driver
- Crankshaft Hall sensor (B70), engine rpm
- Knock control, transmission overload protection, overheating protection
A maximum boost pressure of 900 mbar is built up in wide open throttle operation.
To reduce the boost pressure in partial-load range, the exhaust flows that drive the turbine wheels 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 flaps over a linkage, 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 turbine wheels, thereby 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.
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 distributor 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 ATL 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 actuator (M16/6).
Shown: the flow pattern of the intake air
Shown: flow pattern of the intake air/charge air
Shown: flow pattern of the charge air
Shown: boost pressure control shown with a duty cycle of (t i ) <5%
Shown: boost pressure control shown with a duty cycle of (t i ) >5%
Function sequence for charge air cooling
Through charge air cooling the charge air temperature is kept < 60°C (for engine 278) or < 65°C (for engine 157) for a 20°C ambient temperature.
The cooled air downstream of the charge air coolers has a 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 water/charge air cooler. The water/charge air cooler is attached to the low-temperature circuit with the low-temperature cooler and charge air cooler circulation pump (M44).
If the charge air temperature >35°C the charge air cooler circulation pump is actuated by the ME-SFI [ME] control unit via the ATL relay (F58kO).
If the charge air temperature falls below 25°C, the charge air cooler circulation pump is switched off again.
The charge air temperature is detected between the charge air cooler and the throttle valve actuator by the charge air temperature sensor and reported to the ME-SFI [ME] control unit in the form of a voltage signal.
Shown: low-temperature circuit
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