Thermal Management, Function - GF07.10-P-1012MMG

ENGINE 276.9 in MODEL 166 up to model year 2016 

Function requirements for thermal management, general points 

• Circuit 87M (engine management ON)
• Engine runs

Thermal management, general 

The coolant temperature of the engine is regulated with the thermal management controlled by the ME-SFI [ME] control unit (N3/10). The following advantages arise from this:

• Rapid reaching of the optimal operating temperature
• Reduction of the exhaust emissions
• Fuel saving (up to about 4%)
• Improved heating comfort

The controlling of the thermal management is dependent on the following sensors and signals:

• Coolant temperature sensor (B11/4)
• Intake air temperature sensor (B17)
• Intake manifold intake air temperature sensor (B17/1)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Accelerator pedal sensor (B37), accelerator pedal actuation (how quickly and how far → vehicle type quiet or sporty)
• Crankshaft Hall sensor (B70), engine rpm
• Temperature sensor in the ME-SFI [ME] control unit
• Instrument cluster (A1), speed via the chassis CAN 2 (CAN E2) and chassis CAN 1 (CAN E1)
• SAM control unit (N10), outside temperature via the interior CAN (CAN B) and chassis CAN 1
• Automatic air conditioning control and operating unit (N22/7), air conditioning system status over interior CAN and chassis CAN 1
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN 1
• Fully integrated transmission controller unit (Y3/8), status of transmission oil temperature via drive train CAN (CAN C)

Function sequence for thermal management 

The thermal management is described in the following points:

• Function sequence for heating the two-disk thermostat 
• Function sequence for fan control 
• Function sequence for radiator shutters 
• Function sequence for overheating protection 

Function sequence for heating the two-disk thermostat 

The temperature of the coolant can be controlled variably by the heatable two-disk thermostat. There is a coolant thermostat heating element (R48) in the two-disk thermostat which is actuated a required by the ME-SFI [ME] control unit using a ground signal.

The two-disk thermostat can take four positions:

• Full throttling 
• Bypass mode 
• Mixed-fuel mode 
• Radiator operation 

Positions of two-disk thermostat 

Courtesy of MERCEDES-BENZ USA

Position for full throttling 

• Heating element deenergized, coolant temperature < 65°C The coolant thermostat is closed.

Position for short circuit mode 

• Heating element deenergized, coolant temperature < 100°C
• Heating element energized, coolant temperature < 65°C

According to the meaning of optimal in-engine friction and therefore fuel saving the coolant temperature can be increased to about 105°C in partial-load range (heating element deenergized).

Therefore the friction power can be improved due to a higher engine oil temperature and the mixture formation improved due to less fuel condensation on the cylinder barrels.

Position for mixed-fuel mode 

• Heating element deenergized, coolant temperature 100 to 115°C
• Heating element energized, coolant temperature 65 to 100°C

Position for radiator operation 

• Heating element deenergized, coolant temperature < 115°C
• Heating element energized, coolant temperature < 100°C

Through heating the two-disk thermostat (heating element energized) opens this and the coolant is led through the engine radiator.

For wide open throttle the two-disk thermostat is very quickly opened.

The coolant temperature can be lowered to about 80°C whereby best possible engine cooling and knock-free combustion are achieved.

Above an about 115°C coolant temperature the two-disk thermostat is always fully open independent of the flowrate through the heating element (limp-home function).

Function sequence for fan control 

The ME-SFI [ME] control unit actuates the fan motor (M4/7). Here the target fan speed is prescribed over a pulse width modulated signal by the ME-SFI [ME] control unit.

The duty cycle of the pulse width modulated signal is 10 to 90%.

Here for example the following mean.:

• 10% fan motor off "OFF"
• 20% fan motor "ON", minimum rpm
• 90% fan motor "ON", maximum rpm

For faulty actuation the fan motor rotates at its maximum rotational speed (fan emergency mode).

The AAC control and operating unit transmits the status of the A/C to the ME-SFI [ME] control unit via the interior CAN and chassis CAN 1.

Delayed fan switch off 

The fan motor runs on for "ignition OFF" for up to 6 minutes if the coolant temperature or the engine oil temperature has exceeded the prescribed maximum values.

The duty cycle of the pulse width modulated signal for delayed fan switch off is a maximum of 40%.

If the on-board electrical system voltage drops down a lot, the delayed fan switch off is suppressed.

Function sequence for radiator shutters 

The radiator shutters is closed in order to lower the fuel consumption (through having a lower aerodynamic drag).

This also causes reduced engine compartment cooling off and a dampening of external noise of the engine.

The radiator shutters actuator (Y84) is actuated by the ME-SFI [ME] control unit after the engine start by means of a ground signal. In this way the vacuum in the vacuum unit is built up and the radiator shutters closed by means of a linkage.

The radiator shutters are opened when the coolant temperature reaches 106°C and closed again at 98°C.

Function sequence for overheating protection 

In a case of thermal overload the overheating protection protects the catalytic converters against engine damage and overheating damage.

If the coolant or intake air temperature is too high, the ME-SFI [ME] control unit no longer fully opens the throttle valve actuator (M16/6), depending on engine speed and load. The ME-SFI [ME] control unit shortens the injection period of the fuel injectors (Y76) according to the lower air mass.

The ME-SFI [ME] control unit also actuates the coolant thermostat heating element so that the two-disk thermostat is fully open and all the coolant is cooled by the engine radiator.

If the coolant temperature is too high, a warning message is shown in the multifunction display (A1p13) on the instrument cluster (). To do this, the ME-SFI control unit sends the corresponding signal via chassis CAN 1 and chassis CAN 2 to the instrument cluster.

	Electrical function schematic for heat management		PE07.10-P-2712-97NAE
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