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

Engine 276.8 in model 217, 222 

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

Thermal management controlling is dependent on the following sensors and signals:

• Coolant temperature sensor (B11/4), coolant temperature
• Charge air temperature sensor (B17/8), charge air temperature
• 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
• Climate control, control unit (N22/1), status of A/C via the interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)
• IC (A1), vehicle speed via the user interface CAN (CAN HMI), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis FlexRay, powertrain control unit and drive train CAN
• Fully integrated transmission control unit (Y3/8n4), status of transmission oil temperature via drive train CAN

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 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:

• Position for full throttling 
• Position for short circuit mode 
• Position for mixed-fuel mode 
• Position for radiator operation 

Courtesy of MERCEDES-BENZ USA

Positions of two-disk thermostat 

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

Position for radiator operation 

• Heating element deenergized, coolant temperature < 115°C
• Heating element deenergized, 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 a coolant temperature of approx. 115°C, the two-disk thermostat is always fully opened (limp-home function) irrespective of the energization of the heating element).

Function sequence for fan control 

The powertrain control unit actuates the fan motor (M4/7). The actuation occurs here via the drive LIN (LIN C1) and all rpms between 0 and 100% can be set.

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

The climate control, control unit send the status of the A/C via the interior CAN, electronic ignition lock control unit, chassis FlexRay to the powertrain control unit and via the drive train CAN to the ME-SFI [ME] control unit.

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. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.

Function sequence for overheating protection 

In case of thermal overload, the overheating protection protects against engine damage and overheating damage to the catalytic converters (three-way catalytic converters).

If the coolant or intake air temperature is too high, the ME-SFI [ME] control unit no longer fully opens the throttle valve of the throttle valve actuator (M16/6), dependent 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. Furthermore the heating element in the coolant thermostat is actuated by the ME-SFI [ME] control unit so that the two-disk thermostat is fully opened and the whole coolant is cooled over the engine radiator.

If the coolant temperature is too high, a warning message in instrument cluster (A1). To do this the ME-SFI [ME] control unit transmits an appropriate signal via the drive train CAN, powertrain control unit, chassis FlexRay and electronic ignition lock control unit and via the user interface CAN (CAN HMI) to the IC.

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