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

Engine 276.8 in model 172.4 

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
• IC (A1), vehicle speed via chassis CAN 1 (CAN E1), the front SAM control unit with fuse and relay module (N10/1) and the chassis CAN 2 (CAN E2)
• Front SAM control unit with fuse and relay module, outside temperature via chassis CAN 1
• AAC control and operating unit (N22/7), status of A/C via the interior CAN (CAN B), front SAM control unit with fuse and relay module and chassis CAN 1
• Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN 1
• Fully integrated transmission control unit (Y3/8n4), status of transmission oil temperature via the 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 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 

Courtesy of MERCEDES-BENZ USA

Positions of two-disk thermostat 

Full throttling 

• Heating element de-energized, coolant temperature < 65°C

The coolant thermostat is closed.

Bypass mode 

• Heating element de-energized, coolant temperature < 100°C
• Heating element de-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 de-energized).

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.

Mixed-fuel mode 

• Heating element de-energized, coolant temperature 100 up to 115°C
• Heating element de-energized, coolant temperature 65 up to 100°C

Radiator operation 

• Heating element de-energized, coolant temperature < 115°C
• Heating element de-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 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 ME-SFI [ME] control unit actuates the internal combustion engine fan motor and air conditioning system with integrated control (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).

Its status is transmitted to the fan motor as a ground signal over the actuation line.

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 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 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 for cylinders 1 to 6 (Y76/1 to/6) 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 engine oil or 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 [ME] control unit transmits an appropriate signal via the chassis CAN 1, front SAM control unit with fuse and relay module and the chassis CAN 2 to the IC.

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