Thermal management, function - GF07.10-P-1012MMS

ENGINE 157.9 in MODEL 212, 218 as of model year 2014 

ENGINE 278.9 in MODEL 207, 212, 218 as of model year 2014 

Function requirements for thermal management, general 

• 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

Function sequence for charge air cooling

The function sequence for charge air cooling is described in more detail in the document Charging function. 

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

• IC (A1), vehicle speed via chassis CAN 1 (CAN E1) and chassis CAN 2 (CAN E2)
• Coolant temperature sensor (B11/4) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
• Charge air temperature sensor (B17/8)
• 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)
• Oil sensor (oil level, temperature and quality) (B40) (for engine 157)
• Crankshaft Hall sensor (B70), engine rpm
• Temperature sensor in the ME-SFI [ME] control unit
• Front SAM control unit with fuse and relay module (N10/1), outside temperature via the chassis CAN 1
• AAC control and operating unit (N22/7), status of A/C via the interior CAN (CAN B) and chassis CAN 1
• Electronic Stability Program control unit (N30/4) (except code 233 (DISTRONIC PLUS) or Electronic Stability Program Premium control unit (N30/7) (for code (233) DISTRONIC PLUS), wheel speed signal 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 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 
  Fig 1: Thermal Management Function Diagram

  Courtesy of MERCEDES-BENZ USA

Positions of two-disk thermostat 

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 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"
• 20% fan motor "ON", minimum rotational speed
• 90% fan motor "ON", maximum rotational speed

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 

After "ignition OFF", the fan motor continues to run for up to 6 min. if the coolant temperature or engine oil temperature is above the specified maximum value.

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

If the battery 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 charge air temperature is too high, the ME-SFI [ME] control unit no longer fully closes the boost pressure control flap depending on engine speed and load. Furthermore, the throttle valve of the throttle valve actuator (M16/6) can no longer be opened fully. 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 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.

	Electrical function schematic for heat management	MODEL 218	PE07.10-P-2712-97XAG
		MODEL 207	PE07.10-P-2712-97EAM
		MODEL 212	PE07.10-P-2712-97DAP
	Overview of system components for gasoline injection and ignition system with direct injection	ENGINE 157.9 in MODEL 212, 218 as of model year 2014 ENGINE 278.9 in MODEL 207, 212, 218 as of model year 2014	GF07.70-P-9998MM