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

ENGINE 272.9 (except 272.982) in MODEL 204.0/2 as of model year 2009 

ENGINE 272.9 (except 272.983) in MODEL 212 

ENGINE 272.9 (except 272.984) in MODEL 207 

ENGINE 272.9 in MODEL 204.9 

ENGINE 273.9 in MODEL 207, 212 

Function requirements for thermal management, general points 

Thermal management, general 

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

Thermal management is performed based on the following sensors and signals:

Function sequence for thermal management 

The thermal management system is described in the following steps:

Function sequence for cutout of the heating system (for engine 272) 

To heat up the engine more quickly, the ME-SFI [ME] control unit switches off the heating system coolant circuit by actuating the heating system shutoff valve (Y16/2).

Function sequence for heating the coolant thermostat 

The coolant temperature can be varied by the heatable coolant thermostat (Y110). For this purpose the heatable coolant thermostat is fitted with a heating element which the ME-SFI [ME] control unit actuates with a ground signal as required.

When heated, the three-disk thermostat opens in the coolant thermostat. In this way the coolant temperature of 80 to 100°C is regulated via the duty cycle.

The three-disk thermostat can be set in four positions:

Position of the three-disk thermostat 

Fig 1: Identifying Three-Disk Thermostat Position
G10084289Courtesy of MERCEDES-BENZ USA

Full throttling 

For a cold start the coolant thermostat is not heated. The heating circuit is also switched off for engine 272 by the heating system shutoff valve when the vehicle heating is switched off.

The coolant in the engine now warms up very quickly. The engine oil is warmed up over the heat exchanger at the front on the engine. The closing plate on the three-disk thermostat opens but dependent on the pressure (by the rotating coolant pump) from about 3500 rpm (short circuit operation).

Bypass mode 

From an outside temperature >12°C and a coolant temperature of 45°C or from a coolant temperature of > 70°C, switching to short-circuit operation takes place.

For short-circuit operation the coolant thermostat is heated less and part of the coolant flows back into the engine circuit. Short-circuit operation can be 'choked', so that the heater responds more quickly.

Mixed-fuel mode 

The mixed-fuel operation is enabled if the coolant temperature reaches 98°C for the first time after the start.

For mixed-fuel operation the coolant thermostat is heated in such a way that the coolant flows through the engine radiator and the engine circuit.

At partial load, the three-disk thermostat regulates at an increased coolant temperature of around 100°C.

In order to prevent critical coolant temperatures from occurring, the range of increased coolant temperature is lowered under the following conditions:

The coolant temperature is thus lowered according to outside air temperature. If outside air temperature is below 12°C, the temperature is lowered to about 90°C and if outside air temperature is above 12°C, it is lowered to about 80°C.

Cooler mode 

The coolant thermostat is heated constantly during radiator operation. The coolant only flows through the engine radiator.

If coolant temperature is above about 110°C, the three-disk thermostat is open continuously, irrespective of heating (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).

The specified fan speed is set by the ME-SFI [ME] control unit with a pulse width modulated signal (PWM signal).

The duty cycle of the PWM signal is 10 to 90%.

This means, for example:

0% fan motor "OFF"

0% fan motor "ON", minimum rpm

0% fan motor "ON", maximum rpm

If actuation is faulty, the air fan motor rotates at the maximum rotational speed (fan emergency mode).

The automatic air conditioning control and operating unit transmits the air conditioning status via the interior and chassis CAN to the ME-SFI [ME] control unit.

Delayed fan switch off 

With "ignition OFF", the fan motor runs on for up to 5 min. if the coolant temperature or engine oil temperature (calculated from the temperature model) has exceeded the specified maximum values.

The PWM signal duty cycle is 40% maximum while the delayed fan switch off is active.

If the battery voltage drops too much during this time, delayed fan switch off is stopped.

Function sequence for overheating protection 

In case of thermal overload, the overheating protection protects against engine damage and overheating damage to the firewall catalytic converter.

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 time of the injection valves (Y62) according to the lower air mass.

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

IMPORTANT If engine oil or coolant temperature is too high, a warning message is shown in the multifunction display (A1p13) on the instrument cluster (A1). For this purpose, the ME-SFI [ME] control unit transmits the appropriate signal over the chassis CAN to the instrument cluster.

  Electrical function schematic for heat management MODEL 204 PE07.10-P-2712-97FAB
MODEL 207 PE07.10-P-2712-97EAB
MODEL 212 PE07.10-P-2712-97DAB
  Overview of system components motor electronics (ME-SFI) fuel injection and ignition system   GF07.61-P-9997MI
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