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




GF07.10-P-1012MG Thermal Management, Function
ENGINES 271.8 in MODEL 204.0 /2 /3, 207.3 /4, 212.0 /2

Function requirements for thermal management, general points
^ Circuit 87 M ON (engine timing ON)
^ Engine running

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

- The optimum operating temperature is reached faster
- Reduction of the exhaust emissions
- Fuel savings (up to around 4%)
- Improved heating comfort

As of YoM 11
At cold temperatures the wide open throttle operation vent line heater element (R39/2) is actuated by the ME-SFI [ME] control unit. This prevents freezing of the crankcase ventilation system and any associated engine damage.

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

- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- Pressure sensor downstream of throttle valve (B28/7), engine load
- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far driver Model calm or sporty)
- Crankshaft Hall sensor (B70), engine speed
- Front SAM control unit with fuse and relay module (N10/1), outside air temperature via the chassis CAN (CAN E)
- Automatic air conditioning control and operating unit (N22/7), air conditioning system status over interior CAN (CAN B) and chassis CAN
- Instrument cluster (A1), vehicle speed via chassis CAN
- Electrically stability program control unit (N30/4) (except code (233) DISTRONIC PLUS) or Premium electrically stability program control unit (N30/7) (with code (233) DISTRONIC PLUS), wheel speed via chassis CAN

The Electronic Stability Program control unit (N30/4) will be introduced into service as of 1.3.2011 (model 204.0/2) or as of 1.6.2011 (model 204.3) in 2 variants:
- Electronic Stability Program control unit, basis variant (except code (233) DISTRONIC PLUS)
- Electronic Stability Program control unit, Premium variant (except code (233) DISTRONIC PLUS)

Up to 28.2.2011 or 31.5.2011 only the Electronic Stability Program control unit Basis variant will be used.

Function sequence for thermal management
The thermal management system is described in the following

^ Function sequence for heating system switch-off
^ Function sequence for heating the coolant thermostat
^ Function sequence for fan control
^ Function sequence for radiator shutters
^ Function sequence for overheating protection

Function sequence for heating system switch-off
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
Depending on the operating conditions (as a function of a characteristic map), the ME-SFI [ME] control unit actuates the heating element in the coolant thermostat (R48) using a ground signal. The voltage is supplied through circuit 87 M2
Heating causes the two-disk thermostat located in the coolant thermostat to open. In this way the coolant temperature of 80 to 105°C is regulated via the duty cycle.

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

^ Full throttling
^ Bypass mode
^ Mixed mode
^ Cooler mode





Two-disk thermostat positions

1 Coolant from engine
2 Coolant back to engine
3 Coolant to engine radiator
4 Coolant to heater heat exchanger

A Full throttling
B Short-circuit mode position
C Mixed mode position
D Radiator mode position

Full throttling
For a cold start the coolant thermostat is not heated.

No circulation of the coolant occurs whereby the coolant standing in the engine is warmed very quickly.

The heating circuit is also switched off by the heating system shutoff valve when the vehicle heating is switched off.

Bypass mode
From an outside temperature greater than 12°C and a coolant temperature of 45°C or from a coolant temperature of greater than 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.
The closing plate on the two-disk thermostat opens but dependent on the pressure (for the rotating coolant pump) from a pressure differential of greater than 0.7 bar (motor rpm greater than 4000 rpm).

Mixed-fuel mode
The mixed-fuel operation is enabled unheated if the coolant temperature reaches 103°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. The two-disk thermostat already opens heated at a coolant temperature of 80°C.

At partial load, the two-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:

- Intake air temperature greater than 38°C
- engine speed greater than 3000 rpm
- engine load greater than 30%
- Sporty driver

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 8 0°C.

Cooler mode
The coolant thermostat is heated constantly during radiator operation. The coolant only flows through the engine radiator.
If the coolant temperature is above about 110°C, the two-disk thermostat is open continuously, irrespective of heating (limp-home function).

If the 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 sends the appropriate signal over the chassis CAN to the instrument cluster. appropriate signal over the chassis CAN to the instrument cluster.

Function sequence for fan control
The ME-SFI [ME] control unit actuates the 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:

10% Fan motor "OFF"
20% Fan motor "ON", minimum rpm
90% Fan motor "ON", maximum rpm

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

The automatic air conditioning control and operating unit sends 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 radiator shutters
The radiator shutters are closed in order to lower the fuel consumption (by producing a lower aerodynamic drag). This also causes reduced engine compartment cooling and a dampening of engine noise emissions to the outside.
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 111°C and closed again at 99°C.

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 temperature or charge air temperature are too high the ignition timing is adjusted in the direction "retarded", dependent on the motor rpm and load. The correction by retarding the ignition timing is map-controlled by the ME-SFI [ME] control unit.

The retardation of the ignition timing point commences at a coolant temperature of approx. 90°C and a charge air temperature of Examples of ignition angle correction towards "retard":
- for coolant at 100°C, charge air at 20°C, and at full load ->2° crank angle
- for coolant at 100°C, charge air at 60°C, and at full load ->8° crank angle
- for coolant at 125°C, charge air at 60°C, and at full load ->11°

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.