GF07.10-P-1012MAW Thermal Management, Function
GF07.10-P-1012MAW Thermal Management, Function
ENGINES 156.9 in MODEL 204.0 /2 /3, 212.0 /2
Function requirements for thermal management, general
^ Circuit 87M (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
Thermal management is performed based on the following sensors and signals:
- Oil temperature sensor (B1)
- LH and RH hot film MAF sensor (B2/6, B2/7), engine load
- Coolant temperature sensor (B11/4)
- Intake air temperature sensor (B17)
- Accelerator pedal module (B37), load request by driver
- Crankshaft Hall sensor (B70), engine speed
- AAC control and operating unit (N22/7), outside air temperature and air conditioning system status over the interior CAN (CAN B) and chassis CAN (CAN E)
- Electronic stability program control unit (N30/4) or Premium electronic stability program control unit Premium (N30/7) (on model 212 with DISTRONIC PLUS), vehicle speed via chassis CAN
Function sequence for thermal management
The thermal management system is described in the following Operation steps:
^ Function sequence for heating system switch-off
^ Function sequence for two-disk thermostat heating
^ Function sequence for fan control
^ Function sequence for engine cooling (except code (P98) Black Series)
^ 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 two-disk thermostat heating
The coolant temperature can be varied by the two-disk heated thermostat. For this purpose, the two-disk thermostat contains the coolant thermostat heating element (R48), which the ME-SFI control unit actuates with a ground signal as required.
The two-disk thermostat can be set to three positions:
^ Bypass mode
^ Mixed mode
^ Cooler mode
Two-disk thermostat positions
A Short-circuit mode position
B Mixed mode position
C Radiator mode position
a Coolant from engine
b Coolant to radiator
c Coolant back to engine
Short-circuit operation position
Heating element deenergized Coolant temperature less than 100°C
Heating element energized coolant temperature less than 60 °C
To optimize in-engine friction and thus save fuel, the coolant temperature can be raised to about 100°C in the partial-load range (heating element is deenergized).
The friction power is reduced by the higher engine oil temperature and mixture formation is improved by reducing the fuel condensation in the cylinder barrels.
Mixed fuel operation position
Heating element deenergized Coolant temperature 100 to 115°C
Heating element energized Coolant temperature 60 to 100°C
Radiator operation position
Heating element deenergized Coolant temperature greater than 115°C
Heating element energized Coolant temperature greater than 100°C
Heating the two-disk thermostat (heating element energized) causes it to open and the coolant passes through the engine radiator.
At wide open throttle, the two-disk thermostat can be opened very quickly. The coolant temperature can be lowered in the process to about 85°C whereby the best possible engine cooling and knock free combustion is achieved.
When coolant temperature is over about 115°C, the two-disk thermostat is always fully open (limp-home function), whether the heating element is energized or not.
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 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 engine cooling (except code (P98) Black Series)
The ME-SFI control unit detects the engine oil temperature through the oil temperature sensor.
If the engine oil temperature is too high, the ME control unit actuates the oil cooler fan motor (K25) through the oil cooler fan motor relay (M4/1). This cools the engine oil in the auxiliary engine oil cooler.
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 front and rear throttle valve actuators (M16/3, M16/4) are no longer fully opened by the ME-SFI control unit, 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 heating element so that the two-disk thermostat is fully open and all the coolant is cooled by 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 (A1). For this purpose, the ME-SFI [ME] control unit transmits the appropriate signal over the chassis CAN to the instrument cluster.
