GF07.61-P-4012MAR ME Thermal Management, Function
GF07.61-P-4012MAR ME thermal management, function
- refinement package
- as of model year 09
Function requirements for thermal management, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
Thermal management, general points
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:
- Operating temperature is reached faster
- Reduction of the exhaust gas emissions
- Fuel savings (up to around 4%)
- Improved heat comfort.
Thermal management is performed according to 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 sensor (B37), accelerator pedal actuation (how fast and how far ->driver type calm or sporty)
- Crankshaft Hall sensor (B70), motor speed
- AAC [KLA] control and operating unit (N22), outside air temperature and air conditioning status over the interior CAN (CAN B) and engine compartment CAN (CAN C)
- ESP, SPS [PML] and BAS control unit (N47-5), vehicle speed over the engine compartment CAN
Thermal management function sequence
Thermal management consists of the following subfunctions:
^ Heating system switch-off function sequence
^ Two-disk thermostat heating function sequence
^ Fan control function sequence
^ Engine cooling function sequence
Heating system switch-off function sequence
To heat up the engine more quickly, the ME-SFI control unit switches off the heating system coolant circuit by actuating the heating system shutoff valve (Y16/2).
Two-disk thermostat heating function sequence
The coolant temperature can be varied by the two-disk heated thermostat. For this purpose, the two-disk thermostat has a two-disk thermostat heating element (R48), which can be actuated when necessary by the ME-SFI control unit by means of a ground signal.
The two-disk thermostat can be set to three positions:
^ Bypass mode
^ Mixed mode
^ Radiator operation
Component Identification:
Short-circuit operation position
Heating element deenergized Coolant temperature <100 °C
Heating element energized Coolant temperature <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 >115 °C
Heating element energized Coolant temperature >100 °C
Heating the two-disk thermostat (heating element energized) causes it to open and the coolant passes through the engine radiator.
At full load, the two-disk thermostat can be opened very quickly by heating. 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.
Fan control function sequence
The ME-SFI control unit actuates the engine and air conditioning electric suction fan with integrated control (M4/7). The nominal fan speed is specified via a PWM signal by the ME-SFI [ME] control unit. The duty cycle of the PWM signal is 10 to 90%.
Meaning:
10% Fan motor "OFF"
20% Fan motor "ON", minimal rpm
90% Fan motor "ON", maximum rpm
If actuation is faulty, the air fan rotates at the maximum rotational speed (fan emergency mode).
The AAC [KLA] control and operating unit sends the air conditioning status over the interior and engine compartment CAN to the ME-SFI control unit.
Delayed fan switch off
After "ignition OFF", the fan motor continues to run for up to 5 min. if the coolant temperature or engine oil temperature is above the specified maximum value.
The PWM signal duty cycle is 40 % maximum while the delayed fan switch-off is active.
If the battery voltage is dropping too much, the delayed fan switch-off is stopped.
Engine cooling function sequence
The engine oil temperature is detected by the ME-SFI [ME] control unit via the oil temperature sensor (B1).
If the engine oil temperature is too high, the ME-SFI control unit, through the additional engine oil fan relay (K25), actuates the oil cooler fan (M4/1). This fan cools the engine oil in the additional engine oil cooler.
If the engine oil or coolant temperature is too high, a warning message is displayed on the left multifunction display (A1p13) of the instrument cluster (A1). To do this the ME-SFI [ME] control unit sends an appropriate signal via the engine compartment-CAN to the instrument cluster.
