ME thermal management, function - GF07.61-P-4012MAS
ENGINE 156.984 in MODEL 216.377, 221.077 /177 as of Model Year 09 /AEJ 08
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), load request by driver
- Crankshaft Hall sensor (B70), motor speed
- AAC control unit (N22/1), outside air temperature and air conditioning status over the interior CAN (CAN B) and chassis CAN (CAN E)
- ESP control unit (N47-5), vehicle speed over the chassis 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 contains the two-disk 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
- Radiator operation
Two-disk thermostat positions
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 specified fan speed is set by the ME-SFI control unit with a pulse width modulated signal (PWM signal).
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 control unit sends the air conditioning status over the interior CAN and chassis 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 by the oil temperature sensor.
If engine oil temperature is too high, the ME-SFI control unit actuates the engine coolant circulation pump (M45) through the circulation pump relay (N10/2kQ). This pumps coolant through the engine oil heat exchanger, thus cooling the engine oil.
If engine oil or coolant temperature is too high, a warning message is shown on the multifunction display (A1p13) of the instrument cluster (A1). To do this, the ME-SFI control unit sends the corresponding signal over the chassis CAN and central CAN (CAN F) to the instrument cluster.
| Electrical function schematic for thermal management | Model 216 | PE07.61-P-2791-97CAC | |
| Model 221 | PE07.61-P-2791-97SAC | ||
| ME-SFI [ME] control unit, component description | N3/10 | GF07.61-P-6000MAS |