Thermal management, function - GF07.10-P-1012MMW
ENGINE 276.9 in MODEL 212.095 as of model year 2014
Function requirements for thermal management, general points
- Circuit 87M (engine timing ON)
- Engine running
The function requirements "internal combustion engine running" includes all function sequences of the fuel low pressure and high-pressure circuit, as described in the function "fuel supply".
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:
- Optimum operating temperature is reached faster
- Reduction of the exhaust emissions
- Fuel savings (up to approx. 4%)
- Improved heat comfort.
Thermal management is performed based on the following sensors and signals:
- Coolant temperature sensor (B11/4)
- Intake air temperature sensor (B17)
- Intake manifold intake air temperature sensor (B17/1)
- Pressure sensor downstream of throttle valve (B28/7), engine load
- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far driver type calm or sporty)
- Crankshaft Hall sensor (B70), engine speed
- Temperature sensor in the ME-SFI [ME] control unit
- Front SAM control unit with fuse and relay module (N10/1), outside air temperature via chassis CAN 1 (CAN E1)
- Automatic air conditioning control and operating unit (N22/7), status of air conditioning system via interior CAN (CAN B) and chassis CAN 1
- IC (A1), vehicle speed via chassis CAN 2 (CAN E2)
- Regenerative braking system control unit (N30/6), wheel speed via the chassis CAN 1
- Fully integrated transmission control unit (Y3/8n4), status of transmission oil temperature via drive train CAN (CAN C)
Function sequence for thermal management
The thermal management system is described in the following steps:
- Function sequence for two-disk thermostat heating
- Function sequence for fan control
- Function sequence for radiator shutters
- Function sequence for overheating protection
Function sequence for two-disk thermostat heating
The coolant temperature can be variably controlled by the heatable two-disk 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-fuel mode
- Cooler mode
Two-disk thermostat positions
Short-circuit mode position
Heating element deenergized for coolant temperature <100°C
Heating element energized for coolant temperature <65°C
To optimize in-engine friction and thus save fuel, the coolant temperature can be raised to about 105°C in 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 mode position
Heating element deenergized for coolant temperature 100 to 115°C
Heating element energized for coolant temperature 65 to 100°C
Radiator mode position
Heating element deenergized for coolant temperature >115°C
Heating element energized for 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 wide open throttle, the two-disk thermostat can be opened very quickly. The coolant temperature can be lowered in the process to about 80°C whereby the best possible engine cooling and knock-free combustion is achieved.
When coolant temperature is above 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 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 "OFF"
- 0% fan motor "ON", minimum rotational speed
- 0% fan motor "ON", maximum rotational speed
If actuation is faulty, the air fan motor rotates at the maximum rotational speed (fan emergency mode). Its status is transmitted to the fan motor as a ground signal over the actuation line. The automatic air conditioning control and operating unit transmits the air conditioning status via the interior and chassis CAN 1 to the ME-SFI [ME] control unit.
Delayed fan switch off
After "ignition OFF", the fan motor continues to run for up to 6 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 on-board electrical system voltage drops too much during this time, delayed fan switch off is stopped.
If actuation is faulty, the air fan motor rotates at the maximum rotational speed (fan emergency mode).
Its status is transmitted to the fan motor as a ground signal over the actuation line. The automatic air conditioning control and operating unit transmits the air conditioning status via the interior and chassis CAN 1 to the ME-SFI [ME] control unit.
Delayed fan switch off
After "ignition OFF", the fan motor continues to run for up to 6 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 on-board electrical system 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 off 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 106°C and closed again at 98°C.
Function sequence for overheating protection
In case of thermal overload, the overheating protection protects against engine damage and overheating damage to the 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 on the throttle valve actuator (M16/6), depending on engine speed and load. The ME-SFI [ME] control unit shortens the injection time of the fuel injectors (Y76) according 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. To do this, the ME-SFI control unit sends the corresponding signal via chassis CAN 1 to the front SAM control unit with fuse and relay module and via chassis CAN 2 to the IC.
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