GF07.10-P-1012MMC Thermal Management, Function
GF07.10-P-1012MMC Thermal Management, Function
- ENGINES 157.9 in MODEL 216.3, 221.0 /1
- ENGINES 278.9 in MODEL 216.3, 221.0 /1
Function requirements for thermal management, general points
- Circuit 87M (engine timing unit 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:
- The optimum operating temperature is reached faster
- Reduction of the exhaust gas emissions
- Fuel savings (up to around 4%)
- Improved heat comfort.
- Optimal main combustion point for a high load
Thermal management is performed based on the following sensors and signals:
- Coolant temperature sensor (B11/4)
- Intake air temperature sensor (B17)
- Pressure sensor downstream of throttle valve actuator (B28/7), engine load
- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far driver type calm or sporty)
- Oil sensor (oil level, temperature and quality) (B40) (for engine 157)
- Crankshaft Hall sensor (B70), engine speed
- Temperature sensor in the ME-SFI [ME] control unit
- AAC control unit (N22/1), status of the A/C and outside air temperature via the interior CAN (CAN B) and chassis CAN (CAN E)
- ESP control unit (N47-5), wheel speed via the chassis CAN
- Electric controller unit (VGS) (Y3/8), status of the transmission oil temperature via the drive train CAN (CAN C)
Function sequence for thermal management
The thermal management system is described in the following steps:
- Function sequence for heating system switch-off up to 05/2011
- Function sequence for two-disk thermostat heating
- Function sequence for fan control
- Function sequence for overheating protection
Function sequence for heating system switch-off up to 05/2011
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).
Function sequence for two-disk thermostat heating
The coolant temperature in the engine 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 adjusts the thermostat disc positions as needed and actuated for this by the ME-SFI [ME] control unit by means of a ground signal.
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 65°C
To optimize in-engine friction and thus save fuel, the coolant temperature can be raised to about 105°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 65 to 100°C
To optimize in-engine friction and thus save fuel, the coolant temperature can be raised to about 105°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 65 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 full load, 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 over about 115°C, the two-disk thermostat is always fully open (limp-home function), whether the heating element is energized or not.
If 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 via the chassis CAN and central CAN (CAN F) to the instrument cluster.
Function sequence for fan control
The ME-SFI [ME] 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 [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 AAC control unit sends the air conditioning status via the interior CAN and chassis CAN to the ME-SFI [ME] control unit.
Delayed fan switch off
The fan motor runs on for "ignition OFF" for up to 6 minutes if the coolant temperature or the temperature of the ME-SFI [ME] control unit has exceeded the prescribed maximum values or the heat input into the engine block before switching off the engine was very high.
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 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 ME-SFI [ME] control unit no longer fully opens 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).
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 on the multifunction display (A1p13) of the instrument cluster (A1). To do this, the ME-SFI control unit sends the corresponding signal via the chassis CAN and central CAN (CAN F) to the instrument cluster.
