Thermal Management, Function - GF07.10-P-1012MNL
Engine 176.9, 177.9 in model 217
Engine 176.9, 177.9 in model 222
Engine 177.9 in model 290
up to model year 2021
Function requirements, general
- Engine runs
The ME-SFI [ME] control unit (N3/10) detects the engine running via the evaluation of the crankshaft Hall sensor signals (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.
Thermal management, general
The ME-SFI [ME] control unit regulates the engine coolant temperature via the heat management.
The following advantages arise from this:
- Rapid reaching of the optimal operating temperature
- Reduction of the exhaust emissions
- Fuel savings
- Rapid heating of the vehicle interior
The ME-SFI [ME] control unit reads in the following signals to the control the heat management:
- Coolant temperature
Coolant temperature sensor (B11/4)
- Charge air temperature
Left charge air temperature sensor (B17/14)
Right charge air temperature sensor (B17/15)
- Engine load
Pressure sensor downstream of left throttle valve (B28/22)
Pressure sensor downstream of right throttle valve (B28/23)
- Accelerator pedal position
The powertrain control unit (N127) reads in the accelerator pedal sensor (B37) signals directly, and transmits the accelerator pedal position via the drive CAN (CAN C1) to the ME-SFI [ME] control unit.
- Engine speed
Crankshaft Hall sensor
- Temperature sensor in the ME-SFI [ME] control unit
The ME-SFI [ME] control unit also evaluates the following variables:
- Status of the air conditioning system for rotational speed and torque adjustment
The climate control, control unit (N22/1) transmits the status via the interior CAN (CAN B), the electronic ignition lock control unit (N73), the suspension FlexRay (Flex E), the powertrain control unit, and the drive CAN to the ME-SFI [ME] control unit.
- Vehicle speed
The instrument cluster (A1) transmits the vehicle speed via the user interface CAN (CAN HMI), the electronic ignition lock control unit, the chassis FlexRay, the powertrain control unit and the drive train CAN to the ME-SFI [ME] control unit.
- Wheel speed
The Electronic Stability Program control unit (N30/4) transmits the wheel speeds via the chassis FlexRay, the powertrain control unit and the drive train CAN to the ME-SFI [ME] control unit.
- Transmission oil temperature
The fully integrated transmission control unit (Y3/8n4) or electric controller unit control unit (Y3/8n4) (for model 290) transmits the transmission oil temperature via the drive CAN to the ME-SFI control unit.
- Outside temperature
The front SAM control unit (N10/6) transmits information on the outside temperature via the interior CAN, electronic ignition lock control unit, suspension FlexRay, powertrain control unit and drive CAN to the ME-SFI [ME] control unit.
Schematic diagram of the high temperature circuit
The thermal management is described in the following points:
- Coolant thermostat closed-loop control
- Charge air cooling
- Fan control
- Overheating protection
Coolant thermostat closed-loop control
The temperature of the coolant can be controlled variably by the heatable two-slide thermostat. There is a coolant thermostat heating element in the two-slide thermostat which is actuated as required by the ME-SFI control unit using a ground signal.
The two-slide thermostat can assume five positions:
- Closed
- Bypass mode
- Mixed mode
- Radiator operation
- Fail-safe mode
Closed
At a coolant temperature < 80°C and an engine speed < 3000 rpm, both valves on the two-valve thermostat are closed completely.
Shortening of the engine warm-up phase by stationary coolant leads to fuel saving and therefore reduction of the CO2
output.
Bypass mode
- Heating element deenergized (coolant temperature 80 to 105°C)
- Heating element energized (coolant temperature 40 to 65°C) In partial-load range, the coolant temperature can be raised to approx. 105°C (heating element deenergized). Therefore the friction power can be improved due to a higher engine oil temperature and the mixture formation improved due to less fuel condensation on the cylinder barrels.
Mixed mode
- Heating element deenergized (coolant temperature 105 to 120°C)
- Heating element energized (coolant temperature 65 to 90°C)
Radiator operation
- Deenergized heating element (coolant temperature > 120°C)
- Energized heating element (coolant temperature > 90°C) Through heating the two-slide thermostat (heating element energized) this opens and the coolant is led through the engine radiator. For wide open throttle the two-slide thermostat is very quickly opened. The coolant temperature can be lowered whereby the best possible engine cooling and knock-free combustion are achieved.
Fail-safe mode
To avoid damage, the failsafe operation is initiated for stationary coolant and an engine speed > 3, 000 rpm. The coolant is passed back over the differential pressure disc to the engine (short circuit).
Above a coolant temperature of about 120°C, the two-disk thermostat is always fully open independent of the supply to the heating element (limp-home function).
Charge air cooling (engine 176.9)
The charge air cooling keeps the charge air temperature < 60°C at 20°C ambient temperature. The cooled air downstream of the charge air coolers has a higher density. This increases the cylinder charge, and therefore engine performance.
The tendency to knock is reduced due to lower exhaust temperatures and there is reduced development of nitrogen oxides (NOx ). Each cylinder bank has a coolant-cooled charge air cooler, which is connected to the low temperature circuit.
The coolant in the low-temperature circuit is constantly circulated to prevent overheating at certain points in the circuit. For this purpose, the low-temperature circuit circulation pump 1 (M43/6) is steadily controlled as required by the powertrain control unit via the drive LIN (LIN C3).
The closed-loop control depends, among other things, on the following variables:
- Ambient temperature
- Charge air temperature
- Engine load
The coolant temperature in the low-temperature circuit is detected via the low-temperature circuit temperature sensor (B10/13), which sends its signal to the powertrain control unit.
The charge air temperature is detected in the charge air cooler by the left and right charge air temperature sensors and sent to the ME-SFI control unit with a voltage signal.
For the appropriate distribution of the flow volume of the coolant in the low-temperature circuit, the low-temperature circuit switchover valve (Y73/1) is actuated by the powertrain control unit via the powertrain LIN.
Schematic diagram of low-temperature circuit (engine 176.9)
Charge air cooling (engine 177.9)
In engine 177.9, the ME control unit and the transmission oil heat exchanger for the automatic transmission and the transfer case are also connected. In addition, a wheel arch cooler is integrated in the low-temperature circuit to increase the cooling surface.
In addition to low-temperature circuit circulation pump 1, low-temperature circuit circulation pump 2 (M43/7) and low-temperature circuit circulation pump 3 (M43/8) are integrated into the low-temperature circuit and ensure an appropriate flow volume for providing the required cooling output.
To ensure correspondingly consistent distribution of the flow volume, the low-temperature circuit switchover valve is also actuated by the powertrain control unit via the powertrain LIN.
Schematic diagram of low-temperature circuit (engine 177.9)
Fan control
The powertrain control unit communicates via the powertrain LIN with the fan motor (M4/7). For actuation, the powertrain control unit transmits the target fan rotation speed to the fan motor. The fan motor transmits its status to the powertrain control unit.
In the case of a fault in the signal line (loss of frequency) by the powertrain control unit the fan motor switches itself to the maximum rpm (fan emergency mode).
The climate control, control unit transmits the status of the air conditioning system and a fan request via the interior CAN, electronic ignition lock control unit, and suspension FlexRay to the powertrain control unit. If the powertrain control unit does not receive a valid fan request, the fan motor is actuated at maximum rpm.
Delayed fan switch off
The fan motor runs at ignition off for up to 5 minutes if the coolant temperature, the temperature of the ME-SFI control unit, or a characteristics map calculated based on engine load, coolant temperature, vehicle speed, and outside temperature (averaged over the last 6 min) have exceeded the specified limits. If the battery voltage drops down a lot, the delayed fan switch off is suppressed.
The delayed fan switch off is not broken off by "ignition ON". When starting the engine in delayed fan switch off the fan regulation for normal operation is suppressed until the delayed fan switch off is completed.
Overheating protection
In a case of thermal overload the overheating protection protects the catalytic converters against engine damage and overheating damage. To do this, the ME-SFI control unit reads in the signals of the coolant temperature sensor and the oil sensor (oil level, temperature, and quality) (B40) directly.
The following measures are taken for overheating protection:
- Ignition control in "retarded" direction depending on the engine load and engine speed from a coolant temperature of approx. 90°C and a charge air temperature of approx. 20°C.
- The opening of the throttle valves is downsized via the left throttle valve actuator motor (M16/60m1) and the right throttle valve actuator motor (M16/61m1) depending on engine load and rotational speed.
- The injection duration is adjusted to the lower air mass. To do this the ME-SFI [ME] control unit actuates the following assembly parts:
- Cylinder 1 fuel injector (Y76/1)
- Cylinder 2 fuel injector (Y76/2)
- Cylinder 3 fuel injector (Y76/3)
- Cylinder 4 fuel injector (Y76/4)
- Cylinder 5 fuel injector (Y76/5)
- Cylinder 6 fuel injector (Y76/6)
- Cylinder 7 fuel injector (Y76/7)
- Cylinder 8 fuel injector (Y76/8)
- The injection quantity is reduced at a coolant temperature of 106°C on the basis of the characteristics map.
- The slide valve in the coolant thermostat is opened completely by actuating the coolant thermostat heating element.
If the engine oil or coolant temperature is too high, a warning message in instrument cluster is shown. To do this, the ME-SFI control unit transmits a corresponding request via the engine CAN (CAN C), powertrain control unit, suspension FlexRay, electronic ignition lock control unit, and user interface CAN to the instrument cluster.
| Electrical function schematic for heat management | Engine 177.9 in model 290 up to model year 2021 | PE07.10-P-2712-97XBA | |
| Engine 176.9, 177.9 in model 217 Engine 176.9, 177.9 in model 222 | PE07.10-P-2712-97SEL | ||
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