Thermal Management, Function - GF07.10-S-1012TRJ
Engine 274 in model 447.6/7
with code XM0 (Facelift)
Function requirements for thermal management, general points
- Circuit 87M ON (Engine management ON)
- Engine running (3).
Thermal management, general
The coolant temperature of the engine (3) is regulated by means of thermal management controlled by the ME-SFI [ME] control unit (N3/34).
This is dependent on the following sensors and signals:
- Coolant temperature sensor (B11/21)
- Charge air temperature sensor upstream of throttle valve (B17)
- Charge air temperature sensor downstream of throttle valve (B17/16)
- Intake manifold pressure sensor (B28/24)
- Accelerator pedal module (B37/4)
- Crankshaft Hall sensor (B70/2)
- Signal acquisition and actuation module control unit (SAM) (N10/1), outside temperature
- Air conditioning system control and operating unit (AAC-V & AAC-H) (S98) (with code HH4 (THERMOTRONIC automatic climate control) or with code HH9 (Semiautomatically controlled air conditioning system, TEMPMATIC)), air conditioning system status
- Electronic Stability Program (ESP) control unit (N30/4) for wheel speed
- Fully integrated transmission control (VGS) electric controller unit (N15/11) (Automatic transmission with code G42 (7G-TRONIC PLUS)), transmission oil temperature
- Fully integrated transmission control (VGS) electric controller unit (N15/15) (Automatic transmission with code G43 (9G-TRONIC)), transmission oil temperature
Coolant circuit, shown schematically
Heat management
The thermal management is described in the following points:
- Coolant thermostat regulation
- Overheating protection
- Fan control
Coolant thermostat regulation
The opening and closing of the ball rotary valve (48b) in the coolant thermostat (48) is realized by temperature-influenced expansion and contraction of the wax expansion element (48a) in a temperature range from approx. 98 to 108°C.
In addition, actuation of the coolant thermostat heating element (R48/4) can be used to perform the opening and closing of the coolant thermostat (48) variably and depending on the engine requirements.
For this purpose, the ME-SFI [ME] control unit actuates the thermostat heating element (R48/4) with a ground signal depending on the operating conditions.
The coolant thermostat (48) can take the following positions dependent on the coolant temperature and the actuation by the ME-SFI [ME] control unit (N3/34):
- Closed
- Open (mixed-fuel mode)
- Open (radiator operation)
View of coolant thermostat closed
Closed
The ball rotary slide (48b) of the coolant thermostat (48) is closed if the following conditions are fulfilled:
- Coolant temperature below approx. 98°C
- Thermostat heating element (R48/4) de-energized
- No wide open throttle request
In this position the coolant flows through the engine circuit and the heater heat exchanger as required (4). The engine radiator (1) is not flowed through.
Open (mixed-fuel mode)
The ball rotary slide (48b) begins to open if one of the following conditions is fulfilled:
- A coolant temperature of approx. 98°C is reached for the first time after starting (no full load request).
- Thermostat heating element (R48/4) is energized.
In a coolant temperature range of approx. 98 to 108°C or depending on energization of the thermostat heating element (R48/4), the wax expansion element (48a) starts to expand and actuates the ball rotary valve (48b). This releases the connection to the engine radiator (1). The opening cross-section of the ball rotary slide (48) is adapted according to the temperature of the expanding wax element (48a). The coolant flow to the engine radiator (1) is varied in this way.
Open (radiator operation)
Where a coolant temperature of approx. 108°C is exceeded, the ball rotary valve (48b) is fully opened and the coolant can flow via the radiator (1) in an unrestricted manner.
For a coolant temperature of greater than 85°C and an open circuit request the ball rotary slide (48) also opens through heating of the expanding wax element (48a) fully.
In order to avoid reaching critical temperature ranges the coolant temperature is lowered under the following conditions:
- Intake air temperature above 38°C
- Engine speed above 3000 rpm
- Engine load above 30 %
The coolant temperature is lowered here dependent on the air outside temperature the heating of the expanding wax element (48a):
- Outside temperature below 12°C to approx. 90°C
- Outside temperature above 12°C to approx. 80°C
Overheating protection
In the event of thermal overload, the overheating protection protects against engine damage and overheating damage to the near-engine mounted catalytic converter.
The following measures are taken for overheating protection:
- Map-dependent firing-time shift in the "retarded" direction, depending on the engine load and speed, from a coolant temperature of approx. 90°C and a charge air temperature of approx. 20°C
- Less opening of the throttle valve actuator (M16/50), dependent on the engine load and rotational speed
- Shortening of the injection period according to the lower air mass
- Energization of the thermostat heating element (R48/4) by the ME-SFI [ME] control unit (N3/34) for full opening of the ball rotary slide (48)
In the case of an excessively high coolant temperature a warning message is displayed over the coolant temperature warning lamp (A1/1e54) by the IC control unit (IC) (A1/1). For this purpose, the ME-SFI [ME] control unit transmits a corresponding signal to the instrument cluster control unit (IC).
Fan control
The ME-SFI [ME] control unit (N3/34) actuates the electric fan (M91). In this connection, the request "nominal fan speed" is specified by the ME-SFI [ME] control unit.
The duty cycle of the pulse width modulated signal is 10 to 90 %. In this connection, the following statuses among others are generated:
- 10%: Electric fan OFF
- 20%: Electric fan ON, min. speed
- 90%: Electric fan ON, max. speed
A fault in the electric fan is transmitted to the ME-SFI [ME] control unit.
For a fault in the signal line (frequency failure), the electric fan automatically switches to max. speed (fan emergency mode).
The air conditioning system control and operating unit (AAC-V & AAC-H) (S98) transmits its status to the ME-SFI [ME] control unit.
Delayed fan switch off
In the case of "ignition OFF", the electric fan runs on for up to 5 min if the coolant temperature or the engine oil temperature have exceeded the specified maximum values.
The duty cycle of the pulse width modulated signal for delayed fan switch off is a maximum of 40 %. If the on-board electrical system voltage drops down a lot, the delayed fan switch off is suppressed.
| Function schematic for thermal management | PE20.00-S-2502-97TRM | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-S-9998TRJ |