Thermal Management, Function - GF07.10-S-1012TRC
Engine 274 in model 447, 448
except 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) over direct line
- Charge air temperature sensor upstream of throttle valve (B17) over direct line
- Charge air temperature sensor downstream of throttle valve (B1716) over direct line
- Intake manifold pressure sensor (B28/24) over direct line
- Accelerator pedal module (B37/4) over direct line
- Crankshaft Hall sensor (B70/2) over direct line
- SAM control unit (N10/1), outside temperature via the interior CAN (CAN B)
- Automatic air conditioning control and operating unit (KLA-V & KLA-H) (S98), status of A/C via interior CAN (CAN B) (with code HH4 (THERMOTRONIC automatic air conditioning)) or with code HH9 (Semiautomatic regulated A/C, TEMPMATIC))
- Electronic Stability Program control unit (N30/4), wheel speed via the chassis CAN (CAN E)
- Fully integrated transmission control electric controller unit (VGS) (N15/11), transmission oil temperature via the drive train CAN (CAN C) (for an automatic transmission)
Coolant circuit, shown schematically
Thermal management
The thermal management is described in the following points:
- Coolant thermostat regulation
- Overheating protection
- Fan control
Coolant thermostat regulation
Opening and closing the ball rotary slide (48b) in the coolant thermostat (48) takes place by means of temperature-influenced expansion and contraction of the expanding wax element (48a) in a temperature range of about 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.
Depending on the operating conditions, the ME-SFI [ME] control unit (N3/34) actuates the heating element in the thermostat (R48/4) using a ground signal.
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 (48) closed
Closed
The ball rotary slide (48b) of the coolant thermostat (48) is closed if the following conditions are fulfilled:
- Coolant temperature 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:
- Reaching a coolant temperature of approx. 98°C for the first time after starting (no full-load request).
- Thermostat heating element (R48/4) is energized.
Within in a temperature range of coolant of about 98 to 108°C or according to the energization of the thermostat heating element (R48/4) the expanding wax element (48a) begins to expand and actuates the ball rotary slide (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)
For exceeding of a coolant temperature of about 108°C the ball rotary slide (48) is opened completely and the coolant can flow unheeded over the engine radiator (1).
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 up to about 90°C
- Outside temperature below 12°C up to about 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:
- A characteristics map-dependent ignition angle setting in the direction "retarded", dependent on the engine load and-engine speed, as of 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). To do this the ME-SFI [ME] control unit (N3/34) sends an appropriate signal via the chassis CAN (CAN E) to the IC control unit (IC) (A1/1).
Fan control
The ME-SFI [ME] control unit (N3/34) actuates the electric fan (M91). The target fan speed request is made via the drivetrain-LIN (LIN C3) by the ME-SFI [ME] control unit (N3/34).
The duty cycle of the pulse width modulated signal is 10 to 90 %.
This means, for example:
- 10 %: electric fan (M91) "OFF"
- 20 %: electric fan (M91) "ON", minimum rotational speed
- 90 %: electric fan (M91) "ON", maximum rotational speed
A fault in the electric fan (M91) is sent by the ME-SFI [ME] control unit (N3/34) via the drivetrain-LIN (LIN C3).
In the case of a fault in the signal line (loss of frequency) by the ME-SFI [ME] control unit (N3/34) the electric fan (M91) switches itself automatically to the maximum rpm (fan emergency mode).
The A/C control and operating unit (KLA-V & KLA-H) (S98) (with code HH4 (THERMOTRONIC AAC) or with code HH9 (Semi-automatic regulated A/C, TEMPMATIC)) transmits its status via the interior CAN (CAN B), electronic ignition lock control unit (EZS) control unit (N73) and chassis CAN (CAN E) to the ME-SFI [ME] control unit (N3/34).
Delayed fan switch off
After "ignition OFF", the electric fan (M91) continues to run for up to 5 min. if the coolant temperature or engine oil temperature is above the specified maximum value.
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.
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