Function requirements for thermal management, general points
Engine runs
Circuit 87M ON (Engine management ON)
Thermal management, general
The coolant temperature, exhaust temperature and fuel pressure of the engine are regulated by the thermal management system controlled by the CDI control unit (N3/9). The following advantages arise from this:
Rapid reaching of the optimal operating temperature
Reduction of the exhaust emissions
Fuel savings
Improved heating comfort
The controlling of the thermal management is dependent on the following sensors and signals:
Hot film mass air flow sensor (B2/5), engine load
Intake air temperature sensor (B2/5b1)
Charge air pressure and temperature sensor (B4/32), engine load
Coolant temperature sensor (B11/4)
Temperature sensor upstream of diesel particulate filter (B19/9)
DPF differential pressure sensor (B28/8)
Accelerator pedal sensor (B37), accelerator pedal actuation
Crankshaft Hall sensor (B70), engine rpm
Fuel temperature sensor (B50)
Engine fuse and relay module (K40/8), status of circuit 87
Circuit relay 87M (K40/8kN), status of circuit 87
Front SAM control unit (N10/6), outside temperature via the interior CAN (CAN B), electronic ignition lock control unit (N73) via the chassis FlexRay (Flex E) to powertrain control unit (N127) and drive train CAN (CAN C1)
Climate control control unit (N22/1), A/C status via interior CAN, electronic ignition lock control unit via chassis FlexRay to powertrain control unit and drive train CAN
Electronic Stability Program control unit (N30/4), wheel speed via chassis FlexRay to powertrain control unit and via drive train CAN to CDI control unit
Fully integrated transmission control unit (Y3/8n4), gear range via drive train CAN (CAN C) (for A/T)
Function sequence for thermal management
The thermal management is described in the following points:
Function sequence for post-start phase
Function sequence for coolant thermostat
Function sequence for fan control
Function sequence for radiator shutters
Function sequence for overheating protection
Function sequence for post-start phase
In the post-start phase circulation of the coolant is prevented by a shutoff valve in the coolant outlet connection. In this way the coolant heats up quicker to the desired operating temperature. For a coolant temperature of about 80°C the shutoff valve coolant thermostat pressure transducer (Y88) is actuated by the CDI control unit CDI , in this way the shutoff valve is opened in the coolant outlet connection and the coolant can flow to the coolant thermostat. From this point in time circulation of the coolant is possible.
Function sequence for coolant thermostat
The expansion material thermostat opens as of a coolant temperature of about 85°C and therefore frees up the large coolant circuit. From this point in time the coolant delivers thermal energy over the engine radiator to the ambient air.
Function sequence for fan control
The powertrain control unit (N127) actuates the fan motor (M4/7). The fan nominal speed is specified via the drivetrain LIN (LIN C3) by 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 sends the air conditioning status via the interior CAN and suspension FlexRay to the powertrain control unit including a fan requirement. If the powertrain control unit does not receive a valid fan request from the climate control control unit, the fan motor is actuated at maximum rpm.
Delayed fan switch off
The fan motor runs on for up to 5 min. for "ignition OFF" if the coolant temperature, the temperature of the CDI control unit or a thermal input integral calculated based on an engine load, coolant temperature, vehicle speed and outside temperature (averaged over the last 6 min.) has exceeded a prescribed threshold value. If the battery voltage drops too far here, 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.
Function sequence for radiator shutters
The radiator shutters is closed in order to lower the fuel consumption (thorough having a lower aerodynamic drag). This also causes reduced engine compartment cooling off and a dampening of external noise of the engine. The radiator shutters actuator motor (M87) is actuated by the powertrain control unit after engine start via the drivetrain-LIN. The radiator shutters are opened when the coolant temperature reaches 106°C and closed again at 94°C.
Function sequence for overheating protection
The overheating protection protects against engine damage if there is a thermal overload. At a coolant temperature above 106°C the injection quantity is reduced based on the characteristics maps stored in the CDI control unit. The reduction takes place dependent on the coolant temperature. To do so, the CDI control unit reads in the coolant temperature sensor and the temperature sensor upstream of the turbocharger (B19/11) (turbocharger protection). After evaluating the input signals, the CDI control unit regulates the fuel pressure in the rail over the quantity control valve (Y94) and the injection period over actuation of the fuel injectors (Y76).
If the coolant temperature is too high, a warning message in instrument cluster (A1). To do this, the CDI control unit sends a corresponding signal via the drive train CAN, the powertrain control unit via the chassis FlexRay, the electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster (A1).
Thermal management shown schematically |
1 | Expansion reservoir |
2 | Motor |
3 | Heater heat exchanger |
4 | Coolant thermostat |
5 | Coolant outlet connection |
6 | Engine oil heat exchanger |
7 | Engine radiator |
8 | Coolant pump |
9 | Exhaust gas recirculation cooler |
A | Coolant cold: |
B | Coolant, warm |
C | Coolant circuit ventilation |
M43/6 | Low-temperature circuit circulation pump 1 |
P20.00-2530-76
Referenced documents
- gf0716p9997orb Overview of system components for common rail diesel injection (CDI)