Function requirements for thermal management, general points
Circuit 87 (Engine management ON)
Engine runs
Thermal management, general
The thermal management as controlled by the CDI control unit (N3/9) regulates the engine's coolant temperature, exhaust temperature and the fuel pressure. The following advantages arise from this:
Rapid reaching of the optimal operating temperature
Reduction of the exhaust emissions
Fuel saving (up to about 4%)
Improved heating comfort
Component protection for a high engine load
Thermal management controlling is dependent on the following sensors and signals:
Engine oil temperature sensor (B1)
Left hot film mass air flow sensor (B26), engine load
Left intake air temperature sensor (B2/6b1)
Right hot film mass air flow sensor (B27), engine load
Right intake air temperature sensor (B2/7b1)
Boost pressure sensor (B51), engine load
Coolant temperature sensor (B11/4)
Charge air temperature sensor (B17/8)
Temperature sensor upstream of diesel particulate filter (B19/9)
DPF differential pressure sensor (B28/8)
Accelerator pedal sensor (B37), accelerator pedal actuation (how quickly and how far vehicle type quiet or sporty)
Fuel temperature sensor (B50)
Crankshaft Hall sensor (B70), engine rpm
Front SAM control unit (N10/6), outside temperature via interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)
Climate control control unit (N22/1), A/C status via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN
Electronic Stability Program control unit (N30/4), wheel speed via the chassis FlexRay, powertrain control unit and drive train CAN
Fully integrated transmission control unit (Y3/8n4) (with code 427 (7G-TRONIC) or (with code 421 (9G-TRONIC), gear range via the drive train CAN
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 maximum heating combustion
Function sequence for fuel preheating system
Function sequence for fuel tank protection
Function sequence for fan control
Function sequence for radiator shutters
Function sequence for charge air cooling
Function sequence for overheating protection
Function sequence for post-start phase
In the post start phase, the coolant circulation can be interrupted by switching off the coolant pump with the aid of a coolant pump switchover valve (Y133).
The coolant pump switchover valve is actuated in the process by an output stage switching to the ground connection in the CDI control unit and controls a bypass in the coolant pump using vacuum. The engine is warmed up quicker in the process and the exhaust emissions are reduced.
The coolant pump is switched off for a cold start for a maximum of 300 s if the following conditions are fulfilled:
The limit values stored in the CDI control unit for the intake air and coolant temperature as well as for the injected total fuel quantities are still not reached from the engine start.
No "heating" is requested by the climate control control unit.
The engine speed or injection quantity has not exceeded its established limit value.
If the conditions for shutoff of the coolant pump are no longer fulfilled the maximum switching time of 300 s is reached and the CDI control unit ends actuation of the coolant pump switchover valve.
The coolant pump switchover valve is ventilated over the ventilation connection and the bypass in the coolant pump is closed again. The coolant pump is therefore switched on and the coolant circulation is achieved again. If the coolant pump was activated once, it remains active in the entire ignition sequence.
Function sequence for coolant thermostat
The two-disk thermostat can take the following positions:
Short-circuit mode position; t < 87°C; coolant flow in engine only, a flow through the passenger compartment heater is possible
Mixed mode position; 87°C < t < 102°C; the two-disk thermostat opens, the coolant throughflow begins
Radiator mode position; t > 102°C; the two-disk thermostat is opened, full radiator throughflow
The following advantages result from regulating the coolant temperature of the engine:
Operating temperature is reached faster
Emissions reduced
Improved heating comfort
Component protection for engine high load
Schematic diagram |
67 | Coolant thermostat |
A | Position for short circuit mode |
B | Position for mixed-fuel mode |
C | Position for radiator operation |
K | To the radiator |
M | From engine |
W | To the coolant pump |
P20.10-2196-04
Function sequence for maximum heating combustion
With the maximum heating combustion more heat is introduced into the coolant by a new combustion strategy on the engine side.
The following function conditions must be met simultaneously:
Accelerator pedal position reported by the accelerator pedal sensor is below 80% (partial throttle)
Diesel particulate filter (DPF) not in regeneration mode
At least 90% heat output is requested from the climate control control unit
Outside air temperature under 7°C (renewed cut-in takes place at 4°C by the front SAM control unit)
Coolant temperature from coolant temperature sensor is below 82°C (renewed cut-in takes place at 74°C)
During maximum heating combustion, a higher exhaust temperature is achieved by means of 2 preinjections from the fuel injectors (Y76) using a much greater fuel quantity, plus a retarded main injection. This process, in combination with exhaust gas recirculation (EGR), causes more heat to be transferred to the coolant inside the engine, allowing for more rapid attainment of the optimum operating temperature and improved warming of the vehicle interior. To do this the exhaust gas recirculation actuator (Y27/9) is actuated by the CDI control unit.
The CDI control unit regulates, stabilizes and increases the idle speed depending on operating conditions and engine loads if the accelerator pedal is not actuated.
Function sequence for fuel preheating system
Fuel preheating is achieved using the following regulation strategies:
Pressure regulating valve (Y74) regulation
2-control concept regulation
Quantity control valve (Y94) regulation
Pressure regulating valve regulation
The fuel pressure is regulated by the pressure regulating valve during the starting procedure and for fuel heating. The quantity control valve is opened in a controlled manner.
Pressure regulating valve regulation takes place under one of the following conditions:
Up to 30 s after the engine starts in idle
Up to a fuel temperature of 20°C
Pressure regulating valve regulation causes the cold fuel to be heated rapidly by the fuel being forced at high pressure through a narrow gap in the pressure regulating valve.
2-control concept regulation
The fuel pressure is jointly regulated in idle and in deceleration mode by the pressure regulating valve and quantity control valve.
Quantity control valve regulation
Fuel pressure regulation over the quantity control valve takes place from 30 s following engine start and from a fuel temperature of 20°C.
With the 2-regulator design and with regulation by the quantity control valve, the fuel is heated less than is the case with pressure regulating valve regulation.
Function sequence for fuel tank protection
Increasing the fuel pressure via the high-pressure pump from 4.5 bar up to 1800 bar also increases the temperature of the fuel.
To protect the fuel tank from overheating, the CDI control unit reads in values from the fuel temperature sensor and thus monitors the temperature of the fuel delivered to the high-pressure pump. If the temperature of the fuel delivered to the high-pressure pump rises above 90°C, the CDI control unit reduces the injection quantity and the fuel pressure using the pressure regulating valve.
This causes less fuel to be compressed.
The CDI control unit causes the excess fuel to return to the fuel tank via the quantity control valve.
When the temperature of the fuel delivered to the high-pressure pump drops below 90°C, the protection function is deactivated by the CDI control unit.
Function sequence for fan control
The powertrain control unit (N127) actuates the fan motor (M4/7). The fan nominal speed is specified steplessly 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 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.
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 engine external noise emissions to the outside. The radiator shutters actuator motor (M87) is actuated by the powertrain control unit after engine start via the drivetrain-LIN. In this way the radiator shutters is closed over a linkage. The radiator shutters are opened when the coolant temperature reaches 106°C and are closed again at 94°C.
Further opening conditions are:
Request for delayed fan switch off
Request for basic ventilation of the A/C
Charge air temperature above the threshold value
Request to lower the coolant temperature for component protection
Function sequence for charge air cooling
The wayter-cooled charge air cooler is connected to the low-temperature circuit with the low-temperature cooler and the low-temperature circuit circulation pump 1 (M43/6).
If the charge air temperature is > 35°C the low-temperature circuit circulation pump 1 is actuated via the engine CAN (CAN C), the powertrain control unit and via the drivetrain LIN by the CDI control unit.
If the charge air temperature falls below 25°C, the low-temperature circuit circulation pump 1 is switched off again.
The charge air temperature is detected in the charge air distributor by the charge air temperature sensor and sent to the CDI control unit using a voltage signal.
Only open the cap in the low-temperature circuit when the charge air temperature is increased (lack of power) and the engine is cold. The coolant must reach up to the cap.
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. Reduction occurs depending on the coolant temperature and oil temperature. To do this the CDI control unit reads in signals from the coolant temperature sensor, the engine oil temperature sensor and the temperature sensor upstream of ATL (B19/11) (turbocharger protection).
After evaluating the input signals, the CDI control unit regulates the fuel pressure in the rails via the quantity control valve and the pressure regulating valve, and controls the injection period by actuating the fuel injectors.
If the engine oil or coolant temperature is too high, a warning message is shown in the instrument cluster (A1). To do this the CDI control unit transmits an appropriate signal via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) to the IC.
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