GF07.10-P-1012OGG Thermal Management, Function

GF07.10-P-1012OGG Thermal Management, Function
- as of model year 09

Function requirements for thermal management, general points
^ Circuit. 87 ON (engine control ON)
^ Engine running

Thermal management, general points
The coolant temperature of the engine is regulated by the controlled thermal management from CDI control unit (N3/9). This has the following advantages:
- The optimum operating temperature is reached faster
- Reduction of the exhaust gas emissions
- Fuel savings (up to around 4%)
- Improved heat comfort.

Thermal management is performed according to the following sensors and signals:
- Hot film mass air flow sensor (B2/6), engine load
- Intake air temperature sensor (B2/6b1)
- Hot film mass air flow sensor (B2/7), engine load
- Intake air temperature sensor (B2/7b1)
- Charge pressure sensor (B5/1)
- Coolant temperature sensor (B11/4)
- Charge air temperature sensor (B17/8)
- Accelerator pedal sensor (B37), accelerator pedal operation (how fast and how far ->driver type calm or sporty)
- Fuel temperature sensor (B50)
- Crankshaft Hall sensor (B70), engine speed
- Temperature sensor in CDI control unit
- AAC [KLA] control and operating unit (N22) (except code (581) Comfort automatic air conditioning) or comfort AAC control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning), outside temperature and status of the air conditioning via the interior CAN (CAN B), central gateway control unit (N93) and engine compartment CAN
- ESP control unit (N47-5), vehicle speed over the engine compartment CAN

Thermal management function sequence
The thermal management is described in the following points:
^ Function sequence for coolant thermostat heating
^ Maximum heating combustion function sequence
^ Tank protection function sequence
^ Fan control function sequence
^ Overheating protection function sequence

Function sequence for coolant thermostat heating
The CDI control unit actuates the two-disk thermostat heating element (R48) (dependent on the performance map) depending on the operating conditions (except code (U42) BlueTEC (SCR) diesel exhaust treatment and with code (494) USA version) using a ground signal.
The voltage is supplied through "circuit 87 ".
When heated, the two-disk thermostat opens in the coolant thermostat. In this way the coolant temperature of 55 to 110 °C is regulated via the duty cycle.

Maximum heating combustion function sequence
For the "hot burning process" more heat is conducted into the coolant on the engine side due to a new combustion strategy.
The following function conditions must be met simultaneously:
- Accelerator pedal position of accelerator pedal sensor lies under 80% (partial load)
- No regeneration operation of diesel particulate filter (DPF)
- At least 90% of the heat output is requested by the AAC [KLA] control and operating unit (except code (581) Comfort automatic air conditioning) or from the comfort AAC control and operating unit (with code (581) Comfort automatic air conditioning)
- Outside air temperature below 7 °C (new cut-in occurs at 4 °C) from the AAC [KLA] control and operating unit (except code (581) Comfort automatic air conditioning) or from comfort AAC control and operating unit (with code (581) Comfort automatic air conditioning)
- Coolant temperature from coolant temperature sensor lies under 82 °C (renewed cut-in takes place at 74 °C)

During the hot burning process a significantly higher exhaust temperature is achieved through 2 preinjections by the fuel injectors (Y76) and a later main injection generates an increased exhaust temperature. More heat is given up to the coolant inside the engine in combination with the exhaust gas recirculation (AGR) which allows more rapid attainment of the optimum operating temperature and improved warming of the vehicle interior.

Tank protection function sequence
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 the fuel temperature sensor and thus monitors the temperature of the fuel delivered to the high-pressure pump.
If the temperature of the fuel to be delivered to the high-pressure pump rises above 90 °C, the CDI control unit increases the injection quantity and the rail pressure using the quantity control valve (Y74). This causes the fuel less to be less compressed.
The quantity control valve (Y94) diverts excess fuel back into the fuel tank.
If the temperature of the fuel delivered to the high-pressure pump drops below 90 °C, the tank protection function is deactivated by the CDI control unit.

Fan control function sequence
The CDI control unit actuates the engine and air conditioning electric suction fan with integrated control (M4/7). The specified fan speed is set by the CDI control unit with a pulse width modulated signal (PWM signal).
The duty cycle of the PWM signal is 10 to 90%.

Meaning:
10% Fan motor "OFF"
20% Fan motor "ON", minimal rpm
90% Fan motor "ON", maximum rpm

If actuation is faulty, the air fan rotates at the maximum rotational speed (fan emergency mode).

The AAC [KLA] control and operating unit (except code (581) Comfort automatic air conditioning) or the comfort AAC control and operating unit (with code (581) Comfort automatic air conditioning) transfers the status of the air conditioning to the CDI control unit via the interior and engine compartment CAN.

Delayed fan switch off
With "ignition OFF", the fan motor runs on for up to 5 min. if the coolant temperature or engine oil temperature (calculated from the temperature model) has exceeded the specified maximum values. The PWM signal duty cycle is 40 % maximum while the delayed fan switch-off is active.
If the battery voltage is dropping too much, the delayed fan switch-off is stopped.

Overheating protection function sequence
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 according to the performance maps stored in the CDI control unit.
Reduction occurs depending on the coolant temperature and oil temperature.

To this end, the CDI control unit reads in the coolant temperature sensor (), oil temperature sensor (B1) 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 rails via the quantity control valve and the pressure regulator valve, and controls the injection timing by actuating the fuel injectors.