CDI thermal management, function

General function requirements

 Circuit 61 ON

Common rail diesel injection (CDI) thermal management, general

The thermal management function encompasses the following subfunctions:

 Overheating protection function sequence

 Maximum heating combustion function sequence

 Tank protection function sequence

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Overheating protection function sequence

To protect the engine from thermal overload, in addition to the air conditioning electric suction fan with integrated control (M4/7), when coolant temperature is above 110 °C, engine torque is limited depending on coolant temperature, engine oil temperature and engine speed, according to performance maps stored in the CDI control unit (N3/9) .

To do this, the CDI control unit reads the coolant temperature sensor (B11/4), oil temperature sensor (B1), crankshaft Hall sensor (B70) and temperature sensor upstream of the turbocharger (B19/11). After evaluating the input signals, the CDI control unit regulates fuel pressure in the rail via the quantity control valve (Y94) and pressure regulator valve (Y74) and controls injection timing by actuating the fuel injectors (Y76).

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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 (B37) lies under 80% (partial load)

- No regeneration operation of diesel particulate filter (DPF)

- At least 90 % of heat output required by the AAC control unit (N22/1)

- Outside air temperature below 7°C (renewed cut-in takes place at 4°C), from outside temperature indicator temperature sensor (B14)

- Coolant temperature from coolant temperature sensor lies under 82°C (renewed cut-in takes place at 74°C)

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During the hot burning process a higher exhaust temperature is achieved through 2 preinjections with a significantly increased fuel quantity and a later main injection. In combination with the exhaust gas recirculation (EGR), more heat is released to the coolant inside the engine which leads to improved vehicle interior heating.

Tank protection function sequence

Through increasing the fuel pressure via the common rail high pressure pump by 4.5 bar up to 1800 bar the temperature of the fuel also increases. To protect the fuel tank from overheating, the CDI control unit reads the fuel temperature sensor (B50) and thus monitors the temperature of the fuel delivered to the common rail high-pressure pump.

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If the temperature of the fuel delivered to the common rail high pressure pump goes above 90°C the injection quantity and rail pressure are automatically reduced. This compresses the fuel less. The quantity control valve diverts excess fuel back to the fuel tank.

If the temperature of the fuel fed to the common rail high pressure pump drops below 90°C. the tank protection function will be deactivated by the CDI control unit.