CDI function when driving

When driving, one of the basic tasks of common rail diesel injection (CDI) is to provide the amount of engine torque that corresponds to the accelerator pedal position. Optimum smooth running characteristics are also required, with reduced fuel consumption and low exhaust gas emissions. For this purpose, the CDI control unit must adjust the electronic diesel control (EDC) and the air and exhaust system to each other, according to the stored performance map data.

When driving, the CDI controls the following functions through the CDI control unit:

 Exhaust gas cleaning on Group 3 low-emission engines EU4

 Refrigerant compressor shutoff, with automatic air conditioning or regulated air conditioning (Tempmatic)

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 Quantity Control

 Charging

To do this, the CDI control unit reads the following parameters from the associated components:

 On vehicles with Group 3 low-emission engines EU4, the intake air mass and temperature from the hot film MAF sensor and the integrated intake air temperature sensor.

 Current rail pressure, from the rail pressure sensor

 Current boost pressure, from the boost pressure sensor, the pressure sensor downstream of the air filter, and the charge air temperature sensor

 Coolant temperature from the coolant temperature sensor

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 Accelerator pedal position, from the pedal value sensor

 Fuel temperature, from the fuel temperature sensor

 On vehicles with Group 3 low-emission engines, the EU4 exhaust residual oxygen content from the O2 sensor

 Engine speed from the crankshaft position sensor

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The CDI control unit also communicates with the following control units over the Class C (engine compartment) Control Area Network bus (CAN C) to obtain the values for other parameters:

 Using the instrument cluster as interface to the Class B (interior compartment) Controller Area Network bus, for example to allow processing of the winter tire maximum speed setting, or activate the Electronic Stability Program (Electronic Stability Program) (ESP) in roll test mode.

 In vehicles with 722.6 transmission and ETC control unit, for example to obtain information about the gear currently selected (actual gear engaged).

 In vehicles with 722.6 transmission and electronic selector lever module control unit, for example to obtain the selector lever position "P" or "N" information.

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 With the ESP control unit, for example to obtain the wheel speed.

 Using the EIS control unit as interface to the CAN B, for example to obtain the switching status of the air conditioning systems, on vehicles with automatic air conditioning or regulated air conditioning (Tempmatic).

Refrigerant compressor shut-off

As a function requirement, the air conditioning system must be active.

Through the Class C (engine compartment) Controller Area Network bus (CAN C), the CDI control unit receives the "KOMP_EIN" message (refrigerant compressor activated) from the EIS control unit.

At engine speeds below 2000 rpm and if the pedal value sensor value is above 95 %, the CDI control unit interrupts actuation of the refrigerant compressor and places the "KOMP_AUS" message (deactivate refrigerant compressor) on CAN C. The refrigerant compressor is then actuated again by the CDI control unit.