Engine torque request, CDI function

General function requirements

 Circuit 61 ON

Common rail diesel injection (CDI) engine torque requirement, general

The CDI control unit (N3/9) intervenes with an external quantity intervention if an increase or decrease on the engine speed and engine load is requested from another system.

-----------------------------------------------------------------------------------------

To do this the CDI control unit communicates with the following control units:

- Fully integrated transmission control unit (VGS) (Y3/8n4) over the drive train CAN

- ESP control unit (N47-5), over the chassis CAN

- AAC control unit (N22/1), through the interior CAN, central gateway control unit (N93) and chassis CAN

-----------------------------------------------------------------------------------------

The engine torque demand is comprised of the following subfunctions:

 Transmission overload protection function sequence

 Switching line shift function sequence

 Engine torque request function sequence over the Electronic Stability Program (ESP)

 Refrigerant compressor (A9) shutoff function sequence

Transmission overload protection function sequence

The transmission overload protection protects shift elements of the transmission from excessive thermal stress during load changes in the upper engine speed range. The engine torque is reduced on request of the fully integrated transmission control, control unit (VGS). The CDI control unit reduces the injection quantity. In order to adapt the injection quantity, the fuel pressure in the rail is decreased by the pressure regulator valve (Y74) and the quantity control valve (Y94) via the CDI control unit. At the same time the actuation time of the fuel injectors (Y76) is shortened appropriately.

-----------------------------------------------------------------------------------------

Switching line shift function sequence

Switching line shift brings the oxidation catalytic converter more rapidly up to operating temperature and supports diesel particulate filter (DPF) regeneration. On request from the CDI control unit, the fully integrated transmission control control unit (VGS) electronically shifts the switching lines so that the partial load switchings take place at a higher engine speed or higher vehicle speed.

Torque request by ESP function sequence

In order to secure vehicle stability, the ESP control unit sends the request to reduce engine torque or to increase engine torque to the CDI control unit. The CDI control unit increases or decreases the injection quantity. In order to adapt the injection quantity, the fuel pressure in the rail is increased or decreased by the pressure regulator valve and the quantity control valve via the CDI control unit. At the same time the actuation time of the fuel injectors is extended or shortened appropriately.

-----------------------------------------------------------------------------------------

Function requirements for refrigerant compressor shutoff

 Air conditioning system is in operation

Refrigerant compressor shutoff function sequence

The CDI control unit receives the "KOMP_EIN" message (refrigerant compressor activated) indirectly from the AAC control unit over the chassis CAN.

If the following conditions are present, the CDI control unit interrupts actuation of the refrigerant compressor:

- Engine speed < 2000 rpm

- Value from accelerator pedal sensor (B37) > 95 %

If the function requirements for the refrigerant compressor shutoff are no longer met, the refrigerant compressor is actuated again by the CDI control unit.