Calculating engine specified torque, function

W30.35-1082-81

1 Vehicle CAN bus

2 Engine CAN bus

A3 Drive control (FR) control unit

A6 MR/PLD control unit

A10 ABS control unit
- Vehicles with code (B02) brake system, antilock brake system (ABS)

A11 BS/EPB control unit
- Vehicles with code (BB1) brake system (BS) or with code (BB8) brake system (BS) with ASR

B1 Foot throttle actuator

B17 Speed sensor

P1 Tachograph

Z1 CAN star point cab dash support

a Accelerator pedal position

b Vehicle speed

c Condition of the antilock brake system (ABS) or the Acceleration Slip Regulation (ASR)

d Maximum possible engine torque

e Calculated and (if necessary) limited specified engine torque

* Vehicles up to vehicle ident. end no. 472725

* * Vehicles as of vehicle ident. end no. 472726

General information

The specified engine torque is a purely calculated value based on the driving requirements of the driver.

This value is primarily dependent upon the position of the gas pedal and mainly needed by the engine control (MR) for regulating the load while driving.

This specified engine torque can, however, be limited in the drive control (FR),
for example to maintain the legally prescribed maximum speed or for a regulating intervention by the antilock brake system (ABS) or the acceleration slip regulation (ASR), and in the engine control (MR), for example to protect the engine.

Function

The drive control (FR) first determines the accelerator pedal position (a). This occurs with the aid of an electronic foot throttle actuator (B1) which detects the position of the gas pedal and converts this into PWM (pulse-width-modulated) signals. These PWM signals are sent to the drive control (FR) control unit (A3), which derives the specified engine torque on this basis.

In addition to the accelerator pedal position (a), the drive control (FR) also monitors other boundary conditions such as the legally prescribed maximum speed or a regulating intervention by the antilock brake system (ABS) or the acceleration slip regulation (ASR).

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

This means that the drive control (FR) can limit the specified engine torque according to the vehicle speed (b) or according to the condition of the antilock brake system (ABS) or the acceleration slip regulation (ASR).

Furthermore, the specified engine torque is always only selected within the maximum possible engine torque (d) range, which is in turn determined by the engine control (MR) and sent via the engine CAN bus (2) to the drive control (FR).

The maximum possible engine torque (d) is primarily dictated by the data set in the MR electronics and is thus dependent on the model designation of the engine. It can also be additionally limited, however, according to the operating conditions of the engine (engine temperature, speed etc.).

The specified engine torque (e), which has been calculated and (if necessary) limited in this way, is finally sent via the engine CAN bus (2) to the engine control (MR).

The specified engine torque is additionally limited in the engine control (MR) as required (for example to protect the engine) and corrected, while taking account of the actual mass of the fuel which can be derived from the fuel temperature or a performance map, before the delivery or injection beginning point and the delivery end of the unit pumps are finally calculated.

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

 The specified engine torque (e) that is calculated and (if necessary) limited by the drive control (FR) is not always positive:

If the gas pedal is in the idling position, the specified engine torque is "0".

It can even be negative during a thrust operation.

The specified engine torque can also be influenced by variables from the automatic AT/AGE control unit, the GS/EPS control unit, the retarder control unit, the PSM control unit or the WSK control unit (depending on vehicle equipment), for example, which can be received via the vehicle CAN bus (1).