Speed control driving, function

W07.15-1356-81

4 Engine CAN bus

A3 Vehicle engine control (FMR) control unit

A6 MR/PLD control unit

B1 Foot throttle actuator

Y6 Cylinder 1 unit pump

Y7 Cylinder 2 unit pump

Y8 Cylinder 3 unit pump

Y9 Cylinder 4 unit pump

Y10 Cylinder 5 unit pump
- Only for engine 906.9 and 926.9

Y11 Cylinder 6 unit pump
- Only for engine 906.9 and 926.9

If the drive control (FR) does not request neutral or working speed control then this represents normal driving operation.

The torque delivered by the engine in driving mode is primarily dependent on the position of the accelerator pedal and thus the position of the foot throttle actuator (B1).

The engine control (MR) selects the respective regulator type or the characteristic stored for this type of regulator and compares the incoming specified engine torque from the drive control (FR), which can also be derived from the position of the foot throttle actuator (B1) and that provided over the engine CAN bus (1) with the current actual engine torque, which represents the actual operating conditions of the engine.

If the current actual engine torque differs from the specified engine torque, the engine control (MR) controls the fuel quantity in such a way that the actual engine torque matches the required engine torque.

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Thus if the required engine torque is less than the current actual engine torque the engine control (MR) reduces the fuel quantity and if the required engine torque is greater than the current actual engine torque then it increases the fuel quantity.

The engine control (MR) is therefore always attempting to get the actual value to match the specified value.

While this matching process is being performed, the MR/PLD control unit (A6) adjusts the start of injection in order to compensate the ignition delay which can have a negative effect, particularly at higher engine speeds, and to keep the pollutant emissions as low as possible.

The engine control (MR) will not actuate the solenoid valves in the unit pumps if the required engine torque is negative, as for example when decelerating. This a way to use the braking effect of the engine.

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 The engine control (MR) can limit the specified engine torque sent by the drive control (FR) to protect the engine, for example if the coolant temperature exceeds an impermissibly high value or the engine has reached its upper or breakaway speed. The engine control will adjust to and set the highest possible engine speed in the latter case.

There is also a specified engine torque correction taking place in the engine control (MR) which takes account of the mass of fuel. To do this it uses the fuel temperature which is determined either via a fuel temperature sensor or via a performance map.