Torque Control

Torque Control








General
Engine torque control is used to ensure the correct engine torque is supplied by the engine. ECM controls engine torque by regulating the air mass per combustion (cylinders' capacity) and also by regulating the ignition timing.

The maximum engine torque allowed for the engine is stored as a table in the control module memory. The table specifies the highest torque the engine is allowed to generate at various engine speeds.

Engine torque is primarily calculated using air mass per combustion and engine speed. But, ignition timing and current lambda value also affect the torque calculation. Retarded ignition timing generates lower engine torque. This is the case in knock control. As regards the lambda value, there is an optimal lambda value for each operating point. If the engine runs richer or leaner than the optimal value, engine torque reduces.





Note that a lambda value lower than the optimal value (richer mixture) produces lower torque.

The calculation also takes the engine's own torque consumption, i.e. internal friction, into consideration. The following values are used for this calculation:
^ Air mass
^ Engine speed
^ Coolant temperature
^ Idling torque

Fast engine torque control, increasing load
The fast method of control is used when the engine load changes rapidly, e.g. idle when turning the steering wheel rapidly so that the power steering pump puts a load on the engine. The increased torque requirement from the engine must then be compensated by a rapid increase in engine torque or the idling speed will drop. This fast compensation is done using previous ignition timing, giving higher torque.





After the fast compensation, ECM will gradually increase the throttle area in order to get more air mass into the engine while the ignition is retarded slightly. This allows ECM to maintain a torque reserve so that it can again perform fast compensation for changed engine loads.





Slow torque control, load change
Slow engine torque control is used when driving under constant load, i.e. when the load does not vary or varies slowly. In this case, ECM operates mainly with throttle area to regulate the engine torque.





For higher torque requirements, turbo control will also be used to increase the air mass in the engine so that it produces the requested engine torque.