Adaptive Functions

Adaptive Functions
The tolerances of certain components such as the mass air flow (MAF) sensor, injectors, air leaks in the intake manifold or blockage of the air cleaner (ACL) will affect the fuel/air mixture. To compensate for this, the engine control module fuel trim function incorporates adaptive (or self-learning) functions. When the engine is new the integrator varies cyclically around a nominal median (A) 1.00 with, for example, a ± 5% change in injection period when heated oxygen sensor control is operating.

If there is an air leak the integrator is quickly displaced to a new position (B), operating between 1.10 (+10%) and 1.20 (+20%) for example, (still with an amplitude of 5%, but displaced in relation to the original median (A). The injection period has increased to compensate for the increased volume of air.

This increase is corrected for by the adaptive functions so that the integrator operates around its new median (B) with its full control range ±25% available.

Adaptation is a measure of the difference (C) between the original integrator median (A) and the new median (B).

The Adaptive Functions Consist Of Two Elements:

^ The first element (an additive term) can increase or decrease the injection period by 0.5 ms. This adaptation operates when the engine is running at idling. It corrects the integrator to its median within a few minutes. This is the method used by the engine control module to adjust CO content when the engine is idling.
^ The second element (a multiplier) can increase or decrease injection period by 25%. This adaptation operates when the engine is running at partial load.

The adaptive adjustments to the injection period, called long-term fuel trim, are stored in the engine control module after the engine has been stopped. This means that the correct mixture is achieved immediately after the engine is started, before the heated oxygen sensor has reached operating temperature.