An algorithm for the calibration of wall-wetting model parameters

Spark-ignited engines equipped by a three-way catalyst require a precise control of the air fuel ratio fed to the combustion chamber. A stoichiometric mixture is necessary for the proper working of the catalyst in order to meet the legislation requirement. A critical part of the air fuel ratio control is the feed-forward compensation of the fuel dynamics. Conventional strategies are based on a simplified model of the wall-wetting phenomena whose parameters are stored in off-line computed look-up tables. Unfortunately, errors in the parameters calibration over the whole engine map deteriorate the control performances in terms of emissions. In this paper an automatic procedure for a rapid and efficient identification of the wall-wetting parameters is presented. The whole procedure has been experimentally tested on a vehicle by using a test bench. Using the identified parameters values, a significant reduction in the air fuel ratio excursion has been achieved during rapid throttle transients with respect to the same vehicle equipped by a commercial ECU with resident engine maps computed by traditional calibration activity. Moreover, the algorithm can be also on-line used to improve air-fuel ratio control performances.