| In order to meet future standards regarding tailpipe emissions from spark-ignited engines, precise control of air-fuel ratio during transient engine operation is essential. However, current industrial controllers perform poorly during transients, partly because they rely heavily on empirical feedforward control schemes. In response, controllers have recently been developed in which the compensation is based on physical models of the air and fuel flows into the engine. These model-based controllers have demonstrated good transient regulation of air-fuel ratio, provided accurate values of specific dynamic parameters associated with the air, fuel, and sensor dynamics are known. Since these parameters may possibly change with engine speed, load, ambient conditions, and age, a method of periodically updating the parameter values is required to maintain high performance at all times.;In this work, an adaptive air-fuel ratio control system was developed for a single-cylinder CFR engine in which the parameters of a physics-based engine model were identified and incorporated into a model-based controller and estimator. A recursive, nonlinear least squares identification technique was used to provide accurate values of model parameters from data collected during normal engine operation. The inputs were the control signals for an electronic fuel injector and drive-by-wire throttle, and the output was the measurement from a UEGO sensor mounted in the exhaust manifold. Sensor characteristics and airflow parameters were identified by imposing small dithers about the nominal throttle angle during periods of relatively steady engine speed and load. Dithers in the fuel injector pulsewidth were applied during similar steady-state conditions to identify fuel puddle parameters. The identified values were then used in a model-based control system to control air-fuel ratio over a range of throttle angles and engine speeds. Using this self-tuning regulator structure, air-fuel ratio was controlled within 0.5% rms of the commanded stoichiometric value during 10... |
