A/F ratio estimation and control based on induced engine roughness

A new estimator for A/F ratio is described, which is based on inducing crankshaft speed fluctuations by modulating the fuel injection pulse widths in a predetermined manner. The fuel pulse width modulation produces a corresponding modulation of the instantaneous combustion A/F ratio and IMEP, which in turn modulate the crankshaft velocity. Event based measurements of crankshaft velocity provide a metric that, together with other engine state parameters, can be used to estimate A/F ratio independent of data from an exhaust gas oxygen sensor. The estimator can be used to supplement the exhaust gas sensor during cold start or warm start engine operation when the sensor may not be available. This paper discusses the design of the A/F ratio estimator, the transient performance of the estimator during both engine cold and warm start operation, and the transient performance of a closed loop A/F ratio control system using the estimator for A/F ratio feedback