Abstract
AbstractA lot of effort has been put into estimating sideslip angle in varying road friction conditions, but the problem of estimating the tire-road friction coefficient under small tire slip angles has been rarely addressed. An inaccurate estimate of the tire-road friction coefficient, when applied to the estimation of sideslip angle, could cause large errors in the result. This paper studies the estimation of the tire-road friction coefficient in the context of adaptive estimation of the sideslip angle. The nonlinear observability theory is used to analyze the local observability of the system with an augmented state vector that includes the tire-road friction coefficient. The connection between local observability and lateral tire force characteristics is established based on the results of the observability analysis. By studying the performance of the combined state and parameter estimator under weak observability conditions, a modification to the estimator is proposed to keep the observability of the system in an acceptable level even when tire slip angles are small, so that the tire-road friction coefficient can be properly estimated. Test results show that the modified algorithm can effectively improve the accuracy of estimating the sideslip angle under complicated road friction conditions.KeywordsNonlinear observabilityFriction coefficientDual extended Kalman filterSideslip angle
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