Competitive degradation process based monitoring of steer-by-wire system under unknown degradation features

Abstract Monitoring of steer-by-wire (SBW) system under intermittent faults is challenging since it is difficult to obtain the priori knowledge of monotonous degradation feature of intermittent fault due to its stochastic nature. To deal with this issue, this paper develops a prognosis method for the SBW system under unknown degradation features based on the concept of competitive degradation process (CDP). With the aid of fault diagnosis module, the possible faulty components can be determined, where the fault isolation estimators and the expanded analytical redundancy relations are used to improve the isolabilities of sensor faults. For each faulty component, three degradation features are defined and the monotonicity of each feature is unknown beforehand. To judge the monotonicity of the feature, the competition index is developed in the CDP and the feature is applicable (i.e. monotonous) if the predefined criterion can be satisfied using the established dataset of the feature. Once the applicable features are determined, the corresponding degradation models are built for remaining useful life prediction. Experiment results are presented to illustrate the performance of the proposed method.