Reliability improvement of electric power steering system based on ISO 26262

Electric power steering (EPS) systems have been more and more widely used in medium and large cars. As a safety-critical system, its safety and reliability are uttermost important. ISO 26262 adapted from IEC 61508 provides a V-model as a reference process model for different phases of product development. In this paper, DFMEA (design failure mode and effects analysis) and FTA (fault tree analysis) complied with ISO 26262 are taken to analyze the safety aspects of EPS so as to enhance the safety and reliability of EPS. Firstly, the EPS system is decomposed into subsystems and components, and the familiar failure modes and undesired top events are separately divided into several categories. Then a comprehensive DFMEA for every single potential failure mode is carried out without omission as far as possible. The qualitative FTA is put into practice to identify the weak link as well. Since the DFMEA and FTA for EPS are finished, countermeasures for each potential hazard should be taken to guarantee the safety and reliability of EPS which are always achieved by fault detection and fault isolation algorithms of EPS hardware and software. Besides, some preventive actions are also taken in the early design stage to find out the potential causes.