Computation of Safety Architecture for Electric Power Steering System and Compliance with ISO 26262

Technological advancement in the automotive industry necessities a closer focus on the functional safety for higher automated driving levels. The automotive industry is transforming from conventional driving technology, where the driver or the human is a part of the control loop, to fully autonomous development and self-driving mode. The Society of Automotive Engineers (SAE) defines the level 4 of autonomy: “Automated driving feature will not require the driver to take over driving control.” Thus, more and more safety related electronic control units (ECUs) are deployed in the control module to support the vehicle. As a result, more complexity of system architecture, software, and hardware are interacting and interfacing in the control system, which increases the risk of both systematic and random hardware failures. In order to reduce these risks and minimize any potential failure or loss of control, ISO 26262 Standard provides guidance to the automotive original equipment manufacturers (OEMs) and suppliers (tier 1) to ensure an adequate and acceptable level of safety procedures is implemented in the vehicle control modules. This study focuses on the electric power steering (EPS) system and its automotive safety integrity level (ASIL) assignment. It was found that new challenges have emerged recently for the EPS system such as higher forces at the steering rack and more Advance Driver Assistance Systems (ADAS) functionalities; Consequently, The ASIL computation has shifted for the EPS system because any sudden loss of assistance (LOA) may lead to catastrophic accidents. The definition of controllability in ISO 26262 is not fully mature and needs some modification in the light of the above given facts of the functional safety of an EPS system. The study proposed a new metric to relate a range of torque magnitudes to the controllability class C0 - C3 in table B.6 part 3 ISO 26262 Standard.