Brake-by-wire architecture design and analysis in accordance with functional safety standard

Abstract

The brake-by-wire (BBW) system is one of the safety-critical components of intelligent vehicle chassis, and ensuring its reliability requires a comprehensive functional safety design process. Although many studies have been conducted on electro-mechanical braking (EMB), there is a lack of relevant content on electro-hydraulic braking (EHB), another scheme of BBW system. And the key components affecting EHB system reliability need to be further explored. To address these issues, a system-architecture for EHB with fail-operational capabilities based on ISO 26262 is proposed. Additionally, Fault tree analysis (FTA) and Bayesian network (BN) are used for assessing its reliability. Fault tree (FT) is established to quantitatively calculate the Automotive Safety Integration Level (ASIL). Then FT is mapped into BN, and the conditional probability table is modified to express the polymorphic and uncertain logical relationship of events. To mitigate the dimensional disaster caused by numerous risk factors in the joint probability distribution, a Noisy-or gate method is applied in the BN to address this problem. Finally, the crucial events of system reliability are analyzed. The results indicate that the proposed EHB architecture can meet the safety and reliability requirements of ASIL D and can provide essential reference for the design of EHB related fail-operational system.