Brake-by-Wire System Redundancy Concept for the Double Point of Failure Scenario

Brake-by-wire (BbW) systems are one key technology in modern vehicles. Due to their great potential in the areas of energy efficiency and automated driving, they receive more and more attention nowadays. However, increased complexity and reliance on electric and electrical components in BbW systems bring about new challenges. This applies in particular to the fault tolerance of the brake system. Since drivers cannot form a fallback layer of braking functions due to the mechanical decoupling of the brake pedal, known BbW concepts provide a redundant system layer. However, driving is significantly limited in the event of a failure in the BbW system and is only possible under certain restrictions. The reason for that is a further possible failure (double point of failure scenario), which can result in a significant loss of braking performance. To improve the availability level of the braking functions, a principally new redundancy concept for the double point of failure scenario is presented. This allows for a less restricted driving operation when the BbW system is subject to failures. For this purpose, a central electric motor (CEM) and modified electronic parking brake (EPB) actuators are used on the front axle of a vehicle to form a separate redundancy layer. Strategies for deceleration and wheel slip control are developed for the individual actuators as well as for their simultaneous operation. The performance of the different brake modes is evaluated in road tests. The analysis shows that especially the combined operating mode of the CEM and EPB leads to high deceleration levels and robust operation in low road friction conditions.