Fail-Safe Study on Brake Blending Control

Battery electric vehicles (BEV) share the ability of regenerative braking since they are equipped with two independent types of deceleration devices, namely the electric motor working as a generator and the friction brakes. Correct interaction of these systems in terms of driving safety and energy efficiency is a function of the Brake Blending Control. Individual electric motors for each wheel and a decoupled brake system provides the Brake Blending with a high design flexibility that allows significant advantages regarding energy consumption, brake performance, and driving comfort. This paper is focusing on the fail behaviour and analyses the robustness and redundancy abilities of such systems against various error scenarios. For this purposes, a distributed x-in-the-loop environment, consisting of dedicated simulation and hardware testing components, is introduced. The investigation is carried out based on a high-fidelity real-time simulation model of an electric sport utility vehicle with four in-wheel motors (IWM) and decoupled electro-hydraulic brake system. This model can be used for a detailed analysis of vehicle dynamics in case of brake system fails. The electro-hydraulic decoupled brake system is implemented through a Hardware-in-the-loop test rig, which allows a realistic fault injection. The vehicle stability and controllability is investigated under the circumstances of various brake system failures in the regenerative and friction brake system, respectively. These studies are presented according to standardized test scenarios like Straight line braking (DIN 70028) and Brake-in-turn (ISO 7975). With obtained x-in-the-loop simulation results, the impact of a failure on vehicle dynamics is discussed in the final part of the paper.