Driving Safety of Electric Vehicles with Unconventional Service Brake Topology

The increasing market share of electric vehicles (EVs) leads to novel questions regarding brake system design. To maximise efficiency and cover strict particulate emission standards, a novel and disruptive braking system concept could be beneficial, in which the conventional friction brakes of the rear axle are replaced by a central axle brake module integrated into the driveline. This arrangement eliminates wheel-individual service brake intervention on the rear axle, which are generally used for electronic stability control (ESC). This thesis discusses the driving dynamics potentials and challenges of such a system.

To demonstrate the lateral dynamics potential of the new brake system topology, a proposal for a dedicated vehicle dynamics controller (VDC) is introduced into a software-in-the-loop simulation environment. The investigations on lateral dynamics identify certain limitations in under- and over-steering-critical situations. Performance degradations during braking and acceleration on inhomogeneous (µ-split) surface are also discussed. Especially the acceleration case represents a clear physical limitation that can only be solved by bespoke hardware measures, e.g. limited slip differentials (LSDs).

This work puts special emphasis on the development of a methodology for the assessment and selection of passive LSDs. It extends known approaches for the quantification of driving dynamics properties such as the Milliken-Moment-Method, but also considers the impact of LSDs in daily driving conditions. As an alternative, a novel parking brake concept is presented that combines conventional parking brake functionality but also supports climbing ability on µ-split. This multi-disc brake concept is mounted on the differential housing and is acting on the axle shafts.