Studies on brake blending and developing of braking control strategies to maximize performances and energy efficiency for a Formula SAE electric vehicle

The present thesis comes from the interest on electric vehicles that was born from my experience in Formula Student team of Politecnico di Torino for seasons 2018/2020. Electric vehicles are becoming more and more widespread as car companies are investing on them. Part of the investment comes from the need to redesign some important systems of the ICE vehicles. The braking system is one of them since the braking ability of the vehicle is now shared between the friction and electric systems. This work has the aim to search the best way to implement regenerative braking in coexistence, also called blending, with friction braking and get a better understanding regarding to what extent a regenerative brake system can recover energy and how it will affect vehicle stability and manoeuvrability along with changes for the typical brake systems. To do so, the thesis first focuses on ideal brake studies to understand the principles of brake system design and the duality between ideal performance and real system performance. The effects of unbalanced braking and braking out of ideal conditions is so studied by also the presentation on typical systems used to increase brake efficiency along with more modern systems like ABS and EBD. These studies are important to understand the effect of regenerative and the need for increasing efficiency that require the forces to be away from ideal line, a requirement that is opposite to brake balance and shortest brake distance. Regenerative braking is presented by the analysis on its characteristics and limitations coming from the other, eventual, elements inside electric powertrains. The way the regenerative braking and friction braking can coexist are presented by first division upon legislation definitions and then addressed by presenting two different layouts, based on the level of technology present in vehicles and the respective logics to blend the braking effects are explained. Results are finally collected based on the analysis on typical brake power and energy used in WLTP and NEDC test procedures that are standard used for automotive in Europe. These studies let understand the eventual impact and performance windows required in braking and the pros and cons of each hybrid braking system. Finally, the same approach is presented on the formula SAE vehicle of Squadra Corse PoliTO that, being a formula vehicle, presents new design constraints and needs that focuses mostly on performance but on the other side, present higher forces and accelerations that could lead to higher regenerative efficiency. The regenerative impact is studied based on typical Formula Student events data, and the target values are developed along with a deep study on the eventual use of regenerative strategy on accelerator pedal, following what is typically called “Single pedal control”.