Hydraulic Brake Systems for Electrified Road Vehicles: A Down-sizing Approach

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Electrification of road vehicle powertrains is currently emerging as a global trend in automotive industry. This transformation does not affect powertrain systems solely, yet it entails revolutions in the remaining vehicular elements as well. In this framework, new research trends have recently arisen in the field of braking concerning the optimal control of regenerative braking and the optimal re-sizing of hydraulic systems for electrified vehicles. Despite the first topic is being adequately assessed in literature, few works have been presented regarding the optimal design of hydraulic brake systems for electrified road vehicles. Nevertheless, thanks to the regenerative braking torque provided by the electrical powertrain, remarkable opportunities are offered to downsize the components of current hydraulic brake systems and allow them operating at enhanced efficiency.

The authors of this paper have recently proposed an optimization framework for hydraulic brake systems of conventional (i.e. non electrified) road vehicles. Safety homologation standards were evaluated from EU regulations and implemented as design constraints. Then, optimization criteria were set in identifying optimal brake system layouts for different vehicle parameters. Design parameters included the master cylinder diameter and stroke, the vacuum booster diameter, the amount of wheel cylinders for both front and rear brakes and their diameters.

This paper aims at extending the developed optimization methodology to hydraulic brake systems for electrified vehicles. Particularly, particle swarm optimization (PSO) is adopted here as exploration algorithm for the design space. Then, several numerical simulations are performed for each retained sizing candidate by implementing a complete vehicle model in Amesim® software. The performance of hydraulic brake system sizing candidates can be thus assessed by simulating time-based braking maneuvers from safety standards for both fully loaded and lightly loaded vehicle conditions. Finally, the optimal layout can be determined by minimizing a size function for the overall hydraulic brake system.

A comparison is performed between two case studies considering a pure electric powertrain and a conventional internal combustion engine powertrain for the same vehicle body. Results demonstrate that, in the case of an electrified powertrain, the hydraulic brake system can be effectively downsized in order to reduce weight and cost. The proposed sizing methodology could thus potentially find implementation in computer-aided engineering (CAE) tools for designing the future hydraulic brake systems for electrified road vehicles.

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