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

Down-sizing hydraulic brake systems can is made possible in electrified road vehicles thanks to the braking torque contribution provided by electric machines. Benefits in terms of weight and cost of the system can be ensured in this way. Nevertheless, appropriate care should be taken not to excessively deteriorate the overall electrical energy recovery capability of the electrified vehicle during braking maneuvers. For this reason, a multi-target optimization framework is developed in this paper to down-size hydraulic brake systems for electrified road vehicles while simultaneously maximizing the braking energy recovery capability of the electrified powertrain. Firstly, hydraulic brake system, electrified powertrain and vehicle chassis are modeled in a dedicated simulation platform. Subsequently, particle-swarm optimization is employed as search algorithm to identify optimal sizing parameters for the hydraulic brake system. Sizing variables particularly include diameter and stroke of the master cylinder, electrically assisted booster diameter, front brake piston diameter and rear brake piston diameter. The simulation of homologation tests for safety standards ensures that retained combinations of sizing parameters complies with regulatory requirements. A case study proves that the developed methodology is flexible and effective at rapidly producing several sub-optimal sizing options for both front-wheel drive and rear-wheel drive layouts for a retained battery electric vehicle.