Optimal braking force allocation for a four-wheel drive fully electric vehicle

Control allocation can be used onboard fully electric vehicles in order to maximise the regenerative power produced during braking manoeuvres. In this study, the efficiency characteristics of an electric motor are used in conjunction with constraints from European braking regulations in an offline optimisation procedure aimed at maximising the regenerative power yielded at different motor speed and braking demand conditions. The resulting optimisation data are used in a simple online control allocation approach via a look-up table. Simulation results highlight significant motor power loss reductions and small increases in regenerative power under various levels of braking demand in comparison with a wheel torque allocation scheme in which the front axle-to-total braking force ratio is maintained at a constant level. The approach does not rely on complex online optimisation schemes and can thus be practically implemented in real time on fully electric vehicles.