Design and testing of a braking control logic for independently driven electric wheels

Anti-lock braking control strategies have the aim of avoiding the wheel locking condition, in order to reduce the stopping distance and preserve the handling of the vehicle during the braking manoeuvres. Furthermore, the spreading of electric vehicles offers the possibility of adopting new powertrain layouts. Among those, the most interesting is represented by vehicles with independently driven wheels, i.e., one motor per wheel. This paper proposes a braking control logic particularly intended for independently driven electric wheel, in which the electric motor brakes the wheel and handled the wheel dynamics to avoid locking in braking. The control strategy is based on the estimation of the longitudinal force exchanged between the tyre and the road made possible by the motor torque estimation. The knowledge of the braking force allows to improve the braking performance with respect to conventional acceleration based strategies. The effectiveness of this strategy has been verified both in numerical simulation with a full car vehicle model and in a dedicated test-bench that reproduces the quarter car longitudinal dynamics.