Braking force control strategy for electric vehicles with load variation and wheel slip considerations

The braking system plays an important role in electric vehicles. In order to achieve high energy regeneration efficiency and also ensure driving safety at the same time, the regenerative braking system should be well coordinated with the mechanical braking system. As the brake-by-wire technology is developed, individual control of braking force on each wheel can be realised, which is suitable for the future electrified vehicles. This paper aims to investigate the braking force control strategy for electric vehicles under a low road friction condition. In order to further improve the braking force control accuracy and eliminate the effect of the vehicle load variation, a vehicle load estimation method is proposed. The standard hybrid braking force control strategy of electric vehicle is introduced for comparison with the proposed control strategy. To prevent a front wheel lock-up and maximise the regenerative braking efficiency under a low tyre-road friction condition, a revised control strategy is presented with the front wheel slip ratio consideration. Simulation results indicate that by using the proposed strategy, the vehicle braking performance under the low tyre-road friction condition is guaranteed and the regenerative braking force on front axle is fully utilised compared with the standard control strategy.