Master cylinder pressure reduction logic for cooperative work between electro-hydraulic brake system and anti-lock braking system based on speed servo system

Abstract

As one feasible solution of brake-by-wire systems, electro-hydraulic brake system has been made available into production recently. Electro-hydraulic brake system must work cooperatively with the hydraulic control unit of anti-lock braking system. Due to the mechanical configuration involving electric motor + reduction gear, the electro-hydraulic brake system could be stiffer in contrast to a conventional vacuum booster. That is to say, higher pressure peaks and pressure oscillation could occur during an active anti-lock braking system control. Actually, however, electro-hydraulic brake system and anti-lock braking system are produced by different suppliers considering brake systems already in production. Limited signals and operations of anti-lock braking system could be provided to the supplier of electro-hydraulic brake system. In this work, a master cylinder pressure reduction logic is designed based on speed servo system for active pressure modulation of electro-hydraulic brake system under the anti-lock braking system–triggered situation. The pressure reduction logic comprises of model-based friction compensation, feedforward and double closed-loop feedback control. The pressure closed-loop is designed as the outer loop, and the motor rotation speed closed-loop is drawn into the inner loop of feedback control. The effectiveness of the proposed controller is validated by vehicle experiment in typical braking situations. The results show that the controller remains stable against parameter uncertainties in extreme condition such as low temperature and mismatch of friction model. In contrast to the previous methods, the comparison results display the improved dynamic cooperative performance of electro-hydraulic brake system and anti-lock braking system and robustness.