Abstract: For the convenience of mechanical automation for traditional automobile brake pedal, an automatic brake pedal mechanism with circular section is designed according to the general automobile brake pedal structure form. A kinematics model of the automatic braking pedal is established using the principle of mechanism kinematics. A method for determining the optimal section arc size is proposed based on geometric constraints of the pedal structure. Take a brake pedal of an electric vehicle as an example, the optimal section arc size is calculated, and compared with the CATIA DMU model and the bench test data in which the correctness of the established model is verified. A practical vehicle brake test is carried out, and the feasibility of the designed automatic brake pedal mechanism is explained. The results show that the computational results of the established kinematics model are completely consistent with the results of CATIA DMU model, and are also very close to the bench test data. In the brake simulation for the optimal section arc size, the maximum horizontal deviation between the tangency points and pin vertexes is less than 0.54 mm, which means the mechanism can transfer smooth and continuous braking force. In the real vehicle brake test, the designed automatic brake pedal can be effectively implemented in braking processes such as the slow brake, fast brake and man-machine separated brake of a self-driving vehicle.

Key words: brake pedal, mechanism design, kinematic geometry, self-driving