Abstract: In order to improve the vehicle dynamic stability, the driving and braking force distribution between the front and rear axles for 4WD electric vehicle is investigated. According to the friction circle of tyre force, the ideal force distribution ratio is obtained, at which the wheels of the front and rear axles reach the adhesion limit simultaneously when the vehicles operate at various conditions. The vehicle handling stability under different distribution methods is analyzed by simulation using 4WD vehicle model. Simulation and theoretical analysis results show that the idea distribution method proposed in this work can improve utmost the lateral stability of the vehicle under the premise of ensuring the current longitudinal acceleration. In addition, for 4WD electric vehicles, the change of turning radius with longitudinal acceleration is minimized and the vehicles have the best maneuverability. Furthermore, the ideal distribution method is simple in calculation and relies little on the vehicle state information, so is easy for application in real vehicles.

Key words: vehicle engineering, force distribution between axles, handling stability, four-wheel-drive, electric vehicle