The Influence of the Magnetic Force Generated by the In-Wheel Motor on the Vertical and Lateral Coupling Dynamics of Electric Vehicles

摘要

For the in-wheel motor (IWM)-driven electric vehicle, the drive motor is directly integrated in the wheel. The magnet gap deformation of the motor can be generated due to road surface roughness (RSR) excitation, uneven load, and other reasons. The magnet gap deformation will lead to unbalanced magnetic force, which is a critical vibration source to the vehicle dynamics. Focusing on this problem, an IWM-driven electric vehicle without a speed reducer is considered as the research subject, and an 11-degree-of-freedom dynamics model is developed and verified to study the magnetic force influence on vehicle vertical and lateral coupling dynamics. The effect of magnetic force on the vehicle dynamics is analyzed under two operation conditions first. The results show that the magnetic force makes all dynamic response variables deteriorate in different degrees, regardless of the operation conditions, which indicates that the magnetic force has some negative influence on both the vertical and lateral vehicle dynamics. The results also show that even if the hub bearing stiffness is 5 MN/m, the maximum magnet gap deformation of the IWMs can still reach a big value. Therefore, the hub bearing stiffness should be designed to be stiff enough to conquer the magnet gap deformation under permitting conditions. In addition, extended study is performed with different motor speeds to further investigate the vehicle coupling dynamics. The results show that all the root-mean square (RMS) values of the evaluation indexes increase with the increase in motor speed. This result contributes to both RSR and magnetic force, since the motor speed is not only related to road excitation but also concerns magnetic force. For electric vehicles driven by IWMs, magnetic force must be considered as one of the important factors in the system design. This study can provide some theoretical basis for the design, optimization, and coordinated control of the IWM-driven electric vehicles.