考虑机电耦合的电动轮系统纵向振动特性建模及验证

为了研究机电耦合对电动轮系统的纵向振动特性的影响,该文首先建立了电动轮纵扭耦合动力学模型,基于该模型分析了考虑机电耦合前后电动轮系统模态特征的变化,并通过轮毂电机驱动电动轮系统的振动特性试验,验证了该动力学解析模型的准确性;其次分析了机电耦合对电动轮系统纵向振动的影响,指出转矩波动引起定转子发生相对运动,导致电机发生偏心,从而产生不平衡磁拉力。不平衡磁拉力的作用导致非簧载部分纵向振动出现不同程度的恶化,当轴承刚度为12.5 MN/m时,在定子纵向平移模态频率下电机的定转子、轮胎纵向振动加速度分别恶化113.35%、105.69%、27.15%,影响其使用寿命和结构安全,而对于簧载部分纵向振动的影响较小。

Modeling and validation on longitudinal vibration characteristics of electric wheel system considering electromechanical coupling

Abstract: Recently, distributed-drive electric vehicle has become one of the development directions of future vehicle with the advantage of miniaturization and high performance. The electric wheel system is a key component of distributed-drive electric vehicle. The longitudinal dynamics of electric wheel system caused by torque ripple of the in-wheel motor is more significant than vertical. The existing studies on longitudinal vibration analysis of electric wheel system are always taking stator and rotor as a whole. Actually, the electric wheel is a complicated electromechanical coupling system. The longitudinal vibration of electric wheel system causes the relative displacement of rotor and stator, resulting in unbalanced magnetic pull (UMP) that acts on the surface of rotor and stator. The induced UMP by electromechanical coupling changes the characteristics of the longitudinal vibration and deteriorates the performance of the electric wheel system further. Therefore, it is important to consider the effects of UMP caused by electromechanical coupling on the longitudinal vibration of the electric wheel system. Longitudinal vibration characteristics of an electric wheel system considering electromechanical coupling was studied in this paper. Firstly, the electric wheel longitudinal-tensional coupling dynamic model was established, and the variation of the modal characteristics for the electric wheel system with and without electromechanical coupling was analyzed. It needs to indicate that the modal shapes of the electric wheel system are identical considering the UMP, but the fifth order modal frequency is decreased obviously. This mode was characterized as the longitudinal translation of the stator. The accuracy of the analytical dynamic model was verified through vibration test of a one-quarter electric wheel system. The electric wheel system adopted a double-wishbone suspension and was installed on the experiment bench developed by the research group. During the test, the tire was driven by the in-wheel motor and directly contacted with the drum. The load on the tire was exerted by the drum to simulate the resistance in the course of vehicle running. The longitudinal acceleration of tire was measured by an acceleration sensor. Time frequency map of the tire longitudinal vibration was then extracted. Three main resonance regions could be found near 48, 94 and 141 Hz, which were consistent with the modal frequencies obtained by the established analytical model. This verified the accuracy of the analytical model on longitudinal dynamics of electric wheel system. When longitudinal vibration frequency of the vehicle driven by in-wheel motor was near 2-3 Hz, it significantly affected the riding comfort as people are sensitive to low-frequency longitudinal vibration. While the high frequency longitudinal vibration is not favorable to the motor. Finally, the longitudinal vibration characteristic of the electric wheel system considering electromechanical coupling was studied. The time and frequency domain acceleration of vehicle body, stator, rotor and tire were obtained by simulation. It inferred from the quantitative analysis that torque ripple caused the relative displacement of stator and rotor, resulting in eccentric of the motor and UMP. The UMP is regarded as external force for the stator and rotor of the motor, while it is regarded as internal force for the vehicle body and tire. As a result, the unbalanced magnetic pull had little influence on the longitudinal vibration characteristic of sprung mass. However, it deteriorated the longitudinal vibration characteristic of unsprung mass sharply, which was harmful to the service life and structure safety. Therefore, it is necessary to consider the unbalanced magnetic pull caused by electromechanical coupling in the development of electric vehicle. This study provides guidance for the design of electric vehicles driven by in-wheel motor.