A Physical Simulation Platform of Bump Motion for Test of In-Wheel Motors

The bump motion of in-wheel motors (IWMs) is a key concern in addition to motor vibration, which have significant influence on motor's mechanical and thermal dynamics. In comparison to motor vibration, the frequency of bump motion is considerably lower, whereas its amplitude is significantly higher. This paper develops a physical simulation platform to experimental simulate the bump motion of an electric vehicle (EV) on a standard sine-wave track, and the mechanical and thermal dynamic characteristics of IWMs under bump motion could be further tested. A cam-roller mechanism is designed to drive the tested IWM system up and down vertically, according to the specifications of an automotive proving sine-wave track constructed by BYD, an EV manufacturer located in Shenzhen, China. The target vertical amplitude of bump motion is designed as 4.5 cm, and the maximum vertical frequency of bump motion is 1.59 Hz at the cam's rotation speed of 95.4 r/min. By adjusting the profile and rotation speed of the cam, the desired vertical amplitude and bump frequency can be modified to meet various test requirements. A speed control algorithm with torque feedforward is proposed for a 3 kW, 1435 r/min asynchronous motor equipped with a gear reducer, which is used to compensate the variation of the cam's load torque and ensure the highly stable rotation speed of the cam. An online torque feedforward correction method is proposed to compensate errors in parameters of torque feedforward calculation, and avoid frequent manual parameter calibrations. Moreover, the parametric sensitivity of torque feedforward is analyzed. Simulation and experimental results demonstrate that the cam rotates smoothly at the maximum speed of 95.4 r/min under a full heavy load of 415 kg. The measured speed fluctuation is less than 2.04%, and the measured displacement, velocity, and acceleration curves of the tested IWM system in the vertical direction are consistent with the target values of IWMs on the sine-wave track.