Vertical vibration analysis on electric vehicle with suspended in-wheel motor drives

In-wheel motor drive (IWMD) is currently a hot topic in electric vehicle research and development for its remarkable advantages. But the extra wheel mass from the motor worsens vehicle ride comfort and road holding. Motor vibration is another problem, which does harm to motor performance and service life. As a trial response to the above problems, a 1/4 car model is established for electrical vehicles driven by suspended in-wheel motors. Five indexes are then employed or defined to evaluate vehicle performances and motor vibration, which are the road holding, vehicle suspension deflection, motor suspension deflection and vertical vibration accelerations of the body and the motors. After sensitivity analysis on motor suspension parameters, optimization is then performed with two different cost functions defined in terms of the amplitude-frequency characteristic of each of the indexes. One function, noted as A-Opt, is the area enclosed by a characteristic curve and frequency axis. The other function, noted as P-Opt, is the summation of the peak values of the characteristic curve. Both the transfer function and the variance of the response are used to describe the vehicle performance. With the former function, focus is mainly put on the frequency response characteristics of the vehicle. With the latter one on the other hand, attention is paid to average amplitude variation for the vehicle on a typical road. Results are compared with those of equivalent electrical vehicles driven either by a centre motor or by fixed in-wheel motors. Results demonstrate that a properly designed motor suspension can effectively improve the performances of vehicles with in-wheel motor drive, including ride comfort, road holding and motor working condition. Furthermore, the second optimization strategy has advantages over the first one with regard to vibration reduction and resonance elimination.