Control-oriented modelling and experimental modal analysis of Electric Vehicles with geared In-Wheel Motors

Electric Vehicles (EV) equipped with independent drives are capable of controlling the car body motion in multiple degrees-of-freedom with driving force distribution through the suspension reaction force. These electric powertrains could thus suppress primary (1 - 3Hz) and secondary (4 - 10Hz) resonant modes improving ride comfort, road holding and safety of passenger cars. On-Board-Motor (OBM) drivetrains can subdue primary vibrations including the heave, pitch and roll modes, but are limited by the torsional resonance of the half-shaft. In-Wheel-Motor (IWM) drivetrains alleviate the torsional restriction potentially reaching higher bandwidths and thereby improving road holding and passenger comfort. However, the additional unsprung mass aggravates the secondary vibration urging for an appropriate motion control design. This research proposes a dynamic model in multiple degrees-of-freedom for vibration suppression control and an experimental validation of both primary and secondary dynamics in EVs. In this work, the vibration performance of both powertrains are compared on a test vehicle in experimental and operational conditions. Moreover, the modal coupling between the torsional, longitudinal and vertical motions are analysed and the slip-ratio dependency assessed. The deterioration in dynamic behaviour using IWMs is demonstrated and a precise parametric model identified for vibration suppression control of geared In-Wheel-Motor drivetrains.