I. Introduction
Electric vehicles (EVs) are becoming important, not only as an environmental measure against global warming but also as an industrial policy [1]. In order for them to be used widely, the next-generation EVs must be safe and perform well. The propulsion force generation mechanism (i.e., motor-drive structure), which strongly influences the safety and running performance of the vehicle, is crucial to meeting such requirements. However, completed systematic research into the propulsion force generating mechanism of EVs has been limited [2]–[5], and studies on failsafe control in the event of failure of the electronic parts that constitute the drive systems of EVs [6]–[10] are nearly completed. Since the unexpected behavior of the vehicle that occurs at the time of failure may induce a serious traffic accident, the failsafe structure of the drive systems that generates the propulsion force should also be examined, taking vehicle stability at the time of failure into consideration. In addition, the drive structure should be constituted so that the running performance is sufficient in vehicles that must continue running in a stable way on various road surfaces.
Propulsion force generation mechanisms in conventional EVs and the FRID EV. (a) Front- or rear-wheel drive-type EV. (b) Two or four in-wheel drive-type EV. (c) FRID EV.
Issues on the safety occurring during running on low- road surfaces. (a) Steering operations. (b) ABS operations.