An electric vehicle (EV) drive system with dual low output motor can high efficiency drive on the wider conditions than a drive system with a high output motor. Gears, clutches, and brakes for merging multiple driving force are important drivetrain elements, and they are studying by a number of automotive companies and research institutes. This paper proposes a dual-motor EV drive system with planetary gear set and unique dog brake for changing drive mode. A dog rotor of this brake is composed to two-piece of dog ring and coil springs. A drive dog ring and a regenerate dog ring are connected by springs each other, and these springs are extended when dog engaging and disengaging. This brake can be in one of the following three states: 1. An engaged state for single-motor drive, 2. A disengaged state for dual-motor drive, 3. A stand-by state for changing the drive mode from single-motor drive to dual-motor drive. The combination of double dog rings and spring force make benefits of reducing power and NV when EV drive mode changes. The dual-motor EV drive system with the proposed dog brake can expand the operating region compared to the previous drive system. In addition, the brake can be disengaged simultaneously with starting of the motor like as an one-way clutch. Moreover, the proposed dog brake absorbs the energy of the rotating parts, because the timing of brake engagement is controlled when the EV drive mode changes. We prototyped the new dual-motor EV drive system and evaluated its basic performance. The results of these study indicated that when the drive mode was changed, the driving torque gap was reduced by up to 53% by control of the engagement timing. Therefore, its application to pure EV as well as drivetrains for several vehicle (PHEV, FECV) drivetrains may be beneficial.

Dr. Eng. Isamu Shiotsu, Researcher, Toyota Central R&D Labs., Inc.