Proof of concept for dog clutch-based electric transmission system via preview control

Abstract

Commercial electric vehicles require a transmission for efficient driving and motor downsizing because of their large mass and significant vehicle load changes. However, existing transmissions are unsuitable for electric vehicles due to low power transmission efficiency, so new electric transmission is required. Since the dog clutch has a simple configuration and excellent power transmission efficiency, it is suitable for electric transmission. However, the dog clutch has a problem of torque hole, which power is cut off because speed synchronization and engaging process are required during the gear shift. Therefore, in this paper, the torque hole is minimized through four-wheel-drive architecture and preview gear shifting using forward information to show the applicability of the dog clutch for the electric transmission. First, present an architecture that can minimize the torque hole that occurs during gear shifting. The proposed architecture comprises a front motor and a rear motor with a transmission. This architecture can minimize the overall torque hole by controlling the front motor during gear shifting, and efficient driving is possible through power distribution between the two motors. Next, using the dynamic programming method, a global optimization method, the occurrence of torque holes is minimized. This result was compared and evaluated with the existing gear shifting method without forwarding information and confirmed that the proposed method could significantly reduce the torque hole. Therefore, if the forward prediction is possible, the possibility of using the dog clutch in electric transmission was verified through preview gear shifting.