Development of two-speed dual-clutch transmission for seamless gear shifting in EVs

•The control object is a two-speed DCT for electric vehicles, which controls the motor and two clutches.•Theoretical equations that enables seamless gear shifting was derived.•Simulations have shown that by shifting gears based on the derived theoretical equations, shocks associated with gear shifting can be reduced and seamless gear shifting is possible. In recent years, there has been a shift from gasoline-powered vehicles to electric vehicles (EVs) owing to the tightening of fuel consumption and emission regulations in many countries. One of the challenges of using EVs is their short driving range, and transmissions are being designed especially for EVs to solve this problem. The installation of these transmissions should increase the driving power, efficiency, and maximum vehicle speed, resulting in improved driving performance. However, one of the problems of EV transmissions is the generation of shocks owing to the large gear ratio for the second speed. The magnitude of the shifting shock can be controlled by adjusting the amount of force applied to the clutch friction member, and seamless shifting can be achieved by controlling the motor torque based on the clutch-passing torque. However, the clutch-passing torque is not easy to estimate, as it depends on several factors, such as the difference in the rotational speed, temperature, and time-related deterioration. Therefore, in this study, a new system was developed to directly monitor clutch torque using a dual clutch transmission (DCT). Specifically, to achieve seamless shifting of a two-speed DCT for EVs, a system was devised to monitor the clutch transmission torque using a torque sensor, and seamless shifting by controlling the motor torque and the two clutches was investigated. First, a theoretical equation was constructed to elucidate the input–output relationship for the transmission. Next, it was confirmed that seamless gear shift control is possible based on this theoretical equation. Finally, a delay was added to the motor torque to verify if seamless gear shifting was possible.