Modeling and control of ball-ramp electromechanical clutch actuator for in-wheel AMT of electric vehicles

A novel ball-ramp electromechanical clutch actuator (BR-ECA) based on the in-wheel two -speed transmission topology for electric vehicles is proposed in this study. It is compact, lightweight, and installed within the wheel to achieve accurate gear shifting. Moreover, the actuator motor is parallel to the transmission central axis and mounted on the knuckle, thus freeing the limited arrangement space. A ball-ramp self-energizing mechanism is designed to enhance the clutch normal force, which allows for a lower-torque motor. In this study, the physical structure and dynamic model of the BR-ECA are described in detail. Furthermore, considering the strong nonlinear characteristics in the system, a triple-step nonlinear controller is designed for clutch position tracking. Finally, the good continuous controllability and tracking accuracy of the actuator are validated through simulations and experiments. The complete engagement/disengagement time is less than 0.3 s, and the steady-state error is less than 0.05 mm. Compared with the PID, the tracking error of the continuous step response is reduced by 6.4% and the sinusoidal response at 1 Hz is reduced by 10.09% under the triple-step nonlinear controller.