Abstract:

Multi-gear clutchless automated manual transmissions (CLAMTs) are increasingly used in electric vehicles (EVs), as the electric motor can operate in a higher efficiency zone under various driving conditions compared to fixed-ratio gearboxes. A novel unilateral Harpoon shift is developed as an alternative for conventional cone-type synchronizers used in electric vehicles equipped with multi-speed CLAMT, aiming to improve the gearbox's efficiency and performance. Harpoon shift can overcome the drawbacks of traditional synchronizers, including friction loss and wear, and simplify gearshift control. A detailed dynamic model of Harpoon shift is established to investigate the transients of the proposed synchronizer during engagement. Also, an experiment is performed to evaluate the engaging performance of Harpoon shift and validate the effectiveness of the model. Besides, the effects of rotating speed and speed difference on the torsional shock during engagement are analyzed quantitatively. Results show that the rotating speed has no significant impact on the torsional shock during engagement, whereas the speed difference plays an important role in Harpoon-shift performance. The proposed unilateral Harpoon shift has obvious advantages over the traditional synchronizers, and it is desirable for electric vehicles to improve the transmission’s efficiency, reduce the overall energy consumption during gearshifts, and consequently extend the driving range.