Gearshift Analysis for an Electric Vehicle with a Novel Synchronizer Mechanism
- Publication Type:
- Thesis
- Issue Date:
- 2020
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Multi-speed clutchless automated manual transmission (CLAMT) can offer many benefits for electric vehicles (EVs). It improves the driving efficiency and transmission performance compared to single-speed EVs. Currently, most multi-speed transmissions use conventional cone-type synchronizers for speed synchronization. However, these friction elements are a major source of inefficiency in multi-ratio gearboxes. Friction losses and heat dissipation can significantly influence transmission performance. In addition, frictional wear has a considerable impact on the service life and shifting performance of traditional synchronizers.
To overcome these drawbacks, the concept of unilateral Harpoon-shift synchronizer is introduced in the study. It aims to improve the gearboxes’ efficiency and riding comfort, meanwhile, simplify the shift control logic for EVs with the multi-gear transmissions. A detailed dynamic model of the unilateral Harpoon shift is built to study the engaging performance of the proposed synchronizer. Besides, to investigate the powertrain transients, an original dynamic model of the CLAMT power-train system which integrates the Harpoon shift model is developed in the study. Also, to guarantee a smooth gear change, torque and speed profiles are designed using a modified step function for the torque control and active speed synchronization of the electric motor (EM) in EVs. Up- and down-shift simulation results verify the effectiveness of the proposed models as well as control logic. Furthermore, to reduce the jerk during gear shifts, the Harpoon-shift torque spring stiffness in each gear is optimized via quantitative analysis. Also, the impacts of rotating inertia and speed difference on the vehicle jerks are quantitatively investigated. In addition, an experiment is conducted to study the engaging performance of the unilateral Harpoon shift and prove the effectiveness of the dynamic models.
To improve the performance of the unilateral Harpoon shift, a new concept of bilateral Harpoon shift is proposed for the multi-speed EVs equipped with CLAMTs. Then a detailed and original multi-body model of the bilateral Harpoon shift is established, aiming to capture the synchronizer's transient behavior during the engagement. In the model, the engaging process is defined as six stages, and it can cover the interacting cases between the engaging-related parts, including guide ring, sleeve, and dog gear. Then the model is integrated into the established model of the powertrain system to analyze the gearshift vibrations, allowing to investigate the engaging performance of the bilateral Harpoon shift based on the shifting shocks. Based on the integrated model, gearshift simulations are conducted and the impacts of the torque spring stiffness and tooth chamfer angle on the shifting shocks are comprehensively analyzed, and the two significant parameters are then optimized. Furthermore, comparisons are performed to demonstrate the superiority of the proposed torque profile over its counterpart based on the modified bump function. Results show that the proposed Harpoon shift can achieve high-quality gear change for EVs and meanwhile overcome the friction-related drawbacks of traditional synchronizers. Besides, the Harpoon shift greatly simplifies the shift control strategy due to its special engaging mechanism.
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