Dynamics and control of gear shifts in a two speed electric vehicle

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Conference Proceeding
Advances in Applied Mechanics Research, Conference Proceedings - 7th Australasian Congress on Applied Mechanics, ACAM 2012, 2012, pp. 698 - 707
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Electric vehicles have become an alternative to conventional and hybrid electric passenger vehicles, with the capability to provide higher overall powertrain efficiencies through the omission of conventional combustion engines. However, as a result of lower battery energy density as compared to fossil fuels, electric powertrains have limited range capabilities, leading to a phobia of electric vehicles and limited consumer acceptance. Furthermore, small electric motors typically cannot achieve the diverse functionality of conventional vehicles, most particularly for vehicle performance and grade climbing in comparison to vehicle range. As a result, multi-speed transmissions have been suggested as one strategy to improve the powertrain performance and increase the functionality of electric vehicles. By increasing the number of gear ratios the motor can operate under higher efficiencies for a wider range of vehicle speeds. The vehicle can then be designed to operate at a more diverse range of operating conditions, increasing the speed range and torque deliverable at lower speeds. To realise this objective there is a necessity to provide gear shift strategies unique to electric vehicles, delivering high quality gear shifts without relying on conventional vibration isolators such as torque converters or torsional dampers. This paper presents modelling, simulation, and control of a two speed electric vehicle. Demonstrating through enhanced precision of torque estimation and control in the electric machine it is possible to minimise powertrain response during and after gear shift transients, thereby improving driver comfort. The contents of this paper will therefore provide a detailed framework for powertrain modelling with electric vehicles, identify appropriate shift strategies for stepped automatic EVs, integrate these to develop shift control algorithms, and finally provide simulation results for up shift transients. Results demonstrate that it is possible to both improve post shift transient response of the powertrain and reduce the inertia phase of gear shift using the proposed methods.
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