Abstract
The prospect of physical exertion commonly acts as a deterrent to the adoption of cycling for everyday transport. A battery powered assistance torque electric motor could alleviate such physical exertion by reducing the effort required by the cyclist. This study investigates the potential effectiveness, efficiency, and energy saving of electrically-assisted cycling when assistance torque of a switched reluctance motor is designed to vary in accord to the cyclist instantaneous torque at the pedal cranks. Specifically, the modulated motor assistance torque is delivered at the least efficient human input torque points on the cycle. For a representative short distance cycling schedule modulating the instantaneous torque of the on-board electric motor causes the electric energy expenditure to not exceed that of the assisted cycling mode of an identical constant-torque motor. Furthermore, for the same speed profile cycling journey with added road gradient and head wind resistance, the energy expenditure of the modulated torque motor is equal to the constant torque motor. These findings indicate significant improvements in the cycling experience.
Highlights
Assisted bicycles (e-bikes) require pedaling, and permit the rider to switch on battery-powered motor to reduce pedaling effort
Commercial e-bikes are generally heavier than conventional bicycles due to the additional battery, the motor in these bikes is engaged by pedaling, and the level of assistive power given by the motor can be adjusted
In this paper we introduce a Switched Reluctance Motors (SRMs) torque controlled by the time-varying torque generated by the cyclist
Summary
Assisted bicycles (e-bikes) require pedaling, and permit the rider to switch on battery-powered motor to reduce pedaling effort. In this paper we introduce a SRM torque controlled by the time-varying torque generated by the cyclist This torque is expected to improve the overall efficiency and reduce cycling effort. In [22] instantaneous electromagnetic torque waveforms of the SR machines are calculated based on a simple vector analysis of the flux-linkage map to avoid integration, non-linear curve fitting or geometrical series summation The novelty of this investigation is in the idea of providing motor assistance during the instantaneous human torque fluctuations within one crank revolution, rather than providing the constant torque assistance as with traditional e-bikes. The contributions of this work are: (a) Human torque is considered as part of the SRM design process to reduce the effort that the cyclist needs to put into cycling This will achieve better performance and lower energy consumption. A like-for-like comparison is performed for the modulated and constant assistive motoring torque modes in order to demonstrate the advantages the modulated assistive mode can offer
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