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The aim of this paper is to present an innovative electromechanical device which integrates a brushless DC (BLDC) hub motor with a speed-changing wheel hub stored on the rear wheel of an electric bicycle. It combines a power source and a speed-changing mechanism to simultaneously provide functions of power generation and transmission for electric bicycles. As part of the proposed integrated device, the wheel hub consists of a basic planetary gear train providing three forward speeds including a low-speed gear, a direct drive, and a high-speed gear. Each gear is manually controlled by the shift control sleeve to selectively engage or disengage four pawl-and-ratchet clutches based on its clutching sequence table. The number of gear teeth of each gear element of the wheel hub is synthesized. The BLDC hub motor is an exterior-rotor-type permanent-magnet synchronous motor. Two-dimensional finite-element analysis (FEA) software is employed to facilitate the motor design and performance analysis. An analysis of the power transmission path at each gear is provided to verify the validity of the proposed design. The results of this work are beneficial to the embodiment, design, and development of novel electromechanical devices for the power and transmission systems of electric bicycles.

In view of the oil leakage failure of the joint surface of the transmission case of an electric vehicle, a contact non-linear finite element method was used to analyze the tightness of the joint surface of the transmission case of an electric vehicle. Based on the workbench software, a finite element model of the transmission case is established. Determining the sealing performance of the case by calculating the distribution of the surface pressure and the opening of the case under static and high-speed conditions. Two optimization methods are proposed. The first method is to widen the box contact area of the oil leakage area; the second method is to increase the tightening bolts in the oil seepage area. After comparing the data obtained by the two optimization methods with the original data, it shows that reducing the sealing bolt spacing and widening the sealing surface where the sealing performance is poor makes the sealing performance greatly improved. This method provides an effective way to determine the tightness of the transmission case, provides a basis for optimal design, and lays the foundation for experimental research.