Study And Development Of In-wheel Drive System For Electric Bicycle

China is a big country in the use of electric bicycles.After years of development,there are multiple types of bicycle drive systems and mature technologies.However,the market is chaotic,and over-standard bicycles have appeared frequently.With the enactment of the new laws and regulations "Electric Bicycle Safety Technical Specifications",the market will be strictly limited.Therefore,it is of great significance to develop a new in-wheel drive system that meets the requirements of laws and regulations and can achieve higher power density and smaller size and lighter weight.In this paper,the new in-wheel drive system will be studied from the theoretical calculation and simulation analysis.The motor is designed by field-circuit combination method.The two-stage planetary traction reduction bearing is designed by finite element simulation method.The rationality of the design structure is verified from the theoretical level.The main research contents are as follows:(1)A new in-wheel drive system configuration is proposed.The characteristics of the existing wheel drive system for electric bicycles are compared and analyzed.Combined with the dynamic performance requirements of electric bicycles and the layout of the body structure,a new type of wheel drive system configuration is proposed.It is driven by a high-speed outer rotor motor and is decelerated and twisted by a two-stage planetary traction reduction bearing.The two-stage deceleration is used to improve the motor design speed and improve the power density.The dynamic analysis of the electric bicycle was completed,and the design specifications of the motor and the reduction bearing were determined.(2)Design and analysis of motor structure and electromagnetic scheme.For the determined design indicators,the motor parameters are analyzed and calculated by the magnetic circuit method.Firstly,the effects of different winding schemes and different pole slot ratios on the motor are analyzed.The design of 12/10 pole slot ratio and double layer concentrated winding is selected.The design of the permanent magnet was completed,and the suitable permanent magnet material was selected.The structural arrangement and magnetization mode of the permanent magnet were determined,and the permanent magnet size was determined by parametric analysis.The parametric design of the air gap length is carried out to optimize the air gap magnetic density waveform.Select the appropriate yoke magnetic density to calculate the stator size and the size of the inner groove of the stator.The motor winding turns and back EMF are calculated and calculated.Finally,the results of the above design are optimized by Ansoft Rmxprt magnetic circuit calculation software,and the parameters are adjusted repeatedly to obtain the optimal results.(3)The performance of the motor was simulated and analyzed in Maxwell 2D finite element simulation software.Through the simulation of the static magnetic field,the magnetic field distribution and the air gap magnetic density waveform of the motor are obtained,and the motor is further improved and optimized through the simulation results.The performance of no-load start-up and no-load stable operation is analyzed,and the no-load counter electromotive force is obtained.The cogging torque of the motor is calculated and optimized.Analyze the running characteristics of the motor load and the rated load conditions to obtain the rated speed,rated torque and rated power of the motor.The results show that the design is achieved.The loss of the motor was analyzed and the motor efficiency was calculated to be 93.6%.(4)Completed the design and simulation of the two-stage planetary traction reduction bearing.Combined with the dynamic index of the electric bicycle and the output performance of the motor,the structure and size of the two-stage planetary traction reduction bearing are designed.The minimum wall thickness of the rolling element and the outer ring of the decelerating bearing was analyzed by the Workbench software,and the minimum interference after assembly was designed by the amount of deformation obtained by the simulation.On this basis,the structure and detailed dimensions of the decelerating bearing are designed,and the strength check under rated conditions is checked.The contact stress and bending stress are analyzed,and the results meet the strength requirements.Finally,the modal analysis of the reduction bearing is carried out to determine that the system does not generate resonance when working.