Thermal-mechanical Coupling Analysis Of Drum Brake

The braking performance of electric bicycle drum brakes seriously affects driving safety.In 2018,the new national standard of "Safety Technical Specifications for Electric Bicycles" was promulgated,which puts forward higher requirements on the braking performance of brakes.Due to the non-uniform frictional contact between brake drum and friction plate under working situation,some phenomenon such as local hot spots and non-uniformly distributed temperature field appear on friction pair.Because of thermal expansion,both brake drum and friction plate would be deformed randomly so that the parameters like contact area,contact stress and friction coefficient of friction pair are constantly changing.As a result,greater braking jitter and concentrated wear of friction plate are caused.This article focuses on the 80-type drum brake of electric bicycle,and analyzes the distribution of temperature field and stress field of its friction pair under different braking conditions.Through physical experiments,the influence of brake drum speed and brake holding force on the temperature rise of the brake friction pair is tested and analyzed.In order to improve the problems of brake jitter and excessive local wear of the friction plate,brake optimization suggestions are proposed based on the results of thermal-mechanical coupling analysis and experimental testing under different braking conditions.The main research work is as follows:(1)Analysis of the working condition of the brake.The working principle of 80 drum brake is discussed.The contact state of the friction pair is analyzed using a combination of graphic method and numerical calculation method,the analysis result shows that the brake drum and the friction plate are in non-uniform contact,and the middle position of the outer surface of the friction plate is the first and main contact area.Using classical mechanics theory,brake force analysis is carried out.(2)Dynamic performance analysis of brake.Using 3D modeling software,the geometric model of 80 drum brake was established.Based on the brake geometric model,the brake rigid-flexible coupling dynamics simulation model was established using dynamics software.Under two typical working conditions of continuous braking and emergency braking,the propulsion force of the brake cam to the leading and follower shoes is solved by simulation,and the dynamic performance of the brake is analyzed.The theoretical calculation results of the propulsion torque are compared with the propulsion torque indirectly calculated through the rigid-flexible coupling simulation results,and the correctness of the rigid-flexible coupling dynamics simulation model is verified.(3)Physical experiment measurement of temperature at specific points of friction plate.Based on the similar principle,a temperature measurement platform with equidistant measurement points of the friction plate in the circumferential direction was built.The influence of the brake drum speed and brake holding force on the temperature rise of the friction plate measurement points was tested and analyzed.The results show that the temperature rise at the measuring point in the middle of the friction plate is the largest,and the location where friction contact occurs is mainly located in the middle of the friction plate,which is consistent with the non-uniform contact analysis result of the friction pair.Under long-term continuous braking,the middle position of the friction plate is prone to excessive wear.(4)Thermal-mechanical coupling simulation analysis and optimization suggestions for drum brakes.Using finite element software,a thermal-mechanical coupling simulation model of the drum brake was established.The distribution of temperature field and stress field of the brake under two typical working conditions is analyzed.The influence of the material characteristics of the brake drum on the temperature rise of the brake friction pair is explored.In order to improve the problems of brake jitter and excessive local wear,the following optimization suggestions are proposed based on the results of thermal-mechanical coupling simulation analysis and experimental testing: for brake drums and friction plates,materials with large specific heat capacity and thermal conductivity should be selected comprehensively;the material of the friction plate with large rigidity should be selected;the outer surface of the friction plate in the width direction is designed as a concave arc surface.