Design And Meshing Performance Analysis Of Rack And Pinion Steering With Variable Ratio

The steering gear is the most important part of the steering system,which undertakes the main function of the steering system.The traditional constant ratio steering gear can not meet the two indexes of steering portability and steering sensitivity at the same time,that affects the vehicle handling stability.The mechanical steering with variable ratio not only meets the requirements of steering portability and steering sensitivity,but also has the advantages of high reliability,low cost and strong versatility,so it has been paid more attention by researchers.Among the existing design methods of rack and pinion of mechanical gear with variable ratio,the answer is not unique in solving the tooth surface equation with analytical method,while the machining simulation method generates trace of cutting,resulting in inaccuracy.For this reason,this thesis studies the accurate design method and meshing performance of the rack and pinion of mechanical gear with variable ratio.In this thesis,the design requirements of variable ratio curve are analyzed from the perspectives of vehicle steering performance and steering function to get the variation characteristics of variable ratio curve,the general term formula of variable steering ratio curve function is established and the selection basis of various parameters and the calculation method are studied.In addition,the evaluation methods of steering portability and sensitivity of variable ratio steering were analyzed to vertify the correctness and effectiveness of the design method of variable steering ratio curve.Secondly,with the relevant theory of non-circular gear,the mesh principle of rack and pinion with variable ratio is studied,and a discretization envelope design method for the rack and pinion with variable ratio is put forward,the mathematical model of the rack and pinion with variable ratio is established and an efficient and accurate extraction algorithm is put forward for extracting rack tooth profile point.At last,a GUI system is developed for the design of rack and pinion with variable ratio,which reduces the design difficulty and improves the design efficiency.Then,three kinds of 3D models of the rack and pinion with variable ratio are designed,and the corresponding relationship between geometric structure and transmission ratio is analyzed,which verifies the rationality of the design method.The virtual prototype model is established for kinematics simulation to verify the feasibility and correctness of the discretization envelope design method of rack and pinion with variable ratio.Through the finite element simulation of the rack and pinion with variable ratio,the mechanical properties in the meshing process are analyzed.And,in order to facilitate the subsequent dynamic analysis of the rack and pinion with variable ratio,the calculation method of time-varying meshing stiffness is improved.The research in this thesis is of great theoretical value for improving ratio curve’s design theory and modeling efficiency and accuracy of the rack and pinion with variable ratio,and is of great practical significance for promoting the complete localization and popularization of mechanical steering with variable ratio.