Research On Digital Design Method Of Variable Ratio Pinion For Recirculating Ball-type Variable Speed Ratio Steering Gear For Agricultural Vehicle

Improving the operating conditions of drivers and strengthening the production safety of agricultural machinery is an important goal in promoting the high-quality development of China’s agricultural equipment.Agricultural vehicles are frequently steered due to complex and changing road conditions,and often need to be loaded with agricultural equipment for highload operations.The contradiction between steering portability and steering sensibility is becoming more and more prominent,which is very likely to cause driving fatigue and even lead to major accidents.As a reliable solution,the recirculating ball-type variable ratio steering gear has significant advantages for further improving the handling stability,driving comfort and driving safety of the vehicle.However,the complex tooth geometry of the variable transmission ratio beveloid pinion,the core component of the recirculating ball-type variable ratio steering,makes it difficult to balance efficiency and accuracy with the current mainstream design methods.Therefore,in order to explore the transmission characteristics of the newly developed recirculating ball-type variable ratio steering gear and to further enrich the design theory of the variable transmission ratio pinion,this paper takes the variable transmission ratio beveloid pinion in recirculating ball-type steering gear as the research object,combines the "gear element" discrete concept and CAD software to study an efficient and accurate design method for variable transmission ratio beveloid pinion,and validates such design method from multiple perspectives.Firstly,the basic principles and design procedures of the current mainstream gear design methods,CAD envelope method based on imitation machining and analytical method based on meshing theory,are elaborated,and corresponding examples of variable transmission ratio thickened gears are designed with the aid of CATIA software and MATLAB software,and the application characteristics,advantages and disadvantages of these two methods are comprehensively analyzed.Then,the gear element method is proposed for the generation of tooth surface points of variable transmission ratio beveloid pinion,the gear element model of the variable transmission ratio beveloid pinion and straight rack shaper is constructed,and the tooth surface constraint equations of variable transmission ratio beveloid pinion are derived.With the preset initial value and the parallel computing capabilities of MATLAB are introduced,which leads to the development of an efficient algorithm for the solution of the variable ratio tooth surface points,and a mesh-type variable transmission ratio tooth surface point cloud with an approximately uniform distribution is yielded.Subsequently,a method for calculating the normal error in the evaluation of the accuracy of the gear element method for solving the tooth face points is proposed in conjunction with the analytical method based on the meshing theory.And a highquality modelling of the variable transmission beveloid pinion has been completed using CATIA software.Finally,based on the finite element method,the transmission characteristics and transmission errors of the variable transmission beveloid pinion and straight rack pair are analyzed under two input torques and four preload assembly conditions.A prototype of the variable transmission beveloid pinion is manufactured by CNC end-milling and a transmission ratio test is carried out.The transmission error and the ratio test error were combined to verify the correctness of the variable transmission ratio beveloid pinion design method proposed in this paper.The paper establishes a direct "bridge" between tooth surface point generation and tooth surface fitting modelling,further promoting and improving the application of the "gear element method",which can improve the design of variable ratio gears for recirculating ball-type variable ratio steering gears.It is of great theoretical significance in promoting the research and application of recirculating ball-type variable ratio steering gears.