The Improvement Design And Optimization Of Micro-hillside Tractor

The study of micro hillside tractor is of great and strategic significance to realize agricultural modernization, accelerate mountain farming and social development in our nation. As one of the most important components in the micro hillside tractor, the gearbox which is composed of tight structure and small size is in charge of transferring power and controlling the steering. The velocity of gear must satisfy the requirement of farm work such as ditching and rotary tillage. Aiming at dealing with such weaknesses of gearbox as surplus structure size and insufficient gear in low velocity zone, the research has put forward plans to improve the gearbox. Based on modern design technologies, such as the combination of Virtual Prototyping, finite element analysis and optimal design, the research completed the three dimensional model of the improved gearbox on which finite element analysis and optimal designing have been conducted. By applying the Modern Design Methodology to optimize the gearbox, not only has its structure been improved but also the period of its research and development shortened, the efficiency of its design enhanced and the practicability of micro hillside tractor strengthened. The concrete research content and conclusions are as follows:(1) The structure formation and transmission project of the improved gearbox in micro hillside tractor have been conformed. PRO/E, which is a three-dimensional modeling software, has been applied firstly in the parametric modeling of all vital parts of gearbox in the micro hillside tractor, and secondly in the virtual assembly of those parts. Interference analysis and motion simulation have also been carried out.(2) By taking working conditions of gearbox in the micro hillside tractor when it is under the top gear as example, traditional mechanics analysis has been carried out on gear and shaft of the gearbox to check the strength of the shaft, the contact strength of gear surface and bending strength of dedendum. Thereby, whether the strength of gear and shaft fulfill work requirement can be tested and verified.(3) By leading the three-dimensional model which is established by PRO/E into NSYS WORKBENCH and then defining material properties, meshing and applying load and constraints, the linear static and contact analysis of gearbox of the micro hillside tractor can be achieved. In addition, stress and strain nephograms on the structure of gearbox can also be obtained. The comparative analysis between the obtained stress data and the results of theoretical calculation can verify the reliability of finite element analysis.(4) The constraint modal analysis on output shaft of gearbox in the micro hillside tractor provides a solid basis for kinetic analysis. By analyzing the results, the first ten natural frequencies and its corresponding modal shape can be got. By comparing the highest frequency of working gearbox and the natural frequency of each order, the fact that resonance is unlikely to occur in output shaft when it is working can be verified.(5) By stipulating the lightest weight and minimum volume as the objective functions and the design parameters and the strength requirements of wheel gear as the constraint conditions as well as making use of the optimization toolbox which comes with Matlab to optimize all the gear pairs when gearbox is under the top gear or shifting, optimal parameters of it can be received to reduce the weight and the manufacturing cost of gearbox.