Designing And Testing Of A Differential Steering Gearbox For Crawler Combine Harvesters

China has about 30 million hectares and 200 million tons total output of rice.Crawler combine harvester is gradually developing towards large-scale,high-capacity and light-weight with the increase of single yield of rice.In order to overcome the problems of low steering efficiency,low service life and reliability and damage to soil quality caused by single-side braking steering of traditional crawler combine harvester in heavy clay field,a differential steering gearbox is to be designed,which is matched with a full-load 7-ton crawler combine harvester and can realize pivot steering and free radius steering.The main research work of this paper is as follows:1.A differential steering gearbox for crawler combine harvester was designed and its principle was verified by kinematic simulation.Based on the requirements of 7-ton capacity and steering mode of the harvester,the transmission principle was designed.Also,the ratio and the distribution of gear teeth number at all levels were completed.After checking,the fatigue strength of all gears met the requirements.Then,the topology of the gearbox end layout was extracted to optimize with the minimum end area of the transmission system as the objective function.The end area was reduced by 15.4%.Moreover,the kinetic characteristic of planetary gear differential mechanism was analyzed theoretically and the kinematic simulation was carried out.The results show that the crawler combine harvester runs in a straight line and the speed of left and right output half-axis is proportional to the output speed of the driving Hydrostatic Transmission(HST)which works alone.The crawler combine harvester turns at the original point when steering HST works alone and the speed of left and right output half-axis,which increases with the output speed of the steering HST,is equal but the direction is opposite.The crawler combine harvester turns with free radius when driving HST and steering HST works simultaneously.Similarly,the speed and direction of two HSTs affect the turning radius and turning direction of the harvester respectively.2.The parametric model was established and the structural optimization design and static analysis of gearbox body was carried out.Based on the response surface method,the size of the gearbox body was optimized with the purpose of minimum mass,minimum maximumdeformation and minimum maximum-stress.In addition,the fitting curve,sensitivity correlation and response surface parameters were analysed and the results show that the wall thickness has the maximum effect on the objective function.Then,the static analysis of the finite element model of the gearbox body before and after optimization was carried out.The results indicate that the mass,maximum deformation and maximum deformation was reduced by 12.7%,17.8%,7.6% respectively.Eventually,the light-weight design is realized while the strength and stiffness of the gearbox body are improved.3.The key gears of planetary gear differential mechanism were modified microscopically.Conceptual model and detailed model of planetary gear differential mechanism were established by Romax Designer software.According to different working conditions of crawler combine harvester,power flow and load spectrum were defined and set.Then,the tooth profile and flank profile of sun gear and output gear were modified after simulation analysis.After the micromodification,the maximum load of per unit meshing length on the surface of sun gear and output gear tooth was reduced by 51.5% and 47% respectively,while the transmission error of sun gear and output gear was decreased by 34.8% and 31.8% respectively.Meanwhile,the stability of the transmission and the bearing capacity of the gear were improved after modification.4.Trial-manufacture,assemble and bench test were carried out on the differential steering gearbox.The gearbox was processed by 3D print as the same-size ratio,using Photosensitive Resin,which was assembled and installed on the test bench.A test scheme was designed in order to verify the relationship between the input and output speed of the gearbox.The principle of the differential steering gearbox was proved to be correct by the test.