Structural Optimization Design Of Hydro-mechanical Continuously Variable Transmission Box Of Heavy Tractor

As an important agricultural equipment to promote the development of agricultural mechanization in China,tractors appear more and more in China’s agricultural production and operation.Transmission is an important part of the tractor power train,and as the transmission assembly in the mass,the largest volume of the transmission box,is an essential part of the tractor transmission system,directly affect the working performance of the entire tractor.In the process of tractor operation,due to the bad working environment,the box not only bears the action of the alternating load caused by the internal gear meshing,but also bears the vibration excitation caused by the complex terrain.If the transmission box is damaged,it will not only affect the performance of the vehicle,but also affect the driver’s life safety.Therefore,should have enough stiffness and strength to ensure the normal operation of the transmission.However,in engineering design,in order to guarantee the reliability of the box body,enclosure structure design tend to be conservative,directly caused the housing materials of waste and the increase of the overall quality,will make the transmission is too heavy,not only adds to the cost of production,and makes the vehicle fuel consumption will also increase at the same time.Therefore,the reasonable design of transmission box is an important guarantee to improve the working performance of tractor.In view of the design and optimization of the hydro-mechanical continuously variable transmission box(HMCVT)of heavy tractor,the research work in this paper is as follows:(1)Structure design of HMCVT box.Based on the schematic diagram of HMCVT,the layout of the whole transmission system is determined by considering the support of transmission parts inside the gearbox and the assembly sequence of parts in the later stage.Considering the connection requirements,space requirements and transmission cooling,lubrication and control requirements of the HMCVT box mounted on the heavy tractor,the overall structure of the HMCVT box was determined,and the three-dimensional model of the HMCVT box was established and the two-dimensional engineering drawings were drawn by using the relevant drawing software.(2)Structural characteristics analysis of HMCVT box.According to the schematic diagram of HMCVT,the rigid-flexible coupling virtual prototype model of the HMCVT system was established.Combined with the vibration test and theoretical calculation of the tractor under different driving conditions,the dynamic excitation of the bearing hole of the HMCVT box under different loading conditions was obtained.The statics analysis of the box structure was carried out to obtain the maximum stress and maximum displacement of the gearbox under different working conditions,and to judge whether the stiffness and strength of the gearbox meet the service requirements.The modal analysis of the transmission box was carried out to obtain the first ten natural frequencies of the transmission box.Combined with the vibration test of the tractor transmission box,the resonance of the transmission box during the operation of the tractor was judged.The dynamic analysis of the gearbox was carried out to obtain the stress variation history of the dangerous parts of the gearbox,and the S-N curve was modified to calculate the fatigue life of the gearbox by comprehensively considering the factors such as stress concentration,size effect,surface quality and load characteristics.(3)Topology optimization of HMCVT box.A compromise programming method is used to establish the comprehensive objective function of six sub-objectives,including three static stiffness conditions and three dynamic low-order natural frequencies.Then,the weight ratio of six sub-targets was taken as the design variables,and the Latin hypercube method was used to design the experiment,and 30 experimental samples were obtained.The proxy model was constructed based on the experimental samples,and the optimal weight ratio of each target was obtained by using genetic algorithm.Finally,the weight ratio obtained is substituted into the synthetic objective function for topology optimization.According to the results of topology optimization,the gearbox was redesigned,and the structural performance of the designed box was compared with the original box to verify the optimization results.