The Structure Optimization And Reliability Analysis Of Small-scale Combine's Gearbox Shell

As China's important agricultural crops,rice and wheat have been harvested by the largescale harvesting machinery in the northern region.However,the paddy fields are small and uneven in the southern hilly region.It is difficult to move and turn for a large harvester in such terrain conditions that the combine cannot works.While the small size combine has a unique advantage in the hilly areas because of its smaller quality and volume.This requires that the small size combine has high compact structure so that installation space of shell of the gearbox is extremely limited.The high reliability is required for the long time continuous operation and severe impact of the combines,what's worse the loads is large in the deep paddy fields during the harvest season.The shell of the gearbox can provide a closed space for internal gears,shafts,bearings and other parts,playing the protect and installing role.But the gear meshing precision will be influenced by the load stresses and deformations of the shell of the gearbox under the large transfer power.Therefore,to ensure the strength and stiffness of the shell is the design focus.However,the thickness of gearbox is often made larger to guarantee the performance index at the expense of increasing the mass and degrading the all combine performance in the conventional design.Meanwhile the structural reliability of the gearbox housing is affected directly by the transmission housing size parameters,material properties and working loads that are all uncertain.In this thesis,the combine harvester gearbox shell as a research object has been designed for structure topology optimization to achieve minimum structure supple degree,getting the optimal layout of reinforcement;and been designed for size optimization to achieve a minimum quality and amount of deformation of the shell under meeting the stress and frequency requirement.The static and dynamic characteristics of the gearbox shell before and after optimized are analyzed by finite element numerical simulation,and then the finite element modal analysis is verified by modal test.The analysis showed that the strength and rigidity,dynamic characteristics are enhanced for the optimized gearbox with reducing the mass in 16.7%.Finally,the shell of the gearbox has been assessed by structural reliability analysis,achieved the design optimization and a reasonable assessment.