| Gear transmission is the most widely used transmission type at present.With the development of material industry and the continuous improvement of lightweight requirements for products,plastic gear is gradually widely used,such as auxiliary transmission system,latch,reducer,printer and so on.Compared with metal gear,plastic gear has the advantages of light weight,vibration absorption,self-lubrication and easy production and processing,but at the same time,plastic gear is not as strong as metal gear and more sensitive to temperature,so it is easier to fail in work than metal gear.In this paper,the helical gear pair in the transmission system of an automobile electric power brake is taken as the research object,the metal gear is taken as the driving wheel,and the plastic gear made of POM is taken as the slave wheel.The theoretical analysis and finite element simulation of this kind of gear pair are carried out,and the following work is mainly completed:(1)The contact characteristics of metal and plastic were analyzed,the viscoelastic mechanics model of plastic gear was established,the contact pressure model of metal and plastic helical gear pair was analyzed,the contact mechanics of the gear pair was theoretically analyzed by using Hertz contact theory.(2)UG software was used to establish a three-dimensional model of the gear pair,and the model was imported into ANSYS software to carry out the finite element contact analysis.Through simulation,the stress,strain and distribution of the gear pair under different torques were obtained,and the maximum contact stress law of the gear pair under different contact friction coefficients was obtained.(3)The steady temperature field finite element numerical simulation of plastic gear was carried out,and the friction heat flow model of helical gear pair meshing was established.According to the temperature field theory of gear meshing,the friction heat flow of gear pair under certain working conditions was calculated,and the single tooth finite element model of plastic gear was established.By calculating the boundary conditions,the temperature distribution of plastic gear single tooth under different speeds and loads was obtained,and the influence law of the maximum temperature of plastic gear under different working conditions was analyzed.(4)Based on the structural analysis and temperature field analysis,the thermalstructural coupling analysis of the gear pair was carried out.The maximum equivalent stress and strain under the coupling field were obtained by introducing the thermal load into the structural field,and the stress and strain obtained under the same working condition were compared and analyzed with the structural field.Then the stress and strain of the gear pair with or without the elastic modulus affected by temperature change are analyzed and discussed respectively.(5)Through the simulation analysis of the finite element model,it is found that the stress concentration at the tooth root of the plastic gear is the cause of the tooth root fracture.Therefore,the structure of the plastic gear is improved by the method of transiting the fillet radius through the tooth root.Combined with the finite element comparative analysis test,the radius of the plastic gear root transition fillet was obtained,and the optimal modification radius was calculated.The stress-strain distribution law of the structural field and coupling field before and after modification was compared,which verified the feasibility of the modification method and improved the strength of the plastic gear. |
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