The Finite Element Reaerach On Meshing Performance For The Small Modulus Gears Of Vechile Door Locking Devices

In the transmission of vechile door locks with a locking device, the majority of small modulus gears are paired by metal gears and plastic gears, and the metal gear mainly for the driving wheel. This type of gear not only has the light weight of plastic gear, low noise transmission, self-lubricating, it also can improve gear heat by the good thermal conductivity of metal materials. However, plastic materials with low elastic modulus, poor thermal conductivity, high thermal expansion coefficient. These characteristics limit the application of plastic gears. And the design and application of plastic gear, had not a single reference standard, and according to the metal gear will bring a greater difference. And, the research on such small modulus gear pair analysis is relatively little.Therefore, the analysis on this kind of gear meshing behavior of systematic and effective, has a certain theoretical and practical significance for the application of this kind of gear pair, also has higher economic effect to the enterprise, and has an important significance to the design criteria and research method on the gear. So, in this paper a car door locking device of small modulus gear pair was taken as the research object, firstly made gear model in the CAXA, then the theory of finite element analysis and finite element analysis software ANSYS12.0were used to undertake relatively comprehensive analysis and research on the performance of gear pair meshing. The main contents include:(1) The finite element analysis on the contact of gear pair:the establishment of a precise gear contact pressure model to study the gear in a meshing cycle and contact stress distribution of junction displacement, summed up in a mating cycle distribution, the result was:the maximum contact stress of gear pairs was obtained for the4.197MPa, the maximum strain was7.035μm, and occured in the gear pair meshing in node.(2) The finite element analysis on the bulk temperature field of plastic gear:detailed discussions the transmission process of heat generation and propagation in the gear pair, systematically introduced some definitions of heat transfer and basic equation of thermodynamics finite element analysis, the friction heat flow of the gear pair was calculated; a plastic gear single tooth model was established:the maximum temperature was42.447degrees when plastic gear working, the highest temperature appeared in the vicinity of pitch circle when temperature rised up to7.447degrees, the friction heat of metal gear distribued the heat flow of total frictional (as meshing at nodes up to91%)(3) Analysized the hot-stress coupling performance of the meshing gears in the node, based on structural analysis and thermal analysis, and discussed influence of thermal expansion coefficient and elastic modulus (decreases with increasing temperature) on the meshing performance; The contact stress was gotten in consideration of two factors thermal structure coupling analysis of maximum (10.449MPa) and in the only test elastic modulus affects thermal structure coupling analysis of minimum (3.950MPa), the main factor which affected the gear side thermal structure coupling performance was the thermal expansion coefficient of plastic gear.(4) The finite element was used to analysize the contact fatigue life of plastic, the failure mode and failure mechanism of plastic gear was discussed; The contact fatigue fatigue life when the gear meshing at the node was analysized; the plastic gear fatigue life up to52130(less than the actual requirement of60000), while the cumulative fatigue coefficient was1.91844.(5) The gears for durability experiment to test the results of finite element analysis were correct and reliability; The optimization of such gear ideas put forward direction: including gear size-parameter optimization, enhancement of plastic gears, better performance replacement materials.In conclusion, contact strength and heat resistance performance of gear can meet the job requirements, but also the larger redundancy. But the contact fatigue performance was not up to the work need, contact fatigue life can not meet the design requirements, which was one of the main reasons of the gear failure.