| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 101 === Involute gears have advantages such as simple manufacturing process, low sensitivity due to the center distance deviation, and high transmission efficiency etc., so it is widely applied in various power transmission equipments. However, vibration, noise, and even tooth surface damage will occurr during the gear mesh because of variation of mesh stiffness and tooth tip corner contact. Therefore, profile modification on gear teeth is a commonly method to reduce the violent change of loading on teeth and to avoid tooth contact on tip corners beyond the normal line of action. But the profile modification is equivalent to a special kind of tooth profile deviation, it is necessary to analyze the loaded tooth contact stress of the gear pairs with or without profile modification to understand the influence of different profile modification design on the performace of gear drives in practical application.
The aim of this study is to analyze the influence of tip relief, a common profile modification method for involute spur gear, on tooth contact stress. This study includes (a) identification of occurrence of tooth tip corner contact and analysis of contact stress distribution of the involute spur gear pair without profile modification, and (b) the influence of different tip relief types on load sharing and contact stress distribution of involute spur gear pairs. At first in the thesis, occurrence of tooth tip corner contact of involute spur gear pairs without profile modification under different loads is identified based on the geometric relation of gear mesh. Then static load sharing and tooth contact stress distribution of spur gear pairs without and with different tip relives are analyzed by using stiffness method and influence coefficient method respectively. The types of tip relief discussed in the study include linear long and short tip relief, tip rounding, parabolic tip relief, etc.
The results of the load sharing analysis show that linear tip relief and parabolic tip relief can improve problem of the violent load change, but tip rounding or other tip chamfer types can not improve it.
According to the results of the loaded tooth contact analysis, non-Hertzian contact of tooth pairs occurs at the positions before the theoretical contact begin and after the theoretical contact end of the tooth pair without tip relief. The values of the corresponding contact stress are much larger than the value of normal contact. The maximum contact stress occurs at the position nearby theoretical contact begin and end position. The type of non-Hertzian contact can be avoided effectively by using the linear tip relief and the parabolic tip relief, but tip corner contact of tooth pair with tip rounding still occurrs. In addition, stress concentration can be also found at starting position of the tip relief, if the tip relief curve is not smooth.
The analysis results show that the calculation modules for load sharing and loaded tooth contact analysis developed in this study are reliable and time-saving for calculattion, so they can be used for tip relief design and analysis efiiciently.
Keywords: Tooth Tip Corner Contact, Tip Relief, Tip rounding, Load Sharing, Tooth Contact Stress
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