Finite Element Contact Analysis Of Helical Gears With Surface And Shaft Deviations

Involute cylindrical gears are commonly used in industry, especially in the wind turbine gearboxes, which requires better performance. Modifications can be very useful to improve the loading capacity of gearboxes. Surface and shaft deviations are important errors which can greatly affect gear strength. A pair of helical gears in wind turbine is studied in this paper using finite element contact analysis. Moreover, modification methods are researched and the influences of surface and shaft deviations are evaluated.Firstly, the formulas of continuous profile curves are educed from the formulas of the cutter profile curves, so the profile of helical gears can be fast and accurately created. Part model and full model are separately built for different modifications. Meshing and loading methods are discussed for the analysis of helical gears, and comparisons with other loading methods are also included to validate the usability of this loading method for part model.Secondly, the theories of different modification methods, including profile modification, longitudinal flank crowning and helical slope, are investigated by analyzing the relationship and aim of various deformations, based on the results of contact analysis of part model and full model. The results of part model with profile modification and full model with modifications show that the modification method can avoid the scratch of tooth tip and the impact when entering and exiting, and greatly decrease the end effect and load offset.Finally, the influences of surface and shaft deviations on load distribution along the contact lines are studied. Surface deviations assigned with grades 5 and 7 are divided into five basic types, including single pitch deviation, profile form deviation, profile slope deviation, helix form deviation and helix slope deviation. The results of part models with different surface deviations show that their influences are various on transverse load distribution and face load distribution. Furthermore, they're changeable in different deviation grade and load magnitude, and additive to a certain extent. Shaft deviations including center distance deviation, shaft parallelism deviations and bearing clearance are researched based on full models. By comparing their different influences, suggestions are made to improve the recommended formulas of shaft parallelism deviations. The method of involving bearing clearance in full model does well in determining the position and direction of shaft which is in better agreement with the real condition. The finite element method for helical gears focuses on the celerity and accurateness of modeling and loading. The modification values derived in this thesis are utilized in practice with good results. The classified research of surface and shaft deviations in this thesis is more detailed than in former researches, so differences and similarities of their influences on load distribution can be revealed clearly, to support the further research on influences of errors and design of high performance gearboxes.