Abstract A method for calculating dynamic root stresses of helical gears is proposed,based on local mesh refinement approach of tooth root,analysis of dynamic behaviours of gear transmission system and 3 D FEM.In order to improve greatly the accuracy of computation,following factors are taken into consideration:simultaneous engagement of three pairs of teeth;influence of deformation of rims and webs of gears;influence of deformation of shafts and bearings;gear base pitch errors and tooth profile errors.The transient responses of dynamic root stresses are replaced by the root stresses under dynamic loads.In this case it is possible to avoid the complicated natural vibrational behaviours and dynamic response analyses of gear teeth.Experiments of the dynamic root stresses of the helical gears are carried out to verify the validity and reliability of the presented numerical method.The calculated results are in agreement with experimental ones.The calculations and the experiments show that the distributions of the dynamic root stresses of the helical gear teeth in meshing have basically three stress peaks.The maximum dynamic stress of the tooth root and stress fluctuations will increase with the increase of the rotational speed.As the input torque increases,the dynamic stresses of tooth root increase.But their dynamic stress factors have a decreasing tendency as the elastic deformation of the gear structure will increase with increasing the input torque.
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