Analysis On Bending Fatigue Stress Of Involute Helical Gear And Research On Test Method

The gear transmission has the advantages of accurate transmission ratio,high work efficiency,compact structure,reliable operation and long service life,which has become the most widely used mechanical transmission form in engineering field.Cylindrical helical gears(hereinafter referred to as helical gears)are the most widely used cylindrical gears,that are superior to spur gears with the same modulus in terms of transmission stability and load-carrying capacity.The occurrence of bending fatigue failure of helical gears can be reduced and prevent by studying the bending fatigue stress and accurately estimating its fatigue life.The reliability and power density of gear transmission system will be also improved.For the calculation and verification of the stress and life of helical gears,it is the commonly used method at present that calculating indirectly according to the calculation method given in the standard based on the S-N curve of gear material by the results of spur gear bending fatigue stress test.However,the calculation method of helical root stress in the national standard is empirical formula,which has some limitations.For the calculation of the stress of the large helical gear and the finite element simulation analysis,there is a large deviation,so the life calculation is unreliable.Firstly,the calculation method of the tooth root stress of the involute cylindrical helical gear in national standard GB/T 3480 is studied in this paper.The maximum tooth root stress of two groups of involute helical gears with different helical angles when transmitting the same torque is calculated.At the same time,Romax Designer software is used to establish the three-dimensional meshing model of these two groups of helical gears with different helical angles.Based on the finite element analysis method,the root stress of meshing gears is analyzed,and the root stress change process of meshing gears with the same torque and different helical angles during the meshing process is obtained and the maximum root stress is extracted.Then,the root stress calculated by the national standard method is compared with the maximum stress extracted by the finite element simulation analysis.The results show that there are obvious differences between the results of national standard method and the results of finite element analysis for helical gears with large helical angle,and the maximum is more than 20%.This indicates that there is an unreliable risk in indirectly calculating and evaluating the bending fatigue life of helical gears by the calculation method given by the national standard,so it is necessary to carry out bending fatigue stress test for helical gears.In order to complete the bending fatigue stress test of helical gears,according to the test requirements of GB/T 14230,this paper studies the method of simulating the meshing process of helical gears by finite element method to determine the position of loading line and loading load.This method can effectively determine the test parameters required for single-tooth bending fatigue stress test of helical gears,and provides a theoretical and methodological basis for single-tooth bending fatigue test of helical gears.In this paper,a set of bending fatigue test fixture,which can ensure uniform loading,is also designed.Through the finite element method,the biased load condition is simulated and analyzed.The gear fracture is uniform and tidy by using the new test fixture in the bending fatigue stress test,which verifies the rationality of the fixture design.It provides equipment basis for bending fatigue test of heliacal gears under single tooth loading in the future.