Modeling And Analysis On Contact Stress Of Helical Gears In Heavy Automotive Transmission

Helical gearing is widely applied into the mechanical transmission, which iswidely adopted due to its high efficiency and stable transmission. Teeth surface pittingfrom stress concentration and gear fatigue damage caused by excessive contact stress inthe course of transmission gears will shorten the gear design lifetime. So the gearcontact stress is very import for gear transmission, it’s necessary to study the dynamicand static contact stress of helical gear in order to improve its lifetime and contactstrength. The main contents includes1) An parametric model of involute helical gear was built based on UG software.The model can be easily changed in terms of gear geometric parameters. And a highquality finite element grid model was established based on HyperMesh software.2) In order to analyze the errors of the results between part teeth and whole bodymodels, five finite element models of a pair of helical gears which include three teethmodels with or without wheel rim, five teeth model with or without wheel rim and awhole body model were established and the static and dynamic contact simulation of thehelical gears were completed with finite element method. The results show that the fiveteeth model gives more accurate results than the three teeth model regardless of themodel with or without wheel rim in the static analysis. Whereas both the three teeth andfive teeth models with wheel rim have much less errors than those without wheel rim inthe dynamic analysis.3) The static contact finite element analysis of involute helical gear based onANSYS software was conducted, and the equivalent stress of gear and stressdistribution could be calculated. The result showed that the gear sharp edges createstress concentration seriously.4) the dynamic contact finite element analysis of involute helical gear based onANSYS/LS-DYNA was also conducted in this paper. The change rule of equivalentstress and stress distribution with time could be calculated. Then the influences ofdynamic contact performance by different tooth flank clearances of gear wereresearched, which showed that the contact stress of gear is larger with the clearanceincrease.5) The dynamic contact stress analysis model of gears in a heavy vehicletransmission four gears was established; the influence of dynamic contact stress by the stiffness of supporting shaft were researched. The results showed that the shaft bendingdeformation is apt to cause the gearing mesh unstable, and is easy to produce largerstress.6) Because the maximum contact stress due to stress concentration is bigger thanallowable stress which was caused by the gear sharp edges. Based on the modificationtheory, this paper researched gear profile and drum modification. Dynamic finiteanalysis on the model of a heavy vehicle transmission four gears after modification wasconducted. After modeling and analysis, comparison results before and aftermodification revealed that: gear contact stress decreased and the shock and stressconcentration decreased obviously after the modification, and the distribution of contactstress is uniform, which is satisfied with the intensity requirement.