An overview of calculation methods of load carrying capacity of gears is given in the paper. The standard procedure for determining tooth-root and contact stresses in spur gears is defined in ISO 6336 standard. Tooth-root stress is approximated by bending stress caused by tangential force component, while compressive stress, caused by radial force component, and shear stress are neglected. The whole force acting on one tooth is used in calculations. This simplification of calculation is taking into account by using numerous influence factors in formulae. Finite element method is the most commonly used numerical method for determining tooth-root stresses in gears' teeth. Linear analysis or nonlinear contact analysis can be used. In linear analysis the whole force acting on one tooth is used for the calculation. The procedure for determination of load distribution on teeth in simultaneous contacts is given to improve the accuracy of this numerical method, especially when high contact ratio gears are analysed. The application of nonlinear contact analysis of gears in mesh gives very accurate results, without necessity of previously known load distribution. Instead of the force applied on one point on the tooth flank, the load is applied by putting the pinions' and wheels' teeth in contact and applying the torsion moment on the pinion. The formulations for these analyses are presented in the paper.

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