Effect of the ISO 6336-3:2019 Standard Update on the Specified Load Carrying Capacity Against Tooth Root Breakage of Involute Gears

Part 3 of the ISO 6336 standard contains a verified specification for calculating the tooth bending strength of involute gears. In November 2019, an update of the previous version from the year 2006 was issued, which includes more detailed calculation methods based on the most recent research findings. For an optimal gear design, gear engineers need to be aware of how the changes in the standard affect the overall calculation result, since the revised standard can yield a higher or lower safety factor against tooth root breakage. This paper provides a detailed summary of the key changes in ISO 6336-3:2019, outlines their overall effects on the basis of a calculation study, and presents a comparison of the results to the previous version of the standard, ISO 6336-3:2006. The key changes in ISO 6336-3:2019 are a new load distribution influence factor that accounts for the effects of high overlap ratios and a more precise consideration of the helix angle on the stresses. Furthermore, the standard now also covers the determination of the tooth root geometry of internal gears by means of a shaper cutter. To investigate these changes and their overall effect, we vary the contact ratio by using gears with different transverse contact ratios and overlap ratios as a basis for computing the specifications of the standard. In addition, by simultaneously varying the transmission ratio and the tool tip radius, we investigate the effect on the calculation of internal gears with different tooth root geometries. The findings of this research give a detailed insight into how the update enhances the ISO 6336 standard and how they affect the load carrying capacity calculation.