Contact Fatigue Design of Helical Gear by Spur Gear Equivalency

Abstract

Contact fatigue failure or pitting is a common mode of gear failure. High speed gearing is therefore prone to pitting and scoring failure modes. A simplified contact stress capacity model that is explicit in the representation of helical gear design parameters is developed. The model gives estimate of the contact stress expected in a helical gearset during meshing. Also, the model clearly reveals the direct influence of the base helix angle on contact stress and normal module size estimates. Contact stresses for five design Examples from different references are computed using the new contact stress capacity model and compared with AGMA estimates. The results show very favorable comparisons because the percentage variances between the new model and AGMA contact stress estimates are within -10% to 6% in this study. The Examples cover a wide range of the helix angles which spans 15 The new model appears to give slightly higher contact stress values in general so that for preliminary design, it offers the advantage of providing conservative solutions. The new contact stress capacity model was modified for design sizing and its application is demonstrated in Example 6. Comparison of the service load factor values for design sizing and design verification indicates a difference of only 0.9% in Example 6. The new model may be used for contact fatigue design of spur gears if the helix angle is taken as zero degree.