Abstract
The popular kinds of tooth surface deviations of helical gears, i. e. Profile slope deviations, Lead slope deviations, Bias, Lead crowning, Profile crowning, Tip relief and so on, do not always have a good correlation with gear noise by themselves. So, even if all inspected factors of tooth surface are within the allowable tolerance, gear noise could be often bad, and even if all inspected factors of tooth surface are without the allowable tolerance, gear noise could be often good. In this paper, the most important factor of tooth surface that has a good correlation with gear noise is discussed. At first, many kinds of tooth surface deviations are investigated. It is found that gear noise is very sensitive to the slope along the path of contact and the convex curvature along the path of contact has a good correlation with gear noise. Next, the design method of tooth modifications is proposed. When the slope deviation along the path of contact could be large as the limit of the tolerance, the level of gear noise is in the worst condition. In this condition, a gear pair with some large convex curvature along the path of contact is quieter than with small convex curvature. Therefor, the convex curvature along the path of contact should be determined by the allowable tolerance of tooth surface slope.
