The Purpose of this paper is to estimate the root bending stress of a helical gear tooth. and to present factors and formula which can be used practically to appraise the stress accurately. Most methods for estimating the stress have been mainly based on analysis and test results for spur gears, and have not been sufficiently accurate. In order to estimate the stress more accurately, the finite element method, in which the calculated load distribution is applied to the 3-dimensional finite-element model, was introduced. After verifying the method through several tests with strain gages, factors and formula were derived using the method to estimate the stress in the range of automotive transmission gear dimensions. The accuracy of the methods were then confirmed through several examples.
