A simplified design method (SDM) for spur gears is presented. The Hertz contact stress and Lewis root bending stress capacity models for spur gears have been reformulated and formatted into simplified forms. A scheme is suggested for estimating the AGMA J-factor in Lewis root bending stress for spur gears from a single curve for both pinion and gear instead of the conventional two curves. A service load factor is introduced in gear design that accounts for different conventional rated load modifier factors. It represents a magnification factor for the rated load in a gear design problem.

Two design examples are considered for applications of the stress capacity models. In Example 1, the Hertz contact stress of the SDM deviates from AGMA value by 1.95%. The variance in Example 2 between the contact stress of the SDM and FEM is 1.184% while that between SDM and AGMA is 0.09%. The root bending stress of AGMA and SDM for the pinion in Example 1 differs by 1.44% and that for the gear by 6.59%. The difference between the root bending stress of AGMA and SDM for pinion and gear in Example 2 is 0.18%. These examples suggest that the new simplified method gives results that compare very favorably with both AGMA and FEM solutions. The simplified method developed is recommended mainly for preliminary design when quick but reliable solutions are sought.

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