Full contact analysis versus standard load capacity calculation for cylindrical gears

Modern gear design is driven by full tooth contact analysis to determine adequate gear microgeometry. Engineers strive to optimize load distribution and make use of the full load carrying capacity of the gear set. Local stress levels in the tooth contact and the tooth root are important calculation results. But reliable values for the limits of the load carrying capacity are available for standard methods, e.g., ISO 6336. Therefore, the relevant power ratio and safety factors are still determined by standard methods that use traditional approaches. Combining both provides a possibility for further optimizations. Tooth root breakage and flank damage by pitting and scuffing have been covered in international standards for some time. Recently, ISO standards have been created that cover additional gear failure modes (micropitting, tooth flank fracture). Again, for these the question of how to combine tooth contact analysis methods with standard calculations has to be answered. In this paper, local tooth contact analysis and standard calculation are used to determine the load capacity for the failure modes pitting, tooth root breakage, micropitting, and tooth flank fracture. Analogies and differences between both approaches are shown. An example gear set is introduced to show the optimization potential that arises from the use of a combination of both methods. Difficulties in combining local approaches with standard methods are indicated. The example calculation demonstrates a valid possibility to optimize the gear design by using local tooth contact analysis while satisfying the requirement of documenting the load carrying capacity by standard calculations.