PSI - Issue 42

Omar D. Mohammed et al. / Procedia Structural Integrity 42 (2022) 1607–1618 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1617

11

microgeometry modifications the stress and PPTE results can be significantly improved. Microgeometry design can significantly affect fatigue life and damage status. The design considerations were studied, different microgeometry designs and load cases were presented, and the safety factors were obtained to assess the design status. In this section, the four studied considerations can be discussed further as follows. The double dependency case was studied. It is important to understand that the macro- and the microgeometry design parameters of the common gear (the driven ring gear) must be set to match the design of both Gear 1 and Gear 2. Furthermore, the final gear geometry must fulfil all the design requirements of both engagements, Gear 1-Ring and Gear 2-Ring. It is not an easy task to design such dependent gears, however, there are industrial needs for this type of design layout in different applications. The two opposite tooth flanks have different design requirements because of the different load and misalignment on each flank. Tooth microgeometry asymmetry, which means having different microgeometry design sets for the drive and the coast flanks, can entail the benefits of obtaining the best possible results in terms of durability and NVH. The PPTE which acts as an excitation in the gear system is important to be reduced as low as possible over the torque range to meet the design requirements. Different designs were studied, and it is clear that having a gear geometry that offers a good contact pattern of the lowest possible contact stresses does not necessarily fulfil other requirements of having acceptable root bending stresses and PPTE over various torque levels. The design must be compromised in order to obtain the optimal results that fulfilling the different design requirements. The case of misalignment variation with different rotation positions was studied. Gear misalignment which is directly related to the stiffness of the connected rotating parts and the structural housing, is usually compensated by the tooth microgeometry. Thus, the microgeometry design will be even more complicated in the case of stiffness variation. The obtained misalignment can be changing with different rotating positions, and then the microgeometry design should be selected by considering different misalignment cases. 6. Conclusions • Gear design has several aspects and considerations that need to be covered to deliver a compromised design that meets all the design requirements. • The macro- and the microgeometry design of the common gear (Ring Gear) must be set to match the design of the driving gears, Gear 1 and Gear 2. Furthermore, the final gear geometry must meet the design requirements of both engagements, Gear 1-Ring and Gear 2-Ring. • Having different microgeometry sets for the drive and the coast flanks can entail the benefits of obtaining the best possible results in terms of durability and NVH. • Having a gear geometry that offers a good contact pattern of the lowest possible contact stresses does not necessarily fulfil other requirements of having acceptable root bending stresses and PPTE over various torque levels. • The PPTE results should be balanced over the torque range to meet the requirements. • In the case of stiffness variation, the obtained misalignment can be changing with different rotation positions. Then the microgeometry should be designed by considering different misalignment cases. • The design requirements can conflict with each other, and then a compromised design should be obtained to meet all the design requirements. • The safety factors in ‘cycles’ and ‘stress’ are both representing the same damage status of a certain designed gear which is subjected to a certain load spectrum, and both should equal at least 1.0 for safe operation. • Design A_G1- C shows SF’s lower than 1.0 in stress, which implies unsafe design of possible failure. • Changing the microgeometry design can significantly affect the predicted fatigue life and damage. References Artoni, A, Guiggiani, M, Kahraman, A & Harianto, J 2014. “Robust optimization of cylindrical gear tooth surface modifications within ranges of torque and misalignments”. ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Portland, USA. Beghini, M, Presicce, F & Santus, C 2004. “A method to define profile modification of spur gear and minimize the transmission error”. American Gear Manufacturers Association, Virginia, USA. Bibel, G, Reddy, S & Savage, M 1991. “Effects of rim thickness on spur gear bending stress”. The 27th Joint Propulsion Confer ence cosponsored