PSI - Issue 42

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

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As mentioned earlier, design considerations such as backup ratio, tooth flank modifications, misalignment, helix angle, among others, have been under investigation. To conduct those efforts, the current article discusses the considerations of dependency, tooth microgeometry asymmetry, PPTE and misalignment variation. Moreover, it discusses how to select a microgeometry design accordingly to meet the design requirements and investigates the effect of changing the design on the resulting fatigue life. 2. Gear System Model A double dependency gear system is adopted in the current article as a case study to offer the possibility of studying the dependency in gear design. As illustrated in Fig.1, the studied gear system consists of two small driving gears, Gear 1 and Gear 2, and one driven Ring Gear. The studied system model has a layout similar to the final drive gear system used in the DCT automobile transmissions, which consist of two output shafts providing the output load to a ring gear connected to the differential mechanism. In this system, different load magnitudes can be applied either on Gear1 or Gear 2, while the output torque must be taken from the driven ring gear. Table 1 explains the main macrogeometry data used in the studied gear system model. The gear system was modelled in MASTA to obtain the generated misalignment, and then LDP software tool was used for stress and PPTE calculations. The main tooth flank modification parameters were defined for both engagements Gear 1-Ring and Gear 2-Ring, as explained in Table 2. The microgeometry design of both the drive and the coast flanks were studied for Gear 1-Ring engagement. In addition to Design A and B, presented in Table 2, the case of no microgeometry modifications, which is named Design 0, was also studied to compare with. 3. Gear Design Method Gear design is not a straightforward task and without a precise experience in this multilateral field, it is not feasible to cover the various design aspects and meet all the design requirements. Gear design consists typically of two major parts, namely the macro- and the microgeometry designs. A macrogeometry design proposal needs to be selected, in which meets the given centre distance and gear ratio requirements. The microgeometry modifications should be introduced after that to improve the tooth contact pattern for better stress and PPTE results. Several design loops can be implemented until reaching the best possible design that fulfils the design requirements and shows the lowest possible stresses and PPTE. To avoid any possible gear failure, safety factor calculations must be performed to assess gear durability based on the given load collective cycle. Gear performance depends directly on the macro- and the microgeometry design. The current article studies the considerations of dependency, tooth microgeometry asymmetry, PPTE and misalignment variation, as follows.

Fig.1 Studied gear system model