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Gear tooth optimization for nonstandard cylindirical internal and external aerospace gear pairs

Karaca, Orhan Nuri
Aerospace gears are produced by grinding method and can have arbitrary addendum circle and dedendum circle radii and rounded gear root as opposite to the gears produced by traditional method such as rack and pinion generation method. The aerospace gears have also nonstandard module, pressure angle and helix angle. In this study, helical external and internal aerospace gear pairs are optimized by considering bending stress, contact stress and scuffing limitations. Pinion and gear number of teeth, normal module, helix angle, pressure angle, pinion shifting coefficient, center distance, pinion addendum radius, gear addendum radius, pinion dedendum radius and gear dedendum radius are taken into consideration as the design parameters which are to be optimized. Pinion and gear rotational speeds, input power, Young Modulus and Poisson ratios of the pinion and gear material, Contact and Bending strength of the gear material are taken as input parameters. All the possible gear pairs are considered in terms of contact stress, bending stress, scuffing temperature, tiff clearance, top land thickness, root form radius and tip clearance limitations. AGMA 908-B89 is used for evaluating the contact stress geometry factor. AGMA 2001-D04 is used for evaluating the bending and contact stress. The rounded gear root evaluation is conducted for cylindrical gear pairs. The bending stress geometry factor is implemented for gear pairs which have rounded gear root. AGMA 925 is used for evaluating the flash temperature and scuffing evaluations. The analytical method is conducted in MATLAB. All the obtained results are compared with KISSOFT commercial tool and it is observed that KISSOFT uses only the transverse plane in the gear root evaluation and does not consider the backlash effect on the bending stress geometry factor evaluation. The minimum center distance optimization has a crucial role in aerospace applications to decrease the weight of an air vehicle. The minimum weight design solutions are obtained by using the minimum center distance optimization.