ABSTRACT
This chapter describes stress analysis and rating of asymmetric tooth gears defined by Direct Gear Design. Maximum gear contact stress, characterizing tooth surface pitting and wear breakage, is traditionally calculated by the Hertz equation. The tooth load is consequently applied to each flank finite element node from the lowest node near the root fillet to the highest one for the driving pinion and from the highest node to the lowest one near the root fillet for the driven gear. Rating of helical asymmetric gears by the existing rating standards employs the same approach as for the spur asymmetric gears. The standard design of helical symmetric gears is based on parameters of the virtual spur gears that represent normal sections of the helical gears. In some industries, like aerospace, which are accustomed to using gears with nonstandard tooth shapes, rating of these gears is established by comprehensive testing.
