The paper represents the results of accomplished research projects directed atreduction of noise caused by misalignment
of the following gear drives: double- circular arc helical gears, modifed involute helical gears, face- milled spiral bevel
gears and face- milled formate cut hypoid gears. It is proven by the authors that due to misalignment, periodic almost
linear discontinuous functions of transmission errors occur, The period of such functions is the cycle of meshing when
one pair of teeth is changed for another one. Due to the discontinuity of such functions of transmission errors high
vibration and noise are inevitable. The authors propose to predesign a parabolic function of transmission errors that is
able to: (i) absorb linear discontinuous functions of transmission errors, and (闻) tur out the resulting function of
transmission errors into a continuous one. The proposed idea was succesfully tested by the Gleason Works and NASA
Lewis Research Center for a set of spiral bevel gears manufactured by the Bell Helicopter Co. It was found out that the
noise was reduced at 12 -18 decibels in comparison with the existing design. The idea of the predesign of a parabolic
function is applied forthe reduction of noise ofhelical andhypoid gears. Theeffectiveness of the proposed approachhas
been investigated by developed TCA (Tooth Contact Analysis) programs. The bearing contact for the mentioned above
gears is localized. Conditions that allow to avoid edge contact for tie gear drives have been determined. Manufacturing
of helical gears with new topology by hobs and grinding worms has been investigated.

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