A modified geometry of face-milled spiral bevel gears with uniform and tapered teeth that provides a localized bearing
contact, reduces the level of noise and increases the strength of the teeth has been developed. The modified geometry is
based on application of specially developed machine-tool settings and the generation of the gears is accomplished by
application of the commercially available equipment and tools.
The main ideas proposed are the followings:
(1) The optimization of the geometry is based on the local synthesis of the gear tooth surfaces that provides: (i) a
localized bearing contact in the longitudinal and across the surface directions, (ii) areduced level of transmission errors
of a parabolic type, and (iii) the desired magnitude of the major axis of the instantaneous contact ellipse. The
optimization is achieved by the mismatch of the surfaces of the generating tools.
(2) The increase in tooth strength is due to the inherent increase in the total tooth contactratio producedby theoptimized
geometry. The stress analysis is based on solid modeling of the tooth and finite element analysis.
(3) The theory developed was tested by a Tooth Contact Analysis (TCA) computer program. Prototypes of the gears
with tapered teeth were manufactured and vibration, noise and stresses have been measured experimentally. In
comparison with the existing design, the level ofnoise was reduced by up to 18 decibels, at the spiral bevel meshing
frequencies, and the vibration levels were reduced by 50%. The total stress level for the gear setwas reduced enough to
permit an increase in the maximum operating torque level.

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