Page 252 - Gear Technology Solutions

18 Eight Selective Crowning Sections

18.1 What is Selective Crowning?

Selective crowning means that in every region of the Ease-Off there is the re-
quired amount of crowning. The traditional length and profile crowning is not
adjusted to the path of contact or quantified in each region of the flank to the
requirements of this region. For example, the flank center of each bevel and
hypoid gearset should be conjugate and provide a large contact area with a
large load sharing between neighboring tooth pairs. This center conjugacy
makes a gearset quiet and the power density high. Along the top and the root
transition, there should be a defined relief in order to prevent edge contact and
root fillet interference. In the toe and heel area there should be a local relief,
protecting the flank surfaces from toe and heel edge contact and also acting
against tooth contact movements as result of manufacturing tolerances as well
as deflections under load.

The software suite of selective crowning corrections offers all the above-
mentioned types of crowning and reliefs, and also has corrections for spiral
and pressure angle as well as tooth size and depth. The most remarkable as-
pect of selective crowning is the fact that these are coupled, yet independent
corrections. This means that gears cut or ground with one cutter or grinding
wheel in completing (convex and concave flank at the same time with identical
basic settings) can be corrected independently. This is a mathematical and
kinematical phenomenon which was discovered by Gleason [1].

18.2 Universal Motion Concept - UMC

The Universal Motion Concept (UMC) offers a selection of higher order flank
form corrections. The principle of the UMC corrections is based on a concept,
where eight of the basic settings of the virtual bevel gear machine in Figure 1
become “alive” and change their magnitudes depending on the roll position
throughout the generating roll. The UMC influenced basic settings are:

q… Roll angle
s… Radial setting
i… Tilt angle
j… Swivel angle (orientation of the tilt angle)
Em… Machine offset
Xb… Sliding base

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