17.2.3.A Effective Tooth Width, bH(mm)
The narrower face width of the meshed gear pair is
assumed to be the effective width for surface strength. However, if there
are tooth modifications, such as chamfer, tip relief or crowning, an
appropriate amount should be substracted to obtain the effective tooth
width.
17.2.3.B Zone Factor, ZH
The zone factor is defined as:
(17-15)
where:
bb =
tan-1(tanb
cosat)
The zone factors are
presented in Figure 17-2 for tooth profiles per JIS B 1701, specified in
terms of profile shift coefficients x1, and x2, numbers of teeth
Z1 and Z2
and helix angle b.
The "+" symbol in
Figure 17-2 applies to external gear meshes, whereas the "-"
is used for
internal gear and external gear meshes.
(17-16)where:
n = Poisson's Ratio, and E = Young's Modulus
Table 17-9 contains
several combinations of material and their material factor.
17.2.4 Contact Ratio
Factor, Ze
This factor is fixed at 1.0 for spur gears.
For helical gear meshes, Ze
is calculated as follows:
Helical gear:
When eb
£ 1,
(17-17)
where: ea
= Radial contact ratio
eb
= Overlap ratio
