T-42
Fig. 4-9a
The Meshing of Standard
Fig. 4-9b
The Meshing of Profile
Spur Gear and Rack
Shifted Spur Gear and Rack
(a = 20°, z1 = 12, x1 = 0)
(a = 20°, z1 = 12, x1 = +0.6)
SECTION 5 INTERNAL GEARS
5.1 Internal Gear Calculations
Calculation of a Profile Shifted Internal Gear
Figure 5-1 presents the mesh of an internal gear and external gear. Of vital importance is the
operating (working) pitch diameters (dw) and operating (working) pressure angle (aw). They can be
derived from center distance (ax) and Equations (5-1).
z1
ü
dw1 = 2ax –––––––
ï
z2 – z1
ï
ï
ï
z2
ï
dw2 = 2ax –––––––
ý
(5-1)
z2 – z1
ï
ï
ï
db2 – db1
ï
aw = cos–1(–––––––––)
ï
2ax
þ
Table 5-1 shows the calculation steps. It will become a standard gear calculation if x1 = x2 = 0.
d
db
a
d
––
2
H
ax
xm
d
db
a
d
––
2
H
a
