T-148
The coefficient of friction has a great effect on the transmission of a worm gear.
Equation (16-21) presents the efficiency when the worm is the driver.
T2 Fu2
cosancosg – msing
hR = ––– = ––– tang = –––––––––––––––––– tang
(16-21)
T1i Fu1
cosansing + mcosg
16.5.2 Worm Gear as the Driver
For the case of a worm gear as the driver, the forces are as in Figure 16-14 and per
Equations (16-22).
Fu2 = Fn(cosancosg + msing)
ü
ï
ï
Fa2 = Fn(cosansing – mcosg)
ý
(16-22)
ï
ï
Fr2 = Fnsinan
þ
When the worm and worm gear are at 90° shaft angle, Equations (16-20) apply.Then,
when the worm gear is the driver, the transmission efficiency hI is expressed as per
Equation (16-23).
T1 i Fu1 cosan sing – m cosg
1
hI = ––– = –––––––– = ––––––––––––––––––– –––––
(16-23)
T2 Fu2 tang
cosan cosg + m sing
tang
The equations concerning worm
and worm gear forces contain the
coefficient m . This indicates the
c o e f f i c i e n t
o f
f r i c t i o n
i s
v e r y
important in the transmission of
power.
Fig. 16-14 Forces in a
Worm Gear Mesh
16.6 Forces In A Screw Gear Mesh
The forces in a screw gear mesh are similar to those in a worm gear mesh. For screw
gears that have a shaft angle S = 90°, merely replace the worm's lead angle g, in Equation
(16-22), with the screw gear's helix angle b1.
F2
Fn
Fr2
Fu2
F2
Fa2
Fnm
g
an
