Power Transmission Devices

Belt Drives

Some terms:

Consider a belt drive,

d = diameter of the driving pulley, mm


D = diameter of the driven pulley, mm

n = speed of the driving pulley, r.p.m.

N = speed of the driven pulley, r.p.m.

t = thickness of the belt, mm

V = linear speed of the belt, mm/s

i = speed ratio or velocity ratio

Linear speed of the belt,

$V = {πdn}/{60}$


or

$V = {πDN}/{60}$

$n/N = D/d$

Speed ratio, or velocity ratio,

$i = {\text"Speed of driving pulley"}/{\text"Speed of driven pulley"}$

$i = n/N = D/d$

if thickness of belt is considered

Speed ratio, $i = n/N = {(D + t)}/{(d + t)}$

Gears

Some terms:

i = speed ratio or gear ratio


$z_p$ = number of teeth on pinion


$z_g$ = number of teeth on gear


$d_p$ = pitch cricle diameter of pinion, mm


$d_g$ = pitch circle diameter of gear, mm


$n_p$ = pinion speed, r.p.m.


$n_g$ = gear speed, r.p.m.


m = module, mm

$i = {z_g}/{z_p} = {m z_g}/{m z_p} = {d_g}/{d_p}$


or


$i = {n_p}/{n_g}$