Gears have been used since the 16th century to transfer power between rotating shafts. There are different types of gears that transfer power in parallel shafts or at 90 degree angles, including spur gears, helical gears, bevel gears, worm gears, and planetary gear sets. Gears work through their teeth and gear ratios which determine the input and output rotation directions and speeds.

2. Gears
 They have been around
for a while!
 In the 16th century
Leonardo di ser Piero da
Vinci came up with this
idea... A self propelled
vehicle

3. Gear ratio rules
 The DRIVE GEAR is the gear that supplies the power
 The DRIVEN GEAR is the one that receives the power

4. Gear Ratio rules
 2 EXTERNALLY mated gears will always rotate in
OPPOSITE directions
 2 INTERNALLY mated gears will always rotate in the
SAME direction
 An idler gear allows 2 externally mated gears to rotate
in the SAME direction

5. Gear Ratio rules
 To find the gear ratio DIVIDE the #of teeth or the
pitch diameter of the DRIVEN GEAR by the number of
teeth or pitch diameter of the drive gear.
 To find the overall gear ratio (trans & final drive)
MULTULPLY the ratios to gether

6. Gear terminology
 Annulus Gears
 Teeth cut on the
inside of the gear
 Pitch
 The working
diameter of the gear
 Face
 Working surface of
gear
 Root
 Base of tooth
 Heel
 Outside of gear
tooth
 Toe
 Inside or gear tooth

7. Thrust from gears
 Axial or Side Thrust
 Force on the axis of the
gear
 Spiral cut gears have
AXIAL THRUST and
will force gear in
different directions
depending on rotation

8. Thrust from gears
 Radial Thrust
 Force 90deg to the axis of
the gear
 Spur gears create RADIAL
THRUST trying to separate
gears

9. How gears are made

10. Gear Types
 Spur Gear
 Straight cut teeth
 Inexpensive to produce
 Noisy
 Not as strong as helical
gear
 Transfers power in
parallel shafts

11. Gear Types
 Helical Gear
 Quiet
 Strong
 Transfers power in
parallel shafts

12. Gear Types
 Bevel Gears
 Can be both SPUR and
BEVEL
 Transfers power in
shafts at 90deg
 Bevel gears axis
intersects at centerline

13. Gear Types
 Hypoid Gears
 Variation of SPIRAL
BEVEL gear
 Gears intersect off –
center of axis
 Found in differentials

14. Gear Types
 Worm Gear
 Transmits power at
90deg
 Most common use is
speed sensor

15. Gear Types
 Planetary Gear Set
(Simpson)
 4 Components
 Ring Gear
 Planetary Gears
 Planet Carrier
 Sun Gear
 One planetary gear set
can achieve 9 gear
variations