Spur gear

1
Kinematics of Gears
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Gears!

• Gears are most often used in transmissions to
  convert an electric motors high speed and low
  torque to a shafts requirements for low speed
  high torque
• Speed is easy to generate, because voltage is
  easy to generate
• Torque is difficult to generate because it
  requires large amounts of current
• Gears essentially allow positive engagement
  between teeth so high forces can be transmitted
  while still undergoing essentially rolling
  contact
• Gears do not depend on friction and do best when
  friction is minimized
• Basic Law of Gearing
• A common normal (the line of action) to the
  tooth profiles at their point of contact must, in
  all positions of the contacting teeth, pass
  through a fixed point on the line-of-centers
  called the pitch point
• Any two curves or profiles engaging each other
  and satisfying the law of gearing are conjugate
  curves, and the relative rotation speed of the
  gears will be constant

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Spur Gears

• Teeth are parallel to the axis of the gear
• Advantages
• Cost
• Ease of manufacture
• Availability
• Disadvantages
• Only works with mating gear
• Axis of each gear must be parallel

4
Helical Gears

• Teeth are at an angle to the gear axis (usually
  10 to 45) called helix angle
• Advantages
• Smooth and quiet due to gradual tooth engagements
  (spur gears whine at high speed due to impact).
  Helical gears good up to speeds in excess of
  5,000 ft/min
• More tooth engagement allows for greater power
  transmission for given gear size.
• Parallel to perpendicular shaft arrangement Fig
  8.2
• Disadvantage
• More expensive
• Resulting axial thrust component

5
Helical Gears

• Mating gear axis can be parallel or crossed
• Can withstand the largest capacity at 30,000 hp

6
Worm Gears
worm gear

• Gears that are 90 to each other
• Advantages
• Quiet / smooth drive
• Can transmit torque at right angles
• No back driving
• Good for positioning systems
• Disadvantage
• Most inefficient due to excessive friction
  (sliding)
• Needs maintenance
• Slower speed applications

worm
7
Bevel Gears

• Gear axis at 90, based on rolling cones
• Advantages
• Right angle drives
• Disadvantages
• Get axial loading which complicates bearings and
  housings

8
Spiral Bevel Gears

• Same advantage over bevel gears as helical gears
  have over spur gears!!
• Teeth at helix angle
• Very Strong
• Used in rear end applications (see differentials)

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Why Use Gears?

• Reduce speed
• Increase torque
• Move power from one point to another
• Change direction of power
• Split power

Generally this functionality is accomplished by
many gears mounted in a gear box!
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How a differential works http//en.wikipedia.org/
wiki/Differential_(mechanical_device)