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Spur gear

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Classification of gear – PowerPoint PPT presentation

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Title: Spur gear


1
Kinematics of Gears
2
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

3
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)

9
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!
10
How a differential works http//en.wikipedia.org/
wiki/Differential_(mechanical_device)
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