PLANETARY GEARS

1
PLANETARY GEARS

• Chapter 4
• Page 61
• Classroom Manual

2
PLANETARY GEARS SHAFTS

• Describe how different gear ratios are obtained
  from a planetary gear set.
• Identify components of a planetary gear set
  their operation.
• Describe the different designs of compound
  planetary gear sets.
• Describe the construction and operation of
  typical Simpson gear train.

3
INTRODUCTION

• Automatic Transmissions provide different gear
  ratios for performance and economy over the
  entire driving range.
• Ratios are selected manually (driver) or
  automatically (hydraulically).
• A planetary gear set consists of a sun gear, a
  planet carrier, internal gear.

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SIMPLE PLANETARY GEAR SETS

• Planetary gear sets are typically helical cut
  gears.
• Sun gear is in the center.
• Planet gears rotate around the sun gear.
• The Ring, Annulus, or Internal gear is the outer
  gear of the set.

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SIMPLE PLANETARY GEAR SETS
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SIMPLE PLANETARY GEAR SETS

• Planet gears are in constant mesh with the Sun
  and Internal gears.
• Number of planet gears depends on the load the
  transmission was designed for.
• A planet gear set can provide (1) gear reduction,
  (2) overdrive, (3) direct drive, (4) reverse, or
  a (5) neutral position.

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SIMPLE PLANETARY GEAR SETS

• When a smaller gear drives a larger gear, output
  speed is decreased.
• When a larger gear drives a smaller gear, output
  speed is increased.
• When a external gear drives another external
  gear, output direction is reversed.

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SIMPLE PLANETARY GEAR SETS

• When a external gear is in mesh with an internal
  gear, the two gears will rotate in the same
  direction.
• Clutch packs and bands are used to hold or
  release the members of the planetary gear set to
  get the proper direction of rotation and/or ratio.

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GEAR REDUCTION

• When the output gear turns at a slower speed then
  the input gear, gear reduction has occurred and
  results in increased torque output.
• 2 ways to get reduction
• Hold sun gear, drive internal gear.
• Hold internal gear, drive sun gear. Lower ratio.

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OVERDRIVE

• When output speed is greater than input speed,
  overdrive is achieved.
• 2 ways to get overdrive.
• Hold sun gear, drive planet carrier.
• Hold internal gear, drive planet carrier. Higher
  ratio overdrive.

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DIRECT DRIVE

• Input and output speed are the same.
• Drive any two members of the planet and the
  result is direct drive.

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REVERSE

• Input rotation direction is reversed.
• 2 ways to get reverse.
• Hold planet carrier, drive planet carrier.
• Hold planet carrier, drive sun gear. This is
  reverse overdrive.

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NEUTRAL

• Input but no output.
• When no member of the planetary set is held or
  locked to another, there will be no output
  regardless of which member receives the input.

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