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PLANETARY GEARSPLANETARY GEARS

Chapter 4 Page 61 Classroom Manual

PLANETARY GEARS & SHAFTS

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.

INTRODUCTIONINTRODUCTION

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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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.

2



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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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 REDUCTIONGEAR 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. Page 63

OVERDRIVEOVERDRIVE

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 DRIVEDIRECT 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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REVERSEREVERSE

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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NEUTRALNEUTRAL

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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