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# Gears - PowerPoint PPT Presentation

Gears. Inter American University of Puerto Rico Mechanism Design MECN 4110. Chapter 9. Mechanical Transmissions. Belts. Chains. Gears. Types of Gears. Spur Gears. Pinion. Gear. Spur Gears - Types. External Set: Opposite Movement. Internal Set: Movement in the same direction.

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## PowerPoint Slideshow about 'Gears' - jayme-branch

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### Gears

Inter American University of Puerto Rico

Mechanism Design

MECN 4110

Chapter 9

Mechanical Transmissions

Belts

Chains

Gears

Spur Gears

Pinion

Gear

Spur Gears - Types

External Set: Opposite Movement

Internal Set: Movement in the same direction

The Fundamental Law of Gearing
• The angular velocity ratio between the gears of a gearset remains constant throughout the mesh.
• The angular velocity ratio (mV) is equal to the ratio of the radius of the input gear to that of the output gear
• The torque ratio (mT)
The cycloid and the involute: curve characteristics

The involute is a curve which can be generated by unwrapping a taut string from a cylinder (called the evolute). Features of this involute curve:

The Involute Tooth Form
The Involute Tooth Form
• The string is always tangent to the cylinder.
• The center of the curvature of the involute is always at the point of tangency of the string with the cylinder.
• A tangent to the involute is then always normal to the string, the length os which is the instantaneous radius of curvature of the involute curve.
Contact Ratio

If mp is 1, then one tooth is leaving contact just as the next is beginning contact. Spur gears [1-2]. The minimum contact ratio for a smooth operation is 1.2. A minimum contact ratio of 1.4 is preferred and larger is better. Most spur gearsets will have contact ratios between 1.4 to 2.