Gears Inter American University of Puerto Rico Mechanism Design MECN 4110 Chapter 9

Mechanical Transmissions Chains Belts Gears

Types of Gears

Pinion Gear Spur Gears

Spur Gears - Types External Set: Opposite Movement Internal Set: Movement in the same direction

Pinion and Gear

The Fundamental Law of Gearing The angular velocity ratio between the gears of a gearset remains constant throughout the mesh. The angular velocity ratio (m V ) is equal to the ratio of the radius of the input gear to that of the output gear The torque ratio (m T )

The Involute Tooth Form 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 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.

14.5 o, 20 o and 25 o

Gear Tooth Nomenclature

Contact Ratio If m p 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.