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Transcript of Gears
GearsGears
Inter American University of Puerto Inter American University of Puerto RicoRico
Mechanism DesignMechanism Design
MECN 4110MECN 4110
Chapter 9Chapter 9
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)
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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.
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.