Gears Gears Inter American University of Inter American University of Puerto Rico Puerto Rico Mechanism Design Mechanism Design MECN 4110 MECN 4110 Chapter 9 Chapter 9
Gears Inter American University of Puerto Rico Mechanism Design MECN 4110 Chapter 9.
Jan 12, 2016
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GearsGears
Inter American University of Puerto Inter American University of Puerto RicoRico
Mechanism DesignMechanism Design
MECN 4110MECN 4110
Chapter 9Chapter 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 (mV) is equal to the ratio of the radius of the input gear to that of the output gear
The torque ratio (mT)
out
in
out
in
in
outV d
d
r
rm
out
in
out
in
in
outV d
d
r
rm
in
out
in
out
out
inT d
d
r
rm
in
out
in
out
out
inT d
d
r
rm
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.
14.5o, 20o and 25o
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
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.
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