Theory of Machines: Unit II: Gears and Gear Trains
contact ratio
Gears and Gear Trains - Theory of Machines
The contact ratio is the average number of teeth that are in contact at any instant.
CONTACT RATIO • The contact ratio is the average number of teeth that are in contact at any instant. • The contact ratio is defined as the ratio of the length of the arc of contact to the circular pitch. We know that, circular pitch, pc = π . m, where m = module • The contact ratio must exceed 1 because contact between gears must not be lost. • A contact ratio of 1.2, for instance, indicates that one pair if teeth is always in contact, and a second pair of teeth is in contact 20% of the time. • The greater contact ratio values result in smoother action because another gear tooth shares the load for a longer duration during the engaging/disengaging process. • In addition, with more teeth sharing the load, greater power may be transmitted. • The most direct manner in which the contact ratio can be increased is to use larger gears. This is in direct contrast to most design goals of compactness. Note where circumference of pitch circle of pinion = 2πr where circumference of pitch circle of wheel = 2 π R
Theory of Machines: Unit II: Gears and Gear Trains : Tag: : Gears and Gear Trains - Theory of Machines - contact ratio
Theory of Machines: Unit II: Gears and Gear Trains
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Theory of Machines
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