41 Transmission 1 A Gears Gear ratios C Types of gear wheel

A Gears

Gear wheels, or gears, are wheels with teeth (or cogs). The teeth interlock (fit together) with those of other gear wheels. When one gear wheel revolves, the other revolves with it - in the opposite direction as their teeth mesh together. Gears are normally fitted to shafts. They transmit rotary motion from one shaft to another that is, they transmit drive. Drive, usually supplied by an engine or motor, causes a shaft to revolve. A shaft connected directly to an engine or motor is called a driveshaft or an input shaft. A gear wheel on a driveshaft is called a driver. The second gear wheel, which meshes with the driver, is called a follower the driver drives the follower. assembly of several shafts and gear wheels is called a gear train or transmission system. It begins with an input shaft and ends with an output shaft. The system may contain idler gears (or idlers). These change the direction of a follower.

Gear ratios

Gears can provide a mechanical advantage (see Unit 33) by using different gear ratios. In the diagrams above, the driver has 20 teeth and the follower has 60 teeth. Therefore the driver rotates three times to make the follower rotate once. So the gear ratio is 3:1 (three to one). This means that if, for example, the input speed that is, the speed of the driver is 3,000 rpm, the output speed (of the follower) will be 1,000 rpm.

In some machines, a gearbox is used to provide a number of different gear ratios. A gearbox has a gear selection system, which allows gears to be changed (or shifted) while the transmission is running. This may be a manual gearbox, where gears are changed by a person, or an automatic gearbox, which automatically selects a higher gear or lower gear, as needed.

C Types of gear wheel

• Spur gears are the simplest gears. The teeth run straight across the wheel.
• Helical gears have curved teeth, so that they mesh together more smoothly.
• Bevel gears allow drive to be transmitted through an angle - often 90°.
• Crown gears transmit drive through 90°, often to a small gear called a pinion.
• Worm gears transmit drive through an angle. They also allow a low output speed relative to the input speed of the worm. They can provide a 'one way' drive, as a worm can drive a gear but a gear cannot drive a worm (the mechanism will lock).

Ответ: See above

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