gear train

A system of interconnected gears.

A combination of two or more gears used to transmit motion between two rotating shafts or between a shaft and a slide. In theory two gears can provide any speed ratio in connecting shafts at any center distance, but it is often not practical to use only two gears. If the ratio is large or if the center distance is relatively great, the larger of the two gears may be excessively large. Moreover, an additional gear may be necessary simply to give the proper direction to the output gear. Belt, rope, and chain drives are frequently used in conjunction with gear trains. See also Belt drive; Chain drive; Gear; Planetary gear train.

The most important distinction in classifying gear trains is that between ordinary and epicyclic gear trains. In ordinary trains (illustration a), all axes remain stationary relative to the frame. But in epicyclic trains (illustration b), at least one axis moves relative to the frame. In illustration b, gear B, whose axis is in motion, is called a planet. The gears A and C are sun gears.

Gear trains. (a) Ordinary. (b) Epicyclic.

A simple gear train is one in which each gear is fastened to a separate shaft, as in illustration a. If at least one shaft has two or more gears fastened to it, the train is said to be compound. The train is a reverted gear train when the input and output shafts are in line. If the input shaft does not line up with the output shaft, the train is said to be nonreverted.

If a machine must be operated at any one of several output speeds, a multiple-speed gearbox, or transmission, may be used as a component part. Machine tools and motor vehicles are familiar instances of the need for transmissions. The speed of the output shaft of a transmission can be varied by sliding gears in and out of contact or by connecting gears in continual mesh to shafts by means of clutches. See also Automotive transmission.

A gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another.

Gear trains consists of:

• Driving gears - attached to the input shaft

• Driven gears - attached to the output shaft

• Idler gears - interposed between the driving and driven gear in order to maintain the direction of the output shaft the same as the input shaft or to increase the distance between the drive and driven gears. A compound gear train refers to two or more gears used to transmit motion.

Examples of Gear Trains

Types of gear trains
1. Simple gear train
2. Compound gear train
3. Epicyclic gear train
4. Reverted gear train

See also

• Powertrain

Gears
Gear systems	Spur gear systems • Worm gear • Rack and pinion • Epicyclic (planetary) gearing • Harmonic drive • Cycloidal drive • Non-circular gear
Gear shapes	Straight cut gear • Bevel gear • Helical gear • Hypoid gear
Geartooth profiles	Involute • Cycloid
Gear mechanics	Transmission • Differential • Gear coupling • Gear train • Bicycle gearing • Continuously variable transmission • Offset (gears)
See also	Ball screw • Leadscrew • Jackscrew • Belt drive • Chain drive • Gear manufacturing

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