An example of when a compound gear is a better choice than e

An example of when a compound gear is a better choice than epicyclic gear and vice versa. Fully describe and justify.

Solution

Epicyclic gear trains are generally used for automatic transmission, overdrives, and final drives. The most commonly used gear trains in automatic transmission system are three-speed Simpson gear train and two-speed Ravingeau gear train.

Epicyclic gears are very widely used in automatic transmission because,
(a) they are always in constant-mesh
(fc) engagement of these gears may be obtained smoothly and quietly by the application of brake bands, and
(c) considerable variation in gear ratios both forward and reverse can be obtained through epicyclic gear trains.

Compound Gear Train-

In a compound gear train at least one of the shafts in the train must hold two gears.

Compound gear trains are used when large changes in speed or power output are needed and there is only a small space between the input and output shafts.

The number of shafts and direction of rotation of the input gear determine the direction of rotation of the output gear in a compound gear train. The train in Figure has two gears in between the input and output gears. These two gears are on one shaft. They rotate in the same direction and act like one gear. There are an odd number of gear shafts in this example. As a result, the input gear and output gear rotate in the same direction.