A reduction gear is an arrangement by which an input speed can be lowered for a requirement of slower output speed, with same or more output torque. Reduction gear assembly consists of a set of rotating gears connected to a wheel work. The high speed incoming motion from the wheel work is transmitted to the set of rotating gears, wherein the motion or torque is changed. The number of gears used in the reduction gear assembly depends on the output speed requirement of the application.The reduction gear assembly is usually known as reduction gear box.
Why is a Reduction Gear Used?
To understand why a reduction gear is used in a particular machinery we will take an example of a ship using high speed turbines. It is a basic requirement of a ship that in order to have high efficiency the steam turbine should operate at a relatively high range of rpm. However, the effective functioning of a propeller requires a relatively low rpm range. For this reason, a reduction gear is used, which reduces the high speed motion of the steam turbine into low rpm range required by the propeller.
Types of Reduction Gears
There are mainly two types of reduction gears:
- Single reduction gear
- Double reduction gear
Single Reduction gear
This arrangement consists of only one one pair of gears. The reduction gear box consists of ports through which the propeller shaft and engine shaft enters the assembly. A small gear known as a pinion is driven by the incoming engine shaft. The pinion directly drives a large gear mounted on the propeller shaft. The speed is adjusted by making the ratio of the speed reduction to the diameter of pinion and gear proportional. Generally, a single gear assembly has a gear double the size of a pinion.
Double Reduction gear
Double reduction gears are generally used in applications involving very high speeds. In this arrangement the pinion is connected to the input shaft using a flexible coupling. The pinion is connected to an intermediate gear known as the first reduction gear. The first reduction gear is then connected to a low speed pinion with the help of one more shaft. This pinion is connected to the second reduction gear mounted directly on the propeller shaft. Such arrangement facilitates the reduction of speed to a ratio as high as 20:1 .