GEAR BOX DESIGNG.Gopinath – AP/SRIT

Gear Box Gearbox often referred as transmission is

a unit that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.

Gearboxes are employed to convert input from a high speed power sources to low speed(Eg. Lift, Cranes and Crushing Machine) or into a many of speeds(Lathe, Milling Machine and Automobiles).

A gearbox that converts a high speed input into a single output it is called a single stage gearbox. It usually has two gears and shafts.

A gearbox that converts a high speed input into a number of different speed output it is called a multi-speed gear box.

Multi speed gear box has more than two gears and shafts. A multi speed gearbox reduces the speed in different stages.

Preferred Numbers or Preferred Step Ratio

In order to get a series of output speeds from a gearbox, geometric progression is used.

By using geometric progression the speed is reduced uniformly in different stages.

Geometric progression, also known as a geometric sequence, is a sequence of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio (called as progression ratio or step ratio in gear box design).

Step Ratio In gearbox design a set of preferred step

ratio or preferred numbers is used to obtain the series of output speed of gearbox.

The preferred step ratio is mentioned as basic series named as R5, R10,R20,R40 and R80. Each basic series has a specific step ratio. 

Structural Formula

A kinematic layout is a pictorial representation of a gearbox, describing the arrangement of gears. It provides information like number of stages, number of shafts used, number of gear pairs and its arrangement. The following diagram is the kinematic arrangement of a 12 speed gear box.

Kinematic Layout

A ray diagram is a representation of structural formula. It provides information such as speed in each stage, the transmission ratio in each stage, The total number of speeds and its values. The following diagram is a ray diagram of a 12 speed gearbox.