Page 98 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Gear train

A gear train is a mechanical arrangement of gears that transmit rotational motion and torque from one part of a
machine or system to another. It consists of two or more gears meshed together, forming a series of interconnected
rotating elements.
Gear train is an arrangement of gears meshing with each other in order to achieve some level of torque conversion
between the driving and driven shaft. Gearbox is the housing in which all these are enclosed.

The teeth on gears are designed so the gears can roll on each other smoothly (without slipping or jamming). In
order for two gears to roll on each other smoothly, they must be designed so the velocity at the point of contact
of the two pitch circles (represented by v) is the same for each gear.

Mathematically, if the input gear G has the radius r and angular velocity w and meshes with output gear G of
A
A
B
A
r and angular velocity w then:
B
B
v= r w = r w B
A
A
B
The number of teeth on a gear is proportional to the radius of its pitch circle, which means the ratios of the gears’
angular velocities, radi, and number of teeth are equal. Where N is the number of teeth on the input gear and N
B
A
is the number of teeth on the output gear, the following equation is formed:
A rB N B
B rA N A
This shows that a simple gear train with two gears has the gear ratio R given by: R A N B
B N A
This equation shows that if the number of teeth on the output gear overline G is larger than the number of teeth
B
on the input gear G then the input gear G must rotate faster than the output gear G B
A
A

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CITS : WCS - Mechanical - Exercise 8 CITS : WCS - Mechanical - Exercise 8