A gear train is made up of five spur gears as shown in the figure
A gear train is made up of five spur gears as shown in the figure. Gear 2 is driver and gear 6 is driven member. N2, N3, N4, N5 and N6 represent number of teeth on gears 2, 3, 5 and 6 respectively. The gear(s) which act(s) as idler(s) is/are
A. only 3
B. only 4
C. only 5
D. Both 3 and 5
Please scroll down to see the correct answer and solution guide.
Right Answer is: C
SOLUTION
Explanation:
Gear Train:
Two or more gears are made to mesh with each other to transmit power from one shaft to another. Such a combination is called a gear train.
When there is only one gear on each shaft, it is known as a simple gear train.
Since the gear 1 drives the gear 2, therefore gear 1 is called the driver and the gear 2 is called the driven or follower.
Idler Gear:
The purpose of an idler gear used in gear trains is to have the required direction of rotation at the output shaft.
- It is used for changing the direction.
- It does not change the velocity ratio or torque.
- It may be noted that when the number of intermediate gears (idler gear) is odd, the motion of both the gears (i.e. driver and driven or follower) is like.
- But if the number of intermediate gears is even, the motion of the driven or follower will be in the opposite direction of the driver.
The ratio for the given gear train is given by the following formula
\(\frac{{{{\rm{\omega }}_2}}}{{{{\rm{\omega }}_6}}} = \frac{{{{\rm{\omega }}_2}}}{{{{\rm{\omega }}_3}}}\frac{{{{\rm{\omega }}_3}}}{{{{\rm{\omega }}_5}}}\frac{{{{\rm{\omega }}_5}}}{{{{\rm{\omega }}_6}}} = \frac{{{{\rm{N}}_3}}}{{{{\rm{N}}_2}}}\frac{{{{\rm{N}}_5}}}{{{{\rm{N}}_4}}}\frac{{{{\rm{N}}_6}}}{{{{\rm{N}}_5}}} = \frac{{{{\rm{N}}_3}{{\rm{N}}_6}}}{{{{\rm{N}}_2}{{\rm{N}}_4}}}\)
∴ Only Gear(5) is the Idler gear, as the number of teeth on the wheel '5' does not appear in the velocity ratio.
