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Gear Train: - Simple - Compound - Epicyclic

Gear trains can be simple, compound, or epicyclic. Spur gears transmit torque with little sliding action, making them very efficient (0.98-0.99). Helical gears are slightly less efficient due to more sliding. Gear ratio relates input and output angular velocities. A compound gear train ratio is the product of individual gear ratios. Planetary gear trains use a sun gear, planet gears that mesh with the sun and ring gears, and an optional rotating arm. Common gear failure modes are bending fatigue at tooth roots and surface fatigue from sliding contact.

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Gaurav Agarwal
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94 views18 pages

Gear Train: - Simple - Compound - Epicyclic

Gear trains can be simple, compound, or epicyclic. Spur gears transmit torque with little sliding action, making them very efficient (0.98-0.99). Helical gears are slightly less efficient due to more sliding. Gear ratio relates input and output angular velocities. A compound gear train ratio is the product of individual gear ratios. Planetary gear trains use a sun gear, planet gears that mesh with the sun and ring gears, and an optional rotating arm. Common gear failure modes are bending fatigue at tooth roots and surface fatigue from sliding contact.

Uploaded by

Gaurav Agarwal
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Gear Train

Simple

Compound

Epicyclic

1
Gear Train Efficiency

Ideally , gears will transmit 100% of torque


In reality this does not happen because of losses due to the sliding
action of the gear teeth
Spur gears generally are very efficient (0.98 to 0.99)
because there is very little sliding action involved*

Helical gears will be slightly less efficient,


due to larger sliding component

2
Gear ratio
Conjugate Action:
1
1 O2 P
=
Constant Angular Velocity Ratio: =C 2 O1 P
2
P IS FIXED

r1
1 O1 Pitch Point O2
P
2
r2

Pitch Circle 1

Pitch Circle 2

3
Gear Ratio
N2
Gear ratio mG
N1

applies to angular velocity and transmitted torque


1
Angular Velocity Ratio mV
2

2
= 2
Gear ratio mG
1 1

4
Simple Gear Train
N1
Angular Velocity ratio mV:
2 N1 N2
mv = = in
1 N2
N3
Train ratio (velocity ratio):

N4

out N1 out N5
=
in N5
5

5
Compound Gear Train
Train ratio (velocity ratio):

N2 N4
N1
N3
in

N driving _ gears
out
N driven _ gears

6
Example
Design a Compound spur gear train

Problem:
Design a compound spur gear train with overall train ratio of 32:1.
Pressure angle is 20o, two stages only, module of 2.5 mm.

7
Planetary Gear Train
Planetary Gearset

arm= 0 N1
N2
arm
in

P G out
Conventional Gearset

arm 0
N2
N1
out
arm
in planet gear

Sun gear

8
Planetary Gear Train
Planetary Gear Train from Screwdriver

Photo courtesy: www.howstuffworks.com


9

9
Planetary Gear Train
Planetary Gear Train with Ring Gear

N4

N1 arm
N2

arm
sun
planet gear

Sun gear ring

10

10
Example
Problem:
s
Determine the train ratio between sun gear and arm for the planetary
train. Ns=20, Np=40, Nr=100. arm
The arm is the input arm, the sun is output s, the ring gear is held stationary.
Assumption: the first gear is the sun gear, the last gear is the ring gear.

Nr

Ns arm N
P
arm
sun
ring=0

11

11
Gears Failure
Modes of Gear Failure

Fatigue Failure

Surface Failure

AGMA Method for Bending Stress

AGMA Method for Surface Stress

12

12
Loading on Spur Gears
Two regions of high-stress:
Root of Tooth and Point of Contact

13

13
Modes of Failure

BENDING STRESS

SURFACE STRESS
(mostly more critical than bending stress!)

Common practice is to design gears for surface fatigue failure


rather than fatigue-fracture.

14

14
Bending Fatigue Failure

Photo courtesy: Systematic Analysis of Gear Failures, L.E. Alban, ASM, 1985
15

15
Bending Fatigue Failure

Photo courtesy: Systematic Analysis of Gear Failures, L.E. Alban, ASM, 1985
16

16
Surface Failure

17

17
Surface Failure

(b), Courtesy New Departure-Hyatt Bearing Division,


General Motors Corp.

(a), Courtesy AGMA,

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