nomenclature gears

8/12/2019 Nomenclature Gears

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Nomenclature

Smaller Gear is Pinion and Larger one is the gear

In most application the pinion is the driver, This reduces

speed but it increases torque.


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Internal Spur Gear System


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pitch circle, theoretical circle upon which all calculation is based

p, Circular pitch, p the distance from one teeth to the net, along

the pitch circle. p!"d#$m, module!d#$ pitch circle#number of teeth

p! "m

P, %iametral Pitch P!$#d

pP! "


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&ngle ' has the values of () or (* degrees. &ngle +.*have been also used.

Gear profile is constructed from the base circle. Then

additional clearance are given.


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How Gear Profile is constructed

&+-+!&+&), &(-(!( &+&), etc


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Standard Gear Teeth

Item ()ofull depth ()oStub (*ofull depth

&ddendum a +#P ).#P +#P

%edendum +.(*#P +#P +.(*#P

Clearance f ).(*#P ).(#P ).(*#P

/or0ing depth (#P +.1#P (#P

/hole depth (.(*#P +.#P (.(*#P

Tooth thic0ness +.*2+#P +.*2+#P +.*2+#P

3ace width 4#P5b5+6#P 4#P5b5+6#P 4#P5b5+6#P


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Gear Trains

))()((

5

4

4

3

2

1

1

5

N

N

N

N

N

N

n

n=


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Planetary Gear train

You can get high torque ratio in a smaller space

There are two inputs to the planetar7 gears, 8P9 of sun and 8ing,

The out put is the speed of the arm.


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Example of planetary Gear train

Gear +, sun , 8P9 +()), $umber of teeth (),

Planet Gear , $umber of teeth 6)

8ing Gear, 8otates 8P9 +(), and teeth of ),

: horse power, find the speed of the arm and torque on the ring.

&lternativel7 7ou ma7 have Certain ;ut put Torquerequirements


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Transmitted oad

< !ith a pair of gears or gear sets" Power istransmitted #y the force de$eloped #etween

contacting Teeth


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d in, 8P9 rev.#min, =

in#sec

d in, n rpm, = fpm

95491000

33000

63000

12

60

2*2/

sin

cos

TnVFKW

V

hpF

Tnhp

dnV

RPMddV

FF

FF

t

t

nr

nt

==

=

=

=

==

=

=

Toque lb>in

= fpm

T! $.m, = m#s, 3 $ewton

These forces

have to be

corrected for

d7namic effects ,

we discuss later,

considering&G9& factors


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Some %seful &elations

< '())***hp+, , fpm English system

< -etric System< .!(/',0+1***(Tn+2342

< ' newton" , m+s" n rpm" T" N5m

< hp( ',+64356(Tn+6171


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8ending Strength of the a Gear Tooth

23 612/2/)(

bt

F

bt

tLF

I

Mc tt ===

?arlier Stress &nal7sis of the Gear Tooth was based on

& full load is applied to the tip of a single tooth

The radial load is negligible

The load is uniform across the width

$eglect frictional forces

The stress concentration is negligible

This equation does not consider stress concentration,d namic effects etc.


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9esign for the 8ending Strength of a Gear

Tooth: The ;G-; -ethod

=

=

=

=

=

=

=

=

=

=

=

=

J

K

K

m

b

P

K

K

F

J

KK

bmKKF

JKK

bPKKF

m

s

v

t

ms

vt

msvt

0

0

0

0.1

@.S. Customar7

SI units

-ending stress at the root of the tooth

Transmitted tangential load

;verload factor

=elocit7 factor

%iameteral pitch, P

3ace width

9etric modue

SiAe factor

9ounting factorGeometr factor


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Your stress should not exceed

allowa#le stress

=

=

=

=

=

=

R

T

L

t

all

RT

Lt

all

K

K

K

S

KK

KS

&llowable bending stress

-ending Strength

Life factor

Temperature factor

8eliabilit7 factor


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9ynamic 'actor = .$

>?ven with stead7 loads tooth impact can cause shoc0 loading>Impact strength depends on qualit7 of the gear and the speed of

gear teeth Bpitch line velocit7

>Gears are classified with respect to manufacturing tolerancesD

>Ev6 F 2, commercial qualit7

>Ev F +(, precision>Graphs are available which chart vfor different qualit7 factors


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oad 9istri#ution 'actor = .m

>3ailure greatl7 depends on how load is distributed across face

>&ccurate mounting helps ensure even distribution

>3or larger face widths even distribution is difficult to attain

>$ote formula depends on face width which has to be estimated for initial iteration

>3orm goalD b 5 %pH 1 5 bP 5 +1


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&elia#ility 'actor = .&

>&dJusts for reliabilit7 other than 44K

> 8! ).1* F ).)2*4 ln B+>8 ).* 5 8 5).44

> 8! ).*) F ).+)4 ln B+>8 ).44 5 8 5 ).4444


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;G-; Geometry 'actor = >

>@pdated Lewis 3orm 3actor includes effect of stress concentration at fillet>%ifferent charts for different pressure angles>&vailable for Precision Gears where we can assume load sharing Bupper curves

>PSTC F highest point of single tooth contact>&ccount for meshing gear and load sharing Bcontact ratio M +

>Single tooth contact conservative assumption Bbottom curve>N ! ).6++ ln $ O ).+* B() degree

>N ! ).612 ln $ O ).()+1 B(* degree


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8ending Strength No5 ? St"'atigue #ending strength

>Tabulated %ata similar to fatigue strength

>8ange given because value depends on Grade

>-ased on life of +)2c7cles and 44K reliabilit7


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St? ;nalytical Estimate

>Through hardened steel gears

>%ifferent charts for different manufacturing methods

>Grade + F good qualit7

St ! 22.6 -O +(,))

>Grade ( F premium qualit7

St ! +)( -O +1,))


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8ending Strength ife 'actor= .

>&dJusts for life goals other

than +)2c7cles

>3atigue effects var7 with

material properties and surfacefinishes

>L! +.16+ $>).)6(6$M6?1

$oteD ())) rpm reach 6

million c7cles in + da7 of

service


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Example:

A conveyor rive involvin! "eavy#s"oc$ %orsional loain! is opera%e &y an

elec%ric mo%or' %"e spee ra%io is 1:2 an %"e pinion "as (iame%eral pi%c" )*10in#1' an n+m&er o, %ee%" -*1 an ,ace /i%" o, &*1.5 in. "e !ear "as rinnel

"arness o, 300 "n. in %"e maxim+m "orspo/er %"a% can &e %ransmi%%e'

+sin! A4A ,orm+la5


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Gear 8ox 9esign


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nomenclature gears

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