gears_ch_29.ppt

8/9/2019 gears_ch_29.ppt

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Chapter 29 – Black Book

Chapter 2 – Chek Chart



Objectives

Explain design characteristics of gears

Explain torque multiplication

fundamentalsExplain Overdrive fundamentals

Explain ear Operation



ears !urpose

"ransmit rotating motion

#ormall$ mounted on shaft

"ransmits rotating motion from oneparallel shaft to another



%nteraction

ears and &hafts can interact three

'a$s

&haft can drive the gear ear can drive the shaft

ear can free'heel on shaft



ear (esign

ears must have same

pitch to operate

together

ear !itch "he number of teeth per

given unit of pitch

diameter

"o determine pitch) divide

number of teeth b$ thepitch diameter of the gear



"ooth (esign



"$pes of ears

&pur ear Cut &traight across

&pur gears onl$ have

one tooth in contactat a time

*inimi+es chance ofpopping out of gear

,andles torque 'ell -sed for .everse



,elical ear

/re quieter than spur

gears

"'o teeth at a time

contact ,as a tendenc$ to

move shaft for and aft

/re left and right

handed Opposites on parallel

shafts



&pur ears vs0 ,elical ears

&pur gears are

straight cut parallel

to shaft

,elical gears are

angle cut to gears

axis of rotation



%nternal ear

"eeth

*ost gears areexternal0 1teeth onthe outside

%nternal gear used'ith pinion gears

External gearrotates samedirection of internalgear

External gearrotates opposite'ith anotherexternal gear



%dler ears

3ocated bet'een drive and driven gear

-sed in reverse gear trains"ransfers motion 'ithout changing

rotational direction



ear .atios

Can multipl$ torque and speed Can reduce torque and speed &ame si+e and number of teeth 4 no change

in output Equal si+e gears create equal output

&mall drive gear to larger driven gear 4driven gear speed decreases

3arger drive gear to smaller driven gear 4driven gear speed increases



ear .atio Calculations

ear .atio can be found b$ dividing

number of teeth on driven gear b$ the

number of teeth on the driving gear0

Ex) 56 driven teeth ) 76 drive teeth 4

80 gear ratio

Page 740



ear .eduction

&peed decreases "orque %ncreases:hen speed is

halved; torquedoubles

*ost manualtransmissions are

speed reducing;torque increasing



ear Overdrive

&peed %ncreases "orque decreases:hen speed is

doubled; torque ishalved

-sed for fuel milage <actor$ overdrives

vs0 /ftermarketoverdrives



"orque

"orque is calculated b$ multipl$ing forceapplied b$ the distance of the force from a

center of a pivot point0 ears appl$ torque Ex) 8= ft lbs applied to 8 foot drive gear to a 2

foot driven gear 4 2= foot lbs torque

Page 740



"orque *ultiplication

-sed for lo'er gears

in a manual

transmission

equipped car 7)6 4 lo' gears

<or /cceleration

2)6 4 high gears <or mileage



External ears

:hen t'o external

gears mesh; the$

rotate in opposite

directions



Bevel ears

Change the direction

of rotation

&pider gears are

straight cut bevelgears

"ransfer motion

bet'een t'o shaftsat an angle to each

other



.ing and !inion

BE>E3 E/.&

-sed as a final drive

in .:( vehicles



.ing and !inion <inal (rive



:orm ear

(rives a spur gear

!rovides maximum

tooth contact

-sed in recirculating

ball steering boxes

&peedometer cable

drive mechanisms

gears_ch_29.ppt

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