presentation transmission

8/6/2019 Presentation Transmission

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Transmission


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Need ofTransmission

To provide for disconnectingthe engine fromthe driving wheels.

To enable the leverage betweenthe engineand driving wheelstobe varied.

Itmustreduce the drive-line speed fromthatofthe engine tothatofthe driving wheelsinaratioofsomewhere betweenabout 3 : 1 and

10 : 1 ormore, accordingtothe relative size ofengine and weightofvehicle.


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Turnthe drive, ifnecessary, through 90 or

perhapsotherwise realignit. Enable the driving wheelstorotate at

differentspeeds.

Provide forrelative movementbetweentheengine and driving wheels.

Whenthe engine isrunning, to enable the

connectiontothe driving wheelstobe made

smoothlyand withoutshock.


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Typesoftransmission

Mechanical

Hydraulic

hydrostatic

hydrodynamic

Electricand electromagnetic


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Mechanical Transmission

Clutch, gearboxand live axle.

Clutch, gearboxand dead axle.

Clutch, gearboxand axle less

transmission


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Clutch, gearbox and live axle transmission


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The engine isatthe front, withitscrankshaft parallel tothe

axisofthe vehicle.

The d

rive

istransmitt

edthrough

a

clutch

an

da

short

shaft

(c)

tothe gearbox.

Fromthe gearbox, a propellershaftor cardanshaft witha

sliding jointatone end and auniversal jointatboth ends

takesthe drive toa live backaxle.

A live axle isone through whichthe drive istransmitted, while

a dead axle isone that doesnottransmitthe drive. Bevel or

wormgearing (g) withinthe axle turnsthe drive through 90,

and differential gears divide it equallybetweenthe two drive

shafts, orHalf shafts ( j), whichtake itouttothe wheels.


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A clutchisused for disconnectingthe engine fromthe driving

wheels.

Itmustalso enable the drivertoconnectthe engine, whenitisrunning, withoutshocktothe driving wheels.

The clutchiskeptin engagementbyaspring-loading

mechanismand is disengaged by pressure ofthe footona

pedal. Soitcannotbe disengaged except whenthe driverisinthe

vehicle.

Whenthe driver wantsto leave the vehicle withthe engine

runninghe hasto disconnectthe engine fromthe drivingwheelsbyuse ofthe gear-shift lever, whichhe setsina

neutralorgears-disengaged, position.


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The propellershafttransmitsthe drive ontothe backaxle.

The universal jointsatits endsallow boththe engine-and-

gearboxassemblyand the backaxle tomove relative tooneanother, astheirspring elements deflect.

The sliding joint, usuallyintegral withone ofthe universal

joints, accommodatesvariationsin lengthofthe propeller

shaftasitsrear end risesand fallsvertically withthe backaxle

and itsfront end pivotsaboutthe universal joint justbehind

the gearbox.

Gearing (g), in whatiscalled thefinal drive unit, turnsthe

drive through 90 and reducesthe speed inaratioofabout 4 :

1, since the driving wheelsmustrotate muchmore slowlythanthe engine.


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Layout of rear-engine vehicles with live

axles

Mainlyused inbusesand coachestosetthe

floorat low level.

Thisadvantage makesitthe bestconfiguration

foruse inthe formulacars.


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Engine placed transverselyatthe back


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Description

The engine and gearboxare builtasasingle

unit, whichisinstalled transverselybehind the

rearaxle.

The clutchisinterposed betweenthe engine

and gearbox, while atthe other end ofthis

boxisabevel gear pairtermed the transfer

drive.


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Totransmitthe drive tothe rearaxle, the driven

gearofthe bevel gear pairiscoupled bya

universal joint. The final drive unitisincorporated atone side of

the axle toavoid the complicaciesthatmight

occurincase the drive isgivenatthe center,

instead ofnearitscentre.

The drive isturned throughmuch lessthan 90

fromthe propellershaftatbothitsfinal drive and

transfer drive ends, whichsimplifiesthe designofboth pairsofgears


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Engine placed longitudinally


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Gearbox placed behind the axle


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Disadvantagesofrearmounted engine

The lengthsofthe control runsfromthe

driving positiontothe back.

The drivermaynotbe able tohearthe engineand judge itsspeed, forchanginggear,

especiallyinnoisyurbantraffic.


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Frontmounted rear wheel drive


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Description

Engine ismounted longitudinallyforward of

the front wheelsand the gearboxtothe rear

ofthem, the final drive beinginterposed

betweenthe two.

Itsoutputshaftisbelow itsinputshaft,

instead ofthe more commonarrangementin

whichthe twoare in line.


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Frontmounted front wheel drive


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Frontmounted front wheel drive


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Description

The axesofall the shaftsare transverse

relative tothe longitudinal axisofthe car.

Spurgearstransmitthe motionfromclutchtogearboxand fromgearboxtothe final drive

unit.

The gearbox, the final drive unitand the

engine all sharingthe same lubricantthat

fromthe oil sump itself.


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Four wheel drive


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Description

A transferboxisinterposed betweenthe gearboxand backaxle unit.

The functionoftransferboxistotransferthe

drive fromthe maingearboxtoboththe frontand rearaxles.

Pinion A is drivenbyacouplingfromthe gearboxoutputshaft.The pinion, throughan

intermediate gear B, drivesathird gearC,mounted onthe cage ofa differential gearassembly


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Fromthe differential gears, one shaftistaken

forward tothe frontaxle and the other

rearwardstothe backaxle.

Boththe axleshouse theirown differentials

and final drive gears.

Atthe frontouter endsthere are universal

jointsD, whichare necessarytoallow the

front wheelstobe steered.

presentation transmission

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