Automobile Engineering- Unit-3-Transmission system of Automobile (gear box)

Automobile Engineering.
Unit-3-Transmission system of Automobile.
Gearbox- Sliding Mesh, Constant Mesh, Synchromesh Gearbox).

1. AUTOMOBILE ENGINEERING
Unit-III-Transmission system of
Automobile
(Gear Box)
By,
Dr.S.SURESH,
Assistant Professor,
Department of Mechanical Engineering

2. WHATISGEARBOX
Whenwedrivethevehicle,wedonotdrivethe
vehiclealwaysatthesamespeed.Thevehiclemust
beoperatedatalowerspeedwhenitneedsmore
pullingpower.
Moreover,basedontheoperatingconditions,the
vehiclerequiresdifferentspeedsandtorque.
Toperformthis,aboxcontainingdifferentgears,
shafts,andbearingsisrequired.Thisboxiscalledthe
gearbox.

3. NECESSITYOFGEARBOX
1. For reducing the engine speed and increasing the
torque.
2. For reducing the engine torque and increasing speed.
3. For the selection of speed levels according to the
driver’s requirement.
4. For pushing the vehicle in the backward direction.
5. For neutralizing the vehicles when there is no need to
transmit the engine power

4. TYPESOFGEARBOX
Manual Transmission
Sliding Mesh Gear box
Constant Mesh Gear box
Synchromesh Gear box
Automatic Transmission

5. 1. SLIDINGMESHGEARBOX
Itissimplesttypeofgearbox
spurgearsarechangedbyslidingonegearontheother.
Thisgearboxconsistsofthreeshafts:
➢mainshaft,clutchshaftandacountershaft(or)layshaft
Inafourspeedgearbox(whichincludesonereversegear),the
countershafthasfourgearswhicharerigidlyconnectedtoit.
Clutchshafthasonegearandmainshafthastwogears.
Thegearsonthemainshaftcanslideinthehorizontaldirection
alongthesplinesofthemainshaft.However,thegearsonthe
countershaftcannotslide.

6. CONT..
Theclutchgearisrigidlyfixedtotheclutchshaft.Itis
alwaysconnectedtothecountershaftdrivegear.
Thegearsonthemainshaftcanslidebytheshifter
yokebyoperatingtheshiftlever.Thesegearscanbe
meshedwithcorrespondinggearsonthecountershaft
withthehelpofshifteryokeandshiftlever.
Shiftleverisoperatedbyhandinfourwheelersfor
changingthegears.Areverseidlergearismountedon
another(third)shaftandisalwaysinmeshwith
reversegearoncountershaft.

7. LINEDIAGRAMOFSLIDINGMESHGEARBOX

9. Firstgear
FirstGearisusedatthetimewhenvehiclestartsitsmovementinforward
direction.
Providesmaximumtorqueandminimumspeed.
Thesmallestgearonthelayshaftmesheswiththebiggestgearinthemain
shaft.
Secondgear
SecondGearisobtainedwhenthesecond-largestgearofthesecondsmallest
gearoflayshaftmesheswiththemiddlesizegearofthemainshaft.
ProvideslowertorqueandhigherspeedthanFirstGear.
Thirdgear
ThethirdgearisthelastgearortopgearoftheSlidingMeshGearbox.This
gearisobtainedwhenthebiggestgearoflayshaftmesheswiththesmallest
gearofthemainshaft.
Providesmaximumspeedandminimumpower.
Reversegear
ReverseGearisusedwhenthevehicleneedstomoveintheopposite
direction.

10. 2. CONSTANTMESHGEARBOX
Allthegearsonthelayshaftandmainshaftareinconstant
meshwitheachotherandthedogclutchdecidesthe
transmissionoftherequiredgeartobeengaged.
Thespeedofmainshaftgearsandthedogclutchmustbe
equalforsmoothengagement
Components
1.Shafts
Clutch shaft
Lay Shaft
Main Shaft
2. Gear Lever
3.Dog clutch
4.Gears

11. LINEDIAGRAMOFCONSTANTMESHGEARBOX:

12. *Thevehiclemovesslowlyinthefirst
gear&acquiresmaximumtorque.
*Drivingshaftgear(layshaft)issmall
comparedtothegearofthedrivenshaft
(MainShaft).
*Thedogclutch(D1)slidestowardsits
leftonthemainshaftandmesheswith
the1stgear.
*TheTorqueacquiredissmallerandthe
speedacquiredislargerthanthefirstgear.
*Thedogclutch(D2)slidestowardsitsright
andengageswiththe2ndgearonthemain
shaft.

13. *providesMaximum speedand
MinimumTorque.
*Thedogclutch(D2)slides
towardsitsleftandengageswith
the3rdgearonthemainshaft
whichisindirectcontactwiththe
clutchshaft.
*Idlergearistobeplacedin
betweenthebiggerdiametergear
ofthemainshaftandsmaller
diametergear(G)ofthelayshaft.

14. 3. SYNCHROMESH GEARBOX
LatestversionofConstantmeshtype.
Itisamanuallyoperatedtransmissioninwhichchange
ofgearstakesplacebetweengearsthatarealready
revolvingatthesamespeed.
Inthistypeofgearbox,gearscanrotatefreelyoritis
lockedonlayoutshaft.
Synchromeshisanimprovementondogclutch.
Thesynchronizeristhemainpartofthisgearboxthat
stabilizesthespeed.
Asynchronizerisakindofclutchwhichlets
componentsturningatdifferentspeeds.
Tosynchronizethespeedsconefrictionisused.

15. PRINCIPLE:
Inagearbox,thereisalwaysadifficultyinengagingthestationary
gearwiththegearsalreadyrotatingatahighspeed.
Theprinciplestatesthat”Beforeengagingthegearstheyare
broughtinfrictionalcontactwitheachotherandafter
equalizingthespeedtheengagementisdone.”
Construction:
The synchronizer is placed between two gears. So, we can use one
unit for two gears.
G1 and G2 are the ring-shaped members who are having the internal
tooth that fits onto the external teeth.
F1andF2are the sliding members of the main shaft.
H1, H2, N1, N2, P1, P2, R1, R2are the friction surface.

16. Main shaft Gears
Lay Shaft Gears
Clutch Shaft
Cone Synchromesh
Synchronizers

18. Advantages
*ThenoiseproblemduringtheengagementofGearshas
beenminimizedintheSynchromeshGearbox.
*DuetothepresenceofSynchronizers,thequickshiftingof
gearsispossible.
*Duringtransmission,thereisnolossofTorqueduetothe
presenceofsynchronizers.
Disadvantages
*Impropergearchangingwillleadtothefailureofgears.
*Itisexpensivecomparedtotheothergearboxduetothe
usageofSynchronizers.