gear boxes in automobiles presentation

8/2/2019 gear boxes in automobiles presentation

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GEARBOXES IN

AUTOMOBILES

SUBMITTED BY:-

CHANDRA BHAN SINGH HADAMOOL SINGH CHOUHANNAGESH CHOUDHARYAMIT TIWARYBRIJESH RAJ(II yr. MECH. B.TECH IV SEM)

Academic session2011-2012


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INTRODUCTION Gearboxes are used in almost every industry right from

power to marine, and also include agriculture, textile,automobiles, aerospace, shipping etc.

There are different types of gearboxes available for varyinguses. These gearboxes are constructed from a variety ofmaterials depending on their end use and the kind ofindustry they are being used in.

The product has numerous industrial applications forproviding high torque and smooth speed reductions.

These gearboxes are also manufactured keeping certainspecifications in mind, which will also vary depending onthe application.


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DEFINATION A gearbox, also known as a gear case or gear head, is a gear

or a hydraulic system responsible for transmittingmechanical power from a prime mover (an engine or

electric motor) into some form of useful output. It isreferred to the metal casing in which a number of gears aresealed.

Its also known as manual transmission.

A gearbox is also a set of gears for transmitting power fromone rotating shaft to another.

Their main function is to convert the input provided by anelectric motor into an output of lower RPM and highertorque.


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FUNCTIONAt low speeds, the torque produced by an I.C. engine is

very small, which increases with increase of speed,peaks at some optimum speed and starts decreasingbeyond that.

The transmission also provides a neutral position sothat the engine and the road wheels are disconnected

even with the clutch in the engaged position.A mean to back the car by reversing the direction of

rotation of the drive is also provided by thetransmission.


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NECESSITYVariation of resistance to the vehicle motion at various

speeds.

Variation of tractive effort of the vehicle available atvarious speeds.


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TOTAL RESISTANCE


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Tractive effort

The curve 1,2 and 3respectively in figrepresent the tractive

effort in first, secondand top gearsrespectively.


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Superimposing the total resistance

and tractive effort curves for different

gears:-

When tractive effort is greater

than total resistance, thanvehicle is accelerated.

When the necessary speed hasbeen obtained , we may shiftinto higher gears, becausethen the vehicle speed has tobe simply maintained and noacceleration is required.


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TYPES OF MANUAL

TRANSMISSION SLIDING MESH GEARBOX

CONSTANT MESH GEARBOX

SYNCHROMESH GEARBOX EPICYCLIC GEARBOX


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SLIDING MESH GEARBOX1.main drive gear

2.counter shaft

3.main shaft

4.I gear

5.II gear6.III gear

7.top speed engaging

dogs

In this type of gear box, gears are engaged and disengaged by slidingof the gear wheels. Gear wheels on the main shaft engage with gear wheels on the layshaft or counter shaft by sliding themselves.


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Sliding mesh gear box

I gear position


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II gear position


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III gear position(TOP GEAR)


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reverse gear position


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Disadvantages Only Straight cut (Spur) can be used. So more

wear

Straight-cut gears had to be matched in speedbefore being brought into mesh together. Theresult was a horrible grinding noise - crashing thegears, as it was known

changing gear requires considerable skill


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Constant mesh gear box


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Constant mesh gear boxConstant-mesh gearboxes are quieter and slicker,

also less wear because of Helical gears

More frictional losses due to meshing of all gearsall time

But you still have to match the spinning speedsbefore you could engage the chosen gear, i.e.

need for double-de-clutching


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Constant mesh gear boxAdvantages of Constant mesh gearboxover Sliding mesh Gearbox:

Helical and herringbone gear can be employed in these gearboxes and,therefore, constant mesh gearboxes are quieter.

Synchronizing devices can be easily incorporated. Since the gears are engaged by dog clutches, if any damage occurs while

engaging the gears, the dog unit members get damaged and not thegear wheels.

By suitably designing the dog clutch, the gear changing can be madeeasier.

Damage to the dog clutch is less likely because all the teeth are engagedat a time.


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Double de-clutching This is to match the speed of the rotating parts of the

gearbox for the gear you wish to select to the speed of theinput shaft driven by the engine. Once the speeds arematched, the gear will engage smoothly.

To perform it, the clutch is pressed and the gearbox shiftedinto neutral gear. The clutch is released, the throttle is"blipped" which applies power to the disengaged gearbox,thus speeding it up internally. The clutch is pressed for thesecond time and the gear lever moved (smoothly) to thedesired gear. The clutch is released again, and the drive

continues. This operation is suitable for a down change. For an upchange, it is usually sufficient to allow the gear

lever to rest momentarily in neutral and no "blip" isapplied.


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Synchromesh GearboxThe green cone-shaped areais the syncho collar. It'sattached to the red dog gearand slides with it.

As it approaches the helicalgear, it makes friction contact

with the conical hole.

The more contact it makes,the more the speed of theoutput shaft and free-spinning helical gear areequalized before the teeth

engage.


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Synchromesh gear boxIn a synchromesh gearbox, gears canfreely rotate or be locked to the shaft

It consists of a sliding collar whichbridges between two circular ringswith teeth on them - one travels withthe gear, one with the shaft. Whenthe rings are bridged, the gear islocked to the shaft. To match thespeed of the gear to that of the shaft

as the gear is engaged, the collarinitially applies a force to a coneshaped clutch which is attached tothe gear. This spins the gear up ordown in speed to match the shaftprior to engagement of the collar.


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Epicyclic Gearbox

In such gear boxesepicyclic gear trains areemployed to get the

various gear ratios.

The characteristicfeature of an epicyclicgearing is that at least

one wheel not onlyrotates about its ownaxis but also rotatesabout some other axis.


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Epicyclic GearboxAutomatic gearboxestypically use one or morecompound planetarygearsets instead ofchaining regular gearsetstogether.They look just like aregular planetary gearsetfrom the outside, but

inside there are two sungears and two sets ofintermeshing planet gears.There is still only one

ring gear though.


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Epicyclic Gearbox

gear boxes in automobiles presentation

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