Gear box is to maintain engine speed on all conditions of loadand vehicle speed, the gear box uses a system of leverage ofkeeping the speed of engine up while scarifying some roadspeed.Types of Gear boxes1) Sliding mesh gear box2) Constant mesh gear box3) Synchromesh gear box a) Three speed gear box b) Four speed gear box4) Preselective gear box5) Epicyclical gear box6) Auxiliary gear box7)The freewheel drive8)Five speed gear box
Sliding mesh…It is the oldest and simplest form ofgear box.In order to mesh gears on the splinedmain shaft with appropriate gears onthe lay shaft for obtaining differentspeeds, they are moved to the right or tothe left.Splines are provided on the main
Sliding mesh….For meshing the pinions with themating gears on the lay shaft, the pinionsare slided along the spine.When the main shaft is driven from thelay shaft the gear reduction is providedby the first pair of gears which are alwaysin mesh.They are usually known as constantmesh gears.
2) Constant mesh gear box 1)I speed gear 2)II speed gear 3)main shaft 4)III speed gear 5)top and III speed engaging dogs 6)top gear 7)primary shaft or main drive gear 8)counter shaft/cluster gear
Constant mesh…All the gears whether of the countershaft or the main shaft are in constantmesh with each other.It also known as a silent or quite gearbox.It gives a quiteter operation and makesgear changing easier by employinghelical gears for the constant mesh.
Constant mesh….In constant mesh gear box generallyfour or more pairs of gears and two ormore sliding coupling members arethere.The coupling member is mounted aswell as slided on the splined teethmachined gear box main shaft.A selector fork fitting in to a groove inthe coupling member moves the sliding
Synchromesh…To bring the speeds of both the enginedriven and the gear box out put shaftdriven gears which are to engaged to therotational speeds for moving their dogclutches or their equivalent meshing unitsin to engagement readily and quietly.The gear wheel s which are to bepositively connected are first brought in tofrictional contact and when the friction hasequalized their speeds, the positiveconnections are made.
Synchromesh….The basic requirements areA braking device such as cone clutch.To permit easy meshing means ofreleasing pressure on the clutch beforeengagement of gears.
a) Three speed gear box 1)Main shaft 2)Planetary gear shafts 3,4,7)Internal gears (5) poking spring (6) gear regulating ring (8) Gears (9) planetary gear shafts (10) main shaft (11) planetary gears (12) fixed internal gear (13) intermediate gear disk (14), (15), (17) planetary gears
Three speed….It is simple form of gear box in whichengaging of gears is done by means of dogclutch.All the three forward speeds aresynchromesh.In this case the teeth of the sliding memberengage with corresponding teeth on the fixedposition rotating member.To engage the dog clutch with thecorresponding dog member on the enginedriven shaft it is slide along the splined gearshaft.A special hub provides the first(low) gear.
b) Four speed gear box
Four speed…For better performance in comparison tothe three speed type gear boxes, many of thelower powered cars are necessarily using afour speed gear box. With comparison three speed gear box inthe driving car, it fails to climb a hill on topgear while on a slightly lower gear ratiowould climb easily.
4) Preselective gear box
Preselective…•It is developed type of gear box used inDaimler and armstrong siddelely cars.•It employs wilson pre selective gearprinciple.•In this gear box the gear lever is dispensedwith and is replaced by a small lever mountedon the steering wheel.
Preselective….•The gear control lever provided moves in anarc to marked position relating to reverse ,neutral, first, second, third and fourth or topspeeds.•The control lever is moved to the required gearposition marked on the steering wheel selectorby hand for changing from one forward gear toanother gear above or below it.
5) Epicyclical gear box
Epicyclical…•Epicyclic gear box is known as planet gear box.•These were initially fitted to Lanchester and the fordcars.Advantages of Epicyclic gear boxIn these gear boxes, no dog clutches or slidinggears are used because the planetary gears are inconstant mesh.External contracting had brakes or multipleclutches of relatively small dimensions are used formaking gear changes.
Epicyclical….In stead of having the load only on a pair of gears,it is distributed over several gear wheels.To distribution of loads, a greater area of geartooth contact can be used by this gear box.In comparison three speed or four speed gear box,gears and gear housings of this gear box can bemade smaller in overall dimensions.It provides a more compact unit operating about acommon central axis because the epicyclic gearsoperate within an annuals or ring gear with itsexternal surface of cylindrical form.
6) Auxiliary gear box
Auxiliary gear box…
Auxiliary….An auxiliary gear box in order to form singleconstruction is either made as an entirelyseparate unit or is built on or attached to themain gear box.It is generally used by providing two gearratios.On e ratio is used in vehicles for “off theroad “ while the other is used for crosscountry use.
7) The freewheel drive
Freewheel..The free wheel drive is based on theprinciple similar to that used on a bicycle.It transmits a driven in one direction only,it is known as a unidirectional or one wayclutch.It is designed as a separate main unit.It consist of no of rollers.
8)Five speed gear box
. Five speed… It is mixed type of gear box having first and second speeds provided by sliding mesh gears and others provided by constant mesh gears. It has a shaft coupled to the driven shaft of the clutch with a pinion integrally attached to it. The lay shaft having four gears splined to it is driven by the pinion. The main is supported differently at the centre and the left as well as at the right.