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Gear boxes

Updated on May 3, 2012


Necessity ofgearbox:

As is known, in internal combustion engines, the expansive force of the gases generated by the explosion of the mixture is applied on the piston head which exerts a force greater, the higher the amount of explosive mixture. This force which is transmitted to the journal of the crankshaft by connecting rod, it generates the torque, which represents the effort of rotation which is capable of developing the motor saw forces which opposes its movement. When the value of these forces is equal to the torque developed, the vehicle moves at a constant speed. If the effort applied to the wheel rotation is less resistance to overcome the vehicle in gear, this will slow to a halt, and if it is higher, will gain speed.
The engine torque multiplied by the number of rotations makes the power developed. From there it follows that the power of an engine varies primarily with the engine speed, the higher values ​​corresponding to higher regimes, because despite the fact that the torque decreases in these margins, the number of explosions per minute gradually increase, which leads the significant growth in the power developed by the engine.
Whereas a rotation speed between the maximum torque value and the maximum power which corresponds to a given torque then, when increasing the resistance to overcome the movement of the vehicle (for example a uphill) there is a decrease in speed but in addition it gives an increase in the torque developed, necessary to overcome the increased resistance imposed now to vehicle motion, thereby obtaining a new equilibrium condition, a system lower.
If we consider a rotation speed of the engine below the value which is obtained the maximum torque, the operation of the same cannot be stable because of the small increases to overcome the resistance to movement of the vehicle, the engine speed decay, and thus, considerably reduces the torque and power developed, with which it can obtain a new balance at a lower speed and thus the engine loses gradually the rotation until it goes off.

These conditions results clearly the need for a mechanical organ, such as a gearbox, permitting operation of the engine speed in the range of stable, regardless of the resistance encountered by the vehicle during operation.


Attaching thegearboxin the vehicle:

In older vehicles, the gearbox was placed between the clutch and rear axle. In other cases, the powertrain, consisting of engine, clutch and gearbox, is located on the front, which is the current trend for vehicles of average type. We can also see the gearbox at the rear, coupled to the rear axle, or coupled to the motor, in this case placed at the rear. In any case, the functions and qualities of a gearbox are the same, whatever its placement on the vehicle.


Main typesof gearboxes:

• Unsynchronized gears boxes;
• Synchronized gears boxes;
• Semi-automatic gear boxes;
• Automatic gear boxes;
• Continuously variable transmission CVT


Unsynchronized gears boxes:

This box consists basically of four shafts (primary, secondary, intermediate and reverse), a number of sprocket, two forks and two forks of the shafts.
The shaft is directly connected to the metallic disc clutch. At its end, which enters the gearbox there is a reel and short teeth and strong.
The secondary shaft is in alignment with the shaft and is connected to the shaft of the motor. It is square or grooved and includes sprocket which can move along it by means of the forks. On one side rests in a bearing housing and the other an ear which rotates a bronze on the end of the shaft.
The intermediate shaft is located alongside the other two shafts, and there are fixed a number of sprocket, which together constitute the fixed rail.
The sprocket or a gear box of four forward gears are at least ten: a primary shaft, the three secondary shaft, five in the fixed rail and the reversing reel on a shaft itself.
The forks slide along axes or guides the fork and forked end.
The shaft or guides of the forks are at the top of the box and attach them to the forks.


Howit works:

The end of the sprocket shaft is always meshed with a reel shaft means. Therefore, with the engine in gear, the train turns constantly fixed. When you want to get a change, push the clutch level and move up the gear lever. This pulls the front or back of a fork that will require a reel of the secondary shaft to engage in the respective spool shaft through. Thus, when clutch again, the secondary shaft is forced to rotate also.
To get the fourth in a four-speed gearbox is not necessary gear sprocket. In such case, the teeth of the end of the shaft which mesh with the teeth of the end of the secondary shaft, thus causing direct transmission of movement, as primary and secondary shafts formed a single shaft.
The reverse is obtained by means of an auxiliary interposed between a reel spool of the intermediate shaft and the secondary shaft. Thanks to this reel through the direction of movement of the secondary shaft is reversed.
There positions of gear lever such that no secondary spool shaft sprocket is meshed with the intermediate shaft nor the transmission occurs directly. In this position called neutral.
It is thanks to the position of the reels in neutral it is possible to stop the car without disengaging or stop the engine.


Synchronized gears boxes:

Can be regarded as traditional gearbox formed by the shaft, to which belongs the pinion, which is constantly geared to a gear train fixed, it is built, also the speed of reels, which are therefore sympathetic to the shaft. With these the sprocket gear mounted on the secondary shaft nuts, with the interposition of bushes of brass so that rotate freely about the shaft, dragged by the respective pairs of the intermediate train.
The input shaft receives the motion of the motor via the clutch and secondary transmission and movement, therefore the wheels. All the shafts are supported in the shielding housing by means of bearings, causing it to the shaft end inside the secondary shaft with the interposition of a needle bearing.
To transmit the movement that comes from the primary to the secondary shaft, it is necessary to do this came from solidarity to any of the reels mounted mad about it. Thus, the rotation is transmitted from the primary to the fixed rail, or through, through the pair of reels takes constant, resulting in the drag of the secondary sprocket meshing with them, which rotate about this shaft nuts. If any of the gears to be sympathetic to the shaft, it will be in rotation.
The gear shift is achieved by means of synchronizers, composed essentially of a part mounted on a grooved secondary shaft, on which in turn mounts the crown also on grooved and can be moved laterally a distance.

Synchronizer:

Due to theconstitution of aconventionalsynchronizedgearbox, in which the intakevelocityis obtainedby moving thecrown of thesynchronizer,whichhasinternaltoothmeshingwith thetoothof theselected speed, it is understood thatit is necessary tomatch thespeedsentrained by thesecondary shaftthroughtrainwhich runsin turndriven by theengine from theshaft.
With themoving vehicle, the driverwhen operatingthe gear leverto selectanew relationship, it produces the immediatedisengagementof the gearcorresponding to thespeedwith which theywentto move, leaving the gearbox in neutral. This operationis simple to perform, because only occursto movethesynchronizerof the crown, to which itgivestherelevant technicalmeshinggearspeed.Still,to get a newgear, it is essential to match thespeedsof the parts toengage, or synchronize yourmovements, otherwise toproduceshocksinindentationsthat can grow tocausenoiseand even fractures.

As theentrainedsecondary shaftrotatesthe wheelsinthe neutral positionof the box andnuts isgeardrivenby the enginethrough the primaryandintermediatetrain, to achieve synchronizationis requireddeclutching, whereby theshaftis free, without being movedby the motor, its speed of rotationdue toinertiacan be synchronizedwiththe secondary shaft. For this reason, the speed changesto bemade​​declutchthe motorto returnthegearprogressivelyachievedsincethe selection of thenewdesired relationship.The action ofslow and progressivegearavoidspullinginprogress.
The function of asynchronizeris thereforeequal the speedofthe secondary shaftgearmad, withthisshaft.This is achieved byinterposingbetween these twomoving partsofaclutchdevicethat takesthe speed ofgearprogressivelycloser to thewildthe secondary shaft. The synchronizerthat bestmeets theseconditions of useis thetypeof frictionclutchcone.

The synchronizer of the simplest type is formed by a cube, which rib is mounted on the secondary shaft, so that it can move a certain route. In its side faces are formed cone female thread and on its outside there are a toothed radial slots in which to house the fixing balls, spring-mounted.
Streaked on the hub is mounted on the crown, provided with an internal circular groove in which balls are housed in fixing the neutral position. In its exterior is constructed another circular groove, which lodges the fork command.
Against the side of the hub attaches to the spool, nuts mounted on the secondary shaft and provided with a male taper and a small toothed, which engage respectively with the female taper of the synchronizer and the internal tooth of the crown, the selection of maneuvers speed.
In the neutral position the cores are uncoupled allowing the independent rotation speed difference and the synchronizer hub (entrained by the shaft) and the reel nuts (driven by the intermediate train.
In the maneuvering speed of change, to introduce the new relationship, the conductor takes the gear lever to the desired position and, with this action produces the displacement of the crown, and carried the synchronizer hub through balls housed within the groove crown. Accordingly, the female taper of the synchronizer in contact with the male taper of the spool, and due to contact between them, the speeds of rotation of the reel and the synchronizer become equal.
Later, during the maneuver, if we continue to apply force on the crown, since the cube is already leaning on the reel, the crown will slip on the cube winning the fixing action of the spheres, which lurk in their living winning the action of the springs. In this way produces the internal gear of the toothed crown of the reel, being this being integral with the secondary shaft, whereby to produce the clutching, the motor rotation is transmitted from the sprocket to the secondary shaft nuts through the synchronizer .
There is also the absolute synchronizer which displays in the conventional certain significant variations, among which can stand the use of a female taper synchronization position, instead of being built in the cube.


Semi-automatic gear boxes:

Inthesemi-boxes speed selectionis madebeforehandby means ofa leverplaced on asectorexistingin the passenger compartment. Maneuveringthis lever, the box is preparedfor the speedto andthenshallthe time beingmore convenientfor simpleoperation of apedal.
Epicyclicgearboxwithmechanicalbrakes: This boxconsists of:fourepicyclicgearsand theircrosses, fourdrums withbandbrakes, aclutchfordirect, onecamshaftforthe brake controlleversand foursystemsof springsand fasteners.
The drumsare formedon the outsideof the crowns, exceptthe drumof the 3rdspeed.
Themotor shaftisfixed on himthe maleclutchpasses freelyin the planetariumof the 3rdspeed andis rigidly connectedtotheplanetary2ndand 1stgears.Theshaftis connectedto the crossheadof the satellitesof the 1stspeed andreverse gear.
The numberof teeth of theplanetaryand satellitecrowns arecalculatedso that theymake the necessaryratio reduction.
Theplanetarythe 1stand 2ndare constitutedby a singlegear.

The control of the brake drum is made of the carrier by means of the lever pre-selective. This lever, through an appropriate system, drives the camshaft from the box. This shaft acts on a system of levers and springs, one for each drum.
Depending on the position of the lever pre-selective, and are prepared each change of speed.
Once prepared the change of gear, drives up the box in time by a pedal which corresponds to the ordinary vehicle clutch.
During the march, mixed up with the speed, you can prepare another speed, driving back the lever pre - selective, making it impossible to be impossible to produce any damage to careless handling.
To obtain each change of speed, twisters speed of the drum in order to immobilize the respective crown.
Operation: 1st gear: In 1st gear, when you press the pedal, lock up the drum corresponding to immobilize their crown. The planetarium, driven by the shaft, it rotates the geared satellites that are also required to go through the sprocket teeth immobilized. Thus, the crosshead of the satellite is driven in a rotational movement properly scaled which it conveys the drive shaft to which it is connected.
2nd speed: In 2nd gear, when you press the pedal, the drum hangs up the second corresponding to immobilize the crown, getting all the other free. The planet spins the satellites, which are then required to go through the immobilized crown. Thus, the movement of the second crosshead is transmitted to the crown of the first to which it is connected. The appropriately scaled motion is transmitted to the crosshead of the first shaft.
3rd speed: In 3rd gear, when you press the pedal, the drum is immobilized in the third. As the third planetary shaft is loose, the movement is scaled by the gear of the 1st, 2nd and 3rd gears.
4th gear or directly: The direct clutch closes and the motor shaft rotates through the clutch drum and the third planetary. As all the drums are free relative movements are impossible and turns around together with the speed of the drive shaft.
Reverse: In reverse, when you press the pedal, the crown is immobilized in reverse. The drive shaft drives the planetary first and rotates the satellites of the first and reverse, which crosspieces are connected to the shaft. As the heads of the reverse gear is immobilized and the crown is connected to the first planetary reversing, it is apparent that the satellites of the reverse gear undergo an inversion of the movement communicating the crosshead connected to the drive shaft.
Neutral: In neutral, the drums are all free. The drive shaft drives the planetary the 2nd and 3rd speeds that are turning their satellites. These in turn make the crowns corresponding rotate. How these are linked to the 3rd planet and reverse shafts that are free, the movement is not transmitted to the drive shaft.
A semi-automatic box may have some differences will be mentioned here, namely the main difference consists in employing electrical brakes instead of drum mechanical immobilize the crowns.

Automatic gear boxes:

Theautomatic transmissionis one in whichthegear shiftingis accomplished withoutthe intervention of thedriver.
Anautomatic transmissionhas threemain parts:
•Atorque converter: replacing thecurrentfrictionclutch.
•One or moresets ofplanetary gears, which replace thesprocketteethof thenormalboxes.
•hydrauliccontrols.
Atorque converteris formed byan impellerconnected rigidlyto theend of the crankshaftanda rotorintegral with theshaftof the gearbox. These two bodiesareprovided withinnerlugsand are mountedopposite oneanotherin a housingfilled with oil.Among thesethere are one ormorereactionmemberscalledstators.These are essentiallyformed byfinsorientedin order to changethe direction of theoil.
Operation: When the engine operatesat leastengine speed, theoilprojected by thevanesof the impelleragainst thefins of therotoris not strongenough to printrotational forceto the rotor.Loading, however, the accelerator, the speedincreasesand the rotorisforced torotatein the same directionof the impeller.
Asthe rotor speedis close to theimpeller, the statortorquedrops to zero, so that the change isgradualrather thanin steps, as when going fromoneother combinationgearboxes,reelsbehavior.
Theplanetary orepicyclicgearsare identicalto theexistingsemi-automatic boxes. Butthere is anotherinwardlymultiple discclutchbetweenthe crossheadand the crownof the satellites, to fix thesetwo bodiesto oneanother whenrequired for thedirect transmission.

When fixing the crown with the brake, the satellites revolve about the planet, covering the sprocket teeth. This results in a reduction in motion, and therefore an increase of pulse to the drive wheels of the vehicle.
When the brake band is loosened and the crosshead of the crown and satellites are fixed by means of multiple-disk clutch, both of these bodies rotate as a unit on the planet, thereby providing direct transmission.
Operation ("Hydromatic box"): 1st gear: Both the brakes on and both clutch free interior. The gearing operates in two sets of gears.
2nd speed: Brake and clutch 2nd game of the first connected, the brake of the 1st game and the second clutch free. The gearing operates only in the 2nd game.
3rd gear, brake the 1st game and the second clutch connected, brake and clutch 2nd game of the first books. The gearing operates only in the 1st game.
4th speed or direct: Both free brake and both clutches connected. Not operating gear ratio.
Reverse: 1st game of the brake on the reel and reverse jam, lock the 2nd game and both clutch free. The gearing operates in the 1st game and in the reverse gear.
Neutral: Both brakes and clutches both free. The movement is not transmitted.
The hydraulic controls the automatic operating oil pressure is maintained by appropriate valves. To maintain this pressure is required right driving force, resulting in a gas consumption slightly higher.
In the cabin there is a dial with a lever that allows four or five positions. Maneuvering conveniently this lever and pushing the gas pedal, make changes gradually without any driver intervention.
Four positions of the lever:
• N (neutral): neutral.
• Dr (driving): four positions in the regular brand forward which engage automatically.
• Lo (low): low gears only work in which the 1st and 2nd speeds, exceptional for use on steep slopes or in the way of bad floor.
• R: reverse.


Continuously variable transmission CVT:

For several yearsis being used inpassenger carsandsmalldisplacementscooters, adrivesystemforautomaticcontinuousvariablespeed.
Thisisa transmissionsystemthat suitsyourperformance soconstant as a functionofvehicle motionconditionsand requirementsof driving.To achieve thisithasin twopollsofvariableeffective diameter, joined byametalbelt.
Thepolycan modifythe width oftheir throatsmovement ofone of its facesonthe other (side), which is obtainedby applying toa particularmobilesideoil pressure,which is providedby a pumpinstalled in thegearboxitself. Thus, it appears that the diameter of thepolyis variable, corresponding to each ofa givenvariationrate of speed, and since there isan infinite numberof variations,thatis obtained withaninfinitenumber of gearsas well, ie, acontinuous variationof thespeed ratio.
When the twofacesofpolyclientare separate from, those ofpolyaresenttogether andthere is a significantspeedgear ratio. Theopposite occurs whentheincreaseof engine speed, the oil pressureincreases, moving the faceof themobileclientpolyincreasing the diameter, whilethepolysentis forcedagainst the action ofa powerfulspringto decreaseits diameteradjusted by thelengthof the belt.Accordingly,it produces amultiplication ofthe motor.
This type ofboxhasanelectromagnetic clutchorcentrifuge.


Gear box controls:

The most common systemto drivea gearboxisa system of levers, cables, bearings, shafts, etc., or a mechanical system.
Agearboxcan alsobe controlledin other ways,in particularthree capstanhydraulic or pneumaticsystems.

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