Differentials

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By: tara.chand01234 (91 month(s) ago)

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Differentials:

Differentials When you make a car go around a corner, the outer wheels travel further than the inner wheels.You'll notice that the rear wheels take a different path to the front wheels, but the other thing to notice is that because the car's wheels are describing different radius arcs, the further away from the centrepoint of the arc, the larger the distance that gets travelled. In car terms, that means the outer wheels need to turn more times than the inner ones every time you go around a corner, because they're describing a larger arc.

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I f the outer and inner wheels were joined together with a solid axle, one of them could not turn more times than the other - they'd have to turn at the same rate.Differentials basically allow two wheels on the same axle to turn at different rates..

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On a two-wheel-drive car only the driven axle needs a differential. The undriven wheels are not connected to each other. .For four-wheel-drive or all-wheel-drive vehicles, then yes, both the front and rear axles will have differentials because they are both driven axles. Technically, a differential is a torque-splitter - it splits the input torque two ways to two output shafts, each of which can turn at a different rate.

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For full-time all-wheel-drive, there is often a third differential in the driveline from the front to the rear of the vehicle, to allow the entire front and rear axles to spin at different speeds to each other

Open Differentials :

Open Differentials They're the easiest to explain, they're the most common, and they supply the same amount of torque to each output. Open differentials have a few essential components, illustrated below.

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The input pinion gear is the gear that is driven from the drivetrain - typically the output shaft from the transmission. It drives the ring gear which, being larger, is what gives that final gear reduction . Attached to the ring gear is the cage, containing two captive pinion gears that are intermeshed with the two output pinion gears, one connected to each axle. The captive pinions are free to rotate how they wish.

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As the input pinion spins, it meshes with the ring gear. The ring gear spins, spinning the cage and the two captive pinions. When the vehicle is travelling in a straight line, neither drive pinion is trying to spin any differently from the other, so the captive pinions don't spin and the turning of the ring gear is translated directly to both drive pinions. These are connected to the driveshafts to the wheels, so effectively, the ring gear spins the wheels at the same speed that it is turning. When the vehicle starts to turn a corner, one of the wheels is going to want to spin more quickly than the other. At this point, the captive pinions come into play, allowing the two drive pinions to spin at slightly different speeds whilst still transmitting torque to them.

Limited-slip differentials :

Limited-slip differentials It still has all the components of an open differential but there is two crucial extra elements. The first are spring pressure plates which are a pair of springs and pressure plates nestled in the cage between the two drive pinions. These push the drive pinions outwards where the second extra element comes into play - clutch packs. The backside of the drive pinions have friction material on them which presses against clutch plates built into the cage. This means that the clutch is always going to try to behave as if the car was moving in a straight line by attempting to make both output pinions spin at the same speed as the ring gear and cage

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. However, when a car with a limited-slip differential goes into a corner, there are enough forces at play that the drive pinions begin to slip against the clutch material, thus allowing them to turn at different speeds again. The stiffness of the spring pack coupled with the friction of the clutch pack together determine the amount of torque required to overcome the clutch.

Torsen differentials :

Torsen differentials Torsen differentials are a derivative of open differentials. They derive their name from their function - Tor que- Sen sing. When the torque going to both outputs is the same, a Torsen differential essentially works just like an open differential. The change comes when the torque going to each output begins to change, for example as a result of a slippery road surface under one wheel. When this happens, what's known as an Invex gear train (inside the differential) begins to bind together. The Invex gear train is designed with a torque bias ratio in mind that determines the ratio of torque that it can split between the outputs as the geartrain begins to bind together.

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Torsen differentials are normally used in-line between the front and rear drives for performance all-wheel-drive vehicles, to split the torque between the front and rear axles, rather than the left and right wheels

Locking differentials :

Locking differentials Locking differentials are another derivative of open differentials but with an electronic, pnuematic or hydraulic actuation system that locks the two drive pinions together as if they were a solid axle. This is for use in serious off-roading, where a vehicle will spend a lot of time with one wheel per axle in the air. By locking the differential, it behaves like a solid axle and both wheels are spun together.

The exceptions that prove the rule :

The exceptions that prove the rule A good example of a vehicle with no differential would be a NASCAR or Indy car racer. To save weight, those cars have no differential. But they go around corners so they must have differentials ! With the exception of street courses, NASCAR and Indy car racers always turn left, and this is Good News for the engineers. When you know that a vehicle is always going to be turning one direction, you can make the outer tyres physically larger than the inner ones. This gives them a greater circumference, and that in turn means that for every turn of the axle, the outer tyre is going to try to travel further than the inner one - precisely what you need in a corner.

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