Point of Center Differential?

[SpitFireV12RR]

Hey dudes,

I can't find an action that the center diff. does! I thought all a Differntial did was turn the vertical rotations to horizontal rotations(IF you look at it from a birds eye view). I just don't get it and thought one of you could help me understand.

Thanks,
Todd

 

[Plaidfish]

A DIFFERENTIAL gear allows the 2 output shafts to spin at different RPMs....the center differential allows the front and rear differentials to get power as they need it rather than forcing power to both sides equally....it keeps the car planted on the ground instead of yanking the front end in the air by allowing excess forces to be absorbed and redistributed through tthe driveline......

 

[Plaidfish]

the pinion gear / ring gear set out side of the differntial cup are what transfer the rotation...

 

[kx250ryder]

Yeah, a front or rear diff allows one side of the car to spin faster than the other, since the outside wheels have a longer distance to travel around a corner than the inside wheels.

EDIT: If this seems a bit fuzzy when you read it, imagine walking a lap around a pole. Now walk a full size car width out from the pole, and walk another lap. Notice how many more steps it took. That is why a differential is necessary here. Otherwise, one of the two wheels would have to spin faster/slower than the ground is actually going by. If you ever notice an old street rod that squeals its tires when it goes around a corner, even if it is going slow, it is because it has a solid rear axle, with no differential. The same thing happens with a sport atv (not the utility ones, because they usually have 4wd and diffs).

The center diff allows the front and rear diffs to spin at different speeds. This is handy under braking for a corner, when you may want your rear wheels to lock up, but not your front ones, to induce a slide. I have the brake bias set up on my buggy such that my rear wheels can lock, but my front ones almost never do (if they lock, you have no steering).

 

[Jeep]

The center differential applies the same amount of torque to the front and rear differentials, but if the front end as a whole has more traction than the rear, then the rear end as a whole will experience more rotational velocity, and vice-versa.
On hard acceleration the weight of the vehicle will shift to the rear and thereby apply more traction to the rear than the front, when that happens and both front and rear differentials see the same torque input but less traction on the front, the front wheels will begin to spin, and torque applied to the rear end will reduce acceleration due to the rear end, which will temporarily slow overall acceleration until the front end gains more weight and traction and then the vehicle will accerelate harder again. All of this weight transfer and accleration due to front to rear rotational velocity happens very, very quickly.
And, as said earlier, it allows for a different amount of braking percentage front and rear.

On the other hand, if there were no center differential at all, the front diff input and rear diff input will both experience the same exact rotational velocity input.

Jeep

 

[Dhutch]

The others have covered the basics, but heres some back ground reading.

http://auto.howstuffworks.com/differential.htm
http://en.wikipedia.org/wiki/Differential_gear


Daniel

 

[rocknbil]

Also all of the above can be controlled by different weights of oil in the front or rear, for example, if you have equal oil weights front and rear, and the rear wheels tend to slip more than the fronts, one way to adjust this is to use a lighter oil in the rear than front. Most buggies wind up with heavier weight in front than rear due to the weight shift mentioned above.

 

[Dhutch]

Also all of the above can be controlled by different weights of oil in the front or rear, for example, if you have equal oil weights front and rear, and the rear wheels tend to slip more than the fronts, one way to adjust this is to use a lighter oil in the rear than front. Most buggies wind up with heavier weight in front than rear due to the weight shift mentioned above.

And then its common to run something heavyer again in the center diff