5 ms·

There are a variety of mechanical systems used to combat this problem, not just thick grease. Limited Slip differentials can be employed to ensure that one whe

There are a variety of mechanical systems used to combat this problem, not just thick grease. Limited Slip differentials can be employed to ensure that one wheel can only slip so far before the differential locks and then both wheels are forced to rotate together. LSDs can be employed in 3 positions front, rear, and center. The front and rear will lock left and right wheels together, the center one will lock the rotation speed of the front and back axles. You can also add manually selectable locking differentials in any of those positions instead. Frequently, you see LSDs in front and back and manual lockers in the center. In off road applications it is more common to see manually selectable lockers in every position. Because of the lack of differentials, though, manual lockers put a lot of load on the drivetrain if the surface isn’t slippery. The alternative, traction control can use variable differentials to send different power amounts to different wheels, typically by employing the brakes on the slipping wheel to force power to distribute evenly. Obviously, there is a lot to this, but highlights some of the options.

pitaj 9y ago
There's also the Torsen differential [1] [1]: https://youtu.be/JEiSTzK-A2A https://youtu.be/JEiSTzK-A2A
- bigiain 9y ago
  And for those on a budget - what we in Australia call "The CIG Locker"... http://www.billzilla.org/diffs.htm http://www.billzilla.org/diffs.htm (They _kinda_ work on rally cars and hillclimbers...)
- lathiat 9y ago
  It takes a while to get your head around how these work but they are fantastic. Fortunately there are a few videos on it now to help.
mtreis86 9y ago
The Viscous Coupling is really neat. The design consists of a series of plates with holes cut in them and relies on a dilitant fluid (silicon paste) filling the holes to have a significant resistance to shearing. This allows the outputs to run at different speeds than each other, up to a point where the paste gets hot from shearing and the pressure increase locks the plates to each other. When the output speeds are similar, the diff doesn't lock up but will allow one to overspeed the other. One main benefit to this design over others, is that by changing the number of plates you can change the amount of torque sent to the outputs. When installed with twice as many discs to the rear than the front you end up with twice as much torque to the back wheels, as in the transfer case of a E30 BMW 325iX. Effectively there is no mechanical connection between the engine and the wheels until the transfer case input starts moving which starts to lock up and transfer torque to the rear. The rear diff outputs are not mechanically connected until the shearing in it causes an increases in pressure. But the increase in pressure happens so quickly, lockup being within milliseconds, that you wouldn't know it while driving.

pitaj 9y ago

There's also the Torsen differential [1] [1]: https://youtu.be/JEiSTzK-A2A https://youtu.be/JEiSTzK-A2A

bigiain 9y ago
And for those on a budget - what we in Australia call "The CIG Locker"... http://www.billzilla.org/diffs.htm http://www.billzilla.org/diffs.htm (They _kinda_ work on rally cars and hillclimbers...)
lathiat 9y ago
It takes a while to get your head around how these work but they are fantastic. Fortunately there are a few videos on it now to help.

mtreis86 9y ago

The Viscous Coupling is really neat. The design consists of a series of plates with holes cut in them and relies on a dilitant fluid (silicon paste) filling the holes to have a significant resistance to shearing. This allows the outputs to run at different speeds than each other, up to a point where the paste gets hot from shearing and the pressure increase locks the plates to each other. When the output speeds are similar, the diff doesn't lock up but will allow one to overspeed the other. One main benefit to this design over others, is that by changing the number of plates you can change the amount of torque sent to the outputs. When installed with twice as many discs to the rear than the front you end up with twice as much torque to the back wheels, as in the transfer case of a E30 BMW 325iX. Effectively there is no mechanical connection between the engine and the wheels until the transfer case input starts moving which starts to lock up and transfer torque to the rear. The rear diff outputs are not mechanically connected until the shearing in it causes an increases in pressure. But the increase in pressure happens so quickly, lockup being within milliseconds, that you wouldn't know it while driving.