3 ms·

>Torque goes to whichever of the four wheels has the least grip. That should be the tire with the most grip. If torque goes to the wheel where the tire on it h

>Torque goes to whichever of the four wheels has the least grip. That should be the tire with the most grip. If torque goes to the wheel where the tire on it has the least grip the tire still has no traction torque doesn't make grip appear out of nowhere. In four-wheel or all-wheel drive one wheel where a tire has no grip the other three wheel with tire that have grip move the vehicle isn't that the entire point of 4WD and AWD?

singlow 10y ago
He is talking about what happens when there is no lock. He goes on the clarify what happens when there are locks or viscous couplings.
rwmurrayVT 10y ago
>To counteract this, the better AWD cars are fitted with a center differential that contains a clutch or viscous drive unit. This splits torque front-to-rear, directing it away from the spinning wheel. The differential contains a nifty little clutch. When the vehicle detects no traction, it engages and sends the torque to the correct location. Otherwise you'd end up in a situation similar to engaged cruise control with no traction. Limited slip differentials and locked differentials cause much confusion.
johngalt 10y ago
Mechanically a drivetrain has no means of differentiating between a tire that is slipping vs a tire at that's on the outside of a turn. A 4wd car with three open differentials will absolutely send all of the engine power to one slipping wheel. The author is describing the tricks used to get around that fact. Namely locking differentials or limited slip differentials. The end result is a fraction of the torque makes it to other Wheels depending on the design of the drivetrain. The author spent a lot of time on locking differentials when those are rare. Limited slip differentials are more common. Most awd cars will have a LSD in the center diff. There are torsen diffs which do what you describe but they are rare.
- kinofcain 10y ago
  Even a torsen diff, or similar helical/gear type limited slip diffs are "torque multiplying", they need a load on one wheel in order to send the "multiplied" load to the wheel with traction. Modern stability/traction systems equipped with helical diffs will apply the brake to the "free" wheel in order to provide a load to the mechanical diff. You can also apply the brakes yourself if you have a torsen diff but no electronics. A clutch-based diff or some other type of locking diff would otherwise be required to solve the "wheel in the air" problem without applying an artificial load to the free wheel.
  - lathiat 10y ago
    There is at least one mechanical design which (claims to?) solve this problem, Wavetrac. Don't want to embarrass myself trying to explain it, so click "how it works" on this page: http://www.wavetrac.net/technical.htm http://www.wavetrac.net/technical.htm
mindslight 10y ago
This article is careless with physical terms. What it means to say here is that rotation (or energy) goes to whichever of the four wheels has the least grip. The torque of all the wheels is basically equal [0]. The ones that are gripping are creating linear force, but not enough to move the car. The wheel that is spinning freely has its torque going into dynamic friction and rotational acceleration. When that wheel has accelerated to as fast as possible (which happens awfully quickly because a wheel isn't that massive), the engine's rev limiter kicks in and cuts the total torque down to 4x the dynamic friction. [0] Assuming ideal naive differentials.

singlow 10y ago

He is talking about what happens when there is no lock. He goes on the clarify what happens when there are locks or viscous couplings.

rwmurrayVT 10y ago

>To counteract this, the better AWD cars are fitted with a center differential that contains a clutch or viscous drive unit. This splits torque front-to-rear, directing it away from the spinning wheel. The differential contains a nifty little clutch. When the vehicle detects no traction, it engages and sends the torque to the correct location. Otherwise you'd end up in a situation similar to engaged cruise control with no traction. Limited slip differentials and locked differentials cause much confusion.

johngalt 10y ago

Mechanically a drivetrain has no means of differentiating between a tire that is slipping vs a tire at that's on the outside of a turn. A 4wd car with three open differentials will absolutely send all of the engine power to one slipping wheel. The author is describing the tricks used to get around that fact. Namely locking differentials or limited slip differentials. The end result is a fraction of the torque makes it to other Wheels depending on the design of the drivetrain. The author spent a lot of time on locking differentials when those are rare. Limited slip differentials are more common. Most awd cars will have a LSD in the center diff. There are torsen diffs which do what you describe but they are rare.

kinofcain 10y ago
Even a torsen diff, or similar helical/gear type limited slip diffs are "torque multiplying", they need a load on one wheel in order to send the "multiplied" load to the wheel with traction. Modern stability/traction systems equipped with helical diffs will apply the brake to the "free" wheel in order to provide a load to the mechanical diff. You can also apply the brakes yourself if you have a torsen diff but no electronics. A clutch-based diff or some other type of locking diff would otherwise be required to solve the "wheel in the air" problem without applying an artificial load to the free wheel.
- lathiat 10y ago
  There is at least one mechanical design which (claims to?) solve this problem, Wavetrac. Don't want to embarrass myself trying to explain it, so click "how it works" on this page: http://www.wavetrac.net/technical.htm http://www.wavetrac.net/technical.htm

mindslight 10y ago

This article is careless with physical terms. What it means to say here is that rotation (or energy) goes to whichever of the four wheels has the least grip. The torque of all the wheels is basically equal [0]. The ones that are gripping are creating linear force, but not enough to move the car. The wheel that is spinning freely has its torque going into dynamic friction and rotational acceleration. When that wheel has accelerated to as fast as possible (which happens awfully quickly because a wheel isn't that massive), the engine's rev limiter kicks in and cuts the total torque down to 4x the dynamic friction. [0] Assuming ideal naive differentials.