Open Differential theory of operation???

Boy it's confusing :-)

I guess to sum it up, Is that when go> Anyone have any links (Bill?) that describe exactly

This describes the "ideal" open differential, which doesn't exist. All differentials have a certain amount of internal friction, which makes the behavior less ideal. Because of this, you can get off of ice with a thin film of water on top of it, which is the slipperiest road surface that I have encountered. Other things to keep in mind, are the effect of "stiction", which is a physical concept, that says that you have more traction, if you are not spinning your wheels, and the ability of a quick tap on the brakes, to restore the state, where there is more traction than power.

Earle

Basically 100% of the torque goes to 'both' rear wheels in an open diff 'all' the time.

Where you get into trouble is when one wheel is say on ice and the other is on dirt. Then 100% of the torque still goes to both wheels but the torque needed to make the ice wheel spin is really low, say only 1 or 2 foot lb. so the same really low 1 or 2 foot lb. goes to the dirt wheel and you go nowhere.

To overcome this you can apply the emergency brake (according to the Jeep owners manual) or as I do and hit the brake pedal so you add a pile of resistance to the ice wheel. This raises the torque needed to turn the ice wheel and it can/will get high enough to break the dirt wheel free so you drive off shooting two rooster tails.

With practice this works really well. I have managed to go from one front and one rear wheel spinning on ice with me stopped and the boys laughing and going for straps, to me pulling away with all 4 tires shooting rooster tails. Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

FrankW wrote:

You're both right.

Power is applied eaually to both wheels UNTIL one wheel breaks loose, then it gets all of the power.

They both get equal 'power' Jeff. The spinning wheel just needs very little power to spin, so the stopped wheel also gets the same very little power.

It 'acts' like you state though.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jeff Strickland wrote:

I can see that you remember at least some of your high school or college physics courses. You are right, in that the wheel that is not turning, is not getting or dissipating any power. However, if you could magically look inside the differential while this is happening, you would see that the stopped side is in fact using some power, by virtue of gears and internal friction, which I mentioned earlier. In the case where you are stuck, the torque on both wheels is roughly the same. Torque is similar to pressure or mechanical force, while power is the energy dissipated by something that is subject to torque, and moving. You have to be moving, against some resistance, in order to be dissipating mechanical power.

In the stuck and wheel spinning case, so little energy is being dissipated, that friction plays a bigger part, as I mentioned earlier. If you could measure the torque or the power, you would then find that they are not equal, but pretty darn close. Strictly speaking, you are right, and your boss is wrong. The wheel that is not turning, has no power applied. It does have some torque on it, enough to balance the torque on the spinning wheel. And there is some power being applied on that side, enough to spin the gears against internal resistance. So maybe you are both right.

Confused yet? I hope so. I certainly don't want to have to format the equations in ASCII!

Earle

Figure for easy numbers that a wheel spinning on ice only needs 10 foot lb of power or torque to break free and spin. You barely have to touch the gas pedal to send that much power back.

That would mean the other side wheel is still only getting 10 foot lb., but it is on dirt so it just stays still. It would need 'say' 100 foot lb. to break free and spin.

Now if you slam down on the brake pedal and mash the gas to the floor, it tries to stop the wheel spinning so the power or torque needed to compensate for the drag of the brake shoe goes up really high under full throttle. Once the torque on the spinning wheel passes the 100 foot lb. the stopped wheel needs to break free, away you go with both wheels spinning and the engine just a roaring.

Come along on one of our winter runs and we can practice it. It works neat.

Mike

FrankW wrote:

Because if it only takes 15 foot pounds of torque to spin a tire, then that's all that gets delivered. The tire that has traction needs 20 foot pounds of torque to move the vehicle, but the tire that is spinning can spin with 15 foot pounds, so 20 foot pounds is never delivered to the tire that has traction.

So, both tires get the same amount of power -- expressed as torque -- but when one tire starts spinning uselessly then it get what is effectively all of the torque, and the other tire gets nothing. Mike was saying that the other tire doesn't really get nothing, but it dopesn't get what it needs to move the vehicle, so it may as well get nothing.

Now, there is a strategy that the driver can employ that involves tapping the brakes to change the power distribution and get the vehicle moving, but the open diff left to its own devices will effectively deliver all of the engine torque to both tires equally when both have traction, but to the tire with the least traction if traction is compromised.

Jeeps, or at least mine are Right Rear vehicles still Bill. That is why they state in a 5 tire rotation that the spare goes to the RR with the RR going to the RF and the RF going back to the spare. The three wheel rotation on one side will balance the two wheel left side rotation for wear.

Mike

"L.W.(ßill) Hughes III" wrote:

Would a Miller or Hobart locker work as well or should I stick with Lincoln?

Frank,

Maybe this will help you out.

Andy