4 wheel drive question

[wvpolekat]

Not meaning to be difficult here, just wondering if you get that they are receiving equal torque and unequal speed with an open differential and unequal torque but equal speed, with a locked diff.

What it also means is that it is incapable of sending enough torque to the wheel(s) with usable traction and therefore, ability to DRIVE the vehicle. Rendering them no longer drive wheels.

Equal torque to all wheels is only useful when enough of it can be applied to the wheels with the traction to convert it to movement. Meaning, that under this system, in all conditions, all wheels are not capable of being drive wheels.

Use of the word "drive" in this case is semantics, and I suspect you know that.

 

[TripleR]

I love threads like these. I Jeep. I hardcore Jeep. I have a complete understanding of differentials, lockers, limit slips, etc.

I find that those who get caught up in "word perfect" terminology tend to have the least amount of practical application under their belt.

When you are stuck in 4wd and open diffs and are walking for help because you are spinning only two tires and not moving, you can think of plenty of things to "call" it.

Sometimes, but not always, some professions insist on absolute correctness in terminology. Some professionals also use only correct terminology when speaking with their peers and maybe not so much when speaking with others. I dealt with legal matters mostly and you darned well better use the exact precise terminology as it was going to wind up in court or some government office to be read by many and open to misinterpretation and challenge.

I saw a recent discussion of the use of "gun" by Soldiers/Marines/Sailors. I would never refer to a S&W revolver as being a pistol to some of my friends as a pistol, it is a "revolver", our Glocks are "pistols". We won't get into the whole military thing.

As to my understanding of differentials, until recently I thought maybe there were hamsters on wheels in there or maybe elves. Actually, I have helped my brothers and knew there were gears in there, but it beat the heck out of me as to how they worked; interesting thread.

 

[Egon]

When you are stuck in 4wd and open diffs and are walking for help because you are spinning only two tires and not moving, you can think of plenty of things to "call" it.

In this situation is it still "Four Wheel Drive"?:laughing::laughing::laughing:

 

[Raspy]

The basic problem (aside from not enough traction and getting stuck) is the notion that seeing a wheel spin, somehow equates to "it is the only one getting power" misconception. You can't see torque, but you can see spinning. In other words, if I can't see it, it doesn't exist. "That non-spinning wheel is just sitting there and not being driven at all. Must be, because I can't see anything happening. It's one wheel drive". The quick human analysis, even with one wheel up off the ground and spinning helplessly, is that that wheel is the only one getting power.

Next comes the argument. "Yes it is one wheel drive and I can prove it." Then the solution from someone else: "well, my Daddy used to just step on the brake when he spun a wheel and just drive right out".

Man, I love all the stories and ways to describe how four wheel drive is really two, etc. These days, machines are so user friendly that we don't have to know anything about how they work, then we push them out of their envelope and ............uh, oh. But instead of trying to figure it out, it's time to argue about "one wheel drive", or get out the dictionary and argue definitions.

So, let the stories continue. :thumbsup:

 

[Gary Fowler]

I just have 1 more thing to say on this with regard to tractors, If it is too icy or muddy for your tractor to move in "3 WD" then perhaps you should be home by the fireside or kicked back with a cold one rather than out on the tractor to start with. I have had my tractor stuck once in "bottomless" soil when I tried to mow across fresh landfill in a slough area and again in a dried up pond we were digging out and when the frame is under the dirt, it really doesnt matter if you have 1 wheel or 8 wheel drive, you aint going nowhere. When all the wheels are spinning and the FEL cant help push you out, it's time for another piece of equipment.
I rarely get into situations where "3 Wd" and FEL wont get me out with differential locked on the rear. I think you would be asking for disaster to the front drive system to have a front lock on a tractor should you engage it and then try to turn. It would be like trying to turn a dozer by hitting the brakes without disengaging one of the drive clutches.

 

[JoelD]

Did you take one wheel off? Did you disconnect one wheel from the power train? Which "three" does it "run".

Not meaning to be difficult here, just wondering if you get that they are receiving equal torque and unequal speed with an open differential and unequal torque but equal speed, with a locked diff.

How is it unequal torque with lockers?

This is a great thread

Thanks
Joel

 

[wvpolekat]

The basic problem (aside from not enough traction and getting stuck) is the notion that seeing a wheel spin, somehow equates to "it is the only one getting power" misconception. You can't see torque, but you can see spinning. In other words, if I can't see it, it doesn't exist. "That non-spinning wheel is just sitting there and not being driven at all. Must be, because I can't see anything happening. It's one wheel drive". The quick human analysis, even with one wheel up off the ground and spinning helplessly, is that that wheel is the only one getting power.

The problem is that you are trying to apply a textbook answer to a real world question. ON PAPER, there is power to both wheels. In reality, the wheel with enough traction to produce work is not getting enough power to allow it to do so. Technically, you are right, in reality, it doesn't matter because they are still stuck with one wheel on dry pavement and the other on ice.

Next comes the argument. "Yes it is one wheel drive and I can prove it." Then the solution from someone else: "well, my Daddy used to just step on the brake when he spun a wheel and just drive right out".

And this is a 100% valid way of getting a open diff to work. It causes it to send enough torque to both wheels to give the one with traction enough to move the vehicle. They may not understand why it works, but they have learned to manipulate the system to do what they want, to overcome it's biggest weakness.

Man, I love all the stories and ways to describe how four wheel drive is really two, etc. These days, machines are so user friendly that we don't have to know anything about how they work, then we push them out of their envelope and ............uh, oh. But instead of trying to figure it out, it's time to argue about "one wheel drive", or get out the dictionary and argue definitions.

Except you are arguing for the sake of arguing. The "proof" is right there in plain sight. Regardless of what is technically happening, the reality is that the wheel without traction is spinning and the one with traction is sitting there like a bump. The why of this doesn't matter except to you. To the user, the system has failed them by not delivering sufficient power to the wheel with traction to allow the vehicle to move.

I don't think anyone here has said you are wrong about the operation of an open diff. What I think is you are fighting a lot of windmills because people say something that is technically wrong, but true in reality. Nobody is going to say that they got stuck because the amount of torque required to loose traction on the right wheel was not enough to produce enough work from the one with traction to move forward.

 

[QRTRHRS]

Sometimes, but not always, some professions insist on absolute correctness in terminology. Some professionals also use only correct terminology when speaking with their peers and maybe not so much when speaking with others. I dealt with legal matters mostly and you darned well better use the exact precise terminology as it was going to wind up in court or some government office to be read by many and open to misinterpretation and challenge.

I saw a recent discussion of the use of "gun" by Soldiers/Marines/Sailors. I would never refer to a S&W revolver as being a pistol to some of my friends as a pistol, it is a "revolver", our Glocks are "pistols". We won't get into the whole military thing.

As to my understanding of differentials, until recently I thought maybe there were hamsters on wheels in there or maybe elves. Actually, I have helped my brothers and knew there were gears in there, but it beat the heck out of me as to how they worked; interesting thread.

This is my weapon, this is my gun. This is for fighting, this is for fun.

 

[slowzuki]

Diff Locker = equal speed at each tire, not equal torque
Open diff = equal torque at each tire limited by the tire with the least traction

Differentials not as common in tractors:
Torque biasing = think of as a differential without a 1 to 1 ratio between the opposing tires but rather say 10 to 1. The torque on the spinning side is multiplied by the gears to the other side but not locked. Hummers have this type of diff.
Limited slip = clutches that have a minimum torque to overcome before letting the two sides turn at different speeds.


There are lots more too but not found at all in tractors.

 

[Egon]

The horses have come to the trough. They are not drinking as the water is not to their knowledge or understanding. :thumbsup:

Surprisingly; many of the Horse's, understand the equal torque bit on an open differential. They can also understand why there "MAY" be unequal torque on the axles of a locked differential. Some of them have gone as far as blocking one rear wheel, jacking up the other wheel an open differential and using it for a prime mover of various different tool's they use in the course of their work.:thumbsup:

Slowzuki, thanks for a real simple expalation.:thumbsup: