[DirtyDan]

Oh, yeah, to solve the dilemma of the tree in a forest....if you define "noise" narrowly as that which is heard by the human ear then, if there are no humans present there is no "noise". But if you define "noise" as some strange spiked lines on graph paper produced by a scientific instrument...then you are probably going to get lots of "noise" if you put the instrument near a falling tree. Semantics. It should be noted that even the techies with the scientific instrument have to draw inferences from their graph paper spikes to the human ear.

Analogously, if you define "torque" as only present if a wheel has a certain traction then you will get one set of inferences. If you define "torque" as a product of the motor turning a shaft, you will get another set. Which is right? Depends on what you want to do.

When auto manufacturers write the specs for their vehicles, they list torque as a function of the ability of the motor to turn a shaft. They do not write torque specs as the ability of a wheel to move...if it has x,y,z modes of traction and power. However, this does not mean that the concept of torque as defined such is useless or wrong.

[Blue Thunder]

Originally Posted by Samurai

...Torque is the least force required to turn something on an axis.
...

I am no physics expert, but I dont think torque is defined that way.

[DirtyDan]

Originally Posted by Samurai

Dan, this is not a quibble. This thread is under technical section, so we can get technical here.

Torque is a physics concept, it can't be re-interpreted in many ways like art. There is no way to have different opinions about it.

I beg to differ. Physics can give us many interpretations, many models of reality. Quite often physics gives us two or more contradictory theories each proven by publically observable experiment. I site the "particle" theory of light and the "wave" theory of light. Both proven in experiment, but contrary to each other. Rarely do we have the good forture to happen on a crucial experiment or observation that decides an issue cleanly in physics. I refer you to Thomas Kuhn's book The Structure of Scientific Revolutions and Carl Hempel's treatice entitiled The Theoreticians Dilemma.

I urge you to read them....if you are dead from the waist down.

[Samurai]

Originally Posted by Blue Thunder

I am no physics expert, but I dont think torque is defined that way.

It is just the reworded version of this:

Torque, also called "moment" or "moment of force", is a measure of how much a force acting on an object (a wheel) causes that object to rotate. The object rotates about an axis.

In case of a fully locked differential, 100% torque goes to the wheel with traction: http://www.awdwiki.com/en/torque+spl...on_up_to_100__

Thus, Physics is satisfied. I rest my case.

[Sutripta]

Hi,
I'm with Samurai, 1100D, and Sudev on this.

And so to this question

Originally Posted by dhanushs

If ^^ is right: Then assume one of the rear axles is not connected to one rear wheel and is spinning freely, if so, with the Eaton locker locked, and with only one axle in function, the vehicle should accelerate just like it would do with two wheels powered?

I'll say yes. (Ignoring details like that the vehicle, left to its own devices, will try to turn. Because these details are not relevant to the discussion at hand. And assuming that traction is not an issue.)

Anyone here seen one of those old 'line shaft' factories. You know the ones which were powered by a single prime mover.

Regards
Sutripta

[DirtyDan]

Originally Posted by Samurai

It is just the reworded version of this:


In case of a fully locked differential, 100% torque goes to the wheel with traction: http://www.awdwiki.com/en/torque+spl...on_up_to_100__

Thus, Physics is satisfied. I rest my case.

Your diff is locked, your vehicle is jacked into the air so that neither wheel touches the ground, neither wheel has traction and the motor is in gear just buzzing away. Do you still have torque?

If you think traction is necessary for torque then you ain't got no stinkin' torque.

If you think traction is not necessary for torque, just a spinning shaft is sufficient, then you gots lots of stinkin' torque because your shaft is merrily spinning away....

Either way Physics is satisfied and I rest your case....too.

[Sutripta]

^^^
What about an asymmetric case: Both wheels jacked up, Diff locked, brakes applied lightly on one wheel, hard on the other? Both halfshafts will carry ?? torque.

Regards
Sutripta

[Samurai]

Originally Posted by DirtyDan

Your diff is locked, your vehicle is jacked into the air so that neither wheel touches the ground, neither wheel has traction and the motor is in gear just buzzing away. Do you still have torque?

Yes, just enough to freespin the wheels, inertia of the drive-train is the only load in this situation. Traction at the wheels is what gives the real load to the engine. Without load, engine can't generate torque.

Originally Posted by DirtyDan

If you think traction is not necessary for torque, just a spinning shaft is sufficient, then you gots lots of stinkin' torque because your shaft is merrily spinning away....

This is your belief, not mine.

Ok, let's just ask the experts. Behram and Sutripta, let's hear it from you.

Can the engine generate maximum rated torque at no load? Can you send loads of torque to a shaft with no load?

[lucifer1881]

Originally Posted by Samurai

I too have to disagree then. Torque is the least force required to turn the wheel. If traction is high, more torque is required to turn the wheel. If there is no traction (wheel in air), very little torque is required to turn the wheel. One can never deliver more torque than required, that is once the wheel starts slipping.

Your understanding is incorrect.

Torque is not a force. It is the moment of force. In simple formula:

Torque = (Force) x (length of the lever arm connecting the axis to the point of force application) x Sin (angle between the force vector and the lever arm)

To extend your pole and pen example to a door. It is possible to open a door by pushing very close to the hinges. The force required to push is very high in this case. Hence, door handles are placed far away from the hinges.

In other words, the torque to open a door is constant. The force varies depending on the distance from the hinges.

For a wheel spinning at X rpm, the torque required is constant whether the wheel is free-spinning or on tarmac or stuck in the mud. The force required to generate that torque changes.

Similarly, if an engine is rated for 240Nm at 2000 rpm it will generate that torque irrespective of whether the transmission is engaged or in neutral. The engine, in case of transmission being in neutral, would be running on almost no load since the force required to generate that torque is very low. If the transmission is engaged and the car is moving forward then the engine will be under load conditions depending on weight of the car, traction of the wheels, etc. This is one of the reasons why stop-start traffic gives you lower mileage because the engine has to work on higher loads to get a car moving from standstill than to keep a moving car in motion. This is because coefficient of rolling friction is less than coefficient of static friction.

To summarise:

Torque required for a given rotation is constant. If a wheel has to spin at 10rpm then it will need the same torque whether it is spinning in the air or vacuum or submerged in jelly.

The force and angle of force are the variables that can be changed to achieve that torque.

[ex670c]

Originally Posted by Samurai

I can't agree with this statement. If the diff is locked and one wheel is in air, all the traction necessary for torque generation is coming from the other wheel. So we have to admit that the entire torque from the propeller shaft is going to the wheel with traction.

Check the last paragraph under diff locks in here: http://www.4wdonline.com/A/Diff.locks.html

I don't know mechanical stuff like you, I am entirely depending on Physics here.

Hi Sharath,

The last Paragarah is about "CENTRE DIFF-LOCK"

Also in a Locked Differential, with one wheel in the air, the Torque is being distributed equally to both Wheels, because both Wheels will rotate with the same speed, may not be visible

Also in case of an Automobile, Traction is not necessary for Torque generation, but co-efficient of Friction is necessary for Traction.

Do you mean to say a vehicle spinning its wheels in mud or ice is not generationg torque?

Regards,

Arka

[Samurai]

Originally Posted by lucifer1881

Torque = (Force) x (length of the lever arm connecting the axis to the point of force application) x Sin (angle between the force vector and the lever arm)
.
.
.
In other words, the torque to open a door is constant. The force varies depending on the distance from the hinges.

This statement defies mathematics too, let alone physics.

T = f(F) [i.e. torque is a function of force]

And then you say force varies, but torque remains constant.

Originally Posted by lucifer1881

Similarly, if an engine is rated for 240Nm at 2000 rpm it will generate that torque irrespective of whether the transmission is engaged or in neutral.

Shall we wait for some real professionals answer this question?

Originally Posted by ex670c

Do you mean to say a vehicle spinning its wheels in mud or ice is not generationg torque?

It is generating just enough torque to free spin the wheels, no more. I was made to understand this stuff when I was learning to drive on icy/snowy roads of NJ, about 20 years back. Don't think the science has changed.

Can I request we wait for the professionals who actually understand the underlying theory to answer this question? Behram, Sutripta, Spike_Arrester, star_aqua are some of those who can speak with authority on this.

[lucifer1881]

Originally Posted by Samurai

This statement defies mathematics too, let alone physics.

T = f(F) [i.e. torque is a function of force]

And then you say force varies, but torque remains constant.

Shall we wait for some real professionals answer this question?

Samurai, before being condescending please read the formula carefully.

T = F x L x Sin(A)

Torque is a function of force, distance and sine of angle. Let me dumb it down.

Say we need to achieve a torque of 10Nm. This can be done in multiple ways.

1. F=2N, L=5m, Sin(A)=1; Torque = 2N x 5m x 1 = 10 Nm
2. F=10N, L=1m, Sin(A)=1; Torque = 10N x 1m x 1 = 10 Nm
3. F=3N, L=10m, Sin(A)=1/3; Torque = 3N x 10m x 1/3 = 10 Nm
4. Etcetera.

Where is it defying mathematics? Please read my post carefully.

[Samurai]

Originally Posted by lucifer1881

Torque is a function of force, distance and sine of angle. Let me dumb it down.

Say we need to achieve a torque of 10Nm. This can be done in multiple ways.

1. F=2N, L=5m, Sin(A)=1; Torque = 2N x 5m x 1 = 10 Nm
2. F=10N, L=1m, Sin(A)=1; Torque = 10N x 1m x 1 = 10 Nm
3. F=3N, L=10m, Sin(A)=1/3; Torque = 3N x 10m x 1/3 = 10 Nm
4. Etcetera.

Where is it defying mathematics? Please read my post carefully.

Does L and A change for a given vehicle?

[lucifer1881]

Originally Posted by Samurai

Does L and A change for a given vehicle?

L & A do not change for a vehicle. They are constant.

I used the formula to explain the concept of torque. The first thing to understand is that torque is not force. It is the moment of force.

If a wheel is stuck in the mud, then the engine will be working on higher load to impart any rotation to the wheel.

I understand I made one gaffe in my earlier post:

For a wheel spinning at X rpm, the torque required is constant whether the wheel is free-spinning or on tarmac or stuck in the mud. The force required to generate that torque changes.

I should have stated that the load on the engine to generate the force required to achieve the torque to spin the wheel changes.

This load depends on how much traction the wheels have. The torque required to spin the wheels does not depend on traction.

Another example. In my car I achieve 80kmph in fifth gear at 2000rpm. Whether I drive uphill or downhill, 2000rpm in fifth gear results in 80kmph. Torque required is the same in both cases. However, the engine load is higher uphill than downhill.

[1100D]

Originally Posted by lucifer1881

Your understanding is incorrect.

Similarly, if an engine is rated for 240Nm at 2000 rpm it will generate that torque irrespective of whether the transmission is engaged or in neutral.

The torque generated by the engine at any RPM is also a function of the quantity of fuel being fed. That quantity of the fuel is based on calculations (from dataset) as well as the throttle position.

Torque generated by an idling engine is much less than the torque generated by the same engine at the same rpm, engaged in gear and rolling, so is the fuel feed.

The much lower torque generated by the engine, when the driven wheels are spinning (or in air) goes to counter the rolling friction of the powertrain components (GB, Propshaft bearings, diff, axles etc), this torque is anyway there when the wheels have traction, and the tractive effort is added to this (rotational frictional component).

As an experiment, please raise both driven wheels of any vehicle on jacks and try to rotate them using engine power and see for yourself, how much little throttle inputs are required to accelerate the spinning wheels. Compare with the acceleration felt, when the vehicle is on road,
the answer will be very clear.