Locked or spool differentials

[Jersey Tom]

A spool equalises wheel speed but not torque delivery. It is possible (common even) for the L:R torque split to be 0:100

Torque delivery to the diff output is equal with a spool diff.

I think I liked Gruntguru's description better. Halfshaft torque on the diff side and wheel side can't be different values unless it's accelerating (even then, left and right half shafts will be accelerating at same rate).

[autogyro]

A spool equalises wheel speed but not torque delivery. It is possible (common even) for the L:R torque split to be 0:100

Torque delivery to the diff output is equal with a spool diff.

I think I liked Gruntguru's description better. Halfshaft torque on the diff side and wheel side can't be different values unless it's accelerating (even then, left and right half shafts will be accelerating at same rate).

I know what you mean JT, I simply dislike the way most people consider torque in power trains.
Torque is measured against a brake of some sort.
Just because the rpm is equal on both sides it does not mean there is any torque being applied to the road.
GG is of course correct, he usually is.

[strad]

the antithesis of an F1 differential
https://www.youtube.com/watch?feature=p ... Afy42hFYBk

[gruntguru]

Something he didn't discuss in that video - although the rear is (was) a beam axle, the hubs are driven by CV joints allowing the rear wheels to have adjustable camber and toe. I say "was" because the V8 Supercars now run IRS and a transaxle gearbox.

[J.A.W.]

Yeah, & again the vid commentary goes on about "Diffs" ( even though it aint) instead of "final drive"..

[gruntguru]

I know Mark Dutton fairly well. He holds a bachelor of mechanical engineering and is probably the best race engineer in the Supercar competition. He is nonetheless a humble man and would no doubt apologise profusely if riff_raff was to point out his inappropriate use of the word "diff".

PS. I just noticed the thread topic contains the same contradiction - tut tut.

[riff_raff]

Any engineer would agree that technically a spool is not a form of a mechanical differential device, since it provides no differential function. A spool is simply a rigid shaft coupling. A mechanical differential is a device that allows two outputs to turn at different speeds or direction of rotation from a common input, or two inputs rotating at different speeds or directions to connect to a common output. It is basically a mechanical adding machine.

With a conventional gear differential the sum of the two output speeds must always agree with the input speed. With a spool the two outputs always have the same direction of rotation and speed. With a spool or a conventional gear diff, the two output torques must always be in balance with the single input torque.

Why would any engineer use a term like "spool diff" whose two words have opposite meaning? It's basically an oxymoron.

[gruntguru]

Why would any engineer use a term like "spool diff" whose two words have opposite meaning? It's basically an oxymoron.

Let me see . . . perhaps because in common parlance a "diff" is "a big cast iron thing that keeps the rear wheels apart". (as opposed to "a device that sums angular displacements".)

Or did it grow from the term "locked diff" which is amost identical but not in the slightest oxymoronic. That is because a locked diff could be a diff which has been un-diffed - using perhaps an arc welder or maybe even a spool. Oh well, engineers can abuse the English language as "good" as anyone.

Ever heard an engineer use the term "AC current"?

[autogyro]

Ahhhh yes, applaud le 'diff' erance.

[strad]

I think the choice of terminology throws people off.
,
https://www.youtube.com/watch?v=gwJEU7p9U2Q
.
https://www.youtube.com/watch?v=MCxqUJCZGNU
.
https://www.youtube.com/watch?v=ujsxq9WBllU

[riff_raff]

Let me see . . . perhaps because in common parlance a "diff" is "a big cast iron thing that keeps the rear wheels apart". (as opposed to "a device that sums angular displacements".)

Or did it grow from the term "locked diff" which is amost identical but not in the slightest oxymoronic. That is because a locked diff could be a diff which has been un-diffed - using perhaps an arc welder or maybe even a spool. Oh well, engineers can abuse the English language as "good" as anyone.

Ever heard an engineer use the term "AC current"?

Here's Wikipedia's definition of an automotive differential, which would seem to qualify as "common parlance":

"In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other."

A "spool" is a rigid shaft coupling composed of a single monolithic part. A 'diff" is mechanical device usually composed of a set of bevel gears that functions as described above. A spool is not a diff, and a diff is not a spool. The term differential implies a device that has certain capabilities. If you were to weld the bevel gears of a common auto diff together, thus disabling the differential function of the device, logically it would no longer meet the definition of a differential. So why would you continue to call it a diff?

If you castrate a bull, obviously it is no longer a bull. It is a steer. But according to your logic it should be called a bull steer. Can't be both things, just like a spool diff.

[Cold Fussion]

While we are on the subject of semantics, why are heat exchangers referred to as radiators? If anything they should be called convectionators.

[autogyro]

No riff raff a differential is simply the difference between two or more things.
Your definition of a vehicle differential does not explain a 'central' geared differential which establishes a difference between four or more wheels not just two.
A spooled differential still establishes a difference between two 'or more' wheels be they at the same rpm and 'potential' torque delivery.
Locked slipper or spool differentials are simply types of differential.

As to bulls and steers.
An F35B is an aeroplane but it is also a 'dog'.

[strad]

A spool is no differential..it locks the two wheels together .. THIS is a spool

[gruntguru]

Let me see . . . perhaps because in common parlance a "diff" is "a big cast iron thing that keeps the rear wheels apart". (as opposed to "a device that sums angular displacements".)

Or did it grow from the term "locked diff" which is amost identical but not in the slightest oxymoronic. That is because a locked diff could be a diff which has been un-diffed - using perhaps an arc welder or maybe even a spool. Oh well, engineers can abuse the English language as "good" as anyone.

Ever heard an engineer use the term "AC current"?

Here's Wikipedia's definition of an automotive differential, which would seem to qualify as "common parlance":

"In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other."

A "spool" is a rigid shaft coupling composed of a single monolithic part. A 'diff" is mechanical device usually composed of a set of bevel gears that functions as described above. A spool is not a diff, and a diff is not a spool. The term differential implies a device that has certain capabilities. If you were to weld the bevel gears of a common auto diff together, thus disabling the differential function of the device, logically it would no longer meet the definition of a differential. So why would you continue to call it a diff?

If you castrate a bull, obviously it is no longer a bull. It is a steer. But according to your logic it should be called a bull steer. Can't be both things, just like a spool diff.

rr's finest moment.
https://www.youtube.com/watch?v=c3y0CD2CoCs