Talk:Differential (mechanical device)

From Wikipedia, the free encyclopedia

Contents

[edit] Pinion Gear Rotation

Neither of the pics makes sense to me. If the pinion gear is indeed interfacing between each side gear, then for one to turn, the other must be turning in the opposite direction. The pic seems to indicate that if the ring gear receives torque in the illustrated direction, the left driveshaft will necessarily spin in that direction. If the pinon gear interfaces with the left side gear, then the pinion gear will necessarily spin counterclockwise (looking from above, as in the pic). If the pinion gear interfaces with the right side gear, this will necessarily drive the right side gear in the opposite direction from the left side gear. What am I missing? JunkCookie 21:58, Aug 20, 2004 (UTC)

  • Yeah, the pics could stand to be clearer. The top image is meant to show that the entire assembly rotates forward; picture it without the ring gear for a moment, and imagine the green pinion gear rotating around the other two gears. The pinion gear is pushing against both side gears, so the pinion gear itself can't rotate unless one of the side gears meets some kind of resistance. When there is resistance on one side (as in the second picture), the pinion gear starts rotating, turning the other side with additional speed. The link to the HowStuffWorks version is much better at explaining this than what we currently have here, unfortunately. -- Wapcaplet 23:51, 20 Aug 2004 (UTC)
I figured out what I was missing. I didn't realize that the cage to which the pinion gear is mounted actually rotates with the ring gear. Somehow I had it in my head that the ring gear was fixed to the left side gear, and that the pinion is used to transfer the rotation to the right side gear. The animated pics at HowStuffWorks gave me the 'Aha!'. JunkCookie 20:59, Aug 23, 2004 (UTC)
And the fact that you needed another site to figure it out underscores that our figure is unclear. The figure does for instance not make clear that the cage is separate from the left side gear. Anybody up for making an animation? - Mglg 23:24, 4 June 2006 (UTC)
The problem with making an animation is that the politically correct thought police will only allow certain file formats to be loaded. I suspect that given the time that it would take to build the model, and then go through all the hoops required to turn it into an acceptable file format that very few people know of (ogg video) will put them off. Leastways it does me.Greg Locock (talk) 22:14, 26 January 2008 (UTC)

[edit] Torque

When the ring gear causes the planet gears(green) to push the sun gears(red & yellow) is there a ratio involved?Does the torque on the axle as a whole equal to the torque on the ring gear(purple) multiplied by the sun to planet ratio?(only on a straight road)

I don't know anything about torque, but the ratio of ring gear to axle as a whole is 1:1. Ring gear turns once, both sides also turn once; when both sides are going at the same speed, the effect is the same as having one long, solid axle, since none of the gears are moving with respect to one another. -- Wapcaplet 16:41, 22 Aug 2004 (UTC)
There is a ratio not shown in the diagram, the ratio of the drive pinion to the ring gear, but the drive pinion is missing from the diagram (and the teeth on the ring gear are on the wrong surface). But as said above, the ratio of ring gear to axle is 1:1. (The ratio of drive pinion to ring would typically be in the range 3.5:1 - 4.5:1, and yes it multiplies torque by reducing speed.) RB30DE 21:37, 20 June 2006 (UTC)

[edit] "Gear" vs. "Device"

I don't see any reason that a differential has to be composed of gears. Saying that "...a differential is a gear..." kind of implies that it's one gear, rather than several; while I am not well-versed enough in mechanics to know for sure, I can imagine that a differential could just as easily be implemented using a set of disks that interact through friction, through some kind of fluid coupling, or through a magnetic field. The term "device" seems much more general, and thus a better choice. I have changed the article to read "...a device, usually consisting of gears..." -- Wapcaplet 22:54, 28 Aug 2004 (UTC)

I believe that in fluid coupling limited slip differentials, the gears are eliminated, and exactly what you describe occurs. Thanks for the edit! Scott Paeth 07:09, 8 August 2007 (UTC)

[edit] What is this moon thing?

Some one put something about the phases of the moon in text. That has to be fixed.

Why? It seems like a perfectly acceptable addition to the article to me, if you actually read it in context. Graham 22:52, 8 August 2005 (UTC)
I agree. Please read the article Antikythera mechanism to see why it makes perfect sense.

[edit] Torsen

How about mentionning and linking to the Torsen --Olivier Debre 12:08, 30 August 2005 (UTC)

The article in question should be limited slip differential - looks like Torsen should be merged in there as there is already some duplicaiton. Graham 23:24, 30 August 2005 (UTC)

[edit] Rename "Differential (mechanical)"?

I propose this page be moved to "Differential (mechanical)". The current name implies it's about "Differential" in the field of mechanics. (I can only guess that would be a differential element of volume.) In reality, this article is about the mechanical device known as a differential. Comments? —BenFrantzDale 23:37, 13 January 2006 (UTC)

I agree with this idea. Any objections? Geometry guy 13:47, 21 February 2007 (UTC)

Disambiguation terms are generally plural nouns, not adjectives. "mechanics" is used elsewhere for this purpose, e.g. Transmission (mechanics). The term differential element is clearly part of mathematics, even though it may be used in mechanics. I don't see a great benefit in making this change.--agr 13:57, 21 February 2007 (UTC)
How about Differential (mechanisms)? This is one of the categories. Geometry guy 14:10, 21 February 2007 (UTC)
Are disambiguation terms really plural nouns? I can't think of one... Some disambiguators are descriptive nouns—words such as "band" and "artist"; others are field names such as "physics" and "mathematics"; none of these are plural nouns. —Ben FrantzDale 23:58, 21 February 2007 (UTC)
Further to this, I checked out WP:disambiguation: a disambiguation term should usually be a class, subject or context (hence a noun), but they rarely seem to be plural; when they are, it is usually because they are referring to a subject area like mechanics. I guess you are using the term "mechanics" to mean "The body of theoretical and practical knowledge concerned with the invention and construction of machines, the explanation of their operation, and the calculation of their efficiency; mechanical engineering." rather than "The branch of applied mathematics [and physics] that deals with the motion and equilibrium of bodies and the action of forces, and includes kinematics, dynamics, and statics." (Both from OED.) However, the mechanics article concerns the second definition and differentials are used all of the time in this subject. The disambiguation term (mechanics) is also used in a number of classical mechanics articles. So I think it is unfortunate that a number of articles about mechanical devices refer to "mechanics" or even link to the mechanics article.
This suggests "Differential (mechanism)" would be better, but the term mechanism is still ambiguous, so perhaps the clearest disambiguation would be "Differential (mechanical device)". Geometry guy 15:21, 21 February 2007 (UTC)
I just noticed that "mechanical" is used for Bearing (mechanical); how about we just go with that? I can't see that being confusing. —Ben FrantzDale 23:58, 21 February 2007 (UTC)
I found eight "(mechanics)" articles and have left messages on some of the talk pages. I think we should use a noun (mechanical device is still my favourite choice) if at all possible. On the other hand, I also found eight "(mechanical)" articles. Both lists are in my user space User:Geometry guy/Mechanics. I'll wait for other responses before moving. Geometry guy 09:56, 22 February 2007 (UTC)

[edit] Active Differentials

This section is unclear, and should among other things explain what "DOF" means. Now DOF links only to a disambiguation page that does not list any relevant page. - Mglg 23:24, 4 June 2006 (UTC)

Based on context, I'm going to change it to Degrees of freedom (engineering), as that seems to be the correct interpretation. Still, it's a poor paragraph, butr at least I've resolved some of the confusion. --Bdoserror 07:48, 4 October 2006 (UTC)

[edit] Three wheels?

I know that saying differentials are only found on four-wheel vehicles is incorrect (cf three wheeled car) but I'm not sure how to reword the summary without destroying what it's getting at. Axled vehicles? Do motorcycles have axles? It's not something I specialize in. Scott Paeth 07:17, 8 August 2007 (UTC)

[edit] Changed video link from YouTube to Internet Archive

Changed the link to "Around the Corner" (1937 Chevrolet film explaining how a differential works) from YouTube to the Internet Archive. The film is rather overproduced for the topic, but anyone who watches it will understand how a differential works. --John Nagle (talk) 02:15, 16 April 2008 (UTC)

[edit] Recent edits; wrong illustration

The article was fascinating to find; I've been a mechanical technician, and very interested in mechanisms all my life. Indeed, a differential (especially as a "torque splitter", as used in cars) is a tricky thing to describe. While searching for an illustration of a spur-gear differential, I came across several descriptions.

As I found the article, it implicitly assumed automotive emphasis, which bothered me somewhat. Differentials are found in many places, most of them not well-known, however, but, their "torque splitter" use in cars is atypical, if one were to make a comprehensive list of their applications. I tried to rewrite the introduction while also trying not to eliminate the original wording any more than seemed necessary; that's an editing courtesy to the author. As it is, I wish it were simple to keep more of the original at that point.

The planetary (epicyclic) differential (power split device) in the Prius drive train interconnects three major entities: the engine and one motor-generator, another motor-generator, and the differential for the front wheels. It's not quite simple. A really first-rate description is by Graham Davies, at <http://www.ecrostech.com/prius/original/Understanding/Contents.htm> He assumes some technical and scientific education, which permits him to offer a really-good explanation. Perhaps this link could be included in the Differential article, but it seems mostly off-topic, although the planetary differential is quite essential.

Perhaps, not incidentally, the Prius does not contain a CVT; that's technically incorrect. A CVT is a very different, variable-ratio mechanism. However, the Prius apparently feels as though it has a CVT.

As to a Google image search for a good, clear illustration of a spur-gear differential, I looked at maybe 25, perhaps more pages of images, and they became increasingly irrelevant. There were some images, but they were engineering drawings that were really not suited for the article.

[I just realized that I have a computing differential, could take a picture of it, and add it to the article. No promises, though! It doesn't look dramatically different (it's much like the one at the reference I gave). The spider is very easy to see.]


[Wrong illustration; sorry!]

As to the illustration "Reconstructed 19th century carding mill differential", it looked pretty odd. When I clicked on the little icon to learn more, it turns out that this is really, truly unlikely to be a differential! Its title is "Ox powered treadwheel". It's a rugged, strong turntable, and you can just about see a set of "bevel" gears near the ground. The gear on the shaft has individual pins that point down and mesh with a smaller gear on a shaft that looks like a log. That shaft goes down to the right, to power the mill.

The cage-like structure at upper left is probably where the ox was tethered; as he walked on the turntable, he made it rotate -- one ox-power.

I didn't want to act like a bull (or ox?) in a china shop and delete the image, but I do hope that someone who's been more connected with this article will do so!

Regards, Nikevich (talk) 08:53, 9 May 2008 (UTC)