Witchcraft

"Cé hé sin" (michael-m-mouse) 04/09/2015 at 18:20 • Filed to: Mercedes, automatic

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Here we have a Mercedes 7 speed automatic box.

And here we have the newer 9 speed.

So, one has seven sets of gear wheels and the other nine.

No. Oh, no.

The eagle eyed will spot that while having detail differences each has four gear trains (admittedly the seven speed has three with a kind of double arrangement for one of them with two sets of planet wheels). The process of extracting seven and nine gears from these indisputably involves the craft of witches and probably sorcery as well.

scoob > Cé hé sin 04/09/2015 at 18:21

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what am i looking at

StoneCold > Cé hé sin 04/09/2015 at 18:22

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Modeling these must be one of the greatest exercises in patience and spatial awareness.

Cé hé sin > scoob 04/09/2015 at 18:23

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The internal workings of two automatic boxes. Only about three people in the world understand these.

DrJohannVegas > scoob 04/09/2015 at 18:23

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Gears.

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > Cé hé sin 04/09/2015 at 18:24

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Automatic transmissions are very weird. I tore apart a Chrysler A413 from a Neon once. Even though it was only 4 gears, lining everything back up for reassembly was equivalent to brain surgery.

RamblinRover Luxury-Yacht > Cé hé sin 04/09/2015 at 18:25

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Something dearly missing in autos of the ancient past - lockup of multiple concentric shafts in different combinations. Sequential and alternating combinations are powerful.

Cé hé sin > StoneCold 04/09/2015 at 18:26

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Indeed, but I saw a diagram some time ago of a Napier turbocompund aircraft engine. Done about seventy years ago with nothing other than pen and paper and it made either of these look almost simple.

Cé hé sin > RamblinRover Luxury-Yacht 04/09/2015 at 18:28

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Yes, and the availability of modern electronic controls plays a part too!

tromoly > Cé hé sin 04/09/2015 at 18:28

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Nope, just planetary gear trains working in series. Had a discussing at my old job about this very concept a couple months ago, actually.

PS9 > Cé hé sin 04/09/2015 at 18:29

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Nah, not witchcraft. Just clutching in/out the various sun/ring/planetary gear sets. I do like that chain driven fluid pump though. That's pretty neat!

TheHondaBro > Cé hé sin 04/09/2015 at 18:30

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My mind is full of fuck. I have no clue how to transmission.

Cé hé sin > tromoly 04/09/2015 at 18:34

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Sounds easy, doesn't it? Each epicyclic is only providing a direct and one other gear (and a reverse in one case) but it's the combination of all the different elements that makes your head hurt.

JR1 > Cé hé sin 04/09/2015 at 18:35

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EL_ULY > Cé hé sin 04/09/2015 at 18:37

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just gears, no biggie

ly2v8-Brian > Cé hé sin 04/09/2015 at 18:40

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Not that complicated.

SidewaysOnDirt still misses Bowie > Cé hé sin 04/09/2015 at 18:49

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This one?

Cé hé sin > SidewaysOnDirt still misses Bowie 04/09/2015 at 18:51

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That would be it, or one of them. They were two iterations of it, neither successful.

That's Engineering? > Cé hé sin 04/09/2015 at 19:05

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Haha you would have loved my engineering class then! The final was, given the ZF 8-speed, derive all gear ratios, gear speeds, and all torques on the clutches and brakes in the transmission. The semester project was to design a 5-speed automatic transmission, only given required gear ratios.

That's Engineering? > Cé hé sin 04/09/2015 at 19:07

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Yep. On its own, a planetary gear set is really sime. Designing an automatic transmission, where you have multiple sets, clutches, and brakes which all work together to create the actual gear ratio... Pretty miserable. Designing a 5 speed automatic was a project in one of my classes. Not fun.

That's Engineering? > TheHondaBro 04/09/2015 at 19:09

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Try and find a drawing where you just have the gear sets, clutches, brakes and connections shown. It's a lot easier to digest that way.

norskracer98-ExploringTheOutback > Cé hé sin 04/09/2015 at 20:03

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Definitely interesting. Here's a drawing of GM's new 8L90 8 speed box.

XSeriesWalkingDead > Cé hé sin 04/09/2015 at 20:07

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That looks like $$$$$

wafflesnfalafel > Cé hé sin 04/09/2015 at 21:51

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didn't Lexus do that first? (using varying combinations of existing ratios to make additional ratios in the same box.)

AMGtech - now with more recalls! > Cé hé sin 04/09/2015 at 21:54

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Definitely witchcraft. The factory special tool for repairing these is actually a magic wand.

Cé hé sin > wafflesnfalafel 04/10/2015 at 06:08

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If you have more than about four speeds I think everyone designs them that way.

BloodlessWeevil > Cé hé sin 04/10/2015 at 10:37

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An explanation of how to get several ratios out of a single planetary gear set can be found here:

http://science.howstuffworks.com/transport/engi…

Clutches control what is the input, output, stationary, or locked together. From there it is just a matter of stacking those together with slightly different ratios. That is, reduction/overdrive gives a different ratio than overdrive/reduction. I might label one of these so you guys can see it visually if I have time later.

Cé hé sin > BloodlessWeevil 04/10/2015 at 10:52

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Oh, I know about epicyclics - you can in theory get five forward and two reverse gears from one - it's the interaction of different geartrains that make the brains of us poor mortals hurt.

Have a Wilson pre selector. Four geartrains, four brake bands and one clutch.