“Fluid gears” invention offers promise for improving mechanical devices | Hacker News Reader

“Fluid gears” invention offers promise for improving mechanical devices

phys.org

33 pointsvlachen54 comments

The phys.org article and headlines are misleading, the authors did not investigate systems to actually transmit torque. From what I gather, the interesting findings are the parameters for co-rotation and counterrotation of the driving and driven cylinder, depending on the Reynolds number, distance and so on. To illustrate one of the images of their publication: https://i.imgur.com/m8P2iVw.png

That would make much more sense then what the article seems to imply (scientists reinvent a 100 year old torque converter! But worse!!). Of course that headline isn't nearly as fun (scientists develop better model for fluid dynamics in torque converter).

Can someone suggest a better (i.e. more accurate and neutral) title?

Mapping out How Fluid Mechanical Spin-coupling Interactions Depend on Proximity, Confinement, and Flow State

Alternate: New Ways to Understand, Control, and Exploit Hydrodynamic Spin-spin Interactions in Applications

The article doesn't really deliver on either headline, but that's the fault of the article, not the study.

The limit is 80 chars and I'm not sure how to squeeze those in. I've taken a crack at something simpler in the title above. Does it work?

From the original source: Scientists Put Teeth Into Water-Driven Gears https://www.nyu.edu/about/news-publications/news/2026/januar...

(Can't tell what the submission title was, but the byline (with quotes) works too: “Fluid gears” invention offers promise for improving mechanical devices)

Ok, let's try the second one. Thanks!

But these things exist though. https://en.wikipedia.org/wiki/Fluid_coupling

Check out what this dude came up with 120 years earlier: https://en.wikipedia.org/wiki/Hermann_F%C3%B6ttinger

Died at age 68 on April 28, 1945 in Berlin, from shrapnel. The Soviets had begun shelling of Berlin on April 20.

This sort of coupling was used to drive the supercharger on the German BF 109, enabling it to maintain manifold pressure from sea level up to 20,000 ft. with a single stage supercharger without throttling. Use of such couplings in automobiles didn't occur until after the war.

https://www.youtube.com/watch?v=NcI67pZe_Ss

I'm not a fan of the bias towards "Gears are old tech, and that makes them bad" but I can see a lot of interesting possibilities with fluid coupling. The variables involved in power transmission for these things would be pretty wild to characterize, and the article video clearly shows inefficiencies in the system with the driven cylinder having counter rotational flow against it.

> I'm not a fan of the bias towards "Gears are old tech, and that makes them bad"

If the gears don't at least require an app with a subscription and regular updates to use, they must be old tech

/sarcasm

Ever driven a vehicle with an automatic transmission rather than a manual gearshift with a clutch? Then you almost certainly used a fluid coupling: basically two fans in a can with oil so turning one turns the other.

The article is so full of hype it doesn't bother to explain how this is different from the "fluid gears" invented in 1905.

As immortalised in the 1978 song "Greased Ligthnin'" from the film Grease:

    Well, this car is automatic
    It's systematic
    It's hydromatic
    Why it's greased lightnin' (greased lightnin')

I am pretty sure that "hydromatic" there is actually "Hydramatic" (https://en.wikipedia.org/wiki/Hydramatic).

If it’s a hydramatic, be careful to only lubricate it with snake oil.

1978 film (based on a 1971 musical) set in 1958 with the high school kids repairing a beaten up 1948 model year car.

Except a fluid clutch actually works, and a torque converter works even better and has three fans inside it ;-)

I can see the "passive" cylinder getting dragged around a little by viscosity but I don't see how this could transfer even the tiniest amount of power.

Yeah, and like it's name a torque converter can actually not only transmit torque as well but also convert rpms to torque. Running the engine at high rpm at standstill converts revolutions of the input shaft to torque on the output shaft, thus allowing the car to start accelerating at slow speed but with high torque, operating without a clutch.

That's as close to fluid gearing as you can imagine.

Yup. You can hold the RPM steady and watch the road speed climb as the inner blades "catch up" with the outer ones.

Not as funny as with CVTs though where you can have the road speed increasing as the engine RPM decreases. Or there was a guy about 20 years ago who had a Volvo 340 automatic fitted with a Volvo 760GLT 2.3 litre turbocharged engine, which he used to compete with at drag races at the local raceway. It did not too bad against similar vehicles in its class, but it sounded pretty funny because it would just race up to about 4500RPM and stay there for the whole run, as you had a rising howl from the drive belts at the back.

Of course my car has a torque converter and two viscous couplings - the TC between the engine and gearbox, one viscous coupling that makes the centre diff act like a very stiff LSD, and of course one that works the other way (eases off as it slips) to let the cooling fan stay at a steady speed.

> Ever driven a vehicle with an automatic transmission rather than a manual gearshift with a clutch? Then you almost certainly used a fluid coupling

Are you sure?

https://en.wikipedia.org/wiki/Continuously_variable_transmis...:

“The most common type of CVT uses a V-belt which runs between two variable-diameter pulleys.

[…]

A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by enabling the engine to run at its most efficient speed regardless of the vehicle's speed.

[…]

Disadvantages of a hydrostatic CVT include:

Reduced efficiency. Gears are one of the most efficient methods of mechanical power transmission, with efficiencies as high as 90 percent in many cases. In contrast, few hydrostatic transmission systems achieve more than about 65 percent efficiency”

CVT != Automatic transmission (which is generally hydraulic)

https://en.wikipedia.org/wiki/Automatic_transmission#Hydraul...

Not sure why you are making this statement.

> "A continuously variable transmission (CVT) is an automatic transmission ..."

https://en.wikipedia.org/wiki/Continuously_variable_transmis...

CVT is not the same as "automatic transmission", but it is a subtype of automatic transmission, i.e. CVT is a kind of automatic transmission, but there are also other kinds of automatic transmissions, which are more frequently used.

"Automatic transmission" just means that you do not change gears manually, which is also true for CVT.

There are also DCTs which IIRC don't use a torque converter. But chances are pretty good that an automatic transmission car uses a torque converter.

A hydrostatic CVT is not a torque-converter transmission (which is hydrodynamic). A hydrostatic CVT is basically a hydraulic pump, control valves plus hydraulic motor. So what you would typically find on construction or forest equipment.

Many automatics these days are manual transmissions with a computer controlling the clutch. They have nothing in common with the slushboxes of old, the oil is just for lubrication.

Even slushboxes tend to aggressively lock up the torque converter. It's usually only in a "fluid dynamics" mode for brief moments. (Except maybe on a gentle hill start)

It's worth mentioning hard acceleration causes a torque multiplication to occur in torque converters vs a slow acceleration does not (check me on that). Once locked up, multiplication no longer occurs. Thank you hot rod magazines of the 90's.

ZF 8HP is still a traditional torque converter transmission. Most high performance or high torque applications use that design. Dual clutch automatics or automated manuals can't take it.

Virtually every truck has an automated manual transmission, every EV 2-speed is a DCT, Porsche uses PDKs etc.

Every truck? Like which ones?

As an American (land of the pickup truck) I can't think of any

I think GP meant eighteen-wheelers and the like.

> American (land of the pickup truck)

More like SUVs with beds

But yes, sibling is correct, I'm talking about commercial vehicles.

Citation needed. By truck if you mean commercial truck (lorry, artic, etc.) then no, Allison still makes hydraulic automatics which are very common in vocational work the world over.

Tremec makes DCTs that are used in 800hp Mustangs and 1000hp Corvettes

I mean, certainly the VAG group likes to use their dual clutch automatics, but "true" torque converters are still very common. ZF makes them for like a million different cars, and AISIN makes them for the Volvo and Geely group.

Maybe in sports cars but the majority of vehicles still come with hydraulic autos or CVTs.

As what efficency? The artical doesn't say, but hydraulics and automatic transmissions have been around for a long time and are less efficient than regular gears or electric motors. Cars got a good efficieny boost then the locking torque converter was developed.

Virtually zero torque right?

I don't see how it could even have any measurable torque.

You could improve it by making the cylinders have sticky-out bits that would scoosh the fluid around better, like little paddle wheels, and if you wanted to get some serious torque transfer you'd push the two paddle wheels so close together that the paddles actually kind of intersect.

you could increase fluid viscosity

Indeed, then this design will truly have come full circle.

That's a slippery slope that leads right back to traditional gears.

Nice to see that they have discovered the Torque converter https://en.wikipedia.org/wiki/Torque_converter

Used since the 60s lol

Torque transfer through a fluid, per se, is old hat: it's been deployed in automatic transmissions starting in the 1940's. Buick's "Dynaflow", etc.

I’m super confused how this any more useful than an oil based hydrodynamic torque converter like you’d find in a “slush box” automatic transmission. The video in the article shows such a low rate of transmission it’s crazy, I can’t think of a purpose!

Do we understand fluid mechanics well enough now to just design things like this from scratch, or is it still mostly trial and error? TFA seems to imply the latter, but....

This could have been designed in CFD in an afternoon. Building it in real life is always somewhat cool but the amount of hype they're putting on this is crazy.

https://en.wikipedia.org/wiki/Torque_converter

There must be some reason PRL chose to publish this, but it's not apparent to me from TFA or the abstract, and I'm not interested enough to login via my institution.

It's not new that you could set up co- or counter-rotation in such a system. This seems like the sort of thing G. I. Taylor had as a bath toy.

Maybe impossibly tiny and unresponsive torques are useful somewhere?

How is this different from slushomatics? Sounds exactly like old school fluid couplings.

Or slushboxes …

Ehm, isn't it the same thing as https://en.wikipedia.org/wiki/Torque_converter ?

reminds me of a tesla turbine -- only less efficient

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