New CVT design

[u/titowW]

https://youtu.be/mWJHI7UHuys?si=gm5QxoWa7YGvxHM6

Do you think this design can be adopted massivement by big constructors around the world or it will stay niche ? It seems to be promising but i can't tell by myself.

[u/ModernRonin]

The small planet gears inside the small ring gear have one-way clutches so they only pull the ring forward, and don't push it backward. Therefore, as one of the YT comments correctly observes:

This seems like an obfuscated ratcheting CVT, these have been around for a while. There's a bunch of extra gears and levers to make it seem like something new and different, but really it's just a ratcheting cvt, the animation around 13:00 really makes it clear as thats the same motion and link as in a ratcheting cvt.

Nothing wrong with ratcheting CVTs, if they are implemented correctly. Whether this one is implemented correctly? I'm not a mechanical engineer, so I can't say for sure. The small gears with the one-way clutches do accelerate and decelerate as they move the ring gear around, so that might cause vibration at higher RPMs.

In general, though I love CVTs, I do think that they're not as useful as they used to be. Piston engines are rather peaky in their torque delivery, so a CVT pairs well with a piston engine, for the reasons mentioned in the video.

However, my hope is that the future is mostly electric motors. Mainly because electric motors are generally about twice as efficient as gasoline engines. But also, electric motors have a much flatter torque curve. Usually a 2-speed gearbox is way more than enough for an electric motor. So any CVT that's more expensive, complicated, or less reliable than a 2-speed gearbox is going to be a bad pairing for an electric motor.

Having dreamed up a chain-based planetary "MRT" ("many ratio transmission") myself, I do like CVTs and I think they're neat. But I'm just not sure they're the kind of future that I want to move towards. It seems like the grass is greener over in the lithium-ion battery and AC induction motor pasture...

Edit I had that backward.

[u/wildwildwaste → u/ModernRonin]

I worked for a supercharger company a while back and helped develop a CVT gearbox for their street superchargers. Pretty neat as it mostly eliminated the lag associated with superchargers that have fixed ratios, and therefore fixed impeller speed relative to the engine speed. This device allows you to operate at a target impeller speed instead. Unfortunately I don't think it took off as well as they expected, but I am a bit out of the loop on these things now.

I will say, our biggest issues were efficiency and heat. The two biggest hurdles in any forced induction setup.

[u/Snellyman → u/ModernRonin]

The reason that electric motors work without a transmission isn't due to the flat torque curve but rather that above base speed they output a constant HP with the torque decreasing proportional to the speed increasing (just like a CVT). The back EMF of the motor makes an inherent gearbox. Also if that is too limiting the windings of the motor can be switched from star to delta to electrically create a 1.7 gear ratio change without any mechanical parts.

[u/func600 → u/Snellyman]

You can also do field weakening, to get extra speed out of the same motor by reducing some of that back emf at the cost of extra current.

Having messed with electrical motors in PEV's, drones, trains and cars for years now, I love how simple electrical motors are. Yeah, the drive circuitry is complicated, but the mechanical simplicity coupled with the smooth power delivery you get from a 3 phase motor is simply awesome. Sometimes I turn off the stereo in my EV and just listen to the quiet song from the inverters as I tear up and down a twisty mountain road. Never buying another ICE vehicle again.

[u/ModernRonin → u/func600]

Oh, don't worry. The idiotic, technologically illiterate, greed-maxxing, myopic fuccbois in the C-Suites of major US car companies will definitely find a way to completely degrade and ruin EVs. (Elon has already created the CyberTruck!)

[u/ZeroGravityDodgeball → u/ModernRonin]

Near the end of the video, he mentions that the ratcheting mechanism is only for the bicycle application (where you don't want the pedals to spin when rolling downhill), and that that the company has produced a non-ratcheting version for automotive applications.

I am not a deep expert in this field, so I may be thinking about two different ratchets.

Edit: I was wrong. Per comment from the OOP:

NOTE: One-way ratcheting/ motion is an essential feature of this transmission and not bicycle specific as I mentioned in the video. Wothout a one-way bearing or a ratchet or other similar mechanism the small planet gears would just roll back and forth on the ring gear leading to no output. This is something I should have emphasized more in the video.

[u/SimplifyAndAddCoffee → u/ZeroGravityDodgeball]

the ratcheting on the input bearings is for bicycles, the ratcheting on the output is necessary just by virtue of the design to drive the transmission

[u/Mshaw1103 → u/ModernRonin]

Well, had this video in my watch later playlist. Sounds like I’ll be removing it if it’s nothing special

[u/davey-jones0291]

I saw this, the issue it has will be vibration and creating pulses of power as reach ratchet takes over from the last. I saw that can be minimised by using elliptical gears on the ratchet but not sure it will be perfectly smooth. Interesting though

[u/TheBizzleHimself]

One of the coolest CVT designs I’ve seen was for an older lathe. I forget the brand but it used a movable ball between two discs.

It did suffer from people using the wrong oil (once the drive slips, the surface finish is ruined and no longer functions well)

But it was simple and beautiful in function.

[u/sonorguy → u/TheBizzleHimself]

Was it a Reeves drive? Delta-Rockwell and Powermatic are the common companies that made wood lathes with them. I'm less knowledgeable about metal lathe manufacturers.

[u/throwaway21316 → u/TheBizzleHimself]

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

[u/HCTriageQuestion]

Rube Goldberg's ratchet CVT.

[u/Zorbick]

I think this is a clever evolution of CVT designs and I'm cautiously optimistic on this. I have some applications where even the 14-speed Rohloff isn't quite a perfect fit. If it can be more efficient than a Nuvinci CVP, say 90+%ish, at roughly the same mass, then I'm all in.

Sure, an eCVT is probably going to have a higher market share, but an encapsulated CVT for bicycles, scooters, and the like would be incredibly handy for a lot of different situations.

[u/k-mcm]

It doesn't allow engine braking so that would be death on a few ultra-steep hills that exist. A hybrid could use regen after this, but hybrid + this CVT is way too much complexity.

Also, there's no way those little ratchet gears will survive for long. Their total output may be reasonably smooth but each one of them is getting hammered.

[u/KiloClassStardrive]

the only issue i see with this is the computer controlling it, we need to move away from computer controls and go to mechanical vacuum controls systems, why you may ask, mechanical control systems are cheaper in the ling run, a transmissions will survive longer without the electronics, we all know all too well that electronics have a predetermined service life, just so many electrons can flow through an ecteronic system before it fails. i do like this transmission, great move foreword, but the engineers put way to much faith in electronic control systems. it's OK to have sensors to monitor function, it's not OK for computers to control the engine and transmission functions. if the computer goes bad, you can still drive the car without a diagnostic system.