Hyundai Uni Wheel electric drive system could revolutionize EV design
autoblog.com
autoblog.com
The gears will be turning at a large multiple of wheel speed, so will require roller bearings except for low power and speed use: a radial and thrust bearing for each end of each gear, or 22 of each per wheel. Increasing torque also increases the level of thrust support required for the moving gear carriers handling all of those helical gears.
It's a neat idea for highly space constrained applications that have to package a drivetrain very close to a wheel, which does end up being a rather niche use case. Mars rovers, perhaps. Trying to compete against CV joints in passenger vehicles with this would be quite difficult.
That seems like an easier sell.
I'm not sure if we're talking past each other but you wouldn't need an axle to deflect. The motor drive could attach directly to the 'uni wheel' which is in turn connected directly to the wheel. If you're talking about the motor drive shaft, then surely you'd just be moving thrust bearings from the gearbox to the motor (if motors don't already have them)
Thrust bearings are for the gears. The depictions show helical gears, which would surely be necessary when operating at transportation speeds for noise reasons. Helical gears experience axial forces, which would need to be handled for each gear. Mainly on one side for ICE drivetrains, since coasting loads are small, so one side could get away with a ground and hardened rub surface. EV's using regenerative braking would need robust thrust handling on both sides.
Herringbone gears would eliminate the axial thrust issue, at substantially more expense. The easiest method is to separate the gear areas with a central runout groove so you'd have a hope of grinding in a decent surface on the faces, then it's only a little more than double the work; effectively cutting two gear shapes per gear plus the runout.
This is really cool for rear wheels. I don't know why their demo shows it on all 4, since it has to be able to steer (note that the demo does show a CV joint in the axle on the front, but that seems like it would limit steering angle severely, since it is just 1 joint. They're probably planning to apply torque to steer).
You're suggesting placing the ring-gear in the chassis and running the axle to the wheel? That would involve two reduction gearsets in the chassis instead of the current "one plus a CV gear," which kind of defeats the purpose of reducing chassis space usage.
> The gears will be turning at a large multiple of wheel speed, so will require roller bearings except for low power and speed use: a radial and thrust bearing for each end of each gear, or 22 of each per wheel. Increasing torque also increases the level of thrust support required for the moving gear carriers handling all of those helical gears.
I imagine the final product would use herringbone gears, since the large number of thrust bearings would all add to unsprung weight.
The designs seems to cover all the motion of the wheel in the suspension - but I don't see how this could accommodate steering.
Is this for back wheel drive only?
Curiously the animations shown in the video, show the uni wheel used in the front of a front wheel drive car - but without ever showing how the wheels steer.
How is that supposed to work?
You'd have an added complication of making the shock absorber the pivot point, and attaching the motor to the top point. Or having a separate pivot point where the motor or wheel can slide up and down.
This does raise the question of why not just attach the motor straight to the wheel.
The standard response to that is a hand wavey "unsprung mass". But has it actually been tried and shown to be an issue?
So, that's probably not it.
I think this only works with RWD, because the turning wheels can't be sprung without also having to rotate the springs.
It would be a better suspension (closer to racing suspensions) than standard, because wheels wouldnt toe in/out when they moved down/up. Looks expensive as hell though
"This does raise the question of why not just attach the motor straight to the wheel. The standard response is ...unsprung mass"
Afaik with high performance motors, if you want optimal performance and space efficiency you take the unsprung mass for granted and move everything in wheel and try to reduce the mass as much as possible. As a bonus you do not need joints, just a planetary gear system.
A motor per wheel simplifies everything.
No diff, no CV joints, you don't need this, just a simple planetary gearbox.
You gain space, lower manufacturing costs (theoretically, assuming multiple motors doesn't offset the other cost reductions, although as you could base a 2wd and 4wd high performance version on the same motor, that's an even harder case to make).
Benefits according to the article: "reduced packaging size, improved ride quality, greater durability and, importantly, increased efficiency."
That somehow seems a weird choice for a device that's all about improving space efficiency.
Just look closer at the animations in the video if you want to see how the space is being used
I'm actually surprised they would even need the gearbox. Why not just put four Outrunner[1] motors, one on each wheel, and let the wiring be the only thing that has to flex when the wheel is steered.
1. https://fr.wikipedia.org/wiki/Moteur-roue_d'Hydro-Qu%C3%A9be... (in French only, sorry!)
They're common in electric scooters, bikes and bicycles though.
the sound is not coming from EMF, but rather from speakers due to safety regulations for pedestrians
It actually doesn't. A wheel's camber changes as it moves up and down, which is why race cars typically have negative camber when going straight, so the tire's entire contact patch is used when going around a turn, which compresses the suspension of the outside wheel.
This design doesn't appear to handle this case at all. I'm not sure how a traditional suspension setup could be modified only move a wheel up and down, without any change in the camber, considering the fixed attach points of the various control arms.
I think this could have worked with an ICE, but there is no real point: the CV joint is simple and the advantages to this don't apply when you have a single large power source.
I think the tradeoff is between more flexibility & fewer parts (no cv joints) but possibly more rolling resistance.
But watch the video, this uni-wheel thing is different. It isnt an in-wheel motor, more of a cv-joint alternative?
Motor scooters have unsprung motors, the motor is a significant proportion of the mass.
The issue is that it scales poorly, unsprung weight is bad enough that on some cars the disc brakes live 'inboard' on the front wheels (older hydraulic suspension cars).
Essentially the larger the unsprung mass the bigger the hit every time the road surface irregularities cause the wheels to move relative to the vehicle body. The larger the mass the more energy gets imparted, and the more energy that gets imparted the bigger the impact and all that energy then needs to be absorbed so you'll need a stronger (and heavier) suspension system, roughly half of which is unsprung mass!, and a larger battery to compensate for the losses in the suspension which also adds weight (harder suspension -> bigger range but less comfortable ride). So it feeds back on itself and that's why it scales so poorly.
See upthread links and subsequent updates
https://news.ycombinator.com/item?id=38485097.
Note that more unsprung weight has other effects as well, such as poor handling because the wheel bounces higher and so will be out of contact with the road for a longer time when it encounters an obstacle. If you think of the weight of the wheel as the weight on a pendulum it is easy to see why that would affect the period of the swing.
We have developed the first production car to use in-wheel hub motors. https://mwmotors.cz/luka-ev/
This car maybe too, as far as I understand it. A Russian UAZ on steroids: https://www.youtube.com/watch?v=RCOf_33C1qc
Still, very impressive achievement and a nice testbed for this kind of tech, it may also make sense for motorcycles and for vehicles that are not meant for highway use.
Why should the airflow be cleaner?
As far as I know, this Czech company uses in-wheel motors:
All that being said it could be a good niche solution. A small city car would benefit from the space savings and does not need to go high speeds over less than perfect roads. Nor does it rack up that many miles in wear and tear. In general I think electric will bring more diversity in car designs depending on purpose.
But uni-wheel changes paradigm!
They also gloss over "splitting the motor". It looks like 4 individual wheel motors, which would indeed be optimal for the torque vectoring that they mention.
Still, looks like a very cool development. I hope it works out to be a real advance
There still needs to be a CV joint to allow steering, but short of hub motors[1] There isn't much you can do about that.
What I would be interested to see is how lubrication works. Do you think they just have a bunch of oil in the bottom and rely on centrifugal force to fling it to the ring gear? Then let surface tension transmit it to the sun gear?
[1] They are heavy and heavy wheels affect ride quality, as suspension works essentially by allowing a light wheel to move up and down dampening against the mass of the heavy body. If the body is light, then you need to have less dampening, which means more shock/impulse is transferred into the main body of the car/
Naw, because if you look closely in the video you can see that the motors turns with the wheel. With small EV motors that’s not unreasonable.
Presumably the motor is free to tilt up and down a bit as well to deal with changing camber.
> but short of hub motors[1] There isn't much you can do about that.
I mean, it is pretty much a hub motor that has been decouple in the vertical motion so it doesn’t contribute to unsprung mass, and with a good reduction gear as a bonus.
that being said the tradeoff might not be too bad in this case.
Quad-motor all-wheel torque vectoring sounds awesome tho.
I assume that means they still need a CV joint for the front wheels regardless, and that it gains no camber when cornering.
Reminds me of the head of a waterpic toothbrush - a packet of tiny gears, the weakest point in the device, constantly wearing out.
How much would damaging a wheel cost?
Hopefully they are able to work out these details, and eventually provide a real physical demonstration of these use-cases.
I think this would make most sense with an axial flux motor. That’d keep the package quite compact.
I’m guessing the camper changes mentioned could also be handled by the motor pivoting up and down as well. But I can’t say for sure if that makes sense.
When you turn the wheels the axles need to flex somehow around that rotation. This is one of the things CV joints do well: they can handle not just moving up and down, but also the wheel turning left/right. This thing is a bunch of gears and seems to handle only wheels moving up and down and not turning.
That aside, it would interesting if someone made a 3d model one could print to try this out at home for small robots.
The more interesting question to me is what happens if you get a flat tire? Does everyone need to carry a spare uniwheel, or wait to get towed?
A lot of cars don't have a spare wheel now, why would they start carrying one in the future?
As for flat tires.. the last time that happened to me was a few years ago. Not common these days. Except on some particular roads in the region.. the locals have complained for years that they get flat tires all the time. And that's an island, there are no towing services nearby.
With all those extra gears, the efficiency should be comparable? Would only work for real wheels of course.
Non-spinning-shaft power transmission (doesn't really need to be electric, could as well be something like fluid power transmission like hydraulic or pneumatic power) dodge this by putting the power plant in a way the angle between power plant and wheel can't change.
If you have to end up with 4 "normal sized engines" or "normal sized clutches" to implement this, you now are in net gain of wasted weight/space.
https://en.m.wikipedia.org/wiki/List_of_Hyundai_transmission...
For a regular car this is useful because the space all the shafts taking power from the ICE to the wheels can be used for something else. For a race car there is plenty of space for those shafts and you don't have anything else to put into that space if you could. This the reason this was developed doesn't apply to race cars.
Of course for race cars they are concerned about weight and performance. Not having those shafts may be better for weight and thus worth it (assuming a EV race care), or it might not make a difference. This might have some other advantage in racing applications that the designers haven't even realized yet.
And gears close to wheel used in off-road vehicles looong time, to create more clearance but they was headache, because need much additional mechanic time, and there was huge losses.
…except when large SUVs are bought as a status symbol, or the race to drive the biggest tank on the road in defense from the other tanks or the road.
Drivers discount that because they like to think that those are things they control and just won’t do, but every year some fraction of people will hit ice, be distracted or angry, etc.
Minivans are a good option for some families. But they suck for towing trailers, and the ground clearance is terrible if you ever have to drive on a dirt road.
I am all in on retrofitting a 1973 Ford Country Squire faux-wood-panel-in-green station wagon with a set of Kia uniwheels.
It's a lot bigger than my Prius, and that happily takes 4 (5 with a squeeze) climbers with all their gear!
I still find it crazy that no station wagon exists other than Volvo.. like Audi does not export their A4/A6/A8 estate version? Skoda, Mitsubishi, Toyota neither?
I can understand if you live in an area where roads are not well maintained or mostly dirt, SUV is really alluring. But for city driving is a massive (literally) problem for everyone.
Meanwhile, I can fit four people and some light cargo comfortably in my hatchback, or put all the seats down and carry more cargo than the typical SUV.
Now show me a modern EV that has similar specs, and you are talking about a large SUV that's up around the $100k price range.
It's a simple fact that while modern EVs are often styled as SUVs, the inside is comparatively tiny since the battery pack takes up a lot of space.