There’s 2 significant inaccuracies in the article and 1 large oversight in the official video.
Differentials are not one wheel drive. They can seem to drive only one wheel when spinning the wheels as one let’s loose and the other stays still, but it’s not driving one wheel. It’s still driving both. The problem is the free wheel is spinning at twice the speed indicated on the speedometer and the other is at 0. The driveshaft puts in a certain number of turns, the wheels, together, must add up to an equal output (multiplied by the gear ratio). If the car is going straight with full traction, then they turn the same. If you floor it in snow, one is probably spinning 40% over it’s share and the other 40% under. This is not unique to rwd either as fwd cars still very much have a functioning differential. To throw some numbers at it to help clarify the function, let’s say the engine is asking the wheels to spin at 30rpm each in a straight line. In a left turn, the right wheel travels further and needs to spin at 35rpm while the inner spins at 25rpm. It still adds up to 60rpm, same as a straight line. Mash it in the snow and it might be 60rpm in the left and 0nin the right or 0 in the left and 60 in the left. It could be 5/55, 40/20, or any other combo as long as it totals 60.
PS: differentials are irrelevant when the wheels aren’t connected to each other. Individual-motor wheels, as shown in the video, don’t need a diff. The non-drive wheels in a 2-wheel drive vehicle do not have a differential on the non-drive axle.
Cv joints are not specific to fwd as nearly all modern rwd cars with independent rear suspensions have CV joints. I don’t know of any trucks still using U-joints either since big trucks are solid axle. Cv joints function the same as U joints. The difference is C.V. joints output constant velocity whereas U-joints (what you’ll see often under trucks on the driveshaft, two square C shaft ends with an X link between) have lopey output that gets worse with greater deflection angle. If you own a u-joint bit for your socket wrench, I invite you to play with it. Instead of a solid pinned X between the U ends, CVs have free-rolling balls that can roll inboard and outboard to maintain the link between the shaft’s cup and the wheel’s cone.
The article is inaccurate but the video ignores this part, so I don’t fault The writer. The CV joints are said to be a poor design, yet, it ignores the part where the video reinstalls them at 4:20 and 5:10 for the front wheels. This mechanism does not allow angular deflection between the motor and hub, as it’s shown, without a CV joint. Lateral displacement, yes, but not angular - as in it can’t steer. This may be an overall improvement by reducing how often it needs to bend (only when steering), but it doesn’t eliminate it. And even then, the rear suspension is still designed to change camber as it changes ride height. Camber is the angle of the wheel as measured top to bottom, as in what you see from looking at the wheels from the front of the car. It keeps the wheels flat on the ground as you lean the car in a corner. You may see an overloaded car’s rear wheels look like /—\ as viewed from the rear or -–/ when hanging free on a lift.
Look, I’m not an engineer at Hyundai (or even a competitor) but this doesn’t quite pass the sniff test. Cool idea for sure, but it smells a little like marketing is clamoring for something edgy to display. Even as displayed, the motors and original reduces were already very compact and in close proximity to the wheels compared to a normal engine. The slightly reduced footprint of this uni wheel and slightly increased friction of a bunch of additional gears makes me think this is a fractional improvement in practice rather than a revolutionary improvement.
I’d be concerned with the amount of unsprung weight this adds, too. You’re basically taking the transmission and adding that mass to the hub. Seems like it would be pretty crashy on rough surfaces.
I considered that but couldn’t make any conclusions. The driveshaft and sun gear are not added to the unsprung. I’d guess only half the weight of planets and carriers is added. It definitely adds the weight of the ring gear to the unsprung mass.
I’m also curious how this affects rotational mass. So while every component spinning with the wheel from tire to motor shaft has rotational inertia, small-diameter components such as drive shafts have relatively little rotational inertia. Wheels and even brake discs have a lot more. I don’t have numbers obviously but I’m curious if the rotational mass of the ring gear ends up being detrimental compared to a heavier-weight lower-inertia cv setup.
Isn’t the ring gear the wheel body (or whatever it’s called), that is, even a fixed axle would have weight there, the gearteeth even provide stiffness. CV joints also contain unsprung mass, I’d say there might be a bit of a difference but nothing drastic. With modern fancy biomimetic wheel body geometries and everything you’ll probably definitely be lighter than 80s steel rims. What happened to spoked wheels, anyway.
The CV only contributes half it’s mass to unsprung weight, and this system still requires a drive shaft and either a CV or u-joint. But with more mass at the hub.
Typical hubs are still lighter than this, because this setup still requires the hub structure, it’s just adding gearing out there.
Half of the hub is unsprung, the transition between sprung and unsprung is at those fancy articulating planetary gears. The drive shaft is definitely sprung, it and the motor is completely static relative to the battery and everything.
Trucks used these as far back as pre-WWII. It a great solution for off road vehicles to gain clearance. At low speeds, even universal joints work fine for this setup, because the shaft rotates at 1/3 wheel speed, like a drives haft does going into a differential.
Meh, it’s still a portal hub, where you put the input shaft is a minor difference. It’s still putting the gearset in the hub, increasing the total weight of the vehicle, and increasing unsprung weight.
Calling it a new thing is a lie. All they’ve done is switch it to planetary gears. I’d bet lots of money this was tried a long time ago, and was shelved in favor of an offset input shaft.
I noticed they conveniently didn’t talk a lot about steering…
The claim of “one wheel drive” I think is meant to highlight what happens if traction is lost. It sounds like something I have heard on 4wd off-road forums. I agree the phrase “one wheel drive” is perhaps not a great way to explain the disadvantages of differentials vs limited slip differentials vs locking differentials vs individually driven wheels.
The idea of “one wheel drive” as I have seen it used, is that in a vehicle with one powered axle assembly (what we normally call 2wd-- either front or rear wheel drive) is that if you lose traction with either drive wheel, the vehicle no longer moves because all power is diverted to the slipping wheel.
If you have a limited slip differential, there is a limit to how much power is diverted to the slipping wheel. With a locking differential, you only stop moving if you lose traction to both drive wheels.
Anyway…
The design is really interesting.
You also bring up a good point about how camber changes with suspension position. Also the effective track width changes, such as with my 4Runner which has upper and lower control arms, a Double wishbone suspension. If the motor remains in a fixed position, the wheel will move onboard and outboard relative to the motor depending on suspension location.
I don’t quite get how these two effects are addressed with this new design. Or are the suggesting a different suspension technology that they didn’t discuss?
As for steering, I wonder if the design rotates the motor along with the wheel. In that case no CV is needed but I would guess there are some downsides to such a design.
I agree the video seems kind of… premature. The mechanism is cool but I don’t get the sense that its applications haven’t exactly been nailed down yet.
Individual motors on each wheel will still slip, just with half the power. So sure, it’s an improvement by an unrelated mechanism, but not having the wheels connected with a limited slip means it’ll still need a traction control system. And even still, the “half” power is a relative term because every car has a different output. That goes for not connecting left to right as much as it goes for front to back. So, not different than a traditional open diff or 2wd. There have been advances in brake-based traction control so they don’t just cut power and apply single brakes like the 00s, they can properly modulate pressure to get equal propulsion.
That’s a good point you’ve mentioned as well - the wheel will change distance to the motor as it goes through it’s motions. The only way to avoid that is to place the motor at the effective pivot point of the suspension which is, in a properly design suspension, inside the other wheel to mimic the level dynamics of a solid axle. That of course defeats the short halfshaft design direction. So something has to allow variation in distance. In the non-steer wheels, maybe this could be as simple as a telescoping spline drive. However, the video shows a small black joint at the same time stamps above on the rear and still has those normal-looking cv boots on the fronts.
Or maybe they’re ditching good handling and going with perfectly vertical suspension travel. Give it hard eco tires and it’ll slide before the suspension shows it’s flaws.
The steering wheels’ hubs rotate in two directions. The steering action rotates through a vertical axis while the typical suspension rotates in a front-to-back axis pinned approximately through the other side of the car. So unless they abandoned common suspension design to let tires lean in turns more than a reasonable amount, there needs to be an allowance for angular deflection. A pinion gear arrangement sounds like it would take up a lot of the space they’re trying to save but still not solve the multi-axis problem found at all 4 wheels. I’m trying to not take their video so literally but it’s not like it’s a dealership rep spouting incomplete info here
Now imagine there is a handle sticking out of the crankshaft that needs to rotate around the shaft with the hand crank as it gets turned. That is the motor.
The video never showed the motor moving along with wheels turning, only the up and down part. In fact, when they showed space savings they showed the motors as stationary with no clear way to turn.
With how small the motor is you could also pivot it alongside with the wheel, after all, something pivoting with the wheel doesn’t mean that it has to be unsprung.
There’s 2 significant inaccuracies in the article and 1 large oversight in the official video.
PS: differentials are irrelevant when the wheels aren’t connected to each other. Individual-motor wheels, as shown in the video, don’t need a diff. The non-drive wheels in a 2-wheel drive vehicle do not have a differential on the non-drive axle.
Cv joints are not specific to fwd as nearly all modern rwd cars with independent rear suspensions have CV joints. I don’t know of any trucks still using U-joints either since big trucks are solid axle. Cv joints function the same as U joints. The difference is C.V. joints output constant velocity whereas U-joints (what you’ll see often under trucks on the driveshaft, two square C shaft ends with an X link between) have lopey output that gets worse with greater deflection angle. If you own a u-joint bit for your socket wrench, I invite you to play with it. Instead of a solid pinned X between the U ends, CVs have free-rolling balls that can roll inboard and outboard to maintain the link between the shaft’s cup and the wheel’s cone.
The article is inaccurate but the video ignores this part, so I don’t fault The writer. The CV joints are said to be a poor design, yet, it ignores the part where the video reinstalls them at 4:20 and 5:10 for the front wheels. This mechanism does not allow angular deflection between the motor and hub, as it’s shown, without a CV joint. Lateral displacement, yes, but not angular - as in it can’t steer. This may be an overall improvement by reducing how often it needs to bend (only when steering), but it doesn’t eliminate it. And even then, the rear suspension is still designed to change camber as it changes ride height. Camber is the angle of the wheel as measured top to bottom, as in what you see from looking at the wheels from the front of the car. It keeps the wheels flat on the ground as you lean the car in a corner. You may see an overloaded car’s rear wheels look like /—\ as viewed from the rear or -–/ when hanging free on a lift.
Look, I’m not an engineer at Hyundai (or even a competitor) but this doesn’t quite pass the sniff test. Cool idea for sure, but it smells a little like marketing is clamoring for something edgy to display. Even as displayed, the motors and original reduces were already very compact and in close proximity to the wheels compared to a normal engine. The slightly reduced footprint of this uni wheel and slightly increased friction of a bunch of additional gears makes me think this is a fractional improvement in practice rather than a revolutionary improvement.
I’d be concerned with the amount of unsprung weight this adds, too. You’re basically taking the transmission and adding that mass to the hub. Seems like it would be pretty crashy on rough surfaces.
I considered that but couldn’t make any conclusions. The driveshaft and sun gear are not added to the unsprung. I’d guess only half the weight of planets and carriers is added. It definitely adds the weight of the ring gear to the unsprung mass.
I’m also curious how this affects rotational mass. So while every component spinning with the wheel from tire to motor shaft has rotational inertia, small-diameter components such as drive shafts have relatively little rotational inertia. Wheels and even brake discs have a lot more. I don’t have numbers obviously but I’m curious if the rotational mass of the ring gear ends up being detrimental compared to a heavier-weight lower-inertia cv setup.
Isn’t the ring gear the wheel body (or whatever it’s called), that is, even a fixed axle would have weight there, the gearteeth even provide stiffness. CV joints also contain unsprung mass, I’d say there might be a bit of a difference but nothing drastic. With modern fancy biomimetic wheel body geometries and everything you’ll probably definitely be lighter than 80s steel rims. What happened to spoked wheels, anyway.
The CV only contributes half it’s mass to unsprung weight, and this system still requires a drive shaft and either a CV or u-joint. But with more mass at the hub.
Typical hubs are still lighter than this, because this setup still requires the hub structure, it’s just adding gearing out there.
Half of the hub is unsprung, the transition between sprung and unsprung is at those fancy articulating planetary gears. The drive shaft is definitely sprung, it and the motor is completely static relative to the battery and everything.
Yep.
Trucks used these as far back as pre-WWII. It a great solution for off road vehicles to gain clearance. At low speeds, even universal joints work fine for this setup, because the shaft rotates at 1/3 wheel speed, like a drives haft does going into a differential.
This puts a diff at each wheel.
Edit: These are called Portal Gears
Not quite portal gears, that has the input shaft fixed at the top. This is like an adjustable portal gear.
Meh, it’s still a portal hub, where you put the input shaft is a minor difference. It’s still putting the gearset in the hub, increasing the total weight of the vehicle, and increasing unsprung weight.
Calling it a new thing is a lie. All they’ve done is switch it to planetary gears. I’d bet lots of money this was tried a long time ago, and was shelved in favor of an offset input shaft.
I noticed they conveniently didn’t talk a lot about steering…
The claim of “one wheel drive” I think is meant to highlight what happens if traction is lost. It sounds like something I have heard on 4wd off-road forums. I agree the phrase “one wheel drive” is perhaps not a great way to explain the disadvantages of differentials vs limited slip differentials vs locking differentials vs individually driven wheels.
The idea of “one wheel drive” as I have seen it used, is that in a vehicle with one powered axle assembly (what we normally call 2wd-- either front or rear wheel drive) is that if you lose traction with either drive wheel, the vehicle no longer moves because all power is diverted to the slipping wheel.
If you have a limited slip differential, there is a limit to how much power is diverted to the slipping wheel. With a locking differential, you only stop moving if you lose traction to both drive wheels.
Anyway…
The design is really interesting.
You also bring up a good point about how camber changes with suspension position. Also the effective track width changes, such as with my 4Runner which has upper and lower control arms, a Double wishbone suspension. If the motor remains in a fixed position, the wheel will move onboard and outboard relative to the motor depending on suspension location.
I don’t quite get how these two effects are addressed with this new design. Or are the suggesting a different suspension technology that they didn’t discuss?
As for steering, I wonder if the design rotates the motor along with the wheel. In that case no CV is needed but I would guess there are some downsides to such a design.
I agree the video seems kind of… premature. The mechanism is cool but I don’t get the sense that its applications haven’t exactly been nailed down yet.
Individual motors on each wheel will still slip, just with half the power. So sure, it’s an improvement by an unrelated mechanism, but not having the wheels connected with a limited slip means it’ll still need a traction control system. And even still, the “half” power is a relative term because every car has a different output. That goes for not connecting left to right as much as it goes for front to back. So, not different than a traditional open diff or 2wd. There have been advances in brake-based traction control so they don’t just cut power and apply single brakes like the 00s, they can properly modulate pressure to get equal propulsion.
That’s a good point you’ve mentioned as well - the wheel will change distance to the motor as it goes through it’s motions. The only way to avoid that is to place the motor at the effective pivot point of the suspension which is, in a properly design suspension, inside the other wheel to mimic the level dynamics of a solid axle. That of course defeats the short halfshaft design direction. So something has to allow variation in distance. In the non-steer wheels, maybe this could be as simple as a telescoping spline drive. However, the video shows a small black joint at the same time stamps above on the rear and still has those normal-looking cv boots on the fronts.
Or maybe they’re ditching good handling and going with perfectly vertical suspension travel. Give it hard eco tires and it’ll slide before the suspension shows it’s flaws.
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The steering wheels’ hubs rotate in two directions. The steering action rotates through a vertical axis while the typical suspension rotates in a front-to-back axis pinned approximately through the other side of the car. So unless they abandoned common suspension design to let tires lean in turns more than a reasonable amount, there needs to be an allowance for angular deflection. A pinion gear arrangement sounds like it would take up a lot of the space they’re trying to save but still not solve the multi-axis problem found at all 4 wheels. I’m trying to not take their video so literally but it’s not like it’s a dealership rep spouting incomplete info here
But you need a CV or Universal on that drive shaft to accommodate suspension travel (or steering if needed on that wheel).
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Now imagine there is a handle sticking out of the crankshaft that needs to rotate around the shaft with the hand crank as it gets turned. That is the motor.
The video never showed the motor moving along with wheels turning, only the up and down part. In fact, when they showed space savings they showed the motors as stationary with no clear way to turn.
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Suspension movement still requires flex in the shaft. There’s no way around it unless the engine moves with the suspension
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Unrelated comment, but holy shit I am a huge fan of the M8. So wild to see you on Lemmy, and this comment section is exactly what I’m here for.
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With how small the motor is you could also pivot it alongside with the wheel, after all, something pivoting with the wheel doesn’t mean that it has to be unsprung.