Where are all the in-wheel (hub) motors?
Discussion
Before EVs became commonplace, there was a lot of talk about the use of in-wheel or hub motors. However, I've yet to see these implemented in a production car. Does anyone know why this is? I'm assuming it comes down to cost? Or, is it that they're still not a proven, fully-tested technology?
The benefits of in-wheel motors are clear. They free up even more space within the vehicle itself, providing extra passenger or storage capaity, or even allowing for the realisation of some truly groundbreaking body shapes. Yet, as mentioned, I don't know of a single production car that makes use of this technology.
The benefits of in-wheel motors are clear. They free up even more space within the vehicle itself, providing extra passenger or storage capaity, or even allowing for the realisation of some truly groundbreaking body shapes. Yet, as mentioned, I don't know of a single production car that makes use of this technology.
I'm not sure they free up much space in the car itself. Of the chassis I have seen the motors are all in between the suspension arms or chassis structure, they don't stick up or out much at all. I wonder/speculate that form a practical viewpoint the motors aren't strong enough to withstand the hammering wheels get from the roads.
I'd guess it's a combination of unsprung weight, cooling (usually via some sort of liquid coolant, rather than just air), longevity of cables (near constant flexing leading to mechanical fatigue), longevity of the motors themselves (would be subject much harsher vibration than a chassis-mounted motor), and probably quite difficult to package along with mechanical brakes.
As one of the previous posts points out, current EV motors are so compact that there's not much to be gained in terms of packaging through making them wheel mounted.
As one of the previous posts points out, current EV motors are so compact that there's not much to be gained in terms of packaging through making them wheel mounted.
Not just unsprung mass, just mass in general.
A decent hub motor can easily be over 30kg, and might just give you 100hp.
So you'd need at least two for a modest car (also, otherwise you'd end up with a left-wheel drive car like some Spira), and nearly impossible to scale for more power unless you drive all 4 wheels, adding well over 100kg of unsprung weight.
Conversely, a boggo Tesla Model 3 SR motor makes 5x the peak power whilst weighing less than two of those hub motors.
In board they can be designed to be a lot more efficient without the geometry constraints. In short, the copper to kg ratio is much higher.
Add to that that violently shaking an electric motor all the time might also not be beneficial to longevity, but that's my take so no source on that.
A decent hub motor can easily be over 30kg, and might just give you 100hp.
So you'd need at least two for a modest car (also, otherwise you'd end up with a left-wheel drive car like some Spira), and nearly impossible to scale for more power unless you drive all 4 wheels, adding well over 100kg of unsprung weight.
Conversely, a boggo Tesla Model 3 SR motor makes 5x the peak power whilst weighing less than two of those hub motors.
In board they can be designed to be a lot more efficient without the geometry constraints. In short, the copper to kg ratio is much higher.
Add to that that violently shaking an electric motor all the time might also not be beneficial to longevity, but that's my take so no source on that.
malaccamax said:
Guessing its reliability in a harsh environment - lot of load going through when you hit a pothole. They would give a sports car a LOT more boot space though. One reason Alpine is using hem for the next A110
Well, this was my thinking? Even if the space saving was minimal, in certain situations, even a little is a lot! But, you're saying the Alpine will use in-wheel motors in the next A110?Edited by gtwilliams on Thursday 21st August 16:34
Roguexcess said:
Cooling the motor cant be easy especially that close to the brakes
Assuming the brakes are there too. It could have inboard brakes.From my R/C car days the electric motors could easily lock the wheels if you applied a bit of reverse throttle and so I wonder how long before we need brake discs at all.
malaccamax said:
Guessing its reliability in a harsh environment - lot of load going through when you hit a pothole. They would give a sports car a LOT more boot space though. One reason Alpine is using hem for the next A110
Wow! You're correct - https://www.autocar.co.uk/car-news/new-cars/alpine...So, they are being introduced into the industry. Love it!
Jonny_ said:
I'd guess it's a combination of unsprung weight, cooling (usually via some sort of liquid coolant, rather than just air), longevity of cables (near constant flexing leading to mechanical fatigue), longevity of the motors themselves (would be subject much harsher vibration than a chassis-mounted motor), and probably quite difficult to package along with mechanical brakes.
As one of the previous posts points out, current EV motors are so compact that there's not much to be gained in terms of packaging through making them wheel mounted.
You would also need a reduction gearbox for each motor.As one of the previous posts points out, current EV motors are so compact that there's not much to be gained in terms of packaging through making them wheel mounted.
It'll be interesting to see how Alpine get on with the idea. It presents some pretty serious engineering challenges to overcome.
I'm dubious of that article's claim that it will make the cars lighter. By everything I understand of the engineering behind it, I'd have expected the opposite.
I'm dubious of that article's claim that it will make the cars lighter. By everything I understand of the engineering behind it, I'd have expected the opposite.
Edited by kambites on Thursday 21st August 18:52
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