>> In addition to the poor handling aspects of so much more unsprung weight, it would have to deal with much more vibration. Seems like a tough sell.
I did some work with hub motors a while back. The unsprung mass is still under debate, but moving all that mass to the corners of the vehicle is actually a good thing. I would think putting the inverter in the hub would make for terrible durability problems, but who knows.
Anecdote: The hub motors I wrote code for had integrated planetary gear, so they ran 6000rpm at the motor. The rotor was on a rather large bearing and we had all sorts of runout and alignment issues. It's was really hard to package in that space. We had peak power of 40KW per wheel, but you only got that for about 30 seconds before needing to cool off for 5 minutes (it was also water cooled, but not well - packaging again). Because of the heating and alignment issues, nobody could make much progress on doing the software calibration (motor mapping) on it. It was the only motor we had that required my new algorithm to get it up and running. It made light work of the calibration, compensated for the alignment and eccentricity issues, and ran the hell out of that thing. Sometimes I miss working on that stuff ;-)
Whenever I read car magazines they are always talking about the need to reduce unsprung weight. Supposedly, high unsprung weight causes a harsher ride - so this is not a given?
Depends. If you hit a bump or a pothole, you need the wheel to move vertically very quickly. But on smooth roads it's not a problem and having the mass at the corners increases the vehicles rotational (pitch, roll, and yaw) stability. I have not formed a personal opinion on it yet, so I listen to both sides. My suspicion is that the unsprung mass is bad and the arguments to the contrary are partly wishful thinking by hub-wheel advocates ;-)
I always wonder whether it is really inspiring weight, or the ratio of sprung va unsprung?
In an application I have lots of experience with, mountain biking suspension, the overall sprung weight relative to the frame/rideris so low that even doubling the wheel weight or cassette weight doesn’t really effect suspension performance. (Pedaling rotating mass is a different story)
In a car or truck, where the overall mass of the car is very large, adding more unsprung mass might not matter so much. The car still has a lot more inertia than the wheels. You should be able to make up for the heavier wheels with better suspension valving and improved shims. Problem being that most factory standard suspension is really bad.
The unsprung weight thing is usually a bit overstated, though it is true. It doesn't sport luxury cars from sometimes having extremely heavy wheels for the sake of looks at times, for instance.
I did some work with hub motors a while back. The unsprung mass is still under debate, but moving all that mass to the corners of the vehicle is actually a good thing. I would think putting the inverter in the hub would make for terrible durability problems, but who knows.
Anecdote: The hub motors I wrote code for had integrated planetary gear, so they ran 6000rpm at the motor. The rotor was on a rather large bearing and we had all sorts of runout and alignment issues. It's was really hard to package in that space. We had peak power of 40KW per wheel, but you only got that for about 30 seconds before needing to cool off for 5 minutes (it was also water cooled, but not well - packaging again). Because of the heating and alignment issues, nobody could make much progress on doing the software calibration (motor mapping) on it. It was the only motor we had that required my new algorithm to get it up and running. It made light work of the calibration, compensated for the alignment and eccentricity issues, and ran the hell out of that thing. Sometimes I miss working on that stuff ;-)