Maker of In-Wheel Electric Car Motors Goes to China
spectrum.ieee.org
spectrum.ieee.org
It's hard to tell whether the subject of the article, Protean, is having success with the in-wheel motor. Their website is vague about who their customers are: http://www.proteanelectric.com/about-us/
At the end of the article they mention that China set a goal of 500,000 non-fossil fuel cars on the road by 2015, it looks like they probably got there: https://en.wikipedia.org/wiki/Electric_car_use_by_country#/m...
They also stated the goal is to have 5M on the road by 2020, which also looks like they'll get close since there were 352,000 sold in 2016: https://qz.com/972897/china-is-selling-more-electric-vehicle... and what looks like a 72% growth rate over 2015. That would mean (if the 72% growth holds, it could even increase):
Current: ~600K 2017: 600K sold 2018: 1M sold 2019: 1.72M sold
Total: ~4M
ps: also that design has no absorbing element in the wheel.. I would have done it differently.
However, it also avoids a lot of weight due to the lack of gearbox and axles, and efficiency losses in the gears. It can make sense especially in applications that require lower power output - for example virtually all solar cars use hub motors for efficiency.
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 ;-)
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.
Also the hub motors need to spin at the wheel RPM, which might not be in the peak efficiency for motors of that size or dimension, so it becomes a challenging engineering problem to try to match efficiencies with chassis mounted motors, which can be geared to run at their peak efficiency ranges.
Still problematic though.
LeTourneau built some huge off-road "land trains" for the U.S. Army. The biggest used multiple gas turbine engines and had 58 powered wheels.[1]
https://en.wikipedia.org/wiki/Active_Wheel
Their rival Continental have something a lot more interesting:
https://cleantechnica.com/2017/08/14/continental-new-wheel-c...
They have an aluminium disc with the rotor on the inside, not the outside, plus the 'spokes' of the wheel hold this oversized disc. The disc does not rust so it suits EVs where the brakes really should not be needed outside of emergencies, and when that happens you don't want the wheels to go round a few times clearing off rust before actual braking kicks in.
I am sure that this can also be combined with better aero so that the hub cap is designed to radiate heat rather than direct air in to the brake.
I imagine a future where vehicles have an extremely flat and low floor with the wheels pushed to the corner and definitely 'cab-over' to some extent as no bonnet needed. This will be great for users of wheelchairs, pushchairs and hand carts. Particularly if the vehicle drives itself and knows where all the potholes are and has the active suspension to deal with it.
A car can go without brakes in the rear, but front brakes are crucial in the front. This is specially true in emergency situations. I doubt an electric motor can provide enough braking power to stop any car at highway speeds in the distance required by most countries
A typical passenger car would have two such motors, while a heavy-duty or high-performance vehicle could have a motor in each of its wheels.
So the question of how reliable braking is achieved is still open.
This really isn't a problem. A hub motor should have no problem providing more stopping force than the tire/road interface can manage.
Heat is no problem either. Either dump the excess energy into a battery or just design a motor housing that can cool itself well enough. You have way more area and mass in a hub motor than in a brake rotor. You'd almost have to try to screw it up.
Maximum stopping distance laws are a complete joke. Anything can stop fast the first time. It's the 5th, 6th, 7th time that's a problem. Electric motors actually have the advantage in that situation because they fade more linearly than a hydraulic system.
The fall-off on braking performance on worn tires is crazy bad.
Brake rotors have less thermal mass, but can get red-hot without damage.
I suspect you can only install these motors on the rear wheels so the front wheels can have normal brakes.
Megawatts of braking for 1 or 2 seconds is very much doable, if designed for that.
Directly connect the motor to a bank of resistors (maybe use the same system in an electric car that is used for AC anyway so you don't waste the heat) or into supercaps, and if you want really enormous braking power apply the power in reverse. You will need brakes though for the last few km/h and for parking brake.
An extra 70lb at the wheel is going to make the already terrible durability of low profile tires worse (and you can't design for a smaller rim because you need space for the motor).
It's even a problem on trains - early electric trains had connecting rods between the motors and wheels just like steam trains. Later ones have the motors in the bogeys, but the motors are sprung and can swivel on the same axis as the drive gear.
Now replace the entire car with a 75lb electric motor in each corner and you've got the same problem but less extreme. It beats the crap out of the rim and tire. This wouldn't be too big of a deal but the hub motor all but forces you to use big rims and low profile tires which are already not that durable for reasons you can Google.
The tire wants to go in a straight line (inertia).
When a tire bounces over a bump, the springs push it back down onto the road. The heavier the wheel and the arms, the longer the tire has poor (or no!) contact with the road. No contact = no handling.
It's like hydroplaning on a dry road. Scary shit. Potentially fatal on a curve.
Technically it's easy, much easier to control, much cheaper, but you need the loading infrastructure (no hybrid, limited range) and strong political support. Since Israel cancelled their nationwide e-car project, nothing much happened since, but Tesla.
Having the engine there if these weaknesses are managed effectively would be quite disruptive to the industry. Maybe they won't make it work, but they obviously think they can.