This article is from 2014 so I thought it would be interesting to see how things are going.
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/
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
Surely they wouldn't move the motors into the wheels for actual full-size cars, right? 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.
>> 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.
Yeah, the unsprung weight, handling issue and reliability due to vibration and road impacts are problems. The amount of space it actually saves isn't that large. The Tesla motors essentially fit along the axels. Seems to me like a dead end.
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.
It also requires the motors to be larger because motor size mostly corresponds with torque output, not power output, and there is no gear reduction.
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.
It's not a bad idea for heavy trucks. LeTourneau heavy equipment used in-wheel motors from 1958. They built some monster earthmoving machines with that technology. It was Diesel-electric all-wheel drive, like a locomotive. Works fine at big scale, driving very slowly.
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]
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.
I'm also dubious. My first impression of the render is, where do the brakes go?
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
> I doubt an electric motor can provide enough braking power to stop any car at highway speeds in the distance required by most countries
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.
Some military vehicles have the brakes installed on the output shafts of the differential (see the hmmwv), but this would defeat the advantages of using hub motors in the first place.
I suspect you can only install these motors on the rear wheels so the front wheels can have normal brakes.
Yes, putting brakes on shafts of differentials is probably a pain to design for. Finding space would probably be impossible for most applications of this since the vehicles would probably use Forward Wheel Drive
With a PMDC electric motor, instant braking power is usually limited by the maximum current rating of ones mosfets/switches, as long as the vehicle is going fast enough.
Megawatts of braking for 1 or 2 seconds is very much doable, if designed for that.
Really? I'm no expert by any means, but I'm very much interested in this field. Could you point to any readings, examples on how to design a motor for such a load?
> I doubt an electric motor can provide enough braking power to stop any car at highway speeds in the distance required by most countries
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.
Hitting the brakes in a 2500 kg car at 100 mph generates a megawatt of braking energy (100 * 1607/3600 * 2500 * 9.8 * 0.9 = 984 kW). Plausibly sized hub motors can't handle this even momentarily.
Brake rotors have less thermal mass, but can get red-hot without damage.
How many actuations is the motor good for? The mosfets? Brakes are great, work for a very long time, and have lots of redundancy, they are also easy to fix without diagnosing issues with mosfets, windings, switches, and wires.
I've never been to china but what's their city road quality like?
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).
Sorry if this is a stupid question, but why would 70lbs in the wheel be any different from that same weight resting above the wheels, as in a normal car?
On the wheel, it's unsprung mass. That extra mass hurts the ability to the wheel & suspension to quickly respond to bumps, and causes energy to be lost into the suspension and tire.
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.
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.
Other people answered the hanlding question but there are also durability problems because of the additional shock loading introduced by the extra weight. You wouldn't drive a car without suspension at highway speed. It would kill tires or other components in short order.
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 wheel must change direction and move quickly to follow imperfections in the road surface. Increasing this weight decreases the wheel's ability to follow the undulations. Increased mass also contributes to centripetal force, inhibiting the wheel's ability to change yaw (turn). It acts like a gyroscope.
Afaik Magna designed a similar car concept 8 years ago already, but nobody picked it up. German car makers prototyped similar designs but they had to move to Chinese companies to get them actually built.
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.
Engineering at this level would require a somewhat intelligent engineering team and so I'm assuming this is their starting point and that they are expecting to significantly lower the weight.
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.
Between resistance from the chemical, oil and auto industries, their bought government, and the more favorable conditions in China, this might be another core tech we lose forever if we don't pay attention now.
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