Pkoning, am first time hearing about vehicle with motor on wheels and I don’t know how centralized control is possible for all independent motors. Any idea? Why you are telling that efficiency is not going to change-any particular reason.
I don't remember speaking of efficiency. But electric drive efficiency is pretty high; there's not much margin between today's numbers and 100%. The area for improvement is in batteries; the problem there is that it's not clear how.
As for control, what's the problem? For starters, each wheel wants to have torque delivered to it. Then you can look at traction control (anti-skid) which of course is inherently a per-wheel activity; conventional cars have to approximate that because they have centralized drive, and per-wheel drive makes it much easier.
If you're not doing traction control, the whole thing is trivial. Consider that electric trains (the motor car style) have had per-wheel drive for close to a century.
Wow! Everything about this prototype sounds great – thanks for sharing, Ann Thryft! The motors in this EV's wheel are no doubt an exciting development, but it's the use of lightweight plastics that really give the extended drive range of this vehicle a serious boost. And because plastics are also known for their strength, we can expect this automobile to be safe in addition to fast and efficient. Can't wait to see this one in production in 2014! PS College for Creative Studies (CCS) students in Detroit have for years been "dreaming" fly by wire technology like this for the wheels! Here you've found it in reality and shared it with us. We will share it with them!!!
Jeff, you're right that the design approach isn't novel. However, as several commenters (including me) have pointed out below, those early cars with motors in their wheels weighed an insane amount due to battery size and weight, nearly two tons.
RobKrebs, thanks for the enthusiastic response. And the reminder that the point of the article wasn't EV design but the range extension made possible at least in part by plastics. OTOH, you might want to let those automotive design students know about the history of the motors-in-the-wheels idea, which can be found sprinkled throughout these comments.
Torque Steer is not a product of giroscopic forces, but the "torque-steer" you felt in the steering wheel of your Honda front wheel drive is a different phenomena, arising from manufacterer using different lenght (and mass) half shafts (unequal-lenght shafts).
Now, an electric motor installed completely inside the wheel will put a much heavier rotating mass than using a motor centrally or inside the car towards the chassis. Many unsuspecting owners have taken the absurd Too-Large wheel vogue, by going to 19", 20" or even larger aluminum wheels with correspondingly low tire profiles (not always keeping the external overall diameter). The deleterious effect on acceleration and fuel economy is not small. Even a few pounds of weight when located in the outer portion of the rotating assembly, will represent an unusual increase in rotating inertia, penalizing acceleration and braking more than other things, like unsprung weight, that mainly affects tire adhesion on uneven pavement. The only way to avoid a large penalty would be to keep rotating mass as lowest as possible, maybe by using advanced electric motor designs to keep inertial rotating mass and inertial moment to the minimum. In the old days, racers used to say that every pound added in a tire-wheel was "like adding ten or so pounds in car weight".
There are some articles on this subject, like SAE Paper Number: 900760. Amclaussen.
I have to disagree with the cause of the torque steer mentioned previously. Torque steer is an effect that arises from one wheel absorbing all the engine torque in a turn. This happens as a result of the differential putting all torque to the outer wheel. If the car had a posi-traction type differential that delivered equal torque to the driving wheels there would be no torque steer.
Presumably with a wheel motor on each of the 4 wheels the onboard computer would monitor relative rotation rates and torque demand from the driver to insure all wheels were optimally engaged in either breaking or accelerating.
The rotating mass of the wheel has little effect on the overall forces required to brake and accelerate. Rotational mass effects are small comared to the overall forces involved in accelerating and decelerating a 3500 lb car.
The unsprung mass of the wheel/motor/tire combination has the most effect on the suspension characteristics. A lower unsprung mass compared to the mass of the vehicle is desirable for smoothing the ride. In this respect, I believe the lower tire mass is intended to compensate for more wheel diameter. The overall effect should be to reduce the weight of the wheel and tire. Unfortunately as my new Hyundai Genesis demonstrates, the very low profile tires create a very stiff suspension overall since there is considerably less flex in the tires.
or purchase the SAE paper mentioned by me above. If you still disagree, maybe you are referring to another different thing. Otherwise, you'll have to go and tell a lot of SAE guys they were wrong for a lot of time! :)
(it could be that you are referring to a lack of centering of the steering wheel during a turn when accelerating at the same time, but that is certainly not called "torque-steer").
The "pull" to one side you feel at the steering wheel when accelerating hard is what is called "torque-steer". What you are probably referring with your Honda (a sensation when accelerating AND turning) is NOT universally recognized as "Torque-Steer".
What the car community calls "Torque-Steer" is felt mostly in higher powered Front Wheel Drive vehicles when acccelerating hard from standstill or low speeds. It's causes are not fully corrected by the differential type, but with a better designed transaxle and driveshafts set geometry, rigidity, and mass distribution. Not all front wheel drive cars use equal-lenght shafts and favorable geometry struts, and since it is most notable in higher powered cars with more torque at launching RPM's, and is often incorrectly attributted to a "powerful car" by car aficionados, it is not corrected in all models. Why don't you take a look under your Honda to asess if it has equal lenght shafts or not? Another big player in Torque-Steer is the Strut and Steering Knuckle geometry (a good introductory discussion to this is at http://www.caranddriver.com/features/ford-revoknuckle-and-gm-hiper-strut-explained-tech-dept article. Different left side wheel vs right side wheel "Scrub radius" often result from unequal lenght halfshafts car design.
And regarding limiting slip differentials, Car and Driver even critizised its use in FWD cars stating that "And when a limited-slip differential is employed in a front-driver, these effects are sometimes amplified as the diff decides which wheel to favor with power..." (http://www.caranddriver.com/columns/slowly-but-surely-horsepower-is-killing-front-drive ). This article mentions something about that sensation you probably felt and believed to be "torque-steer" when talking about the Dodge SRT-4 lack of steering wheel centering or more properly, Self-centering force when turning and applying a large torque at the same time during a turn. Please read more on this and we can discuss it better as long as all of us use the same term for the same concept. Respectfully, Amclaussen.
Well said Bunter (Dennis), Unsprung weight is important (independently of what some guy at Lotus recently said)... But there are other things that need to be considered here. The matter of rotational mass (Polar moment of inertia) is one of them. Maybe the diameter of the motor assembly is small or the heaviest component is placed inside (either magnets or coil windings could be placed inside or outside depending on motor type selection, varying the rotational inertia).
In a perfectly flat road (never saw that where I live), placing the motors directly into the wheel is of little consecuence, but I guess that in a world full of huge potholes, the design of the tire will have to take into account a larger bump absorption capability than present day designs provide. Your suggestion about using a short shaft seems to me the best compromise perhaps. Amclaussen.
In straight line acceleration the Honda with 265 Hp does fine. I could not detect any problems with unequal torque being applied to the front drive wheels. The steering effort to keep it straight was negligible. The acceleration is very impressive in a relatively light car. I was referring to the Honda EX V6 with a 6 speed manual transmission, 2 dr coupe I bought new in 2005. In a turn and under hard acceleration the car would pull very strongly in the direction of the turn, so much so that an inexperienced driver could easily be overwhelmed and create an issue. It surprised me more than once and took some getting used to.
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