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Ivan Kirkpatrick
User Rank
Platinum
Re: Now we are talking same language!
Ivan Kirkpatrick   3/4/2013 3:42:41 PM
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I remember the torque steer on the honda as being in effect in either direction of a turn.  Left or right the car would pull significantly in the direction of the turn.  I attributed this to the outside wheel receiving more if not all of the engine torque.  Perhaps front wheel differentials are different than the rear wheel ones I used to deal with.  the differentials I am familiar with only supply equal torque when the rotations of the output shafts are identical.  If one wheel is rotating slower than the other in a turn then the torue is essentially applied to the faster wheel only.

Your explanation would indicate the torque from the engine is applied equally at least as far as the differential output shaft and varous other factors produce the torque steer effect.  

I guess there are still some issues I don't quite follow regarding the front wheel differentials.  the papers you referred to would seem to indicarte that torque steer is a usually subtle affect based on steering geometry and torsional stiffness of the drive train on each wheel.  I thought it was a rather direct function of the differential.

Amclaussen
User Rank
Platinum
Now we are talking same language!
Amclaussen   3/4/2013 3:31:11 PM
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I am confident that the loss of self-centering (restoring) force on the steering wheel that you previously referred as "torque-steer" is a result of front wheel drive non-optimal geometry when subjected to simultaneous turning and large torque application.  It is the same sensation referred in the Car and Driver article when describing the lack of return-to-center of the steering wheel in the powerful dodge SRT-4 that did not returned to center when accelerated. That the SRT-4 did NOT pull in the same direction of the turn means that in that respect, the overall steering design of the Dodge is better done than that V6 Honda, no doubt!

The sensation is VERY unpleasant, to say the least...  specially when the lock to lock ratio has many turns in it.  I clearly remember one of my first cars, a 2-door Valiant Duster (the mexican version of the Plymouth Duster) with the slant six 225 engine, manual steering with 24:1 ratio... in a slow turn, if I suddenly applied more than half accelerator without holding the steering wheel, the damn thing turned the steering into the turn until reaching the lock end!  It turned out that that was a new model platform, and that the factory did a mistake and set the front suspension on entirely wrong settings.  Once corrected camber/caster and toe (partially), that maddening tendency was subdued but not entirely fixed.  Best Regards.

 

Ivan Kirkpatrick
User Rank
Platinum
Re: Torque steer true causes.
Ivan Kirkpatrick   3/4/2013 2:21:58 PM
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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.

I will read the papers you are referring to.

Amclaussen
User Rank
Platinum
Re: Novel design approach, will still need to address several things.
Amclaussen   3/4/2013 2:16:02 PM
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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.

Amclaussen
User Rank
Platinum
Torque steer true causes.
Amclaussen   3/4/2013 1:57:04 PM
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IVAN: I don't want to start a discussion on what is Torque-Steer, so I respectfully invite you to read a lot more on the subject. You can start with Jens Dornhege (Ford Werke AG) paper on this at http://web.mscsoftware.com/support/library/conf/adams/euro/2002/papers/005_EUC_008_FORD.pdf

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.

 

Ivan Kirkpatrick
User Rank
Platinum
Re: Novel design approach
Ivan Kirkpatrick   3/4/2013 11:58:28 AM
NO RATINGS
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.

 

Amclaussen
User Rank
Platinum
Re: Novel design approach
Amclaussen   3/4/2013 11:42:38 AM
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.

Ann R. Thryft
User Rank
Blogger
Re: Everything about this prototype sounds great
Ann R. Thryft   9/20/2012 12:09:42 PM
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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.

Ann R. Thryft
User Rank
Blogger
Re: Novel design approach
Ann R. Thryft   9/19/2012 3:16:42 PM
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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
User Rank
Iron
Everything about this prototype sounds great
RobKrebs   9/19/2012 1:34:22 PM
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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!!!

For more on lightweight plastics in cars, visit: http://www.facebook.com/plasticcar and http://www.plastics-car.com/Todays-Automobiles/Automotive-Safety/Lightweight-Plastic-Fibers.pdf

Rob Krebs, Market Innovations, American Chemistry Council

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