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All wheel drive

Discussion in 'Tesla Motors' started by TEG, Jun 1, 2007.

  1. TEG

    TEG TMC Moderator

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    The Roadster is rear wheel drive.
    Tesla has mentioned that 0-60 times are "traction limited" because the rear wheels would slip if they tried to accelerate much faster.
    0-60 time could be (theoretically) improved if they had some powery deliver to the front wheels as well.

    Tesla has said that the Roadster ESS is able to soak up all the regen braking they get from the eMotor.
    When you hit the brakes, the weight distribution shifts to the front tires, and brake portioning will have more braking going to the front calipers.
    So, much braking energy (particularly under hard braking) is wasted as heat on the front discs. If there was a regen system on the front wheels it could possibly capture more regen energy.

    Now, with all that said, I still think they are doing the right thing with the roadster. The Lotus chassis wasn't designed for a lot of mechanism up front, and having no drive shafts there helps keep a "pure" steering feel on such a light, small sports car.

    Whitestar, on the other hand, could probably benefit from AWD for the above reasons, as well as for foul weather traction.

    I wonder if Tesla is considering it.

    It would think a small self-contained system could be a very marketable item. A small eMotor with Ultracaps, that only charges from regen, and only provides eBoost during hard acceleration. It wouldn't be a primary drive source... Only an aux source for energy "recapture" and "playback" during hard braking and hard acceleration.
    The main source would drive one set of wheels, and the aux unit would drive the other. Toyota does something a little like this with their AWD Highlander Hybrid, although in their case both electric drive motors share the same traction battery pack.
     
  2. WarpedOne

    WarpedOne Supreme Premier

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    Just a reminder: electric motor in "generator mode" (regen braking) is just as powerfull as in "normal mode".
    Putting small (weak) eMotor infront would mean it could capture only small amount of regen energy at braking.

    The best option would be to have two same eMotors, one front and one rear, each with fixed transmission - single speed, no gearbox with electronic intelligence monitoring front/rear power delivery and regen. I think this will happen arround 2015, when first real EV SUVs are born.

    Edit: "first real EV SUVs" meaning 150Hp+, 100mph+, 300miles range, 5-seaters
     
  3. TEG

    TEG TMC Moderator

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    Toyota's AWD Highbrid Highlander has something a bit like what you describe:
    LexusHybridBatteryMonitor.jpg
    (But it has a gas motor up front as well so you never need to plug it in)

    Their system works very well.

    Warped one wrote:
    Highlander Hybrid meets all those criterion but they put a gas engine instead of extra batteries.
    If it weren't for the Cobasys NiMH restrictions it would have made a great replacement for the old Rav4-EV.

    Highlander Hybrid AWD front electric motor (65hp):
    http://www.hybridsynergydrive.com/en/electric_motor.html

    Highlander Hybrid AWD rear motor (65hp):
    http://www.hybridsynergydrive.com/en/rear_electric_motor.html

    Plus they have a 200hp+ V6. Theoretically they have 200+65+65=330hp, but they rate the whole system at only 270hp I think because their little battery can't drive both e-motors at full output continuously. In any case, for an SUV, the thing really scoots.


    By the way, check this out:
    http://www.uwspace.uwaterloo.ca/bitstream/10012/2735/1/Thesis_for_formatting_review+-+revised.pdf
     
  4. Michael

    Michael Member

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    That would be such a shame. I had already started saving for the WhiteStar with an assumption that 4 wheel drive will be available at least as an option!
     
  5. TEG

    TEG TMC Moderator

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    More on AWD:

    How about this article on the Carrera 4?
    www.roadandtrack.com/article.asp?section_id=6&article_id=2595
    …”the new C4 understeers less, feels sportier and laps the Nürburgring as quickly as the Carrera 2 despite being 121 lb. heavier. ..”

    Lamborghini also builds race worthy street cars, and offers AWD…
    www.seriouswheels.com/cars/top-2006-Lamborghini-Murcielago-LP640.htm
    “Just like its predecessors, the Murciélago LP640 features permanent four-wheel drive, based on the reliable Lamborghini VT (Viscous Traction) system. The system is self-governing and does not feature any electronic controls. The drive force is usually divided between the front and rear axles in the ratio of 30 to 70. An independent control circuit adjusts the distribution of the drive force depending on dynamic oscillation, weight distribution and the relative friction factor in perfect synchronization with the Visco clutch. In extreme cases, up to 100% of the drive force can be applied to a single axle.”
    (The AWD Murciélago reportedly does 0 to 60 in 3.4, so the AWD can’t be hurting it much in a straight line at least)

    www.clublexus.com/forums/archive/index.php/t-151157.html
    …”Those of you who believe that AWD cars are designed primarily for driving conditions that are less than optimal are greatly misinformed about this marvel of automotive engineering. Don’t confuse AWD with off-road, 4-wheel drive systems. AWD systems simultaneously and continuously “sense” road conditions under each of the four wheels and apply proportionate power as appropriate. In addition to sure-footedness on slippery roads, AWD generally improves/enhances handling and performance. That’s why Audi Quattros were banned from racing circuits in the late `80s (RWD vehicles could not touch them), and why Porsche and Lamborgini now produce vehicles that feature AWD. “…

    findarticles.com/p/articles/mi_m3165/is_4_41/ai_n13675707
    …”Grip And Grin …
    Audi insisted AWD had another advantage: improved handling - even on dry tarmac. The auto maker made its point over the years by dominating several forms of racing, sometimes thrashing 2-wheel-drive competition so emphatically that AWD was banned.
    In the real world, engineers and enthusiasts agree AWD usually is superior to either front-wheel drive or rear-wheel-drive in wet, ice and snow, but they debate AWD’s ability to “improve” handling or cornering behavior on dry roads.
    Mechatronic technology, until now largely unheralded, advances AWD to a new level of dynamic ability far beyond its reputation as a traction enabler for foul-weather driving.
    That technology has a name: torque vectoring. The engineering that enables torque vectoring is not uncharted territory, but a new showcase, the Super Handling All-Wheel Drive (SH-AWD) system that’s standard for Honda Motor Co. Ltd.’s ‘05 Acura RL sedan, has grabbed the attention of driveline and chassis engineers and buyers.

    Whether in low-traction conditions or in the dry, many who have driven the Acura RL say SH-AWD’s performance adds an eye-opening new dimension for AWD. Toss the RL into a corner and bury the throttle: The aggressive torque transfer between rear wheels creates the driving sensation of a car on rails.
    The RL’s torque-vectoring system has auto maker and supplier engineers buzzing. Some debate the technology’s ultimate impact from a volume perspective, but most agree torque-vectoring is a formidable new advance in AWD development.
    More telling, perhaps: Almost every auto maker and AWD-connected supplier is actively evaluating torque-vectoring AWD technology.
    …etc…”

    Subaru makes a big deal about all of their cars being AWD:
    www.drivesubaru.com/SubaruDrive-Sum02/AWD-Demystified.asp
    www.subaru-global.com/about/awd/physics/index.html
    www.subaru-global.com/about/awd/cornering/index.html
    …”Conversely, with rear wheel drive and front wheel steering, turning is sharper, but somewhat less stable.
    Apply too much throttle in this case, and the car will tend towards oversteering in corners.”…

    Power on oversteer isn’t for everyone. I love “fishtailing” (oldschool term for drifitng) a RWD car on a track, but most people are better off not hanging the rear end out in a wet intersection on the way home from school with the kids. The Roadster isn’t a family car, but Whitestar may well be.
     
  6. WarpedOne

    WarpedOne Supreme Premier

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    Overstear: it scares passangers
    Understear: it scares the driver
    "Train": no one is scared :)

    Classic AWD is plaqued with problems regarding power and torque transfer. Delicate differentials, clutches, electromechanical couplings etc. But its advantages are evident. Hub electric motors are ideal for AWD but come with their own set of problems. 2 Tesla's drivetrains wheigh less then most bigger ICE engines and transmission. I would be very interested in Tesla's view on feasbility of such configuration.
     
  7. danny

    danny Administrator

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    I have been investigating this subject myself. I like to have clear answers but so far i cannot figure out which is better on dry track, rwd or awd.....
    So far i've gathered this:
    RWD-less complicated, more maneuverability, better steering fee, lighter, cheaper
    AWD-More grip, advantage in pretty much every situation besides dry road, easier to get power down, power lost during conversion to wheel horsepower, heavier, loss of steering feel(not sure how much) due to differential(or something like that).

    I've asked why if awd is better why they don't use it in racing. But I don't get a clear answer on that from people on forums. I would love to talk to some engineers about it and see what they think. Its hard to imagine that AWD won't take over, i mean 2 extra wheels just seems to make sense to me, however this will depend on whether they can continue to make advanced awd systems and computers.

    RWD may be more fun but my question has been about which is fastest.
    What is interesting is how awd systems are getting very advanced sending torque from front to back and i think they might be sending torque from side to side. What would be interesting is to have a car where you can customize the system for where you are and the conditions. And even be able to push a button and get rwd if you feel like drifting. Then you would be able to program the awd for what would be fastest.
     
  8. Michael

    Michael Member

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    I have read that there is a lot of interest being generated with other vehicle makers in regards to the vectoring method used on the SH-AWD system in use by Acura.

    Seems like somehing that would more easily be accomplished using individual wheel motors instead of gears. Now if only those motors could be kept from contributing to unsprung weight (inboard). I also wonder if making something this seemingly complicated is actually simpler utilizing electronics or is it still too complicated?
     
  9. WarpedOne

    WarpedOne Supreme Premier

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    They could be mounted onto the chassies so they do not contribute to unsprung weight at all. Like inboard disk brakes here http://teslamotorsclub.com/forum/index.php/topic,599.0.html
    In this way they also suffer much less vibration and shocks, they can be liquid cooled etc.

    Perfect configuration?
     
  10. TEG

    TEG TMC Moderator

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    Yeah - 4 inboard motors (with a disc brake attached to each motor output shaft) sounds good to me.
    You could have one long battery box with 2 motors and 2 brake discs at each end. You then just run 4 half shafts to the wheels, add a few suspension bits (torsion bar + shock absorber) and away you go.

    It fits well with the idea of keeping the weight low and near the center of the car. Also to keep the weight unsprung.
     
  11. WarpedOne

    WarpedOne Supreme Premier

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    Should I / we patent it? :D
     
  12. TEG

    TEG TMC Moderator

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    I bet it has been done before.

    Here was an article that more or less discusses the concept:

    http://www.evworld.com/article.cfm?storyid=914
    "The most significant difference between the GM EV1 and its prototype (the Impact) was that the Impact had two inboard electric motors,
    each driving a front wheel, while EV1s have a single large inboard motor driving both front wheels though a conventional differential.
    The main concern that caused the change was the possibility of sudden motor failure throwing the vehicle off the road or into the path of oncoming traffic. "
    ...
    "the ride could be improved further by bringing the disk brakes inboard.
    This is far from novel, either on the track or on the road.
    One reason why the Jaguar XJS had such a good ride for a sports car was its inboard rear brakes."

    and this:

    http://www.autoblog.com/2005/08/24/mitsubishi-testing-lancer-evo-with-in-wheel-electric-motors/
    " Alistair @ Dec 18th 2005 11:06PM
    You could use the four-wheel electric motors to handle ABS, stability control, and traction control.
    You could also drop the mechanical connection between the motor and the rear wheels to save weight.
    Inboard electric motors with driveshafts would sidestep the (unsprung weight) issue..."

    and this:

    http://www.cypenv.org/smf/index.php?PHPSESSID=f0a1465838ab66a32cfed3d71a18feb8&topic=61.new
    "Re: Citroen and Peugeot HDi Hybrid
    « Reply #4 on: March 12, 2006, 02:56:36 am »
    having four inboard electric motors (important to reduce the unsprung weight) reduces the complex and heavy mechanical transmission (gearbox/differentials)
    with a computer optimising the relative speeds for each wheel under any given conditions - especially good for optimum traction in snow/ice, dosing that
    "lotsa torque" to avoid any slippage."

    I always assume that everything is already patented, so knock yourself out if you want to test that theory.
     
  13. WarpedOne

    WarpedOne Supreme Premier

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    I suppose this could happen if the motor failure would block the wheel. I am sure this problem could be solved with a simple centrifugal clutch. One per wheel.
     
  14. TEG

    TEG TMC Moderator

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    Someone else pondering "inboard hub motors":

    [​IMG]
     
  15. AGR

    AGR Member

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    Any AWD vehicle requires an additional differential for the front axle (assuming it was originally a rear wheel drive), it also requires an additional "power divider" between the front and the rear axle. Usually the weight of the vehicle increses by a few hundred pounds.

    If a manufacturer is producing a car with "massive power" and is looking for an additional claim to fame they will consider an AWD version. Porsche Carrera 4 or a Lambo has it been mentioned.

    Under adverse climatic conditions (snow) AWD vehicles are very popular, and useful in certain circumstances. Mercedes-Benz / BMW / Audi all have AWD versions of several of their models, and everyone has a different name.

    More than 1 motor, who would deal with the product liability if the elctronic controller for the motors develop a glitch, and the vehicle lost control because 1 motor was no longer synchonised with the other.

    Inboard brakes, most consumers have absolutely no desire to pay excess labor charges to do a brake job on any vehicle, inboard brakes by their nature create additional labor charges. On many high performance cars the discs have become so large (14 inch diameter) they are now ceramic discs, and the vehicle has 18 inch wheels just to clear the disc / caliper.
     
  16. WarpedOne

    WarpedOne Supreme Premier

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    Who would deal with the product liability if ABS/TC controller goes nuts and blocks both left wheels on a highway?
    And then almost all cars have ABS / TC / you name it. What is so special about ** that ** electronic controler?

    If break pads last for 150-200k miles I do not care much about ** doubling ** the cost of brake jobs.
     
  17. AGR

    AGR Member

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    ABS in and of itself does not apply the brakes on any car, you still need to push on the brake pedal to apply the brakes.

    Traction control will apply the brake on the spinning wheel, when one of the wheel loses traction. Same with an Electronic Stability Program which will apply the brakes selctively if a vehicle initiates a sideways skid.

    Mercedes a few years ago developed SBC brakes which was literally brake by wire, it was installed on a few models, and subsequently dropped.

    On the majority of high performance cars brakes pads, and tires have a brief life expectancy, front pads last 30K miles front discs 60K miles. There is a reason these cars have massive brakes.

    If a vehicle with an electric motor would have "regen braking" which is comparable to a downshift up to a point...you still need the brakes.
     
  18. TEG

    TEG TMC Moderator

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    I suspect that rumors of high cost for inboard brake jobs is really just concern that it is different, not inherently harder.

    Actually with inboard brakes you don't even have to remove the wheel(s) which normally takes extra time.

    As long as you have a proper lift (or pit) to make sure the car is over your head, there isn't much trouble replacing pads on inboard disc brakes.
    Yes, changing the rotors is a bit more trouble, but you don't have to do that as frequently as pad replacement.

    And as was mentioned you shouldn't need to work on the brakes much because the regen does a lot of the work instead.
     
  19. vfx

    vfx Well-Known Member

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    I drove the Ebox in it's prototype stage. There was a slide lever for setting the regen amount. Slide it one way and the brakes did miost of the stopping-work. No Regen.
    Slide it the other way and the instant you let off the pedal the car would come to a near brake slamming stop. There were no brakes working at all. Just motor resistance. A very smooth VERY quick stop. Like riding your bike into deep sand.
     
  20. shark2k

    shark2k Member

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    Did a search and found this so I figured it would be better bringing this thread back to life than start a new thread. I was wondering if anybody had any ideas how AWD would affect efficiency. To be more specific I am wondering if having an AWD car would result in lower range/more power consumption since all the tires are being turned.

    I was wondering this because I was thinking how it would be really nice for the Model S to have AWD (or at least an option for it). I live in Jersey (as it says under my name) and we get snow in the winter so I was thinking how AWD would be nice for the winter. I figured with RWD or FWD during snowy/icy weather the would probably be more apt at losing power quickly if you get stuck spinning your tires. I figured an AWD car would help reduce this by the fact you have all 4 wheels to get traction, not just 2.

    -Shark2k
     

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