TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Elon Musk: Model X will have 4 wheel Drive!

Discussion in 'Model X' started by de704, Nov 2, 2011.

  1. de704

    de704 XP268

    Joined:
    Dec 6, 2009
    Messages:
    355
    Location:
    Lawrenceville GA
    I just listened to the "Tesla Motors, Inc. Third Quarter 2011 Financial Results Q&A Conference Call" (http://ir.teslamotors.com/).

    Elon Musk said the Model X will have 4 wheel Drive!

    Woo Hoo!!! :biggrin:


    Your Thoughts?!
     
  2. AnOutsider

    AnOutsider S532 # XS27

    Joined:
    Apr 3, 2009
    Messages:
    11,923
    Wouldn't have it any other way! Being so used to Audi, I hope their system is comparable or better.
     
  3. JRod0802

    JRod0802 Member

    Joined:
    Dec 15, 2010
    Messages:
    661
    Location:
    Boston, MA
    I believe Elon said something like "It will be the best four wheel drive in the world" during the conference call.
     
  4. dpeilow

    dpeilow Moderator

    Joined:
    May 23, 2008
    Messages:
    8,572
    Location:
    Winchester, UK
    Of course...
     
  5. AnOutsider

    AnOutsider S532 # XS27

    Joined:
    Apr 3, 2009
    Messages:
    11,923
    Is this supposed to be standard or "available"?
     
  6. Robert.Boston

    Robert.Boston Model S VIN P01536

    Joined:
    Oct 7, 2011
    Messages:
    7,842
    Location:
    Portland, Maine, USA
    I understood it to be "available."
     
  7. NigelM

    NigelM Recovering Member

    Joined:
    Apr 3, 2011
    Messages:
    13,257
    Location:
    Sarasota, FL
    I had read in one of the reports that 4 wheel drive will be an option.
     
  8. PopSmith

    PopSmith Saving for a Model 3

    Joined:
    Jan 22, 2010
    Messages:
    608
    Location:
    Utah
    Hopefully that means it's torque vectoring. Given that statement (which I expect from Elon) I'd love to see all wheel torque vectoring similar to (hopefully even better than) Audi's quattro or Acura's SH-AWD.
     
  9. VolkerP

    VolkerP EU Model S P-37

    Joined:
    Jul 6, 2011
    Messages:
    2,455
    Location:
    Germany
    The 4WD option possibly is not available right from the start of Model X. Tesla might chose to start production as early as possible, and ramp up to volume while development of the 4WD option is under way. They need to add a 2nd motor to drive the front wheels, an additional PEM, and they need to beef up the control software to distribute power according to drive situation.
    If Model X comes to customers late 2013, I guess that 4WD is available from mid 2014. No, I have no facts on that, just guesswork.
     
  10. NielsChr

    NielsChr Member

    Joined:
    Oct 18, 2011
    Messages:
    264
    Location:
    Denmark
    4wd in a electric car could be "simple" to build - it dosn't even require at new or extra PEM og a "power disribution system" - the way electronic motors works in combination they will automatically distribute power to the wheels in need of power...., they (the 2 motors) will drag the power needed - the wheel with most resistance will drag the most power, if front or back is spining the other wheelset will automatically take/have more power - this is by physic lows, no need to advanced electronic handling this.
    If you have a electric motor, and try stoping it turning, the motor will try work agains this change by draging more power, if the motor is spining without any resistance, it will drag less power.
    So a 4 wheel drive EV will basically be a matter of adding a second motor to the front wheels and redesign the wheel base/suspension. When this is done, you need to deside 1 out of 3 options:

    1. you chose to connect in serial, your 2 ev motors will share the electrical voltage evenly under normal situations by 50%/50%, both having the same amp - but if one motor for any reasoon requires more torqe it will "take" more voltage (and thereby power)
    (this will ofcouse only work if the pressent PEM does not use motor/whell spin feedback in such case the PEM need to control the power distribution)

    2. you chose to run them in parallel, they will both have the same voltage, but will split the amp in a 50/50 - if one motor for some reasoon reqire more torqe, it will try drain more power (amps) leaving less amps to the other - as far as I know Telsa is amp controlled, so this will be the most likely setup, of option 1 or 2
    (this will ofcouse only work if the pressent PEM does not use motor/whell spin feedback in such case the PEM need to control the power distribution)

    3. you add a second PEM witch give the abbility to dynamically (e.g. by the touchscreen) distribute power to front or rear in any torqe combination they like.....you chose while driving 10/90 or 90/10 with a slider like the sun roof... :).
    (this option is as far as I can see required if the PEM does recive motor/wheel spin feedback to control need of power, and in such case it could be difficult to control correctly - basically the 2 wheels could drive with different speeds and wear your tyres fast, and waste a lot of energy)

    if option 1 or 2 is used, tesla could by design chose how tourqe spilt should be by default when all whells are force with same drag (runing on a road), simply by having different gearings front/rear - thereby insure that in normal driving the front whell will e.g. drag aprox 40% while rear wheels will drag 60% - if front or rear wheel "meets" more resistance (or less) it will automatically adjust the torqe ration..you do not need to change any thing

    if option 3 is used, I will suspect they will use same gearing in front/rear and control the torqe spilt fron back/rear by software - thereby having the abbillity to let the driver dynamically select witch ration they like e.g. 20/80 or 75/25 - it will simply be a matter of software. (btw. the 2 PEM's will not nessesarlly need to be as big as the one in Models S, they could go for 2 smaller, say 600 amp each - wich will be 1200 amp together (same amp as models S sport))

    if price is a matter, tesla should go for the option 2, while if they aim for the most flexible solution they should go for option 3 - sine the PEMs could be smaller, it will not nessesarlly be that mutch more expesive in HW, but will cost more to develop and test/fine tune.

    all options could by drivers choise offer 100% 2WD rear or back at any time - option 3 will reduce total horse power, while option 1 or 2 could be with full horse power in 2wd since the limitation is most likely in the PEM and the cooling of the EV motors
     
  11. VolkerP

    VolkerP EU Model S P-37

    Joined:
    Jul 6, 2011
    Messages:
    2,455
    Location:
    Germany
    Chris,

    I'm afraid I have to point to some fundamental flaw in your solution 1+2. Your description works for DC motors. But the drive motors run on 3 phase AC.
    The PEM controls frequency + voltage amplitude. The frequency is in sync with motor rotation and, through fixed gear set, with wheel rotation. When driving curves, front wheels take bigger radius than rear wheels (and outer wheels bigger than inner wheels, but that is handled by differential gear).
    The frequency of the two drive motors will go out of sync and you want to have it that way or loss of traction is imminent.

    That leaves us with solution 3: two different PEMs.

    I don't see an advantage in splitting the Model S Sport 1200A capable PEM into 2x600A. Model S Sport 4.5s acceleration 0-60mph is not traction limited, but torque/power limited. 2.5s would be traction limit. We need more watts to the wheels. To maintain 1g acceleration at 60mph in a 4000lbs car, you need >500kW.
     
  12. Robert.Boston

    Robert.Boston Model S VIN P01536

    Joined:
    Oct 7, 2011
    Messages:
    7,842
    Location:
    Portland, Maine, USA
    Niels' post raised a related question in my mind: how does Tesla replicate the role of the differential gear in the Model S? The two wheels certainly can't be forced to rotate at the same speed.

    Does the answer to this question then answer the question of how a 4WD system could/should work?
     
  13. doug

    doug Administrator / Head Moderator

    Joined:
    Nov 28, 2006
    Messages:
    15,912
    Location:
    Stanford, California
    Err... via a differential (transaxle). I.e. mechanically. Similar to the Roadster.

    Not really since Tesla's solution will clearly be electrical (meaning no driveshaft down the spine). Likely they will have a second inverter for the front motor.
     
  14. Kevin Harney

    Kevin Harney Active Member

    Joined:
    Apr 30, 2008
    Messages:
    2,052
    Location:
    Herndon, VA
    I think they must have an air or electrical lock between the wheels on each axel which can be activated when necessary in order to have the "most advanced 4WD system" that Elon talks about. It does not get more advanced than controlling each wheel individually for optimum traction . In 4WD systems it is often advantageous to have the wheels on the same axel FORCED to operate at the same speeds while off road. Yet as pointed out you need them to operate at different speeds on road.
     
  15. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

    Joined:
    Jun 27, 2011
    Messages:
    627
    Location:
    Atlanta
    Is there any reason why they can't have four smaller electric motors which each have traction control? That would seem like the most advanced 4WD system!
     
  16. doug

    doug Administrator / Head Moderator

    Joined:
    Nov 28, 2006
    Messages:
    15,912
    Location:
    Stanford, California
    Tesla hasn't made any indication that they'd go in that direction, and in the past (early Roadster days) has given reasons why they wouldn't. At the Model S premiere in 2009, Elon said AWD would be possible by adding a second motor (with diff implied) to the front. I wouldn't expect them to change their minds at this point, but you never know.


    Selectable locking differentials (via solenoids) is certainly a possibility and shouldn't be too hard to implement. Though with ABS, TC, and ESC you can probably get away with using a mechanically open differential. It's a good question and makes me wonder what they're using in the Model S.
     
  17. neroden

    neroden Happy Model S Owner

    Joined:
    Apr 25, 2011
    Messages:
    3,529
    Location:
    Ithaca, NY, USA
    The complexity involved in a working differential which interlocks with the steering is almost certainly why the Model S is rear-wheel-drive. Individual wheel motors for left and right actually make this a lot simpler. On the most advanced trains (with separate left and right axles), the wheel motors are actually sprung, but swing on the same axis as the wheels, so they have a very simple pair of universal joints connecting them to the wheels; this has to be simpler than a differential interlocked with the steerable front wheels. It does require a fair amount of space, but the Model X will have the room. But Tesla could go either way.
     
  18. W.Petefish

    W.Petefish Active Member

    Joined:
    Apr 29, 2011
    Messages:
    1,059
    Location:
    North Texas (DFW)
    IF they do a trans-axle it needs to be electronic locking. 4 motors make sense IF they are DC. AC induction motors require significantly more control circuitry, so that isn't feasible.

    Keep in mind that e-locking differentials have been out on the market for years, and the simple fact that Tesla is using tried and proven tech, means that this is the way that they are probably going to do it. More than likely though it will include some sort of Electro magnetic locking and/or drive mechanism.
     
  19. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,249
    Location:
    Silicon Valley
    All of this begs the question - just how "off road" capable will Model X be?

    Hybrid highlander comes in an AWD flavor with a lone rear motor and small diff to provide rear power completely separate from the front hybrid drivetrain.
    Fine for pulling out of an icy driveway, but not recommended for real off-roading over boulders and such.

    I am going to guess that ModelX will have limited off-road capability, but we will find out soon enough.
     
  20. AnOutsider

    AnOutsider S532 # XS27

    Joined:
    Apr 3, 2009
    Messages:
    11,923
    If the model x is supposed to be a crossover or minivan-type vehicle, I'm pretty sure they're not aiming at offroading.
     

Share This Page