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

Dual drive techincal questions

Discussion in 'Model S' started by TEG, Oct 17, 2014.

  1. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,252
    Location:
    Silicon Valley
    I think the performance, efficiency, and top speed improvements were bigger than many expected.
    Questions have been asked about how they did it, without real answers (yet.)

    Asking some pointed questions here in case we can someday get more info:

    #1: What are the gear ratios of the front and rear gearboxes?
    #2: What are the RPM ranges for the front and rear motors?
    #3: What do the horsepower and torque graphs look like for both motors over the full speed range (0-155MPH) of the P85D?
    #4: Is the 691hp figure just a sum of front & rear motor max HP at different RPMs, or is there actually a time when the car is producing the full 691hp at a specific speed?
    #5: How long/far can the dual motor cars actually drive at 155MPH?



    Are these assumptions correct?:
    The rear motor has shorter gearing for better 0-60 acceleration, and the front motor has taller gearing for higher top speed and highway efficiency...?
    There is no clutch/decouple device on either motor, so the rear motor is forced to "freewheel" past power red-line when the front motor is pulling for top speed...?
     
  2. LittoDevil

    LittoDevil Member

    Joined:
    Nov 17, 2013
    Messages:
    51
    Location:
    San Francisco, CA
    When I get my "D" I'll let you know how long and far you can drive at 155 MPH considering I've done 135 MPH in my P85+.. ;)

    A lot of people thought the P85+ was limited in top speed due to gearing but now it proves that it wasn't the gearing or max rpm but the power required to drive it even faster. With another motor and more power, the rear motor doesn't have to work as hard by itself to go over 130 MPH.

    The whole rear motor is forced to freewheel and front wheel pulling was actually a problem that the engineers were working on the prototype ones. It all came down to software and calibration. The car would shake when you accelerate due to the oscillations between the front and rear motors, I wasn't suppose to see it but I have seen it when it was in prototype stage. Noise was also another concern they had to tackle with.

    Larry
     
  3. wycolo

    wycolo Active Member

    Joined:
    May 16, 2012
    Messages:
    2,423
    Location:
    WY
    Red line could be higher when motor is 'off'.
    --
     
  4. GSP

    GSP Member

    Joined:
    Dec 28, 2007
    Messages:
    1,996
    Great questions TEG. Tesla is still shy about publishing tech specs. Perhaps they will open up after the cars hit the street and the competition can just buy one and find out.

    I also would like to know:

    1) Maximum Battery power available for 60, 60D, 85, 85D, P85D. I want to know how much of the advertised "motor power" can be used.

    2) EPA range for each of the above, for the 19" and also the 21" wheels.

    3) Torque curves for all four motors: including big and small motors for the other models, as well as the P85D motors.

    GSP
     
  5. GaryREM

    GaryREM Member

    Joined:
    Jul 16, 2013
    Messages:
    324
    Location:
    Fairfax, VA
    I think the horsepower numbers are somewhat misleading.

    As far as I understand Tesla is now publishing the horsepower ratings of the motors themselves which is why the horsepower ratings on single motor cars look higher, but performance ratings are same. I.e. same motors, different spec being reported.

    That makes the 691 hp number a little suspicious because adding the 2 horsepower ratings of the individual motors doesn't tell you much about what is really happening.
     
  6. Kardax

    Kardax Member

    Joined:
    Jun 8, 2007
    Messages:
    258
    Location:
    Minnesota, USA
    My thought is that both motors are geared taller than in single-motor configurations.
     
  7. Luis Mengual

    Luis Mengual Member

    Joined:
    Sep 16, 2014
    Messages:
    16
    Location:
    Spain
    Completelly agree, and in this particular case; as soon as you have more torque/power available and specifically from two sources (Twin motors) you are pushed to get a large gear ratio if you want overcome bigger mass penalty.

    Furthermore... The cool thing of dual motor is, when you are developing this smart D project, you must consider different ratios in these different sized motors, in order to improve the perfomance depending instant speed, torque and position of the accelerator, changing the frecuency in just few ms of each motor, reducing power demand according the efficiency curve of each motor, "not considering full load".

    I have other questions like:

    -More power, bigger cooling system? how much is the difference compared to the single one?
    -How Dual motor works logically? This will be amazing to know how they do it.
    -What percent in terms of kinetic regenerative braking is taking from each motor?
    -In ofroad, snow, sand, how is its behavior, some video discovered will be a great stuff?
     
  8. tdelta1000

    tdelta1000 Active Member

    Joined:
    Jul 19, 2009
    Messages:
    1,667
    Location:
    South Florida
    The hamster wheels TEG. On a serious note I too would like to know how?
     
  9. gnelson

    gnelson Member

    Joined:
    May 26, 2013
    Messages:
    557
    Location:
    Houston
    My 2001 Corvette convertible with about 375 hp topped out at 150 mph in 5th gear. I had to shift from 6th to 5th to go above 120 mph.
     
  10. uselesslogin

    uselesslogin Enthusiast

    Joined:
    Jun 13, 2013
    Messages:
    1,300
    Location:
    Omaha, NE
    Well I read some of the patent. In the patent the gear rations may or may not be different and the gearboxes may or may not be multi-speed. I think we can safely say it is two single speed transmissions since shifting is something I would think one would notice. Figures 2 and 3 shows that the main motor/transmission has a similar torque curve to the single drive while the second motor is considered an assist motor which has a completely flat torque curve. I would assume this would have to be done through gearing but I don't know enough about electric motors to know if there were some other way of doing it. But to me I would guess it is like a 10:1 gear ratio on the main drive and a 5:1 on the secondary front motor or something like that. Maybe the main drive needs a lower ratio so that it can get to top speed but I don't know if it was a limitation of the motor or a limitation of the power the battery could put out that limits the rpm of the motor.

    Control System For An All-wheel Drive Electric Vehicle
     
  11. LittoDevil

    LittoDevil Member

    Joined:
    Nov 17, 2013
    Messages:
    51
    Location:
    San Francisco, CA
    Oh nice.. so 6th gear was like over drive then.. to keep rpm low on highway speeds. So it didn't go faster than 120mph in 6th gear or it just took too long to go any faster?

    Larry
     
  12. gnelson

    gnelson Member

    Joined:
    May 26, 2013
    Messages:
    557
    Location:
    Houston
    Shifting down raised the rpm's and engine produced more hp as the rpm's increased.
     
  13. LittoDevil

    LittoDevil Member

    Joined:
    Nov 17, 2013
    Messages:
    51
    Location:
    San Francisco, CA
    Yea I'm sure it's single speed, the packaging for two speed transmission is much larger and they had the problem of it breaking due to such a big torque output from the motor. Gearing could definitely be different though. The current P85+ is software limited as far as top speed goes since the amount of power it takes to continue to output 320 KW. If it didn't limit the power to the motor it would definitely go faster than 135 mph. I want to say it's the limitation of the electronic drive controllers, wiring and etc to sustain such high power output. Just like how it takes exponentially more power to increase the speed of the vehicle in a normal gas powered car.. to do that with an electric vehicle it would take much thicker wires, cooling, electronic control units that can sustain such high power demand and all that comes with $$$ heh.

    I want to bet it takes the combination of rpm and power from both motor combined to reach that type of velocity (155 mph). I also can't wait to get the D to see if it's current limited like in the P85+ which I assume it is...

    Larry


    - - - Updated - - -

    Oh yea that I know, your closer to your peak torque curve. I just wasn't sure if it stopped accelerating around 120 mph in 6th gear or it just took too long. Some cars you could accelerate in 5th gear to red line then shift to 6th just to have the car slow down because it doesn't have the power to continue to accelerate while others... you would shift to 6th after reaching redline in 5th gear just to have the car continue to accelerate but very slowly to reach top speed. I turbocharged my smart car and my experience with that was the latter, but before I turbocharged it, in 5th gear (it only has 5), it would actually slow down since it didn't have enough power to continue to accelerate lol.

    Larry
     
  14. scottf200

    scottf200 Active Member

    Joined:
    Feb 3, 2013
    Messages:
    1,271
    Location:
    Chicagoland ModelX S603
    Are the front motors the same on the 85D (aka S85D) and the P85D? Inverter make the performance different?
    Why the 295 vs 275 mile range difference? Different efficiencies in the motor(s)? Gearing?

    cX1axEk.png

    Tesla Model S Dual Motor Specs (vs comparable single-motor model)
    Note: The Tesla Model S P85D specifically has 50/50 weight distribution and 1 g maximum lateral acceleration.

    Torque
    S85D: 362 lb-ft — 181 lb-ft front, 181 lb-ft rear
    P85D: 687 lb-ft — 244 lb-ft front, 443 lb-ft rear

    Electric Motor Output
    S85D: 376 hp—188 hp front, 188 hp rear (vs 380 hp rear only)
    P85D: 691 hp—221 hp front, 470 hp rear (vs 470 hp rear only)

    Weight
    S85D: 4824 lbs (+ 176 lbs)
    P85D: 4936 lbs (+ 291 lbs)

    Battery Range
    S85D: 295 miles (vs 285 miles)
    P85D: 275 miles (vs 285 miles)

    http://www.roadandtrack.com/go/first-looks/first-look-tesla-model-s-p85d-dual-motor

    Aside: interesting PDF on inverters
    http://net.grundfos.com/doc/webnet/boosterpaq/BoosterpaQ%20CD/Misc%20Tech/Inverted%20Fed%20Motors%20-%20Baldor.pdf
     
  15. gjunky

    gjunky Waiting for the Model ☰

    Joined:
    Mar 26, 2012
    Messages:
    695
    Location:
    Scottsdale, AZ
    I am also curious to see if you can set a fwd/rwd preference. It would be possible to change the fwd/rwd tendency through software, something that is not easily done in an ICE. This would give the driver more control over the feel of the car sending more power to the front or the rear based on their setting (50:50 or 40:60 for instance).
     
  16. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,252
    Location:
    Silicon Valley
    Thinking something a simple as higher performance tires on P85D with more rolling resistance...
     
  17. scottf200

    scottf200 Active Member

    Joined:
    Feb 3, 2013
    Messages:
    1,271
    Location:
    Chicagoland ModelX S603
    But it didn't make a on the single motor version here?

    4BFY2GD.png
     
  18. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,252
    Location:
    Silicon Valley
    Here is an image from that patent, with the curves relabeled to (hopefully) make more sense than numeric legends:
    patent-graph.jpg

    So, it looks like the redline & rev range there are similar.
    Maybe the idea of rear motor being geared shorter and front being geared taller is wrong, and it is just a matter of front motor having different characteristics that emphasize high RPM power and don't try to focus so much on low end (since the existing rear motors already provide plenty of low end torque for 0-60 performance.)

    Maybe both motors are geared tall now to support the 155MPH top speed, and the 0-60 improvement is all due to the extra traction (of having 2 more drive wheels) and the additional torque assist... (?)

    - - - Updated - - -

    Front motor is more efficient at high speed, but that benefit isn't fully realized on P85D due to tires?
    I don't know - maybe gearing different between the two. The top speed differences is probably a clue of some sort.
     
  19. ra-san

    ra-san Member

    Joined:
    Dec 26, 2008
    Messages:
    292
    Location:
    San Diego, CA
    I was told at the event, talking to the drive train engineer, that the front is geared slightly (his word) taller (er, as in will top out higher ground speed at lower rpm) than the rear. I think he even told me gear ratios. I don't remember the numbers exactly, but iirc they were both 9 point something, differing in the tenths. If that sounds completely wrong, then I'm probably recalling incorrectly. I don't think this stuff was meant to be secret. I've got some more questions to ask, but still need to get them composed to send off. I expect any customer or potential customer could find out some of these details just by asking a few tesla folks. Might take a bit to get to someone that can and will answer, but I'm sure they will all be answered eventually.
     
  20. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,252
    Location:
    Silicon Valley
    Yeah, I asked here in a public forum since I expect this info to be released eventually.
     

Share This Page