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Modified 60D same range as 100D

Discussion in 'Model S' started by Zagorac, Jan 28, 2017.

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  1. Zagorac

    Zagorac Member

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    I think that tesla is not using efficiently energy from battery packs, on D models if you have two motors and two transmissions then why not to use them at different speed separately and at peak efficiency. If tesla would use only rear motor to speed of 55mph at standard 9.87 gear ratio and front from speed of 55mph at gear ratio 4.2, then 60D range would nearly duble range and be like standard 100D at ever day use. I think this would make huge differnece in ev market and make Tesla more even more efficient.

    As we can see tesla is nearly all time using just rear motor-
    2:14 at this video, so if it uses rear to 55mph and just front with modified gear ratio to 4.2 from speed of 55mph, than the range would nearly duble in every day use.
    Also aerodynmics should be taken in consideration, but i think car would nearly double the range at highway speeds.
     
  2. sorka

    sorka Active Member

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    You're mistake is assuming that gear ratio and hence motor RPM somehow equates to power used. You couldn't be more wrong.

    That said, the D cars do have a feature called torque sleep that essentially turns them into front wheel drive only cars at constant cruising speed which is more efficient which is why the 60D gets better range than the 60 does.
     
  3. Zagorac

    Zagorac Member

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    You miht be right ,but car is most efficent at 24.2mph and that is around 2800rpm at motor shaft, so if you just cange gear ratio to 4.2, than at 55mph motor would run at 2800rpm.
     
  4. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    Sorka is correct. Yes, the motors, as geared now, are most efficient at a certain speed, and less efficient at other speeds, but the difference in efficiency is small.

    Energy is energy. Sure, gearing it differently may result in operating the motor in a more efficient range, but you still must provide the same amount of energy to travel.

    In the following example, I am assuming some rough numbers to illustrate the point, they may not represent actual figures for the Model S.

    Example: Operating motor at 5600 RPM, 88% efficiency, 55 MPH, required power to overcome all air resistance and tire rolling resistance at constant speed = 15 kW. At 88% efficiency, input power to the motor is then 15/0.88 = 17 kW.

    Now we change gear ratio.

    Operate motor at 2800 RPM, 92% efficiency, still 55 MPH. Required power to overcome all air resistance and tire rolling resistance at constant speed still = 15 kW. Now at 92% efficiency, input power to the motor is 15/0.92 = 16.3 kW.

    Net improvement = (17-16.3)/(17) = 4 % improvement in range.

    The price you pay is significantly reduced torque off the line and lower efficiency during hard acceleration.
     
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  5. Zagorac

    Zagorac Member

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    But if we lock at this chart efficiency at 24mph and efficiency at 80mph is not just cuple of persents. Because in europe 80mph is highway speed limit in many countries, so range can be problem at that speed, then every percesnt is important. Hence not many people buys D model for acceleration and if you want acceleration you probably don't care about efficiency at that moment.
     

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  6. sorka

    sorka Active Member

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    That chart has nothing to do with motor efficiency. It's how many wh / mile are consumed by the entire car moving through the atmosphere. The curve you see is the result of overcoming drag at any particular speed:

    [​IMG]

    The roadster has less drag than the model S...not to be confused with the cd which is the ratio of drag, not the actual total drag. You could have a mountain sized car with a cd of .24 but it would still have far more drag than any car ;)

    Further more, the front motor's 9.34 gear ratio is slightly taller than the rear 9.73 which allows the front to stay smack in the middle of the efficiency zone at typical US highway cruising speeds.
     
  7. Zagorac

    Zagorac Member

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    Ok but, middle of efficiency zone at typical US highway cruising speeds is not same as in europe. In europe 55mph is for trucks, 75mph is half of europe and 80mph is for other half on highways. So if gearing is snack on at 75mph then European cars should have different gear ratio then American at front motor.
     
  8. sorka

    sorka Active Member

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    You and I are talking about completely different things here :eek:
     
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  9. Zagorac

    Zagorac Member

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    Sorka tank you,I honestly tough that if you put 4.2 gear ratio in front you would cut energy consumption in half from 400wh to 200wh per mile, and now i see that i am wrong. But at the end if somebody see this from Tesla, they should know that speed limits are different in Europe then in USA, so from my no sense of physics there is still something that might help tesla.
     
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  10. sorka

    sorka Active Member

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    The bigger issue with the Tesla in Europe is when driving extended 120 MPH speeds for a long time as the DU and battery cooling systems can't keep the drivetrain cool like ICE cars.
     
  11. Zagorac

    Zagorac Member

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    Actually I don't personally see that as a probelm since in most european countries there is more speed cameras then traffic signs and police chase cars that look like civilan, but when they stop then its fun. Probably prison and you life is ruined but off course except Germany. It is mecca for car lovers since there is no speed restrictions on some parts of autobahn. I think Tesla should make new roadster that is going to be best over the best and lessons like overheating batteries and motors should be on pages of history(imagine what could happend in middle east at track at 50*C). I belive in electric cars and i belive in Tesla and know that their next product is going to be best in front of best. 400kw superchagee with 2170 battery is going to be EV pornography. And inverter motors and battery cooling should all ready be at testing phase for future Tesla products that should be more refined, reliable, nicer, much more sophisticated and build like spaceships.:cool:
     
  12. jareade

    jareade Supporting Member

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    Just looking at that equation made me break out in a cold sweat. Time for a scotch. :)
     
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  13. sorka

    sorka Active Member

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    The only thing in that's important is v^3 :)
     
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  14. Zagorac

    Zagorac Member

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    And off course if you put gear ratio 3.8 at 180mph, motor rpm is going be around 8000rpm like at 70mph. So gear ratio change on front motor is not i think so bed idea:D. Rimac croatian electic car company changes gears on rear wheels soo tesla its on you.:rolleyes:


    Equation: density of air x speed x speed x speed x aera of car x drag coefficient /2



    simple:D
     

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