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Instant Torque (Electric Cars vs. Gas/Diesel Cars)

  1. Sep 22, 2013 #1
    So I hear a lot about how electric cars are great because electric motors get instant max torque at 0 RPM.

    However, can't the same be done with an internal combustion engine if you have a clutch?
     
  2. jcsd
  3. Sep 22, 2013 #2
    No. Run an ICE to slow and it will stall. Even below about 2000rpm in most engines, there is very little torque.
     
  4. Sep 22, 2013 #3

    SteamKing

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    That pesky transmission is there for a reason, and it's not to give you an extra hand rest.
     
  5. Sep 22, 2013 #4
    I'm not familiar with stick shift cars at all (or car mechanics in general) so bare with me as I have no idea what I'm talking about. But can't you rev up the engine to its max torque almost instantly using a clutch without moving the car and THEN hit the pedal to get that same feeling of instant torque that you would get from an electric car?
     
  6. Sep 22, 2013 #5

    OmCheeto

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    Yes, but this involves the clutch slipping. If you do that a lot, the clutch will wear out prematurely. Have you ever changed brake pads? Changing the clutch disk is about 100 times worse, as it involves removing the engine, transmission, or both.

     
  7. Sep 22, 2013 #6

    SteamKing

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    More likely, you'll stall the engine.

    Hit what pedal?

    With a manual transmission, the clutch is disengaged to allow the engine to run without load. Consequently, it takes very little throttle to rev the engine to its max. torque RPM. If you put the transmission into its highest (1:1) ratio and engage the clutch, the engine still must overcome the inertia of the car before movement can take place. More often than not, doing this will stall the engine rather than getting the car to move. Also, since the clutch is a friction device, engaging it repeatedly at high RPM will rapidly burn out the friction plates, requiring a costly clutch replacement.

    Doing the same thing with an automatic transmission may not stall the car, but soon you will need a new transmission, which is even more costly to replace than a clutch.
     
  8. Sep 22, 2013 #7
    I think the main point to take is that there is a difference between having torque being produced at a specific high RPM and slipping something to achieve pull away, and having produced at zero RPM.
     
  9. Sep 23, 2013 #8
    Ryuk1990, Yes, what you're talking about is possible. You can just dump the clutch at peak torque. You will get the results above though....fast wear and broken parts. You could also use a slipper clutch that will only lock-up above a certain rpm. It's not instant, but will allow the engine to rev up before being loaded at peak torque (or whatever rpm you set it for). You could also use a high-stall torque converter. It doesn't hammer the drivetrain like a clutch, but creates a whole lot of very hot transmission fluid, so you'll need a good cooler. Driveablitlity would be poor with a slipper clutch or converter that stalled that high, so daily use wouldn't be possible. Is there a point beyond a theoretical question? It's going to be a loooooooong time before a Prius can pull a travel trailer, or before an electric truck can pull a semi-trailer for 500 miles a day. ICE vehicles overcome the lack of instant torque through gearing, so there is really no need to turn an ICE into an electric motor.
     
  10. Sep 23, 2013 #9
    It was more about having that fast smooth acceleration that the Tesla Model S offers with an ICE car.
     
  11. Sep 23, 2013 #10

    SteamKing

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    Most cars with automatic transmissions accelerate quite smoothly from stop to highway speeds. The shift points of the transmission provide a momentary change in the sound of the engine as the revs drop, but other than that, everything is quite smooth. Also, new transmissions have up to eight speeds, rather than the three or four or older transmissions, making the process even smoother, as the engine revs do not need to drop as much between shifts.

    It might be you are thinking of the so-called Continuously Variable Transmission (CVT), which doesn't operate using conventional reduction gears.

    http://en.wikipedia.org/wiki/Continuously_variable_transmission

    These transmissions allow the engine to maintain a constant speed as the vehicle accelerates. Although such transmissions have been used in a variety of automotive applications, several factors have kept them from replacing conventional transmission designs (see the article above for more details).
     
  12. Sep 23, 2013 #11

    AlephZero

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    Tesla S: 0-60 in 5.4 sec, top speed 125 mph, "handles like a sedan" (to quote the Tesla website)
    Porsche 911S turbo: 0 - 62 mph in 3.1 sec, 0-124 mph in 10.3 sec, top speed 200 mph, handles like a car.
     
  13. Sep 23, 2013 #12

    AlephZero

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    That depends on the design of the clutch. Back in the 1970s I used to drive a british-designed sports car with a 6 speed gearbox. More accurately, it had a 4 speed conventional box and pedal-operated clutch, and a separate epicyclic gearbox and clutch that was operated electrically from a switch in the top of the gearstick, to switch between gears 3 and 4, or 5 and 6. (The manual box and clutch selected either 1,2,3,5 or 1,2,4,6).

    The epicyclic gear change was designed to operate at any engine RPM and throttle position, and changed gear in less than a second. Floor the throttle, flip the switch, and get a kick in the back ... (or on a bad hair day, over-rev the engine when changing down without first engaging brain).
     
  14. Sep 24, 2013 #13
    It doesn't make any difference on design, a slipping friction clutch transmissting lots of torque will wear prematurely.

    And a British 70's sports car in the US.... an MGB?
    What you are describing is an overdrive in 3rd and 4th.

    The solenoid should automatically disengage the overdrive in 2nd and 1st. If/when it fails, and you can engage the overdrive in the lower gears, it slips and wears the cone clutch out. Also the overdrive is not designed to give you 'a kick in the back'. It's designed for cruising.

    The reason for the lurch when you engage the overdrive whilst still having the throttle open is that wheels suddenly wanted to be travelling much faster than the road speed (as overdrive is effectively a longer gear). Two things can happen in this case, the wheels slip or the overdrive clutch slips to synchronise the road and engine speed. As it's rather dangerous for the wheels to start slipping at high speed, the clutch was designed to slip first.

    This abuse of the overdrive clutch is what caused MG to stop the overdrive from engaging in 3rd on later cars
     
  15. Sep 26, 2013 #14
    The technique asked about by the OP involves flooring the throttle and then controlling the clutch pedal to ensure RPMs stay around max torque (gradually engaging it as car speed builds) - if you're stalling the engine you're engaging the clutch too quickly.
     
  16. Sep 26, 2013 #15

    SteamKing

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    Perhaps so, but it is a maneuver which I think could only be accomplished with not a little skill and a fairly robust clutch. All in all, even with the best technique, I still see a much shorter clutch life, perhaps shorter engine life to boot.
     
  17. Sep 26, 2013 #16

    cjl

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    That's not really a fair comparison though, since the Tesla is a much different car in a completely different category of size and performance (and is half the price of a 911 Turbo S). A BMW M5 or Audi RS6 would be a much better comparison (and should still win in all performance metrics).
     
  18. Sep 26, 2013 #17

    Averagesupernova

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    Interesting. I just drove a Volvo semi-tractor with a Detroit diesel in it and it governs out when it approaches 2000 RPM. ALL the torque is below 2000. Yes, the thread is about diesels too.
     
  19. Sep 26, 2013 #18
    It's ironic that you picked two cars with pretty much the same power as the 911 turbo s. New Golf R. 300bhp and 0-60 in 4.8 with the DCT.

    Hot hatch progress... its mind bending.
     
  20. Sep 26, 2013 #19

    NigelTufnel

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    Generally with ICE the larger the displacement the lower the rpm at which it makes max torque. If you want more torque without having to rev the engine just get a bigger engine.

    Here's a 14 cylinder diesel that makes over five million foot pounds of torque at only 102 rpm
    http://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C
     
  21. Sep 27, 2013 #20
    Isn't this what everyone does when they try to pull away "quickly" in a manual transmission (eg pulling out onto a busy road)? You rev the engine up a bit (to around max torque), then release the clutch in a controlled manner whilst pressing the accelerator harder to keep the rpms more or less constant. In most cars the clutch will only slip for a fraction of a second until the car is moving fast enough to match the 2000-3000rpm. Yes it does wear the clutch more than a slower pull-away, but it's not going to destroy anything. Try the same technique in 2nd or 3rd gear, then you'll smell the clutch burning away :-)
     
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