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Toyota Prius hybrid car

  1. Oct 31, 2005 #1
    prius is a car combining an electric engine with a gasoline engine.
    http://en.wikipedia.org/wiki/Toyota_Prius

    can someone please explain whats the benefit of a hybrid car like this over a regular one? since the accumulator of the electric engine is charged using the regular gasoline engine wouldn't it just be better to scrap the electric engine and use the fuel needed to charge the accumulator for speed?
    why should this car be anymore fuel economic than a regular gasoline car?
     
  2. jcsd
  3. Oct 31, 2005 #2

    Pengwuino

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    In a normal car, when you break, a lot of heat is generated. Hybrid cars incorporate a generator as a break so that instead of breaking, you simply turn on a generator which causes the driveshaft to slow down and come to a stop. That generator thus charges batteries contained within the car.

    The electric motor will be used for power at low speeds (up to around 15mph) while hte gasoline engine will take over at greater speeds. This pretty much means that these cars are a waste on long drives in say, the countryside while they are excellent for stop-and-go traffic in the cities. Depending on where you normally travel, the fuel economy can be a tad bit better then regular cars or dramatically better.

    The regeneration efficiency is only something like 4% though which kinda sucks.
     
  4. Oct 31, 2005 #3

    Cliff_J

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    Anzas - the efficiency of the gasoline motor is far from ideal under most operating circumstances.

    It has to have enough power to move the car up steep hills with a full load. But yet 99% of the time it will not operate at that load and is oversized to simply cruise down the road.

    With a full hybrid, the gas AND electric motors work together to provide this reserve power for the 1% of the time the car would need that power. And for low power situations like stop-n-go traffic, the gas motor can recharge the batteries in a few mintues rather than run continously. So if it could recharge in 15 minutes for 1 hour of driving, that is a large improvement in gas consumption.

    Large ships or trains run incredibly large diesel engines that have very high efficiencies. But they almost always run under the same conditions so the engine is highly optimized for that load. Their efficiency can exceed that of a fuel cell vehicle in terms of extracting energy and delivering it to the ground.

    But the reality of car driving prevents us from enjoying the same one-load-one-speed operating condition, and the hybrid works well to optimize the sporadic nature of car speeds.
     
  5. Oct 31, 2005 #4

    russ_watters

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    Really? That's surprising - do you have a source for that?
     
  6. Nov 1, 2005 #5

    Cliff_J

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    I don't have a source for it Russ, but as I recall reading something similar about 5% regen efficiency and the arguement presented for the it was somewhat simple. Here's my recollection of it: On a level surface it will take X watts to maintain velocity, on the uphill its X+Y watts to maintain velocity. On the downhill its Y-X watts leftover to charge the battery since the X is constant. Now the additional watts Y-X will manifest itself as an increased back-EMF but the voltage only gets to climb so much if maintaining a constant velocity and this low voltage differential causes the most notable efficiency drop. As I recall it went on to postulate that if you regen-braked down to a stop that the efficiency would be better but still not that great.

    It seemed contrary to my inital logic too, if x=10A and y=30A the I^2R losses are roughly 4x greater on the uphill than the downhill assuming our battery has a low enough ESR to be charged at ~20A just above its float voltage. (I'm assuming the voltage hasn't swung too much to make the amperage calcs from power too radically different, but it does need to swing a lot to actually charge the battery so out go the back-of-the-napkin numbers) Its almost like the cascaded efficiency losses of chem-elec-mech and mech-elec-chem seem to work against regen in both directions mostly because of the chem-elec portion.

    I think I'm not alone to say I'd love to see some well-controlled empirical data! Or what could be done with some of the new super-caps with really low ESRs that could maybe capture the energy better. Fast switch to regen on caps in parallel and switch back to series to extract the energy back out.
     
  7. Nov 1, 2005 #6

    Pengwuino

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    I'm pretty sure you were the one who told me that...
     
  8. Nov 2, 2005 #7
  9. Nov 2, 2005 #8

    Pengwuino

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    Man... getting to a point where the entire history of 20th century technology can be found inside a car.
     
  10. Nov 2, 2005 #9

    Cliff_J

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    Wasn't it one of the big three american companies (I think Ford) that had a nuclear powered show car? It'd be like buying the lifetime supply of gasoline if they set it up like a Navy sub/carrier reactor.

    And I bet you would not have anyone following you too closely...
     
  11. Nov 2, 2005 #10
  12. Nov 2, 2005 #11
    It's been like this for 100 years. Cars have had computers longer than homes.
     
  13. Apr 6, 2011 #12
    There is no car like a 4WD which eats gazillions of liters of fossil fuels per 100. Just my opinion ofc :P
     
  14. Apr 6, 2011 #13

    phyzguy

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    I drive a Prius and it's a great car. I routinely get ~45 mpg, and sometimes over 50 mpg. As has been said, there are four main reasons why it gets better mileage:
    (1) Regenerative braking - collecting and reusing some of your kinetic energy.
    (2) The gas engine can be smaller.
    (3) The gas engine can operate closer to its optimum efficiency
    (4) It can (and does) shut the gas engine off when you don't need it - like in stop-and-go traffic and sitting at a stop light.

    Usually small fuel efficient cars have poor acceleration, but when you tromp on the gas pedal in the Prius it turns on both the gas engine and the electric motor, so it accelerates pretty well.
     
  15. Apr 7, 2011 #14
    American?
     
  16. Apr 7, 2011 #15

    S_Happens

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    Dang, this thread waited 5.5 years for a worthless revival like that?
     
  17. Apr 7, 2011 #16
    If I would live in USA, I would probably buy an American product for my car, yeah.
     
  18. Apr 7, 2011 #17

    Borek

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    It was reopened by a spammer whose post is gone. But DanP answered and whole thing started again.
     
  19. Apr 7, 2011 #18

    S_Happens

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    We can always count on you (to count). :tongue:
     
  20. Apr 7, 2011 #19

    Borek

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    Locked to not waste more bytes.
     
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