1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Mythbusters 6/12/2013 - Hypermiling and Crash Cushion

Discussion in 'Now Playing - TV Show Talk' started by GoPackGo, Jun 13, 2013.

  1. john4200

    john4200 Active Member

    4,571
    8
    Oct 31, 2009
    You astound me with your lack of surety! :rolleyes:

    Perhaps you will share some more words of wisdom. Do you suppose the gas mileage of a car will be lower if you drive it immediately after a crash? Do you think a crash you can walk away from is better than one where you end up in critical condition at the hospital? Is someone with a sense of humor more likely to survive a crash than someone lacking in that department? :D
     
  2. RonDawg

    RonDawg Well-Known Member

    20,293
    104
    Jan 12, 2006
    Rather than continue to sidetrack this thread with any more futile attempts at rational discussion with you, I will just ignore you from now on.
     
  3. RonDawg

    RonDawg Well-Known Member

    20,293
    104
    Jan 12, 2006
    A friend of mine test drove one and found it totally...underwhelming.
     
  4. john4200

    john4200 Active Member

    4,571
    8
    Oct 31, 2009
    So, no more words of wisdom about how crashing is bad, then? :(

    (I would have gone with "no more running this thread out of control" myself)
     
  5. cwerdna

    cwerdna Proud Tivolutionary

    9,887
    17
    Feb 22, 2001
    SF Bay Area, CA
    Well, you get at least 1 or 2 presses of the brake power assist w/the engine off, but yeah, there is the loss of power steering.

    To me, it'd be not too terrible if to shut off the engine when approaching a traffic light that's only straight ahead and you know how well the car's speed scrubs off when the engine's off, so that you don't need the brakes at all/much.

    It's not too weird anymore, but then again, I've had my Prius for over 7 years now. For me, it drives me nuts to be in a regular car w/the stupid engine idling away when stopped. And, it irks me greatly to be in such a car and using the brakes, to know all that kinetic energy is being thrown away as heat and brake dust.

    The BMW 3-series cars that I drove w/auto-start stop have a comical restart noise. I heard it from other BMWs on the test drive loop. It was just hilarious to me (from someone having driven hybrids from Toyota, Nissan (well it's Toyota HSD based), Ford, Honda and Kia).
     
  6. cwerdna

    cwerdna Proud Tivolutionary

    9,887
    17
    Feb 22, 2001
    SF Bay Area, CA
    No, but its fuel economy are disappointing along w/its straight line performance.

    See how it did in CR's FE tests at http://www.consumerreports.org/cro/2012/02/the-most-fuel-efficient-cars/index.htm?loginMethod=auto. It scored too low in their tests to recommend.

    In their tests, it did 0-60 in 9.3 seconds so ok it's faster than a Prius but a Camry Hybrid blows it away (http://www.consumerreports.org/cro/2012/01/fuel-economy-vs-performance/index.htm). My mom's Altima Hybrid got identical acceleration times to the '12+ Camry Hybrid (not surprising since they're only 2 hp apart).

    I also wouldn't trust the battery longevity of any Honda hybrid. Their track record is not particularly good. It's unfortunate that Honda's not putting up a better fight against Toyota.
     
  7. Waldorf

    Waldorf Super Duper Member

    997
    0
    Oct 4, 2002
    Phoenix, AZ
    This is in the same vein as what I was thinking of.. he averaged over 106 mpg on a tank:

    http://www.startribune.com/lifestyle/22053954.html

    I think he may have been part of a group of people I saw on another episode of 20/20 or Dateline or something else, but I haven't been able to find it.
     
  8. voripteth

    voripteth User Advocate

    333
    0
    Apr 9, 2003
    We regularly get 100+ MPG but then again we have a Volt. :D
     
  9. verdugan

    verdugan Active Member

    2,415
    2
    Sep 9, 2003
    Sacramento, CA
    The ignore list is a powerful thing. Use it. Shout if you have quesitons on how it works.
     
  10. Waldorf

    Waldorf Super Duper Member

    997
    0
    Oct 4, 2002
    Phoenix, AZ
    How long have you had it / how is it so far? The Volt is a certainly different beast... I remember reading that Jay Leno had 11,000 miles on his Volt and still had half the original tank of gas. :eek:
     
  11. Flop

    Flop Member

    408
    2
    Dec 2, 2005
    Oklahoma
    I can't imagine how that would save any gas. Since the drag on the car is more or less constant at those speeds, it seems you would burn more gas to produce the amount of energy required to accelerate the mass of the car and to overcome drag from air resistance and tire friction than you could possibly save by coasting back down. It's been many years since I took physics, but I believe the power required to overcome aerodynamic drag increases as the cube of the velocity (it might be the square not cube... it's been a while). At high speeds (say going from 65 to 70) that power difference won't be a lot, but it's still additional power required, and you still have to add the power required to accelerate the mass of the car as well.
     
  12. Hank

    Hank AC•FTW TCF Club

    20,972
    25
    May 31, 2000
    Boston, MA
    It's the square.
     
  13. john4200

    john4200 Active Member

    4,571
    8
    Oct 31, 2009
    The third power is correct.

    You are certainly correct about speeding up and coasting being an inefficient technique in general.

    Although I can imagine a more sophisticated technique, that slows down a bit when there is a headwind and speeds up a bit when there is a tailwind, could be effective. It would probably need electronic automation to do it well -- a digital speedometer or GPS to monitor ground speed, an anemometer to monitor airspeed, and a computer to compare them and determine if there is sufficient headwind or tailwind to merit a throttle change.
     
  14. john4200

    john4200 Active Member

    4,571
    8
    Oct 31, 2009
    No. The drag is proportional to the second power of velocity, but the power required to offset the drag is proportional to the third power of velocity:

    P = F * v = ( k * v^2 ) * v = k * v^3
     
  15. RonDawg

    RonDawg Well-Known Member

    20,293
    104
    Jan 12, 2006
    I'm well aware of how it works, thank you.
     
  16. kdmorse

    kdmorse Active Member

    5,076
    14
    Jan 29, 2001
    Germantown, MD
    I wonder about the hypothetical engine/transmission combination that is more wasteful maintaining speed than accelerating. Where accelerating briskly and efficiently for 10 seconds then idling for 50, is more efficient than maintaining speed at an inefficient RPM for 60 seconds.

    Not that it would ever be the case in a modern automobile, but I wonder if it was at least partially the case for some model of 60's/70's vehicles, enough so to generate the idea....
     
  17. alansh

    alansh New Member

    1,177
    0
    Jan 3, 2003
    Phoenix, AZ
    The speed up and slow down thing is "pulse and glide", and may be specific to the Prius or at least hybrids in general.

    The idea of the hybrid is to keep the internal combustion engine at the most efficient point in its power curve, regardless of the amount of power you actually need. So if the ICE is generating too much power, the excess goes into the battery and is used when you need more power than the engine is creating.

    There are losses in the process, so pulse and glide aims to use 100% of the engine's output for acceleration, rather than having an excess that goes into the battery. You accelerate to above your target speed, with the goal of none going into the battery. Once you're above your target speed you coast, with the engine turning off automatically. Once you've slowed enough, you repeat.

    You could theoretically do this in a non-hybrid, but the shifting into neutral and turning off the engine for the glide part is going to be a problem.
     
  18. john4200

    john4200 Active Member

    4,571
    8
    Oct 31, 2009
    While that technique may be able to increase mileage in city driving, I thought we were discussing freeway driving, where such a technique would surely hurt your mileage, for reasons already explained by Flop.
     
  19. alansh

    alansh New Member

    1,177
    0
    Jan 3, 2003
    Phoenix, AZ
    Yes, pulse and glide is typically used around 40mph or less on the Prius. At those speeds, the difference in the power curve is enough to make a bigger difference than the wind resistance. Above 40mph, the gen II Prius has to run the gas engine because of the way the gearing between the electric and gas motors is done, so the engine never really shuts off. I haven't really looked into the difference for the gen III.

    Anyway, as I mentioned, this would be really difficult to do on a non-hybrid.
     
  20. cwerdna

    cwerdna Proud Tivolutionary

    9,887
    17
    Feb 22, 2001
    SF Bay Area, CA
    On Gen 3 Prius, I believe the max speed at which you can drive w/the ICE not turning is ~46 mph, rather than 40 or 41 mph.

    There's also the efficiency map at http://priuschat.com/threads/2010-prius-2zr-fxe-engine-efficiency-map.62586/. 1NZ-FXE is the 1.5L engine used in the Gen 2 (04-09) Prius while the 2ZR-FXE is the 1.8L engine used in the 2010+ Prius liftbacks.
     

Share This Page