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Preliminary 2010 mph vs MPG

Discussion in 'Gen 2 Prius Technical Discussion' started by bwilson4web, May 29, 2009.

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  1. bruceha_2000

    bruceha_2000 Senior Member

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    As Tom (or is it Ray?) would say "Au contraire Pumpkin Puss!"

    The electric motor is engaged any time the computers decide to use it. Interstate speeds or 25 MPH. Could be for more power, could be because the battery is 'full green' to make sure there is 'head room' in case you go down a hill. I have seen EVERY combination of power flow with the CC set at 65 on the Interstate hills of Vermont. From ICE plus Electric to all EV and even pure 'glide'. If you have the right grade, it is all FREE :)
     
    #41 bruceha_2000, May 31, 2009
  2. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Our Prius has an overhead energy cost to run the computers, brake pump and in my case, daylight running lights. As long as the car is 'ON', this energy loss exists. This is the fixed overhead.

    Bob Wilson
     
    #42 bwilson4web, May 31, 2009
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Because we are treating the 1.6L and 1.8L engines as power plants and not looking at the total internal operation. From a mechanical standpoint, the pistons are a primary, internal source of drag but the bearings and valves play a part too.
    This is an entirely different area, the internal performance characteristics of each engine. Although interesting and there is an SAE paper that covers a lot, let's put this off for another day.

    Bob Wilson
     
    #43 bwilson4web, May 31, 2009
  4. SageBrush

    SageBrush Senior Member

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    I'm not following your reasoning. Why talk about piston friction against the cylinder and ignore piston air drag ?
     
    #44 SageBrush, Jun 1, 2009
  5. Celtic Blue

    Celtic Blue New Member

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    There won't be any effective air drag against the piston head. There would be a minor amount against the walls. More important in terms of air would be the pumping losses (compression).

    My off the cuff estimate is that piston friction against the cylinder will be an order or two greater magnitude than air drag along the cylinder walls.
     
    #45 Celtic Blue, Jun 1, 2009
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    My apologies to the community. I just realized that posting a Mach 3 speed vs MPG was probably not the best subject line. We have a Prius, not an SR-71:
    [​IMG]
    Anyone who thinks I screwed up just so I could post this neat photo ... well it wasn't a conscious thought.

    Bob Wilson
     
    #46 bwilson4web, Jun 1, 2009
  7. donee

    donee New Member

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    Hi All,

    I use speed, rather than velocity, as velocity is usually considered the vector of speed.

    Thanks Bob for straightening those guys out.

    That SR71 is just another computer drive-train controled Hybrid, ya know.

    The reason the bigger engine in the 2010 Prius has better mileage, is because the EPA changed the playing field, and put in higher illegal (around here at least) speeds in the mix, and the new Prius has the heat recovery system (the city test is from cold start). And Toyota improved the engine-wheels efficiency by putting the gearing needed for the MG2 between MG2 and the PSD, rather than between the PSD and the axle. This also allowed them to make MG2 ligher, and gear it up even faster.
     
    #47 donee, Jun 1, 2009
  8. Dobey

    Dobey New Member

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    Can you show your calculations on this one? An estimate that ranges from 1 order of magnitude to 2 orders of magnitude is no better than a wild guess.
     
    #48 Dobey, Jun 2, 2009
  9. F8L

    F8L Protecting Habitat & AG Lands

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    Here is a cool study on the subject. :)

    http://www.eere.energy.gov/de/pdfs/conf-05_ares/ares05mit.pdf

    I think MIT does a lot of work on engine efficiency testing with regards to piston friction.
     
    #49 F8L, Jun 2, 2009
  10. fgp

    fgp Active Member

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    you guys are scaring the hell out of me!! its miserable being mathlexic like i am.
     
    #50 fgp, Jul 26, 2009
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