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A Nomograph for my 2008 Prius.

Discussion in 'Gen 2 Prius Technical Discussion' started by ronhowell, Mar 7, 2008.

  1. ronhowell

    ronhowell Active Member

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    Hi All,

    I have re-created in the attached the nomograph originally developed I believe by Robert Snyder, which depicts graphically the relationship between the ICE, MG1 and MG2, for my 2008 Prius. It is based on much of the original work done by Graham Davies and outlined on his website.

    I've also included lines showing the approximate power output required from ICE at various RPM settings for steady speed states assuming level ground, and the relationships for power required to overcome rolling and aerodynamic drag. The latter are based on the the data outlined in some of the blogs on EV WORLD: The Eco-Friendly World of Electric Cars, Hybrids, Plug-In Hybrids, Hydrogen Fuel-Cell Vehicles from Bicycles to Buses, Trucks to Trolleys.. I have assumed an overall drivetrain efficiency of 69% in deriving the constant speed/power lines. The ICE power vs. RPM relationship is estimated from Toyota previously published data.

    From these charts it indicates that at a steady speed of say, 70 mph, the ICE power output is around 30 HP, at a speed of around 2100 - 2200 RPM. does this seem about right to the experts out there?

    I throw this chart out there to the PC group to chew at and comment on as you see fit!!

    ron.
     

    Attached Files:

    #1 ronhowell, Mar 7, 2008
  2. tochatihu

    tochatihu Senior Member

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    Great to see new Prius people who appreciate this side of the car. I would urge you to try out Wayne Brown's calculator at privateNRG for comparisons. My first guess is that your drivetrain effy might be low.

    Hope it's available there now, because he was getting hacked or something recently.

    Also do you have Graham's spreadsheet model for the NHW11? That was the state of the art in 2001 ;) Way ahead of his time. O'course back then we had people showing movies on their MFDs. Giants walked the Earth, and few remember it anymore.
     
    #2 tochatihu, Mar 7, 2008
  3. ronhowell

    ronhowell Active Member

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    Thanks DAS. Yes, I have to admit the drive-train efficiency assumption is just a guess, based on an article in NewEnergyNews that assumes an electric motor efficiencies of 90%, as a generator 90% and mechanical drivetrain of 85%. I happen to think the latter is on the low side. Most modern gearing is upwards of 90% or more. I am also familiar with Wayne's excellent work at privateNRG.

    Not familiar with Graham's spreadsheet. I did use the gear tooth ratios and equations developed in his website writeup, but measured my own drive wheel rolling radius at 11.5" rather than the 11.1" he used. So my numbers are slightly different.
     
    #3 ronhowell, Mar 7, 2008
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I don't know if this helps but it is based upon the earlier, NHW11 with data points from my 2003 Prius:
    [​IMG]
    The NHW11 has a reported, software MG1 limit of 6,500 rpm in normal operation and engine limit of 4,500 rpm. But I've noticed the chief determinant on vehicle efficiency is drag. With the exception of the boundary around 42 mph, the vehicle pretty well follows a drag derived efficiency curve. The one interesting aspect is looking at the nomograph for 60 mph and the 6,500 rpm MG1 limit.

    My thinking is that the best transmission keeps the ICE running in the maximum efficiency range. For my older, NHW11, it looks like anything under 2,600 rpm is pretty good and it rapidly falls off above 3,150 rpm:
    [​IMG]
    The negative values come from an artifact of the data collection and should be ignored. As of today, driving our Prius engine does not create gasoline.

    I am less worried about the specific speed ranges as long as the over all effect of a good transmission and engine system is efficient engine operation. So when I look at ICE efficiency, there are speed ranges that seem to do better than others:
    [​IMG]
    BTW, there is an interesting dip between 1,650 and 1,850 that still has me scratching my head. I don't know what is going on here but it shows up time and time again in my data.

    Bob Wilson
     
    #4 bwilson4web, Mar 7, 2008
  5. ronhowell

    ronhowell Active Member

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    Hi Bob,

    You have obviously done a lot of testing across the entire spectrum of the NHW11, the original THS model, but do similar charts exist for the latest version of Prius propulsion system, the 2005 - 2008 model THS II system?

    I'd be interested to learn if similar data exists.

    ron
     
    #5 ronhowell, Mar 8, 2008
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Sad to say, no, but there is an approach that could work.

    We can take the coefficient of drag ratio, .29 for the NHW11 and .26 for the NHW20, and come up with a similar drag and MPG profile. However, the real problem is the absence of constant speed, benchmarks.

    Last summer, some guys on vacation sent some high-speed Prius cruise data that I was able to incorporate in this graph:
    [​IMG]
    But the problem is getting folks to do controlled tests under any sort of standard conditions. Yet it is so simple:
    • on relatively flat highway with documented wind and temperature
    • set cruise control to a given speed
    • after at least 45 minutes, record the MPG
    • change the speed by 5 mph and repeat
    Actually the key is control the speed and route during the test and report the results. Just avoid speed changes, performance at a constant speed for long enough to get reproducible results.

    Bob Wilson
     
    #6 bwilson4web, Mar 8, 2008
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