Modeling Clarity PHEV MPG

Discussion in 'Clarity' started by Steven B, May 31, 2018.

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  1. Steven B

    Steven B Active Member

    @bwilson4web ,
    I've come across your charts for Prius efficiency and think some of us on this Clarity forum might be interested to see a similar graph for our vehicle: MPG as a function of mph. However, I'm not sure which explicit values that you utilized are unique to Prius. Can you explain more about these numbers:
    375 (in Drag_HP calc)
    49.1 gallons per horsepower hour
    EPA efficiency factor 92% (chart y axis says 15% E-factor)

    Since we also don't have hard values from Honda, other numbers such as transaxle loss, engine thermodynamic efficiency, and vehicle overhead (power consumed when READY) would likewise require estimation.
    EPA Test data:
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  3. bwilson4web

    bwilson4web Well-Known Member Subscriber


    The process:
    1. Start with the three EPA roll-down coefficients:
    2. Add a column of mph speeds. Typically start at 5 mph and increase by 5 mph to 100 mph.
    3. Use the following formula for the drag power: ($A10*(B$3 + (B$4*$A10) + (B$5*$A10*$A10)) / 375)+B$6
      1. $A10 - speed in mph
      2. B$3 - Target Coef A
      3. B$4 - Target Coef B
      4. B$5 - Target Coef C
      5. B$6 - overhead in HP, 746 W ~= 1 HP
    4. Make a shadow table converting HP to kW: 746 W ~= 1 HP or 0.746 kW ~= 1 HP times efficiency factor (*)
    5. Use formula to generate kWh/100 mi: $U$8*L10/$U10
      1. $U$8 - 100 miles for scaling to EPA metrics
      2. L10 - the previous table kWh
      3. $U10 - speed in mph
    (*) - the drag power is measured at the road-to-tire interface. The efficiency metric accounts for tire, bearing, gear, inverter, and motor loss. For a rough order of magnitude, I used 95% although 88-90% is more likely the loss. Also, some drag effects are not linear with speed so a more complex formula would be needed. For example, around 85 mph, the tire drag increases exponentially. Also, motor efficiency is different between PM and induction motors and varies with rpm.

    The original thread:

    Be sure and read the full thread as I'd made a math mistake in the first version.

    Bob Wilson
    Steven B likes this.
  4. Steven B

    Steven B Active Member

    @AnthonyW ,
    So a couple datapoints that would help those of us interested in the true efficiency of the Clarity that your Scangauge might provide:
    1) Instantaneous kW consumption at 30 mph and 60-75 mph. I suppose this would be a conversion from the HVC value reported.
    2) Vehicle overhead consumption (what the vehicle requires just to sit in the READY state). I suppose a best case scenario would be with all accessories off: lights, radio, A/C. Again, based on HVC value.

    There are probably others that will surface.
  5. bwilson4web

    bwilson4web Well-Known Member Subscriber


    These curves are theory but you need some benchmarks to tweak the overhead and efficiency:
    • 20 mph for 10 miles - this is used to set the vehicle overhead in the kWh/100 mi scale.
    • 65-75 mph for 10 miles - this is used to set the vehicle efficiency so both benchmarks are on the curve.
    • Tweak the values until both points are on the curve.
    Benchmarks need to be done carefully to minimize altitude, wind, vehicle warm-up (i.e., tires), and reasonably close to a "Standard Day" temperature.

    Bob Wilson
  6. AnthonyW

    AnthonyW Well-Known Member

    Here are the the overhead values. I have included 3 controls.

    -DC-DC Converter Temp should directionally indicate the temp of the battery pack. It’s the last of the 3 components in the IPU to be cooled so I figure the battery pack temperature will be less than the DCT temp. If that holds true then we can conclude that this measurement was taken while the battery was within its target temperature range. IPU cooling system was not running.

    -Air Temp Outside of Vehicle. Don’t imagine these would have much impact on current until it gets really cold outside (or really hot).

    -Current Battery Voltage. I assume we will be using nominal voltage for our baseline but I included this just in case. I’m sure current will be the same at nominal but I can charge up to nominal tonight and check the values again in the morning.

    All accessories, lights, climate controlled were off. IMG_3782.JPG

    Sent from my iPhone using Inside EVs
    Last edited: Jul 27, 2018
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  8. AnthonyW

    AnthonyW Well-Known Member

    Bob or Steven,

    Could one of you build me a spreadsheet with all the formulas already input and Fisher Price what you want me to fill in?

    Sent from my iPhone using Inside EVs
    bwilson4web likes this.
  9. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Later this weekend.

    Bob Wilson

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