MPG in Hybrid Mode

Discussion in 'Prime Technical Discussion' started by CEJ, May 13, 2019.

  1. CEJ

    CEJ Member

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    Here's some data: I zeroed the mileage, reset the mi/kwh DM2 reading to zero, fully charged the battery and then drove 34.5mi in EV before exhausting EV charge and switching to HV. Then I fully replenished the battery, requiring 6.47kwh from the wall. So the total mi/kwh (including energy which never reaches the wheels--AC/DC conversion, fan, trickle charge, etc. that have been mentioned) comes to 34.5/6.47=5.33mi/kwh. Using SK's favorite estimate for the energy which is actually available for EV driving (5.46kwh) the result is 34.5/5.46=6.32mi/kwh. The final reading on DM2 was 5.9mi/kwh which is about half-way between the two.

    My assumption has been that the DM2 reading should in principle agree with the 6.32. To get this agreement the energy consumed in EV driving would need to be 5.84kwh instead of 5.46kwh, which, perhaps, is not that far off. I'll probably try it again to see how much the result fluctuates.

    P.S. My latest GOM reading on full charge was 40.4mi.
     
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  2. jb in NE

    jb in NE Senior Member

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    This may be a case of overthinking. When you run your car in ICE mode, are you tracking the losses in the wheel bearings, driveshafts, transmission? No. You put in gas and measure the miles driven per gallon. Do the same with EV mode. How many miles from how many KwH from your wall.
     
  3. Salamander_King

    Salamander_King Senior Member

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    Very interesting. Thank you for trying the experiment. I'd love to see you repeat the experiment. Unfortunately, I can not try the method myself for I do not want to reset the DM2 data. It is the only place I can see cumulative EV efficiency, I do not want to lose that data.

    A few questions. Is 34.5 mi in EV actual miles driven in EV mode? What was the EV range indicated on GOM? Did you just drive the car on EV mode and did not switch back and force between HV until all the EV range is depleted?

    I do not know how the car computes miles/kWh value in DM2 and the Eco Diary. Since we can not know the actual amount of kWh of battery used for given EV miles driven easily, we can't confirm the accuracy of this value. I have a suspicion that the value may not be that accurate just like the MPG display in the car. Of course, if one assumes the mi/kWh value is more optimistic than the actual just like the MPG values are, then the number 5.9miles/kWh may be high, thus making 6.32mi/kWh even far off from the real value. Would be interesting to see if the value of the energy consumed in EV driving, 5.84kwh, you deduced would fluctuate much each try. As I mentioned before, using Hybrid Assistant App, there was a single data point reported that this value is 5.22kWh. I will try using the APP next time I do longer than EV range drive.
     
    #283 Salamander_King, Jul 9, 2019
    Last edited: Jul 10, 2019
  4. CEJ

    CEJ Member

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    I wanted to get an accurate estimate of electrical usage for EV driving and thought using the DM2 reading would be a convenient way. This shows that it would probably give a result that is about 10% too low.
     
  5. CEJ

    CEJ Member

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    Yes, 34.5 mi was actual miles indicated on Main display speedometer and all driving done in EV (no switching back and forth) until EV range was exhausted at which moment I quickly noted the mileage. The GOM was originally around 40, I think, but I was using AC (very hot here) and am not sure what the GOM indicated when using AC (probably close to the 34.5 above). I just stuck with the actual mileage. The AC drain was just folded into the running of the car and, of course, lowered the numbers somewhat.

    Yes, the 5.9 seems high. But could that be because it can't take into account the energy lost in the transfer from the wall?

    Yeah, I'll definitely try again and we'll see how reproducible the results are.
     
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  6. Salamander_King

    Salamander_King Senior Member

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    Could you do me a favor and check your Eco Diary of the day you did that experiment. Is your Eco Diary "Average miles/kWh" for that day match your DM2 number of 5.9 miles/kWh? In your experiment, you have reset the DM2, so only number it should have registered is for that 34.5 miles of EV run. And if you did not recharge on the same day after the experiment and drive again in EV mode, the Eco Diary value for that day should be exactly the same as DM2.

    How the car actually measures EV range (miles) and electric energy used (kWh) for EV drive is total mystery to me. I also do not know how it "averages" the number over time. I have not come across any technical note on this. I just know it is just for the EV mode portion of EV drive and not including any "EV" portion under HV mode. In any case, the true value of electric energy (kWh) used for 100%-0% EV SOC seems to be somewhere between 5.2 - 5.8 kWh. That's 59% to 67% of the total capacity of the traction battery (8.8kWh).
     
    #286 Salamander_King, Jul 10, 2019
    Last edited: Jul 10, 2019
  7. CEJ

    CEJ Member

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    It shows 6.1 ave mi/kwh with AC load ratio of 3 (whatever that means) for July 9. However, it is probably not appropriate to compare this directly with the 5.9 since I didn't drive all 34.5mi yesterday, but some the day before. On July 8 the values were 5.6 and 22 (AC load ratio), when I believe I started the experiment. And you notice 5.9 is almost exactly the average of 6.1 and 5.6, so that seems signficant.

    I agree the GOM is aptly named. Sometimes I check it by zeroing trip A or B when I start out on full charge and then see if the sum of mileage on the MD and GOM reading remain close to constant as I travel to see how close I am realizing the full (guessed) EV range. This is straight-forward if AC and fan are off. Usually, I lose some of the predicted EV range but this clearly depends on one's driving tendencies.
     
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  8. Salamander_King

    Salamander_King Senior Member

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    Yeah, Eco Diary value from different day is not very useful. If you don't remember when you did the experiment or it is days ago that no longer the Eco Diary record exist (IIRC, it keeps past 32 days record), will you try to compare the DM2 value and Eco Diary value next time when you redo this experiment?

    Yap, the AC for both cool and heat really makes the estimate off. For routine commuting my driving condition day to day is fairly constant and during summer time GOM is very accurate on estimating actual miles driven. During winter, GOM seems to constantly guesstimate longer than actual EV range for me. I have been experimenting increasing daily miles/kWh under EV MODE by switching EV and HV mode to favor the EV range extension. I got average over 6 miles/kWh in month of June, and over 8 miles/kWh for July so far. The problem is that with switching EV/HV, I can no longer measure actual EV range accurately.

    IMG_20190708_160516.jpg
     
  9. CEJ

    CEJ Member

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    Do you agree that averaging 6.1 for July9 and 5.6 for July 8, the two days over which the 34.5mi driving occurred and getting about 5.9, is probably significant?
     
  10. Salamander_King

    Salamander_King Senior Member

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    Oh, that was the date you did the driving. So, did your drive actuary happened over two days in two separate drivings?
     
  11. CEJ

    CEJ Member

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    I started the experiment by driving on July 8 and finished July 9, with a total of 34.5mi. Eco Diary gave 5.6 mi/kwh for July 8 and 6.1 for July 9. The simple unweighted average of these two figures is 5.85, close to the 5.9 on DM2 for both days. Next time I do this (and I have already started today), if the total mileage is spread over more the one day, I will try to remember to note the mileage for each day and then compute a weighted average, which, I suspect, will agree with the DM2 number. Sound reasonable?
     
  12. Salamander_King

    Salamander_King Senior Member

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    OK, that sound perfectly good explanation. Yes, I think DM2 value is in agreement with the average of 2 days of EV drives, which is assuring that both monitors are using the same input from the car.

    I just played with my Hybrid Assistant App on my car, and found out that I don't really need to do a single trip to finish ALL EV SOC to calculate the total amount of kWh used. As it turned out, admittedly I have not explored this function before, the app has fantastic Report generating feature, which provides all the details of EV drive for each trip I make from the START to OFF. I have to spend more time reading the report to understand what they mean, but it seems to track very accurately distance of EV drive (not just EV MODE, but also provide map to depict segments of HV and EV), change in SOC, and amount energy (kWh) used and regenerated during the trip.
     
    #292 Salamander_King, Jul 11, 2019
    Last edited: Jul 11, 2019
  13. CEJ

    CEJ Member

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    Not sure I understand how you get higher mi/kwh by switching from EV and HV. Is this because you get charging in HV mode?
     
  14. Salamander_King

    Salamander_King Senior Member

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    Getting recharge from ICE is one factor, but in my case, I avoid climbing big uphills with EV. EV AUTO mode will shift to HV if you quickly accelerate into RED ZONE or you do high-speed driving but does not help low to moderate speed steady acceleration on a hill climbing. That hill climbing is the most energy-intensive segments of my daily commute and uses far more kWh than flat terrain. By switching to HV and using ICE to climb those hills I can conserve much more battery capacity for the rest of the road thus extends EV range greatly. One thing is that this is by no mean the most cost-effective or energy-efficient way of driving in many cases.
     
  15. Tideland Prius

    Tideland Prius Moderator of the North
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    Do you find EV Auto working at > 50% SOC? Cause I find it works the same in EV or EV Auto for the first half or so... below 50%, then maybe it'll make a difference (it fired up the engine at 32% SOC in EV Auto at 70mph to preemptively warm the engine before it got to 0%)
     
  16. Salamander_King

    Salamander_King Senior Member

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    To tell the truth, I don't know how "EV AUTO" behaves. I have not used that mode except for the first few weeks I was trying out. I gathered from others posting that "EV AUTO" pretty much do nothing except when you floor the gas pedal which I almost never do. Let me try using "EV AUTO" on my way to work today >50% SOC. I will report back.
     
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  17. drash

    drash Senior Member

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    Have to admit, I use the EV Auto button on longish trips (~>30 miles) because it’s easier to hit than remember what mode you selected with using just the EV/HV button. In winter I found it will fire up the ICE repeatedly to produce heat as the SOC approaches 50% if it’s really cold out and I’m using cabin heat. But it could be doing it to preemptively warm the ICE before it gets to HV level as you’ve pointed out. These are places I do banking and shopping that I can usually do in all EV mode during late Spring through early Fall.

    Maybe I should update the wish list to include voice confirmation when selecting buttons or screen commands, ha ha. Sorry but sometimes I don’t want to read anything if I have to glance down when I’m driving. The HUD is my new best friend but I wish it had other info like modes.


    iPad ? Pro
     
  18. Salamander_King

    Salamander_King Senior Member

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    Here is my morning commute today. I did all the way in EV AUTO Mode. 18 miles of rural highway with moderate elevation change. I drove fairly aggressively today but the ICE never fired up the entire way from EV SOC100% to 31% resulted with only 4.5miles/kWh. I even had AC heat on today to defog the windows. Yeah, HEAT, the morning temp was 58F, and was raining. The AC was set at 71F to blow warm air to windshield to defog the glass without using the front defroster. When I manually switched EV/HV for this exactly the same commute yesterday morning to avoid using EV on uphill, I ended up with 66% in EV Mode with change of EV SOC100% to 91% which resulted in whooping 21.2miles/kWh. According to Hybrid Assistant App, this trip used 0.19 gal of gas during the manually turned on HV segments which cost me $0.49 at $2.60/gal. This saved 3.22kWh of energy stored in the battery from the wall charge at $0.195/kWh or $0.63 cost. Or net gain of +$0.14. In reality the actual wall charge cost was higher than this value considering ~80% charge efficiency, making the cost saving even more like +$0.175.

    elevation 7-12-19.png
    EVauto vs EVHV-vert.jpg
     
    #298 Salamander_King, Jul 12, 2019
    Last edited: Jul 12, 2019
  19. CEJ

    CEJ Member

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    I have now done the earlier experiment two more times. Here is a summary of results:
    1. First time used 6.47kwh from wall to go 34.5 mi, so actual mi/kwh (including losses) was 34.5/6.47=5.33. DM2 (consistent with Eco Diary) gave 5.9mi/kwh which would require 5.847 kwh for 34.5mi (suggests this may be the amount used for EV driving).
    2. Second time 6.67kwh from wall for 32.1mi, giving 4.81mi/kwh. DM2 gave 5.6 which translates into 5.73kwh for 32.1mi.
    3. Third time 6.62kwh from wall for 32.4mi, giving 4.84mi/kwh. DM2 was 5.5 which translates into 5.89kwh for 32.1mi.
    The numbers 5.87, 5.73 and 5.89 are pretty close and seem to suggest this is the amount actually used for EV driving. Averaging them (5.83) gives 5.83/8.8 or 66% of battery charge available for EV.
     
    #299 CEJ, Jul 13, 2019
    Last edited: Jul 13, 2019
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  20. Salamander_King

    Salamander_King Senior Member

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    Great work. Assuming the DM2 is reporting the distance traveled per kWh of energy from the battery accurately, I do agree with your conclusion that ~5.83kWh was used for the full range of EV drive for your three trials. However, I don't think this amount of energy is the actual total energy stored in the traction battery from the wall. One question, were the three trials driving condition very similar?

    The reason I am still wondering about is this. The total amount of traction battery energy used for a full range of EV drive is actually not all from the stored energy (kWh) from the wall. I have been looking at the report generated by Hybrid Assistant App, and as it turned out even when you do all EV MODE drive there is a substantial amount of electric energy (kWh) generated during a drive that goes back into the traction battery. This amount is highly dependant on the driving conditions such as temperature, terrain, road surface, speed, and others. I don't have many data points yet, but I have done a few times. One such result from my commuting I did all in EV MODE for ~18 miles of drive, the app measured 3.926kWh from the battery, but it also showed 1.586kWh went to the battery, resulting in the battery energy balance of -2.341kWh. If DM2 report is based on this delta battery balance which I think it is and it should. I don't think you can use the number to calculate the total battery charge available for EV. What do you think?
     
    #300 Salamander_King, Jul 13, 2019
    Last edited: Jul 14, 2019
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