Engine only MPG

Discussion in 'Prime Fuel Economy & EV Range' started by Salamander_King, May 2, 2022.

  1. Rmay635703

    Rmay635703 Senior Member

    Joined:
    Oct 16, 2016
    2,161
    1,373
    0
    Location:
    Somewhere in Wisconsin
    Vehicle:
    2013 Chevy Volt
    Model:
    N/A
    So in effect the fuel economy you get when driving with an empty battery?

    The theoretical “load level” economy that happens with cycling is sort of meaningless
     
  2. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    "empty" as in dead traction battery which Prius is not capable of, not the "empty" as in still can drive on HV mode.
     
  3. Rmay635703

    Rmay635703 Senior Member

    Joined:
    Oct 16, 2016
    2,161
    1,373
    0
    Location:
    Somewhere in Wisconsin
    Vehicle:
    2013 Chevy Volt
    Model:
    N/A
    Yep so everything I mentioned is 100% accurate

    With a “dead” hv battery I can definitely decelerate in a way that makes the motor shut off and “glide “ with minimal regeneration .
    Likewise I can accelerate in a way that doesn’t appear to dig into the battery buffer while not being a total wet blanket and charging during acceleration

    Even in the Volt I can do the above and in the Gen IV I tested ditto

    I see no reason that old school economy couldn’t be calculated driving without plugging in at different average speed tankfuls. Just time consuming

    Also likely on “gas only” you will find as stated a hump above and below which economy is worse.
    Every other PRII I tested had that Goldilocks speed
     
    #23 Rmay635703, May 4, 2022
    Last edited: May 4, 2022
  4. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    I did not say your statement was inaccurate. It was just irrelevant to answering my question.

    In any case, Jerry's explanation satisfactorily answered my question. The only thing left which is testable is to see if I actually get "worse" ICE-only mpg using my calculation method if I obtain the same type of data with above 75mph only speed. If Jerry's theory is correct, then the ICE-only mpg should drop at a very high speed, which I don't usually do.

    Just out of curiosity, how can you drive a PP with a "dead" hv battery? I thought that was not possible.
     
  5. mmmodem

    mmmodem Senior Taste Tester

    Joined:
    Nov 17, 2011
    2,680
    1,653
    0
    Location:
    Bay Area, CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    So we both agree with @jerrymildred. The PiP has a trip meter-ish menu for EV miles and kWh used. I never reset mine so it's a lifetime usage for my PiP sans whatever the dealer did for the first 50 or so miles.

    I'm curious why your EV ratio isn't zero if you trip has no stops and average speed is above 43 mph. I haven't driven a Prime so I'm not versed in it. But in the PiP, if the EV portion of the battery is depleted and one never stops or goes below 43 mph, then on your two example trips EV ratio would be zero as the ICE never turns off. Does the Prime engine turn off at higher speeds?
     
    Salamander_King likes this.
  6. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    I have never driven Pip, but I had Gen3 before PP. The PP is way more efficient in HV mode than Gen3 was. In my driving condition, I can go to EV (not the EV mode but EV under HV mode) up to ~65mph without an effort. The engine does actually stop and propel the car in EV with the M1 electric motor only if the terrain is flat. If it is on a downhill, I can go longer on EV without the engine firing. The 72mpg with a 51% EV ratio was obtained that way. But at speed above ~65mph, the engine was on most of the time unless it was very steep downhill which I did not have on this route. That was the way I drove on the trip 54mpg with a 19% EV ratio. I would say above 70mph, the engine never shuts off making the EV ratio to be near 0%, but sustained 70mph or faster has not been tested. Maybe for my next trip on the interstate, I will try that on the segment of the trip recording only while the sustained speed is 70mph or above.
     
    #26 Salamander_King, May 4, 2022
    Last edited: May 4, 2022
    mmmodem likes this.
  7. Gokhan

    Gokhan Senior Member

    Joined:
    Oct 5, 2008
    1,603
    739
    0
    Location:
    Paramount CA
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    It's probably a warmup effect. You're seeing poor mpg because of a cold engine in short trips with a lower average speed.
     
    #27 Gokhan, May 4, 2022
    Last edited: May 4, 2022
    Rmay635703 and Salamander_King like this.
  8. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Well... No. But that's OK. I already got a Good Answer. LOL

    upload_2022-5-4_18-45-13.png
     
    Gokhan likes this.
  9. Gokhan

    Gokhan Senior Member

    Joined:
    Oct 5, 2008
    1,603
    739
    0
    Location:
    Paramount CA
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Salamander_King likes this.
  10. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    10,744
    13,103
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    First, let me say that I'm flattered that some of you like my theory. But it is just a theory. I'm not 100% sure it's right.

    But regarding the quotes I have here, having driven both the PiP (2 years) and Prime (3 years), I really miss that feature on the PiP that told you exactly how many miles you drove in HV mode and how many in EV mode plus the kWh used. It's not relevant to @Salamander_King's question, but it's nice to have. Instead, the Prime says, in percentage, how much of your driving is with the ICE on and how much with it off regardless of the mode chosen by the driver. Also interesting info. I wish I could have both.

    As for the difference in when the two cars have the ICE on or off in HV mode, it's pretty amazing. The Prime is seemingly eager to shut off the ICE. We have lots of very flat roads here. At 50 mph, my ICE is off nearly 50% of the time. That percentage increases at lower speeds. It still shuts off a lot at 60 mph, but above that it needs a tail wind or downslope.

    Because of the one way clutch between the engine and transaxle in the Prime, MG1 can help MG2 in powering the car in EV mode. That allows EV speeds up to 84 mph. That's not possible in a PiP or even a regular Gen 4 Prius.
     
    Hicksite, mmmodem and Salamander_King like this.
  11. Gokhan

    Gokhan Senior Member

    Joined:
    Oct 5, 2008
    1,603
    739
    0
    Location:
    Paramount CA
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
  12. FuelMiser

    FuelMiser Senior Member

    Joined:
    Jun 29, 2008
    1,039
    732
    0
    Location:
    Monument, CO
    Vehicle:
    2016 Prius
    Model:
    Touring
    My thoughts exactly! There is no such thing as ICE only.
     
  13. mmmodem

    mmmodem Senior Taste Tester

    Joined:
    Nov 17, 2011
    2,680
    1,653
    0
    Location:
    Bay Area, CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Interesting. I used to keep ~0.5 mile of EV in reserve in my PiP on trips where I know there are declines. This allows me to coast with the ICE off up to 62 mph instead of 43 mph. The trips have always been too irregular to accurately measure whether there was any benefit at all. Learn something new everyday, thanks. (y)
     
  14. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    OK, I have a plan. On my next interstate trip, I will record the segment of the trip with sustained 70mph or above speed with 100% SoC (thus no room for recharge).
    If Jerry's theory is correct, then this sustained 70mph or above speed segment of the trip should show a 0% EV ratio, no SOC change, and no charing from the engine, thus no conversion loss. And we all predict the ICE-only MPG calculated the same way as I did would show decreased MPG than the average speed 61mph data with 19% EV ratio I recorded previously.
     
    mmmodem and jerrymildred like this.
  15. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    OK, I was able to do the experiment I planned, which is to record the segment of the trip with sustained 70mph or above speed with 100% SoC (thus no room for recharge). I was able to do multiple segments on my trip on the interstate highway at sustained speed above 65mph. Those data points are added to the previous graph. The data points inside the red circle in the graph are the new data.

    upload_2022-5-10_14-14-31.png

    The result is not conclusive, but I can see a trend of ICE Only MPG calculated the way I did drop a little when the sustained speed was above 70mph. Here is one example of a segment (1 hr continuous drive) on CC set at 78 mph, resulting in the sustained speed of 75mph with the EV ratio of 0%. At any point, the speed did not go below 74mph in this segment.

    It is remarkable that even at this speed and presumably with no traction battery helping the car to propel, the engine alone was able to maintain 46.3mpg.

    upload_2022-5-10_14-18-45.png
     
  16. Ovation

    Ovation Active Member

    Joined:
    May 11, 2021
    146
    113
    0
    Location:
    Quebec
    Vehicle:
    2021 Prius Prime
    Model:
    Base
    As I make several 200 mile round trip commutes a week and gasoline here (as of yesterday’s fill-up) is 7.83$/gal (2.07$/litre), I’m ecstatic about the fuel efficiency, whatever mode I’m in. This breakdown noted above is quite interesting and also reassuring regarding my decision to buy my 2021 Prime. In one year and 3 weeks of driving, I have about 47,000km/29,000 miles, so my happiness with the car is genuine.
     
    Salamander_King likes this.
  17. vvillovv

    vvillovv Senior Member

    Joined:
    Mar 19, 2013
    2,464
    886
    1
    Location:
    NY
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Sal is ignoring me so wouldn't see this post and Quote it again, but he forgot to mention if he noticed any SOC changes during the trip (which he started at 100% SOC (thus no room for recharge)) as stated in post # 34 and 34 . On longer trips that I start at 100% I typically notice SOC changes, not that I'm actually looking for that stat. So I agree with Jerry that it's at least Very hard to calculate ICE only mpg in a Prius Prime if not near impossible. I for sure haven't figured out a way to do it.
    edit I'll do my best to honor Sals request to ignore his posts as well in the future. And I hope this doesn't offend anyone else.
     
    #37 vvillovv, May 12, 2022 at 12:47 PM
    Last edited: May 12, 2022 at 12:59 PM
    bisco likes this.
  18. mmmodem

    mmmodem Senior Taste Tester

    Joined:
    Nov 17, 2011
    2,680
    1,653
    0
    Location:
    Bay Area, CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    That is remarkable. I recall the worst fuel economy I ever got for my PiP was on a drive between San Francisco and San Diego on mostly flat Hwy 5: 43 mpg. This was with a speed limit of 70 mph and frequent jaunts to 85 mph when I could find a shiny BMW to follow in the fast lane. This is with a full car with luggage for a week vacation. I unfortunately didn't log what average speed was.

    As flat as Hwy 5 is, I think the traction battery did play a role on fuel economy on small elevation changes. Charging on the way down and providing a little oomph on the way up.
     
    Salamander_King likes this.
  19. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    9,909
    7,852
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    I should have noted that the segment records from my previous comment were with 4 adults in the car. With a cargo, I would estimate around 750lb of load on the car. The weather was good, had A/C on AUTO 70F. There was some wind, and yes, there were some segments that did have elevation both incline and decline but not extremely hilly.

    One thing is that for the segment recording, I used TripB by resetting the trip meter at the beginning of the segment and taking the photo record of the Drive Monitor data at the end of the segment. Each segment was either 1-hour duration or 30 min duration. Here is the complete set of data I added to the graph above. Note that CC was done with cruise control and MA was done by manually controlling the speed. Since there is no starting acceleration and no engine warm-up, the fuel efficiency is purely for the traction of the car for the given average speed.

    upload_2022-5-16_15-15-50.png

    One another observation I made during the experiment was that, with CC, there was very little speed variation but with manual control, the speed varied much wider. And the car would go into EV (engine shuts off) every time I decelerate the car and speed hit the 72mph. This "72mph" EV switch did not happen with the CC on. Even if the DRCC decelerated the car down below 72mph, it would not go into EV. It had to go much lower speed or the car has to be on a long downhill for it to go into EV while on CC. That is one of the reasons that even at the same average speed, MA driving almost always had a better EV ratio and thus better MPG. Because of this reason, my impression was that PP does better on overall mpg without DRCC for the same average speed.
     
Loading...