The 4 modes and the quest to the best MPG

Discussion in 'Prime Technical Discussion' started by pakitt, Sep 8, 2021.

  1. pakitt

    pakitt Senior Member

    Joined:
    Aug 10, 2009
    1,993
    1,205
    0
    Location:
    Colorado
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Six months have gone by, and I am starting to get a hang out of my new 2021 Prime. This is my 3rd Prius. The first one to own on US soil, the other two being owned in Germany.

    I have driven 4600k mi so far and long enough trips to see how she behaves when the ICE gets used. I also experimented a bit on some drives to see what happens with EV Auto and HV+EV modes.

    I also made an excel table to see how much 30 or so miles in EV mode affect the cost of a trip vs. using HV only.
    My assumptions are 31.8mi of EV range on a full charge (ideal); local gas costs of $3.35/gal average; electricity cost of $0.146/kWh; EPA average of 54 MPG (ideal).
    The table tells me that I save 15%-50% depending on trip lengths of less than 100 miles. After that, the savings go down to 3% with trips of up to 500mi.
    Of course, the fewer EV miles are driven (because of speed, terrain, temps, etc.), the lower the overall trip cost benefits.

    I am still wondering, though, if it is possible to improve the MPG on longer trips (more than the EV range) by using the different modes. In this regard:

    1. I am still very perplexed by EV Auto: EV mode on the Prime is "strict," meaning that you can press the gas pedal as much as you want, and the ICE will not fire up (which is actually nice). So by default, the Prime starts in EV mode to drain the battery, and then switches to HV mode no matter how I drive. EV Auto, with my driving patterns, behaves exactly the same. I also never really experienced a behavior for EV Auto like the one explained in the user manual (i.e., to give you "an extra oomph"). At highway speeds up to 85mph the Prime merrily uses the SOC, as if in pure EV mode, instead of switching to HV mode, which I would think to be more efficient. EV Auto seems pretty useless to me. I am reading on other posts/threads that starting up the Prime in HV mode, getting the ICE warmed up, and then switching to EV Auto will change its behavior and be more helpful. Is that a fact? And in general, should EV Auto mix HV and EV mode to work like an "enhanced" HV mode or an "extended" EV mode? What is EV Auto for at all? Is it a gimmick, like EV Mode in the Gen 3 and Gen 4 is? (The EV-only range and management on the Gen3/4 is essentially useless; you can simply accelerate lightly on a decent SOC and achieve the same result as EV mode. If you accelerate too much, EV mode will be disabled anyway. I used EV mode on the Gen3/4 only to move the car within a parking lot or a driveway, to avoid warming the ICE up.)
    2. CHG Mode: is it known how much extra fuel is getting burned to charge the battery to x%? Is there a situation in which burning fuel to charge the battery is more helpful to improve overall MPG? How does it compare to simply use up all the EV range and then go into HV to achieve the best MPG?
    3. Based on my excel table, and this is more of a statement than a question, it is clear that using up all the EV range before coming back home to charge it up is the best way to save fuel vs. HV mode only. My impression is that the best MPG is achieved if you can get to 0% SOC during a trip before the next recharge. Those 30 miles of EV range bring a tangible benefit on overall gas costs for trips up to 100mi. The question is, using CHG mode during a trip can further improve that? Can EV Auto improve that? Otherwise said: in a trip longer than the EV range, how can one achieve the best MPG by managing the SOC and "mode" depending on the type and length of the trip? What advice do you have based on your personal experience? In "vanilla" Gen 3/4 Prii, one had to hypermile. What do you do with a Prime? Hyper-switching modes? Can one simply "drive it" and get the best MPG, or does one need to fuss with switching modes all the time depending on where and how you drive?
    PS: If you are interested in having the excel table to calculate how much x miles of EV range saves you on a trip of overall y miles, please let me know.
     
    jerrymildred and Tideland Prius like this.
  2. schja01

    schja01 One of very few in Chicagoland

    Joined:
    Apr 22, 2005
    1,454
    990
    0
    Location:
    Chicagoland
    Vehicle:
    2018 Prius
    Model:
    Prime Advanced
    EV Auto is EV but if you really goose it the ICE will get added for more power. In pure EV under 85mph the ICE won’t be used assuming the heater/defroster are not being used.
     
    pakitt likes this.
  3. m8547

    m8547 Senior Member

    Joined:
    Aug 8, 2018
    918
    596
    0
    Location:
    Colorado
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    If the engine is already warned up, EV auto will take advantage of it a little more. Usually going uphill on the highway.
     
  4. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    8,600
    6,902
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    With my limited experience, with DRCC engaged, the EV Auto mode does trigger the ICE to fire up more frequently when power demand is high such as going steep uphill. Someone suggested this in another thread. I don't usually use DRCC on my normal driving condition, but when I did use DRCC and EV Auto on my regular commuting route, it did start the engine during a hill climb. But without DRCC, you are quite correct in that EV Auto is exactly the same as EV mode.

    As for the CHG mode usefulness, the only time it may be useful is if you have no charging capability at the destination but having a near-full (80%) battery charge will help to keep the cabin cooler or warmer while parked without starting the engine, like sleeping/camping in a car. But MPG-wise, I can not see any reason using CHG mode will beat the simple HV mode under the same driving condition. In your situation with higher gas prices and lower electricity, you should always aim to empty the full charge before the next charge session. If you live in an area with a higher electric rate, this is not always economical. Our current gas price is $3/gal and electricity is at $0.21/kWh. For now, it is cheaper to drive on EV mode, but when the gas price gets below $2.85/gal, it becomes cheaper to drive HV.
     
    pakitt likes this.
  5. pakitt

    pakitt Senior Member

    Joined:
    Aug 10, 2009
    1,993
    1,205
    0
    Location:
    Colorado
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    I tried this morning to start the car in HV mode, get the engine to warm up, and when I saw that it was done I switched to EV Auto. I tried accelerating a bit more aggressively up to 55mph (the max I could do on my route) and nothing happened. Merrily going on in EV, no a blip from the ICE.
    I think with DRCC on and EV Auto selected the ICE will fire up because the DRCC has the bad tendency to accelerate very aggressively to keep up the speed. Not very environmentally (or MPG) friendly, IMO. I remember on the Gen3 and Gen4 I owned, that if you put the car in Eco mode (or power) it will respect the setting in accelerating while trying to keep the speed in DRCC.

    Long story short - for me EV Auto is useless and it is a pity to drive a 21st century drivetrain, with software from 1990. Like the the entertainment huge screen in the middle of the console with pretty basic graphics and tiny space for Car Play - what a waste. I rented a Gen4 basic last month, and the screen was nice and wide, better than this useless "thing" in the prime. Toyota marketing...

    Yes, I agree, goal of the game is to come back home always with SOC to zero (assuming one drives more than the 30 or so miles EV Range). And in the case you describe, with my table, the advantage to drive EV and then HV for the rest of the trip, goes down significantly (6-17% savings vs driving HV only, instead of 15-50% in my case, for trips shorter than 100 mi)
     
  6. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    9,945
    12,213
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    The Prime kind of hyper-miles all by itself. Unless you're going over 60 mph, fighting a headwind, or climbing a hill, it'll keep switching the ICE on & off its own. When it's running the ICE to recharge what it had been borrowing from the battery, it'll run at the most efficient speed and throttle setting it can manage while still meeting the requests from your right foot. For example, every other week, we have a 42 mile round trip to make. We are at our destination long enough for the ICE to cool quite a bit, so I don't run it at all on the way over there. On the way back, I stay in EV till the range is used up. The ICE turns on and I continue on my merry way. Speeds are mostly 50 mph with some residential speeds at each end. If I reset a trip meter when the ICE comes on, it'll show close to 70 mpg for the HV part of the trip. If you keep starting & stoping the ICE manually, you might not be running at optimal temperatures or RPM.

    Same story with mine. Warmed up ICE. Stand on the accelerator as long as I dare to, not a peep from the ICE.
     
  7. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    8,600
    6,902
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Try the DRCC with EV AUTO mode. I tried it on mine and I observed the engine starting on the uphill going 40mph on my usual commuting route. I don't know if that is a more efficient and smoother ride than going all on EV, but at least for the first time, I experienced how the EV Auto works. The same route if I drive without DRCC ann EV AUTO, the engine does not come on at any point.
     
    pakitt and jerrymildred like this.
  8. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    9,945
    12,213
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    "Uphill" ... lessee here. Oh yeah! I remember that from our trip to Maine a few weeks ago. I have no idea when I'll see another hill. Probably if we go to Ohio next spring. :LOL:
     
    Salamander_King likes this.
  9. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    8,600
    6,902
    0
    Location:
    New England
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Oh, I forgot you are a flat-earther. :ROFLMAO::ROFLMAO::ROFLMAO:
     
    jerrymildred likes this.
  10. Old Bear

    Old Bear Senior Member

    Joined:
    Sep 15, 2017
    663
    1,001
    20
    Location:
    Boston, Massachusetts USA
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    There is really no virtue in "warming up" the engine. Please see my earlier post and the article which it cites.

    However, if you do start the Prime's ICE, it will run for several minutes to warm up the catalytic converter before shutting down on its own. I discovered this behavior when I mistakenly pressed the front windshield defrost button for clear some minor interior fogging. Since then, in similar conditions, I usually just turn on the A/C and set the fan speed to high for a minute or so, thus avoiding several minutes of unnecessary gasoline burning.

    The Prime is pretty smart about when it needs the ICE for supplemental power -- and that is on rare occasions and usually at higher speeds. I don't believe the ICE would add much to acceleration response because the torque of the electric motor is greater. Possibly someone with greater mechanical engineer knowledge can confirm or deny this.
     
    mountaineer likes this.
  11. pakitt

    pakitt Senior Member

    Joined:
    Aug 10, 2009
    1,993
    1,205
    0
    Location:
    Colorado
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    Yesterday I did a round trip to Denver. Started with EV mode on a full charge before entering the highway. The drive to the ramp is about 7mi of very hilly terrain. As I started to go down the last hill, I activated HV mode to make sure the ICE was warmed up before I took the highway. I don't know how "smart" the Prime is in warming up the ICE from EV mode to HV mode, while driving at 60+ mph...

    When I arrived in Denver, I turned on EV mode for the city driving section of the trip.
    On my way back I did the same, EV mode in the city, HV on the highway.
    When I started going downhill on the highway before getting to my off ramp heading home, I turned EV Auto. To my surprise the ICE turned on and pushed the car at speeds of about 50mph (I kept the accelerator pedal in the same position as I made the switch between the modes) and my battery was over 50%.
    So, meh, still confused about EV Auto mode...
     
    vvillovv likes this.
  12. vvillovv

    vvillovv Senior Member

    Joined:
    Mar 19, 2013
    1,685
    613
    0
    Location:
    NY
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Keeping track of all the data you gather is the fastest way to get a handle on how the Prime works.
    The thing I'm noticing lately while switching between HV/EV during one driving session -> (Ready mode - drive - Park and shutdown) is that the Prime hardly ever does the same things, even when driving the same route and driving it the same way. perplexed....
     
  13. Old Bear

    Old Bear Senior Member

    Joined:
    Sep 15, 2017
    663
    1,001
    20
    Location:
    Boston, Massachusetts USA
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    To understand the internal operation of the Prius Prime, you cannot view it as an isolated and autonomous element of technology. You need to consider it within the larger context of the astral universe.

    This chart may be of assistance:

    astrology-chart.jpg

    Then again, it may not.
     
Loading...