Prime- Forced regen trick.

Discussion in 'Prime Fuel Economy & EV Range' started by Gen3PP, Apr 29, 2019.

  1. Gen3PP

    Gen3PP New Member

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    We know about the holding HV-EV to get a forced regen. From a YouTube video... you will get around a 32mpg equivalent from this forced regen for later EV use scenario (don't quote me). If the engine is cold you will get much less.

    I am not able to charge often. I would like to be able to EV on my short trips ( less than 3 miles round trip) to avoid the ICE warm up mpg hit.


    If you forget to engage your Hybrid mode when you start your car, your battery will drain down in one of the default HV-EV or EV modes I have found that if you toggle between to HV-EV to Hybrid and back to HV-EV, you can reset your Hybrid target battery level to the currently displayed level. For instance, when you come to a regenerative stop or go down a long hills your battery charge in general will be above your current target level of battery charge (this is not displayed, but your car is working to maintain this level in hybrid mode). If you toggle out of and then immediately back into hybrid mode, the new target battery charge will be the one you have on your display. if you keep doing this you can ratchet up your target battery charge. This should be done when the ICE has warmed up.

    Since this is not an all out forced charge, the Prime seems to be more efficient doing the Regen this way. From what I can tell, the Prime is still making above 50mpg equivalents!??!
     
  2. Gen3PP

    Gen3PP New Member

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    To follow up. I have started this experiment with 156 miles at 72.4 mpg with 4.2 miles of charge remaining, I am now at 252 miles at 72.2 and 4.4 mile of charge remaining (All work trips). At one point, I was up to 10 miles of charge with 71.4 mpg showing. I have generated around 12 extra miles of charge using this trick for 3 short EV trips. So it looks like there are almost no perceivable hit for doing this. I believe this is because you are basically stealing regen miles just after they have been produced. The car is not put in position where it has to catch up with charging in an inefficient way. I would say there is no mileage hit for doing this trick except for the fact you have to keep pressing buttons.
    I guess that the 12 miles in EV saved me from starting ICE 3 times.

    I could see using the battery reserve in a camping situation away from charging stations where you wanted AC and didn't want the ICE to start up during the night.
     
  3. jb in NE

    jb in NE Active Member

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    Somewhere along here you lost me. What is the trick? And on what vehicle are you doing this?
     
  4. kevin.c

    kevin.c Junior Member

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    Probably talking about Charge Mode by holding the HV button
     
  5. Tideland Prius

    Tideland Prius Moderator of the North
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    It’s not CHG mode but it sounds like he’s employing some sort of PiP trick in the Prime. But I, too, don’t understand why he needs to “reset the target battery level”. Or why it’s moved in the first place. The Prime can charge up the battery in HV mode such that you can go back into EV mode but I guess if you didn’t want to be in EV and save the charge, you could switch back to HV mode.

    But yeah I’m still not clear on this purpose.
     
  6. Gen3PP

    Gen3PP New Member

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    Yes...Prime. Talking MPG savings. ...Forced charge (shortest amount of time) has a big MPG penalty Vs Toggling in and out of hybrid only mode just after regen stops when the EV miles to go meter has just moved up (This latching up takes a lot longer than the forced charge way) ..Note in the Charging mode, ICE is on all the time no mater what you are doing ( no mpg optimization).. ... Your mileage will vary.
    Hybrid mode only (HV)... The problem with understanding this is that the miles to go EV meter is always moving above and below the target Miles to go target. This target is not displayed, you only know what this number is when you see the miles to go number on your display with you toggle in and out HV mode. You must remember what that number was when you pushed the button. In my experience you will see your Miles to Go To will vary between .3 above and below .3 this set target.

    Example(not exact numbers)..I am in HV only mode cruising at at 50 mph and the EV miles to go is showing 5.5 miles. I hit the HV-EV button twice so I am go out of HV and then back into HV (toggle HV). I now know my target EV miles to go is 5.5 because I just set it (the computer has stored this value even though the meter values you see are varying from 5.2 to 5.8 mile to go ( +.3 to - .3 miles). I now brake and come to a stop using regen braking. The meter reads 5.9 miles to go. I now toggle out and back into HV using the HV-EV button to set 5.9 miles to go as the new target level. The car after this point will try to keep the miles to go center around 5.9 miles to go (+.3 to -.3 miles or 5.6 to 6.1). if you repeat this process over and over when you come to stop, you can move up your miles to go meter all the way up to its max allowable level.
     
    #6 Gen3PP, May 1, 2019
    Last edited: May 1, 2019
  7. jerrymildred

    jerrymildred Senior Member

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    I see what you mean. I used to do that sometimes with my PiP. I also called it "ratcheting." Usually on longer trips on back roads when I expected to have some lower speed EV driving ahead. I could build up several miles of EV range by going from HV to EV and right back after stopping at a stop sign or something like that.

    However, there is still a hit because now you've locked that energy into the battery and next time the car uses electricity to help out the ICE, it'll have to charge the battery back up to that new and higher level. So, while I think it does help some, it might not help a lot except in special circumstances. Having it available to avoid a cold start the next day might be one of them, but I'm not sure it's more efficient than charge mode. Either way, the ICE has to make the electricity. It is kind of fun, though. :)
     
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  8. Tideland Prius

    Tideland Prius Moderator of the North
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    Ohhh ok I see what you mean now. It is similar to the PiP trick. (Although if you switch to Drive Monitor 2, you can see the distance remaining anyway).
     
  9. bruceha_2000

    bruceha_2000 Senior Member

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    I didn't follow it the first time around but the explanation made sense. I don't know how all this works but from my observations, when you go from EV to HV the car does generally try to maintain that level of charge on steady state driving. So if the quick switch from HV to EV and back sets the "battery charge set point", I can see how it would work. I'll have to try it some time though a lot of my drives longer than I can EV only are EV to the interstate, HV, EV off the interstate and around town, HV back to interstate 'start' point, EV home.nothing there to test this theory.
     
  10. Gen3PP

    Gen3PP New Member

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    Update..... I noticed that you cannot do the charge trick if you have already drained your battery all the way down to the point where "_" is showing in your EV miles to go display; it will be stuck there. The work around is to get into the forced charge mode (Hold HV-EV button until see the flashing "Charge" symbol, then let go). Once you have any amount of Miles to go showing you then can then do the trick.
     
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  11. Gen3PP

    Gen3PP New Member

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    20 miles to work to collect 2 miles of EV. The car cools down. Then use the 2 miles of EV only to Mickey Ds (no cold low milage ICE). Note, If you do the tick to the extreme, it will be just like doing a forced charge.
     
    #11 Gen3PP, May 9, 2019
    Last edited: May 9, 2019
  12. jerrymildred

    jerrymildred Senior Member

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    I haven't tried it with the Prime yet, but in the PiP you could do the ratchet trick with no EV range if you had a big enough hill. I did it in the Smokies a few times last year. It would suddenly just from no EV to about 0.6 miles instantly. But, yes, in normal driving, you'll never get enough in the battery from braking/coasting to push it up into that charge area.
     
  13. Pdog808

    Pdog808 Active Member

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    I did this coming down the Grapevine (I-5 in CA) last year. Since it's so steep, I drop the car from HV to EV and switch to B-mode (versus D-mode) and can gain up to 15% back into my battery. Note, I believe if your battery is over 80% (not sure about this) and you switch to B-mode, the engine may turn on even though you are in EV mode in order to apply regenerative braking.

    If you leave the car in HV mode after you go downhill, the extra 15% will get "trimmed" back down to the battery level you were at the top of the hill. You pop it into EV to have the car "remember" the new level and keep it there for use at a later time.
     
  14. Gen3PP

    Gen3PP New Member

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    I am guessing that if you repeat the HV-EV to EV and back a few times going down this hill, you may get allot more, but I have not tried it.

    In the equation somewhere in the B mode, is the fact the computer is forcing/allowing the engine to rev high to act as a drag so the battery does not overcharge and also slows the car down. On my gen 3, I had a scan gauge with a RPM tack mode, which confirmed this (not tried on the prime). Did you every notice the signs for the big rigs to use low gears going down the hill and when you pass them going down the hill you can hear their engines scream from the high revs (more of an old school manual trans thing). In the same vain, but more extreme are the Jake brakes on trucks (google).
     
    #14 Gen3PP, May 13, 2019
    Last edited: May 13, 2019
  15. Pdog808

    Pdog808 Active Member

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    I drop it into EV then B mode so that I don't have to apply the brakes as much on the downhill. I leave B mode on when doing all EV driving (see @stevepea posts on driving in B mode when in EV (only)).
     
  16. ReDave

    ReDave Junior Member

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    Is using the B mode better than using the cruise control? I've been using the CC for my daily downhill speed control, and battery charge up for years. I LOVE how the new prime has like a super brake mode, not the DRCC, but if i tap down the CC lever a couple of times, it BOOM, goes into super slow down mode, which, i assume, is charging the battery.
     
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  17. Pdog808

    Pdog808 Active Member

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    Not sure about using CC. But I believe that B mode will do what you are simulating in CC and with more control.

    B mode in pure EV just ups the regen rate and allows you to slow down by minimizing brake pedal usage when you let up on the gas pedal. In my opinion, this helps avoid loss of regen by reducing the chance that you will engage the brake pads and thus waste energy (as heat between the pads and rotor) that you could have "gained" back as regen.

    Perhaps the better way to explain it is when you are in EV and change from "D" to "B" mode, the car decelerates much more aggressively when you let up on the gas pedal. This deceleration is your regen. You get a gentler deceleration curve when the car is in "D".

    Bleh - hope this makes sense.
     
  18. bruceha_2000

    bruceha_2000 Senior Member

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    But if the hill isn't steep enough to hold speed in B mode, you have to apply some go pedal. Does that just ease up on the B mode braking?
     
  19. Pdog808

    Pdog808 Active Member

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    Adding brakes doesn't ease up on B mode braking but just adds to total regen. The key is to keep the regen meter from "maxing" out. When regen is maxed, it means that you are using brake pads to augment the deceleration (and wasting energy).

    It would have to be a very steep hill to overcome B mode deceleration (i.e. the Grapevine on the I5 for example).
     
  20. Gen3PP

    Gen3PP New Member

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    I have boosted mileage up to 28.0 EV miles to go using this trick. The battery meter shows all but a pixel's worth to max EV. It seem like it was harder to make the last 5 miles to 28.0 EV. After hitting 28.0 the meter never moved above 28.0 and rarely moved below it when locked into HV mode. This is probably bad for the battery to stay at max charge while charging. Toyota seems to have engineered the car to drain the battery down to lower levels unless the driver hits the HV mode button at every startup.
     
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