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Driving in "B" Mode Regularly

Discussion in 'Prime Main Forum (2017-2022)' started by stevepea, May 25, 2017.

  1. stevepea

    stevepea Senior Member

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    I know people are just trying to be helpful, but please realize that the Prime is a different car than the old PiP or a regular Prius.

    I have seen posts online recently from people with the normal Prius stating that the "B" on the normal Prius wastes energy instead of adding regen. Since I don't have the normal Prius, I can't and won't comment on it. But for those who do not actually have the Prime, I will tell you, that when you use "B" on the Prime, the regen meter goes on substantially. Instead of just a sliver (as in "D"), it's quite a bit the moment you take your foot off the gas -- and if you then press the brake just a bit, it's practically the full thing.

    To your replies:

    (1) "If the battery is full, then engine braking is the only choice."
    This is a moot point. As I stated from the beginning, I recommend using the "B" for flat driving only in EV Mode, NOT HV Mode. And as soon as one goes into EV mode, your battery will immediately start depleting. You'll never have a "full" battery after just a couple seconds in EV Mode. But if you're going to be doing any stops or slow downs in EV Mode (even in flat driving), having it in "B" will make that battery last longer than if you have it in D (and if you're just driving and not stopping, no effect either way as long as you're in EV Mode). That's been my experience so far.

    (2) The possible danger with the brake lights not coming on.
    This is a valid point, however while the amount of regen-stop with "B" is much stronger than the paltry amount with "D", it's not an immediate stop (if one needed an immediate stop, one would have to apply the pedal, showing the lights). For the last 12 years I've had a Civic Hybrid that had default, unchangeable regen very similar to "B" on the Prime (without the lights going on) and I never got into any accidents. It's one of those things where you really have to try it on the Prime yourself to see. On a scale of 1-10, if the Prime's "D" is a "1" then the "B" might be a "4" (and all the Civic Hybrids out there on the roads a 3.5).

    I'm hoping others with a Prime (should they feel like it) try it and see if they have the same results I've seen or not (those who have said they'd give it a try, I appreciate it!) It makes no difference to me how others want to drive their car, but I posted what I did because my observations so far -- for the Prime in EV Mode -- have convinced me enough to where I now drive in "B" regularly when in EV Mode (unless I know it's going to be all 100% fast freeway driving). I say that as someone (a) used to similar-to-B regen braking (without lights) from my old Civic Hybrid, and (b) someone who wants to extend the range of the battery as much as possible. Whether that's your style or not is up to you.

    I honestly appreciate everyone's help and comments, but please keep in mind that the Prime is a different car than the old PiP and normal Prius.

    -------------------------------
    Those with a Prime who'd like to give it a try to see if your results are similar, here's what I observed again:

    *When in EV Mode with "B" on all the time: no loss of efficiency under any circumstance (stop-and-go or fast freeway), though you'll only see the benefit if it's stop-and-go/city/typical rush hour commute driving. Benefit is that "B" mode will extend the battery longer than "D" mode with major regen for the battery (and super-high regen if you also press on the brake). Whatever the cause (even if it's merely due to the fact that with "B" the regen is immediate, but with "D+braking" there's always a delay before one can press the brake) -- whatever the cause, the battery range winds up lasting longer in "B". (And possibly saving wear on the brakes, though that's not the main focus). As far as the ICE, observed no difference (stayed completely off in EV Mode whether in "D" or "B").

    *WHen in HV Mode with "B" on: though the higher-regen is still the same, the end effect is lower MPG because I observed the Prime doesn't alternate to short EV bursts as much, and tends to stay in "gas" mode more. Also, no real need to make the battery last longer once in HV Mode, since, well, you're in HV Mode (and your EV charge has most likely already been depleted).
     
    #21 stevepea, May 29, 2017
    Last edited: May 29, 2017
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  2. giora

    giora Senior Member

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    You are giving a recommendation to others which is a wrong one.
    No matter if B is used or D with brake pedal, amount of regeneration depends on the difference between initial and final kinetic energy and the decelerating rate. this is physics that even the Prime must obey.
    In fact, using D position in stop-an-go situations, accelerating 'smoothly' and then releasing the 'go pedal' early and in timely manner is the most efficient way of using battery electrons in stop-and-go as the max. kinetic energy is the lowest and deceleration rate is the lowest this way.
     
    #22 giora, May 29, 2017
    Last edited: May 29, 2017
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  3. Bob Comer

    Bob Comer Active Member

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    I don't have my Prime yet to try, hopefully within a month, but it's not wrong logically if you are using more EV regen (electric motor braking) instead of just dumping the energy to the physical brakes. Sure, if you never use the brakes when slowing down to stop in D, it would be the same, but you'd have have a lot of people cussing at you from behind if you're slowing down too early, which i think you'd have to to make the regen do anything.

    I never slow down like that in my current prius, I'd get run over.

    In any case, my commute is not stop and go enough to make much of a difference, and I wouldn't want to not use the DRCC, so it would be a situational thing for me if I'm somehow out of my normal commute.
     
  4. stevepea

    stevepea Senior Member

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    Folks,
    I'm not going to get into an endless argument with someone who does not even have this car, cannot drive it to see for themselves, yet feels the need to insist that my observations are wrong, so I will just say the following:

    For those interested (who actually have the Prime and can actually test it out in the real world)...
    If you want to, please give it a try -- and let us know what your results are, either way!

    What I have said all along, was I have observed -- firsthand -- that the EV charge seems to last longer when driving in "B" when in EV-MODE, especially in City/Rush-hour traffic. Whatever "theoretically" should happen, the real world is not a laboratory. Whatever the cause (driving patterns... delay... [the strong "B" regen is immediate, whereas in "D"+Brake, most people let up on the gas with a pause before you can move your foot over the the brake pedal]... perhaps it's that with "B" it's all regen, with "D" some of it might indeed be brake pads... or maybe it's just little blue men from Saturn) --- whatever the cause, I wouldn't take the time to write this and change how I drive myself if I didn't notice a definite difference in the real world, with the actual car. With "B" seeming to help extend the battery charge more than "D".

    So I wrote up what I observed, and asked others curious and willing to try it, to post their findings.

    Perhaps it's some strange way I drive. Perhaps it's that the stretches/times I had it in "B" (each and every single time, by some heavenly miracle) were all more favorable than the stretches/times I had it in "D". I don't know, which is why I posted what I observed and asked others who want to try what their results are. But I'm convinced enough from my own real-world observations that I have started putting it in "B" when doing EV City/rush hour driving, because it seems to indeed make the charge last longer.

    So why don't we hit pause for a moment, and give others who actually have the car and want to try it, time to see if they get the same results or not. Please let us know either way! (Longer Charge... No Difference... Shorter Charge... whatever you observe!) EV-Mode only.
     
    #24 stevepea, May 30, 2017
    Last edited: May 30, 2017
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  5. giora

    giora Senior Member

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    OK, let's see what the folks that not only drove the car but actually designed and engineered it - are saying on the subject of stop-and-go and heavy traffic driving:

    In driving tips (page 97)
    .
    .
    Shift the shift position to D when stopped at a traffic light, or driving in heavy traffic etc...
    .
    .
    ● Drive your vehicle smoothly. Avoid abrupt acceleration and deceleration. Gradual acceleration and deceleration will make more effective use of the electric motor (traction motor)
    ◆ When braking
    Make sure to operate the brakes gently and a timely manner. A greater amount of electrical energy can be regenerated when slowing down this way.

    When driving in a traffic jam, gently release the brake pedal to allow the vehicle to move forward slightly while avoiding overuse of the accelerator pedal. Doing so can help control excessive electricity and fuel consumption.

    In tips for extending EV driving range (page 101):
    .
    .
    ● Maintain a safe distance from the vehicle in front and avoid unnecessary acceleration and deceleration

    Cannot find any mention of B position in those circumstances...
     
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  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Hummm, interesting observations but testing will be a challenge.

    My first thought was to use this benchmark loop:
    [​IMG]
    • 10 loops on cruise control+B+EV - measure before and end %SOC
    • 10 loops on cruise control+D+EV - measure before and end %SOC
    • 10 loops on cruise control+N+D+EV - measure before and end %SOC
    This loop is 1.1 miles and posted at 30 mph and a little more than a mile from some L2 EVSEs. I'll head over and put a full charge on the car with a late lunch and then drive to the loop. After the first loop, clockwise, I'll have to choose my START/STOP which can be either the lowest point, the exit from the western curve or the highest, the eastern curve. In the middle of the afternoon, the temperature should be constant and traffic low.

    Comments? Suggestions?

    The "N+D" means using N on the down grade and when the speed decays to the cruise control set speed, switching back to D and hitting resume to climb. In effect, there will be no regeneration. Neither will the brakes be used.

    Bob Wilson
     
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  7. giora

    giora Senior Member

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    I am not sure I understood the details completely as I don't see use of brake pedal on any of the tests?
    Why not several loops EV+B and no CC trying to maintain the desired constant speed by the throttle pedal (and brake pedal if and where B alone is not enough), and repeating same loops and speed in EV no B (and no CC)?
     
  8. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I have no way to quantify the brake pedal application but cruise control handles the regeneration consistently. If there is an enhanced regeneration in B over D, we should see a measurable difference.

    Bob Wilson
     
  9. Lee Jay

    Lee Jay Senior Member

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    In the real world, this is not true, and I do have a Prime. Braking a little in D mode is the same as not braking at all in B mode.
     
  10. giora

    giora Senior Member

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    I think (but not sure) CC cancels B (and replaces it with 'variable' B)?
     
  11. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I have made the assumption that cruise control works in B. I don't think cruise control worked with our Gen-3, 2010 Prius.

    Bob Wilson
     
  12. Lee Jay

    Lee Jay Senior Member

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    Cruise control does not work in B mode at all on the Prime.
     
  13. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Rats! That means I'll have to do some early morning testing but not on that slow-speed loop.

    I'll have to get on Research Blvd after midnight:
    • max acceleration to speed limit+10 mph, 75 mph
    • foot off until reaching minimum speed, 45 mph
    • repeat between fixed START/STOP points, once in D and then in B
    Bob Wilson
     
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  14. Trollbait

    Trollbait It's a D&D thing

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    First off, the ones writing the owner's manual of a car are not the ones that engineered and designed it.
    This paragraph also tells you to shift into P when parking, and not use N because the ICE is on but doesn't generate electricity. B gear is not addressed, but it is the same paragraph from the hybrid driving tips section of the plain Prius manual. So differences between the hybrid and plug in were not considered. At a quick glance, it appears these driving tips sections are the same between the two manuals.

    This sound advice for any car with regenerative braking regardless of which pedal controls that braking. With the gen2 Prius, I was able to control the amount of regen generated by the accelerator to the point of having it turned off. Does putting the Prime in B mode change the control over regen that the driver has in D?

    Does putting the car in B deactivate the simulated automatic transmission creep?

    This is true for any car, regardless of what gear it is in. If a Prime driver that follows this advice in D, why would they change their behavior when shifting to B.

    You should look into one pedal driving. From user descriptions, it sounds like B gear on the Prime is just a limited version.
    Only if the CC algorithms deemed they need for greater braking was needed to maintain set speed.

    The different gears aren't changing the amount of regenerative braking the car has available, just how the driver implements it. So any test that follows a deceleration rate map isn't going to show any difference. With B supply the same amount of braking with foot off as D with light brake pedal application, which one is better is going to come down driver preference. What regen settings do you prefer on the i3, Bob?

    In heavy traffic, I have put the Sonic's automatic into manual and kept in 2nd or 3rd gear; the turbo can start the car from a stop in these gears. I can use one pedal driving for much of time in those conditions. Can the driver behind hit me because I slowed down faster than they expected of the car without braking? Only if they weren't paying enough attention to what was going on in front of them. On the flip side, I'm not coasting up as much onto the bumper of the car in front of me, because greater engine braking means less distance covered by the car during the delay between foot off accelerator to foot on brake.

    Those seeing an increase in EV range while using B are likely just finding it easier to drive efficiently with it. Some have found using PWR mode in the hybrid let them get better fuel economy. If somebody is reaching the efficient driving end goal, does it matter how they do it?
     
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  15. stevepea

    stevepea Senior Member

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    For those wishing to see if they also experience the same better charging of the EV battery while driving in "B" (during EV Mode only), please remember that the benefit comes from starting and stopping, so using cruise control likely won't give you any discernible difference (though I observed no loss of efficiency when driving fast in B as long as you're in EV Mode, the gain came from rush hour type traffic). I was always in ECO, with both CC and A/C off (how I normally drive, at any rate those were the settings for both B and D). Besides controlled tests (also welcome) I'd welcome others to do some actual driving (city/rush hour) in B vs D mode (perhaps with CC off for that kind of driving) and report their findings in real-world driving. For whatever reason, I've personally observed enough difference to satisfy myself to do the extra thing of putting it in B for such drives, and (those unable to stop being absolutely sure of themselves aside), would again be interested in what others observe (whatever the results may be) while doing real-world city/rush hour driving.
     
    #35 stevepea, May 30, 2017
    Last edited: May 30, 2017
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  16. SaraBBrown94

    SaraBBrown94 Active Member

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    I tried the B mode going down a big hill land got a solid 1.5 miles (it was probably 2 miles down). I can't usually check it since it's usually pretty congested on that road

    Posted via the PriusChat mobile app.
     
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  17. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I'm about to head out to do some benchmarks but I noticed that the BMW i3-REx has no "B" mode. It has:
    • D - drive
    • N - neutral
    • R - reverse
    • P - park
    One reason is the regeneration is almost as strong as the acceleration. In fact, regeneration was reduced in early versions. But dynamic cruise control works in "D". This suggests that Prius Prime "B" may be somewhat similar to BMW i3-REx "D", a stronger regeneration.

    To test this hypothesis, I'll do some benchmarks of both Prius Prime "D" and "B". Assuming the ice does not come on and there is no other energy dumping mechanism, this may be the closest the Prime can come to BMW i3-REx driving. Except, the BMW i3-REx will come to a complete stop.

    Later,
    Bob Wilson
     
  18. stevepea

    stevepea Senior Member

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    Yes, that's what the "B" seems to me as well coming off the Civic Hybrid (which had strong regen as soon as you took your foot off the pedal) -- simply strong regen with no energy dumping, other than recharging the traction battery. Though I noticed a drop in efficiency when in HV Mode (because of the gas staying on more), I personally saw NO drop in efficiency at all in EV Mode (I also put the left-side, scrollable-up-and-down "MPG Monitor" display onto "miles/kwh" in EV Mode to monitor it, and would then switch back and forth between D and B for short spurts when keeping the speed the same... could see no loss of efficiency at all.

    Over the last couple days, I've continued to drive in "B" for my city and/or heavy-traffic-freeway trips with very good success. Again, this driving style may not be for everyone (especially those not used to higher regen when taking your foot off the pedal -- remember, I'm coming off of a car that had it for 12 years), but it certainly seems to be keeping the battery charged longer in EV Mode more than D (and when you need to actually press the brake while in B, the recharge level then goes almost all the way -- higher than doing so in D, it appears).

    But that's why I'm interested to see what others get when they try. Thanks for giving it a go... let us know what your results are, either way! (Remember to keep it in EV Mode/ECO) :)
     
    #38 stevepea, Jun 1, 2017
    Last edited: Jun 1, 2017
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  19. bwilson4web

    bwilson4web BMW i3 and Model 3

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    First I had to understand 'creep' in "D" and "B". Both appear to have a target energy shooting for 5 mph. However "D" will on shallow grades will reach 7 mph. In contrast, "B" clamps it to 5 mph.

    My next test we're to 30 mph and letting it slow to creep. There was a 3 to 1 difference in the distance with "D" having the longer coast down. So "B" has about 2-3x more regen than "D". You can set a rough idea by descending a grade and shifting between "B" and "D" to see how much regen is going on. I did it while in coast down and it appears (no photos, yet) to be 2-3x stronger in "B".

    If you are used to a stronger regen, use "B". It should work slightly better in traffic. I don't have enough to quantify the effect as driving style and traffic conditions also play a roll. Personally, I find dynamic cruise control, a safety feature, more rewarding in my driving.

    Bob Wilson
     
    #39 bwilson4web, Jun 1, 2017
    Last edited: Jun 1, 2017
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  20. giora

    giora Senior Member

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    Can you define better in this context?
    Suits better to the driving style?
    Higher efficiency?
    Better safety?