B mode: What is the advantage to use B mode when driving, more regeneration? more economy?

Not to change the direction of the topic but I wonder (and I will find out soon enough) how much current is going back into the battery. I know on my '16 Prius that I traded in it would get about 100-120 amps (at around 208-240 volt) which didn't last long because in a few minutes the battery would be charged. I can definitely tell that the regenerative braking is more aggressive over the other Prius so I'm going to guess that it is twice the current going in.

I also notice in HV mode that the ICE will rev up a little bit more under certain conditions and I know it is not because the car weighs a couple hundred more pounds, I suspect that the ICE charges the traction battery at a faster rate. The regular Prius I recall would charge at 20-30 amps.

All that is from a OBDII scanner, I would watch a lot of live data, most monitoring battery SOC and temps and whatnot.

 

Yup, the scanner will give you your data. When I was in the Smokies a few weeks ago I got some pretty big regenerations coming down off Clingman's Dome and Newfound Gap, and my PiP battery was not quite big enough to take it all. Your Prime probably could absorb all that charge if you ran down your EV range going up. Some of that was in B and some in D depending on how steep it was.

 

Yep, that's what mind looked like... So we have Cowee mountain and Winding Stair Gap to go up and down. My thoughts are to use EV going up and then regen down. I racked up from 0% EV to 50% between the two mountains. So something around 3 kWh? Perhaps obsessive data hoarding can confirm lol

edit: Now clingman's dome on the other hand yeah you'll have enough to power a small town on lol

 

Maybe apples/oranges, regular Prius vs Plug-In, but anyway: if you're coming down a long hill, where the battery's going to top-up and the car fall back on friction brakes only, B will delay that happening, reduce the brake wear?

FWIW, even with our regular Prius, coming down Mount Seymour, mostly in B, the car indicated it was charging all the way to the bottom. Maybe without B it would have hit the limit, don't want to find out.

 

I wonder if anyone can confirm or deny what I noticed today about "B" mode (or even in general) when braking downhill from a full charge. We just bought a house in the hills above the town. I was doing some work getting ready to move in and figured I'd top off the Prime for a couple hours while there. I got to a full charge. When I left, the "guessometer" said 32.6 miles left. I then went down a short but fairly steep hill in 'B' mode that usually restores 0.6 to 0.7 miles of range (takes a little over a mile off on the way up). The guessometer remained at 32.6 miles all the way down, as if it didn't recapture any charge down the hill. BUT -- I drove for at least half a mile before it clicked down to 32.5 and then downward normally.

I could be wrong, but it seems to me like the Prime is saving the extra regeneration even if doesn't report a guessometer more than 100% "full" (knowing that full isn't really "full" to preserve battery life) -- and uses that excess until back under what it considers a full charge, and only then the guessometer starts ticking again.

Anyone else observed anything like this? Just curious if that's how it is supposed to work.

 

I found for myself, using B mode gives me more EV range than D, in the Prime.
Even if on paper they should be the same, the real world, with varying factors, is often different than paper equasions (amount of brake pads vs engine brake, even the delay time between moving you foot from gas to brake if in D vs the instant braking of B)... whatever the factors are, I have found in multiple real-world tests between B and D, that I get better range and m/kw readings when in B over D -- in EV mode, of course. In HV mode, I have found B to use more gas than D (naturally, but I verified it with my own non-scientific tests) and should basically just be used for going down hills.

But once again, whatever the additional factors might be, for my own personal driving (and trying my best to keep it the same when I compare), "B" has constantly given me better range and numbers than "D" for city and/or stop-and-start driving. If it didn't (and continue to do so) then I wouldn't bother with the extra effort of always putting it in "B" (and then having to put it back to "D" when the EV range runs out). Not worth the effort if there's no benefit, but I can tell you, in the Prime anyway, and using EV, I see a difference.

So what I suggest is people try it a couple times and compare. If they see no difference, just stick to "D" then (not worth the bother). But if you do see a difference as I have, whatever factor(s) might be causing it, you might decide to do what I've done for almost two years now, and do all my city drives in "B".

So okay, I took a pic with my camera of my readings for the last couple days. None of these are "cheats" (ie, one way down a hill). They're all round trips on normal city streets. No freeway driving (that of course will lower the numbers) but this is what I got over the last few days using "B" for normal city driving (not even in rush hour). A/C off, normal flat city roads. For Sept 15th (6.8 reading) I went 28 miles (14 miles to a shop, then returned the 14 miles back home an hour later, for 28 miles).

 

One question I do have (as I have yet to use 'B' in my Prime) is whether or not shifting into 'B' causes the ICE to start while in EV mode? If not, then yes I can totally see how using 'B' would yield more EV range.

 

I really wish Toyota would provide a more comprehensive explanation of "B" mode, like a huge fold out brochure that explains ONLY it's recommended function and what it is doing. ( For each model if there are differences )

Because for whatever reason, people seem to like to attach what they "think" it is doing or what they would like to imagine it's benefits are in usage in a wide variety of situations. Many of which I think are chimerical and not worth doing.

With my standard Gen 3 Prius? The owners manual recommended usage on long down hill situations. That is basically all I ever used "B" for.
I didn't use it in stop and go traffic.
I didn't use it to simulate shifting down.

Like almost all automatic transmission vehicles "D" means drive, and that's what I used 99% of the time I was driving.

 

All I can say about 'B' is in regards to my 2016 Prius (regular NiMH) that I traded in.

ICE kicks on. Does charge the battery at a faster rate.

Under normal coasting in 'D' the charge rate is around 25-30 A
When in 'B' and coasting the charge rate is around 35-40 A. When the battery would reach maximum charge, the ICE would rev up higher to a maximum of about 5100 RPM.

Speed doesn't make much difference, the charge rate and ICE RPM is about the same whether you're going 30 MPH or 70 MPH, the car adjusts the ratios to prevent motor/ICE over speed.

That is all valid for the regular Prius. I won't have a chance to put this to the test in the Prime until this Friday and I will be able to see live data from the OBDII scanner. From that I can conclude whether or not 'B' has any benefit for downhill grades that are 9% or less.

 

Going down big hills, that's true. But that side conversation was about using B on flat ground, where it has no impact on brake wear.

I can't say for sure on the Prime, but on the PiP, going to B in EV does not start the ICE. I don't know why Prime would be different there. But it will start it in HV mode on the PiP. Not burning gas, but still spinning and, iirc, going through its warmup routine. Other models may be different.

 

Those look like great numbers. I suspect that you're also doing something a little different when in B, but whatever the reason for the higher efficiency, it's there, so it's working for you and that's a good thing.

 

@jerrymildred So that suggests that the Prime would do the same then and if that's the case 'B' would be slightly better, being that you would get a smooth charge rate rather than coast, brake, coast, brake, etc. Of course if you're going down something very steep, something like 12%...15% then you would need to be in 'B' and hitting the brakes (one of the mountains near where I live has to be something like 30% I've spun tires going up on my '16 Prius after hitting a hump lol)

 

The whole concept of no brake lights in stop and go traffic is an accident waiting to happen IMHO.
J

 

I would have to agree with that... Going down a mountain or something is different and is really what 'B' is intended for.

 

If govt. regulations did not REQUIRE a selectable low gear to be present.......B probably wouldn't even be there.

It should be a fairly trivial matter to program the car to recognize a heavy, continuing declaration condition and "engage" engine braking on it's own. They already DO that if cruise is engaged.

I think there would be less confusion if it was labeled L like all other vehicles.......including my Ford hybrid.

 

Here are pictures of my EV m/kw numbers on the Prime over the last month, using "B" when in EV. A few (the lower ones, in the low 5s) included freeway driving as well as city driving. The rest were city driving. Note that these are all "roundtrips" (no cheats). One day had a bit of A/C usage (you can see which one) but for most the A/C was off. These are the EV numbers I get all the time by using "B" and driving in a smart fashion (no hard accels, etc). Even with some freeway on some of the days, they're ALL in the 5 and 6 range.

To answer someone's question, using "B" does NOT turn on the ICE on the Prime.

Sorry if I put up too many pictures, but for information people can consider, I wanted to show exactly what my m/kw numbers have been over a good period of time so people can see I'm not fudging. About 1/4 to 1/3 had some freeway as well, the rest were all city driving. Oh, and about half of them had a passenger as well.

 

I like that you can load multiple pictures in one action now, or any other document type, say pdf, excel spreadsheet. Kudos to the site maintainers.

 

I agree that the steepness is a big factor. If it's not steep, then you're modulating the throttle in B. If it's really steep, then you're modulating the brake in B, but not as much as in D. This is something I don't get to do in normal driving since our biggest "hills" are overpasses and bridges.

 

It certainly would IF......the HV battery is full and the grade is still steep.
That is exactly what it is there for.

 

That would more likely not be the case. I did go from 0% to 50% going down two mountains... I don't know of anything nearby (maybe Clingman's Dome?) where I would regenerate 100% charge. Would be nice, nothing better than free electric lol