Now that our P.Prime, which I call "El Primo," has arrived (yeehah!), I tried "B"raking mode in EV. First, as you folks mentioned, it does indeed appear to only add more regen upon lifting you foot from the ... gas-free ... gas pedal. Not a huge increase, but enough to help a bit with descending hills. However, probably not surprisingly in hindsight, one thing I've noticed you can't do in "B" mode is set the cruise control. Other than for descending hills, it may be good for driving around in neighborhoods. iPhone ? Pro
Oh man, you got there first, or I would have jumped on it!!! Har, har. Mine would have been something like, "You have to let the Prime dry before you can put on the Finish (not Swedish!) coat! Har, har! .
I personally have never used B mode. When going down long hills, I set the DRCC, and it applies the correct amount of regeneration or power necessary to maintain the set speed and clearance to the vehicle ahead.
My understanding of how DRCC behaves is that it is pretty much equivalent to human application of the throttle or brake pedal. Applying the brake pedal uses varying degrees of regeneration, up to the limit of regeneration, or until the battery is full, at which point the friction brakes are used. So if the human knew exactly how much brake or throttle to apply at every instant, they could duplicate the effect of DRCC. The ability to slow you down is one of the big advantages of how cruise control works in a Prius (DRCC or conventional cruise control) over how it works in conventional ICE cars, where it only controls the throttle, and thus you can speed up going down a hill. B mode applies a fixed degree of regeneration over what is the normal "idle" drag, but with cruise control, the amount of "drag" is variable. B mode is a way to simulate "downshifting to a lower gear" in an ICE car.
On older model liftbacks, the owner's manual explicitly calls out that cruise control works only in 'D' mode. But why would you need to set both? With cruise control turned on and set, the computers should have access to all the 'B' mode mechanisms and adjustment range that the car needs to keep speed down to the set speed.
I haven't used the B setting yet, but a few times a year, work where I have to drive up a long steep climb (for LA area), then go down it afterwards. Am I correct in reading your comment that if you're going down a steep hill and put it in "B", the car will only regen if your foot is OFF the brake (not ON the brake?) To me that doesn't make sense (as even with a bit of regen, if you're going down a steep hill you need to press the brakes now and then). So let me ask you folks then... in a situation where you have about a mile going up a steep hill, then going down the hill on the way home, what's the setting for the downward direction? Should I use B, or just keep it in D for the most regen (since going down that hill, I'll be pressing the brake somewhat frequently). Would of course like to have the most regen as possible...
Using the brakes in B mode in Ev will just add regeneration until you're at max regen. Using B mode down a large hill is the way to go unless you're using cruise control.
That agrees with my best understanding: DRCC can't, for example, engage regen instead of brakes. iPhone ? Pro
That agrees with my best understanding as well. I'm also finding that it feels more controllable in residential areas in B too, and probably gives a tiny bit more regen as well. iPhone ? Pro
I only use B on long downhills where I want the car to slow down on its own. Mind you this is on my older 2014 Prius. I wouldn't use it around town in the flats.
Best I can tell so far, in EV mode, "B" mode increases the gas-pedal off regeneration rate, and precludes using cruise control. I do see the regen rate increase even farther with brake application. Several folks have said that when you apply the brake, it avoids entirely applying the friction brakes until regen runs proves insufficient. I'd like to see some documentation on that. If I were an engineer at Toyota, as a fail-safe for fault-tolerance, I'd be reluctant to put any sort of conditionality into the application of friction braking. My best impression is that friction braking applies at pretty much the same amounts relative to pedal position, but regenerative braking varies depending upon battery level and other factors: Light brake application does not engage any significant amount of friction braking (possibly even none at all), but does apply substantial regenerative braking (again, unless the battery is full), and both generally increase from there toward greater pedal depression. I'm not sure of that, however... iPhone ? Pro
There's no good reason to apply friction braking unless regeneration is insufficient to meet the demand, and I'm pretty sure that's what it does. That's how I got almost 150,000 miles out of just 20% of pad thickness on my 2004. If friction brakes were being applied anytime the pedal is pressed, there's no way the pads would have worn so little. Control systems now can be multi-fault tolerant and self-checking so there's no good reason not to use them to control critical systems like brakes. That's how fly-by-wire commercial airplanes can be safe despite no mechanical connections between pilot and control surfaces.
OK, good to know, so when I'm driving down that long hill I'll move it to B. Should one typically drive in B mode then, if it's more regen-friendly, even on the freeway? That's the one thing I found strange with the Prime vs my old Civic Hybrid -- you lift your foot off the pedal and there's only a little bit of regen on the Prime. Any downside to using "B" for everyday driving then? (City or highway) Will it try to mimic low gear in a regular car (in which case not a good idea unless you really need the braking, like going down a hill) or is it simply more use of regen, in which case it might not be a bad idea to use all the time? Sorry, I haven't used it at all yet because never had a Prius before, never encountered it. If all it does is make it regen more when your foot's off the pedal, that's what I'm used to (from the Honda Civic) for the last 12 years, so maybe I should drive all the time in B? (For me, regen is good) Your opinions on this please..
At my previous job, we supplied microcontrollers for braking systems, and those people are always super-conservative. In Toyota's position, I would be less concerned about electronic failures than mechanical failures. If I were to design in any sort of component that could in any sense disconnect the mechanical brakes from the pedal, I'd be really scared of it breaking... Modulating it, fine, but disconnecting it... That makes those guys reeeally nervous. iPhone ? Pro
Nervous or not, that's what it does. It has to. Otherwise, regeneration would add to friction braking and change the feel (a lot) between HV and EV modes, which it doesn't. Also, friction braking would dramatically reduce re-captured regenerated energy making regeneration almost pointless. The presentation on my 2004 Prius showed this in no uncertain way.
