Was coming up on a toll plaza at about 65 mph and shifted to B out of D. Car seemed to rev but wondering if there is a speed you don't want to do this over.
Unlike with conventional cars, shifting to B does not do anything mechanical in the Prius (plug-in or standard). It just puts the control unit into a mode where it more aggressively regenerates when you have the foot off the pedal. I think that it will trigger engine compression braking if the battery is full and regeneration is thus not possible. Pretty much the same as pressing the brake pedal moderately. (I am sure more knowledgeable Prius-geeks will correct me if these details are not correct. ) Why would you want to shift into B mode when approaching the toll plaza?
I believe the common thought process is similar to downshifting it slows the vehicle, while perhaps offering a little more battery regeneration. I don't do this. I only use B on long down hill drives. I do not use it in the above described manner.
My understanding is that using B only kicks in engine compression and doesn't give any extra regeneration. I only use it if I want to save my brake pads in a situation such as a long stretch down the side of a mountain where you might over heat your brakes. If going at a high rate of speed down a steep decline, I would definitely use it. However, it is best to plan your decent. When coming down Pike's Peak, they check your vehicle's brake temperature. You should easily pass the test if you started out using B.
Putting the car in B results in less regen - that is it's purpose. It takes energy to spin the ICE, energy that would otherwise be dumped into the battery. The proper use of B is only when the battery is full or not otherwise accepting the full output of the generator because of some other reason like temperature extremes. This will prevent the friction brakes from being used to slow the vehicle resulting is less wear on the rotors and pads. And even then B might not be better - your only saving brake wear and tear at the expense of ICE wear and tear.
There is not upper limit to when you can use B as it does not shift to a lower gear, if it did, I bet they would have labeled it L for Low gear, not B for engine Braking. B under the D in the Drive gears? | PriusChat
Kinda glad I seldom use it. I think I'd rather wear and tear on the brakes than the ICE. In anycase, I'm NOT one of those that likes to use it "like" a downshift to slow the vehicle. I've read several posts where people admit to using it in that capacity.
From my observation: In EV mode, regardless of engine status or speed, switching to B will slow the vehicle down by increasing regen period. When in HV mode, switching to B will pump the engine to slow down the car, thus wasting regen potential. There will be no ICE wear nor Brake wear if in EV mode and on B.
I had full regen since I was on the interstate for a long time and the toll plaza was down a hill. I guess I used it properly since I didn't want to step on the brakes so hard as to go into the pads. Regen braking wouldn't have been a benefit. I guess there is no top speed restriction from using B then from the replies.
B does increase regen, you can see CHG bar grow a bit. Anyone with a scangauge to confirm that? I agree.
For best MPG, you did if you were at the top of a descent of over 600 feet, otherwise, no. But it is always safe, even where it is not wise.
The B-mode in the PiP is somewhat confusing, as the manual makes it look like you really don't want to use it unless you HAVE to (going downhill, battery full), while in the Nissan LEAF, Honda Fit EV, it just means more aggressive regeneration, and encourages single-pedal driving. Really wish Toyota called it something else.
I have put PiP from D to B at 60 mph. ICE did not kicked in. It was pure regen back into the bigger PHV pack. It is my belief that the EV mode in PiP will not use the gas engine compression braking in B gear. Edit: If it is in HV mode, ICE will do compression brake above 25 mph (it seems... don't quote me on the exact speed).
One reason that there even is a B mode is legal. Seems that there is some government mandate that says that vehicles with multi-gear transmissions must support a "low gear" that provides significant engine braking, to supplement friction brakes that may have "faded" due to overheating. I am not sure, but I thought "fading" went away with the adoption of disc bakes, but the rules persist. I don't know how this point applies to the regulations in other countries. Engine braking is more of an issue with the standard Prius, with its much more limited battery capacity to store regenerated energy. It can be an issue if one charges the car at the top of downhill run, and the battery is full at the start of the run.
