PRIUS C regen-braking-regeneration explanation- B mode

Use either Eco Score or Eco Savings screen to instantly view how much regen you are achieving. Initial brake pedal application is 100% regeneration, and if you push harder it will also use the friction brakes. It is of course speed dependent, per the torque curve of the regeneration motor.

Have you read your owners manual yet? Please do! It contains actual information and isn't some sort of compromise to your masculinity.

"B" mode on the shifter is pretty much useless unless you specifically need more ICE braking, fuel economy be damned.

 

Just a note on the B mode. If your battery is full (or even if it's not) when you go into B mode, and your going down say, a mountain pass, it's very functional. When you coast in B mode, the car uses engine braking as much as possible, so you can control your speed without using the friction brakes. Really cool feature IMO.

 

B under the D in the Drive gears? | PriusChat

is my best effort to explain B mode.

 

Pressing the brake pedal does not automatically cause friction braking. It does cause the brakes to prepare for braking, but doesn't apply pressure unless one of the following conditions is met:

1) The amount of braking requested exceeds the capacity of regen. The total capacity of regenerative braking is limited by the size of MG2, the capacity of the battery and charging system, and the ability of MG1 to burn excess charge by spinning the ICE as an air pump. B mode is more aggressive about burning charge through MG1/ICE spinning.

2) Panic stop. If you quickly mash the brakes, the braking ECU assumes a panic stop situation and employs "brake assist", where the system immediately goes to high level friction braking. Essentially it applies the brakes faster than the driver.

3) Loss of traction. When traction is lost on either front wheel during braking, the braking ECU drops regeneration and switches to four wheel ABS friction braking. This is what causes the short loss-of-braking or surge sensation that Prius drivers sometimes experience when braking over bumps.

4) Failure. Several failure modes cause the braking system to fall back on friction braking.

So if you want maximum regeneration during braking, brake hard enough to fully utilize the regenerative system without forcing engine braking or friction braking. You will need additional instrumentation to do it with certainty, but that is really overkill for ordinary driving.

Tom

 

I think qbee42 has probably explained this better, but any time you are within the blue regen portion of the HSI and not in one of the exceptional cases that qbee42 described, then you will be using regen brakes. There is one additional exception which is at very low speeds the regen braking is ineffective and only friction brakes are used.

Outside of those cases, it is only when you push the pedal far enough to cause you to hit the bottom of the HSI that friction braking kicks in.

Ha... I'm a nerd and this reminds me that we see the world differently. In nerd world, failure to read the manual is compromising your masculinity. I'd read the whole US manual online before I went in to pick up my car here. I was teaching the dealer stuff when he foolishly tried to give me a walk-through.

I have also been known to read at least part of the manuals of hire cars I have driven, but I acknowledge this as overkill.

 

Early 2010 Prius had a software fix as the braking transition was not seamless enough, but mostly you can't tell.

 

The slower the regen the more you capture as well? That's when I get my best stop scores anyway.

 

I wouldn't say so. The trick to maximum score on your stop is to have two elements - 1. regen braking only until the friction brakes kick in as you come to a halt and 2. A nice consistent braking run - essentially getting just the right amount of pedal pressure that takes you from cruise speed to stopped in the right place, without needing to make any big adjustments on the way. This is difficult to achieve on shorter stopping runs.

 

It's all about power. At high speed it doesn't take much braking effort to exceed the capacity of the regenerative system. At lower speeds you need more braking force to develop the same amount of power.

Short physics lesson: Power equals work per unit time. Work equals force times distance. Higher speed means more distance for the same time, so more power for the same force.

Tom

 

Worth noting that this information predates the HSI - the graph which in the C appears on the ECO Score display, as I discussed in an earlier post in this thread. The HSI means everyone has the information they need to keep to regen braking. It is true that as you slow down you will be able to press a little further down on the pedal without causing the HSI to bottom out, but this doesn't become significant until near the end of your stopping run (it seems to be an exponential relationship) and if you are focussing on the "stopping score" for some reason, the car seems to generally not like you making use of this and seems to prefer a steady stop (though IMO it makes no difference).

On reflection, it might be possible that the programming logic of that score feels that if you are braking harder - even on regen brakes - there's an implication that you came off the accelerator later than you should have, which cerainly would be in keeping with the "Drive Without Brakes" school of thought - I just find that a hardline interpretation of DWB is impractical most of the time in the city.