Driving in "B" Mode Regularly

Works on Prime too, but it's tough to stay dead-on zero.

 

Dead on is not really necessary, close to zero the in/out current is very minute.

 

The EV1 may have worked that way, but absent the prevalence of hill start assist, there can be greater roll back.

One pedal operation is the KISS solution to regenerative braking, and it was used on diesel electric locomotives long before hybrid and electric cars made a comeback. Its just called dynamic braking when there isn't a way to store the electricity generated.

The mid position of the accelerator is a neutral, glide with not energy being produced or consumed. Depress from there and you have acceleration. Let off, and you get regen braking, with maximum when the foot is off the pedal. Which is heavy braking that could bring the car to a complete spot. Brake lights are operated based on the deceleration rate. The brake pedal operates the friction brakes only.

Having friction and regen braking operated by the brake pedal raises the issue of trying to have the two braking systems work seemlessly together. Having acceleration and deceleration on the same pedal is easier because the driver isn't going to be calling for both at the same time.

Did the site ever have a sticky post with the lexicon on community terms?

 

Shifting into "N" works perfectly fine but should only be used by those who also know how to drive a manual transmission car. It is a different way of thinking and driving.

Bob Wilson

 

There were some glossaries, but they are now deeply buried under more recent archeological strata:

PriusChat Glossary | PriusChat
Acronyms and Abbreviations Glossary | PriusChat
Acronym/Glossary (Updated) | PriusChat
Acronyms and Abbreviations Glossary | PriusChat

 

Wayne Gerdes (of cleanMPG site) was doing a third gen hypermiling tutorial, and was telling the instructee to put it in Neutral quite frequently.

Still, I think it depends on your level of enthusiasm, I'm fine to just rest a foot on the gas pedal, if it seems like regen is going to (for example) prevent me rolling to a red light without needing to give more gas.

 

Except N results in ICE idling when in hybrid mode, when a glide results in energy use by the engine nor motor.

I thought there was, but I vaguely remember a loss of posts during a major software upgrade or switch.

The lower EV speeds of early Prius gens meant the need to spin the ICE at those speeds. A true glide wasn't possible, and neutral with idling ICE could mean less energy spent than spinning the the ICE with a M/G. A gen4 Prius should get the same results with less shifting to N.

It's all about knowing the capabilities of your car.

 

Didn't in my 2004 40mph and below. Don't know about the Prime. It's either in Ev or at high speed out on the highway in Hv.

 

I had no problem getting my 2005 to glide at those speeds.

Now my knowledge is rusty, but shifting the neutral at speeds above 40mph will result in the ICE idling even when the speed drops below that. It could also shut off all ability to regeneratively brake.

 

I meant it didn't idle in neutral, up to 40.

 

Using B position with the Prime in EV mode in city and rush-hour drives is solely a matter of convenience for those who are more aggressive on the go pedal.
It is not more efficient in those circumstances (edge cases excluded) but can be less, regeneration has its losses so the less is the better, you do not regenerate what you did not spend.
It can also be less safe as no brake light with B.
In fact, with the Prime in EV mode, B is only a matter of convenience also for steep downhill drives, short or long (edge cases excluded) with same efficiency as D+brake.

This post is not meant to argue with feelings as feelings (though important) are not evidence.

 

It can slightly be more efficient. There is that fraction of a second delay when switching the foot to the brake pedal. With B, you have more effective regen braking for that period of time. Those tiny intervals can add up while in traffic.
While the regen is less efficient, the driver wouldn't be moving their foot to the brake pedal if they weren't intending to brake.

The most efficient way to drive in traffic is to maintain a large enough buffer between you and the car in front so that you make the most out of gliding and avoid brake use. I have not seen any statements to the effect that using B in a Prime in EV mode makes this difficult than being in D. Then the variables of traffic can make this hard to accomplish, and the slightly heavier regen of B could be of fuel efficient and safety benefit.

 

. . . in a Prius Prime.

I agree with @stevepea that what counts is experimental data, direct observations, of the object under discussion. I'm OK with proffers of math models provided they have some association with observations. So I've done mph vs MPG studies using the EPA roll-down coefficients without having a Volt or other models in my hands. Speculations about what might be going on, as long as we agree they need experimental testing, is weak tea.

So I did some testing of "B" vs "D" and was able to observe how it is a weak version of BMW i3-REx, single-pedal driving. My understanding is GM has adopted 'paddle modulated' regeneration and when in EV mode. In contrast, the Prius Prius EV mode has these regeneration modes:

• "N" - no regeneration at all
• "D" - default regeneration
• "B" - 2-3x regeneration based on local benchmark testing

I have no idea of what the PiP does in EV using "D" or "B" but think it would be helpful. It has a different set of control laws.

Bob Wilson

 

I defer. Regeneration starts at the moment you lift off your foot from the go pedal, the strength is smaller in D until brake but so is the kinetic energy reduction. A scenario in which you lift off in D and only after 2-3 seconds (as traffic allows) using brake, when speed is much lower, is less efficient than being in B in your opinion? If yes, then you are contradicting yourself in your last paragraph.

This is in the convenience department IMO.

I agree but not to the 'difficulties' and 'could be' mentioned later on in your post.

 

We have not seen any experimental set of data from @stevepea yet, only initial 'observations' which may be a trigger to experiments which may prove or disprove the subjective observations.

PiP behaves exactly the same. What make you state it has a different control laws?

 

That is how science often proceeds. First informal observations followed by more formal studies.

It is a different code-base as the Prime is substantially different from the earlier generation Prius. Not having one, I look forward to experimental verification by those who own a PiP. What is the relative effect of using "B" versus "D" on a straight, level road.

Bob Wilson

 

Which may disprove the subjective observations.
Further, not everything needs empiric data set, when the physics laws are clear one can count on them.

About 2-3 times the strength, and the exact value is not that important.