Driving in "B" Mode Regularly

makes me wonder how Engineering works at Toyota for the Prius/Prime ... if it's the same group that engineers Gen4 and Prime, the have something in mind for B and might not even think about that in the Prime you can use B in EV and it is something very different. I know that there is an account on PChat is using but they are probably not monitoring, wonder if someone has a way to get their attention to this topic ...

 

Do you perceive that DRCC has braking controls that a human driver does not, notably that it can command more regeneration before friction braking engages than the human driver can with the brake pedal?

I presume, but I don't know for sure, that DRCC has the same braking controls as the human driver.

I perceive there to be two minor but "nice" values to EV "B" mode: First, you can get a little closer (albeit not much) to the proverbial "one-pedal driving." Second, that additional braking force, albeit only a little, does not involve friction braking; it is almost certainly entirely regenerative. When you depress the brake pedal, it's hard to know at what point friction braking gets involved.

I perceive these advantages would both be more interesting if the amount of added regen was considerably greater, like that on a Tesla, BMW i3, or Chevy Volt/Bolt in "low."


iPhone ? Pro

 

The Toyota PriusChat account (PriusTeam) is for Toyota USA Marketing, which used to be based in Southern California, but is now based in Texas. The design and engineering is done in Japan, and unless you are fluent in Japanese, you would would probably have trouble communicating with them.

 

I don't know for sure, but I suspect that DRCC is like the bake pedal, biased toward using regeneration whenever possible.

 

DRCC well wait to long to use regen and use the regular brakes to much I believe. Because off the sprang clutch I do not believe that the ice in the prime we'll do any braking going down hill in B mode. But I donot live on a steep hill to check when battery is full. I know it uses both gen/motors to send electricity to the battery.

Now my 16 four touring can really waste energy spinning the engine going downhill. The Prime just ads juice to the battery.

 

Do any of the priuses have resistors to send excess electricity to?

 

We'll have to disagree about this because the clutch is on the engine shaft relative to the engine block. It prevents the engine from turning in the reverse direction.

Bob Wilson

 

Does this mean when acting as a motor it spins one direction and when acting as a generator it spins the other direction?

 

No. Both MGs need to act as a motor and as a generator in the same spin direction.

 

This is a misconception. If the situation requires friction brakes, system will activate them no matter which mode you are in (i.e. 'B' or 'D'). This will happen in 'emergency' or very strong braking situations whereby you will use the brake pedal while being in 'B'.

 

Agree, and will add:
'D'+brake pedal is "Dynamic Human Cruise Control" - DHCC which will be more efficient than fixed fixed amount of regeneration in "quite few" situation of the dynamic traffic.

 

I know of no evidence that any form of Prius has what diesel-electric locomotives call "dynamic braking."


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I am only talking about foot -- both human and electronic "foot" -- off the brake and off the gas, in EV B mode.

Do think it would ever apply the friction brakes in that scenario? I'd be very surprised if so.

With foot on the brake though, when exactly friction braking engages is … more involved.

iPhone ? Pro

 

Here is the misconception. It is not more involved, it is simply non existent - up to a point of max. regeneration allowed - which is far more braking strength than 'B' alone (without brake pedal) is capable.

 

Nope, the Prius doesn't need to spare its friction brakes from stopping thousands of tons of mass.
This raises a question about locomotives with regen braking, do they have synamic braking also?

Why the assumption that B has all or none braking, and not have driver control over the amount through the accelerator pedal?

 

So, yes, we both agree that the additional regen braking of EV B mode is way below what would engage friction braking.

When you apply the brake pedal though, the circumstances that will result in friction braking being engaged seem ... involved. According to Questions about the Prius Braking System, there's a regen braking limit of 55A, and any greater braking force than that is for-sure friction braking.

I periodically see graphs of this nature, which suggest that there is more friction braking at first than regen:

However, the context for this chart is hard to find. This presumably describes a case where more braking force is demanded than this 55A limit.

However, I think it's a safe bet that the extra deceleration of taking your foot off the gas in EV B mode is entirely non-friction, which is all I was saying earlier (well, that plus it gets us a little -- accent on "little" -- closer to Tesla-style single-pedal driving).


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You are bringing a reference dated 2004 which corresponds to Gen2 (or 1?) maximum regenerating max. current was drastically improved in the following generations.
The absolute value is, however, not relevant here. what is relevant is the fact that up to the maximum 'D'+brake pedal is purely regeneration and when needing more, it will activate friction both in 'B' (+brake pedal) and in 'D'+brake pedal. 'B' alone is way less than the maximum, so is 'D'+brake for same braking effect.

 

In stop and go traffic if there is car in front one can engage DRCC when fully stopped and DRCC will hold the car and one can take the foot of the brake - I found it very convenient. So per say I would want this functionality not the DRCC per say.

 

I agree that DRCC renders B vs. D (largely) irrelevant.

My comment earlier mentioning not being able to use DRCC as a disadvantage of B mode, is that you have to remember to take it out of B mode before you turn on DRCC. That makes it harder to "normally" drive in B mode.

I've had that happen several times: I try to engage DRCC, and it just pops up the "only for freeway use" banner. I'm like, "yeah, I'm on the freeway, so why aren't you engaging..., ah, crap" flip the shifter over to D mode.


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Why does the ICE come on in EV mode when the battery is full.... if the battery is full and you're in EV mode, surely, you can just drive more in EV mode without firing up ICE? I don't get why ICE has to ever kick-in if battery is "too full" ... am I missing something?