Regenerative Braking - D or B ?

You don't need to alternate. Just press the gas pedal enough to reduce the amount of B-mode regen/engine braking to the desired level.

There is no need or advantage to taking your foot off the gas pedal while in B-mode.

 

So, unlike in D mode where you press the brake pedal to augment the Regen until the brakes have to kick in, in B mode, you (lightly) press the gas pedal to reduce the Regen so you keep moving at the speed you want. That's it?

 

Yes.

Initially, some drivers find it a bit disconcerting when they discover themselves in this narrow set of circumstances where pressing the pedal down a bit causes the engine to spin slower, not faster. But it is a narrow range, and easy to get accustomed to.

 

Sounds similar to the one pedal driving in Tesla, except there it can bring the vehicle to a stop. Still, I'll give this a try as I very much like that one pedal driving.

 

I find D has quite a bit of regen, just about perfect. The brakes need to be used a little, as when coming to a stop can hear them the last few feet. Otherwise discs get rusty. Not using at all the brakes, not good at all.

 

I haven't yet driven any Tesla, but suspect that the Prius version is significantly milder than the Tesla one-pedal driving.

Note that used in this mode on flat roads, the Prius MPG will likely decrease. The Tesla version doesn't waste any of its electric braking energy as ICE compression braking, or as ICE idling while stopped, as the Prius will. B-mode will prevent ICE auto-shutoff, shorting circuiting one of its fuel saving measures.

 

When I drove a Model S around 2014 - 15 , regen was adjustable. I believe I've seen youtubes of other models witht eh same adjustable regen in the settings on screen. And yes, it's can be adjusted way beyond what B mode give us in the prius. I remember before I learned how much braking I could get in B I used to hold the joystick in the B position dreaming I could get more regen braking that the prius allowed.

 

In newer Tesla, you can't adjust it anymore. It's always full Regen when you let go the accelerator. I don't know why they removed it. Older vehicle still have the option for Low Regen but not newer one.

 

I understand the concept, but doesn't that use gas necessarily? If you're able to not press the gas pedal at all, wouldn't that be an advantage?

 

I guess it depends, just like when you start to press the brake pedal, you don't actually apply the physical brake, you start by using more and more Regen, until it can't Regen at any faster rate. I guess the same applies to the accelerator in B Mode. Between full throttle off and engine kicking in, there is a region where Regen will be used at different level.

 

@GeoJ you have to remember that B while in EV is much different than B in HV or how it work in the regular prius. It's very confusing to new Prime owners trying to understand how B is working for them when they read how B works in the regular prius, which is very much like (if not identical to ) how B works in the Prime while in HV mode. Hope this helps a little.

 

When using engine compression braking in B-mode (or also D-mode), fuel is completely cut off. None is burned. This is true of most modern non-hybrid engines too, ever since 'DFCO' (deceleration fuel cut-off) was added decades ago.

Now, once you press the pedal far enough to get propulsive power, then it will burn either battery charge or gasoline. Or when you come to a full stop in B-mode -- at least with the older generation non-plug-ins -- the engine will stay on in Idle, which does burn some gas.

 

I watched one of my long time subscribed Tesla youtube channels Out of Spec Motoring do a review of the bz4x and Kyle mentioned near the end that the bz wouldn't stop without using the brake pedal. Granted it was his first time driving the car, but later watching the Alex on Auto review of the lower trim bz he mentioned there was a one pedal button on the dash, but did not include a demonstartion of how it works while he was driving the car or even show the button while filming the dash segment.

Thanks for mentioning that Tesla has discontinued the adjustable regen feature they used to provide. When I turned regen all the way up in the Model S, it was a significantly different driving experience than when regen was set more to the middle of it's range..

 

Would you say the Regen in B mode is similar to what low Regen on the Model S was?

 

Sir I get what you are saying, but what about the following: could it be better for the battery (and combustion engine) to be charged through minimal regenerative braking instead of letting the engine charge the battery? Because when one "glides" and cancels out regenerative braking, after a certain while the combustion engine will activate in order to charge the battery. Is there something to say about the wear and tear occuring in such occasion?

 

If anything, the car is likely to use higher charging currents in regen braking than in charging using the engine.

Prius HEVs strive to keep the battery at a nice intermediate level of charge (60%, in NiMH models at least) and usually stay spot on or near that number in sustained cruise. The most efficient way they can use gasoline is when the motive power load can be supplied directly by the engine running in an efficient region of its power map.

When the battery state of charge needs to be raised, often that happens not by starting the engine when it's otherwise stopped, but by just slightly increasing its output when it is already running to move the car, and sending the slight excess power to the battery.

 

I thank you for your reply, sir.

As someone owning a car for the first time, I got quite excited about trying to "pulse & glide" with a Gen 4 Prius (HEV), but deciding I want to keep the car for as long as possible, I assumed that for the life of the battery (as well as the engine), charging the battery with minimal regenerative braking might be the better choice. But now I ought to know better.

The idea of P&G causing extra wear and tear creeped in when I kept reading instructions that acceleration when going for an effective "pulse and glide" ought to be firm.

I'm sadly not knowledgeable on the subject, but the thought behind a bit more "spirited" acceleration might be basically because of what you typed above sir; it being an efficient way of using gasoline. And perhaps in an HEV to skip the ultimately relatively inefficient way of accelerating with electricity (due to what I believe is described as convertion losses).

It initially sounds a bit strange for someone unlearned like me, but it seems to be known that combustion engines operate efficiently (as to what is gained from gasoline) under a certain load, which one doesn't really seem to reach when accelerating in quite a slow way.

I don't wish to waste your time but perhaps there is another misconception you would be able to clear sir: wouldn't this increased load, resulting in a more efficient use of gasoline, come with the downside of added wear and tear on the engine? An assumption not based on much, but I would assume accelerating with lower RPM (without lugging the engine) would cause the least wear and tear.

Perhaps I'm wrong and it is actually (not coincidentally) under so called optimal load where there is the least wear and tear.

And even if there is a bit more wear and there, with the right maintenance it might not even be significant as far as the lifetime of the engine is concerned.

Hearing about clogged up engines due to too slow and gentle of a driving, it becomes clear that slow is not always the answer. Not sure if the Gen 4 Prius EGR is prone to such problems.

Anyway, I thank you for your valuable time and knowledge.

 

Nope, not al all. B uses engine braking, which substantially worsens the fuel economy.

 

Never use the B mode unless you really need it, as it substantially worsens the fuel economy because it uses engine braking.

Only use the B mode in needed situations such as for slowing down without using friction brakes when going downhill.

Don’t worry about the regenerative boost. It seems to be more like an accelerator-pedal modulation that changes where the regenerative braking starts and doesn’t seem to increase the amount of maximum regenerative power available, which is limited by the capabilities of the hybrid system.

 

things have changed in 2 years