Is EV really that useful? Also, is B fine to always use?

EV is great for moving your car out of the garage onto the drive to wash it but that's about it. It's a play thing, a gimmick. It has limited use and if you do over use it and run the battery down, then the engine has to work harder to put that energy back - affecting mpg.

The 'B' option is mainly for use on steep hills. I only use it on one particularly long hill near me, otherwise I don't bother.

 

EV mode is great when moving a car across a parking lot or other extremely short trip where there is no point to warming up the engine.

B wastes energy with more engine braking, less regeneration than D. So long as gas mileage is not one of your goals, you can run it all the time. Most Prius owners value gas mileage.

If you are on a downhill with more than 600 feet of vertical drop, the HV Battery will fully charge, so no more regen can happen. At that point D will have to use friction braking, while B can slow the decent with engine Braking.

This downhill into Warsaw NY may be a good use of B. After the incline, there is a sharp turn under a bridge, you will want fresh brakes.
Google Maps

 

Nope. No more aggressive charging is possible without damaging the battery. Here is Hobbit's detailed explanation, but it can be summarized by 'B stands for engine Braking'

http://www.techno-fandom.org/~hobbit/cars/b-mode.html

 

That's good advice - normal regen is preferred most of the time, but for long hills it's better to use engine braking.

I suppose the ideal would be to use regen braking while watching the battery - when it gets near full, flip into B.

 

Basically, B mode uses the "suction" of the engine to create drag on the wheels. It isn't burning gas, but it is wasting energy that could be captured by regen instead - provided you have somewhere to put it (i.e.: "space" in the battery)

My question is:
Why aren't the Prius electronics smart enough to switch into B mode automatically when the battery is full?

 

That is a great idea. That would save brake pads and in rare conditions make the car safer by having cooler brakes! (such as times when the user SHOULD have manually selected B mode on a long downhill) I don't think Toyota is ready to add more complexity to its software though.

 

Depending on the hill, you can try to use the cruise control.
Cruise control will try to decelerate using regenerative braking - but when the batteries are full or if braking power is not sufficent ICE engine brake kicks in as well. I did not use B - just D.

Martin (from Austria where there are a lot of mountains)

 

Why have a manual way of selecting B? When you pass signs like this Select B NOW!



Once they start telling truckers to slow down to 18 MPH, there is going to be a hill!

http://www.oregon.gov/ODOT/MCT/docs/EmigrantHill.pdf

 

With regard to

actually, it more or less does. Once you're topped, the engine is
brought to spinning anyway [generally, with no fuel injected].
Then, if you flip to "B", a lot *more* spinning happens and that's
when you're sailing down the hill with the "jet roar" coming from
under the hood.
.
What I generally do is use "B" as needed if on a long downhill to
try and balance regen vs. brake use, and then try to stay mostly
in "D" once the battery is topped [and the engine is spinning
anyway] for the rest of the run, unless I *really* need to take
a load off the brakes and I'm at fairly low speed already. It
takes a little predictive thinking about how long and steep the
downhill is going to be. This is why mountain driving is such
a blast; I refer to it as the "regen game". The real challenge
is to try being close to *empty* as you crest the hill, but that's
almost impossible if there's traffic behind you.
.
_H*

 

The ideal way to use B mode is to shift into B early on a downhill, but only on a downhill where regeneration will max out. The problem with that, of course, is that you need to know the characteristics of the hill and battery SOC in advance, so most of the time you can only guess, unless it's a hill you often drive.

If you wait to shift into B, it's pretty much the same as letting the Prius do it automatically.

Some drivers also use B mode on long down grades for simplicity. It makes it easy to control speed with just the gas.

Tom

 

What makes you say that? I'd have assumed that doing that versus shifting to B late would be roughly equivalent: Shifting early, you might charge the battery more slowly on the way down (Maybe? I have yet to use B in my 2-week-old Prius...), but in both cases, you'd start with the same charge, end with a full battery, and use no gas on the way down (though if you're in B most of the way, the engine will be using compression braking for longer).

 

It actually does, the occasions where this might happen are pretty rare, but I have induced it by staying in D down a long steep downhill - once the battery gets fully (80 percent) charged the rpms will rise on regen coasting and braking. Shifting into B maximizes this effect.

You can also think of B = bad mileage, if you use it when you don't need it. :madgrin:

 

You are forgetting friction braking. You are correct that both scenarios end up with a full battery, and the gas consumption is the same, assuming you actually needed to brake. But in the first case the friction brakes take a beating.

As you brake down a hill the Prius uses regeneration to capture the braking energy that would otherwise be wasted. When the HV battery gets charged up to the high limit, the Prius stops regeneration and switches to engine and friction braking. This is equivalent to B mode, except the HV battery is already at the high limit.

When you shift to B mode, the Prius immediately starts using engine braking along with regeneration. This pushes back the point where friction braking must be used, saving wear on the friction brakes and helping to eliminate brake fade.

It takes a pretty steep hill before any of this makes any difference, but on a long steep hill shifting to B mode early will help save the friction brakes.

Tom

 

This thread raises a couple of interesting questions for a circumstance that I have yet to encounter.

1. When your traction battery is fully charged (I haven't encountered this yet), does the brake regen no longer engage when braking, or does regnen still work for braking, with the recaptured electrical energy sacrificed as heat?

2. Is the feel of the brakes different when the traction battery is fully charged?

Thank you

 

I can confirm all the above. I use B very sparingly and mainly on steep declines, in the same way I would shift to a lower gear on the manual gearshift of my previous car. I can also confirm that the Prius will start engine braking even in D when battery is full (it happened to me on the highway once).

The regen drag is "strong" enough to be used in town without the need to brake the whole time or use B (my father has a Honda Jazz/Fit with CVT, and you need to brake the whole time or shift from D to L to get some engine braking).

The EV mode is useful, after 9000km driving, only when wanting to move the car from a cold start from A to B (e.g. between parking lots, as mentioned above to wash the car on the driveway, etc.). I see it perfect in the US to go from one store to another between parking lots of huge shopping malls (often spread between 2 or more roads): in summer the engine, after a longer stop, might still not do the warm-up procedure, but in winter, if battery is full enough, you can avoid it altogether and move the car with 0 fuel consumption.

Other than that, with the capacity of the battery we currently have, EV is mostly a marketing gig. You can go "EV" also without selecting it if you are light on the gas pedal, drive slow and have enough charge (more than 2 bars).

EV will not engage, if you don't have at least 4 bars, if I remember correctly.

 

So the Prius does automatically use engine braking when the HV battery is "full".

That tells me not to bother with B mode unless I know a hill will definitely max out the battery. (pretty much what the manual says in far less detail)

 

In the technical sense regenerative braking stops when the HV battery hits the high limit. MG2 is still used for engine braking, which is really a form of dynamic braking. Instead of electricity going from MG2 to the HV battery, the electricity goes from MG2 to MG1 and is used to spin the ICE as a big air pump. The ICE really revs up to a high speed, but it is not burning fuel.

If you are familiar with your car you can feel a difference when regeneration stops. Likewise you can hear the ICE start spinning.

Correct. There is no reason to use B mode unless the HV battery will max out, with two possible exceptions:

1) On a very, very steep hill you may want a lot of braking. Using B mode allows for regeneration and engine braking at the same time, instead of one at a time.

2) Some people like B mode for a feeling of improved control when descending a hill. Mostly this is because it is easy to control speed in B mode: lift your foot off the gas, things slow down; press on the gas, things to faster.

Tom