Best Use of B mode

When the battery is charging it puts a 'load' on the motor (or engine) and will increase braking effect. When the battery is fully charged, the load is minimal.
Have a small toy motor around. . .try spinning it with the battery leads disconnected. . .the motor spins freely.
Now short the leads together and try to turn it. . .most likely, you can't.

 

I used the B mode for the first time this past weekend.

Going over the hills from SoCal to AZ, I reached a full BSOC and still had 2+ miles of ~6% down hill to go. In any other car, I would have downshifted so that I wouldn't risk "cooking" my brakes. Using the B mode was surprisingly loud (was doing 65-70 mph) but it did keep the car from accelerating without using the brakes.

I was under the impression that this was the ONLY reason/purpose of B mode. Is this correct? Or is there a way to get better MPG using it?

 

It will if you are pressing on the brake. Just that in 'B' mode, you are less likely to do so.

 

kkister1492 you have a good point there. but you also have to realize that deceleration in B mode is very gradual that most would notice unless they came from behind you waaaay back. in that case, they are probably building up ramming speed and brake lights wouldnt help you anyway.

 

When dirving in B mode, can you also accelerate? I have a long and curving downhill drive and I tried using it this morning. I have a long drop with speed humps inserted and then a flat spot before another decent. Should I shift out of B for the flat spot? I noticed that I had slowed too much to make it through the flat curve and had to increase speed a bit. Please, someone explain the correct procedure to me.

 

The B mode is so misunderstood. Don't use it. Use your brake peddle as lightly as needed to maintain your speed. Check your battery level. Once your state of charge reaches 8 bars, regenerative braking will no longer occur. At this point all braking will have to come from the friction brakes. This is the only time you ever need to use the B mode. B mode will use the compression of the engine to slow the vehicle and will take other actions to avoid overcharging the traction battery. B mode will not help save gas under any circumstance. (Japanese mileage freaks notwithstanding)

 

"The only concern I have about using the B mode in stop and go traffic is that the brake lights don't illuminate - correct? If someone isn't paying attention....smack!"

Same as any stick shift car-- no brake lights until you near a stop and actually press the brake pedal.

 

In summary B may stand for Bewildering.

Some of us won't use it, many use it going downhill, some of us use it to assist our braking for stoplights, and the technical people - well - what the heck is an EV switch? And it seems like the jury is still out on it too.

I'd like to hear from politically corrupt if he eventually blows out his engine by continuing to pop it into B at 45 mph. How much higher would you push it? Don't take it out on the car.

 

at 45 mph heck I've put it in to B at 120 km which is about 70 mph and the ICE only revs to 3400 RPM. How's that going to blow the engine when it's electricaly limited to 4500 RPM, I'm 1100 below red line.

 

Hey Frank, what do I know? Like many - I am ignorant. Like too few - I will admit it. I'd be afraid to pop it into B at 120km. Why would you do it at that speed?

 

it will only rev up to the RPM you would normal be at at the speed your travelling. 19KM of 9% grade and full battery and pretty soon your doing 120 klicks. Put it in B and slowed back down to 110 and it stayed there. With the Mini Scanner I can now see the O2 temps and BSOC and HV battery voltage and current draw so now use that data to make more informed decision to use B or brakes.

 

Well I could ask too many questions but I have two.

To what purpose all of this monitoring? Is your "...more informed decision to use B or brakes" in order to reduce gas consumption?

What is a Mini Scanner?

 

I mostly use the scanner to know what the car is doing and just to get my head around all the output from the computers in the car. My main use is to know the temp of the ICE to get the car into S4 as soon as possible to get the best mileage. Unfortunately there still isn't a commercially available scanner for the 2k4-5 Prius. Check out Graham Davies ecrostech site and have a look. If you read thru the manual you can see all the data available from the car. I don't use all of it but have looked at all of the outputs.
http://www.ecrostech.com/Products/MiniScan...anner/Intro.htm

 

Well, this has been very interesting. A whole new technical perspective of my car has opened up. I may consider a Mini Scanner when it's available for the 05.

Right now I'm pretty happy with the average of 51 mpg on my third ever tank of gas and playing with the B Mode - without knowing what effect it's having.

 

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eh, I wouldn't go much past 55, when going down hills I'll use B with the brakes. I drove a standard all my life so I mean I wouldn't just shift into 3rd gear going 55 but I would going 40 and use the brakes with 3rd gear if I was speeding up going down a steep grade. I'lll let you know though, I think a lot of people are baby-ing their cars I refuse. True test right here.

 

I read somewhere the main purpose of the "B" mode was to comply with safety rules requiring engine braking be available and just using the brake pedal in the Prius for this was unacceptable to meet the rule (don't remember where or if the source was credible).

Many agree while B mode increases regen braking, it doesn't do so any more than pressing the brake pedal (up to kicking in the friction brakes) and has a greater potential to hurt than help your mileage. A number feel you can try to get better MPG with it. Using B mode when the engine brake kicks in definately hurts mileage. Coastal Dave's soon to be released device to illustate how much regen you're currently getting would prob be a more efficient way to maximize regen. I read (prob somewhere in this forum or Graham DAvies website) "low and slow" gives max regen since the battery is the limiting factor - it can only accept so much charge at once. The MGs can demand or produce more than this amount.(slower battery charge than discharge) But since regen is fairly inefficient anyway the best way to get max MPG is to avoid stopping in the first place. Careful planned driving will beat regen or B mode any day.

There may be hills steep enough to need B mode, but probably not many... On my last car I don't remember taking it out of 5th gear too often due to incline, I do not know about automatics.. prob the main time I ever used engine braking with it is going down the ramps in the parking garage when Im' on the top floor. With regen braking, you can lean on the brake pedal until the battery is 100% and still have cool brake pads. This type of long, slow brake leads to quick fade in regular brakes (I learned it's better to do short brake bursts in this situation instead of slow and constant) but is what I do instead of B mode, since its easy and going this stepp downhill I don't like giving up control to cruise control.

I DO use B mode occassionally when my foot is tired and I've been in stop and go traffic for awhile (unfortunatly too often in Chicago). I am sacrificing MPG for comfort since I can keep more precise MPG saving control in D, but when going 5-10MPH B mode slows the car so quickly I usually don't have to move my foot (Plus at speeds this slow the MPG impact is hard to measure) If traffic gets moving more steadily I try to shift out as quick as possible, getting up to speed and forgetting will hurt MPG, thou usually the altered feel of driving reminds me right away.

You can shift between D and B anytime you want, no need to worry about using the shifter and hurting the car. Since all you're doing is sending a message to the computer, not actally moving anything (by wire), the computer won't let you hurt anything. LIke if you try to shift to R while moving forward, it won't let you.

If you hit the gas while in B it feels like all braking stops and the car drives like in D. As soon as you lift your foot you feel the drag. Based on feel, it seems like there would be no need to shift out of B to go "up the valley" so to speak... but I don't know if any changes invisible to the driver go on.

 

Right you are, B is simply changing the programming, along with adding a little 'reverse ICE'. Don't worry about what speed you are using B in, it doesn't matter. It is no different than driving at 55, ICE will turn the same or slower either way. Remember, you aren't changing actual gears like you are in a manual or auto transmission, where in that case you are over-reving your engine, and/or placing undue load on the gears.

But using B for stop and go, it may make you drag faster without brake, but I found it also prevents or at least retards the shutting down of ICE. I do believe I was seeing a measurable MPG when 'coasting' in B, which means ICE was being fueled, not just turned.

 

Dan your partially right on the injection of fuel when in B mode, the O2 sensor voltage starts to drop and then raise back and then drop again indicating that fuel is being injected. But by the same token on a long down grade in D the O2 temps rise and fall indicating the injection of fuel as well. The O2 sensors are what has a major control over the ICE stopping when in S4 at a stop. If you coast down a long hill and stop at the bottom and the ICE takes it's own sweet time to shut off it's probably because the ICE was in pumping mode and the O2 sensors cooled down and you hit it right at the wrong time. It injects a bit of fuel to keep the ICE running and the O2 sensors warm fairly quickly and then the ICE stops.

 

Hmm. That would explain then what happened this morning. Was running about 45-50 MPH, some stop and go. Was coasting (or creeping), and saw my MPG show that ICE had to be running. Stppped for a few seconds and ICE shut down. Then I could drive in stealth. SOC was green at 7 bars too.