Best Use of B mode

B mode uses the compression losses of the cylinders for engine braking. The higher the RPMs, the greater the losses and the more resistance provided. People who drive cars with standard transmissions will understand this as the reason they downshift when approaching a stoplight or going down a long grade.

Bottom line: it's normal for the Prius.

 

Thank you Bob - You are helping me to understand the B "gear" mode and "engine braking." Not many hills here but when I misjudge - and have to break more agressively coming to a stoplight - I will pop it into B.

I know there are other threads on this but what is the advantage - other than saving on brake wear, for doing this often? Is it detrimental technically?

You do have to make sure there is no idiot tailing you because you do slow down quickly with no brake lights.

Thank you.

 

Okay, I'm back after reading some previous B threads. So we get less regeneration in B because the ICE continues to run? Is this constant no matter what speed we engage B? Therefore someone who uses B a lot will have poorer mileage?

 

B mode isn't as simple as most think. 8 - 25mph it uses the electric motors as the main slow down method. Above 25, it uses the engine's compression to slow down the car. both are farily decent at regenerating electricity. I would say my breaking methods are better.. but breaking methods take a lot of work.

If you come to a stop with B gear still on... then you are waisting electricity that has to spin the engine. If momentum won't spin it.. the electric motors will. the ICE will always spin when B Gear is enabled. This explains poor gas mileage. It does get a little more complicated.. but either way, it has to spin and takes valuable energy if you are not going down a hill. you can use electric mode by lightly applying pressure to the gas pedal.. However.. same concept, ICE will still be spinning. Imagine having the A/C on while in a standard car. It takes energy away.

B gear seems to have no ill effect, no matter how much you use it. There shouldn't be any problems. I have not heard of any problems either. Everything i've heard says you can use it as much as you like. Keep in mind your mpg could go down in used inproperly.

 

i think B mode should never be used. realize that unlike a normal car, applying the brakes and slowly increasing pressure will increase regen to the battery without any wear and tear on the friction brakes (or minimal)

 

use B all the time and regen is almost identical to brake regen. Long steep hill it'll hold the car at the same speed as the nomal traffic and not use the brakes at all. Yes the ICE is running but if you look at the fuel flow data it's miniscule. I just put it back in D when at the bottom or when traffic allows.

 

Let me tell you when our Japanese mileage freaks is using B mode.

There is only one situation of using B mode as follows...

1. When you are approaching a stop sign or a red signal.
2. Keep in D mode when vehicle is more than 35km/h(22MPH).
(The ICE will run using B mode above 35km/h(22MPH).
3. Shift to B mode when vehicle is lower than 35km/h(22MPH).
(The ICE won't run and we get better regenerating.)

Above 35km/h(22MPH), the ICE is always running on B mode and you are losing energy by friction of the ICE.

Using B mode on downhill is same thing. Using only brake on downhill means more regenerating.
When you see full green on downhill, it means Prius can't save generating energy any more, then Prius decides to run ICE to waste the energy and to save battery life.

Regards,
Ken@Japan

 

Slow'n'go driving along the freeway (typically under 22mph) is a good time for B-mode. It slows the car down using gas pedal modulation instad of hopping from gas to brake and back. Saves wear and tear on ME!

 

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No. The 35km/h(22MPH) point never change whether we engage the EV switch or not.

Regards,
Ken@Japan

 

once the BSOC is 80%, full charge (all green) there is no regen at all just friction brakes. At that time put it in B and the ICE kicks in and it forces MG1 to start putting an electrical load on the HV battery to reduce the BSOC to less than 80% at which time you put it in D and it'll regen charge the HV battery. On a long hill 13KM of 9% grade the car will start to accelerate because of the loss of regen till you put it in B. I've tried to drive it like the gas milage freaks in Japan and all that happens is people blow the horn at you and pass wildy and give you the finger. Two distinctly different cultures.

 

I never understood spinning the engine when exceeding 8 bars. Why don't they just not use energy from any MG and use straight friction brakes for the time being, like any other car?

I have also noticed, once stopped while using B, ICE is still running and consuming fuel (Instant MPG low), even with BSOC in 6 bars. When I switch back to D, ICE stops.

 

when your coming down hill and BSOC is 80% when you put it in B and the ICE starts the fuel injector on time is very short and the amout of fuel injected is so miniscule that I'm sure that the mixture is so lean you get lean misfire and the hydrocarbons exit the ICE and get consumed in the cat's as the temp reading for the cat's doesn't drop, which would happen if the ICE was just pumping air, it stay's the same or slightly climbs. The computer takes this temp data and probably stops the fuel injector on time. The load the ICE puts on the planet carrier is what MG1 holds agains to provide the retardation on the drive train to slow the car. With out going back thru my posts if memory serves me right I think the current draw of MG1 was 19 amps. This pulled the BSOC down to 60% in about 1 mile.

 

I go up and down a large hill (sepulved pass for those of you in LA) every day during my commute to work. After getting to the bottom of the hill I have a very flat half mile left to the parking lot.
Since my battery is completely charged by the time I get to the bottom of the hill I like to put the car in EV mode and go the last stretch without using any gas. However, sometimes the car will not let me enter EV mode. I'm guessing its because everything gets cooled down while coasting down the hill.
When I use B mode to control my speed coming down the hill I don't have this problem. It's probably just because leaving the car in B mode keeps the engine running and therefore warm.

 

It has been reported that it won't go into EV mode if the battery is too full.

 

Not true in my experience. When I come off the hill on my way to work my battery is almost always completely full (all the green bars lit), and a lot of the time I don't have any problem putting it in EV mode. So I'm thinking in my case it has more to do with the engine temp (or something else) than with the state of the battery.

 

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!

 

I'm a real nice person with this car. I mean I paid for the extended warrenty and they made me wait forever and a day for it and I had to get the most expensive one, so I beat the hell out of it.

Used the B going 45 mph, it charged my battery all the way up, the car actually works better when the battery is all the way filled up. Doesn't last long though, the charge fades quickly. Don't worry if you use it, but I would suggest it for slowing up to stoplights the most, just make sure you switch back to D

 

I believe the SOC level was not so high in your case.
Many people are experiencing that they could not go into EV mode when the battery level was at the top of 8.
The SOC range is about 76% to 80% for battery level 8.

Regards,
Ken@Japan