I am a new owner and am shifting into "B" to slowdown for stoplights in lew of using my brakes. I always shift out of B when the light changes or if i have to come to a stop. Is their anything wrong with this process. I live in Colorado and i understand the intended use of B. I am assuming that using B when i need to slow down increases MPG and saves on brakes.

 

additional note from rod i average 52.7 to 53MPG to and from work. the trip is hilly with few stops. 15 miles each way

 

Hi,

I have a Graham miniscanner and I find light braking increases the regenerative braking current substantially more than using "B". However, "B" is excellent for descending large hills without having to use the brakes. On a 6% grade, I'm typically seeing speed hold about 65-70 mph with "B". But for energy recovery, a light brake pressure can't be beat.

Bob Wilson

 

Here is a good explanation of the B mode as well.
http://techno-fandom.org/~hobbit/cars/b-mode.html

 

As Bob posted, using "B" will actually end up wasting a bit of energy. "B" forces use of the engine for braking as well as regeneration. So you will loose some regeneration energy (because the engine braking dissipates the energy, not the regeneration). You WILL notice better braking performance, but at a loss of recoverable energy.

There is one exception. When the SOC (state of charge) meter is at full green, the car can't use regeneration to charge the battery (though it can use it to spin the ICE - internal combustion engine). So use of "B" when the battery it displayed as full, will probably not loose you use of energy because the system can't store it anyway.

The trick to recover maximum energy is to anticipate when you will have to stop at least a block in advance. Brake slowly using gentle pressure. This will maximize the times you will actually not have to stop, as the light will change before you get there, and will maximize the amount of energy you will recover to the battery.

Be aware, the "recovery" of kinetic energy through regeneration is only around 50% efficient (an estimate from those with instrumentation). The motor generator is only perhaps 80% efficient. Battery charging is only perhaps 70% efficient. And finally, when you go to use the electric energy, removing the energy from the battery is not 100% efficient, and the motor is perhaps 80% efficient at using the energy. To make matters a little worse, you can't recover the last bit of energy (below 7 MPH vehicle speed) as regeneration shuts down and friction braking takes over.

You shouldn't worry about the Prius brake wear. If anything, they don't wear fast enough.

 

My 2007 let's me coast above 42 mph with no use of battery pack (P&G kind of). I rarely use highways anymore, but I was wondering if it would do any harm. Say you have an extended downhill where B braking is not needed, but at the same time normal regen (D mode) will slow you down and coasting will use battery. Any suggestions?

 

I'm not really sure what you're asking. Could you clarify it?

Bob Wilson

 

Fluteman, what you are describing is called "warp stealth". The engine is spinning, btw, but consuming no fuel. It will do no harm. In fact, it is the technique the hypermilers sometimes use, though they usually try to stay slower than 42 MPH.

The engine has to spin to avoid overspinning MG1 (motor generator 1).

Also, just for your info., "stealth mode" is coasting below 42 MPH, where the engine doesn't have to spin.

As a final note, the car will not let you harm it. Don't worry, just drive.

 

I perfer to just use a light break pedal while going down a hill rather than using "B", this way you keep the battery charged. I'd say my indicator is green a good third of the time.

I am thinking of doing the EV mod.

 

Your mileage will increase dramatically if you try depleting the
charge your last mile or two before arriving home (or wherever). You're just wasting fuel working to keep your display green so much. Mine is almost never green. My mileage is on my signature (real, not computer)