Using B often...Good or Bad?

hmmmmm.. I use the brake and listen technique. It keeps my hands on the wheel and allows me to prepare for a speed increase when the light turns green.

[I work for a software company that coordinates traffic lights. ]

 

Yes, you are reducing your efficiency somewhat. Using "B" uses the engine to slow the car. Just leave it in "D." Look ahead, and see what the lights are doing. Coast as often as possible in traffic. Right now, I'm beating my combined EPA figure by 9.6 mpg in my classic. EPA combined for my car is 48, and the computer is stating 57.6. While my computer is optimistic, this will still be a new high tank for this car.

 

use it 4 day's a week, I have a hill on the way to work that is 13% grade for 3/4's of a mile and there is a traffic light at the bottom. Pop it into B and it will hold me at speed (no increase) and it keeps the SUV's a cars off my bumper, then use D and brakes to slow to a stop. I'm one who goes with the flow, and the gas for the Prius is a lot less than the Tundra.

 

Did it ever occur to anyone that if Toyota thought it was a good idea to use engine braking to decelerate from 20 to 6 they would have programmed the computers to do it already?

 

I've tried this, 20mph is VERY slow and the minimal improvement in regen vs. the risk of being rear ended...[/quote]

I agree with this concern, many people aren't paying enough attention on the road. The brake lights serve to inform those behind that you are slowing down and 'B' will slow the car more than average. Someone behind might not notice the 'increased' decrease in speed. Of course, I guess one could be on the brake pedal just enough to activate the lights for safety.

 

The "If Toyota had Wanted You To...." arguement is fallacious most times for one reason.

In an automated system, the designers go for a middle ground.

Take an Automatic Transmission for example. It shifts at a certain Load/RPM because that's optimal for a combination of factors: Mileage, Acceleration, Noise.....

That DOES NOT imply that the chosen shift point is optimal for all situations.

That's why someone with a Stick can Downshift and up the Revs when they want, or Upshift sooner to save fuel when they want.

The Human Mind is an amazing thing. It can take all kinds of complex variables, and process them in combinations that computers still can't. Not to mention the fact that the computer can't read your mind, or know what is ahead on the road, or what is behind you.

Toyota clearly couldn't make "B" mode the default because of lots of reasons. It is less mileage efficient, and if you took your foot off the gas in traffic, instead of a slow coast/down you'd slow like a you had an anchor out. That's clearly not appropriate for ALL situations.

But, that in no way implies that there's any problem with doing something different when you know the road ahead, and there is no one behind you, and you know what you're doing and why.

We know that B below 20mph DOES regenerate more vigorously, and this gives us a choice.

Choice is good, as long as it's applied with the proper brain power behind it to avoid making stupid choices.

Just as someone with a Manual Tranny wouldn't downshift with a Semi 2 feet off their rear bumper, we have to assume that an operator wanting to use B mode has just as much common sense as someone driving a Stick Shift

And, to flip the arguement around:

If Toyota hadn't wanted you to use B mode, they wouldn't have put it there!!!!!

 

I find it hard to reconcile these two statements. Does slowing below 20 using B regenerate more power? If so, surely it's more mileage efficient.
I must confess I don't quite understand what people are trying to achieve by using the B button.

No, that's not what I mean. I mean they could have programmed it so that if you lightly pressed the brake pedal below 20, it acted like B mode.

 

It is designed to be used when going downhill to slow the car down instead of using your brakes. This is especially important when traveling in the mountains where on steep downhill slopes, brakes can burn out. I personally don't see that you need to use it during other times. On "normal" hills like those here in the Denver area, B mode is unnecessary and I don't use it.

 

Above 20 MPH, B Mode is indeed "Engine Braking". It bleeds off power by spinning the ICE, presumably with varying degrees of Fuel-Less compression.

Below 20 MPH, the B mode is NOT "Engine Braking". It does not spin the ICE, but instead relies on increased resistance from the MG(s), which in turn produces greater electricity regeneration.

Thats why you see the Japanese 'Power Mileage Drivers' who have this particular peculiarity down to a science using it when slowing below 20 MPH.

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And no, it's not contradictory to say that having B mode engaged all the time is more fuel-inefficient, because there are times you want to lift off the accelerator and NOT slow down.

Lightly pressing the brake below 20MPH results in much less braking that B mode. It's a significant amount of slowing, and cannot be modulated, so that's not an option.

If B were engaged all the time, you would only have two options, accelerate or brake, unless you were the perfect 'featherer' finding the dead zone when you wanted to not accelerate or maintain speed.

 

Aha. So how's that different from pressing the brake pedal slightly harder? Don't the first few stages of braking rely purely on adjusting the MG load? The Toyota blurb suggests that the hydraulic brakes aren't activated at all until fairly heavy deceleration is required.

 

Without exact data, who knows exactly how much regeneration can be obtained by the brake pedal before the mechanical brakes engage, or if B mode provides more regeneration than the system would allow through brake pedal manipulation before putting pad to metal.

Maybe one of the Japanese researchers has some hard data.

But, in any case, low speed B mode ensures that you are not engaging the mechanical brakes, and that all your decelration is producing electricity.

If you were doing it yourself via the brake pedal, you would not know when you have started using the mechanical brakes and thus lost some amount of regenration.

So if you slow using B mode, you can safely say that you have maximized regeneration, which is not something you can be sure of using the Brake Pedal.

 

I was reading a post somewhere that one person keeps bumping it into "B" whilst on the freeway (by accident) and the car immediately decelerates with no brakelights posing a traffic risk. He says it's happened 3 times by accident.

Does anyone have any thoughts on how to avoid accidental selection of "B" at high speed. My car hasn't arrived yet, so I am also curious about how to "dissengage" B rapidly if it was selected by accident.

 

Hmmm... I'm hard pressed to figure out why anyone would ever intentionally leave "D" in freeway traffic, and thus accidently bump it into "B". No reason with a Prius to put the car in neutral in stop-and-go traffic.

Unless somebody kept bumping the shift knob? I haven't been in a Prius enough to know if that's likely.