So, as I have said before, I have an hour commute to work. It's mostly on the turnpike, but when I exit I have about a 7-10 minute drive down a longggg steep hill. I thought instead of braking the whole way down, I'll put the car in B mode (or however you would say it!). Well, the car started getting really loud and of course I got scared, so I put it back into drive. Was I going too fast for it to be in B mode? I'd say I was going about 55ish...I mean, I don't think I should be breaking the whole time but I'm not sure how to handle this hill. Should I put Preston in cruise control???
What was the battery state of charge at the time it got loud? There have been reports that if the battery gets really full then the Prius will work to burn off some of the extra charge. This has never happened to me so I don't know what it sounds like. But you said that most of the drive is on the turnpike. I know that sometimes when I'm driving on the highway the battery can get up to 6 bars or even 7. If you start coasting and regenerating on top of this it could fill the battery.
The "loud" noise was your engine acting as a brake, as if you would have downshifted in a standard car. As the battery reaches the upper limit of it's state of charge, the engine will spin even faster to "absorb" the excess energy, usually right up to it's maximum operating RPM (which is perfectly safe). If you were to floor it, you'd get the same "loud" sound. Nothing to be concerned about.
The noise you describe is normal, as the others have explained. Seeing you are from Pennsylvania, I can't imaging a hill long enough to warrant the use of B mode. B mode throws away energy by spinning the engine. Generally it is better to recapture that energy by using regenerative braking. Just press on the brake pedal and stay in D. If you find that the battery is fully charged after the downhill, the next time you might consider using B. Otherwise normal braking was the correct choice. Tom
It's fine. You should hear it coming down the side of the mountain! It sounds like a twin prop coming in for landing!
If by the bottom of the hill the engine is going very loud you have topped out the battery so using B mode is the right thing to do. The computer will look after your engine so stay in B until you get to the bottom of the hill. Engine revs will never exceed 5,000RPM which isn't high by todays standards, the same capacity engine in a Yaris would redline at over 6,000RPM.
In western PA I haven't shifted into B. Generally I go as far as Breezewood and have not found it needed on the Turnpike. Going south from Ebensburg to Portage or on PA164 I'll fill the battery but don't brake down the mountains. The mountain going south on I-80(?) from State College is much steeper. B mode may be a better option as I do brake most of the way down.
On long hills in New Hampshire where I know that "B" is not enough to prevent the battery from reaching full charge, I turn on the headlights to "HI". This burns off some of the recharging and lets the car go further before the battery reaches full charge. On really nasty hills (Mt Washington), I may also turn on the air conditioner to "HI" as well. This use of electrical energy helps prevent the mechanical brakes from working and subsequently overheating once the battery is full and the engine is revved to the wall. Actually, the Prius can do pretty well on the Rockpile's 4,700 foot drop from the summit. A lot of them go up and down.
Yea, I know what hill you're talking about near State College! The hill I drive down isn't on the Turnpike; it's after I exit...315 to 81 North towards Scranton. Familiar with that particular area? It's what I like to call "One hill of a hill"!!! But basically if I see my battery is pretty close to charged then I SHOULD go down the hill in B? Is that right? Not to play the "girl card" but I don't really know much about cars...I bought Preston for my commute, but I'm trying to learn as much as I can through this site!! FYI: I passed THREE other Prius' today on the turnpike and not one of them even glanced my way..BOO!!! =( PLUS, they all passed me...which, am I the only one who stays slightly under the speed limit to get the best mpg? It surprises me to see Prius' whizzing past me on the Turnpike...it's like, an oxymoron or something.... (at least in MY book!)
B mode delays the onset of friction braking in the event that engine braking alone can't provide enough braking. When you don't use B mode, the Prius will still resort to engine braking once the battery becomes charged, it just waits longer and isn't quite as aggressive about it. You seldom *need* to use B mode unless you are driving in the mountains. Many people *like* to use B mode for ease of control and a perceived sense of better control, but that is a subjective choice. I suspect in your case you don't need B mode. Once again, if you find that the battery consistently charges to the point that engine braking occurs automatically, then you can consider engaging B mode as you head down the hill. You can tell when engine braking kicks in because the engine will sound like it is racing, so if you get this when in D consider using B next time. Otherwise just use D which will maximize your mileage. Tom
There is no such thing as "too fast for B mode." B mode is engine braking, but unlike downshifting a conventional car (which could over-rev the engine) the Prius's computer keeps everything under control. Unfortunately, cruise control will not slow down the car, so it's useless when you are going downhill on a hill steep enough to require braking. I agree with this. Not absolutely the only one, but just about! Note that not only the Prius, but all cars get better mileage going slower (though the Prius's best mileage is at a slower speed than other cars). Most drivers are in such a hurry to get where they're going that they don't care how much gasoline they burn. Consider those big, square SUVs going 5 to 10 mph over the speed limit. They are burning gas like nobody's business. Most folks think the speed limit is the slowest permissible speed, rather than the fastest. It's that sort of attitude that has gotten us into the mess we are in now. Good for you for driving a little under the limit!
Nope :_> "B" is used only to avoid riding the brakes. There is never any need for the driver to use "B" to manage the battery; the car takes care of battery management all by itself.
