Can you shift too much?

[HarleyMYK]

In my first couple days with my new 2004 Prius I have been using the shift to B frequently to use the Generator / Engine braking and recharge and then shifting back to D. Is there a downside to this? Can you shift too much?

Also, what is the downside to leaving the car in B? Higher revs and poorer gas milage?

[efusco]

In my first couple days with my new 2004 Prius I have been using the shift to B frequently to use the Generator / Engine braking and recharge and then shifting back to D. Is there a downside to this? Can you shift too much?

Also, what is the downside to leaving the car in B? Higher revs and poorer gas milage?

Very poor gas mileage if you use it at any time besides steep downhills. There is no indication to use it at all most of the time, but if you're tired of using the brake pedal on steep long downhills you can drop into "B", but this will actually result in lower overall mileage due to the engine braking involved.

You can also use it at speeds below 20mph if you really want to, when slowing, without the ICE kicking in and it should, theoretically, maximize regenerative braking. It's hard to imaging it makes much difference though, and no regen braking occurs below 9mph anyway.

[Wolfman]

In my first couple days with my new 2004 Prius I have been using the shift to B frequently to use the Generator / Engine braking and recharge and then shifting back to D. Is there a downside to this? Can you shift too much?

Also, what is the downside to leaving the car in B? Higher revs and poorer gas milage?

Well, it does defeat the purpose of the system. As Evan stated "B" is used for heavy mountain driving, and even then, only when it's needed to safely keep the car at speed downhill.

Personally, I've never used the "B" selection, even on 6 and 7 percent grades. My car typically stays within 5 mph of the posted limit, and has only required a light touching of the brakes on occasion to bring that down. For normal everyday use, just leave it in "D" and forget about it.

[AlphaTeam]

Ok sorry n00b here.
What is "B" anyway?
I saw that and thought it might be a parking brake.
But since you guys drive with it, I'm guessing its not.

Alpha

[efusco]

"B" is for engine braking. Basicly it acts sort of as a "Jake Brake" where the back pressure of the ICE helps slow the vehicle. However, in the Prius it also maximally engages regenerative braking (MG1) to reclaim some of that kinetic energy.

[jamarimutt]

I find that B is only useful when going downhill for a long time, as on a long and twisty country road several miles long. In this case, B could keep the brakes from overheating. The rest of the time there's no need to use B (may be useful, though, if you're bored and want to play with the shifter).

[ggood]

I use B every work day coming down a 6 story spiral parking garage ramp. Keeps me from having to ride the brake. Of course, for a quick thrill, I don't use B or the brake!

[Ken Cooper]

Excuse the ingnorance of an old retired engineer here, but please explain to me what it is about 'B' mode that would cause gas mileage to suffer when using it. If you watch the monitor when in 'B' mode as you use it slow your speed going down hill, the engine isn't fired up and the battery is being recharged through regeneration.

Jake brake reference has been used, but that entails using engine compression with no fuel applied (air compressing on each stroke and released at the top of that stroke).

If no fuel is applied to the engine in 'B' and regeneration is occuring in 'B', how on earth is this going to affect gas mileage?

I'm sure I'm missing something here. Please enlighten me.

Ken

[DaveinOlyWA]

being in B mode would only hurt your gas mileage if you were trying to increase your vehicle's speed by accelerating. accelerating in B mode would feel similiar to accelerating in 1st gear in a normal automatic transmission ICE.

you should also know that B mode creates unnecessary wear on the transmission and should not be used for long periods of time.

although many people here seem to think that the Prius slows down fairly rapidly when coasting in Drive, i feel that it doesnt. many times when i am coming to a stoplight i do not want to start coasting too early especially if traffic is heavy so i will use the B mode as it basically slows the vehicle at a much greater rate. and as an experiment, i decided to use it as often as was possible in town to see if there was a noticable change in my gas mileage. since i just started this experiment this weekend and havent tested it enough to say for certain, it does appear that my mileage has increased due to more regen power being captured. for the first time in recent memory, i achieved 150 Wh of recharge in a segment, then got a 100 Wh charge in the next segment. this was achieved on level road at speeds from 35-45 mph. as 50% of the stops were stop signs, couldnt avoid the complete stop.

as it looks so far, im nearly 2 mph over my typical in town average of 49 mpg. like i said its still early and will have a better picture of it after a few weeks of trying the B mode.

[Ken Cooper]

How does 'B' mode create unnecessary wear on your transmission (power split device that is always working in one way or the other anyway).