Who Uses the "B" Setting on the Shift Lever??
#31
09-12-2006, 05:21 PM
Re: Who Uses the "B" Setting on the Shift Lever??
I have used "B" mode only once when decending a steep grade on I-75 Southbund out of Chatanooga mph was at 65 and increasing to 80. "B" mode slowed it down quickly. I am certain if the speed was too fast for this the computer would not let it engage.
Can't think of any place it would be needed in Florida, not even on thrill hill
As far as having a thermos bottle, I concur that is only on the Prius. The TCH has an electric heating element (I think) to rapidly bring the coolant up to operating temperature but not sure if that function is available without the climate control set to a high temperature requesting heat.
Can't think of any place it would be needed in Florida, not even on thrill hill
As far as having a thermos bottle, I concur that is only on the Prius. The TCH has an electric heating element (I think) to rapidly bring the coolant up to operating temperature but not sure if that function is available without the climate control set to a high temperature requesting heat.
#32
10-08-2008, 06:49 AM
Re: Who Uses the "B" Setting on the Shift Lever??
The "B" mode is the same as downshifting a gear with a manual transmission, thus allowing the transmission to "hold back" the engine's power while coasting down a slope. Great for safety reasons (no runaway car on steep slopes), but has little to do with fuel economy.
#33
10-09-2008, 03:30 PM
Re: Who Uses the "B" Setting on the Shift Lever??
I live two miles up a steep-ish mountain in CA. That gives me plenty of practice with B mode. When starting out cold, B mode spins the ICE without gassing it, but it lubricates and warms it naturally from activity and compression in the cylinders.
From the outset in B mode, mileage is virtually pegged at maximum.
By the time I've gone about half a mile, switching to Drive shows it to be at its most efficient. By this point the mileage shows about 70 ish averaged.
If I start off in Drive, the first half mile or so brings constant wheel braking/regenerating for the whole distance, but only shows as about 30 mpg. Obviously, the engine has been sucking some gas to warm up and get ready to ramble.
Coming down the west side of the Rockies during a road trip, I used it to bleed energy on endless downhills when it seemed that constant foot braking might be detrimental, should overcharge conditions cause brake-only slowing.
The theory being that once the batteries are full to the brim, the brakes no longer divert energy into the battery, so they either spin up the ICE to bleed energy (and you can hear it whine when that condition kicks in) or put the entire weight and momentum on brake pads, potentially leading to fading. Instead of that, the B mode was selected, and although the ICE whined in fast-spin mode, a comfortable 60 was maintained for miles and miles with no apparent issues.
My conclusion is that B mode is really only helpful down hill. And only when engine braking is obviously a Good Thing. It extends my milage when the car is cold, but doesn't seem to change the overall charge level's point of full up as I continue down hill.
Now that I see the questions posed here, I'll try it in other ways to see if different behaviors from my habit will produce consistent alternative results over this two mile test bed.
From the outset in B mode, mileage is virtually pegged at maximum.
By the time I've gone about half a mile, switching to Drive shows it to be at its most efficient. By this point the mileage shows about 70 ish averaged.
If I start off in Drive, the first half mile or so brings constant wheel braking/regenerating for the whole distance, but only shows as about 30 mpg. Obviously, the engine has been sucking some gas to warm up and get ready to ramble.
Coming down the west side of the Rockies during a road trip, I used it to bleed energy on endless downhills when it seemed that constant foot braking might be detrimental, should overcharge conditions cause brake-only slowing.
The theory being that once the batteries are full to the brim, the brakes no longer divert energy into the battery, so they either spin up the ICE to bleed energy (and you can hear it whine when that condition kicks in) or put the entire weight and momentum on brake pads, potentially leading to fading. Instead of that, the B mode was selected, and although the ICE whined in fast-spin mode, a comfortable 60 was maintained for miles and miles with no apparent issues.
My conclusion is that B mode is really only helpful down hill. And only when engine braking is obviously a Good Thing. It extends my milage when the car is cold, but doesn't seem to change the overall charge level's point of full up as I continue down hill.
Now that I see the questions posed here, I'll try it in other ways to see if different behaviors from my habit will produce consistent alternative results over this two mile test bed.
#35
10-09-2008, 08:52 PM
Re: Who Uses the "B" Setting on the Shift Lever??
Wow -- so much confusion. The B mode is designed for long down-hill descents. Once the traction battery reaches its maximum allowable state of charge (SoC), without the ability to shift the "empahsis" to engine braking, the friction brakes would be forced to bear the entire load themselves, as the drive system in its normal operating mode provides little, if any, actual engine braking. I don't know the numbers for the TCH yet, but in the Gen-II Prius, which I used to drive, the ECU would not let the traction battery SoC exceed about 80%. If you're still screaming downhill after the SoC reaches that level, you're going to suddenly be on the friction brakes alone. At first, this confused me, until I realized that in the conventional cars, you always have the engine braking effect present; in the HSD cars, you lose the generator drag when you hit 80% SoC.
Of course, I live in FL, where the highest elevation is about 350 feet MSL, so it's a moot point for me -- B is useful, however, for brake-light-free decels (preceded of course by a look in the rearview...) when the V1 goes off abruptly!
Of course, I live in FL, where the highest elevation is about 350 feet MSL, so it's a moot point for me -- B is useful, however, for brake-light-free decels (preceded of course by a look in the rearview...) when the V1 goes off abruptly!
Last edited by ekpolk; 10-09-2008 at 08:55 PM.
#36
10-09-2008, 11:48 PM
Re: Who Uses the "B" Setting on the Shift Lever??
Wow -- so much confusion. The B mode is designed for long down-hill descents. Once the traction battery reaches its maximum allowable state of charge (SoC), without the ability to shift the "empahsis" to engine braking, the friction brakes would be forced to bear the entire load themselves, as the drive system in its normal operating mode provides little, if any, actual engine braking. I don't know the numbers for the TCH yet, but in the Gen-II Prius, which I used to drive, the ECU would not let the traction battery SoC exceed about 80%. If you're still screaming downhill after the SoC reaches that level, you're going to suddenly be on the friction brakes alone. At first, this confused me, until I realized that in the conventional cars, you always have the engine braking effect present; in the HSD cars, you lose the generator drag when you hit 80% SoC.
Of course, I live in FL, where the highest elevation is about 350 feet MSL, so it's a moot point for me -- B is useful, however, for brake-light-free decels (preceded of course by a look in the rearview...) when the V1 goes off abruptly!
Of course, I live in FL, where the highest elevation is about 350 feet MSL, so it's a moot point for me -- B is useful, however, for brake-light-free decels (preceded of course by a look in the rearview...) when the V1 goes off abruptly!
#37
10-10-2008, 01:00 AM
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Join Date: Jun 2007
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Re: Who Uses the "B" Setting on the Shift Lever??
I read the Brake position is similar to 2nd and Low gear of a regular gas powered car. It said in the brake position is uses the generator to gear down till the traction battery reaches full charge. Then it switched to the engine and continues the gearing down. This may be when your at 45 mph and higher.
If the engine can't gear down enough then the computer gently applies the brakes trying to keep the car at a steady slower speed.
If the engine can't gear down enough then the computer gently applies the brakes trying to keep the car at a steady slower speed.
Last edited by rburt07; 10-11-2008 at 12:32 AM.
#39
10-10-2008, 06:07 PM
Re: Who Uses the "B" Setting on the Shift Lever??
No, seriously, B is meant specifically for when you've been going downhill so long that you max out the traction battery's SoC. Once that happens, B helps take some of the burden off of the friction brakes. It can also be used for added drag under less critical situations. Hope that's more clear than my last ramble...
#40
10-11-2008, 05:18 AM
Re: Who Uses the "B" Setting on the Shift Lever??
Short version - "Use B when going down a long steep grade - it helps keep your brakes from overheating and failing at the worst possible moment. Otherwise, don't worry about it."
