Best Use of B mode

DanThePodGuy · 03-26-2005, 05:28 AM

I live of a small hill and use the B mode when going down the hill. It seems to work fine. However on longer down grades when I use the B mode the engine reve very high. What is up with this. The times I ahve noticed it is when the battery is fully charged.

Is this a problem with the car or normal. Why the high revs?

8AA · 03-26-2005, 06:59 AM

B mode uses the compression losses of the cylinders for engine braking. The higher the RPMs, the greater the losses and the more resistance provided. People who drive cars with standard transmissions will understand this as the reason they downshift when approaching a stoplight or going down a long grade.

Bottom line: it's normal for the Prius.

geminirat · 03-26-2005, 09:32 AM

Thank you Bob - You are helping me to understand the B "gear" mode and "engine braking." Not many hills here but when I misjudge - and have to break more agressively coming to a stoplight - I will pop it into B.

I know there are other threads on this but what is the advantage - other than saving on brake wear, for doing this often? Is it detrimental technically?

You do have to make sure there is no idiot tailing you because you do slow down quickly with no brake lights.

Thank you.

geminirat · 03-26-2005, 10:21 AM

Okay, I'm back after reading some previous B threads. So we get less regeneration in B because the ICE continues to run? Is this constant no matter what speed we engage B? Therefore someone who uses B a lot will have poorer mileage?

V8Cobrakid · 03-26-2005, 10:42 AM

B mode isn't as simple as most think. 8 - 25mph it uses the electric motors as the main slow down method. Above 25, it uses the engine's compression to slow down the car. both are farily decent at regenerating electricity. I would say my breaking methods are better.. but breaking methods take a lot of work.

If you come to a stop with B gear still on... then you are waisting electricity that has to spin the engine. If momentum won't spin it.. the electric motors will. the ICE will always spin when B Gear is enabled. This explains poor gas mileage. It does get a little more complicated.. but either way, it has to spin and takes valuable energy if you are not going down a hill. you can use electric mode by lightly applying pressure to the gas pedal.. However.. same concept, ICE will still be spinning. Imagine having the A/C on while in a standard car. It takes energy away.

B gear seems to have no ill effect, no matter how much you use it. There shouldn't be any problems. I have not heard of any problems either. Everything i've heard says you can use it as much as you like. Keep in mind your mpg could go down in used inproperly.

DaveinOlyWA · 03-26-2005, 11:14 AM

i think B mode should never be used. realize that unlike a normal car, applying the brakes and slowly increasing pressure will increase regen to the battery without any wear and tear on the friction brakes (or minimal)

Frank Hudon · 03-26-2005, 11:23 AM

use B all the time and regen is almost identical to brake regen. Long steep hill it'll hold the car at the same speed as the nomal traffic and not use the brakes at all. Yes the ICE is running but if you look at the fuel flow data it's miniscule. I just put it back in D when at the bottom or when traffic allows.

ken1784 · 03-26-2005, 12:21 PM

Let me tell you when our Japanese mileage freaks is using B mode.

There is only one situation of using B mode as follows...

1. When you are approaching a stop sign or a red signal.
2. Keep in D mode when vehicle is more than 35km/h(22MPH).
(The ICE will run using B mode above 35km/h(22MPH).
3. Shift to B mode when vehicle is lower than 35km/h(22MPH).
(The ICE won't run and we get better regenerating.)

Above 35km/h(22MPH), the ICE is always running on B mode and you are losing energy by friction of the ICE.

Using B mode on downhill is same thing. Using only brake on downhill means more regenerating.
When you see full green on downhill, it means Prius can't save generating energy any more, then Prius decides to run ICE to waste the energy and to save battery life.

Regards,
Ken@Japan

DanThePodGuy · 03-26-2005, 03:52 PM

Ken,

Thanks for the info. If you have an EV switch do the speed points change? That is will the 22 MPH change to be 35 MPH with the ev switch on before the ICE kicks in?

The time I obsevered the high reving was after a long trip when the battery was in the green. I assumed the engine was running to sluff off the entra energy.

DanThePodGuy

KTPhil · 03-26-2005, 03:56 PM

Slow'n'go driving along the freeway (typically under 22mph) is a good time for B-mode. It slows the car down using gas pedal modulation instad of hopping from gas to brake and back. Saves wear and tear on ME!

03-26-2005, 05:28 AM	#1
DanThePodGuy Join Date: Feb 2005 Posts: 9 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Best Use of B mode I live of a small hill and use the B mode when going down the hill. It seems to work fine. However on longer down grades when I use the B mode the engine reve very high. What is up with this. The times I ahve noticed it is when the battery is fully charged. Is this a problem with the car or normal. Why the high revs?

03-26-2005, 10:42 AM	#5
V8Cobrakid some guy... Join Date: Jun 2004 Location: San Jose, CA Posts: 2,519 My Car: 2004 Prius Package: #9 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 4	B mode isn't as simple as most think. 8 - 25mph it uses the electric motors as the main slow down method. Above 25, it uses the engine's compression to slow down the car. both are farily decent at regenerating electricity. I would say my breaking methods are better.. but breaking methods take a lot of work. If you come to a stop with B gear still on... then you are waisting electricity that has to spin the engine. If momentum won't spin it.. the electric motors will. the ICE will always spin when B Gear is enabled. This explains poor gas mileage. It does get a little more complicated.. but either way, it has to spin and takes valuable energy if you are not going down a hill. you can use electric mode by lightly applying pressure to the gas pedal.. However.. same concept, ICE will still be spinning. Imagine having the A/C on while in a standard car. It takes energy away. B gear seems to have no ill effect, no matter how much you use it. There shouldn't be any problems. I have not heard of any problems either. Everything i've heard says you can use it as much as you like. Keep in mind your mpg could go down in used inproperly. __________________ Silver 9 as of June 12th '04 (over 101k Miles now) Decals, Mud Flaps, BT Tech Rear Brace, coastaletech 2" receiver hitch, and 215/45/17 tires.

03-26-2005, 12:21 PM	#8
ken1784 SuperMID designer Join Date: Dec 2003 Location: Yokohama, JAPAN Posts: 1,347 My Car: 2004 Prius Package: G Touring Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 2	Re: Best Use of B mode Let me tell you when our Japanese mileage freaks is using B mode. There is only one situation of using B mode as follows... 1. When you are approaching a stop sign or a red signal. 2. Keep in D mode when vehicle is more than 35km/h(22MPH). (The ICE will run using B mode above 35km/h(22MPH). 3. Shift to B mode when vehicle is lower than 35km/h(22MPH). (The ICE won't run and we get better regenerating.) Above 35km/h(22MPH), the ICE is always running on B mode and you are losing energy by friction of the ICE. Using B mode on downhill is same thing. Using only brake on downhill means more regenerating. When you see full green on downhill, it means Prius can't save generating energy any more, then Prius decides to run ICE to waste the energy and to save battery life. Regards, Ken@Japan

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03-26-2005, 06:59 AM	#2
8AA Senior Member Join Date: Feb 2004 Location: Maryland Posts: 492 My Car: 2004 Prius Package: #9 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	B mode uses the compression losses of the cylinders for engine braking. The higher the RPMs, the greater the losses and the more resistance provided. People who drive cars with standard transmissions will understand this as the reason they downshift when approaching a stoplight or going down a long grade. Bottom line: it's normal for the Prius.

03-26-2005, 09:32 AM	#3
geminirat Join Date: Mar 2005 Location: Downriver, Michigan Posts: 31 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Thank you Bob - You are helping me to understand the B "gear" mode and "engine braking." Not many hills here but when I misjudge - and have to break more agressively coming to a stoplight - I will pop it into B. I know there are other threads on this but what is the advantage - other than saving on brake wear, for doing this often? Is it detrimental technically? You do have to make sure there is no idiot tailing you because you do slow down quickly with no brake lights. Thank you.

03-26-2005, 10:21 AM	#4
geminirat Join Date: Mar 2005 Location: Downriver, Michigan Posts: 31 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Okay, I'm back after reading some previous B threads. So we get less regeneration in B because the ICE continues to run? Is this constant no matter what speed we engage B? Therefore someone who uses B a lot will have poorer mileage?

03-26-2005, 11:14 AM	#6
DaveinOlyWA Opps !! I Did it Again!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 9,521 My Car: 2006 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 4	i think B mode should never be used. realize that unlike a normal car, applying the brakes and slowly increasing pressure will increase regen to the battery without any wear and tear on the friction brakes (or minimal)

03-26-2005, 11:23 AM	#7
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	use B all the time and regen is almost identical to brake regen. Long steep hill it'll hold the car at the same speed as the nomal traffic and not use the brakes at all. Yes the ICE is running but if you look at the fuel flow data it's miniscule. I just put it back in D when at the bottom or when traffic allows.

03-26-2005, 03:52 PM	#9
DanThePodGuy Join Date: Feb 2005 Posts: 9 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Ken, Thanks for the info. If you have an EV switch do the speed points change? That is will the 22 MPH change to be 35 MPH with the ev switch on before the ICE kicks in? The time I obsevered the high reving was after a long trip when the battery was in the green. I assumed the engine was running to sluff off the entra energy. DanThePodGuy

03-26-2005, 03:56 PM	#10
KTPhil Senior Member Join Date: Jan 2005 Posts: 1,213 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Slow'n'go driving along the freeway (typically under 22mph) is a good time for B-mode. It slows the car down using gas pedal modulation instad of hopping from gas to brake and back. Saves wear and tear on ME!