Regenerative Braking

donwjaco · 03-11-2007, 04:27 PM

I have had my Prius since late December I love it. I am wondering about the regenerative braking. Does it charge more quickly when the brake peddle is depressed aggressively or is it better to ride the brake pedal as you are rolling to a stop or slow down? At what point do the actual brake pads start pressure on the disks? With hard braking or just at slow speeds near the stop?

NoMoShocks · 03-11-2007, 04:36 PM

I can tell you that with agressive braking, that is when the mechanical brakes come into play. Coasting or gentle braking regenerates the maximum power, without using the mechanical brakes.

I would like to have one of the more experienced posters expand on what they might know as far as the actual threshold between gentle braking and harder braking when the mechanical brakes kick in.

Also, would appreciate if someone can confirm, as I understand, gentle braking down a hill will regenerate power, but use of the B position of the shifter uses the ICE to brake. Therefore, the B should not be used unless agressive braking requiring the mechanical brakes is needed to maintain speed on a hill, which seems like it would be very rarely. Am I correct?

usbseawolf2000 · 03-11-2007, 04:40 PM

Don't stop aggressively. Start braking as soon as possible. Don't do it too early so drivers behind you get annoyed.

If you have EV button installed, engage and accelerate as hard as you can before HSD cancel out of EV mode and resume normally. Remember the "G" you feel from the pull on battery alone. That is how much power the battery can absorb back. So, brake around that "G" and you should be able to recover probably 90% of the energy and you may see more green bars.

Edit: I have yet to confirm the charge rate is the same as the discharge rate.

dmckinstry · 03-11-2007, 04:51 PM

<div class='quotetop'>QUOTE(NoMoShocks @ Mar 11 2007, 01:36 PM) [snapback]403860[/snapback]</div>

Quote:

I can tell you that with agressive braking, that is when the mechanical brakes come into play. Coasting or gentle braking regenerates the maximum power, without using the mechanical brakes.

I would like to have one of the more experienced posters expand on what they might know as far as the actual threshold between gentle braking and harder braking when the mechanical brakes kick in.

Also, would appreciate if someone can confirm, as I understand, gentle braking down a hill will regenerate power, but use of the B position of the shifter uses the ICE to brake. Therefore, the B should not be used unless agressive braking requiring the mechanical brakes is needed to maintain speed on a hill, which seems like it would be very rarely. Am I correct?
[/b]

Yes I'd like to see that information in terms of % braking as displayed by CAN-View (or probably ScanGauge).
Can we have agressive braking defined in terms of such a percentage?

P.S. I just noted that my time stamp is screwed up. See the 12:51 PM at the top of the page (may be changed now that I'm editing). It's 1:54 PM according to my computer, and I see other posts indicating it's just before 2:00 PM. What gives?

Well, that's strange. After exiting and looking it says 1:51 PM now.
Dave M.

qbee42 · 03-11-2007, 05:16 PM

Very aggressive braking, in the form of a panic stop, will cause the brake system to abandon regen braking and switch to friction brakes. For best regen, brake early with modest pressure. As you increase the brake pressure, the current levels rise, which causes less efficient charging of the battery. The most efficient braking is no braking at all; coast as much as possible, but be safe and don't annoy other drivers.

The regen system drops out at about 7 mph, after which the friction brakes take over.

Tom

daniel · 03-11-2007, 06:37 PM

It's always most efficient (as with any car) to drive with moderation: Don't baby it, but don't push it either. I've seen over 100 amps going into the battery, so it can take a pretty fair amount of regen.

B mode uses engine braking to slow the car, like using low gear on a manual transmission, or jake brakes on a semi. The only time you should use B mode is when an extended downhill will rise the SOC of the battery as high as the computer will permit (about 80% of capacity, or something more than "full" on the screen icon) because once the battery will accept no more charge, then friction braking is used. B takes some of that job off the brakes and puts it on the engine. Friction brakes and engine compression braking both waste energy by dissipating it as heat, so you only want to do that when the battery is full -- or, in the case of friction braking, when you need to make a very quick stop.

It's really difficult to put into words how hard you can step on the brakes and still have 100% regerative braking, especially since that will depend on factors like SOC and battery temperature. I think the best description is "moderate." Neither too gentle nor too hard.

ken1784 · 03-11-2007, 11:10 PM

I think this should be placed on the FAQ list somewhere.

http://vassfamily.net/ToyotaPrius/CAN/brindex.html
Attila's experiment shows pedal value 17 (13% on CAN-view) is the best.

Ken@Japan

TheForce · 03-11-2007, 11:15 PM

<div class='quotetop'>QUOTE(ken1784 @ Mar 11 2007, 11:10 PM) [snapback]404016[/snapback]</div>

Quote:

I think this should be placed on the FAQ list somewhere.

http://vassfamily.net/ToyotaPrius/CAN/brindex.html
Attila's experiment shows pedal value 17 (13% on CAN-view) is the best.

Ken@Japan
[/b]

Ahhhh. 13 for us Can-View owners. I was wondering how he was getting a 22 sec stopping time with 17. I was stopping a lot quicker when I used 17. I'll try 13 now that I know this.

That brings up a question. How do you know its 13? Am I missing a conversion somewhere?

ken1784 · 03-12-2007, 01:40 AM

<div class='quotetop'>QUOTE(theforce @ Mar 12 2007, 12:15 PM) [snapback]404019[/snapback]</div>

Quote:

That brings up a question. How do you know its 13? Am I missing a conversion somewhere?
[/b]

Attila's brake pedal value 17 is the raw number on CAN and the max is 127.
CAN-view shows it 0-100%, so 17/127=0.13 or 13%.

Ken@Japan

TheForce · 03-12-2007, 01:52 AM

<div class='quotetop'>QUOTE(ken1784 @ Mar 12 2007, 01:40 AM) [snapback]404066[/snapback]</div>

Quote:

Attila's brake pedal value 17 is the raw number on CAN and the max is 127.
CAN-view shows it 0-100%, so 17/127=0.13 or 13%.

Ken@Japan
[/b]

I see now. Thanks.

03-11-2007, 04:36 PM	#2
NoMoShocks Electrical Engineer Join Date: Jan 2007 Location: Camas, WA Posts: 1,024 My Car: 2007 Prius Package: #5 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I can tell you that with agressive braking, that is when the mechanical brakes come into play. Coasting or gentle braking regenerates the maximum power, without using the mechanical brakes. I would like to have one of the more experienced posters expand on what they might know as far as the actual threshold between gentle braking and harder braking when the mechanical brakes kick in. Also, would appreciate if someone can confirm, as I understand, gentle braking down a hill will regenerate power, but use of the B position of the shifter uses the ICE to brake. Therefore, the B should not be used unless agressive braking requiring the mechanical brakes is needed to maintain speed on a hill, which seems like it would be very rarely. Am I correct? __________________ Lightning Green McQueen, and owner Larry 2007 Pkg 5, Jan 2007 with modifications: Toyota Mudguards Feb 2007 LED Signal mirrors March 2007 Wheelskins Leather Steering Wheel March 2007 ScanGuage II, March 2007 BT Tech Stiffening Plate, March 2007 Nokian WR 195-60R-15 tires, Nov 2007 Solar Gaurd window tint, Feb 2008 Fog Lights on idependant of headlamps, Feb 2008 BT Tech Strut Tower Brace, April, 2008

03-11-2007, 04:40 PM	#3
usbseawolf2000 HSD PhD Join Date: Sep 2004 Location: Queens, NY Posts: 1,636 My Car: 2006 Prius Package: #3 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 47	Don't stop aggressively. Start braking as soon as possible. Don't do it too early so drivers behind you get annoyed. If you have EV button installed, engage and accelerate as hard as you can before HSD cancel out of EV mode and resume normally. Remember the "G" you feel from the pull on battery alone. That is how much power the battery can absorb back. So, brake around that "G" and you should be able to recover probably 90% of the energy and you may see more green bars. Edit: I have yet to confirm the charge rate is the same as the discharge rate. __________________ Prius shaped the form of future cars. Hybrid Synergy Drive is the engine of change that moved us forward. Kyowa KR206 17" Black Chrome Lips \| Sherwood Wood Dash (Birds Eye) \| EV Button \| Auterra Dyno Scan \| Fumoto Valve (F-103) \| Garmin Nuvi 250W GPS \| Philips Vision Plus

03-11-2007, 06:37 PM	#6
daniel Cat Lovers Against the Bomb Join Date: Feb 2004 Location: Spokane, WA Posts: 9,148 My Car: 2004 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	It's always most efficient (as with any car) to drive with moderation: Don't baby it, but don't push it either. I've seen over 100 amps going into the battery, so it can take a pretty fair amount of regen. B mode uses engine braking to slow the car, like using low gear on a manual transmission, or jake brakes on a semi. The only time you should use B mode is when an extended downhill will rise the SOC of the battery as high as the computer will permit (about 80% of capacity, or something more than "full" on the screen icon) because once the battery will accept no more charge, then friction braking is used. B takes some of that job off the brakes and puts it on the engine. Friction brakes and engine compression braking both waste energy by dissipating it as heat, so you only want to do that when the battery is full -- or, in the case of friction braking, when you need to make a very quick stop. It's really difficult to put into words how hard you can step on the brakes and still have 100% regerative braking, especially since that will depend on factors like SOC and battery temperature. I think the best description is "moderate." Neither too gentle nor too hard. __________________ Daniel ---------------------- Primary car: Zap Xebra SD: 100% electric car. 1.9 cents per mile, using electrons generated from water power. (The Prius is my gas guzzler, used when I have to travel farther than 35 miles in a day.) "If voting changed anything, they'd make it illegal." -- Emma Goldman "Anyone who has ever looked into the glazed eyes of a soldier dying on the battlefield will think long and hard before starting a war." -- Otto von Bismarck

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03-11-2007, 04:27 PM	#1
donwjaco Join Date: Mar 2007 Posts: 2 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I have had my Prius since late December I love it. I am wondering about the regenerative braking. Does it charge more quickly when the brake peddle is depressed aggressively or is it better to ride the brake pedal as you are rolling to a stop or slow down? At what point do the actual brake pads start pressure on the disks? With hard braking or just at slow speeds near the stop?

03-11-2007, 05:16 PM	#5
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 5,691 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 6	Very aggressive braking, in the form of a panic stop, will cause the brake system to abandon regen braking and switch to friction brakes. For best regen, brake early with modest pressure. As you increase the brake pressure, the current levels rise, which causes less efficient charging of the battery. The most efficient braking is no braking at all; coast as much as possible, but be safe and don't annoy other drivers. The regen system drops out at about 7 mph, after which the friction brakes take over. Tom

03-11-2007, 11:10 PM	#7
ken1784 SuperMID designer Join Date: Dec 2003 Location: Yokohama, JAPAN Posts: 1,391 My Car: 2004 Prius Package: G Touring Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 3	I think this should be placed on the FAQ list somewhere. http://vassfamily.net/ToyotaPrius/CAN/brindex.html Attila's experiment shows pedal value 17 (13% on CAN-view) is the best. Ken@Japan