Transaxel braking

PatapscoPete · 07-13-2006, 02:03 PM

Here's just the type of question you might expect from a new owner (purchased July 4, 2006, White Package #6 ... maybe I should change my moniker to PatriotPete).

Does it make sense to use the Transaxel Brake whenever possible to increase regenerative braking? Is the best usage just to slow the vehicle, or does the increased ICE revolutions increase regeneration? If it increases regeneration, does the increase in power recorvery outweigh the wear and tear that increased revs cause to the ICE and trans?

john1701a · 07-13-2006, 05:35 PM

<div class='quotetop'>QUOTE(PatapscoPete @ Jul 13 2006, 01:03 PM) [snapback]285748[/snapback]</div>

Quote:

Does it make sense to use the Transaxel Brake whenever possible to increase regenerative braking?[/b]

No, it does exactly the opposite. Having the engine absorb some of the kinetic energy takes away from the potential available for the electric motors. This has been proven too, numerically with a scanner.

By the way, the "transaxel" is almost always referred to as the PSD (Power Split Device). All motion is directed through that, whether it is engine or motors. But I knew what you meant.

**efusco** · 07-13-2006, 05:36 PM

It's best to not use it at all. It serves very little useful purpose and will not maximize regeneration, you can do better with your foot on the brake. Plus, it forces the ICE to spin to create drag and that's wasteful.

It is convenient to use it on very long grades to reduce the amount you have to use the brake, but that's about it.

john1701a · 07-13-2006, 05:38 PM

I've found "B" mode very effective for graceful deceleration on unexpectedly slippery curves. It reduces the risk of putting too much reliance on the brakes.

barbaram · 07-14-2006, 12:02 AM

It is also helpful if you discover you need to stop much more quickly than you first anticipated! Use both!

hobbit · 07-14-2006, 01:07 AM

Possibly too overwhelming for a new owner and probably makes
reference to many other concepts you have yet to run across, but
http://techno-fandom.org/~hobbit/cars/b-mode.html is my best effort
at a FULL rundown on what B mode is, does, doesn't do, etc.
If you can get through it without falling asleep and then go look
up every term therein that you don't understand yet, you'll get a
good prius-education-by-storm out of it!
.
_H*

PatapscoPete · 07-14-2006, 12:34 PM

<div class='quotetop'>QUOTE(hobbit @ Jul 14 2006, 12:07 AM) [snapback]286091[/snapback]</div>

Quote:

Possibly too overwhelming for a new owner and probably makes
reference to many other concepts you have yet to run across, but
http://techno-fandom.org/~hobbit/cars/b-mode.html is my best effort
at a FULL rundown on what B mode is, does, doesn't do, etc.
If you can get through it without falling asleep and then go look
up every term therein that you don't understand yet, you'll get a
good prius-education-by-storm out of it!
.
_H*
[/b]

An excellent discourse. This clears up several issues I had.

Thanks,
PPete

kimgh · 07-14-2006, 05:32 PM

<div class='quotetop'>QUOTE(PatapscoPete @ Jul 14 2006, 09:34 AM) [snapback]286240[/snapback]</div>

Quote:

An excellent discourse. This clears up several issues I had.

Thanks,
PPete
[/b]

I'd like to know how to tell when to shift into "B" on a long downgrade. Immediately? After SOC is all green? Somewhere before that?

The article hints at an answer, but I don't think it is that clear. I'd be interested in other's experiences, because I'm about to embark on a long trip that will include several mountain passes (Siskyous, Snoqualmie, Owyhee, Donner, Altamont). Any experienced folks? Donner is by far the biggest challenge I would think, so who has taken his Prius over Donner?

hobbit · 07-14-2006, 05:56 PM

Last time I was juggling mountain descents I tried to balance the
process and use enough "B" early in the game to control speed, and
basically would bounce back and forth between "D" and "B" as terrain
demanded. Oh, and I tried to remember to go into EV mode and *empty*
the SOC before cresting, but that's hard to predict sometimes.
.
Basically the battery will hold only so much section of a big hill,
and where along the path you capture that [and waste the rest]
really doesn't matter that much. If you can maximize it by starting
from as low as possible, that's good, but may not be feasible if
you've got someone screaming up behind you at > 33 mph.
.
_H*

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07-13-2006, 02:03 PM	#1
PatapscoPete Join Date: Jul 2006 Posts: 24 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Here's just the type of question you might expect from a new owner (purchased July 4, 2006, White Package #6 ... maybe I should change my moniker to PatriotPete). Does it make sense to use the Transaxel Brake whenever possible to increase regenerative braking? Is the best usage just to slow the vehicle, or does the increased ICE revolutions increase regeneration? If it increases regeneration, does the increase in power recorvery outweigh the wear and tear that increased revs cause to the ICE and trans?

07-13-2006, 05:36 PM	#3
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,247 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 24	It's best to not use it at all. It serves very little useful purpose and will not maximize regeneration, you can do better with your foot on the brake. Plus, it forces the ICE to spin to create drag and that's wasteful. It is convenient to use it on very long grades to reduce the amount you have to use the brake, but that's about it.

07-13-2006, 05:38 PM	#4
john1701a Senior Member Join Date: Jan 2004 Location: Minnesota Posts: 2,719 My Car: 2004 Prius Package: Pioneer #3 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 3	I've found "B" mode very effective for graceful deceleration on unexpectedly slippery curves. It reduces the risk of putting too much reliance on the brakes.

07-14-2006, 12:02 AM	#5
barbaram Senior Member Join Date: Jan 2006 Location: Trenton, NJ Posts: 721 My Car: 2006 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	It is also helpful if you discover you need to stop much more quickly than you first anticipated! Use both!

07-14-2006, 01:07 AM	#6
hobbit Senior Member Join Date: Mar 2005 Location: Bahstahn Posts: 2,989 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Possibly too overwhelming for a new owner and probably makes reference to many other concepts you have yet to run across, but http://techno-fandom.org/~hobbit/cars/b-mode.html is my best effort at a FULL rundown on what B mode is, does, doesn't do, etc. If you can get through it without falling asleep and then go look up every term therein that you don't understand yet, you'll get a good prius-education-by-storm out of it! . _H*

07-14-2006, 05:56 PM	#9
hobbit Senior Member Join Date: Mar 2005 Location: Bahstahn Posts: 2,989 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Last time I was juggling mountain descents I tried to balance the process and use enough "B" early in the game to control speed, and basically would bounce back and forth between "D" and "B" as terrain demanded. Oh, and I tried to remember to go into EV mode and empty the SOC before cresting, but that's hard to predict sometimes. . Basically the battery will hold only so much section of a big hill, and where along the path you capture that [and waste the rest] really doesn't matter that much. If you can maximize it by starting from as low as possible, that's good, but may not be feasible if you've got someone screaming up behind you at > 33 mph. . _H*