Understanding your braking system

[hobbit]

I really hate to start yet another thread about Prius brakes,
but I need to call specific attention to a few clarifying points.
The babble has risen to unmanageable levels and there are far too
many other threads to keep track of, but I see a common trend across
pretty much all the ones on braking [here and on other forums].
.
Integrated regenerative and hydraulic braking systems are unique,
and still a young science. To Toyota's credit they've done a
really nice integration job with the Prius in general, with almost
seamless balancing of the braking force provided by the separate
parts of the system. It requires tight computer communication,
and does its job in very short timeframes under wildly varying
conditions and high mechanical stress conditions. There are
certain unavoidable limits on batteries and inverters that
restrict regenerative braking to a certain "operating envelope",
which the car will not let the driver exceed. Such systems are
bound to have a few quirks in their early stages, and trust me,
even the 2010 Prius is an "early stage" for a lot of this science.
It's not perfect and may never be. Maybe the 2010 system is more
squirrely than the second-gen or maybe it isn't -- I don't know, all
I know is that it's fairly different but the principles of operation
AND LIMITING FACTORS are exactly the same.
.
Fact is, the braking "sag" over bumps is a quirk that has existed
from the 2004 Prius right on down. The "old guard" owners know all
about it and know how to respond and in some cases even prevent it
from happening with sufficiently skillful driving. I see that
virtually all of the recent complaints and new threads on the topic
have come from NEW OWNERS, who have not researched what has, uh,
gone before.
.
Therefore I would urge all new owners to go read my detailed
discussion on the braking system -- you can skip the techie stuff but the
operational observations are near the end, and have been well-documented
even before that article was written in *2005*. Learn your vehicle and
how to control it. It is generically unsafe in any car to try and do
all your braking right at the end of a stop, and much more efficient in
a regenerative system to spread it long and slow over as much distance
as you can predict and make available. The shift between regenerative
and hydraulic is not "acceleration" as so many confused posters have
called it, it is simply a momentary diminishment of overall braking
force *per given pedal demand* as the system compensates for some
limits being exceeded. One is battery current; another is low speed
under which regen isn't practical anymore.
.
New owners have also probably not gone off and read all about the
"B" shift setting, either, still believing some dreck from their
dealers about how it's for "charging your battery". Well, that is
partially right in that "B" does tend to increase regen current,
but also throws away a lot more energy elsewhere. However, it also
offers a way to partially make up for regen loss. If you get the
"sag" over a bump and have already compensated for it with your foot
but want some of your regen back on that stop, whack the shifter down
into "B". You will then feel that you need *less* pedal force to
decelerate at the same rate, as the car sort of falls on its face.
You'll hear the engine spin a bit, you'll see your HSI slam toward
the left, and after the car gets down to around 5 MPH you can just
go back into D since you're on full hydraulics at that point anyway.
[Don't leave it in B or your engine might keep idling if was on.]
.
That's it. Your best means of compensating for regen loss is to
first expect it, and then try to get a little bit of it back with
"B" if you have time. Whether or not you GIVE yourself that leisure
time to decide and act is up to you, and that's where I'd put my
energy rather than whining about the NHTSA. This has been a solved
problem for six years.
.
It was not really an issue on the first-gen Prius because that system
always brings in about half hydraulics anyway giving much less ground
to cover in a "transition". One of the nicest aspects of the PII and
the PIII is that it tries its best to stay *completely* off the
energy-squandering hydraulics until you need them. The rest is up
to the loose nut behind the wheel.
.
_H*

[KK6PD]

Yep!!!
Nicely summed up!!!

[mitch672]

Yes, hobbit, you are exactly correct, and I also posted a short version of what you said in the "Toyota may recall the 2010 Prius" thread. Most new owners are not really aware of the unique differences of the braking systems between the Prius and EVERY other traditional car. Thanks for the eloquent explantion for the newbies.

Mitch

[tpfun]

Is it new or old ?

Toyota spokeswoman Ririko Takeuchi said Thursday that Toyota found out there were design problems and corrected the design for Prius models sold since late January.
Toyota says Prius brakes had design problem - USATODAY.com

[xpcman]

I own both a 2008 and 2010 Prius. I would have to say the the braking problem in the 2010 is MUCH more pronounced. If there is no problem then why did Toyota admit that there IS a problem (read the above USATODAY story). We have to stop being "fanboys" for Toyota and be objective. I expect the car to stop when I need it to stop not when it wants to stop.

[GrumpyCabbie]

Maybe there is a problem with SOME cars but not all. That is why your brakes appear to be safe and seamless and others appear to have issues.

[PaJa]

Originally Posted by tpfun

Is it new or old ?

Toyota spokeswoman Ririko Takeuchi said Thursday that Toyota found out there were design problems and corrected the design for Prius models sold since late January.
Toyota says Prius brakes had design problem - USATODAY.com

It is fresh news based on AP agency. I don't know about any other reference/source stating the same.

[The Electric Me]

Originally Posted by tpfun

Is it new or old ?

Toyota spokeswoman Ririko Takeuchi said Thursday that Toyota found out there were design problems and corrected the design for Prius models sold since late January.
Toyota says Prius brakes had design problem - USATODAY.com

Horrific Blunder. Absolutley terrible news.

How could Toyota recognize that there were design problems to the extent that they "secretly" correct the design for models sold since late January BUT not tell owners that had purchased previously?!!!

I guess I just need to step back and let the news unfold but this is HUGE.

I think the public can be forgiving and understanding about a gas pedal that Toyota openly recalls and repairs A.S.A.P. but I don't know how it's going to sit with most of the public if it is revealed Toyota knew about a problem with the design of Prius Brakes, actually made changes to the model being produced in January but did NOT mention it to owners and buyers that purchased earlier.

You just don't do that. PERIOD.

Still investigating how to inform people who had bought them earlier? Are you kidding me? That's total BS.

Note to Toyota: You know how you inform people who bought them earlier? You inform them! You inform them any way and every way you can!

What was Toyota thinking? Did they hope they could just quietly "fix" the problem and then "moving forward" complaints would decrease and they could just ignore the fact that everyone that purchased a Prius before January had a "design problem"?

I've been optimistic. I really believed Toyota would emerge. I still want to hear more about how this happened and what Toyota intended. But this is horrible news.

Makes you kind of wonder about the timing of the Prius price increase. Wonder if Toyota wanted to secretly correct the design and make new owners pay the price as well.

Tell me it isn't so Toyota, Tell me it isn't so!

[PaJa]

Electric,
stay calm - you are very safe with your current, non-prius, non-hybrid car :-)
Why are you waiting for Prius if you have so bad feeling about TMC? Choose the other car, other manfacturer which will suit to you.
I'm sorry for my reply, but your posts in each other thread look like as from 'Chevy' PR agency.

[GrumpyCabbie]

It would appear it is so!

There was a post on this forum recently from a guy in Japan who said that the latest January models in Japan had been given a software upgrade to solve the braking problem.

One wonders why that wasn't made available to all previous owners. I use my car for my business and if it gets pulled off road for safety reasons I'll be not very happy at all (and that's an understatement).

I am hearing the words class action