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Discussion Starter · #1 ·
I don't own a hybrid, but have had a question about them on my mind:

We know that on hybrid cars like the Prius, during braking the battery is
recharged as the wheels act like generators. But I wonder about two things:

- Is there a conventional braking system pressing metal against metal as a
backup for these cars in case the generator function during braking doesn't
work properly; and
- If so, what kind of wear does this backup braking system endure, in
general (presumably far less than on conventional cars.)

Thanks in advance.
 
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Discussion Starter · #2 ·
"M. Hamill" <[email protected]> wrote in message
news:[email protected]
>I don't own a hybrid, but have had a question about them on my mind:
>
> We know that on hybrid cars like the Prius, during braking the battery is
> recharged as the wheels act like generators. But I wonder about two
> things:
>
> - Is there a conventional braking system pressing metal against metal as a
> backup for these cars in case the generator function during braking
> doesn't work properly; and


There is a conventional braking system but it is brake pad material against
metal, not metal against metal (unless you don't replace the pads after they
are worn).

> - If so, what kind of wear does this backup braking system endure, in
> general (presumably far less than on conventional cars.)
>
> Thanks in advance.


The service brake would have the same or less wear than on a conventional
car.
--
Ray O
correct the return address punctuation to reply
 
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Discussion Starter · #3 ·
In article <[email protected]>
[email protected] "M. Hamill" writes:

> I don't own a hybrid, but have had a question about them on my mind:
>
> We know that on hybrid cars like the Prius, during braking the battery is
> recharged as the wheels act like generators. But I wonder about two things:
>
> - Is there a conventional braking system pressing metal against metal as a
> backup for these cars in case the generator function during braking doesn't
> work properly; and
> - If so, what kind of wear does this backup braking system endure, in
> general (presumably far less than on conventional cars.)


I recently enquired of Toyota UK about the details of the Prius
braking system. Some of my comments have previously been posted
but here goes again...

The Prius subsystem which handles braking is a blend of electric
regenerative and conventional hydraulic technology.

As you tread on the brake pedal the system notes how you did so:
how hard; and how suddenly. From this, it works out (very fast)
what braking force is required. As much of this as possible is
provided by regenerative braking; the rest of done by hydraulic
braking (with the usual brake pads and such).

There are several useful benefits from this.

(a) If either of the available braking methods fails, the other
continues to provide some kind of slowing force. If the electric
side fails, I infer the hydraulic provides all of what's needed.

(b) Regarding your second question, I suppose that the brake pads
experience less wear, because regenerative braking is essentially
"non-contact" and will handle most of the low-force braking (such
as gentle touches on the pedal).

You should realise that much of the Prius is conventional. What
is new is how the old is blended with the new.
--
Andrew Stephenson
 
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Discussion Starter · #4 ·
As an interesting side note, the dealer I work for has ONE recorded case of
replacing brake pads on a Prius. I've seen some with well over 100k miles
and over 50% of the pad lining remaining.
 
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Discussion Starter · #5 ·
"Ray O" <[email protected]> wrote in message
news:[email protected]
>
> "M. Hamill" <[email protected]> wrote in message
> news:[email protected]
>>I don't own a hybrid, but have had a question about them on my mind:
>>
>> We know that on hybrid cars like the Prius, during braking the battery is
>> recharged as the wheels act like generators. But I wonder about two
>> things:
>>
>> - Is there a conventional braking system pressing metal against metal as
>> a backup for these cars in case the generator function during braking
>> doesn't work properly; and

>
> There is a conventional braking system but it is brake pad material
> against metal, not metal against metal (unless you don't replace the pads
> after they are worn).
>
>> - If so, what kind of wear does this backup braking system endure, in
>> general (presumably far less than on conventional cars.)
>>
>> Thanks in advance.

>
> The service brake would have the same or less wear than on a conventional
> car.
> --


One follow up question, does it still have a conventional e-brake/ parking
brake on the Prius ?
 
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Discussion Starter · #6 ·
<[email protected]> wrote in message news:[email protected]
>
> "Ray O" <[email protected]> wrote in message
> news:[email protected]
>>
>> "M. Hamill" <[email protected]> wrote in message
>> news:[email protected]
>>>I don't own a hybrid, but have had a question about them on my mind:
>>>
>>> We know that on hybrid cars like the Prius, during braking the battery
>>> is recharged as the wheels act like generators. But I wonder about two
>>> things:
>>>
>>> - Is there a conventional braking system pressing metal against metal as
>>> a backup for these cars in case the generator function during braking
>>> doesn't work properly; and

>>
>> There is a conventional braking system but it is brake pad material
>> against metal, not metal against metal (unless you don't replace the pads
>> after they are worn).
>>
>>> - If so, what kind of wear does this backup braking system endure, in
>>> general (presumably far less than on conventional cars.)
>>>
>>> Thanks in advance.

>>
>> The service brake would have the same or less wear than on a conventional
>> car.
>> --

>
> One follow up question, does it still have a conventional e-brake/ parking
> brake on the Prius ?

I don't know but a conventional parking brake is the easiest way. By the
way, passenger cars do not have an "emergency brake." They are called a
parking brake because they only apply the brakes to the rear wheels and will
not stop a vehicle as quickly as the service brake.
--
Ray O
correct the return address punctuation to reply
 
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Discussion Starter · #7 ·
In article <[email protected]>
[email protected] "<[email protected]>" writes:

> One follow up question, does it still have a conventional
> e-brake/ parking brake on the Prius ?


The Prius does a good job of emulating a conventional automatic
gearshift car. On the dashboard is a button which has the same
effect as shifting the lever to Park. It locks the transaxle as
usual and is strong enough for level ground. The knob to select
[R]everse/[N]eutral/[D]rive (and new attery-recharge option)
is just below this button, with functions lined up in the same
sequence as on a standard gear lever: imagine the arc which your
hand moves through during operation of a standard shift; the same
arc is followed in a Prius, just higher up at dashboard level.

Above the rest for your left foot is a easy-use foot brake that
engages a very normal mechanical brake. Forget to disengage this
and it obstructs your left foot; there is also a warning light.
--
Andrew Stephenson
 
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Discussion Starter · #8 ·
In article <[email protected]>,
"Ray O" <[email protected]> wrote:

> I don't know but a conventional parking brake is the easiest way. By the
> way, passenger cars do not have an "emergency brake." They are called a
> parking brake because they only apply the brakes to the rear wheels and will
> not stop a vehicle as quickly as the service brake.


But in case of hydraulic failure, the mechanical "parking" brake will
still function as an emergency brake, correct? I've always called it an
"emergency" brake for that reason, and I do practice stopping the car with
it (comes from my training as a naval aviator, I guess).

Merritt
 
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Discussion Starter · #9 ·
"Merritt Mullen" <[email protected]> wrote in message
news:[email protected]
> In article <[email protected]>,
> "Ray O" <[email protected]> wrote:
>
>> I don't know but a conventional parking brake is the easiest way. By the
>> way, passenger cars do not have an "emergency brake." They are called a
>> parking brake because they only apply the brakes to the rear wheels and
>> will
>> not stop a vehicle as quickly as the service brake.

>
> But in case of hydraulic failure, the mechanical "parking" brake will
> still function as an emergency brake, correct? I've always called it an
> "emergency" brake for that reason, and I do practice stopping the car with
> it (comes from my training as a naval aviator, I guess).
>
> Merritt


Yes, in case of total hydraulic failure, the mechanical parking brake will
still function as an "emergency" brake but stopping distances will probably
be at least triple the distance with a normally functioning brake since the
front brakes do most of the braking. Nothing like the stopping power of a
tailhook though!
--
Ray O
correct the return address punctuation to reply
 
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Discussion Starter · #10 ·
On Fri, 09 Dec 2005 04:42:16 GMT, Merritt Mullen
<[email protected]> wrote:

>In article <[email protected]>,
> "Ray O" <[email protected]> wrote:
>
>> I don't know but a conventional parking brake is the easiest way. By the
>> way, passenger cars do not have an "emergency brake." They are called a
>> parking brake because they only apply the brakes to the rear wheels and will
>> not stop a vehicle as quickly as the service brake.

>
>But in case of hydraulic failure, the mechanical "parking" brake will
>still function as an emergency brake, correct? I've always called it an
>"emergency" brake for that reason, and I do practice stopping the car with
>it (comes from my training as a naval aviator, I guess).
>
>Merritt


Naval Aviator?

My hat is off to you and I'd fly ANYWHERE with ya!

Thanks for your service to our country.

--

Scott in Florida
 
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Discussion Starter · #11 ·
Andrew Stephenson wrote:

> The Prius does a good job of emulating a conventional automatic
> gearshift car. On the dashboard is a button which has the same
> effect as shifting the lever to Park. It locks the transaxle as
> usual and is strong enough for level ground. The knob to select
> [R]everse/[N]eutral/[D]rive (and new attery-recharge option)
> is just below this button, with functions lined up in the same
> sequence as on a standard gear lever: imagine the arc which your
> hand moves through during operation of a standard shift; the same
> arc is followed in a Prius, just higher up at dashboard level.


The B position is an engine braking function. Seems to me its only
purpose is to help in long downhill runs, simulating a stick shift car
using the engine to back down a little.

Gary Eickmeier
New Owner
 
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Discussion Starter · #12 ·
In article <[email protected]>
[email protected] "Gary Eickmeier" writes:

> Andrew Stephenson wrote:
>
> > The Prius does a good job of emulating a conventional automatic
> > gearshift car. On the dashboard is a button which has the same
> > effect as shifting the lever to Park. It locks the transaxle as
> > usual and is strong enough for level ground. The knob to select
> > [R]everse/[N]eutral/[D]rive (and new attery-recharge option)
> > is just below this button, with functions lined up in the same
> > sequence as on a standard gear lever: imagine the arc which your
> > hand moves through during operation of a standard shift; the same
> > arc is followed in a Prius, just higher up at dashboard level.

>
> The B position is an engine braking function. Seems to me its only
> purpose is to help in long downhill runs, simulating a stick shift car
> using the engine to back down a little.


Not to be picky, actually it is touted as an optional instruction
to the car to charge the battery using regenerative braking. The
driver will be in a better position to know the road ahead so can
tell the car to recharge (and, incidentally, slow down). Most of
the time, I find this function of little use; but it's nice to be
able to choose. As it happens, I do employ it most to apply some
e-braking where foot-braking is not essential; but that certainly
is not its primary function. Start relying on it and one day you
may find the battery can't take more charge -- then braking won't
be as hard as hoped and you suddenly have to f-brake anyhow. <g>

At least, all of the above is based on recollections of a tedious
trawl through the handbook, as well as general Toyota propaganda.
--
Andrew Stephenson
 
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Discussion Starter · #13 ·
Andrew Stephenson wrote:

> Not to be picky, actually it is touted as an optional instruction
> to the car to charge the battery using regenerative braking. The
> driver will be in a better position to know the road ahead so can
> tell the car to recharge (and, incidentally, slow down). Most of
> the time, I find this function of little use; but it's nice to be
> able to choose. As it happens, I do employ it most to apply some
> e-braking where foot-braking is not essential; but that certainly
> is not its primary function. Start relying on it and one day you
> may find the battery can't take more charge -- then braking won't
> be as hard as hoped and you suddenly have to f-brake anyhow. <g>
>


That can't be right. We all know that the Prius regenerates power
whenever you back off the accelerator. The book also mentions that the B
function shouldn't be used as a practice, because it will get poorer gas
mileage. I see the only purpose as engine braking, but then I am a new
owner (a week or so).

Gary Eickmeier
 
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Discussion Starter · #14 ·
Andrew Stephenson wrote:

> The Prius subsystem which handles braking is a blend of electric
> regenerative and conventional hydraulic technology.
>
> As you tread on the brake pedal the system notes how you did so:
> how hard; and how suddenly. From this, it works out (very fast)
> what braking force is required. As much of this as possible is
> provided by regenerative braking; the rest of done by hydraulic
> braking (with the usual brake pads and such).
>
> There are several useful benefits from this.
>
> (a) If either of the available braking methods fails, the other
> continues to provide some kind of slowing force. If the electric
> side fails, I infer the hydraulic provides all of what's needed.


I question this explanation, and hope you can back it up with further
references of your own or Toyota's. As I said above, I think there will
be engine braking only when you are using the B function of the shift lever.

Gary Eickmeier
 
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Discussion Starter · #15 ·
In article <[email protected]>
[email protected] "Gary Eickmeier" writes:

> Andrew Stephenson wrote:
>
> > Not to be picky, actually it is touted as an optional instruction
> > to the car to charge the battery using regenerative braking. The
> > driver will be in a better position to know the road ahead so can
> > tell the car to recharge (and, incidentally, slow down). Most of
> > the time, I find this function of little use; but it's nice to be
> > able to choose. As it happens, I do employ it most to apply some
> > e-braking where foot-braking is not essential; but that certainly
> > is not its primary function. Start relying on it and one day you
> > may find the battery can't take more charge -- then braking won't
> > be as hard as hoped and you suddenly have to f-brake anyhow. <g>

>
> That can't be right.


If you say not, I suppose that ends the discussion. ;-)

> We all know that the Prius regenerates power whenever you back
> off the accelerator.


Not always. Oddly, I have managed to make the car freewheel by a
very (NB) light touch on the brake, as well as by a similar touch
on the accelerator. Mostly the car decides for itself whether or
not to insist on charging the battery, or not doing so. Keep in
mind, you are not the boss where such matters are involved. Have
you noticed how many gauges are not provided in a Prius? (Such
as engine rpm and temperature.)

> The book also mentions that the B function shouldn't be used as
> a practice, because it will get poorer gas mileage.


That'll be because the overall efficiency of charging the battery
then recovering the charge to drive the electric motor is smaller
than the efficiency of driving the wheels more directly: either
by the petrol (US:gas) engine alone or by the petrol engine via
the generator driving the electric motor -- which happens more
often than some people imagine.

I have a theory, yet to be tested, that one could actually obtain
better mileage by the judicious application of a bit of welly: by
forcing the car to drive directly from the petrol engine and/or
"engine-->generator-->motor", one could cut from the loop the
comparatively lossy battery. But that _is_ still just a theory.

> I see the only purpose as engine braking, but then I am a new
> owner (a week or so).


Hang in there. And look into those manuals again. ;-) In the
end, use it in whichever way works for you. Later versions of
the technology will, I expect, enforce whichever practices have
been found to be best.

Tip, FWIW: the rear lower storage area (ie, beneath the fold-up
panels, where the spare tyre lives) can be made more useful by
placing the (separate purchase) optional Toyota rubber mat over
the spare. You can fold up the rearmost section of the panelling
and sit small/medium coolboxs (up to tall enough for 2-litre soft
drinks bottles) securely in the "slot".
--
Andrew Stephenson
 
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Discussion Starter · #16 ·
In article <[email protected]>
[email protected] "Gary Eickmeier" writes:

> Andrew Stephenson wrote:
>
> > [explanation of the Prius subsystem which handles braking and
> > how it affects the function]

>
> I question this explanation, and hope you can back it up with
> further references of your own or Toyota's. As I said above, I
> think there will be engine braking only when you are using the
> B function of the shift lever.


If you caught my post of a day or two before the above, you may
have seen I mentioned asking Toyota UK for technical data. They
provided lavish documentation with diagrams, which prompted my
synopsis and inferential explanation. If you have another, I'd
be interested to hear it. If your objections are simply that you
prefer not to believe (or you are trolling), I can't help you.
--
Andrew Stephenson
 
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Discussion Starter · #17 ·
In article <[email protected]>, Gary Eickmeier
<[email protected]> wrote:

> Andrew Stephenson wrote:
>
> > Not to be picky, actually it is touted as an optional instruction
> > to the car to charge the battery using regenerative braking. The
> > driver will be in a better position to know the road ahead so can
> > tell the car to recharge (and, incidentally, slow down). Most of
> > the time, I find this function of little use; but it's nice to be
> > able to choose. As it happens, I do employ it most to apply some
> > e-braking where foot-braking is not essential; but that certainly
> > is not its primary function. Start relying on it and one day you
> > may find the battery can't take more charge -- then braking won't
> > be as hard as hoped and you suddenly have to f-brake anyhow. <g>
> >

>
> That can't be right. We all know that the Prius regenerates power
> whenever you back off the accelerator. The book also mentions that the B
> function shouldn't be used as a practice, because it will get poorer gas
> mileage. I see the only purpose as engine braking, but then I am a new
> owner (a week or so).


Welcome, Gary. I forescast ou'll be driving with a smile. I am.

In hilly terrain I use the B setting in lieu of braking on steep
downslopes. Else, I leave it alone. The problem with using B for
slowing in traffic is that it doesn't trigger the brake lights.

The hypnotic energy-transfer animation shows that even on level ground
the gas engine periodically charges the main battery. The book's advice
against using B applies to travel on level ground where indeed the
practice does reduce the gas mileage.

Brent
 
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