Poll: Are Prius brakes a problem?

During my two first weeks of Prius ownership I already experimented this phenomena four times. Unfortunately, here in Rome due to heavy rain and bad maintenance we are plenty of potholes in the streets. Besides, I've got the 17” wheels, that probably does not help. When I experimented the so called "brake loss", I felt that just pressing hard the pedal would have stopped quickly the car, if needed. So it did not worry me much, although I would have preferred a smoother brake, of course.
Regards
Igino

 

Because I understand what is happening and it only happens with light to moderate braking force (when the car is using regenerative braking) and the car senses that it may need to use ABS. That is the condition when this transition occurs. It doesn't happen during panic braking, it doesn't happen during higher speed braking (because you are already using partial or full friction braking). It only happens during a switch from full regenerative braking to full friction braking.

Here is the explanation for what is happening from another thread:

http://priuschat.com/forums/gen-iii...0-felt-brake-cut-out-thing-3.html#post1010260

 

I'm certianly for toyota looking into this or any third party for that matter. I agree as well that my terminology in stating the loss of braking to be a sensation is incorrect. I will agree that the sensation of no braking is because indeed, for that instance, there is no braking.

What I am saying is that I believe this to be a byproduct of design. The Prius has many systems that work in various combinations. Re-gen braking, standard braking, VSC, ABS,etc. In the right conditons the transition from re-gen to standard brakes, the on set of VSC, ABS or what ever, may not be as seamless as we would like.

When braking re-gen is the first system to engage. When you hit loose, broken or uneven pavement and a tire loses contact with the road it will decelerate faster then the tire in contact. At this point the VSC stops re-gen braking which allows both front wheels to equalize there speed. This is where we notice the loss of braking feel. The sensation if you will, because in fact, at that moment in time, there is no braking. Once the wheel speeds equalizes then the standard brakes engage. If ABS engages (which only works with the standard brakes) we don't notice the braking loss because ABS only releases the brake on the wheel that decelerates the fastest. The purpose behind all this is to maintian steering control which is normally lost in a skid.

These transitions have to exist for all these systems to function together. For me, I am satisfied that a safety issue is not present because although it may feel scary, the prius stops quick and stable no matter how hard I try to make it do other wise.

I'm sure there are other cars out there that stop faster them the Prius but I only have the Corolla at my disposal to compare it to. And with that I must say that my wifes Corolla with ABS and the Prius sure made me feel much safer then the 04 Corolla with out ABS did.

The issue for me is can Toyota make these transitions less noticeable. If we could not feel this happen then we would not be debating the issue.

 

I went out to my local "rough road patch" to recreate the problem and take a picture. I went over the spot around 8 times, and recreated the problem 3 times. There was quite a bit of traffic so I was limited on what I could do and I realize this is far from a scientific study.

I tried with varying levels of regen braking and it _seems_ that it occurred when the HSI bar was around the middle of the CHG area. I did varying levels of braking pressure, all within the CHG area, and it never did it near either end of the CHG area, as it always occurred in the middle area.

I, and others familiar with this spot, aim to put a tire over the manhole covers, as the rough area is to the left of the manhole covers. To recreate the problem, I aimed right for the rough area.

 

I think all 2010 Prius's will exhibit the same error on the same spot in the road, using the same amount of breaking and speed. I believe it's a software bug in the breaking logic. It's the same software in all vehicles.

 

I voted 'about once per month' (really twice in six months), and 'not a risk'. But see below ...

The 44 foot comment I saw was not a 'report', but rather a 'prediction' under a certain circumstance and speed. I had to challenge it as not being important, because it involved light braking with an intended braking distance approaching 1000 feet. Anyone intending to stop shorter would skip regen, going directly to friction braking. So far, I've seen no reports of this happening during friction mode.

This is always a possibility, leaving me with some uncertainty that I'm experiencing the same thing.

 

On rare occasion, my 2009 brakes might be a little grabby backing out of the garage, but other than that, the brakes are totally normal.

I enjoy the electric regenerative sound when slowing or stopping.

 

I forgot to mention that I was passing that rough patch at around 20 MPH when attempting to recreate the issue. Again, nothing scientific here and it was difficult to control speed and other factors such as amount of regen due to traffic conditions.

 

Dang, that's one messed up roadbed! But, I looked at the photo and have some questions as to what I'm looking at.

1. How do you know which "tire tracks" were made by the Prius and which were not.
2. The only track I can see that shows "gaps" is the dark thin skid mark. I'm not a forensic scientist, but I would think rubber marks like that can only be left behind if rubber is abraded on the surface of the pavement by the rubber wearing off as it frictionally moves against the pavement surface, as in SKIDDING or BURNING RUBBER. I would think the Prius ABS would prevent said skidding. Also, if this IS from skidding, the gaps would also be caused by the tire returning to normal "rolling" behavior and not by being airborn.

Let's not jump to some conclusion from one photo that's difficult to read let alone interpret the results from.

 

It looks like the GM Volt forum is jumping on the band wagon.

http://gm-volt.com/2010/01/02/third-generation-toyota-prius-regenerative-brakes-flawed/

I'm kinda #&^%$ off that this is getting blown out of proportion in that the media and other websites are referring to this a brake failure when no failure exists.

I guess we won't be happy until the hybrid of choice is the cadillac escalade hybrid. I hear OPEC loves them!

 

GeoDesign,

I get your frustration and concern. I think this is all the more reason why Toyota needs to act quickly on the matter and either state that everything is as designed and users just need to be aware of the loss of pedal pressure/braking sensation or they need to find an adjustment they can make to make this sensation/effect go away for all Prius cars. My dealer certainly never told me about this issue. Nor have I read anything about it in the Prius manual.

 

This forum debate sorta reminds me of the Old Salem Witch Hunt.

If your not Christian! You must be a Witch! Let's burn you at the Stake.

If you don't agree with us your not a Christian! You must be a Witch! Let's burn you at the Stake!

The action wasn't Christian like! You must be a Witch! Let's burn you at the Stake!

 

Or from burning Witches! BURN THE WITCHES, I SAY!!!



Tom

 

Well no, that's quite a sweeping generalization and I for one can guarantee you that it is inaccurate. I have felt this about four times, all while going slow and braking while going over a small bump or pot hole. The first time it was over a small bump caused by a tree root and it was positioned shortly before an intersection that I was approaching, hence the slow speed and light breaking.

Nope. My four instances happened in sunny SoCal weather.

It's not about it feeling the same each time you brake, it's about not having a disconcerting sensation that the brakes failed for a second or that you are accelerating instead of braking. I am grateful that I had read about it before it happened to me since I could just think "oh, that's what they were talking about" instead of possibly panicking as some might do if they aren't familiar with it.

I think Toyota needs to address this issue. One shouldn't have the sensation of acceleration while braking, which is what it feels like even if it's an illusion. Personally I don't feel necessarily unsafe, but like I said, if this happens to someone who is completely unaware of it they could think they were stepping on the gas and move their foot off the brake thinking they aren't on it and perhaps get in an accident. There are a lot of nervous drivers without this, I wouldn't want to have one of them behind me when this happens to them.

p.s. I voted twice for the second part because I didn't feel there was an answer for me. I don't really feel unsafe for myself as driver, but I think Toyota should address this as I do not think it is normal and should be this way. I don't trust that if it happens to someone behind me they won't react in a manner that would cause them to hit me.

 

What about the Warlocks? Men get away with everything. :rant: