One more rant about the lunging brakes

Seriously though...look at it this way.

I think most people want and appreciate the benefits of regenerative brakes. I think most people want them.

I believe there is a different feel and behavior to the entire Prius brake system when it encounters a very specific reality. That is the surfaces that create the "lunge" feel.

How is Toyota suppose to fix this? Since most bumps or suddenly slick surfaces appear totally unpredictably? There is no software update that is going to be able to adjust for sudden stops on manhole covers or going over sudden bumps, when you may or may not suddenly have to brake, because no software is going to be able to magically forecast the appearance of those conditions. Or forecast for your sudden desire to brake or need to brake.

So personally I approach it as YES, I believe it is a condition and feeling that can and will occasionally under very specific conditions manifest. But do I believe it is a condition that results in the vehicle being dangerous to drive? No. It's simply a behavioral symptom of the braking system as it works as a whole.

I've driven my Prius now for 5 months in the rainy suburbs of the Pacific Northwest. Lots of slick manhole covers, covered in rain. I "think" maybe I've experienced the "lunge" feel or affect maybe once, at even though it felt a bit strange it in no way hindered my ability to slow or stop the vehicle safely.

Will I someday rear end somebody in a intersection and be in here complaining about those "damn" Prius brakes? Maybe, but well, I really don't think so.

I'm old enough to remember the transition from just standard brakes, to all vehicles having Anti-Lock brakes. And the first time I slammed on the brakes of an Anti-lock vehicle, and they automatically engaged the anti-lock system, the vehicle behaved and felt different than I expected.

But knowing is MORE than 1/2 the battle here.

The Prius has a different and more complex brake system than most standard vehicles. It can feel and operate under specific situations in a manner that is different than my expectations as trained by "regular" brakes. I do not define this as a flaw in the system...just part of the system.

If I ever experience or am lead to believe this isn't the reality, I won't apologize for the Prius brakes, I'll trade the vehicle in on something I feel more comfortable with.....I am nowhere near believing that at this time.

 

The recall that Toyota did in 2010-2011 (I can't remember which) did a great deal to resolve this issue, at least for my 2010 Prius. So I am surprised this is still an issue to anyone.

 

I experienced the issue on a 2011 prius I test drove, but have never experienced it in the 15k miles I've put on my 2012 prius. I think they did come up with a workable fix for newer model years.

 

Does it ever happen to you during hard or emergency braking? It didn't on my 2010, and I cannot recall any reports from others that it does.

That is the reason I simply got used to it, and didn't complain. It seemed to happen only on light to moderate braking, and seemed to be related to regen getting upset and cutting out.

Pure regen braking is used only in non-emergency situations where plenty of margin should be available. Drivers should always be prepared to escalate to hard or panic braking if the situation changes. Drivers who are using regen (i.e. light to moderate braking) with no safety margin, and/or have no plan to press harder if something changes, are violating defensive driving practices and are asking for trouble in any car.

It seemed to me that the primary hazard was to drivers who, surprised by the unusual feel, respond by freezing, or even releasing the brake in the mistaken belief that the brakes had failed. This is a training issue that can be resolved, and should be addressed no matter what vehicle the driver using. Because I grew up with several old cars that stalled without warning, losing all power assist to steering and brakes (leaky vacuum storage too), it was fairly easy for me to adjust.

I'm willing to change my mind if we find credible reports that this happens during hard / emergency / panic braking.

 

<snip>I then repeated the exercise a third time (and a forth, too). But this time I applied the brakes in drive, heard the whine, then shifted to neutral. There was a much, much faster transition to mechanical braking and more importantly, _there_was_no_surge_ .<snip>

While you shifted from drive to neutral, you continued to brake. This is where it differs. The "surge" is an ABS event.
When a braked wheel skitters over a rough surface, or slips due to low traction, it triggers an ABS event. The ABS system detects one or more wheels decelerating at a faster rate than expected. Braking effort is initially reduced, to allow the slipping wheel(s) to regain traction and speed up to match the other wheels.
In a hybrid such as the Prius, during regenerative braking, the caliper pistons are in the retracted position. When hydraulic braking is called upon, it takes a moment for the pistons to move enough to put the pad into contact with the rotors. This, combined with the initial reduction in braking force initiated by the wheel slip, is the "surge".

 

They fix it via software, as it's an adjustment to the abs system thresholds. They've already improved it greatly; they could certainly do more. I don't believe the issue to be specific to the regen system but rather to the abs.

I live at the top of a hill and at one particularly steep point heading down the hill the road gets very rough just as you approach a stop sign. It's a perfect test of this issue (that is by the way, not exclusive to the Prius). My old Volvo drives over it without even noticing it - no different than braking on smooth pavement. Many other cars, the Prius included, cause it to be a bit of a pucker moment if you don't slow down well in advance of the rough section because you hit the brakes there and the car keeps moving right towards the intersection. On regen or not, the abs works the same way; it monitors the rotation speeds of the wheels, and modulates brake pressure trying to keep them from locking. The Prius' calibration just isn't as good as some other vehicles.

Even if the issue is as described by PriusInParadise above, there is no reason that the piston need be fully retracted. Many cars have been pre-pressuring the pistons in anticipation of needing them for years. Again, it's just software.

 

I'm aware of the software update Toyota applied.

But in reply to the OP's "rant", I'm just not sure they could do much more.

Since Toyota did apply a software calibration update very early in the Gen 3's existence, that would tell me Toyota is fully aware of the operation and perception of their Prius brakes operation.

As an automobile manufacturer, Toyota neither wants dissatisfaction with their brakes nor the suggestion to exist that they operate in an unsafe manner. They can't really afford that.

I think Toyota IS and probably should constantly work towards improvement of all systems within their vehicles, including the regenerative brake system employed on The Prius. So I would hope for generational improvement.

But I think the brakes we have on Prius today? Are pretty much the brakes we are going to have on the Prius today. I don't expect nor desire a recall or another recalibration. I don't think it's justified.

My feeling today? Is that the regenerative braking system on Toyota's hybrids is actually a system much more to be applauded for what it does, than feared or criticized because of a perceived feeling or action that may or may not happen under a very, very specific set of usually very random parameters.

So to anyone I'd just say make a decision. If you are experiencing this reality routinely, regularly, and to you it makes driving the vehicle dangerous or untenable? Get rid of your Prius.

I don't believe this.-- I'm not denying the "sensation" or reality can't manifest, I'm just saying I don't think it is dangerous, nor do I think Toyota can do much to about it.

I guess if that makes me an apologist? It makes me an apologist.

 

I've got 55K miles in type, and the only time I think about this "issue" is when I read about it in this forum, and that is very infrequently.

I am NO apologist for the Prius.
Ask around.
I'm pretty sure that this condition exists in your car, and I'm pretty sure that it will still exist when you sell it or the automotive Grim Reaper comes to take it to Prius Valhalla.
I remember people fussing and cussing when ABS brakes came out, and there were probably people who felt the same way when hydraulic brakes came out in the 20's, or when people stopped yanking on that lever to halt wagons.
Toyota has been in the white hot light of truth before when people were claiming (falsely, IMO) that there was a problem with unintended acceleration. There are other people (morons, IMO) that claim that EMI from the battery pack was/is causing health problems.
Disclaimer: I was a Submariner, so I know something about tooling around in a vehicle with a really REALLY big battery pack, which may lend credance to these claims.
I'm waiting for some jackwagon out there to say that the DC Shooter (name purposely redacted) was a victim of this phenom, since he drove one of these death wagons.


The truth is that our media is pretty good at raking muck.
If there were even a HINT of a brake problem then they would be all over it like a Bum on a bologna sandwich!!
Scott Pelly @ 60 minutes would leave Assad and Kerry alone and be on the FIRST plane to Narita Airport!!!

So.....you're probably going to have to put up with the brakes acting like they're supposed to.

Sorry if this sounds overly adversarial, and I get the fact that you're frustrated, but maybe you should consider another car.

Seriously.
Good Luck!

 

I think a key issue in this discussion is also the Vehicle Stability Control. When the "surge" you describe occurs, you are at the event threshold of VSC kicking in. The car is attempting to correct a situation where loss of traction is occurring. A slick manhole cover momentarily causing a breaking issue is not the fault of the vehicle. It is trying to overcome a potentially dangerous situation. I experienced that many times in my '07, but not once in my '13 with the 17" tires. It may be more prevalent with 15" tires, which have less of a traction patch to the road. Over inflated tires, which I recommend may also contribute to this. Also, when my tires were at there last 10,000 miles of use, the situation occurred more frequently...

Are your tires near there end of life?

I think it's important to understand that LRR tires are not the same when it comes to traction as other vehicles with sticky tires. This may contribute to your "surge" interpretation when the event occurs and you are comparing what's happening to your experience in other vehicles.

 

I experience the transition at the expected times, but still refuse to have the recall done on my '10, because I do not perceive a need and don't want any less regen braking. Whether it is the transition from regen, the ABS, or the VSC (or some combination), I accept it. I also do not think it lasts a half second, though my wife will gladly tell you that I am often wrong.

If a fellow tells me that every time he runs into a wall he gets a concussion, I'd say don't run into a wall unless really necessary. Plan your braking so that you can let up while rolling over the spot (2 feet), then reapply. If it is an emergency stop, it will work as fast as ABS and VSC can allow, and faster than the skidding car without those features.

Different reactions to a common issue. Interesting. Some may deem unsafe and sell. I will trade to a PiP with the same issue, if TMC will ever sell them in my area. It's all good.

 

Can someone explain to me how this relates to the regen system, because it sure doesn't sound like it does from what I understand the issue to be. It seems that Toyota's abs software is a bit overly aggressive in determining that a wheel has locked, which causes it to back off brake pressure, causing a 'surge' or loss of stopping power. ie. a wheel hits a bump, a wet manhole cover, or set of railroad tracks, etc. and the computer interprets that as a wheel lockup, and backs off on the brakes. If anything, the more sensitive this is, the less regen you would get as the computer overcompensates, losing regen while it tries to allow the wheel to spin again.

Braking is exactly the kind of event you can't 'plan' for, when you really need it, you need all of it and right now.

 

I'll bet on 'combination'. Because I believe regen is part of that combination, and regen isn't used for emergency braking, I also accept it.

My understanding was that when these upsets occurred (likely ABS or VSC events), the regen was cutting out, flipping over to pure friction braking.

The vast vast vast majority of my braking is planned, light braking with plenty of safety margin. This is where regen is used. There may still be some corner-case anomalies to be ironed out, but I'm not giving up on regen just to get away from these anomalies.

Only a very small portion of my braking is unplanned, full strength braking where I need all of it and right now. The Prius skips regen in this mode and goes straight to pure friction braking. I remain unaware of reports of this anomaly happening when braking this mode.

The Prius might have a separate issue that seems like a momentary loss of power assist, requiring old-fashioned manual pedal forces. That seems to strike in a different scenario.

 

I believe, if you were to take the LLR tires and rims off of a Prius that experiences this issue and installed them on a non-hybrid vehicle of similar weight and dimensions, you could then reenact the scenario and see if said car experiences an braking anomaly. Because said vehicle does not employ regen, you would probably experience an anomaly, but one you would expect or be used to when compared to your previous experiences. That said, the Prius, while reacting differently, and therefore you, not expecting different, would express this as being a concerned, as the OP is. But, the outcome of said anomaly would most likely be the same... i.e., similar stopping distance, feeling a slide rather than a "surge".

 

I've had the car 1 month and it has happened to me. It is actually an ABS anomaly and several other car manufacturers are dealing with it as well. The worst ones are the large pickup trucks with only rear ABS. The large bump upsets the ABS system and it releases pressure to the brakes momentarily. It can be unnerving during a rapid stopping situation.

 

I agree Vito. I've experienced it in large pickups as well.

 

Just bought my certified 2010 4 months ago - have almost 12k on it. Noticed this 'lunge' or 'lurch' when braking on a bumpy road almost immediately - wasn't sure what to think. Then they announced the brake recall this summer, but nothing matched and didn't get the notice. I looked into it a little more this last week when it happened to me at a stop sign in downtown Baltimore, and scared the crap out of me. I find the info about the 1st brake recall in 2010 - but my car wasn't included in it according to Toyota's site. So I dropped it for service this morning, and they're telling me it's 'normal'. In the meantime, just this morning, Supreme Court is allowing suits against Toyota in Calif for bogus repairs of the problem. Not sure what to do - Car supposedly has no problem, but it's described in boards all over the place and involved in an investigation and a recall - but not MY car. Maybe I'll try and take the service mgr for a ride and show her.

 

Just posted this on another thread, but it probably belongs here as well....
Just bought my certified 2010 4 months ago - have almost 12k on it. Noticed this 'lunge' or 'lurch' when braking on a bumpy road almost immediately - wasn't sure what to think. Then they announced the brake recall this summer, but nothing matched and didn't get the notice. I looked into it a little more this last week when it happened to me at a stop sign in downtown Baltimore, and scared the crap out of me. I find the info about the 1st brake recall in 2010 - but my car wasn't included in it according to Toyota's site. So I dropped it for service this morning, and they're telling me it's 'normal'. In the meantime, just this morning, Supreme Court is allowing suits against Toyota in Calif for bogus repairs of the problem. Not sure what to do - Car supposedly has no problem, but it's described in boards all over the place and involved in an investigation and a recall - but not MY car. Maybe I'll try and take the service mgr for a ride and show her.

 

I experience this too coming up to a specific stop sign, where they are doing street repairs and the top 2 inch surface of the asphalt is milled (scraped off) about 20 feet short of the stop line. I can re-create the described everytime at this stop. Apparently the sudden 2" drop in the road surface elevation likely causes the front wheel rotational speed to suddenly increase for a split second which then causes the "loss of braking" effect which feels far too long especially if there's a stopped car already stopped ahead of you at the intersection.

An experiment for other to try out there, look for a section of road where they have milled the road (with a perpendicular 2" drop) ahead of you and start applying the brakes just a few yards before the 2" or so drop in the road surface. Keep the brakes applied as you go over the drop and see if you experience the same "loss of braking". I consistently experienced this at about 10 or 12 mph at this particular stop but I think it can happen at any speed (and is not related to the 7 mph speed at which regen ceases).

Note: This is quite different from the feeling you get when braking (using regen) and hit some rough bumps and the braking transitions from regen to friction braking which has an almost instantaneous response with a far more secure feeling (although you are then furious why you couldn't capture that potential regen )

 

There are two transitions to friction: 1 at 7 mph, the other whenever ABS kicks in. So just because not at 7 mph, it is still the transition.