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Comments
You thought correctly.
It is perfectly normal for the brake pedal to vibrate violently while ABS is in use.
The problem being expressed concerning ONLY hybrid vehicles is the transition from regen braking ONLY into friction braking at the instant impending wheel lockup due to braking is detected. If the ABS "event" is momentary then all that the driver feels is the brief "lurch" forward for the 100 or so milliseconds it takes to release regen braking and then extend the brake pistons outward to bring the brake pads into contact with the brake rotors.
Since the brake pedal never goes into violently vibrating mode the drivers see this "lurch" as an anomaly when it reality it is uniquely SOP to hybrids.
And yes, on a highly slippery downslope I have often had to apply the e-brake to bring the vehicle to a final full and complete stop.
Toyota’s massive recall of many of its high-volume models has, surprisingly, led to few credible reports of similar symptoms in non-recalled models. Yet a 2004 Toyota 4Runner in California is said to be experiencing exactly the same issues as its recalled brethren.
ABS is capable of PWM, Pulse Width Modulation, down to 10's of milliseconds is good, but does that allow enough time for the wheels to grip and the driver to take advantage of the grip? I have a feeling the Mark/Space ratio might have to be say, 70/30 of brake/"no"-brake to maintain steering. I see that as about 30% less stopping ability. Realistic?
(I've seen estimates of 20% longer stopping distances, but I don't know how this was measured.)
Toyota Prius braking issues may predate 2010 model; other problems reported
Could the apparent braking problems reported on the Toyota Prius – which Toyota admits was an issue on the current model prior to being resolved earlier this year – extend past the recently released 2010 model? According to TheDetroitBureau.com, the answer is a resounding... maybe.
The third generation of the popular hybrid hatchback hit the market in 2009 as a 2010 model, and some 300,000 vehicles are thought to have a software glitch that could cause the car to lose braking power for up to one full second under certain circumstances. But that's not all. Apparently, reports of braking issues have been pouring in since 2005 or even earlier. If true, over a million second-generation Prius hybrids could potentially be affected.
Perhaps it's worth mentioning that previous electronic issues have also been reported, such as headlights that burn out too quickly and malfunctioning traction control system. As pointed out by TheDetroitBureau.com, "ABS, traction control, electronic stability control and various other technologies all rely, at least in part, on braking to improve the stopping, handling and stability of today's cars, including Prius."
I took my Prius in and had them look at it on Dec 15th a couple of weeks after I had the accident. They said that everything checked out fine and that it was probably my anti lock brakes kicking in(I moved to Seatlle from Minnesota and I know what anti locke brakes feel like, that wasn't the problem). Since then going down the same hill the car has accelerated when going over a pothole in the road. I called Toyota back and they said that my car is not part of the recall and that when they looked at my car in December they checked the brakes and the accelerator and all checked out! I feel like there is not much else to do. I called them again today and left a message that I want them to take another look. My insurance company said to just keep bugging them. After reading the other posts, the service guys at Toyota must have been told to tell people that they have never heard of this problem! I also feel Toyota should fix the bumper that was dented from the brakes failing to work! URG
Once frictional braking comes fully online and if impending wheel lockup detection persists then ABS goes into mode 2 and you get that standard vibratory brake pedal feedback "signal".
In the case of a short bump, pertubation, in the roadbed that causes a brief separation of a driven wheel with the roadbed it is highly likely there will be no cause for ABS to enter mode 2.
While electrically/electronically the solenoid voltage can be switched on and off at those rates the mechanical time constants involved only allow a "switch" rate on the order of 100's of milliseconds.
The PWM dutycycle is controlled by the ABS ECU in real-time, and it has two "masters". First, it will not allow the front wheels to slow very much more rapidly than the rear wheels, and vice versa. Second, if it detects that ANY wheel is too rapidly approaching lockup it will instantly release brake fluid pressure on that wheel and will not re-apply pressure until the wheel rotation rate has again risen to some "target" as defined by the current roadspeed.
http://hiwaay.net/~bzwilson/prius/Prius_bump_240.jpg
The pothole, near side, was used for testing: ~4-5 inches deep and 7 feet long. I approached the pothole at ~20 mph since 19 mph is a documented threshold for braking transition. Before the patch, the regenerative indicator showed ~75% but after the pothole it dropped to ~20-15% and there was about a 50% reduction in braking force:
http://hiwaay.net/~bzwilson/prius/Prius_brake_080.jpg
After the patch, the same test scenario showed ~50% regeneration and no reduction in regeneration after the pothole. Accelerometer testing showed no reduction in braking force:
http://hiwaay.net/~bzwilson/prius/Prius_brake_070.jpg
It took a while to realize that the brake pause was not the same as our rain-slick Huntsville streets. I have one more test to run but it will take drizzle wet streets. But based upon the pothole tests run on Saturday, Feb. 13, the patch A0B works.
Bob Wilson
The 2010 has not engaged the VSC or AB as much as the 2007...but it has happened.
I honestly take this as normal...a Prius may start with a P but it ain't a Porsche.
Pushing down harder on the brakes will always help you stop.....EXCEPT if you push so hard or the road is so slippery that ABS activates. There is no condition known to man wherein Anti-lock braking will not extend your stopping distance.
The idea behind ABS is to "reserve" a portion of your front wheels' roadbed traction coefficient for directional control. The bad news is that it will do that regardless of whether you need, or use, that "re-apportioned" lateral traction.
Some day soon I expect that VSC will be used to activate ABS only if it is needed.
That's one of the reasons why it's not good to tailgate.
The car does have brake over-ride. It only works at >30mph. Feet on both accelerator and brake pedals simultaneously will stop the car.
I have not experienced any unanticipated acceleration on this car bought in December, but I know the complaint shows up in NHTSA complaints, but not to the degree of cars being recalled for UA. I had already practiced shifting to N and killing the engine by holding the start button for 3 seconds; yes, I know the brakes can overpower any engine surge.
I continue to like this car a lot and have confidence in the company. The bashing from the GM crowd is pretty entertaining, in any case.
I'm apalled to learn that ABS is highly undesirable when driving on snow or ice or loose sand or loose gravel when what you most want to do is get stopped ! This is particularly aggravating when I think of the $1000 I invested in Toyo ice tires, that are being hobbled by ABS just when they could be most effective. Maintaining directional control seems to be a less frequent occurence to me, although mighty nice when you can benefit from it.
On reflection, it seems to me that ABS may be largely responsible for the recent accounts of runaway Toyotas that couldn't be stopped by standing on the brakes. That's the way ABS is supposed to work ! IE: ABS will prevent wheel lock-up, and it will continue to function until the brakes overheat. At this point ABS shuts off but the brakes are probably too hot to be effective and there is no hope for the driver stop his runaway.
Also horribly ironic when, before the advent of ABS, one good brake application could have brought almost any car to a halt by locking up the brakes in the first place!
Realistic?
Thanks
"..On reflection.."
I myself was somewhat stunned to see that C & D test wherein the Mustang took almost 1000 feet to come to a stop at full throttle and HARD braking. Being RWD I would have thought, at first thought, that the brakes would have been able to bring the front wheels, and therefore the Mustang, to a QUICK stop.
What I forgot was that ABS would have prevented the front wheels from braking heavily with the rear wheels still being "spun" by the engine torque.
Are you saying the BTO only works if your speed is above 30mph....???
On a second issue: BA or Brake Force adjustment seems to be a rather ill-conceived driver aid. Suppose a prudent driver carefully removes his/her foot from the throttle and has it resting on on the brake pedal before maximum braking is required. Since there was no panic switch from throttle to brake does the braking computer remain stuck on minimum brake force? Is it only the inattentive drivers that benefit from automatic extra brake force?
I think BA watches the brake fluid pressure sensor to determine the rate at which brake fluid pressure rises in order to activate BA functionality.
I'm assuming is Emergency/Parking Brake, also comes up short on the 2010 Tacomoa Automatic because it's the foot operated toggle-latching style. So, in an emergency one has to lift one's left foot to find it and then it locks on until you release it and then re-apply your foot to remove braking, then re-apply your foot again to get braking. Not at all a good design for slippery conditions when your trying your best to do threshold braking! (I test drove a standard shift and it had the very nice manual, hand operated proportional brake so I was a bit disapointed on this feature --- more so as I realize how useful it is)
As for BA sensing the brake fluid pressure rate increase, that might still miss the mark if a prudent driver is gradually applying pressure in search of threshold braking. I'll explore this a bit more. Maybe I can build up a few good reflexes.
I'm beginning to think all our vehicles have been designed by "bare roads" designers, (regulators too, as ABS is becoming mandatory on all new vehicles.) Surely no one with winter driving experience would have put such systems (ABS, BA etc) in place. They have no place on slippery roads.
Thanks. Can I make it user choice? Using the parking brake feature is nice, and apparently regular use of the Tacoma parking brake is necessary to maintain it in a functional state (keeps the lubrication moving in the mechanism)
Not just ABS like on older cars. The affect is completely different that just plain-old ABS. There is no basis for comparison.
Some cars come with foot applied/hand released e-brakes. Even then, during driving and braking, one must use a hand to keep the brake from staying engaged.
Not correct. Testing has shown that ABS will extend braking distance in only two circumstances: 1. Loose gravel; and 2. Loose/soft snow. Stopping distances were longer as compared to braking by a very skillful professional driver (yes, I know, we all are better than average drivers). ABS will stop in the same distance as the skillful driver when the road is 1)dry; 2)wet; 3)ice covered; and 4)covered with compacted snow.
Remember that maximum braking deceleration happens not with the wheels locked up, but with 5% rotation.
I think we all underestimate the gap we really need to stop safely.
I have not tested.
I cannot find it in my owners manual, on any Toyota official site or any other car site, in any media story, or in conversation w other Prius owners. I doubt it is true.
If anyone is sure any year Prius has brake override, please tell me. I am a bit hesitant to try it because, among other things, I do not want to damage the car.
I think we all underestimate the gap we really need to stop safely."
There are too many subjective elements I think for anyone to say that there is "no way" I could have stopped in time. I have also used the calculator on http://www.csgnetwork.com/stopdistcalc.html which shows that it should have taken me 19.78 feet to stop. Nonetheless, the real issue is that after testing it as I described above I have real safety concerns, and to me it is not as important whether or not I was actually at fault in that accident - I have real concerns that I hope to have addressed, as I have a 93 mi commute and at this point do not feel safe driving my '07 Prius. BTW, I have nothing against hybrids or anything that can help save our planet - that is the whole reason I owned an '82 Mercedes 240D as I could use biodiesel in it (speaking to those who comment that there is some conspiracy against Priuses/hybrids/whatever nonsense).
""High Rate of Low Speed Brake Failure in 2004-2009 Prius"
by ganderc on April 7, 2009
Pros: Great car except for the brakes.
Cons: Has a rate of low speed brake failures 31 times that of a traditionally-braked car (Corolla). Many result in rear-ending the car ahead with no injury.
Summary: I read that they redesigned the braking systems for the 2010 Prius. That appears to be Toyota's response to the fact that the U.S. Generation 2 Prius (2004-2009) has had low-speed brake failures reported to the National Highway Traffic Safety Administration (NHTSA) at 31 times the rate of such failures reported for the 2004-2009 Corolla, which of course has traditional brakes. Many of the Prius low speed brake failures were in low-speed city traffic, resulting in rear-end collisions without injury. It appears that the several computers that control the complex braking systems were too busy calculating the most efficient way to apply the brakes, and did not get around to actually applying them, until it was too late. Toyota never took responsibility for the problem, but the 2010 redesign indicates they were aware of it. Unfortunately, the NHTSA never initiated an investigation despite the extremely high rate of failures. The detailed failure reports ("complaints") are available to the public on the NHTSA website. The details are these: To April 2009, 2004-2009 Prius has received 44 complaints of low speed brake failure. 2004-2009 Corolla has received 7 complaints of such failures. Given that at least five times more Corollas than Prius were sold during 2004-2009, 44/(7/5) = 31 times the rate of brake failure for the Generation 2 Prius."
Where is the source data for this obvious nonsense?
The problem is anyone can post a message saying any nonsense they
wish. Don't bet your credibility on "ganderc on April 7, 2009" who appears
to have made something up without citing a credible source.
Bob Wilson
Answers to Questions About Prius and the Toyota Recalls
Q. What is the problem that led to the Prius investigations?
A. The investigations focus on a new version of the antilock brake systems on the 2010 Prius, which was introduced in Japan and the United States last spring. There have been 124 reports of problems in the United States, and 77 reports in Japan. The problem does not appear to affect earlier versions of the Prius because the brakes were redesigned for the 2010 model.
In a statement, Toyota said, “Some customers have complained of inconsistent brake feel during slow and steady application of brakes on rough or slick road surfaces when the antilock brake system (ABS) is activated in an effort to maintain tire traction. The system, in normal operation, engages and disengages rapidly (many times per second) as the control system senses and reacts to tire slippage.”
Owners are reporting that the brakes fail to work immediately when the car is on a bumpy or slippery surface, or when it drives over potholes. Toyota said Thursday that it had already identified the cause of the problem and corrected it on cars built since January. Toyota officials in Japan said Friday that the company was considering a recall of 103,000 new Priuses in the United States and 176,000 in Japan, but that a decision had not yet been made.
Are you referring to yet another aspect of the brake complaint on 2010 Prii? I bought mine on December 12--and am generally happy with it.
Also, after listening to Mr. Toyoda's and Mr. Inabe's Congressional testimony last week, I presume that we will offered the installation of brake override--without the formalities of a recall.
While it is possible to specify firmware operation that would give priority to the gas pedal position over regen braking that is NOT very probable. That would not only be a serious flaw in the design but would border on intentional, criminal, action.
Thank you to those who are respectful on this and any forum.
If you go back to that original source, you'll notice I replied with the actual ratio of Prius and Corollas for those model years and the ratio is ~2.6 to 1, not the '5 to 1' ratio used in his numbers. If he can't get the ratio of cars in that model year right, how are we to trust his other numbers?
Understand he may be right about the counts of "reports" but look at his own numbers:
44 - Prius
7 - Corolla
The problem is 7 is not statistically significant. It is too small to draw any useful conclusions. So his ratio itself is suspect, as well as his counting.
I won't complain if you 'do the math' other than if I follow the same procedure we come up with different numbers. Then we'll discuss methodology and make sure we are seeing the same data. But as it stands, that source suffers from a major self-evident problem and a factually inaccurate count of vehicles.
The reason I knew the vehicle count is I've been looking at the Toyota December sales reports for the past couple of years. This has the total number of Prius and Corollas sold:
http://pressroom.toyota.com/pr/tms/toyota-reports-december-and-2009-150487.aspx
Bob Wilson