NHTSA Tracking Braking Loss on Prius Hybrids

If the regen brakes are loss in the front (due to a slip in one or both tires), the rear should continue to brake.

That's why I was asking for accelerometer G read out the moment the front wheels slip.

 

The maximum battery current for the Gen III has been increased to 125A from 100A on the Gen II. This allows more aggressive regeneration.

On the Gen II maximum current only produces very mild braking that drops to about 16A if a bump is encountered. I am not sure what allows full regeneration again - just releasing the brakes and reapplying does not seem to do it.

kevin

 

Regeneration only uses the front wheels so if regeneration stops due to a bump in the road there is no braking until the friction brakes are applied on all four wheels.

Actually the regeneration does not seem to stop completely but reduces to about 16 Amps (from the max of about 100A) .

kevin

 

That anus-clenching sensation when a car loses traction momentarily is nature's way of telling you that you are driving too fast for conditions. Slow down. Or get used to it, or sell the Prius.

 

Right. So if the data is recorded, we'll know exactly how many millisecond and what G it drops to and comes back up, etc... This is with the driver holding the brakes steady.

 

Tom,

Don't know...I have not read anything about differences in breaking between G2 and G3. But will take your word for it. If you have a link that speaks to the different breaking systems, I would appreciate it.

 

ElectricMe,

I find it interesting that you always seem to show up on threads involving issues/problems with the Prius. Yet you don't own one, and probably never will.

If your motive is, in fact, genuine, then that's fine. But it seems that your posts have no substance, or factual information behind them. To me, most of your posts simply look all you are trying to do is fan the fire...

- If you have facts, then fine.
- If you have actual Prius experiences to share, then fine.
- If you have articles, and links to things you have read about the Prius, then fine.
- If your idea is thought out with an ounce of logic, then fine.

But if all you want to do is speculate with little or no knowledge of the problem/possible solutions, then I will continue to question your motives.

Clearly, you are free to post what you want, but know this - I'm not going away, so get use to it. :rockon:

 

From the spec, 2010 MG2 is a high rev motor/generator with lower torque rating with the new speed reduction unit. This SRU multiplies the torque to more than the Iconic model.

Rev: 6,400 vs 13,500 RPM
Torque: 295 vs 153(x2.636) lbs-ft

Since 2010 MG2 spins twice faster, more regen at lower speed can be captured.

More detail specs: Green Car Congress: Toyota Previews Generation III 2010 Prius Hybrid

 

If you believe the reports, the car has a delayed reaction, since it may be disengaging the regen brakes at this time. I was answering the question how could losing brakes for half a second at less than full braking increase your stopping distance. If you don't believe the reports obviously we have nothing to talk about.

If you have read the statistics, normal braking behaviour, pumping the brakes, did increase accidents when abs were added. ABS brakes still may increase stopping distance and nhtsa did say that education was needed. This is a case of losing braking in some situations. Instead of squelching discussion and yelling "la la la la, the prius is perfect" some of us would like to know what these situations are so we can add extra braking distance. We would also like the issue to be investigated and ff possible fixed.

What strawman? I am saying that unexpectedly losing braking may cause an accident. Toyota has said they are looking into it. Much has changed since gen II. I hear you loud and clear. You are trying to squelch discussion. I am unclear about your motivation. I'm leaving the thread now.

 

Hi Kevin. Interesting! It sounds like you've measured the current produced by the regen during a bump. Are you saying that upon hitting a bump, the regen output drops to 16 amps and never goes back up? That sounds more like an electronic reaction rather than the mechanical reaction I hypothesized. I would expect the current to drop momentarily, but recover at least partially when the free wheel grabs the road again. Or, if in response to the brief loss of braking the driver pressed harder on the brake to engage the friction brakes, the perhaps the regen would not recover fully. Do you have a current trace as an example?

 

I think if you are using a ScanGauge to read the HV battery current, then you need to consider the refresh rate for the ScanGauge (i.e. it isn't instantaneous). You might never see the regen drop to zero even if it does for a fraction of a second.

 

My feeling exactly...

Why anyone with absolutely zero experience or knowledge would go on and on paragraph after paragraph with pure speculation on a subject that he or she knows nothing about is a wonderment to me.

Like the OP Becker I see it as a need for attention. It's like the previous thread 'Woe is me I can't decide...' IOW I want attention.

It's an open forum and as long as the rules are followed no one should be excluded but each should be aware that unfounded speculation is likely to be slapped around by facts and experience.

 

Agreed, there may be a transient that drops below the 16A I mentioned.

There are some hills go down and it is difficult to keep the regeneration at a high-level - the slightest disturbance (such as a bump in the road) and it drops from the 50-80A region to about 16A and doesn't recover.

Just releasing the brake and reapplying does not seem to do it (maybe there is a recovery time, or using the accelerator is required, but I have not found a repeatable method).

kevin

 

I know I shouldn't even bother to respond.

But first of all, know this...I'm not going away either, so get used to it, I don't run from bullies.

Secondly, my original post within this thread was a response to FBears post #312, inwhich he communicates the idea that the braking issue isn't a problem because he has experienced it in his generation 2 Prius for many years.

This got me to thinking "Why does it seem to be more significant or to have manifested more acutely in the generation 3?" My idea simply being that perhaps the conditions for this feeling or slippage are met more often as a result of the 3rd Generation Prius having a more powerful engine and more torque available.

Care to explain where I didn't use facts or knowledge? My observations of the "Braking Problem" threads seems to support, to me, that this is more significant within Generation 3. It may be the same "thing" that is happening, but there seems to be reasons why the sensation is more acute in generation 3 and it seems to be happening more often for some owners. This "logically" led me to stronger engine, more available torque.

I never meant the post as an "answer" to the problem. Infact I ended it with just speculating...don't know...so it was never presented as "Hey, I have the answer!".

I actually found your additional information that the suspension in the Generation 3 is also "stiffer" interesting...as it may be a whole picture scenario....stronger engine, stiffer suspension, same braking system as in generation 2...might be why Generation 3 is experiencing this phenonema more often and acutely. Suspension might be the key...

But anyway, my original post was IMO not an unfounded or illogical post at all. But you can believe whatever you want.

As far as my only showing up for negative threads/problem threads...I have posted over 500 times in this forum....yes some negative, yes some positive.

Yes this is "Prius Chat" but I've enjoyed discovery and discussion about many issues not directly involving Prius. Sometimes it's as simple as giving an opinion or advice about a situation....and I don't think Prius Ownership is necessarily needed in many situations.

To be honest, if you can't have the maturity to get over my "Perfect Storm of Doubt" thread...if you are so threatened by it that I become the "evil enemy" that must be beaten down....then I don't care.

READ SLOWLY....I invite you, or anyone that is offended by my posts, or thinks they are invalid for any reason...to simple ignore them. You'll find my Name and a indentifying symbol in the upper left hand corner...so it should be easy to simply bypass. Try scrolling down....

Also..as far as "Facts" and "Experience" I find it funny that an "Engineer" who is TELLING me I don't know what I'm talking about...doesn't even know the difference between "Brakes" and "Breaks". Newsflash: It's called a "Braking System" NOT a "Breaking System" even though lately with Toyota you might be more correct. (Just Kidding! Calm Down)

I'm sorry I've sunk to your level...but it's also not ExASSerbate as you put in one of your posts...it's exacerbate...but again in your case the nice person might be correct.

 

All of these should cause the driver to immediately escalate from light/moderate to hard braking, regardless of vehicle. Do we have reports of Prius failing this escalation?

Without going back to review everything, my impression has been that this quirk is a loss of braking sensation and possibly pedal backpressure, when the driver is trying to hold a constant braking pressure. The event time span is similar to normal human reaction time, so we are missing details about whether or not it prevents escalation to full braking.

Absent such reports, I'm not going to worry much. My two 'loss of braking' incidents involved light braking with large safety margins. In contrast, I've had three hard braking Brake Assist activations, including one this morning when a school kid ran out in the road. While previous cars would have stopped in time in all three incidents, the Prius BA stopped with superior safety margins.

In a half million miles of driving, I've had one boo-boo, stopping just a few feet too late. This Prius stops so fast that it would have avoided that boo-boo. I'm not going back.

Both TC and VSC should be completely inactive under these circumstances when tracking straight. I've seen no evidence that either is involved.

 

Felt the brake failure again the past 2 days. Right after hitting the pothole on my right hand side. Now that I was expecting it, it really feels like it's accelerating the brief few seconds.

Conrad

 

If it is repeatable, do conditions allow you to start playing and experimenting with it?

I'd like to know whether or not you can switch to hard braking in middle of the event. Also, is it still triggered if you hit the pothole with hard (not-regen) braking. I'm sure Bob Wilson will have other scenarios to test.

 

I tested this last week. In my experience the effect is not noticed during a hard braking event. It's hard to say if you can enter hard braking "during" an event because the event is so short in duration. Certainly you can enter hard braking after the event as your reaction time permits.

Someone else on this list opined that the effect is caused by the geared differential trying to spin a front wheel that looses traction. I agree with his analysis and add that the ABS system is designed to minimize tire skidding by reducing braking effort on the skidding wheel. But the only control the system has when in regenerative braking is to reduce the generator drag to the differential, which affects BOTH front wheels. It physically can't modulate one wheel at a time, so has to modulate both, in other words. The system probably makes the decision that when this event happens it will also bring the friction brakes into play, giving the ABS system control of all four wheels. This fraction of a second that we feel must be the sensing of this skid event and the dialing in of the friction brakes.

I hope that the fix for this doesn't involve reducing the effectiveness of the brake regeneration system, but I'm afraid that's exactly what will happen.

 

In my own testing to which I posted over this past weekend, I certianly feel safe and have full confidence in my Prius' braking system. I am now use to the sensation and i'm not at all phased by it now.

I think all the tech replies with regards to the diffirental, the re-gen having to release both front wheels as well as the stiffer supension all may come to play here and it makes perfect sense to me. Having been in the alternative energy business for the past 20 years I am still amazed with regards to the number of people that find fault in our equipment because it behaves diffierently.

I have to admit shame in my self because I was alarmed when I noticed the braking sensations in my Prius. That is why I did my tests against the other cars.

With that said, I would like to address The Electric Me.

In a forum such as this, when questions of a vehicle's safety, the integrity of a new technology, etc, is in question, I truly want to disscuss this with others having first hand experence. I too have to question ones motives to enter into a forum thread of this importance with out owning and with out having experenced what we have.

So, in light of some of my earlier posts, are you a good witch or a bad witch?

Bad Witch's will be burned at the stake!