NHTSA Tracking Braking Loss on Prius Hybrids

Any possibility of providing photos or exact addresses of places that consistently produce this problem?

Thanks,
Bob Wilson

 

I felt some evidence that may back up your hypothesis. See my (too brief) test of wfolta's suggestion yesterday.

 

Nope, I wouldn't call you a troll by your description and some of your followup posts.

The posts that irk me are the ones from newbies that say things like "car lurches forward" and "lurches forward very strongly" and declare it to be a horrible safety problem, the sky is falling, etc.

 

Hummm, this begins to sound familiar and a photo would help. The larger the collection of observations, the better we'll be able to form testable hypothesis.

Thanks,
Bob Wilson

	Column 1	Column 2	Column 3	Column 4
0	link	proposed description
1	140	hard	dirt covered road with lateral "V" dip
2	130	same "V" from side
3	120	approach to "V"
4	110	approach to manhole cover
5	100	manhole cover with yard stick
6	090	sun at back of manhole cover
7	080	prior to repaving	right turn lane cracks
8	070	Google aerial view of dual	manhole covers
9	060	descending street view	San Francisco (?)
10	050	descending New Jersey street	requires leaves in street
11	040	Texas railroad crossing
12	030	right turn lane	broken street surface
13	020	serial manhole covers	lateral patches
14	010	Canadian dual patches	dual manhole covers	lateral patches

Current collection, looking for more, may have missed some - rjw

 

Bob,

Took the same route this morning (see 070 above) and the roads were covered with a sheet of ice. No evidence of anything abnormal about the braking over the manhole covers this morning when slowing down using regenerative braking before making the right turn. No issues at all on my trip over the sheet of ice covered roads this morning with the Prius braking.

Will keep trying to recreate it.

 

Here is another example, with this one being on a flat and level surface with an eroded depression.

 

I have felt the "slide" twice since I leased my Prius II in December.

Both times I was startled, but prepared, having read this thread. It is just a strange sensation that is slightly disconcerting.

It happens when I am comming to a gentle stop and travel over a rough patch in the road. Pedal pressure is the same but the constant rate of decelleration is definitely changed.

I don't tailgate so it is not an issue for me but it would totally freak my Mother in law out if it happened to her while she was in it. Toyota needs to address IMO.

 

So this is interesting news (at least to me). This is the first post that I've read that someone other than a G3 owner has expereienced the phenomena. Further indication the problem has been around for a while...?

 

That is a G3 Model II, not at G2.

 

We had a G2 (2005) and it happened to us also. No big deal but as I used to slowly regenerative brake, at about 7 MPH the regenerative braking released a bit and the frictional braking took over. There was a slight surge. I have always thought of this as normal hybrid braking and was never concerned about it. Same way I feel about the 2010 braking now. Until I experience the magnitude of braking surge talked about on PC, I will assume my 2010 brakes normally. Again, my build date was 11/09 and I'd like to hear from anyone else on PC with a car manufactured in November or later having this problem.

 

It's interesting to see again someone relate this issue to the 7 MPH transition from regen to friction. Having experienced the issue more than a few times, I can say the two events aren't even on the same scale as far as how serious they are. Personally, I believe Toyota has done an excellent job with the 7 MPH transition as I can detect it, but find it barely perceptible. Again, I suspect some folks have never experienced the issue. The issue I have experienced would get everyone's attention, no exceptions.

This is where it will be great when we can quantify this with an accelerometer. I suspect the 7 MPH transition will barely be a blip on a graph, while I expect the braking issue to be much more than a blip.

 

Thanks for posting such a good description. I find it interesting that you mention that you have trouble disengaging cruise control with the brake pedal, since I have the braking problem and also have noticed that it takes quite a bit of brake pressure (maybe 20-30%) to disengage cruise control. It's a very eerie feeling to be applying the brakes at 20% and still be speeding up, though not as scary as "losing" brakes for a split second while decelerating

Like you said, I don't know that these two are related but we won't know unless people mention it

 

I will be very interested in the results from that too.

 

Happened again yesterday, in a very dramatic way. The situation was flat road, in town, rainy day. We were approaching a stop light under light braking, probably about 20mph, although I was not staring at the speedometer. As I approached the light, we passed over a pavement joint - one of those metal expansion joint thingies, which was obviously slick from the rain. That little instant of wheel slip produced quite the effect. As the transition occurred, it caused something in the rear brakes to change rapidly enough to produce an audible 'bang'. At the same moment, the overall braking level was instantly and dramatically reduced to near zero, producing a subjective feeling of acceleration. That feeling of sudden acceleration, combined with the bang from the rear brakes was sufficient to scare my passenger into believing we had been hit from behind. She turned around to look and nearly got out of the car to check for damage before I could explain the phenomenon. It was quite something, and nothing at all like the normal 7mph transition. In fact, until today, I had never even been able to detect the 7mph transition. I did feel it once today, but it was a tiny little thing that you wouldn't even notice if you weren't an enthusiast. But yesterday's event... boy howdy... that would have caused some drivers to lose control of bodily functions, if you know what I mean. Again, I was prepared for it, so with an increase in pedal pressure I safely brought the car to a timely stop without any drama. But I was glad to have some extra stopping distance available and none too pleased about having to calm down a panicked passenger. I think I'm going to take it into the dealer, even though they won't be able to duplicate it, just to have it on record.

 

Can you give me a street address to use with Google Map?

Thanks,
Bob Wilson

 

Have you tried Wfolta's suggestion of shifting to N during light regen-only braking, to see if the response is similar to this braking problem? The rear 'bang' shouldn't happen, but any car-to-car correlation between the braking problem and a shift-to-N reduction in braking force might be useful to tracking down the problem.

Shifting to N, my car has had a variable response. Most trials show a mild or moderate loss of braking force, but some trials show none, and no trials have shown a serious loss. I still haven't done it enough to figure out a pattern.

If these two phenomena are related -- right now, we just don't know -- then my car probably won't be one of the better test beds for replicating the brake problem.

 

It was 6th Ave in Troy, NY, just north of Rt. 7. I appreciate what you're trying to do Bob - I have great respect for the scientific method. But believe me when I tell you there was nothing at all unique about this place and the road itself had nothing do do with it. It was just a slippery spot, the only relevant thing perhaps is that it was wide enough for both sides of the car to cross simultaneously. But really, it was just a run of the mill pavement joint like millions of others.

R7

 

Wfolta's test idea is a dang good one and I keep meaning to try it. So far, the only time I remembered under the suitable light regen, I was going about 50mph. At that speed the transition was seamless. Will update with slower speed results as soon as I can make myself remember I have a hunch that it won't be replicated though, because I am fairly certain the skid control ECU is coming into play when the issue occurs for real, and that ECU would not be in control during a neutral shift event. But still very much worth the test.

 

Something like this?

Route 7, - Google Maps

Thanks,
Bob Wilson

 

Something similar. I believe it may have been a block or two north, at the next light I think, and I was heading the other way (going northbound). I apologize for my lack of precision in recording the location - bad, bad, R7. The road just seemed so unremarkable and I was on my way to hockey practice, so I had other things on my mind. There were no major bumps though, just a change in surface either metal or tar-patch material, that was less than a foot wide and stretched the width of the lane.