2010 brake system

Hi folks,

In light of the announced, upcoming 2010 fix, I'd like to first:

Thank YOU!
​

for everyone who contributed:

1. Addresses and locations of the problem places
2. Accurate descriptions of what happened
3. Patient with my plodding pestering about more details

Of course on this great day, I finally got the accelerometers I'd ordered to debug the problem. But that is OK, I have another use for them ...

CLEAN UP

My plan is to:

1. Collect the last of the brake problem location photos and images.
2. Ask folks who contributed to report "before" and "after" impressions. In engineering we call this 'regression testing.'
3. Low-keyed collaboration on understanding more engineering data - I have these accelerometers and a couple of months before . . .

So this is a happy day, a fix is coming, and I couldn't be happier. Hummm, guess I should clean out my "Ignore list" of the folks who only added noise, no facts and data, . . . or maybe not.

Thanks again,
Bob Wilson

 

Well my Gulf Coast Data Concepts, X6-2, arrived today ... just in time to get detailed data about what happens when a ZVW30 Prius drives over a speed bump at ~30-20 mph while the brakes are lightly applied:

This is the first set of data also used to understand the device, calibration and orientation. The Az is gravity and as the car hits the speed bump, there is an initial acceleration up. Once the car is headed up, it returns at a partial G until it impacts the pavement again. There may be a dampened shock absorber cycle or possibly some part of the rear wheels impacting the speed bump.

During these G variations, the stopping force varies but only up and down from zero to the approximate braking force. Then as the car suspension begins to recover, the braking force evens out. There is no evidence in this test of any reduced braking effect beyond the actual bump. But this is not definitive but just a single observation.

I'm not ready to loan these recording accelerators until I have some software to reduce the data, handle calibration, and minimize noise. Also, a secure mount is needed and clear instructions. I also need to study our ZVW30's data to see if there may be some testing profiles that may replicate the reports of others. Although Toyota plans to release a fix, it is always nice to have a baseline to compare before and after data.

Obviously, I have too many fun toys for boys.

Bob Wilson

 

Thanks!

Like this, looking NorthWest:
41.924503,-87.810038 - Google Maps

Or this, looking SouthEast:
41.924503,-87.810038 - Google Maps

BTW, I am not going to comment on the quality of those streets since no doubt those who travel them already have ... strong opinions.

Bob Wilson

 

The posted graph is normal braking going over a speed bump. The blue line is braking acceleration, actually deceleration of the car. There is no evidence of a delay in braking force after having passed over the speed bump. During the bump there are some changes but they have more to do with loss of traction than anything else.

This first graph is just to get the data and get a feel for how the instrument works. More will be coming but I have to hack a Perl program to reduce the data.

I have a volunteer who can replicate the anomaly. His data should show the problem. But first I have to 'master the tool.'

Bob Wilson

 

Are you willing to spend $90 on an accelerometer and a couple of hours to document it?

If so, contact Gulf Coast Concepts and order their cheap accelerometer. I'll be happy to share "lessons learned'.

Bob Wilson

 

It is the difference between flying by seat of the pants and using instruments ... say airspeed indicator. Let me give an example with one of my first measured speed bumps recorded by the accelerometer. :

The red line is vertical acceleration and the force of gravity. The blue line is acceleration along the axis of the car. Due to the orientation, a positive value is application of the brake. So the bump is the variation in vertical acceleration but other than temporary, momentary brake force changes, after the bump, the car continued to decelerate. We have engineering units that can be used to quantify exactly what is going on. A "siezed" brake would show a very sharp, deceleration.

Now you may remember from physics that:

• integrating acceleration -> velocity + constant
• integrating velocity -> distance + constant

So using the same data, I was able to generate this chart:

The "blue line" is the double integration of the acceleration and shows when the front tires hit the speed bump, the struts compress and the cabin rises ~2.5 cm. Then the rear wheels hit and suddenly the cabin is 5 cm. higher ... the height of the speed bump.

Now the reason I bring this up is an accelerometer converts imprecise words into numbers, engineering units. You no longer have to say "seize" but instead:

• normal reverse braking is "n meters/second**2"
• abnormal reverse braking is "m meters/second**2"

One thing I didn't ask, have you gotten the maintenance manual that covers the brakes? In particular, the parking brake adjustment mechanism? Parking brakes are typically self-adjusted by braking while in reverse.

If you can get the maintenance manual, you might be able to figure out what is going on. Perhaps even jack up the rear, take the tires off and inspect the parking brake adjustment mechanism. But none of this has anything to do with the "brakes going away after light braking over some road surfaces."

This is the "Prius Technical Forum," which typically means not just reporting a problem but doing something about ... mastering the technology. So you have options.

Bob Wilson

 

Well finally it happened to me so I voted. This after 8,500 miles and spending the last six weeks trying to replicate the problem. Fortunately, I had the accelerometer running and captured the event.

CONDITIONS

Friday morning, ~8:30 AM, light drizzle, approaching the Martin Road entrance to Redstone Arsenal. There are two speed bumps and the first one exhibited the braking anomaly:

The "red" markers are gravity and the speed bumps. The "blue" line is negative for braking and positive for acceleration. It includes coming to a complete stop for the badge check. BTW, I've been over that speed bump many times without a problem.

Expanding the scale a little better:

This clearly shows braking ceased and then came back. I had a sliding sensation that is common on rain slick, Huntsville streets. Even now, I don't know if the braking system stopped or the tires just slid until they regained traction. Regardless of the specific mechanics, there was a definite pause. But some of the linear data points suggest brief acceleration.

I expanded the scale again and ran trendlines that averaged 16 points together:

The trend line shows no evidence of 'acceleration' but it is clear braking forces ceased for about 800 milliseconds.

I'm uploading the spreadsheet with the data. Feel free to join in data analysis.

Bob Wilson

 

I believe the brake pressure was constant. I was approaching the gate and needed to reduce my speed. So I was braking before hitting the speed bump and it is not my practice to try and modulate the brakes when going over a speed bump. You'll notice that when braking force returned it was similar to the pre-bump level.

I remember no evidence of ABS activation but within the interval of transiting the speed bump, I personally couldn't tell. That is one reason for using the accelerometer. Once the speed bump is past, I felt a slipping motion (aka., slip and slide.)

Bob Wilson