2010 brake system

[bwilson4web]

Hi,

Part of problem diagnosis is to understanding the system so we can map symptoms to potential failure modes. The poll associated with this posting is to ask about subtle items that may or may not have any bearing on the brake anomolies. These are just hypothetical mappings but an important step. One of the best source are Toyota's New Car Features:

• BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: BRAKE CONTROL SYSTEM: DETAILS (2010 Prius), Doc ID: RM000004221000X
• BRAKE CONTROL / DYNAMIC CONTROL SYSTEMS: BRAKE CONTROL SYSTEM: GENERAL (2010 Prius), Doc ID: RM00000421Y000X

This is just a brief summary of the details.

OVERVIEW

The Prius brake system is an integrated system that balances regenerative braking, hydraulic braking, traction control, antilock skid control, and balance into a simple to operate system:


Now one of the symptoms reported is an extended 'loss of braking force.' Considering the curve above, it is likely this is a hydraulic system release. Given the time-scale, this chart suggests the effect occurs in an early braking condition versus a longer, braking interval when regenerative braking force might be a higher percentage.

It is a fairly sophisticated system that also adjust braking force based upon the vehicle loading:


So one question is whether or not the vehicles experiencing the braking symptoms may have or not had a load in the rear.

SIGNIFICANT ELEMENTS

Assembly	Part	descriptions
Master Assembly	Brake Actuator	4 switching solenoid valves
	Brake Actuator	2 linear solenoid valves
	Brake Actuator	8 control solenoid values
	Stroke Simulator	generates pedal stroke per driver's input
Skid Control ECU		manages system
Stroke sensor		detects brake pedal operation, analog
Speed sensors		one for each wheel
Power ECU		responds to regen request from skid control ECU
Power ECU		sends regen value to skid control ECU
Power ECU		controls motive force per skid control ECU
Elect. Brake Dist.		adjusts front and rear and left/right braking
Stroke sensor		contact type variable resistor, stroke position
yaw rate sensor		left and right acceleration
acceleration sensor		forward and backward acceleration

Of these elements, I tend to wonder about these sensors:

• brake stroke - there is history of wiper-based, sensors being a little weak. It is one reason Hall effector sensors are used more commonly.
• acceleration sensor - something we'll measure with the USB sensor.

Thanks to the help from those who have experienced the problem, we have a growing list of surface conditions that seem to trigger the symptom:

http://hiwaay.net/~bzwilson/prius/Prius_bump_010.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_020.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_030.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_040.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_050.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_060.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_070.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_080.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_090.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_100.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_110.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_120.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_130.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_140.jpg
http://hiwaay.net/~bzwilson/prius/Prius_bump_150.jpg

You can help by posting photos or Google Street view or Google map addresses of the places this happens. The key to diagnosis will be finding a way to replicate the problem at will. Then we can do things like:

1. swap Prius - if one vehicle always has the problem and another does not, it means finding out what is different between the two
2. quantify the problem - we need engineering units that document time, duration and magnitude

Bob Wilson

[georgew]

REALLY appreciative that so much energy is going into researching this.

FYI, Each time I've had brake loss/pause, there has been zero load in the rear of the car..

One street near me that would cause brake loss almost every time was caused from what I think was a bulge in the road from a tree root while stopping at a stop sign. Shouldn't be too hard to recreate if we can think of a way to create a similar bump in the road. I've since adjusted my driving habits to avoid this but I'll see if I can get the prius toexperience brake loss at that spot later this week and will take some pictures if i can along with speed, brake force, etc..

[Airbalancer]

the only time I have feel anything funny braking is when I have cruise on, it feels like the car is not stopping
And it could be is I am not pressing hard enough on the pedal to dis engage the cruise, as soon as I press harder it starts to brake
It think it just a matter of knowing the car better

[spiderman]

Interesting... I have never had the breaking issue (that I know of) but then I have never had a payload either... I wonder if that has something to do with it.

[FLP]

Mine happens at a speed bump as I turn into my cul de sac. I just make sure I'm going very slowly, so that I don't have this occur.

[qbee42]

Keep in mind that there isn't just one braking issue. Among the possibilities are:

1) Sticky brakes in reverse.

2) Soft pedal pressure.

3) Regenerative braking to friction braking transition.

4) ABS.

Some issues may be a combination of the above. Compounding and confusing the various issues keeps these threads lively.

Tom

[bwilson4web]

Hi,

I'm really interested in the slow-speed, stopping anomalies as these are often close to other objects (aka., bumpers, walls, curbs, walkways.) Also, understand I'm using the "New Car Features," NM1291U, and the "2010 Maintenance Manual," EM1291U, as my source materials. I'm not a Toyota trained technician and my reading and interpretation is likely to have unintended errors. But this is my best understanding ... today ... and I appreciate corrective posts so we can all advance our knowledge and understanding.

BACKGROUND

A non-error code, braking anomaly has been reported by some 2010 Prius Chat members:

• ~18% report "scary, safety issue" (18)
• ~41% report occurs (40)
• ~59% report not experienced it (57)

It seems to be a low speed phenomena:

• ~47% report speeds 20 mph and slower

Typical report:

Modest braking that passes over a manhole cover, railroad crossing, patched surface, or pothole that leads to a longer period of reduced braking.

Survey From Maintenance Manual

System architecture:


These are bits that suggest interesting aspects that may apply to our braking system:

"Do not remove or install electronically controlled brake system parts such as the steering angle sensor, yaw rate and acceleration sensor or brake pedal stroke sensor except when required, as they cannot be adjusted correctly after removal or installation." (BC-1)

I'm still reading the brake section, over 300 pages. But I wanted to start the conversation. More details to follow.

Bob Wilson

[bwilson4web]

Hi,

Originally Posted by FLP

Mine happens at a speed bump as I turn into my cul de sac. I just make sure I'm going very slowly, so that I don't have this occur.

You could help by giving us a Google address of the speed bump. If there is not Google Street view, take a photo and post it here ... with a yard stick or scale so we can understand the shape. But a simple "me too" post without technical details or even a photo ... wastes everyone's time:

• ours because we already know something is going on
• yours because you already knew something was going on

Please, provide additional technical details and be part of the solution.

Bob Wilson

[DetPrius]

Bob, I checked both at the beginning and after a bit as when I made my repeated attempts to recreate it a couple weeks ago, it didn't seem to matter, but this is a gut feel response to the question as I was not looking to answer that specific question. I also checked no load but that is my normal operation of the car.

[namasteflc]

I am disappointed in the Prius 2010 ABS. Although the car does stay straight while stopping in slick snow, the ABS only seems to pulse twice a second. My previous car(Benz) seemed to pulse eight times per second- like going over a series of warning speed bumps. At least i can use front wheel drive to power-steer(the Benz was rear wheel drive). Should i add weight to the rear of my Prius? How much weight? We used to put #80 of salt in the front 'trunk' of our Corvairs- balanced the cars well.