I am not sure the average consumer appreciates how revolutionary the braking system of the modern hybrid is. For 100 years the only way to stop a car was to rub metal and ceramic parts together, generating heat, noise, and brake dust. It is all parasitic waste. Sure it is implemented a bit better than on Fred Flintstone's car, but it is still essentially a crude system unchanged for more than a century.

On our hybrids, breaking doesn't carry with it all that penalty.

Since I got interested I have been looking for documents on details about how the FEH braking system is designed. Does anyone have a detailed schematic? Is the brake pedal linked directly to a master cylinder or is that driven in another way, and what role/dependence does the computer play?
I note that the gas pedal seems to be all fly-by-wire, but I don't think the brake is. Is this correct?

Any answers appreciated?

 

MrCrank — I don't have any specific FEH information, but I'm attaching the braking system descriptions from the 2007 Toyota Camry Hybrid's "New Car Features Guide." The system is indeed very complex! I'd expect Ford's system to have many aspects similar to Toyota's.

Stan

 

Hi Alan,

I would like to explain how Prius's brake system is implemented since the FEH is licensed by Toyota's THS system.

Basically, the brake system is brake-by-wire.
Your brake force is received by the brake pedal stroke simulator converting to an electric signal.
The skid control computer receives the signal including signals from each four wheel speed sensors, yaw-rate-sensor, G-sensor and steering-sensor, then it sets the regenerating braking force and friction brake force.

The vehicle has oil pressure accumulator for the friction brake and each wheel has solenoid valves for that.

Therefore, your brake input will cause regenerating brake first, then goes to friction brake if you need more braking force.

There is a fail-safe system.
If the vehicle lost 12V power, there is an electric power back-up supplying by super capacitor.
If the vehicle lost everything, your brake force applies mechanical force to front brakes.

Please to refer to following page...
http://www.toyota.co.jp/en/tech/envi...s2/system.html

Regards,
Ken@Japan

 

Under most cases, and for most of the brake pedal travel, it is all Brake-by-wire. There is a mechanical linkage to the hydraulic brakes as a back up, but this will take considerable effort from the driver, and is not used normally.

Place a book on the passenger seat and brake.
If the book stays on the seat, friction pads ARE NOT being used.

If you brake hard enough for the book to slide off, some friction pad effort is probably being used.

-John

 

I don't have specs but there will be a new system on the 2009 models per:

"A new brake system also provides a more seamless transition from regenerative braking to traditional braking. It incorporates a new pedal sensor that gives the driver better feedback and pedal feel similar to that of a traditional vacuum-assisted hydraulic system."

http://www.ford.com/about-ford/news-..._autoshow_2008

 

Woah. I thought that things were more complex than was empirically obvious, but I hadn't thought that this much engineering went into it. Thanks for the PDFs I'll read through them tonight.

 

Lots of information. Ford is going to have electronic stability and roll over stability on their hybrids for the first time. Ford's AWD system on hybrids is different than Toyota's use of a second electric motor to power the rear wheels. Will have to wait for Ford's documents on this issue.

 

The stopping system is entirely brake-by-wire, here is Ford's description from the early FEH shop manual. This is the system used on the '05s thru the '08s.

 

Thanks for the posting -- do you know where an up-to-date shop manual can be had?

It is interesting they use an accelerometer instead of using tachometers on the wheels.

 

Remember, accelerometers can most directly measure the rate of change in speed of the vehicle (how fast is the truck stopping?). I assume the Brake System Control Module (BSCM) uses information from the ABS sensors at each wheel as well as data from other speed sensors.

Big software changes are in store for the '09 if they truely can incorporate VSC (Vehicle Stability Control) (I believe Ford calls it "ControlTrac"?) into the brake-by-wire system in the FEH. At least it would finally silence all the FEH naysayers who swear nobody should ever operate a vehicle without VSC - lest they die a horrible death.

Do a search on this forum for "shop manual" and there are several links to ebay sources, etc. I chose to get the DVD version supplied to dealers - for around $70.