Willard, come on, you have got to be kidding. It is common knowledge that the FEH is brake-by-wire....there is no "direct connection to a master cylinder" from the brake pedal. The hydraulic brake system is constantly at a state of pressure (pump and accumulator) - ready to be engaged.

It is left to the computer to decide what combination of regen and hydraulic braking to use......depending on vehicle speed, deceleration rate, and brake pedal position inputs. Your choice to say that friction braking is blocked during regen is just not accurate. The computer's choice not to engage a braking system is different than "blocking" that system.

It may be semantics but electronic "blocking" or "unblocking" a system is not really the same as engaging and disengaging.

Ford has gone to great lengths to make this braking system appear to stop the vehicle like a traditional foundation (hydraulic, friction) brake system. As far as the driver is concerned, the command is given, through the brake pedal, for the vehicle to slow or stop...and the vehicle responds accordingly.

 

Okay, I give...

The FEH is unique in that it has the ability with a system failure of leaving the frictional brakes completely disengaged.

 

Brake Pedal Assembly — Hybrid
Hybrid vehicles are equipped with a brake pedal assembly that utilizes driver input and electronic components to apply the brakes. The brake booster push rod has an elongated slot that attaches to the brake pedal with a clevis pin. The elongated slot allows for a small amount of pedal travel (freeplay) to occur without the brake pedal applying pressure on the booster push rod. This freeplay allows regenerative braking to occur. To compensate for the freeplay, the pedal assembly is equipped with a hydraulic brake pedal feel simulator that provides the same feel and resistance as a conventional brake pedal. On light or normal brake applications, sensors attached to the brake pedal assembly measure brake pedal angle and the amount of pressure applied to the brake pedal. The sensors send signals to ABS module which activates a solenoid inside the brake booster. The solenoid draws the booster push rod into the booster, applying pressure to the master cylinder piston which then applies hydraulic pressure to the brake system. On hard brake applications, the brake pedal will travel to the end of the elongated slot, eliminating the freeplay and physically engaging the booster push rod, operating the brakes similar to a conventional brake actuation system.

Active brake booster (hybrid vehicles)

The active brake booster uses vacuum supplied by an engine mounted electronic vacuum pump and is similar to a conventional vacuum assist brake booster with the addition of a brake booster (vacuum) solenoid, a brake booster travel sensor and a vacuum sensor. If it is necessary to apply the vehicles friction brakes, the ABS module will send a signal to the brake booster solenoid that is proportional to the amount of brake torque requested. The booster solenoid will open to allow vacuum to draw the booster diaphragm and pushrod towards the master cylinder piston, building hydraulic pressure. The brake booster vacuum sensor is used by the ABS module to monitor vacuum maintained inside the brake booster. The brake booster travel sensor is used to monitor the performance of the brake booster.

 

So the FEH is not fully brake-by-wire...?

The description reads pretty much the same, including the brake pedal "feel" simulator, as the Toyota HSD system, Prius, etc.

As a failsafe the brake pedal does push on the master cylinder...??

 

My earlier post was worded too strongly.....it's fair to say the brake pedal controls the hydraulics in failsafe mode. See attached.

 

This matches the Ford service literature that my service rep at my Ford dealer gave me after our 2010 Mariner had the 'brake pedal to the floor' problem. Since the nature of this problem is a safety 'next time someone could get killed' problem, I am not giving up until Ford convinces me that this won't happen again. My dealer is terrific and has treated me very well for many years, so I am counting on their help in working with Ford. One question is WHY this happened when my car was manufactured after all the fixes to this problem had been dialed into the factory. Why is this still occuring?

 

We have a 2009 FEH, and are currently suing Ford under the Lemon Law to get a replacement vehicle. Our brakes failed 4+ times and each time we took it in for repair and the Ford dealership swore the brakes were repaired. My father actually drove the car through our house, because of the brake failure. Now we have a killer car that we can't even drive, but are paying the note on. Also NTSB, will not post this problem on line, but there have been complaints. It is time for a class action/recall. Please contact me if you have similar brake problems. Thanks!

 

I have a 2008 Mercury Mariner Hybrid. Brakes failed in Nov for my wife and in Dec for me. I have taken all the ground points from the Neg of battery to where they connect to the body and cleaned them. One is below the battery, one is on the passenger side of engine, on the wheel well and one you need to remove the driver side front tire to redo. I think it is an electrical problem. I have not had a failure since. 4-14-12

 

Brakes can fail short for a number of reasons. You should take actions to prevent braking mechanism failing, but if you ever find yourself in a driving situation where your brakes not work. Unfortunately, manufacturers are not always as cautious as they should be, and a automobile may be outfitted with defective braking systems that can fall short suddenly.