When do the physical brakes kick in? We live on a mountain and since the car rolls well, I use some brake getting off the mountain. I assume that light braking pressure is regenerative and the physical brakes don't kick in until you actually have to stop at a red light. Correct?

 

As I under the system the frictional braking may not be used at all except once fully stopped, depending on the specific situation. The more rapid the stop the more likely the frictional brake will be used/required.

 

First IIRC the rear brakes always are used only the fronts are varied. The electro braking force is about as strong as moving something like a dictionary off the front seat, at the point the book moves is about the limit of the regen.

 

New "invention".

I'm making this statement only "presumptively". No actual direct knowledge of the FEH braking system other than what I read and past experience with other vehicle braking systems.

Insofar as brake fluid pressure, frictional braking, is concerned the front and rear braking systems use a COMMON brake pressure source. Most modern day vehicles have "dual" brake pressure sources, systems are "split" diagonally such that if one system fails you still have adequate braking capability.

That means, excepting VSC/TC, that once frictional braking is used on one wheel it applies to all.

But keep in mind that rear braking capability is typically mechanically compromised vs the front. This is because the lows of physics come into play for any serious level of brake application. Plus you NEVER want the rear of the vehicle to "out-brake" the front.

So, 100 lbs of brake pressure in the "system" is 80% more effective at the front vs the rear.

Unless Ford is using the front wheel ABS/TC solenoids to isolate the front brake calipers/pistons from brake pressure in this instance it is not possble to have rear frictional braking without having ~4 times as much, effectively, at the front.

I suspect that is one of the reasons, foundations, for believing Ford has put the Patent covering this issue into use. On an adverse roadbed the use of regen braking at the front absent an appropriately "equal" level of braking at the rear could have dire consequences. Given the potential, HIGHER potential, for encountering these conditions when the OAT is near or below freezing, it becomes easy to understand when the design would allow for friction braking to come into use much sooner in those conditions.

 

Below information was posted elsewhere as a result of a question about a Highlander Hybrid rear-ending another car when a "bump" caused the ABS to activate.

"..sensitive to "bumps" when stopping...

All Anti-lock Braking systems have this "sensitivity", undesirable as it may be.

The "bump" pushes the wheel upward and the shock does not allow it to rebound right away. As a result the wheel loses traction with the roadbed momentarily and the "braked" (Regen ONLY..??) wheel's resulting rotational rate reduction causes an ABS activation.

The only fix would be to disable ABS...

Or modify ABS such that it doesn't activate unless VSC indicates the need. ABS has no functional purpose, NONE, unless directional control is somehow threatened during braking. If the vehicle isn't or doesn't yaw during braking, or the driver doesn't need to make corrective directional maneuvers, ABS activation not only serves NO purpose, but can be detrimental, as can be seen here.

Obviously this effect might be much more detrimental on a modern day FWD hybrid. Up until hitting the bump the braking may be PURELY from Regen, and therefore ONLY on the front wheels. Regen MUST be DISABLED the very instant ABS activates otherwise ABS functionality would be reduced, or maybe even non-existent.

In point of fact since frictional braking may not have been in use AT ALL at the time of the "bump" the instant disabling of same results in NO BRAKING AT ALL until brake fluid pressure can "arrive".

There is an indication, Ford has a US patent concerning this, that the Escape/Mariner/Tribute substantially reduces Regen capability when the OAT is below ~34F to reduce the potential for this happenstance.

 

"There is an indication, Ford has a US patent concerning this, that the Escape/Mariner/Tribute substantially reduces Regen capability when the OAT is below ~34F to reduce the potential for this happenstance."

It is 15 F today at 3:55 pm Central time. I am driving 30 mph on a snow and ice covered roads from a ski location. I lift my foot off the gas pedal, shift into "L" and my FEH immediately slows downs to approximately 12mph.

How many more times do we have to read that the FEH operations are disabled due to colder temperatures?

 

I have to agree with Billyk... -5 deg C here in Toronto today, lots of snow and ice on the side streets, and still plenty of regen braking and regen "engine" brake when foot comes off the gas (with ICE on or in EV)... ABS seems to function just fine as well, with no issues.

Also, I would say that the statement about ABS being NO use during a stop unless you are trying to turn is not correct... ABS will reduce the straight line stopping distance vs full braking resulting in a skid.

 

Regen capability substantially reduced does not equate to disabled...

 

Sounds like your instincts are correct.

The attached page from the 2006 shop manual describes the brake-by-wire system in the FEH and suggests that the braking system is capable of using any combination of Regen and "Friction Pad" brakes....depending on the vehicle speed/deceleration and brake pedal position inputs. So the answer to the question is, "It depends." and "The computer decides."

Note: I'm fairly sure this write up is an accurate description of the 2009 system (other than the parking brake and rear brakes now being full drum brakes). I don't know if VSC (Ford calls it AdvanceTrac RSC) changes this description.

 

"still plenty of regen braking(1) and regen "engine" brake(2).."

You seem to be implying you are using "B" mode, in which case...OF COURSE.

"ABS seems..."

Of course, just as your owner manual states, regen is disabled whenever ABS activates.

"ABS will reduce..."

Never happen, do the research.

ABS will NEVER reduce the straight line stopping distance but will often help to prevent a "skid"... loss of directional control.