PDF file of the official CHP report on the Sikes affair

Even if you assume the frictional brakes were fully functional you still have to take ABS activity into consideration. With the drive system applying a strong forward force to the front wheels simultaneous with frictional braking the braking at the front would have undoubtedly been less than expected.

The braking at the rear may have been compromised by the Anti-lock braking systems efforts to keep the rear wheels rolling, rotating, at some speed very close to that of the front wheel.

Then the e-brake tipped the balance of the equation toward stopping the Prius.

 

This statement is rubbish. The wear on the brakes shows that they were working. The "e-brake", which is really a parking brake, added nothing to the braking power in this situation.

Tom

 

Keith

 

The rear brakes and the e-brake are one and the same.

 

There is nothing that indicates the gap is a computer failure. Based on everything I've read the system performs exactly as designed, and based on my GenII experience the gap is not at all unpredictable. In any case, it turns out that the design was very slightly flawed, and the programming was modified.

 

Is it that unpredictable? I have the 2010 Prius. I can re-create the "gap" pretty much at will at a speed bump. I've never failed to stop, and I can't imagine with common sense driving safety practice, that it would ever really put me in much jeopardy of a serious accident. The "gap" only occurs during gradual braking, not during full force emergency type braking. And the "gap" happens so quickly (split second), I can't imagine me gradual braking so close to something where it would cause a collision.

 

It's actually very predictable. You can reproduce it consistently by braking over the same imperfection in the road.

I experienced it again this morning on my way to work (no, I haven't had the fix done).

 

Heat and wear the friction brakes down a lot faster.

 

Be very quiet about this, one "lucky guy" will call you a liar all because you can reproduce it.

 

Misunderstandings...

The Prius, all Toyota HSD models, have a brief, momentary, 100-200 millisecond, braking gap when ABS activation causes the transition from regen + frictional, or regen only, to ONLY frictional braking.

According to the 2010 Prius recall this same gap will sometimes, rarely, be extended to 1-2 seconds and that has apparently resulted in a few rear-enders.
.

 

Okay, not "failure" just poor computer coding initially...

 

I believe any rear-enders were not the result of this gap, but people not stopping in time. People get rear-ended all the times due to human error (happened to me in my brand-new Prius too and had the rear bumper replaced). They just like to shift their blame to something else.

 

I don't recall reading that anywhere and it is not in any of the Toyota documentation or the sticky thread here. But since I don't have a GenIII I didn't follow the issue closely. Surely you have a link to documentation?

 

Nothing was said in the quote you referenced about the frictional brakes not working. With the HSD drive system in WOT runaway mode there can be no question that the frictional braking on the front wheels might have been severely compromised.

And frictional braking at the rear might well have been compromised by the anti-lock or skid control system.

The drum type rear e-brake is separate from the normal rear braking and operates strickly mechanically.

I initially came away puzzled on reading about the 500HP Mustang taking 4-5 times the normal stopping distance with WOT throttle drive and EXTREME braking. The Mustang is RWD so the front brakes, PRIMARY braking, 70-80%, would not have been compromised by having to overcome the engine driving force.

So why did it take so long to stop...??

Most likely because the anti-lock system prevented the front wheels from slowing more rapidly than the rear wheels. So the front brakes, braking ability, ended up being compromised by ABS activation.

 

Who/what is your question about..???

 

No, the parking brake (it's not an e-brake) runs exactly the same drum in the rear. There is no difference other than the mechanical actuation.

If you are going to speculate about the systems in the Prius you need to have a basic understanding of how they work.

I'm sorry to put such a sharp point on it, but I stand by my original assessment.

Tom

 

I'm pretty sure the later Prius models have disc brakes all around.

But even if not the point I was trying to make is still valid. The rear e-brake (emergency brake) is mechanically actuated, push on the pedal, (or lift the lever, whichever) the e-brake engages. The normal frictional braking system is under control of the skid control computer and therefore subject to all aspects of VSC/TC/EBD/BA/Etc.

 

"the frictional brakes not working."

Should read:

the Fictional "brakes not working".

 

Regen is not capable of providing hard or severe braking at any speed. To get hard braking, the front brakes must go into friction mode.

 

'Later' in this case means MY2010. In the U.S., 2009 and earlier models still had drums in the rear.