I checked the BTO out a little more thoroughly, and it appears that the engine does continue to rev under light braking with throttle applied. However, when the brake peddle was pushed further, the engine did return to idle. Felt like it took about 1/2 of the brake peddle travel to engage BTO.

 

Thanks to cp_tch for the thoroughness and for stating the observation so clearly !

I had noticed something similar in my informal tests, but I had not thought it out this clearly.

Now this latest observation would, at least qualitatively, explain why the inherent BTO functionality in the Camry Hybrid (as well as in the Prius) has proven inadequate to prevent the mat-induced UA incidents in which the mat became trapped under the brake pedal and on top of the accelerator pedal.

It would also explain why it makes sense for Toyota to do the carpet and pedal modification recall on the TCH in spite of the fact that the car has the inherent BTO functionality.

Excellent work, cp_tch ! Thanks again for sharing your observation.

 

The Toyota HSD's ICE can be revving at 5,000RPM and not deliver a single erg of energy to the drive wheels.

 

In my observation, the engine did feel like it was delivering power to the wheels until the rev's dropped. However, my experiment was pretty "informal" also...

 

Thanks to cp for posting this clarification.

My own obsrevation was similar.

Hence my conclusions,

"Now this latest observation would, at least qualitatively, explain why the inherent BTO functionality in the Camry Hybrid (as well as in the Prius) has proven inadequate to prevent the mat-induced UA incidents in which the mat became trapped under the brake pedal and on top of the accelerator pedal.

"It would also explain why it makes sense for Toyota to do the carpet and pedal modification recall on the TCH in spite of the fact that the car has the inherent BTO functionality."

 

What about the inverse of this, floor the pedal THEN shift to neutral.
I expect the same to happen, ie the engine does not continue to rev.

 

Upon shift to neutral, the ICE will be either idled or shut off, depending upon temperature and state of charge. It will do this regardless of accelerator pedal position or engine speed or car speed.

This is why in the TCh this is absolutely the best way to manage a UA event. I know this from first hand experience.

 

My understanding of the toyota HSD planetary gear system is that a MG1 must be operating in order for the engine to provide any power to the drive shaft. This is different from a standard transmission that could, possibly, in theory, "torque lock" or not shift to neutral at very high speed or engine rev levels (any gearheads that could explain this would be greatly appreciated).
When a HSD is shifted to neutral the hybrid control system simply cuts power to MG1 which causes the planetary gear to freewheel after a second or two depending on the speed. with the planetary gear "unlocked" from the drive shaft only MG2 (drive motor) could move the vehicle, but the control system would not power the motor since the shift selector is not in Drive.
Given this gear setup, I dont believe a torque lock would be possible as in a standard transmission, since there is nothing physically shifting in a HSD planetary gear system, just gears syncing or freewheeling and the ratio of which controls transfer of power from the engine to the drive shaft.

taken from http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

 

Modern transmissions will shift to neutral at high rpm or under a high load condition. The shifts are done by solenoids and controlled by the ECU unit. The only other "control" mechanism in the tranny is the valve body which controls the fluid flow. I will defer to a Toyota transmission expert but the ones I am familar with will not suffer from "torque lock". It might happen, but I very much doubt it.

 

So in a car with a gas engine and an automatic transmission, even in a wide open throttle condition, it should always be possible to put the transmission into neutral removing power from the wheels.

There has been so much (mis)information thrown around in the press about this whole unintended acceleration problem, "brakes not having any effect", "shifting to neutral does nothing", I'm trying to get a better technical understanding what failure modes really do exist.