Low Pump Capacity?

[wwest]

What if the engine hesitation problem is the result of low transaxle hydraulic pump capacity??

All of the clutches, including the lockup clutch, are actuated by hydraulic pressure via the pump driven with a cam on the input shaft.

Suppose that the unusual shifting sequence, QUICK sequence, exhausts the hydraulic pressure just enough that the NEW shift sequence cannot occur absent a few turns of the engine to "rebuild" hydraulic pressure?

You're in the acceleration lane, low gear engaged appropriate to acceleration, Lockup disengaged to take advantage of the torque multiplication. Now you get slightly off the gas and briefly enter "cruise" mode. The engine RPM declines to idle, the tranmission upshifts into the most appropriate gear and the lockup clutch is engaged. But now you lift the gas pedal completely and apply the brakes and the lockup clutch must be disengaged.

And NOW...you apply the gas sharply because you wish to accelerate.

Ooops!

Hydraulic pressure was exhausted during your previous efforts and now it will take many turns of the engine, input shaft hydraulic pump cam, to build enough pressure to be certain of the newly required downshift sequence.

When Toyota and Lexus decided to use the lockup clutch in the same manner a person would use a REAL clutch did the engineers consider the extra duty, capacity, this would require of the transaxle's hydraulic pump.

[ColinBarber]

I would have thought they would be able to compensate for this by altering the line pressures within the ECU software and therefore would have fixed, or at least improved, the situation.

I would also have thought a low line pressure would produce an error code to be stored within the ECU.

[wwest]

Low line pressure...error code.

I'm sure there would be if they had a feedback sensor to measure line pressure with, or some derivative method.

[jgr7]

It appears your theory is working in slow motion, the output of the pump I'm sure is many times greater than any opperations the transmission might require. You can't really believe that the R&D guys didn't think of everything that you have, can you? I know that you have put alot of time and thought into this, but unless Toyota/Lexus is willing to admit a flaw no service dept in the world is going to give anything you say any weight. Have fun with your research it makes one think about these complex machines.

Jeff

[monarch]

The hesitation issue doesn't affect the Canadian emission standard RX models. Therefore the root cause of the hesitation has to do with the USA emission system design and programming

I'm from California and we have had to deal with and accept the reality of emission system related drivability issues for over 30 years because of our extra tough emission standards.