Engine Hesitation.....

[wwest]

but only because the transmission ECU told it to.

2001 RX300 Repair Manual, Volume 1, page DI-191, (Input Turbine Speed Sensor):

"CIRCUIT DESCRIPTION

This sensor detects the rotation speed of the input turbine. By comparing the input turbine speed signal NT) and the counter gear speed sensor signal (NC), the ECM detects the shift timing of the gears and appropriately CONTROLS THE ENGINE TORQUE and hydraulic pressure in response to various conditions, thus performing smooth gear shifting."

In other words the RX300 shifting sequence is completely an open loop servo system. Once the transmission ECU energizes the correct electrical solenoids for the new gear position the only feedback to verify new gear engagement completion is via the comparison of the transmission input shaft speed and the output shaft speed.

And I would imagine the engine torque output is controlled via the "throttling" of the fuel injectors since my 01 does not have DBW/e-throttle.

So, let's assume I'm at 21-24(19-23{AWD})MPH and fully close the throttle while waiting for a merge opening on the freeway. The system detects the coastdown circumstance and begins the upshift sequence (page SS-22, same volume) from 3rd to 4th just as I depress the gas pedal to mid-point to accelerate and merge.

Being open loop means that the upshift must complete and the upshift must be "verified" via the correct rotation ratio comparison between transmission input and output. And now once that shift completion is verified a new downshift command will be issued and verified.

In the meantime the engine torque is suppressed via fuel injector "throttling".

And this is for an 01 RX300.

So, now the question becomes when did Toyota/Lexus discover that these transmissions were failing prematurely due to the "too quick" reapplication of engine torque.

Remember that while the engine is being starved for fuel via closed injectors I may have the throttle control valve wide open resulting in an extremely LEAN mixture. The knock sensors will be complaining mightily!

Could they extend the dethrottling period for the fuel injectors without affecting the emissions requirements?

Could the engine, or engine related components, suffer premature failure due to short periods of extremely lean mixture over just a few years of operation?

Certainly not if as of 04 Toyota/Lexus uses DBW/e-throttle and shuts down fuel and air flow during these 1 to 2 second double shift sequences.

[wwest]

Quotes from:

AAAWORLD.COM

January/February 2005

Snake Oil by Peter Bohr

Corporate Average Fuel Economy, CAFE for short, a US law that requires automakers to build vehicles that meet certain standards. Automakers are desparate to meet them, or they have to pay millions in penalties.

{Hmmm....

MILLIONS IN PENALTIES....$$$$.}

Meeting CAFE standards might be a cinch if Americans favored little gas misers. But we don't; the ten most fuel efficient cars account for just 1 percent of total cars sales. Moreover, automakers are thrilled to indulge our taste for BIG IRON. Were it not for high-profit---but often, thirsty-, SUVs and pickups, some automakers would have pretty bleak balance sheets.

Roger Clark, a senior manager at General Motor's Tech Center...."We scour the Earth for ways to save gasoline." "Eager to have their cake (avoid CAFE penalties) and eat it too (sell highly profitable vehicles), GM and other automakers employ thousands of engineers to devise and evaluate fuel-saving possibilities."

Paul Williamsen, Toyota executive, speaking of cheap gizmos advertised on TV to improve fuel ecnomy....."We'd use any inexpensive device--we'd use it even if it were expensive. The grief our engineers go to in order to save a mile per gallon would blow you away!"

After a friend loaned me his Prius for a week, in return for his having my Porsche, I went out and bought a 2003 model. The Prius has a control function that allows you to set a mode wherein actual engine compression braking is used when you let off the gas, during coastdown. There is a note of caution concerning use of this function that says that fuel economy will suffer...

The Prius normally uses regenerative braking to simulate, give the feel of, engine compression braking. So, use engine compression braking, but when you do your batteries don't get charged.

From this all blessing (engine hesitation symptoms) flow.

The next time you're out cruising in your Sienna, say at about 65MPH, let off the gas completely and time how long it takes to coast down to say 40MPH. Now repeat that but pull the shifter down into 1st. See how much quicker you get down to 40MPH?

All Toyota is trying to do is save you a bit of pocket change.

Anytime you touch the brakes, the presumption being that the throttle valve is fully closed, why shouldn't the transmission be "upshifted" via unlocking the torque converter, slightly reducing engine compression braking. Even if you only release the gas pedal, why shouldn't the transmission be upshifted to extend your fuel mileage?

So what if you suddenly change your mind and decide to accelerate quickly? Your transmission now has a mind of its own and at this particular moment it wants to go in the other direction. Guess who wins, EVERY TIME!

Sorta like a two-headed snake....

What, how much, positive effect do you suppose this might have had on Toyota's CAFE with the hundreds of thousands of vehicles, Camry, Solara, ES330, HL, RX300, RX330, etc, sold since they started (2000?, 2001??) the upshift program?

How much, do you suppose, that would add up to in CAFE penalties should Toyota agree to fix each and every vehicle shipped using this technique?

[wwest]

:chairshot: