Last post on Nov 09, 2013 at 5:09 AM
You are in the Toyota Camry
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Toyota Camry, Sedan
#2206 of 5646 Re: Camry's accelerator software [alan_s]
Oct 18, 2006 (2:55 pm)
alan s wrote: "Automotive News reports Toyota has tackled a problem with the 2007 Camry's accelerator software. In four-cylinder Camrys, the software allegedly learns the driver's style, and those drivers with a frugal right foot get less response over time. Sudden demands for power – like a quick shift into the passing lane – can confuse the system and leave drivers with less power than they need."
This is where I have a big problem with the "learning transmission" argument here. I also have a 1994 Dodge Grand Caravan ES with a "learning" electronically-controlled 4-speed automatic transmission, and I've never had to teach "myself" how to drive this vehicle. Both my wife and I regularly drive the van, and we've never experienced any drivability anomalies with this transmission. Learning transmissions are not new technology per se; Toyota's implementation yes, but the basic conceptual design - no.
Personally, I don't think it's so much of a Toyota "learning transmission" problem, rather a real problem with the firmware for the drive-by-wire throttle. Hence, the reflashing TSB.
#2207 of 5646 Play it again.....
Oct 18, 2006 (3:15 pm)
The only firmware solution possible is to totally eliminate the lift-throttle, throttle fully closed, upshifting of the transaxles.
For the RX series they started using that technique, for sure, with the 2001 model year, possibly earlier. While the use of this technique would undoubtedly be beneficial to FE, I have come to quite firmly believe that it is being used, predominantly, to alleviate instances of loss of directional control due to engine compression braking should the roadbed happen to be somewhat slippery.
Ford Motor Company has just been granted a patent which appears to impinge, be important, in this regard. The patent involves the use of a technique whereby a hybrid vehicle's regenerative braking effort is significantly reduced if the prevailing OAT hovers near or below freezing.
Within the same patent a technique is described wherein regenerative braking is disabled the instance ABS activates.
If regenerative braking, already lowered due to OAT, can still interfere with ABS activation, how can anyone say that ICE compression braking would not, most especially with FWD? Not saying this to denigrate FWD especially, but the fact of the matter is that ABS is much more important at the front wheels since the front brakes do provide ~70-80 of the braking HP.
So IMMHO Toyota and Lexus are "hobbled" by the EPA and CARB with regards the FE improvement, and most likely the automotive insurance industry with regards the improved safety of FWD or front biased AWD via use of the lift-throttle coastdown upshift technique.
Within the PR news of the new Ford Edge, also a FWD or front biased AWD SUV, there is a note indicating it is equipped with a variable displacement ATF pump to improve efficiency.
In the past the greatest "challenge" for the ATF pump was to provide enough pressure/flow for quick and firm upshifting during acceleration. Big DEAL. The engine is always at a fairly high RPM during "these" upshifts.
Now that Toyota and Lexus have adopted this lift-throttle upshifting technique the transaxle will often need to preform two shift sequences in quick succession.
Example: The driver lifts the accelerator pedal fully just long enough for the transaxle to begin an upshift. The engine RPM quickly drops to idle but now the driver re-applies pressure, a significant level of pressure, to the accelerator pedal.
Since the ATF pump capacity with the engine at idle cannot provide enough pressure/flow the DBW system has been adopted (RX350) so the onset of engine torque could be delayed until enough pressure/flow is provided.
Rather than increase the FIXED pumping capacity of the ATF pump and suffer the horrible loss of transaxle efficiency thereby, Ford has chosen to use a variable displacement pump. HIGH volume during shift sequences and low volume, or maybe even zero volume at times.
My guess is that we will not see a final fix for the delay/hesitation symptom until Toyota and Lexus adopt a like or simuliar. ATF pressure/flow "make-up" technique.
#2208 of 5646 Re: Play it again..... [wwest]
Oct 18, 2006 (4:07 pm)
Perhaps I am seeing this too simplistically, but it would appear that logic to avoid compression braking on FWD (which is only hazardous in snow or rain) would be be better determined by using the same logic as ABS - if the front wheels are turning more slowly than the rears, then the front wheels are slipping, and only then shift the transmission to neutral. In other words, all this "safety logic" should be set to kick in at certain thresholds, not all the time.
I was reading an old 2002 copy of a Car and Driver road test of a Lexus IS300 and LS430 and they mentioned this hesitation in both vehicles, so I don't think this affects only Toyota's FWD vehicles. Is it really intentionally implemented to avoid FWD compression braking or for some other reason?
#2209 of 5646 Re: Play it again..... [alan_s]
Oct 18, 2006 (5:04 pm)
When braking, most especially severe/panic braking, the front wheels, accounting for the majority of braking, almost ALWAYS turn slower than the rear. That's why ABS is disabled when the center diff'l is locked on a 4WD/4X4.
The ABS control firmware "watches" the rate at which each individual wheel is slowing due to braking and if one, two, or all slow faster than a target rate based on initial entry speed, vehicle weight, etc, the wheel(s) with impending lockup has/have the brake released momentarily. All this is happening hundreds of times per second so the relatively slow shifting transaxle would have had to be in neutral as soon as the brakes were applied.
If the transaxle could be shifted into neutral in as short a moment as the ABS' electric solenoid can release brake pressure then yes, your idea would work.
There are really two desparate times, instances, wherein upshifting will occur that might result in the need for a following quick downshift.
The first and foremost of those we have all encountered virtually forever, or for at least as long as automatic transmissions have been around. That is when it is the driver's actual intent to entry cruising mode, simple drive along at the currently attained speed. Now think about how few times you do that and then suddenly, quickly, change your mind and decide you wish to accelerate, quickly, no less.
Rare, yes, but those do occur.
Prior to the adoption of this lift-throttle upshifting technique I am quite confident that most if not all automatic transmissions, on FULL lift-throttle, would remain in the currently selected gear ratio. In the past FULL lift-throttle would almost always indicate a desire to coast down to a lower speed and most of us, for all that time, considered the resulting engine compression braking to be an asset, if we even considered, thought about it, at all.
What has happened is that these new transaxles quickly upshift on any lift-throttle situation. So if you intent was for only a momentary coastdown then now when you re-apply the gas you will oftentimes encounter the delay/hesitation.
Give us back our clutch pedal seems to be the only obvious solution.
Test drive a BMW X3 and "FEEL" the STRONG engine compression braking effect at 60 MPH in FULL lift-throttle.
#2210 of 5646 Re: Canadian TSB for I4 5 speed AT [jamiecar]
Oct 19, 2006 (6:45 am)
Hey guys..... had the ECM on my 2007 Camry reflashed yesterday afternoon as per the TSB that came out (in Canada on Oct. 18/06). The car seems to accelerate a little better but I'm still experiencing some hesitation. The "flat spot" that was evident when slowing down and reaccelerating has disappeared. I'm hoping the little hesitation that is left is just part of the "learning" process. I don't have the actual TSB number yet nor do I know the wording of it..... will let you know when I find out.
#2211 of 5646 Hmmm....
Oct 19, 2006 (9:51 am)
Just thinking out loud.
Why couldn't toyota use the DBW system to match engine RPM to current gear ratio/roadspeed upon FULL lift-throttle and thereby eliminate engine compression braking?
Adverse effect on FE so probably not.
Then again look how rare these instances seem to be, FULL lift-throttle coastdowns vs partial lift-throttle for entering cruising mode. If nothing else this technique could be used for the first few hundred milliseconds of FULL lift-throttle, thereby delaying the transaxle upshift, in case a quick return to acceleration is indicated.
But then how would drivers react to the resulting engine RPM "flare" during FULL lift-throttle events?
#2212 of 5646 Re: Hmmm.... [wwest]
Oct 19, 2006 (5:13 pm)
#2213 of 5646 Re: Camry's accelerator software [captain2]
Oct 19, 2006 (5:19 pm)
Agreed - what a mess Pat made of the Avalon forums, sorry Pat nothing personal. It is like trying to read a phone directory and I'd rather not.
#2214 of 5646 Time for the car to "learn" its driver
Oct 19, 2006 (8:40 pm)
I spoke to the service manager at my Toyota dealership today. I asked if he had heard of the TSB for the hesitation. He was genuinely
startled and said "for this model?". He had not realized the 07 Camry had the problem. Then he said that he believed the car took about 800-1000 kilometres( this is Canada, so divide by 1.6, or 500-600 miles)to learn the driver's style, and he suggested that instead of the gentle break-in I have begun that I drive as aggressively as I normally would so the car doesnt think it has a wimp at the wheel.
I did that for the rest of the day - much more fun. No hesitation so far.
Also, this wouldnt apply to most of this forum's readers but he added that many people with automatic transmissions never use the gearbox and have no idea how much more responsive the car can be.
He drives the V6. I rather wish I did.
Hope this info may be useful.
#2215 of 5646 Re: Time for the car to "learn" its driver [workingstiff]
Oct 20, 2006 (3:24 am)
i'm fairly sure the "learning" which is done is done pretty quickly. it would have to be this way, otherwise the multiple driver problem arises... i would think classification of the driver would happen within a few stop-and-go cycles.
now then driving it agressively may help short-term learning by classifying you in a such a manner as to counter-act a suspected lean condition on quick throttle application - and perhaps mitigate the hesitation, but that would mean you'd be contradicting the whole effort to improve FE with the smart programming.
but - if your vehicle is more responsive, till they get the programming refined, maybe you've got a workable solution.
i'd wager people with the problem would gladly toss the extra MPG or two to have a responsive vehicle.
i highly doubt people with ATs are gonna embrace using the shifter. i think that's a bad idea for most folks but if it works for you... you don't know if it may have transmission longevity consequences though.
interestingly the manufacturer and some dealer reps seem to have been advising drivers to take it easy on the accelerator. you're service manager's advise and your observation is a bit contrary to the tide.
it therefore may be very helpful to others. let us know how it goes.