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From: Bob Cooper on 16 Jul 2010 05:55
In article <b2648f19-54f7-4d7e-b8e2-
af76934b592c(a)r27g2000yqb.googlegroups.com>, drnwnr(a)hotmail.com says...
>
> 2006 Corolla, when it's downhill and I press the brake pedal above a
> certain braking power, it shifts down the transmission. I was trying
> to figure out if that's a feature of the transmission and how does it
> know that the car is travelling downhill.
> It's probably intended for adding engine braking but sometimes it's
> just annoying since revs go up and it strains the engine and
> transmission.
> BTW, no down shifting when braking on a level road.

It's called "grade logic control." Sometimes "grade logic system (GLS)"
Below is a Honda description. Looks like they tout it more than Toyota,
and have used it longer. Standard on autos since 1997.
Here's a Toyota reviewer reference to it for the 2005 Camry.

http://toyotabuyersguide.theautochannel.com/news/2005/03/24/020359.html
"Perhaps the most important upgrade is to four-cylinder models - a new
five-speed automatic transmission with electronic grade logic control
replaces the old four speed, for improvements in both performance and
economy."

Looks like your Corolla got a version the next year.
Personally, I like making the shift choice myself.
There's a big honking shift lever for that.
I would also find that Corolla shifting annoying.
My GM car freewheels down long, steep grades, exceeding the cruise speed
setting. A little braking takes care of that and the trans never
shifts.
Fine with me, since I'm hardly ever on those grades.
But a case can be made for its usefulness to downshift while in cruise
control.
Some who often drive grades often might like grade logic to keep cruise
control working.
You might make a case for using it on heavier vehicles which tow, as a
safety feature.
And when you think about it, a properly and quickly working system
should reduce braking distances in emergency stops done when in 2nd gear
or higher on any car.

But I like having the choice whether to use brakes or a lower gear to
maintain speed.
You should complain to Toyota.
At least they could put a disable function on the nanny shifting
for those who find it annoying or worse, or refine it somehow.
There are plenty of complaints about it, and some who like it.
Others start out not liking it, but quickly adjust to it.
Like all complexity added to control systems, errors occur.
Excessive engine braking while approaching a stoplight is one complaint
that is too common.
Here's a few Honda complaints, probably caused by bad programming or
sensors.
http://www.aboutautomobile.com/Complaint/2008/Honda/Civic/Automatic+Tran
smission



***********************************************************************
Grade Logic Control
To reduce gear "hunting" and unnecessary shifting, Grade Logic Control
and Shift Hold Control systems are integrated into the shift programming
of Accord automatic transmissions. Grade Logic Control alters the 5-
speed automatic's shift schedule, reducing shift frequency while
traveling uphill or downhill. Using inputs monitoring throttle position,
vehicle speed and acceleration/deceleration, Grade Logic compares the
operating parameters with a digital map stored in the transmission
computer. When the system determines the Accord is on a hill, the shift
schedule is adjusted to automatically hold the transmission in a lower
gear for better climbing power or increased downhill engine braking.
From: Clive on 16 Jul 2010 14:26
In message <AkN%n.33667$Ls1.25198(a)newsfe11.iad>,
=?iso-2022-jp?q?Hachiroku_=1B$B%O%A%m%=2F=1B=28B?= <Trueno(a)e86.GTS>
writes
>It should be freewheeling. The only time it should downshift is when the
>rpms and the speed gets below a certain level, and I'm not sure what that
>would be for your car. It seems you should be going fairly slow before the
>trans downshifts.
>I would have the operation of the trans ECU checked.
I don't know about the US, but I'm pretty sure that free-wheeling is
unlawful in the UK. You'd certainly fail your driving test if you
selected neutral before coming to a stand and engaging the hand brake.
--
Clive
From: Hachiroku ハチロク on 16 Jul 2010 14:58
On Fri, 16 Jul 2010 19:26:03 +0100, Clive wrote:

> In message <AkN%n.33667$Ls1.25198(a)newsfe11.iad>,
> =?iso-2022-jp?q?Hachiroku_=1B$B%O%A%m%=2F=1B=28B?= <Trueno(a)e86.GTS> writes
>>It should be freewheeling. The only time it should downshift is when the
>>rpms and the speed gets below a certain level, and I'm not sure what that
>>would be for your car. It seems you should be going fairly slow before
>>the trans downshifts.
>>I would have the operation of the trans ECU checked.
> I don't know about the US, but I'm pretty sure that free-wheeling is
> unlawful in the UK. You'd certainly fail your driving test if you
> selected neutral before coming to a stand and engaging the hand brake.

Not frewheeling that way, but the clutch packs allow the transmission to
spin more freely until certain revs are attained, and then the car
downshifts.

If you're doing 50MPH down a hill, the trans should stay in the highest
gear.



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