Auto transmission torque converter lockup

[OilUzer]

Assuming a 6 speed auto trans with torque converter (TC) lockup in 4th,5th and 6th.

Q1:
If you are in 5th and locked, and cruising on flats and not accelerating ... car shifts from 5th to 6th ...
Does it go from 5th & locked directly to 6th and locked? Is that mechanically possible?

Or does it go from 5th & locked to 6th & unlocked then 6th & locked. Or
from 5th and locked to 5th and unlocked then to 6th and unlocked then 6th and locked?

Q2:
I think for a downshift (e.g. From 5th & locked to 4th) the trans always unlocks since it needs the power.
For this example, it will go to 5th & unlocked the down to 4th & unlock. It that correct?

 

[SnowDrifter]

It's possible to shift with a locked converter. I know some of the big power guys do it, particularly diesels. But their transmissions are build to handle it

As to your case, I'd expect it would be a case of how the transmission is programmed to behave. Why do you ask?

 

[OilUzer]

Just curious how it works. I've always driven manual trans and not familiar with how auto trans works!

 

[tiger862]

I watch rpms and don't let torque converter kick in to early. Last car 4 speed with lock up at 46 and now my 62te is at 44. In a 45 mph speed zone I do 43 at 1500 rpm instead of 45 mph at 1000 rpm.

 

[supton]

Originally Posted by tiger862
I watch rpms and don't let torque converter kick in to early. Last car 4 speed with lock up at 46 and now my 62te is at 44. In a 45 mph speed zone I do 43 at 1500 rpm instead of 45 mph at 1000 rpm.

Why not let it kick in? Lower rpm, less fuel burn.

My truck likes to unlock rather than downshift. I guess it saves on trans wear... but there's a few hills where I can have lower engine rpm after a downshift. Less slippage means less heat which means less loss.

 

[DriveHard]

The auto's I own go from 5th locked to 6th locked or 7th locked to 8th locked.

Unlock when needing more power or downshifting.

 

[SnowDrifter]

Originally Posted by OilUzer
Just curious how it works. I've always driven manual trans and not familiar with how auto trans works!

Ahh


For for your average auto trans, inside you bell housing is something called a torque converter. It's what automatics use in lieu of a clutch. It's a fluid filled drum with vanes in it, with a fairly sharp speed-torque transfer coefficient. That's why you can idle with the car in gear without the engine stalling - and the little bit of drag present moves the car forward when you let off the gas.

Inside the torque converter is a hydraulically actuated clutch. Its job is to mechanically link the input and output of the torque converter together so its no longer slipping due to the nature of a fluid filled turbine. It improves thermal efficiency and as a result, fuel economy.

Inside the transmission itself, instead of finding a standard input and output shaft with gears lined up on them, an automatic transmission will generally favor planetary gear reductions. That allows the input and output to be kept inline. The gear selection is decided by actuating one or more of these planetary gearsets. Shifting / gear actuation is carried out by hydraulically actuated clutch stacks. They're not unlike a motorcycle clutch if you've ever had one apart.

Here's a cross section of a trans. You can see the planetary gearsets
https://www.allpar.com/photos/mopar/transmissions/ZF-8-speed/ZF.jpg

Another one that shows the torque converter a bit better
http://www.corvetteblogger.com/images/content/2014/071014_4.jpg

And the clutch packs
https://2k8ugo7vg0ythyc326851m1c-wp...ads/2016/10/72960-06K_ComboSonnaxWeb.jpg

 

[Linctex]

Originally Posted by tiger862
In a 45 mph speed zone I do 43 at 1500 rpm instead of 45 mph at 1000 rpm.


I do the opposite - - I push my F150 up over 45 MPH - then briefly let off the gas just long enough to get the computer to make the TC lock.

My truck makes plenty of torque and is happy tooling along at 1100 rpm at 45 mph.

I really, REALLY wish there was a "LOCK NOW" momentary button on the dash. My transmission shift points are always generally too high.

 

[KrisZ]

All of the mentioned combinations are possible, but it all depends on how the transmission is programmed. If the transmission is equipped with a strong clutch for the TC lockup, then shifting while locked is not a problem.

 

[Linctex]

Originally Posted by supton

My truck likes to unlock rather than downshift. I guess it saves on trans wear... but there's a few hills where I can have lower engine rpm after a downshift. Less slippage means less heat which means less loss.



Same.

What's strange is the different programs on cruise control, of by foot.

If I am operating the far right pedal gingerly, I can get over some pretty big hills without hearing the converter unlock.....
But with the cruise on, the computer unlocks it every little bump in the road, and i hate that. So I seldom use the cruise.

 

[StevieC]

My Highlander will bang through all the gears before doing the multi-stage lock-up if I'm moderate to aggressive on the accelerator.
If it's light throttle it will lock up in the lower gears past first gear. I think Toyota's goal with this transmission was performance when you want it but RPM limiting fuel economy as soon as possible.

 

[OilUzer]

Good info. Thank you all!

 

[tiger862]

I am old school. While lower rpm might mean fuel mileage it also means more wear. I've worked in dealerships most of my life and can't tell you how many times I've seen transmission problems from worn torque converter. The benefit of 1 mpg in city from lockup is not worth extra heat and load. If on open road no lights 45 mph speed zone I do 50 mph which I think is a better rpm for motor. If fuel mileage is what I am after then a.c. would be off. I have econ button that lets rpm drop with sooner lockups but shift points are not correct as engine is always loaded. Most of my driving is 35-45 mph and I tried to let lockup occur early just didn't like feel as it felt like i was pulling heavy trailer. I get 18 mpg with Caravan under these conditions.

 

[StevieC]

My Santa Fe had Multi-stage lock-up and did fine.

 

[PimTac]

The SkyActiv transmission on our Mazda has around a 90% lockup. My understanding is that just over 5mph it locks. I have found it to be the most responsive auto transmission I've driven. It always seems to be in the right gear for the situation and it automatically downshifts going down a hill or slowing to a stop.