# AC motors and automatic transmissions



## Richard Wood (Jun 27, 2008)

While I am at it, are there any issues in operating regen through an automatic transmission?


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## Anaerin (Feb 4, 2009)

Yes. Regen with an Automatic box is next to impossible. You know how you get negligible engine braking (Also called "Compression braking") with an automatic gearbox? Know how you can't push-start an automatic? The same thing will happen with your electric motor. I believe you can force some Regen if you manually select a gear, but then you're turning the car into a semi-automatic rather than an automatic.


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## Coulomb (Apr 22, 2009)

Anaerin said:


> Yes. Regen with an Automatic box is next to impossible.


Errr, really? I don't drive automatics, but surely once they are in a gear, if the torque direction changes, that torque goes through to the motor and regeneration happens.

From *The Reasons why Automatic Gearboxes WILL Work with EV's & how to do it..*:

"Regeneration: Yes, the wheels will backfeed torque through the transmission to capitalize on Regen if using the AC drive system and appropriate controller(s)."

Are you saying that an automatic transmission is likely to change to change down a gear when you take your foot off the accelerator pedal? Or just as the car slows down? Wouldn't that generate more regenerative current with the motor running faster? Or are you saying that it will shift down, and the sudden speed change will be too jerky?

Perhaps it depends if you keep the torque converter, and if it isn't the lock-up type, or hasn't gotten to top gear yet where the lock-up happens.

Sorry about the many questions, but I couldn't let the answer as above stand unchallenged, when it seems to directly contradict the thread linked to above.


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## JRP3 (Mar 7, 2008)

Some autos, such as in my RAV4, even down shift from overdrive when you hit the brakes which gives some compression braking. In any transmission higher gears will give you less regen but you can still get it with an auto.


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## major (Apr 4, 2008)

Richard Wood said:


> While I am at it, are there any issues in operating regen through an automatic transmission?


Hi Richard,

You have to know what you are doing. Always good advice, I guess  We did a 3 speed hydromatic with ACIM years ago. Lost the torque converter and used external pump. Had full regen. We really didn't know what we were doing, so kept burning up second gear clutches. Finally figured out that reverse torque on a band and drum will produce more force than the piston so the band would loosen and burn. 

Our solution was to only regen in third. This took an electronic circuit to sense gear selection and turn off regen. Finally worked great. We were controlling shifts anyway. So we just didn't downshift until we came to a stop. Regen worked very well in third anyway. At higher speed is where you get the most from regen. And our AC system had strong enough regen torque that it provided enough torque even in high gear.

So regen with automatic transmission is possible, although it may not be simple or easy 

Regards,

major


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## Anaerin (Feb 4, 2009)

Coulomb said:


> Errr, really? I don't drive automatics, but surely once they are in a gear, if the torque direction changes, that torque goes through to the motor and regeneration happens.
> 
> From *The Reasons why Automatic Gearboxes WILL Work with EV's & how to do it..*:
> 
> ...


AIUI, (When in "D"), when there is a difference between motor RPM and gearbox input RPM, the torque converter slips (This is assuming a non-locking, or non-locked torque converter). The less the difference between RPM, the less slip occurs. So, for instance, in an ICE, when driving down the road, if you take your foot off the accelerator pedal, the engine RPM drops to idle while the gearbox coasts at it's needed speed, with the torque converter slipping to allow this.


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## esoneson (Sep 1, 2008)

Also, let us not forget the infamous PowerGlide transmission. A small change to provide torque from the drive shaft to the motor. Done all the time in circle-track applications.

I'm not the tranny expert, but I agree with JPR3 that regen is probably not out of the question.

Eric


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## Richard Wood (Jun 27, 2008)

Thanks Major and all, 
Sounds like it may be that regen is possible but best applied selectively in the higher gears to save strain on the lower ones?
I'm agreeing any regen would be handy but don't have to get every last drop if it risks the transmission.
If one keeps the torque converter, when is the lock-up generally applied/released? Does it automatically release at a point that protects the transmission anyway?
I'm specifically wondering about the tranny in my 95 Honda Accord but let's keep in mind all readers.
And what about my broader starter question - what are the pros/cons of a combination of AC and Automatic? 
It seems to me that there are loads of automatic donors around and AC drives seem to becoming more price competitive.


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## JRP3 (Mar 7, 2008)

I wonder about the problem of using lower gears in an auto for regen with a modern transmission. Certainly I down shift my auto for engine braking at times with no issues, why would it be any different with regen? It probably depends on the specific transmission being used and how it's setup.


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