How effcient are current automatic transmissions

[dadof275103]

I have just read that the Chrysler 904 Torque Flite is one of the most effcient automatic transmissions in use. Is this true?

How is this tested?

Are automatics still 4% to 6% less effcient than a manuel transmission?

Michael
dadof275103

 

[MikeHalloran]

Most of them have lockup torque converters now, so you're only faced with gear losses most of the time.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

Traditional automatics also have a hydraulic pump that's running all the time, to generate the hydraulic pressure that's used for holding the internal clutches engaged. Nowadays, this is a variable-displacement pump, to cut the parasitic loss to a minimum - but it's a loss that's not there with a manual.

Volkswagen's new 7-speed DSG with dry clutches is supposed to be equal in efficiency to a manual - no compromise. The 6-speed DSG (with hydraulic "wet" clutches) is really close. No torque converter on those. But even torque-converter-equipped transmissions can have good efficiency IF they have an aggressive lock-up program. The new transmissions with many closely-spaced forward gears (5 or more) don't need to unlock the torque converter to fine-tune the engine RPM, and they can use the drive-by-wire throttle to cover up variations in torque output that a torque converter normally masks when changing gears.

In many cases, if you go by the EPA ratings, the modern designs have negligible difference between automatic and manual.

 

[romke]

efficiency of automatic transmissions may vary quite a bit depending on the driving pattern. as mike and brian point out a lot of steps are taken to enhance the efficiency, but if the driver has a heavy right foot most of those enhancements come not into play, since the torqueconverter is heavily used without lockup. especially in urban driving and stop&go traffic the penalty may be still high and also when the "sports" type of shifting is selected by the driver. nevertheless, modern 5,6 or 7 speed tranmissions are more efficient then previous types with 4 or less gears. they will not however, as long as a torqueconverter is used as a flexible ratio component, be as efficient as mechanical or "robotosized" mechanical tranmissions like the VW DSG transmissions.

 

[dgallup]

I've seen quite a few vehicles with 6 & 7 speed automatics with HIGHER EPA fuel economy ratings than the manual gearbox. That may be a ratings fluke & your mileage may vary but obviously they have gotten very good.

I would not classify any DSG gearbox as an "automatic" even though they have taken over the shifting. Unfortunately, it is another case of language not keeping up with technology & being imprecise. When most people use the term "automatic" they are thinking "torque converter".

 

[GregLocock]

Yes, that's an interesting point. Sorry I'm feeling lazy, does anybody know how the shift schedule for manual gearboxes is set for EPA testing?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kchan711]

Hey Greg,

You may want to check out the following link from EPA on test procedures.

http://www.epa.gov/otaq/cfeis.htm

Kyle

Kyle Chandler

http://www.chiefengineering.net

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[ivymike]

When most people use the term "automatic" they are thinking "torque converter".

I doubt that most people even know what a torque converter does. When they say "automatic" they mean "I'm not shifting it."

 

[Warpspeed]

The later automatics with six or even seven available ratios, also typically have more aggressive overdrive ratios in the top two gears.

That alone will drop light throttle engine rpm when up to the required road speed. The transmission itself may be more or less mechanically efficient, but what probably matters more, is the overall package and how it is programmed to operate.

 

[patprimmer]

More and more ratios make the drive line more efficient, but I would expect a law of diminishing returns to apply.

On the other hand, more and more ratios increase weight and that decreases fuel efficiency in direct proportion to the overall weight increase of the car. There must be a crossover point where the extra weight fully offsets the extra drive line efficiency.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[romke]

the latest automatic transmissions with more then 5 speeds use a very sophisticated setup combining several planetary gear sets in such a way that both the number of physical gears and the required number of clutches and brakebands is less then in previous designs. this way the overal dimensions of a modern 6 speed automatic can be substantially smaller and lighter then previous designs with 4 speeds. therefore there is not necessaryly a weight penalty in using more gears. there is a tendency though to design more heavy vehicles to comply with various safetyrequirements and luxury wishes, and that usually takes the fuel consumption into a higher bracket, notwithstanding more efficient engines and transmissions.

 

[GregLocock]

Well, kinda, sorta. Engineering being the art of compromises it seems unlikely that a smaller, more complex, device will outperform in all respects, such as strength, for example.

Either way there is no doubt that the six speed boxes are more efficient that the 4 speed boxes, whether that is from better mechanical efficiency or better shift scheduling.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[BrianPetersen]

Local newspaper today had an overview of the new Mazda 6 in it, and for the 4 cylinder model, the auto-trans model has better Transport Canada consumption ratings (9.7 L/100 km city 6.7 highway) than the manual-trans model (10.4 city 6.9 highway). Both 6-speeds.

 

[GregLocock]

So my point about the manual shift schedules is that it seems to be defined according to the number of gears you have if I have not misinterpreted the last file on kchan's link, whereas for an auto you get to use whatever you feel is appropriate.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

About 6-speed shift schedules:

Camaros so equipped since 1992 have a shift lockout, with solenoids in the transmission, controlled by a computer, that forces a 1-4 shift instead of a 1-2 or 1-3 shift at certain speeds at moderate throttle settings. It's clearly intended to improve ratings in the EPA drive cycle (and briefly documented as such in the owners manual).

Some other upshifts are also locked out, but I've only hit one once that I know of; it feels like a really balky synchro.

The computer graciously illuminates a lamp (not prominently placed) on the dash to tell you what it's doing. If you don't notice the lamp and/or act soon enough, the 1-4 shift produces a major bog. Since ~1997, disconnecting the solenoid produces a check engine code and lamp.

Tactics to deal with the unmodified system include:
- Short-shift even earlier. The LS1 tolerates it; the LT1 was less polite.
- Wait 5 seconds (typically while coasting through an intersection with the car behind you still accelerating), at which time the lamp goes out and the transmission will go into the gear you want.
- Drive it hard, and you'll never see the lamp.. and never get near the EPA numbers.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

Corvette had the same idiotic system. They also had an 'interesting' attitude to the driveby noise tests. I learned a lot about Federal Government and big business on that program, can't say it improved my opinion of either.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[DSMer]

For off road use only of course...

http://www.pfyc.com/mm5/merchant.mv...Code=PFYC&Category_Code=VTUNDER&a_aid=froogle

 

[murpia]

Apologies if this is too off-topic...

There's mention somewhere above about variable-displacement hydraulic pumps in modern automatic transmissions. Can anyone point me to a link to a supplier?

Also, does anyone know if any modern shift strategies need to use PWM or similar control of hydraulics solenoids, maybe for shift smoothing? Or is the electronic side of the control simply on / off?

Thanks, Ian

 

[BrianPetersen]

I know that Stackpole (now a division of Gates) builds transmission oil pumps of many different designs, and I'm sure there are other suppliers.

PWM is widely used nowadays. A lot of the time, the line pressure is controlled that way. Sometimes the torque converter lockup is like this.

 

[Thecardoc]

Modern CVT's are achieving efficiency that exceeds even the manual trans-axles. Check out AUDI's newest design for the A6.