why so many multi speed automatics?

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The more gears the easier it is to keep the engine in its sweet spot whether for power of mpgs.
 
Originally Posted By: CT8
The more gears the easier it is to keep the engine in its sweet spot whether for power of mpgs.

I find it amazing though that there is any significant difference in MPG between a 6 speed auto and an 8 speed auto with a VVT engine? Or especially a turbo VVT engine...
For normal acceleration, the difference in average engine rpm, going up through the gears might be less than 100 more for a 6 speed than the 8?
I'd like to see some SAE papers on the difference in performance, both MPG and towing.
 
Originally Posted By: MCompact
I read an article that interviewed a BMW powertrain engineer, and at this point Munich is holding at 8 speeds; the ZF 8HP is an outstanding bit of design, and the engineer stated that adding a ninth gear might increase fuel economy by 1%- and that gain could well be offset by the increased weight that adding another gear would cause. The 6HP and 8HP boxes are the first automatics that I like just about as well as a DCT/DSG- and the first ones I found to be as responsive as the 1975 3HP22 in my '02.
That said, I still prefer three pedals in all but big sedans and SUVs.


Yep, BMW, Audi, Bentley, Jaguar, Mopar and others love that little ZF slushbox.

In my new Ram it is already yielding GREAT mpg and the most wonderful effortless feel to the truck. Short gears (3.91 posi) and two overdrives combined with awesome programming really enhance the driving experience.

IMO everyone should drive one before making all these suppositions about them. Truly superior to the older designs...
 
Originally Posted By: supton

On a tangent: how long do you expect that transmision to last? I've always thought those transmissions were good for like ever. Abuse aside that is. I've heard of doing in-frame engine rebuilds and whatnot; but never thought about the rest of the drivetrain wearing out. Different world from passenger cars!


As long as any other commercial truck transmission, at least that is not abused. I currently have 335,000 mile of this 18 speed factory rebuilt. It regularly gets workouts to 80,000 lb gross weights and fighting some hard pull hills here and there. Nary an issue. Don't expect one for a considerable time either.

Most times, drive train components on commercial trucks are a million mile deal. Except when abused by idiots. U-joints and axles seals will usually be the only issues.
 
Just wondering when the auto/pickup OEM's decide to go more for dual clutch automated manual transmissions since they are continuing to pile on the gears.
 
GM's newer 8L designs are very compact, so is the ZF. Allegedly this new 10 speed is also small. The 8L also shifts faster than many automated manuals.

Once a dual clutch design is rated for 400 foot pounds or more then the size and weight becomes a factor. Packaging issues are why the new Vette has the 8L90E instead of a dual clutch box.

As with any slushbox the programming is really important. Our new Ram can scarcely be felt changing gears, it is a wonderful programming job, very responsive and eager to shift down for you. The same trans has been panned in V6 apps...
 
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Has anyone ever felt like gears are only to make up for insufficient torque?
With enough twist and a wide, flat curve, you only need direct drive..
 
Originally Posted By: needsducktape
Its like Gillette constantly adding blades for a "closer shave"
The best razor I ever owned was the 2 blade Gillette Sensor, what are they up to now nine blades?!

Or adding megapixels to cameras...

At somepoint it is the law of diminishing returns.

My sisters 1993 accord with a 4 speed- returned AMAZING gas mileage... (And it was bulletproof)

Just sayin'


That 93 Accord must have better trans than a 95 Civic because I always thought that was the weak link on those cars. (Hondas)
 
Originally Posted By: edwardh1
why just recently do you see more 5, 6, 7 ? speed automatics? Has there been some break thru in auto trans design in the last 5 years that did not exist in decades past?


Quest for better city mpg's basically.
 
Originally Posted By: Olas
Has anyone ever felt like gears are only to make up for insufficient torque?
With enough twist and a wide, flat curve, you only need direct drive..


Well, an electric car would need but one gear.

Makes me wonder. I know the big rigs have run 13 and 18 speed trans for decades. You'd think they were headed for 20 plus if "more gears is better" was true. The tipping point must be before then.
 
Originally Posted By: Olas
Has anyone ever felt like gears are only to make up for insufficient torque?
With enough twist and a wide, flat curve, you only need direct drive..

The only car I've ever been in, which that may work, was a 2001 Viper... 1st is good for near 60mph and I suppose with a torque converter, you could run it 3rd gear all the time, but it would get like 8 mpg.
 
Packard did that. Fluid coupling IIRC, but it also had a lockup function. No shift shock. But somewhat thirsty and slow.
 
Originally Posted By: supton
Originally Posted By: Olas
Has anyone ever felt like gears are only to make up for insufficient torque?
With enough twist and a wide, flat curve, you only need direct drive..


Well, an electric car would need but one gear.

Makes me wonder. I know the big rigs have run 13 and 18 speed trans for decades. You'd think they were headed for 20 plus if "more gears is better" was true. The tipping point must be before then.


Diesels had a narrow "sweet spot" for horsepower and torque. Numerous gear ratios were required to stay in that narrow range.

Gasoline engines generally have a wide useful rpm range and don't need so many gears. The large number of gears in modern cars is an attempt to maximize fuel economy. IMO there is not much of a performance gain past a 5 speed transmission.
 
Originally Posted By: TiredTrucker
…….. I currently have 335,000 mile of this 18 speed factory rebuilt. It regularly gets workouts to 80,000 lb gross weights and fighting some hard pull hills here and there. Nary an issue. Don't expect one for a considerable time either………..


How often do you change gear oil in the transmission?
 
So the 2015 Silverados finally get 8 speed transmissions, and I'm just jealously sitting here with my 4l60e, wondering why trucks need more than 4 speeds.

4L60E---8L90E Gear ratios
3.06----4.56
1.63----2.97
1.00----2.08
0.70----1.69
--------1.27
--------1.00
--------0.85
--------0.65

Not sure if this is logical but I tried finding the avg gear ratio of some of the 6L90 gear ratios and see if it's similar to one gear in the 4L60.

4.56+2.97+2.08/3 = 3.20 would make up 1st gear, close to 3.06
1.69+1.27/2 = 1.48 would make up 2nd gear, close to 1.63 or 4L80 1.48
1.00 1:1 3rd gear
0.85+0.65/2 = 0.75 would make up 4th gear, close to .70

With todays transmission being so smooth and advanced shift logic, you probably won't notice the transmission shifting though 5 gears to get into 6th gear vs a built 4L60e with 2 neck snapping shifts into 3rd gear (direct drive gears.)
 
Nice to see "deep" gearing for first. Can run reasonably tall gears out back, taller than one could in the past. And I bet that will bump up mpg's better than say a 0.4:1 over drive pushing 4.56 gears -- have to figure the losses in the ring and pinion are not negligible.

Actually, I'd think getting the transmission into direct drive (1:1) would be best for mpg's. In a car that would make sense (RAV4's I4/4spd auto did that in later years, or nearly so). In a truck though I could see 1:1 in a lower gear so as to try to bump mpg while doing actual work. Less friction while hill climbing.

Although stupid tall gears that the vehicle can't push on flat ground might be nice for hill descents...

One question though: what is reverse geared at? Usually I think of reversing something big and heavy as the hardest work a transmission has to do.

*

Something I find kinda interesting is that while first gear is getting more deeply geared, top gear isn't. And, based upon complaints of double-downshifts in some of the six speeds, it's almost as if these transmissions are downshifting on hills like the old 4spds did. From OD to DD. When power is needed, usually it's more than a minor bump in rpms (since now it's so tall geared it's spinning slow indeed). I'm slowly gaining some respect for how the gear ratios for 4spds were decided on. [I realize it's more complex than just picking ratios, as both planetaries come into play, but you get the idea.]
 
Direct is more fuel efficient for general highway use, but not practical for many applications. I use an 18 speed manual in my commercial semi, tied to 2.64 diff ratio. I run in direct (16th) and the mpg improvement is documented. But it did require the 18 as opposed to the 10 or 13, because I had to have deep reduction on the bottom. I do not ever use the overdrives, but then there are parasitic losses when one steps up to the overs. By running in direct, transmission stays considerably cooler with heavy loads on long pulls on the hottest days. Not an ideal application for everyone, but it has done quite well for me up to the 80,000 lb gross weights I run.
 
I wish they'd put my dipstick back on (are u listening dipstick Jimmy?). I want to check the fluid on my DD but no dipstick. Although sealed, I don't know fluid level and how it looks/smells.
Doesn't make it easy to drain/re-fill fluid.

Having multiple gears, at least when I go from automatic to sport paddle shifting, at least in the dash cluster it tells me what gear I'm in (1st, 2nd, 3rd, 4th, 5th) but if in automatic, it's just "D" for drive, and doesn't say when in OD. Oh, when not in automatic, the "ECO" light never comes on no matter engine load.
 
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