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These new transmissions really are impressive engineering. The more speeds a unit has (up to a point) the more reliable the unit can be, and the better the fuel mileage.

If you look at the curb weight of some of today's vehicles it is significantly higher per square inch of volume than older cars. Mostly that's due to all the gadgetry being crammed into these pigs.

Having more ratios reduces stresses within the transmission. A case in point consider Turbo-Glide which sent all the torque through the same path. The thing was a disaster that blew apart under stress.

If torque is being split more ways the components can be made smaller and lighter. Computer control also reduces problems inherent in so many synchronous shifts.

The result is that my 20 year old modern car with less horsepower and weight doesn't do as well as the same price bracket pig being sold today which is heavier and has twice as much horsepower. However, recently I told one of the engineers they really need to figure out how to sell transportation because that market is underserved. I use a car to get where I want to go for the least hassle. If I hand my choice I would walk. Which I did for a while.

As for the Kimes book, I don't think that is an accurate presentation. The lock up clutch is there because the only way to handle the low efficiency of the unit was to use sharper vain angles which creates problems during coupling phase. Thus, the addition of a lock up clutch. Chevrolet got around this problem by replacing the original Powerglide (a total slush box) with a two speed trans. Buick added a second turbine with reduction to make Dynaflow acceptable. Packard still had torque converter only with a low range via the front sun gear. To get a three speed unit they needed a redesign using either a Simpson gear train or Ravigneaux set up like BW.

These new transmissions really are impressive engineering. The more speeds a unit has (up to a point) the more reliable the unit can be, and the better the fuel mileage. If you look at the curb weight of some of today's vehicles it is significantly higher per square inch of volume than older cars. Mostly that's due to all the gadgetry being crammed into these pigs. Having more ratios reduces stresses within the transmission. A case in point consider Turbo-Glide which sent all the torque through the same path. The thing was a disaster that blew apart under stress. If torque is being split more ways the components can be made smaller and lighter. Computer control also reduces problems inherent in so many synchronous shifts.

The result is that my 20 year old modern car with less horsepower and weight doesn't do as well as the same price bracket pig being sold today which is heavier and has twice as much horsepower. However, recently I told one of the engineers they really need to figure out how to sell transportation because that market is underserved. I use a car to get where I want to go for the least hassle. If I had my choice I would walk. Which I did for a while, and (for the benefit of the wise guys out there) it was because I lived within walking distance of work and not because I didn't have a driver's license.

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I don't know anything about sun gears, Simpson gears or Ravignequx --maybe you went to automatic transmission school?--but the Ultramatic torque converter did have two turbines. In addition, the Twin Ultramatic torque converters in the Caribbean and 400 were tweaked with special vanes ("sharper vane angles"?) (same Kimes reference, pg 588).

Speculation about "why" the lock up clutch was used doesn't seem to me to contradict the accuracy of the Kimes presentation of "how" the Twin Ultramatic shifts. The description is the way I remember it, and the quote doesn't seem to be making any claims for the trans that are not accurate.

The Hydramatic, when it came out, did have eight forward speed, so we are once again revisiting the mid 20th century for today's "improved technology" in automatic transmissions. Computerized shifting does make a lot of this more practical, I suppose, but it's still pretty amazing how much was accomplished back when vacuum and linkage did most of the shift point selection--along with your accelerator foot.

As an aside:
Personally, I think the newer computerized transmissions have a mind of their own and get confused a lot. "Smoothness" is still a big thing (one reason for the demise of the multiple speed early Hydra-Matic was all those noticeable shifts). The newer transmission I have experienced will sometimes balk, "thinking" it should stay in a lower gear, or else upshift too quickly through a gear it doesn't like during acceleration. (Usually a gear I like a lot.) In short, these transmissions seem harder to control with your accelerator foot, wanting to do things "their way." You pretty much have to ignore the tachometer and let the trans do what it wants, even if it doesn't suit you... because it'll be smooooooth, I guess. And I suppose the mfr will argue that the gas mileage is better that way, too.

I have a 2013 VW Beetle TDI with the 6-speed DSG and I find it to be most enjoyable and controllable. I can let it shift for itself in either of two modes, a regular and a sport. The sport mode moves up the shift points for more lively performance. And, I can shift it myself either on the steering wheel paddles or shift lever. A good marriage of an automatic- and manual-shift transmission. There is an expensive service every 40,000 miles for filter and fluid change.

(o{}o)

The second turbine in the Ultramatic was not the same as in the dual ratio Dynaflow. The second turbine in the Dynaflow used a planetary gearset to provide reduction. The second turbine in the Ultramatic was merely an attempt to compound the directed force. Modern torque converters don't use them because they are not efficient.

The need for the direct clutch to prevent problems during coupling phase is not a change in ratio. Without the lockout the converter will slip with higher power loss than a torque converter with lower blade angles. Buick used a solenoid operated two range stator to offset this problem. The so-called "Switch Pitch" Dynaflow would increase the angle for acceleration and reduce it for cruise.

A comparison between the original Powerglide and Ultramatic is shown below. Even after correction for the power to weight ratio, the Ultramatic torque converter is more efficient at low speeds and less efficient at high speeds. The forced lock out at 56 mph for the Packard means these figures are a comparison of torque converter efficiency. The Packard is faster at breakaway (even after correction for power to weight) but the Powerglide is more efficent the higher the speed. So the direct clutch in the Packard eliminates this problem.

...........1951 Chevrolet.................1951 Packard 300
.............Powerglide

Horsepower........105............................150

Weight...........3405...........................4380

LBS/HP...........32.4...........................29.2

0-60 mph High..24.84........................20.80
.Low and High..20.15........................18.30

0-30.....Low.....6.8............................5.4

Mileage at 60.....19...........................13.6


Hope this helps explain what is going on.

Quote:

Hope this helps explain what is going on.

Yeahhh, I think so.

Taken from your last post and an earlier one you made, I think these two quotes together give me a better understanding:

"Without the lockout the converter will slip with higher power loss than a torque converter with lower blade angles."

"The lock up clutch is there because the only way to handle the low efficiency of the unit was to use sharper vain angles"


I will rephrase them this way:

"Without the lockout (clutch) the converter will slip with higher power loss at increased speeds than a torque converter with lower blade angles."

"The lock up clutch is there because the only way to handle the low efficiency of the unit at low ("breakaway") speeds was to use sharper vain angles."

(I don't know quite why the Ultramatic "unit" itself was "low efficiency" to start out with, but I can live without that... probably has something to do with sun gears, or solenoids, or something else that's part of the graduate level course.)

So anyway, as I understand it, the Ultramatic vs the Powerglide gives "faster breakaway" because its sharper vain angles give it better torque at low speeds, but these sharp vain angles are not efficient at high speeds, hence, use a clutch at higher speeds.

I would expect that the sharper angle blades would become less efficient at higher speeds for the same reason that boat propeller blades with a steeper "pitch" give good torque off the line but start to cavitate (lose efficiency) as the boat speeds up. Whether it's water or ATF, flailing around in a churning liquid isn't efficient.

BTW, we used to call Powerglides "Powerslides" and Hydramatics "Slidramatics" although the Hydramatics were definitely better. That is, they were better for normal driving. Back in those days, Powerglides were often said to be the transmission of choice for dragsters that used automatics. Don't ask me how or why. (If we start talking about "stall speed" and stuff I'll probably go cross-eyed.)

It's interesting how many different ways automatic transmissions have been configured to do what they do. I seem to remember the Buick "Switch Pitch" torque converter was around for quite a while after the Dynaflow was history. Into the mid-'60s I believe.

The best automatic I've experienced in one of my own vehicles was a plain old 3-speed OD in my '96 Dodge Dakota. I knew WHEN it shifted, WHY it shifted, and I had decent control over HOW it shifted using only the accelerator. I could even feel it downshift firmly into second and first when slowing down to a stop. It wasn't rough, but you could feel it. I don't even know what Chrysler Corp. called it. It had to have had some computer controls, but they seemed to work very well, and the feeling was not that different from a good vacuum/accelerator controlled unit.

Tim,

Care to point out the holes in that last post for me? I hate to leave my mistakes unanswered, and a lot of it was conjecture. Sorry for the length.