Quote:
Tim Cole wrote:
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. ... 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.
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.
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