Kevin, I have often admired planetary gear arrangements. They look complex and are strangely beautiful compare to other mechanical systems. If I recall correctly, the Toyota Prius synergy drive system uses planetary gears systems. Is that correct?
Nope. That is one thing that is sort of on my bucket list of car repairs. I have done more car work than I would like to admit, but I have always stopped short of pulling an automatic. I have done manual's, way back, but never an automatic. Looks like a swiss watch. One of my co-workers fixed his Chrysler Caravan transmission, and he was quite pleased with his accomplishment. It had one planetary stage froze up, I think. It took some effort, but he got it going.
my experience is with older cars. We had a similar car (a Chrysler Town & Country) which had the transmission fail (after 12 years). We decided not to fix it (it was my wife's car and she needed something right away). It might have been interesting, though.
When I had the transmission rebuilt for my Dakota, the shop owner told me without Chrysler he would be out of business. If regular maintenance has not been performed, every minivan needs a new transission at 80,000 miles he tells me. So I asked him, why do carmakers design transmissions that cannot be drained and put filters where they are not readily changed?
I heard a lot of that. We had at least three and others we know had them and I never heard of one having the problem until ours. Now, we had lots of miles on that vehicle (well over 100K). I don't doubt that there were plenty that had problems, but they also sold a lot. At one point (and perhaps today) they had over 50% of the minivan market. Just about every family where I live had a minivan and a sedan, at least. It would be interesting to know what the relaibility numbers really were.
ttemple. In my younger days when I felt invincible, I tried pulling the transmission from my third-hand 4 door Ford. I enlisted a buddy of mine one Saturday morning to help me with the task thinking it would be a one day job. We actually did have an IPB (illustrated parts breakdown) of the transmission with all of the internal working parts. I'm going to make this short--three weeks later, we finally got the transmission back together. To our credit, it actually worked--the first time. We would go to class, work on the transmission, go to class, work on the transmission. You get the picture. The bottom line, never again. Never again. Excellent post Kevin.
I was responding to the statement that "almost every automatic transmission has planetary gears". I thought that it was quite obvious that automatics must have planetary gears. The only alternative that I have ever heard of was the "Funk-o-matic", marketed by the Funk transmission company back in the 1960's era. I think that it used air cylinders to shift a standard transmission, at least t5hat is what I recall.
Planetary gearsets have certainly been a very handy way to achieve multiple ratios at the best cost/weight/complexity point, and they will probably stay in the front for a while.
Those continuously variable systems seem to lack some of the long life that is found in the discrete-step systems, and I am not convinced that the CV is really needed. Yes, it is "cool", but is it worth the cost?
And by the way, my very first response was an attempt at humor. I won't make that mistake again.
Sorry for not picking up on your humor. Sometimes it is not obvious in written form. If we were talking face to face, I probably would have gotten it.
On the CV issue, it seems like the "new way" to deal with it is going to more "speeds" in the transmission instead of making it constantly variable. Chrysler went to 8 and 9, I think, and GM also stepped up to 8 or something like that. I suppose that this effort is evidence that keeping the motor at a good operating point is worth the cost of adding more and more gears. It also seems to say that the planetaries end up being more efficient than the stuff they have come up with for constantly variable versions.
I drove a car with a CV transmission once. It was strange sounding because the engine would stay at the same pitch, but the car would accelerate. It didn't sound like the car was accelerating, and it was hard for me to get used to.
I recently rode on a Chrysler 200 CVT, which I presume had a CV transmission, although I am not sure. It was very smooth, but then most expensive new cars are smooth, and this one only had 375 miles on it, about as new as can be.
If additional gars can be added to the transmissions without causing reliability problems then it should be a benefit, since the engines will indeed be able to have a smaller speed range. I do wonder about the weight of the package, though. And of course the new multispeed transmissions can only work with electronic controls. The original hydraulic analog computer would be way to complex for one of these.
One thing in the article that I missed is about that beautiful cutaway view of what looks like a hub-mounted multispeed transmission. That device would certainly be worthy of an article of it's own.
I have a 1920 Model T with the normal 2 speed trans with reverse. All planetary, plenty of parts and plenty of supporting documentation. Once I took one apart following the book, the design was very elegant, reassembly was simple and reliability has been excellent. My Dodge PU has needed 2 rebuilds in 5 years, I hired the first and did the 2nd myself. It is POSSIBLE to rebuild a modern automatic transmission yourself but it is not for the faint of heart, nor is it simple. A lot of reading and a little luck seem to be necessary. Some snap rings have a beveled and a flat side; it's important to keep little subtleties like this in mind because your transmission won't work properly if you have inserted one (of about 10) upside down.
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