Transmissions speeds 4? 5? 6?

For a number or years, automatic transmissions have been mostly four speed. Now I'm seeing five and six speed, plus Nissan Maxima has a constant velocity on the '07 models (shades of Turboglide?)
In theory, the more speeds the smoother acceleration and ease of staying in a power range of the engine. In practice though, does it really make difference? Any thoughts on what is "best"?
--
Ed
http://pages.cthome.net/edhome/



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Edwin,
In theory, the best would be an electronically controlled CVT, where you have infinite ratios available and, by sensing engine load, throttle position, road speed, etc. get a "perfect" match of engine power to need, also taking into account fuel economy and emissions.
Needless to say, such a system would be complex and expensive. I'm glad to see Nissan bite the bullet and try that sort of system in the Maxima (though I'd not want to be one of the "test subjects" to try it out in the real world unless they'd guarantee that transmission for say 150K miles).
As far as conventional multiple speed transmissions, you have a trade off of added cost, complexity, the added weight of the additional gearsets and servos required to operate it as you increase the number of speeds VS the improvement in mileage and emissions the additional transmission gears provide. Modern electronics makes it easier: a silicon computer works much quicker and with less complexity that a hydraulic one can (electrons can move much faster than hydraulic oil, valves and springs).
One real-world example I could use is to compare the operation of a GM 4T60 with a 4T60E (drive a 1992 Buick Regal, then try a 1993: about the only mechanical difference between those 2 cars is the 1992 has a 4T60, which has no electronic control except converter clutch lockup, the 1993 has a 4T60E which has electronic controlled shifting) - gearsets and such are the same, but the 4T60E operates sooooooo much better. The later 4T65E better yet - even more of the hydraulic controls where replaced by software in the PCM.
. Also, the "hype factor" has to be taken into consideration as well - all the auto makers, both foreign and domestic, are in a game of "keeping up with the Jonses". Those marketing folks always want new and better things to tout and hate the idea that they don't have what the other guy is offering (or maybe something even better).
The old Chevrolet TurboGlide was a great idea conceptionally, but suffered in the execution due to the state of the art available in 1958. It was highly complex internally and a real bitch to work on. I've always wondered if the concept might fare better given modern computer-aided design technology, but I still believe that CVTs are the wave of the future.
Regards, Bill Bowen Sacramento, CA

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I pretty much agree with you, Bill. Making a durable CVT is a bit of a challenge, but I think of it in the same light as making a durable 4-wheel drive system. In the old days, 4-wd systems existed and were desirable but they wore out quickly, they used extra fuel, and needed a good bit of service. Now, they have largely been tamed.
Autotrannies can get better in just the same way, and they are much better today than they used to be , except for the occasionally runs of units which have not been well developed by the manufacturers in their haste to market.
My next car is going to be a manual transmission Volvo, and that doesnt disappoint me either. ( A new development, for me. I am coming out of retirement for a few years of foreign service, and this car is already leased and ready to go.) I will continue, I hope, to be able to keep in contact via these groups, and will let you know how it does.
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Let's talk about that some Bill. Since CVT is all about centrifugal force it is easier to keep the proper "gear ratio" simply based on the load placed on the engine. I'm not sure we would need as many of the electronic monitoring and control functions since the tranny is more self regulating than a multiple speed gearbox.
I'm wondering what the thing actually looks like inside. In my imagination, I'm seeing this large-ish snowmobile belt humming away...
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CVTs have been around in cars for many years. The DAF used a CVT in the sixties. They have been around at least since the thirties, on stationary engines, that drive machinery. It is only recently that technology as made it possible to use a CVT on engines that operate at higher RPMs
mike hunt

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The very same question ran through my mind lately Ed. The Nissan commercial brought it forward in my mind. CV transmissions are certainly nothing new and they are a pretty proven technology. I'm not sure if the technology has proven itself to scale up to car size applications but I suppose the Nissan will show whether it does or not. If I'm not mistaken, isn't there a Honda that uses CVT also? Seems to me that Ford tried this not so long ago also. It's certainly a much more simple transmission design.
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AWD Ford 500s and Freestyles currently have a CVT tranny.
mike hunt

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There have been a number of CVT applications around, and Honda is one of them, I believe.
One of the first designs I saw commercialized was the Dutch DAF unit, years ago. DAF was never popular over here, and the application was, IIRC, a rather low powered one, so I can't speak with any real experience to their durability.
I am not convinced yet that they are as durable as we, as consumers, will want, especially in the higher horsepower versions. And to say that they are simple might be misleading as well. But I do think that new designs and materials will eventually evolve that will make them attractive and less of a gamble.
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High winding engines are more fuel efficient and develops more HP. The Japs like to advertise the HP their engine produce. The problem with that however is the torque band and the HP band are too far apart. It works fine when one has a manual tranny and uses the gears to stay on the proper torque band but in the US most buyer prefer automatic trannys. If one does not keep their foot in the throttle, the vehicle dies on the grades. That is why the 4 cy Camry is a dog on the grades. To improve the situation the answer is more gears or a CVT. Many say the 500 is under power with the CVT. It is not, IF driven properly. When starting out with a CVT, or climbing a grade, one must floor the throttle to take advantage of the tranny ability to stay in the torque curve. If one simply uses part throttle, it is like starting out in a higher gear with a manual tranny. The Nissan commercial is deceptive. It shows the RPMs climbing, when it actually would be at it peak the way the driver is driving. ;)
mike hunt

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Thanks for the interesting replies

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The '05 Impalla 4sp 3.4L sure could have used more gears, the top gear was so high and 3 rd so far below it.
The CVT seems best if it stands up. It's only recently been used in larger more powerful vehicles. Volvo used it some years ago in a smaller car in Europe. Now BMW, Ford, Nissan and Chrysler (Caliber), plus others are using it. Ford's 500 application is slow because of the heavy vehicle with a smallish engine; the CVT isn't the problem.
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I would be inclined to agree, it would be a good set up, provided it's durable and has some provision for a "power" setting for when you are climbing grades, etc so it keeps it up at a higher rpm, since most 4 cylinders seem to thrive at 4000 and above. I would imagine you could make a real rocket out of it with a small block 350, but I doubt the CVT would last long behind one of those. But it seems everyone is trying to get larger hp numbers and better fuel efficiency, so they tune and tweak the engine more and more, to achive dyno results. However, real world dictates you seldom get something for nothing. While driving my gf's Acura TSX this is quite apparent. It has the 4 cylinder engine, rated for 200 hp. Meanwhile, it doesn't seem to have much more oomph than her 93 Accord 4 cylinder had unless you really wind it up, and there goes your fuel mileage then anyhow. So I fail to see the benefit. Only real benefit her 2006 TSX seems to have is a better shifting 5 speed, but while climbing hills in PA this past weekend I found the top gear severly lacking in power unless you were cruising at 80 or more, and to downshift to 4th with the sport shift option it ran the rpms up around 3500-4200 to keep about 65-70 mph. During which time, the instant fuel mileage gauge dropped below zero, while cruising on flat ground it was more like 35-40 mpg. So I think it could benefit from a little better spacing. But once again, never get something for nothing. I'll be curious to see if Nissans attempt is more successful with the aid of modern materials and computer technology. And what real world performance it delivers and what kind of MPG ratings go along with it.
Gus
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IIRC, Volv used the DAF unit I spoke of earlier.
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Super Turbine 2 speed in my 68 LeSabre seemed okay, back in the day. 350 - 2bbl V8.
harryface
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Harry Face wrote:

I meant more of a hi-po 350, like a semi race motor, kind of like a CVT version of a power glide in a strip car.
Gus
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