mmarshall

Makes you wonder if the engine will end up lugging in some of them. Automatic transmissions, of course, are supposed to kick-down under a set-amount of pedal-pressure to prevent lugging and give better acceleration, but some are much-better at it than others. The taller the overdrive ratio, of course, the more likely lugging is to occur if a downshift does not occur. That's also why many automatics today have sport-shift manual levers/paddles.

Sulu

Why develop automatic transmissions with a greater range of gear ratios instead of continuously-variable transmissions (CVT)?

Planetary gearset automatic transmissions are old technology so it is easier to develop new ones with greater number of ratios: just add planetary gearsets. All transmission manufacturers know how to design planetary gear automatic transmissions to fit from the smallest FWD super-minis to the largest RWD full-size premium cars, so technology is not a problem. The problem would be shoehorning everything into a compact, transversely-mounted FWD transaxle, but ZF will be introducing a 9-speed transversely-mounted FWD transaxle very soon, so a 10-speed FWD transaxle may not be that far off.

No manufacturer, however, has yet to introduce a CVT that can handle the torque of larger engines. The highest capacity CVTs are the ones used by Nissan on its 3.5-litre V6 engines. There are other CVT designs being researched, but the common one now is the pulleys-and-belt type: a metal band (belt) strung between two variable-diameter pulleys. As the diameter of one pulley gets larger, the other gets smaller, to vary -- infinitely -- the drive ratios between two limits. Because of the lack of toothed gears, great torque inputs (the limit seemingly being roughly the 270 ft.lb of torque of the Nissan 3.5-litre V6) will cause the belt to slip.

If any transmission manufacturer squeezed 10-speeds into the gear range of the current 6- or 8-speed automatic transmissions, that may be overkill, but if they used it to extend the range from an ultra-short 1st-gear to an ultra-long 10th-gear, you could theoretically have both low-end power (great torque magnification with the ultra-short low gears) AND high-end fuel economy (with the ultra-overdrive of the ultra-long high gears). Automatic transmissions with greater than 6 gear ratios should probably come with sophisticated computer software programming that allows the transmission to skip gears when downshifting (Mercedes-Benz' 7-speed automatic can skip gears when downshifting for greater engine braking), and possibly when upshifting also. Needless to say, the programming should also allow for 2nd- or 3rd-gear starts to prevent wheelspins in winter conditions (this is common now).

Planetary gearset automatic transmissions, being older, proven technology, will be cheaper to develop into greater numbers of gear ratios. CVTs, being relatively newer technology, will be more expensive to develop, especially for larger, more powerful engines.

Blackraven

Man, with the way things are going, it looks like automobile gearboxes/trannies are going the way of trucks and bicycles.

Haha so introducing the MY 2044 Lexus LS460 with 40-speed automatic transmission............by SHIMANO (with three gears for reverse :P)

P.S.
@Sulu

You're right though about how the challenge for current CVTs which is with regards to how much torque the unit can handle. The highest I've seen are those used by Nissan in the Murano Z51 with all-wheel-drive (as a stand-alone system) or the one used in the Lexus LS600 hybrid (which is a mated link-up with hybrid propulsion system).

Oh btw, I forgot about the Toroidal CVT





It was produced by Jatco (a wholly-owned subsidiary of Nissan Motor Corp.) and was said to be the pinnacle of CVT technology back in the day.

It was touted as the WORLD'S FIRST EIGHT-SPEED CVT (March 2002) when it made its debut on the V35 model range

Nissan Skyline 350 GT-8 (Japan)


http://www.autoexpress.co.uk/carrevi...yline_gt8.html

It was the very first application of the TOROIDAL CVT in any 21st century automobile

mmarshall

I don't know of any bicycles with automatic trannies. Do you?

ydooby

There are quite a few actually, first invented in 1974. Here's a 3-speed auto bike that you *could* buy between 2007 and 2009 (not sure why it isn't sold anymore, as it won awards when it made its debut).
http://www.trekbikes.com/us/en/bikes/2009/archive/lime
http://www.youtube.com/watch?v=hi17HhgRaRg

*Batman*

This doesn't make sense to me. At that point you may as well have a CVT.

scgt652

That is actually a noticeable problem with Hyundai's new 8 speed transmission.

rominl

iTrader: (4)

well when ls460 debut a lot of people said that about the 8 speed too

ydooby

Yup, and now when everyone has 7 or 8 speeds people (myself included) start saying 6 speeds (on the new GS350) just aren't enough.

Sulu

Blackraven: Toyota and Lexus hybrid vehicles (e.g. Prius, Camry Hybrid, Highlander Hybrid, RXh, LS 600h) do NOT use a real continuously-variable transmission (CVT). It is neither a belt-and-pulleys CVT nor a toroidal CVT.

In fact, the Hybrid Synergy Drive is not available with a conventional variable-ratio transmission (you cannot change gear ratios with either the stubby gearshift or on-the-floor gearshift lever). It only seems to operate as a CVT because the gasoline engine always spins at a constant, most-efficient RPM. The Power Split Device, which is the HSD's transmission, controls road speed with an electric motor, which is always connected to the drive wheels -- if you want to go faster, the computer directs the electric drive motor to spin faster. The gasoline engine is NEVER directly (mechanically) connected to the drive wheels, unlike in a normal car (with or without a CVT). Because the gasoline engine is never connected to the drive wheels, it can spin at a constant, most-efficient rpm, just like a car with a real, continuously variable-ratio transmission, regardless of the road speed of the vehicle. The PSD allows the gasoline engine to add torque to the electric drive motor when needed.

On the topic of multi-speed bicycles... Despite being called 10-speed or 15-speed bicycles, they are really 5-speed transmissions with a low-range and high-range (10-speed), or a low-range, medium-range and high-range (15-speed) secondary transmission, just like true 4WD trucks have a second gearbox that offers a low-range and a high-range. But how many people really use all 10 (5x2) gears on a 10-speed bicycle? If a normal FWD or RWD car offered 10 gears through a primary 5-speed gearbox and a secondary low- and high-range gearbox, how many people would use all 10 gears? I am willing to bet that most people would just stick to high-range, thus limiting themselves to 5 gears only.

Finally, Hyundai may be designing a 10-speed automatic transmission merely to prove that they can do it (they are still trying to prove to the rest of the world that they are serious, modern auto manufacturers). But just because you can do it does not necessarily mean that you should do it -- or have to do it.

adamls2

as if the 8-speeds I have already are not mind boggling enough :/ for me 7 speeds is perfect. One of the only thing that i dislike about my car is that it is more confused than an experimental teen-age boy...BUT, I have noticed that over the course of driving through the decades that cars have been getting better and better therefore we tend to cruise at higher speeds which is really helpful when you have an extra few overdrive gears to save on MPG's and wear on the engine...so lower RPM's at higher speeds = the solution. i guess the 10-speed will be very helpful on the autobahn?? depends on the gearing