it's all about gears!

[mcrews]

Drove my gf 2011 Lexus RX 350 for several days this week.
It has an 8 speed automatic transmission.

What a difference compared to the Kia's 5 speed automatic tranny.

Given my personal experience w/ upsizing to lower rpm and the joy of driving an 8 speed, I can't understand why the industry has been so slow in increasing the gearing in their eco-models.

I remember the 1984 corvette had the first 6 speed and got 27mpg on the hwy all day long.

I really thing 6-8 speed auto trannies are the secret to improving mpg.

[cbaber]

Auto's have come a long way, that is for sure. My gf's 1999 Sunfire has a 3-speed automatic for crying out loud. That thing is terrible.

You don't need all those gears to get good MPG. The reason they keep adding gears is because the more gears you have to use from 0-70 mph, the less RPMs have to build up to satisfy the average driver's need for acceleration. Lower RPM = higher MPG. It all comes down to building technology that forces drivers to improve their driving techniques.

[gone-ot]

Why 6-8 gears?

A stout, reliable CVT would have infinite-gearing possiblities, so would (theoretically) be better. Take your pick: cones, belts, planetary gears, etc.

[mcrews]

Originally Posted by Old Tele man

Why 6-8 gears?

A stout, reliable CVT would have infinite-gearing possiblities, so would (theoretically) be better. Take your pick: cones, belts, planetary gears, etc.

Despite being a BIG Infiniti guy...I know nothing about the cvt trannies

[usmclowrider]

Originally Posted by Old Tele man

Why 6-8 gears?

A stout, reliable CVT would have infinite-gearing possiblities, so would (theoretically) be better. Take your pick: cones, belts, planetary gears, etc.

I'm with you on the CVT. I love driving the wife's Civic Hybrid. No jerky shifts, when I'm cruising it never goes above 2k rpm except up hills and I think they are just plain fascinating. I don't know why more companies aren't using them.

[user removed]

CVTs basically are two pulleys with a connecting belt. Both pulleys are adjustable as far as width. One pulley gets wider as the other gets narrower thus changing the ratios. Although the ratios are infinite between the two extremes there is a limit as to how low and high the ratios can be.

My invention is much closer to an infinitely variable transmission. Theoretically the top ratio could be almost infinite, then zero (neutral) and reverse, by changing the stroke position alone, no clutch or torque converter, your start in a super high ratio then reduce the ratio (in milliseconds) to get moving and reverse the stroke, which has to go past neutral to reverse which reverses the flow of fluid in the high pressure circuit and is captured for future acceleration events.

US#7677208 the full document is on the web.

http://www.google.com/patents/US7677208

regards
Mech

[Cobb]

8?!?!?!? And I hated 4 speeds as they often hunt between 3/4.

+1 on the cvt and ecvt. I never find myself between a gear too high or gear too low. I also like puzzling my passengers as to why my car never shifts gears.

[mcrews]

remember it is an automatic.
It actually shifts effortlessly. and when I'm on the freeway and need power....it just goes!!!!
never feel the downshift.

[Thenorm]

reading a review about the new Cherokee with teh 9 speed. they said they never saw it engage 9th and that it doesnt even come into play on the EPA cycle (has to be down hill, low throttle above 70mph or something rediculous)

so maybe we've hit the limit of # of gears?

[gone-ot]

To be HONEST, I was (previously) NOT a CVT fan, however, since getting our '14 Prius with eCVT, I've sudden had to learn MORE about them, and, in-the-process, have become to believe they're definitely OK...especially, the eCVT, in this Prius.

Instead of the normally thought-of dual "cones & belts" CVT, the eCVT is actually a planetary (ring, idler, and sun) gear arrangement, so the gear 'teeth' are ALWAYS engaged...so, unlike the "cones & belts" system, physical "slippage" is totally NOT possible, unless something is broken.

The PriusChat (PC) forum has a neat animated illustration of *how* the eCVT works:

• PC thread: http://priuschat.com/threads/toyota-...ission.127864/

• animation: http://eahart.com/prius/psd/

• CVT history: http://groups.engin.umd.umich.edu/vi...Miller_W04.pdf