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Automotive Why not CVT? Its ingenious to say the least.

  1. Feb 25, 2012 #1
    Most of us are familiar with the continuously variable transmission. Disregarding reality for a minute, I think one should understand that the crucial components of making something (anything) turn at variable speeds requires that of a POWER SOURCE.. (engine) and its counterpart of a MEANS TO MAINTAIN OPTIMUM EFFICIENCY (transmission). correct me, if thats not as accurate as modern reality.

    I dont want to make this a broad topic as it could be so im sticking with the realistic truth. CVTs are used on snow mobiles, and a few cars today such as Toyota, Nissan, and Honda. All of which I have driven and show no sign of inconvenience when compared to the performance of most all other economical cars.

    The modern car engine is pretty set and stone, and apart from the hybrid scene, they seem to be doing fine and are getting more efficient/economic by the year.. But the question here is why have we invested so much study/application in the automatic transmission whereas the CVT hasn't been much of even a suggestion.

    As a part time technician in the field, i understand maintenance is rarely an issue just due to the far reliability of them in general. (Biggest wear and tear component being the belt.)
    And in essence, the CVT is a perfect solution for maintaining a precise optimum engine speed depending on the load of the engine... its gotta be perfect when put in combination with todays electronics of of strictly variable fuel feed depending on the cars physical state etc...

    The biggest problem i see is just the fact that todays CVTs are not durable under a heavy load. They havent yet been engineered (at least in mass production) in high performance vehicles which is another story alone.

    Any feelings? clarification? opinions?
    Iv discussed this with some techs in the field, and it just sounds like there's not enough money being put into their development due to the success of todays automatic transmissions. which are in my opinion (the most complex part of a car in engineering BY FAR).
  2. jcsd
  3. Feb 26, 2012 #2
    Costs more.
    Less reliable/requires more maintenance.
    Only really suitable for lowered powered models.

    European customers just don't seem to like it. CVT's sell well in Japan though.

    I've driven the CVT in the Honda Jazz. I really, really didn't like it, even in it's 'fake manual' mode. Where they make the CVT go in steps to emulate gears (defeating the whole point).

    The technical issues can be engineered out (apart from cost maybe), but the biggest factor over all is that noone is going to spend millions developing a gearbox that most customers don't like.
  4. Feb 26, 2012 #3

    jim hardy

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    Buick produced a hydraulic turbine CVT from 1948-1964 called "Dynaflow". I had one in my '49 Roadmaster.

    Performance wasn't much - a friend's 62 Buick with that huge V8 took 15 seconds 0 to 60....
    and my '49 with 320 in^3 straight-eight you clocked with a calendar.

    But they were smoother than silk, absolutely no shift..
    There's a few Dynaflow shop manuals on Ebay
  5. Feb 26, 2012 #4
    Ehh, "costs too much:" sounds like a market based answer. It just seems like the materials used are so much more simplified than automatic transmissions.

    I actually drove one today in a nissan maxima before aligning.. just the typical 3.5l found in most (PLENTY of power by the way... just saying), this thing was smoother than any automatic transmission I've driven. I personally find that many automatic transmissions are way too jumpy when shifts are taking place.. Sure the manual shift feature in the CVT is JUNK.. defeating the purpose, but i mean all it is is a slight reprogramming of the Transmission control module and an additional switch mounted in the center console- aka marketing gimmick in action.

    I mean, if only someone, for example those rich formula 1 teams would just invest some money in the engineering of CVTs, they could be big. They aren't high maintenance. They just may be more expensive to maintain when things go wrong, especially in the extremely common case that people don't replace their CVT fluid at designated intervals like they should. There is extreme potential for this theory of infinite gear ratio and manufactures haven't shown enough interest simply because in this day in age its just plain cheaper to bolt an automatic transmission to a vehicle.

    Anyone who has driven a cvt and doesnt have taste in them, probably feels this way just because of the lack of high rpm at lower vehicle speeds. Apart from the gradual increase in engine RPM as vehicle speed increases (giving the driver a feeling of having no control over engine speed whatsoever) this feature is almost JUST the same as an automatic transmission in the drivers seat, if not better, in the case of consumers interested in fuel economy as opposed to performance of course.

    its funny, its almost comparable to the transition from throttle cable to "drive-by-wire" (electronic controlled throttle) systems, in that after they made the switch with most all cars, due to the fact that the vehicle can better control fuel consumption. Just as a CVT may replace an automatic transmission. On the corporate profitability side of this theory, Today automatics are cheaper. but the value of the materials and complex parts and assembly is totally not. If you look in a factory service manual, the engineering of CVTs really isn't that complex. It took me Weeks in school just to understand how exactly the electronics decided when to make shift points, how fast to make them, and how much hydraulic fluid should precisely be sent to specific holding and locking components in an automatic transmission. Taking note to the fact that there is so much more susceptibility to wear and tear leading to ultimate failure than their is in CVTs.
    (This is disregarding my personal dislike in throttle-by-wire systems due to their slow response times. But later, of course, im sure they will be improved. They're still somewhat new technology to the decade.)

    Bottom line, I think there should be deeper investigation into this idea of CVTs.
  6. Feb 26, 2012 #5

    jim hardy

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    What mechanical arrangement do you forsee to provide infinitely variable ratio?

    BTW - i repaired computers too long to ever get in an automobile that has one in control of the throttle, steering or brakes. Transmission - maybe.
  7. Feb 27, 2012 #6
    cvts are banned in f1. Williams made one in 93.

    Bottom line is, manufacturers wont develop something with no market. In europe we like manuals, the us likes autos. So the two biggest markets are unlikely to shift.

    If driven sensibly the gains are only fairly small anyway. But there is no technical reason why we shouldnt all have cvts.
  8. Feb 27, 2012 #7

    Ranger Mike

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    The cost to develop a new product is a major factor in the introduction of new ( newer) technology. If the market is not there, you will fail. Note billions were dumped into the electric car and it is a huge flop.

    You have to know the market..American market now is 51 % women by population. Women can not dial cell phones and shift gears as easy in a manual trans car..ergo..the love for the automatic..me...give me a stick any time...
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