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10475539 发表于 2012-3-31 21:44 
cvt 是否有问题？
http://www.dogandlemon.com/articles/automatics-cvt-transmissions
CVT Transmissions
Back in the 1950s, some automatic transmissions had only two gears. Two-speed transmissions were a pain, because when you were going up a hill you only had two options: first or second gear; it screamed in first gear or lost power in second. Then, as you went faster, the transmission was screaming because it needed an extra gear but didn’t have one.
Two-speed automatics were not only inconvenient to use, but they robbed the car’s engine of much of its power and drank fuel like there was no tomorrow.
You may never notice it, but your four or five-speed automatic suffers from the same problems as the two-speed one described above: it never gets the gears quite right. That’s why cars with conventional automatics never put out quite as much power as those with a manual gearbox and almost always use more fuel.
In the 1950s, a Dutch company called DAF came up with a new type of automatic transmission that solved the problems described above. Instead of having a small, fixed number of gears, DAF’s gearbox simply made up the gearing as it went along; the DAF transmission could change itself internally to produce a wide range of different gears, each one perfectly suited to the road conditions and driving style of that vehicle. The Continuously Variable Transmission (CVT) was born.
There are no fixed gears (e.g., first, second, third, and so on) in a CVT. The transmission simply invents the right gear at the right time. In theory a CVT is the ideal gearbox.
In practice, however, most modern CVT gearboxes suffer from the same problems as their ancestors: because they don’t have gears (like on the back wheel of a bicycle), many CVTs use belts instead, like the one that goes around your waist. The problem is, these transmission belts break, no matter how well they’re made. When they break, the whole transmission has to come out, generally for a complete overhaul at great expense. CVT gearboxes that use chains are better, but they still break.
The carmakers knew this when they put these CVT transmissions onto the market, but they also knew that most of the CVTs wouldn’t break until the vehicle was out of guarantee, meaning it wouldn’t be the carmakers’ problem. However, even that scam didn’t work: both Nissan’s and Honda’s CVTs have been subject to multiple recalls, some on almost-new vehicles. It’s possible that someone will eventually figure out how to build a CVT transmission that lasts as long as a conventional manual gearbox, but we’re not holding our breath. In the meantime, the evidence to date suggests that CVT transmissions can easily become a nightmare for car owners.
The fact that many CVT transmissions die young shouldn’t be your problem; the easiest option is to simply avoid CVT transmissions entirely! |
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发表于 2012-3-31 20:36:09
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