AutoblogGreen

There is another type of continuously variable transmission, one that uses one or more planetary gearsets and two motor/generators. It is the heart of full hybrids from Toyota, Ford, Nissan, and the GM dual mode hybrids.

The planetary geared CVT has several advantages over cone-and-belt CVT, including higher torque handling, fewer moving parts, less wear, greater durability and much greater reliability.

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I think that it's the best transmission type to match to an hcci( homogeous charge compression ignition )engine as the engine operate at a steady rpm. So hcci + cvt can increase fuel economy 30%-40% with good drivability.

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Speaking of reliability: you can tell Nissan deals with the French.

I mean, sure they throw a ton of great features for the amount of money your forking, but they've been having terrible reliability problems lately.

From what I read, the Versa is the least reliable 'subcompact' (it competes in that segment, even though it really isn't one) you can get.

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CVTs are popular in Japan is because they are cheaper to build than conventional ATs. New cone ring designs from e.g. GIF should be cheaper than the better-known belt-and-pulley systems pioneered by DAF. Manual transmissions are not popular in the Japanese market, in part because of the near-permanent traffic jams.

It is, however, a misconception that CVTs necessarily maintain constant engine speed - that's just one of many possible control strategies. HCCI does not require constant engine speed.

The primary customer gripe to belt-and-pulley type CVTs is the 'rubberband effect'. Most people are used to hearing an engine speeding up at the same rate as the vehicle does, with step changes in the frequencies during gear shifts.

With an optimally controlled CVT, the transmission ratio is adjusted instantly in response to allow the engine to speed up before the vehicle does. This 'slide-down' is analogous to the discrete kick-down of a conventional AT during hard acceleration events. This lets a smaller engine deliver the desired power level. The acceleration is smooth and instant, but the higher pitch and volume of the engine sound advertises the cheapness of the solution.

Since Japanese consumers who cannot prove they have a parking spot of their own are limited to the kei car market and its 660cc displacement limit, they have learned to live with the rubberbanding effect.

Kei car engines typically feature 3 or 4 tiny cylinders and therefore suffer from relatively high losses due to heat transfer into the coolant. Switching to parallel twins with inertial compensation (cp. Rotax 804, used in the BMW F800 motorbikes) would increase cylinder size.

In Europe and the US, CVTs could be used to optimize a 1.0-2.0L engine's operating point for any given desired power level wrt fuel eocnomy.

Intelligent sales & marketing could persuade consumers to associate rubberbanding with efficiency and hygiene (low CO2 emissions) rather than cheapness. The message would be easier to convey if the accelerator pedal - currently linked to torque - was redefined as a power pedal, providing direct feedback on fuel consumption. In addition, maintaining high power levels would require drivers to maintain an uncomfortable foot position, so for high-speed cruising they would engage cruise control. Frequent acceleration events at autobahn speeds guzzle a lot of fuel.

An additional trick would be to synthesize additional volume at engine order 0.5 to create the illusion of a bigger engine. Fortunately, that might not be necessary for engines with small turbochargers whose optimum speed for the typical low-to-medium power levels is anyhow at a quiet but sonorous 1500-2500 RPM.

Of course, automated/automatic transmissions with discrete gears could approximate the efficiency-centric control strategy described above.

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I'm more worried about longevity than road feel...but Nissan doesn't seemed to be concerned. I wonder if this expanded use of the transmission will hurt sales...especially since all the other manufacturers are dropping the CVT.

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