Nissan's "Hyper CVT"

[wedgepilot]

I recently drove a car with one of these, and I have to say it was "interesting". The engineer in me likes the idea of the engine staying at it's optimum point in the rev range for the job in hand, but it took a while to get used to. It also had a pronounced 'lag' while the engine moved to the required point in the rev range - I'd imagined it would be faster revving for some reason.

It can also be put into 'tiptronic' mode where it behaves just like a regular box, so I guess it's the best of both worlds.

Any experts out there who can comment on this setup? Is it more/less reliable than a more conventional box? Is it all it's cracked up to be? And if it's so good, why don't more manufacturers offer it as an option? Just curious.

Cheers,
Alan

[Sparks]

Sounds like a CVT (Continuously Variable Transmission). They have been around for years (Daf/Volvo had one, affectionately known as the 'rubber band' over 20 years ago).
Several manufacturers have them, including Ford, Fiat and more recently Audi, who have beefed it up to take more power. This was always the biggest drawback, and was limited to small, low torque cars.

Basic principal is a band linking the drive to a 'double cone' arangement, that varies the size of the output 'cog' to vary the ratio. Generally reasonably reliable, as the power outpus of CVT equiped cars was low. Audi has developed a much stronger 'band' which is available on some of their diesels.

I think there is extra maintenance involved, which outweighs the cost saving over proven auto technology that most use. I like the idea, as the power delivery should be smooth, stepless, and it hold the power/torque maximum. Takes some getiing used to (not that I have driven one) but I think it may be the way forward, if audi can get the costs down.

I am sure more technical discussion will be along soon


Sparks

>> Edited by Sparks on Tuesday 31st January 12:32

[Frik]

The "double cone" isn't the only method of CVT out there, but it is the most successful(!).

There are number of systems that seem to be constantly "in development" and have been for years. Torotrak anyone?

[d-man]

Williams tried a CVT in an F1 car back in the early nineties. Must have worked well as the FIA promptly banned it.

[Andrew Noakes]

I always thought Torotrak sounded a great idea. Another alternative is a hydraulic system with a central pump and hydraulic motors in the wheels, but there are problems with noise and efficiency, and perhaps unsprung weight.

A bigger problem is probably with customer acceptance. Most enthusiastic drivers will shy away from any sort of auto gearbox in favour of a manual, but a CVT with a good control strategy offers enormous performance gains.

[Pigeon]

Andrew Noakes said:

Another alternative is a hydraulic system with a central pump and hydraulic motors in the wheels, but there are problems with noise and efficiency, and perhaps unsprung weight.

This is an idea I like. I don't think efficiency is too much of a problem compared to a normal transmission, especially a "normal auto". It's a pity this development seems to have sunk without trace.