CVT transmissions

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spider
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CVT transmissions

Post by spider » 16 Nov 2013, 18:27

I'm not aware of any PSA vehicles that use these (thankfully!)

I don't personally like the 'effect' of them, its a bit strange as there are no gears I guess merely a sliding cone or strap to generate a near infinite number of ratios, although the fact that they are high revving to initially move cannot really aid fuel economy.

I also note they tend to only fit them to smaller engines, possibly the torque of a larger unit would pull them to bits internally :D :oops:

Anyway I was thinking about this the other day, given the way they work in theory they could go as fast in reverse as forward no ? (not that I'd want to even try it!) :-k

Some info for the curious > http://en.wikipedia.org/wiki/CVT_transmission" onclick="window.open(this.href);return false; , there may be more detailed sources elsewhere.

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CitroJim
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Re: CVT transmissions

Post by CitroJim » 16 Nov 2013, 20:09

Indeed, they used to say the Daf variomatic would go as fast backwards as forwards..

Their take on the CVT actually worked very well but yes, it was odd how the engine revved constantly as the speed rose.

Given they all work on a friction drive basis I guess they are limited in how much torque they can transmit. A lot could make it slip I'd imagine.

Curious fact was that the Volvo 340 was originally driven by a Daf variomatic transmission and that was essentially a transaxle. The car biody was expressly designed for it so had no maningful transmission tunnel. When the manual 340s appeared they had a manual transaxle fitted so the bodyshell did not need any modification from that used with the variomatic.

AFAIK, all PSA cars have always used conventional automatics although there was much work done in the 60s to try and perfect a gearless hydraulic drive for the DS but it was not a success. Ditto the original Traction was inteneded to have a clever gearless drive but that never worked either. It was going to be produced and all the gearbox castings were already made for it when the idea was abandoned. The clever engineers managed to use the same castings for a conventional manual gearbox...

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Timmo
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Re: CVT transmissions

Post by Timmo » 16 Nov 2013, 21:18

Nissan used that on some of the micras if I remember correctly, do remember driving an auto micra that didn't ever change gear, guess was one of these!

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Re: CVT transmissions

Post by Hell Razor5543 » 16 Nov 2013, 21:24

David Coulthard tested one in the early 90s, but the FIA banned it;

http://www.f1fanatic.co.uk/2007/05/03/b ... ssion-cvt/" onclick="window.open(this.href);return false;

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mooseshaver
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Re: CVT transmissions

Post by mooseshaver » 17 Nov 2013, 09:47

Lexus use one on their LS600h. 5.0 v8 and hybrid.
I thought these boxes were always supposed to be at the right revs all the time and somehow better than normal autos?

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spider
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Re: CVT transmissions

Post by spider » 17 Nov 2013, 14:51

The Micra's are CVT from what I remember Timmo.

Jim, I do remember the 340 series were a bit strange in that the engine was front mounted and the transmission was rear so the "prop" was always turning as it was the link between engine and transmission. I guess for weight distribution purposes it may of worked well, not sure.

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Re: CVT transmissions

Post by isisalar » 17 Nov 2013, 14:55

During a short spell selling Nissans, sorry they were still Datsuns then, in the 70's, a Cherry model had some sort of semi auto gearbox which involved two settings, town and highway. After almost having an order cancelled while trying to explain how to use the box on handover I found it far easier to just tell the mostly elderly female customers to just leave it in the H setting. Never any comebacks.
I think this was some sort of CVT with a high and low ratio, at least that was what it felt like.
Those were the days, unbelievable reliability for the time, and then they'd crumble before your eyes at about 6 or 7 years old, sooner if they'd had any repair work done.
Bet there's not many Cherry's left on the road.
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CitroJim
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Re: CVT transmissions

Post by CitroJim » 17 Nov 2013, 16:47

spider wrote: Jim, I do remember the 340 series were a bit strange in that the engine was front mounted and the transmission was rear so the "prop" was always turning as it was the link between engine and transmission. I guess for weight distribution purposes it may of worked well, not sure.
That's it, a light alloy prop turning at engine speed.. A weakness as it had clamped splines at each end and if the pinch bolts worked loose it wore the splines and you ended up with no drive.

Happened to me and stranded us in Bicester. Damage to the splines was too bad to repair and the car was scrapped in favour of a Metro...

Which in turn led to a 405 and the rest is history...

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spider
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Re: CVT transmissions

Post by spider » 17 Nov 2013, 16:53

CitroJim wrote:
spider wrote: Jim, I do remember the 340 series were a bit strange in that the engine was front mounted and the transmission was rear so the "prop" was always turning as it was the link between engine and transmission. I guess for weight distribution purposes it may of worked well, not sure.
That's it, a light alloy prop turning at engine speed.. A weakness as it had clamped splines at each end and if the pinch bolts worked loose it wore the splines and you ended up with no drive.

Happened to me and stranded us in Bicester. Damage to the splines was too bad to repair and the car was scrapped in favour of a Metro...

Which in turn led to a 405 and the rest is history...
So you owe it all to the 340 then. Just kidding. :)

Worked out well in the end. Can't go far wrong with a good 405 (preferably XUD/XUDT) even these days if you get a decent one. Clutch is a right "£$£"$"£ on the later ones with A/C though, I remember it was one of the first clutches I did it took me hours and hours :oops: :oops: :oops: , not a nice "introduction" really.

Although very picky (but as you're looking at it, it annoys me) the facelift models the speedo and tacho fonts / styles on the instruments do not match which is a shame. The 205TD (with tacho like mine) did then again it was similar to the pre-facelift 405 design.

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nametooshort
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Re: CVT transmissions

Post by nametooshort » 23 Nov 2013, 21:25

I drove the volvo version of that CVT once and I found it really odd, its like driving one of those little mopeds, they use the same transmission.

It IS based on friction, but then again so is a conventional clutch, and conventional automatic transmissions are even worse since they have no connection between the wheels and the engine at all, apart from fluid (ok later ones have a lockup, but older ones mostly don't).

I guess, as transmissions go, the CVT is as close to perfect as you can get, its actually much more ideal in the way it works than manual or automatic transmissions, since assuming the transmission is correctly set up for the engine, it will always keep engine RPM at the either most efficient or most powerful point, depending on the position of the gas pedal.

Northern_Mike

Re: CVT transmissions

Post by Northern_Mike » 23 Nov 2013, 23:48

The modern CVT in my dad's Honda Jazz is a lovely gearbox. Seems reliable too, and has a flappy-paddle mode where it'll pretend to be a seven speed manual so one can play at being a racing driver on the Greek mountain roads, which ia fun for about 10 minutes.

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