The Technical Questions Thread

[f6fhellcat13]

CVTs seem to be a bit of a conundrum for car companies. On the one hand it should be possible to make a CVT that's more efficient than any other kind of gearbox, because you can (in theory) always maintain the most efficient revs for the task at hand. It should also mean that you always have power when you need it, for the same reason. The 'box will just be where it is needed. On the other hand, you have the focus groups telling the marketing department that CVTs are weird and no one wants them, so the budget goes to making 8/9/10 speed autos instead, now that CVTs with a setting that emulates a conventional gearbox haven't worked.

From an enthusuist perspective I appreciate that manual, conventional gearboxes add to the fun of driving, but I don't see why CVTs aren't being developed for things like a Merc S-Class or a Roller, where smoothness is key and the engine is not there for fun. Or for a Smart type application, where economy is king [and the extant gearboxes suck anyway]. People seem fine with scooters, they've all had CVTs for years.. why not all small city cars?

I agree entirely. They also seem like they would work well on diesels with their more-limited torque band.

The only problems I'm aware of are that CVTs can't handle oodles of power and I would assume, but I have no basis for this, that CVTs are less-efficient than other gearboxen that we've had almost a century to perfect and optimize. I guess the only reason I think they're less efficient is that I imagine the internals are all squidgy, soft, and loose. I know they aren't actually, but I think of them as being so.

EDIT: It seems that a Japanese tank features a CVT, so maybe they can handle larger forces? Though, I could swear that I remember reading that they cannot.

[Ferrer]

Nah, sometimes they publish stuff from their forum (or whatever it's called) to the front page. They're a bit too much the stereotypical American car fans of the internet for me; everything is wagon this, or 883cc diesel hatchback that, and moaning about how everyone else gets everything cool.

I have to say, you people in North America, make me laugh.

Having said that, over to the topic in hand.

First of all the manual will still take decades to be erased completely. It will possibly happen at the same time cars stop using petrol as fuel.

As for CVTs, yes in theory the idea is brilliant, but in the real world it doesn't seem to work as well. They are not especially smooth at low speeds and if you want a lot of performance you get a lot of noise, which would be odd in a luxury car. I have tried them with a diesel and even there it's a no go.

Some city cars have them, mainly Japanese ones for some reason, but I guess the reason why they haven't caught up is quite possibly cost. In a cheap car prices are key and I guess that it is much cheaper to offer an automated manual (structurally the same as a conventional manual) than a CVT. By the way, automated manuals are ludicrously awful and all cars that have them should be terminated with fire. All of them.

My choice would possibly be a dual clutch if you have a small not very powerful engine (say under 200bhp) and torque converter auto for the ultimate smoothness with big powerful engines. Oh and I think that paddles are just gimmicky and that they aren't needed at all. The point of going for an auto is, well, its automaticness, so wanting manual control is kind of defeating the point...

[henk4]

As for CVTs, yes in theory the idea is brilliant, but in the real world it doesn't seem to work as well. They are not especially smooth at low speeds and if you want a lot of performance you get a lot of noise, which would be odd in a luxury car.

I think it is a matter of adjusting your throttle operations, don't floor it, but just keep it where the engine does not start screaming. On our national Autoweek website the would-be journos always blame the CVT for making too much noise, but these only know one throttle position. And by the way is not Audi offering a CVT for at least their A6 models?

I have to say that I never drove one, not even a DAF in period as they were considered ladies cars, and there was always something odd about them, in the sense that the DAF's marketing department had decided to call the gear shifter (for forwards and backwards engagement) "het pientere pookje" which does more or less translate as "the clever stick" (without the alliteration). It does not require much imagination that that term could also be applied to very specific male body part.

The guys in the Huron as far as I know did not need to adjust too much (it is not like the early turbo F1 engines that you had to keep on song to avoid the turbo lag) Next time I see him I will ask Simon Hadfield who restored the Huron for Van Doorne (the grandson of the CVT inventor).

[pimento]

CVTs don't make noise, thrashing something with poor NVH supression causes noise. Also, cost will go down and sophistication will go up with the economies of scale and development that come with these things.

[Ferrer]

Possibly yes, but its odd that variations in road speed and engine speed do not match.

If we weren't used to stepped gearboxes maybe it wouldn't be a problem, but being used to them a gearbox with no gear ratios feels strange.

It would probably work better with bigger, torquey, more powerful engines, because you'd have enough speed at the lower end of the rev range but if CVTs aren't designed to be able to stand those kind of situations...

[henk4]

Possibly yes, but its odd that variations in road speed and engine speed do not match.

If we weren't used to stepped gearboxes maybe it wouldn't be a problem, but being used to them a gearbox with no gear ratios feels strange.

It would probably work better with bigger, torquey, more powerful engines, because you'd have enough speed at the lower end of the rev range but if CVTs aren't designed to be able to stand those kind of situations...

that is the same effect in a torque converter, but it will last shorter because it is is connected to a stepped gearbox. And as somebody mentioned above CVTs have been used in a tank, so the initial idea that it could only be used for small engines is not valid.

[drakkie]

Nowadays a pushbelt CVT is usually coupled to a torque converter in the first place. Some designs have the electronics create a kind of 'stepped' feeling for the driver. As far as I know the pushbelt CVT is suitable for production vehicles upto about 450Nm at the moment. In the late '80's they tested a pushbelt CVT on a Williams F1 car even. The gearbox is cut open and is in one of the meeting rooms in Tilburg. Was nice to look at during my job interview some time ago

What kind of CVT was used in the tank?

[henk4]

Nowadays a pushbelt CVT is usually coupled to a torque converter in the first place. Some designs have the electronics create a kind of 'stepped' feeling for the driver. As far as I know the pushbelt CVT is suitable for production vehicles upto about 450Nm at the moment. In the late '80's they tested a pushbelt CVT on a Williams F1 car even. The gearbox is cut open and is in one of the meeting rooms in Tilburg. Was nice to look at during my job interview some time ago

What kind of CVT was used in the tank?

Van Doorne is restoring the Williams for static display. Is it ready?

[drakkie]

The car has been at the main entrance for years. The gearbox itself is 'cut in half' so to speak and in a meeting room. Every room has a different piece of history displayed.

[henk4]

The car has been at the main entrance for years. The gearbox itself is 'cut in half' so to speak and in a meeting room. Every room has a different piece of history displayed.

last year we spoke with Van Doorne and he mentioned that they were going to put everything together to show the car at other occasions. I am sure it would make some impression at let's say the Festival of Speed.

[drakkie]

last year we spoke with Van Doorne and he mentioned that they were going to put everything together to show the car at other occasions. I am sure it would make some impression at let's say the Festival of Speed.

Now that would be a very interesting vehicle to see driving! I remember I tried so hard not to get up in the meeting and ask dozens of questions about the 'box when I was there last time.
Talking of Van Doorne, our company is having an interesting event the first weekend of October, displaying many not-often seen DAF trucks and cars. It's held partly on our company's grounds and partly in the museum:

http://www.dafmuseum.nl/NL/news/Page...-techniek.aspx

If your interested, let me know and I'll get you some more info and free tickets.

[Magnum9987]

I'll have you guys know the M1 Abrams tank has a jet engine, paired to an allison torque converter CVT transmission. But that uses a heavy duty chain drive set up, which is durable yet uselessly complex and expensive for any kind of mainstream car. It lends itself well to a jet engine and torque converter because the torque multiplication needed to get a 70 ton tank moving is huge, and then on to 60 miles per hour!

I've always liked the idea of a fluid-type CVT, which is basically two torque converters put together, and each one varies stall speed so the engine is always at a correct speed. The problem with those is while around town, pumping losses are huge, and the heat produced is huge as well. But these aren't much different from a conventional automatic transmission because it needs some kind of planetary gear set so it can engage reverse....

[RacingManiac]

I think one of the reason for the less popularity is you can't get enough ratio spread on the CVT design. Yes its infinitely variable, but the range which that happens is still limited. Also the NVH thing, most of the CVT are still somewhat limited in their torque capacity, and thus confiines them to smaller/cheaper car which tend to have poor NVH performance to begin with, coupled with engines that are not so smooth. So its one bad thing adds one another.

Nissan is making pretty strong headway though, most of the Front drive Nissan in US now uses CVT as their auto. Honda will probably follow suit now following the success of the new Accord. I think they still makes more sense than making complicated 9-10 speed auto....

The whole "stepped" feeling of the geared car will probably eventually be an non-issue. Especially when EV become more mainstream...

[Matra et Alpine]

Was an issue in the re-introduction that drivers didn't like the "natural" CVT operation so they had the computer control mimic gear ratios with change points and engine rev increasing

An optimally configure cvt car revs to the max torque point and lets the transmission sort it all out. Most folks don't like the acceleration with NO matching increase in revs

[f6fhellcat13]

I think one of the reason for the less popularity is you can't get enough ratio spread on the CVT design. Yes its infinitely variable, but the range which that happens is still limited.

Could a pair of CVTs in series give it that necessary range without adding too much complexity?