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DifferentPointofView 12-04-2008 11:27 PM

CVT Disadvantages
 
lol, the disadvantages that wikipedia has listed are quite humorous as they pretty much are advantages in reality. That and it describes the Typical American thought process when it comes to the way things should work.

Advantages

  • CVTs operate smoothly since there are no gear changes which cause sudden jerks.
  • Very few problems have been reported with the CVT transmission, lowering the cost of ownership.[citation needed]
  • The fluids do not have to be changed as often as in an automatic transmission.[citation needed]




    Heres the oddity that makes it seem like they couldn't find a good
    enough reason to down the CVT, so they scrapped together this
    Info. This explains why the regular american driver looks down at
    his foot and goes "What the F***!!!" when they use the CVT
    for the first time.

Disadvantages

  • CVTs operate smoothly and efficiently, without spending energy to jerk the car during a shift. This can give a perception of low power, because many drivers expect a jerk when they begin to move the vehicle. However, the expected jerk of a non-CVT can be emulated by CVT control software, thus eliminating this marketing problem.[citation needed]
  • Since the CVT keeps the engine turning at constant RPM over a wide range of vehicle speeds, pressing on the accelerator pedal will make the car move faster but doesn't change the sound coming from the engine as much as a conventional automatic transmission gear-shift. This confuses some drivers and, again, leads to an impression of a lack of power. This can be considered a disadvantage if the driver desires to hear the engine change tone.
  • CVT torque-handling capability is limited by the strength of their transmission medium (usually a belt or chain), and by their ability to withstand friction wear between torque source and transmission medium (in friction-driven CVTs). CVTs in production prior to 2005 are predominantly belt- or chain-driven and therefore typically limited to low-powered cars and other light-duty applications. Units using advanced lubricants, however, have been proven to support any amount of torque in production vehicles, including that used for buses, heavy trucks, and earth-moving equipment.

SVOboy 12-04-2008 11:30 PM

I didn't know the jerk during a shift was because the car was using so much power! Thank goodness I learned this *rollseyes*

DifferentPointofView 12-04-2008 11:37 PM

lol, when I accelerate in a normal Auto car, you don't feel the shifts cause of how little I'm using the gas. That and I keep my Jeep running good :thumbup:

I didn't know that having a smooth running car was an advantage! wait.. its also a disadvantage??? WTF!? *brain explodes*

trebuchet03 12-05-2008 02:54 AM

Quote:

Originally Posted by DifferentPointofView (Post 76681)

I didn't know that having a smooth running car was an advantage! wait.. its also a disadvantage??? WTF!? *brain explodes*

The cursed double edged sword....



Seriously, what's wrong with a double edge sword? I'd have more of a problem with the hilt-less sword :p

MazdaMatt 12-05-2008 08:43 AM

So... CVTs are used in heavy equipment!?!?!? I thought they were not in high production because they couldn't handle torque?! Why aren't all the EV people jumping all over this tech? Why aren't all the elctric motor companies offering computer controlled CVTs matched to their motors????? I love driving standard, but hell, a CVT would be sweet...

I would love to see a car with a "manual cvt" ... instead of a gear shift, a smooth lever :)

dichotomous 12-05-2008 09:08 AM

Quote:

Originally Posted by MazdaMatt (Post 76743)
So... CVTs are used in heavy equipment!?!?!? I thought they were not in high production because they couldn't handle torque?! Why aren't all the EV people jumping all over this tech? Why aren't all the elctric motor companies offering computer controlled CVTs matched to their motors????? I love driving standard, but hell, a CVT would be sweet...

I would love to see a car with a "manual cvt" ... instead of a gear shift, a smooth lever :)

audi offers this as a "6speed" program on their CVT TT. to ives the driver the thrill of shifting gears, even though its fastest just leaving it to do its job

MazdaMatt 12-05-2008 09:13 AM

Bleh, that's gross... i want a smooth lever that allows me to control the CVT ratio infinitely. Why on earth would anybody who knows anything about driving a sports car WANT to force the tranny to a ratio where the revs drop out of the prime zone?

bikin' Ed 12-05-2008 09:16 AM

I hate 'em
 
My wife has an altima V-6 with CVT. Just getting off of the gas pedal is akin to applying the brake. It has no coast in gear kind of affect. I also believe that if I were shifting a manual, I'd almost always be in a higher gear than it chooses for me. Both of these cost me at the pump.:(

MazdaMatt 12-05-2008 09:19 AM

That is entirely caused by bad software. Do you know if the gas pedal is cabled to the throttle plate? I would think that a truely perfect CVT system would use a computer controlled ratio AND throttle plate, making the pedal only a "speed setting" pedal... keep your foot where it is and the control system should align its throttle position and RPM on the best BSFC location for cruising.

dichotomous 12-05-2008 10:54 AM

the biggest problem CVT's have with people operating them is actually the "motorboating" effect. you press the pedal and the engine speeds up but you dont, untill it gets the ratio's and friction setup right. there are many out there now that dont do this. my sister loved hers in her saturn ion

MazdaMatt 12-05-2008 11:11 AM

So in effect, ALL of the dissadvantages are in user PERCEPTION? And the advantage is that it makes the car more powerful and fuel efficient? Well we got used to replacing horses with engines, i think we can get used to the motorboat effect and coasting with your foot on the gas.

DifferentPointofView 12-05-2008 11:28 AM

My mom's caliber has CVT with "Autostick"

Basically, its a clutchless manual sort of thing. when your shifting manually, you can control what gear you want it to be in. The quietness is a factor when using the autostick option because you have to look at your Tachometer cause the car is so dang quiet.

But I love it. when you accelerate, it goes to just under 2000 RPM and stays there, and when you get to 55, it is still there. and its so smooth. *drools* I can't wait till I get it, I'll be 2 years into college, but It'll still be better than driving my Jeep around thats for sure. I can pull the max out MPG's on my jeep by driving like an idiot. I don't know how people complain about getting like 23 mpg in it. How do they do it??? I got 30.6 driving 75 from here to Kansas city and when I got there thats when we filled up.

Also, when your listening to music, the details from your music really sing.. mmmm

MazdaMatt 12-05-2008 11:32 AM

What is Autostick and how does it relate to CVT?

DifferentPointofView 12-05-2008 02:00 PM

Its a feature that the Caliber R/T's CVT2 transmission has that allows you to shift like its a manual, but on an automatic transmission. It creates simulated Gear ratios that allow you to control the ratio of the CVT's belt/pully's whatever type of CVT it is so that you can have more control in situations like snow, acceleration, and want an overall Manual transmission experience without the actual manual transmission. Makes it good if you like driving stick but your wife has no idea how to drive stick. You can also keep it in a high gear ratio around town to lower RPM's.

When using the Autostick feature in the Caliber, 1/4 mile times are faster and you don't have to wait for the computer to decide what position the V belts need to be at in order for the best gear ratio, you decide that, and launches are faster. Autostick is only available on the higher end models, mostly for performance applications. But you can also use it in town or while coasting downhill for better coasting and lower RPM's for better fuel economy. You gotta know how to drive it though.

MazdaMatt 12-05-2008 02:04 PM

I wish i had funding dollars because i could totally develope a control algorith that would be way more advanced that anything that you all are telling me that production cars do.

It is absolutely SILLY that this autostick mode would have a faster quarter mile than CVT mode. CVT mode should simply lock the engine RPM at max power and change the gear ratio to suit wheel speed. It should not be beatable in acceleration OR mpg.

dichotomous 12-05-2008 02:09 PM

Quote:

Originally Posted by MazdaMatt (Post 76805)
I wish i had funding dollars because i could totally develope a control algorith that would be way more advanced that anything that you all are telling me that production cars do.

It is absolutely SILLY that this autostick mode would have a faster quarter mile than CVT mode. CVT mode should simply lock the engine RPM at max power and change the gear ratio to suit wheel speed. It should not be beatable in acceleration OR mpg.

so you'd need a unit that could handle intense torque on a sliding ratio, not easy to put together, and you'd need to know exactly what the driver wanted, right then, all the time, and how the engine and transmission should be configured for best performance either way, and you'd need to factor in the differences in people driving, and make sure it all works best, and lighter than the manual, and reacts just as quickly, and costs about the same. otherwise it either wont work or people wont buy it. hence the case with the cailber.

DifferentPointofView 12-05-2008 02:13 PM

yea, the main reason is price. otherwise, it will either not sell or no one will buy it. they kept it simple and went with nissan's already developed technology.

MazdaMatt 12-05-2008 02:17 PM

All i'm proposing is a better control system for the CVT, no mechanical changes... except that i would want the gas pedal to be an elctronic input and have actuators at both the throttle plate and the cvt gear so both engine and tranny are in my control.

I think the only hurdle is that people are dumb... which really blocks most of the world's progres... it would just feel "different" and that my drive off the idiots. It would always cruise at the throttle/rpm that would produce the required HP to maintain speed while being at the most efficient available point on the BSFC chart, and at pedal positions above neutral it would seek points on the chart with scaling hp, so at full throttle it would seek its way to the greatest hp output.

Hard to describe in 500 words or less, but I understand myself so it must be possible :)

extragoode 12-07-2008 04:08 PM

I agree with Matt 100%! CVTs are great, in concept, but all the stupid people of the world that think they need to jackrabbit everywhere have made the execution way off target for efficiency. They're capable of being lighter, smaller, more efficient, more quiet, and have a wider total spread of ratios compared to a geared transmission regardless of all the available ratios in between min and max. The ONLY disadvantage I see them having is the slightly limited torque handling which could make low speed, high ratio driving difficult/a little less efficient/damage the trans, but I'm talking <20mph, top gear/ratio/whatever. I can also kind of understand the weird sensation of watching the speedometer rise and not the tach, but I would think the hoards of drones that have been driving mushy automatics forever would be used to this. I, being a 12 year veteran of the 5 speed, automatically think "Great, there goes my clutch!" This is just something that will seem more natural with time for me and the rest of society. I don't understand why the programming on the CVTs is fixed. Sports cars have buttons for their automatics that allow them to shift quicker. I don't even need manual slide ratio control like Matt wants even thought that would be sweet! All I need is a button (like sport shift or 4wd) or a selector (like the knob that chooses defrost or floor, does any vehicle use those anymore) that would let me choose "granny" mode or "lead-footed idiot" mode and maybe even another option in between. That's what it would take to get me out of my manual.

Anything that's programmed for the status quo and unchangeable is not for me, because I am not the status quo and I don't think anyone else here is either. If someone here is satisfied with the status quo why are they on a modding website of any kind?

DifferentPointofView 12-07-2008 07:26 PM

Quote:

The ONLY disadvantage I see them having is the slightly limited torque handling which could make low speed, high ratio driving difficult/a little less efficient/damage the trans, but I'm talking <20mph, top gear/ratio/whatever.
"have been proven to support any amount of torque in production vehicles, including that used for buses, heavy trucks, and earth-moving equipment."

New CVT's use advanced lubricants that allow them to do this. Tractors now Use CVT. Old CVT's before 2005 had the low torque problem, but that has now been fixed.

jamesqf 12-07-2008 08:37 PM

Quote:

Originally Posted by extragoode (Post 77113)
Sports cars have buttons for their automatics...

Sorry, but sports cars don't have automatics, by definition. Put an automatic in one, and it stops being a sports car.

DifferentPointofView 12-07-2008 08:43 PM

...technically isn't a sports car with paddle shifters technically an automatic?

dichotomous 12-08-2008 10:40 AM

Quote:

Originally Posted by jamesqf (Post 77148)
Sorry, but sports cars don't have automatics, by definition. Put an automatic in one, and it stops being a sports car.

tell this to ferrari and porcshe.... I think they are pretty well set in the definition of "sports car" and so anything they do, automatically means its a sports car.

or do you want to call the 4 wheel drive, selectable automatic, rear engine ungodly fast cars they produce "non-sports cars"?

I remember hearing that "sports car" was defined by a manual transmission, front engine rear drive 2 door car. which would make the top sporty cars, not sports cars, but the miata fits... seems a little backwards.

or wait, well, they DID come up with another term..... "super car" which I belive the ferraris and porcshes and the lambo's fit into (well the lamb is more of a hypercar - all show with a big engine but not "fast" like a supercar)

jamesqf 12-08-2008 10:58 AM

Quote:

Originally Posted by dichotomous (Post 77223)
or wait, well, they DID come up with another term..... "super car" which I belive the ferraris and porcshes and the lambo's fit into (well the lamb is more of a hypercar - all show with a big engine but not "fast" like a supercar)

Exactly. Going ungodly fast is not a requirement for a true sports car. I could argue that it's even a detriment: I doubt my old Austin-Healey Sprite could hit 100 mph even on a downhill, and many classic sports cars weren't all that much faster. It's the difference between autocrossing and drag racing...

dichotomous 12-08-2008 11:02 AM

Quote:

Originally Posted by jamesqf (Post 77228)
Exactly. Going ungodly fast is not a requirement for a true sports car. I could argue that it's even a detriment: I doubt my old Austin-Healey Sprite could hit 100 mph even on a downhill, and many classic sports cars weren't all that much faster. It's the difference between autocrossing and drag racing...

no, its the difference between autocrossing and track time trial racing. drag racing favors rwd cars. oddly enough, the 4 wheel drive aspect is only better at lower speeds, its the higher speeds you dont want your front wheels under power. ever see a 4wheel drive formula 1 car? or can-am car? nope

MetroMPG 12-08-2008 11:38 AM

DPV - can you coast engine-off with the Caliber's CVT? What does the user manual say about towing?

DifferentPointofView 12-08-2008 11:42 AM

... I'd have to check that out actually. I'll make a note of that in the back of my noggin...

I know that when you have your foot off the gas fuel cutoff is pretty much instant and it doesn't seem to kick back on until around 15 or so mph. once in MO i was going down a steep grade using no gas for about 2 miles and it kept around 65-70mph, but the thing slows down so much when you take off the gas pedal you never really have to use your brakes if you slow down early like I do (save money 2 ways! woo)

wagonman76 12-08-2008 12:41 PM

Quote:

Originally Posted by DifferentPointofView (Post 77133)
"have been proven to support any amount of torque in production vehicles, including that used for buses, heavy trucks, and earth-moving equipment."

New CVT's use advanced lubricants that allow them to do this. Tractors now Use CVT. Old CVT's before 2005 had the low torque problem, but that has now been fixed.

Sure it can be designed to handle the torque. But will it fit under the hood?

DifferentPointofView 12-08-2008 01:56 PM

CVT tranny's are lighter and smaller than their automatic counterparts.

And the Caliber uses these type of lubricants, so its not just earthmoving equipment that uses the "new" lubricants.

andylaurence 12-08-2008 05:08 PM

Quote:

Originally Posted by MazdaMatt (Post 76751)
Bleh, that's gross... i want a smooth lever that allows me to control the CVT ratio infinitely. Why on earth would anybody who knows anything about driving a sports car WANT to force the tranny to a ratio where the revs drop out of the prime zone?

I had a Ford Focus CVT that had a virtual 7 speed semi-automatic gearbox. The automatic function had three possible modes; Economy, Normal and Sport. The difference in the three modes was how eager the 'box was to keep the revs high. In Economy (my favoured mode), the revs dropped off immediately when the throttle was closed. It was great for economy but awful for a sporty drive. The semi-automatic mode meant that I could control the revs as I saw fit, either for economy or for performance (holding the revs through the bends). Sadly, the gearstick was crappy, so it was hard to use.

Usefully, when changing virtual gears, the change was slurred. This allowed the revs to stay within about 2-300rpm when going through the gears. Aside from the awful 5 second pre-programmed start routine, the gearbox was the best I've ever driven. Here's a clip of the car in action:

Focus CVT in action

Cheers,
Andy

jamesqf 12-08-2008 09:10 PM

Quote:

Originally Posted by dichotomous (Post 77229)
no, its the difference between autocrossing and track time trial racing.

Yes, that's a better comparison: my brain's not quite up to speed that early in the morning. You get my point, though? A real honest-to-gawd sports car is something you'd have fun driving on English country lanes, or on California Hwy 1 south of Big Sur - with the top down, of course :-)


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