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Car Tech: Continuously Variable Transmissions


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Ever wonder what's inside a CVT, or how it works, and how it's different from other automatic gearboxes?

Wonder no more. Here's a look inside Nissan's unit.

And while this is quite a brilliant piece of engineering, it's generally considered to be NON-REPAIRABLE because parts, specs, and procedures aren't available...but that's not exactly the reality.

 

 

Edited by Ace-Garageguy
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Dung to drive, can’t fix, impossible to have fun driving one. Rather have a root canal and drive a slippy power glide than those. 

Edited by keyser
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2 minutes ago, keyser said:

Dung to drive, can’t fix, impossible to have fun driving one. Rather have a root canal and drive a slippy power glide than those. 

Agreed, but for your basic low-T consumer who gets as involved with the function of his vehicle as he does with his fridge, they have their place.  B)

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They were developed to help meet the Federal CAFE mileage standards and have a life expectancy of about 100,000 miles, depending on how they are driven/serviced. I have owned/driven 2 Nissans and 2 Hondas with a CVT and have mixed reviews about them. Currently own 1 Nissan but have a lifetime warranty on the trans so should any issues come up, I should be okay.

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Reminds me of an old '53 Buick I owned. Only cost me $50 in the late '60's. The main claim to fame was its ability to get around in snow, and nobody wanted to park to close to it in a parking lot.  

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CVT in my 2019 Outback works fine.  Better than the transmissions in my 2001 and 2004 Tauruses, 2014 Focus and 2016 Fusion.  On the other hand the auto trans in my 2011 Fusion has 165,000 miles, has never been touched and still works quite well.

 

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Well, I'm not a fan of CVT but to say its only for those who don't care about cars is a stretch. I have one in my 2011 Altima and though it doesn't snap my neck with every gear it does do what I need it to do when I need it. Also, its been more reliable than three GM cars I've owned, drove the same yet had tranny trouble in each.

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3 hours ago, mikemodeler said:

They were developed to help meet the Federal CAFE mileage standards...

Exactly, and the continuously variable trans that holds the engine (theoretically) at its torque peak most of the time is a good way to achieve that. It's pretty cool engineering to boot.

But it's simply not something for spirited driving (as in "precise car control"), or with anything like a "high performance" level of power.

Edited by Ace-Garageguy
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The CVT has a poor reputation but I was told by a Nissan tech that they will outlast the car with a simple oil change every 30K miles. I have over 130K on my 2010 Altima and the CVT works just fine.

I use the simple method to change the fluid through the dipstick tube. Use a pump to suck out as much fluid as possible and replace it with the same amount of fluid (to the ounce.) I use the Valvoline CVT fluid in mine. As always, your mileage may vary 😉

 

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I have an Outlander Phev 2019 with the 2,4l petrol engine and these have the CVT transmission. Since its being hybrid the CVT proabobly is the logic transmission to have in it. But its sutch a strange setup driving it. The Petrol engine revs allot, allways, and you cant feel any shifts. And the engine noise is realy akward both from inside and outside.. not much good to say about the car exept for my wife can drive to work on the battery and its the right size for us. 

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Nissan's CVTs have a bad reputation (likely due to lack-of maintenance by the vehicle's owner), and are horrible in real world settings.
Toyota's CVTs have been quite good; reliable, and not as "revvy-and-obnoxious" as the models used by Nissan

Somebody please feel free to mention the suppliers/manufacturers of Nissan's CVTs and Toyota's CVTs, et al.

My personal experiences with CVTs are few: first was my friend's 2005 Prius. Like others have mentioned, a CVT is perfect for hybrids -- the one in that Prius worked well (including traversing the Cajon Pass, etc., to-and-from Las Vegas).
Where I used to work; firstly were a couple of brand new Chevy [Suzuki] Sonic "things". 
Absolute junk.
Then a few Nissan Leaf 4 door liftbacks. More junk, but not nearly as bad as the Sonic et al. CVT.
In 'defence' of the Nissan Leafs' CVTs: received the vehicles used, and with +/- 35,000 miles on them.
I mentioned to the manager of the auto parts store where I was working, that they need to drain-and-fill the CVTs in both cars, as there's more than 30,000 miles on them, with unknown history.
"You worry too much.", they'd told me.
Fine.
You're right.
Six months and 17,000 miles later, guess what happened? BOTH of those Leafs' CVTs were overheating, due to low fluid (no way for the everyman to check the CVT's fluid level), excess miles, past-due servicing, and abject abuse.

Personally, I prefer a good old planetary gear set transmission, with a full-quadrant (none of these 'P', 'R', 'N', 'D' only settings!). Travelling downhill in a CVT-equipped car just plain sucks! No way to 'compression-brake' the engine by selecting a lower gear! 
That's where the real world failures/deficiencies present themselves with CVTs.

With all of that being said: I admire the engineering and theoretical-function of CVTs. 

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22 hours ago, 1972coronet said:

Nissan's CVTs have a bad reputation (likely due to lack-of maintenance by the vehicle's owner), and are horrible in real world settings.
Toyota's CVTs have been quite good; reliable, and not as "revvy-and-obnoxious" as the models used by Nissan

Somebody please feel free to mention the suppliers/manufacturers of Nissan's CVTs and Toyota's CVTs, et al.

My personal experiences with CVTs are few: first was my friend's 2005 Prius. Like others have mentioned, a CVT is perfect for hybrids -- the one in that Prius worked well (including traversing the Cajon Pass, etc., to-and-from Las Vegas).
Where I used to work; firstly were a couple of brand new Chevy [Suzuki] Sonic "things". 
Absolute junk.
Then a few Nissan Leaf 4 door liftbacks. More junk, but not nearly as bad as the Sonic et al. CVT.
In 'defence' of the Nissan Leafs' CVTs: received the vehicles used, and with +/- 35,000 miles on them.
I mentioned to the manager of the auto parts store where I was working, that they need to drain-and-fill the CVTs in both cars, as there's more than 30,000 miles on them, with unknown history.
"You worry too much.", they'd told me.
Fine.
You're right.
Six months and 17,000 miles later, guess what happened? BOTH of those Leafs' CVTs were overheating, due to low fluid (no way for the everyman to check the CVT's fluid level), excess miles, past-due servicing, and abject abuse.

Personally, I prefer a good old planetary gear set transmission, with a full-quadrant (none of these 'P', 'R', 'N', 'D' only settings!). Travelling downhill in a CVT-equipped car just plain sucks! No way to 'compression-brake' the engine by selecting a lower gear! 
That's where the real world failures/deficiencies present themselves with CVTs.

With all of that being said: I admire the engineering and theoretical-function of CVTs. 

You make an interesting point beyond the basic vehicle maintenance. The ability to even check the transmission fluid level. The two Dodge Chargers I have owned since 2010 and neither of them have a dip stick for the transmission. The tube is there and a removable plug but no dip stick. With the lube jockey usually being the lowest paid employee, you have to wonder how it's done at the dealership. Your experience with not having a transmission dip stick might be more common than you realize.  

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On 7/28/2022 at 5:54 PM, sfhess said:

CVT in my 2019 Outback works fine.  Better than the transmissions in my 2001 and 2004 Tauruses, 2014 Focus and 2016 Fusion.  On the other hand the auto trans in my 2011 Fusion has 165,000 miles, has never been touched and still works quite well.

 

X2 on the Focus transmissions. I was going in for a clutch pack replacement every 20-25,000 km with my 2014, and ended up selling it before the extended warranty ran out. I replaced the Focus with a Kia, and haven't had any issues.

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My mother bought a 2009 Maxima with the CVT to replace her '04 Maxima with a standard torque-converter auto. Great engine yoked to a whiny, horrible, laggy draggy drudge of a trans. She only kept the car for a couple of years because she hated the transmission so much. I had a rental Kia Forte with CVT a few years back when my Soul was in the shop after I got rear-ended and it seemed... better? Not as bad, anyway. Could be because it was a 10-year-newer car or because the low power of the Forte engine masked the inherent laziness of the CVT. 

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I drove a 1999 Honda Civic HX coupe with an automatic CVT transmission for 14 years.  That transmission has to be the worst ever made.  I bought the car new in 1999 and about one month after the factory warranty expired, the car would shudder when I hit the gas pedal.  Turns out the issue was a problem with the transmission.  When I bought the car new from the Honda dealership, I also got the extended warranty which at the time I regretted.  Now the extended warranty paid for the transmission repairs.  A year later the same shuddering problem occurred so back to the dealership it went.  This time they had to replacement the transmission and it was paid for by the extended warranty.  Fast forward to late 2013 and I was at a stoplight and hit the gas pedal and the car barely crossed the intersection and then it would not move forward anymore.  I had the car towed to the dealership and they told me it needed a new transmission.  I did not want to spend $3,000 to repair a car that was worth $2,000.  I sold the car to the Honda service advisor who was going to repair it for this teenage daughter.  The last I seen this car it was on its 3rd CVT transmission.  It was a nice little car with excellent gas mileage but lousy transmission.

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CVTs continue to evolve and improve, like all technology does over time.

But the CVT has an inherent limitation, and that's the "traction" the steel belt can achieve working on the variable steel sheaves. This limitation is often the cause of faults in operation, from belt slippage.

And any belt stretch in a CVT is a potential failure mode, as is poorly synchronized variation of the driving sheave and the driven sheave, both problems resulting in belt slippage as well.

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Conventional automatic gearboxes use special friction surfaces, or "linings", on bands and clutches to progressively decrease and finally eliminate slippage between components that actively transmit power. These surfaces wear away over time, eventually failing completely. When they wear away enough so there's metal-to-metal contact, the trans slips because these parts are no longer able to transmit torque.

But older 3-speed auto gearboxes like GM's TH350, TH400, Ford's C4, C6, and Chrysler's 721 Torqueflites would routinely make it to 200,000+ miles with no problems if they weren't abused, and rebuilding was straightforward, with parts readily available.

Newer auto boxes of conventional design are failing much earlier across the board, as the increased number of "speeds" means that internal components are smaller, and more highly stressed...leading to earlier failure, and parts availability can be a serious problem.

The CVT may ultimately solve that issue, if the inherent limitations of the design can be overcome in a way that's cost-effective for relatively inexpensive, mass-produced vehicles.

Edited by Ace-Garageguy
CLARITY
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Daf created long ago, crept thru Honda Nissan and Audi. Rented Altima cvt. Zero change in velocity, just noise, like a blender. 
Audi A6 cvt another gem. Loaner, cannot imagine spending 50k on a car with cvt. Boite de merde. 
https://en.m.wikipedia.org/wiki/Variomatic#:~:text=Variomatic is the continuously variable,developed by Hub van Doorne.

Edited by keyser
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7 hours ago, Ace-Garageguy said:

But older 3-speed auto gearboxes like GM's TH350, TH400, Ford's C4, C6, and Chrysler's [904 & 727, et al., Torqueflites] would routinely make it to 200,000+ miles with no problems if they weren't abused, and rebuilding was straightforward, with parts readily available.

Each one a solid gearbox (except for the TH-200/250, neither mentioned). Each had their strong points and weak points - 904 & 727 Torqueflites' overrunning clutch ("Sprag") was pressed-in at the factory; a bolt-in 'sprag' eliminated that problem (that unintentional factory/engineering fact was also the reason why a reverse-patten manual valve body was recommended by Tom hoover et al.).
Ne'er-the-less - easy to rebuild & modify, rock-solid gearboxes.

Newer auto boxes of conventional design are failing much earlier across the board, as the increased number of "speeds" means that internal components are smaller, and more highly stressed...leading to earlier failure, and parts availability can be a serious problem.

The electronic-shifting of newer/revised planetary gearset autos certainly helps with reliability - no more bands, only solenoid-trigger shifting (though I seem to recall that Ford's 5R55E [?] still had a high gear apply servo which would "oval-out" in its bore, causing gear-slipping). The biggest issue with the 6-10 speed [!!!!] planetary gearset autos is their overt complexity. From what I can recall, the 'TCM' permits for "gear-skipping", dependent upon the load demand. Never having operated a vehicle with one of those gearboxes, I can't attest to their practicality - but, I can imagine that, much like CVT's, the theory doesn't hold water (except as means to please the EPA et al, in lab settings, that fuel economy is "improved"). 

Much of the problem, too, is that the dealer-salesman-manufacturer tell customers that the "Transmission has a lifetime guarantee!" without disclosing whose lifetime (i.e., "lifetime" of the vehicle's powertrain warranty). As a result, most folks never have those International Space Station automatics serviced every 10,000 miles/ one year, whichever happens first. 

 

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I’m driving my 2014 Maxima, with 58,000 miles, Ive had the fluid changed as recommended. My old 2007 Maxima also had one, which was well maintained as well, and when I traded it in for my 14, it had over 100,000 miles. The ONLY reason I traded it in was because the 14 was a leftover and I saved $10 grand right off the sticker. Plus my trade in, so in short,  I bought a new Maxima for less than a new Altima with a four banger would cost. I hear Nissan merged with Renault, and their CVTs are made by JATCO, and are supposed to be junk, but I don’t see it. I don’t drive my daily drivers like I drove the drag car, but these Maximas still put a smile on my face every time I mash the pedal. 

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Not all CVTs are the same. Subaru has been working with CVT since the 1980s (an option on the 1989 Subaru Justy). Subaru manufactures their own CVT designed for their cars, where many other automakers outsource theirs from a 3rd party, Jatco supplies many automakers including Nissan who has developed a very poor reputation for its CVTs. CVTs are less complex, smaller and lighter weight than automatic transmissions which makes then well suited to small cars.

I prefer a manual but we have a CVT in our Forester and it works just fine, I don't find it any better or worse than most other automatic transmission cars I've driven / owned. It keeps the car in its optimum power band when accelerating so makes the most of the engine power, and it drops to a low RPM when just maintaining speed on the highway for better fuel economy.

It absolutely does allow compression braking, when I set the cruise control on a downgrade it does a fantastic job of maintaining my desired speed, and in fact it does a better job of holding speed than even a manual transmission on a downgrade, because it just keeps adjusting the transmission to maintain just the right amount of engine compression. Now actually slowing down with compression braking a manual does better, but just holding speed, I'm impressed at how well the CVT does and I do a lot of hill and mountain driving.

CVT is apparently not a great choice for a large vehicle, or for serious towing but they work fine for small to midsize cars. 

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