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Continuous variable transmission engines are now common. What this appears to mean (do correct me) is that instead of matching a specific pair of discrete gears (for 1st speed, 2nd speed, etc), there is a continuous gear (of what form; helical?) that is matched to a gear. This means that CVTs have effectively a continuous, or infinite, number of "gears", rather than a finite/discrete set.

On traditional (manual) transmission, when I engage cruise control on 4th speed on country roads or 5th speed on the highway, I do not think twice about maintaining this gear engagement for an hour or more. The gears will take it.

But with CVT I'm no longer so sure.

If I engage cruise control, I imagine that a small section of that magical helical transmission will engage. Stressing just this one section of the CVT for an extended period sounds like a recipe for it to deteriorate more rapidly, ultimately leading to failure of the transmission.

Is continuous variable transmission (CVT) averse to extended cruise control? In other words, do I have to be careful to engage cruise control for, say, 10 minutes, then change the speed slightly up or down, and then engage again for another 10 minutes, and so on?

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  • Cruise control isn't about gearing, but maintaining a fixed speed with throttle control, and on a grade, if there isn't enough torque to maintain the speed, the gear ratio will be adjusted. There isn't a 'special gear' or 'magical helical transmission' for cruise control. With a manual transmission you have to change down yourself. Commented Oct 17, 2023 at 21:09
  • @WeatherVane Cruise does affect the transmission. My old car (2005) activated a different shift map for cruise use that held top gear longer for fuel efficiency. It sucked going up hills because it would lug then shift down and the revs shoot up. In my new car, the cruise will command the transmission to downshift for engine braking, it works quite well.
    – user71659
    Commented Oct 18, 2023 at 5:32

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TL DR: No, you really shouldn't worry about it.

Here's an image of what the working parts of a CVT look like (not exact, just an idea of what they look like):

enter image description here

Note: Image pulled from this site.

In the image, you can see two separate CVT belt/pulley combinations. In both, the primary pulley is on the top. It is driven by the engine. The secondary is pulley is at the bottom, which pushes power out to the drive wheels. The belt is what rides on both and transmits the power.

At slower speed, what you see on the left side of the image is what it would look like. As the vehicle speeds up, it will start moving the primary pulleys in towards each other and the secondary pulleys out, as on the right side of the image. This is how it continuously changes the ratio between the two.

If you notice in both sides of the image, how the belt sits on the pulley never changes. The angle of the pulley sides allows the belt to sit flush at all times. Because it sits flush at all times, there is no difference in how it engages at any time during operation. The amount of surface contact will change on either end because the amount of belt which is being presented to the pulleys will change, but the area from bottom of the "V" to the top will still be the same.

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  • That clarifies it. Sequel: Traditional transmission 1- touches some oil bath, and 2- is all metal. If the belt in CVT is rubber, does this mean it needs to be replaced every n km/miles?
    – Sam7919
    Commented Oct 17, 2023 at 18:05
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    @Sam7919 - I'm sure it varies between makes, but yes, it'll need to get changed. And, BTW, they aren't completely rubber. Most have metal "V"s which actually come in contact with the pulleys, so the wear is a lot better over time. Regular automatic transmissions aren't "all metal". There are a lot of fiber clutches inside which are wear parts. Then a manual transmission has a clutch which is a wear part as well. No mechanical device is built to last forever, especially cars. You know the manufacturers want to make more money by selling you another car down the road (pun intended). Commented Oct 17, 2023 at 19:34
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enter image description here

To my knowledge, the only rubber belted cvt are in snowmobiles. There is another application of these same rubber belts used to drive a postal letter sorting machine in the '70s; 160 aluminum letter carts, each cart divided into twelve openings to hold one letter, coupled to a three level conveyor chain, driven by a one hp, 3-phase electric motor. These rubber belts never wore out, using a small electric motor to vary pulley sheaves while the conveyor was in motion. Snowmobiles in severe cold temperatures usually carry a spare belt for field replacement otherwise overnight camping may be the last resort in subfreezing temps.

CVTs in every four wheel vehicle use all metal segmented belts. Hydraulic pressure controls varying two pairs of pulley sheaves for an infinite number of speeds. Subaru utilizes CVTs in almost every model with only one using a conventional manual transmission. CVTs have their own unique problems but belt wear isn't one of them. Unfortunately, when a cvt fails, rebuilding isn't cost effective unless diagnosed early and replacement parts are made before long term damage occurs. Several years ago, only one xmission shop was willing to reveal on youtube, a total disassembly and rebuild with modifications made but never followed up on results. The cvt was a discontinued brand after a two year run in Saturn Vues using the 2.2l 4-cyl engine. A dismal failure but not representative of Subaru, Nissan and others using Jatco and other CVTs.

As a new Subaru owner, I was amused to find out that my Crosstrek Sport 2.5L cvt has eight speeds(?). Typical cvt operation; speedometer ramps up but there's never any jerking motion from gear shifts since none exists, as the tachometer shows rising rpm while accelerating in everyday driving. A truly shiftless automatic that is smooth whether flooring it for stoplight racing or quiet driving in everyday situations. The unknown fact of cvt operation is the invisible and silent hydraulic controls; increasing one pulley diameter while simultaneously decreasing the other pulley to vary output speed to the drive wheels. All done silently as opposed to geared xmissions exhibiting slight jerking as each gear is automatically selected with the tach rpm dropping as much as 1k rpm between gear shifts.

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The issue isn't cruise control. The issue is cruising.

If you're spending large blocs of time going 70 MPH on the flat, your car is going to spend a lot of time in the same power band and gear ratio. It doesn't matter whether you're holding the pedal with your foot or letting the computer hold it. The transmission sees the same wear either way.

So no, the enemy is not cruise control. The enemy is driving.

The gears will take it.

No they don't. I've worn out the 5th gear in a manual transmission.

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    Curious: what was the mileage on the engine when the 5th gear was worn out?
    – Sam7919
    Commented Oct 19, 2023 at 13:03
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    @sam over 200k. Commented Oct 21, 2023 at 2:17

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