In the FX series, The Strain, there is a character who is not quite human and not quite vampire. He battles the vampires on behalf of the humans. He is Mr. Quinlan – aka The Born.
The Continuously Variable (CVT) transmission is like him, in that it was unnaturally conceived – as a way to keep the government at bay.
CVTs do that by slightly increasing gas mileage vs. conventional automatic transmission. Which they do by maintaining optimum leverage for any given road speed or load on the engine. Which they do by continuously varying the relationship between how fast the engine spins and the wheels turn.
Conventional automatics have to continuously shift – up and down – to alter the mechanical driveline ratio for road speed/load. Each gear is a compromise and “just right” for only a given road speed/load. As the speed/load changes, the transmission must shift up – or down – and it’s the in-between these shifts that isn’t as efficient.
The difference in mileage vs. a CVT is about 3 MPG on average. It’s not a big difference but it is a necessary difference – for the sake of not incurring the fines for failing to reach the government’s mandated MPG average, currently set at about 35 MPG.
All new cars must achieve this unnaturally decreed average – their combined city/highway mileage – else the car company that makes them gets fined and passes the cost of the fines on to its customers in the form of a higher sticker price.
The CVT’s job is to prevent that.
It’s an unnatural bargain because it’s one made not between the car company and the car buyer – as would be natural in a free market – but instead it is made between the car company and the government. In balder words: The car buyer didn’t demand the CVT but he gets it anyhow.
He’ll be getting more of them, too – if the Ecuarico-style “election” stands.
The next government has given fair warning that it plans – in the words of the media-anointed El Presidente – “robust” increases in the mandatory minimum MPG regs. (Which raises another interesting point worth discussion some other time about how it came to be that it no longer requires a law being passed by the representatives of the people for government bureaucrats to “mandate” mandatory MPG minimums.)
Well, what’s so bad – and is there anything good – about the CVT?
The main good, of course, is that there is a gas mileage benefit. Which may become more of a benefit once El Presidente-select adds two or three dollars to the cost of a gallon of gas, as he has implied he will do and as he must do if he intends to “end” fossil fuel use in this country, as his crew is champing at the bit to do.
There is also smoothness, arguably the CVT’s most appealing attribute and the one which might have resulted in its success on the market in certain types of cars (ironically, luxury rather than economy cars) absent any government pressure to build them into cars.
CVTs are smooth – a desirable attribute in luxury cars especially – because they don’t shift. They transition from range to range. You depress the accelerator and the car accelerates in a linear progression for as long as you press on the accelerator. Even if you press the accelerator all the way to the floor and hold it there, there’s just the forward thrust without any interruption.
In the same car with a conventional automatic, there is a noticeable transition at each shift from gear to gear; engine speed goes up, then down, then up again. In between a slight pause as the transition occurs and a little snap – forward and then back. This is the “coffee spilling shift shock” which CVTs eliminate – and tout.
Which brings up some of the bad things about CVTs, the first of which is their mushy characteristic precisely because they do not shift.
The firm feel of gear-to-gear is replaced by a forward surge that can feel like a conventional automatic that’s broken and slipping because it isn’t shifting. In cars with not-very-powerful engines, the surge may not subside until you back off the accelerator, because the engine has to be kept at a fairly high RPM to maintain the wanted acceleration. This is often accompanied by additional noise – of the engine, revving and holding revs – along with the CVT’s own sounds.
So there is CVT sturm und drang – as the German saying goes.
Interestingly, it is much-ameliorated if the engine bolted to the CVT is powerful, especially one with lots of low end torque like a big V8. because then there is no necessity to make the engine rev as high – or hold revs as long – to get (and keep) the car going. Ironically, though, CVTs are most prevalently used in cars without powerful engines as a way to improve their efficiency – at the cost of sturm und drang.
But there is another reason why CVTs are mostly used in cars with not-very-powerful engines. It is that CVTs are not as sturdy as conventional automatics. They cannot take heavy loads as reliably and tend to break sooner when used hard.
Ironically – again – they tend to get used harder precisely because they are most often paired with marginally powerful engines. The little four cylinder engine is revved and worked – and so is the transmission. A conventional automatic bolted to a big V8 that easily moves the car without having to dig deep and spin like an Indy car engine just to get the car up to merging speed doesn’t load the transmission as much, which tends to increase the life of the tranny.
CVT reliability has improved but the nature of their design is such that they are more vulnerable to failure if worked hard and when the fail, it is usually permanent. The band in between the adjustable pulleys breaks and sends shards of metal throughout the unit.
Most CVTs are not designed to be repaired but replaced and the replacement cost is often the value of the car itself, since a post-warranty failure at ten years out and with 120,000 miles on the clock isn’t worth paying for – because the car isn’t worth much more than the cost of the replacement transmission.
Such are the pros – and the cons – of the unnatural transmission.
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