Motoring along in a new direction
CVTs, LIKE THE ONE IN THE 2015 SUBARU WRX, don’t have gears but their growing popularity is probably a good thing
Benefits of a CVT include the ability to maximize acceleration by holding an engine at peak output.
Ever try to heel and toe in a pair of wooden shoes? Me neither, but I’ll bet it’s no picnic. And yet, more and more manufacturers would have you shift gears in a manner first popularized by the Dutch motor industry: the Continuously Variable Transmission (CVT).
Hoo boy, that phrase cleared the gearheads out in a hurry. One of Harry Potter’s wand-flinging semi-Latinate exhortations doesn’t have the magical auto-enthusiast-repulsion of a good Continuous Variableus! Mostly, people who like to drive don’t like to drive ’em.
But wait, here’s Subaru offering a CVT in its entirely new WRX, a car that many are praising as one of the best rally-rocket Subies to come along in years. Has the world gone mad?
Not at all. In fact, the CVT’s spreading popularity as the automatic transmission of choice is actually probably a good thing. Your fuel economy goes up. You can keep the engine singing in its powerband.
While you won’t find a sketch of a scrappy fourbanger in Leonardo da Vinci’s notebook, you will find the plans for a stepless transmission with a theoretically infinite range of ratios. It’s hardly new technology — Leo jotted down the idea in 1490.
Early uses included poweroperated milling and sawing, and the device was used in cars and motorcycles as early as the late 1800s. While the CVT was first popularized in low-powered scooters and the like, its first widely accepted automotive appearance was in the Dutch-built DAF 600.
DAF called its version the Variomatic, and it would give the tiny, 590 cc-engined family car some very odd characteristics.
First though, a look at what a continuously variable gearbox is, because they aren’t all the same. For instance, the Prius can claim to have an infinite number of gears between its highest and lowest ratios, but that’s a result of its planetary drive taking in a number of power outputs (from both electric and gasoline sources), and shunting the power around as needed.
More commonly, when we’re talking about a CVTequipped passenger car with a conventional engine, the transmission in question is a belt-drive. Imagine, if you will, an 18-speed bicycle where the front and rear sprockets have been replaced by a pair of fattish cones. Instead of the stepped 18-speeds, you suddenly have gears like fifteen-and-a-half, or twelve-and-three-quarters.
Inside a CVT transmission, that’s essentially what’s hap- pening. Instead of cones, you get a pair of V-sectioned pulleys that can each squeeze or expand to change their diameter. Because the belt must always stay the same length, as one shrinks, the other grows, in an infinite number of variations between top gear and lowest gear.
In the little DAF, that drive was an actual rubber belt, and it wasn’t exactly the most reliable thing in the world
That wasn’t the only weird thing about the daffy DAF. Because reverse involved simply running the transmission backward, it had the same top-speed in both directions. At the now-defunct annual Dutch backward driving world championships (yes, really), the DAF proved itself unbeatable. There was also a control on the dash that would allow increased vacuum to cause the CVT to hold lower gears and enhance engine braking — you could literally turn up how much it sucked.
Because each of the DAF’s rear wheels was propelled by its own drive-belt CVT, you had a sort of weird limitedslip arrangement. Handling in icy conditions was euphemistically described as “interesting,” even though power from the 590-cc flattwin engine was very modest.
Later, DAF would be snapped up by Volvo, which would eventually coincide with the CVT’s appearance in a motorsport that dovetails nicely with our so-equipped WRX: rallycross.
For some reason, Volvo decided its DAF-engineered 343 (a rear-drive hatchback we never got here) needed a bit more rough-and-tumble to its image. Volvo therefore entered it in the European rallycross championships in the late 1970s, equipped with a 1.6L turbocharged engine and a DAF-designed CVT. Surprisingly, it did pretty well.
For most Canadians, our earliest experiences with a CVT transmission came aboard a snowmobile. Makes perfect sense, then, that the first CVT-equipped car to reach Canadian shores in any numbers was the humble little Subaru Justy.
The odds of stumbling across a Justy today are pretty darn slim, as it wasn’t very popular. Part of the issue was a production bottleneck at the Van Doorne manufacturing plant — descendant of DAF — which could only produce so many metallic link belts for the transmission. The other part of the problem was that it wasn’t a very pleasant car to drive, performing like an office chair with a chihuahua attached to it with a bungee cord. Happily, things got better.
Benefits of a CVT include the ability to maximize acceleration by holding an engine at peak output. Under light acceleration, they can also keep revs down and thus maximize fuel economy by constantly shifting gears rather than raising rpms.
Drawbacks? Well, reliability has certainly been an issue. While early efforts relied on rubberized belt- drives that often broke, most modern CVTs are made of woven metal chains, and are thus extremely strong. That’s not to say issues don’t crop up, and when they do, a rebuild is far more complex than with an ordinary automatic transmission.
However, as the CVT has become widespread, its dependability has improved immeasurably. Its ability to handle higher torque applications is becoming more widespread, and the fuel-saving benefits increase as efforts are made to decrease the friction losses inherent in a beltdrive system.
Moreover, manufacturers have come up with solutions to the principle issue facing the CVT: feel. Because of the way a CVT holds constant engine speed, drivers often complain of a droning or a slack, rubber-band feel.
The solution seems to be simulating the feel of an ordinary stepped automatic transmission. With Subaru’s CVT WRX, activating the most aggressive throttle mapping allows access to eight gear ratios through the paddle shifters — because the transmission need not swap gears, but merely jump to a preset ratio, it shifts with the rapidity of a dual-clutch automatic, if not quite the crispness.
Leave everything as it is, and the CVT functions like a sort of a slingshot, with the turbocharged engine spooling up and the car snapping off after it. All-wheel-drive versions of the Nissan Juke function in much the same way, and because there’s no shifting, boost pressure is maintained at a constant.
Cast an eye on something with much less power, such as the Mitsubishi Mirage, and you won’t find much in the way of driving engagement. However, the combination of a CVT and a gentle right foot can net some excellent fuel-economy benefits. The slower your acceleration, the lower the revs. With greatly reduced friction losses, CVT transmissions regularly beat manual transmissions, even in stop-and-go traffic.
Nissan embraced the CVT fairly early on, and now offers it across the range. First to get the transmission was its Murano crossover, and while early versions did suffer from some reliability issues, it was considerably smoother and more efficient than a Pathfinder equipped with the same V6 engine. With the Versa, Sentra, and Altima, continual improvements in shift programming have reduced the laggy, rubberband feel of Nissan’s CVTs, and considerable effort has been made to reduce friction losses.
As for Subaru’s decision to go for a CVT in its WRX, well, no one who loves driving a stick is going to be swayed over to the dark side.
With a quick-spooling 2.0-litre direct-injection boxer engine that provides 258 lb-ft of torque as low as 2,000 rpm, the CVT-equipped WRX drives like a fired slingshot. Always on the boil in Sport Sharp mode, the driveline makes the most of the power, and on a twisting back road it is no barrier to enjoyment.
Need further convincing? At the launch of the new vehicle, four-time World Rally Champion Tommi Mäkinen admitted he’d actually prefer if the current generation of STI had the WRX’s variable transmission in it.