The future of CVT
Is it a thing of the past?
CVT or continuously variable transmission has its roots at the beginning of the 20th Century, first coming to prominence courtesy of Dutch manufacturer DAF. At the 1958 Amsterdam motor show, the company launched its Variomatic transmission in the 600 model. The system continued to be used by DAF and then Volvo in its 300 Series until 1992. Indeed, the very last Volvo 340 off the production line was a Variomatic model.
CVT was developed for DAF by another Dutch company, Van Doorne, and essentially consisted of two rubber belts driven via pulleys that could vary their width and circumference, and hence the ratio, as the belt moved up or down the pulley. Later systems swapped to more reliable steel belts but the operation remained the same, resulting in one infinitely variable ratio without the individual steps – or gears – contained within a conventional gearbox.
Benefits included relative simplicity and the ability to allow the engine to operate in its most efficient power band, thus boosting economy. The downside was that by keeping the engine at its most efficient operating speed, any meaningful call for acceleration caused revs to soar, often disproportionately to the road speed achieved and to the detriment of cabin refinement. Although later CVT transmissions would see the adoption of virtual ‘steps’ in an attempt to mimic a conventional gearbox, the answer for many car-makers was to develop and adopt the dual-clutch transmission. Although complex, these combine impressive efficiency and performance with rapid shift times, and feel more natural to drivers used to torque-converter automatics.
That should have been enough to see CVT relegated to the technological history books, but the reality couldn’t be more different. Last year, the Japanese transmission manufacturer JATCO (Nissan own a majority stake with Suzuki and Mitsubishi also shareholders) announced that it had produced 30 million CVT ’boxes since production started in 1997 and that they can still be found in a wide range of Japanese models. Catering for front, rear and hybrid drive applications, the company continues to spend time and money on developing CVT, with work focusing on further reductions in frictional losses and improving efficiency and driveability.
Not all manufacturers are convinced, though, with Audi phasing out its multitronic CVT back in 2014, telling us: “With the latest S tronic technology we have been able to surpass the efficiency benefits offered by multitronic without compromising on the rapid step-off and virtually instantaneous shift characteristics that have long been the hallmarks of our dual-clutch transmissions… [with] emphasis placed on driving refinement, performance and agility.”
Keeping the faith
One of the car-makers to have kept faith in CVT is Subaru, dubbing their version the Lineartronic. According to the company, 93% of Japanese cars and 79% of European models sold are thus equipped. It’s perhaps no surprise given they’ve been using CVT since the Justy model in 1989, but why stick with it today? They told us it had numerous benefits, including stronger economy at cruising speeds thanks to the use of longer ratios, and that being relatively light and compact allowed it to be mounted lower down, improving the centre of gravity. The design also allowed for a shallower driveshaft angle and a lower transmission tunnel, reducing the impact on cabin space.
Mind you, not all reviews have been favourable. Auto Express road-testers said the CVT gearbox was “clumsy and slow to respond – while the whine from the transmission can get tiresome quickly.” Claimed economy and emissions of 39.8mpg and 164g/km were nothing to write home about either.
Still, Subaru aren’t the only manufacturer choosing to avoid the populist dual-clutch route. Last year’s Geneva Motor Show previewed the 10thgeneration Honda Civic, which goes on sale this month. That will be available with an optional CVT transmission that Honda says is simply the most effective way of keeping the engine in its most efficient operating range. The company also points us in the direction of the current Jazz, which claims 61.4mpg combined economy and CO2 emissions of 106g/km, an improvement of 4.9mpg and 10g/km less than versions equipped with the six-speed manual gearbox.
And there’s another big proponent of CVT: Lexus. Their version, dubbed E-CVT, does away with belts and pulleys, and instead utilises an electronically-controlled epicyclic gear set, but its essential operation remains the same. They say their hybrid systems simply aren’t designed to work with dual-clutch gearboxes and, in any case, reckon their customers prefer the smoother, more relaxed manners of CVT. Lexus also told us that there are further benefits in terms of both cost and weight versus other self-shifters.
Customer preference aside, what’s especially interesting here is that Lexus have indisputably pinned their colours to the CVT mast and are pressing ahead with the next generation of transmission that’s set to make its debut in the LC500H. A muscularly-styled two-door coupé, the new flagship model premiered at the 2016 Geneva Show and launched in February 2017 with deliveries expected in the summer, featuring what the company calls its Multi Stage Hybrid System. Said to “achieve a more direct connection between the accelerator pedal and vehicle acceleration” – ie, minimising the ‘rubber band’ effect suffered by most CVTS – the new powertrain incorporates not only a six-speed CVT transmission but also a more conventional four-speed automatic gearbox fitted behind it. This will provide the driver with a choice of 10 manually-selectable ratios, the highest of which is an overdrive that Lexus say combines the efficiency benefits of a continuously variable transmission with the response and acceleration of a dual-clutch unit. In manual mode, shifts are said to be completed in less than 100 milliseconds.
It’s an enticing prospect and one that could revolutionise the way continuously variable transmission is employed in helping to meet ever more stringent emissions legislation. Not bad for a technology that started life as a pair of rubber bands.