Welcome to the final installment of Trans Wars, a three-part miniseries exploring the automatic transmission. So far we’ve compared torque-converter and dual-clutch units, but these two gearboxes aren’t the only ones on the market today.
CVTs are something of a dark horse in the automatic transmission world. Functionally they’re completely different from their main rivals but ultimately they achieve the same goal: sending engine torque to the road as efficiently and effectively as possible.
“From a pure delivery of power to the wheels the CVT is the best way to go” said Jim Friedline, senior manager of research and development at Jatco USA Inc. This Japanese transmission company is mostly owned by Nissan, though Mitsubishi and Suzuki are also stakeholders.
Unlike the other two major kinds of automatic transmission, CVTs don’t have preset gears. Instead they feature a pair of variable-diameter pulleys that are connected by a special metallic belt. By varying the diameter of the drive and driven pulleys the transmission can change ratios.
“I think everybody’s realized it’s a driver for fuel-economy improvement,” said Friedline. The advantage of a CVT is that you’re not limited to fixed ratios. In a regular transmission “you have to pick the provided ratio, not the optimal ratio,” he said.
Paradoxically, these units are actually LESS efficient than either a torque-converter automatic or a dual-clutch gearbox. “The hydraulic system of a CVT drains more power from the engine just to run the transmission, but by allowing the engine to run at a more efficient point it more than makes up for the power that the transmission is consuming,” said Friedline.
Comparing Jatco’s latest CVT8 to a conventional six-speed automatic transmission – arguably the industry standard today – Friedline said the continuously variable unit can result in an efficiency improvement of about 5 percent.
SEE ALSO: Trans Wars Episode I: The Phantom Pedal
Because of this benefit, the competition is really starting to take notice. “We’re getting calls from all the automakers on a regular basis,” he said. Of course Jatco CVTs have found their way into a wide variety of non-Nissan vehicles from Chrysler products like the Jeep Compass and Patriot to vehicles from Renault and Chevrolet. The Bow Tie brand’s Spark city car features Jatco’s CVT7.
But one of the major concerns with these transmissions is how they perform. Some drivers may not like the slipping sensation provided by a CVT, something automotive journalists have been keen to point out over the years.
Friedline said, “One of the benefits I enjoy is the comfort; there are no shift events at all.” But he also mentioned this sensation is alien to a lot of customers, especially in the U.S. where the torque converter has reigned supreme for decades.
Despite their efficiency benefits these transmissions aren’t perfect. Friedline said the technology “does have its limitations,” which is why you don’t see it in heavy trucks. They also tend to cost more than competing transmissions because of how precisely everything has to be made for them to offer lasting performance.
If CVTs are used in smaller vehicles, Friedline said “there are no durability issues at all.” Beyond this, he also mentioned they they’re basically maintenance free, with no specified fluid-change intervals.
MAY THE CHOICE BE WITH YOU
Every driver may have their preferred type of automatic transmission; each one has its own benefits and drawbacks. Torque converter-equipped models are the established leader. Often they’re very slick but efficiency isn’t necessarily the best. Dual-clutch automatics offer lightning-fast gear changes for sporty driving and enhanced economy but they tend to be a little rough. Finally, CVTs are terrific at cutting consumption and eliminating “shift shock” but added cost and potential drivability issues can turn people off.
“What ZF has seen is that automatics will continue to dominate” said Johnson, adding that they feel dual-clutch transmissions will likely focus on performance vehicles in the future. He also said, “We’ve pretty much stepped aside on CVTs,” focusing on advanced torque-converter automatics instead.
Skorupski agreed, saying “there’s no real silver bullet for this transmission solution. I can see all three of these transmissions existing going forward.” When the DSG was launched, he said they thought conventional automatics might go away, but obviously that hasn’t happened because they keep getting better – smoother, faster and even more efficient.
Finally, Friedline noted that stepped-ratio transmissions will never really go away, but that he sees CVTs continuing to increase their market share as automakers struggle to deliver ever-greater economy.
Still, there are plusses and minuses to each configuration. “Obviously a CVT is not going to be a very good choice for a performance car,” said Friedline. However he also noted, “The dual clutch is a very good manual transmission, but it’s not really acceptable as an automatic.” Issues including shift quality have kept them from really taking off in North America.
Praising torque converters Skorupski said, “The only real disadvantage to a conventional automatic is the efficiency.” But where fuel economy and sporty driving count, dual-clutch units have an edge. He mentioned that VW’s DSG has been really popular in Germany, a country that, along with the rest of Europe, is still a stronghold of the manual transmission.
With so many good options these days it seems inevitable that more and more drivers are going to opt for self-shifting gearboxes. Prognosticating a little Johnson said, “I think the volume for automatics will remain steady if not grow [in the future].”