By Paul Duchene, Special to Tribune Newspapers
4:22 PM PDT, May 20, 2010
Every so often, the Big Earth Clock makes a giant tick, and something that was considered experimental becomes common.
For example, the first mention of scissors seems to be about 3000 B.C. in Egypt, but mass production waited until 1761, thanks to Robert Hinchcliffe in Sheffield, England.
Automobiles puffed into the public consciousness with Frenchman Nicolas Cugnot's steam tractor in 1769, but Henry Ford is credited with bringing the modern version to life with his Model T in 1908.
In a much shorter arc, the dual-clutch transmission has gone mainstream after developmental work by Porsche in its 1983 Le Mans 956 and 962 race cars and in the Audi Quattro S1 rally car. Volkswagen introduced the first DCT for road use in the Golf R32 pocket rocket in 2003.
The theory is fairly simple; the execution had to wait for electronics that were small, efficient and robust enough.
Most DCTs use two gear sets and two clutches, one each for odd and even gears. Clutches may be arranged concentrically or side by side, like the gear clusters.
They can operate in full automatic mode or be shifted manually.
Oil-based, or "wet," clutches are favored for the most powerful engines. They weigh more because of their hydraulic lines, pumps and coolers. Dry clutches, generally used in smaller applications, are less likely to drag and weigh some 30 pounds less than a conventional 4-speed automatic.
The DCT's key difference from conventional manual and automatic transmissions is operating speed. The electronic gearshift in the DCT takes only about 1/100th of a second to act.
And they do all that without a torque converter, saving another 20 pounds by eliminating the 12-inch disc between the engine and transmission. Add this reduction to the compactness of the DCT and its wider range of gears and you improve mileage and power measurably.
And while Environmental Protection Agency tests show a DCT might subtract 1 or 2 mpg from manual transmission figures, it is expected to add 10 percent to an automatic.
The first evidence of DCT thinking dates to Adolphe Kegresse, a Frenchman known for half-track Citroen trucks that set all kinds of obscure records in the Sahara in the 1930s.
Though he never built a DCT, Citroen tackled the idea of quick-shifting transmissions in the DS19 of 1955, using a powered hydraulic system to achieve a quick shift.
"The key to the DCT is its improvement in efficiency with no power loss," said Colin Price, Nissan's manager of technology communications in the U.S., whose baby book includes the GT-R, a dual-clutch whiz that does zero to 60 in less than 4 seconds and tops out at 193 mph. "The cool thing is, you plant your foot and pull the lever; there's none of that delay in changing gears, no letup in acceleration."
"A manual transmission is a nice interactive experience, but the DCT is here to stay," said Dan Edmunds, director of vehicle testing for Edmunds.com. "Manuals have been on the decline for a long time, with fewer people bothering to learn them, and that's especially true here (in the U.S.). In Europe, people like to shift gears, and they're reluctant to adopt automatics."
Dave Buchko of BMW's Advanced Powertrain and Heritage Communications put his finger on the other advantage of the new DCT transmissions.
"The fact the transmission can shift quickly thanks to auto-tronics was a big advantage in competition, but downshifting is where there's significant potential for a missed shift. These transmissions make that virtually impossible. On the race track going from 4th to 2nd would cause the engine to over-rev. The computer won't allow that; it just waits until the car slows down."
The technology can add from $1,575 in a 2011 BMW 135i coupe to $2,900 in an M3, a small price for what Buchko called a Jekyll and Hyde profile: commuting in automatic calm and a full Formula One experience in manual mode.
Besides, the real DCT magic probably lies with hybrids. For example, a hybrid diesel 5-Series BMW seems likely to deliver around 70 mpg, or better, with the technology.
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