The Power of Two: Dual Clutch Transmissions

A Smart Solution For Medium Duty Trucks

Sometimes two really is better than one. Like Aces in a card game. And what good is a single work glove? But can the same logic apply to clutches in an Automated Manual Transmission (AMT)?

Eaton has developed a Dual Clutch Transmission (DCT) initially intended for medium-duty applications with frequent starts and stops, which could potentially improve fuel economy by 8 to 10 percent over the torque converter-style automatics that are currently prevalent in the segment.

DCTs also have the added benefit of providing a more car-like driving experience.  As the name implies, a DCT employs two clutches and actuators; one performs shifts out of the odd-numbered gears while the other takes care of the even-numbered shifts. This allows one clutch to stay engaged at all times, and eliminates the power interruption that typically occurs when an Automated Manual Transmission changes gears. Fuel that today is consumed to recover momentum lost during these torque interruptions no longer needs to be spent.  Meanwhile, a DCT with a wider gear spread allows the gears to engage more quickly than does a torque converter, providing a smoother shifting experience and greater fuel economy over torque converter automatics.

 

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Eaton Procision™ 7-Speed dual clutch transmission.

The Eaton Procision™ 7-speed dual clutch transmission is slated to be released in medium-duty trucks beginning mid-2015. It is currently undergoing field-testing with customers and the results have been favorable when compared to an automatic transmission with torque converter.

 

Jerome Palazzolo, engineering specialist with Eaton’s modeling and simulation group, has been working on the project and so far, likes what he sees. The fuel savings combined with the smoother driving experience could be enough to make the DCT a mainstream specification in certain applications, he said.

Meanwhile, the simplicity of an automated manual gearbox – relative to a torque converter automatic – is maintained, which will make the Procision transmission easy to  service, if required.

 

“The Dual Clutch Transmission allows you to have better efficiency through launch and through the shifting of gears,” Palazzolo explained. “In a torque converter automatic, the hydraulic system is more complex and because of that complexity, there are additional seals that cause drag in the transmission and whenever you have more drag, that equates to greater parasitic losses, which increases fuel consumption.”

The torque converter-style automatic transmission has gained prominence in the medium-duty truck market because of its car-like feel and smooth shifting. The DCT matches or surpasses this, improving fuel economy as well, Palazzolo noted.  “In automated manual transmissions, you feel the torque interrupt during the gear changes.  With the all-new Procision dual clutch transmission,  you can’t feel the shifts, so it’s like driving a car,” said Palazzolo. “I think drivers will appreciate the confidence-inspiring driving characteristics, but the improved fuel efficiency is what’s going to help it take off in the market.”

The 8.5 percent fuel economy improvement recently touted in a white paper published by Eaton, is based on dynamometer testing; however, about 30 test units currently being run by Eaton and its customers have also performed well, with 650,000 miles amassed.

 

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Dual clutch transmissions are well suited for start-and-stop applications.

Applications that are suited for the dual clutch transmission are numerous - and may even include Class 8 linehaul - but it’s initially being designed for the medium-duty market and duty-cycles with plenty of starts and stops. This is where the Procision delivers the greatest value, Palazzolo said.  “Essentially, stop-and-go applications enhance the region of operation of the dual clutch where it outperforms the torque converter automatic,” he explained. “So instead of having efficiency losses dictated by the torque converter, we’re able to use another gear but in the same respect, we’re able to shift through those gears and lock up quicker than a torque converter is able to lock up.”

 

The Dual Clutch Transmission, with its second clutch and actuator, could be the next big breakthrough in the evolution of commercial vehicle transmissions. As a result, there will  be two clear winners: the driver, who will benefit from a smoother driving experience thanks to its power-shifting, and the truck owner who foots the fuel bill.