NASHVILLE -- The large gap between combination trailers can now be decreased at highway speeds to reduce aerodynamic drag and save fuel with Silver Eagle Manufacturing’s T-Dolly, the company says.

The dolly’s tongue automatically retracts 28 inches to close the trailer-to-trailer gap from 40 inches to 12, explained Gary Gaussoin, Silver Eagle’s president. Retraction occurs at 45 mph, as measured  by the vehicle's anti-lock braking system, and extends as it slows past 40 mph to allow sharp turns. A hydraulic mechanism does the pulling and pushing.   

Fleet testing with double- and triple-trailer combinations shows the T (for telescoping, T-shaped tongue) Dolly improves fuel economy by 2.5% to 3.5%, Gaussoin said. Reduction in turbulence and closer coupling between trailers improves stability and reduces the “wiggle” effect, especially after lane changes, something that test drivers remarked on, he said during the official announcement during the Technology & Maintenance Council's annual meeting.

"The only reason to have a large gap between trailers is to make a sharp turn at low speed,” Gaussoin said. “Just think of how little you turn the steering wheel at highway speeds to change a lane; there is a very small steering angle in those situations.”

The T‐Dolly concept was first brought out in 2007 for Future Truck Exposition of the Technology & Maintenance Council of ATA. In 2008 a manually adjustable dolly was tested in Texas, where appreciable fuel savings came from reducing the gap between trailers. Next, wind tunnel tests verified energy savings.

Then the difficult work of creating the mechanical components and methodologies to be fully automatic and autonomous began, Gaussoin said. It needed to work regardless of the equipment to which the dolly was hooked.

“From the beginning we were very aware that the T‐Dolly had to fit into the fleet like any other dolly, and it had to ‘fail safe’ and return to the normal extended position,” said Kevin Sternes, Silver Eagle’s lead engineer.

Mature components and technologies were used throughout the design, he said. Examples are the sliding drawbar system that the company has used for decades; speed readings from the anti-lock braking system; and proven hydraulic cylinders and pumps.

UPS agreed to test the T‐Dolly and has worked through several iterations, employing them in regular service between Portland, Ore., and Everett, Wash.

“The T‐Dolly will play an important part in reducing fuel consumption in our fleet.” said Bill Brentar, UPS director of maintenance and engineering for transportation equipment. “UPS drivers who use these dollies preferred the way they feel in the closed position, and that they settle down right away when changing lanes.”

“An additional benefit of the single telescoping tongue has been better ergonomics for maneuvering the dolly into position, and air and electrical hook ups.” said Brian MacKenzie, Silver Eagle’s director of sales. “This additional open space gives greater clearance for a tight turn and reduces the chance of a bent tongue.”

During fuel efficiency testing on the Ohio Turnpike, a test driver declared, “Triples pull like double 45-foot trailers,” a combination known to be stable, Gaussoin said.

Fuel savings were measured by Type IV testing for double- and triple-trailer combinations. The supervisor was Chuck Blake, an applications engineer for Detroit Diesel and one of the authors of the TMC-SAE test procedures more than 20 years ago.

“This is a no brainer, isn’t it?  Geater stability (less wag) and improved fuel economy, especially in windy yaw angles,” Blake commented. “Even in no-wind conditions the savings are significant and very measurable.”

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