Dana engineers are working on a Spicer Dual Range Disconnect tandem rear axle that combines the traction advantages of a dual-drive 6x4 configuration with the fuel economy of a single-drive 6x2. Executives showed off the concept on Wednesday, the eve of the Mid-America Trucking Show in Louisville, Ky.

The design goes beyond a “clutched” rear or forward axle to enable a single-drive tandem, they said, by introducing the effect of a low and high range. But it does so without using old-style two-speed axles.

“New fuel economy regulations for linehaul trucks are on the immediate horizon, and truck manufacturers are already addressing the challenge of reducing fuel consumption beyond the levels that can be achieved through today’s conventional powertrain systems,” said Mark Wallace, a Dana executive vice president and group president of Dana On-Highway Driveline Technologies.

“Our advanced Spicer AdvanTek Dual Range Disconnect concept enables truck manufacturers to achieve substantial gains in fuel economy with a system that still performs dependably in adverse driving conditions.”

The design employs a “slow” (high-numerical) ratio in the rear axle for startup and low-speed maneuvering, and on slippery pavement, he explained. Planetary-gear action in the interaxle differential mixes that with a “fast” (low-numerical) ratio in the forward axle to get a combined ratio, such as 3.10. The tandem then operates as a 6x4.

At a pre-determined speed, electronic controls switch to the forward axle’s ratio, such as 2.21, to lower engine revs at higher road speeds. The rear axle is disconnected using a sliding dog clutch at each end of the interaxle driveshaft, and the interaxle differential is bypassed. The tandem then operates as a 6x2.

Power and torque flow directly to the forward axle, eliminating meshing and fuel-burning drag of the additional gear sets. The concept supports “downspeeding” of the truck’s engine, which could cruise as low as 900 rpm – a trend that’s developing – for additional fuel savings, Wallace said.  

Because the range switch must be done precisely, the concept works best with an automatic or automated transmission, Wallace’s colleagues said. But it can work with a manual transmission.

Dana engineers have been evaluating a prototype Advantek 40 tandem with the Range Disconnect feature for the last two and a half years, Wallace said. Engineers plan to install copies in truck chassis for further testing later this year.