First revealed at the Mid-America Trucking Show in March, Dana's Dual Range Disconnect drive axle system gives users the fuel savings benefit of a downsped 6x2 drivetrain as well as the traction and performance benefits of conventional 6x4 setup with a mid-range axle ratio. How's that possible you ask?
The key word here is disconnect. While running at speeds up to about 54 mph, the system functions as a 6x4 with torque going to all four wheels for optimum traction. It also runs at a 3.10:1 ratio for better performance and startability. Above 54 mph, the interaxle driveshaft disengages, leaving the driving to only the forward drive axle. Interestingly, the axle ratio of the forward axle is 2.26:1, which lowers engine rpm and in effect creates a downsped drive train. The benefit, of course, is better fuel economy resulting from a 300-400 rpm drop in engine speed.
Dana calls it "Dual Range Disconnect" and it will soon be available on Spicer AdvanTek 40 drive axles. How it works is a bit tough to get your head around, but this video helps to explain what happens.
The benefits of the "downsped" configuration at highway speed coupled with the reduction in torque stress on the rest of the driveline at low speed and the advantages of 6x4 traction when it required suggests to me that Dana is now able to offer fleets all the advantages of 6x2 and downspeeding with few, if any, of the problems associated with these proven fuel saving strategies.