Fortunately, it’s easier to describe the performance of Dana’s Spicer AdvanTEK Dual Range Disconnect concept than to explain how it works.
I had an advance test drive on a truck equipped with a DRD concept drive axle at Dana’s Maumee, Ohio, facility. It was one of three test trucks equipped with the system. Were it not for the little video screen on the dash used by the engineers to monitor the system, I wouldn’t have known it was there.
At this point in the development and testing phase, the DRD is designed to disengage the rear axle of the tandem at a predetermined speed, somewhere between 52 and 54 mph. Steven Wesolowski, the senior director of global advanced engineering at Dana Holding Corp., explains that’s the optimal speed for the powertrain/drivetrain they are working with now, but notes that the axle shifting strategy could change as engineers further refine the system.
At 54 mph, when a mechanical clutch disengages the numerically-higher-ratio rear axle, the “blending” effect of the planetary gears combining the two axle ratios (2.26:1 front; 4.88:1 rear; 3.10:1 combined) is uncoupled and numerically-lower-ratio front axle becomes the sole driving axle. This effectively puts the truck into 6x2 configuration with a 2.26:1 drive axle ratio.
Still with me?
Steve Slesinski, Dana’s director of global product planning, explains that the Dual Range Disconnect provides benefits of a numerically higher ratio 6x4, including full four-wheel traction, slightly livelier response from the engine and less torque-induced stress on the driveline while at lower speeds, and fuel-saving performance of a lower-ratio 6x2 at highway speed. There’s also a slight benefit from the reduction in mechanical drag with the inter-axle driveshaft and the rear-axle gearing being physically disconnected.
“Depending on your starting point, the DRD axle system can improve powertrain and driveline efficiency somewhere in the range of 2% to 5%,” he says. “You’ll also get the downsped 6x2 efficiency at highway speed, and better low-speed performance for startability or when backing a trailer into a dock. There, you can go one or two miles per hour rather than three or four with a low-ratio axle.”
Without getting too far into the mechanical details, for all intents and purposes, the Dual Range Disconnect feels like a modern-day 2-speed rear axle. When the axle-range shift occurs, automatically of course, the driver feels nothing different from a normal 9th to 10th gear shift. The engine decelerates to break the torque, the rear axle disconnects and the inter-axle stops rotating, and the engine rolls the power back on about 400 rpm slower than it was prior to the shift.
It feels the same during a downshift. At the predetermined speed, the engine revs up by about 400 rpm, the rear axles re-engage and the truck is now back in 6x4 configuration with combined axle ratios producing a final drive ratio of 3:10:1.
We were bobtail for the test drive of the DRD system, so I couldn’t really compare the performance difference of the two configurations, but I did notice the drop in engine speed when the rear axle disconnected, and I also noticed the difference in creep speed in reverse between the two ratios while moving at idle.
Going strictly by the numbers, that 400 rpm reduction in engine speed provides a functional downspeed setup, which could produce fuel savings on the order of up to 4%, based on the assumption of 1% savings for every 100-rpm drop in engine speed.
That, along with the reduction in torque stress on the rest of the driveline, and the advantages of 6x4 traction when it’s required, suggests to me that Dana might be onto something here.