@Dept:
Freightliner's R&P Steering
Rack and pinion provides a solid feel, and it's an inexpensive option.
Rack and pinion steering is a common feature on today's automobiles, where it offers preciseness and a decent feel of the road, even with power assist. But R&P is new to heavy trucks, where Freightliner is making it available on certain models.
Heavy Duty Trucking magazine's Nifty Fifty list, and it was a finalist in the Truck Writers of North America's annual Technical Achievement Award competition for 2006.
Awards are fine, but does rack and pinion steering do anything for the driver of a big rig? The answer is yes, judging from a brief trip in a Century Class tractor during the Mid-America Trucking Show in Louisville.
The tractor, hitched to a loaded 53-foot van, served as a demonstrator for press reporters and potential customers. Christoph Hofmann, Freightliner's director of product strategy, rode along to explain the R&P system, which I could concentrate on because the tractor had an Eaton Fuller UltraShift automated transmission that did most of the work.
And I did have to listen to Jennifer Edwards, Freightliner's public relations manager, as she issued driving directions from the "back seat"– actually the sleeper's bunk. She directed me out the Kentucky Fair & Expo Center's front gate and onto Interstate 264 west, which we rode for a few miles before exiting onto a series of streets that took us back to the center complex. She was assisted by colleagues Susan Gallik and Kim Pupillo, who work for the builder's advertising and PR agency, so there was really no chance of me getting lost.
Highway speeds sometimes put considerable stresses on the front axle's wheels and steering mechanisms, so the open road is where you most notice the improvements of rack and pinion steering. These include a solid feel in the steering wheel instead of the mushiness you get in some integrated hydraulic power systems, and less tendency to wander. Therefore, I had to make fewer on-center corrections, as Hofmann had promised in his pre-drive briefing.
I wondered if I was reacting to suggestions he had planted in my head or if the improved sensations were real, and I finally decided that yes, R&P does have those benefits. I could take my hands off the wheel and the rig would continue to track straight and true, at least as long as the pavement wasn't overly crowned or rutted. And I didn't have to constantly move the wheel left and right to keep the rig in my travel lane. That converts to less fatigue as the minutes turn into hours. It also makes driving more pleasant and allows you to enjoy your chatty companions, if you have any.
But back to business: R&P works better because it uses fewer mechanical parts and pivots to transmit your inputs to the wheels. There's still a hydraulic power steering pump, but gone is the integrated steering's frame-hung gear box, along with the pitman arm and drag link that connect it to the steering geometry. This cleans up the left frame rail adjacent to the engine and allows easier access to other things. It also saves about 45 pounds.
R&P's gearing and toothed rack are mounted on the axle, where they can act directly to move the wheels in either direction. Up to 80 percent less force is needed to produce king-pin torque, according to engineers' measurements, which reduces effort at the steering wheel and should cut wear on the pump and hoses, as well.
You might argue that integrated hydraulic power steering is a known system that requires little maintenance, while rack and pinion steering for heavy trucks is new and untested. Not exactly, Freightliner would answer. R&P prototypes are being tested on its track in Indiana, and as of April, had accumulated 63,000 "torture miles," equivalent to 5.2 million road miles. Some 400 test units have been in customers' hands since late 2004, running about 80 million reliability miles "without concerns." Individual units have gone as far as 450,000 miles.
For now, rack and pinion steering is limited to 12,000-pound-capacity steer axles, but Hofmann said that a version for 14,600-pound axles might be in the works. It doesn't cost much – a little more than $100 as an option on Century Class S/T tractors and several other models, including Freightliner's new Cascadia highway model.
Would I order it? You betcha, even without directions from Ms. Edwards and her friends.
Tom Berg
Senior Equipment Editor
