When Ford Motor Co. sources first confirmed '03 Lincoln Navigator would have independent rear suspension (see WAW — May, '01, p.13), it was as if a gauntlet had been thrown at the feet of its competitors.
Now Lincoln is dropping both gloves, hockey-style, with the revelation that its re-engineered fullsize SUV will be equipped with an automatic load-leveling air suspension system. And its Ford twin, Expedition, will offer the same feature as an option sometime during the fourth quarter.
“We were looking for an improved ride. It's a natural progression,” says Russ Norton, an engineer with Ford's Outfitters suspension design team.
Cadillac Escalade and Lexus LX 470 have solid-axle rears, though Escalade's features hydraulic load leveling, and LX470 has a manually operated air suspension that raises and lowers all four corners at the touch of a button.
“We looked at that, and we chose not to,” Navigator/Expedition Suspension and Steering Supervisor Dave Zinn says in defense of automation. Focus groups showed disdain for a system that required activation by the operator, he says.
Instead, Navigator responds to loads automatically. Data collected by three sensors — two in front, one at the rear — are sent to a controller that determines which of three pre-set heights the vehicle's body must attain for optimum utility and performance. Then the system, supplied by Continental Teves, responds automatically.
The cycle begins when the vehicle is at rest — or “kneel,” as Ford calls it. The design of '03 Navigator, scheduled to roll out in spring, only enhances this feature because the new model already sits 1 in. (25 mm) lower than its predecessor — a victory for ingress and egress.
As soon as the transmission is engaged, in either reverse or drive, the system seeks what Ford calls the “trim” position — for optimum handling. “And as you drive down the road, the vehicle will try to maintain that trim position,” Zinn says.
The third setting, which is 1 in. (25 mm) higher than trim, is available only when the vehicle is traveling under 20 mph in 4-wheel drive or all-wheel drive.
“People never put their vehicles in 4×4 low unless you are really, really, truly off-road,” Zinn admits, “or, occasionally, people use it pulling boats out of the lake on a boat ramp.”
“Even heavy payloads and towing do not compromise suspension geometry and vehicle attitude,” Lincoln says. “Each air spring is designed with a separate load path from its companion shock absorber (from Bilstein), which reduces loads on the top mount and improves isolation from road surface imperfections, such as tar strips, frost heaves and expansion joints.”
This could also have positive implications on issues such as vehicle life and re-sale value, says Continental Teves, which also supplies the air suspension system for the Audi Allroad.
“When you bottom out,” says Detlev Borchert of Continental Teves, “you could possibly damage all your other suspension systems — the spring, the damper, jounce bumper. At least over lifetime, your fatigue cycle probably looks much worse.”
With Navigator's air suspension system, he adds: “You don't bottom out. The total jounce and rebound travel that is designed into the vehicle is always kept constant, which gives you a better chance to survive a severe pothole if your vehicle is almost fully loaded, compared to a steel-spring vehicle.”
Continental Teves was mindful of durability, which was problematic for Lincoln's previous attempt at employing air suspension. Once featured on the Continental, it was subject to leakage.
“In particular, we looked at the spring, at the bellow, because that is the part that is next to the wheel where it's the dirtiest,” Borchert says.
As with Allroad, Navigator's system features a dryer that, during the venting process, purges it of potentially corrosive moisture. And unlike systems built previously by Continental Teves competitors, the purging process also refreshes the dryer, eliminating the need for regular replacement.
Unlike Allroad, however, '03 Navigator does not have “aero” mode between kneel and trim. That's because Ford engineers opted for a different approach.
“Our shocks have rebound springs which contribute significantly to the vehicle's roll stiffness,” says Ford's Norton. The rebound springs, he says, make it counterproductive to go into aero mode on the highway, where lowering would mitigate against the rebound springs, compromising the Navigator's initial roll stiffness. “This is undesirable from a vehicle dynamics or sportiness feel.”
