"We've taken several steps to further refine the Lincoln Navigator's NVH qualities to deliver the performance we're looking for," explains Craig Williams, supervisor of ongoing development, NVH, for the Lincoln Navigator. Apparently these steps were the right ones as the Navigator scored highest as the "Quietest" SUV for the second year running. Best Ride judges found the large, luxury sport-ute "extremely quiet, even on rough roads," also noting its "solid feel," and "smooth ride."
Though already working from a quiet base, the 2000 Navigator sports several enhancements, according to Williams. The first is called a "tunnel shield," fiber-glass material mounted outside the vehicle in the tunnel area above the transmission. "We did this to address not only powertrain noise but also to give the cab a little better barrier against road noise," he says.
Engineers also added a constrained layer mastic patch to the fender to damp noise from the power plant that was actually making it resonate. Another action was to bolster the cam cover isolators and add a secondary exhaust resonator to the tailpipe. Based on customer input, engineers also respecified the U-joint articulation torque to cut driveline vibration, which was noticeable at about 45 mph.
Says Williams, "We measure NVH in terms of the maximum noise output during a wide-open throttle, first-gear run. We also measure steady-state noise at 80 mph to really look at wind and road noise, and then steady-state cruise at about 45 mph. We primarily attack noise peaks, looking for a smoother, more-linear response level."
The wind tunnel lets engineers look specifically at wind noise in the absence of powertrain or road noise. It also lets them vary temperature and change vehicle altitude. Mirrors are often big noise generators, so engineers start working with them early in the design, says Williams. "We have specific requirements for pivoting mirrors and the sealing of the mirrors to the overall vehicle," Williams points out. "All are individually tuned in the wind tunnel."
An Aachen head device, named for a research laboratory in Aachen, Germany, helps gauge noise in the passenger compartment. It looks like a human head with microphones in each ear. Engineers strap the device into a vehicle then drive on different roads, all the while recording noise during steady-state, part throttle, or wide-open throttle. The process helps determine whether small changes significantly reduce overall interior noise.
Engineers take special note of power features that make driving a luxury vehicle a pleasure. Features such as power windows, locks, and adjustable pedals, along with the actual track mechanism that moves seats forward and backward all get scrutinized for NVH. One new feature for 2000 is a first for full-size SUVs — climate-controlled seats that heat or cool both the driver and front passenger. Noise is a factor for the compact heat pump and small fan that circulates cabin air through the seats. "The technology of applying forced air through the seat with fans is measured during a worst-case scenario," Williams explains. "We go through a series of refinements specifically looking at the NVH to get the overall noise below what we believe to be the customer's objection level."
Moving outside, road noise as well as noise at the tire/road interface are primary NVH contributors. Measurements get taken in both dry and wet conditions with the vehicle loaded and unloaded. "We benchmark to determine whether there are deficiencies or opportunities to improve, but we feel the Continental tires on the Navigator are very competitive in the NVH arena," he says.
Once all systems onboard have been tested and retested, Ford's assembly plants take a last look. Ten vehicles daily see wind noise audits to gauge static ultrasound and dynamic conditions. Says Williams, "Those guys are our last bastion of support in consistently getting the customer a quality product."