Silence of the cams

Anyone who remembers the 1994 Jeep Grand Cherokee commercial in which the vehicle's window rises to eliminate the sound of a background waterfall understands that quiet sells in today's automotive marketplace.

Automakers discovered several years ago that safety sells, now they are becoming aware that silence is golden as well. Instead of using Band-Aid fixes at the assembly plant or relying on the radio volume knob to cover noise, vibration and harshness (NVH), smoothness and quiet are now being engineered into entry-level and luxury models alike.

Oldsmobile's Aurora and Buick's Riviera boast a stiff chassis resulting in a smoother and quieter ride. The new Ford Taurus and Mercury Sable have been redesigned using a stiffer frame with the same consequence. The redone Chevrolet Cavalier/Pontiac Sunfire platform claims similar chassis frequency readings as Aurora and Riviera.

"Customers are demanding quieter cars but not silent cars," says Cadillac Chief Engineer Ed Zellner. "You can make an environmental system blower motor totally silent, but when customers get in a hot or cold car they want to hear the air blowing around."

Mr. Zellner says certain sounds give a car character. "We've engineered in engine noise on our STS and Eldorado Touring Coupes so customers can hear those 300 hp when they step on the gas," he explains. "But they're quiet when just cruising around."

As OEMS try to soothe NVH through design and engineering they are asking their suppliers to solve problems at the component level.

"Automakers are moving from a reactive position to a proactive stance on NVH," says Matt Bolten, an account representative at DuPont Automotive. "It's putting a lot of pressure on the suppliers, particularly those that supply windows, doors, instrument panels and seating."

Mr. Bolten adds that squeak-free specifications are being written into supplier system contracts and that one automaker is even scrutinizing the noise a seat belt makes when it rubs seat upholstery.

Why are automakers pushing NVH issues? Perhaps the more important question is why are consumers suddenly so concerned about quiet cars? Gerald Jusco, executive vice president at insulation component manufacturer Rieter Automotive Globe Inc., has hypotheses for both questions.

"The sounds people hear in a vehicle consciously and subconsciously affect their perception of the quality of the vehicle," says Mr. Jusco. Consumers, on the other hand, "are buying more premium sound systems and they want to be able to hear them," he adds. "They want their automobiles to be quiet places for conversations, talking on the phone and relaxation."

Designing a stiffer chassis solves one NVH problem and prevents another. The smoother ride it offers not only makes the occupants more comfortable but also keeps components from shaking loose and rattling. Still, suppliers are doing a variety of things to keep those components in place and to eliminate objectionable noises while operating.

Plastics companies have proven that molding components from plastic can eliminate parts, which reduces the opportunity for things to shake loose. General Motors Corp.'s Delphi Interior and Lighting Systems Div. and GE Plastics earlier this year introduced the Super Plug door module, which consolidates 61 parts into one. Besides reducing system cost, mass and assembly time, the Super Plug eliminates many attachments that could loosen over time and create rattles.

Some plastics by their nature also dampen noise, so molded parts can be a double-edged weapon in the war against NVH. New materials and component refinements also are joining the battle.

To stop a torsion bar noise on an undisclosed Big Three sport/utility vehicle, DuPont developed a unique rubber sheet material that is a mix of four existing products. Called Wearforce, it eliminates noise when fastened to one of two rubbing pieces of metal.

"Wearforce combines the wear resistance of Kevlar fiber, the conformability of Lycra spandex, the temperature resistance of Viton fluoroelastomer and the lubricity of Teflon," says Sandy Horner, business development manager at DuPont, who adds that the success of this composite should lead to further blending of DuPont materials.

Other DuPont NVH solutions include XTC-U, Thermolite and Keldax. A derivative of XTC recs.cled thermoplastic sheet, XYC-U (the U stands for unconsolidated) is drape-formed over a three-dimensional shape rather than compression molded. The result is a structural foam-like material for door panel interiors, package trays and hoodliners that can be spot-molded to strengthen attachment points or speaker mounts, says John Fisher, a DuPont development engineer.

Thermolite, normally a thermal insulation for gloves, boots, jackets and sleeping bags, debuted as acoustical insulation on 1995 Chrysler Concorde, New Yorker and LHS and the Dodge Intrepid and Eagle Vision upper and lower rear quarter trim panels. DuPont says automakers are testing the material for use in dash-liner, wheel-well, door-panel, quarter-panel and hoodliner-applications.

Cadillac Products' Soundloc essentially is a watershield material that doubles as a noise insulator, with the help of DuPont's Keldax thermoplastic, on the Jeep Grand Cherokee, Chrysler's new minivans, the Neon, the 1996 Sebring convertible, Ford's Mustang and many Cadillac models.

Always an area of NVH concern is the vehicle's glass, which can work loose over time and rattle. DuPont's Alcryn melt-processible rubber serves as window lace trim on the Acura Legend, Mazda 626, Toyota Corolla, Dodge Intrepid, Eagle Vision and Ford Probe. Its low-temperature flexibility and energy absorption help eliminate the rattles, says DuPont.

3M Corp. introduced a new film earlier this year designed specifically to reduce interior noise, vibration, squeaks and rattles. 3M Brand 9343 Conformable Sound Management Film is a high-performance acrylic adhesive, says the company, which fits intricate, irregular part geometries for long-term bonding.

Seemingly unimportant components such as carpet backing, also can be key in the NVH battles. ICI Polyurethane's Rubiflex acoustical foam can be tailored to a range of stiffnesses depending on the end use. The company says it offers reduced weight and improved fit and finish in carpet underlay and dash insulator applications.

Once interior noises are eliminated or isolated through engineering, other noises become more noticeable. Many times the offending noises can be traced to the engine compartment. More often these days, engineers will attack the noise at its origin rather than covering it up with a shield of some sort.

Drivetrain vibration, which is transmitted into the chassis, can be reduced with composite driveshafts and acoustic constant velocity (CV) joints, says GKN Automotive AG. GKN can replace the standard two-piece driveshaft with a one-piece design made of carbon fiber, eliminating the intermediate bearing and joint.

GKN's fixed CV joints have up to a 50% larger working angle, which, it says, offers a larger joint interior, longer spring travel paths and smaller turning circles for smoother operation.

The Spicer Driveshaft Div. of Dana Corp. is using a tunable aluminum grapwte that allows the company to adjust or fine-tune certain characteristics of the driveshaft assembly to increase stiffness to control noise. This material is being used on GMC pickups, says a Spicer spokesman.

Spicer also is developing metal matrix composites (MMC) to reduce vibrations. MMC consists of tiny aluminum oxide particles that are added to aluminum driveshafts to increase component strength, much the same way pieces of metal are added to cement to bolster concrete.

To quell engine vibration, New Jersey-based ContiTech Group North America, a division of Germany's Continental AG, has developed hydraulic engine mounts. These mounts, says ContiTech, are made of a highly elastic elastomer support that bears static weight. Inside the.mount, hydraulics control the degree of cushioning, depending on the negative pressure exerted on the vehicle. Negative pressure activates the system.

ContiTech also advocates supporting a vehicle's propeller shaft on elastic bearings. These bearings are a combination of elastomer and metal parts designed to work together to provide optimum support and isolate the vibrations.

When engine noise and vibration is isolated, still other chassis noises crop up. Freudenberg-NOK General Partnership, which manufactures several NVH-reducing parts, replaced a rubber suspension strut spring isolator with one made of microcellular polyurethane, which "significantly improved noise" on the Chrysler LH platform, says a Freudenberg-NOK spokesman.

Despite all the best engineering in the world, engines and most other vehicle mechanical components make noise. That's where companies like Mr. Jusco's Rieter Automotive Globe and Perstorp Components Inc. enter the picture. Both suppliers deliver noise absorption, barrier and dampening systems. Perstorp, a Swedish company, recently moved into new headquarters/technical center facilities in Plymouth Township, MI.

The new facility features a hemianechoic (sound absorbant) chamber with a chassis dynamometer, among other equipment, to test for and isolate vehicle noises. Rieterautomotive Globe has similar equipment that it uses not only to test its components but to benchmark. "We have a library of NVH data from vehicles from around the world," says Mr. Jusco, illustrating the importance of NVH to the global industry.