Less Weight, More Quiet
Customers want quieter vehicles. They also want cars and trucks that have better fuel economy. Until now, the two goals were mutually exclusive because making a vehicle quieter meant adding more layers of heavy insulating materials. The weight of these materials might run from 55 lb. on a smaller vehicle, to as high as 135 lb. on a luxury sedan at a time when engineers are chasing ounces elsewhere in the car. If that isn't enough, larger pieces–like dash panel sound insulators–are often so heavy (15 to 20 lb. isn't unusual) and flexible that it takes two people and multiple fasteners to install them on an assembly line.
"Our Ultra Light technology," says David Westgate, president and CEO of Rieter Automotive Systems' Americas business unit (Farmington Hills, MI), "can take an average of 30 lb. out of a vehicle, and lower the weight of a typical dash panel by as much as 70%." (Rieter claims weight savings of between 15 lb. and 90 lb. on the 20 production vehicles currently using the system.) He proves the point by putting the current dash panel from a new Japanese mid-size car, and its Ultra Light replacement on a scale. The formed Ultra Light pad weighs 12 lb. less than the 17 lb. standard insulator, and needs five fewer fasteners. "The current unit takes two people to lift into place and secure," says Jeff VanBuskirk, v.p., Systems Engineering and Development, "while ours can be fitted by one person in less time, which frees that worker to perform other tasks."
Reducing the weight of the typical sound barrier material increases the amount of noise that is transmitted to the vehicle interior. "Conventional materials are designed to smother unwanted sounds," says VanBuskirk, "and they need the mass to do that." Ultra Light, a patented multi-layer material, absorbs sound and makes cable runs and other noise infiltration paths–including windows–less critical. "You don't want to build a sound-proof box," says VanBuskirk, "because any sound that does leak through turns the interior into a reverberation chamber. The idea isn't to keep sound from entering the cabin, but to absorb it as quickly as possible so that it doesn't become an annoyance." Anything that can cut weight and noise infiltration in this manner must be pretty special.
"There's nothing special about the materials we use," says Westgate. "These are combinations of high- and low-density fiber and foam products, though the Ultra Light carpet does use a patented weaving process." The carpet sits on a micro-porous absorbing layer over a lightweight acoustic foam/felt, and has as typical specific weight of 1.8 kg.m2, or 2.2 kg/m2 less than an insulating floor module. It is molded to the contours of the vehicle floorpan, and installs as a single unit. According to VanBuskirk, "The OEMs tell us the Ultra Light floor module sits and looks better without any degradation in acoustic performance." This has helped the company get more business earlier in the design process.
Rieter has acoustic integration responsibility on a 2003 GM platform. In this role, the company determined the best location for its materials, oversaw the suppliers, and controlled the interfaces for maximum acoustic performance. "We weren't limited to just covering existing insulation areas with our materials," says VanBuskirk, "which gave us the opportunity to negotiate the real estate we needed, cascade this down through GM and the suppliers, and defend our turf." The result, he claims, was well worth the effort: "According to GM, this is the first time a prototype at the beta build ever met the acoustic targets. There are no noise issues heading into production." This is quite a feat considering that noise issues are often at the root of vehicle launch delays. Westgate and VanBuskirk say this is just one example of what is possible through early involvement in a project.
"We removed 22 lb. of PVC undercoating on the Mercedes A-Class, and replaced it with a lightweight multiple-piece underbody shield," says Westgate. In addition, multi-piece heat shields were consolidated into single-piece acoustic units, under-vehicle air dams were eliminated, and hinged sections designed into the shield to ease servicing. "We had to pay careful attention to the panel shapes, fastener placement, and the transitions between panels so that we didn't introduce any wind noise or negatively affect the aerodynamics," says VanBuskirk. Though specific acoustic values weren't given for the A-Class, Rieter claims the underbody shield typically produces an aerodynamic improvement of about 10%, as much as a 12dB reduction in noise levels, and a 10% improvement in speech intelligibility. The Cd on the A-Class dropped from 0.32 to 0.27 with the addition of the underbody shielding.
Because Rieter's noise reduction is achieved without resorting to high-tech materials, the company often finds it must prove its claims to skeptical OEMs. "We are often asked to do an A-to-B comparison on a vehicle that is an automaker's worst application," says Westgate. "This includes showing them how much weight we saved, and having them drive the car back-to-back with an unmodified version they provide. No one has been disappointed yet." Or, for that matter, unimpressed with how less material can result in greater quiet.
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