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Windshields, with their low internal damping, are an acoustical weak link in automotive glazing. In the past, acoustically-enhanced glass products were typically achieved by utilizing solid and mass product design elements to increase the glass thickness. This is no longer acceptable as automakers are interested in weight savings, especially as they develop vehicles that are more fuel-efficient. Laminated safety glass, with a standard polyvinyl butyral (PVB) interlayer, is used extensively for automotive windshields and side glazing, and offers improved acoustical performance over tempered glass. However, the standard PVB interlayer is not designed specifically for acoustical and Noise, Vibration and Harshness (NVH) purposes. Studies of the parameters affecting acoustical properties and actual noise reduction capability of standard laminated glass led to the development of an acoustical grade PVB interlayer.

The growing trend in demand for vehicles with diesel engines, especially in Europe, is a result of consumer demand for vehicles that offer greater fuel economy. This trend is gaining attention in North America as well. However, diesel vehicles are notorious for their NVH issues including engine vibrations that reverberate through the passenger cabin and noise that transmit through windshields as both structure-borne noise and airborne noise. Windshields, normally seen as the big hole in the front of the vehicle through which noise passes into the vehicle cabin, can be transformed to provide noise-mitigating properties by redesigning the PVB interlayer to reduce noise entering the vehicle. In essence, an acoustical windshield can help dissipate noises to a significant degree. NVH testing was performed on vehicles with diesel engines and acoustical-grade windshields, and vehicles with diesel engines and windshields made with standard PVB.

Several windshield constructions are designed and tested for the objectives of weight savings and improved vehicle wind noise. They include standard windshield constructions representing typical production windshields installed on most vehicles today, and acoustic windshield constructions of different glass thickness with weight saving and NVH improvement as the design objectives. The acoustic windshields contain an acoustically enhanced polyvinyl butyral (PVB) interlayer, Vanceva™ Quiet. The windshield constructions are tested for transmission of external airborne noise in laboratory and wind noise and road noise on high-speed test tracks. Laboratory study shows significant opportunities for both improved acoustics in 1500 Hz to 6000 Hz frequency region - a key range for wind noise and airborne noise transmission - and weight savings.

Noise-vibration-harshness (NVH) design optimization problems have become major concerns in the vehicle product development process. The Body-in-White (BIW) plays an important role in determining the dynamic characteristics of vehicle system during the concept design phase. Finite Element (FE) models are commonly used for vehicle design. However, even though the speed of computers has been increased a lot, the simulation of FE models is still too time-consuming due to the increase in model complexity. For complex systems, like vehicle body structures, the numerous design variables and constraints make the FE simulations based optimization design inefficient. This calls for the development of a systematic and efficient approach that can effectively perform optimization to further improve the NVH performance, while satisfying the stringent design constraints.

Noise transmission through automotive windshields is the subject of extensive laboratory acoustic and full scale high-speed track NVH evaluation. Standard windshields transmit structure-borne noise through resonances at low frequencies, and wind noise and airborne noise due to coincident effect at high frequencies. Approaches to enhance windshields NVH performance and to improve vehicle interior noise quality are explored. The study shows that the most effective approach is to design a new interlayer for windshields. This leads to the development of an acoustic grade PVB interlayer. To quantify the noise reduction by windshields with the new PVB interlayer, Solutia commissioned NVH testing of the windshields installed on cars, comparing these with factory-equipped standard windshields. Dynamic responses of the windshields were studied in laboratory on a dynamometer and resulting frequency response functions measured.