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An investigation of the effects of changes to the interlayer material in a windshield is described. While the program covered a broad range of measurements to assess the performance different interlayer materials, this paper will focus on the development of a raindrop test that could accurately simulate noise performance in a rainstorm. For the purpose of this test a unique device was developed to simulate rainfall. This test apparatus is described. When using this device, the resulting interior noise was found to be quite similar to that experienced in the natural environment. The difference between interlayers was found to be significant using this rain drop tester. Both objective and subjective measures showed differences that were in some cases easily detectable by the average listener.

The development and validation of a brake pad insulator damping measurement procedure by the SAE Brake NVH Standards Committee is described in this paper. The details of the test procedure, test set-up and recommendations for proper test practices are described. The description provides an excellent foundation for evaluating the damping properties of a shim over a range of frequencies and temperatures. To document the repeatability of the measurement process, a Gage R&R study was conducted. The results show that a high level of repeatability is achieved over a range of temperatures and damping properties. An example application is described to illustrate the usage of the procedure. This example provides an excellent illustration of how this procedure can be used to select the best shim for a specific application. Conclusions as to the applicability of this procedure and its value to brake noise control are provided in the final section.

There is a growing emphasis on the transfer of testing from the proving ground to the laboratory. The rapid evolution of test technology has been a key to making such transfers possible. This paper presents a description of the methods, including the critical data acquisition and the control parameter generation processes, developed to efficiently perform the move from the proving ground to the laboratory. Software tools are described that permit the user to collect vehicle control and response inputs on the road and convert these to test system control parameters. The process of collecting data is shown to be straight forward with a great deal of flexibility in terms of the type and number of channels to be collected. The conversion of these data to control parameters is described with examples. Parameters included in these studies include speeds, loads, vehicle inclination, accelerations, temperatures, torques, pedal positions, pedal force, time and distance.

A thorough examination of the use of inertia simulation to provide dynamometers capable of accurately representing vehicle performance is presented. A description of a dynamometer system for brake testing using inertia simulation is provided. The models used to properly represent inertia losses, and both the programs and the results from experimental verification are described. The limitations due to motor power and existing fixed inertia in the system are described. Vehicle and dynamometer characteristics discussed include linear inertia, tire rolling resistance, bearing losses, windage, inclines, and motor field effects. Inertia simulation is shown to accurately model both steady state and transient vehicle performance.

A summary of the committee engaged in the development of a revised SAE J57 Truck Tire Noise Measurement Standard is presented. This discussion reviews the evaluations of the current standard, current and proposed international standards, and the key changes in the proposed revision to SAE J57. A major expansion to the scope of the current standard tackled by the committee was the effect of environmental conditions. The effects of road surface temperature, ambient air temperature, and wind are discussed. The measurement limitations and corrections implemented to address these factors are also described. Another key issue discussed is the effect of pavement surface. Cited references indicate that the effects of road surface variation can be greater than tire design differences. The committee developed a specification for a standardized surface to address this concern. Another improvement of the current standard is in the specification of tire operating conditions.

A description of the confirmation tests conducted by the Tire Noise Standards Committee for the revised J57, Truck Tire Noise Measurement Standard is presented. The goal of these tests was to determine the repeatability and variability associated with the procedures and ranges of parameters specified in this revision. Two sets of tires were tested over a range of measurement parameters. The parameters examined included tire type, ambient temperature, pavement surface temperature, coast-by speed, and trailer drawbar length. Finally, the total coast-by noise measurement variability according to this new procedure is estimated.

It is difficult to quantify the portion of coasting vehicle noise that is due to tire-pavement interaction alone. There are often contributions from aerodynamic noise of the vehicle, transmission whine, noise from suspension components, and other miscellaneous sources. The towed-trailer method used in the revised SAE J57 standard has been shown to be an effective means of isolating tire-pavement noise for truck tires. This paper reports the results of a test program conducted by SAE Tire Noise Standards Committee to evaluate the feasibility of towed-trailer coast-by testing of passenger and light truck tires. The results of tests conducted in April 1996 at the Ohio Transportation Research Center are described and they indicate that accurate measurements are possible for towed-trailer testing of passenger tires. It is shown that a key aspect of performing such a test is reducing the noise of the tow vehicle and that sufficient reduction is possible even for extremely quiet test tires.

As part of the development of a New SAE Recommended Practice for Brake Natural Frequency and Damping Measurements, the US Working Group on Brake NVH conducted a series of Round Robin tests and developed detailed recommendations for such measurements. The results of these tests are summarized in this paper. Initial results showed that there were difficulties with the identification of the types of modes being measured. However, when the results were carefully categorized, the measured natural frequencies agreed quite well. The measured damping coefficients showed much larger variations. In some instances, differences of more than 200% were found between testers. The steps taken to improve the consistency of results and subsequent Round Robin tests are described.

As commercial acoustic intensity measurement devices are introduced to the market place, it is essential that the limitations of the two-microphone technique used in these devices are well defined. This paper presents an analytical study of measurement errors due to the finite difference approximation in the intensity formulation. Unlike previous studies which treated only ideal point sources, this study investigates errors associated with finite sources. The sources considered include a pulsating sphere, an oscillating sphere, and a general two-source model. Errors determined for measurements with these sources are plotted for typical measurement conditions. Errors are found to closely resemble those for ideal point sources with the exception of the general two-source model.

The character and level of noise in a vehicle has changed significantly from the 1970s to today. In the 1970s the challenge was to permit communication from the front seat to the rear at highway speeds. In the last decade, the challenge has grown to provide a vehicle that provides the right "type" of sound while isolating the occupants from disturbing exterior noise. This may involve adding engine noise simulation and sculpting the interior sound to meet customer expectations. More recently, the challenge has been to modify noise controls for extreme light weighting exercises and electric vehicles. In addition, electric vehicles present a different sound environment and the challenge of determining what an EV should sound like. This paper will attempt to discuss these challenges and talk about the future of vehicle interior noise.

As other vehicle systems have become more refined, more attention must be placed on brake NVH issues because they can cause a negative customer experience. From the laboratory to the road, the use of technology as well as further study by engineers is helping to lessen noise, judder, and vibration in cars. This book provides readers with a fundamental understanding of current practices for measuring and testing brake NVH. From coverage of basic definitions and concepts to in-depth analysis of on-road testing procedures, it will serve as a comprehensive reference guide for brake test technicians, test engineers, lab managers, and others who work on making brakes quieter, smoother, more refined, and more reliable. Readers will learn how to test for brake noise, what tools to use, and which recent standards and practices have led to the successful measurement of brake noise and vibration.