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The acoustic and performance characteristics of an automotive centrifugal compressor are studied on a steady-flow turbocharger test bench, with the goal of advancing the current understanding of compression system instabilities at the low-flow range. Two different ducting configurations were utilized downstream of the compressor, one with a well-defined plenum (large volume) and the other with minimized (small) volume of compressed air. The present study measured time-resolved oscillations of in-duct and external pressure, along with rotational speed. An orifice flow meter was incorporated to obtain time-averaged mass flow rate. In addition, fast-response thermocouples captured temperature fluctuations in the compressor inlet and exit ducts along with a location near the inducer tips.

In the thermal expansion valve (TXV) refrigerant system, transient high-pitched whistle around 6.18 kHz is often perceived following air-conditioning (A/C) compressor engagements when driving at higher vehicle speed or during vehicle acceleration, especially when system equipped with the high-efficiency compressor or variable displacement compressor. The objectives of this paper are to conduct the noise source identification, investigate the key factors affecting the whistle excitation, and understand the mechanism of the whistle generation. The mechanism is hypothesized that the whistle is generated from the flow/acoustic excitation of the turbulent flow past the shallow cavity, reinforced by the acoustic/structural coupling between the tube structural and the transverse acoustic modes, and then transmitted to evaporator. To verify the mechanism, the transverse acoustic mode frequency is calculated and it is coincided to the one from measurement.

The effect of aerodynamically induced pre-swirl on the acoustic and performance characteristics of an automotive centrifugal compressor is studied experimentally on a steady-flow turbocharger facility. Accompanying flow separation, broadband noise is generated as the flow rate of the compressor is reduced and the incidence angle of the flow relative to the leading edge of the inducer blades increases. By incorporating an air jet upstream of the inducer, a tangential (swirl) component of velocity is added to the incoming flow, which improves the incidence angle particularly at low to mid-flow rates. Experimental data for a configuration with a swirl jet is then compared to a baseline with no swirl. The induced jet is shown to improve the surge line over the baseline configuration at all rotational speeds examined, while restricting the maximum flow rate. At high flow rates, the swirl jet increases the compressor inlet noise levels over a wide frequency range.

We report measurements of interior automotive cabin forced acoustical response (SPL) as a function of frequency from 1 Hz to 200 Hz. The acoustical response was measured at eight positions in the vehicle tested, approximating the positions of passengers and points in between passengers. Variances in experimental data arising from the manner in which measuring equipment is setup in a particular vehicle are reported, and variations in data taken in similarly equipped vehicles are also reported. The purpose of these tests is to determine the measurement variability of a typical vehicle acoustic test.

A series of tests have been performed on a production vehicle to determine the characteristics of the external turbulent flow field in wind tunnel and road conditions. Empirical formulas are developed to use the measured data as source levels for a Statistical Energy Analysis (SEA) model of the vehicle structural and acoustical responses. Exterior turbulent flow and acoustical subsystems are used to receive power from the source excitations. This allows for both the magnitudes and wavelengths of the exterior excitations to be taken into account - a necessary condition for consistently accurate results. Comparisons of measured and calculated interior sound levels show good correlation.

The application of SEA (Statistical Energy Analysis) to the sound package design for a convertible is presented. SEA modeling was used optimize the soft-top construction and the acoustic insulation in the top-stack area (where the soft-top is stored) which were shown to be important transmission paths for tire noise. Correlation between measurement data and predictions from the SEA model is presented and good agreement shown. It is concluded that SEA can be applied to determine the special sound package requirements for convertible vehicles.

As automotive manufacturers continue to increase their use of thermoplastics for interior and exterior components, there is a likelihood of squeaks due to material contacts. To address this issue, Ford's Body Chassis NVH Squeak and Rattle Prevention Engineering Department has developed a tester that can measure friction, and any accompanying audible sound, as a function of sliding velocity, normal load, surface roughness, and environmental factors. The Ford team has been using the tester to address manufacturing plant issues and to develop a database of polymeric material pairings that will be used as a guide for current and future designs to eliminate potential noise concerns. Based upon the database, along with a physical property analysis of the various plastic (viscoelastic) materials used in the interior, we are in the process of developing an analytical model which will be a tool to predict frictional behavior.

The Indirect Boundary Element Analysis is employed for developing a computational pass-by noise simulation capability. An inverse analysis algorithm is developed in order to generate the definition of the main noise sources in the numerical model. The individual source models are combined for developing a system model for pass-by noise simulation. The developed numerical techniques are validated through comparison between numerical results and test data for component level and system level analyses. Specifically, the source definition capability is validated by comparing the actual and the computationally reconstructed acoustic field for an engine intake manifold. The overall pass-by noise simulation capability is validated by computing the maximum overall sound pressure level for a vehicle under two separate driving conditions.

This paper presents the upgrades and improvements needed to bring an old and seldom used reverberation room test suite up to current standards. The upgrades and improvements included eliminating a below-floor pit that was open to the reverberation room, improving the acoustical diffusion within the room, enlarging the opening between the reverberation room and an adjacent anechoic chamber, renovating the anechoic receiving chamber, constructing an innovative sound transmission loss test fixture, and installing of a high power reverberation room sound system.

Vehicle interior acoustic performance is an important part of customer satisfaction. Radiating panels enclosing the vehicle cabin are very important for vehicle interior quietness. One of the most critical vehicle panels for the engine noise propagation to the vehicle interior is the dash panel. Most of the engine noise propagates through the dash panel to the vehicle interior. The dash material density, thickness and its damping properties significantly influence the dash panel sound transmission performance. In this study, the dash design of “Vehicle A” has been evaluated using the Statistical Energy Analysis (SEA) modeling and NVH testing tools. SEA and physical testing of 2′×2′ square sample panels were conducted on different dash materials and lamination materials. Dash component level and vehicle level SEA to TEST correlation results are reported to highlight the NVH performance of the dash design as well as the SEA prediction capability and its applicability in vehicle design.

The acoustical frequency response of an automobile audio system, measured at the listener position, is usually far from ideal. It is therefore desirable to equalize this response electronically in the audio system. Equalization can be implemented with common analog filter circuits, but these are susceptible to performance variations due to temperature and part tolerances. As a result, the design of an analog equalization circuit can be time consuming, requiring several design, build and test iterations to achieve the desired response. In addition, due to limits in analog circuit capabilities, the design may only yield an approximate response correction. Frequency response modification, particularly for the purpose of equalization, is a popular application of digital signal processing (DSP). This paper describes a DSP-based vehicle equalization design system. It uses a DSP unit in the vehicle for performing the equalization, and a personal computer (PC) for controlling the unit.

Sound attenuation and flow loss reduction are often two competing demands in vehicle breathing systems. The present study considers a full vehicle exhaust system and investigates both the sound attenuation and the flow performance of production configurations including the catalyst, the resonator, and the muffler. Dynamometer experiments have been conducted with a firing Ford 3.0L, V-6 engine at wide-open throttle with speeds ranging from 1000 to 5000 rpm. Measurements including the flow rates, the temperatures and the absolute dynamic pressures of the hot exhaust gases at key locations (upstream and downstream of every component) with fast-response, water-cooled piezo-resistive pressure transducers facilitate the calculation of acoustic performance of each component, as well as the determination of flow losses caused by these elements and their influence on the engine performance.

This paper describes an investigation into the sound quality of passenger car and light truck closure sounds. The closure sound events that were studied included side doors, hoods, trunklids, sliding doors, tailgates, liftgates, and fuel filler doors. Binaural recordings were made of the closure sounds and presented to evaluators. Both paired comparison of preference and semantic differential techniques were used to subjectively quantify the sound quality of the acoustic events. Major psychoacoustic characteristics were identified, and objective measures were then derived that were correlated to the subjective evaluation results. Regression analysis was used to formulate models which can quantify customers perceptions of the sounds based on the objectively derived parameters. Many times it was found that the peak loudness level was a primary factor affecting the subjective impression of component quality.

This paper describes a test-based process used to identify structural characteristics of a vehicle windshield wiper system that contribute to customer impression of the sound. The method of paired comparisons determined which wiper system sounds customers preferred. Annoyance ratings of sound components then identified contributors to customer preference. Wiper motor noise was identified as the major annoyance factor affecting system sound quality. This information guided a study of the structures responsible for radiated motor noise. Laser based test methods were used to interrogate the structures clearly identifying transmission paths into the surrounding structure. Paths were then modified reducing structure-borne motor sound as measured with acoustic retests. Thus, a logical technique for hardware testing and modification guided by customer perceptions is presented allowing efforts to be focussed on the most critical aspects of vehicle sound quality.

Vehicle interior sound quality is regarded as a major quality attribute by automobile consumers and manufacturers. Whining noise, due to its steady state and tonal nature, is easily perceived as an annoyance to normal driving comfort. The blower motor in the climate control air-handling system can be a source of whining noise, especially when the motor is located in the passenger compartment. This paper describes a systematic case study carried out to identify the major noise generating mechanisms of a whining noise from the climate control air-handling system. The paper discusses the use of commonly available tools and techniques to resolve typical automotive NVH concerns resulting in improved sound quality. Particular measurement and analysis techniques presented include sound field mapping using acoustic intensity, resonance identification using transfer functions, three-axis spectrum analysis, and some physical modifications to the source and propagation paths.

Panel acoustic contribution analysis (PACA) is an advanced engineering tool to improve the NVH quality of vehicles. Using PACA areas of vehicle body panels are categorized according to their contribution to the total sound. Positive contribution areas increase the sound level as vibration amplitude increases, negative contribution areas decrease the sound level as vibration amplitude increases, and neutral areas have no significant effect on the sound level. This knowledge is important to guide vehicle NVH refinement. This paper presents the technical approach of PACA and the results of an experiment used to validate the PACA techniques. Vehicle application results to improve NVH quality and reduce weight are also included.

This paper presents a validation project carried out by the Ford Motor Company and Numerical Integration Technologies (NIT) concerning the numerical prediction of engine noise radiation. The importance and the difficulty of building a structural model (predicting accurate vibration data) are discussed. A new methodology has been developed. This method consists of a modal expansion of experimental data and allows to introduce experimental vibration measurements in the numerical approach to enhance the quality of the predictions. Provided that the structural behavior is correctly assessed, the project has shown that the BEM-based acoustic predictions agree remarkably well with test data.

The Ford Motor Company Advanced Engineering Center contains 100,000 square feet of sound and vibration laboratories, induding full vehicle chassis dynamometers, powertrain dynamometers, and sound quality evaluation chambers. The facility houses the first U.S. All-Wheel-Drive NVH Chassis Dynamometer (4 independent motor drive), the first U.S. All-Wheel-Drive NVH Powertrain Dynamometer (4 independent motor drive) and other unique elements, such as innovative wedge construction for the acoustic chambers.

A robotic sound intensity data acquisition system has been developed to overcome the problems of manual data acquistion. The system has the following performance: Accurate and repeatable positioning of the intensity probe Regular five and six sided rectangular measurement surfaces Irregular measurement surfaces around the complete powerplant, or individual components Continuous scanning or fixed point measurements Probe motion, data measurement, and storage of acoustic and geometric data integrated within the acquisition system database.

For vehicle interior noise abatement and noise treatment, it is desirable to quantitatively determine sound power contribution from each vehicle component because: (1) Sound packages can be designed with maximized efficiency if sound power contribution into a vehicle is known; (2) Acoustic leakage inside a vehicle can be determined by comparing sound power contributions from adjacent vehicle components; and (3) Sound power flow information can be used to verify Statistical Energy Analysis (SEA) model. Simple sound pressure measurement does not produce any information about sound power flow and is unsuitable for these purposes. This paper describes an in-situ determination of sound power contribution inside a vehicle using sound intensity measurements. Sound power contribution from each vehicle component was determined for engine noise at idle speed. Acoustic leakage in the vehicle was also determined.