Search Results

Grazing flows over open windows or sunroofs may result in “flow buffeting,” i.e. self-sustained flow oscillations at the Helmholtz acoustic resonance frequency of the vehicle. The associated pressure fluctuations may cause passenger fatigue and discomfort. Many solutions have been proposed to solve this problem, including for example leading edge spoilers, trailing edge deflectors, and leading edge flow diffusers. Most of these control devices are “passive” i.e. they do not involve dynamic control systems. Active control methods, which do require dynamic controls, have been implemented with success for different cases of flow instabilities. Previous investigations of the control of flow-excited cavity resonance have used mainly one or more loudspeakers located within the cavity wall. In this study, oscillated spoilers hinged near the leading edge of the cavity orifice were used. Experiments were performed using a cavity installed within the test section wall of a wind tunnel.

To consider the acoustic quality in car design, a scientific methodology is developed in order to give an objective notation. To obtain a good correlation between the subjective and objective judgments, the first point is the choice of recording points that represent the signature of each sound sources that the human ear detects in space. Then, the information about the sound quality is extracted from signals with the computation of different appropriate parameters like “shock balance” and “roughness”. From these metrics, a notation system similar to a neural network gives a single note. At last, the processing of parameter is different for engine in stationary or run-up conditions.

In the design of Recreational Vehicle generators, a particular challenge arises from marketing and engineering teams' desire to ensure that their products meet “best in class” sound quality characteristics. Furthermore, it is desirable to know these characteristics in measurable engineering terms in the product design stage, preferably before prototypes are built and tested. Using a combination of product engineering knowledge and sound manipulation techniques, this paper shows how several generator sounds were produced. These new hybrid real/ synthetic sounds along with actual competitive generator sounds were then used for consumer jury tests to determine their preferences. The sounds include a target “best in class” sound based on mechanical design criteria. Since published A-weighted sound levels can be a useful marketing tool, in one study a few different sounds were presented to juries at varying levels of loudness.

Product sound quality is becoming increasingly critical in recent years. To help improve customer satisfaction and product quality, Delphi Automotive Systems has taken a proactive approach to address sound quality issues. The first step is to identify customers' expectations. This paper describes a sensory approach to develop sound quality criterion for a power product. To identify critical sound quality characteristics, a large number of sound samples were recorded. Jury (focus group) evaluation was conducted to identify the acceptance level and preference of each sample. Then, critical objective measures, and the criterion level of each measure, were identified via correlation analysis with subjective responses. This article presents a practitioner's point of view on how to apply sensory engineering method to engineering practice.

In the assessment of vehicle noise quality, sound characteristics caused by modulation play an important role because they contribute significantly to the perceived annoyance. The sensations can be roughness, rumble or fluctuation strength depending mainly on the modulation frequency range. The proposed generalized model for modulation parameters was developed as part of a research program with the aim of establishing an onboard analysis system for vehicle interior noise quality based on objective sound parameters. The model can be adjusted by model parameters to calculate versions of roughness, thereby accentuating different psychoacoustical assumptions. The model was successfully tested as reported in [1].

A finite element-based acoustic-structure interaction analysis tool has been developed to determine the noise transmission loss characteristics of door seal systems. This tool has been applied to determine the effects of the individual parameters, such as seal material density, seal constitutive model, separation distance between seal layers, external cavity shape, and seal prestress field, on noise transmission characteristics. Our findings indicate that the external and internal cavity shapes, seal material density, and deformed seal geometry are the key factors affecting the noise transmission through seal system. Increasing seal material density decreases the resonance frequencies and increases the overall sound transmission loss. Changing the separation distance between seal layers changes the sound transmission characteristics without changing the compression load deflection behavior of the seal system.

In an effort to better understand the effectiveness and durability of P.F.P.E.(k) fluids in solving automotive squeak and vibration problems, a test method has been developed that permits an accelerated, quantitative assessment of their impact on a variety of commonly used automotive materials. This paper describes the apparatus and method developed to conduct this testing, as well as presenting data generated to date as the impact of key fluid properties and parameters on various combinations of materials are explored. This information should allow automotive engineers to solve these problems with a much greater degree of precision and confidence.

An experimental analysis is performed on structure-borne sound in the low-frequency range under 50 Hz by applying an acoustic excitation test to a fully trimmed vehicle. This analysis makes use of the structural-acoustic reciprocity technique in which the vibration distribution of the car body is measured while the vehicle is being acoustically excited by a loudspeaker placed at the position of a passenger's ear. This paper explains why the concept of reciprocity should be applied to the study of low-frequency structure-borne sound, and discusses the causes of road noise, a typical problem in structure-borne sound associated with passenger cars.

The current ability of the Virtual Aerodynamic/ Aeroacoustic Wind Tunnel to predict interior vehicle sound pressure levels is demonstrated using an automobile model which has variable windshield angles. This prediction method uses time-averaged flow solutions from a lattice gas CFD code coupled with wave number-frequency spectra for the various flow regimes to calculate the side window vibration from which the sound pressure level spectrum at the driver's ear is determined. These predictions are compared to experimental wind tunnel data. The results demonstrate the ability of this methodology to correctly predict wind noise spectral trends as well as the overall loudness at the driver's ear. A more sophisticated simulation method employing the same lattice gas code is investigated for prediction of the time-accurate flow field necessary to compute the actual side glass pressure spectra.

Sound propagation in a typical automotive air handling system was studied using the finite element and boundary element methods. The focus was on sound propagation characters and critical resonant frequencies of the system. A given sound source was applied as the excitation to the system. Frequency response analyses were performed, emphasizing the low and mid frequency ranges. The predicted critical frequencies, associated modal configurations, and corresponding sound pressure level fields were investigated. Both the finite element and boundary element methods were applied, and results by the two methods were compared and discussed.

A sound simulation technique has recently been developed that allows the NVH engineer to subjectively and objectively predict the passenger compartment noise levels due to radiated transmission gear noise. By using the simulation technique, a noise evaluation can be performed in the early stages of vehicle development, allowing NVH analysts and design engineers to address potential noise concerns well before production of the vehicle is scheduled to begin.

A building-block method, often used for simulating automotive systems, is described in this paper for simulating a driveline system. In the method, a driveline supplier's design responsible components are modeled with explicit FE models. Model accuracy is verified by testing and correlating the components in a free-free condition. Non-design responsible components are modeled using lumped parameters and/or modal models. These components and the validated design responsible components are integrated into a system model and connected using simple lumped parameter connections. Correlation at the system level is performed by making adjustments to the connection parameters and to the parameters of the non-design responsible components. The resulting system model has been used to accurately predict operating responses in a driveline system.

This paper describes a bench test evaluation method for vibratory forces caused by a propeller shaft. Most of the vibratory forces are usually generated at the joints of a propeller shaft. They are classified as vibratory forces of axial, radial and moment directions. Axial force can be easily evaluated by measuring the load washer outputs. On the contrary, radial and moment forces can not be analyzed enough clearly even though the outputs are measured, because the load washer for both forces is the same and the outputs depend on the sum of these forces. In this paper, an algorithm for the evaluation method is described. In this method the outputs, as a sum of the forces, are by computation translated separately into kinds of forces which are generated at each joint. The translated results are calculated using an inverse matrix of influence coefficients between the forces and the outputs. Using this method, the evaluation is effective for analyzing the mechanism of the forces.

We have developed a vibration damping technique for the Oil Pan to reduce radiation noise. This technique makes use of oil viscosity. To increase vibration damping of oil pan, we use oil viscosity by forming a thin oil film between the oil pan bottom and an added inner plate. This paper presents the results of vibration tests that were conducted to study the oil damping mechanism and results of applying to a small high-speed diesel engine.

An anti-backlash camshaft gear has been developed for the Cummins B Series 4-cylinder diesel engines. This gear reduces the gear train impact to result in lower engine noise levels and improved engine sound quality. The greatest benefit is at the low idle condition, where an engine noise reduction of about 2 dB(A) has been observed. Noise reductions throughout the engine speed and load range are also significant. The first application of this noise reduction gear is for a light duty pickup truck.

Due to improving levels of vehicle refinement and the growing importance of vehicle sound quality, transmission whine is an issue of increasing interest to vehicle manufacturers. This paper describes the development of a set of novel tools for the prediction of gear whine from spur and helical external gear systems. Transmission whine is primarily generated by transmission error, which is a deviation of meshing gears from a perfectly conjugate (smooth) motion due to manufacturing tolerances, tooth corrections and elastic deflection due to transmitted torque. The transmission error excites the geared shaft and bearing system leading to dynamic forces at the bearings, which in turn excite the transmission casing causing it to radiate noise.

Gear whine can be reduced through a combination of gear parameter selection and manufacturing process design directed at reducing the effective transmission error. The process of gear selection and profile modification design is greatly facilitated through the use of simulation tools to evaluate the details of the tooth contact analysis through the roll angle, including the effect of gear tooth, gear blank and shaft deflections under load. The simulation of transmission error for a range of gear designs under consideration was shown to provide a 3-5 dB range in transmission error. Use of these tools enables the designer to achieve these lower noise limits. An equally important concern is the dynamic mesh stiffness and transmissibility of force from the mesh to the bearings. Design parameters which affect these issues will determine the sensitivity of a transmission to a given level of transmission error.

In the NVH design optimization of automotive structures, the spectral properties of dynamic forces transmitted from rotating machinery to its housing is of primary interest. This paper describes the application of an indirect dynamic force estimation technique, more commonly known as transfer path analysis, to an operational transfer case. Through the implementation of an inverse transfer matrix technique, dynamic forces transmitted to a transfer case housing are estimated at a discrete number of locations. This paper describes the experimental and analytical methodology employed for dynamic force estimation as well as statistical techniques for solution optimization. Good correlation is shown to exist between frequencies of known physical phenomena and estimated dynamic forces for a total of nine (9) operational variations of transfer case speed and torque.