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Technical Paper

Frequency Optimization Technique Based on the Anti-Resonance Sensitivity Method

1991-05-01
911076
There are two analytical methods for optimizing automotive structural dynamic characteristics to improve vehicle ride quality and minimize structural mass for improved fuel economy. The first method, the traditional approach, is to move the undesired structural resonant frequencies out of the range of the forcing functions by modifying the mass and stiffness parameters appropriately. However, in some cases the resonant frequencies are insensitive to parameters; these cases normally are difficult to improve. Fortunately, there is a second method, based on the natural phenomena that an anti-resonance exists for each resonant frequency. Furthermore, the sensitivity of these anti-resonance nodes to the structural parameters of mass, stiffness and damping are uniquely different. It is this difference in sensitivity that permits cases to be solved, which resist solution by the traditional first method.
Technical Paper

A Development Process to Improve Vehicle Sound Quality

1991-05-01
911079
Vehicle sound quality has become an important basic performance requirement. Traditionally, automobile noise studies were focused on quietness. It is now necessary for the automobile to be more than quiet. The sound must be pleasing. This paper describes a development process to improve both vehicle noise level and sound quality. Formal experimental design techniques were utilized to quantify various hardware effects. A-weighted sound pressure level, Speech Intelligibility, and Composite Rating of Preference were the three descriptors used to characterize the vehicle's sound quality. Engineering knowledge augmented with graphical and statistical techniques were utilized during data analysis. The individual component contributions to each of the sound quality descriptors were also quantified in this study.
Technical Paper

The Application of Noise Simulation Techniques to Conceptual Automotive Powertrain Design

1991-05-01
911077
Abstract Noise and Vibration Simulation techniques are becoming increasingly important as refinement continues to be one of the major issues in passenger vehicle design. Concentrating on in-vehicle noise, this paper hopes to show how simulation can be used at a conceptual stage to demonstrate the relative benefits of structural modification. Audible reproduction of the simulated noise making the assessment easier.
Technical Paper

On Combustion Noise and Working Stability of 6130Q Diesel Engine

1991-05-01
911072
In this paper, the authors analyse the effect of combustion process upon the combustion noise and working stability of 6130Q D.I. diesel engine, and point out that the higher combustion noise is caused by excessive premixed combustion. In order to improve engine noise it is need to decrease the injection quantity in delay period. The fluctuation of working cycles is mainly effected by the injection pump rack shaking and auto-advancer oscillating. By improving the matching of spring rigidity and mass the working stability can be improved.
Technical Paper

Noise and Vibration Refinement of the Ford 3.8 Liter Powertrain

1991-05-01
911073
Continuous improvement of the NVH performance of current production powertrains is a necessary goal of domestic auto makers. In order to maintain a competitive product, it is necessary to re-evaluate proven hardware against demanding NVH performance targets established by the competition. This paper describes an NVH investigation of component modifications to the Ford 3.8 liter powertrain. The hardware investigated includes: ribbed and isolated rocker covers, drop-in roller fulcrums, forged steel and cast iron crankshafts, crankshaft bending damper, full skirt girdle, one piece bearing cap (bearing beam), reduced weight pistons and rods, ribbed sump, and alternate crank pulleys and water pump. At the conclusion of these investigations, a complete powertrain was assembled based on the recommendations generated in this project. The NVH features included in this “quiet” 3.8 liter engine and the rationale behind the decisions are described.
Technical Paper

A New Method for Car Body Design Optimization

1991-05-01
911074
The object of this study is to present a newly developed optimization method for car body design. In the case of designing car body without roof, lowering of the bending and torsional rigidities which lead to a lowering of resonant frequencies should be considered. In order to overcome these problems, a new optimization method has been developed and applied successfully. This method is based on the pseudo least square method and all the sheet elements in the finite element method are treated as design variables.
Technical Paper

Improving Interior Noise Produced During Acceleration

1991-05-01
911078
The interior noise produced in a car while accelerating was studied from the aspect of sound quality. The quality of interior noise produced in various types of cars was first assessed subjectively by Semantic Differential method. These data were then compared with the data obtained by objective assessment. Two types of cars having two types of sound quality were then produced by making necessary modifications on the basis of the comparison. The new information gained on sound improving technology which is very effective in setting up pleasant sound environment, has been discussed in this paper.
Technical Paper

The Power Injection Method for Vibration Damping Determination of Body Panels with Applied Damping Treatments and Trim

1991-05-01
911085
The use of the Power Injection method for measurement of loss factors of complex panels with different trim systems is described. The basic theory is reviewed including the use of frequency response function measurements instead of direct measurement of input power and mean square response. The fundamental errors are presented. Practical considerations for reliable results are discussed and examplified. Examples of loss factor measurements on trimmed automotive panels are included.
Technical Paper

The Effects of Dynamic Strain Amplitude and Static Prestrain on the Properties of Viscoelastic Materials

1991-05-01
911084
The dynamic material properties of viscoelastic materials are known to be sensitive to a variety of environmental factors. A great deal of attention has been given to characterization of the effects of temperature and frequency. However, for thorough design of some noise control schemes, such as isolation systems and tuned damper devices, it is often necessary to characterize the properties of viscoelastic materials as a function of dynamic strain amplitude and static prestrain, as well as temperature and frequency. Included is a description of test techniques utilized to characterize these properties, presentation of sample properties, and discussion of the applicability of the data to the design of noise control systems.
Technical Paper

Panel Vibration Control for Booming Noise Reduction

1991-05-01
911086
For the booming noise reduction by vibration mode control, structural and acoustic analyses or optimization procedure have been studied. For obtaining know-how to reduce booming noise, it is necessary to understand the mechanism of vibration phenomenon, and then to simplify the phenomenon. In this paper, it is presented that the booming noise should be reduced by using the simplification of panel vibration mode of vehicle body. Simplification is obtained by considering that panels are forced and vibrated by the body frame of the vehicle, and that panel vibration is decided by frame movement and stiffness and mass distribution in the panel. The simplification about panel vibration control by the appropriate mass and stiffness distribution is confirmed by using floor vibration. By appropriately controlling the stiffness distribution in the dash panel, booming noise caused by the dash panel vibration was reduced.
Technical Paper

Statistical Evaluation of an Annoyance Index for Engine Noise Recordings

1991-05-01
911080
Abstract The object of this paper is to describe a statistical approach to objectively evaluate the subjective perception of the annoyance caused by engine noises using multiple regression analysis based on subjective data and given physical parameters. About 300 test persons were involved in rating the annoyance of engine noises. 60 representative engine noises, each of them characterized by 48 physical parameters, were studied. This study selects an optimal set of parameters, estimates the regression coefficients so as to minimize the deviation between calculated annoyance scores and real ratings given by test persons and thus reproduces subjective annoyance scores by means of selection and combination of objective physical parameters.
Technical Paper

Development and Application of an Evaluation Technique to Assess the Subjective Character of Engine Noise

1991-05-01
911081
This paper describes the development of a software based technique to obtain by measurement objective parameters to define the annoyance of engine noise. This task requires the application of advanced digital binaural measurement techniques. On the basis of noise data recorded via an artificial head system, fully digital data processing techniques and statistical evaluation methods for the subjective ranking procedures were developed and verified with numerous test personnel. This method lead to the ultimate development goal of being able to describe and assess engine noise character by a combination of objective parameters. Using such, an assessment procedure for subjective noise character, the necessary improvements can be made to achieve given target values. This is demonstrated by examples of application of the technique for the improvement of the noise character of power trains and vehicles.
Technical Paper

The Development of Vibration Damping Steel Sheets for Inner Panels of Automotive Vehicles

1991-05-01
911083
Vibration damping steel sheets (VDSS), which have sandwich structures with intermediate layers of resin, have been studied. The most important characteristics of VDSS for inner panels of automotive vehicles are the vibration damping properties, press formability and spot weldability. Vibration damping properties, which are quantified by loss factor,η, were influenced by both tanδ, which indicates damping capacity of resins, and elastic modulus of core resin. From a view point of vibration damping properties, resins with larger tanδ and relatively lower elastic modulus were favorable. Because these mechanical characteristics vary considerably with temperature, it is important to select the most suitable resin for the service temperature range. The relationship between noise reduction effect and loss factor of VDSS were also studied. It was experimentally confirmed that noise reduction effect of VDSS is proportional to the logarithm of their loss factor.
Technical Paper

Diagnosis and Objective Evaluation of Gear Rattle

1991-05-01
911082
The objectives of this work were to establish a method to diagnose the source of gear rattle and to evaluate the rattle objectively. The methods are described in detail, applied to two passenger cars as an example. Investigations were conducted into transmission rattle under transient conditions. By analysing the transmission casing vibration with respect to the engine flywheel angle, and presenting the data in the form of contour maps, it was shown that the two vehicles had different characteristics of gear impacts. Further measurements of the angular motion of each gear revealed the impact conditions at the input mesh in the transmission largely controlled the character of the rattle and were fundamentally different between the two vehicles. A rattle index was developed, based on the casing vibration under transient driving conditions.
Technical Paper

Study on Test and Product Variations of Noise Reduction Capabilities of Headliners

1991-05-01
911092
This paper discusses the importance of studying different variabilities (test and product variations) that may affect the noise reduction capabilities of automotive headliners, constructed from different materials. For this purpose, interior noise measurements were made at a position approximating the operator ear level, with different headliner materials under various operating conditions. For better understanding of the effect of different variabilities on acoustical performance, various single number values were computed from the measured data reduced in 1/3 octave band frequencies. Statistical data analyses show that the acoustical performance evaluation of headliners is affected by the product variation from one headliner to another, as well as experimental variation due to vehicle performance and test variation.
Technical Paper

Design Optimisation of MDI-Based Polyurethane Foam Backed Automotive Carpet Systems

1991-05-01
911087
This paper describes procedures being used to rank the acoustic performance of all-MDl (diphenylmethane di-isocyanate) foam backed automotive carpet systems. The procedures are based on the airborne noise Insertion Loss of the carpet composite measured under laboratory conditions and well established criteria used to assess human response to noisy environments, such as annoyance and speech perception. Data are presented which demonstrate how the interior noise spectrum might be influenced by the unit mass of the heavy layer, and the thickness of the foam backing layer. It is shown that although low modulus isolating systems are predicted to give superior Articulation Index performance other criteria indicate that for incident airborne noise the best overall performance should be achieved with a system having a resonance frequency within the 1/3 octave bands centred at 260Hz and 315Hz.
Technical Paper

A Shock Absorber Vibration Analysis - High-Frequency and Low-Frequency

1991-05-01
911068
The vibration characteristics of the shock absorber/strut is one of the key factors for vehicle NVH. In order to build a model of the strut, excitation tests were conducted on the struts alone to examine the mechanism causing the “cocking phenomenon” of struts at high frequencies and the “stick-slip phenomenon” at low frequencies. As a result, strut models that accurately reproduce these phenomena were constructed using the NASTRAN code and the ADAMS program, respectively.
Technical Paper

Some Results Concerning the Effect of Stochastic Parameters on Engine Mount System Behavior

1991-05-01
911054
Vehicle noise, vibration, and harshness (NVH) development typically assumes that the vehicles behave deterministically, both individually and among vehicles of the same model line and equipment level. While the deterministic assumption is true in neither case, for NVH development on an individual vehicle, the vehicle can be considered as a deterministic system responding to stochastic inputs. However, even among nominally identical vehicles, the allowable assembly and parameter tolerances result in some variability in vehicle characteristics and responses. Characterizing the expected variability would provide a number of benefits, such as helping to identify system parameters that NVH behavior is sensitive to, determining how well a NVH vehicle system model should be expected to correlate with test, and providing guides to determine when vehicle NVH behavior is significantly abnormal enough to merit a diagnostic investigation.
Technical Paper

Investigating Calculated Loudness ISO 532 for Evaluating Impulsive Sounds

1991-05-01
911088
Because of the multitude of impulsive sounds that can occur in automobiles it would be valuable to have a method for evaluating these sounds that relates well to customer response. Loudness Calculation based on ISO 532 Method B ( Zwicker' s method) was investigated for its potential as such a method. Problems occurred in obtaining valid 1/3 octave band spectra from conventional real time analyzers for the input to the calculation routine. A conflict arises between the short averaging times needed to track the impulse and the uncertainty principle (BT product rule) for the lower frequency bands. Since Zwicker' s method is based on critical bands, a four-pass analysis procedure was devised using an external filter set for the width of a critical band. The calculation routine was modified to directly accept critical band data.
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