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Technical Paper

Effects of Vehicle Windshield Defrosting and Demisting Process on Passenger Comfort

2001-05-15
2001-01-1729
This paper describes an investigation into the fluid flow and heat transfer on the windshield as well the effect of the air discharge from the defroster vents on passenger comfort. The investigation is both experimental and computational. Full-scale tests are conducted on a current vehicle model using non-intrusive diagnostic methods. The results presented are from numerical simulations validated by experimental measurements. The numerical predictions compare well with the experimental measurements. The locations of maximum velocity and pressure, as well as width and length of re-circulation regions, are correctly predicted.
Technical Paper

2002 Pontiac Montana Frequency Improvements Employing Structural Foam

2001-04-30
2001-01-1609
This paper documents a joint development process between General Motors and Dow Automotive to improve primary body structure frequencies on the GM family of midsize vans by utilizing cavity-filling structural foam. Optimum foam locations, foam quantity, and foam density within the body structure were determined by employing both math-based modeling and vehicle hardware testing techniques. Finite element analysis (FEA) simulations of the Body-In-White (BIW) and “trimmed body” were used to predict the global body structure modes and associated resonant frequencies with and without structural foam. The objective of the FEA activity was to quantify frequency improvements to the primary body structure modes of matchboxing, bending, and torsion when using structural foam. Comprehensive hardware testing on the vehicle was also executed to validate the frequency improvements observed in the FEA results.
Technical Paper

A Method to Determine the Power Input Associated with Rain Excitation for SEA Models

2001-04-30
2001-01-1625
Statistical Energy Analysis is used to predict the sound pressure level (SPL) in the interior of the vehicle. This is accomplished by knowing the energy sources (tire, engine, wind, etc) affecting the interior as well as the acoustic performance (absorption and transmission loss) of the interior trim components (headliner, door panels, instrument panel, etc). One of the noise sources that has not been seriously examined to-date is panel excitation by precipitation. The excitation of the roof due to raindrops can be a major noise source. Knowing how to properly model this power input would help analyze different headliners or roof treatments to minimize the SPL in the interior cavity. This will involve computational determination of mass, speed, and energy of standard water droplets for one of rain condition. A power spectrum is presented for one rain intensity condition on a test fixture.
Technical Paper

A New Method for Calculating Fluctuation Strength in Electric Motors

2001-04-30
2001-01-1588
In assessing the sound quality of electric motors (e.g., seat, mirror, and adjustable pedal motors), the sensation of Fluctuation Strength - a measure of intensity or frequency variation - has become important. For electric motors, it is typically caused by variation in the load, creating frequency modulation in the sound. An existing method for calculating Fluctuation Strength proved useful initially, but more extensive testing identified unacceptable performance. There were unacceptable levels of both false positives and false negatives. A new method is presented, which shows improved correlation with perceived fluctuation in sounds. Comparisons are made to the previous method and improvement is shown through examples of objective-subjective correlation for both seat motor sounds and adjustable pedal motor sounds. The new method is also shown to match subjective data from which the original measure of Fluctuation Strength was derived.
Technical Paper

Disc Brake Rotor Squeal Suppression Using Dither Control

2001-04-30
2001-01-1605
“Dither” control recently has been experimentally demonstrated to be an effective means to suppress and prevent rotor mode disc brake squeal. Dither control employs a control effort at a frequency higher, oftentimes significantly higher, than the disturbance to be controlled. The control actuator used for the work presented in this paper is a piezoelectric stack actuator located within the piston of a floating caliper brake. The actuator is driven in open-loop control at a frequency greater than the squeal frequency. This actuator configuration and drive signal produces a small fluctuation about the mean clamping force of the brake. The control exhibits a threshold behavior, where complete suppression of brake squeal is achieved once the control effort exceeds a threshold value. This paper examines the dependency of the threshold effort upon the frequency of the dither control signal, applied to the suppression of a 5.6 kHz rotor squeal mode.
Technical Paper

Advances in Complex Eigenvalue Analysis for Brake Noise

2001-04-30
2001-01-1603
Brake squeal has been analyzed by finite elements for some time. Among several methods, complex eigenvalue analysis is proving useful in the design process. It requires hardware verification and it falls into a simulation process. However, it is fast and it can provide guidance for resolving engineering problems. There are successes as well as frustrations in implementing this analysis tool. Its capability, robustness and reliability are closely examined in many companies. Generally, the low frequency squealing mechanism is a rotor axial direction mode that couples the pads, rotor, and other components; while higher frequency squeal mainly exhibits a rotor tangential mode. Design modifications such as selection of rotor design, insulator, chamfer, and lining materials are aimed specifically to cure these noise-generating mechanisms. In GM, complex eigenvalue analysis is used for brake noise analysis and noise reduction. Finite element models are validated with component modal testing.
Technical Paper

Analysis of Instabilities and Power Flow in Brake Systems with Coupled Rotor Modes

2001-04-30
2001-01-1602
Recent investigations by others have indicated that the dynamic response of automotive brake rotors in the squeal frequency range involves the classic flexural modes as well as in-plane motion. While the latter set creates primarily in-plane displacements, there is coupling to transverse displacements that might produce vibrational instabilities. This question is investigated here by analyzing a modal model that includes two modes of the rotor and two modes of the pad and caliper assembly. Coupling between in-plane and transverse displacements is explicitly controlled. Results from this model indicate that the coupling does create vibrational instabilities. The instabilities, whose frequencies are in the squeal range, are characterized by power flow through the transverse motion of the rotor.
Technical Paper

Roll-Down Considerations in Idle Quality

2001-04-30
2001-01-1501
Idle quality is a complex phenomenon, involving both the average vibration amplitude perceived by the occupants and also its unsteady, erratic shake amplitude (here referred to as lumpiness). Besides the periodic combustion torque produced by an ideal engine, cycle-to-cycle combustion variation causes a random torque component. Together, these torque components cause periodic and random vibration response components. The random component, by its nature, has modulating amplitude. Further, depending on their dominant frequencies and amplitudes, the random and periodic components can modulate with each other. The resulting sudden change in amplitude is often interpreted as an engine “miss” or partial burn, when in fact it may not be. This and other idle phenomenon are also highly affected by the sensitivity of the vehicle, as determined by the powertrain mounting and body structure.
Technical Paper

Frame Resonance of High Air Flow Resistivity Plastic Foams: Properties to Improve Acoustical Absorption of Composite Multi-Layered Systems

2001-04-30
2001-01-1558
The optimization of acoustical properties of multi-layered materials used in the automotive industry requires a good understanding and characterization of the various component layers. This is a particular concern in the case of headliners where performance must be balanced with packing space demands. These composite structures when used with flexible urethane foams provide good stiffness and light weight, but their acoustic performance can be sub-optimal. Measurements undertaken with poro-elastic high airflow resistivity foams highlighted frame resonances which, if exploited, might significantly improve the acoustical performance of this system. A new modeling technique based on a pseudo-macroscopic description of the poro-elastic material in the framework of a four-pole network will be used to explain these frame resonances. This formulation exploits the electro-acoustical analogy in transmission line theory.
Technical Paper

Towards a Standard for Material Friction Pair Testing to Reduce Automotive Squeaks

2001-04-30
2001-01-1547
Today vehicle owners perceive squeaks and itches inside a vehicle cabin as a major negative indicator of vehicle build quality and durability. Manufacturers struggle to bear the high costs of squeak and rattle (S&R) related warranty. Although the benefits of structural integrity and tight manufacturing tolerances with respect to the prevention of S&R are known, today's cost, weight, crash requirements, aesthetic demands and environmental/fire hazard rules quite often dictate the design of S&R prone sub-systems. Even sub-systems with the best possible structural design and manufacturing tolerances are not immune to extreme environmental conditions, and mating materials can initiate contact leading to S&R. One method of minimizing the possibility of squeaks is by the judicious selection of mating material pairs. This paper describes a test process aimed at the quantification of material pair compatibility.
Technical Paper

Validation and Improvement of Body Panels FE Models from 3D-Shape and Vibration Measurements by Optical Methods

2001-04-30
2001-01-1536
In this paper, we propose a strategy for validation and improvement of structural finite elements (FE) models using vibration and 3D-shape optical measuring method. The main advantage of these methods is to provide a whole field information allowing to speed-up the measurements, combined with an high spatial resolution ensuring updating quality. This strategy is especially adapted to the improvement of light weight body panel structures. Several application examples are presented.
Technical Paper

Reduction of the Vibration Transmission in a Front Wiper System

2001-04-30
2001-01-1478
This paper presents an experimental methodology used to attenuate the vibration transmission. It is applied to a front wiper system mounted on a car in order to reduce the noise due to the motor wiper system in the passenger compartment. It gives information on the rubber grommet behavior.
Technical Paper

Polyurethane Foam Systems For NVH and Improved Crashworthiness

2001-04-30
2001-01-1467
Recently, automotive engineers have been looking at rigid polyurethane foam systems for the advantages their application brings to vehicle design and performance. The benefits range from NVH management achieved through effective body cavity sealing and improved structural dynamics, to enhanced vehicle crashworthiness. These benefits can be realized through application of polyurethane foam systems designed for energy management. These systems offer multifunctional, low cost solutions to traditional approaches and can be modeled early in the vehicle design stage. In many cases, the overall vehicle mass is reduced as reinforcements are eliminated and/or sheet metal thickness is decreased. Dow Automotive has developed a family of water blown polyurethane foams specifically for these applications. Development has focused on foam systems designed for impact optimization, allowing OEM's to optimize the body structure content.
Technical Paper

Material Damping Properties: A Comparison of Laboratory Test Methods and the Relationship to In-Vehicle Performance

2001-04-30
2001-01-1466
This paper presents the damping effectiveness of free-layer damping materials through standard Oberst bar testing, solid plate excitation (RTC3) testing, and prediction through numerical schemes. The main objective is to compare damping results from various industry test methods to performance in an automotive body structure. Existing literature on laboratory and vehicle testing of free-layer viscoelastic damping materials has received significant attention in recent history. This has created considerable confusion regarding the appropriateness of different test methods to measure material properties for damping materials/treatments used in vehicles. The ability to use the material properties calculated in these tests in vehicle CAE models has not been extensively examined. Existing literature regarding theory and testing for different industry standard damping measurement techniques is discussed.
Technical Paper

Understanding Laboratory Versus In-Vehicle Performance of Sprayable and Sheet Applied Damping Materials

2001-04-30
2001-01-1465
Liquid spray applied damping materials have potential advantages over conventional sheet damping materials in automotive body panel vibration applications. In order to understand the acoustical impact, a laboratory based NVH study was conducted to compare the damping and stiffness performance characteristics of various sprayable damping materials versus the production damping treatment. Based on this comparison, a criteria was developed to select potentially viable sprayable damping materials for vehicle testing. In-vehicle tests were also performed and compared to the laboratory findings to understand how well the results correlate. This paper discusses a criteria for selecting sprayable damping materials based on bench-top tests for vehicle applications, and the potential benefits of sprayable materials.
Technical Paper

Using Polyester Fibers for Improving Acoustics and Saving Weight in Automotive Applications

2001-04-30
2001-01-1457
With today's push towards quieter and more fuel-efficient vehicles, the automotive industry must seek alternative materials for use in applications where the same material technology has been used for many years. Polyester fibers offer an excellent option as a material alternative to address the needs of this industry now and in the future. Polyester fibers can provide improved acoustics and lighter weight in many of the same applications as traditional decouplers and absorbers such as foam, cotton fiber (shoddy), and fiberglass. When designed properly, the polyester insulator/absorber can be used in underhood applications such as hood absorbers, engine side dash insulators, tunnel insulators, trim panel absorbers, watershields, headliner absorption, underpads, and dash insulators, to name a few. The purpose of this paper is to demonstrate the superior effectiveness of polyester products over traditional insulators.
Technical Paper

Sound Absorption Performance of Membrane Covered Insulators

2001-04-30
2001-01-1455
Molded fiberglass hood insulators (hoodliners) and engine side dash insulators (dashliners) are widely applied in vehicles for noise control. These absorptive components reduce reverberant “build-up” in the engine compartment and thus cut the noise transmission into the passenger compartment. Due to restrictions of underhood space, the hood and dash insulators normally have limited thickness (under 1.5 inches), which results in inadequate noise absorption coefficient in mid and low frequencies (100Hz - 2000 Hz), where the peak of engine compartment noise spectrum exists. It is known that covering the porous absorptive panel (at the noise incident surface) with an impermeable membrane will increase the mid-low frequency absorption coefficient of the panel at the cost of some high frequency absorption coefficient loss.
Technical Paper

Numerical Modeling of the Damping Effect of Fibrous Acoustical Treatments

2001-04-30
2001-01-1462
The damping effect that is observed when a fibrous acoustical treatment is applied to a thin metal panel typical of automotive structures has been modeled by using three independent techniques. In the first two methods the fibrous treatment was modeled by using the limp frame formulation proposed by Bolton et al., while the third method makes use of a general poro-elastic model based on the Biot theory. All three methods have been found to provide consistent predictions that are in excellent agreement with one another. An examination of the numerical results shows that the structural damping effect results primarily from the suppression of the nearfield acoustical motion within the fibrous treatment, that motion being closely coupled with the vibration of the base panel. The observed damping effect is similar in magnitude to that provided by constrained layer dampers having the same mass per unit area as the fibrous layer.
Technical Paper

New Developments on Glazings

2001-04-30
2001-01-1461
Increase of size and bending of glazings, and general improvements concerning NVH, has made of glazings one of the weak points to be treated. No specific acoustic solutions existed. First question was to determine exactly concerning which problems glazings were involved, and then what and how solutions could be found. Main problems were found concerning booming noise, transmission of airborne external noise and aerodynamic noise. To dispose of good specifications concerning products, simulations had to be done and validated: finite elements code for low frequency behavior (booming and airborne), SEA and modal superposition concerning medium and high frequency (aerodynamic and airborne). This was done for monolithic and laminated glass with their shape, free-free and taking into account boundary conditions: glues, extrusion, encapsulation.
Technical Paper

Numerical Analysis of the Flow Over Convertibles

2001-05-14
2001-01-1762
In the present study, the exterior air flow over convertibles together with the interior flow in the passenger compartment has been calculated using the commercial CFD program STAR-CD. The investigations have been performed for a SLK-class Mercedes with two occupants. The computational mesh consists of about 3 million hexahedra cells. The detailed informations of the calculated flow field have been used to elaborate the characteristic flow phenomena and increase the physical understanding of the flow. The influence of different geometrical modifications (variations of roof spoiler, variations of the draft stop behind the seats etc.) on the flow field and the air draft experienced by the occupants has been analyzed. To proof the accuracy of the numerical results, wind tunnel experiments in a full scale and 1:5 scale wind tunnel have been carried out for the basic car model as well as for several geometrical variations.
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