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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

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

Comparison of Performance between Several Vehicle Windshield Defrosting and Demisting Mechanisms

2001-03-05
2001-01-0582
The safety and comfort aspects of passenger cars are significant sales argument and have become a topic of rising importance during the development process of a new car. The objective of this study is to compare the performance of several current model vehicles, highlight the drawbacks of current defrosting/demisting systems and point the way to improved passive mechanisms. The investigation is experimental. The experiments are carried out using full-scale current vehicle models. The results show that the current designs of the defroster nozzle give maximum airflow rates in the vicinity of the lower part of the windshield, which decrease gradually towards the upper parts of the windshield. This hinders and limits the vision of the driver, particularly at the top of the windshield, which can be uncomfortable and indeed dangerous.
Technical Paper

Conditions for Incipient Windshield Fogging and Anti-Fog Strategy for Automatic Climate Control

2001-03-05
2001-01-0583
This paper describes a strategy, suitable for use in a climate control ATC (Automatic Temperature Controller) for predicting the onset or existence of fog (or misting) conditions and automatically taking action to avoid or reduce such conditions. Two variables currently measured by the ATC, cabin air temperature and ambient (outside) temperature are combined with cabin air relative humidity information provided by an additional sensor to allow the calculation of a degree of likelihood of windshield/window fogging. As fogging conditions are approached, a staged alteration of climate control strategy can relieve or even avoid altogether windshield fogging.
Technical Paper

A Magnetorheological Door Check

2001-03-05
2001-01-0619
Several shortcomings of mechanical door checks are overcome using a magnetorheological damper. Because the damper is electrically actuated, it can check in any desired position. The logical decision to activate or release the door check can be made either by passive circuitry based on input signals from switches attached to door handles or under microprocessor control, in which case the decision can take into account a variety of unconventional input factors, including the magnitude of the force applied to the door, the rate of change of the applied force, and the angle of door opening. With the addition of an appropriate proximity sensor, the controllable damper can prevent the door from inadvertently hitting a nearby obstacle. Details of the damper mechanism are described, and several implemented control strategies, both passive and microprocessor based, are discussed.
Technical Paper

The Emerging Fabric of Seamless Mobility

2000-11-01
2000-01-C033
Consider this recent data about the "speed'' of the information age: In a sixty-month window beginning in the year 1995, the number of cellular phone subscribers increased from 90 million to 330 million, the number of people on the internet went from about 5 million to just under 200 million, and not surprisingly the number of websites grew from a few thousands to 50 million. Now further consider that almost every cellular phone subscriber is also an automobile user, be it as a driver or a passenger. A fabric of mobility soon emerges --- one that is formed by the meshing of the strands of information mobility with those of personal mobility. In this paper we explore a "new frontier'' --- a "territory'' on this multidimensional fabric that is defined by the demands of seamless mobility. The typical daily cycle of events in our lives involve many different modalities and time-phases of mobility. We examine the rapidly increasing demands of seamless mobility in this context.
Technical Paper

Friction Induced Paint Damage: The Role of Coating Attributes

1996-02-01
960914
The recent inclusion of painted plastic fascias/bumpers into automotive applications has necessitated the evaluation of potential in-service damagability. One failure mode that has been identified, that of friction-induced paint/substrate damage, has been simulated in a laboratory environment. Our goal was to evaluate the effects of coating attributes, both thermal and mechanical, on subsequent performance of painted thermoplastic olefin (TPO) materials. It was determined that the most significant parameters in the paint which contributed to damage were the glass transition temperature, the secant modulus at break, and the static coefficient of friction. This paper will discuss techniques and results used to reach these findings.
Technical Paper

Finite Element Prediction of Backlite Molding Squeak Noise

1997-02-24
970584
The backlite molding squeak noise is caused by the stick-slip type of friction between the window molding and the body panel. To predict if the molding would squeak a finite element analysis technique which uses the nonlinear explicit code LS-DYNA3D has been developed. The three dimensional finite element simulation technique is based on the threshold displacement velocity spectrum and the relative movement of the window glass with respect to the body panel. Comparisons between FEA analysis and tests are also presented in this paper.
Technical Paper

Intrusion Factors and Their Effects on Steering Column Movements During Vehicle's Frontal Impact Testing

1997-02-24
970573
Significant dashpanel intrusion is seen in some cars after severe frontal crashes at high speeds or after offset impact with rigid barrier or both. This intrusion may also result in severe steering column displacements and rotation. Knowledge of both responses is critical for designing an efficient vehicle front end that will respond well in crash. The intrusion has an effect on deciding the car front end length, while the column movements have an effect on the driver dummy's response. For reasons of developing efficiency and safety in vehicles and due to lack of published research, studies were conducted to understand the nature of the intrusion phenomenon as well as the mechanics of the steering column movement in the presence of intrusion. This paper describes an experimental investigation on intrusion and steering column movements.
Technical Paper

Development of a Door Test Facility for Implementing the Door Component Test Methodology

1997-02-24
970568
This paper describes the development of an automated Door Test Facility for implementing the Door Component Test Methodology for side impact analysis. The automated targeting and loading of the door inner/trim panels with Side Impact Dummy (SID) ribcage, pelvis, and leg rams will greatly improve its test-to-test repeatability and expedite door/trim/armrest development/evaluation for verification with the dynamic side impact test of FMVSS 214 (Occupant Side Impact Protection). This test facility, which is capable of evaluating up to four (4) doors per day, provides a quick evaluation of door systems. The results generated from this test methodology provide accurate input data necessary for a MADYMO Side Impact Simulation Model. The test procedure and simulation results will be discussed.
Technical Paper

High Strain-Rate Tensile Testing of Door Trim Materials

1997-02-24
971064
The objective of this study was to determine dynamic tensile characteristics of various door trim materials and to recommend a practical test methodology. In this study, Polypropylene (PP) and Acrilonitryl Butadiene Styrene (ABS) door trim materials were tested. Slow speed (quasi-static-0.021 mm/s) and high speed tests were conducted on a closed loop servo-hydraulic MTS system. The maximum stress of these materials increased from quasi-static to dynamic test conditions (as much as 100%). The dynamic stiffness of PP increased two times from quasi-static tests. No significant change in stiffness was observed for ABS during quasi-static and dynamic tests at different strain-rates. Quasi-static and medium strain-rate (10-20 mm/mm/s) tests may be adequate in providing data for characterizing the dynamic behavior of trim materials for CAE applications. Strain gages can be used to measure the quasi-static and in some cases, dynamic strain.
Technical Paper

Application of a Laser Vibrometer for Automotive Aeroacoustic Analysis

1997-05-20
972065
The Scanning Laser Vibrometer can make full field, high resolution measurements of the normal surface velocity of automotive door glass and sheet metal vibrations. These properties make the vibrometer a very useful tool for locating compliant and noisy areas on the surface of a vehicle, generated by exterior wind noise. An advantage of the vibrometer is that it measures the vibration of the surface, capturing the transfer of noise through the surface, rather than simply measuring the exterior wind noise. Methods of experimental setup, testing, and problem analysis on outside rear view mirror/A-pillar/Sideglass configurations and body panel vibrations are discussed in the paper.
Technical Paper

A CAE Methodology for Reducing Rattle in Structural Components

1997-05-20
972057
Squeak and rattle has become a primary source of undesired noise in automobiles due to the continual diminishment of engine, power train and tire noise levels. This article presents a finite-element-based methodology for the improvement of rattle performance of vehicle components. For implementation purposes, it has been applied to study the rattle of a glove compartment latch and corner rubber bumpers. Results from the glove compartment study are summarized herein. Extensions to other rattle problems are also highlighted.
Technical Paper

Measures to Quantify the Sharpness of Vehicle Closure Sounds

1997-05-20
971910
Impulsive sound events (i.e. door closing) are often characterized as being undesirably sharp sounding. A high degree of perceived sharpness is normally related to large amounts of high frequency energy relative to the low frequency energy. In this project third octave data generated from a filterbank was used to calculate the center of gravity (cg) of the third octave bands. The result is the frequency corresponding to the centroid of the third octave data. Sounds with substantial high frequency energy have a centroid location that occurs at a higher frequency. The mean of the third octave cg over the duration of the transient event was investigated, in addition to sharpness as defined by Aures [1] and calculated on a commercially available analyzer. Correlation analyses to subjective data indicate that the mean third octave cg and the commercially available method produce comparable results for the vehicle closure sounds studied here.
Technical Paper

A Predictive Model for the Interior Pressure Oscillations from Flow Over Vehicle Openings

1997-05-20
971906
An analytical model based on “vortex sound” theory was investigated for predicting the frequency, the relative magnitude, the onset, and the offset of self-sustained interior pressure fluctuations inside a vehicle with an open sunroof. The “buffeting” phenomenon was found to be caused by the flow-excited resonance of the cavity. The model was applied to investigate the optimal sunroof length and width for a mid-size sedan. The input parameters are the cavity volume, the orifice dimensions, the flow velocity, and one coefficient characterizing vortex diffusion. The analytical predictions were compared with experimental results obtained for a system which geometry approximated the one-fifth scale model of a typical vehicle passenger compartment with a rectangular, open sunroof. Predicted and observed frequencies and relative interior pressure levels were in good agreement around the “critical” velocity, at which the cavity response is near resonance.
Technical Paper

Modelling the Dissipative Effect of Seal Air Hole Spacing and Size on Door Closing Effort

1997-05-20
971901
Door weather strip seals are designed with ventilation holes spaced at regular intervals along the seal system to expedite the flow of air from the seal system during the door closing process. The flow of air through the ventilation holes represents a nonlinear damping mechanism which, depending upon hole size and spacing, can significantly contribute to door closing effort. In this study we develop one- and two- dimensional versions of a nonlinear damping model for seal compression load deflection (CLD) behavior which incorporate the effects of seal damping response due to air flow through the ventilation holes. The air flow/damping models are developed from first physical principles by application of the mass and momentum balance equations to a control volume of entrapped air between consecutive air ventilation holes in the seal system.
Technical Paper

Acoustic Analysis of Vehicle Ribbed Floor

1997-05-20
971945
Ribbed floor panels have been widely applied in vehicle body structures to reduce interior noise. The conventional approach to evaluate ribbed floor panel designs is to compare natural frequencies and local stiffness. However, this approach may not result in the desired outcome of the reduction in radiated noise. Designing a “quiet” floor panel requires minimizing the total radiated noise resulting from vibration of the floor panel. In this study, the objective of ribbed floor panel design is to reduce the total radiated sound power by optimizing the rib patterns. A parametric study was conducted first to understand the effects of rib design parameters such as rib height, width, orientation, and density. Next, a finite element model of a simplified body structure with ribbed floor panel was built and analyzed. The structural vibration profile was generated using MSCINastran, and integrated with the acoustic boundary element model.
Technical Paper

Experimental Assessment of Wind Noise Contributors to Interior Noise

1997-05-20
971922
Wind noise reaches the interior of a vehicle through a variety of mechanisms including: aerodynamic excitation of vibration and reradiation from the greenhouse surfaces; acoustic transmission through door seals including gaps and glass edge leaks, and due to airborne transmission of noise generated by wind interaction with body panels. This paper presents experimental results that quantify contributions to interior noise from individual greenhouse surfaces and from airborne sources on the underbody. The measurements were carried out on a production vehicle in a wind tunnel. Greenhouse surfaces, in addition to the driver window are important contributors to interior noise along with airborne transmission of noise generated due to the flow over and through the vehicle underbody.
Technical Paper

An Alternative Approach to Robust Design: A Vehicle Door Sealing System Example

1997-05-20
971924
Designing a high-quality door sealing system at low cost is an economic and technological engineering challenge. Robust design is a systematic and efficient technique to meet this challenge of design optimization for performance, quality, and cost. This technique, also called parameter design, focuses on making product and process designs insensitive (i.e. robust) to hard-to-control variations called noise factors. In this paper, we illustrate and apply the principles of robust design using a response model approach to a door sealing system design problem where vehicle interior sound is the primary response being studied. The Appendix contains a glossary of all italicized words for reference.
Technical Paper

Use of FCRASH in a Door Openability Simulation

1997-04-08
971526
During frontal and rear end type collisions, very large forces will be imparted to the passenger compartment by the collapse of either front or rear structures. NCAP tests conducted by NHTSA involve, among other things, a door openability test after barrier impact. This means that the plastic/irreversible deformations of door openings should be kept to a minimum. Thus, the structural members constituting the door opening must operate during frontal and rear impact near the elastic limit of the material. Increasing the size of a structural member, provided the packaging considerations permit it, may prove to be counter productive, since it may lead to premature local buckling and possible collapse of the member. With the current trend towards lighter vehicles, recourse to heavier gages is also counterproductive and therefore a determination of an optimum compartment structure may require a number of design iterations. In this article, FEA is used to simulate front side door behavior.
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