Search Results

This paper presents a case study on reducing road noise of a passenger vehicle. SEA, insertion loss and sound intensity measurements were the tools used in the study. A SEA model was constructed to predict the primary paths (panels or area) contributing to the overall interior sound field. Insertion loss measurements were used to verify the primary contributing paths identified using SEA. To provide further details of the primary paths, intensity maps of identified panels were measured allowing detailed reconstruction of the contributory panels. The SEA model, insertion loss, and intensity maps aided in providing possible design fixes that will effectively reduce road noise. Finally, comparisons of predicted results versus actual results at both a subsystem and a full vehicle level are included in this paper.

Sound absorption is one way to control noise in automotive passenger compartments. Fibrous or porous materials absorb sound in a cavity by dissipating energy associated with a propagating sound wave. The objective of this study was to evaluate the acoustic performance of a cotton fiber absorbing material in comparison to a new polypropylene fibrous material, called ECOSORB ®. The acoustical evaluation was done using measurements of material properties along with sound pressure level from road testing of a fully-assembled vehicle. The new polypropylene fibrous material showed significant advantages over the cotton fiber materials in material properties testing and also in-vehicle measurements. In addition to the performance benefits, the polypropylene absorber provided weight savings over the cotton fiber material.

Noise due to the flow over an automobile A-pillar rain gutter in isolation was computed using a two step procedure. Initially the flow solution was obtained by solving the Reynolds Averaged Navier Stokes (RANS) equations. Acoustical Sources were extracted from the flow solution and propagated to the far-field using the Lighthill-Curle equation. Experiments were conducted to evaluate the computations. Compared results include steady pressures, time dependent pressures, and sound intensity levels. Computed results and experimental data were reduced in a similar way to ensure a one to one comparison. Computed results are in good agreement with the experimental values. A-weighted noise levels are predicted reasonably well.

Elastomeric isolators are used in a variety of different applications to reduce noise and vibration. To use isolators effectively requires the product design and development engineer to satisfy multiple objectives, which typically include packaging restrictions, environmental criteria, limitations on motion control, load requirements, and minimum fatigue life, in addition to vibration isolation performance. An understanding of elastomeric material properties and the methods used to characterize elastomeric component behavior is necessary to achieve desired performance. Typical design criteria and functional objectives for various isolator applications, including powertrain mounts, suspension control arm bushings, shock absorber bushings, exhaust hangers, flexible couplings, cradle mounts, body mounts and vibration dampers are also discussed.

This paper describes an axle gear whine noise reduction process that was developed and applied using a combination of experimental and analytical methods. First, an experimental Transfer Path Analysis (TPA) was used to identify major noise paths. Next, modeling and forced response simulation were conducted using the Hybrid FEA-Experimental FRF method known as HYFEX [1]. The HYFEX model consisted of an experimental FRF representation of the frame/body and a finite element (FE) model of the driveline [2] and suspension. The FE driveline model was calibrated using experimental data. The HYFEX model was then used to simulate the axle noise reduction that would be obtained using a modified frame, prior to the availability of a prototype. Hardware testing was used as the final step in the process to confirm the results of the simulation.

It is well known that lining reduction through wear affects contact pressure profile and noise generation. Due to high complexity in brake noise analysis, many factors were not included in previous analyses. In this paper, a new analysis process is performed by running brake “burnishing” cycles first, followed by noise analysis. In the paper, brake lining reduction due to wear is assumed to be proportional to the applied brake pressure with ABAQUS analysis. Brake pads go through four brake application-releasing cycles until the linings settle to a more stable pressure distribution. The resulting pressure profiles show lining cupping and high pressure spots shifting. The pressure distributions are compared to TekScan measurements. Brake noise analysis is then conducted with complex eigenvalue analysis steps; the resulting stability chart is better correlated to testing when the wear is comprehended.

Brake squeal has been a persistent quality issue for automobile OEMs and brake system suppliers. The ability to model and measure brake squeal dynamics is of utmost importance in brake squeal reduction efforts. However, due to the complex nature of brake squeal and the wide frequency range in which it occurs, it is difficult to accurately correlate and update analytical models to experimental results. This paper introduces a systematic and rigorous correlation and updating process that yields FE models, which can accurately reproduce high-frequency brake squeal dynamics.

This paper discusses a standard procedure to reduce brake squeal using CAE and robust synthesis & analysis techniques. There are several techniques available to evaluate the stability of a system. Complex eigenvalue analysis is used for predicting and reducing squeal propensity. The complex eigenvalue method was implemented using SOL110 in version 2001 of MSC/NSTRAN for this study. We applied the signal to noise ratio using an orthogonal matrix to evaluate the main parameter effects and minimize the sensitivity.

Appropriate road noise levels are critical to perceived quality in today's highly competitive automotive industry. Tire noise is often one of the dominant sources. In order to provide effective noise control schemes it is imperative to fully define the noise paths. In this paper, a case study of an experimental lab method is presented that allows definitive understanding of the structure-borne and airborne spectral contributions of tire noise. For this study, interior noise data were collected using a 10 ft road wheel. Data were collected for the front and rear tires. These measurements contained both the structure-borne and airborne contributions. The same test was performed with the tire physically disconnected from the vehicle structure. This measurement contained only the airborne contribution. The structure-borne contribution was then calculated as the difference in noise levels between the two cases.

This paper presents a study of roof rack wind noise using commercial Computational Fluid Dynamics (CFD) software. The focus is to predict the noise generated from the roof rack cross bars mounted on a realistic vehicle geometry. Design iterations are created by altering the cross bar orientation. Results from the CFD simulations include frequency spectra of Sound Pressure Level (SPL) for comparison to typical wind tunnel measurements. Aerodynamic results of body lift, drag, and transient flow visualization are also produced to support the noise data. The CFD and physical experiments compare very well with respect to tonal noise generation, tonal frequency content, and relative magnitudes. It is concluded that the CFD method is suitable for predicting relative performance, ranking design concepts, and optimizing large scale geometry parameters of vehicle roof racks in a production-engineering environment.

The new regulations to reduce emissions have resulted in the development of new techniques to maintain or enhance competitive performance. A requirement for the manifold is to help meet the reduction in cold start emissions, particularly during the transient conditions from start to 100 seconds following the Federal Test Procedures for vehicle emissions. Finite element computer models were developed to predict inner and outer wall temperatures, and to determine structural soundness. Tests were performed to assure that noise levels were minimized. Dynamometer lab and field tests were performed to verify that the manifold would meet the design requirements. From the results of these tests and analyses, modifications were made to the weld and manufacturing techniques to improve product life and reduce noise. Dual wall manifolds have proven durability to meet high exhaust gas temperatures up to 1650°F (900°C), while meeting the performance, noise, and weight reduction goals.

A structural-acoustic finite-element model of an automobile trimmed-body is developed and experimentally evaluated for predicting body vibration and interior noise for frequencies up to 200 Hz. The structural-acoustic model is developed by coupling finite element models of trimmed-body structure and the passenger-compartment acoustic cavity. Frequency-response-function measurements of the structural vibration and interior acoustic response for shaker excitation of a trimmed body are used to assess the accuracy of the structural-acoustic model.

In the last thirty years the automotive industry has seen the transition from drum brakes to disc brakes. This transition was made with the intent of improving performance and reducing mass. Concurrent with this transition has been an all out effort to improve both quality and perceived quality of automobiles. A key component of quality/perceived quality of disc brake systems is disc brake squeal. In the past five years a tremendous amount has been learned about disc brake squeal, through analytical techniques, dynamometer testing, and on vehicle testing. This work has culminated in the identification of at least three families of brake squeal, each having its own set of countermeasures. This paper attempts to capture most of the recent findings, including the identification of the three families of disc brake squeal, a system to diagnose them, and a discussion of the appropriate countermeasures. A discussion on how to go about designing a ‘squeal free’ system is also included.

The stringent 1978 emission standards of 0.41 gm/mi HC, 3.4 gm/mile CO, and 0.4 gm/mi NOx may require the use of a dual catalytic converter system (reducing and oxidizing catalyst). These emission requirements have been achieved at low mileage with such a system, but it is complex and has exhibited poor durability. This system also results in the loss of fuel economy at the 1978 emission levels.

At the early design stage it is easier to achieve impacts on the brake noise. However most noise analyses are applied later in the development stage when the design space is limited and changes are costly. Early noise analysis is seldom applied due to lack of credible inputs for the finite element modeling, the sensitive nature of the noise, and reservations on the noise event screening of the analysis. A high quality brake finite element model of good components’ and system representation is the necessary basis for credible early noise analysis. That usually requires the inputs from existing production hardware. On the other hand in vehicle braking the frequency contents and propensity of many noise cases are sensitive to minor component design modifications, environmental factors and hardware variations in mass production. Screening the noisy modes and their sensitivity levels helps confirm the major noisy event at the early design stage.

The International Organization for Standardization (ISO) has developed a new measurement procedure, ISO362:200X, for vehicle exterior noise. This proposed standard covers motorcycles, light duty vehicles, and heavy-duty vehicles. The intent of the new procedure is to measure vehicle noise consistent with typical urban operation. SAE has conducted a cooperative research program to evaluate the new ISO procedure for light duty vehicles with regard to the intent of the procedure, technical, and practical considerations. The results of the cooperative research program indicate the new ISO procedure meets the intent of measuring typical traffic noise and does so in a technically correct and practically achievable manner.

Vehicle evaluations and model calculations were conducted on a vacuum-insulated catalytic converter (VICC). This converter uses vacuum and a eutectic PCM (phase-change material) to prolong the temperature cool-down time and hence, may keep the converter above catalyst light-off between starts. Tailpipe emissions from a 1992 Tier 0 5.2L van were evaluated after 3hr, 12hr, and 24hr soak periods. After a 12hr soak the HC emissions were reduced by about 55% over the baseline HC emissions; after a 24hr soak the device did not exhibit any benefit in light-off compared to a conventional converter. Cool-down characteristics of this VICC indicated that the catalyst mid-bed temperature was about 180°C after 24hrs. Model calculations of the temperature warm-up were conducted on a VICC converter. Different warm-up profiles within the converter were predicted depending on the initial temperature of the device.

This paper presents four methodologies for modeling gear mesh excitations in simple and compound planetary gear sets. The gear mesh excitations use simplified representations of the gear mesh contact phenomenon so that they can be implemented in a numerically efficient manner. This allows the gear mesh excitations to be included in transmission system-level, multibody dynamic models for the assessment of operating noise and vibration levels. After presenting the four approaches, a description is made regarding how they have been implemented in software. Finally, example models are used to do a comparison between the methods

Three-way catalysts provide a means of catalytically achieving lower NOx emission levels while maintaining good control of HC and CO emissions. However, very accurate control of air-fuel ratio is necessary. The precise air-fuel ratio control required is accomplished by employing a closed loop fuel metering system in conjunction with an exhaust gas sensor and an electronic control unit. To gain production experience with this type of system, General Motors is introducing it on two 1978 engine families sold in California. One is a 2.5 litre L-4 engine and the other is a 3.8 litre V-6 engine. Closed loop controlled carburetors are used on both systems. This paper discusses these 1978 systems. The components used on both systems are described and emission and fuel economy results are reviewed.

The main objective of this paper was to determine if the vehicle performance can be maintained with a reduced mass cradle structure. Aluminum and magnesium cradles were compared with the baseline steel cradle. First, the steel chassis alone is analyzed with the refined finite element model and validated with experimental test data for the frequencies, normal modes, stiffnesses and the drive-point mobilities at various attachment mount/bushing locations. The superelement method in conjunction with the component mode synthesis (CMS) technique was used for each component of the vehicle such as Body-In-White, Instrument Panel, Steering Column Housing & Wheel, Seats, Cradles, CRFM, etc. After assemblage of all the superelements, analysis was carried out by changing the front and rear cradle gauges and the material properties. The drive-point mobility response was computed at various locations and the noise (sound pressure) level was calculated at the driver and passenger ears.