Search Results

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.

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.

A subjective in-vehicle evaluation system is generally used to evaluate brake noise. This approach is quite dependent on analysis procedure, individual hearing abilities, individual tolerance level to the noise, the vehicle condition, road conditions and weather conditions. Due to the resultant subjective rating's dependence on these non-controllable factors, it was decided to develop an empirical laboratory technique using the brake dynamometer with sensitive noise measuring equipment to collect sufficient data on brake noise to allow engineers to study brake noise problems.

European legislation covering noise, smoke emission and industrial pollution, all seeking to improve the environment are not addressed in this paper, which takes only exhaust emission and fuel complexity as its subjects. It describes how this complexity can inhibit the development capacity, thus restricting the model offering of a major european automobile manufacturer. The paper concludes that general benefit would be derived from genuine pan european emission legislation, particularly if that legislation was established at levels of control that allowed the development and use of modern engine technology.

A new method to predict brake squeal occurrence was developed by MSC under contract to Ford Motor Company. The results indicate that the stability characteristics of this disc brake assembly are governed mainly by the frictional properties between the pads and rotor. The stability is achieved when the friction coefficient of the pads is decreasing as the contact force increases. Based on the results, a stable brake system can be obtained without changing the brake structure by incorporating the appropriate frictional coefficient in the brake system. The method developed here can be also used as a tool to test the quality of any brake design in the early design stage.

The present work discusses an objective test and analysis method developed to quickly quantify steering gear rattle noise heard in a vehicle. Utilizing envelope analysis on the time history data of the rattle signal, the resulting method is simple, fast, practical and yields a single-valued metric which correlates well to subjective measures of rattle noise. In contrast to many other rattle analysis methods, the approach discussed here is completed in the time domain. As applied to rattle noise produced by automotive electric steering systems, the metric produced with this analysis method correlates well with subjective appraisals of vehicle-level rattle noise performance. Lastly, this method can also be extended to rattle measurements at the component and subcomponent level.

Powertrain mounts are one of the important design characteristics of a vehicle. Powertrain is mostly mounted to the front subframe and once installed in a vehicle, powertrain mounting has an important role in determining the vehicle vibration characteristics. A good mounting system isolates engine input vibration from the vehicle body and minimizes the effect of road inputs to the customer. This paper discusses results of several dynamic models as they relate to noise, vibration and harshness (NVH) and compares the accuracy of these models. Various powertrain models are studied and their accuracy in comparison with full a vehicle model is discussed.

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.

Nonlinear finite element analysis has been applied to determine the conditions conducive to seal system aspiration. Aspiration noise occurs and propagates into the passenger compartment of a vehicle when there exists a gap between the seal and sealing surface due to pressure differential between the vehicle interior and exterior. This pressure differential is created by the vehicle movement which reduces the pressure acting on the exterior surface of the vehicle, and it is on the order of , where ρ and U∞ are the density of air and vehicle speed, respectively. The pressure difference is also created by turning on the climate control system which pressurizes the passenger cavity. Since aspiration increases door seal cavity noise level and creates a direct noise transmission path without any significant transmission loss, the presence of an aspiration noise source can dominate the vehicle interior noise level if it is close to the driver or passenger's ears.

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.

Closed cell foam has been used for filling vehicle pillar cavities at select locations to block road noise transmitted through pillars. In the past, most pillar foam implementations in vehicle programs were driven by subjective improvements in interior sound. In this study road test results are used to correlate a detailed CAE (Computer-Aided Engineering) model based on the statistical energy analysis method. Noise reduction characteristics of pillar with a number of foam block fillings were then studied using the CAE model. The CAE models provided means to model and understand the mechanism of noise energy flow through pillar cavities. A number of insightful conclusions were obtained as result of the study.

With the adoption of large-scale vehicle system models for NVH analysis, it has become possible to optimize the properties of chassis components to minimize the perception of vibration and/or sound in a vehicle. It has been found that these analytical optimization procedures are useful both in the early concept stage of the vehicle design/development process and in the subsequent component detailed design stage. While the process is rather complex and costly, it can be less costly than the alternative — the building and testing of multiple prototype parts or vehicles. From this standpoint, it may be that analytical optimization is the only practical way of evaluating the many combinations of design parameters that could lead to improved vehicles. To reduce the complexity of the analytical procedure, the vehicle modeling process has been automated and software pre and post-processors have been produced to supplement the primary analysis and optimization codes.

The intent of this paper is to summarize the work of the V8 power plant intake manifold radiated noise study. In a particular V8 engine application, customer satisfaction feedback provided observations of existing unpleasant noise at the driver's ear. A comprehensive analysis of customer data indicated that a range from 500 to 800 Hz suggests a potential improvement in noise reduction at the driver's ear. In this study the noise source was determined using various accelerometers located throughout the valley of the engine and intake manifold. The overall surface velocity of the engine valley was ranked with respect to the overall surface velocity of the intake manifold. An intensity mapping technique was also used to determine the major component noise contribution. In order to validate the experimental findings, a series of analysis was also conducted. The analysis model included not only the plastic intake manifold, but also the whole powertrain.

This paper describes a system modeling technique for predicting passenger compartment “boom” for a specific car design prior to the building of a prototype vehicle. Since “boom” — defined here as auditory response in the 20 Hz to 80 Hz frequency range — is dependent on body panel vibrations as well as air acoustic properties, three-dimensional finite element models of both body and air are constructed. These models are incorporated in existing vehicle models which include powertrain and chassis representations of the type previously used for performing shake and harshness analyses. To avoid non-symmetric mass and stiffness matrices, a modal method using auxilliary variables is utilized to couple the acoustic and body models. Included in the paper are discussions of modeling issues unique to structural acoustic simulation as well as several examples of studies in which sound pressure level response to realistic inputs is predicted and reduced by simulated design modifications.

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.

This case study presents a new automated production noise test for power steering pumps. The test included adaptive noise cancellation, and a neural network implementation. The result mapped the pump acceleration signature into an objective repeatable noise metric. The test algorithm was a distributed DSP architecture designed for real-time measurement and decision processing. It was implemented with no increase in test cycle time. It accomplished the correlation of in-vehicle power steering pump noise to it's vibration characteristics, and retrofitting of accelerometers in place of microphones for acceptance testing.

The purpose of this paper is to describe the growth and the trends of automotive convenience products. These products contributed to make the driving experience more pleasurable. Electronics have contributed to this growth since the sixties, and its contribution and prospects will be the prime focus of this paper. With the continuing advance of electronic products in the consumer and industrial sectors, the consumer wants' and expectations are changing, especially with the “Baby Boom” generation. More new convenience features will be developed by the prudent use of electronics. The development of these future products require a thorough understanding of consumer wants and needs through market research, careful adaptation of the emerging technology to avoid gimmickry, and dedicated application of engineering know how to design package efficient, cost effective and reliable products.

Vehicle interior sound quality is regarded as a major quality attribute by automobile consumers and manufacturers. Whining noise, due to its steady state and tonal nature, is easily perceived as an annoyance to normal driving comfort. The blower motor in the climate control air-handling system can be a source of whining noise, especially when the motor is located in the passenger compartment. This paper describes a systematic case study carried out to identify the major noise generating mechanisms of a whining noise from the climate control air-handling system. The paper discusses the use of commonly available tools and techniques to resolve typical automotive NVH concerns resulting in improved sound quality. Particular measurement and analysis techniques presented include sound field mapping using acoustic intensity, resonance identification using transfer functions, three-axis spectrum analysis, and some physical modifications to the source and propagation paths.

A CAE method has been developed to address engine tonal noise and whine due to the excitation from a gerotor oil pump. The method involves a multidisciplinary approach including CFD, frequency-response structural analysis and acoustic analysis. The results from the application of the method applied to a couple of pumps with different designs are discussed. Engine tonal noise improvement through reduction in the excitation source from the pump and also stiffening the excitation path from the pump to the engine are studied. The effect of component modal alignment with oil pump orders is addressed as well.

This paper describes experimental methods for simulating and analyzing road noise using an artificial road surface mounted to a chassis dynamometer. The nature of the relationship of road noise to road surface is discussed, including the nature of sound produced by the artificial surface mounted to the dynamometer. A method is described for converting the harmonics usually produced in a chassis rolls test into a continuous spectrum. This method also smoothes statistical fluctuations which arise due to the short length of road simulated. Dynamometer techniques are shown to be particularly effective in separating sound contributions from the front and rear suspension, and in separating contributions due to road surface and the tire tread.