Papers included in this collection cover the systems engineering experience required to achieve ultra-low emission levels on gasoline light-duty vehicles. Emission system component topics include the development of advanced three-way catalysts, the development of NOX control strategies for gasoline lean burn engines, the application of high cell density substrates to advanced emission systems, and the integration of these components into full vehicle emission systems.
This technical paper collection will focus on ‘Advances in NOx Reduction Technology’. The topics covered will include: new materials for lean NOx traps (LNT) and Selective Catalytic Reduction (SCR); system integration and durability; advances in NOx catalyst substrates, novel reductants and mixing designs.
The main use of FRC in automobiles, with the exception of a few specialized low volume vehicles, has been until now in semistructural parts. One of the most promising process in development today, that may play major role in future structural composite fabrication, is based on SRIM technology. The rapid and extensive introduction of this process goes also through the development of deeper theoretical knowledge of the process and the development of computer simulation to aid mold design and choice of proper processing parameters. To contribute SRIM advancement, a preliminary model has been developed for viscosity changes, extent of the reaction and temperature rises, associated with the mold filling stage, as well as a simple software to evaluate the pressure drop through different combinations of reinforcements.
Synthesizing different customer and functional requirements into an acceptable design configuration within a given space constraints is a challenging task for design engineers. The principles for designing efficiency, noise levels, maneuverability, safety, durability, etc. into the product are well understood. However, designing for reliability, maintainability and quality turns out to be a long-drawn laborious process due to unavailability of simplified design procedures. The author in this paper develops the understanding of reliability, maintainability and quality design principles and methods for products, with specific reference to vehicle designs.
Over the last years, SEA has been recognized as a useful tool to model and analyze the high-frequency vibro-acoustic behavior of fully assembled complex structures. This paper discusses the experimental derivation of the loss factor model of a passenger car. The paper outlines the different steps which need to be taken to obtained a fully validated experimental SEA model. This includes the subdivision into subsystems, the PIM measurement campaign, the derivation of the loss factors and their associated confidence levels and the model validation. The paper further details how the experimental SEA model was used to quantify and investigate the airborne and structure-borne contributions to the interior noise level for a road noise test condition. The operational power inputs to the vehicle were indirectly determined from operational response measurements. A contribution analysis showed that airborne noise sources dominated structure-borne noise sources above 500Hz.
Vehicle sound package serves two basic functions: general acoustic insulation and local problem treatment. The former is often done at the up-front phase of the vehicle development process, and the latter at the downstream phase when representative prototype hardware becomes available and specific noise problems are identified. This paper examines the goals and key tasks of practical SEA CAE applications in the two phases of the sound package development process. Topics on CAE model requirement, typical analysis applications, and ways to improve the effectiveness of SEA applications to compliment hardware testing are discussed.
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.
This paper discusses the methods of reducing weight of sound package through a new approach in sound absorption and insulation. In contrast to conventional sound package theory, a light porous material with high absorption (Ultra Light material) is used to replace a conventional porous/barrier sandwich material (classic), which results in an equivalent or better noise reduction in-vehicle with significant weight reduction. A Noise Reduction (NR) test was conducted with a box equipped with both the Ultra Light material and classic material. A SEA model of the same setup was also analyzed. Results from both the test and the analysis show that it is possible to achieve weight reduction by replacing conventional porous/barrier sandwich materials with light porous materials with high absorption.
Transfer Path Analysis (TPA) is a widely used methodology in Noise, Vibration and Harshness (NVH) analysis of motor vehicles. Either it is used to design a vehicle from scratch or it is applied to root cause an existing NVH problem, TPA can be a useful tool. TPA analysis is closely related to the concept of partial contribution. The very basic assumption in TPA is that the summation of all partial contributions from different paths constitutes the total response (which could be either tactile or acoustic). Another popular concept in NVH analysis of vehicles is the component sensitivity. Component sensitivity is a measure of how much the response changes due to a change in one of the components of the system, i.e., the thickness of a panel or elastic rate of an engine mount. Sensitivity rates are more popular among CAE/Simulation community, simply because they are reasonably easy to calculate using mathematical models.
Environmental concerns as well as regulatory requirements are driving the development of alternative vehicle propulsion systems. Electric vehicles (EV's) are attractive because they emit no pollutants. In this paper, we examine the sound quality characteristics of wind and powertrain noise in electric vehicles. Sound quality is an important attribute of EV's, because the expectation is that they will be very quiet due to the absence of an internal combustion engine. As we show in this paper, the absence of engine noise is both a blessing and a curse for sound quality. For wind noise, the results show that electric and gasoline vehicles have equivalent wind noise loudness levels at all speeds. However, at lower speeds (50-60 mph), the EV is judged to have more wind noise even though the level was the same as the gasoline vehicle! The difference is that, in the EV, there is no engine noise to mask the wind noise.
Chemically and heat reactive, expandable sealants are used as “acoustical baffles” in the automotive industry. These acoustic baffles are used to impede noise, water and dust propagation inside of structural components and body cavities. Use of these sealant materials has grown significantly as the demands to improve vehicle acoustic performance has increased. Various test methods have been developed to quantify the performance of these materials through direct comparison of material samples. These investigations use standardized testing procedures to characterize the acoustic performance of a material sample on the basis of controlled laboratory test conditions. This paper presents a step in the progression of evaluating acoustic baffle performance in the vehicle. Standard experimental techniques are used to investigate the influence of the baffles on the vehicle acoustic performance.
This paper presents a software-driven procedure for continuous assessment facilitating an evaluation of non-stationary sound quality. The noise stimuli are presented to the test persons via headphones and a subwoofer from a personal computer. The key feature of the rating procedure is the “zonal pairwise comparison” for the time zones at the beginning and the end of the noise sequences. Evaluation of data together with time variant objective parameters by means of statistical methods is described. The results and models from multiple regession analysis are given.
The area in the neighborhood of the package tray can be a significant path for road noise and exhaust noise. Air extraction routes and loudspeakers add to the difficulty of effective system design. A variety of designs were prototyped and their transmission loss measured in a standard SAE J1400 sound transmission loss suite. The performance of the various designs was compared to an untrimmed piece of sheet metal with embedded air extraction holes. The addition of trim added from 1 dB to 14 dB to the transmission loss. Statistical energy analysis (SEA) models of a variety of package tray systems will also be shown. Both of these techniques can provide design guidance at an early stage of vehicle program development.
This paper discusses four general attributes which quantify the character of an impulsive sound event. These attributes include the time duration, amplitude and frequency content of the impulsive noise. A three dimensional plot relating time, frequency and amplitude have been developed for the presentation of the measured data. This format allows graphic illustration of the noise event, providing fast interpretation and communication of the measured sound. Application of this methodology to the sound of an automotive door closing event is presented here. Representative door closing sound events are analyzed, with correlation presented between the attributes above to dynamic events of the physical hardware within the door and vehicle systems. Modifications of the door-in-white, internal door hardware, seal systems and additional content are investigated for their effect on the sound quality of the door closing event. Finally, recommended values for these attributes are presented.
In noise and vibration control, damping treatments are applied on panel surfaces to dissipate the energy of flexural vibrations. Presence of damping treatment on the surface of a panel also plays an important role in the resulting vibro-acoustic characteristics of the composite system. The focus of this study is to explore possibilities of reducing the weight of damping treatments by means of perforation without sacrificing performance. The power injection concept from Statistical Energy Analysis (SEA) is used in conjunction with Finite Element Analysis (FEA) to predict the effect of perforated unconstrained layer treatments on flat rectangular panels. Normalized radiated sound power of the treated panels are calculated to assess the effect of varying percentage of perforation on structural-acoustic coupling.
An approximate analysis method for brake squeal is presented. Using MSC/NASTRAN a geometric nonlinear solution is run using a friction stiffness matrix to model the contact between the pad and rotor. The friction coefficient can be pressure dependent. Next, linearized complex modes are found where the interface is set in a slip condition. Since the entire interface is set sliding, it produces the maximum friction work possible during the vibration. It is a conservative measure for stability evaluation. An averaged friction coefficient is measured and used during squeal. Dynamically unstable modes are found during squeal. They are due to friction coupling of neighboring modes. When these modes are decoupled, they are stabilized and squeal is eliminated. Good correlation with experimental results is shown. It will be shown that the complex modes baseline solution is insensitive to the type of variations in pressure and velocity that occur in a test schedule.
Brake squeal, which is a noise, occurs in the range of frequencies 1 to 16 kHz is an important task for research to develop the vehicle passenger comfort. This phenomena has been studied many years theoretically and experimentally to gain better performance of brake and eliminating the squeal problem. The work presented here is focusing on the effect of the brake pad manufacturing on the generation of brake squeal. A simple proposed three-degree of freedom model has been used in the study to simulate the brake components (pad, caliper, and disc). The brake squeal and frequency response of brake pad has been measured at different working conditions (pressure, sliding speed, and brake pad type). A comparison between the theoretical and experimental work has been made and a good agreement was found between the theoretical prediction of the brake assembly natural frequency and the experimental measurement.
In recent years there has been much interest in problems involving the noise prediction and reduction inside and outside the vehicle. Tire/road exterior noise has been considered to be the major vehicle exterior noise source. However, this paper describes an investigation into the characteristics of the air pumping noise mechanism in terms of source locations and directionality. Some rubber tire/road air pumping noise measurements are presented, whereas some predicted results are computed based on the boundary element method (BEM) to display some parameters which are found to be difficult to be obtained experimentally.