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This study was initiated to evaluate the thermal characteristics of a vehicle underbody using math-based computational fluid dynamics (CFD) simulation based on 3-D configuration. Simulations without heat shields were carried out for different vehicle operating conditions which placed several areas at risk of exceeding their thermal design limits. Subsequently, simulations with several heat shield designs were performed. Results show that areas at risk without shields are well within thermal design limits when shielded. Part of the CFD simulation results were compared with experimental data, with reasonable correlation. The CFD approach can provide useful design information in a very short time frame.

Concepts for dual density materials for usage as absorbers and decouplers are based on well-established layered media principles and have been applied for many years in non-automotive applications. Balancing the mass, air flow resistance, and thickness allows for improved noise attenuation in the low to mid frequency range which is of particular interest for automotive NVH management. Using these principles, products were tuned via mass and airflow resistance to reduce noise levels while also significantly reducing mass. Validation in various vehicles confirmed that up to a 55% reduction of a sound package's mass is possible. The considerable weight reductions of dash insulators and carpet systems are possible at the same times as the sound level in the vehicle interior is at least maintained and frequently improved.

In order to engineer Squeak & Rattle (S&R) free vehicles it is essential to develop an objective measurement method to compare and correlate with customer satisfaction and subjective S&R assessments. Three methods for exciting S&Rs -type surfaces. Excitation methods evaluated were road tests over S&R surfaces, road simulators, and direct body excitation (DBE). The principle of DBE involves using electromagnetic shakers to induce controlled, road-measured vibration into the body, bypassing the tire patch and suspension. DBE is a promising technology for making objective measurements because it is extremely quiet (test equipment noise does not mask S&Rs), while meeting other project goals. While DBE is limited in exposing S&Rs caused by body twist and suspension noises, advantages include higher frequency energy owing to electro-dynamic shakers, continuous random excitation, lower capital cost, mobility, and safety.

This paper describes the design, synthesis-analysis and development of the unique vehicle structure architecture for the fifth generation Chevrolet Corvette, ‘C5’, which starts in the 1997 model year. The innovative structural layout of the ‘C5’ enables torsional rigidity in an open roof vehicle which exceeds that of all current production open roof vehicles by a wide margin. The first structural mode of the ‘C5’ in open roof configuration approaches typical values measured in similar size fixed roof vehicles. Extensive use of CAE and a systems methodology of benchmarking and requirements rolldown were employed to develop the ‘C5’ vehicle architecture. Simple computer models coupled with numerical optimization were used early in the design process to evaluate every design concept and alternative iteration for mass and structural efficiency.

This paper presents a method for modeling large deformations of structures using scale plastic models. The method was used to predict the dynamic barrier crash performance of a proposed vehicle structure with the aid of a computer simulation of the collision. The use of the technique can provide design direction in the early stages of the vehicle design process.

Microcomputer technology has added a new dimension to the design of test instrumentation, but the connotations of the name microcomputer have a tendency to build barriers rather than offer solutions to problems. Historically, computers have been treated as systems or identifiable subsystems in instrumentation applications. The implications of complex hardware and mystical programming is often sufficient to direct the user to alternate technologies. In a new light, clear of earlier prejudices, the microcomputer becomes a functional module like other LSI devices. Flexible and economical systems involving logical control, data gathering, and numerical calculations are possible utilizations of these relatively new devices. This paper discusses a facility to assist the designer in development of test instrumentation. Emphasis is placed on use of the microcomputer as an integral part of system design. Test instrument applications are cited.

A front suspension laboratory test procedure was developed to reproduce time-correlated fatigue damaging events from a light truck road durability test. Subsequently, the performance of front suspension systems for the GMT 400 light truck program were evaluated in terms of customer reliability. Both prototype and pilot testing, as well as computer modeling, were used in the evaluation.

Aspirating airbag modules are unique from other designs in that the gas entering the airbag is a mixture of inflator-delivered gas and ambient-temperature air entrained from the atmosphere surrounding the module. Today's sophisticated computer simulations of an airbag deployment typically require as input the mass-flow rate, chemical composition and thermal history of the gas exiting the canister and entering the airbag. While the mass-flow rate and temperature of the inflator-delivered gas can be obtained from a standard tank test, information on air entrainment into an aspirated canister is limited. The purpose of this study is to provide quantitative information about the aspirated mass-flow rate during airbag deployment. Pressure and velocity measurements are combined with high-speed photography in order to gain further insight into the relationship between the canister pressure, the rate of cabin-air entrainment and the airbag deployment.

Recent effort has focused on correlating random incidence absorption coefficients obtained in different sizes of reverberation rooms based on round robin testing of identical samples in a database driven approach. An alternate approach presented here is to correlate random incidence sound absorption coefficients among different reverberation rooms using an apparent linear relationship between sound absorption coefficients and a geometric property of the test samples. Linearity can be judged in relation to the uncertainty of each individual measurement. The study will encompass experimental work on three different sizes of reverberation rooms for both a single layer material and a multi-layered material. By examining the different sound absorption coefficient values from each size of room, as a function of geometric parameters, we illustrate the quantitative correlation that might be established between the different sizes reverberation rooms.

Passive star networks have been shown to be the best architecture for high speed vehicle networks. This paper attempts to describe how problems in passive star networks can be diagnosed in the field. The potential physical layer failure modes for passive star networks are detailed, and a network test tool is described which is capable of determining whether a media fault exists and locating the position of that fault. The application of the test tool to potential failure modes is discussed.

This paper documents the development process of the 2001 Pontiac Aztek body structure for improved noise & vibration performance. Successful vehicle development under an accelerated timing schedule demands clearly defined body structure vibration performance targets and critical dependence on the math based modeling process. Specifications for global body structure vibration performance were generated through a two step process. First, a benchmarking activity was undertaken to comprehend competitive vehicle performance. Secondly, a frequency domain “mode map” was constructed to minimize vehicle subsystem interaction. Computer simulation models were developed to predict the body structure performance. A coarse full body structure model was used to define body structure section size and joint requirements. Detailed analysis models of body joint areas were used to synthesize the joint design.

In performing stochastic simulations using computer models, the method of sampling is important. It affects the quality and the convergence speed of the results. This paper discusses one special case: sampling of spot-weld locations from potentially thousands of spot welds on a vehicle body. This study is prompted by the need of evaluating the effect of missed spot welds on the structural integrity, identifying critical welds, and optimizing weld locations. A balanced random sampling algorithm based on the concept of Latin-Hypercube sampling is developed for this application. We also present a case study in which the efficiency of three different sampling methods is compared using a car joint stiffness example. The new method, called the Balanced Latin-Hypercube Sampling (BLHS), has shown significantly faster convergence over the other two.

The approaches used to develop an NVH package for a vehicle have changed dramatically over the last several years. New noise and vibration control strategies have been introduced, new materials have been developed, advanced testing techniques have been implemented, and sophisticated computer modeling has been applied. These approaches help design NVH solutions that are optimized for cost, performance, and weight. This paper explains the NVH practices available for use in designing vehicles for the new millennium.

Indoor or laboratory testing of tire tread wear offers many advantages over vehicle fleet testing. Advances in test equipment capabilities and the technologies for defining and simulating meaningful tire loading histories has made indoor tread wear testing a reality. Tire loading histories are influenced by vehicle characteristics, wear course and driving style, and tire stiffnesses. Methods for independently characterizing each of these are reviewed. A simulation technique, TS-Sim, is also described that combines specific vehicle, course and tire characterizations to create a tire load history. The vehicle characterization is critical to the process since both wear rate and various forms of uneven and irregular wear are strongly dependent on vehicle suspension/steering characteristics and on dynamic load transfer behavior. The characterization process involves mapping the vehicle over a practical range of acceleration, deceleration and cornering maneuvers.