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As an important class of nonlinear system, polytopic bilinear system is investigated. Combined with the properties of convex polytope, the nonlinear control for polytopic bilinear system is formulated by synthesizing nonlinear H∞ controller which is designed for polytopic bilinear system at vertices. For a semi-active suspension system with controllable damping and variant stiffness elements, it is easily modeled as a polytopic bilinear system model. In this case, the desired nonlinear control properties are pursued in making effective use of the changeable damping property while the variant stiffness is taken as the affine parameter of polytopic model. Therefore, polytopic bilinear system model could be reduced to a feasible problem by polytopic convex decomposition. Then the control problem of bilinear system model is to find a solution of nonlinear H∞ control.

As automotive manufacturers continue to increase their use of thermoplastics for interior and exterior components, there is a likelihood of squeaks due to material contacts. To address this issue, Ford's Body Chassis NVH Squeak and Rattle Prevention Engineering Department has developed a tester that can measure friction, and any accompanying audible sound, as a function of sliding velocity, normal load, surface roughness, and environmental factors. The Ford team has been using the tester to address manufacturing plant issues and to develop a database of polymeric material pairings that will be used as a guide for current and future designs to eliminate potential noise concerns. Based upon the database, along with a physical property analysis of the various plastic (viscoelastic) materials used in the interior, we are in the process of developing an analytical model which will be a tool to predict frictional behavior.

Buzz, Squeak, and Rattle (BSR) tests are commonly employed in the automotive industry as a diagnostic. The resulting signals are typically analyzed using established (historical) metrics such as A-weighted SPL or stationary loudness (ISO532B). However, due to the non-stationary nature of these signals, traditional metrics often fail to fully describe the signals in question. Compounding the issue is the fact that some specifications state that the test specimen is to produce ‘no objectionable noises’ when subjected to representative excitation. This is a very vague and debatable statement that normally cannot be settled by subjective observations alone. Within this paper, sound quality and statistical metrics are employed for several BSR signals acquired during forced response testing of a seat. Results are presented for two different boundary conditions and alternative signal processing tools are presented.

This paper describes the use of numerical methods in the rattle noise prediction of a seat belt sensor mechanism, requiring the solution of transient and highly non-linear acoustic radiation parameters. Hence, the computational model involves flexible body dynamics and boundary element acoustic codes. The predicted sensor motion and the acoustic response have been correlated with experimental results.

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.

Novel acoustical materials have been developed. The materials are thermoplastic foams extruded from blends of a polypropylene (PP) resin with an ethylenic polymer resin. One material is an open-cell sheet product made from a blend of a PP resin and a polyolefin elastomer (POE). Another is a large-celled plank foam of substantially closed-cell structure made from a blend of a polypropylene resin and a low density polyethylene (PE) resin. The foam materials are of lightweight, hydrophobic, dust free, recyclable and withstand the temperatures prevailing in automotive uses.

In many manual transmissions, conditions for the onset of vibro-impacts from an unloaded gear pair are more likely than from an engaged set. Although some of the general characteristics of neutral gear rattle are known, no specific analytical models are available in the literature that can explain interactions between unloaded and loaded gear pairs in the drive rattle mode. For the sake of illustration, a particular problem for a light duty truck is studied in this paper and dynamic interactions are investigated. Some experimental measurements are first presented to define the unloaded gear rattle problem. Linear and non-linear mathematical models of the driveline are developed to understand, quantify and control the rattle problem. Trends predicted by simulations are compared with those observed in experiments. The effects of various gear run-ups and vibratory drag torques are investigated.

The continual trend towards weight reduction resulted in the implementation of molded polyurethane carpet underlay at a density of 43 kg/m3 in early 2000. Now, through new formulation developments, coupled with the production introduction of carbon dioxide co-blown technology, additional weight reductions have been achieved. This has resulted in molded densities of 34 kg/m3 to be reached in prototype moldings. In addition to weight reductions, there has also been a renewed focus on improving the acoustical performance of the sound insulation material. As a result, a new family of formulations has been developed which have shown acoustical improvement while not sacrificing weight. This paper will showcase these new developments and highlight the benefits of polyurethane in sound insulation applications.

The optimization of acoustical properties of multi-layered materials used in the automotive industry requires a good understanding and characterization of the various component layers. This is a particular concern in the case of headliners where performance must be balanced with packing space demands. These composite structures when used with flexible urethane foams provide good stiffness and light weight, but their acoustic performance can be sub-optimal. Measurements undertaken with poro-elastic high airflow resistivity foams highlighted frame resonances which, if exploited, might significantly improve the acoustical performance of this system. A new modeling technique based on a pseudo-macroscopic description of the poro-elastic material in the framework of a four-pole network will be used to explain these frame resonances. This formulation exploits the electro-acoustical analogy in transmission line theory.

This paper describes a pilot benchmarking study of polyether foams for acoustical applications. The study investigates the differences in sound absorption performance that result from two different foam manufacturing methods: thin sheet casting and bun manufacturing. A basic conjecture that is examined in this work is that thin sheet cast foams have the following advantages over bun stock manufacturing: higher sound absorption performance and lower variability of the physical properties that determine acoustical performance. It is shown that the sound absorption performance of thin sheet cast urethane foam is 40% and 67% higher than the best performance of bun stock foam when evaluated by the Average Normal Sound Absorption Coefficient (ANSAC) and the noise reduction coefficient (NRC) respectively. In general, the computed variabilities for the properties of thin sheet cast urethane foam are lower than those for the bun stock foams.

The designs of vehicle seats have significant impact on interior acoustic modes as well as sound pressure level inside the vehicles. Seats trimmed with elastic porous materials are especially critical to the acoustic behavior of the vehicles due to the sound absorption of the materials. This paper demonstrates how seating materials affect the acoustic performance of an earh-moving cab. To accurarely simulate the sound absorption of the seat, the seat was modeled as a bulk reactive absorber instead of a local reactive absorber.

Dynamic properties of flexible polyurethane foam materials for car seats are highly complicated. In this paper, characterizations of dynamic stiffness of several foam specimens based on static stiffness obtained from IFD(Indentation Force Deflection) curve measurements are presented. It is observed that dynamic stiffness and its drift with static loading duration in logarithmic scale are proportional to the static stiffness at a given static loading regardless of types and dimensions of the foam. A three degree-of-freedom model of seated human body based on apparent mass measurements together with the characteristics of foam materials were incorporated for transmissibility prediction of the passenger-seat system.

To meet legal requirements vehicle manufacturers have to use a standard drive-by noise acceleration test conforming to relatively easily specified procedures (gear, approach speed etc). However, due to the transient conditions occurring during the test, predicting maximum drive-by noise levels from the contributions of vehicle systems is difficult. As manufacturers need to identify early in the design of a vehicle those available systems which will ensure legal requirements are met, a technique is required that can predict the contribution of each system. The technique has to be able to accept system target & CAE data as well as test data in order that it can be used in all stages of a vehicle program.

The Indirect Boundary Element Analysis is employed for developing a computational pass-by noise simulation capability. An inverse analysis algorithm is developed in order to generate the definition of the main noise sources in the numerical model. The individual source models are combined for developing a system model for pass-by noise simulation. The developed numerical techniques are validated through comparison between numerical results and test data for component level and system level analyses. Specifically, the source definition capability is validated by comparing the actual and the computationally reconstructed acoustic field for an engine intake manifold. The overall pass-by noise simulation capability is validated by computing the maximum overall sound pressure level for a vehicle under two separate driving conditions.

Analysis of the contribution of each pass-by noise source to the overall pass-by noise is an important issue for reduction of pass-by noise. A technical approach for analyzing pass-by noise is used to identify the principal noise sources of the pass-by noise in this study. Wave propagation theory and decoupling tests are employed and the near-field measurements are carried out to obtain the characteristics of each noise source. Since the Doppler phenomenon causes a frequency shift during a pass-by noise test, the Doppler correction and time delay effects are incorporated into the estimation of pass-by noise. Combining the entire data from the action of the prior tests, a simulation program was developed for analyzing each noise source contribution and predicting the overall pass-by noise as a function of the vehicle location. Finally, the developed program can furnish an indepth understanding of the effect of each noise source to pass-by noise.

The paper outlines and discusses the possibilities of a new instrumentation tool for the analysis of engine and gearbox noise radiation and the prediction of pass-by noise from powertrain test cell measurements. Based on a 32 channel data acquisition board, the system is intended to be quick and easy to apply in order to support engineers during their daily work in the test cell. The pass-by prediction is a purely experimental approach with test cell recordings being weighted by measured transfer functions (from the powertrain compartment to the pass-by point).

“Dither” control recently has been experimentally demonstrated to be an effective means to suppress and prevent rotor mode disc brake squeal. Dither control employs a control effort at a frequency higher, oftentimes significantly higher, than the disturbance to be controlled. The control actuator used for the work presented in this paper is a piezoelectric stack actuator located within the piston of a floating caliper brake. The actuator is driven in open-loop control at a frequency greater than the squeal frequency. This actuator configuration and drive signal produces a small fluctuation about the mean clamping force of the brake. The control exhibits a threshold behavior, where complete suppression of brake squeal is achieved once the control effort exceeds a threshold value. This paper examines the dependency of the threshold effort upon the frequency of the dither control signal, applied to the suppression of a 5.6 kHz rotor squeal mode.

Brake squeal has been analyzed by finite elements for some time. Among several methods, complex eigenvalue analysis is proving useful in the design process. It requires hardware verification and it falls into a simulation process. However, it is fast and it can provide guidance for resolving engineering problems. There are successes as well as frustrations in implementing this analysis tool. Its capability, robustness and reliability are closely examined in many companies. Generally, the low frequency squealing mechanism is a rotor axial direction mode that couples the pads, rotor, and other components; while higher frequency squeal mainly exhibits a rotor tangential mode. Design modifications such as selection of rotor design, insulator, chamfer, and lining materials are aimed specifically to cure these noise-generating mechanisms. In GM, complex eigenvalue analysis is used for brake noise analysis and noise reduction. Finite element models are validated with component modal testing.

A new experimental methodology has been developed to quantify spindle loads of a vehicle under actual operational conditions. The methodology applies an indirect six degree-of-freedom (6 DOF) frequency response function (FRF) measurement technique to obtain three translation/force and three rotation/moment FRFs of the suspension system of the vehicle. The Inverse Frequency Response Function (IFRF) method estimates the spindle loads under operational conditions. The feasibility and applicability of the developed methodology for vehicle road NVH applications was experimentally demonstrated. The results show that the methodology provides accurate spindle load estimation over a broad frequency range. This methodology can be used for benchmarking and target setting of spindle loads to achieve desired road NVH performance as well as for diagnosing root causes in problem solving applications.

This paper presents an experimental investigation of methods for disc brake squeal source localization. The underlying data for the localization methods considered here was obtained through the use of a sound intensity probe and a scanning laser vibrometer. The ability to correctly identify the squeal sources is an essential first step in diagnosing brake squeal. Localization methods based upon the use of sound intensity and laser vibrometry, when used together, are shown to converge successfully upon squeal sources. The sound intensity probe is used to spatially locate regions of airborne squeal noise in the near field of the brake rotor and caliper system mounted on a brake squeal dynamometer. The scanning laser vibrometer is then used to further investigate the vibration behavior of the brake assembly within these suspect regions.