Automotive NVH

ABSTRACT For (benchmark) tests it is not only useful to study the acoustic performance of the whole vehicle, but also to assess separate components such as the engine. Reflections inside the engine bay bias the acoustic radiation estimated with sound pressure based solutions. Consequently, most current methods require dismounting the engine from the car and installing it in an anechoic room to measure the sound emitted. However, this process is laborious and hard to perform. In this paper, two particle velocity based methods are proposed to characterize the sound radiated from an engine while it is still installed in the car. Particle velocity sensors are much less affected by reflections than sound pressure microphones when the measurements are performed near a radiating surface due to the particle velocity's vector nature, intrinsic dependency upon surface displacement and directivity of the sensor. Therefore, the engine does not have to be disassembled, which saves time and money. An array of special high temperature particle velocity probes is used to measure the radiation simultaneously at many positions near the engine of a compact class car. The particularities of these probes, the mountings used, and the actions taken to cope with disturbances such as airflows are described in this paper. The effective sound pressure is calculated with a particle velocity based transfer path analysis method and a novel sound power based method. To validate these techniques, the data obtained is compared to the results acquired in an anechoic room with a dismounted engine. It is shown that similar results can be obtained with both methods but that the sound power based methodology seems more practical. It is a straightforward and fast approach to characterize the average sound pressure level at certain distance.

Viscoelastic material is commonly used in the passive treatment of structural vibration of the vehicle structure, to introduce damping and reduce vibration level at resonance frequencies. In a passenger vehicle chassis it is usual to add around 10 kg of these viscoelasctic patches. The effectiveness of such damping treatment depends on design parameters such as application location, area, thickness, and choice of the type of damping material. This paper describes an experimental procedure implemented to evaluate the performance of two different layers of damping material, when they are applied to a passenger vehicle chassis (white body). Results are presented for the white body chassis: 1) without damping added, 2) with asphalt pad added and 3) with liquid applied sprayable damper. The results are discussed through a comparison with adequated mapping of the responses and by results from beamforming tests in a chassis prototype, in terms of its efficiency for the damping of vibrations.

Noise and vibrations from an engine form important benchmarks from customer satisfaction view while choosing an automotive car. There are several sources of noise and vibrations emissions from an engine installed in a car. Some of these sources include: combustion noise, exhaust flow noise, aero dynamic noise as well as noise due to mechanical motion of parts etc. Each of these sources of noise depends on some factors which includes fuel injection parameters, design of engine, lubrication regime, operational parameters like speed and load. Motion of piston skirt form a major source of noise and vibrations in an automotive car. Apart from normal reciprocating motion of skirt, there can be secondary motion along the lateral direction. This motion is known as piston slapping motion. There are several factors that affect this lateral motion of skirt which includes the design of piston, type of lubrication as well as the speed of engine. In the present work a numerical model of lateral motion of skirt has been proposed. The proposed model was applied for a dual cylinder water cooled diesel engine. Effects of various design parameters like piston-liner clearance, skirt length, mass of skirt, and location of piston pin has been analyzed. The proposed methodology can be used to optimize the design of skirt in order to reduce the noise and vibration emissions arising due to lateral striking motion of skirt with liner.

In this paper, metamodeling and five wellknown metaheuristic optimization algorithms were used to reduce the weight and improve crash and NVH attributes of a vehicle simultaneously. A high-fidelity full vehicle model is used to analyze peak acceleration, intrusion and component’s internal-energy under Full-Frontal, Offset-Frontal, and Side crash scenarios as well as vehicle natural frequencies. The radial basis functions method is used to approximate the structural responses. A nonlinear surrogate-based mass minimization was formulated and solved by five different optimization algorithms under crash-vibration constraints. The performance of these algorithms is investigated and discussed.

Brake Analysis and NVH (Noise, Vibration and Harshness) Optimization have become critically important areas of application in the Automotive Industry. Brake Noise and Vibration costs approximately $1Billion/year in warranty work in Detroit alone. NVH optimization is now increasingly being used to predict the vehicle tactile and acoustic responses in relation to the established targets for design considerations. Structural optimization coupled with frequency response analysis is instrumental in driving the design process so that the design targets are met in a timely fashion. Usual design targets include minimization of vehicle weight, the adjustment of fundamental eigenmodes and the minimization of acoustic pressure or vibration at selected vehicle locations. Both, Brake Analysis and NVH Optimization are computationally expensive analyses involving eigenvalue calculations. From a computational sense and the viewpoint of MSC.Nastran, brake analysis exercises the CEAD (Complex Eigenvalue Analysis Dmap) module, while NVH optimization invokes the DSADJ (Design Sensitivity using ADJoint method DMAP) module. In this paper, two automotive applications are presented to demonstrate the performance improvements of the CEAD and DSADJ modules on NEC vector-parallel supercomputers. Dramatic improvements in the DSADJ module resulting in approx. 8-9 fold performance improvement as compared to MSC.Nastran V70 were observed for NVH optimization. Also, brake simulations and experiences at General Motors will be presented. This analysis method has been successfully applied to 4 different programs at GM and the simulation results were consistent with laboratory experiments on test vehicles.

“Mass Properties Analysis and Control” is Part 5 of a ten part presentation series "Automotive Dynamics and Design". The intent is to form a comprehensive series of lectures providing instruction in the design of automobiles from both a practical and a stylistic viewpoint. The ten segments constitute the core (reading assignments, homework, and test material not included) of a class to be given over a period of about twelve weeks. The ten course segments are:
1) "Automotive Dynamics and Design"
2) "Longitudinal Dynamics"
3) "Lateral Dynamics"
4) "Vertical Dynamics"
5) "Mass Properties Analysis and Control"
6) "Tire Behavior"
7) "Aerodynamics"
8) "Advanced Topics"
9) "Design (Styling)"
10) "Summary"
Part 1 is essentially an introduction to, and a syllabus for, the course of study. Part 2 constitutes a study of automotive acceleration, braking, and crash deceleration. Part 3 constitutes a study of oversteer, understeer, directional stability, rollover, lateral acceleration: transient and steady state. Part 4 constitutes a study of springing, damping, shock attenuation, road contact, road vibration transmissibility, ride motions. Part 5 constitutes a study of the ten mass properties equations, the ten mass properties uncertainty equations, standard deviation, normal distribution, regression analysis, coefficient of determination, correlation, degrees of freedom, total weight estimation, unsprung weight estimation, sprung weight estimation, estimation of the total weight c.g., estimation of the unsprung weight c.g., estimation of the sprung weight c.g., estimation of the total mass moments of inertia,  estimation of the unsprung mass moments of inertia, estimation of the sprung mass moments of inertia, estimation of the total products of inertia, estimation of the sprung roll moment of inertia.

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http://www.researchmoz.us/global-and-china-automotive-wiring-harness-industry-report-2013-report.html

The global automotive wiring harness market value climb 2.3 percent to USD40.3 billion in 2013, and is expected to reach USD41 billion in 2014, up 1.6% over 2013. The slow growth is caused by many reasons. The market share of two major Japanese players of automotive wiring harness totals more than 50%, while Japanese Yen devaluates by 24% in 2013, resulting in a significant decline in the market value counted in the U.S. dollar. Also, due to the decline in copper prices as well as the continuous lawsuits against wiring harness price manipulating, manufacturers are forced to reduce prices to please customers.

The basic intent of this paper is to counter the commonly held simplistic concept of the role mass properties play in determining ride and road-contact. For those that have never undertaken any study of the matter, the general presumption seems to be that all that is required to achieve optimum performance is to minimize the weight and to obtain a balanced mass distribution. The reality is that there are many aspects to automotive performance, and what constitutes an optimum mass properties condition is generally a very complex matter which often necessitates difficult compromises. Tailoring some mass property parameters so as to achieve a desirable level of behavior with regard to one performance criterion will often adversely affect other performance criteria.

Although this paper is restricted to mass properties issues related to performance resulting from motion in the vertical direction, occasional reference will be made to those mass properties requirements necessitated by performance considerations associated with the longitudinal (acceleration, braking) and lateral (maneuver, roll-over, and directional stability) directions, as revealed in the previous investigations noted earlier. To do otherwise would be to work in a vacuum; the nature of reality tends to be such that all things are ultimately interrelated. To the fullest extent possible, the greater intent herein is to approach reality through the totality of the papers and articles written by this author on the subject of mass properties and automotive performance.

After decades of investigating brake noise and despite the application of advanced tools and methods of investigation, brake squeal remains a general problem of the automotive industry. Finite Element Analysis (FEA) has been employed as the main tool in numerous studies recently, mainly using the Complex Eigenvalue Analysis (CEA) to predict the occurrence of brake instability and, hence, brake squeal. However it has been shown that not all instabilities predicted by CEA do occur in reality. The effective (negative) damping ratio (expressed in percentage terms) is used as a measure of the strength of instabilities. The level of effective damping ratio of the predicted instabilities below which the instability is not prone to cause noise is set at different levels by different researchers with 1% being an average value in the industry. However, in this study, the acceptable effective damping ratio percentage is set to be 0.5% and any instability predicted with an effective damping rat...

Take-up judder is the first rigid body torsional mode of the clutch system, which occurs during clutch engagement. This phenomenon is induced by stick-slip oscillations at the friction lining interfaces between the clutch disc and flywheel, and the pressure plate. The phenomenon is influenced by the clutch lining friction characteristics, the topography of the mating-sliding surfaces and the operational conditions during the engagement process.
Therefore, the interfacial characteristics are affected by contact pressure, interfacial slip speed and surface temperature. Take-up judder causes driver and vehicle occupant discomfort, as well as gradual wear of contacting surfaces. The response frequency of the system is reported to be in the range 5-20Hz, depending on the clutch system and vehicle inertia. In this paper the measured interfacial friction characteristics together with clamp load variation (contact pressure) under different surface temperatures are included in a multidegree of freedom dynamic analysis to obtain torsional vibrations of the system, pertaining to take-up judder conditions. Such an in-depth investigation has not hitherto been reported in literature. The paper shows that take-up judder is omnipresent under all clutch engagement conditions, but its poignancy is most evident at cold surface temperatures. It is also shown that the transient judder response has a broader spectral content that is generally acknowledged.

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SEA models are used to predict the performance of acoustic packages when assessing the performance of vehicle level
or body noise reduction targets. One of the challenges faced by CAE engineers is the ability to estimate the performance of
different materials used in the sound package at the design stage. Analysts can use measured data in the form of insertion
loss and random incidence absorption if available or can predict the performance of materials using a Biot type description.
The use of the full poro-elastic Biot model for materials requires knowledge of the fluid and elastic properties, however a
limp or rigid model can be used to describe the material based only on the fluid properties and this is often sufficient to
describe fibrous materials.
In this paper a method will be outlined which will allow the material properties of fibrous materials to be estimated
from basic normal incidence data that is provided by material suppliers. This approach will then allow the effect of
compression on the material properties to be predicted and the impact on the acoustic performance to be estimated. In
addition it will allow the analyst to estimate the effects of increasing or reducing the fiber weight. Predictions will be
compared with measured data.

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The overall process of low-noise engine design is outlined. Computational techniques for the analysis of engine noise are considered: the finite element method for the vibratory analysis of the engine structure, the boundary element method for the acoustic analysis of the bare engine and the boundary and shell element method for the prediction of the effect of noise shields. Results from the application of the techniques to an engine-like structure or to test problems are given.

Lightly damped non-linear systems such as vehicular drivelines undergo a plethora of Noise, Vibration and Harshness (NVH) problems. The clonk phenomenon is one concern which occurs as the result of impulsive torque input in the form of sudden clutch actuation or throttle tip-in and back-out. The resulting impact of meshing gear pairs propagate structural waves down the driveline. With lightly damped thin-walled tubes having high modal density, elasto-acoustic coupling occurs. High frequency noise emission is of metallic nature and quite disconcerting to vehicle occupants as well as passers-by. It is perceived as structural failure and/or poor-quality build. Therefore, the occurrence of the phenomenon is a concern to vehicle manufacturers and progressively constitutes a warranty concern. This paper investigates the clonk phenomenon through use of a long-wheel base rear drive light truck test rig. The investigation uses psychoacoustic metrics to establish the severity of clonk noise in different maneuvers. This is an attempt to quantify the effect of transient clonk event which is usually ascertained through subjective evaluation ratings in a customer/jury clinic in industry. Alternatively, detailed numerical analysis is carried out with parametric studies to quantify different clonk events, a very time consuming approach which is not usually correlated with occupants' perception of the event. Therefore, the experimental NVH monitoring-psycho-acoustic approach is new for the case of clonk and not hitherto reported in literature. The study corroborates the results and conclusions of previous work, pointing to the loudness and sharpness of high frequency short-lived "metallic" response, which is attuned to human aural perception. The psychoacoustic analysis has shown this to be as the result of short duration hard impact (accelerative period). This hard impact duration accounts for the bulk loudness and sharpness of the overall event. Therefore, effective palliation should focus on the attenuation of particular frequency bands, which carry the main contribution to loudness and sharpness.

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