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Wind noise is one of the most influential NVH attributes that impact customer sensation of vehicle interior quietness. Among many factors that influence wind noise performance, the amount of dynamic door deflection under the pressure load due to fast movement of a vehicle plays a key roll. Excessive deflection could potentially lead to loss of sealing contact, causing aspiration leakage, which creates an effectual path through which the exterior aerodynamically induced noise propagates into the vehicle cabin. The dynamic door deflection can be predicted using CFD and CAE approaches which, in addition to modeling the structure correctly, require a correct pressure loading composed of external and internal pressure distributions. The determination of external pressure distributions can be fulfilled fairly straightforward by using commercial CFD codes such as Fluent, Star CCM+, Powerflow and others.

Nowadays, by the introduction of significant advances in automotive industries, noise, vibration and harshness (NVH), in the position of the main comfort attribute, plays a crucial role in marketing and passenger satisfaction. In order to cope NVH problems, three main actions are taken by NVH engineers for reducing perceived level of noise in cabin: Noise reduction in sources, Noise path treatment and Noise control at receiver. Among these approaches, those pertain to modification of noise pass, through structure and air, to the cabin are more prevalent in automotive applications. Accordingly, identification of noise paths that dominantly contribute to sound and vibration transfer to cabin phenomenon should be dealt with importance. In practice, engine vibration transmitted through sub-frame attachments to body can induce high level of noise and vibration to the passenger cabin.

Acoustic Diagnostic Network Algorithms (DNA) are experimental methods that extract airborne acoustic characteristics from a motor vehicle and decompose this information into a set of networks from which the source, path and receiver noise sources and paths can be determined. Unlike traditional transfer path analysis Acoustic DNA takes the problem into the fine detail. It answers questions such as what, where and how does a vehicle's acoustic systems need to be changed in order to achieve any given objective. This paper describes the fundamental methodology and features together with how it has been implemented into a computer program that has been used successfully in over 50 vehicle projects within the Authors Research and Development group on a wide range of motor vehicles.

The increasing trend toward electric and hybrid-electric vehicles (HEVs) has created unique challenges for NVH development and refinement. Traditionally, characterization of in-vehicle powertrain noise and vibration has been assessed through standard operating conditions such as fixed gear engine speed sweeps at varied loads. Given the multiple modes of operation which typically exist for HEVs, characterization and source-path analysis of these vehicles can be more complicated than conventional vehicles. In-vehicle NVH assessment of an HEV powertrain requires testing under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. Generally, it is necessary to assess issues related to IC engine operation and electric motor operation (running simultaneously with and independent of the IC engine), under both motoring and regeneration conditions.

Acoustic material testing is becoming increasingly relevant to engineers, designers and manufacturers from a broad range of industries. This paper presents comparisons between material absorption measurements made using the traditional approaches of the reverberation room method and the fixed impedance tube using a sample holder, with those obtained using a lightweight portable flanged impedance tube method. The portable tube allows fast non-destructive in-situ material measurements. It may therefore be used to measure the impact of the installed lay-up (e.g. effects of facing sheets, curvature, material compression, bagging, etc.). Results are presented for both non-locally reacting and locally reacting materials. The flanged tube results are compared directly with in-tube data. They are also corrected for random incidence to allow comparison with the diffuse field reverberation room data.

Acoustic performance of auto interiors is definitely important to control the NVH (noise, vibration, and harshness) performance inside a vehicle, and it is determined by the material parameters, such as density (ρ), thickness (d), open porosity (OP), airflow resistivity (σ), tortuosity (T), viscous characteristic length (VCL), thermal characteristic length (TCL), young's modulus, poisson's ratio, and damping coefficient. Firstly, by making different felt samples (of different surface density and thickness), the sound absorption performance and related parameters were obtained. Then the correlation between the parameters and the sound absorption coefficient (SAC) was summarized. Through this method, database of acoustic parameters and the corresponding SAC for porous materials can be established and sound package design and adjustment can be easily conducted based on the database.

Over the past decade damping materials have contributed major improvements to passenger comfort. Noise Vibration and Harshness (NVH) engineers have further shaped material specifications to reflect key targeted properties that improve vehicle design. The specified damping material is then applied to the formed surfaces of the vehicle body to provide optimal performance and achieve the required results. This paper describes how liquid dampers have advanced to meet increased performance requirements through improved loss modulus of the final coating. Data generated by dynamic mechanical analysis shows that this viscoelastic behavior is what drives the performance in damping materials. Through the correlation of loss moduli to damping performance of Oberst bars, the mechanism can be further quantified and explained.

Active vibration control is the most effective method used for suppressing vibrations from external sources. This paper presents the particle swarm optimization (PSO) algorithm to search about the optimum feedback controller gains for the active mount suspension, for the first time, to reduce the vibrations level of a structural system. It consists of vibrating mass and flexible beam subjected to an external disturbance. A mathematical model and the equations of motion of the structure system with an active mount suspension are simulated using Matlab/Simulink software. The active controller was designed to control the first three modes of the structure. The proposed PSO algorithm aims to minimize the acceleration of the suspended mass as the objective function with constraint of the actuator force. Vibrations level is examined theoretically in order to assess the effectiveness of the proposed controller.

Random vibration control systems produce a PSD plot by averaging FFTs. Modern controllers can set the Degrees of Freedom (DOF), which is a measure of the amount of averaging to use to estimate the PSD. The PSD is a way to present a random signal-which by nature “bounces” about the mean, at times making high excursions from the mean-in a format that makes it easy to determine the validity of a test. This process takes time as many frames of data are collected in order to generate the PSD estimate, and a test can appear to be out of tolerance until the controller has enough data to estimate the PSD with a sufficient level of confidence. Something is awry with a PSD estimate that achieves total in-tolerance immediately after starting or during level changes, and this can create dangerous over or under test conditions within specific frequency bands and should be avoided.

Finite element analysis (FEA) is commonly used in the automotive industry to predict low frequency NVH behavior (<150 Hz) of structures. Also, statistical energy analysis (SEA) framework is used to predict high frequency (>400 Hz) noise transmission from the source space to the receiver space. A comprehensive approach addressing the entire spectrum (>20 Hz) by taking into account structure-borne and air-borne paths is not commonplace. In the works leading up to this paper a hybrid methodology was employed to predict structure-borne and air-borne transfer functions up to 1000 Hz by combining FEA and SEA. The dash panel was represented by FE structural subsystems and the noise control treatments (NCTs) and the pass-throughs were characterized via testing to limit uncertainty in modeling. The rest of the structure and the fluid spaces were characterized as SEA subsystems.

In order to reduce high-frequency harmonic noise produced by the blower in the auxiliary system of a fuel cell vehicle (FCV), a narrowband active noise control (ANC) method instead of conventional passive mufflers is adopted since the blower demands clean air condition and expects good acoustic performance. However, in ANC practical applications, the frequency difference between reference signal and actual primary signal, i.e., frequency mismatch (FM), can significantly degrade the high-frequency performance of narrowband ANC system. In this paper, a new narrowband ANC system is proposed to compensate for the performance degeneration due to the existence of FM and improve noise reduction at high frequencies. The proposed system consists of two parts: the Filtered Error Least Mean Square (FELMS) algorithm filtering the primary signals at wide frequency range other than those at the targeted frequencies, and the FM removal algorithm proposed by Yegui Xiao.

Powertrain and driveline systems interaction in rear wheel drive vehicle development has recently gained attention for the improvement of interior noise and vibration in emerging markets. The driveline is a significant path for engine-generated noise and vibration to reach the interior occupant interfaces, where it affects refinement perception. The interaction of powertrain excitation orders and driveline resonant responders covers a wide range of frequency and vehicle operating conditions. This interaction poses significant challenges during vehicle development. With recent increased demand for higher specific power from diesel engines, driveline refinement has become even more challenging, especially for rear wheel drive vehicles. Two driveline related refinement issues were observed during evaluation of a RWD vehicle. Root cause analysis determined that the first issue (lower rpm boom noise and vibration) was due to engine torsional excitation of the driveline.

A combined lumped parameter, finite element (FE) and boundary element (BE) model is developed to predict the whine noise from rear axle. The hypoid geared rotor system, including the gear pair, shafts, bearings, engine and load, is represented by a lumped parameter model, in which the dynamic coupling between the engaging gear pair is represented by a gear mesh model condensed from the loaded tooth contact analysis results. The lumped parameter model gives the dynamic bearing forces, and the noise radiated by the gearbox housing vibration due to the dynamic bearing force excitations is calculated using a coupled FE-BE approach. Based on the predicted noise, a new procedure is proposed to tune basic rear axle design parameters for better sound quality purpose. To illustrate the salient features of the proposed method, the whine noise from an example rear axle is predicted and tuned.

Reduction of the drag torque and longevity of the clutch assembly are the most important factors for vehicle transmission improvement. The decreasing trend of the drag torque with speed after its peak is a common characteristic of the clutch assembly. Several theoretical models have been presented by the researchers describing the drag torque characteristics at lower clutch speed. However, very little study has been made on the drag torque behavior at very high clutch speed (6000∼10000+ rpm). The alarming jump of the drag torque at high speed operating condition remains unexplained till date. In this paper, we investigated the possible reasons of torque jump up at high rotation speed and solution to overcome this problem. We presented an analytical correlation of torque jump up with the excessive decrease of local static pressure and assumed that vacuum formation is the possible reason of high speed torque rising and associated vibration.

In this paper the power hop phenomenon is analyzed and important influencing factors are investigated. The results of driving tests on various road surfaces with different types of cars with longitudinal and transversal mounted engines as well as with front and rear wheel drive are presented. In order to understand and quantify the power hop effect the rotational speed of the individual wheels and the engine are measured. Additionally, the drive shaft torque, the engine movement in its bearings and the vertical deflection of the wheel with respect to the chassis are determined to get detailed knowledge about physical dependencies. It is shown that the rotational speed of the driven wheels is not a sufficient indicator to assess the occurrence of power hop by measurements. Alternatively, the measured longitudinal acceleration at the seat rail provides a good quantification.

Developing a quiet brake system has been a constant task for OEMs as well as their brake suppliers. As a major component in the brake system, the rotor plays a significant role in brake noise performance. Owning to the cost and damping property advantages, gray iron is still the most widely used material for brake rotor application. When pads/rotor coupling is examined to address noise issues, however, most efforts have been on pads and insulators. Rotor specifications are rather general and the component is typically accepted based on grades defined by mechanical property minimum (mostly in G3000 SAE J431). Nevertheless, we have found that gray iron within a grade can have wide microstructure variations, and the deviation (especially on the rotor friction surface) can critically affect the noise propensity in addition to friction output performance and wear characteristics. In this work, the impact of brake disc material on brake noise and output performance is investigated.

Rear disc brake squeal test results confirm the disc wear - brake squeal correlation reported earlier on front disc brakes. A significant amount of Fe transferred from the disc to the NAO pad surface is detected and the distribution of the transferred Fe is very non-uniform on the pad surface. The pad surface formulation reaches that of Low-Steel Lomets. Disc pads from a noisier brake retain more transferred particles than from a less noisy brake. The pad surface retains more transferred Fe after noise test procedures than after performance test procedures. The transferred Fe particles are either barely visible or invisible. During brake noise test procedures, discs wear in weight as much as disc pads. No correlation is found between average in-stop Mu, maximum in-stop Mu or in-stop delta Mu and brake squeal.

Regenerative braking coupled to small high power density engines are becoming more and more popular in motorsport applications delivering improved performances while increasing similarities and synergies in between road and track applications. Computer aided engineering (CAE) tools integrated with the telemetry data of the car are an important component of the product development. This paper presents the CAE model developed to describe the race track operation of a LMP1-H racing car covering one lap of the Le Mans circuit. The friction and regenerative braking is discussed.

The present work presents evaluation of the sliding surface morphology of brake pads during stick-slip. A low-metallic (LM) and a Non Asbestos Organic (NAO) brake friction materials were subjected to slide against a brake disc under conditions favorable to produce stick-slip phenomenon. The experiments were conducted in a laboratory-scale tribometer, which was especially designed to test brake pads used in vehicle. Delta torque divided by slip time (dT/dtslip) was the parameter used to quantify stick-slip propensity. In addition, optical microscope images of the material's surface were obtained at different stages of the braking test. These images were post-processed in appropriate computational software and by means of the segmentation technique, the real contact area, size and amount of contact plateaus related to the brake pad surface were estimated. This technique was effective to quantify the differences in the sliding surface morphology during low speed braking test.

The dynamic friction behavior of automotive brakes is generated by the boundary layer dynamics between pad and disk [OST01]. A key component of the Friction Interface is the influence of mesoscopic surface contact structures known as patches, upon which the friction power is concentrated, and whose sizes vary with time. Through this dynamic process, time and load history-dependent effects come about, which cause, for example, the brake moment behavior commonly observed in an AK-Master test. In recent years, several simulation tools have been developed in order to predict the complex friction behavior caused by the patch dynamics in the friction boundary layer. Such simulations are often based on a two or three-dimensional spatial grid, where the explicit physical phenomena at all locations in the boundary layer are modeled by time-consuming calculations of local material dependent balance equations.