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2015-01-14
Technical Paper
2015-26-0126
Prince Shital, Chiranjit Ghosh, Harveen Talwar, Avnish Gosain, Praneet Shanker Dayal
Three-cylinder Engine without balancer shaft is a recent trend towards development of lightweight and fuel-efficient power train for passenger car. In addition of that, customer's expectation of superior NVH inside driver cabin is increasing day by day. Engine mounts address majority of the NVH issues related to transfer of vibration from engine to passenger cabin. Idle vibration isolation for a three-cylinder engine is a challenging task due to possibility of overlapping of Power train’s rigid body modes with engine's firing frequency. This Overlapping of rigid body modes of power train can be avoided either by modifying mount characteristic or by changing the position of mounts based on multi body dynamics (MBD) simulation. This paper explains about two types of engine mounting system for a front-wheel drive transversely mounted three-cylinder engine. The base vehicle was having three-point mounting system i.e. all three engine mounts were pre-loaded.
2015-01-14
Technical Paper
2015-26-0125
Sambhaji Keshaw Jaybhay, Sudhakara Naidu, Prasanna Nagarhalli, J Saiprasad
LCV AC buses market is rapidly growing up in India; major requirement is for staff pick-up and drop, school applications and private fleet owners. The air-conditioning system is typically mounted on bus roof top and located laterally and longitudinally at center. It is an easiest and most feasible way to package air conditioning system to cater the large passenger space (32 to 40seats) with the conditioned air. This makes air conditioning duct design simple and commercially viable. Most of the LCV buses are with front engine configuration which adds more heat and noise to Driver and passenger compartment, this demands for isolation of Driver’s area from passenger area by means of partition in between. Without partition engine noise is more dominant in passenger area, but in case of with partition, blower noise of roof mounted AC system is more perceivable in passenger area.
2015-01-14
Technical Paper
2015-26-0128
Vikram MR, Ramesh Patil, Shashidhar Chattanahalli, Vijay H Meti
TORSIONAL VIBRATION DAMPER DEVELOPMENT FOR EMERGING MARKET RWD VEHICLE Vikram MR, Ramesh Patil, Vijay Meti, Shashidhar Chattanahalli General Motors Technical Centre India Automotive manufacturers are facing unprecedented cost challenge across globe. Market requirement has become very competitive with demand for higher performance and low cost solutions. This is encouraging automotive manufacturers to develop dampers with local suppliers, as there is huge component cost advantage and also logistic cost savings. However, in emerging markets, supplier capability to develop the component for solving particular NVH problem of OEM is not matured as compared to developed market suppliers. Challenge lies with auto makers to develop supplier, who can give right performance, durability and lower cost components.
2015-01-14
Technical Paper
2015-26-0127
Gaurav Paliwal, Naveen Sukumar, Umashanker Gupta, Saurav Roy, Hemantkumar Rathi
The main emphasis for a Commercial vehicle design which was focused on fuel-economy and durability does not fulfill the increasing customer expectations anymore. Commercial vehicle designers need to focus on other vehicle aspects such as steering, ride comfort, NVH, braking, ergonomics and aesthetics in order to provide car like perception to truck, bus drivers and passengers during long distance drives. Powertrain mounting system must perform many functions. First and foremost, the mounting system must maintain & control the overall motion of the powertrain, to restrict its envelope reasonably, thereby avoiding damage to any vehicle component from the potential impact. This requires the mount to be stiff. Second the mount must provide good vibration isolation to have a comfortable ride to the vehicle occupant. This requires the mount to be soft.
2015-01-14
Technical Paper
2015-26-0130
Pradeep Kumar Singh
Gear noise and vibration in automobile transmissions is a phenomenon of great concern. Noise generated at the gearbox, due to gear meshing, also known as gear whine, gets transferred from the engine cabin to the passenger cabin via various transfer paths and is perceived as air borne noise to the passengers in the vehicle. This noise due to its tonal nature can be very uncomfortable to the passengers. Optimizing micro-geometry of a gear pair can help in improving the stress distribution on tooth flank and reducing the sound level of the tonal noise generated during the running of the gearbox when that gear pair is engaged. This technical paper contains the study of variation in noise level in passenger cabin and contact on tooth flank with change in micro-geometry parameters (involute slope and lead slope) of a particular gear pair. Further scope of study has been discussed at the end of the paper.
2015-01-14
Technical Paper
2015-26-0129
Kapil Gupta, Vikram MR, Eugenio Manta
ABSTRACT A turbocharger unit mainly consists of a centrifugal compressor and a turbine coupled together by a solid shaft. This is employed to boost the charge air pressure of engine. Turbocharging in modern diesel and gasoline engines have become a common and essential operation to result higher power outputs, lower emissions, improved efficiency and refinements from a similar capacity of naturally aspirated engine. The automotive turbocharger system is a source of synchronous and asynchronous noises which are particularly very disturbing for the passengers. This need to be eliminated or reduced for passenger comfort. Subjectively, a high whistle noise was audible at passenger cabin during in mid-rpm range drive in all gears in a 4 cylinder diesel vehicle. Objective noise and vibration data confirm the issue as unbalance whistle.
2015-01-14
Technical Paper
2015-26-0122
Herman Van der Auweraer, Karl Janssens, Fabio Bianciardi, Filip Deblauwe, Kumaraswamy Shivashankaraiah
Certification of vehicle noise emissions for passenger vehicles, motorcycles and light trucks is achieved by measuring external sound levels according to procedures defined by international standards such as ISO362. The current procedure based on a pass-by test during wide-open throttle acceleration is believed to be far from actual urban traffic conditions. Hence a new standard pass-by noise certification is the new ISO 362:2007 is being evaluated for implementation that puts testing departments through their paces with requirements for additional testing under multiple ‘real world’ conditions. The new ISO standard, together with the fact that most governments are imposing lower noise emission levels, makes that most of the current models don’t meet the new levels which will be imposed in the future. Therefore automotive manufacturers are looking for new tools which are giving them a better insight in the Pass-by Noise contributors.
2015-01-14
Technical Paper
2015-26-0124
Vilas Deoolkar
Pass – by testing is increasingly done In-door in a hemi-anechoic environment. Advantages of this method are high repeatability and independence of weather conditions. Often rooms smaller than the standardized size will provide accurate results. Product optimisation work often requires information about the noise contribution from the different vehicle noise sources. In this presentation different room sizes are discussed and an accurate time - based contribution analysis method is explained and documented with results from a practical example. Time domain has a number of advantages. The calculations are simple and hence the data are available for processing in other domains. It is possible to directly listen to the individual component contributions when working on exterior brand sound.
2015-01-14
Technical Paper
2015-26-0123
Yogesh Surkutwar, Mahesh Anand Patwardhan, Nagesh Voderahobli Karanth, Atul Gaikwad
Use of Combined CAE and Experimental Testing Approach for Engine Noise Reduction Y. V. Surkutwar, A. A. Gaikwad, M.A. Patwardhan, N.V. Karanth, ARAI Pune Abstract The work presented in this paper deals with the use of combined CAE and experimental testing approach for reducing engine noise. The paper describes a systematic approach for giving solutions to structure borne engine noise related problems. Noise Source Identification (NSI) was carried out on diesel engine to identify noise radiating sources, ranking of noise sources was carried out and contribution of individual engine component in radiated Sound Level (SWL) was computed. Detailed Finite Element model of Engine assembly was developed and model was correlated in terms of natural frequencies and transfer functions by performing modal testing. Correlated FE model was used for predicting surface vibration velocities under various engine speeds and loading conditions in frequency domain.
2015-01-14
Technical Paper
2015-26-0134
Jayant Sinha, Ajit Kharade, Shrihari Matsagar
An interior sound quality is one of the major performance attribute, as consumer envisage this as class and luxury of the vehicle. With increasing demand of quietness inside the cabin, car manufactures started focusing on noise refinement and source separation. This demand enforces hydraulic power steering pump to reduce noise like Moan and Whine, especially in silent gasoline engine. To meet these requirements, extensive testing and in-depth analysis of noise data is performed. Structured process is established to isolate noises and feasible solutions are provided considering following analysis. a) Overall airborne noise measurement at driver ear level (DEL) inside the cabin using vehicle interior microphone. b) Airborne and Pressure pulsation test by sweeping pump speed and pressure at test bench. c) Waterfall analysis of pump at hemi anechoic chamber for order tracking and noise determination.
2015-01-14
Technical Paper
2015-26-0137
Himanshu Agrawal, Abhishek Arun Kakade, Arun Kumar Singh, Sandeep N Shetty
Fan is generally used for cooling of alternator and an undesirable side effect of these fans is generation of flow induced noise. With stricter regulations and growing importance on acoustic comfort in present day market, its very important for companies to address flow induced noise problems early in product development stage. With physical testing, it would not be possible to get information on source strengths thus, limiting its usage. Whereas simulation on the other hand would be able to provide source strengths, directivity pattern and source ranking. This paper focuses on numerical simulation of alternator’s fan for prediction of air- borne noise. For this purpose, Computational Fluid Dynamics (CFD) based transient analysis is performed with high fidelity turbulence model using commercial software package, ANSYS Fluent. Ffowcs Williams and Hawkings (FW-H) model is used for modeling sound propagation.
2015-01-14
Technical Paper
2015-26-0135
Kalpesh Mistry, Steve Fisher, Nitin Badhe
Vehicle level Acoustic sound pack sensitivity and Test correlation by utilising Statistical Energy Analysis (SEA) technique for Premium SUV Kalpesh A. Mistry, Atul D. Pol, Ajay Virmalwar Tata Technologies Ltd., Pune, India Steve Fisher Jaguar Land Rover Ltd., Gaydon, UK SAE SIAT at India,2015 Abstract Due to increased awareness by customer perceived sound characteristics, advance simulation technique emerged in NVH domain for mid-high frequency like BEM, Hybrid and Statistical Energy Analysis (SEA). Structure-borne noise simulation primarily relies on the finite element (FE) technique and due to wide knowledge base, it is in position to get correlated results and prediction. One of the most widely and accepted practice is SEA to assess and optimize Acoustic sound pack for Air Borne Noise (ABN) in the range of 400 Hz to 10,000 Hz typically for Powertrain and Tyre Patch Noise Reduction. As Prof.
2015-01-14
Technical Paper
2015-26-0141
Ravishastri Gadasu, Anshul Khatri, Aashish Parmar
With increase in product diversity in passenger car market, the need for NVH comfort has gained very strong foothold in every segment. This needs in depth analysis for limiting the noise at part level. Radiator Fan Module is one of such part which contributes to Cabin comfort in major way. In this paper, author is focusing on designing of RFM in order to have low noise. Primary objective of RFM is to meet Heat rejection requirement with optimized air flow. Radiator Fan is primarily responsible for meeting air flow requirement within specified noise limit. For flow inducing components like Radiator Fan, there is always a trade-off between the functional requirement and the noise from various sources (Electrical / Mechanical / Flow). Design of Fan blades and Motor Support ribs in RFM is critical to improve Flow noise, i.e. Air cutting noise.
2015-01-14
Technical Paper
2015-26-0139
Pradeep Kumar Singh
Noise generated in the driveline is mainly transferred inside the passenger cabin through air (air borne noise) and through the vehicle body structure, engine mounts, cables etc. Source of the noise generation in the vehicle is mainly through the engine fluctuation (engine combustion excitations). Any change in the engine characteristics results in the change in passenger cabin noise. Also, influence of the vehicle body structure due to change in material properties also affects the NVH performance. This technical paper explains the effect of change in engine characteristics as well as change in the transfer path due to design change on the NVH performance of the gear box and subsequently the NVH performance of vehicle.
2015-01-14
Technical Paper
2015-26-0140
Milind Ambardekar, Adatiya Yogesh, Sudhakara Naidu
A Power-train Mounting System [PTMS] of a passenger car or a Truck provides isolation and damping against excitations from engine and driveline to the vehicle-body to assure low levels of tactile vibrations and structure-borne noise for the passengers. In a competitive market where faster product development is expected, design sign-off for is needed much before Final Design Judgment of the vehicle. This Paper discusses robustness needed in the Design Validation Plan [DVP] of PTMS to capture Voice of Customer against a typical case like idle-shake of a high powered Truck [Fig. 1]. Production variations of Truck vibrations were measured and then analyzed through an Ishikawa diagram. Noise Factors, Error Status and Control factors of the Truck under study were indentified. Modal Alignment of PTMS was studied by an in-house developed multi-body dynamics tool.
2015-01-14
Journal Article
2015-26-0136
Deepak Mahajan, Arnab Sandilya, Lokesh Khandelwal, Sameer Srivastava
Automotive floor carpet serves the purpose of insulating air borne noises like road/tire noise, transmission noise and fuel pump noise etc. Most commonly used automotive floor carpet structure is - Molded sound barrier (PE or vinyl etc) decoupled from floor pan with an absorber such as felt. With increasing customer expectations and fuel efficiency requirements, the NVH requirements are increasing as well. The only possible way of increasing acoustic performance (Specifically Sound Transmission Loss, STL) in the mentioned carpet structure is to increase the Barrier material. This solution, however, comes at a great weight penalty. Theoretically, increasing the number of decoupled barriers layers greatly enhances the STL performance of an acoustic packaging for same weight. However, practically this solution presents problems like- ineffectiveness at lower frequencies, sudden dip in performance at modal frequencies.
2015-01-14
Journal Article
2015-26-0131
Abhishek Verma, M. L. Munjal
In this work, the noise attenuation characteristics of a three-chamber U-bend hybrid muffler have been investigated. Acoustic performance is quantified by the Transmission Loss (TL) parameter. One-dimensional transfer matrix based muffler program (TMMP) and three-dimensional finite element method (FEM) have been used for the prediction of the TL of the muffler. Presence of perforated baffles in geometry necessitates use of the Integrated Transfer Matrix (ITM) approach for the one-dimensional analysis because the sound fields in the elements would be coupled with each other, and for the 3D FEM analysis LMS Virtual Lab software has been used. The mean flow distribution in each of these configurations has been evaluated by means of a lumped flow resistance network. The resulting values of the grazing flow and bias flow have been used in the expressions for acoustic impedance of the perforates.
2014-11-11
Technical Paper
2014-32-0061
Rama Subbu, Baskar Anthony Samy, Piyush Mani Sharma, Prasanna Mahendiran
Abstract Ride comfort, driving stability and drivability are vital factors in terms of vehicle performance and customer satisfaction. Crankshaft unbalance is a source for the vibration that reduces the vehicle performance and it needs to be controlled to some extent such that the vehicle performance will be improved. The IC engine is made up of reciprocating and rotating parts. They produce unbalance forces during their operation and produces vibration in Vehicle. The vibration reduction will be possible by minimizing these unbalance forces and by optimizing the crankshaft of the two wheeled vehicle engine design. Many researches were made to find the causes for the vibration and to reduce it. But still there is a research gap on the testing and simulation of engine components (crankshaft, connecting rod and piston assembly). In this study, an attempt is made to represent the engine vibrations and its isolation to provide a gate way for the future work on it.
2014-11-11
Technical Paper
2014-32-0063
Daniela Siano, Fabio Bozza, Danilo D'Agostino, Maria Antonietta Panza
Abstract In the present work, an Auto Regressive Moving Average (ARMA) model and a Discrete Wavelet Transform (DWT) are applied on vibrational signals, acquired by an accelerometer placed on the cylinder block of a Spark Ignition (SI) engine, for knock detection purposes. To the aim of tuning such procedures, the same analysis has been carried out by using the traditional MAPO (Maximum Amplitude of Pressure Oscillations) index and an Inverse Kinetic Model (IKM), both applied on the in-cylinder pressure signals. Vibrational and in-cylinder pressure signals have been collected on a four cylinder, four stroke engine, for different engine speeds, load conditions and spark advances. The results of the two vibrational based methods are compared and in depth discussed to the aim of highlighting the pros and cons of each methodology.
2014-11-11
Technical Paper
2014-32-0047
Mohamed El Morsy, Gabriela Achtenova
Abstract Using the PULSE platform for vibration analysis, which has been developed as an advanced solution for vibration measurements, the Robust Diagnostic Concept (RDC) was elaborated. The PULSE setup is designed to aid in fault diagnosis of a vehicle gearbox - the main part of a vehicle powertrain. Time Domain, Continuous Wavelet Transformation Technique (CWT), FFT and order analysis measurements are used for detection of an artificial pitting defect in a gear by tracking the gearbox response at accelerated speed and different loads. The test stand is equipped with three dynamometers; the input dynamometer serves as the internal combustion engine, the output dynamometers introduce the load on the flanges of the output joint shafts. The pitting defect is manufactured on the tooth side of the fifth speed gear on the intermediate shaft. The effect of temperature on the vibration measurements was also investigated to study its impact on the fault diagnosis.
2014-11-11
Technical Paper
2014-32-0105
Atsushi Maruyama, Gaku Naoe
Abstract For a small general purpose engine, the authors have studied on “combustion noise”, the mechanical noise originating from combustion. The purpose of this study is to clarify the mechanisms of combustion noise generation. The engine used in this study was a 4-stroke air-cooled single-cylinder engine with the typical characteristics of 3.5 kW-class small general purpose engines, which was specifically designed for experiments. We analyzed the operational behaviors of parts such as the crankshaft, the flywheel and the crankcase during the time of occurrence of combustion noise. Results of the analysis showed that the primary component of combustion noise in small general purpose engines is radiated from the flywheel connected to the crankshaft, and that the vibration mode that radiates the noise is excited by bending deformation of the crankshaft under explosion load.
2014-11-11
Technical Paper
2014-32-0132
Hiroki Ikeda, Norimasa Iida, Hiroshi Kuzuyama, Tsutomu Umehara, Takayuki Fuyuto
Abstract A combustion method called Noise Canceling Spike (NC-Spike) Combustion [1, 2] has been reported in the co-author's previous paper, which reduces combustion noise in PCCI with split injection. This NC-Spike Combustion uses interference of the following “spike” of pressure rise on the preceding peak of pressure rise. The overall combustion noise is reduced by lowering the maximum frequency component of the noise spectrum. The period of this frequency is two times of the time interval between the two peaks of the pressure rise rate. This maximum load range of conventional PCCI combustion is limited by the combustion noise, since the maximum pressure rise rate increases as the amount of injected fuel increases. The NC-Spike Combustion has a potential to extend of the operating range of PCCI combustion.
2014-11-11
Technical Paper
2014-32-0121
Kazuhiko Tanaka, Haruomi Sugita, Hibiki Saito, Masahiko Sekita
Abstract Recently, it has been widely practiced in motorcycle developments that the same type of engine is commonly applied to various vehicle categories. Accordingly, it is drawing more attention to develop the methodology for creating the best suitable sound for each individual vehicle category regardless of restriction from the engine configurations. In our study, we aimed to establish a procedure to control exhaust sounds beyond the borders across the inherent sound qualities originated from their engine configurations. Firstly, we conducted subjective tests in order to extract essential factors, depicted by adjectives that appear in verbal expressions commonly used to illustrate sound qualities in general. The results enabled us to conduct quantitative evaluations of the exhaust sound qualities of various motorcycles. Next, we clarified the relationships among the individual factors of sound qualities under our study and physical parameters in waveforms of the sounds.
2014-11-11
Technical Paper
2014-32-0120
Sara Gronchi, Riccardo Maccherini, Raffaele Squarcini, Fabio Guglielmo, Emanuela Ligarò
Abstract In the modern engine of both small and large size, the acoustic emission is a very important matter increasingly studied as per specific international standards. This paper presents the study of the acoustic emission of a hydraulic rotary oil pump by means of measurement techniques and numerical approaches. This activity aims at showing a complete test-case in which both methods are used to face a noise issue and highlighting also the “weight” of the hydraulic excitation in both cases. In particular, an oil pump has been completely characterized on a test bench to verify the hydraulic performances and the noise radiation. A structural modification has been suggested with the target of altering the noise spectrum of the pump, achieving an optimization of the noise generation. From this assumption, experimental and numerical activities have started in parallel.
2014-11-11
Technical Paper
2014-32-0123
Vishnu Kumar Kuduva Shanthulal, Kannan Marudachalam, V Pattabiraman, S Jabez Dhinagar, Chandramouli Padmanabhan
Abstract The diesel power train (engine and transmission) is the most significant mass contributor in a three- wheeled vehicle. High idling vibrations from the engine get transmitted to the structure and the body panels through the engine mounts. Isolation of these vibrations by proper design of rubber mounts is the most effective engineering approach to improve ride quality of vehicle. In the present study, a mathematical model of the powertrain and mount system is developed; with the engine and transmission being assumed to behave as a rigid body (6 degrees-of-freedom) and the compliance comes from the mounts. As a first step, the modes and natural frequencies are obtained. Following this the response to unbalanced inertial forces for an excitation frequency range of 20-60 Hz (1200-3600 rpm) has been obtained. The model is validated by comparing its results with results of previous published research work.
2014-11-11
Technical Paper
2014-32-0129
Giancarlo Chiatti, Erasmo Recco, Ornella Chiavola, Silvia Conforto
Abstract In the last years, the increasing concern for the environmental issues of IC engines has promoted the development of new strategies capable of reducing both pollutant emissions in atmosphere and noise radiation. Engines can produce different types of noise: 1) aerodynamic noise due to intake and exhaust systems and 2) surface radiated noise. Identification and analysis of noise sources are essential to evaluate the individual contribution (injection, combustion, piston slap, turbocharger, oil pump, valves) to the overall noise with the aim of selecting appropriate control strategies. Previous paper focused on the combustion related noise emission. The research activity aimed at diagnosing and controlling the combustion process via acoustic measurements. The optimal placement of the microphone was selected, where the signal was strongly correlated to the in-cylinder pressure development during the combustion process.
2014-11-11
Technical Paper
2014-32-0026
Alessandro Franceschini, Emanuele Pellegrini, Raffaele Squarcini
Abstract Nowadays the challenge in design of auxiliary devices for automotive small engines is focused on packaging reduction and on the increase of the performance. These requirements are in contrast to each other and in order to fulfil the project specifications, new and more refined design tools and procedures need to be developed. This paper presents a calculation loop developed by Pierburg Pump Technology Italy S.p.A. (PPT). It supports the design of a variable displacement oil pump component for engine applications. The work is focused on the fatigue life evaluation of a joint, which transmits the drive torque from the engine to the oil pump. The aim of the procedure is to calculate the onset of the surface fatigue phenomenon in the hexagonal joint which drives the oil pump, taking into account the axes misalignment and the flat-to-flat clearance. The study has involved several matters, experimental measures, CFD, MBA and FEM analyses.
2014-11-11
Journal Article
2014-32-0018
Kenichi Morimoto, Kenichi Tanaka
Abstract There have been a number of attempts to clarify the relationship between motorcycle specifications and shimmy phenomenon. Some of such efforts are based on equations of motion. The methods used in those efforts are suitable for analyzing motions in a fundamental structure. However, when the degree of freedom is large, it is extremely difficult to deliver an equation of motion. Therefore, a practical method cannot be found generally when applying the methods employing equations of motion. We also conducted the analysis of shimmy using multi-body dynamics simulation. The yielded results were useful only for clarifying the differences in shimmy levels among motorcycles. However, they were not helpful to understand the relationships between specifications and shimmy phenomenon.
2014-11-11
Journal Article
2014-32-0053
Yoshihiro Nakagawa, Shinya Takahashi, Mikihito Masaki, Ranju Imao
Abstract In brake squeal analyses using FE models, minimizing the discrepancies in vibration characteristics between the measurement and the simulation is a key issue for improving its reproducibility. The discrepancies are generally adjusted by the shape parameters and/or material properties applied to the model. However, the discrepancy cannot be easily adjusted, especially, for the vibration characteristic of the disc model of a motorcycle. One of the factors that give a large impact on this discrepancy is a thermal history of the disc. That thermal history includes the one experienced in manufacturing process. In this paper, we examine the effects of residual stress on the natural frequency of motorcycle discs. The residual stress on the disc surface was measured by X-ray stress measurement method. It was followed by an eigenvalue analysis. In this analysis, we developed a unique method in which the residual stress was substituted by thermal stress.
2014-11-11
Journal Article
2014-32-0059
Antonio Agresta, Francesca Di Puccio, Paola Forte, Gabriele Benigni
Abstract NVH simulations for an automotive component industry represent a convenient mean to compare different solutions and make decisions on design choices based on the predictions of the component vibro-acoustic behavior. This paper presents the vibro-acoustic characterization and comparison of two fuel rail assemblies (FRAs) by mean of simulations in Ansys Workbench & LMS Virtual.Lab. These simulations required a preliminary finite element (FE) modal analysis on the FRAs. To verify the reliability of the FE models, an experimental modal analysis was performed on one of the two fuel rails in free-free condition. The correlation between FE and test models highlighted some differences: a sensitivity study proved that the differences depend on the modeling of some brazed joints. The results of the following NVH simulations were checked by performing an acoustic impact test on the two FRAs in free-free condition inside an anechoic chamber.
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