Browse Topic: Noise, vibration, and harshness standards and regulations
Tire exterior noise has become increasingly critical in vehicle acoustics due to two key developments: updated pass-by noise regulations, which amplify the relative contribution of tire noise, and the rise of Battery Electric Vehicles (BEVs), which lack traditional powertrain noise. Design trends in BEVs—such as increased vehicle mass from battery packs and the widespread use of large-diameter, wide, low-profile tires—further intensify tire noise due to stiffer constructions and altered contact dynamics. A common method for predicting tire noise is the source-transfer-receiver model, where the tire is represented by a set of monopoles with volume velocity Q derived from near-field measurements. Acoustic propagation is modeled via p/Q transfer functions. Despite its simplifications, this approach is practical for vehicle development, enabling clear separation between source and transfer mechanisms and facilitating targeted noise control strategies. In previous work, we proposed a rigorous framework to optimize both the spatial distribution and strength of the monopole sources. Positions were identified using an L1-norm regularization via the Lasso algorithm, promoting sparsity and physical interpretability. Strengths were estimated using an L2-norm Tikhonov regularization, which stabilizes the solution against measurement noise. While the Tikhonov regularization parameter was previously tuned manually through trial and error, we now enhance predictive accuracy by selecting it via a cross-validation technique, ensuring a more robust and data-driven optimization. Besides this, compared to the previous work the approach here is validated for the prediction of both indoor and outdoor pass-by noise, as well as for multiple tire types providing different noise levels. Results demonstrate the method’s robustness, accuracy, and applicability for acoustic development in modern vehicle platforms.
This study focuses on the numerical analysis of weather-strip contact sealing performance with a variable cross-sectional design, addressing both static and dynamic behaviors, including the critical issue of stick-slip phenomena. By employing finite element modeling (FEM), the research simulates contact pressures and deformations under varying compression loads, DCE (Door Closing Efforts) requirements, typical in automotive applications. The analysis evaluates how changes in the cross-sectional shape of the weather-strip affect its ability to maintain a consistent sealing performance, especially under dynamic vehicle operations. The study also delves into stick-slip behavior, a known cause of noise and vibration issues, particularly improper/ loosened door-seal contact during dynamic driving condition. This study identifies key parameters influencing stick-slip events, such as friction coefficients, material stiffness, surface interactions, sliding velocity, wet/dry condition. Numerical simulations are used to predict stick-slip tendencies, and potential improvements, such as optimizing material properties or altering geometric profiles, are proposed. The results demonstrate that optimizing the variable cross-section can significantly enhance sealing performance, leading to better noise, vibration, and harshness (NVH) characteristics. Additionally, adjustments to material properties and geometric profiles are shown to reduce stick-slip effects, contributing to quieter and more reliable weather-strip systems in automotive applications. The findings of this study offer valuable insights for the design of more effective weather-strip systems in modern vehicles
ABSTRACT When we assess compliance of crew exposure to vibration within a military tracked vehicle we use international standards, these are ISO 2631 and BS 6841. Within these standards, weighting factors based on research carried out 40 years ago are applied to the measured vibration. These weighing filters attenuate and remove vibration above 80Hz. After conducting tests for over 30 years, it is the author’s intention to prove that these filters are no longer fit for purpose and the standards need revisiting.
Exhaust system of an automobile is primarily employed in automobile to purify exhaust gases and reduce noise due to combustion. However, a side-effect of the above function is the increase in backpressure. As specified in various literatures, an increase in backpressure can lead to a deterioration on engine performance (Power & torque). Benefit of backpressure reduction can be further taken in terms improving the power & torque of engine or improving the fuel economy. With growing concerns related to global warming and CO2 emissions, reducing exhaust back pressure is one of the promising areas in engine design in order to improve the fuel economy of the automobile and achieving carbon neutrality targets. However, reducing the back pressure generally tends to deteriorate the noise attenuation performance of the Exhaust system. Hence, it is imperative to reduce backpressure of an Exhaust system while at the same time ensuring adequate noise attenuation, for passenger comfort and noise regulations. This paper analyses impact of various components in exhaust system on backpressure and provide optimal solution for reduction of the same. The backpressure reduction resulted in an improvement in engine efficiency, which was then further harnessed for improving the fuel economy of the engine. Subsequent sections explain the approach for study and the results.
Reducing the emitted noise from vehicles is a primary issue for automotive OEMs due to the constant evolution of the noise regulations. In the context of electric powertrains, virtual prototyping has proven to be a cost-efficient alternative to the build-test process, especially in early design stage and/or if optimization is targeted. Due to the multiphysics nature of the model, the full simulation chain involves multiple components, each having its own specific modelling attributes. The difficulty then resides in the parts assembly, solving issues like mesh-to-mesh projections, time to frequency-domain transformation, 2d-axisymmetric to 3d mapping, data formatting and management, unit and local coordinate systems… This paper presents an environment that allows for the prediction and analysis of the noise radiated by electric automotive powertrains. The stator-rotor electro-magnetic behavior is represented by time-dependent forces applied on stator teeth. Transfer functions from structural modes to acoustic pressure describe the vibro-acoustic behavior and ensure a fast synthesis of the radiated noise. It is demonstrated how and where harmonic and space order decompositions are introduced in the computational process to deliver efficient and powerful analysis means to drive design decisions. As such, the workflow operation does not require deep expertise neither in electro-magnetic nor vibro-acoustic simulation. The proposed workflow, implemented in the Actran acoustic simulation environment, is finally used to obtain and analyze results on a typical industrial electric powertrain model.
The exhaust system design and development need to be more flexible and easily adaptable for the requirement of dynamic changes to meet the upcoming emission and noise regulations. Durability of exhaust system components are evaluated through conventional bending moment testing using specified standard load conditions. Road load re-production test is an improvement of the conventional approach to predict component weld durability. It involves the systematic and sequential process of acquiring road load data such as sensor instrumentation, strain measurement at the test track, data processing and input to Bi-Ax testing. S/N Curve testing is introduced recently as an alternate method to minimize the use of road load reproduction testing. It involves prediction of rough force using transient response analysis followed by Bi-Ax testing for the derived high and low load forces to meet the target number of cycles to failure. Targeted fatigue damage factor (< 1.0) is evaluated by comparing S/N curve low load force with RLDA maximum force magnitude. Fatigue damage factor, which is the deciding parameter for road load reproduction test, is established with simulation and component S/N curve testing for a representative exhaust system. This method is preferred when the failure mechanism is not clearly known. It also helps to propose maximum sustainable load caused by engine vibration. The maximum force from RLDA is found to be less than the S/N curve low load force and the calculated fatigue damage factor 0.95 (which is <1.0) and therefore fatigue failure will not occur.
In recent times there has been rising demand for noise level reduction in commercial vehicles. Vehicle engine exhaust system is one of the key sources of noise at driver ear, especially in smaller wheel base vehicles, as well as critical for meeting pass by noise regulations. Several techniques are used to reduce the noise level of an exhaust system such as resonators, dissipative mufflers for low & high frequencies respectively. In this paper sound transmission loss (STL) measurement for a LMD bus exhaust system was carried out at rig level. It has been found from the measured data that noise attenuation of current exhaust system is poor in low frequency zone & therefore lower STL frequencies were identified. To attenuate the noises at identified frequencies Helmholtz resonator was introduced, which is particularly effective for low frequency noise attenuation. A design is conceptualized and developed based on Helmholtz resonator calculation for target frequencies and duty cycle gas temperatures. Further, effect of designed resonators on exhaust back pressure in CFD was analyzed. Prototypes were developed & NVH performance trials were carried out at vehicle level. It has been observed from the results that noise reduction can be achieved at passenger ear level (PEL) & in pass by noise (PBN) test. This paper covers complete NVH development cycle for a real-time noise scenario i.e. measurements & analysis, design, development & final verification on vehicle level. It explains possible measures for decreasing exhaust noise and can be used as guideline for related applications.
Along with the global trend for electrification, also motorcycle industry is entering new spheres of highly advanced products and is increasing customer demands for electric mobility. Beside hard facts such as performance, driving range, durability and ease of use, also the brand specific attributes such as styling, driveability and even sound for electrified 2-wheeler are very emotional, unique selling prepositions. To determine the subjective parameters for driveability and acoustics, AVL has developed dedicated tools and methods to quantify these attributes with high maturity. In terms of acoustics and NVH there are several crucial noise sources within electrified powertrains, which have to be treated with high attention from the initial development phase to avoid any kind of unforeseen annoyances: E-motor with inverter, transmission and secondary drive are most relevant. This issue becomes even more important with the ongoing market trend of products featuring increased power. Electrified motorcycles commonly are expected to offer supreme acceleration performance, but even this attribute may lead into driver's disappointment if throttle response and overall vehicle driveability parameters are inhomogeneous. The driveability and the corresponding parameters have to be calibrated in perfect match of all powertrain components along with the given vehicle architecture. AVL has developed unique measurement equipment AVL-DRIVE to validate the relevant criteria and to support best suitable vehicle driveability development. This paper describes the process of adding the capabilities to assess these tasks with AVL driveability and acoustic NVH measurement tools and gives examples how these tools support the increasing effort in development tasks for electrified motorcycles.
Vehicles with lower noise levels and better levels of vibratory comfort for passengers made the area of noise, vibration and harshness (NVH) one of the main areas related to the perception of vehicle quality. Several approaches on the contribution of transfer paths have been studied to define the propagation energy in vehicular structures. Transfer Path Analysis (TPA) is a tool to improve NVH performance with the primary goal of reducing and improving perceived vibrations and noise in the cabin vehicle by occupants. Indirect methods are especially important in cases where the force signals are immeasurable in practice in terms of cost and space for sensor couplings, in the measurement configuration, and particularly in the case of distributed forces. The matrix inversion method, perhaps the most popular classic TPA, identifies operational forces using passive body acceleration. However, removal of the source can change the dynamic characteristics of the assembled structure and increase the time of the experiment, which results in misleading information in the measurements. For this reason, the inversion operation of the acceleration matrix can give erroneous results, where the condition number of the inverted matrix gains considerably high values, especially in the resonant frequencies. Thus, this paper proposes the comparative study of force estimation techniques and transfer paths, based on the matrix inversion method with and without the application of strain techniques and compares with the computational model of the system. In order to carry out this work, an academic test bench simulating a vehicular powertrain was used. The results showed a good compromise between forces and transfer paths and a significant improvement in some frequencies using sensor fusion techniques.
It is well known the difference between development levels and engineering investment applied to passenger car brake pads when compared to Original Equipment Manufacturer (OEM) and items sold in the Independent Aftermarket (IAM). Based on these differences, the objective of this paper is to propose a simple evaluation for the IAM that can provide at least some level of the understanding of frictional material behavior. Based on a tripod of variables, or three Dimensions Development, described in this work as Performance, Comfort (NVH) and Durability; and using internationally and established testing procedures to measure these dimensions in order to meet the IAM demands for the cost-benefit engineering investment. An important part of the proposed tool is to position friction material against competition for market known issues, and, more importantly, to ensure end product safety and reliability.
With fast pacing development of automobile industry and growing needs for better driving experience, NVH performance has become an important aspect of analysis in new driveline product development especially in hybrid and electric powered vehicles. Differential bevel gear has significant role in the final drive. Unlike parallel axis gears such as spur or helical gear, bevel gear mesh shows more complicated characteristics and its mesh parameters are mostly time-varying which calls for more extensive design and analysis. The purpose of this paper is to conduct design study on a differential bevel gear unit under light torque condition and evaluate its NVH characteristics. Unloaded tooth contact analysis (UTCA) of those designs are conducted and compared for several design cases with different micro geometry to investigate their pattern position and size variation effects on NVH response. Loaded tooth contact analysis (LTCA) that is based on semi-analytical and semi-FE method is used to compare other mesh parameters such as mesh point, line-of-action (LOA) and mesh stiffness. For experimental study, several 11x16 gear pairs are tested at multiple gear positions to study the robustness of each micro geometry design. Both pattern and transmission error(TE) are correlated and compared. Result of this study proves the effectiveness and accuracy of modeling and supports the design optimization predictions.
A major challenge in automotive NVH engineering is to approach complex structure-borne sound and vibration problems with sufficient accuracy but reasonable experimental effort. Typical issues encountered are poor correlation between objective component performance criteria tested for during bench validation and corresponding subjective targets evaluated during system validation in the actual vehicle. Additional challenges arise from the need to impose assumptions on sophisticated physical vibration problems to reduce the complexity to a level feasible for conventional experimental test methods. This paper addresses all mentioned issues by elaborating on a system NVH engineering approach employing Virtual Acoustic Prototyping (VAP) (related to what is now often called component Transfer Path Analysis) to synthesize time domain sound and vibration responses of vibrating machinery operated in a virtual vehicle environment. One crucial step of VAP is to characterize the strength of vibrating machinery by independent quantities at the significant coupling degrees of freedom (DoF). This study puts special focus on the measurement of free velocity, suitable for machinery operated when resiliently mounted as per ISO 9611, and the in-situ measurement of blocked forces, applicable for sources connected to any type of receiving structure during operation, as per ISO/DIS 20270. In order to reduce complexity of the underlying measurements this paper investigates the possibility of using collocated sensor arrays and methods to validate assumptions imposed to abstract away from rotational coupling DoF. An electric power steering (EPS) system inducing vibrations into a sub-frame-type structure is considered as a representative automotive source-receiver installation to investigate the feasibility of free velocity and in-situ blocked force approach with respect to independent source characterization for component Transfer Path Analysis (TPA) and VAP. The obtained Virtual Acoustic Prototype is expanded using an algorithm to synthesize realistic time domain data, enabling NVH engineers to conduct reliable objective and subjective design evaluations.
Today’s trend of combustion engine development for cars is characterized with; high torque, low engine speed, low weight, high degree of cyclic irregularity, low excitation frequency due to fewer cylinders active e.g. 4-cylinder or less. This implies in respect of vibrations that it is crucial to control powertrain rigid body modes and place these were they cannot be reached and induced by the low exciting harmonic frequencies for low engine speeds or idling. It is also important to control the overall flexible vibration modes. A mathematical CAE model is created in simulation software AVL-EXCITE in order to handle the vibration phenomenon as a first step. But it is absolutely necessary to “verify” these models with real measurements in respect of NVH and if needed upgrade the CAE model if there are detected deviations. The NVH-test is done with testing tool DEWESoft. The purpose of below paper is to do model verification on a concrete example in respect of powertrain vibrations. Volvo Cars in-line 4-cylinder VEA diesel engine in rig installation is the object for the paper of model verification. Method of this work has been to do simultaneously NVH measurements of vibrations, torque and cylinder pressure traces during different engine load conditions. Also bump test with a modal hammer has been done in order to find rigid body mode frequencies. The measured cylinder pressure is applied as input to the simulation model in order to have consistent input load between test and simulation. This is important when comparing the output vibrations. Verify and compare crank angle based time domain vibrations signals from CAE model with NVH-testing on a real engine. This is the results of the work.
The paper will present an integrated approach to system NVH analysis, which gives an insight into the system response in an EV driveline due to electrical and mechanical excitations; namely rotor mechanical imbalance, electrical machine torque ripple, and stator radial force shapes. The paper will address the fact that, as part of a practical design exercise, different subsystems and components may achieve design maturity at different times. It is therefore important to understand to what extent various drivetrain components may be considered in isolation, and at what point it becomes necessary to consider the interactions present in the full system. The paper will compare predicted NVH performance of a representative EV traction motor when different boundary conditions are considered; for example, when considering the motor being bested in isolation as part of a typical test setup, and when included in a representative drivetrain. For each configuration, the response to mechanical and electro-mechanical noise mechanisms will be assessed, and the fidelity of simulation required to achieve an appropriate engineering insight will be considered. From these studies, the best practice for the assessment of NVH as part of a holistic design process will be discussed. Consideration will be made of the factors which may influence the choice of simulation approach; for example, the level of design maturity, the availability and reliability of system data, and the design targets which are to be addressed.
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