Search Results

Powerplant NVH decisions are sometimes made looking only at how the change impacts either the source radiated noise level or the source vibration. Depending on the engine configuration, those can be good approximations, but they can also be very misleading. By combining both noise sources into a vehicle equivalent noise level a much better analysis can be made of the impact of any proposed design change on the customer perceived loudness. This paper will investigate several different scenarios and identify how the airborne and the structureborne paths combine for I4, V6 and V8 engine configurations. Similar relationships will be shown for path as well as the source contributions.

Realistically experiencing the sound and vibration data through actually listening to and feeling the data in a full-vehicle NVH simulator remarkably aids the understanding of the NVH phenomena and speeds up the decision-making process. In the case of idle vibration, the sound and vibration of the idle condition are perceived simultaneously, and both need to be accurately reproduced simultaneously in a simulated environment in order to be properly evaluated and understood. In this work, a case is examined in which a perceived idle quality of a vehicle is addressed. In this case, two very similar vehicles, with the same powertrain but somewhat different body structures, are compared. One has a lower subjective idle quality rating than the other, despite the vehicles being so similar.

A deeper understanding of the complex phenomenology associated with the multiphase flow-induced noise and vibration in a dynamic valve is of critical importance to the automotive industry. To this purpose, a two-dimensional axisymmetric numerical model has been developed to simulate the complex processes that are responsible for the noise and vibration in a poppet valve. More specifically, an Eulerian multiphase flow model, a dynamic mesh and a user-defined function are utilized to facilitate the modeling of this complicated two-phase fluid-structure interaction problem. For a two-phase flow through the valve, our simulations showed that the deformation and breakup of gas bubbles in the gap between the poppet and the valve seat generates a vibration that arises primarily from the force imbalance between the spring and the two-phase fluid flow induced forces on the poppet.

Modal parameter identification is used to identify those parameters of the model which describe the dynamic properties of a vibration system. Structural dynamic methods and technologies have been used with great success by the automotive industry. Experimental Modal Analysis is the process of determining the modal parameters (modes, natural frequencies, damping factors) of a linear, time-invariant system. One common reason for experimental modal analysis is the verification or correction of the results of the analytical approach. Another reason to extract the modal parameters experimentally is due to its use for future evaluations such as structural modifications. This paper presents the Experimental Modal Analysis of a car in trimmed body configuration which represents a complex system due to the systems attached to it, increasing its damping and measuring noise. Both frequency and time domain system identification methods are studied to obtain the main modes of the structure.

NVH requirements are critical in new driveline developments. Failure modes due to resonances must be carefully analyzed and potential root causes must have adequate countermeasures. One of the most common root causes is the modal alignment. This work shows the steps to design and optimize a new plastic bracket for an automotive half shaft bearing. This bracket replaces a very stiff bracket, made of cast iron. The initial design of plastic bracket was not stiff enough to bring natural frequency of the system above engine second order excitation at maximum speed. The complete power pack was modeled and NVH CAE analysis was performed. The CAE outputs included Driving Point Response, Frequency Response Function and Modal analysis. The boundary conditions were discussed deep in detail to make sure the models represented actual system.

Each more the consumer uses the vehicle noise, vibration, and harshness (NVH) attributes to define the vehicle model when purchasing a car, so the sound quality development is very important to guarantee the automaker success in a competitive market. Several vehicle components contribute to the consumer sound quality perception, as engine, gearbox and exhaust systems. So those components improvement is necessary in order to enrich the sound perception. In this article will be developed a case study that evaluates the contribution and the characteristics of the irradiated noise from the power steering system, which was classified as moan, whine and hiss noise, defines objectively each phenomena and evaluate the proposed systems.

Vehicle noise and vibration (NVH) is among the important attributes of the vehicle. This attribute has to be designed for in the product development process. This produces challenges that are usually overlooked by researchers in the field. These challenges are assessed in this manuscript. The emphasis here is on the NVH phenomenon at the vehicle level. Little work is being done to study the vehicle noise and vibration from a system or customer perspective. This manuscript brings to the attention of researchers and the NVH community at large the various NVH challenges that constitute complexities to the development engineer and may deserve closer attention.

Chapters written by professional and academic experts in the field cover: analytical modeling and analysis, CEA modeling and numerical methods, techniques for dynamometer and road test evaluation, critical parameters that contribute to brake squeal, robust design processes to reduce/prevent brake squeal via up-front design, and more.

In order to effectively evaluate automatic transmission gear noise and vibration performance using a hemi-anechoic test facility, it is essential to understand the coupling mechanism between the transmission internals and the dynamometers and associated shafting. Once this coupling mechanism is well understood, each major frequency response of the resulting torsional vibration operating data can be properly categorized according to the source: transmission-internal, facility, or driveshaft. This knowledge helps noise and vibration engineers properly manage vibration peaks in transmission operating data by ensuring that the issue of concern is not inadvertently influenced by the facility system. Analytical simulations and tests were performed on a transmission operated in a hemi-anechoic facility to evaluate gear vibration using various driveshafts, followed by a program of vehicle testing.

Powertrain mounts are one of the important design characteristics of a vehicle. Powertrain is mostly mounted to the front subframe and once installed in a vehicle, powertrain mounting has an important role in determining the vehicle vibration characteristics. A good mounting system isolates engine input vibration from the vehicle body and minimizes the effect of road inputs to the customer. This paper discusses results of several dynamic models as they relate to noise, vibration and harshness (NVH) and compares the accuracy of these models. Various powertrain models are studied and their accuracy in comparison with full a vehicle model is discussed.

Pump whine as well as other NVH issues related to power steering system can become customer concerns at the vehicle level. In order to avoid that, proposed treatment of the pump structure and its installation on the engine should be performed. This is particularly important because most vane pumps have a wide range of excitation that can reach 1000 Hz (30th order @ 6000 rpm). This requires maximizing the ‘as installed’ frequencies of the pump to avoid coincidence with the engine and other FEAD harmonics.

Mastic material, constrained or non-constrained with doublers, is the traditional method in adding vibrational damping to a steel structure with the goal of reducing panel vibration and radiated sound. With the use of laminated vibration damped steel (LVDS), Ford has been able to reduce the dash panel vibration and optimize sound package design for powertrain noise attenuation. These NVH benefits are presented as the result of a study completed with a laminated dash on a Ford Taurus.

The objective of this project was to develop a methodology for the diagnosis of vibrations of the vehicle's steering wheel. This paper will describe an attempt at developing a systematic approach for describing the vibrations felt, what the sources might be, and how various steering system parameters might affect the vibrations.

Seat Effective Amplitude Transmissibility (SEAT) values can be obtained from direct measurements at seat track and top or estimated from transmissibility data and seat track input. Vertical transmissibility was measured for sixteen seats and six subjects on the Ford Vehicle Vibration Simulator, and these 96 functions used to estimate the seat top response for rough road input. SEAT values were calculated, and good correlation to values computed from direct seat top measurements obtained (R2 of 0.86). Averaging transmissibilities and direct seat measurements over the 6 subjects to obtain correlations for the 16 seats improved R2 to 0.94, validating this approach.

This paper provides a systematic approach to identify the root cause of the squeal noise of a disc brake by using advanced experimental tools. Modal analysis was used to identify the modal participation factors when the brake was squealing according to the reproduced squeal phenomenon and acquired operational displacement shape (ODS) using pulsed electronic speckle pattern interferometry. Modal coupling between the disc and pad/caliper assembly is found to be the key to produce squeal. It has been demonstrated that using mass loading/damping can de-couple the modes between the disc and pad/caliper assembly and reduce the assembly vibration from which the squeal is eliminated.

The object of this paper is to develop a random vibration laboratory test specification for automotive subsystems using the Power Spectral Density (PSD) method. This development is based on the 150k mile field data collected from vehicle proving grounds. The simulated vibration bench test will be used to simulate the energy of the 150k mile field data. The developed specification will include 3 axis random vibration profiles of appropriate duration. The Power Spectral Density method converts the time-domain field data into the frequency-domain data. The Enveloped Energy method groups the similar road PSD profiles to produce a generic PSD profile. The Inverse Law allocates an adjusted duration to the desired PSD energy level. The Road Test Specification provides the duration time for the developed bench test. The n-Soft tool [1] is utilized for data reduction analysis. The Bench Test Specification of the Fuel subsystem is a pilot for this development.

In order to further reduce vehicle cold-start emissions, the use of catalytic converters that are “close-coupled” to the exhaust manifold is increasing. To understand the vibrational environment of close-coupled and underbody converters, a laboratory study was conducted on several passenger vehicles. Catalytic converter vibration spectra were measured on a chassis dynamometer with the vehicle operating over a variety of test conditions. Vehicle operating conditions included hard accelerations and extended steady-state speeds at distinct throttle positions over zero-percent and four-percent simulated road grades.

This case study presents a new automated production noise test for power steering pumps. The test included adaptive noise cancellation, and a neural network implementation. The result mapped the pump acceleration signature into an objective repeatable noise metric. The test algorithm was a distributed DSP architecture designed for real-time measurement and decision processing. It was implemented with no increase in test cycle time. It accomplished the correlation of in-vehicle power steering pump noise to it's vibration characteristics, and retrofitting of accelerometers in place of microphones for acceptance testing.

Wind noise reaches the interior of a vehicle through a variety of mechanisms including: aerodynamic excitation of vibration and reradiation from the greenhouse surfaces; acoustic transmission through door seals including gaps and glass edge leaks, and due to airborne transmission of noise generated by wind interaction with body panels. This paper presents experimental results that quantify contributions to interior noise from individual greenhouse surfaces and from airborne sources on the underbody. The measurements were carried out on a production vehicle in a wind tunnel. Greenhouse surfaces, in addition to the driver window are important contributors to interior noise along with airborne transmission of noise generated due to the flow over and through the vehicle underbody.

Ribbed floor panels have been widely applied in vehicle body structures to reduce interior noise. The conventional approach to evaluate ribbed floor panel designs is to compare natural frequencies and local stiffness. However, this approach may not result in the desired outcome of the reduction in radiated noise. Designing a “quiet” floor panel requires minimizing the total radiated noise resulting from vibration of the floor panel. In this study, the objective of ribbed floor panel design is to reduce the total radiated sound power by optimizing the rib patterns. A parametric study was conducted first to understand the effects of rib design parameters such as rib height, width, orientation, and density. Next, a finite element model of a simplified body structure with ribbed floor panel was built and analyzed. The structural vibration profile was generated using MSCINastran, and integrated with the acoustic boundary element model.