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Predominant brake noise evaluation and rating was developed many years ago and no longer fulfills the need of modern development work. An extended description of a noisy brake event (European expert group guideline EKB 3006) and a standardized test data exchange format, allowing the comparison of different source test results (EKB 3008) are presented. Today's noise rating systems are described and compared by selected examples. The paper proposes an open 4 level noise rating system (EKB 3007). It starts with simple occurrence statistics, noise rating based on sound levels, situational noise rating including duration and finally based on the human perception, described by psychoacoustics.

In a vehicle's development process, Transfer Path Analysis (TPA) is commonly used for identifying sound sources and their transmission to a receiver. Forces acting on the structure are the reason for the structure-borne sound share of the vehicle interior noise. In practice it is not possible, or too extensive, to measure operational forces directly. Instead, they are often calculated indirectly from accelerations and from additionally measured inertances. As the car body is a strongly coupled system, a force acting at one position results in accelerations throughout the structure. This crosstalk must be considered by using a dense inertance matrix consisting of the ratios between each force excitation and the accelerations at every sensor position. Then a matrix inversion is performed to solve the system of equations describing the coupling of the structure.

Since NVH is always a property of the whole system, one must have a deep understanding of the dependencies and all the components that interact. The well known in-situ Transfer Path Analysis (TPA) provides methods to separate different components of an acoustical system such as source and receiver. The source including excitation and structural dynamics of the exciting subsystem can be described independently of the structural dynamics of the receiving structure by means of the in-situ blocked forces. The Experimental Modal Analysis (EMA) is a common method as well and aims to identify the structural dynamics of a structure. This paper addresses the combination of both methods using the example of an e-drive of an electric car, which has been analyzed on a test rig. The combination of modal analysis and TPA yields a better understanding of the system and its dependencies.

For many years in vehicle and other product noise assessments, tonality measurement procedures such as the Tone-to-Noise Ratio, Prominence Ratio and DIN 45681 Tonality have been available to quantify the audibility of prominent tones. Especially through the recent past as product sound pressure levels have become lower, disagreements between perceptions and measurements have increased across a wide range of product categories including automotive, Information Technology and residential products. One factor is that tonality perceptions are caused by spectrally-elevated noise bands of various widths and slopes as well as by pure tones, and usually escape measure in extant tools. Near-superpositions of discrete tones and elevated narrow noise bands are increasingly found in low-level technical sounds. Existing pure-tone methodologies tend to misrecognize an elevated noise band as general masking lowering the audibility of a tone in the measured vicinity, whereas perceptually they add.

The powertrain noise of cars has been reduced in the last decades. Therefore in many cases, rolling tires have increasingly become the dominant sources of vehicles' interior noise. For sound design or a reduction of tire-road noise it is important to know the individual noise shares of the tires and their transfer paths. Authentic tire-road noise can only be measured on a real road, not on a roller dynamometer. So far measurements have been performed during a coast-down on the road with the engine switched off, avoiding the influence of engine noise. Operational Transfer Path Analysis (OTPA) can be used to remove the uncorrelated wind noise, and to synthesize structure-borne and airborne tire-road noise based on input signals measured with microphones at the tires and a triaxial accelerometer at each wheel carrier. Simultaneously, the interior noise is recorded by an artificial head.

Interior vehicle sound is an important factor for customer satisfaction. To achieve an optimized product sound at an early stage of development, subjective evaluation methods as well as analysis and prediction tools must be combined to provide reliable information relevant to product quality and comfort judgments. Binaural Transfer Path Synthesis (BTPS) is a well-known method to calculate interior noise and vibrations based on multi-channel input measurements. Recent enhancements of the BTPS method enable taking into account also simulated excitations, for example engine mount vibrations calculated using MBS and/or FEM simulations, allowing the prediction of interior noise even if the engine is not available in hardware. Interactive evaluation of the generated sounds in a vibro-acoustic driving simulator helps to increase understanding of customer responses and perception of target sounds.

Diesel impulsiveness (so called Diesel knocking) present in the cabin of diesel vehicles is perceived as unpleasant because of its impulsive time structure. JD Power data clearly show the customers preference of vehicles with little Diesel knocking over those with severe knocking. Corresponding objective descriptors that reflect the customers' perception are introduced. The occurrence of such noise patterns is influenced by the combustion process itself as well as by all excited mechanical components within the power train. Further the transfer characteristics of the engine structure and various vehicle noise paths do contribute to a poor Diesel Sound Quality. It is essential that all these factors have to be considered in combination. This paper provides an overview about suitable methods and technologies, including Binaural Transfer Path Analysis and Synthesis. The potential of the approach is demonstrated by an example.

Sound quality of vehicle is more and more an important product feature which significantly influences the perceived product quality. Over recent years, the broad variety of new models, which resulted in increased competition, has lead to rising customer demands with regard to NVH (Noise, Vibration and Harshness) aspects. Apart from the indispensable troubleshooting, the acoustic engineer's scope of work is extended to NVH design engineering. Thus, innovative, ambitious measurement technologies were developed to meet these new, challenging tasks and to maintain a competitive advantage.

The development of a new method to evaluate the NVH quality of diesel combustion noise bases upon following questions by regarding typical driving modes: Driving behavior with diesel vehicles Which driving situation causes an annoying diesel combustion noise Judgment of diesel combustion noise as good or bad A suitable test course was determined to regard typical driving situations as well as the European driving behavior. Vehicles of different segments were tested on that course. The recorded driving style and the simultaneously given comments on the diesel combustion noise results to a typical driving mode linked to acoustics sensation of diesel combustion noise. The next step was to simulate this driving mode on the chassis dynamometer for acoustical measurements. The recordings of several vehicles were evaluated in listening test to identify a metric. The base of metric was objective analyses evaluating diesel combustion noise in relevant driving situations.

Vehicle interior noise consists of a superposition of broadband contributions from powertrain, wind, and tire-road noise. Tire-road noise has become increasingly important referring to overall acoustic comfort, especially for (luxury) sedans with pleasant low-noise engine sounds. An interior noise recording during a coast-down (engine switched off) contains different components: a mixture of wind along with airborne and structure-borne tire-road noise shares. Separating the mixture into these components requires appropriate algorithms and additional measurements. Therefore, structure-borne excitation signals as well as the airborne noise radiation of all four tires are measured simultaneously to an artificial head recording in the vehicle interior during a coast-down test from maximum vehicle speed to standstill.

Sound quality of vehicles has become very important for car manufacturers. This feature is interpreted as among the most relevant factors regarding perceived product quality. Since the development cycles in the automotive industry are constantly reduced to meet the customers' demands and to react quickly to market needs, ensuring product sound quality is becoming increasingly difficult. Moreover, new drive and fuel concepts, tightened ecological specifications, increase of vehicle classes and increasing diversification, etc., challenge the acoustic engineers trying to create and preserve a pleasant, adequate, harmonious passenger cabin sound. Another aspect concerns the general pressure for reducing emission and fuel consumption, which lead to vehicle weight reductions through material changes also resulting in new noise and vibration conflicts.

Feeling and hearing the results of engineering decisions immediately via a “virtual car” - simultaneous engineering - can significantly shorten vehicle development time. Sound quality and discrete vibration at the driver's position may be predicted and “driven” before the first prototype is built. Although sound cannot yet be predicted in an unknown chassis, the sound and vibration behavior resulting from a new engine, never previously installed in a given vehicle, may be predicted, heard binaurally and felt in an interactive “drivable” simulation based on transfer path analysis. Such a simulation, which includes the binaural sound field and discrete vibration of steering wheel and seat, can also include wind and tire noise to determine if certain engine contributions in sound and vibration may be masked.

Since the brake colloquium in 2004 the role of climatic conditions and their relations to noise occurrence, sound pressure level and friction coefficient level is widely discussed in the US and European working groups on brake noise. A systematic study has been started to investigate the influence of relative humidity, absolute humidity and temperature on brake noise and the corresponding friction coefficient level. In this study an enormous effort was taken to keep the influences of the brake parameters, e.g. lining material, Eigenfrequencies and dimensions of the different components as small as possible to investigate the climatic influence only. Strategic humidity and temperature levels were tested according to the Mollier-Entropy-Enthalpy-Diagram which are corresponding to the seasons in the various international regions. A regression analysis evaluates the correlation and the influence of each parameter to noise and friction coefficient level.

The sound sources of modern road vehicle can be classified into three components, driving sound (sound generated through normal driving patterns and events), operating sound (sound generated through actuated components not related to driving), and generated synthetic sound (electronic warning / interactive feedback). The characteristic features of these sounds are dependent upon customer expectation and usage requirements. Additional development complexities are introduced due to each market's cultural and regional differences. These differences in preference must be considered for the establishment of the target sound quality in the early vehicle development process. In this paper, a sound quality goal setting procedure based on user preference is introduced. The sound targets are created as a result of the user preference investigation and validated by intercultural comparison.

With the exact knowledge of the current positions of the microphones in an array and the potential noise sources, it is possible to compensate a relative motion between them. In the past, techniques exploiting this knowledge have been used successfully, e.g., for the measurement of wind turbines and airplane flyover measurement. In this paper, these ideas are applied and modified for the development of a traffic flow observation system. The main purpose of a vehicle pass by measurement is to extract the continuous noise levels of the dominant sources. With the use of advanced video processing or additional sensor information (radar, light barrier) it is possible to create a continuous tracking model of the vehicle. The scan grid in the beam forming algorithm is then recalculated to compensate the movement. In the resulting acoustic video, the vehicle is fixed and the evolution of the sound sources can be observed and auralized for psychoacoustic evaluations.

Today several international brake acceptance tests exist, like the Los Angeles City Traffic test (LACT) or the Mojacar Noise Route in Spain. During these tests noise evaluation is done subjectively by test drivers, which can cause discrepancies. Sometimes noise data are recorded and evaluated by different, mostly company-specific methods but a procedure that considers the human perception of brake squeal is missing. To fill this gap, the procedure BONI (Brake Objective Noise Index) detailed in this paper is developed based on subjective ratings acquired in hearing tests. It provides reliable prediction of squeal annoyance with high correlation to human perception.

In the development process of products there is at present only one approved method for the “prediction” of sound quality: It is the subjective evaluation by hearing or by binaural playback of Artificial Head recordings. This method is possible in the prototype stage at the earliest. Due to the feet that the development processes in industry become shorter and the tasks - especially in the fields of acoustics and vibrations - become increasingly complex, there exist strong requests for time- and cost saving prediction of the expected sound quality. For this purpose a method can be used that is based on binaural recordings and the determination of vibro-acoustical characteristics of components on test facilities. The combination with a (binaural) transfer path database allows a simulation that describes the effects of modifications of the particular characteristics or transfer paths on the resulting sound situation for the listener.

Since currently a technological shift from automobiles with internal combustion engines now to electric vehicles occurs, new challenges in vehicle acoustics must be met. Although, one of the core duties of NVH engineers will still be the prevention and treatment of disturbing noises, the targeted creation of intended and designed sounds will gain in importance significantly. This sound design task is no longer a choice but a necessity. In the scope of hybrid and electric cars a new kind of acoustic feedback must be created. Surely, the simple electric motor sound, the “tram on wheels”, will not be the final solution accepted by customers. Besides the mandatory use of technical methods like transfer path analysis enabling the reliable identification of the reasons for acoustical problems by separation of sources and transfer paths or binaural panel contribution analysis, investigations of customer preferences on the basis of simulated and real test drives will become more important.

Besides powertrain and aerodynamic noise, tire-road noise is an important aspect of the acoustic comfort inside a vehicle. For the subjective evaluation of different tires or vehicles in a benchmark, authentic sound examples are essential. They should be recorded on a real road rather than on a roller dynamometer (avoiding artificial and periodic sounds, especially in the case of a small roller circumference and a smooth surface). The challenge of on-road measurements is the need for separating the components of the interior noise generated by rolling tires, aerodynamic flow and powertrain. This allows for individual judgment of the noise shares. A common approach for eliminating the engine sound is shutting the engine off after acceleration to the desired maximum speed. Operational Transfer Path Analysis (OTPA) can then be used to auralize the tire-road noise at a certain receiver location, where an artificial head records the interior noise during this coast-down.

Pass-by measurements on a test track are a standard test procedure for every new vehicle. Since there are only a few test tracks and the measurements are depending on the environmental conditions two indoor test procedures have been developed using a chassis dynamometer in a semi anechoic chamber. The first procedure delivers the standard pass-by analyses as well as monaural and binaural time signals using a far field array measurement. The second procedure delivers more detailed information about the different noise sources at the vehicle. Near field measurements of the main noise sources of the vehicle are combined with the airborne transfer functions between these sources and a far field observer position to get a simulated far field microphone signal of the whole vehicle or any set of components