Practical Methods for Managing the Gear Whine Phenomena

Tonal powertrain noise can have a strong negative impact on passengers’ quality and comfort perception in the interior of electric vehicles. Therefore, in the vehicle development process, the assessment of the perceptibility of tonal powertrain noise is essential. As wind and tire noise can possibly mask tonal noises, engineers use modern masking models to determine the masking threshold of tonal powertrain noise from vehicle interior measurements. In the presently used method, the masking threshold is mostly generated with torque-free deceleration measurements. However, the influence of torque on masking tire noise must be considered. As this requires time-consuming and costly road measurements, an extension of the method is being developed, which will also enable the use of roller dynamometer measurements for the assessment. For the extension of the method, however, the influence of the torque must also be considered. This paper presents a novel calculation method that quantifies the influence of torque on the masking threshold and converts masking thresholds from an arbitrary torque level to another. By identifying the frequency and speed range that is mainly affected by the torque-dependent tire noise, a regression model with respect to the tractive force on the tires can be used to calculate a torque-dependent correction factor. The developed method can significantly improve the validity of masking thresholds and quantitatively, the method generalizes well across different vehicle segments. The error can be reduced to below 2 dB above 2000 rpm and to below 1 dB above 4000 rpm. By using this method, more valid target level settings for tonal powertrain noise can be derived.

<div class="htmlview paragraph">Gear whine can be reduced through a combination of gear parameter selection and manufacturing process design directed at reducing the effective transmission error. The process of gear selection and profile modification design is greatly facilitated through the use of simulation tools to evaluate the details of the tooth contact analysis through the roll angle, including the effect of gear tooth, gear blank and shaft deflections under load. The simulation of transmission error for a range of gear designs under consideration was shown to provide a 3-5 dB range in transmission error. Use of these tools enables the designer to achieve these lower noise limits.</div> <div class="htmlview paragraph">An equally important concern is the dynamic mesh stiffness and transmissibility of force from the mesh to the bearings. Design parameters which affect these issues will determine the sensitivity of a transmission to a given level of transmission error. These dynamics are studied through the use of detailed finite element models of the transmission internals.</div> <div class="htmlview paragraph">A systematic approach to gear element design will be presented to optimize the gear blank design from the perspective of the influence both the transmission error and system dynamics on operating noise. The correlation of model predictions with measured operating data on prototype transmissions will be presented. The model results will be used to illustrate how the use of proper tuning of gear blank resonances can be used to further reduce noise levels by 5 - 10 dB.</div>

Gear whine of automotive transmissions should be controlled since it is of a nuisance. While many methods are used to control gear whine at gear design stage, this paper deals with it in transmission manufacturing process including gear manufacturing and transmission assemblies. There are high percentages of effects on transmission error and gear whine in these two processes. Idle gear whine noise can be reduced by the introduction of hard finishing which can optimize the gear shapes and surfaces. Bending of helical gear is found playing an important role in generating high frequency gear whine. It is significant for transmission assemblies to study the correlations of End of Line (EOL) and vehicles. The satisfying correlations can identify and control gear whine of an assembled transmission. All the methods mentioned above have been applied in transmission manufacturing process and good results have been achieved.

Noise and vibration performance of a gear system is critical in any engineering industry. Excessive vibrational amplitudes originated by the excitations at the gear meshes propagate to the transmission housing to cause noticeable noise, while also increasing gear tooth stresses to degrade durability. As such, gear designers must generate designs that are nominally quiet with low-vibration amplitudes. This implies a gear pair fabricated exactly to the specifications of its blue print will be acceptable for its vibration behavior. Achieving this, however, is not sufficient. As the manufacturing of gears require them to be subject to bands of tolerances afforded by the manufacturing processes employed, the designers must be concerned about variations to the performance of their presumably quite baseline designs within these tolerance bands. This research aims at demonstrating how one type of manufacturing error, random tooth spacing errors, alter the vibratory behavior of a spur gear pair. Two pairs of spur gears are tested for their dynamic transmission error performance. One gear pair with no tooth spacing errors form the baseline. The second gear pair contain an intentionally induced random sequence of spacing errors. The forced vibration responses of both gear pairs are compared within wide ranges of speed and torque. This comparison shows that there is a clear and significant impact of random spacing errors on spur gear dynamics, measurable through examination of their respective transmission error signatures. In the off-resonance regions of speed, vibration amplitudes of the random error pair are higher than the no-error baseline spur gear pair. Meanwhile, at or near resonance peaks, the presence of random spacing errors tends to lower the peak amplitudes slightly as compared to the no-error baseline spur gear pair. The presence of random spacing errors introduces substantial harmonic content that are non-mesh harmonics. This results in a broadband frequency spectrum in addition to an otherwise well-defined frequency spectrum with gear-mesh order components, pointing to an additional concern of noise quality.

This paper will present results from a systematic investigation into functional and aesthetic audio quality of speech recordings degraded by wind noise. The major source of wind noise tested comes from velocity fluctuations interacting with the transducer, generating pressure fluctuations at the microphone diaphragm. To better understand the effect of this type of noise, a perceptual experiment was designed to assess task performance and perceptions of quality when speech and simulated wind noise are presented together. A wind noise simulator was developed, which produces realistic audio from anemometer data, to allow the noise to be isolated from other ambient sounds, and also enable salient parameters to be controlled. Two key components of wind noise in recordings were evaluated, the average level and its temporal variance or “gustiness.” Eight levels of wind noise were factorially combined with three levels of gustiness. Each of these permutations was then presented with one of 24 randomly assigned, grammatically correct, nonsense sentences. Participants were asked to type the sentence they heard, rate the difficulty of the task, and indicate overall quality of the clip. Each sentence contained four keywords—correct identification of which was used for scoring performance.

<div class="section abstract"><div class="htmlview paragraph">Electric vehicles (EVs) present a distinct set of challenges in noise, vibration, and harshness (NVH) compared to traditional internal combustion engine (ICE) vehicles. As EVs operate with significantly reduced engine noise, other sources of noise, such as motor whine, power electronics, and road and wind noise, become more noticeable. This review paper explores the key NVH issues faced by EVs, including high-frequency tonal noise from electric motors, gear meshing, and vibrations. Additionally, it examines recent advancements and trends in NVH mitigation techniques, such as active noise control, improved material insulation, and advanced vibration isolation systems. Furthermore, this paper discusses the role of computational tools, simulation technologies, and testing methodologies in predicting and addressing NVH concerns in EVs. By providing an in-depth analysis of the challenges and the latest innovations, this review aims to contribute to the ongoing development of quieter and more refined EVs.</div><div class="htmlview paragraph">EVs pose unique challenges in the realm of noise, vibration, and harshness (NVH) that differ from those encountered in traditional internal combustion engine (ICE) vehicles. With the significant reduction in engine noise in EVs, other noise sources—such as motor whine, power electronics, and road and wind noise—become more prominent. This review paper delves into the primary NVH challenges associated with EVs, including the high-frequency tonal noise produced by electric motors, gear meshing, and vibration issues. It also explores the latest advancements and trends in NVH mitigation techniques, such as active noise control, enhanced material insulation, and advanced vibration isolation systems. Additionally, the paper highlights the role of computational tools, simulation technologies, and testing methodologies in predicting and addressing NVH challenges in EVs. Through a comprehensive analysis of these challenges and innovations, this review aims to support the ongoing efforts to develop quieter and more refined EVs</div></div>

<div class="htmlview paragraph">A new laboratory method has been developed to evaluate the acoustical properties of expandable and other automotive sealants. These materials are used to reduce wind, road, and powertrain noise transmission into passenger compartments. In the new method, ASTM E 1050 absorption measurement equipment is used along with a new sample holder, a downstream microphone holder (providing two additional microphone locations) and an anechoic termination. These additions permit measurement of normal incidence transmission loss as well as absorption. It is intended to encourage adoption of this method as a standard way of quantifying the acoustical performance of sealants and sealing composites in automotive noise control applications.</div>

<div class="section abstract"><div class="htmlview paragraph">The aeroacoustic development of vehicles is still mainly carried out in wind tunnels under steady flow conditions, although the real situation is different. However, as discussed in several earlier publications, a vehicle experiences unsteady, turbulent flow on road, which results for example from natural wind, wakes of other vehicles, or obstacles at the roadside in combination with side wind. The resulting temporal variations of the wind noise inside the cabin affect the passengers’ comfort and safety through fatigue. To be able to also consider the unsteady aeroacoustics in the vehicle development process, a comprehensive method has been developed that is presented in full for the first time in this paper. The on-road situation is simulated in a realistic and reproducible manner in the full-scale wind tunnel of the University of Stuttgart by means of an active turbulence generator, developed by FKFS. The turbulence generator allows to dynamically vary the flow angle with frequency components of up to 10 Hz. By comparing the unsteady wind noise for different flow situations and different vehicles, a flow scenario has been derived which leads to representative and meaningful aeroacoustic results. The measured temporal wind noise variations are investigated using modulation analysis, which has been adapted to show only relevant information in a comprehensible way. Finally, a psychoacoustic metric for rating the annoyance of unsteady, as well as steady, wind noise has been developed based on listening studies. The metric describes the subjective perception and allows evaluation and optimization of the aeroacoustic behavior specifically regarding the passengers’ comfort. With this new method all wind noise aspects, steady as well as unsteady, can be determined and taken into account for vehicle development. The evaluation and comparison of vehicles and variants is comprehensive and is focused on the passengers’ comfort.</div></div>

The quality and comfort perception in vehicles is strongly influenced by the overall sound quality of the vehicle. Besides aerodynamic and tire noise, tonal powertrain noise plays an important role and can have a strong negative impact on sound quality. An assessment of the perceptibility of tonal noise with respect to masking noise is therefore essential for the vehicle development process. Due to the absence of masking by the internal combustion engine in electric vehicles and the wider frequency range of the powertrain noise, new methods are required for this purpose. In order to evaluate state of the art masking models and a newly developed method regarding the audibility of tonal components, masking thresholds for tonal noise in the vehicle interior are experimentally determined in listening tests. A currently developed extension of the method will also allow roller dynamometer measurements to be used for the evaluation. Currently, the masking signals are mostly generated with torqueless coast down measurements to consider the worst-case scenario. However, a torque dependency has to be taken into consideration. In this paper the torque dependency of the masking noise and the resulting influence on masking threshold is shown for road and roller dynamometer measurements.

<div class="section abstract"><div class="htmlview paragraph">As the vehicle and wind speeds and directions change, the unsteady flow creates non-stationary wind noise. To investigate people’s perceptions of non-stationary wind noise, a method to simulate the non-stationary wind noise is needed. Previously, a method was developed that used stationary recordings taken at several speeds and directions to create a set of sound pressure level predictions in each one-third octave band that are a function of wind speed and direction. These functions are used to create time-varying filters based on provided wind profiles. A reference wind noise measurement is then filtered to produce the sounds. A drawback of this method is that many stationary wind condition measurements are needed to form accurate sound pressure level functions, which can be time consuming. A method requiring fewer measurements was investigated. At each yaw angle one non-stationary noise measurement and one stationary reference measurement are used to estimate the relationship between sound power and wind speed. The accuracy of the estimation was validated by comparing wind noise simulations with wind tunnel measurements, A further improvement is to use partially correlated white noise signals to simulate binaural sounds that have a similar coherence structure between the left and right ear sounds to that observed in binaural measurements in the vehicle.</div></div>

Predictors of people's responses to noise inside cars are used by car companies to identify and address potential noise problems. Because significant advances have been made in the reduction of engine, powertrain, and tire/road noise, it is now important to pursue reductions in wind or aerodynamic noise. While models of loudness are commonly used to predict people's responses to stationary wind noise, some wind noises are less acceptable than is predicted by the loudness metric. Additional sound characteristics may account for this. Two listening studies were designed to examine the usefulness of including sound quality metrics in addition to loudness and sharpness in models used to predict acceptability for non-stationary wind-noise sounds, particularly noise with the kind of variations that are expected from wind gusts. Test sounds were based on recordings made in cars in a wind tunnel. A simulation method was implemented to generate sounds with controlled gusting features by modifying stationary noise recordings. A gusting metric was designed to predict subjects' acceptability responses based on the strength, modulation rate, and duration of the gusts.

<div class="section abstract"><div class="htmlview paragraph">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.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Electric vehicles offer cleaner transportation with lower emissions, thus their increased popularity. Although, electric powertrains contribute to quieter vehicles, the shift from internal combustion engines to electric powertrains presents new Noise, Vibration, and Harshness challenges. Unlike traditional engines, electric powertrains produce distinctive tonal noise, notably from motor whistles and gear whine. These tonal components have frequency content, sometimes above 10 kHz. Furthermore, the housing of the powertrain is the interface between the excitation from the driveline via the bearings and the radiated noise (NVH). Acoustic features of the radiated noise can be predicted by utilising the transmitted forces from the bearings. Due to tonal components at higher frequencies and dense modal content, full flexible multibody dynamics simulations are computationally expensive. Based on previously developed metrics for sound quality, a methodology is proposed with the requirements to design a reduced order model, coupling analytical solutions for the electrical motor along with lumped parameter powertrain modelling. Namely, for an adequate representation of the tonal content, the proposed model considers the harmonic excitations of the electric motor and torque ripple, time-varying stiffness and backlash for the meshing gears and flexibility of the housing at the bearing connection points. The reduced order model predicts the transmitted bearing forces, enabling an overview of the sound quality of the radiated noise with lower computational time and complexity.</div></div>

Reliability-based evaluation of automotive wind noise quality

<div>In this article, the method based on the combination of the acoustic perturbation equations and the statistical energy analysis has been used to simulate and optimize the interior aerodynamic noise of a large sport utility vehicle model. The reliability of the method was verified by comparing the analysis results with the wind tunnel test. Influenced by the main noise sources such as A-pillar, exterior rearview mirror, and front sidewindow, the wind noise of the model was significantly greater than that of the same class. To improve the wind noise performance, the side mirror was optimized with the method, including the minimum distance between the rearview mirror and the triangle trim cover, the angle between the rearview mirror and the front sidewindow, and the shell groove of the rearview mirror. The simulation results show that the overall sound pressure level in the car decreases by 2.12 dBA and the articulation index increases by 4.04% after optimization. The development target of wind noise performance was achieved finally. The research demonstrates that the method combining the acoustic perturbation equations and the statistical energy analysis could be effectively utilized in the design optimization of the exterior shape to improve the wind noise performance of the vehicle during the conceptual design stage of the vehicle development.</div>