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08.05 Transmission & Drivetrain Noise

Psycho-acoustic evaluation of the automotive acoustic comfort using vibro-acoustic prediction methods
Time: 12:20 pm


Abstract ID: 1630

In the automotive industry, the acoustic comfort is considered as a selling point of utmost importance. To help the OEMs improve the acoustic comfort in cars, as a one-tier supplier of automotive glazing, Saint-Gobain is currently working on the acoustic comfort within the cabin in order to propose the right set of glazing consistent with the OEMs’ specifications. The characterization of the acoustic comfort mostly relies on physical demonstrators required for carrying out the relevant measurements. It is however not available early in the project phase, delaying the subjective analysis late in the development phase. To have the opportunity to develop effective solutions, the acoustic comfort has to be investigated as early as possible in the design process. Saint-Gobain is thus currently developing relevant acoustic models in order to predict the mid-high frequency airborne interior noise generated by the wind excitations. The subjective acoustic comfort has then to be assessed using the predicted interior sound pressure levels converted into audio soundtracks for the auralization purposes. In this paper, we briefly present the Statistical Energy Analysis model developed by Saint-Gobain. The psychoacoustic methodology deployed to evaluate its reliability for the subjective evaluation of the automotive acoustic comfort is detailed.

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Design of an In-cabin Personal Audio Zone System Using an Optimized Acoustic-Contrast-Control-Pressure-Matching Algorithm
Time: 7:00 am

Author: Zhe Zhang

Abstract ID: 1805

This paper presents the design of an in-cabin personal audio zone (PAZ) system that enables the driver and one rear-row passenger to listen to different audio programs with acceptable mutual disturbance. The system is designed predicated on a modified acoustic-contrast-control-pressure-matching (ACC-PM) algorithm, which is optimized using the genetic algorithm (GA) to find out the optimum tradeoff between performance indices including the acoustic contrast (AC) and error performance (Err) and the numerical stability of the algorithm. Comparison with the traditional ACC-PM algorithm reveals an increased contrast and improved reproduction quality. In addition, perhaps more importantly, the numerical stability of the optimized algorithm is substantially enhanced, making it possible to involve more loudspeakers into the PAZ system to achieve an even better sound compartmentalization performance.

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Suggestive Sound Design – How to use Active Interior Sound Design to improve traffic safety
Time: 7:40 am

Author: Manuel Petersen

Abstract ID: 1874

Active sound design becomes an important addition to the newest generation of premium class electrical vehicles to enhance the emotionality of the driving experience. Musicological research indicates that emotions are altered by certain harmonic sets of pitches, whereas results in traffic psychology show that emotions can influence the driving behavior. Despite these findings, there is no research done on how changes to an active vehicle sound could influence the driving behavior. In this paper, we describe an approach for a suggestive sound design. It’s based on the hypothesis, that the chosen safety distance by a driver could be altered by changing the inherent dissonance of an active interior vehicle sound based on the current safety distance. The suggestive sound design is based on an additive synthesizer utilizing the Shepard-Risset glissando. The sound can be controlled by external signals e.g. CAN signals from real or virtual vehicles. To verify this hypothesis, a driving simulator was built in which the driving experience with a suggestive sound and the resulting driving behavior can be validated through subject studies within an immersive and reproducible virtual reality environment. The research aims at improving road safety by influencing the driver through changes in the interior vehicle sound.

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Acceleration sound design for vehicles using distortion products
Time: 6:20 am

Author: Yu Aburagi

Abstract ID: 2154

When considering the acoustic design of automobiles, low-frequency sounds can increase the excitement levels for users. However, there are several problems accompany an increase in the low-frequency levels of an engine sound. For example, it is difficult to create a balance between silence and excitement when a sound’s different order components are changed. It is also difficult to generate heavy bass engine sounds in practical scenarios. Thus, the application of distortion products in the auditory system of the cochlea is considered. Distortion products are perceived when two or more sounds with slightly different frequencies are played simultaneously. This study was conducted to examine the possibility of achieving powerful engine sounds using distortion products. At first, the relationship between different combinations of complex sounds and the pitch perception of distortion products was investigated. As a second step, the application of distortion products to the acceleration sound was also considered. The results suggested the possibility of synthesizing a low-frequency component using distortion products inside a cochlea.

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Low excitation spur gears with variable tip diameter
Time: 6:40 am

Author: Joshua Götz

Abstract ID: 1799

One important source of noise in drive trains are transmissions. In numerous applications, it is necessary to use helical instead of spur gear stages due to increased noise requirements. Besides a superior excitation behaviour, helical gears also show additional disadvantageous effects (e.g. axial forces and tilting moments), which have to be taken into account in the design process. Thus, a low noise spur gear stage could simplify design and meet the requirements of modern mechanical drive trains. The authors explore the possibility of combining the low noise properties of helical gears with the advantageous mechanical properties of spur gears by using spur gears with variable tip diameter along the tooth width. This allows the adjustment of the total length of active lines of action at the beginning and end of contact and acts as a mesh stiffness modification. For this reason, several spur gear designs are experimentally investigated and compared with regard to their excitation behaviour. The experiments are performed on a back-to-back test rig and include quasi-static transmission error measurements under load as well as dynamic torsional vibration measurements. The results show a significant improvement of the excitation behaviour for spur gears with variable tip diameter.

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Vibrational Monitoring of Nested Planetary Geartrain with Unground Pinion
Time: 7:20 am

Author: Jianxiong Feng

Abstract ID: 1852

The nested planetary gear train, which has two integrated single-stage planetary gearsets, is one of the newly developed compound gear train that has been successfully applied to the automobile transmissions. In the current study, a certain type of gear fault in the nested gear train, ungrounded pinion, is investigated using a non-destructive approach monitoring its vibration levels. A novel experimental test stand with open and vertical setup has been designed to collect the vibrational data by mounting the accelerometer directly to the gear clutches. Each of the two layers of the compound gear was tested separately. The measured vibrational data were processed with several signal processing techniques, which includes (a) frequency spectrum analysis, (b) time synchronous averaging (TSA) and (c) modulation sideband analysis. The experimental results show that the existence of the ungrounded pinion can be identified with the frequency spectrum analysis of the vibrational data. In addition, the modulation sidebands are also modeled using a modified version of the traditional technique of physical signal modeling. It is shown that the relative phase of the planet and the meshing vibration strength changed by the unground gear is the critical factor for determining the modulation sideband behavior. In addition, the location of the ungrounded pinion can also be determined by the time history processed by TSA.

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A study on the development and application of program for planetary gear design considering planetary gear noise and efficiency
Time: 6:00 am

Author: Hyun Ku Lee

Abstract ID: 1860

In general, gear mechanical loss is associated with the friction of the lubricating contact surface of the gear and bearing that transmit the power, and a no-load spin loss which is load independent occurs due to gear rotation and the interaction of the bearing component with the lubricating element. In order to minimize planetary gear loss, it is desirable to design by checking the efficiency at the concept design stage. However, a design technique that considers the noise and efficiency of a planetary gear set simultaneously has not been achieved so far. In this paper, a program called 'pRMC with EHL' to check together the efficiency and noise that affected by gear specifications has been developed. By using developed program, planetary gear sets specifications have been designed. And through the experimental evaluation, automatic transmission efficiency could be reduced by 0.3% in combination fuel consumption mode and the planetary gear vibration could be also reduced by 10 dB than former design. Through this designing verification and input parameter correlation, a new planetary gear set designing process has been come up with successfully at the concept design stage.

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Acoustical behavior of loss-optimized involute gears
Time: 7:00 am

Author: Sebastian Sepp

Abstract ID: 1876

The progressing electrification of vehicle drive systems focuses more and more on efficient high-speed concepts. Increasing the motor speed leads to a higher power density of the electrified power train and thereby to an increased range for battery electric vehicles. The high rotational speeds cause new challenges in designing gearboxes regarding the efficiency and the acoustical behavior. Most present gearings in conventional vehicles are designed with high tooth depths to ensure low noise excitation behavior combined with the best possible efficiency. By changing the gear geometry to smaller tooth depths with higher pressure angles, it is possible to further decrease gear losses. However, the loss-optimized gear geometry must not jeopardize the beneficial acoustical behavior. In theoretical studies, the acoustical behavior of loss-optimized gears are investigated and compared to gearings designed according to the state of the art. Design calculations of the excitations of all ideal gears without deviations are on similar levels. However, application of such gear geometries faces severe challenges because the sensitivity to manufacturing deviations may be high. In this paper, simulation results and test results between low-NVH gears and loss-optimized gears are documented and analyzed.

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Performance of a friction ring DVA for vibration control of a flywheel
Time: 6:20 am

Author: Xiaodong He

Abstract ID: 2140

A flexible ring DVA with friction contact interfaces (essentially a viscoelastic-friction DVA) is proposed to suppress vibration of a flywheel, two other cases are also studied, i.e., viscoelastic DVA and friction DVA. Based on an equivalent 3 degrees of freedom (DOFs) dynamic model, displacement response of the flywheel-DVA are obtained by using harmonic balance method (HBM). It is shown that all three types of DVA can suppress vibration of the flywheel effectively, bandwidth of the viscoelastic-friction DVA is enlarged due to the existence of friction interface. Performances of the DVA are evaluated by analyzing the displacement responses and forces (i.e., spring force, damping force and friction force). It is shown that the frequency corresponding to the turning point on the response curve is the critical frequency at which dynamic vibration absorption takes place, and it is also the frequency at which the friction force begins to take effect. In the process of emergence and disappearance of the dynamic vibration absorption, the friction force plays a role similar to a

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An experimental methodology to study engine gear rattle problems
Time: 7:40 am

Author: Ata Donmez

Abstract ID: 2377

Gear induced noise represents a major part of overall automotive drivetrain noise. Gear rattle noise is caused by strongly nonlinear dynamic behavior of the gear pair, primarily due to external torque of speed fluctuations under lightly loaded conditions. Such loading conditions cannot be generated by using the conventional gear dynamics test set-ups that employ power recirculating gearbox arrangements or conventional electric motors. In this paper, a new test set-up is introduced to emulate the actual torque/velocity fluctuations of the input and/or output members of a gear train through three-phase synchronous servo-motors.  In addition to establishing backlash boundaries, a pair of absolute encoders are used to measure the relative motions of the gears as well as their impacts along the drive and coast sides flanks or gears.  Torsional vibratory behavior of a gear pair is presented at different backlash values under several input/output fluctuation conditions along with the companion sound pressure measurements.

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