Application of Psychoacoustics on the Machinery Noise Emission of Gear Transmissions Christian Brecher, Markus Brumm, Christian Carl Chair of Machine Tools, Laboratory for Machine Tools and Production Engineering (WZL), RWTH Aachen University, Email: [email protected], [email protected], [email protected]Introduction and objectives Acoustic quality of powertrains becomes increasingly important for the customers' acceptance. The gear transmission is one main functional and acoustic component in stationary (e.g. wind turbines) or mobile (e.g. vehicles) machinery. These systems are confronted with trends like lightweight design or the reduction of masking soundscapes. Therefore, high acoustic quality of the gear transmission is strongly demanded in order to meet the acoustic requirements of the machinery system. But a complete avoidance of gearbox noise often can not be achieved by reasonable means. Consequently, increased acoustic quality needs to be achieved by reduction of perception related annoyance, which can be determined by psychoacoustic metrics. But there is only insufficient knowledge about the correlation between the physical excitation in the gear mesh and the psychoacoustic rating of the radiated noise [1]. This paper discusses the application of psychoacoustics on machineacoustic signals of gearbox noise. This incorporates excitation, surface vibration and air-borne noise. Therefore, two different gearsets, which differ in their manufacturing quality and hence in their excitation, are investigated experimentally regarding the psychoacoustic evaluation. Furthermore, the application of FRFs is discussed to predict the noise emission theoretically. Finally, correlation analyses show possibilities of transfer psychoacoustics to the gear set excitation that represents a foundation for the gear transmission design process. Subject of investigation The main focus of this research activity is the noise characteristic caused by the excitation behaviour of a gearset. Therefore, a new test-fixture has been developed during this project that allows measuring the dynamic mesh excitation, Figure 1. Drive Output Elastomer coupling Constant velocity shaft Angular acceleration Rotation angle measuring system Test Gearbox Drive Output Figure 1: Experimental test fixture and powertrain It combines two angular acceleration rings transmitting the data telemetrically. Integrating and considering the base circle diameters lead to the relative differential velocity: 2 2 1 1 ϕ ϕ & & & ⋅ + ⋅ = b b r r x [m] (1) It is a significant excitation indicator of a gearset connecting the noise emission with the input velocity in the gear mesh [2]. Besides this excitation related vibration signal, also surface vibration and sound pressure level are measured with this test fixture. Therefore, the gearbox is integrated in a powertrain which operates within an anechoic chamber. The drive and the output motor are placed outside the anechoic chamber and connecting powertrain sections from the motors to the gearbox are covered by noise attenuation material. Several different microphone positions have been analysed and for this report a positioning of 0.7 m above the gearbox has been selected. For the following investigations two different gearsets have been analysed that have the same macro-geometry (see Table 1). The only difference occurs in the manufacturing quality. The first gearset has a generally medium quality (Q5 according to DIN 3962) whereas the second one has a low quality (Q10 according to DIN 3962) with high profile angle deviations (f Hα = -9.3μm) and high lead angle deviations (f Hβ = 19.5μm), both on the driving gear. z 25 / 36 a 112.5 mm m n 3.5 mm b com 41.5 mm α n 20.0° ε α 1.75 β 19.3° ε β 1.25 Table 1: Gear data and geometry Physical investigation results The investigated operating conditions of the gearsets include a speed run-up from 150 min -1 to 3500 min -1 with an acceleration slope of 33 min -1 s -1 and a constant partial load torque of 100 Nm, both on the driving gear. Differential velocity Figure 2 shows the excitation measurement results for both gearsets based on differential velocity. 20 40 60 80 0 50 100 150 200 20 40 60 80 0 50 100 150 200 10 30 50 70 100 1000 10000 10 30 50 70 100 1000 10000 Gearset 1 Gearset 2 Differential velocity [1e-6m/s] Frequency [Hz] Frequency [Hz] Order regarding drive [-] Order regarding drive [-] Differential velocity [1e-6m/s] Differential velocity [1e-6m/s] Differential velocity [1e-6m/s] Figure 2: Averaged frequency spectra and averaged order spectra of differential velocity AIA-DAGA 2013 Merano 1095
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Application of Psychoacoustics on the Machinery Noise Emission of Gear
Transmissions
Christian Brecher, Markus Brumm, Christian Carl
Chair of Machine Tools, Laboratory for Machine Tools and Production Engineering (WZL), RWTH Aachen