Elsevier

Applied Acoustics

Volume 172, 15 January 2021, 107621
Applied Acoustics

Acoustic intensity technique applied to monitor planetary gears

https://doi.org/10.1016/j.apacoust.2020.107621Get rights and content

Abstract

Condition monitoring of gear trains by classic techniques based on vibrations and/or extensometry measurements requires the preparation of the sensor contact surfaces and the cables installation. In the case of planetary gear trains, this task is more difficult due to their compactness and the complexity of the relative movements among their different elements. As an alternative, the authors studied the possibility of using acoustic measurements for the planetary gear-set characterisation, as well as for predictive maintenance of this mechanical system. In order to perform this study, a suitable measurement equipment was selected and a bespoke software was developed to control it, to process the data, as well as to represent the results. This informatic tool was used to perform the acoustic characterisation, in which acoustic pressure and intensity measurements were combined with advanced algorithms, such as sincronous-average technique. In this study, two different failures were experimentally recreated in a commercial gearbox, representing the results by frequency and order spectra and intensity maps. The obtained results were compared with those obtained in the box without defect.

Introduction

Gear transmission systems are critical components in many industrial applications (power generation, automobiles, agricultural and construction machinery, helicopters, etc.) [1], [2], [3], [4]. In consequence, the reliability requirements for this type of elements are increasing every day, both due to the economic costs and to the human life risk, to which a system failure can lead [5], [6], [7], [8], [9], [10].

In the last decades, the use of planetary gear trains has increased due to their compactness and lightness, especially when high-torque levels and/or high transmission ratios are involved. The increase in their use has been accompanied by more demanding technical requirements and has led to the need for improving their design, and more specifically, their reliability. Although the vibration sources for planetary gears are the same as in fixed-axe trains, planetary gears have unique features which add complexity to the problem. Regarding this aspect, many researchers have developed models, both theoretical and experimental, in order to predict and optimize their dynamic behaviour under different operating conditions [11], [12], [13]. Likewise, several experimental techniques have been proposed, mainly focused on both the theoretical model validation and the development of predictive maintenance techniques for this mechanical system [14], [15], [16].

Its compactness implies important difficulties in monitoring this kind of gears by means of vibration and/or strain gauges measurements. Specifically, the sensors installation inside the train and their wiring are hampered by the scarce free volume in its interior and by the complex relative movement among its components. Even the use of telemetry systems instead of wires and slip rings is not always a valid solution. Among other drawbacks, its use implies the modification of the mass of the systems and the possible introduction of unbalances. The installation of external sensors is simpler but needs a contact with the device and requires space, which sometimes is unavailable.

The present work aims to offer an alternative to the abovementioned methods, by using acoustic measurements for condition monitoring [17], [18], [19], [20] and its application to predictive maintenance. For the sake of simplicity and in order to offer a competitive alternative, acoustic characterization proposed in this paper is developed by measuring sound intensity [21], [22] and pressure. With this approach, the sensors can be placed in an easier and quicker way and, more importantly, they do not need to be in contact with the components. To guarantee the success of the procedure, it is vital that the acoustic surrounding of the system remains approximately stable, which makes it suitable for a wide range of applications, from monitoring a wind turbine gearbox inside its nacelle to control quality in a gearbox assembly line. In order to achieve this goal, a set of measurements were developed in a planetary test bench [23].

In order to validate the proposed acoustic technique, it has been used to characterise the behaviour in operation of a specific planetary test bench, which were previously developed by the authors, extensively presented in the literature [23], [24], [25] and summarised in Section 2 for the sake of simplicity. The proposed acoustic technique is detailed in the third section. In Section 4, the characterisation results are shown when this acoustic technique is used in a perfectly lubricated gear set, and then compared with those obtained in presence of defects (no lubrication and a notch on the tooth root), which are presented in Section 5. Finally, conclusions of the study are detailed in Section 6.

Section snippets

Test bench set-up

The test bench used in this work was previously designed and built by the research team [23], [24], [25] in order to experimentally validate an advanced computational model of planetary gear transmissions. It is a back-to-back configuration (Fig. 1) with a mechanical power recirculation composed by two identic planetary stages with a sun, three planets, a ring and a carrier each. The teeth number of the sun, planets and ring is respectively 16, 24 and 65. One of the stages is the test specimen,

Measurement tool developed to perform the acoustic characterisation

One of the main tasks of this work was the development of a unified computer tool which allows for the measurement control, the treatment of the registered data and the representation of the resultant parameters. The Matlab® environment was chosen as programming platform for this tool due to its built-in powerful routines of application in each of the aforementioned aspects. The measuring chain that controls the computer tool consists of the following elements: Intensity probe (type-2

Test bench acoustic characterisation

In order to perform the acoustic characterization of the test bench without defects, both intensity and sound pressure measurements were carried out for different operating conditions. For this purpose, 9 load levels were established from 200 Nm to 1800 Nm (besides the level 0 which represents idle conditions) and 3 motor speeds: 300, 600 and 900 rpm. These values were considered to be representative of the potential operating conditions to which the gear train will be subjected in its actual

Maintenance application

Once the acoustic characterization of the test bench was carried out, the application of the tool in the predictive maintenance of gears were assessed. In order to check the validity of these techniques in maintenance applications, two different tests were performed. In the first, a run-out of lubrication was reproduced in the test bench, whilst, in the second, a defective planet was incorporated.

Conclusions

In this study, the use of acoustic measurements of pressure and intensity in the characterization and condition monitoring of planetary gear boxes was assessed. The measurements were carried out on a planetary gearbox installed in a specific test bench. The gearbox was run under normal operating conditions and with two different defects separately. The acoustic results were presented through frequency spectra and intensity maps.

Mesh frequencies are better identified in acoustic pressure spectra

CRediT authorship contribution statement

P. Garcia Fernandez: Conceptualization, Writing - original draft, Writing - review & editing, Supervision, Investigation. Ana de-Juan: Writing - original draft, Writing - review & editing, Investigation. A. Diez-Ibarbia: Writing - original draft, Writing - review & editing, Investigation. J. Sanchez-Espiga: Writing - original draft, Investigation. A. Fernandez del Rincon: Writing - original draft, Supervision, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work has been supported by project DPI2017-85390-P funded by the Spanish Ministry of Economy, Industry and Competitiveness.

References (25)

Cited by (6)

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