Research Papers: Elastohydrodynamic Lubrication

Ultrasonic Measurement of Rolling Bearing Lubrication Using Piezoelectric Thin Films

[+] Author and Article Information
Bruce W. Drinkwater1

Department of Mechanical Engineering, University of Bristol, University Walk, Bristol, BS8 1TR, UKb.drinkwater@bristol.ac.uk

Jie Zhang

Department of Mechanical Engineering, University of Bristol, University Walk, Bristol, BS8 1TR, UK

Katherine J. Kirk, Jocelyn Elgoyhen

School of Engineering and Science, University of Paisley, Paisley, PA1 2BE, UK

Rob S. Dwyer-Joyce

Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK


Corresponding author.

J. Tribol 131(1), 011502 (Dec 03, 2008) (8 pages) doi:10.1115/1.3002324 History: Received December 14, 2007; Revised August 19, 2008; Published December 03, 2008

This paper describes the measurement of lubricant-film thickness in a rolling element bearing using a piezoelectric thin film transducer to excite and receive ultrasonic signals. High frequency (200 MHz) ultrasound is generated using a piezoelectric aluminum nitride film deposited in the form of a very thin layer onto the outer bearing raceway. This creates a transducer and electrode combination of total thickness of less than 10μm. In this way the bearing is instrumented with minimal disruption to the housing geometry and the oil-film can be measured noninvasively. The high frequency transducer generates a fine columnar beam of ultrasound that has dimensions less than the typical lubricated contact ellipse. The reflection coefficient from the lubricant-layer is then measured from within the lubricated contact and the oil-film thickness extracted via a quasistatic spring model. The results are described on a deep groove 6016 ball bearing supporting an 80 mm shaft under normal operating conditions. Good agreement is shown over a range of loads and speeds with lubricant-film thickness extracted from elastohydrodynamic lubrication theory.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Configuration of ball bearing outer-raceway and ball in contact

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Figure 2

Schematic of the piezo thin film transducer on a ball bearing

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Figure 3

Photograph of the instrumented ball bearing

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Figure 4

Amplitude of the reflected signal for 500 successive data points. The oil-film generation from two ball passages have been captured.

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Figure 5

Response of pulse-echo signal obtained from a piezo thin film transducer deposited onto the bearing outer-raceway (total propagation distance 9.0 mm). Signal A is used to extract lubricant-layer thickness and signals B are reverberations in the cable; (a) time domain and (b) frequency domain.

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Figure 6

Reflection coefficient profile measured as the bearing rotates. The center of the lubricated contact occurs at x=0. The horizontal dashed lines indicate the predictions based on Eq. 3.

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Figure 7

The effect of ball location on ultrasonic reflection; (a) the reference signal is recorded when the ball is remote from the transducer location, (b) the ball directly beneath the transducer, and (c) the ball just past the transducer location.

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Figure 8

The undeformed and deformed shape of the contact surfaces; (a) outer-raceway and (b) ball

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Figure 9

The tangent angle as a function of distance across the outer-raceway for a range of bearing loads

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Figure 10

Simulated geometrical reflection coefficient (Rg) caused by the surface deformation alone

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Figure 11

The reflection coefficient profiles obtained when an assumed reflection coefficient (given by Eq. 22) is distorted by the reflection effect caused by surface deformation. The dashed lines indicate the theoretical values based on the oil-film thickness calculated from Eq. 3.

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Figure 12

A comparison of experimentally measured oil-film thickness (including a correction for surface deformation) with EHL theoretical solution (Eq. 3) for a range of bearing loads (W) and speeds (w). Note that label AlN refers to measurements made using the piezo thin film transducer and label Focsd refers to data from Ref. 19 obtained using a highly focused 50 MHz transducer.




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