Operating Limits for Acoustic Measurement of Rolling Bearing Oil Film Thickness (original) (raw)
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Ultrasonic Measurement for Film Thickness and Solid Contact in Elastohydrodynamic Lubrication
Journal of Tribology, 2011
The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact...
Acoustic measurement of lubricant-film thickness distribution in ball bearings
The Journal of the Acoustical Society of America, 2006
An oil-film thickness monitoring system capable of providing an early warning of lubrication failure in rolling element bearings has been developed. The system is used to measure the lubricant-film thickness in a conventional deep groove ball bearing ͑shaft diameter 80 mm, ball diameter 12.7 mm͒. The measurement system comprises a 50 MHz broadband ultrasonic focused transducer mounted on the static outer raceway of the bearing. Typically the lubricant-films in rolling element bearings are between 0.1-1.0 m in thickness and so are significantly smaller than the ultrasonic wavelength. A quasistatic spring model is used to calculate oil-film thickness from the measured reflection coefficient data. An accurate triggering system has been developed to enable multiple reflection coefficient measurements to be made as the contact ellipse sweeps over the measurement location. Experiments are described in which the loading conditions and rotational speed are varied. Lubricant-film thickness distributions measured ultrasonically are described and are shown to agree well with the predictions from classical elastohydrodynamic ͑EHD͒ lubrication theory, particularly at high radial loads and low rotary speeds. A range of parameters affecting the performance of the measurement are discussed and the limits of operation of the measurement technique defined.
A Method for the Measurement of Hydrodynamic Oil Films Using Ultrasonic Reflection
Tribology Letters, 2004
The measurement of the thickness of an oil film in a lubricated component is essential information for performance monitoring and control. In this work a new method for oil film thickness measurement, based on the reflection of ultrasound, is evaluated for use in fluid film journal bearing applications. An ultrasonic wave will be partially reflected when it strikes a thin layer between two solid media. The proportion of the wave reflected depends on the thickness of the layer and its acoustic properties. A simple quasi-static spring model shows how the reflection depends on the stiffness of the layer alone. This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrodynamic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oil film and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oil film stiffness that can be readily converted to film thickness. Whilst the reflected amplitude of the wave is dependent on the frequency component, the measured film thickness is not; this indicates that the quasi-static assumption holds. Measurements of the lubricant film generated in a simple journal bearing have been taken over a range of loads and speeds. The results are compared with predictions from classical hydrodynamic lubrication theory. The technique has also been used to measure oil film thickness during transient loading events. The response time is rapid and film thickness variation due to step changes in load and oil feed pressure can be clearly observed.
Ultrasonic Measurement of Rolling Bearing Lubrication Using Piezoelectric Thin Films
Journal of Tribology, 2009
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 10 m. 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.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2015
The apparent viscosity of oils in the thin layers that exist in machine elements such as gears and bearings is very different to that in the bulk. In addition, oils in lubricating layers are characterized by non-Newtonian behaviour due to the severe thermodynamic conditions that arise. It is this viscosity that determines the film thickness in lubricated mechanical components. This paper describes a novel methodology based on an ultrasonic approach to determine viscosity in situ in a lubricated contact. The methodology considers the lubricant at the solid boundary as a Maxwell viscoelastic fluid and determines its response to an ultrasonic wave. This approach is then compared with existing methodologies in both a static contact and in a rotating journal bearing. The obtained results have shown that the algorithm proposed in this study is most suitable to study lubricants in the range of 0.3–3 Pas and the measurement error has been found to be less than 10%. This viscosity range is c...
Ultrasonic measurement of lubricant film thickness in sliding Bearings with overlapped echoes
Tribology International, 2015
The lubricant film thickness in sliding bearings with a thin liner have previously been immeasurable due to the overlapping of ultrasonic signals making the use of the ultrasonic spring model impossible. In this paper, we firstly modeled the overlapped echoes in terms of superimposed Gaussian echoes corrupted by noise and used the EM algorithms to extract the interested echo. Then the extracted echo was used to obtain the lubricant film thickness by an ultrasonic spring model. A high precision calibrated rig which could form a series of known film thicknesses was set up and the performance of the method was shown to work well.
Calibration of the ultrasonic lubricant-film thickness measurement technique
Measurement Science and Technology, 2005
This paper describes an experimental apparatus and procedure for the calibration of the ultrasonic lubricant-film thickness measurement technique. It also presents a study of the accuracy of the technique. The calibration apparatus is demonstrated on a three layer steel-mineral oil-steel system. This was chosen to be representative of a typical bearing system which is the industrial application of the technique. In such bearing systems the lubricant-film thickness typically ranges from 0.1 to 100 µm. The calibration apparatus uses a high precision piezoelectric displacement translator to controllably displace one of the steel surfaces relative to the other and hence alter the lubricant-film thickness by a known amount. Through-thickness resonant frequency measurements are then used to accurately measure a thick lubricant film (h > 10 µm). These resonant frequency measurements form the starting point of the calibration. The displacement translator is then used to reduce the lubricant-film thickness into the, more practically interesting, low micron range. In this range the amplitude of the measured reflection coefficient is used via a spring interface model to calculate the lubricant-film thickness. Issues of ultrasonic beam alignment and frequency of operation are discussed. A detailed study of the effect of reflection-coefficient errors on the resultant thickness measurement is presented. Practical guidelines for use of the calibration are then defined and calibration is demonstrated experimentally over the range 0.5-1.3 µm.
Ultrasonic oil-film thickness measurement: An angular spectrum approach to assess performance limits
The Journal of the Acoustical Society of America, 2007
The performance of ultrasonic oil-film thickness measurement is explored. A ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is used with a 50 MHz focused ultrasonic transducer mounted on the static shell of the bearing and focused on the oil film. In order to explore the lowest reflection coefficient and hence the thinnest oil-film thickness that the system can measure, three kinds of lubricant oils (Shell T68, VG15 and VG5) with different viscosities were tested. The results
Ultrasonic measurement of lubricant film thickness in sliding bearings with thin liners
Measurement Science and Technology, 2014
The lubricant film thickness in sliding bearings with a thin liner have previously been immeasurable due to the overlapping of ultrasonic signals making the use of the ultrasonic spring model impossible. In this paper, we firstly modeled the overlapped echoes in terms of superimposed Gaussian echoes corrupted by noise and used the EM algorithms to extract the interested echo. Then the extracted echo was used to obtain the lubricant film thickness by an ultrasonic spring model. A high precision calibrated rig which could form a series of known film thicknesses was set up and the performance of the method was shown to work well.
The Measurement of Liner - Piston Skirt Oil Film Thickness by an Ultrasonic Means
SAE Technical Paper Series, 2006
The paper presents a novel method for the measurement of lubricant film thickness in the piston-liner contact. Direct measurement of the film in this conjunction has always posed a problem, particularly under fired conditions. The principle is based on capturing and analysing the reflection of an ultrasonic pulse at the oil film. The proportion of the wave amplitude reflected can be related to the thickness of the oil film. A single cylinder 4-stroke engine on a dyno test platform was used for evaluation of the method. A piezo-electric transducer was bonded to the outside of the cylinder liner and used to emit high frequency short duration ultrasonic pulses. These pulses were used to determine the oil film thickness as the piston skirt passed over the sensor location. Oil films in the range 2 to 21 µm were recorded varying with engine speeds. The results have been shown to be in agreement with detailed numerical predictions.