Development of a novel ultrasonic method for non-invasive measurement of oil films in piston ring contacts (original) (raw)
Tribology and Interface Engineering Series, 2005
The efficiency of a hydraulic motor depends on the lubrication performance of the piston ring. If the film is too thin then wear occurs quickly, if it is too thick then oil is lost into the cylinder and efficiency is reduced. In this paper a technique for oil film measurement based on ultrasonic reflection is investigated. This has the potential to be used non-invasively on real components. An ultrasonic pulse will reflect from a thin film interposed between two solids. The proportion of the pulse that is reflected depends on the stiffness of the intermediate layer. If the acoustic properties of the film material are known, then the stiffness can readily be used to determine the film thickness. This principle has been employed for the piston ring lubrication case. A piston/cylinder test bench has been used to evaluate the ultrasonic method. A focusing piezo-electric transducer is mounted outside the cylinder and ultrasonic pulses reflected back from the inner bore. The variation of these pulses as the piston ring passes underneath is investigated and used to determine oil film thickness. Films in the range 0.7 to 1.3 m were measured; the thickness did not depend strongly on either ring speed or sealed pressure. Several practical aspects were investigated such as, attenuation in the cylinder material, response time, and transducer resolution. Whilst this study demonstrated that film thickness measurement is feasible, there are a number of practical considerations that require further work, principally the focusing and coupling of the ultrasonic transducer and the response time.
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.
ULTRASOUND METHODS APPLICATION FOR ESTIMATION OF AUTOMOBILE OIL CHARACTERISTICS
The aim of the study is to show the possibilities of ultrasound methods for measurement and analysis of different engine oil characteristics. These possibilities are important and understanding them may contribute for considerable benefits as: (i) improvement of the quality of specific auto service, by purchasing and correct usage of ultrasound devices; (ii) expertise improvement of technicians in the auto services; (iii) obtaining important information for oil film thickness in the group piston-cylinder wall, ball and hydrodynamic bearings. The elucidation of different ultrasound methods' applications and analysis of derived oil parameters broaden the knowledge of the lubrication process in automobile engine, which is a significant factor for the correct preliminary service diagnostics. The paper includes ultrasound methods' description for oil film thickness measurement in the groups piston-cylinder wall, ball and hydrodynamic bearings, tribological and rheological oil properties' measurement, oil level estimation in the engine, temperature measurement and presence of air bubbles in the lubricant oil supply and sump lines, oil viscosity circumference profile in journal bearing in-situ .
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.
Ultrasound for the non-invasive measurement of IC engine piston skirt lubricant films
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2014
Measurements of piston skirt film thickness in-recoprocare are relatively scarce and generally require significant modification to a test engine. However, the trend of engine original equipment manufacturers to downsize capacities whilst maintaining power outputs, increases the demands placed on the piston components. As a result, the relative pressure loading on the piston skirt is increasing and requires that lubrication be optimised to maintain low friction. This paper outlines experimental skirt film thickness measurements obtained from a fired single cylinder engine using reflected ultrasound. The profile of the film structure is observed and an insight into some of the motions of the piston can be determined. This study shows that quantitative film thickness measurements can be made using ultrasound and which are comparable with other established techniques.
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
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2013
The contact between the piston ring and cylinder liner is the most important sealing interface in an automotive engine. Understanding the contact interactions and lubricant film formation at this interface is crucial for the development of fuel-efficient and low emission engines. This article outlines the development of an ultrasonic approach to enable non-invasive measurement of the lubricant film thickness formed between piston and cylinder wall of a fired engine. The sensor system consisted of a series of small, low cost piezoelectric elements which were bonded to the external surface of a four-stroke, single-cylinder engine. Each element could be individually energised with a short duration voltage pulse and reflections from the cylinder inner bore recorded. By using high frequency pulsing and data capture it proved possible to image individual ring and skirt contacts at full engine speeds. These captured reflections were processed to give lubricant film thickness directly and w...
Engine Oil Condition Monitoring Using High Temperature Integrated Ultrasonic Transducers
The present work contains two parts. In the first part, high temperature integrated ultrasonic transducers (IUTs) made of thick piezoelectric composite films, were coated directly onto lubricant oil supply and sump lines of a modified CF700 turbojet engine. These piezoelectric films were fabricated using a sol-gel spray technology. By operating these IUTs in transmission mode, the amplitude and velocity of transmitted ultrasonic waves across the flow channel of the lubricant oil in supply and sump lines were measured during engine operation. Results have shown that the amplitude of the ultrasonic waves is sensitive to the presence of air bubbles in the oil and that the ultrasound velocity is linearly dependent on oil temperature. In the second part of the work, the sensitivity of ultrasound to engine lubricant oil degradation was investigated by using an ultrasonically equipped and thermally-controlled laboratory test cell and lubricant oils of different grades. The results have shown that at a given temperature, ultrasound velocity decreases with a decrease in oil viscosity. Based on the results obtained in both parts of the study, ultrasound velocity measurement is proposed for monitoring oil degradation and transient oil temperature variation, whereas ultrasound amplitude measurement is proposed for monitoring air bubble content.
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...
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.
Operating Limits for Acoustic Measurement of Rolling Bearing Oil Film Thickness
Tribology Transactions, 2004
An ultrasonic pulse striking a thin layer of liquid trapped between solid bodies will be partially reflected. The proportion reflected is a function of the layer stiffness, which in turn depends on the film thickness and its bulk modulus. In this work, measurements of reflection have been used to determine the thickness of oil films in elastohydrodynamic lubricated (EHL) contacts. A very thin liquid layer behaves like a spring when struck by an ultrasonic pulse. A simple quasi-static spring model can be used to determine the proportion of the ultrasonic waves reflected.
The Phase Shift of an Ultrasonic Pulse at an Oil Layer and Determination of Film Thickness
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2005
An ultrasonic pulse incident on a lubricating oil film in a machine element will be partially reflected and partially transmitted. The proportion of the wave amplitude reflected, termed the reflection coefficient, depends on the film thickness and the acoustic properties of the oil. When the appropriate ultrasonic frequency is used, the magnitude of the reflection coefficient can be used to determine the oil film thickness. However, the reflected wave has both a real component and an imaginary component, and both the amplitude and the phase are functions of the film thickness. The phase of the reflected wave will be shifted from that of the incident wave when it is reflected. In the present study, this phase shift is explored as the film changes and is evaluated as an alternative means to measure oil film thickness. A quasi-static theoretical model of the reflection response from an oil film has been, developed. This model relates the phase shift to the wave frequency and the film p...
Proceedings of the 21st IEEE Instrumentation and Measurement Technology Conference (IEEE Cat. No.04CH37510), 2004
In the oil industry, many applications require the measurement of more than one liquid level interface, often in challenging environments. In this paper, an ultrasonic technique has been developed to examine the propagation of ultrasonic waves in the oil, water, and mixed oil-water liquids. The technique is expanded to determine the oil, emulsion, and water levels in an oil tank. A dedicated compact, low-cost, and programmable ultrasound-based Multi-layer level measurement (MLLM) device has been designed and implemented. The advantages of the new method over the current methods include contactless distance measurement, higher accuracy, lower cost, user friendly, simpler setup, and using non-nuclear rays. Additionally, the use of ultrasonic waves for the measurement has the advantage over light-based methods of being insensitive to dusty and smoky environment and almost independent of the object material and surface. Preliminary experiments have been conducted on the device. In this paper, the design and operating parameters of this device are discussed and evidence for the satisfactory performance is given.
Sensors and Actuators A-physical, 2009
The interface between the piston rings and cylinder liner plays an important role in total frictional losses and mechanical wear of internal combustion engines and is increasingly coming under scrutiny as legislated particulate emission standards are becoming more and more stringent. The capacitance method is used for measurement of minimum oil film thickness at the piston ring-liner interface in the present investigations. Measurement of capacitance formed between the piston ring and a probe mounted flush with the liner provides an accurate measurement of oil film thickness provided that the region between the probe and liner is flooded with lubricating oil whose dielectric constant is known. This paper presents detailed design of sensor, instrumentation and measurement of lubricating oil film thickness using capacitive micro-sensor. The present investigation is carried out in a motored engine in order to validate the sensor and instrumentation and it can be directly employed in a firing engine also.
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.
SAE Technical Paper Series, 2008
The interface between the piston rings and cylinder liner play an important role in total frictional losses and mechanical wear of internal combustion engine and is increasingly coming under scrutiny as legislated particulate emission standards are getting more and more stringent. The capacitance method is used for measurement of minimum oil film thickness between piston ring and liner interface. Measurement of capacitance formed between the piston ring and a probe mounted flush in the liner provides an accurate means of determining the oil film thickness provided that the region between the probe and liner is flooded with oil and dielectric constant of the oil is known. This paper presents detailed design and measurement of lubricating oil film thickness using capacitive micro sensor in a nonfiring engine simulator. Lubricating oil film thickness was found to vary between 0.2μm to 8μm in the non firing engine simulator. At a particular position, lubricating oil film thickness varies significantly in upward and downward stroke of the engine due to reversal in direction of piston tilt in the two directions of motion.
Condition Monitoring of Lubricant in Static Mechanisms Using Pulse-Echo Ultrasound Technique
Procedia Computer Science, 2016
This paper proposes an active pulse-echo ultrasonic testing method to determine the lubricant condition in static mechanical components and assemblies. An ultrasonic inspection system was constructed to produce and receive back, high frequency ultrasonic pulses. Wavelet transform was used to de-noise the acquired signal and extract features from the feedback waveforms. Features data, from different samples, were analyzed and used to develop a fuzzy inference system to define the lubricant condition. Classification system was then examined, using grease samples, with known condition. The results indicated that the novel pulse-echo technique is a suitable method for the inspection of lubricants condition in various engineering systems.
Piston-ring film thickness: Theory and experiment compared
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology
A review of the published literature has demonstrated a large variability and discrepancies in the measured and predicted values of piston-ring lubricating film thickness in internal combustion engines. Only two papers have been found that compare experiments in firing engines directly with outputs from sophisticated ring-pack lubrication models. The agreement between theory and experiment in these comparisons was limited, possibly because of inadequacies in the models and/ or inaccuracies of measurement. This paper seeks to contribute to the literature by comparing accurately calibrated experimental measurements of piston-ring film thickness in a firing engine with predictions from an advanced, commercial software package alongside details of the systematic analysis of the measurement errors in this process. Suggestions on how measurement accuracy could be further improved are also given. Measurements of oil-film thickness with an error (standard deviation) of ±15% have been achiev...