Measurement Of Oil Film Thickness Research Articles

High-accuracy ultrasonic measurement of oil film thickness in sliding bearings considering surface thin coating

Focusing on the difficulty and inaccuracy of separating reflected waves from overlapping echoes caused by coating when measuring the oil film thickness of coated sliding bearings using ultrasonic. This paper proposes a pseudo reflection coefficient (PRC) constructed using the overall reflected wave and reference wave. And a robust PRC model is constructed to simultaneously calculate the oil film and coating thickness. Acoustic simulations verify the accuracy of the method and reveal that the PRC model has better stability. Application experiments are conducted on an actual aviation fuel gear pump. The good consistency between theory and experiment has demonstrated the effectiveness of the method. In addition, the elastic deformation of the bearing is derived based on the minimum oil film thickness.

Measurement of Oil-Film Thickness and Observation of Oil Distribution in High-Speed Deep-Groove Ball Bearings

Measurement of Oil-Film Thickness and Observation of Oil Distribution in High-Speed Deep-Groove Ball Bearings

Using electrical impedance spectroscopy to identify equivalent circuit models of lubricated contacts with complex geometry: In-situ application to mini traction machine

Electrical contact resistance or capacitance as measured between a lubricated contact has been used in tribometers, partially reflecting the lubrication condition. In contrast, the electrical impedance provides rich information of magnitude and phase, which can be interpreted using equivalent circuit models, enabling more comprehensive measurements, including the variation of lubricant film thickness and the asperity (metal-to-metal) contact area. An accurate circuit model of the lubricated contact is critical as needed for the electrical impedance analysis. However, existing circuit models are hand derived and suited to interfaces with simple geometry, such as parallel plates, concentric and eccentric cylinders. Circuit model identification of lubricated contacts with complex geometry is challenging. This work takes the ball-on-disc lubricated contact in a Mini Traction Machine (MTM) as an example, where screws on the ball, grooves on the disc, and contact close to the disc edge make the overall interface geometry complicated. The electrical impedance spectroscopy (EIS) is used to capture its frequency response, with a group of load, speed, and temperature varied and tested separately. The results enable an identification of equivalent circuit models by fitting parallel resistor-capacitor models, the dependence on the oil film thickness is further calibrated using a high-accuracy optical interferometry, which is operated under the same lubrication condition as in the MTM. Overall, the proposed method is applicable to general lubricated interfaces for the identification of equivalent circuit models, which in turn facilitates in-situ tribo-contacts with electric impedance measurement of oil film thickness – it does not need transparent materials as optical techniques do, or structural modifications for piezoelectric sensor mounting as ultrasound techniques do.

On the effect of temperature in friction force measurements for a simplified piston cylinder set-up: Squeeze film combined with minimum oil film thickness measurements and viscosity index effect

The lubricated interface at the piston-ring and liner and its interaction with different lubricants and testing conditions is examined in terms of experimental measurements that show the minimum oil film thickness developed at the lubricated or depending on conditions partly lubricated conjunction and the surface interaction intensity, as measured from the friction sensor. An analysis is carried out with the use of different parameters for the experiments as well as different lubricants in a simplified piston-ring simulation test rig. This analysis is further enhanced with the squeeze film effect investigations close to the stroke reversals and together with cavitation initiation and load-carrying effect results from previous experimental data, light is shed on the interacting surface’s behaviour at the different lubrication regimes. Another parameter, the viscosity index of the lubricant is used as an indication of the effects of squeeze film shift and friction force measurements and how the load and temperature effect are influencing the squeeze film.

Investigation into injection and falling film flow processes of diesel

The formation and flow phenomena of oil films widely exist in various industrial fields. High-accuracy oil film thickness measurement helps to comprehend the complex heat and mass transfer mechanisms of oil films, and to optimize corresponding industrial processes. Here, 0# diesel was employed as the research object. The absorption spectra of diesel at various temperatures were analyzed, and two optimal wavelengths were chosen. A measurement system based on absorption spectroscopy was then developed to determine the oil film thickness. The measurement accuracy of the system was validated by a calibration tool with known thicknesses. Furthermore, the injection processes of diesel at various injection velocities on a horizontal plate were investigated. The falling film flow processes of diesel at various flow rates on a vertical plate were also studied. It indicated that the system could achieve the high-accuracy measurement of diesel film thicknesses during the injection and falling film flow processes.

Dual experimental-numerical study of oil film thickness and friction in a wide elliptical TEHL contact: From pure rolling to opposite sliding

This study presents a dual experimental-numerical approach to simultaneously investigate oil film thickness and friction in a wide elliptical thermo-elastohydrodynamic (TEHL) contact over sliding conditions ranging from pure rolling to opposite sliding (slide-to-roll ratio SRR between 0 and 4). Experiments are performed on a barrel-on-disk tribometer instrumented for friction and optical oil film thickness measurements. In addition, a TEHL numerical model based on the full system approach is used to predict film thickness and friction response variation with sliding. The trends of film thickness variation with SRR are different for SRR lower and higher than 2 because of the genesis of the thermal viscosity wedge effect at opposite sliding. The friction coefficient measured experimentally increases with increasing SRR and then stabilizes at high SRR. The numerical model can accurately predict the film thickness over a wide range of sliding conditions. Also, the model predicts friction with a good accuracy for SRR>2. In contrast, for SRR<2, numerical results overestimate friction coefficient. In addition, a numerical parametric investigation is realized to understand the effect of varying ambient temperature, normal load, and entrainment velocity on film thickness and friction over a wide range of sliding conditions. Numerical results are then used to create a simple formula for an accurate estimation of the minimum film thickness based on classical dimensionless parameters and SRR for a wide range of sliding conditions (0≤SRR≤4).

Quantification of oil film thickness on the top ring sliding surface by visualization

The oil film thickness of the piston ring at the sliding surface affects oil consumption, friction loss and wear of the ring and liner in internal combustion engines. It is important to know the oil film thickness on the piston ring sliding surface in order to improve the engine efficiency. Accurate measurement of oil film thickness on the piston rings is difficult because the oil film thickness is extremely thin. A modified method is proposed for measuring thin oil film. The authors have measured the oil film thickness on the piston skirt and land to contribute. The optical measurement system and analytic method are improved. The presented method present the oil film thickness on the sliding surface of the top ring from the oil film visualization images. The verification of the measured oil film thickness carried out by comparing with the data obtained from the numerical calculation. For evaluating the effect of the oil characteristics, 0W-20 oil and #8 oil were tested with different engine speeds and different crank angle where different ring loads. It was confirmed that the top ring oil film thickness became thick due to the high engine speed. A large load on the top ring reduces the oil film thickness. The oil film became thick when the oil viscosity was high. The effect of oil viscosity on the oil film thickness of the top ring was clarified. The effect of the viscosity index improver was also discussed. It is shown from the experimental results that the present measurement system for the top ring oil film thickness has enough accuracy.

Ultrasonic measurement of oil film thickness in a four-layer structure for applications including sliding bearings with a thin coating

Owing to the non-destructive feature, ultrasonic techniques have been developed to measure the oil film thickness in sliding bearings. If a bearing has a thick coating, then the ultrasonic reflection from a four-layer structure consisting of pad-coating-oil-steel is equivalent to that of coating-oil-steel, where classical three-layered ultrasonic models can be applicable to estimate the thickness of oil film. However, in the case of thinly coated bearings, the measurement accuracy of existing models deteriorates due to signal overlapping. Despite two signal processing methods that have been attempted to isolate the desirable oil film echoes, the challenge remains when dealing with widely ranged oil film thickness. In contrast, this paper presents a unified ultrasonic model that enables accurate measurements of oil film thickness that is widely ranged in a thinly coated bearing. This model is mathematically derived from multi-layer continuum models with the oil thickness and the complex reflection coefficients correlated. It also takes into account two typical locations of the embedded transducer in the bearing. The viability of the proposed method is experimentally validated using a high-precision calibration rig, showing that the oil film that ranges from 6 μm to 97 μm can be accurately measured in the application to thinly coated (around 400 μm) bearings, where the measurement errors are not greater than 7.4%.

Piston ring oil film thickness measurements in a four-stroke diesel engine during steady-state, start-up and shut-down

Internal combustion engine research predominantly focuses on routes to lower emissions to meet various emission legislation. Lower emissions can be achieved with increased fuel efficiency and less lubricant throw off/lubricant combustion in the piston ring zone. These are all dependent on the oil film that forms between the liner and piston components. This article details the use of ultrasonic sensors to study the lubricant film thickness between the engine liner and piston rings/skirt in a fired diesel two-cylinder YTR engine. The testing regime covered a series of engine speeds and loading levels and found the minimum oil film thickness to vary from 1 to 3.5 μm. Spectrograms (time-varying ultrasonic amplitude spectra) have shown a residual oil film on the liner, first present after the skirt moves above the sensor that peaks at 440 μm, which then dissipates until the next oil control ring passage. Start-up and shut-down captures have visualised the build-up and reduction of the film thickness, in which during start-up typically a 2-s interval between the first ring passage and a consistent film thickness was seen. Whilst the shut-down tests showed a lesser variation, anticipated to be due to the oil pump already operating and is, therefore, less subjective to a reduction in engine speed providing a threshold of oil remains on the liner. Measurements like this help to describe how lubrication occurs in the piston ring zone and hence can optimise component design and an oil injection schedule.

Applying the Hilbert Envelope Method to Refine the Ultrasonic Technique for Piston Ring Oil Film Thickness Measurements in a Marine Diesel Engine

Applying the Hilbert Envelope Method to Refine the Ultrasonic Technique for Piston Ring Oil Film Thickness Measurements in a Marine Diesel Engine

Prediction and Experimental Verification for Oil Transport Volume around Three-Piece Type Oil Control Ring Affecting Lubricating Oil Consumption

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Reducing of lubricant oil consumption (LOC) remains a major issue for internal-combustion engines. Especially in recent years, in order to comply with Particular Number (PN) regulations and lower oil viscosity to reduce friction loss, need to reduce the LOC has increased. Controlling the upward oil flow, that passes the piston and piston rings, is effective in reducing the LOC. In addition, oil control ring (OCR) has significant effect on upward oil flow. Therefore, development of a high-precision prediction method of oil behavior around the OCR is important for prediction of LOC. So, the model of Three-piece type oil control ring (3POCR) motion within the OCR groove and the model of oil behavior around the 3POCR were developed using the computer aided engineering (CAE) method in this paper. These models calculate in detail the upward oil outflow to the 3rd land from the OCR groove, which is based on the relation between the OCR motion and the gas pressure as well as the inertial force of oil. Since factors that greatly affect the prediction accuracy are the gas pressure around the OCR and the OCR motion, these were measured and verified in the actual engine. Furthermore, oil behavior observation using in-cylinder visualization engine, and oil film thickness measurement using optical fiber were conducted for experimental verification of the oil behavior model around the 3POCR. As a result, qualitative tendency of calculated results and measured results showed good agreement. Also, comparison in two different OCR specification, the similarly tendency was obtained. Therefore, the effectiveness of the developed prediction model was confirmed.&lt;/div&gt;&lt;/div&gt;

A finite-element-aided ultrasonic method for measuring central oil-film thickness in a roller-raceway tribo-pair

Roller bearings support heavy loads by riding on an ultra-thin oil film (between the roller and raceway), the thickness of which is critical as it reflects the lubrication performance. Ultrasonic interfacial reflection, which facilitates the non-destructive measurement of oil-film thickness, has been widely studied. However, insufficient spatial resolution around the rolling line contact zone remains a barrier despite the use of miniature piezoelectric transducers. In this study, a finite-element-aided method is utilized to simulate wave propagation through a three-layered structure of roller-oil-raceway under elastohydrodynamic lubrication (EHL) with nonlinear characteristics of the i) deformed curvature of the cylindrical roller and ii) nonuniform distribution of the fluid bulk modulus along the circumference of the oil layer being considered. A load and speed-dependent look-up table is then developed to establish an accurate relationship between the overall reflection coefficient (directly measured by an embedded ultrasonic transducer) and objective variable of the central oil-film thickness. The proposed finite-element-aided method is verified experimentally in a roller-raceway test rig with the ultrasonically measured oil-film thickness corresponding to the values calculated using the EHL theory.

Ultrasonic technique for measurement of oil-film thickness in metal cold rolling

ABSTRACT Lubrication is essential in metal cold rolling operation to regulate friction at the metal–roll interface, reduce energy loss and improve the product surface finish. A novel non-intrusive pitch-catch technique, based on the reflection of ultrasound, was employed on a pilot mill to evaluate oil-film thickness at the metal–roll interface during the metal cold rolling operation. During the metal rolling process, oil-film thickness was measured under varying rolling load and rolling speed. The oil-film thickness increases as the roll speed increases and reduces as the rolling load increases. The values of oil-film thickness obtained from this non-intrusive ultrasonic technique agree with theoretical values. This study is a proof of concept and has shown promising results. If further developed, the technique could be employed for in situ monitoring of lubricant during rolling operation in metal rolling industries.

High-accuracy incident signal reconstruction for in-situ ultrasonic measurement of oil film thickness

The oil film thickness in an oil-lubricated tribo-pair can be measured using reflected ultrasonic waves and various transformation models. Conventionally, this approach requires the incident signal to be calibrated using off-line methods prior to testing, and this limits the on-line measurement of oil film thickness in sliding components such as journal bearings. To enable on-line calibration, we propose a method of reconstructing the incident signal from the easily obtained reflected signal. This involves analyzing the amplitude and phase spectrum of the reflection coefficient to reconstruct the incident signal. More specifically, the following main findings of the amplitude and phase of reflection coefficient at the resonance frequency are reported. 1) There is a zero-crossing at the resonance frequency, and therefore the phases of the incident and reflected signal are the same. 2) If part of the reflected signal is included for calculation, the frequency of the extreme point in the amplitude spectrum of the reflected signal is equal to the resonance frequency only when the extreme point phenomenon occurs at the center frequency of the transducer. At other positions, the frequency of the minimum amplitude in the amplitude spectrum of the reflected signal is not equal to the resonance frequency. Utilizing these relationships, the phase and amplitude of the incident signal can be accurately reconstructed by following the proposed method, provided the thickness of the oil film between the tribo-pairs can be widely ranged to cover both the blind and the resonance zones. Correspondingly, a practical schedule for the on-line reconstruction of the incident signal is proposed, which includes an operation to adjust the oil film thickness within the blind and the resonance zone. This method is validated on a test rig by comparing it with the traditional off-line methods.

Temperature compensation strategy for ultrasonic-based measurement of oil film thickness

Due to non-destructive testing characteristics, ultrasonic-based measurements are regarded as potential strategies in real-time monitoring of varied lubricant film thickness for tribological systems. Different theoretical models have been recently developed to calculate the film thickness from ultrasonic echo waves. However, the temperature influence on ultrasonic systems (for example, the acoustic parameters of materials and piezoelectric elements), which is non-negligible in the continuously running equipment, especially for heavy-loaded lubricated systems, has scarcely been considered. In this paper, the sensitivity of different parameters to the temperature variation is investigated in classical ultrasonic models. With the theoretical error analysis, a comprehensive temperature compensation strategy that considering the acoustic speed, material density, and reference signal, is proposed and integrated into the ultrasonic measurement algorithms. It is worth noting that the amplitude attenuation, waveform expansion, and signal time shift are considered in the compensation of the reference signal. Experimental verification is finally carried out in a calibrated rig with swept lubricant film thickness and different ambient temperatures. Test results suggest that the ultrasonic measurements with the proposed strategy effectively compensates the temperature influence and enables accurate calculations of lubricant film thickness under varying temperatures.

Exact analytical solution to ultrasonic interfacial reflection enabling optimal oil film thickness measurement

The ultrasonic reflection from a lubricated interface has been widely analyzed to measure fluid film thickness, with different algorithms being applied to overcome measurement accuracy and resolution issues. Existing algorithms use either the amplitude or the phase angle of the ultrasonic interfacial reflection. In this paper, a new algorithm (named the “exact model – complex”) that simultaneously utilizes both the amplitude and the phase of the complex ultrasonic reflection coefficient is proposed and mathematically derived. General procedures for theoretical analysis in terms of measurement accuracy and uncertainty are proposed and applied to the new algorithm, the beneficial features of which (as compared to other existing algorithms) can be summarized as: 1) a direct calculation, instead of an iterative approximation, 2) guaranteed maximum measurement accuracy, and 3) acceptable measurement uncertainty. None of the existing methods have showed this combination of benefits. Moreover, two groups of raw data from previous experimental studies are utilized to further validate the practical feasibility of the new algorithm. Overall, the proposed “exact model – complex” algorithm fully exploits the potential of ultrasonic reflection for oil film thickness measurement, with an accurate and a convenient calculation suited to practical implementation.

A time-domain ultrasonic approach for oil film thickness measurement with improved resolution and range

The ultrasonic-based method has been proved to be a practical technique for measuring oil film thickness in the enclosed tribo-pair of a supporting bearing and under dynamic conditions. To cope with the large-scale variations of oil film thickness in engineering applications, frequency-domain based models, being adaptive for different measurement ranges, are widely used. As an improvement, the time-domain approach can further expand the effective range, but suffers from decreased resolution in oil thickness measurement. To address these issues, this paper proposes a unified time-domain model for full-range measurement. First, a cluster of standard echoes with definite film thicknesses in a wide range are pre-constructed, and they are matched with measured echoes to find the most suitable oil film thickness. Further, an optimized interpolation is applied to both the constructed and the measured echoes for better resolution. Aiming for the lowest interpolation error, the windowed sinc function was employed optimally. Using a precision calibration rig, the proposed model was compared to the traditional frequency-domain and the time-domain models. The comparison demonstrates that the proposed model has a larger effective measurement range, covering those of all traditional frequency-domain models and with equal accuracies. In addition, the proposed model shows both a wider effective range and a higher resolution than that of the reference time-domain model. This work contributes to the development of on-line continuous measurement of oil film thickness variation at a large scale.

Measurement of Oil Film Thickness at Contact Point under EHL Condition Utilizing Photochromism in Traction Drives

Measurement of Oil Film Thickness at Contact Point under EHL Condition Utilizing Photochromism in Traction Drives

Simultaneous Measurement of Oil Film Thickness and Breakdown Ratio in EHD Contacts

Simultaneous Measurement of Oil Film Thickness and Breakdown Ratio in EHD Contacts

Oil Film Thickness Measurements Combined with High Temperature Friction Investigations in a Simplified Piston-Ring Lubrication Test Rig

Oil Film Thickness Measurements Combined with High Temperature Friction Investigations in a Simplified Piston-Ring Lubrication Test Rig