Oil Film Thickness Research Articles

An in-situ measurement approach for the oil film characteristics of the spherical valve plate pair in axial piston pumps

The three main ultra-thin oil films at the friction interface of piston pumps operate in a harsh environment of high pressure and speed, which is prone to carrying failure or leakage increase. Real-time monitoring of oil film performance is an ideal way to evaluate the structural design and conduct health management for pumps. However, the measurement scheme to simultaneously capture the oil film thickness, pressure, and temperature is absent. This paper presents a multi-parameter in-situ measurement approach for oil film characteristics, with application to spherical valve plate pairs. The added transition structure between the valve plate and the backend cover achieves both in-situ measurement and maximum protection of the pump's original parts and functions. A sophisticated test rig has been built to capture the oil film's performance at different pressures and speeds. The experimental results show that the approach can effectively assess the friction state of the valve plate pair.

Hybrid lubrication model study of slip ring combination seal under the influence of frictional heat

This paper presents an experimental and theoretical investigation into the factors influencing the sealing performance of combined slip rings. Factoring in the frictional heat from micro convex bodies and convective heat exchange between the slip ring, oil film, and air, we formulate a thermoelastic flow hybrid lubrication model for the combined slip ring seal. This model calculates the distribution of oil film thickness, pressure, temperature, velocity, and viscosity in the sealing zone, drawing on the generalized average Reynolds equation and the transmembrane average energy equation, in conjunction with the heat conduction equation of the slip ring. Utilizing the Archard wear model, we also examine the wear characteristics of the combined slip ring seal, providing insights into seal wear under these conditions. The model enables an analysis of the interplay between parameters and their impact on seal performance. The method proposed accurately predicts friction and leakage in line with experimental data, thereby providing a theoretical foundation for further numerical investigation of seal characteristics.

Dynamic analysis of magnetorheological damper incorporating elastic ring in coupled multi-physical fields

The elastic ring assumes a multifunctional role, crucially providing support and reshaping oil-film thickness distribution in applications such as squeeze film dampers, demonstrating its practical efficacy. In this work, a magnetorheological damper (MRD) incorporating an elastic ring is proposed for the first time to improve the performance of damper. The innovative configuration of the elastic ring magnetorheological damper (ERMRD) is fabricated and integrated into a test platform of rotor system. The multi-filed coupling dynamic model of ERMRD is developed involving magnetic field interactions governed by Kirchhoff law, magnetorheological fluid flow dynamics derived from lubrication theory, and the elastic ring deformation based on thin plate theory. The intricate influence mechanisms of elastic ring and excitation current on oil-film characteristic of ERMRD, encompassing oil-film pressure, oil-film force, oil-film stiffness and damping, are investigated in detail. To substantiate the capabilities of ERMRD, it is implemented within the rotor system and a coupled dynamic model is established using Lagrange equation. This is followed by an in-depth analysis of the dynamic response using the Newmark-β method, including a comparative assessment with the conventional MRD. The results reveal that the elastic ring and excitation current influence oil-film pressure distribution in ERMRD from different perspectives, leading the oil-film force to present diverse variation characteristics. Compared to MRD, ERMRD exhibits weaker nonlinearity and superior damping performance.

Wear analysis of rolling bearing contact surfaces based on finite element method

Wear leads to the roughening of bearing surfaces, increased internal clearances, decreased rotational precision, and amplified vibration and noise, ultimately causing the bearing to fail to meet specified performance criteria. This study employs the quasi-static analysis method to examine bearing sliding behavior. Based on the Archard wear model and Hertz contact theory, a computational model for wear depth in lubricated conditions is established for rolling ball bearings, accounting for both the rolling and sliding of the rolling elements. The distribution law of load and wear coefficient along the raceway circumference are analyzed, along with the characteristics of stress and sliding velocity in the contact region. The study investigates the impact of rotational speed, load, surface roughness, and raceway curvature coefficient on the wear coefficient, wear depth, and minimum oil film thickness. Furthermore, sensitivity analysis is conducted on the parameters of the wear depth model. Finite element analysis, utilizing ANSYS Workbench, is employed to study the evolution of surface wear on the raceway of deep groove ball bearings and explore the dynamic relationship between contact stress and wear depth. These findings offer important theoretical guidance for the design, selection, and maintenance of rolling bearings.

Study on the Lubricating Characteristics of the Oil Film of the Slipper Pair in a Large Displacement Piston Pump

Due to the large size of the bottom surface, the slipper pair of the large displacement piston pump (LDPP) will form a larger linear speed difference in the inner and outer positions of the slipper relative to the center of the swash plate during high-speed rotation. It is more likely to lead to the slipper overturning, which makes the slipper partially worn. To make improvements, the comprehensive performance of the slipper pair of the LDPP, the motion law of the slipper pair of the LDPP was explored. Firstly, a mathematical model of the oil film thickness of the slipper pair of the LDPP under the state of residual compression force is established, based on the consideration of the linear velocity difference formed by the high-speed rotation of the large bottom surface slipper and the theory of dynamics and thermodynamics. Secondly, the impact of rotational speed, piston chamber pressure and oil temperature on the oil film thickness of the slipper pair was simulated and analyzed. Finally, to measure the oil film thickness of the slipper pair, oil film thickness measuring equipment was created, and the accuracy of the mathematical model was verified. The study revealed the changing rules of the oil film thickness and tilt angle of the bottom surface of the slipper pair under various working conditions. The consistency of the simulation and test findings demonstrates that the mathematical model can accurately describe influencing elements and changing rules of the LDPP slipper pair’s oil film lubrication characteristics.

Investigation of oil emission mechanisms in a marine medium-speed dual-fuel engine

Pilot-ignition Otto marine engines are known for greatly reduced emissions of air pollutants (sulphur oxides, nitrogen oxide, particulates) compared to marine diesel engines. However, lubricating oil emissions still are about one order of magnitude higher than in land-based systems. To identify reduction potentials, a better understanding of oil emission mechanisms has to be gained. For this purpose, mass spectrometric oil emission measurements and fluorescence lubricating film thickness measurements were performed on a medium-speed marine engine. With the fluorescence measuring system, the varying lubricating oil film on the cylinder wall can be visualised and analysed in sub-crank-angle resolution. By applying the developed calibration method to the measurement data, the oil film thickness can be determined in µm. It is shown that the oil film left by the piston rings on the liner as it moves down is almost halved after ignition compared to during intake stroke. The authors have further been able to detect and time operating point dependent ring rotation and investigations show a connection between ring rotation and cylinder liner temperature distribution. Aligning ring gaps allow blow-by to happen. This and other high intensity events such as engine knock, load shedding or the transition from diesel-mode to gas-mode, heavily disturb the oil layer and cause peaking oil emissions.

Thermohydrodynamic Lubrication Characteristics of Piston Rings in Diesel Engine Considering Transient Heat Transfer under the Parameterized Surface Texture of Cylinder Liners

The cylinder liner and piston ring form the most crucial friction pair in the diesel engine, contributing 35–40% of its overall friction losses. Recent research indicates that transient heat transfer significantly affects piston ring lubrication. However, the impact of such a transfer on varying surface textures and lubrication traits remains unclear. This paper takes the piston ring–cylinder liner of a certain diesel engine as the research object, which is based on a two-dimensional averaged Reynolds function and Greenwood–Tripp micro convex body contact model; establishes a numerical calculation model of the transient heat fluid lubrication characteristics of a vertical piston ring–cylinder liner assembly by combining the oil film thickness equation, energy equation, lubricating oil viscosity–temperature, and viscosity pressure characteristics; avoids large errors associated with assuming different temperature values for lubricants; and also uses the cylinder liner surface texturing technique to examine the effects of surface texturing on lubrication properties in the presence of transient thermal fluids. The findings indicate that employing transient thermal fluid for determining the mean value of the oil film temperature in isothermal lubrication calculations yields comparable values for minimum oil film thickness and frictional power consumption, while the friction power consumption calculated by the transient thermal fluid is slightly lower. The depth of the recesses on the surface of the cylinder liner should be minimized, while the radius of the texture should be maximized, taking into consideration the current circumstances. Compared with a cylindrical texture, a spherical texture achieves lower friction with good lubrication indexes.

Friction power loss of continuous sine tooth profile planetary reducer

In this paper, a sine tooth planetary reducer with one tooth difference is proposed. For the proposed reducer, the equations of the oil film thickness, the meshing sliding and rolling friction power loss, and the friction power loss of the bearings for the reducer are proposed. Using these equations, the oil film thickness distribution, the meshing sliding and rolling friction power loss of the sine gear reducer plus the friction power loss of the bearings on eccentric shaft section are analyzed. The power loss of the reducer is measured and compared to the calculated values. Results show that the measured ratio of the friction power loss to input power is 27.90 %, and the calculated one is 26.53 %. The difference between them is 1.65 %. This illustrates analysis about lubrication and friction power loss of the reducer.

Thermoelastoplastic hydrodynamic lubrication contact analysis of three dimensional rough tooth surface considering micro-scale effect and thermal effect

The contact properties of gear rough surfaces during meshing are influenced by various factors. The analysis of rough surface thermoelastoplastic hydrodynamic lubrication (TPEHL) considering micro-scale effect and thermal effect has not been addressed in the literature. This study establishes a new TEPHL model with multi-factor coupling of thermal field, fluid lubrication, stress-strain, and geometric profile. Based on strain gradient theory (SG), a new thermoelastoplastic material constitutive considering micro-scale effect is developed. Subsequently, the three-dimensional rough surface TPEHL-SG analysis of gear is conducted. The paper investigates the impact of thermal and micro-scale effects on various parameters during the meshing of gear in the full oil film lubrication condition, including surface pressure, oil film thickness, surface temperature, surface deformation, and friction coefficient.

Combined Retrieval of Oil Film Thickness Using Hyperspectral and Thermal Infrared Remote Sensing

An outdoor experiment was conducted to measure the thickness of oil films (0~3000 μm) using an airborne hyperspectral imager and thermal infrared imager, and the spectral response and thermal response of oil films of different thicknesses were analyzed. The classic support vector regression (SVR) model was used to retrieve the oil film thickness. On this basis, the suitable range for retrieving oil film thickness using hyperspectral and thermal infrared remote sensing was explored, and the decision-level fusion algorithm was developed to fuse the retrieval capabilities of hyperspectral and thermal infrared remote sensing for oil film thickness. The following conclusions can be drawn: (1) Based on airborne hyperspectral data and thermal infrared data, the retrieval accuracy of oil films of different thicknesses reached 154.31 μm and 116.59 μm, respectively. (2) The S185 hyperspectral data were beneficial for retrieving thicknesses greater than or equal to 400 μm, and the H20T thermal infrared data were beneficial for retrieving thicknesses greater than 500 μm. (3) The result of the decision-level fusion model based on a fuzzy membership degree was superior to those obtained using a single sensor (hyperspectral or thermal infrared), indicating that it can better integrate the retrieval results of hyperspectral and thermal infrared remote sensing for oil film thickness. Furthermore, the feasibility of using hyperspectral and thermal infrared remote sensing to detect water-in-oil emulsions of different thicknesses was investigated through spectral response and thermal response analysis.

A Multi-Parameter-Coupled Mixed Lubrication Model for Rolling Interface Analysis: An Investigation on Interfacial Oil Pressure and Oil Film Thickness

Utilizing the average Reynolds equation, lubrication friction theory, metal rolling deformation theory, and temperature energy theory, a multi-parameter-coupling mixed lubrication model considering the influence of surface roughness with Gaussian distribution characteristics under rolling conditions was established. The results show that the stress distribution of the lubricating oil at the rolling interface conforms to the typical characteristics of line contact stress distribution. The oil film pressure does not increase significantly with the increase in the reduction ratio. A second peak pressure appears before the outlet. The second peak pressure reaches its maximum when ε = 0.2. The rolling speed has little effect on oil film pressure, but greatly affects oil film thickness. The influence of rolling speed mainly occurs in the outlet zone and at the second peak pressure location. The oil film thickness increases with rolling speed. During rolling, the temperature rise in the rolls exhibits two peak values. The first peak appears near the neutral point, and the second peak appears near the outlet, which is also where the second peak pressure is located. The influence of temperature will reduce the peak stress on the rolls. The overall stress on the rolls will also decrease.

Numerical Studies On the Oil Film Thickness in the Case of Stratified Flow with Different Oil-Water Flow Combinations Through Sudden Contraction Tube

Abstract Most of the oil transportation industries deal with liquid-liquid flow considering the adiabatic situation. In such applications, film thickness measurement plays a very significant role in understanding the flow characteristics. The distribution of phases for efficient wall treatment and to understand the phase distribution, measurement of film thickness is very important. Among different flow patterns, stratified flow is most common for low and medium viscous oil-water flow. At lower oil velocities, stratified flow is observed downstream of singularity whereas in the upstream section, stratified flow is observed for low to medium oil velocities and high-water superficial velocity. Variation of oil film thickness for stratified flow has been analyzed in the present study. Results show that oil film thickness decreases with the increase in the superficial velocity of water (Us-Water) for a constant oil superficial velocity (Us-Oil). With the increase in the volume fraction of one phase, the film thickness of that phase increases. As Us-Oil increases, the film thickness of oil also increases for a constant Us-Water. Oil film thickness is directly proportional to the viscosity of oils. This means, the more the viscosity of the oil, the more will be the oil film thickness.

A design based on centrifugal inertia of rotational oil film for reducing pressure at shaft hole

Shaft seal covers a very wide range of machinery and applications. Lip seals, which are used for sealing shafts against the exit or ingress of liquids, are a type of shaft seal. Reducing the wear of the sealing ring and extending its service life can increase the time interval for machine maintenance and inspection. In this paper, a disk structure for reducing the pressure difference between the inside and outside of the lip seals is proposed. The disk structure forms a layer of rotating oil film on the seal ring, so the oil pressure near the seal ring is less than in a sealing chamber. First, based on the similarity principle and the hypothesis of von Kármán, a theoretical model of the rotating oil film was established, and the dominant influence of inertia of circumferential velocity and viscosity of radial velocity on pressure distribution was expounded. Then, an experimental device that can measure pressure distribution and temperature was constructed, and a pressure distribution measurement experiment was conducted. Based on theoretical models and experiments, it was proved that the rotating disk could generate a pressure drop and the pressure drop was a function of the square of the rotating speed. The influence of temperature and oil film thickness was studied, and it was found that the increase in the temperature and oil film thickness weakened rotational flow inertia and enhanced radial flow viscosity, increasing pressure within the oil film. Additionally, it was observed that the oil in the sealing chamber produced a sunken liquid level due to the stirring of the rotating disk, which would reduce the boundary pressure at the periphery of the oil film and produce a greater pressure drop inside the oil film.

Numerical and experimental investigations on thermoelastic hydrodynamic performance of planetary gear sliding bearings in wind turbine gearboxes

The application of planetary gear sliding bearings (PGSBs) in large wind turbine gearboxes (WTGs) has become an important development trend for high-power wind turbines due to the advantages of improving power density and reducing failure rates. However, the working characteristics of operating at heavy-load conditions and using helical gears to mesh will induce large deformation, axial misalignment, and non-negligible temperature rise in PGSBs. In this paper, a comprehensive analysis model taking into account the influence of axial misalignment, thermal effects, and thermoelastic deformation was presented for the PGSB in WTGs. A full-size test rig for PGSBs was built and simulation experiments were conducted to verify the model. Both the measured oil temperature and film thickness agreed well with the numerical results. The predictions from the model were compared with the results of the isothermal-EHD and rigid-THD models. The comparison results indicated that the pad deformation and temperature rise had obvious effects on the bearing performance and could not be ignored. The effects of bearing clearance and aspect ratios on thermoelastic hydrodynamic performance were analyzed. The numerical results showed that both a lower clearance ratio and a higher aspect ratio could help to reduce the maximum pressure at the bearing edges.

Study on lubrication performance of engine piston skirt with bionic design

As the main friction pair of engine, the friction loss of piston-cylinder liner assembly in the working process has become the main reason of engine friction power consumption. Many species in the biological world have formed non-smooth forms of resistance reduction after thousands of years of survival and evolution. Many people have applied this non-smooth shape of drag reduction on organisms to the surface of friction pairs in construction machinery. Based on LX108 engine, the wear and erosion resistance of Scapharca subcrenata surface is applied to the piston skirt, which is the main friction pair in the engine. Nine test schemes were designed according to orthogonal test. This design selects three factors, namely, groove distribution type, groove depth and width, groove spacing, and each factor includes three levels. The macroscopic fluid lubrication state of the whole piston skirt with bionic shape is studied. Through the change of oil film thickness caused by thermal-mechanical coupling deformation of skirt, combined with the average Reynolds equation, the hydrodynamic pressure of lubricating oil, shear stress, and skirt friction force are obtained to verify the contribution of bionic shape to piston drag reduction, wear reduction, wetting increase, and friction power consumption. The simulation and test results show that the lubrication of all parts of the bionic groove piston skirt is better than that of the standard piston; When the depth and width of groove is 0.8 mm and the spacing is 10°, the thicker the oil film thickness of skirt is; The bionic piston whose oil film bearing area is 74%–87% of the standard piston has the smallest normal pressure and friction; When the upper end of the skirt is arranged with groove shape and the lower end is arranged with narrow groove shape between wide grooves, the lubrication effect is better.

Dynamic Viscosity-Temperature Characteristics and Models of Various Lubricating Oils

Background: The dynamic viscosity - temperature characteristics of lubricants are the main factors used to determine the oil film thickness and carrying capacity. There are few studies on the factors affecting the dynamic viscosity-temperature characteristics of lubricating oils and the dynamic viscosity-temperature model. Objective: This research aims to analyse the influences of lubricating oil type and initial kinematic viscosity on dynamic viscosity - temperature characteristics and present a new dynamic viscosity - temperature model. Methods: The characteristic curves of dynamic viscosity versus temperature of polyol ester oil, paraffinic mineral oil, and five types of PAO (poly a-olefin) oils with different initial viscosities were obtained by using a kinematic viscosity test device and a density test device. The influences of lubricating oil type and lubricating oil viscosity on dynamic viscosity - temperature characteristics were analysed. Based on our patent technology and repeated verification, a new dynamic viscosity - temperature model was presented. Results: Viscosity - temperature curves of three different types of lubricating oils and viscosity - temperature curves of PAO oils with different initial kinematic viscosities were obtained. A new dynamic viscosity - temperature model η=A×e^(((-T)/n) )⁡+ η_0 was proposed. Conclusion: The dynamic viscosity - temperature characteristics of lubricating oils are not only determined by the type of oils but also determined by the initial kinematic viscosity.The variation of dynamic viscosity of lubricating oils with temperature in the scope of -40~110℃ can be described by the following viscosity temperature model : , which can be used in wider temperature range than the existing models.

Application of the Kriging model combined with the whale algorithm in the optimization analysis of the micro-texture effect on the performance of the engine piston ring/cylinder friction pair

In order to study the influence of microstructure and improve the efficiency of the engine friction pair, the engine piston ring/cylinder liner friction pair is selected as the research object. This paper analyzes and evaluates the influence of microstructural geometric parameters on the performance of friction pair. The Kriging model is used as a parametric model to simulate the microstructural parameters and combined with the whale optimization algorithm to optimize the microstructural parameters. The optimal microstructural parameters of the piston ring/cylinder liner friction pair are obtained as follows: ellipse long half:15.3 μm, short half axis: 14.9 μm, offset: 6.5 μm, depth: 7.7 μm; axial spacing: 45.5 μm, and circumferential spacing: 261.2 μm. Compared with the prototype piston ring/liner friction pair, the average friction coefficients of piston ring/cylinder liner friction pair with unoptimized microstructure and optimized microstructure were, respectively, reduced by 10.88% and 13.99%, the average bearing pressure was increased by 23.75% and 24.12%, the average friction power decreased by 9.24% and 12.89%, the average oil film thickness increased by 0.56% and 7.49%, and the minimum oil film thickness increased by 29.80% and 34.51%.

Investigation of Lubricant Oil Film Thickness on Workpiece under Minimum Quantity Lubrication Milling Process

Investigation of Lubricant Oil Film Thickness on Workpiece under Minimum Quantity Lubrication Milling Process

Experimental Study on the Influence of Stearic Acid Additive on the Elastohydrodynamic Lubrication of Mineral Oil 2137

Using an optical elastohydrodynamic lubrication (EHL) test rig, oil film thickness and the coefficient of friction (COF) were measured, and the influence of stearic acid additive on the EHL performance of mineral oil 2137 was investigated. The results showed that 2137 with 0.3 wt% stearic acid (denoted to as 2137s) achieved the same film thickness as 2137, while the COF of 2137s was significantly lower than that of 2137 when the contact was under conditions of a fully lubricant supply. Under conditions of limited lubricant supply, 2137 base oil was prone to oil starvation with the increase of entrainment velocity. On the other hand, 2137s significantly mitigated the oil starvation. This was attributed to the fact that lower surface energy by the adsorption of stearic acid results in discontinuous oil-droplet distribution on the lubrication track and, therefore, early pressure generation. Moreover, it is interesting to find that less 2137s supply quantity can produce higher film thickness when the contact is at high speeds, which is attributed to the fact that a smaller quantity of 2137s gives smaller droplets on the lubrication track, and the resultant small surface area–volume ratio presents oil more resistance to the centrifugal force and results in less oil escaping from the lubrication track. The addition of stearic acid reduced the average COF of 2137 mineral oil by about 13.3%

A Comparison of Hydrogen and Gasoline Piston Ring Simulations

This paper presents a transient mixed-lubrication hydrodynamic and gas flow simulation model for a piston ring pack for a four-stroke internal combustion engine. The analyses carried out compare two fuel types, hydrogen and gasoline, at a 2000 rpm low engine load (20%), as well as 3000 rpm low (20%) and high (100%) engine loads, to investigate the effects of the different fuels and loading conditions on the ring pack. In particular, the minimum oil film thickness at the top compression ring, the total ring friction of the ring pack, the friction power loss and the blow-by are studied. The simulation shows that, under the high load conditions at 3000 rpm, the hydrogen variant exhibits larger friction power losses, around a 200 W peak difference and larger blow-by throughout the expansion stroke of the engine cycle. A similar trend can be observed for the low loads, where larger friction power losses with peak differences of 30 W and 40 W for 2000 rpm and 3000 rpm, respectively, are observed. The blow-by results for the low load at 2000 rpm show a slight increase of approximately 22% more gas flow into the crankcase, while the 3000 rpm simulation shows a 50% increase in blow-by for the hydrogen variant at low load and a 40% increase at high load. The findings that are presented indicate that, although alternative fuel sources such as hydrogen are very attractive alternatives to fossil fuels such as gasoline, there can be unwanted side effects that could lead to the permanent damage of components through quicker wear or hydrogen embrittlement from the blow-by gas.