Oil Film Pressure Research Articles

Thermal–Elastohydrodynamic Lubrication Characteristics of the Flow Distribution Pair of Balanced Double-Row Axial Piston Pumps

A theoretical model for the calculation of thermal elastohydrodynamic lubrication performance of the flow distribution pair of piston pumps is established, which is composed of the oil film pressure governing equation and energy equation, and solved by means of numerical solution and simulation. We carry out quantitative analysis of the influence of various parameters on the thermal elastohydrodynamic lubrication characteristics of the flow distribution pair. The results indicate that both the oil film thickness and the cylinder tilt angle of the flow distribution pair vary in a periodic manner. The increase in the rotational speed of the cylinder block will increase the film thickness of the oil film and reduce the fluctuation, and the inclination angle of the cylinder block and its fluctuation amplitude will decrease. An increase in working pressure will lead to a decrease in the average oil film thickness, an increase in fluctuations, and an elevation in both the tilt angle of the cylinder block and its fluctuation amplitude. The increase in the rotational speed of the cylinder block and the increase in the working pressure will lead to the increase in the viscous friction dissipation of the flow distribution pair, the increase in the oil film temperature and the increase in the leakage. The reduction in the sealing belt will lead to the reduction in oil film friction torque and leakage.

A novel design of journal bearings for stability under shock loads

Mechanical systems are expected to operate under various load conditions, and it is necessary to use a lubrication system to achieve reliability and stable performance. Journal bearings, which are used to achieve such stable lubrication, are representative of hydrodynamic lubrication bearings. In this study, groove-shaped structures and rubber were applied to the ends of the bearings to ensure stable lubrication performance under conditions where, for various reasons, shock loads are applied in addition to static loads under misaligned conditions. The groove structure and rubber contribute to stable lubrication performance by preventing contact between the shaft and bearing as well as absorbing shock loads through elastic deformation of the groove’s end due to oil film pressure. This novel design, which utilizes groove-type flexible structures and rubber, led to journal bearings that exhibited improved lubrication performance under various shock load conditions. When a shock load is applied to a mechanical system, the design proposed in this study contributes to improving the reliability of the mechanical system by enhancing its lubrication performance.

Full-size experimental investigations on planetary gear journal bearings in high-power wind turbines

Abstract To satisfy the large-scale and high-power demands of wind turbines, planetary gear journal bearings (PGJBs) have been applied in large wind turbine gearboxes (WTGs), as an alternative to traditional rolling bearings, due to their higher reliability and smaller size. To simulate the actual lubrication behaviors of PGJBs and investigate their hydrodynamic performance, a full-size test rig for PGJBs was built in this paper. A multi-parameter detection system coupled with the ultrasonic testing method was developed. Four ultrasonic piezoelectric elements, eight thermistors, two pressure transducers, and one torque sensor were used to obtain the film thickness, oil temperature, oil pressure, and friction torque data of the test PGJB. The rated condition experiment was conducted to investigate the variation of measured lubrication performance with the operating time. Three-dimensional predictions of oil film pressure, temperature, and thickness were presented to analyze the steady-state lubrication characteristic at the rated condition. Moreover, a series of steady-state experiments were also carried out to simulate the normal operations of the test PGJB at different conditions. And the measured results were verified by the numerical predictions. The influence of rotational speed, input load, oil supply temperature, and oil supply flow on the hydrodynamic performance of the test PGJB were explored.

Study on the wear characteristics of cylindrical needle bearings on the crankshaft of RV decelerator

PurposeThe purpose of this study is to systematically analyze the wear of cylindrical needle bearings in rotary vector reducers under temperature rise and identify the influencing factors.Design/methodology/approachBased on the dynamic characteristics of the RV-20E reducer, the time-varying contact force of the cylindrical needle bearing and the entrainment speed of the inner and outer raceways were calculated. A mixed elastohydrodynamic lubrication model of the needle bearing, considering friction and temperature rise, was established using a dynamic rough tooth surface model. The model solved for the oil film thickness, contact stress and wear conditions of the bearing raceway contact area. The effects of the number of rolling needles, the diameter of rolling needles and surface strength on the wear characteristics were analyzed.FindingsThe results of this study show that the oil film thickness, oil film pressure and surface scratches of cylindrical needle bearings exhibit an uneven, patchy distribution under the combined effects of friction and temperature rise. When the radius of the rolling needle is less than 1.44 mm, inner ring wear is less than outer ring wear. Conversely, when the radius exceeds 1.44 mm, inner ring wear is greater. The optimal rolling needle radius is 1.6 mm. Increasing the number of rolling needles and enhancing the yield strength of the contact surface significantly extend bearing life.Originality/valueThis study provides valuable recommendations for optimizing bearing structural parameters and material characteristics in the design of rotary vector reducers.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2024-0242/

Research on lubrication mechanism of plunger pair considering viscosity temperature and pressure effect

Aiming at the key problems such as serious friction and wear and large leakage of aviation piston pumps operating under high-speed and high-pressure harsh conditions, the lubrication characteristics of aviation plunger pumps are studied in this paper. In order to improve the lubrication performance of the plunger pump, as well as its working efficiency and service life, the equations of pressure, the thickness, and the leakage of the plunger pair oil film under the combined actions of viscosity temperature and pressure under pressure flow, shear flow, and cylinder elastic deformation are established. The finite difference method is used to analyze the lubrication characteristics and the leakage of the plunger pair under these four different conditions: considering, respectively, the effect of viscosity temperature and pressure, only considering the effect of viscosity temperature or viscosity pressure, without considering the effect of viscosity temperature and viscosity pressure. As a result, coupled by the effects of viscosity temperature and viscosity pressure, when the temperature increases from 20 to 60 °C, the oil film pressure increases, and the thickness decreases faster. When the temperature increases from 60 to 120 °C, the oil film pressure increases and the thickness decreases slower When the contact length of the plunger pair increases from 17 to 37 mm, the leakage ratio decreases more rapidly, and when it is greater than 37 mm, it decreases more slowly. The following conclusions were obtained: the viscosity of lubricating fluid is greatly affected by temperature and pressure. The viscosity decreases and increases hyperbolically with the increase in temperature and pressure, the maximum oil film pressure when considering the effect of viscosity temperature and pressure was significantly greater than that without considering the viscosity temperature and pressure, and the minimum oil film thickness was much smaller than that without considering the viscosity temperature and pressure. The leakage curve when considering the viscosity temperature and pressure effect was obviously different from when only considering a single factor or not considering the viscosity temperature and pressure effect. The magnitude of leakage in the four cases is: considering the viscosity temperature effect, considering the viscosity temperature and pressure effect, not considering the viscosity temperature and pressure effect, and considering the viscosity pressure effect. This study can provide a reference for the accurate theoretical design and safe and stable operation of the plunger pair in the plunger pump.

Research on the Lubrication Performance of Hydrostatic Thrust Bearings Considering Dynamic Pressure Effect and Oil Film Pressure Loss

A lubrication performance mathematical model considering the dynamic pressure effect and pressure loss is proposed for stepped hydrostatic thrust bearings. The influence mechanism of rotational speed and load on the static pressure, dynamic pressure, pressure loss, total pressure, and total temperature of the clearance oil film is systematically discussed through a combination of theory, simulation, and experiment. The investigation found that the total temperature of the oil film decreases with increasing load and increases with increasing rotational speed. The pressure loss also becomes increasingly significant with higher rotational speeds. The dynamic pressure is not limited by the load but increases with the increase in rotation speed. The oil film pressure loss is jointly borne by static pressure and dynamic pressure within the range of 0 to 160 rpm and mainly borne by static pressure within the range of 160 to 200 rpm. Additionally, the trends of static pressure, dynamic pressure, total pressure, and temperature in the experiment are nearly consistent with those predicted by numerical simulations, thereby validating the effectiveness of the research methodology employed in this article.

Influence of Lubrication Cycle Parameters on Hydrodynamic Linear Guides through Simultaneous Monitoring of Oil Film Pressure and Floating Heights

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity.

Multi-physics field coupling interface lubrication contact analysis for gear transmission under various finishing processes

Surface integrity is crucial for the load-bearing capacity, transmission performance, and service life of gears. Finishing processes can effectively improve surface quality and are widely used in gear manufacturing processes to enhance surface integrity and improve the service performance of gears. Five precision machining tests of form grinding, vibratory finishing, barrel finishing, honing, and abrasive flow machining were conducted on spur gears. High-precision surface integrity characterization methods were used to analyze the surface integrity parameters of the finished gear surfaces, including surface roughness, surface microtopography, residual stress, texture aspect ratio, roughness peak curvature radius. The finishing processes uniformity and effectiveness of the tooth profile surface were also evaluated. By using the finished rough surfaces as inputs and considering the impact of thermal elasto hydrodynamic lubrication on the gear surface, a multi-field coupling contact analysis model encompassing solid, liquid, and thermal fields at the gear meshing interface was established. Lubrication performance parameters such as oil film pressure, oil film thickness, oil film temperature rise, and friction coefficient under various finishing surfaces were compared and analyzed. Experimental results indicate that barrel finishing can simultaneously improve various parameters, such as surface roughness, texture aspect ratio, and compressive residual stress. Finishing processes can effectively reduce surface roughness, improve lubrication performance and reduce the risk of scuffing failure. This approach provided an effective method for the comprehensive evaluation of the effects of various finishing processes. The developed program offers theoretical guidance and data support for the selection and optimization design of gear surface finishing processes.

Study on the mixed lubrication of rough planar extrusion considering surface texture

Surface texture plays a crucial role in fluid dynamic lubrication. The non-Newtonian thermal elastohydrodynamic lubrication problem involving rough surfaces with texture has not been investigated to date. In this paper, a model for non-Newtonian thermal elastohydrodynamic lubrication incorporating rough surfaces and texture morphology is developed, focusing on the problem of mixed lubrication in planar extrusion with texture. The model builds upon the Reynolds equation with flow factor introduced. It considers the effects of rough surface texture, thermal effects, and non-Newtonian effects. The Reynolds equation is numerically solved using the Semi-System method to calculate the oil film pressure in full film region and contact pressure in dry contact area. The DC-FFT algorithm is employed to calculate surface elastic deformation. Comparing the calculated friction coefficient of the present model with the measured values in literature experiments, the average error is only 6.94%. Furthermore, the study investigates the effects of texture, temperature, and non-Newtonian on interfacial lubrication performance under mixed lubrication conditions. It’s found that compared to untextured surface, the average film thickness of textured surface increased by a maximum of 10.8%, and the friction coefficient decreased by a maximum of 67.4%; Compared to Newtonian fluids, shear thinning fluids reduce temperature by 0.18%, and shear thickening fluids are more conducive to improving mixed lubrication performance. A stepped pit texture is designed based on the dynamic pressure mechanism of the texture, indicating that the circular stepped pit texture has the best load-bearing capacity improvement.

Study on the lubrication performance of the pitcher plant–like textured surface with various parameters

PurposeThis paper aims to enhance lubrication performance of the pitcher plant–like textured surface with various parameters.Design/methodology/approachA pitcher plant–like structure surface is fabricated on the copper alloy, and the lubrication performance of the pitcher plant–like structure with various parameters is evaluated. In addition, the pressure distribution and oil film load capacity of the pitcher plant–like surface are simulated based on Navier–Stokes equations.FindingsWhen the direction of motion aligns with the pitcher plant–like structure, the friction coefficient remains lower than that of the nontextured surface, and it exhibits a decreasing trend with the increasing of the texture width and spacing distance; the lowest friction coefficient (0.04) is achieved with B = 0.3 mm, L = 1.0 mm and θ = 45°, marking a 75% reduction compared to the nontextured surface. Simulation results demonstrate that with the increase in texture width and spacing distance, the oil film load-bearing capacity demonstrates an increasing trend.Originality/valueBionic pitcher plants are prepared on the copper alloy to improve the lubrication performance and wear resistance.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2024-0119/

Numerical analysis of lubrication performance of variable cross-section sealing rings

A variable section seal ring is a special type of sealing element that features a regularly changing sealing boundary. This paper proposes a numerical analysis method for calculating the elastohydrodynamic lubrication performance of the sealing surface of a variable section seal, considering factors such as the surface morphology of the seal lip, the initial compression rate of the seal, and the micro-elastic deformation of the rough surface of the seal lip. The three-dimensional distribution of the oil film thickness was obtained. The results show that the oil film thickness on the sealing lip of the variable section seal changes both circumferentially and axially, being thicker in the middle and thinner at the sides when viewed axially, and thicker at the peaks than at the troughs when viewed circumferentially. Higher compression rates of the seal lead to greater friction during operation; different compression rates significantly affect the distribution of the oil film and the oil film pressure on the variable section seal, which directly impacts the lubrication and sealing effectiveness of the seal. Therefore, choosing an appropriate initial compression rate for the seal is very important.

Effect of crescent-shaped texture based on different depths and orientations on the frictional properties of cam tappets

The cam tappet friction pair is one of the three major friction pairs in an internal combustion engine, and the surface of the tappet undergoes severe wear during operation. To improve the wear resistance of the cam tappet friction pair during operation, in this study, crescent-shaped micro-textures were prepared on the surface of the tappet material of GCr15 steel by laser machining technique, and the effects of the orientation and depth of the texture on the friction properties of GCr15 steel were studied. The processed test samples were tested and characterized by friction and wear tests, scanning electron microscopy (SEM), 3D morphometry, and EDS. The flow field simulation model of micro-texture was established by using Fluent finite element software. The simulation and experimental results show that the crescent-shaped microtexture prepared on the surface of GCr15 steel can play a certain role in reducing friction and wear resistance, meanwhile orientation and depth of the texture affect the friction performance. In the fluid simulation, the positively oriented texture can produce higher oil film pressure than the opposite texture. When the texture depth is 20 μm, it has a better friction and wear reduction effect, and the friction coefficient decreases by 65.81% compared with that of the untextured surface, and the amount of wear decreases by 74.19%. This is mainly due to the existence of texture in the friction process to reduce the contact area and the shallower depth of texture can produce a larger oil film pressure in the oil lubrication state, so it has better tribological performance. The research data provide a certain reference for the design and optimization of the cam tappet friction pair.

Visco-elastohydrodynamic lubrication and wear model amended by deformation velocity

The deformation velocity caused by viscoelasticity is one of the drives of the Lubrication flow field and significantly influences the mixed lubrication and wear characteristics of journal bearings under dynamic loads. However, research considering the deformation velocity has yet to be reported. To address this research gap, we defined three-dimensional (3D) deformation velocities to amend the bearing surface velocity and proposed its calculation method based on the derivative function of the temporal association deformation equation and the finite element method. Therefore, a new mixed visco-elastohydrodynamic lubrication model amended by 3D deformation velocities was built and a nested solution method was proposed in which the sub-iterative process for deformation velocities was embedded into the oil film pressure iterative process. Furthermore, the lubrication model was coupled with the Archard model to predict wear. The viscoelastic parameter of the bearing was experimentally measured, and numerical simulations of lubrication and wear were performed for an ordinary bearing under a simple dynamic load and for the crankshaft main bearing of an internal combustion engine (ICE) under impact. The simulation results indicate that the deformation velocities reduce the extrusion effect and increase the contracting effect in the lubrication flow field. This enables the new model to identify the micro asperity contact, impact, and early wear features of bearings more accurately than the traditional mixed lubrication model. In addition, an increase in the ICE load intensifies the early wear of the bearing.

Effect of pocket orientation on PVP lubricated hybrid conical journal bearing system

In a MHCJB (multi-recessed hybrid conical journal bearings), the orientation of the pockets affects the oil film pressure dispersion in the clearance space of bearing thereby it affects the performance of bearing system. This article aims to analyse the influence of pocket orientation on the characteristics of MHCJB operating with PVP (piezo-viscous-polar) lubricant. To analyse the effect of pocket orientation, the study considers two configurations of MHCJB with different pocket arrangement. The modified form of Reynolds equation governing the flow of PVP lubricant in MHCJB is numerically solved by using Galerkin’s technique. The results have been computed for the value of semi-cone angle (γ =10o), piezo viscous parameter (α¯pv= 0.0, 0.3) and polar parameter (l¯cs= 0.0, 0.2). The results indicate that pocket orientation-II offers maximum enhancement of 11.77 % in stiffness coefficient (S¯xx) and 2.45 % in damping coefficient (C¯zz). Further, PVP lubricant offers substantial improvement in stability threshold speed.

Topological optimization and fatigue life prediction of a single pad externally adjustable fluid film bearing

This work focuses on the prediction and comparison of the fatigue life of topologically optimized pads in an externally adjustable fluid film (EAFF) bearing. It integrates one-way/two-way fluid–structure interaction analysis, topological optimization (TO), and design modifications of the pad of an externally adjustable fluid film bearing. The major goal is to create an optimum pad design that minimizes weight and maintains structural integrity, and then to predict and compare the fatigue life of these alternative designs. The outcomes of the present study are as follows: (i) Two-way FSI results show a decrease of 65.64% in hydrodynamic fluid film pressure when compared to one-way FSI results because they take into account modifications in the fluid region's geometry caused by pad deformation; (ii) even though the maximum pad deformation in optimized pad geometry (Type-4) resulting from oil film pressure is relatively small (0.0036551 mm), the influence of pad deformation on the fluid domain due to hydrodynamic fluid film pressure cannot be understated; and (iii) when comparing the TO technique's results with fatigue life results, four elongated holes in the radial direction (Type-4) are most appropriate.

Analysis of Influence of Different Running Speeds on Lubrication Performance of Plain Bearings

Abstract Given the influence of the running speed of rotating machinery on the lubrication performance of sliding bearings, based on the hydrodynamic lubrication theory, a numerical analysis model of hydrodynamic lubrication of rolling bearings is established and solved by the finite difference method. The lubrication characteristics of rolling bearings, such as oil film pressure, oil film temperature, oil film thickness, and temperature rise at different running speeds (10 r/min, 30 r/min, 120 r/min, 160 r/min), are obtained. The results show that the sliding bearing shows different trends at different rotational speeds, the maximum oil film temperature is 70.49℃, the film thickness ratio corresponding to the minimum oil film thickness is much more than 3, and the maximum oil film pressure and temperature rise meet the allowable requirements.

Multidisciplinary design and optimization of journal bearing for high-power wind turbine speed increaser

With the increasing power of wind turbine generators (WTG), the failure rate of rolling bearings in wind turbines due to insufficient bearing capacity increases with the increase of bearing size. To overcome these challenges, this paper proposes a design optimization method for the rectangular groove elliptical sliding bearing (RGEB) of the WTG output shaft. This method can maximize the radial bearing capacity under the premise of ensuring that the oil film pressure is large, the end leakage and the temperature rise are small. The multidisciplinary design and modeling of RGEB are carried out according to the structure and working conditions of WTG. Based on computational fluid dynamics (CFD), the influence of the number of rectangular dynamic pressure grooves on the bearing performance is analyzed. The kriging model, BP neural network model, and SSA-BP model are constructed for each performance index of RGEB, to establish a high-precision combined surrogate model based on global error criterion. After establishing the optimization equation, the PSO and SQP combined optimization algorithm is used to optimize the optimal structural parameters. The results show that the bearing capacity of the optimized RGEB is 95.9% higher than that of the ordinary elliptical bearing (EB) without increasing the size and quality of the bearing. In addition, the combined surrogate model can effectively replace the expensive finite element model to deal with the WTG sliding-bearing optimization problem.

ANALYSIS OF THE MIXED ELASTOHYDRODYNAMIC LUBRICATION CHARACTERISTICS OF DOUBLE CIRCULAR ARC GEARS CONSIDERING MICRO-MORPHOLOGY

Different machining methods result in diverse morphologies on the surface of gears. Under mixed lubrication, the friction and contact behavior of the real morphology interface becomes more complex. This study aims to analyze the influence of different process tooth surface micro-morphologies on the lubrication performance of the meshing area of double circular arc gears. Focusing on elastohydrodynamic lubrication (EHL) characteristics of the double circular arc gears as the research object, the study involved measuring the three-dimensional morphology of the meshing position of the double circular arc gears. Non-Gaussian simulation technology was then used to characterize the micromorphology of the tooth surface resulting from different processes (i.e. hobbing process and skiving process). The tooth surface suction speed was determined based on the meshing characteristics of double circular arc gears. Based on the theory of point contact EHL, Reynolds equation and film thickness equation considering micromorphology were derived, and numerical solutions were obtained using the multi-grid method. A point contact EHL model for double circular arc gears was established considering the micromorphology of tooth surfaces in different processes. Results show that, the oil film pressure is positively correlated with rotational speed and torque. The oil film thickness is positively correlated with rotational speed, and negatively correlated with input torque. The negative of micro-morphology on the tooth surface on the lubrication performance could lead to an increase in pressure fluctuations and the absence of the second pressure peak. The uneven distribution of oil film and the lager roughness value could result in obvious fluctuations. The lubrication performance of the contact area in the gear hobbing process is superior to that in the gear skiving process. This study lays the foundation for further exploring the coupling characteristics between the double circular arc gear transmission system and elastic fluid dynamic lubrication. Keywords: Double circular arc gears, Point contact, Mixed EHL, Lubrication characteristics, Micro- morphology.

Bio-based lubricant with additives: tribological performances in hydrodynamic journal bearing

PurposeThe purpose of this paper is to investigate the performance of bio-based lubricants (BBL), namely, palm mid-olein (PMO) enriched with an antioxidant agent, tertiary-butylhydroquinone (TBHQ) and a viscosity improver, ethylene-vinyl acetate (EVA), in journal bearing (JB) applications.Design/methodology/approachSamples of the BBL were prepared by blending it with TBHQ and EVA at various blending ratios. The oxidative stability (OS) and viscosity of the BBL samples were examined using differential scanning calorimetry and a viscometer, respectively. Meanwhile, their performance in JB applications was evaluated through the use of a JB test rig with a 0.5 length-to-diameter ratio at various operating conditions.FindingsIt was found that the combination of PMO + TBHQ + EVA demonstrated a superior oil film pressure and load-carrying capacity, resulting in a reduced friction coefficient and a smaller attitude angle compared to the use of only PMO or VG68. However, it was observed that the addition of TBHQ and EVA to the PMO did not have a significant impact on the minimum oil film thickness.Practical implicationsThe results would be quite useful for researchers generally and designers of bearings in particular.Originality/valueThis study used PMO as the base stock, and its compatibility with TBHQ and EVA was investigated in terms of its OS and viscosity. The performance of this treated BBL was evaluated in a hydrodynamic JB.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2023-0363/

Optimization of lubrication characteristics of wind turbine’s transmission system based on Newton Raphson method

To improve the reliability and lifespan of wind turbines, this paper takes the two-stage fixed shaft gearbox experimental platform of wind turbines as the research object. Based on Hertz contact theory, the oil film pressure and thickness in the contact area are solved by combining the equations of elastohydrodynamic lubrication and the Newton Raphson method; And the lubrication characteristics of the transmission system were analyzed to verify the correctness of the method; At the same time, in response to partial load phenomenon caused by system coupling deformation, genetic algorithm was selected to modify the gear teeth. The results show that the max unit load on the tooth face and the maximum stress of tooth root decreased by up to 26.48 % and up to 20.35 % respectively after modification which can improve the uneven distribution of oil film and the lubrication performance of the tooth surface.