Search Results (113)

To enhance the operational stability and service life of tapered roller bearings (TRBs), this study investigates the application of surface texturing technology using laser marking to fabricate micro-dimples with controlled diameters and distributions on the TRB outer ring. An orthogonal experimental design was implemented to systematically evaluate the effects of three key dimple parameters—diameter, depth, and angular distribution—on the tribological performance under starved lubrication. The results demonstrate that the textured surfaces significantly improve friction-reducing performance and wear resistance. Optimal dimple parameters (diameter: 200 μm, depth: 10 μm, angular interval: 0.9°) were identified, achieving a 43.6% reduction in the average coefficient of friction (COF) and a 75.7% decrease in wear loss compared to smooth bearings. These findings would offer a practical approach to enhancing the durability and operational reliability of TRBs in industrial applications. Full article

To address wear failure in screw pump stator and rotor friction pairs, this study constructed a numerical model of a rhombus-like micro-dimple texture on friction pair surfaces based on the scale structure of rhombus rattlesnakes. The model was based on the fluid dynamic pressure lubrication mechanism. The CFD method was used to calculate the bearing capacity, friction coefficient, flow field pressure distribution, and flow trace distribution of an oil film carrying surface. The effects of the area rate, depth, shape, and angle of the rhombus-like dimple texture and the actual well fluid viscosity of shale oil on the surface lubrication performance of screw pump stator and rotor friction pairs were analyzed. The results demonstrated that increasing the texture area rate and the angle of the long sides and decreasing the texture angle resulted in a decrease in the oil film surface friction coefficient and an increase in the average pressure and net bearing capacity as well as the hydrodynamic lubrication performance. The average pressure increased and then decreased as the texture depth increased, while the friction coefficient of the oil film surface initially decreased and then increased. At a texture depth of 20 μm, the friction coefficient reached its lowest value while the average pressure and net bearing capacity of the oil film reached their highest value, which resulted in optimal hydrodynamic lubrication performance. When the texture depth became greater than 20 μm, vortices were gradually formed within the texture, which decreased the hydrodynamic lubrication performance. When the area rate of the rhombus-like dimple texture, depth, angle between long sides, and angle were, respectively, equal to 27%, 20 μm, 74°, and 0°, the net bearing capacity of the oil film was maximized, the friction coefficient was minimized, and the hydrodynamic lubrication performance and anti-wear effect reached their highest values. The increase in the viscosity of the actual well fluid could enhance the dynamic pressure lubrication performance and improve the bearing capacity. Full article

Turbulence and instability problems are unavoidable challenges for fluid film bearings as rotation speed continues to rise. This paper investigates the effect of turbulence on the dynamic characteristics of two non-circular journal bearings, hybrid two-lobe bearing (TLB) and hybrid three-step recess bearing (TSRB), under large Sommerfeld number conditions. The linear perturbation method and nonlinear trajectory method are employed in this work. The bearing stiffness coefficients, damping coefficients, and threshold speed are determined by solving the perturbed Reynolds equation using the finite element method. Additionally, the bearing nonlinear trajectories are obtained by solving the motion equation and the dynamic Reynolds equation simultaneously. The threshold speed and trajectory spectrum are utilized to evaluate the bearing dynamic characteristics, and the results derived from laminar and turbulence models are compared. The research on those two different types of bearings has yielded a consistent conclusion: under large Sommerfeld number conditions, the onset of turbulence significantly enhances both the stiffness and damping coefficients of the bearings, as well as the onset speed for the appearance of half-frequency components in the trajectory. The findings suggest that turbulence lubrication is beneficial for improving the dynamic characteristics of these non-circular bearings. Full article

To investigate the lubrication mechanism of phytic acid (PA) solution, a “copper–PA solution–copper” confined model with varying concentrations was established. Molecular dynamics (MD) simulations were employed to model the behavior of compression and the confined shear process. By examining the variations in key parameters such as dynamic viscosity, compressibility, radial distribution function, relative concentration distribution, and velocity distribution of PA solutions under different normal loads or shear rates, we elucidated the lubrication mechanism of PA solutions at the molecular level. The results demonstrate that under standard loading conditions, higher PA concentrations facilitate the formation of denser hydrated layers with decreased compressibility compared to free water, thereby significantly enhancing the load-bearing capacity. The shear stress at the solution–copper interface exhibits a substantial increase as the shear rate rises. This phenomenon originates from shear-driven migration of PA to the copper interface, disrupting the hydration layers and weakening hydrogen bonds. Consequently, this reduction in PA–water interactions amplifies slip velocity differences, ultimately elevating interfacial shear stress. The load-bearing capacity of the PA solution and the interfacial shear stress between the PA and copper are critical factors that influence the lubrication mechanism at the PA/Cu interface. This study establishes a theoretical foundation for the design and application of PA solution as a water-based lubricant, which holds significant importance for advancing the development of green lubrication technology. Full article

This research addresses the issue of lubricant performance degradation in the main shaft bearings of wind turbines. Through multi-temperature accelerated aging tests, the static thermal degradation patterns were elucidated, and an aging model was developed. Initially, 176 samples were prepared at temperatures of 80 °C, 100 °C, 120 °C, and 140 °C using the static thermal degradation method, with 44 samples at each temperature point. Subsequently, key parameters such as the quality change rate, penetration, oil separation rate, and evaporation amount of the lubricant were systematically measured. Ultimately, the mathematical aging model of the lubricant was derived by fitting the aging kinetics model. The results indicate that as aging time and temperature increase, the degradation characteristics of the lubricant, such as quality change rate, penetration, oil separation rate, and evaporation amount, exhibit discernible patterns. The mathematical aging model was successfully fitted, with the maximum deviation generally within 20% of the error margin, meeting the established criteria. This research provides a theoretical foundation for the establishment of a lubricant condition monitoring system in wind farms. Predicting the performance inflection point of the lubricant can effectively prevent unplanned bearing shutdowns resulting from lubrication failures, thereby offering significant engineering value in enhancing the operational reliability of wind turbine units. Full article

This study presents an experimental analysis of a turbocharger equipped with a semi-floating bearing system, with a particular focus on the bifurcation phenomenon within the subsynchronous vibration spectrum. A predefined design of experiments (DoE) methodology was employed to determine the measurement domains to be analyzed, where the primary input parameters included the lubricant supply temperature and pressure values. The bifurcation phenomenon in relation to the physical parameters of the system is observed via vibration and displacement sensors in two directions, enabling the collection of subsynchronous frequency data for further insights into the influence of lubricant parameters on the rotor system. While the nonlinear effect of oil temperature is well studied in the literature. However, the combined effect of oil supply temperature and pressure was not yet examined, which was the focus of the present study. This paper aims to investigate its coupled effects on the bifurcation phenomenon associated with both lubricant temperature and pressure. The occurrence of the introduced phenomenon is further examined to enhance the understanding of the uncharted behavior of turbocharger rotors and other rotor-bearing-based machinery. Full article

Lubrication is a well-established strategy for reducing interfacial frictional energy dissipation and preventing surface wear. Various lubricants have been developed, including mineral oil materials, vegetable oil materials, polymer-based materials, and solid lubrication materials. Among these, polymer-based lubrication materials have gained significant interest due to their versatility, leading to the development of tailored strategies to meet diverse application demands. In load-bearing scenarios, polymer-based materials enhance interfacial hydration, exhibiting exceptional frictional properties, including extremely low friction coefficients, high load-bearing capacity, and superior wear resistance. In contrast, in non-load-bearing scenarios, polymer-based coatings improve interfacial hydrophobicity, promoting boundary slip and reducing frictional resistance at the solid–liquid interface (SLI), making them an important strategy for drag reduction. Despite substantial advancements in polymer-based lubrication and drag reduction (PBLDR), the underlying microscopic mechanisms remain incompletely understood. Therefore, this review aims to provide a comprehensive analysis of the fundamental principles governing PBLDR. The main topics covered will include the following: (1) the fundamentals of the surface forces and hydrodynamic force, (2) the mechanisms underlying hydration lubrication, (3) joint lubrication and polymer brush lubrication, (4) the friction tuning and interfacial drag reduction via polymer coating design, and (5) the potential and limitations of polymer-based materials. By summarizing recent advancements in PBLDR, this work will provide valuable contributions to future research and applications in related fields. Full article

The setae structure of geckos’ toes can create a strong adhesion force, allowing geckos to climb almost vertical walls. Inspired by this, carbon nanotubes–graphite (CNTs-Gr) was prepared by microwave technology, where CNTs like the setae structure grew in situ on the surface of Gr flakes. Compared to the Gr, the coefficient of friction (COF) and wear rate of CNTs-Gr decreased by 44% and 46%, reaching 0.10 and 1.18 × 10⁻⁵ mm³·N⁻¹·m⁻¹, respectively. Even if the load increased from 5 N to 35 N, the CNTs-Gr maintained a low and stable COF of 0.12. The excellent tribological properties were attributed to the unique setae structure of CNTs-Gr. This structure enabled the adhesion force of CNTs-Gr to the worn surface to increase threefold, improving the coverage of the lubricating film and significantly enhancing the lubricating film’s pressure resistance. The gecko setae structure proposed in this article provides researchers with a new idea for designing lubricants with excellent lubrication performance and high load-bearing capacity. Full article

Bidirectional rotating thrust bearings are critical components for the development of bidirectional equipment. This paper presents the design and numerical study of an oil-lubricated bidirectional rotating thrust bearing with novel herringbone grooves, which consists of three groups of spiral grooves. The lubrication mechanism of the novel herringbone grooves is revealed. The static characteristics of the thrust bearing are numerically investigated by solving the Reynolds equation applying the finite element method. The influences of the radial width, depth, angle, circumferential width ratio, and number of the groove on the bearing performance are analyzed. The results show that there exists an optimal combination of groove radial widths that ensures equal load capacities in both rotation directions while achieving their maximum values. Furthermore, optimal values for the depth, angle, circumferential width ratio, number of the grooves can also enhance the bearing’s load capacity, maximum film pressure, and energy efficiency. Additionally, it is found that groove radial width has the most significant influence on the bearing performance difference under different rotation directions, followed by the effects from the angle, number, circumferential width ratio, and depth of the groove. The conclusions obtained can provide a valuable reference for the research and application of bidirectional thrust bearings. Full article

This study investigates the influence of idler roller diameter on indentation rolling resistance and idler rotating resistance in belt conveying systems, crucial for long-distance bulk material transport. It encompasses the impact on grease-lubricated rolling bearings, grease-filled labyrinth seals, and lip seals, with the aim of optimizing energy consumption. Experimental devices were used to refine predictive models, demonstrating that larger idler rollers reduce both resistances, leading to a 40% to 55% efficiency improvement. The study offers a detailed breakdown of friction losses under various operating conditions and provides valuable insights for lubricant selection and system enhancement, highlighting the significance of idler roller diameter in reducing energy costs and enhancing system performance. Full article

The excellent lubrication and load-bearing synergistic modulation of the meshing interface has been well recognized, as the microtextured tooth surface seems to be a punished area in deep-sea gear thermal elastohydrodynamic lubrication (TEHL). This is mainly because of the traditional perception of the anti-scuffing load-bearing capacity (ASLBC) and the similarity of the interfacial microelement configurations. Microtextured contact can be applied to the meshing interface to adjust the time-varying TEHL characteristics and enhance the meshing load-bearing performance. In this study, the analytical homogeneous equivalent micro-hydrodynamic contact multiscale parameters are determined, and the dispersed micro-flow real distribution area of the texturing interface is indicated, revealing the TEHL friction characteristics of the rolling–sliding line contact microelement, which is regarded as a bridge connecting the micro-dynamic pressure discrete contact friction behavior and the TEHL textured interface meshed-gear load-bearing. The contact model mentioned theoretically predicts the evolutionary time-varying characteristics of the micro-thermoelastic lubrication behavior of the textured contact interface under hydrodynamic conditions and demonstrates that the microtextured configuration parameters of the molecular scale meshing interface are the most influential structural parameters for the load-bearing problem of the homogeneous flow pressure film layer between the gear pair tooth surfaces, especially for deep-sea gear meshing load-bearing reliability under limited lubrication space. Full article

This study proposes an in-wheel assembly with a variable speed-reduction device designed to maximize torque and vehicle speed, enabling high-performance vehicle-level driving characteristics in front-engine, rear-wheel drive (FR), internal combustion engine (ICE) vehicles, where conventional EV motors cannot facilitate e-4WD. The proposed system integrates a motor and speed reducer within the wheel while avoiding interference from braking, steering, and suspension components. Through various innovative approaches, concepts for an integrated wheel-bearing planetary reducer and a variable speed planetary reducer were derived. The developed system achieved twice the maximum torque and a 35% increase in top speed compared to previously developed in-wheel systems, all without altering the front hard points. Multi-body dynamic analysis and component testing revealed wheel lock-up issues during reverse driving, and instability in the one-way clutch at high speeds. To address these issues, the power transmission structure was improved, and the type of one-way clutch was modified. Additionally, deficiencies in lubrication supply to the friction surface of the one-way clutch were identified through flow analysis and visualization tests, leading to design improvements. The findings of this study demonstrate that even in in-wheel systems where the application of large and complex transmission devices is challenging, it is possible to simultaneously enhance both maximum torque and top vehicle speed to achieve high-performance vehicle-level driving dynamics. Consequently, implementing an in-wheel e-4WD system in ICE FR vehicles is expected to improve fuel efficiency, achieve high-performance vehicle capabilities, and enhance market competitiveness. Full article

The standard procedures for calculating the lifetime of rolling bearings, defined by DIN ISO 281 and ISO/TS 16281, have been revisited in this work with a specific focus on redefining the η factor for cylindrical roller thrust bearings (CRTBs). The new η factor proposed in this study accounts for the additional spinning motion of the rolling elements on the raceway, which affects the lifetime of thrust roller bearings. By considering different spin-to-roll ratios (SRRs), the revised η factor results in a smaller lifetime reduction, improving from a 42% reduction with η = 0.85 to a 27% reduction with η = 0.91. This modification opens industrial opportunities for bearings that can handle higher loads or feature fewer or smaller rolling elements while maintaining the same lifespan target as bearings sized with the original η factor. An analytical and numerical methodology was developed to calculate the η factor for various bearing configurations. Two bearing geometries were selected to assess the influence of the SRR on bearing life. The methodology integrates calculations of the total friction coefficient, 2D and 3D stress distributions, and lifetime predictions based on subsurface-initiated fatigue failure modes. The numerical results demonstrate the impact of contact stresses and bearing kinematics on η. Although this study was based on numerical simulations, it sets the groundwork for experimental validation. Future work includes experimental testing to validate these findings, with a focus on subscale CRTBs subjected to varying γ values. Accelerated testing strategies, including higher rotational speeds and optimized lubrication, are proposed to enhance the accuracy of the results. These experiments would provide further insights into the life expectancy differences between various configurations, contributing to more precise lifetime calculations for CRTBs. Full article

This study presents an experimental analysis of a turbocharger with semi-floating ring bearings, focusing on hysteresis in subsynchronous vibrations. Four automotive oils (SAE 0W-20, SAE 0W-30, SAE 5W-30, SAE 5W-40) were tested across six oil inlet temperatures from 20 °C to 120 °C during ramp-up and ramp-down cycles to examine the effects of lubricant viscosity and temperature on rotor dynamics. Hysteresis and bifurcation points were observed at distinct rotational speeds in both directions, with subsynchronous components providing insights into rotor–lubrication interactions. This study applies the concept of hysteresis loop width for turbocharger rotors, highlighting its nonlinear dependence on oil temperature, an unexpected and unexplained phenomenon. Additionally, the results suggest that vibration sensors could provide real-time feedback on oil supply conditions, offering potential enhancements for turbochargers and other rotating machinery. Full article

The present paper deals with a review on bearing currents in electrical machines, with major emphasis on mechanisms, impacts, and mitigation strategies. High-frequency common-mode voltages from the inverter-driven system have been found to be the main reason for bearing current leading to motor bearing degradation and eventual failure. This paper deals with bearing currents—electrical discharge machining (EDM) currents, circulating bearing currents, and rotor-to-ground bearing currents—and the various methods of their generation and effects that are harmful to the bearings and lubricants of a motor. Mitigation techniques, among which the following have been taken into account, are studied in this context: the optimization of PWM modulation, and the use of shaft grounding brushes, insulated bearings, and passive or active filters. Finally, advantages, limitations, and implementation challenges are discussed. A review comparing three-phase and dual three-phase inverters showed that, due to the increased degree of freedom in modulation strategies, it is possible to eliminate common-mode voltages through active modulation techniques. Such added flexibility will reduce the risk of bearing currents effectively. It also highlights future research directions in bearing current suppression, including the development of multi-phase motor systems, real-time monitoring technologies with artificial intelligence, and the use of new insulation materials for the enhancement of bearing reliability. The results obtained should guide future research and engineering practices in suppressing bearing currents to improve motor durability with high performance. Full article