Search

• Dynamic loaded tooth contact analysis (DLTCA) for computing entrainment speed. • Accurate solution to elastohydrodynamic lubrication (EHL) governing equation. • Discrete convolution and fast Fourier transformation (DC-FFT) for flank elastic deformation. • A separation flow method for iteration of EHL governing equation. • Accurate entrainment effect-based EHL forecasting model for hypoid gears. In full consideration of time-varying meshing performance and oil film characteristics, entrainment effect on elastohydrodynamic lubrication (EHL) is developed for establishing accurate forecasting model of the complex hypoid gears. Firstly, dynamic loaded tooth contact analysis (DLTCA) is employed to determine the meshing interface kinematics, load distribution and entrainment speed under dynamic load condition. Then, entrainment speed is introduced into the EHL governing equation and accurate forecasting model is established. With accurate discretization of EHL governing equation, discrete convolution and fast Fourier transformation (DC-FFT) method is employed to compute the flank elastic deformation. Finally, a hypoid gear set in automotive industrial application is exercised to verify entrainment effect on EHL assessment in the proposed model. [ABSTRACT FROM AUTHOR]

In mixed elastohydrodynamic lubrication (EHL), the load distribution between the gear meshing surfaces is shared by the oil film and the asperities of the gear's rough surface. Based on the load‐sharing concept, this paper proposes a time‐varying meshing stiffness (TVMS) model for gears with mixed EHL. The initial step involves the utilization of the Greenwood‐Williamson model to calculate the contact stiffness of surface asperities, while the lubricating film is assessed using a curve‐fitting formula to investigate the influence of gear surface morphology on TVMS. Subsequently, the incorporation of gear fillet foundation deformation and friction enables accurate TVMS determination. The proposed method is employed to examine the meshing stiffness of the gear pair under both dry lubrication and EHL conditions. Comparative analysis reveals favorable agreement between the proposed model and experimental results obtained under dry lubrication, thereby highlighting the superior performance of the proposed approach. Moreover, the time‐varying friction coefficient under EHL is computed, and the impacts of gear surface morphology parameters, temperature, speed, and load on lubrication conditions and TVMS are investigated. The findings presented in this paper contribute significantly to advancements in gear design and performance. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

Tribological machine elements, such as rolling element bearings and gears, are often used in mechanical components and various industrial applications. The contact interfaces and sliding parts fundamentally consist of two solid and one liquid lubricant, and they are operated under a thermal elastohydrodynamic lubrication (TEHL) condition. The TEHL solution characteristics depend on the operating conditions and lubricant physical properties, as well as the surrounding environment, including the temperature along the solid surfaces and pressure adjacent to lubricated contact. Herein, we numerically examine the influence of both solid temperature and ambient pressure on TEHL solutions at the nominal line contact and discuss the synergistic effects. Any changes in the physical properties of the lubricants are considered either together or separately as functions of temperature and pressure. The high ambient pressure enhances the effects of the solid temperatures on the resultant TEHL solutions. Regardless of the solid temperature and ambient pressure conditions, the TEHL solutions for all the lubricant models are grouped into two in terms of thermal conductivity.

A numerical method is proposed to evaluate the effect of non‐Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non‐Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro‐contact model. The influence of non‐Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper is the second part of a two-part report studying the responses of a typical point-contact elastohydrodynamic lubrication (EHL) system to multiscale roughness mimicked by wavy surfaces. The wavy surfaces are defined by three key parameters: amplitudes, frequencies, and directions. The previous Part I paper focuses on the full film lubrication condition, while the current paper focuses on the partial film regime where asperity contacts occur. A transient thermal EHL model simulates lubrication problems with different waviness parameters, loads, and speeds. The total number of simulations is 1600. Performance parameters, including the asperity contact ratio, minimum film thickness, maximum pressure, central point film thickness, central point pressure, mean film thickness, coefficient of friction (COF), and the maximum temperature rise, are obtained for each simulation. These performance parameters are post-processed in the same manner as those in the previous Part I paper. The influences of the waviness parameters, load, and speed values on the eight performance parameters are discussed.

In this work, a modified numerical algorithm that couples the quasi-static theory with the mixed thermal elastohydrodynamic lubrication (mixed-TEHL) model is proposed to examine the mechanical properties and lubrication performance of the spindle bearing that is used in a high-speed machine tool with spinning. The non-Newtonian fluid characteristics of the lubricant and the non-Gaussian surface roughness are also considered. Moreover, the mechanical properties and lubrication state of the bearing are examined in various service environments. The results indicate that the temperature reduces the lubrication efficiency, which in turn exerts a significant impact on the mechanical properties. The lubrication that either behaves in the manner of Newtonian or non-Newtonian fluid has a relatively negligible influence on the bearing working state, while the non-Gaussian surface roughness significantly alters the oil film thickness and temperature. Calculations with different operating conditions demonstrate that the operating parameters (i.e., axial load, rotation speed) will directly affect the performance of the bearings via the changes in the oil film thickness and the temperature.

Asymmetric polymer gears are used in planetary gear transmission system to cater for the design requirements of compact and lightweight mechanical structure. In order to study the transient elastohydrodynamic lubrication characteristics of the internal meshing teeth of the asymmetric polymer planetary gear transmission, a lubrication model of internal meshing gear transmission of asymmetric polymer planetary gear is established; numerical solution and simulation analysis is completed by the multi-grid method. The similarities and differences between the internal and external meshing geometric parameters of planetary gears are compared and analyzed. The influence of gear operating conditions and different materials of asymmetric polymer planetary gear on transient elastohydrodynamic lubrication is studied. Considering the influence of thermal effect, the temperature distribution of the highest temperature rise and three special instantaneous meshing points in the asymmetric polymer planetary gear was investigated. The lubrication properties of different gear materials under thermal and isothermal elastohydrodynamic lubrication are comparatively studied. The results show that due to the different transmission meshing methods, the geometric parameters of the internal meshing of planetary gears are different from those of external meshing gears. Speed and load have significant influence on the gear elastohydrodynamic lubrication performance. The bearing capacity and isothermal elastohydrodynamic lubrication performance of gears can be improved using asymmetric polymer gear. Polymer gear materials affect tooth strength and heat dissipation at high temperature and heavy load. Asymmetric polymer planetary gears are more suitable for low temperature and low speed environment.

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. [ABSTRACT FROM AUTHOR]

: In order to explore formation and evolution mechanism of lubrication failure of friction pair in mechanical transmission system under harsh working conditions, a point contact elastohydro-dynamic lubrication model was established considering oil film interface slip, and simulation calcula¬ion was carried out. The two-color light interference elastohydrodynamic lubrication test was carried out to study the influences of load on oil film interface slip in elastohydrodynamic lubrication, and hen variation characteristics of entrainment velocity, hydrodynamic pressure, oil film thickness and lip parameters with load were studied under interface slip state. The results show that with the in¬rease of load, the slip amplitude and slip range of interface increase significantly and the entrainment velocity in slip region decreases obviously. The dynamic pressure distribution in slip region tends to be uniform. In addition, slip region produces film thickness accumulation and inlet depression character¬istics. The shape of slip region gradually presents the characteristics of "half crescent". [ABSTRACT FROM AUTHOR]

Based on the meshing principle of the roller enveloped end face worm drive pair， the influence of the center distance， the roller radius， the throat coefficient， and the worm gear diameter are considered comprehensively. According to the elastohydrodynamic lubrication theory， the Newton iteration method is used in Matlab. The Newton-Raphson method is used to solve its numerical calculation， the conjugate teeth of the new transmission pair are studied， and the analysis of the line contact between the conjugate teeth is completed. The schematic diagram of lubricating oil film pressure and oil film thickness under the change of geometric parameters and roughness amplitude of the conjugate tooth surface of the transmission pair is given， and the analysis is completed. The results show that the performance of the transmission pair is good. The important parameters affecting the lubrication are the roller radius and the meshing position， while the throat coefficient and the worm gear diameter have little effect on the lubrication characteristics. Full-film lubrication can be generated between the conjugated tooth surfaces to avoid direct contact， reduce wear and oil temperature， and improve transmission efficiency and anti-glue ability at the same time. Therefore， the necessary theory and application value are given for the development of the new transmission pair.

The present study focuses on investigating the influence of oil and solid body temperatures on elastohydrodynamic lubrication (EHL) film formation. Experimental and numerical simulation methods are employed to examine three heating methods: oil and ball heating, disc heating, and entire system heating. A preliminary comparison between the measured results and numerical simulations confirms the impact of heating methods on film formation while validating the availability of the numerical models. Further numerical analysis reveals that in the case of oil and ball heating, the temperature gradient induced by differences in solid body temperatures plays a more significant role in film formation compared to the conventional thermal-viscosity wedge effect caused by EHL film shear. This effect is further amplified at large sliding–rolling ratios and in steel–steel contacts. The overall film formation is primarily governed by the oil inlet temperature, whereas local film formation characterized by a dimple shape is influenced by both thermal gradient effects and thermal-viscosity wedge effects. This study provides valuable insights for selecting appropriate heating methods in experiments as well as understanding how temperature differences affect film formation in practical engineering.

The transient mixed lubrication behaviors in thermal elastohydrodynamic lubrication (TEHL) contacts during startup and stop are investigated. A transient mixed TEHL model for point contacts under time-varying speed conditions is proposed with comprehensive consideration of surface roughness, thermal effect, and transient behavior. The model is validated by the comparison to available published data. Based on the developed model, significant differences have been found compared with transient EHL and steady TEHL models. In addition, the transient mixed TEHL performance during start–stop with different acceleration rates and surface roughness is investigated. It shows that the lubrication behaviors during start–stop have an irreversible process. The roughness can significantly enhance the transient behavior. The roughness effect has a remarkable impact on lubrication performance in mixed lubrication. The evolution of lubrication behaviors during start–stop is highly related to the acceleration rate and surface topography. [ABSTRACT FROM AUTHOR]