Characteristics Of Lubricant Film Research Articles

Meshing Characteristics of Spur Gears Considering Three-Dimensional Fractal Rough Surface under Elastohydrodynamic Lubrication

Taking the effect of actual surface topography under elastohydrodynamic lubrication (EHL) conditions on the contact state of gear pairs into consideration, a combination model with the analytical sliced method and two-dimensional (2D) EHL model is proposed to characterize the three-dimensional (3D) meshing characteristics of spur gears. Firstly, the surface topology of gears is tested by a surface profiler, which reflects that the topography of tooth surface accords with fractal characteristics. Thus, by adopting the Weierstrass–Mandelbrot (W-M) fractal function, the gear surface is characterized. Secondly, the numerical 2D EHL model with fractal roughness is established, and distributions of oil film pressure (OFP) and oil film thickness (OFT) at different meshing positions are obtained. Finally, considering the different topography distributions in the direction of face width, time-varying mesh stiffness (TVMS) is calculated based on the analytical sliced method. Thus, the influence of 3D surface topography can be considered. The Hertz contact stiffness is substituted by the time-varying lubricating oil film stiffness (OFS). The influences of tooth surface topography and lubricant film characteristics on meshing characteristics are investigated. The results show that the 3D rough tooth surface may be well characterized by a fractal function with random phase. Moreover, there is a great difference in the distribution of OFP and OFT between rough and smooth surfaces, which certainly influences the gear meshing characteristics.

Prediction on Flow and Thermal Characteristics of Ultrathin Lubricant Film of Hydrodynamic Journal Bearing.

This paper focuses on the flow and thermal characteristics of the lubricant film in the micro clearance of a hydrodynamic journal bearing (HJB) at high rotating speed. A thermohydrodynamic (THD) method consists of the Reynolds equation coupled with energy and viscosity-temperature equation with considering the cavitation is put forward. The 3D surface diagrams of the lubricant film thickness, pressure, temperature, liquid mass fraction, flow rate and heat dissipation distributions under different geometric, operating, slip and no-slip boundary conditions are systemically exhibited and analyzed. The results show that with the rise of eccentricity or length diameter ratio, the maximum peaks of pressure, temperature and heat dissipation are rapidly increased, the cavitation is aggravated, and the flow rate is accelerated in different extent. As the bearing speed accelerating, the maximum peak of temperature is strongly increased, whereas, the distinction between peaks of flow rate and heat dissipation is magnified and reduced, respectively. It provides a fruitful inside view of the inner flow and thermal characterizations of HJB for further understanding its flow-thermal interaction mechanisms and offers theoretical support for improving its working performance.

Failure Analysis of Graphite Stationary Ring Utilized in One Type of Mechanical Seal

The loss of kinetic energy of moving parts due to viscous friction of lubricant causes the reduction of piston pump efficiency. The viscosity of lubricant film is mainly affected by the thermal effect. In order to improve energy efficiency of piston pump, this research presents a numerical method to analyze the lubricant film characteristics in axial piston pump considering the thermal effect by the coupled multi-disciplinary model, which include the fluid flow field expressed by Reynolds equation, temperature field expressed by energy equation and heat transfer equation, kinematics expressed by the motion equation. The velocity and temperature distributions of the gap flow of piston/cylinder interface in steady state are numerically computed firstly. Then the distributions are validated by the experiment. Finally, by changing the thermal boundary condition, the influence of thermal effect on the lubricant film, the eccentricity and the contact time between the piston and cylinder are analyzed. Results show that with the increase of temperature, the contact time increases in the form of a hyperbolic tangent function, which will reduce the efficiency of the axial piston pump. There is a critical temperature beyond which the contact time will increase rapidly, thus this temperature is the recommended as a design value.

Modeling and experimental research on engaging characteristics of wet clutch

PurposeTo gain in-depth understandings of engaging characteristics, the purpose of this paper is to improve the model of wet clutches to predict the transmitted torque during the engagement process.Design/methodology/approachThe model of wet clutch during the engagement process took main factors into account, such as the centrifugal effect of lubricant, permeability of friction material, slippage factor of lubricant on contact surface and roughness of contact surface. Reynolds’ equation was derived to describe the hydrodynamic lubrication characteristics of lubricant film between the friction plate and the separated plate, and an elastic-plastic model of the rough surfaces contact based on the finite element analysis was used to indicate the loading force and friction torque of the contact surface.FindingsThe dynamic characteristics of wet clutch engagement time, relative speed, hydrodynamic lubrication of lubricating oil, rough surface contact load capacity and transfer torque can be obtained by the wet clutch engagement model. And the influence of the groove shape and depth on the engaging characteristics is also analyzed.Originality/valueThe mathematical model of the wet clutch during the engagement process can be used to predict the engaging characteristics of the wet clutch which could be useful to the design of the wet clutch.

A Numerical Study on Influence of Temperature on Lubricant Film Characteristics of the Piston/Cylinder Interface in Axial Piston Pumps

The loss of kinetic energy of moving parts due to viscous friction of lubricant causes the reduction of piston pump efficiency. The viscosity of lubricant film is mainly affected by the thermal effect. In order to improve energy efficiency of piston pump, this research presents a numerical method to analyze the lubricant film characteristics in axial piston pumps, considering the thermal effect by the coupled multi-disciplinary model, which includes the fluid flow field expressed by Reynolds equation, temperature field expressed by energy equation and heat transfer equation, kinematics expressed by the motion equation. The velocity and temperature distributions of the gap flow of piston/cylinder interface in steady state are firstly numerically computed. Then the distributions are validated by the experiment. Finally, by changing the thermal boundary condition, the influence of thermal effect on the lubricant film, the eccentricity and the contact time between the piston and cylinder are analyzed. Results show that with the increase of temperature, the contact time increases in the form of a hyperbolic tangent function, which will reduce the efficiency of the axial piston pump. There is a critical temperature beyond which the contact time will increase rapidly, thus this temperature is the considered as a key point for the temperature design.

Effects of thermal and hydrodynamic characteristics of heavy-duty rotary table on the hydrostatic circular pads

The lubricant film of hydrostatic circular pad in the heavy-duty rotary table is affected by the roughness, thermal and hydrodynamic effect, which can cut down the load-carrying capacity and machining accuracy of the heavy-duty machine tool. In this paper, a coupled energy equation with mean Reynolds equation based on the Christensen’s stochastic model of rough surfaces is presented to analyze the temperature rising, pressure distribution and load-carrying capacity of the hydrostatic circular pad. The mean Reynolds equation, momentum equation, continuity equation, and energy equation are coupled and solved using the finite difference method to obtain the characteristics of lubricant film. It is found that the uneven pressure distribution and the temperature rising of lubricant film in resistive oil edge of hydrostatic circular pad are related to the increase of dimensionless hydrodynamic parameter S due to the thermal and hydrodynamic coupling effect. The load-carrying capacity and stability of heavy-duty rotary table is weakened due to the thermal and hydrodynamic effects.

Lubricant film flow and depletion characteristics at head/disk storage interface**Project supported by the National Natural Science Foundation of China (Grant No. 51275124).

The characteristics of lubricant film at head/disk interface (HDI) are essential to the stability of hard disk drives. In this study, the theoretical models of the lubricant flow and depletion are deduced based on Navier–Stokes (NS) and continuity equations. The air bearing pressure on the surface of the lubrication film is solved by the modified Reynolds equation based on Fukui and Kaneko (FK) model. Then the lubricant film deformations for a plane slider and double-track slider are obtained. The equation of lubricant film thickness is deduced with the consideration of van der Waals force, the air bearing pressure, the surface tension, and the external stresses. The lubricant depletion under heat source is simulated and the effects of different working conditions including initial thickness, flying height and the speed of the disk on lubricant depletion are discussed. The main factors that cause the lubricant flow and depletion are analyzed and the ways to reduce the film thickness deformation are proposed. The simulation results indicate that the shearing stress is the most important factor that causes the thickness deformation and other terms listed in the equation have little influence. The thickness deformation is dependent on the working parameter, and the thermal condition evaporation is the most important factor.

Elastohydrodynamic Lubrication Analysis of Conjugate Meshing Face Gear Pairs

This paper investigates the nominal elastohydrodynamic lubrication (EHL) characteristics of the conjugate meshing face gears and predicts the mesh efficiency of the pericyclic transmission system. The meshing face-gear tooth geometries and meshing kinematics are modeled. Hertzian contact and the isothermal non-Newtonian lubricant film characteristics of the meshing face-gear pair are investigated. The friction coefficient is calculated with the effects of lubricant behavior and mesh kinematics. Finally, the pericyclic transmission efficiency is calculated as a function of friction coefficient, mesh loads, and mesh kinematics. The Hertzian contact behavior, film thickness, and friction coefficient values are simulated for an example fixed axis face-gear pair rotating at 1000 rpm with 3.4 kN-m torque. The EHL film thickness ranges from 0.1 to 0.25 μm in this example. The average friction coefficient is predicted as 0.05. The efficiencies of three different 24:1 reduction ratio 760 HP pericyclic transmission designs are investigated. The minimum and maximum efficiency in the given design space are 97% and 98.7%, respectively.

Influence of surface roughness on normal-sliding lubrication

Contact between machine components can involve normal, sliding and rolling motion, either singly or in combination. Combined normal and sliding motion, which occur for example in the meshing of gear teeth and in heavily-loaded rolling elements, can present problems for lubrication. The purpose of the present experimental study was to investigate how surface roughness affects the lubricant film characteristics under conditions of combined normal and sliding motion. The experimental arrar gement consisted of a rotating roller which impacted a stationary ball in the presence of a lubricant. Under the same conditions of normal surface approach, increasing the surface roughness significantly decreased the level of roller sliding that could occur without breakdown of the lubricating film. This behaviour was similar to a step function. Of the several surface roughness parameters investigated, only those which involved the maximum peak-to-valley height correlated well with experimental results. In general, surface roughness had a greater effect on oil film breakdown than did either viscosity or load.

A Study of the Lubricant Film Characteristics of Journal Bearings : 5th Report, Application of the THL Theory to the Bearing Design

A Study of the Lubricant Film Characteristics of Journal Bearings : 5th Report, Application of the THL Theory to the Bearing Design

A Study of the Lubricant Film Characteristics of Journal Bearings : Part 1, A Thermohydrodynamic Analysis with Particular Reference to the Viscosity Variation within Lubricant Film

Recently, a precise estimation of the lubricant film characteristics of journal bearings has become necessary in designing bearings. In almost all the calculations previously performed, however, the effects of the thermal characteristics of a lubricant's viscosity and the effects of operating conditions (for example, journal eccentricity ratio, circumferential velocity and inlet temperature of a lubricant) on journal bearing performances were not taken into account because viscosity variation due to the viscosity dissipation of the lubricant film was not considered. In this paper, as the result of theoretical analysis in which the viscosity variation mentioned above was taken into account, it is shown that both the thermal characteristics of a lubricant's viscosity and the journal velocity have a great effect on the temperature and pressure distributions of the lubricant film and on the bearing load carrying capacity.

A Study of the Lubricant Film Characteristics of Journal Bearings : 1st Report, A Thermohydrodynamic Analysis of Journal Bearing Characteristics with Particular Reference to Viscosity Variation within the Lubricant Film

A Study of the Lubricant Film Characteristics of Journal Bearings : 1st Report, A Thermohydrodynamic Analysis of Journal Bearing Characteristics with Particular Reference to Viscosity Variation within the Lubricant Film