Hydrodynamic Oil Film Research Articles

Research on Meshing Gears CIMT Design and Anti-Thermoelastic Scuffing Load-Bearing Characteristics.

In the process of gear meshing, it is an inevitable trend to encounter failure cases such as contact friction thermal behavior and interface thermoelastic scuffing wear. As one of the cores influencing factors, the gear meshing contact interface micro-texture (CIMT) significantly restricts the gear transmission system (GTS) dynamic characteristics. This subject suggests the contact characteristic model and interface friction dynamics coupling model of meshing gear pair with different CIMT. Considering the influence of gear meshing CIMT on distribution type of hydrodynamic lubricating oil film, contact viscous damping and frictional thermal load, the aforementioned models have involved transient meshing stiffness (TMS) and static transmission accumulated error (STAE). Based on the proposed models, an example verification of meshed gear pair (MGP) is analyzed to reveal the influence of CIMT on the dynamic characteristics of GTS under a variety of micro-texture configurations and input branch power and rated speed/shaft torque conditions. Numerical simulation results indicate that the influence of CIMT on gear dynamic response is extremely restricted by the transient contact regularity of the meshing gear surface. Meshing gears’ dynamic characteristics (especially vibration and noise) can be obviously and effectively adjusted by setting a regular MGP with CIMT instead of random gear surfaces.

Experimental Studies on Friction Processes in Sliding Thrust Bearings

A technique for conducting experiments on determining wear features for thrust slide bearings is presented. The friction coefficient depending on the load and on the rotation velocity of the samples, on the changes in the wear weight fraction, and on the surface roughness parameters are determined. The effect of thickness, propagation, and interaction on the oil film formed in a hydrodynamic friction mode on the wear of friction pairs is considered. An instrumental support of the experiment is described, the results and conclusions are presented. It is noted that the local maximum of the friction coefficient is reached at approximately 900 rpm for all the samples and, for each load level, a corresponding minimum of friction coefficient is observed, which increases with increasing rotation velocity. In the course of testing, the minimum values of friction coefficient have been observed in the ranges of 550–650 rpm and 1050–1150 rpm. For the used testing mode, the smallest change in the surface roughness of the samples amounted to Ra = 0.46–045 μm for steel samples and Ra = 0.75–0.89 μm for bronze samples, respectively. These roughness values have been subjected to changes to a lesser extent, being close to the equilibrium roughness in the course of the testing. It should be noted that the greatest weight wear level of the samples occurs under running-in, and, when equilibrium roughness and the minimum friction coefficient have been reached, the sample wear level exhibits a decrease. In addition, upon the experiments, the distribution of the hydrodynamic oil film pressure over the surfaces of the samples was revealed based on the wear scars in the outer circuit, and its high-pressure belt was expanded in the circumferential direction.

Colloidal PTFE dispersion in commercial engine oil: Lubrication by Pluronic adsorption at the interface

PTFE particles with an average size of ∼300 nm were dispersed in20w40 commercial engine oil using Pluronic® surfactant. The role of series of different Pluronics with varying molecular weight and HLB was investigated. The dispersion stability was checked by UV-Vis-NIR spectrophotometer and by force transducer. The result indicates significant dispersion stability for low molecular weight and low HLB Pluronic, attributed to faster diffusion at PTFE-oil interface and resultant steric stability. L92 based formulation with less than 10% sedimentation even after 48 hrs, was evaluated for further tribological tests, i.e. wear, friction and pressure profile. Hydrodynamic oil film pressure profile using journal bearing showed significant increase in the load carrying capacity owing to PTFE dispersion in engine oil. Four ball tester depicted decreases in wear scar diameter for L-92 stabilised dispersion. Plausible molecular mechanism is proposed based on adsorption of polymers bilayer around PTFE particles through tail-tail interactions between PEO chains.

Optimization of cylinder liner macro-scale surface texturing in marine diesel engines based on teaching–learning-based optimization algorithm

This paper investigates the effect of optimum macro-scale cylinder liners oil groove on the tribological behavior of large bore marine diesel engines. Parabolic bottom shape grooves are selected as the cylinder liner surface texturing. The grooves have been distributed along the stroke in the form of array of circumferential cells with the axial groove centered in each cell. Teaching–learning-based optimization algorithm is applied to get the optimum dimensions of oil grooves, where the objective is to minimize the cyclic average total friction force between the top compression piston ring and the cylinder liner. Numerical simulation based on Reynolds equation is presented to study the effect of optimum grooves’ dimensions on tribological parameters such as hydrodynamic friction, asperity contact pressure, and hydrodynamic oil film pressure. Results showed that the optimum dimensions oil grooves have a significant effect on the total friction force and the cavitation pressure of the oil film.

Simulations of the Influence of the Heat Flux at the Shaft Surface of the Conical Slide Bearing on Its Hydrodynamic Lubrication and Operating Parameters

Abstract The aim of this work is to investigate, how in the adopted model of hydrodynamic lubrication of a conical slide bearing, the change of the heat flux value at the bearing shaft, affects bearing operating parameters. In this research, the authors use, the known from the literature, Reynolds type equation, describing the stationary hydrodynamic lubrication process of a conical slide bearing. The analytical, solutions, that determine the components of the lubricating oil velocity vector and the equation (analytical solution of energy equation) determining the three-dimensional temperature distribution in the lubrication gap, was also adopted from previous works. In order to obtain numerical solutions, the Newton’s method was used, and the derivatives in the Reynolds type equation were approximated by the finite differences. An application of the method of subsequent approximations allowed considering the influence of temperature, pressure and shearing rate on the viscosity of lubricating oil. The considerations were performed by adopting the Reynolds condition of the hydrodynamic oil film. It was tested, how the assumed value of the heat flux on the bearing shaft surface affects the values of the obtained operating parameters, i.e. the transverse and longitudinal component of the load carrying capacity, friction force and coefficient of friction.

Cavitation Bubble Dynamics Induced by Hydrodynamic Pressure Oil Film in Ultrasonic Vibration Honing

During ultrasonic vibration honing (UVH), a thin hydrodynamic oil film formed can seriously affect the cavitation effect in the grinding fluid, but the mechanism is still unclear now. Based on the hydrodynamics theory, a revised cavitation bubble model with oil film pressure is developed, and it has been calculated by the four-order Runge–Kutta method. The calculation results show that the oil film pressure under UVH is a positive–negative alternant pulse pressure, and it can induce the secondary expansion of the bubble, leading to double microjets during the process of the bubble collapsing. The effects of ultrasonic amplitude, ultrasonic frequency, oil film height, and reciprocation speed of the honing stone on the bubble dynamics are discussed. With the increase of ultrasonic amplitude, the amplitude of the bubble expansion is increased, and the oscillation interval is extended. As increasing normalized oil film height, the variation of the bubble first expansion is slight, while the amplitude of the bubble secondary expansion is reduced and the oscillation interval is also shortened. The main effect of ultrasonic frequency and reciprocation speed of the honing stone on the bubble dynamics is connected with the secondary bubble expansion. The bubble secondary expansion is decreased with the increasing reciprocation speed of the honing stone, ultrasonic frequency, and oil film height. The results of the simulations are consistent with the surface roughness measurements well, which provides a theoretical prediction method of cavitation bubbles control.

Experimental study of hydrodynamic pressure distribution in oil lubricated two-axial groove journal bearing

Hydrodynamic pressures in oil lubricated two-axial groove finite journal bearing is measured experimentally using a newly developed test rig. Details of design and fabrication of the test rig is presented. Hydrodynamic oil film pressures were measured using two techniques, viz. pressure measurement with sensor mounted on shaft surface and pressure measurement with sensor located outside the bearing assembly. Pressure measurement with first approach was found to yield only the groove pressures. The maximum pressures obtained using second approach is compared with theoretical values. Maximum experimental pressures are found to have a 20% difference in comparison with theoretical maximum pressures.

Study on micro-surface texture and tribology characters of ground surface in point grinding process

In point grinding process, the characters of surface texture are different from the general cylindrical grinding since point grinding angle exists in the process. The paper sets the model of point grinding texture direction and analyses its characters and influencing factors. The effects on evaluation parameters of surface roughness and the tribology characters are analysed in terms of the measured value and modelled results. Results manifest that evaluation parameters vary with texture direction, whose optimal angles are acquired when the profile is perpendicular to the moving direction. As to surface texture direction, the hydrodynamic oil film between the sliding contact surfaces is formed with better performance. By tribology experiment, the friction coefficient is affected by the ground surface texture direction greatly. The surface texture angle can be obtained by controlling point grinding angle. There is the optimal value for the higher pressure of oil film and less friction coefficient.

Study on CFD Solution Method for Static Characteristics of Hybrid Oil Film Bearing

Reynolds equation is the fundamental equation to solve the static performance for sleeve bearings. For hydrodynamic and hydrostatic oil film bearing with three oil recesses, the specific expressions of the fluid mechanics lubrication Reynolds equation are presented. The gridding model of the bearing is proposed, the boundary condition of the bearing is set, the static characteristics are solved and the pressure distribution of the bearing is plotted by using FLUENT software. The computation results from FLUENT are considerably accordance with the computation results from finite difference method.

Study on the Wear Properties of Hydrodynamic Oil Film Bearing by Finite Element Method

ANSYS as finite element software is used to analyze oil film pressure of hydrodynamic oil film bearing, the stress of bearing bush alloy and the simulation movement of shaft and bearing, and then the reasons of oil film bearing failure and the wear mechanism of bearing bush are illustrated in detail.

Nonlinear Dynamic Behavior of Turbocharger Rotor-Bearing Systems With Hydrodynamic Oil Film and Squeeze Film Damper in Series: Prediction and Experiment

Current trends for advanced automotive engines focusing on downsizing, better fuel efficiency, and lower emissions have led to several changes in turbocharger bearing system design and technology. Automotive turbochargers run faster and use engine oils with very low viscosity under high oil inlet temperature and low feed pressure. The development of high performing bearing systems, marrying innovation with reliability, is a persistent challenge. This paper shows progress on the nonlinear dynamic behavior modeling of the rotor-radial bearing system (RBS) incorporating two oil films in series: a hydrodynamic one with a squeeze film damper commonly used in turbochargers. The developed fluid bearing code predicts bearing rotational speed (in the case of fully floating design), operating inner and outer bearing film clearances, effective oil viscosity, taking into account its shear effect, and hydrostatic load. A rotordynamics code uses this input to predict the nonlinear lateral dynamic response of the rotor-bearing system. The model predictions are validated with test data acquired on a high speed turbocharger RBS of a 6.0 mm journal diameter running up to 250,000 rpm (maximum speed), 5W30 oil type, 150°C oil inlet temperature, and 4 bar oil feed pressure. The tests are conducted at a rotordynamics technology laboratory using a high performance data acquisition system. Turbochargers with four combinations of inner and outer RBS clearances are tested. Prediction and measured synchronous response and total motion are in good agreement. Both demonstrate the nonlinear character of the RBS behavior, including several subsynchronous frequency components across the operating speed range. The nonlinear predictive model aids the development of high performance and optimized turbocharger RBS with faster development cycle times and increased reliability.

Hydrodynamic Pressure Oil Film Modeling and Experimental Study of Ultrasonic Vibration Cutting

On the basis of kinetic characteristic of ultrasonic vibration cutting and the action feature of coolant,the model of hydrodynamic pressure oil film between tool and workpiece is built on the basis of hydrodynamic pressure theory.Through analyzing the variation regularity and distribution state of hydrodynamic oil film pressure on rake face and the process effect of machining experiment,it is proved that high hydrodynamic pressure oil film can be produced in ultrasonic vibration cutting.And the chip can be caused elastic deformation,even extrusion deformation and shear slippage by hydrodynamic pressure of oil film.The process of ultrasonic vibration cutting has two phases,i.e.oil film action and tool contacting with chip.Action of oil film can increase shear angle,make tool sharpened and change contacting state between rake face and chip,and improve the surface quality of workpiece.The influences of the oil film state and the coolant viscosity on the machining result are discussed.

Investigation into the seizure of hydraulic motors

Despite its practical significance, the occurrence of seizure in tribological systems has not been fully understood. In this work, extensive actual tests on hydraulic motors under extreme operating conditions of low viscosity, high pressure and speed have been conducted with a view to investigate and understand the seizure mechanism. Some of the motors failed and they were stopped at different stages of progressive seizure. Based on these investigations, a three stage seizure process has been suggested. Stage 1 involves the breakdown of hydrodynamic oil film between roller and piston which leads to increased friction, thermal expansion and increased leakage. In stage 2, scuffing is initiated either between roller and piston or between piston and cylinder. During stage 3 scuffing propagate to several pistons.

Experimental Characterization of the Influence of Coating Materials on the Hydrodynamic Behavior of Thrust Bearings: A Comparison of Babbitt, PTFE, and PFA

The present paper is the first of a series dealing with the experimental characterization of the coating materials’ influence on the hydrodynamic behavior of thrust bearings. This paper presents a unique set of experimental data characterizing the influence of material coating on hydrodynamic oil films. The data are presented for extensive experimental conditions in which the load, the rotation speed, and the temperature were systematically varied. Seven main parameters characterizing the oil film were recorded. One metallic coating (Babbitt) and two Teflon-based coatings (polytetrafluoroethylene and polyperfluoroalkoxyethylene) were tested. It was clearly evidenced that the nature of the material strongly influences the hydrodynamic behavior. As expected in the hydroelastic regime, coatings with different properties (i.e., metals versus polymers) exhibit strong differences in their hydrodynamic behavior. The originality of the paper lies, however, in that the two polymers showed very different behavior.

A Method for the Measurement of Hydrodynamic Oil Films Using Ultrasonic Reflection

The measurement of the thickness of an oil film in a lubricated component is essential information for performance monitoring and control. In this work, a new method for oil film thickness measurement, based on the reflection of ultrasound, is evaluated for use in fluid film journal bearing applications. An ultrasonic wave will be partially reflected when it strikes a thin layer between two solid media. The proportion of the wave reflected depends on the thickness of the layer and its acoustic properties. A simple quasi-static spring model shows how the reflection depends on the stiffness of the layer alone. This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrodynamic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oil film and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oil film stiffness that can be readily converted to film thickness. Whilst the reflected amplitude of the wave is dependent on the frequency component, the measured film thickness is not; this indicates that the quasi-static assumption holds. Measurements of the lubricant film generated in a simple journal bearing have been taken over a range of loads and speeds. The results are compared with predictions from classical hydrodynamic lubrication theory. The technique has also been used to measure oil film thickness during transient loading events. The response time is rapid and film thickness variation due to step changes in load and oil feed pressure can be clearly observed.

Influences of Wedge Geometry Incorporated Oil-Grooves on Lubrication Characteristics for Crosshead-Pin Bearings

Because the crosshead-pin bearing for large size two-stroke diesel engines oscillates within a small angle at a low speed and is always subject to a high downward load, the hydrodynamic oil film is very thin. The recent tendency to raise the engine power using compact engines continues to increase the lubrication severity of the bearing. It is thus very important to improve the load carrying capacity of the bearing. In the present study, calculations were carried out to clarify the lubrication characteristics for the crosshead-pin bearing with a very low clearance ratio and wedge geometry incorporated oil-grooves. Reducing the bearing clearance ratio is advantageous for enhancing squeeze action on the entirety of the bearing pads, thereby decreasing the oil film pressure. However, this also has a negative aspect of reducing wedge action, causing the oil film thickness to decrease. Even when the clearance ratio becomes very low, incorporating a wedge geometry on both sides of the oil-grooves is an effective means to improve wedge action, and thereby to increase the oil film thickness without a significant raise in the oil film pressure.

A Study of Break-In Film Development with Different Piston Ring Coatings and Correlation with Electrical Contact Resistance Measurements

The film formation including hydrodynamic oil film and chemical boundary films was studied experimentally by using an electrical contact resistance method during the break-in period of coated piston rings rubbing against a cylinder bore segment. A simplified one-dimensional film model was developed to describe the film formation and correlated to the electrical contact resistance measurements. Two scaling factors were determined from the electrical resistance measurement during the break-in film development. The modeling results agreed well with the experimental measurements when the scale factors were selected appropriately in the model. Parameters such as applied normal load, surface roughness, lubricant viscosity, and Young's modulus of the ring coatings were considered in film modeling. The experimental results showed that the behavior of break-in film development was affected by the oil additives. The numerical simulation results showed that the film developed more quickly with decreasing normal load and lubricant viscosity and with increasing surface roughness and Young's modulus. Presented at the 58th Annual Meeting in New York City April 28–May 1, 2003

A Theoretical Analysis of Floating Bush Journal Bearing With Axial Oil Film Rupture Being Considered

A new modified Reynolds equation is derived with centrifugal force acting on the hydrodynamic oil film being considered. This equation, together with a cavitation model, is used to obtain the steady-state equilibrium and calculate the rotordynamic coefficients of lightly loaded floating bush journal bearings operating at very high shaft speeds. The bush-to-shaft speed ratio and the linear cross-coupling spring coefficients of the inner oil film is found to decrease with the increase in shaft speed as the axial oil film rupture develops in the inner oil film. The present model can give reasonable explanation to the steady-state behavior and the stability behavior of the bearing observed in actual machines.

Possibility of slip in hydrodynamic oil films under sliding contact conditions

AbstractIn hydrodynamic lubrication theory, the oil film thickness build‐up increases with increasing sliding speed or oil viscosity, and the viscous resistance or shear stress also increases, both without limit. The entraining force forming the oil film is given by the moving surfaces, or by the adhesive force of the oil molecules on the rubbing surfaces and the interaction force between them. Therefore, the maximum friction force and maximum oil film thickness will be limited by the operating conditions, such as oil properties, rubbing materials, sliding speed, and load. In this study, friction tests were conducted using a plate‐on‐cylinder sliding contact apparatus. It was found that a critical shear stress existed, above which the friction force and oil thickness decreased from theoretical values. Slip in an oil film seems to occur when the theoretical shear stress exceeds the critical value of the oil, according to test conditions. The occurrence of slip in an oil film is responsible for the reduction in the oil film and friction force from theoretical values, leading to the lower‐viscosity components of the oil selectively passing through the conjunction zone.

Journal bearing performance under starved lubrication

The hydrodynamic performance of a journal bearing under starved lubrication conditions is studied theoretically and experimentally. When lubricant is supplied to a journal bearing from an oil groove at an insufficient oil flow rate, the hydrodynamic oil film cannot cover the full width of the bearing at the inlet of the convergent bearing clearance, and the covered width increases gradually with the decrease in film thickness in the circumferential direction. This phenomenon affects the static and dynamic performance of the journal bearing. The oil film boundary in the bearing clearance is calculated numerically for a constant load and a constant speed under the assumption of laminar, iso-viscous lubrication. Measurements are in good agreement with predictions. Some more calculations of journal centre loci are given.