Minimum Oil Film Thickness Research Articles

Effects of Hyperelliptic Bearings Bush on Connecting Rod Big-End Lubrication and Design Optimization

Aiming at the impact of bearing bushes on the lubrication and friction and wear of diesel engine connecting rod big-end bearings, a certain type of diesel engine connecting rod big-end bearing bush was taken as the research object and a multi-body dynamics numerical calculation model of the connecting rod group was built. The connecting rod big-end bearing bushes with four profiles: exponential, hyperelliptic, barrel and trapezoid were used to study the effect on bearing lubrication. The study found that the hyperelliptic bush has the best lubrication performance for the connecting rod big-end bearing. On the basis of the hyperelliptic bush, the bearing clearance, bearing width, journal oil hole diameter and oil supply pressure are used as design variables, using the Box–Behnken experimental design and radial basis function (RBF) neural network method to construct an approximate multi-objective model, which the minimum oil film thickness (abbreviated as MOFT) and average rough contact effective pressure are the objectives. A non-dominated sorting genetic algorithm (NSGA-II) is used for multi-objective optimization. The optimization results show that the bearing clearance remains basically unchanged, the bearing width, journal oil hole diameter and oil supply pressure increase, so that MOFT of the connecting rod big-end bearing rises from 1.56 μm to 1.97 μm, and the average rough contact effective pressure increases from 3.97 MPa decreases to 0.25 MPa. The research results can provide a reference for the analysis and optimization of the lubrication performance of the connecting rod big-end bearing.

On the effect of temperature in friction force measurements for a simplified piston cylinder set-up: Squeeze film combined with minimum oil film thickness measurements and viscosity index effect

The lubricated interface at the piston-ring and liner and its interaction with different lubricants and testing conditions is examined in terms of experimental measurements that show the minimum oil film thickness developed at the lubricated or depending on conditions partly lubricated conjunction and the surface interaction intensity, as measured from the friction sensor. An analysis is carried out with the use of different parameters for the experiments as well as different lubricants in a simplified piston-ring simulation test rig. This analysis is further enhanced with the squeeze film effect investigations close to the stroke reversals and together with cavitation initiation and load-carrying effect results from previous experimental data, light is shed on the interacting surface’s behaviour at the different lubrication regimes. Another parameter, the viscosity index of the lubricant is used as an indication of the effects of squeeze film shift and friction force measurements and how the load and temperature effect are influencing the squeeze film.

Finite element modeling and simulation of mixed elastohydrodynamic lubrication for the finite line contact under tilting loads

Misalignment is a prevalent problem in rotor machinery. This paper proposes a numerical analysis for the mixed EHL of finite-line contacts considering tilting loads based on FEM. The Reynolds and linear elasticity equations, and Greenwood-Tripp contact model are coupled in an iterative process to solve the fluid-solid/solid-solid interaction under the compound external force and moment. Lubrication characteristics at both ends of the cylinder are analyzed and an asymmetric profile design scheme is presented to improve the lubrication performance at the cylinder's lower end. It is found that proper profile parameters can reduce EHL pressure by 40%, increasing the minimum oil film thickness by up to 100%, and thus reduce asperity contact pressure by up to 50%.

Improvement of lubrication performance of sliding pairs with multi-depth groove textures based on genetic algorithm

During the wear and tear process of bearings, the friction coefficient between the friction pairs can be effectively decreased by employing the suitable surface texture on the frition surface. In the study, the distribution and depth variation of the surface texture were used as variables, and the genetic algorithm was used for iterative optimization to obtain the optimal texture distribution and depth. The friction and wear performance of the rectangular texture bearing sliding blocks was optimized. The depth of the texture was represented by a 4-bit binary number, and different binary numbers were set to represent different texture depths. Finally, the genetic algorithm was used for continuous iteration and evolution to obtain the optimal texture combination. The study showed that, compared with the regular texture with a depth of 0.2 μm, the friction coefficient decreased by 15.0% under the optimal texture with a non-uniform depth. Simultaneously, compared with the regular 3 μm deep texture, texture with a optimized depth makes the friction coefficient decreased by 37.5%, and the minimum oil film thickness increased by 0.979 μm. The optimal texture and oil film thickness combination obtained from the study can effectively reduce solid contact force and alleviate mechanical wear.

Lubrication analysis of stern bearing during ship severe turning maneuver

Stern shaft deformation caused by ship maneuvering will lead to stern bearing lubrication failure and wear. Based on the displacement superposition method, the deflection equation of the stern shaft under the action of the interface force and the propeller load was established. The fluid-solid coupling model of the stern bearing was established by using the averaged Reynolds equation, the Greenwood-Tripp model, and the influence coefficient method. The model was experimentally validated. The influence of the shaft bending deformation caused by the propeller load change on the lubrication characteristics is discussed. The results show that the shaft bending deformation leads to the changes in lubrication characteristics along the axial and circumferential directions. Compared with the vertical load alone, the existence of horizontal propeller load will significantly reduce the minimum nominal oil film thickness and friction coefficient. Under hydrodynamic lubrication, the direction of horizontal load has little effect on friction coefficient.

Study on the frictional properties of the top ring-liner conjunction for different-viscosity lubricant

In modern internal combustion engines, the lubricant viscosity affects greatly the friction power loss. To obtain maximum fuel economy of the engines, the lubricants with different viscosities are considered to evaluate the friction properties of the compression ring-cylinder liner conjunction in the engines in this study. To conduct the evaluation, an improved mixed lubrication model is developed with considerations of the cylinder liner deformation, the lubricant thermal effect & transportation, and the change of lubrication condition from full flooded to starve. On this basis, the influence of different viscosity lubricants on the minimum oil film thickness, friction, power loss, FMEP, and wear load are investigated. The numerical result indicates that the low viscosity lubricant is more beneficial to facilitate the change of lubrication condition from starve to fully flooded. Furthermore, the low viscosity lubricant will result in large wear load on the compression ring surface while reducing the friction power loss.

Analysis of Elastohydrodynamic Lubrication (EHL) Characteristics of Port Plate Pair of a Piston Pump

This article presents a steady-state elastohydrodynamic lubrication model for the contact and sliding interface of an axial piston pump’s port plate pair. The wedge-shaped oil film thickness, pressure, viscosity, and elastic deformation distribution of the port plate pair were investigated by using the finite difference method. The elastohydrodynamic lubrication characteristics for different operating parameters and two materials of the port plate pair were analyzed for comparison. Existing conditions for the EHL were calculated, and variations in leakage and friction coefficients were investigated. The results show that the elastic deformation of the interface greatly influences the oil film’s overall performance, which is related to the material, inlet pressure, velocity, viscosity, and the minimum oil film thickness that determines the EHL. The deformation caused by oil film pressure greatly influences the model leakage and friction coefficient, especially when the deformation is equal to the oil film clearance.

Comprehensive analysis of fluid-film instability in journal bearings with mechanically indented textures

This paper theoretically and experimentally investigates the effects of textures produced by a mechanical indentation on the stability of journal bearings. The research primarily aims at lightly loaded journal bearings used, e.g. in vertical rotors and microturbines. The results show that textures located close to the minimum oil film thickness can noticeably improve the stability at low specific loads but have only a negligible effect at a specific load of 0.15 MPa. The texturing also impacts the bearing temperature, which is closely related to the bearing friction. Since the textured journal bearings are prone to the formation of cavities in the oil film, the paper also deals with computational methods. It is demonstrated that an accurate estimate of stability threshold requires very dense computational meshes, which are impractical for mass-conserving treatment of cavitation due to CPU requirements. Interestingly, errors due to non-conservation of mass are up to the same magnitude as uncertainties due to employed numerical algorithms. The results demonstrate that numerical results describing lightly-loaded textured journal bearings are very sensitive to the density of the computational mesh. Hence, the simplified cavitation treatment can be legitimate in applications where the CPU time is a concern, such as the optimisation, iterative algorithms and time-integration of equations of motion.

Effect of the Sliding Element Surface Topography on the Oil Film Thickness in EHD Lubrication in Non-Conformal Contact.

Under hard operating conditions such as high load, low speed and a lack of a sufficient quantity of lubricant, the sliding pairs could suffer serious damage. One of the methods that improves the tribological performance of sliding elements in hard operating conditions is the appropriate surface creation that keeps lubricating substance in cavities. This article presents the results obtained in experimental investigations of the oil film thickness in lubricated non-conformal contact with a different surface topography of the sliding element. The tests were conducted on a ball-on-disc instrument equipped with colorimetric interferometry. Balls of diameter equaled to 19.05 mm were produced from 100 Cr6 steel. To provide hard operating conditions, the glass disc rotated at small speeds in the range of 0.1-0.2 m/s. The tests were carried out at loads of 20 N and 30 N. As a result, in most cases, the highest minimum and average oil film thickness values were obtained when the surface of steel balls was characterized by high negative asymmetry with mainly shallow cavities and some valleys of great depth compared to the height of the peaks. The modified sliding surface that had better performance comprised a comparatively small number of peaks and the curvature of the peaks were large.

Online monitoring of oil film thickness of journal bearing in aviation fuel gear pump

As the key support of aviation fuel pumps, journal bearings are operated under extreme conditions of high temperature, high pressure and low viscosity media, therefore, the broken of the ultra-thin lubrication film is the main cause of lubrication failure and abnormal wear. However, the dynamic hydraulic lubrication (DHL) film is still blind due to the lack of non-destructive online monitoring techniques. This paper presents the study of ultrasonic-based measurement for the dynamic oil film thickness of fuel pump. The circumferential oil film thicknesses in a journal bearing are measured with the complex model and the resonance model, meanwhile, the minimum oil film thickness is extracted by fitting the measured points with the initial circle. Under varying operating conditions, the measured results are verified with classical DHL simulations, and the maximum relative error is shown to be lower than 15%.

A fully coupled tribo-dynamic model for piston-ring-liner system

As key friction pairs affecting the whole engine reliability, the piston-ring-liner system generates more than 45% of the whole engine friction loss. But so far, three-dimensional tribo-dynamic models considering its complex motions are very limited. This paper proposes a new method from the perspective of multi-flexible-body dynamics to realize a fully coupled modeling of the system’s deformation, dynamics, and lubrication characteristics. The study considers the ring-groove contact characteristics and calculates the system boundary loads through the blow-by model. The effect mechanism of ring groove deformation on ring properties is revealed, and the system’s complex tribo-dynamic behaviors such as twisting and fluttering are characterized. After fully coupled modeling, piston deformation at the ring groove position can be 65.80 µm, resulting in a 1.33 µm reduction in the minimum oil film thickness compared to the uncoupled model, and ring wear unevenness is aggravated.

Numerical simulation of oil film dynamic characteristics in the bidirectional thrust bearing of a pumped storage unit

Through the numerical simulation of the internal flow field of the thrust bearing, the distribution of the oil membrane pressure field was calculated using the CFD software Fluent. The effect made by inclination angle and rotor speed on the thrust bearing performance was analyzed. The results show that the inclination angle has a strong impact in pumped storage units. Only when the inclination of the circular direction reaches a certain value, with the increase of the circular inclination, the bearing capacity of the oil film gradually increases, and the pressure center moves to the oil outlet. With the increase of the rotor speed, the bearing capacity of the oil film gradually increases, and the pressure center remains unchanged. Therefore, in the limit of the minimum oil film thickness, running at large inclination angles and rotor speed can improve the performance.

Study on Distribution of Lubricating Oil Film in Contact Micro-Zone of Full Ceramic Ball Bearings and the Influence Mechanism on Service Performance

Compared with metal ball bearings, full ceramic ball bearings have more outstanding service performance under extreme working conditions. In order to reveal the lubrication mechanism and improve the operation performance and service life of full ceramic ball bearings, in this paper, the friction, vibration, and temperature rise characteristics of 6208 silicon nitride full ceramic deep groove ball bearing, under the condition of oil lubrication, are studied experimentally. Based on the test results, and through theoretical calculation and simulation analysis, the distribution of the lubricating oil film in bearing contact micro-zone under different working conditions was simulated. After that, the surface of contact micro-zone of full ceramic ball bearing was analyzed. It was found that there is an optimal oil supply for full ceramic ball bearing oil lubrication in service. Under the optimal oil supply lubrication, full film lubrication can be achieved, and the bearing exhibits the best characteristics of friction, vibration, and temperature rise. Compared with the load, the rotational speed of the bearing has a decisive influence on the optimal oil supply. When the rotational speed and load are constant, the minimum oil film thickness and oil film pressure in the contact area of the rolling body decrease with the increase of angle ψ from the minimum stress point of the rolling body. Under the action of high contact stress, thin oil film will be formed in the bearing outer ring raceway. In the field of full ceramic ball bearings, the research content of this paper is innovative. The research results of this paper have an important guiding significance for revealing the oil lubrication mechanism of full ceramic ball bearing and enriching its lubrication theory and methods.

Prediction of Wear Failure in Journalpin Bearings

Wear damage is a common failure in engine bearing shells. Wear failure induces changes in the bearing geometry and affects the oil film pressure and the durability of bearing shells. In this paper, wear failure in journalpin (main) bearings of a reciprocating engine is studied. Using a dynamic model, forces and torques in the journalpin bearings have been calculated and used in the analysis. To calculate the lubricating characteristics of the bearing, such as minimum oil film thickness and maximum oil film pressure, the Elasto-HydroDynamic (EHD) model that incorporate mass conservation algorithms is utilized. Wear failure in journalpin bearings of a reciprocating engine is assessed and the results are presented. Archard’s model is used as a wear model of journalpin-bearing material. The asperity interaction of two rough surfaces is considered by the boundary lubrication model. The results show that the wear rate at the initial stage of engine running is high. The results indicate that the main reason for wear in the journalpin bearings is the applied torque on the bearing, leading to edge wear. In a V-12 or 6Inline engine, journalpin bearing number 4 has the highest amount of torque applied and therefore has the highest amount of wear.

Effect of surface texturing on rotary vane actuator under different lubrication regimes

In this study, surface texturing was considered to solve the problem of the frictional surface of the rotary vane actuator end seal having difficulty in generating hydrodynamic lubrication. However, the current studies mostly set the minimum oil film thickness as a constant value, which could not reflect the real situation. A lubrication model for textured surfaces under different lubrication regimes was first established in this study based on the mean Reynolds equation and boundary lubrication theory. The model just required assuming the initial value of the minimum oil film thickness, and then the value was automatically corrected by the program in the calculation until the result converged. The rationality of the model was verified by comparing the model results with the friction experimental results. Subsequently, the trend of the friction coefficients for circular and square textures at different speeds and area ratios was analysed to investigate the effects of texture shape, area ratio and speed on the friction of the textured interface under this model.

Study on the moving cross‐hatched textures under starved lubrication based on parallel calculation

AbstractThe oil storage effect of textures is beneficial for lubrication performance under starved lubrication. When the larger of the two surfaces in friction pairs is textured, the moving textures should be considered because the boundary conditions are transiently changed at each moment. This is especially for the cross‐hatched textures, which are manufactured on the cylinder liner while not on the piston ring. However, it means that the calculation cost will be very expensive for engineering friction pairs because the required calculation scale is very large and the required time step is very small. So the dynamic characteristics of moving textures on engineering surfaces are normally neglected in the existing researches. In this study, a starved lubrication model of the piston ring‐cylinder liner (PRCL) system is established considering the oil storage effect, local hydrodynamic effect and dynamic characteristics of the moving cross‐hatched textures. To speed up the calculation, an efficient parallel algorithm is developed. The results show that there is a significant difference in minimum oil film thickness (MOFT), wear load and oil film boundaries between stationary textures and moving textures, so the moving textures should not be simplified. This is helpful to find a better design of textures for engineering friction pairs.

Experimental study on electric corrosion damage of bearing and solution

During the operation of the bearing in the motor, the induced current will inevitably be generated. The bearing raceway will be damaged by current. In this paper, the oil film thickness and capacitance in the bearing are analyzed in detail, and the relationship between oil film thickness, rotational speed, and load is obtained. The oil film thickness increases with the increase of bearing rotation speed and decreases slightly with the increase of load. The minimum oil film thickness of the bearing is between 0.4 μm and 2.9 μm. The capacitance of bearing is influenced by Hertz contact area, oil film thickness, and lubricant quality. It is between 1.9 pF and 34.7 pF. A shaft current test rig was developed. Based on the analysis results, orthogonal tests are set up to study the influence of voltage, rotation speed, and load on bearing operation. By using range analysis and variance analysis, the same conclusion is obtained: the most dominant factors affecting the raceway damage width, surface roughness, and vibration amplitude are voltage, load, and rotation speed, respectively. The mixed ceramic bearing and full-ceramic bearing are used instead of steel bearing to solve the problem of shaft current. Add conductive grease and non-conductive grease, respectively, and analyze and compare the advantages and disadvantages of different combinations from the perspective of temperature and friction and wear. The order from inferior to superior is steel bearing, hybrid ceramic bearing with ceramic outer ring, hybrid ceramic bearing with ceramic inner ring, hybrid ceramic bearing with ceramic ball and full-ceramic bearing. By using non-conductive grease, the damage is reduced by 16%–29%, surface roughness is reduced by 90%–122%, and vibration is reduced by 23%–176%. Under the same conditions, the bearings using non-conductive grease are better than those using conductive grease.

Piston ring oil film thickness measurements in a four-stroke diesel engine during steady-state, start-up and shut-down

Internal combustion engine research predominantly focuses on routes to lower emissions to meet various emission legislation. Lower emissions can be achieved with increased fuel efficiency and less lubricant throw off/lubricant combustion in the piston ring zone. These are all dependent on the oil film that forms between the liner and piston components. This article details the use of ultrasonic sensors to study the lubricant film thickness between the engine liner and piston rings/skirt in a fired diesel two-cylinder YTR engine. The testing regime covered a series of engine speeds and loading levels and found the minimum oil film thickness to vary from 1 to 3.5 μm. Spectrograms (time-varying ultrasonic amplitude spectra) have shown a residual oil film on the liner, first present after the skirt moves above the sensor that peaks at 440 μm, which then dissipates until the next oil control ring passage. Start-up and shut-down captures have visualised the build-up and reduction of the film thickness, in which during start-up typically a 2-s interval between the first ring passage and a consistent film thickness was seen. Whilst the shut-down tests showed a lesser variation, anticipated to be due to the oil pump already operating and is, therefore, less subjective to a reduction in engine speed providing a threshold of oil remains on the liner. Measurements like this help to describe how lubrication occurs in the piston ring zone and hence can optimise component design and an oil injection schedule.

Analysis on the Performances of Misaligned Journal Bearings using Full-Scale Test Rig and Conjugate Heat Transfer Method

Misalignment effects increase the risk of scratch or seizure failure for the journal bearings-rotor system. To investigate the performances of misaligned journal bearings, a full-scale journal bearings-rotor system test rig is designed and journal orbits are tested under different speeds. Then, a THD lubrication model is established to simulate lubrication performances under different misalignment conditions. The results show that for a misaligned journal bearings-rotor system, the center of the orbits of the bearing closing to coupling is fixed around the coupling. The orbits center of the bearing far away coupling is floating gradually with an increasing speed. The vibration amplitude of bearing closing to coupling is larger than that of bearing far away from the coupling. When the minimum oil film thickness is decreasing, the maximum film temperature is increasing except for the bearing closing to coupling. For different misalignment directions, maximum film temperature is determined by the position of the high pressure zone and high temperature zone.

Optimization study of oil-feed parameters to improve the ring pack lubrication performance for a two-stroke marine diesel engine

The piston ring pack is one of the crucial moving parts of two-stroke marine diesel engines because it has essential functions such as lubrication, sealing, and heat conduction. An oil injection lubrication mode for the ring pack through an independent oil-feed system is remarkable for two-stroke marine diesel engines. This study established a lubrication model for the ring pack. The model coupled ring dynamics, ring mixed/boundary lubrication, inter-ring gas dynamics, and asperity contact, especially considering this specific lubrication mode. The influence of lubricating oil-feed parameters (preliminary oil film thickness, oil-feed amount, oil-feed width, oil-feed position, and oil-feed ratio) on the lubrication characteristics of the ring pack was evaluated by the minimum oil film thickness and friction loss power. Finally, the orthogonal analysis method was used to optimize the lubrication characteristics.