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This paper presents comparable sets of the no-load power loss as a product of windage and churning behaviors of a family of various rotating parts (i.e., disc, spur gear, straight bevel gear, and orthogonal face gear). Experimental measurements were carried out under pure air only and under partial immersion in oil to qualify and quantify the windage and churning effects of no-load power losses of a family of spur, bevel, and face gears along with a representative disc as the baseline. Aiming at exploring the influence of gear teeth on the total no-load power losses, two different theoretical analytical approaches are introduced to account for the churning contributions, by which the total power losses are estimated. Both analytical approaches compare well with the experimental findings. Furthermore, a spatial intersecting cross-axis gear (e.g., straight bevel gear and orthogonal face gear) results in higher no-load power losses than that of a representative disc or a parallel-axes gear. The significance of gear teeth (gear vs. disc) on windage behavior is presented, as well as the gear windage effects on the churning phenomenon in a high-speed splash-lubricated gear. [ABSTRACT FROM AUTHOR]

In order to clarify the effect of mixed lubrication methods on the oil flow and power loss of the gearbox, this study adopts a high-precision moving particle semi-implicit (MPS) method to investigate the lubrication of the gearbox under the joint influence of splash lubrication and oil injection lubrication. The accuracy of the numerical method to calculate the churning torque was verified by the constructed test rig. The effects of rotational speed, immersion depth, injection volume rate, and oil injection angle were analyzed and evaluated for lubrication. The results show that better lubrication can be achieved with relatively small churning torques by using a hybrid lubrication method. This provides some references for engineering applications of gearboxes. [ABSTRACT FROM AUTHOR]

With practical physical immersion depth as their joint, the relations between the oil distribution characteristics and the associated no-load power losses for splash-lubricated orthogonal face gears are explored and quantified in this paper. Firstly, a theoretical analytical model is proposed to estimate the churning losses of an isolated face gear considering all the preceding parameters, along with a numerical model of a face gear stirring oil developed based on the sliding mesh strategy. Then the accuracy and correctness of the computational fluid dynamics method are verified with experiments in terms of oil flow behavior and no-load losses. Finally, the physical immersion depth is determined by leveraging the image processing technique and substituted into the theoretical model replacing the static depth with an improvement of prediction accuracy. Last but not least, this practical immersion depth acts as a link to facilitate the communication between the oil distributions and the no-load power losses within the gearboxes. [ABSTRACT FROM AUTHOR]

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission. [ABSTRACT FROM AUTHOR]

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Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING 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.)

The transient lubrication conditions of rolling bearings are different in gearboxes and bearing testers. It has been observed that samples of qualified rolling bearings tested in rolling bearing testers often fail and do not meet lifespan requirements when employed in other lubrication conditions. This may be caused by different factors affecting the bearing in testing and applying lubrication. Needle roller bearings were selected for this study to investigate the causes of this phenomenon in terms of lubrication. Based on the computational fluid dynamics (CFD) method, fluid domain models for the same type of rolling bearings with different lubrication conditions were established. The transient flow fields of rolling bearings with oil jet lubrication in a tester and splash lubrication in a planetary gearbox were simulated. The air–oil transient distribution of rolling bearings in two kinds of lubrication was analyzed. The results indicate that the rotational speed significantly affected the oil jet lubrication of the needle roller bearing. The average oil volume fraction rose by 0.2 with the increase in the bearing speed from 1200 r/min to 6000 r/min and by 0.06 with the increase in the oil jet velocity from 8 m/s to 16 m/s. The splash lubrication of the bearings in the planetary gearbox was directly related to the immersion depth of the rolling bearings in the initial position. Meanwhile, the splash lubrication of the bearings was also affected by other factors, including the initial layout of the planetary gears. The increase in speed from 1200 r/min to 6000 r/min made the average oil volume fraction of splash lubrication decrease by 4.4%. The average oil volume fraction of the bearings with splash lubrication was better than that with oil jet lubrication by an average of 41.9% when the bearing speed was in the low-speed stage, ranging from 1200 r/min to 3600 r/min. On the contrary, the bearings with oil jet lubrication were better than those with splash lubrication by an average of 31.8% when the bearing speed was in the high-speed stage, ranging from 4800 r/min to 6000 r/min. [ABSTRACT FROM AUTHOR]

The distribution of lubricant flow field inside the two‐stage transmission reducer is very complicated during splash lubrication, which is difficult to be visually simulated and analysed using traditional finite element methods (FEM). There are many problems in model processing, algorithm selection, mesh division, and computational workload. Through sufficient investigation and experimental validation based on literature, the moving particle semi‐implicit (MPS) method is proposed to study the splash lubrication characteristics of a rail vehicle reducer. Through this method, the visual simulation calculation of multiple working conditions of reducer with complex structure is realised, and the unreasonable structure of the gearbox body is optimised. The model of oil supply demand in the Hertz contact zone of gear transmission is established, and the time‐domain variation law of oil particles number in the contact zone and oil supply state are analysed. It is found that the optimised reducer model can meet the demand of oil supply under the four typical working conditions of the rail vehicle. The higher the initial oil volume is, the more sufficient the oil supply is. Compared with the working temperature conditions of 20 and 80 °C, the lubrication effect is better at 40 and 60 °C. By analysing the power loss proportion of each gear, it is found that the sum of power loss of gear 1 and gear 2 is dominant under different working conditions, reaching 76%–99.5% of the total churning power losses. [ABSTRACT FROM AUTHOR]

In order to analyze the lubrication characteristics of the planetary gear transmission of shield main drive reducers, a simulation model of splash lubrication of the single-stage planetary gear train is established using the moving particle semi-implicit (MPS) method. By comparing the distribution of lubricating oil particles, velocity field, pressure field, the number of lubricating oil particles in the meshing area of gear teeth and the churning resistance moment produced by each rotating part during the planetary gear train movement under different working conditions, the influence of input speed, initial oil level height and oil temperature on the system lubrication effect and churning loss power are studied. The results show that the oil particle velocity and pressure increase with the increase of the input speed and oil level, and the low speed and oil level height will lead to the uneven distribution of oil particles in the reducer. The number of particles in the meshing zone between planetary gears, sun gears and inner gear rings decreases with the increase of input speed and oil temperature, and decreases with the decrease of oil level height. The meshing area of sun gears is the risk area of poor lubrication. The power loss of the system is most significantly affected by the input speed, and increases exponentially with the increase of the speed, while the influence of oil level height and oil temperature is relatively small. In each working condition, the churning loss power generated by the three planetary gears takes the largest proportion in the total churning loss power.

This paper presents comparable sets of the no-load power loss as a product of windage and churning behaviors of a family of various rotating parts (i.e., disc, spur gear, straight bevel gear, and orthogonal face gear). Experimental measurements were carried out under pure air only and under partial immersion in oil to qualify and quantify the windage and churning effects of no-load power losses of a family of spur, bevel, and face gears along with a representative disc as the baseline. Aiming at exploring the influence of gear teeth on the total no-load power losses, two different theoretical analytical approaches are introduced to account for the churning contributions, by which the total power losses are estimated. Both analytical approaches compare well with the experimental findings. Furthermore, a spatial intersecting cross-axis gear (e.g., straight bevel gear and orthogonal face gear) results in higher no-load power losses than that of a representative disc or a parallel-axes gear. The significance of gear teeth (gear vs. disc) on windage behavior is presented, as well as the gear windage effects on the churning phenomenon in a high-speed splash-lubricated gear.

In order to clarify the effect of mixed lubrication methods on the oil flow and power loss of the gearbox, this study adopts a high-precision moving particle semi-implicit (MPS) method to investigate the lubrication of the gearbox under the joint influence of splash lubrication and oil injection lubrication. The accuracy of the numerical method to calculate the churning torque was verified by the constructed test rig. The effects of rotational speed, immersion depth, injection volume rate, and oil injection angle were analyzed and evaluated for lubrication. The results show that better lubrication can be achieved with relatively small churning torques by using a hybrid lubrication method. This provides some references for engineering applications of gearboxes.

To study the oil film deposition characteristics of splash lubricated gears and determine whether their meshing area is completely lubricated, this study proposes the concept of judging the splash lubrication-deposition characteristics-inlet oil film thickness-lubrication effect. The critical oil film thickness that characterizes the full lubrication of the gear meshing area was obtained as 14.5428 µm by using elastohydrodynamic lubrication (EHL) theory. Based on computational fluid dynamics (CFD) method, based on the renormalization group (RNG) k-ε two-equation turbulence model, dynamic mesh model and volume of fluid (VOF) model, the numerical calculation of the intermediate gearbox in splash lubrication is carried out. The oil film deposition thickness of the gear tooth that was about to enter the meshing area was calculated to be 95.6207 µm. It was found that the meshing area is fully lubricated under the rated operating conditions. [ABSTRACT FROM AUTHOR]

The transient lubrication conditions of rolling bearings are different in gearboxes and bearing testers. It has been observed that samples of qualified rolling bearings tested in rolling bearing testers often fail and do not meet lifespan requirements when employed in other lubrication conditions. This may be caused by different factors affecting the bearing in testing and applying lubrication. Needle roller bearings were selected for this study to investigate the causes of this phenomenon in terms of lubrication. Based on the computational fluid dynamics (CFD) method, fluid domain models for the same type of rolling bearings with different lubrication conditions were established. The transient flow fields of rolling bearings with oil jet lubrication in a tester and splash lubrication in a planetary gearbox were simulated. The air–oil transient distribution of rolling bearings in two kinds of lubrication was analyzed. The results indicate that the rotational speed significantly affected the oil jet lubrication of the needle roller bearing. The average oil volume fraction rose by 0.2 with the increase in the bearing speed from 1200 r/min to 6000 r/min and by 0.06 with the increase in the oil jet velocity from 8 m/s to 16 m/s. The splash lubrication of the bearings in the planetary gearbox was directly related to the immersion depth of the rolling bearings in the initial position. Meanwhile, the splash lubrication of the bearings was also affected by other factors, including the initial layout of the planetary gears. The increase in speed from 1200 r/min to 6000 r/min made the average oil volume fraction of splash lubrication decrease by 4.4%. The average oil volume fraction of the bearings with splash lubrication was better than that with oil jet lubrication by an average of 41.9% when the bearing speed was in the low-speed stage, ranging from 1200 r/min to 3600 r/min. On the contrary, the bearings with oil jet lubrication were better than those with splash lubrication by an average of 31.8% when the bearing speed was in the high-speed stage, ranging from 4800 r/min to 6000 r/min.

As one of the basic energy dissipations for one orthogonal face gear running partially submerged in an oil bath, there is no open literature concerned on the churning power losses of the face gear. This paper proposed a series of formulas to predict the churning losses for one orthogonal face gear running partially submerged in an oil bath. The analytical model of churning drag forces is based on fluid mechanics and boundary layer theory which enables quantitatively calculating the influences of the rotating speed, fluid attributes, and gear geometric construction with the minimum effort. Then, an ad hoc test bench was set up to carry out the specific splash lubrication tests for single face gear at different rotating speeds and initial immersion depth. Finally, considering both the churning and windage effects, a physical-based model adopting the real-time immersion depth instead of the static immersion depth is developed to calculate the total load-independent losses of a splash lubricated face gear. From this, the theoretical results are compared well with sets of directly measured experimental findings. Meanwhile, the model is also exploited to quantitate the contributions of each part in the total load-independent losses for one face gear under splash lubrication condition.

In this paper, a numerical simulation model of the flow field in a gearbox with an oil volume adjusting device is established for the first time to study its influence on the lubrication characteristics of a high-speed electric multiple unit (EMU) gearbox. The moving particle semi-implicit (MPS) method is used to numerically simulate the internal flow field of the gearbox of the high-speed EMU under working conditions. The effects of the velocity of the high-speed EMU, the immersion depth, and the oil sump temperature on the power loss of the gears and the lubricant quantity of each bearing are studied and provide an effective tool for the quantitative evaluation of the lubrication characteristics of the gearbox. The lubrication characteristics of the gearbox under different working conditions are studied when the oil volume adjusting device is closed and opened. The results show that the oil volume adjusting device mainly changes the amount of lubricant stirred by the output gear by changing the flow rate of lubricant from the cavity pinion (Cavity P) to the cavity gear (Cavity G), and thus affects the power loss of gears and the lubricant quantity of each bearing. [ABSTRACT FROM AUTHOR]

Lubricating oil flow characteristics are the primary concern in the main reducer of light helicopters. To improve the lubricating performance of the main reducer, a special lubrication system is innovatively constructed by adding two oil-guiding tubes to the hub of the output gear, and the influence of the oil-guiding tubes is investigated through CFD (computational fluid dynamics) techniques. A CFD model of the gearbox integrated with the VOF (volume of fluid) technique was established to explore the flow characteristics of the oil–air two-phase flow inside the gearing system. To validate the proposed CFD model, a specialized testing rig is devised and manufactured to examine the features of oil distribution. The effects of the structure parameters of the oil-guiding tubes and operating conditions on the lubrication performance are explored. Comparing experimental and numerical findings reveals that the inner diameter of the oil-guiding tube and the rotational speed of the driven gear have a significant influence on the lubrication performance. In contrast, the length of the installation end of the oil-guiding tube, its angle, and the oil-immersion depth show little impact. [ABSTRACT FROM AUTHOR]

Among ever-increasing demands for low power consumption, low weight, and compact reducer systems, an oil-guiding splash lubrication method integrating the oil-guiding cylinder and pipes is suggested to be more suitable for light helicopters, instead of conventional splash or oil jet lubrication. Aiming at improving the lubrication and cooling performance of this special lubrication method, this paper introduces an oil-guiding channel to increase oil quantity reaching the driving gear, bearings, and spline. Firstly, the lubrication and cooling effect of the oil-guiding channel in the main gearbox is investigated at various speeds and oil depths by leveraging with a computational fluid dynamics (CFD) technique. Then, a specialized test bench is set up and utilized for experiments to verify the CFD study. These results show that the numerical results are very satisfactory with the data of experimentation, and the maximum value of relative errors is no more than 15%. What is more, the oil flow rate passing through the monitoring plane with the oil-guiding channel is much greater than that without the channel by about three orders of magnitude. It also suggests that the oil-guiding channel could dramatically increase the lubricating oil in the meshing gear pair, and significantly improve the lubrication and cooling effect. [ABSTRACT FROM AUTHOR]

Despite recognizing the importance of cooling within gear systems, there is a lack of clear design guidelines to minimize churning losses while enhancing heat dissipation performance. This study proposes a reliable approach to modeling using a steady-state approximation methodology based on heat-flow coupling for multiphysics around shrouded gears. Computational analyses reveal a distinctive multiphase flow induced by pressure gradients. The efficacy of the proposed methodology is empirically verified through its ability to characterize lubricant distribution and churning losses in splash lubrication systems. Furthermore, an innovative shroud optimization framework is introduced to regulate friction and collision between fluid particles and gear surfaces, enhancing splash lubrication performance. A genetic algorithm is employed within this framework to obtain shroud configurations for gears with a higher wall heat transfer coefficient (WHTC) and lower resistance torque. Implementing the optimal shroud design achieves a trade-off in terms of a notable 13.7% reduction in resistance torque alongside 11.6% and 4% increments in WHTC for the tooth root face and tooth face, respectively. This signifies enhanced reliability in multiphysics governing gearbox functionality, thereby providing valuable guidance for the design of shrouded gear systems. [Display omitted] • A steady-state approximation modeling methodology based on heat-flow coupling. • The evolution of the resistance torque and wall heat transfer coefficient of the gear with different shroud configurations. • A shroud optimization framework that overcomes the uncertainty of multiple physics. • Reduction in resistance torque by 13.7%. • Improving the wall heat transfer coefficient of the tooth root by 11.6%. [ABSTRACT FROM AUTHOR]

Based on computational fluid dynamics, a two-phase flow model was established to calculate the churning power loss of the spiral bevel gears under splash lubrication. The error between the simulation results and experiment results is only 7.04%. Taking a certain helicopter as an example, the churning power loss of the intermediate gearbox is ∼2.6051 kW, accounting for ∼1.93% of the input power. Besides, the motion mechanisms of free flow, ejection flow and splashing flow of the spiral bevel gear were investigated. The influences of the rotational speed and oil immersion depth on the churning power loss were analysed. The rotational speed and oil immersion depth of the intermediate gearbox should be in the range of 3000–5000 r/min and 17–26 mm, respectively, which can ensure sufficient lubrication and low churning power loss. [ABSTRACT FROM AUTHOR]

During splash lubrication, the distribution of the lubricant flow field inside the secondary transmission gearbox was very complicated. The traditional finite element method was difficult to perform visual simulation analysis. Based on sufficient research and a large number of preliminary calculations, the MPS method was proposed to study the splash lubrication characteristics of the secondary transmission gearbox for rail vehicles. The low field characteristics of the gearboxes under different input shaft speeds, initial lubricating of volumes and ambient temperature were analyzed, and the visual calculation of gearbox splash lubrication was realized. The time-domain variation of the number of off particles at the gear meshing points was analyzed under different operating conditions' and it is found that the number of particles at the meshing points has little relationship with the speed, and was positively correlated with the initial low volumes. The number of lubricating off particles in the meshing area is the largest at 40 °C and the lubrication effectiveness is the best. The gear churning power losses of the gearbox under various operating conditions were analyzed, and it is found that the gear churning power losses are positively correlated with the input shaft speeds and the initial off volumes, and negatively correlated with the ambient temperature increment, and both of the relationship is of nonlinear feature. [ABSTRACT FROM AUTHOR]

Based on the computational fluid dynamics (CFD) method, the performance of the oil-guiding cylinder, a key component in a novel splash lubrication system of the helicopter main reducer, was investigated in terms of three different kinds of structures. The pressure and velocity distribution characteristics were firstly simulated and analysed. The numerical simulations indicated that the oil free surface formed in the rotating cylinder was a paraboloid, meanwhile the structure without a bottom flange can achieve the splash effect constantly. Furthermore, the experimental findings agreed well with the numerical results, it was verified that the cylinder with a cylindrical-shaped lower wall surface gave a better lubrication performance than the conical-shaped. Besides, it was found that the oil volume increased with the rotating speed and oil level increasing, and the geometry parameters of the oil-guiding cylinder and the operating conditions have a great effect on the oil-guiding splash lubrication performance. [ABSTRACT FROM AUTHOR]

• Introduction of a technique for directing splash oil streams via a shroud. • Development of a transient CFD model to illuminate the directional oil transport. • Oil transport driving mechanisms of shrouded wheel. • Effects of shroud design and gear speed on the directional oil transport. Supplying oil to bearings rapidly over long distances presents a challenge for splash lubrication systems in drive axle main reducers (DAMRs), mainly because of inadequate driving forces. To mitigate this issue, a novel strategy was introduced to control the splash oil flow via a shroud, which enabled directional oil transport. We developed a transient modeling framework to comprehensively investigate the temporal and spatial evolution mechanisms of splash oil. This framework, validated through empirical studies, navigates the uncertainties and multiscale properties of the multifaceted physics induced by the dynamic boundaries of a shrouded gear. Several operating scenarios were simulated to investigate the driving mechanism of directional oil transport within the shroud, as well as the effect of shroud design and rotational speed on splash lubrication performance. Results demonstrate that the pressure gradients inside and outside the shroud govern the directional transport of the splash oil flow. The bearings located distally on the sump receive a considerable volume of oil (maximum flow rate exceeding 11 L/min) from the upper passage. Concurrently, the churning losses in the DAMR are reduced by >30 % when the wheel is shrouded in comparison to an unshrouded scenario. Moreover, interactions involving friction and collision between the gear and fluid particles intensify with increasing speed and enhance shroud sealing. This study provides a valuable mechanism for investigating oil transport in splash-lubricated DAMRs. [Display omitted] [ABSTRACT FROM AUTHOR]

Lubricating oil flow characteristics are the primary concern in the main reducer of light helicopters. To improve the lubricating performance of the main reducer, a special lubrication system is innovatively constructed by adding two oil-guiding tubes to the hub of the output gear, and the influence of the oil-guiding tubes is investigated through CFD (computational fluid dynamics) techniques. A CFD model of the gearbox integrated with the VOF (volume of fluid) technique was established to explore the flow characteristics of the oil–air two-phase flow inside the gearing system. To validate the proposed CFD model, a specialized testing rig is devised and manufactured to examine the features of oil distribution. The effects of the structure parameters of the oil-guiding tubes and operating conditions on the lubrication performance are explored. Comparing experimental and numerical findings reveals that the inner diameter of the oil-guiding tube and the rotational speed of the driven gear have a significant influence on the lubrication performance. In contrast, the length of the installation end of the oil-guiding tube, its angle, and the oil-immersion depth show little impact.

Among ever-increasing demands for low power consumption, low weight, and compact reducer systems, an oil-guiding splash lubrication method integrating the oil-guiding cylinder and pipes is suggested to be more suitable for light helicopters, instead of conventional splash or oil jet lubrication. Aiming at improving the lubrication and cooling performance of this special lubrication method, this paper introduces an oil-guiding channel to increase oil quantity reaching the driving gear, bearings, and spline. Firstly, the lubrication and cooling effect of the oil-guiding channel in the main gearbox is investigated at various speeds and oil depths by leveraging with a computational fluid dynamics (CFD) technique. Then, a specialized test bench is set up and utilized for experiments to verify the CFD study. These results show that the numerical results are very satisfactory with the data of experimentation, and the maximum value of relative errors is no more than 15%. What is more, the oil flow rate passing through the monitoring plane with the oil-guiding channel is much greater than that without the channel by about three orders of magnitude. It also suggests that the oil-guiding channel could dramatically increase the lubricating oil in the meshing gear pair, and significantly improve the lubrication and cooling effect.

In this study, we propose a computational fluid dynamics (CFD)-based method to study the lubrication and temperature characteristics of an intermediate gearbox with splash lubrication. A volume of fluid (VOF) multiphase model was used to track the interface between oil and air. A multiple reference frame (MRF) model was adopted to accurately simulate the movement characteristics of the gears, bearings, and the surrounding flow field. The thermal-fluid coupling computational model of an intermediate gearbox with splash lubrication was then established. Combined with experimental results, we verified that the lubricating oil temperature was below the limit requirement (<110 °C). The numerical results revealed that large amounts of lubricating oil were splashed onto the tooth surfaces near the gear meshing area. A large convective heat transfer coefficient corresponds to a low gear tooth surface temperature. The tooth surface temperature of the driving gear is higher than that of the driven gear. The distribution law of oil volume fraction of the bearing roller was jointly affected by the roller rotation direction and gravity. The convective heat transfer coefficient of the roller wall was largely related to the lubrication environment of the roller, including the oil distribution inside the bearing cavity and the flow rate. [ABSTRACT FROM AUTHOR]

The oil distribution and churning loss are the main concerns in the design of a lubrication system for a gear transmission. This article describes a numerical method of simulating the splashing oil flow in a hypoid gearbox, obtaining the oil distribution, and calculating the churning loss. A three-dimensional numerical model is built to simulate the complex oil flow when hypoid gears splash oil inside the box. The volume of fluid (VOF) model is applied to describe the oil-air two-phase flow characteristics. In addition, the flank-moving technique is introduced to overcome the difficulty of generating cells in the tooth-meshing zone. To validate the numerical approach, a test rig is designed to observe the oil distribution in the gearbox and measure the churning loss of the hypoid gears. The comprehensive experimental investigation illustrates that the numerical results correspond well with the measured results. The results of this article show that the numerical method can accurately predict the complex oil flow in a hypoid gearbox and provide a numerical approach for investigating the oil flow and churning loss inside real-vehicle axle housing. This model can serve as a design optimization tool in the future.

In the present study, no-load losses of different splash lubricated spiral bevel gears were measured. The authors used a specific test rig, and a set of gears, to investigate churning losses at higher tangential speeds: up to 60 m/s. An uncommon behavior of the drag torque was highlighted: the torque increased with the rotational speed until a local maximum was reached; then the torque decreased and a local minimum was noticed; at higher rotational speed the torque increased. The torque decrease seems to be linked with a windage phenomenon, which becomes non-negligible at such speeds. In this work, efforts were made to characterize this reduction of gear immersion depth in order to be able to predict no-load losses. It was found that the evolution of oil immersion was linked to a Froude number. Finally a new analytical model of no-load losses was developed for churning losses combined with windage effects. This formulation takes into account several parameters such as rotational speed, gear immersion depth, oil properties, and gear geometrical parameters. [ABSTRACT FROM AUTHOR]

Limited by the space and weight of the reducer, it is difficult to use traditional oil-jet lubrication and splash lubrication for a light helicopter, so an oil-guiding splash lubrication method is adopted as a research object in this paper. Firstly, the lubrication performance of the oil-guiding cylinder in the main reducer under different rotating speeds, oil levels, and flight attitudes is investigated based on the computational fluid dynamics (CFD) method. Then, a specific test rig is developed, and lubrication tests are carried out to verify the feasibility and correctness of the simulation. These results show that oil level, rotating speed, and flight attitude have a great influence on splash lubrication performance.

The splash-lubricated intermediate gearbox of a helicopter is employed to investigate the influence of an oil guide device on lubrication performance in spiral bevel geared transmissions. A CFD (Computational Fluid Dynamics) numerical model of the gearbox which is mainly composed of an oil guide device, spiral bevel gears and the casing wall is built to study the oil distribution inside the gearbox. The present CFD model is validated by comparing experimental results and corresponding simulation ones. Influences of the oil tank capacity, the hole diameter and the fillet radius of oil guide tubes on the oil flow rate in the oil guide tubes are analyzed. It is shown that the hole diameter and the fillet radius of oil guide tubes can exert important influence on oil flow rate in the oil guide tubes while oil tank capacity does the reverse; the oil guide device structure has little influence on the oil flow of contact zone of gear pair and churning power losses in the spiral bevel gearbox. [ABSTRACT FROM AUTHOR]

Transmission efficiency is the main concern in the design of lubrication systems for gear transmission systems, such as the vehicle axle. This paper presents an optimization method to reduce the churning loss and improve the transmission efficiency in an axle based on computational fluid dynamics and the response surface method. A simplified model was applied to determine the optimal solutions to reduce the churning loss of the wheel. The response surface models were constructed based on the numerical and orthogonal experiments to approximate the relationship between the related structures and the churning loss. A multi-objective optimization model was developed to reduce the churning loss at speeds of 50 and 90 km/h. The multi-objective optimization method of non-dominated sorting genetic algorithm-II was applied to determine the Pareto front of the optimal solutions for the churning loss. A comparative experiment was conducted to validate the optimal effect. The measurements indicate the churning loss in the optimal axle was 10.4–12.3% lower than that in the original axle, and the oil temperature in the optimal axle was approximately 2.1°C lower than that of the original axle. [ABSTRACT FROM AUTHOR]

Transmission efficiency is the main concern in the design of the lubrication system for a gear transmission system, such as a vehicle axle. This paper presents an optimization method to reduce the churning loss and improve the transmission efficiency in an axle based on the computational fluid dynamics and the response surface method. In this study, the computational fluid dynamics method was applied to simulate the lubrication flow in the axle housing. A numerical model was built for the splash lubrication system that included the entire structure of the hypoid gears, bearings, oil passage, and other parts. The numerical results provided direct visualization of the oil flow inside the axle housing, and the numerical predictions for the oil distribution and churning loss were determined from the numerical result. Furthermore, the influences of the speed, oil level, and oil temperature on the churning loss were investigated. The oil distribution results from the numerical calculations were consistent with the experimental observations, and the error in the predictions for the churning loss was less than 9.3%. The results of this study provide a foundation for subsequent optimization work on the lubrication system of a vehicle axle. [ABSTRACT FROM AUTHOR]

Abstract To predict the churning power losses in a gearbox with spiral bevel geared transmission, based on the Computational Fluid Dynamics (CFD) method, a numerical simulation model for the splash lubrication of the intermediate gearbox of a helicopter including gear box housing, a spiral bevel gear pair and an oil guide device is established and validated by the churning power losses prediction of experiments showing a good agreement. With the model, churning power losses of a gearbox with spiral bevel geared transmission are obtained; influences of gear rotational speed, oil fill level, oil temperature, oil dynamic viscosity, oil density, and tilt angle of the helicopter, on the churning power losses are analyzed. Highlights • CFD calculations of churning power losses of a gearbox with spiral bevel geared transmission are performed. • The churning power losses increase with the increase of the rotational speed and the oil fill level of gears • The churning power losses increase with the increase of the dynamic viscosity and density of the oil. • The influence of the helicopter tilt angle on the churning power losses is small and regular. • The present numerical model is validated by experimental results. [ABSTRACT FROM AUTHOR]

The oil distribution and churning loss are the main concerns in the design of a lubrication system for a gear transmission. This article describes a numerical method of simulating the splashing oil flow in a hypoid gearbox, obtaining the oil distribution, and calculating the churning loss. A three-dimensional numerical model is built to simulate the complex oil flow when hypoid gears splash oil inside the box. The volume of fluid (VOF) model is applied to describe the oil-air two-phase flow characteristics. In addition, the flank-moving technique is introduced to overcome the difficulty of generating cells in the tooth-meshing zone. To validate the numerical approach, a test rig is designed to observe the oil distribution in the gearbox and measure the churning loss of the hypoid gears. The comprehensive experimental investigation illustrates that the numerical results correspond well with the measured results. The results of this article show that the numerical method can accurately predict the complex oil flow in a hypoid gearbox and provide a numerical approach for investigating the oil flow and churning loss inside real-vehicle axle housing. This model can serve as a design optimization tool in the future. [ABSTRACT FROM AUTHOR]

In this study, we propose a computational fluid dynamics (CFD)-based method to study the lubrication and temperature characteristics of an intermediate gearbox with splash lubrication. A volume of fluid (VOF) multiphase model was used to track the interface between oil and air. A multiple reference frame (MRF) model was adopted to accurately simulate the movement characteristics of the gears, bearings, and the surrounding flow field. The thermal-fluid coupling computational model of an intermediate gearbox with splash lubrication was then established. Combined with experimental results, we verified that the lubricating oil temperature was below the limit requirement (

This study aims to experimentally investigate churning power losses generated by a planetary gear set which is splash lubricated. To this end, a specific test rig has been used to operate a planetary gear train under unloaded conditions in various configurations within a range of the planet-carrier rotational speed. Churning loss is isolated from the measured drag torque and the effects of several parameters (rotational speed, temperature, oil sump level, planet number…) on this source of dissipation are quantified. Beyond the influence of speed or oil level, it is concluded that the number of planets is of primary importance on churning power losses. Moreover, a first assumption is made concerning the oil sump behavior regarding the experiments: an oil ring is created explaining the evolution of the churning losses measured. In addition, this study compares the churning phenomenon occurring in cylindrical gear trains with the one observed during the experiments. It is shown that the approach used for conventional gear trains cannot be used for epicyclic ones: in planetary gear sets the centrifugal effects are predominant whereas the gravity forces have a larger influence on the free surface flows which occur in cylindrical gear sets.

To investigate the influence of the dynamic motion of a gearbox on lubricating flow field and churning power losses under splash lubrication, a computational fluid dynamics (CFD) method based on a combination of the fluid of volume (VOF) method and turbulence model is presented in this paper. A non-inertial coordinate system was employed to simulate the motion of the gearbox, and the feasibility and accuracy of the method was validated by the available experimental results. Numerical models of the gearbox with a spur gear pair under no load operation condition were established, and sinusoidal motions with different frequencies and amplitudes were implemented in the gearbox. The effects of the rotational speed of gears, oil immersion depth, and the frequency and amplitude of sinusoidal motions were studied. The results showed that the dynamic motion of the gearbox can exert a significant influence on churning losses and the oil supply of the gear contacting zone, and the gear pair may be in a loss-of-lubrication state.

A new rotatable test rig is developed to perform oil churning loss experiments to clarify the influence of the relative position of gears and casing wall shape of gear box under splash lubrication condition. Torque losses are measured and photos are taken using a stroboscope to observe the oil behavior. Based on the test results, it has been confirmed that in addition to the well-known factors, relative position and casing wall shape have significant effects on the churning loss and should be considered in the modeling process, which has been neglected in most previous studies. In this article, the importance of the steady-state oil surface profile (SOSP) is emphasized. New ideas are proposed on how other working conditions such as immersion depth and rotation speed influence the churning loss. [ABSTRACT FROM AUTHOR]

In recent years numerical simulation has become one of the most important means to study the complex oil flow within gearbox. Since the gap between tooth surfaces near the gear mesh zone is quite tiny, it's difficult to get high quality mesh grid near such zone. Further numerical divergence frequently occurs along iterative process with dynamic mesh. To overcome this predicament, some researchers have tried different gear modeling methods to simplify the gear model, such as none-teeth method, cutting-teeth method or gear-separation method. Nevertheless these methods have certain limitation. This paper attended to provide a new practical gear modeling methods called teeth-face-moving method. The method was operated by moving each tooth surface slightly. As the tooth thickness was marginally reduced, the gap between tooth surfaces near the mesh zone was increased to 0.5-1 mm, so that mesh generation in the gap became feasible, which was different from the previous methods, i.e. all of teeth profiles and the center distance of 2 gears were kept as same as the original when using the teeth-face-moving method. To certify the reasonability of this new method, a numerical model for splash lubrication in gearbox was built with different gear modeling methods. The volume of fluid (VOF) method was applied to track the air and oil two-phase flow. And RNG k-e model was introduced to describe turbulence flow considering high fluid strain rate and high bending degree of flow line. Standard wall function was applied to deal with the flow near wall region and low Reynolds number flow. Dynamic mesh method with the spring-based smoothing and local remeshing was used to adapt the motion of gears. Due to more concentrating upon mesh zone, the gear-separation method and the teeth-face-moving method required more grid elements and computational resource than other methods. The numerical results of oil distribution and gears' churning loss were comparatively analyzed. Also the simulated results were made a comparison with the existed experiment data. It was easily observed the quantity of oil splashed by gears with none-teeth method or cutting-teeth methods was obviously less than that with gear-separation method or teeth-face-moving method. The similar phenomenon was acquired from churning loss results as well. The churning loss computed with none-teeth method or cutting-teeth method was far less than the related experimental result. On the contrary the churning loss computed with gear-separation method or teeth-face-moving method showed good agreement with the related experimental result. The direct reason was tip diameter and teeth profile had a strong influence on the oil flow in the gearbox. So cutting all or partial teeth may lead unreliable simulation result for splash oil flow. It seemed that the gear-separation method got the result close to the teeth-face-moving method. Unfortunately the center distance of 2 gears had to be increased for the gear-separation method. This was unacceptable in real engineering case because changing the position of gear may lead to related bearings or shaft intersected with other structures, such as bearing base and gearbox housing. So the conclusion is drawn that the teeth-face-moving method not only provides more credible prediction for oil flow in the gearbox, but also has more practicability for complicated engineering situation and hence is superior to the previous gear modeling methods. The teeth-face-moving gear modeling method is quite beneficial to lubrication simulation for real engineering gear system, such as truck axle or vehicle transmission. And further work of applying this new method on complicated machinery is underway. [ABSTRACT FROM AUTHOR]

It is currently assumed that churning losses can be described by using only two physical parameters representative of the lubricant properties; that is, density and viscosity. To verify this hypothesis, a number of transient measurements were carried out on a specific gear test rig over a range of oil temperatures. It appears that, for high temperatures and/or high rotational speeds, the drag torque can suddenly increase with a larger Reynolds number. Based on extensive online lubricant aeration measurements, it is demonstrated that this particular behavior can be related to churning losses when the fraction of air in the lubricant reaches a certain threshold. In order to quantify the influence of oil sump aeration on churning losses, a simplified original model, based on surface tension and lubricant aeration, is proposed. This study shows that density and viscosity are not sufficient to estimate churning losses under some specific operating conditions and the need to account for other physical properties of the lubricant is emphasized. [ABSTRACT FROM AUTHOR]

Limited by the space and weight of the reducer, it is difficult to use traditional oil-jet lubrication and splash lubrication for a light helicopter, so an oil-guiding splash lubrication method is adopted as a research object in this paper. Firstly, the lubrication performance of the oil-guiding cylinder in the main reducer under different rotating speeds, oil levels, and flight attitudes is investigated based on the computational fluid dynamics (CFD) method. Then, a specific test rig is developed, and lubrication tests are carried out to verify the feasibility and correctness of the simulation. These results show that oil level, rotating speed, and flight attitude have a great influence on splash lubrication performance. [ABSTRACT FROM AUTHOR]

To study the influence of dynamic flight attitudes on the splash lubrication performance and churning power losses of the intermediate spiral bevel gearbox in a helicopter, a three-dimensional (3D) simulation model consisting of a spiral bevel gear pair, two bearing caps with oil guide holes and the housing is established, and CFD (Computational Fluid Dynamics) simulations with main flight attitudes are performed. The influences of turning directions, rotational speeds, circling attitude and accelerations on the distribution of lubricating oil, the flow rate of oil guide holes and churning power losses are discussed. A test rig for studying the splash lubrication performance of a gearbox under different dynamic attitudes is developed, and the feasibility of the present simulation method is validated by experiments. • The flow rate of the oil guide holes located on the same side of the turning direction under turning attitude is higher than that of the other side. • The oil inside the gearbox deflects to one side due to the centrifugal force under circling attitude. • The presence of acceleration increases the fluctuation of the oil and the flow rate of the oil guide holes on the driven gear bearing cap. • The churning losses increase as the acceleration of the gearbox increases. • In experiments, the churning losses increase with the increase of the rotational speed of gears under the declination and reciprocating attitude. [ABSTRACT FROM AUTHOR]

To investigate the influence of the dynamic motion of a gearbox on lubricating flow field and churning power losses under splash lubrication, a computational fluid dynamics (CFD) method based on a combination of the fluid of volume (VOF) method and turbulence model is presented in this paper. A non-inertial coordinate system was employed to simulate the motion of the gearbox, and the feasibility and accuracy of the method was validated by the available experimental results. Numerical models of the gearbox with a spur gear pair under no load operation condition were established, and sinusoidal motions with different frequencies and amplitudes were implemented in the gearbox. The effects of the rotational speed of gears, oil immersion depth, and the frequency and amplitude of sinusoidal motions were studied. The results showed that the dynamic motion of the gearbox can exert a significant influence on churning losses and the oil supply of the gear contacting zone, and the gear pair may be in a loss-of-lubrication state. [ABSTRACT FROM AUTHOR]