Gear Power Loss Research Articles

Classification of numerical, experimental, and analytical approaches for gearbox oil flow and no-load gear power loss

The interaction of rotating machine elements with fluid in gearboxes results in fluid flow and no-load power loss. A targeted design of the gearbox lubrication system enables a reliable operation under economical and sustainable use of lubricant. This study focuses on the influence of various parameters on the oil flow and no-load gear power loss of a dip-lubricated single-stage gearbox. Numerical, experimental, and analytical results are presented and compared. A single numerical simulation setup without parameter-specific tuning is applied for a wide range of parameters. The evaluated wetted gear surface strongly depends on the circumferential speed and shows a strong correlation with the resulting no-load gear loss torque. At lower circumferential speed, the wetted gear surface decreases before increasing at higher circumferential speed. Numerical and experimental results show good agreement in terms of magnitude and trend. The analytical approaches underestimate the numerical and experimental results. Nevertheless, they do provide a good representation of the trends in terms of the influence of immersion depth and rotation direction.

Research on characteristics of splash lubrication and power losses of reducer based on MPS method

AbstractThe 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.

Generalized analytical model for evaluating the gear power losses transition changing from windage to churning behavior

Although splash lubrication is usually adopted in the intermediate or tail gearbox of helicopters at low or moderate speed, and it appears that the oil jet lubrication used in a high-speed main reducer of helicopters would be turned into the splash lubrication that only a small part of gears is immersed in the oil sump due to the lubricating oil deposition by the mismatch between the oil feed and return. The classic drag power losses model is either used for the churning behavior of common splash lubrication or the windage behavior of oil jet lubrication, and is no longer suitable for this transition phenomenon of these two behaviors coexist. In this paper, a theoretical analytical method by introducing the windage contribution factor and air-oil ratio evolution model is proposed to predict the associated power losses for one single spur gear rotating partially immersed in an oil bath. To verify the accuracy and correctness, the theoretical calculations are then compared with the existing experimental data from Quiban et al. [33]. Based on this method, a generalized analytical model to evaluate the gear drag power losses for the windage, churning phenomenon and their transition behavior are established.

Studi Efisiensi Sistem Reduction Gear pada Pembangkit Listrik Tenaga Gas

Gas p ower p lants produce electrical energy by a generator driven by a gas turbine through a rotational transmission device called a Reduction Gear. Reduction gear consists of two rotating gears tangent to each other with different diameter sizes. This difference in diameter size makes the output side shaft of the reduction gear, which has a larger diameter, rotate slower than the input side shaft of the reduction gear which has a smaller diameter of the gear. Analysis of the performance of the reduction gear device is done by calculating its efficiency. In this study, the total power loss is 459.18 kW where the gear power loss (Pvz) is 112.53 kW, the bearing power loss (Pvz0) is 342.24 kW, and the power loss due to seals (Pvs) of 4.41 kW. With an input power of 33,000 kW, the efficiency of this reduction gear is 98.61%.

The design of a new type coaxial multilayer rotor helicopter vehicle

Today’s small rotor helicopter vehicles mostly use electric motors and batteries as power sources. Most helicopter power configurations are either front powered or rear powered, causing the center of the helicopter to be offset. This kind of offset should be overcome by structural compensation or by adjusting the angle of attack of the blades, but some lift of the angle of attack will be sacrifice at the same time. This paper proposes a new type of electric helicopter powertrain design. The advantage of new type helicopter design is setting the centre of gravity at the centre position of helicopter. The main shaft of the helicopter through the power transmission method of the electric motor built into the internal gear of the star gear, which improves the design of the center offset of the helicopter. That is improved the flight stability of the helicopter. At the same time, in terms of power transmission, the motor power consumed by the primary gear power of the star gear, while the traditional helicopter power transmission method has three or four gear power losses. The new concept of electric motor with star gear structure proposed in this paper can effectively reduce the transmission power loss of the gear. In addition, the distributed power control system proposed in this paper also reduces the possibility of helicopter crash due to motor failure.

Analysis of a Low-Loss Gear Geometry Using a Thermal Elastohydrodynamic Simulation including Mixed Lubrication

Low-loss gears are an interesting design approach for increasing the efficiency and thermal load limits of gearboxes. The loss-optimized gear geometry concentrates sliding around the pitch point, which results in low load-dependent gear power losses. In this study, a method for modeling transient EHL (elastohydrodynamically lubricated) contacts in gear mesh considering mixed lubrication and thermal effects is introduced and applied to analyze the tribological behavior of a low-loss gear geometry. Special focus is placed on local frictional losses to analyze the role of the thermal effects of the gear mesh. Although a thermal reduction in fluid friction is observed, the overall effect on total frictional losses of the low-loss gear geometry is evaluated to be very small. The edge geometry strongly influences the lubricant film thickness and frictional power losses.

Using the Box–Behnken Response Surface Method to Study Parametric Influence to Improve the Efficiency of Helical Gears

Studying gear power loss theoretically and determining the efficiency of a helical gear drive depend on many geometrical and working parameters, such as rotation speed, tooth number, gear ratio, helix angle, and torque, among others. In this paper, the Plackett–Burman screening design and the Box–Behnken response-surface method are used to consider how the above parameters influence gear drive efficiency, and experimental models are provided to evaluate these influences. The present results can be used to select the efficiency when calculating and designing gear transmissions and to choose the parameters for improving gear transmission efficiency.

Frictional dynamic model predictions of FZG-A10 spur gear pairs considering profile errors

In this work, a nonlinear dynamic model of an FZG-A10 spur gear was investigated by taking into account for the actual time-varying gear mesh stiffness and the frictional effects between meshing gear teeth to evaluate the influence of the dynamic effects on frictional gear power loss predictions. The equations of motion of the generalized translational-torsional coupled dynamic system derived from Lagrange principle was extended compared to authors’ previous work in order to account for time dependent coefficient of friction and profile errors. The dynamic response of spur gears, computed by an iterative implicit scheme of Newmark, is changed due to the presence of coefficient of friction and profile errors. A dynamic analysis was performed and the influence of frictional effect including tooth shape deviations, in particular, was scrutinized since a time-dependent coefficient of friction is deeply related to the gear surface roughness and all parameters dependent on gears error profiles are introduced in the proposed model. The predicted meshing gear power losses with constant and local friction coefficient were compared. The influence of constant and variable profile errors considered in the local coefficient of friction formulation was also studied and their corresponding root mean square (RMS) power loss was compared to the experimental results. The results using FZG A10 spur gear pairs running under several operating conditions (different loads and speeds) validate the superiority of the proposed model against previous similar models.

Thermal Modeling of the FZG Test Rig: Application to Starved Lubrication Conditions

During their lifetime, gears may undergo starved lubrication operating conditions. Starvation has an impact on friction between gears and leads to modified gearbox efficiency. In this article, lubricant starvation tests on an FZG test rig adapted to this condition are presented. Gears were equipped with an embedded thermocouple sensor to measure their operating bulk temperature. An experimental method to isolate the test box power loss of the FZG machine is proposed. A thermal model of this test rig draws up the power loss distribution into the test box for a nominal condition of lubrication. A numerical method based on experimental results is proposed to estimate gear power loss variation during lubricant starvation.

Partial EHL friction coefficient model to predict power losses in cylindrical gears

The accurate prediction of friction coefficient and power losses in the gear mesh is a key subject to several gear-related fields of study. However, there is still not a unified method for large ranges of operating conditions, different gear geometries and lubricant types. The current paper meets this demand by modelling partial EHL friction with an asperity-fluid load sharing approach where fluid traction is calculated with the Ree-Eyring equation and the reference stress behaviour is predicted from piezoviscosity coefficient. It will be shown that only an accurate description of the lubricant’s viscosity behaviour is required to compute friction in gears. Finally, mesh power losses are predicted considering thermal effects and numerical predictions are compared to experimental results showing good agreement.

Numerical modelling of oil distribution and churning gear power losses of gearboxes by smoothed particle hydrodynamics

Sufficient oil supply of all machine elements in gearboxes is usually required to avoid damage during operation. Quite frequently, transmissions are conservatively designed with an oversupply of oil to guarantee operational reliability. An oversupply of oil results in an unnecessarily high amount of oil being kept in motion, which in turn leads to excessive hydraulic gear power losses. In high-speed gearboxes in particular, churning losses can contribute greatly to the total power losses. Further detailed information on the oil distribution in gearboxes is needed in order to increase the efficiency and operational reliability of gearboxes. Computational Fluid Dynamics methods provide a flexible way of investigating oil behaviour in transmissions with almost no restrictions regarding geometry and operating conditions. Generally, there are two main methods of computational fluid dynamics simulation in gearboxes: the traditional finite-volume based method (Eulerian approach) and the mesh-free particle-based method (Lagrangian approach). In this work, a computational fluid dynamics model based on the particle-based smoothed particle hydrodynamics method is built to investigate the oil distribution and churning losses of a dip-lubricated single stage gearbox on an efficiency gear test rig. Results are shown and discussed for different rotational speeds and oil temperatures. The smoothed particle hydrodynamics method provides a high potential of predicting the oil distribution of modern dip-lubricated transmission systems. Comparisons with high-speed camera recordings show good agreement. However, the method shows a need for improvement in churning loss prediction.

Finite element method model to predict bulk and flash temperatures on polymer gears

Abstract A FEM thermal model was implemented to predict the bulk and flash temperature of gears in general and polymer gears in particular. Using the capabilities of a gear power loss model previously validated, a solution for the temperature rise and distribution along the tooth is suggested. The accuracy of the power loss model is decisive for the prediction of gear temperature field by FEM model. The FEM model was validated with experimental results from the literature. The model allows to predict the bulk temperatures for oil jet, dip lubrication or non-lubricated conditions. The FEM model allows an higher accuracy on the calculation of the load carrying capacity of polymer gears, whose mechanical properties are critically dependent on the bulk temperature.

A mixed finite element and analytical method to predict load, mechanical power loss and improved efficiency in non-standard spur gear drives

A reasonably accurate estimation of gear power loss is desirable to maximize gear performance. The load share by teeth pair, contact stress, sliding speed, elastohydrodynamic film thickness and coefficient of friction are some of the most important contributing factors which determine frictional power losses in gears. This paper presents an improvement concept to minimize the load-related power losses (sliding and rolling power losses), which will lead to an enhancement in gear efficiency by selection of non-standard gears. The tooth thickness at the pitch circle of the pinion and gear is different in non-standard gears (kpπm > 0.5 πm and kgπm < 0.5 πm), whereas it is equal in standard gears (kpπm = kgπm = 0.5 πm). In this work, the load share-based frictional power loss and the respective mechanical efficiency have been determined for comparative performance of standard and non-standard gears. Finally, the influence of various gear and drive parameters such as gear ratio, pressure angle pinion teeth number and addendum height factor on gear efficiency has also been investigated and the results of the parametric study are discussed.

Determination of oil distribution and churning power loss of gearboxes by finite volume CFD method

Sufficient oil supply of all machine elements in gearboxes is usually required to avoid damage and to reduce friction during operation. However, dip lubrication and injection lubrication always result in hydraulic gear power losses. Especially in high-speed and dip-lubricated gearboxes with high oil levels, churning losses can represent a significant portion of the total power loss. Current analytical and empirical approaches for examining the churning losses are often limited to certain constraints and operating conditions. Furthermore, they do not provide any information about the oil distribution.CFD (Computational Fluid Dynamics) methods offer a very flexible way to investigate the oil distribution and the churning power losses, with almost no restrictions on the housing shape and operating conditions. In this paper, a CFD model based on the Finite Volume Method (FVM) is built to investigate the oil distribution and the churning losses inside a single-stage gearbox of the FZG back-to-back efficiency gear test rig. Thereby, a three-dimensional finite volume simulation model considering two-phase flow is applied. The results are compared with measurements of the churning losses and with high-speed camera recordings. The comparisons show very good agreement and high potential for predicting the oil distribution and the churning losses in modern transmission systems.

TEHL simulation on the influence of lubricants on load-dependent gear losses

A transient TEHL simulation model based on a finite element formulation and implemented in multiphysics software is applied to study the TEHL contact along the path of contact of spur gears with a focus on load-dependent gear loss of different lubricants. Lubricant properties including the limiting shear stress are based on measurement data. The considered polyalphaolefin and polyglycol oil show significant lower fluid coefficients of friction, maximum TEHL temperatures and local gear power losses than the considered mineral oil. The simulated load-dependent gear power losses of the mineral oil are compared to the measured load-dependent gear power losses in the FZG gear efficiency test rig. Results show very strong correlation when taking into account mixed lubrication.

A comparative study of friction laws used in spur gear power losses estimation

A comparative study of friction laws used in spur gear power losses estimation

Analysis of power losses in an industrial planetary speed reducer: Measurements and computational fluid dynamics calculations

In this work, experimental and theoretical analyses of the power losses in an industrial planetary speed reducer were performed in order to define the weight of the different types of power losses in the global efficiency as well as to understand the appropriateness and the effectiveness of the models and tools available in the literature for the prediction of these power losses. From this investigation, it has emerged that even if for all the kinds of power losses improvements are in principle possible, those for which, at the same time, more improvements seem possible and effective models are lacking are the load-independent power losses. For this reason, a computational fluid dynamics methodology able to evaluate load-independent gear power losses in planetary gearboxes is proposed. The other types of power losses were determined by means of analytical models available in the literature and, together with the calculated load-independent gear power losses, compared with the experimentally determined power losses showing the effectiveness of the adopted calculation models.

Power losses at low speed in a gearbox lubricated with wind turbine gear oils with special focus on churning losses

In this study gear oils were tested for power loss behaviour in a two stage multiplying gearbox, on a back-to-back test rig with recirculating power. The tests were performed at low input speeds and high input torques with oil sump temperature set free.A power loss model simulating the power loss mechanisms was implemented to evaluate gear power losses, but failed to correctly describe the gear churning.Two lubricant flow regimes were identified, which are related to the nature of the fluid circulation, as well as with the gearbox case. A calibration method for the gear churning loss is proposed based on these results and a method to identify the transition between the fluid flow regimes inside the gearbox.

Influence of oil formulation on gear micropitting and power loss performance

This study presents a study of the influence of oil formulation on the protection against gear micropitting and also its influence on gear efficiency. The study had both components because a well-balanced product is necessary and its behaviour must be demonstrated in dedicated tests. The industrial gear oils studied combined polyalphaolefin with ester base oils and had different additive packages. FZG gear power loss tests were performed using 20MnCr5 carburized gears under a wide range of operating conditions. During the tests, the oil and gearbox temperature were continuously recorded and gear oil samples were collected. After the tests, the gear mass loss was measured and oil samples were analyzed by ferrography. Using an energetic model of the FZG test gearbox, it was possible to quantify the influence of lubricant formulation on the average friction coefficient between gear teeth, which will provide a quantitative comparison of lubricants. The gear micropitting protection provided by the oxidized lubricant samples was evaluated in a FZG test rig according to DGMK short micropitting test procedure. During the tests, lubricant analysis, mass loss measurements, surface observation, and topography measurements were performed to evaluate the micropitting evolution along the tests as well as severity of micropitting. The results obtained show that the base oil, the additive package, as well as their combination can have a very significant influence on the efficiency and micropitting performance of industrial gear oil.

Influence of tooth profile on gear power loss

PurposeThe purpose of this paper is to develop innovative geometry for gears aiming low power loss and easy manufacturing.Design/methodology/approachNew gear profiles were developed and studied, and gears were built accordingly and then tested using an FZG machine.FindingsResults from the experimental tests revealed the influence of the profile modifications on the operating temperature, thus on the efficiency of gears (in terms of power loss).Research limitations/implicationsStudied cases were limited to experimental gear models compliant to the FZG machine.Practical implicationsLow‐loss gears can be produced using common technologies and tools. Its design includes power loss minimization besides mechanical strength. The new gears are more environmentally friendly and can operate with lower power consumption, lower temperature, increasing gear and gear oil life.Originality/valueThis work contributes to the development of the “low‐loss gears” concept, adapting it to low‐cost manufacturing technologies. Finally, more efficient gears and gearboxes can be produced only by performing simple geometrical modifications to standard gears.