Numerical and experimental analysis of oil churning lubrication in a face gear drives

To solve the problem of generalized design and batch processing of face gear, a method of tooth surface design and side milling of ruled line face gears is proposed in this paper. First of all, the discrete points of the pitch cone surface of the face gear are calculated, and the straight-line cluster and section curve of the tooth surface is constructed to analyze the deviation of the ruled line face gear. Secondly, the tooth surface model of the ruled line face gear is constructed, and the curvature and contact trace are calculated. Thirdly, the curvature and tangent of the ruled line face gear tooth surface are analyzed, the feed plane of the equidistant surface and the guideline are obtained, the torsion angle of the tooth surface and the distribution of the tangent vector along the generatrix are calculated, and the tool axis position based on the two-point offset method is studied. Finally, the side milling processing test of the face gear is carried out, and the tooth surface of the face gear after side milling is measured. The measurement results verify the correctness of the tooth surface design and the side milling processing method of the ruled line face gear.

Reducing the energy consumption and improving the efficiency of high-speed transmission systems are increasingly common goals; the windage power loss is not negligible in these methods. In this work, the multi-reference frame (MRF) and periodic boundary conditions (PBC) based on the computational fluid dynamics (CFD) method were adopted to investigate the windage phenomena of a single face gear with and without a shroud, and the impact of the gear speed on the windage power loss was analyzed. Furthermore, the effects on the distribution of static pressure due to the distances between the shroud and the gear body in different directions, including the outer radius direction, the inner radius direction, and the addendum direction were investigated. The results indicate that the gear speed significantly affected the windage loss, as the higher the gear speed was, the greater the windage power loss. Additionally, the shroud could effectively reduce the windage power loss, where the optimal distance from the addendum to the shroud was not the minimum distance; however, for the distances from the shroud to the inner radius and the outer radius, the smaller the distance was, the smaller the windage loss. The results can provide a theoretical basis and technical reference for reducing the windage power loss of various face gear drives.

Based on the characteristics of low efficiency and short life cycle of the previous face gear in the clutch, the article puts forward a new type of the face gear. The new face gear can joggle interlaced gear, transfer large torque and extend service life. The article describes the history and recent research of the gear fear, compares the structural characteristics of the previous face gear and the new face gear and analyzes the theory of the strength calculation for the transmission intensity of the new face gear. What's more, simulations based on finite element analysis draw the face gear transmission strength and provide a reliable basis for the strength design of the new face gear.

To further develop the advantages of face gear drives and improve their anti-sticking performance and wear resistance, a novel method using laser cladding as the primary process is proposed; here, grinding processing is used as the secondary process, i.e., achieving tooth surface strengthening of the orthogonal offset face gear using two types of materials to form a material gradient based on a laser cladding technology. Then, grinding processing is performed using a five-axis grinding machining. First, according to the forming principle of the face gear tooth surface, we establish the coordinate system of the orthogonal offset face gear and the gear cutter coordinate system; we also derive the tooth surface equation of the virtual gear cutter and the tooth surface equation of the orthogonal offset face gear. Second, we research the principles of the laser cladding and establish a laser cladding test bed for the orthogonal offset face gear. Based on the analysis of the design of the cladding layer and the process parameters of the face gear, the selection of the scanning path, the heat accumulation during the laser cladding process, and the accuracy control of the scanning position, we perform a laser cladding experiment on the offset orthogonal face gear. Third, we establish the machining coordinate system of the face gear based on the machine tool structure and conduct a grinding experiment for the face gear after the cladding process. Finally, we analyze the morphology and hardness of the face gear after grinding. A bench test verification of the axle face gear transmission system is completed. The results show that the precision and surface hardness of the tooth surface are significantly improved after grinding. Meanwhile, the accuracy and feasibility of the laser cladding surface of the face gear are verified.

In order to further improve the grinding efficiency of face gear, this paper presents a novel method for grinding face gear along contact trace using disk CBN wheel. Firstly, the grinding principle of face gear is studied, and the tooth surface equations of rack and gear shaper cutter are derived, thus formulating the tooth surface equation of disk CBN wheel. Secondly, considering the structure of the face gear grinding machine tool and the impact of the grinding wheel parameters on the face gear tooth surface, the disk CBN wheel configuration is proposed, and the calculation method of the tool position of the face gear grinding is established. Thirdly, according to the structural characteristics of the grinding wheel, the tooth surface contact trace of the face gear is designed, and the face gear development grinding processing method along the tooth surface contact traces is presented. Finally, a test of grinding spur face gear with disk CBN wheel is carried out on a laboratory-made five-axis face gear processing machine. The test results verified the correctness of the face gear grinding. Compared with the dish wheel for grinding face gear, the grinding method proposed in this paper can further improve the grinding efficiency of face gear. This method will break new ground for the engineering application of the face gear.

The machining principle and realization method for the continuous generative grinding face gear by a worm wheel are introduced. Based on a five-axis linked CNC grinding machine, a new method is presented to deprive the equation of face gear error tooth surface by assuming the tool surface as the error surface, where actual tool installation position error is introduced into the equation of virtual shaper cutter. Surface equations and 3-D models for the face gear and the worm wheel involving four kinds of tool installation errors are established. When compared, the face gear tooth surface machined in VERICUT software for simulation based on this new method and the one obtained based on real process (grinding face gear by using a theoretical worm wheel with actual position errors) are found to be coincident, which proves the validity and feasibility of this new method. By using mesh planning for the rotating projection plane of the face gear work tooth surface, the deviation values of the tooth surface and the difference surface are acquired, and the influence of four kinds of errors on the face gear tooth surface is analyzed. Accordingly, this work provides a theoretical reference for assembly craft of worm wheel, improvement of face gear machining accuracy and modification of error tooth surface.

Face gear drive has been widely investigated in the aviation field as a power split device on the helicopter main reducer. However, high-speed and heavy-load condition makes the face gear prone to tooth surface pitting, leading to deterioration of transmission performance. To improve the load-bearing capacity of face gear, this paper proposes a design and modification method based on gear skiving process for face gear drives. First, gear skiving mathematical models for a face gear pair are established, and a continuously profile-shifted modification method is presented based on these mathematical models. Then, the load-bearing capacity of the modified face gear pair is minutely analyzed and discussed through contact analysis. The contact stress of the modified face gear is reduced by 47.78% on the right side and 41.1% on the left side compared with an unmodified face gear. Finally, gear skiving experiments and meshing performance tests of face gear pairs are conducted. The measurement results show consistency with the calculation results. Thus, the proposed design and continuously profile-shifted modification method based on the gear skiving process is feasible and contributes to load-bearing capacity improvement.

Sikorsky Aircraft, under a cooperative agreement with AATD (Aviation Applied Technology Directorate), has launched a four-year program, RDS-21 (Rotorcraft Drive Systems for the 21st Century), to develop face gear transmissions. RDS-21 addresses key technologies needed to enhance the drive systems of the objective force aircraft while developing new technologies to support the development of a new face gear drive system for Unmanned Air Vehicles (UAV) and the Future Utility Rotorcraft (FUR). Some of the initial funding for face gear development came from a partnership with Army MANTECH. This paper presents an overview of the RDS-21 face gear program and summarizes major milestones achieved to-date. Sikorsky has pursued face gear technologies by partnering with two key institutions. The GearLab at The Ohio State University has developed face gear analysis and design software while the other partner, Gleason Pfauter Inc., has developed face gear manufacturing technology. The methods developed for the design and analysis of face gears and some of the results of their application are covered in this paper. A mathematical model of the face gear generation process is created. The model facilitates the calculation of quantities of interest such as sliding velocities and contact ratio. Digital master gears are created for inspection purposes. A gear analysis software package is used to compute the loads and stresses in the gears. Work is continuing at The Ohio State University to create proprietary face gear analysis software for Sikorsky that can quickly run many design configurations.

Calculation of line and point contact ratio for orthogonal spur-face gear drive

Geometry design and tooth contact analysis of non-orthogonal asymmetric helical face gear drives

Skiving is an efficient method for manufacturing face gears, but theoretical machining errors may occur when face gears designed for shaping or grinding are processed by skiving. This study presents a face gear directly designed for the skiving process, eliminating theoretical machining errors. Additionally, a new design approach for the cylindrical gear is proposed to pair with this face gear. The tooth surface models of both the cylindrical pinion and face gear are established. For the pinion, surface modifications are applied in both profile and longitudinal directions, while the face gear’s tooth surface model is tailored for the skiving process to avoid theoretical machining errors. The contact performance, including transmission error, contact stress, and contact pattern, is evaluated through Tooth Contact Analysis (TCA). An optimization model is developed to identify the optimal cylindrical gear tooth surface parameters, targeting improved contact performance. The proposed method is validated by a case study, which shows that the optimized face gear transmission results in lower maximum contact stress and reduced transmission error amplitude.

An advanced CAD/CAE integration method for the generative design of face gears

Face gear transmission is a kind of space-meshing mechanism that is mainly used in the field of aviation. Compared with traditional transmission, it has the advantages of stability, reliability, low noise, and strong carrying capacity. However, owing to its complex tooth surface, there are no means to accurately model the face gear. Likewise, research based on the geometry is difficult. Therefore, the tooth surface equation of the face gear is derived in this article based on the meshing theory. Based on the equations, the point cloud of the face gear tooth surface is calculated, the complex tooth surface is generated, and the face gear is accurately modeled. Moreover, taking tooth surface friction excitation into consideration, a multi-degree-of-freedom nonlinear dynamic model of face gear transmission system is established, using the adaptive variable step length Runge-Kutta method. As shown in the results, the bifurcation diagram, phase diagram, time history diagram, and Poincaré section diagram are combined to analyze the influence of tooth surface friction and meshing frequency on the dynamic characteristics of the system.

A novel transmission using the multistage face gears as the core component is used to realize variable speed with differential gear shifting, there are multiple face gears superimposed on the radial direction, meshing with planetary wheel at the same time, which achieves different outputs speed through braking different face gears. In order to solve the interference problems caused by asynchronous meshing motion between several face gears and the same cylinder gear, this study mainly focuses on the meshing theory study based on the double crown surfaces in tooth profile and tooth orientation. The surface structure of straight tooth and double crown are constructed according to the related surface equations, the corresponding interference conditions are obtained by comparison, every single stage face gear model is designed and assembled. This study shows that the double crown configuration surface structure can easily improve contact characteristics compared with straight tooth surface structure of face gear. In addition, the double crown configuration surface structure can improve the distribution and direction of contact path. This study is expected to establish a new tooth surface model, which can provide the best machining parameters for the face gears.

Purpose During the oil lubrication process of aviation herringbone gears, lubricating oil is injected into and spreads around the tooth surface. Its spreading characteristics directly affect the lubrication state and transmission efficiency of gears. This study aims to investigate the effect of changing the injection parameters and gear operating conditions on the oil film deposition during injection lubrication. Design/methodology/approach The computational fluid dynamics method was used to establish the computational domain for the simulation and optimization using an orthogonal test. The oil film spreading and thickness of the tooth surface were calculated with the change in gear speed, fuel injection distance and fuel injection speed. Optimized oil injection lubrication parameters were obtained, and design ideas were provided for the oil injection lubrication analysis of aviation herringbone gears. Findings Under different operating conditions, such as varying the injection speed, gear rotational speed and injection distance, there were differences in the distribution of the lubricating oil film formed on the tooth surface. The thickness of the oil film decreases as the distance from the injection port increases. The thickness of the oil film deposition can be increased by increasing the injection velocity and reducing the gear rotation speed. The injection distance had a relatively small effect on the spreading thickness of the deposited oil film, affecting only the dynamic spreading process of oil film deposition. Furthermore, the simulation results are compared with the analytical calculation results, and finally the experimental verification is carried out. Originality/value Oil spray lubrication characteristics are important for achieving precise gear lubrication designs in the aerospace field. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2023-0250/