Theoretical Study on the Influence of Planet Gear Rim Thickness and Bearing Clearance on Calculated Bearing Life

Planetary gearboxes are becoming more popular due to their high power density and potentially high efficiency. When the planet bearings are internally mounted, the body of the planet gear has to be hollow. The demand for large outer diameters due to high load requirements might result in a small planet rim thickness. Depending on the rim thickness, its rigidity may become very low. Due to the low stiffness and the special load conditions caused by the double meshing, the deformation of the planet and its bearings are unique. In this paper, the influence of rim thickness on bearing load and lifetime are examined. The analysis is performed with an FEM model of a planet rim with a built-in cylindrical roller bearing. With the resulting planet deformation from the FEM calculation, the load distribution on the rolling elements in the bearing and the bearing lifetime according to ISO/TS 16281:2008 have been evaluated.

Loaded Tooth Contact Pattern Analysis for Strain Wave Gear With Non-Elliptical Wave Generator

This paper presents a new non-elliptical wave generator for strain wave gear to improve its contact pattern quality. The new wave generator has a polynomial profile at one cross section, then crowned along the lead direction. The lead crowning uses a parabolic function with crowning amount controlled by parabolic coefficient. Loaded tooth contact pattern analysis based on finite element method is used to evaluate the new design. The result shows that the new design will avoid the edge contact between wave generator and flexspline, which reduces contact pressure and improve the wearing life of the gear. It also improves the contact pattern quality of the tooth surface. Comparing with elliptical wave generator, the new wave generator with polynomial profile and lead parabolic crowned surface offers more design freedom to improve strain wave gear’s performance. The parametric equation of the new wave generator is defined intuitively, and it can be easily adapted for any type of strain wave gear. Furthermore, the finite element model for the strain wave gear is a new development and application for Loaded Tooth Contact Analysis (LTCA).

Closed Form Calculation of Lead Flank Modification Proposal for Spur and Helical Gear Stages

Due to the growing need for gearboxes to be as lightweight and efficient as possible, it is most important that the gear mesh’s potential is utilized as well as possible. One way of doing that is to define a flank modification that optimally distributes the load over the flank. Best practice for defining a flank modification is to manually check out the load distribution and to define a value of the flank modification. In general, this is an iterative method to get an optimally distributed load. This method can also be automated. To do this, the deformations of the gearbox (shafts, bearings, gear mesh) are calculated. With those results a modification proposal is calculated and applied to the calculation model. As soon as the values for the next additional modification proposal drop under a certain limit, the iteration is finished. This method consumes time and computing power. Additionally, since it is an iteration, does not always converge. A new method for calculating the lead flank modification for all gear stages in the gearbox to be calculated is presented in this paper. The method shown in this paper uses additional degrees of freedom and equations, which are integrated into the linear equation system of the gearbox model. Those degrees of freedom and the equations apply the boundary condition to the model of a constant load distribution. By introducing additional factors in the equations, it is possible to calculate a lead flank modification for an arbitrary load distribution. By integrating these additional degrees of freedom and the equations, only one additional calculation is needed to get a modification proposal. Examples throughout this paper show the results of this method.

Study on Path Planning of Involute Tooth Surface Milling With General Cutting Tool

Milling involute tooth surface with universal cutting tool overcomes the difficult problem of customizing tool for nonstandard gear machining. It is difficult for gear manufacturers to gain an advantage in market competition because of the long cycle of customized cutting tools. In this paper, the milling path of involute tooth surface by a general cutting tool is studied, and how to obtain the uniform surface roughness of involute tooth surface and the cutting path scheme of cutting tool is discussed. The key point of this paper is to put forward the scheme of tool path in the milling process. The end profile of involute gear is modeled by an analytic method, and the equidistant contour of the profile of involute gear is established by using the principle of normal deviation, which provides an accurate position point for the cutting tool.

Energy Dissipation of Damper Rings for Thin-Walled Gears

When the gear generates a nodal mode shape vibration, there are two directions of possible relative displacement between the corresponding points on the contact surface of the damper ring and the damper groove, which are circumferential direction and axial direction respectively. In this paper, the relative displacement of the damper ring and the damper groove are considered in two directions, and the calculation method of energy dissipation is proposed. When the nodal vibration occurs in the gear, due to the existence of the strain difference between the damper ring and the damper groove on the contact surface, circumferential slip of partial area would occur. The energy dissipation in one vibration cycle is accurately determined by analytical solution. Since the aviation gears are mostly thin-walled structures, the axial displacement is large when resonance occurs. Based on the discrete damper ring model which considers interaction between every segment of the ring, the first-order harmonic balance method is used to calculate the axial displacement of the damper ring under the given gear rim amplitude. And then the hysteresis curve area of each discrete segment on the contact surface is summed to obtain energy dissipation in one vibration cycle. In this paper, based on the energy method, the damping effect of the damper ring is predicted. The damping ratio curve obtained by energy dissipation in two directions is compared and analyzed. The occurrence conditions of the two directions of possible relative displacement and the influence of the damper ring parameters on both situations are summarized.

Numerical Simulation for Optimizing Tooth Profile Using Bezier Curve

The research hereby introduces a novel approach to reduce tooth bending stress using a parametric numeric simulation. This Finite Element Method (FEM) is used to determine optimal design variables for an asymmetric root profile of a helical gear defined by a rational cubic Bezier curve. The gear is first modelled using a machine design software and later implemented into a 3D computer aided design (CAD) package to modify the root spline geometry using a script. A nonlinear relationship exists between the design variables and tooth bending stress. Additionally, certain trends exist between the design variables to exhibit a more optimal root profile. The simulation results show that the proposed method is feasible as the general optimization process results in significant bending stress reduction. The numerical simulation demonstrates that bending stress can be reduced by as much as 10.75% by the proposed approach.

Applicability of an Oil Based Calculation Approach for Wear Risk and Wear Lifetime to Grease Lubricated Gear Pairings

Gear pairings often run under very high loads. That can result in different kinds of failure modes limiting their lifetime. Many of the known gear failure modes are tribologically influenced. Especially for gear pairs running with lower circumferential speeds or with different surface hardness, (continuous or slow speed) wear is often the lifetime limiting factor. Slow speed wear appears continuously over a longer period of runtime. In many cases, such applications are lubricated with greases. Since the standardized calculation methods (e.g. ISO 6336) do not cover any determination of wear, one common way to predict the wear lifetime is the calculation method according to Plewe. In the associated Plewe diagram the worn off amount of material is correlated to the minimal lubricant film thickness in the tooth contact. The wear intensity decreases for higher film thicknesses. However, this method has certain limits for greases, because the film thickness of a grease, its bleed oil and the base oil is not necessarily the same. Additionally, the consistency and the flow properties have to be considered, because they influence the lubrication supply mechanism (circulating or channeling). Under certain circumstances channeling could be predominant. Although in theory a grease should build a thicker lubricating film than its base oil, experimental investigations have shown higher wear rates in comparison to oil lubrication.

Influence of the Case Properties After Nitriding on the Load Carrying Capacity of Highly Loaded Gears

The load carrying capacity of highly loaded gears can be increased by thermochemical surface treatments such as nitriding or case hardening. In contrast to case hardening, the nitriding treatment is carried out at lower process temperatures and therefore creates lower distortion. As a result, grinding after nitriding is usually not necessary. Nitrided gears are ordinarily characterized by a thin, high-hardness, a few micrometers thick compound layer of iron and alloy element nitrides directly on the surface and a subsequent diffusion layer reaching more deeply into the material. Nitriding, therefore, provides an alternative to case hardening for distortion-sensitive components and offers potential for cost savings in the production of highly loaded gears. This publication will focus on the influence of nitriding on the load carrying capacity of highly loaded gears. In addition, this paper summarizes the current state of knowledge of nitrided gears and gives an insight into current research in the field of nitrided gears. In particular, the influence of the compound layer on the tooth root bending strength and the flank load carrying capacity achieved within the research project FVA 386 II is discussed.

Tooth Root Shape Optimization of Thin-Rimmed Planet Gears

Planetary gearboxes in highly sophisticated applications such as turbofan engines are required to have a high power-to-weight ratio and excellent reliability. Hence, thin-rimmed gear units need to be designed as compact as possible which, however, is usually limited by the tooth root load capacity. In order to come up with the best design, a tooth root shape optimization process is developed for thin-rimmed planet gears.

Optimization Design and Analysis for Pre-Shift Control Parameters of Wet Dual Clutch Transmissions Based on Dynamic Modeling of Synchronizer

The DCTs have increased in prevalence for achieving power uninterrupted shifting and pre-shift process significantly influences the DCTs shift quality. Research on the multistage and nonlinear characteristics of the gear preselect process is not comprehensive so that there are shortcomings such as high impact, long synchronization time and poor economy. In view of above detrimental phenomenon, control parameters optimization is conducted in order to realize fast, smooth and economic pre-shifting on the basis of analyzing the sensitivity of the factors affecting pre-shift process. Considering the engagement of sleeve, synchro ring and dog gear, the multi-body dynamics theory is applied to establish an accurate synchronizer dynamics model. Based on the model, simulations are conducted to confirm factors like sleeve mass, cone angle fluctuating the pre-shift quickness and smoothness, sorting structure parameters according to factors sensitivity. Furthermore, the formula of energy loss characteristics relating to two control parameters which are pre-shift force and pre-shift trigger time is obtained, deriving from exploring the hydraulic loss caused by pre-shift force and the drag torque energy loss created by pre-shift trigger time. The optimal synchronizer structure parameters are obtained by adopting multi-objective optimization method. Simulation results indicate the optimal control parameters improve pre-shift comprehensive performance including quickness, smoothness and economy compared with conventional scheme.