Below are the 18 papers that will be presented at the 2010 AGMA Fall Technical Meeting.
The papers have been organized around four sessions:
Session I – Manufacturing and Heat Treatment
Session II – Load Capacity Analysis
Session III – Gear Design Considerations
Session IV – Gear Applications
10FTM01. Complete Machining of Gear Blank and Gear Teeth
Author: Dr.Ing. Claus Kobialka, Gleason-Pfauter
Demands for increased throughput, with smaller lot sizes at lower cost have led to the development of an innovative approach to machining of both the gear blank and gear teeth on a single machine.
This paper will discuss the risks and benefits of multi-process machines that are capable of turning, hobbing, drilling, milling, chamfering and deburring of cylindrical gears. It will also discuss the economical potential of combined process technology and a vision for integrated heat treatment is shown.
10FTM02. Improving Heat Treating Flexibility for Wind Turbine Gear Systems Through Carburizing, Quenching and Material Handling Alternatives
Author: Wallace (Jack) Titus, AFC-Holcroft
Handling and process control in heat treating large gears have always been challenging. Growth in Wind Energy technology has focused more attention on this issue in recent years. The vast majority of installations processing such large parts utilize conventional methods via Pit Furnace systems. Such equipment has inherent limitations with respect to quench flow and part handling, making true improvements in areas such as distortion control difficult due to physical limitations of this processing approach. This presentation will explain alternative methods for heat treating large components that allow part distortion to be minimized. Benefits will be quantified regarding cost savings to produce such gearing and quality.
10FTM03. A Novel Approach to the Refurbishment of Wind Turbine Gears
Authors: Mark Michaud, and Gary J. Sroka, REM Surface Engineering and Ronald E. Benson, REM Research Group
Even though they are rated for a maintenance free 20year lifespan, it is not uncommon for multimegawatt wind turbine gearboxes to fail after only a few years due to the demanding environmental conditions in which they operate. These gearboxes experience several types of repairable damage including micropitting, abrasive wear, foreign object debris damage, surface corrosion and fretting corrosion. Historically, grinding is utilized to refurbish these damaged gears. However, high capital investment and the amount of time and skill involved in the grinding process limit the application of this method. This presentation discusses chemically accelerated vibratory finishing, or isotropic superfinishing (ISF), as a low cost option for refurbishing both case carburized and nitrided gears.
10FTM04. Low Distortion Heat Treatment of Transmission Components
Authors: Dr. Volker Heuer, and Dr. Klaus Loeser, ALD, Donald R. Faron, General Motors, David Bolton, ALDTT,
In many applications the high demands regarding service life of transmission components can be reached only by the application of a customized case hardening. This case hardening results in increased surface wear resistance and core toughenss.
However, as a sideeffect the components distort during heat treatment. This distortion has a significant costimpact, because components often need to be hardmachined after heat treatment. Therefore the proper control of distortion is an important measure to minimize production costs.
Low Pressure Carburizing (LPC) and High Pressure Gas Quenching (HPGQ) can significantly reduce heat treat distortion.
This presentation will explain how the successful application of LPC and HPGQ eliminated the need for subsequent machining ring gears for a 6 speed automatic transmission.
10FTM05. Comparison of the AGMA and FEA Calculations of Gears and Gearbox Components Applied in the Environment of the Small Gear Company
Author: Vanyo Kirov, Bucyrus International, Inc.
Current AGMA standards offer calculation methods for loose gears and gearbox components such as shafts, splines, keys, etc. that are based, mostly, on “traditional” methods found in classical textbooks and research papers. The accuracy and reliability of these methods have been proven over many years of design and field tests. However, new methods for calculations of mechanical engineering components like FEA (finite element analysis) are becoming wide spread. Once these techniques were used only by big companies because of their complexity and price, but with the development of computer technology they become more and more accessible to small gear companies.
This presentation offers a comparison between AGMA and FEA in strength and deflection calculations of spur gears and gearbox components, and draws conclusions and recommendations about their effectiveness in the environment of the small gear company.
10FTM06. Finite Element Analysis of High Contact Ratio Gear
Authors: M. Rameshkumar, G. Venkatesan, P. Sivakumar, Combat Vehicles Research and Development Establishment, DRDO
The demand of today’s vehicles for higher load carrying capacity, lower vibration and noise, and less installed volume and weight is increasing more than ever. Although helical gears, for most part, meet this demand, their additional axial thrust makes them less desirable. As a solution, one could consider High Contact Ratio (HCR) gearing for achieving high load carrying capacity with less volume and weight. Contact ratio greater than 2.0 in HCR gearing results in lower bending and contact stresses.
This paper deals with finite element analysis of high contact ratio and normal contact ratio (NCR) gears, with same module and center distance and the comparison of bending and contact stress. A two dimensional deformable body contact model of HCR and NCR gears is analyzed in ANSYS software, and ANSYS Parametric Design Language (APDL) is used for studying the bending and contact stress variation on the complete mesh cycle of the gear pair for identical load conditions.
10FTM07. A New Statistical Model for Predicting Tooth Engagement and Load Sharing in Involute Splines
Authors: Janene Silvers, Carl D. Sorensen, Kenneth W. Chase, Brigham Young University
Load sharing among the teeth of involute splines is little understood. Designers typically assume only a fraction of the teeth are engaged and the load is distributed uniformly over the assumed number of engaged teeth. This assumption provides an unrealistic estimation of tooth loads.
A new statistical model for involute spline tooth engagement has been developed and was presented earlier. This model takes into account the random variation of gear manufacturing processes. Toothtotooth variations cause the clearance between each pair of mating teeth to vary randomly, resulting in a sequential, rather than simultaneous tooth engagement. It predicts the number of teeth engaged and percent of load carried by each tooth pair.
This report presents an extension of the new sequential engagement model, which more completely predicts the variations in the engagement sequence for a set of spline assemblies. A statistical distribution is derived for each tooth in the sequence, along with its mean, standard deviation and skews.
10FTM08. Calculation of Load Distribution in Planetary Gears for an Effective Gear Design Process
Authors: Dr.Ing. Tobias Schulze, Dipl.Ing. Christian HartmannGerlach, DriveConcepts GmBH, and Dr.Ing. Berthold Schlecht, Technical University of Dresden
The calculation of gears especially planetary gears can just be carried out by the consideration of influences of the whole drive train and the analysis of all relevant machine elements. In this case the gear is more than the sum of its machine elements. Relevant interactions need to be considered under real conditions. The standardized calculations are decisive for the safe dimensioning of the machine elements with the consideration of realistic load assumptions. But they need to be completed by extended analysis of load distribution, flank pressure, root stress, transmission error and contact temperature.
10FTM09. Recommendation Reverse Engineering
Author: Charles D. Schultz, Beyta Engineering Service
As America’s manufacturing base has contracted, the need for reverse engineering has grown. Over time, certain pieces of equipment require changes to output speeds or power levels, and new parts have to be designed, built, and installed. And unfortunately, some pieces of equipment don’t measure up to the demands they are subjected to and need redesign or improvement. In many ways, reverse engineering is just as demanding a discipline as original product development with many of the same challenges, but with the additional restrictions of fitting inside an existing envelope.
The typical reverse engineering project begins with very limited information on the existing piece of equipment. This paper will describe a methodology for the reliable measurement, evaluation, re-design, and manufacture of replacement parts for gearboxes and industrial machinery. A step-by-step example will be provided.
10FTM10. Evaluation of Methods for Calculating Effects of Tip Relief on Transmission Error, Noise and Stress in Loaded Spur Gears
Authors: Dr. Mike Fish and D. Palmer, Dontyne Systems, Ltd.
The connection between transmission error and noise and vibration during operation has long been established. Calculation methods have been developed to describe their influence in order to evaluate the relative effect of applying a specific profile modification at the design stage.
This paper explains the theory behind transmission error and the reasoning behind the method of applying profile modifications through mapping the surface profiles and deducing the load sharing. It can be used to explain the results of later experimental validation on various types of tip relief in low contact ratio (LCR) gears. The paper will also demonstrate the importance of application requirements when considering these modifications.
A study of high contact ratio (HCR) gears will be presented to demonstrate why it is often necessary to apply different amounts and extents of tip relief in such designs, and how these modifications affect load sharing and highest point of tooth loading.
10FTM11. PointSurfaceOrigin (PSO) Macropitting Caused by Geometric Stress Concentration (GSC)
Authors: R. Errichello, GEARTECH, C. Hewette, Afton Chemical Corporation, and R. Eckert, Northwest Laboratories, Inc.
PointSurfaceOrigin (PSO) macropitting occurs at sites of Geometric Stress Concentration (GSC) such as discontinuities in the gear tooth profile caused by micropitting, cusps at the intersection of the involute profile and the trochoidal root fillet, and at edges of prior tooth damage such as tiptoroot interference. When the profile modifications in the form of tip relief, root relief, or both are inadequate to compensate for deflection of the gear mesh, tiptoroot interference occurs. The interference can occur at either end of the path of contact, but the damage is usually more severe near the startofactiveprofile (SAP) of the driving gear.
An FZGC gearset (with no profile modifications) was tested at load stage 9 and three pinion teeth failed by PSO macropitting. It is shown that the root cause of the PSO macropitting was GSC created by tiptoroot interference.
10FTM12. Flank Load Carrying Capacity and Power Loss Reduction by Minimised Lubrication
Authors: Dr. Bernd-Robert Höhn, Dr. Klaus Michaelis, Dr. Hans-Philipp Otto
In gearboxes lubricated with immersion methods, the no-load power losses decrease with decreasing immersion depth. The under-load power losses are nearly unaffected. However, the decrease in lubrication depth causes a dramatic increase in gear bulk temperature, which in turn causes a decrease of about 60% in scuffing load carrying capacity. In addition, allowable contact, stress will be decreased due to high local flash temperatures resulting from increased metal-to-metal contact thus increasing the risk pitting failure.
The common pitting load carrying capacity calculation algorithms according to DIN/ISO are only valid for moderate oil temperatures and rich lubrication conditions. For increased thermal conditions, the reduction of the pitting endurance level at increased gear bulk temperatures can be approximated with the method of Knauer. This presentation offers an advanced calculation algorithm for pitting load carrying capacity calculation at high gear bulk temperatures. In addition, the paper will propose a method for the estimation of gear bulk temperature at reduced immersion depth.
10FTM13. Gear Design for Wind Turbine Gearboxes to Avoid Tonal Noise According to ISO/IEC 61400-11
Author: Dipl-Ing. Jörg Litzba, Hansen Transmissions International N.V.
Current wind turbine gearbox design includes one or two planetary gear stages and at least one high speed helical gear stage, which is the most critical stage regarding noise and vibration. Aside from the overall noise of the gearbox and the structure-born noise, tonal noise (tonality) is considered an important issue which, though regulated through applicable international standards, has not been studied in any considerable depth.
A recent investigation has shown that specific gear parameters affect the tonal noise behavior and that a prediction can be made during design stage by simulating the noise by way of state of the art calculation software.
This presentation introduces the definition of tonal noise per ISO/IEC 61400-11 and presents measurement results from test rigs and from the field. It discusses the link between the measurements and various gear parameters. Furthermore, DZP calculation results will be shown along with how tonal noise can be estimated. One or two improved gear sets will be shown, where tonal noise was avoided using the defined gear design parameters.
10FTM14. Analysis and Testing of Gears with Asymmetric Involute Tooth Form and Optimized Fillet Form for Potential Application In Helicopter Main Drives
Authors: Frederick W. Brown, Scott R. Davidson, David B. Hanes and Dale J. Weires, The Boeing Company and Alex Kapelevich, AK Gears, LLC
Gears with an asymmetric involute gear tooth form were analyzed to determine their bending and contact stresses relative to symmetric involute gear tooth designs typical of the main drive gears in helicopters. Asymmetric and baseline symmetric test specimen gears were then designed, fabricated and tested to experimentally determine their single-tooth bending fatigue strength and scuffing resistance. Also, gears with an analytically optimized root fillet form were tested to determine their single tooth bending fatigue characteristics relative to baseline specimens with a circular root fillet form. Test results demonstrated higher bending fatigue strength for both the asymmetric tooth form and optimized fillet form compared to baseline designs. Scuffing resistance was significantly increased for the asymmetric tooth form compared to a conventional symmetric involute tooth design.
10FTM15. Driveline Analysis for Tooth Contact Optimization of High Power Spiral Bevel Gears
Authors: Jesse Rontu, Gabor Szanti, Eero Mäsä, ATA Gears Ltd., Finland
It is a common practice in high power gear design to apply tooth relief to prevent stress concentration near the tooth edges. Gears with crowning have point contact without load. When load is applied, instantaneous contact turns from point into a Hertzian contact ellipse. The contact area grows and changes location as load increases. To prevent edge contact, gear designers have to choose suitable tooth relief considering contact indentations as well as relative displacements of gear members.
In a majority of spiral bevel gears, the extent of spherical crowning is determined experimentally by setting the contact pattern to the center of active tooth flank. Feedback from service, as well as from full torque bench tests, have shown that this method leads to loaded contact patterns which are rarely optimal in location and extent.
Today it is possible to use calculation methods to predict the relative displacements of gears under operating load and conditions. With the help of loaded tooth contact analysis (LTCA), it is possible to compensate for these displacements and determine a special initial contact position that will lead to well centered full torque contact utilizing a reasonably large portion of the available tooth flank area. At the same time, crowning can be scaled to the minimum necessary amount.
10FTM16. Analysis of Load Distribution in Planet-gear Bearings
Authors: Louis Mignot, Loïc Bonnard, Vincent Abousleiman, Hispano-Suiza
In Epicyclic gear sets for aeronautical applications, planet-gears are generally supported by spherical roller bearings with the bearing outer race being integral to the gear hub. This paper presents a new method to compute roller load distribution in such bearings. Based on the well known Harris method, a modified formulation enables the designer to account for centrifugal effects due to planet-carrier rotation and to assess roller loads at any position throughout the rotation cycle. New model load distribution predictions show discrepancies with results presented by Harris, but are well correlated with 1D and 3D Finite Element Models. Several results validate the use of simplified analytical models to assess the roller load distribution instead of more time consuming Finite element Models. The effects of centrifugal forces due to planet-carrier rotation on roller loads are also analyzed. Finally, the impact of the positions of rollers relative to the gear mesh forces on the load distribution is shown.
10FTM17. Self-Locking Gears: Design and Potential Applications
Authors: Alex Kapelevich, AKGears, LLC and Elias Taye, ET Analytical Engineering, LLC
In most gear drives, when the driving torque is suddenly reduced due to power off, torsional vibration, power outage or any mechanical failure, the gears will continue rotating either in the same direction driven by the system inertia, or in the opposite direction driven by the resistant output load due to gravity, spring load, etc. The latter condition is known as backdriving. There are many gear drive applications where the output shaft driving is less desirable. In order to prevent this, different types of brakes or clutches are used. However, there are also solutions which use self-locking gears. The most common one is a worm gear with a low lead angle. However, their application comes with some limitations: the crossed axis shaft arrangement, relatively high gear ratio, low speed, low gear mesh efficiency, increased heat generation, etc.
This paper describes the design approach, as well as potential applications, of parallel axis self-locking gears. Unlike worm gears, they don’t have such application limitations.
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