Gearbox Components Research Articles

Sources of time‐varying contact stress and misalignments in wind turbine planetary sets

AbstractRecent data shows that 90% of large wind turbines include a gearbox, and industry forecasts expect this figure to remain relatively stable. With global annual volumes (2009) of around 18,600 units, the quality, cost and performance of gearboxes is of paramount importance to the wind sector. The industry has been focusing some attention on gearbox reliability, as demonstrated by a growth in the number of specific seminars and collaborative programs on this topic. One aspect that needs to be brought to an industry‐wide forum is the understanding of the complexity of bearing design in the gearbox and the careful attention that needs to be paid to ensure a reliable gearbox design. This paper seeks to address this issue by clear demonstration of design issues using a model of the gearbox from the National Renewable Energy Lab's Gearbox Reliability Collaborative. Detailed models are presented with focus on determining the quality of the function of the planetary gear stages. Key design drivers are discussed such as the quality of alignment at the gears and bearings and the loads and stresses seen on these components. Under a design load case with a significant rotor off‐axis moment the stresses in the planet gears and bearings are investigated. It is shown how the misalignment of the planet pins varies with the rotation of the planetary set and how subsequently time‐varying contact stresses and load distributions occur in the planet gears and bearings. These factors strongly influence the fatigue life of the gearbox components as well as the level of vibration. Design tools are then used to demonstrate how small variations in the clearances of the planet carrier bearings can have a big effect on the quality of the design. Numerical studies show where optimal clearance settings lie and how the misalignment of the planetary set can be improved. Furthermore, a demonstration is made of how redesign of the bearing arrangement and subsequent optimization of the planet tooth geometry further improves the misalignment and results in significantly reduced time‐varying contact stresses, better load distribution and reduced vibration. It is illustrated that small clearances, such as in the carrier bearings, can have a large effect on the performance of the design and a study shows how to identify and reduce time‐varying misalignment and contact stresses resulting in lower vibration, lower fatigue and a more reliable product. Copyright © 2011 John Wiley & Sons, Ltd.

Système hybride pour la conception des boîtiers à broches multiples

In the present paper, we suggest a hybrid system for the determination of a possible kinematics chain of multi-brooches gearboxes which are used in drilling and threading operations of a big series of workpieces (driving blocks, gearboxes cases, etc). The system is based firstly on the representation of the multi-brooches gearbox components and assembly according to an object oriented language. Secondly and according to the different relationships between objects and to a knowledge-base in form of IF-THEN rules, the system try to construct and determine automatically a kinematics chains of the desired multibrooches gearbox.

Application of Oil Debris Monitoring For Wind Turbine Gearbox Prognostics and Health Management


 
 
 Experience has shown that premature gearbox failures are a leading maintenance cost driver that can easily lower the profit margin from a wind turbine operation. Prognostics and Health Management (PHM) techniques offer the potential of effectively managing gearbox health problems by detecting early damage, tracking the severity of damage, estimating the time to reach pre-defined damage limits, and providing key information for proactive maintenance decisions. Experience has revealed that major damage modes of wind turbine gearboxes are bearing spall and gear teeth pitting, both of which release metallic debris particles in the oil lubrication system. Oil debris monitoring is thus well suited to provide an early indication and quantification of internal damage to bearings and gears of a wind turbine gearbox.This paper reviews the application of oil debris monitoring as an effective PHM solution for wind turbine gearboxes. The paper describes the principle of operation of the oil debris monitoring technology and the principle of application for effective PHM of wind turbine gearboxes. The paper explains the common surface fatigue damage mode of bearing and gear rolling elements and the characteristics of the destructive debris that result from this damage mode. The paper outlines a simple means of deriving accumulated debris count damage limits based upon basic gearbox component geometry and the use of moving averages for estimating rates of debris generation as a simple yet effective damage data-driven propagation model. Finally, the application of oil debris monitoring as an effective PHM technology for wind turbine gearboxes is illustrated by presenting actual data obtained from seeded fault bearing and gear tests and fielded gearbox applications.
 
 

Optimization of module, shaft diameter and rolling bearing for spur gear through genetic algorithm

In this study, the dimensional optimization of motion and force transmitting components of a gearbox is performed by genetic algorithm (GA). It is aimed to obtain the optimal dimensions for gearbox shaft, gear and the optimal rolling bearing. GA is a non-conventional useful search technique. In genetic algorithm, the best results can be obtained within the solution space which is formed by the design constraints. With the optimization of the gearbox components, the design with smallest volume which can carry the system load is obtained. The results obtained by GA optimization are compared to those obtained by analytical methods. These obtained results indicate that GA can be used reliably in machine element design problems.

Importance of local microstructure for damage tolerant light weight design of Ti–6Al–4V forgings

Forged parts made of titanium are generally used in aerospace industry, e.g. for engine mounts, pylon fitting and frame parts, housings, gear box components, engine disks and so on. To achieve damage tolerant together with light weight design of such parts the local microstructure resulting from thermomechanical treatment has to be considered. Therefore a new approach is introduced in this paper containing methodologies for the determination of local microstructural-based S/ N-curves. They can be embedded in a lifetime prediction based on local stresses. Long crack growth and fatigue tests were performed on Ti–6Al–4V with different types of microstructures and distinct differences were found in respect of fatigue and crack propagation. It is shown that the microstructural parameters primary α-grain size and ( α + β)-content dominate the fatigue behavior based on rotating bending S/ N-curves whereas the long crack growth is mainly affected by primary α-grain size and connectivity of α-grains. In addition first results regarding characterization of crack initiation phase and short crack growth of mill-annealed Ti–6Al–4V are presented for clarification of the fatigue process in respect of microstructure.

Shifting simulation — Goals, solutions and benefits

Automated gear shifting is becoming an increasingly popular solution for efficient powertrain and gearbox design. In automated systems, such as dual-clutch transmissions for passenger cars or automated gearboxes in trucks, the gearbox layout and components resemble those of the manual gearbox.]

Warm powder compaction substitutes conventionally double pressed and double sintered synchroniser hubs

Within a project supported by the European Union a consortium consisting of the companies Fraunhofer Institute for Structural Durability LBF, AMES, Miba, GKN, Federal Mogul, Höganäs, RWTH Aachen, Peugeot/Citroën and Fiat worked on the realisation of heavyduty gearbox components by warm powder compaction technology. In this paper, part of this work will be reported, namely the manufacturing of synchroniser hubs by this new technology. Until now these hubs were manufactured by the double pressing and double sintering route.Based on service load measurements in a gearbox of a Peugeot 506, vehicle fatigue tests were carried out with conventionally and warm pressed hubs. The results of fatigue tests with hubs as well as the durability tests carried out in the gearboxes of Peugeot/Fiat revealed the same performance for both technologies. As a consequence, the hubs produced by warm powder compaction can substitute for the ones produced conventionally. Further, the new technology reveals economic advantages with regard to the powder price as well as production costs.

Extraction of machining features for CAD/CAM integration

Feature-based CAD/CAM integration is a technology used to realise automatic transmission and conversion of component information among CAD, CAPP and CAM applications. A feature is the medium of information transmission in the integration. Since a process planning downstream application has a different viewpoint from the component designer, feature conversion or feature extraction methodology is used to create a machining feature model based on the design feature model. One of the major difficulties in generating machining features is the preservation of feature integrity because of feature interactivity. The most current research, therefore, focuses on the planar-type form feature conversion. This paper discusses the problem of feature interactivity and proposes a feature-based approach to generating hole-series machining features from a design feature model. Hole-series features are important machining features for gearbox components used in machine tools. These kinds of features cannot be obtained directly from a design feature database. A constraint-based method is developed in this paper to define a hole-series feature model based on the geometric and topological information extracted from the design database. In addition, a STEP file is generated to interface the converted machining feature model with the downstream CAPP application. The implemented feature conversion system is verified by considering its application to some component examples and the developed prototype CAPP system.

Feasibility of a phased acoustic array for monitoring acoustic signatures from meshing gear teeth.

This paper investigates the feasibility of sensing damage emanating from rotating drivetrain elements such as bearings, gear teeth, and drive shafts via airborne paths. A planar phased acoustic array is evaluated as a potential fault detection scheme for detecting spatially filtered acoustic signatures radiating from gearbox components. Specifically, the use of beam focusing and steering to monitor individual tooth mesh dynamics is analyzed taking into consideration the constraints of the array/gearbox geometry and the spectral content of typical gear noise. Experimental results for a linear array are presented to illustrate the concepts of adaptive beam steering and spatial acoustic filtering. This feasibility study indicates that the planar array can be used to track the acoustic signatures at higher harmonics of the gear mesh frequency.

THE DYNAMIC MODELLING OF A SPUR GEAR IN MESH INCLUDING FRICTION AND A CRACK

To improve the current generation of diagnostic techniques, many researchers are actively developing advanced dynamic models of gear case vibration to ascertain the effect of different types of gear train damage. This paper details a simplified gear dynamic model aimed at exploring the effect of friction on the resultant gear case vibration. The model incorporates the effect of variations in gear tooth torsional mesh stiffness, developed using finite element analysis, as the gears mesh together. The method of introducing the frictional force between teeth into the dynamic equations is given. The comparison between the results with friction and without friction was investigated using Matlab and Simulink models developed from the differential equations. The effects the single tooth crack has on the frequency spectrum and on the common diagnostic functions of the resulting gearbox component vibrations are also shown.

Structure-Based Connectionist Network for Fault Diagnosis of Helicopter Gearboxes

A new method of diagnosis is introduced for helicopter gearboxes that relies on the knowledge of the gearbox “structure” and characteristics of the “features” of vibration for component fault isolation. Both the structural knowledge and featural knowledge in this method are defined as the fuzzy weights of a connectionist network that maps each sampled set of vibration features, obtained from a signal analyzer, into fault possibility values associated with individual gearbox components. The structural weights in this network are defined to represent the influence of gearbox component faults on the overall vibration sensed by each accelerometer, and the featural weights are defined to denote the influence of components faults on individual vibration features. Given the extremely complex structure of helicopter gearboxes which prohibits accurate modeling of the effect of faults on their vibration, the structural weights in this method are defined based on the root mean square value of the frequency response of a simplified lumped-mass model of the gearbox. The experimental evaluation of the method based on vibration data from two different gearboxes is included in a separate paper.

An Improved Epicyclic Gearbox for Reduced and Controllable Subsynchronous Vibrations in Gas Turbogenerator Applications

An improvement is made to the design of an epicyclic gearbox that limits the dynamic eccentricities of gearbox components. Gearboxes were manufactured to the new design and tested, showed reduced levels of subsynchronous vibrations at the turbine bearings. The in-situ balancing feature of the gearbox is also found to be very effective in reducing these vibrations further. The improved gearboxes not only assured the service life of the turbine bearings, but also increased the success rate of package testing the first time with substantial cost savings.

What lies ahead for automotive PM?

There are currently over 1000 applications for PM parts in North America cars, ranging from engine and gear box components to mirror supports and seat belt locks. European and Japanese models also include ever increasing quantities of PM. But what are the latest PM parts and materials under development for the automotive industry? Amanda Weaver and Simon Pickering investigate.

Torvac Passes the Test

PLESSEY Aerospace at Titchfield, Hants has installed a Compact 100 vacuum furnace from Cambridge‐based suppliers Torvac. The furnace has just completed the warranty year in operation on a wide range of heat treatments, brazing and degassing applications. The work is generally carried out to the full rigors of aerospace standards including mSR 953, CAA DAI/7591/65 and STAN 05/21. Typical of the jobbing work is the vacuum hardening of bevel gear box components which Plessey manufacture for the AV8B engines used in the Harrier jump jet.

Fatigue Life Analysis of a Turboprop Reduction Gearbox

A fatigue life analysis of the Allison T56/501 turboprop reduction gearbox was developed. The life and reliability of the gearbox was based on the lives and reliabilities of the main power train bearings and gears. The bearing and gear lives were determined using the Lundberg-Palmgren theory and a mission profile. The five-planet-bearing set had the shortest calculated life among the various gearbox components, which agreed with field experience where the planet bearing had the greatest incidences of failure. The analytical predictions of relative lives among the various bearings were in reasonable agreement with field experience. The predicted gearbox life was in excellent agreement with field data when the material life adjustment factors alone were used. The gearbox had a lower predicted life in comparison with field data when no life adjustment factors were used or when lubrication life adjustment factors were used either alone or in combination with the material factors.

A New Method of Modeling Gear Faults

Detailed mathematical models of gear vibrations have appeared in recent years, but to utilize them requires a detailed knowledge of the gearbox components and their dynamic properties. This paper presents an alternative approach which is applicable to the monitoring and diagnosis of gearbox faults based on an analysis of changes in the vibration signal, showing how these can be related back to various classes of fault. Most emphasis is placed on the effects of the various types of faults on the spectrum, but the applicability of two other techniques, viz., synchronous signal averaging and cepstrum analysis, is also discussed comparatively, making use of practical examples.

Reduction of Vibration and Noise Generated by Planetary Ring Gears in Helicopter Aircraft Transmissions

Rotor-drive gearboxes are major noise sources in helicopter aircraft. Narrow-band examination of this noise often indicates the presence of several or more very high, narrow noise peaks, which are located at gearbox mesh frequencies or their multiples. Important exceptions are sideband noise components, located so near the main signal component as to be indistinguishable except by very narrow band reduction. Noise of this type is most effectively treated through a systematic study of the flow of high-frequency vibration energy in the drive train. Such studies should examine the mechanism by which gear meshes generate vibrations, and the vibration response of the gearbox components which support the gears. Results of such calculations are presented for the planetary reduction ring-gear casing elements in the Boeing-Vertol CH-47 forward rotor-drive gearbox and the Bell UH-1D main rotor-drive gearbox. The calculations indicate logical reasons why noise is generated. Typical ring-gear casing design changes are examined for noise reduction.