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If a gear system is run continuously for long periods of time—or if the starting loads are very low and within the normal operating spectrum—the effect of the start-up conditions may often be insignificant in the determination of the life of the gear system. Conversely, if the starting load is significantly higher than any of the normal operating conditions, and the gear system is started and stopped frequently, the start-up load may, depending on its magnitude and frequency, actually be the overriding, limiting design condition.
Recently, there has been increased interest in the dynamic effects in gear systems. This interest is stimulated by demands for stronger, higher speed, improved performance, and longer-lived systems. This in turn had stimulated numerous research efforts directed toward understanding gear dynamic phenomena. However, many aspects of gear dynamics are still not satisfactorily understood.
Micropitting, pitting and wear are typical gear failure modes that can occur on the flanks of slowly operated and highly stressed internal gears. However, the calculation methods for the flank load-carrying capacity have mainly been established on the basis of experimental investigations of external gears. This paper describes the design and functionality of the newly developed test rigs for internal gears and shows basic results of the theoretical studies. It furthermore presents basic examples of experimental test results.
Cubic boron nitride (CBN) finishing of carburized gearing has been shown to have certain economic and geometric advantages and, as a result, it has been applied to a wide variety of precision gears in many different applications. In critical applications such as aerospace drive systems, however, any new process must be carefully evaluated before it is used in a production application. Because of the advantages associated with this process, a test program was instituted to evaluate the load capacity of aerospace-quality gears finished by the CBN process as compared to geometrically identical gears finished by conventional grinding processes. This article presents a brief description of the CBN process, its advantages in an aerospace application, and the results of an extensive test program conducted by Boeing Helicopters (BH) aimed at an evaluation of the effects of this process on the scoring, surface durability, and bending fatigue properties of spur gears. In addition, the results of an x-ray diffraction study to determine the surface and subsurface residual stress distributions of both shot-peened and nonshot-peened CBN-ground gears as compared to similar conventionally ground gears are also presented.
We need a method to analyze cumulative fatigue damage to specify and to design gear drives which will operate under varying load. Since load is seldom constant, most applications need this analysis.
In ParI 1 several scuffing (scoring) criteria were shown ultimately to converge into one criterion, the original flash temperature criterion according to Blok. In Part 2 it will be shown that all geometric influences may be concentrated in one factor dependent on only four independent parameters, of which the gear ratio, the number of teeth of the pinion, and the addendum modification coefficient of the pinion are significant.
Crossed helical gear sets are used to transmit power and motion between non-intersecting and non-parallel axes. Both of the gears that mesh with each other are involute helical gears, and a point contact is made between them. They can stand a small change in the center distance and the shaft angle without any impairment in the accuracy of transmitting motion.
The load capacity rating of gears had its beginning in the 18th century at Leiden University when Prof. Pieter van Musschenbroek systematically tested the wooden teeth of windmill gears, applying the bending strength formula published by Galilei one century earlier. In the next centuries several scientists improved or extended the formula, and recently a Draft International Standard could be presented.
Solutions to the governing equations of a spur gear transmission model, developed in a previous article are presented. Factors affecting the dynamic load are identified. It is found that the dynamic load increases with operating speed up to a system natural frequency. At operating speeds beyond the natural frequency the dynamic load decreases dramatically. Also, it is found that the transmitted load and shaft inertia have little effect upon the total dynamic load. Damping and friction decrease the dynamic load. Finally, tooth stiffness has a significant effect upon dynamic loadings the higher the stiffness, the lower the dynamic loading. Also, the higher the stiffness, the higher the rotating speed required for peak dynamic response.
Because of the better thermal conductivity of CBN abrasives compared to that of conventional aluminum oxide wheels, CBN grinding process, which induces residual compressive stresses into the component, and possibly improves the subsequent stress behavior. This thesis is the subject of much discussion. In particular, recent Japanese publications claim great advantages for the process with regard to an increased component load capacity, but do not provide further details regarding the technology, test procedures or components investigated. This situation needs clarification, and for the this reason the effect of the CBN grinding material on the wear behavior and tooth face load capacity of continuously generated ground gears was further investigated.
The face load factor is one of the most important items for a gear strength calculation. Current standards propose formulae for face load factor, but they are not always appropriate. AGMA 927 proposes a simpler and quicker algorithm that doesn't require a contact analysis calculation. This paper explains how this algorithm can be applied for gear rating procedures.
How should we consider random helix angle errors fHβ and housing machining errors when calculating KHβ? What is a reasonable approach?
Helical gear teeth are affected by cratering wear — particularly in the regions of low oil film thicknesses, high flank pressures and high sliding speeds. The greatest wear occurs on the pinion — in the area of negative specific sliding. Here the tooth tip radius of the driven gear makes contact with the flank of the driving gear with maximum sliding speed and pressure.
A finite elements-based contact model is developed to predict load distribution along the spline joint interfaces; effects of spline misalignment are investigated along with intentional lead crowning of the contacting surfaces. The effects of manufacturing tooth indexing error on spline load distributions are demonstrated by using the proposed model.
In this paper, two developed methods of tooth root load carrying capacity calculations for beveloid gears with parallel axes are presented, in part utilizing WZL software GearGenerator and ZaKo3D. One method calculates the tooth root load-carrying capacity in an FE-based approach. For the other, analytic formulas are employed to calculate the tooth root load-carrying capacity of beveloid gears. To conclude, both methods are applied to a test gear. The methods are compared both to each other and to other tests on beveloid gears with parallel axes in test bench trials.
In some gear dynamic models, the effect of tooth flexibility is ignored when the model determines which pairs of teeth are in contact. Deflection of loaded teeth is not introduced until the equations of motion are solved. This means the zone of tooth contact and average tooth meshing stiffness are underestimated, and the individual tooth load is overstated, especially for heavily loaded gears. This article compares the static transmission error and dynamic load of heavily loaded, low-contact-ratio spur gears when the effect of tooth flexibility has been considered and when it has been ignored. Neglecting the effect yields an underestimate of resonance speeds and an overestimate of the dynamic load.
Flank breakage is common in a number of cylindrical and bevel gear applications. This paper introduces a relevant, physically based calculation method to evaluate flank breakage risk vs. pitting risk. Verification of this new method through testing is demonstrably shown.
This paper will provide examples of stress levels from conventional root design using a hob and stress levels using an optimized root design that is now possible with PM manufacturing. The paper will also investigate how PM can reduce stresses in the root from transient loads generated by abusive driving.
The power of high speed gears for use in the petrochemical industry and power stations is always increasing. Today gears with ratings of up to 70,000kW are already in service. For such gears, the failure mode of scoring can become the limiting constraint. The validity of an analytical method to predict scoring resistance is, therefore, becoming increasingly important.
Helical gears can drive either nonparallel or parallel shafts. When these gears are used with nonparallel shafts, the contact is a point, and the design and manufacturing requirements are less critical than for gears driving parallel shafts.
There is an increasing significance of screw helical and worm gears that combine use of steel and plastics. This is shown by diverse and continuously rising use in the automotive and household appliance industries. The increasing requirements for such gears can be explained by the advantageous qualities of such a material combination in comparison with that of the traditional steel/bronze pairing.
Instances of damage to discontinuous form ground and surface-hardened gears, especially of large scale, have recently increased. This may be attributed partly to a faulty grinding process with negative effects on the surface zones and the surface properties.
Traditionally, gear rating procedures consider manufacturing accuracy in the application of the dynamic factor, but only indirectly through the load distribution are such errors in the calculation of stresses used in the durability and gear strength equations. This paper discusses how accuracy affects the calculation of stresses and then uses both statistical design of experiments and Monte Carlo simulation techniques to quantify the effects of different manufacturing and assembly errors on root and contact stresses.
The contact lines of a pair of helical gears move diagonally on the engaged tooth faces and their lengths consequently vary with the rotation of the gears.
The manufacturing quality of spiral bevel gears has achieved a very high standard. Nevertheless, the understanding of the real stress conditions and the influences. of certain parameters is not satisfactory.
An experimental effort has been conducted on an aerospace-quality helical gear train to investigate the thermal behavior of the gear system as many important operational conditions were varied.
The main theme of this article is high-capacity, high-speed load gears in a power transmission range between 35 MW and 100 MW for generators and turbo-compressors driven by gas or steam turbines.
In this study, the combined influence of shaft misalignments and gear lead crown on load distribution and tooth bending stresses is investigated. Upon conclusion, the experimental results are correlated with predictions of a gear load distribution model, and recommendations are provided for optimal lead crown in a given misalignment condition.
This article presents a new spur gear 20-degree design that works interchangeably with the standard 20-degree system and achieves increased tooth bending strength and hence load carrying capacity.
Influences of Load Distribution and Tooth Flank Modifications as Considered in a New, DIN/ISO-Compatible Calculation Method
This article describes some of the most important tests for prototypes conducted at Winergy AG during the product development process. It will demonstrate that the measurement results on the test rig for load distribution are in accordance with the turbine measurements.
This paper presents an original method to compute the loaded mechanical behavior of polymer gears. Polymer gears can be used without lubricant, have quieter mesh, are more resistant to corrosion, and are lighter in weight. Therefore their application fields are continually increasing. Nevertheless, the mechanical behavior of polymer materials is very complex because it depends on time, history of displacement and temperature. In addition, for several polymers, humidity is another factor to be taken into account. The particular case of polyamide 6.6 is studied in this paper.
The Integral Temperature Method for the evaluation of the scoring load capacity of gears is described. All necessary equations for the practical application are presented. The limit scoring temperature for any oil can be obtained from a gear scoring test.
In epicyclic gear sets designed for aeronautical applications, planet gears are generally supported by spherical roller bearings with the bearing outer race integral to the gear hub. This article presents a new method to compute roller load distribution in such bearings where the outer ring can’t be considered rigid.
In this study, limiting values for the load-carrying-capacity of fine-module gears within the module range 0.3–1.0 mm were determined and evaluated by comprehensive, experimental investigations that employed technical, manufacturing and material influence parameters.
This paper intends to determine the load-carrying capacity of thermally damaged parts under rolling stress. Since inspection using real gears is problematic, rollers are chosen as an acceptable substitute. The examined scope of thermal damage from hard finishing extends from undamaged, best-case parts to a rehardening zone as the worst case. Also, two degrees of a tempered zone have been examined.
The objective of this study was to investigate the limits concerning possible reduction of lubricant quantity in gears that could be tolerated without detrimental effects on their load carrying capacity.
Spiral-bevel gears, found in many machine tools, automobile rear-axle drives, and helicopter transmissions, are important elements for transmitting power.