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Design and manufacturing of spur idler gears of gearbox by means of traditional methods, involves too many times of trial and error and consequently spending too much time and money. Utilizing new technologies such as CAD/CAM will increase productivity and flexibility of the process (PDP). In this paper, different parameters and characteristics of the parametric design process of the spure idler gear using CAD/CAM have been discussed and a method for parametric design has been presented. Using this method, design of parts of the same group can be done within the shortest time and by inputing parameters for any part, a typical design can be achieved. Due to the comlex contours and high accuracy requirements of the gear theeth, gear manufacturing is highly specialized, demanding much machining time and therefore is costly. Material wastage is also another problem in these process. In recent years, there has been increased interest in the production of gears by precision forging. Precision forging enables gear teeth to be manufactured to net or near-net tolerances. Resulting in significant savings in raw material and production time compared with conventional cutting methods. In contrast, precision gear forging is associated with problems related to die design, preform volume and geometry, tooth dimensional accuracy, load and energy prediction, ejection problem and finally tool life. These are also reviewed in this paper. Finally, designed dies for manufacturing a typical spur idler gear, analysed by “Super Forge” software.

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Design and manufacturing of spur idler gears of gearbox by means of traditional methods, involves too many times of trial and error and consequently spending too much time and money. Utilizing new technologies such as CAD/CAM will increase productivity and flexibility of the process (PDP). In this paper, different parameters and characteristics of the parametric design process of the spure idler gear using CAD/CAM have been discussed and a method for parametric design has been presented. Using this method, design of parts of the same group can be done within the shortest time and by inputing parameters for any part, a typical design can be achieved. Due to the comlex contours and high accuracy requirements of the gear theeth, gear manufacturing is highly specialized, demanding much machining time and therefore is costly. Material wastage is also another problem in these process. In recent years, there has been increased interest in the production of gears by precision forging. Precision forging enables gear teeth to be manufactured to net or near-net tolerances. Resulting in significant savings in raw material and production time compared with conventional cutting methods. In contrast, precision gear forging is associated with problems related to die design, preform volume and geometry, tooth dimensional accuracy, load and energy prediction, ejection problem and finally tool life. These are also reviewed in this paper. Finally, designed dies for manufacturing a typical spur idler gear, analysed by “Super Forge” software.

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Gears are one of the important sources of vibrations and noise in industrial rotating machinery and power transmission systems. In order to design and develop an optimal and quiet geared power transmission system, this paper presents the design of an active vibration control for gear-bearing system. A dynamic model of the geared system is presented, where some undesired parameters in the design such as manufacturing errors, teeth deformations, mounting errors as well as external excitations resulting from distributions of applied torque are included. An active control system is presents in order to control and attenuate the disturbance impress on the system vibrations. The idea behind the design of this control system is to reduce vibration transmissibility by the introduction of the excitation forces in the bearing. The controller is investigated and designed by using feedback control and based on the H-infinity control approach. It can be presented as an optimization problem. To solve this optimization problem, Particle swarm optimization (PSO) algorithm is used, which is one of the optimization methods available among artificial intelligence. The simulation results are performed to investigate performance of the control system.

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Gears are widely used to transmit power between two parallel shafts. Study on the lubricant film which is formed between the engaged teeth of pinion and gear is of high importance in predicting the performance of the power transmission system as well as surface failure and wear. Gear surfaces in comparison to rolling element bearings have a higher surface roughness and thus considering the surface roughness is important in gear analysis. In this research, the performance of a pinion-gear system operating under mixed-elastohydrodynamic lubrication is being investigated using load-sharing concept. The contacting asperities might experience elastic, elasto-plastic or fully plastic contact. The engagement of pinion and gear for each point along the line of action is replaced with contact of two cylinders. The radii of these cylinders as well as the exerted load vary along the line of action. Using load-sharing concept, the proposed model can predict the lubricant film thickness, friction coefficient, and portion of the total load that is carried by asperities as well as lubricant film. The predicted results are verified by comparison to other available methods which are published in the literature.

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Gears are one of the most important elements of any power transmission system. Among all types of gears, helical gears are more common due to their high capacity in power transmission as well as lower level of noise. The aim of this study is to present a model for analyzing the contact of teeth of helical gears considering thermal effects and surface roughness. In the present model, each helical gear is divided to several narrow spur gears in which each of the spur gears have a small rotation angle relative to the previous one. Also each contact point of gears is replaced with contact of two equivalent cylinders. Considering the fact that the governing regime for gears lubrication is the mixed-elastohydrodynamic regime, the total load is carried by lubricant and asperities' contact. Meshing and lubrication analysis of a pair of helical gears is conducted based on the load-sharing concept and parameters such as film thickness, friction coefficient and temperature rise are predicted. The predictions based on the load-sharing concept are compared to other published results Acceptable accuracy, short execution time along with considering thermal and roughness effects are some of the major characteristics of this study.

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The accurate evaluation and experimental investigation of the gear dynamic response have indicated some interesting nonlinear phenomena such as bifurcation and chaotic behavior on some system parameters. The chaotic motion is an unusual and unpredictable behavior and has been considered as an undesirable phenomenon in the nonlinear gear vibration systems. Therefore, in order to design and develop an optimal gear transmission system, it is important to control and eliminate these nonlinear phenomena. This paper presents the design of a gear system in order to control and suppress the chaos. A generalized nonlinear dynamics model of a spur gear pair including the backlash and the static transmission error is formulated. The idea behind the design of this control system is applying an additional control excitation force to the driver gear. The parameter spaces of the control excitation force are obtained analytically by using the Melnikov approach. The numerical simulations including the bifurcation diagram, the phase portrait, and the time history are used to confirm the analytical predictions and show effectiveness of the proposed control system for chaos suppression in nonlinear gear systems.

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Nowadays, optimization is becoming one of the most important techniques in engineering and industry to provide competing products in design and manufacturing. Therefore, it is a necessity to search for optimum designs with productibility. In aerospace industry reducing weight and improving reliability of the products are major concerns. As regards the gearbox is one of the most important parts in the helicopter propulsion system, these objects should be more considered. However, most of the existing designs consider only one object, hence, it is vital to implement optimization techniques to include different objectives to improve the existing designs and provide optimum products. In this paper, optimum design parameters including module and face width of gears for the main gearbox of Sikorsky ASH-3D helicopter have been determined (modified) using single and multi-objective mixed discrete- continuous optimization method to minimize weight of the gearbox, increase the safety factor and reduce the difference between safety factors of different gears. The results show that the weight of the gears can be reduced by 27.24% comparing with the existing gearbox. The results of the multiobjective optimization have also been presented as Pareto front diagram wich can be used by the manufacturers to satisfy the prefered requiments.

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One of the major subsystems of each airplane is landing gear system which must be capable of tolerating extreme forces applied to the airplane during landing. Using conservative techniques to find landing loads result in overestimation and unnecessary extra structural weight. New commercial softwares can simulate real landing conditions with acceptable accuracy if detailed mechanical data about landing gear system subparts are provided. Although these softwares work well but due to lack of detailed information about the subparts at the conceptual design phase, complexity and time consuming of modeling, expensive license price, etc. they do not seem to be the best choice for design purpose. In this study, in order to calculate landing loads more precisely than the estimating conservative methods, flight dynamic differential equations of an airplane during landing phase are derived and through numeric and state space techniques are solved for different initial conditions including, three point landing, two point landing and one wheel landing. Each landing gear of the airplane is modeled as a two-degree of freedom mass-spring-damper set. Time history of the airplane center of gravity, pitch and roll angle, vertical landing loads of each landing gear and their spin-up loads for different landing types (different initial conditions) are obtained to show capabilities of this new, fast and accurate landing simulation code, generated.

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In this paper, an optimal active controller is designed to prevent the shimmy vibrations in aircraft nose landing gear. The controller is designed according to the linearized system while the input is implemented on the real non-linear plant. Shimmy vibration is the lateral and torsional vibrations in the wheel that causes instability in high speed performances. Thus, control and suppressing of this vibration is extremely important. In this paper, using the nonlinear dynamics of the nose landing gear system, the equivalent linearized system is extracted and then its related linearized state space is derived. Stability, controllability and observability of the system are investigated based on the linearized model of the system and damping the shimmy vibrations is performed with the least consumption of energy using Linear Quadratic Regulator (LQR). To estimate the states of the system which are not measurable using ordinary sensors, an observer is designed and implemented using separation principal. To verify the performance of the proposed controller, vibration response of the open loop system is compared with the closed loop response of the designed optimal controller. Considerable improvement can be seen in the performance of the closed loop system since not only the vibrations are effectively damped but also the consumption of energy is minimized. Finally, digital control system is extended in order to implement the proposed controller on the discretized model of the system and the effect of sampling rate on the accuracy of the system is studied.

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In this paper, in order to reduce a landing gear vibration two adaptive control systems are designed considering the landing and taxi phases. For this purpose, 6 degree of freedom equations of motion of the landing gear and the related transfer functions are extracted. A reduced order model of the overall transfer functions are given as a result of complicated dynamic model. A Lyapunov based model reference adaptive control is designed to absorb the vibration of front wheel of the landing gear at touchdown. In addition, a minimum variance adaptive controller is designed and implemented on the system to reject the band level disturbances during the taxi phase. The band disturbances are modeled as a colored Gaussian noise and the system parameters as well as noise characteristics are estimated using extended least square approach. Both control systems are investigated to assess the best performance. Numerical simulations of the system in Matlab/Simulink environment show the preferences and satisfactory performances of the proposed vibration control systems. These results are calculated against various inputs including model reference adaptive control and minimum variance approaches

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The position of the planets for the planetary gear systems are in two forms of equally and unequally spaced. This paper investigates free vibration of the planetary gear with unequally spaced planets. The planetary gear set of this study is modeled as set of lumped masses and springs. Each component such as sun gear, carrier, ring gear and planets possesses three degrees of freedom and considered as rigid bodies. Bearing and mesh stiffnesses are modeled in the form of linear springs. Generally, planet, rotational, translational, distinct and degenerate modes are five vibration modes of the planetary gear systems. The results show that the translational mode for the system with numbers of even equally and unequally spaced planets, is different and rotational and translational modes have the same characteristics for the both systems. For the system with numbers of even unequally spaced planets, the natural frequencies of the translational modes have multiplicity one. When the numbers of the planets of the system are odd and the position of them is unequally spaced, the rotational and planet modes are generating and the natural frequencies of the translational modes are not appears. For the distinct and degenerate modes of the system with unequally spaced planets, the planets only have the rotational motion.

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In the present paper, thermal analysis of used spiral bevel gears in main gearbox of helicopter- belong to Iran Aircraft Manufacturing- is investigated. Firstly, with introducing the geometry properties of gears, basic lubrication and thermal analyses are considered based on standards of gear design such as AGMA. Then, in order to create the finite element model, initial and boundary conditions with considering the oil viscosity and calculating the friction coefficient, convection and heat conduction coefficients are determined based on experimental and analytical models in spiral bevel gear. It is noted that, the goal of finite element model is considered to reduce the complex calculation errors and increase the speed of problem solving. Effects of various parameters such as increasing the FLASH temperature and influences of initial temperature on it, contact stresses and heat fluxes, comparison of different mineral oils on the decreasing of temperature and fatigue life are examined. The obtained results of present work show that the FLASH temperature of main gearbox is linear function of initial temperature, so that FLASH temperature increases 56 centigrade in comparison of initial temperature. Also, it is demonstrated that the presence of various mineral oils in this system lead to reduce the solid-solid surface contact and friction coefficient. Moreover, these lubricants cause the cooling in the gearbox and enhancing more temperature, thus the employing these lubricants lead to exceed the system temperature to 90 centigrade.

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The mechanical flow meter is a widely used tool in various industries such as the oil industry. A pair of oval gears is used in the mechanical flow meter. The most important issue in the oval gear is the lack of uniformity in the shape of its teeth. This lack of uniformity prevents the gears from interfering with each other, for this reason, similar to the circular gear, it is not possible to machine.  For the oval gear machining, tool design, or the use of the wire-cut method is required. As a result, it is necessary to know the profile of oval gear teeth. Therefore, in this article, the relations governing oval gears have been investigated. In these relationships, the number of teeth, geometric dimensions, and equations of motion have been investigated. Then, it was modeled using the Gear-Otix software and with the help of the results of the relationships of the gears, the interference conditions of the two gears were checked in this software, and finally, the stress analysis of the gear was done by using Comsol software for the appropriate state. With the help of the created model, it is possible to produce this gear using the wire-cut method.

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When there is a need to transfer power between non-parallel shafts, bevel gears are used. Bevel gears are widely used in power transmission systems such as car differentials and helicopter gearboxes, so knowing and improving the performance of this type of gear is particularly important. It is important and necessary to accurately calculate the machining time of the desired bevel gear in order to reduce time and costs. In this paper, data are collected using Taguchi's test design method in three levels. The amount of machining time was calculated for each test, then with the help of signal-to-noise analysis, the influence of the input parameters on the design of the straight tooth bevel gear on the reduction of the machining time has been investigated. The investigated parameters are conversion ratio, allowable contact stress and allowable bending stress.According to the obtained results, the conversion ratio parameter was found to be the most effective parameter on reducing the machining time. The optimal value of the conversion ratio was reported at level 1 with a value of 1.5.

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Gears are a very important part of mechanical equipment in industry. Due to the fact that in mechanical processes, the teeth are subjected to long-term load, the surface of their teeth is usually rusty, worn out and even broken. Timely fault detection cannot only increase the life cycle of the gears, however it can even prevent property losses and losses due to breakdowns. Therefore, it is necessary to monitor and diagnose the health of the gears to ensure the normal operation of the invaluable machines in industry. In this research, fault detection in polymer gears using audio signal is considered as a non-contact inspection method. Sound signals were recorded from 50 pairs of gears in normal condition, worn teeth and broken teeth at two speeds of 66 and 99 rpm. In the following, using wavelet packet transformation (WPT), the sound signal is analyzed in the time-frequency domain and 12 statistical features are extracted from the 16 coefficients of the fourth level of WPT. In order to study the performance of the fault detection algorithm, four classifications of linear discriminant analysis, K-nearest neighbor, decision tree and support vector machine have been used. The values of accuracy, true positive rate, true negative rate, positive predictive value, negative predictive value, geometric-mean, F1 score, and Matthews correlation coefficient have shown that by using WPT, a significant distinction can be found between normal and faulty gears. Therefore, the proposed method is a suitable approach for timely error detection of polymer gears used in mechanical equipment.