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SPIRAL BEVEL GEAR DESIGN AND DEVELOPMENT -GENERATION AND SIMULATION OF MESHING AND TOOTH CONTACT ANALYSIS (TCA)
FOR IMPROVED PERFORMANCE –FUTURE SCOPE
1ASHOK KUMAR GUPTA, 2DR.VANDANA SOMKUWAR
1Research Scholar (Ph D Mechanical Engineering), AISECT University, Dist: Raisen, Near Bhopal (M P)
2Professor, Mechanical Engineering Education Department, NITTTR, Bhopal (M P)
ABSTRACT:-The procedures needed to develop spiral bevel gear sets for a new product can require months of trial-and-error work and thousands of dollars. In view of increasing global competition for lower priced products, bevel gears are a prime target for the next generation of computerization.
Answering this challenge, it has realized a new modified method through a shift in the way spiral bevel gear development is performed.The Gleason face hobbing process has been widely applied by the gear industry. But so far, few papers have been found regarding exact modelling and simulation of the tooth surface generations and tooth contact analysis (TCA) of spiral bevel gear sets. The developed face hobbling generation model is directly related to a physical bevel gear generator. A generalized and enhanced TCA algorithm is proposed. The face hobbling process has two categories, non-generated (Format ®) and generated methods, applied to the tooth surface generation of the gear. In both categories, the pinion is always finished with the generated method. The developed tooth surface generation model covers both categories with left-hand and right-hand members. Based upon the developed theory, an advanced tooth surface generation and TCA program is developed and integrated into Gleason CAGE™ for Windows Software. Most of the truck manufacturers have been confronted with ever more increasing demands on their products and on the development process. These demands are reflected in higher engine power, lower vehicle noise, higher fuel economy and shorter lead times in development. In most of commercial vehicle, single stage spiral bevel gears are used in the rear axles. In engineering, new product development (NPD) is the complete process of bringing a new product to market.
2 1.1 INTRODUCTION
A spiral bevel gear is a bevel gear with helical teeth. The main application of this is in a vehicle differential, where the direction of drive from the drive shaft must be turned 90 degrees to drive the wheels. The helical design produces less vibration and noise than conventional straight-cut or spur-cut gear with straight teeth. A spiral bevel gear set should always be replaced in pairs i.e. both the left hand and right hand gears should be replaced together since the gears are manufactured and lapped in pairs.
1.1.1 Handedness
Spiral bevel handedness
Zerol handedness
Fig. 1.1 Spiral spiral bevel gears
A right hand spiral bevel gear is one in which the outer half of a tooth is inclined in the clockwise direction from the axial plane through the midpoint of the tooth as viewed by an observer looking at the face of the gear. A left hand spiral bevel gear is one in which the outer half of a tooth is inclined in
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the counterclockwise direction from the axial plane through the midpoint of the tooth as viewed by an observer looking at the face of the gear. Note that a spiral bevel gear and pinion are always of opposite hand, including the case when the gear is internal. Also note that the designations right hand and left hand are applied similarly to other types of bevel gear, hypoid gears, and oblique tooth face gears.
1.1.2 Spiral angle
Fig 1.2 Spiral angle
The spiral angle in a spiral bevel gear is the angle between the tooth trace and an element of the pitch cone, and corresponds to the helix angle in helical teeth. [1-2] Unless otherwise specified, the term spiral angle is understood to be the mean spiral angle. Fig (1.3)
Mean spiral angle is the specific designation for the spiral angle at the mean cone distance in a bevel gear.
Outer spiral angle is the spiral angle of a bevel gear at the outer cone distance.
Inner spiral angle is the spiral angle of a bevel gear at the inner cone distance.
Fig 1.3 Spiral angle relationships
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1.1.3 Comparison of spiral bevel gears to spiral gears
Spiral gears are stronger, operate more quietly and can be used for higher reduction ratios, however they also have some sliding action along the teeth, which reduces mechanical efficiency, the energy losses being in the form of heat produced in the gear surfaces and the lubricating fluid.In older automotive designs, spiral gears were typically used in rear-drive automobile drivetrains, but modern designs have tended to substitute spiral bevel gears to increase driving efficiency. Spiral gears are still common in larger trucks because they can transmit higher torque. A higher spiral offset allows the gear to transmit higher torque. However increasing the spiral offset results in reduction of mechanical efficiency and a consequent reduction in fuel economy. For practical purposes, it is often impossible to replace low efficiency spiral gears with more efficient spiral bevel gears in automotive use because the spiral bevel gear would need a much larger diameter to transmit the same torque. Increasing the size of the drive axle gear would require an increase of the size of the gear housing and a reduction in the ground clearance.[3]
Another advantage of spiral gear is that the ring gear of the differential and the input pinion gear are both spiral. In most passenger cars this allows the pinion to be offset to the bottom of the crown wheel. This provides for longer tooth contact and allows the shaft that drives the pinion to be lowered, reducing the "hump" intrusion in the passenger compartment floor.
However, the greater the displacement of the input shaft axis from the crown wheel axis, the lower the mechanical efficiency.
1.2 OVERVIEW
Computer-based design analysis is nowadays a common activity in most development projects. When new software and manufacturing processes are introduced, traditional empirical knowledge is unavailable and considerable effort is required to find starting design concepts. This forces gear designers to go beyond the traditional standards-based design methods. The results obtained are in agreement with existing knowledge. The transformation has had a vast influence on gear manufacturing as well, providing process
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improvements that lead to higher gear quality and lower manufacturing costs. However, in the case of the gear industry, the critical process of Generation and Simulation of Meshing and Tooth Contact Analysis (TCA) of Spiral Bevel Gears for Improved Performance remains relatively unchanged.
Gearing is one of the most critical components in a mechanical power transmission system, and in most industrial rotating machinery. A gear is a mechanical device often used in transmission systems that allows rotational force to be transferred to another gear or device. The gear teeth allow force to be fully transmitted without slippage and depending on their configuration, can transmit forces at different speeds, torques, and even in a different direction. Throughout the mechanical industry, many types of gears exist with each type of gear possessing specific benefits for its intended applications. Bevel gears are widely used because of their suitability towards transferring power between nonparallel shafts at any required angle or speed. Spiral bevel gears have curved and slope gear teeth in relation to the surface of the pitch cone. As a result, an oblique surface is formed during gear mesh which allows contact to begin at one end of the tooth (toe) and smoothly progress to the other end of the tooth (heel), as shown in Fig 1.4.
Fig 1.4 Spiral bevel gear mesh
Spiral bevel gears, in comparison to straight or zerol bevel gears, have additional overlapping tooth action which creates a smoother gear mesh.
This smooth transmission of power along the gear teeth helps to reduce Heel
Toe
Heel Toe
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noise and vibration that increases exponentially at higher speeds. Therefore, the ability of a spiral bevel gear to change the direction of the mechanical load, coupled with their ability to aid in noise and vibration reduction, make them a prime candidate for use in the automobile industry and others. The American Gear Manufacturing Association (AGMA) has developed standards for the design, analysis, and manufacture of bevel gears. The driving and driven gears are the most important components of the Gear box of any automotive. Modelling allows the design engineer to let the characteristic parameters of a product drive the design of that product. During the gear design, the main parameters that would describe the designed gear such as module, pressure angle, root radius, tooth thickness and number of teeth could be used as the parameters to define the gear. Spiral bevel gears are used to transmit power between shafts that are typically at a 90-degree orientation to each other. The teeth on spiral bevel gears are curved and have one concave and one convex side. They also have a spiral angle. The spiral angle of a spiral bevel gear is defined as the angle between the tooth trace and an element of the pitch cone, similar to the helix angle found in helical gear teeth. In general, the spiral angle of a spiral bevel gear is defined as the mean spiral angle.
Because spiral bevel gears do not have the offset, they have less sliding between the teeth and are more efficient than spiral and produce less heat during operation. Also, one of the main advantages of spiral bevel gears is the relatively large amount of tooth surface that is in mesh during their rotation. For this reason, spiral bevel gears are an ideal option for high speed, high torque applications.
1.3CONCLUSION
The robust and computerized tooth generation approach along with the tooth contact analysis provides a better way to reduce the wear, noise and vibration problems related to spiral bevel gears. Also, the optimization of tooth profile can be done with greater proceedings to the calculations.
Ultimately, we should think of automated soft-wares for designing that would create an optimized model of the gear tooth profile just by inputting
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the basic parameters. The conventional spiral bevel gears are continuously being investigated in order to reduce the failure or increase their transmissible power level, either by developing new composite materials or by modifying the gear tooth geometry. A mathematical model of an ideal spiral bevel and hypoid gear-tooth surfaces based on the Gleason hypoid gear generator mechanism is proposed. Using the proposed mathematical model, the tooth surface sensitivity matrix to the variations in machine–tool settings is investigated. Surface deviations of a real cut pinion and gear with respect to the theoretical tooth surfaces are also investigated. An optimization procedure for finding corrective machine–tool settings is then proposed to minimize surface deviations of real cut pinion and gear-tooth surfaces. The results reveal that surface deviations of real cut gear-tooth surfaces with respect to the ideal ones can be reduced to only a few microns.
Therefore, the proposed method for obtaining corrective machine–tool settings can improve the conventional development process and can also be applied to different manufacturing machines and methods for spiral bevel and hypoid gear generation. In this chapter, an accurate and practical method based on ease-off topography was proposed to perform loaded and unloaded tooth contact analysis of spiral bevel and spiral gears having both types of local and global deviations. Manufacturing errors causing global errors and localized surface deviations were considered to update the theoretical ease-off to form a new ease-off surface that was used to perform a loaded tooth contact analysis. Two numerical examples of (i) face-milled spiral gear set with local deviations and (ii) face-hobbed spiral gear set with global deviations measured by CMM were presented to demonstrate the effectiveness of the proposed methodology as well as quantifying the effect of such deviations on load distribution and the unloaded and loaded motion transmission error.
The robust and computerized tooth generation approach along with the tooth contact analysis provides a better way to reduce the wear, noise and vibration problems related to spiral bevel gears.
Also, the optimization of tooth profile can be done with greater proceedings to the calculations. Ultimately, we should think of automated soft-wares for
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designing that would create an optimized model of the gear tooth profile just by inputting the basic parameters. The conventional spiral bevel gears are continuously being investigated in order to reduce the failure or increase their transmissible power level, either by developing new composite materials or by modifying the gear tooth geometry. A mathematical model of an ideal spiral bevel and spiral gear-tooth surfaces based on the Gleason spiral gear generator mechanism is proposed. Using the proposed mathematical model, the tooth surface sensitivity matrix to the variations in machine–tool settings is investigated. Surface deviations of a real cut pinion and gear with respect to the theoretical tooth surfaces are also investigated.
An optimization procedure for finding corrective machine–tool settings is then proposed to minimize surface deviations of real cut pinion and gear- tooth surfaces. The results reveal that surface deviations of real cut gear- tooth surfaces with respect to the ideal ones can be reduced to only a few microns. Therefore, the proposed method for obtaining corrective machine–
tool settings can improve the conventional development process and can also be applied to different manufacturing machines and methods for spiral bevel and spiral gear generation.
1.3.1 Limitations Of The Research Work
The confines of this research study are as follows;
a. Even though vibration analysis is not suitable for variable speed wind turbine generator where he loads and speeds are not stationary, the random vibration analysis was carried out to located the failure of bearing and it was not included in this doctoral work.
b. As the ice layers in the nordic climate, Inset collision in the warm humid climate, sand blast of blade and mix up of sand particles with the grease lubricant in desert like environment & liable to corrosion by the sea shore climate, the effect of ambient temperature on the performance of wind turbine components is not considered in the present work.
c. Even though time frequency analysis (or) ARMA models and motor current signature analysis are more apt for fault diagnosis in wind turbine gearboxes, because of the restriction to omplete the doctoral
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work within the stipulated time, the scholar has concentrated on that inspite of his own interest.
1.3.2 Scope For Further Research
The present study is done under static condition of the gears. In future, stress analysis shall be carried out for the dynamic state of gear drives.
Also, designing of hob (cutter) can be formulated for the production of composite parole in the helical gears. Technique for improving the gearbox oil cleanliness level shall be done by introducing three stage filter element (5 micron, 10 micron and 50 micron) instead of existing two stage filter element (10 micron and 50 micron) along with an on-line particle counter.
There is a possibility to study the oil cleanliness level in future to improve the life of bearing.
I. Contact stress can also determined for the Face gear
II. Experimental validation of the results predicted by AGMA formula and the Finite element analysis presented in this work Because of the high torque and high loads during operation, considerable amounts of heat is also dissipated. So the heat transfer condition can also be considered in the future analysis of the Face gear.
1.3.3 Future Demands Next Generation Of Standards And Practices In Gear Industry Gear
Manufacturers are moving into an era that will see changes in both engineering practices and industry standards as new end-products evolve.
Within the traditional automotive industry, carbon emission reduction legislation will drive the need for higher levels of efficiency and growth in electric and hybrid vehicles. Meanwhile, the fast growing market of wind turbines is already opening up a whole new area of potential for gearbox manufacturers, but this industry is one that will demand reliability, high levels of engineering excellence and precision manufacturing. Over the coming years, these changes will require new techniques and approaches that will quickly become accepted industry standards.
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Efficiency has become one of the most important factors in the design process for hybrid and electric vehicles. However, optimizing gear designs to be more efficient without compromising other design targets, such as NVH and durability, can be challenging. Having recognized this problem of conflicting design requirements, Romax has carried out significant research and development into simultaneous optimization, so engineers are able to consider efficiency, durability and NVH in the same environment and optimize the system performance to meet all the targets. Another major challenge facing hybrid and electric vehicle designers is that gear noise becomes much more prominent and can be at a high frequency—which is much more noticeable to end users. This makes gear noise in electric vehicles harder both to predict and to solve. Potentially, the gear noise in hybrid and electric vehiclesneeds to be lower over a much wider range of operating conditions than the traditional vehicle. This can be achieved with computer aided optimization of design. As quieter and more efficient automotive gearboxes are required by the end user, this also means that manufacturing standards need to be raised to meet these higher demands.
By using advanced computer-assisted design optimization combined with virtual prototyping, you can give the HEV and ZEV drives of the future the quietest and most efficient experience possible, but this must be combined with tighter and more precise manufacturing techniques and a good standard of quality control. The wind turbine industry is growing and providing a route for many companies to diversify and find new revenue streams. However, whilst component suppliers are welcomed, many are discovering that the wind energy industry demands both quality as well as quantity. The mechanical parts of the wind turbine have to be robust enough to deal with extraordinary forces and stresses, and for this reason, the industry demands exceptional technical ability, as well as high quality from its component manufacturers. Within the area of gearbox transmissions, in particular, reliability problems are widespread, and these issues have to be addressed if the industry is to develop to its full potential.
Manufacturers looking to enter the wind turbine industry can turn to design platforms to support their needs. Design platforms enable manufacturers to
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decrease design time by allowing a variety of concepts to be reviewed quickly and easily, considering all permutations. It also allows different components to be tested in the design stage and the impact on performance, weight and manufacturing to be measured, for example investigating the effects of switching a helical gear for a spur gear. Having the ability to understand the forces and material capabilities enables design decisions to be made before expensive prototyping is performed, ensuring quiet, durable and long-lasting components.For suppliers entering the wind energy market, design platforms can provide a valuable reduction in time and costs to meet the demands for turbine component manufacture, particularly drive train elements such as gearboxes and bearings. For those companies already supplying the wind energy industry, design platforms can offer an opportunity to develop capabilities and improve results. As we move into the future, a new generation of opportunities awaits the gear industry.Going forward, the gear industry will need to utilize and embrace new and developing technologies to ensure that it remains as competitive as possible. The gear industry has a bright future, one that will carve out new practices and standards as we seek to meet the challenges this future brings with it.
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