Technology & Engineering
Gear Train
A gear train is a mechanical system composed of interconnected gears that transmit power and motion from one part of a machine to another. It is used to change the speed, torque, or direction of rotation in a mechanical system. Gear trains are commonly found in various devices such as automobiles, bicycles, and industrial machinery.
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eBook - PDF- Mahmoud A. Mostafa(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
265 6 Gear Trains 6.1 INTRODUCTION A Gear Train is a system of two or more meshing gears. The simplest system consists of a driver on one shaft meshing with a follower on another shaft. If both gears are external, the shafts rotate in opposite directions. If one of the pair is an internal gear, the two shafts rotate in the same direction. Gear Trains are used for transmission of power between two shafts when the dis-tance between them is not too large, and when a certain velocity ratio between them is either necessary or desirable. New trends are toward higher speeds for the prime movers, which necessitate in most cases a step-down in speed for the driven machines. In few cases, a step-up in speed may also be desirable. If the number of teeth on all members of a Gear Train is known, the overall speed ratio between the input and output shafts can be easily determined. However, to find a Gear Train to produce a desired ratio is rather difficult. Gear Trains can be classified into two types, namely, ordinary Gear Trains and planetary Gear Trains. In the ordinary Gear Trains, all gears in a system rotate about fixed axes. In the planetary Gear Trains, some gears rotate about moving axes. The train value e is defined as the output speed divided by the input speed. 6.2 ORDINARY Gear TrainS Ordinary Gear Trains are divided into two types: simple and compound. 6.2.1 S IMPLE G EAR T RAINS In this type of trains, all shafts and axles are fixed relative to the frame and each of the shafts carries only one gear (Figure 6.1). It is clear that all gears have the same diametral pitch or module. The magnitude of the velocity ratio of a simple train depends only on the number of teeth on the input and output gears. The intermediate gears or idlers are used only to bridge a given center distance and to satisfy a desired direction of output rotation.
- Jonathan Wickert, Jonathan Wickert, Kemper Lewis(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
The motion of geartrains and belt or chain drives encompasses mechanical components, forces and torques, and energy and power. Gearsets, simple geartrains, compound geartrains, planetary geartrains, and belt and chain drives are used to transmit power, to change the rotation speed of a shaft, and to modify the torque applied to a shaft. More broadly, geartrains and belt and chain drives are examples of mechanisms commonly encountered in mechanical engineering. Mechanisms are combinations of gears, sheaves, belts, chains, links, shafts, bearings, springs, cams, lead screws, and other building-block components that can be assembled to convert one type of motion into another. Thousands of recipes for various mechanisms are available in printed and online mechanical engineering resources with applications including robotics, engines, automatic-feed mechanisms, medical devices, conveyor systems, safety latches, ratchets, and self-deploying aerospace structures. Quantity Conventional Symbols Conventional Units Velocity v mm/s, m/s Angle u deg, rad Angular velocity v rpm, rps, deg/s, rad/s Torque T N ? m Work W J Instantaneous power P W Diametral pitch p teeth/cm Module m mm Number of teeth N } Velocity ratio VR } Torque ratio TR } Form factor n } Table 8.2 Quantities, Symbols, and Units That Arise when Analyzing Motion and Power-Transmission Machinery Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - PDF- Sparrow Consulting(Author)
- 2021(Publication Date)
- Future Managers(Publisher)
Introduction This module covers gears in more detail, focusing on simple and compound Gear Trains and epicyclic gear systems. Gears are wheels that have interlocking teeth. When one wheel rotates, the other wheel rotates because of the locking action of the teeth. Gears are used in most mechanical machines, such as CNC machines, pumps, generators, cars, and so on. The car gearbox greatly regulates the car’s speed. To increase the speed of the car, the car must be shifted to a smaller gear, such as shifting to the fifth gear on the highway to travel faster. 5.1 Introduction to gear drives As mentioned previously, gears are wheels with interlocking teeth. The interlocking teeth ensure that there is no slip or very little slip between the rotating wheels. Gear systems generally function by converting speed from one shaft to the other. The main purpose of any Gear Train is to either reduce the speed of the driver to the final gear or to increase speed from the driver to the final gear. The speed will also influence the torque (mechanical advantage) exerted on the final gear. Definition Torque – a twisting or turning force that tends to cause rotation around an axis 5.1.1 Advantages and disadvantages of gear drives compared to V-belts and chain drives In almost every factory setup, motors and turbines are used to produce some form of rotational movement to perform different types of tasks. These tasks include drilling, generating pressure and CNC operations. Machines that generate rotational movements 91 N4 Mechanotechnics|Hands-On! need some form of power transmission device to transform the movement from one location to another. The most common types of power transmission devices are belt drives, chain drives and gear drives. Which power transmission device should be selected when the need arises? Here are some of the advantages and disadvantages of these power transmission drives to make the decision easier.
- James Doane(Author)
- 2015(Publication Date)
- Wiley(Publisher)
http://commons.wikimedia.org/wiki/File:Transmission_of_motion_by_compund_gear_train_(Army_Service_Corps_Training,_Mechanical_Transport,_1911).jpg ]Gear Trains allow for a positive drive (no slipping) mechanism to generate a constant ratio modification of speed. Other types of mechanisms, such as belt drives, can modify speed while allowing for slipping. Though slipping is good for dissipation of shock loading, it is very undesirable when exact speed and position relationships must exist between the input and output shafts. Belt drives will offer speed modification at lower costs in some applications that allow for some amount of slipping. Chain drives can also serve as an alternative to Gear Trains.When designing a Gear Train, there will not be just one possible solution. There is not an equation that will result in the best possible gear arrangement. The process of Gear Train design is iterative. A satisfactory solution must consider all design requirements as well as limitations. Though this chapter focuses only on the kinematics of Gear Trains, full design must also consider forces produced in Gear Trains. The gears must be designed so that the gear teeth can withstand the forces. Because gears function due to contact between mating teeth, gear materials must be chosen so that the gears do not have excessive wear. Designing gears for strength and wear considerations is beyond the scope of this textbook. Machine design textbooks can be referred to for more information.8.2 Simple Gear Trains
In a simple Gear Train, each gear is mounted on its own shaft. In other words, all gears in a simple Gear Train are arranged in series. Figure 8.2 shows a general setup for a simple Gear Train with three gears.General simple Gear TrainFigure 8.2For the simple Gear Train shown in Figure 8.2 , we will define gear A as the driver and gear C as the output. The speed of gear B can be determined using velocity ratio equations developed in Chapter 7
- Cho W. S. To, Cho S.(Authors)
- 2022(Publication Date)
- Springer(Publisher)
8.3 Gear TrainS In many applications it is necessary to have large velocity reduction or change the direction of rotation of a gear without changing its angular velocity. This can be accomplished by using a combination of gears which is called a Gear Train. Formally, a Gear Train is a mechanism or system that consists of several mating gears. In general, there are Gear Trains that have their gear centers attached to fixed bodies and those whose centers can be fixed and can be allowed to move. Typical Gear Trains with fixed centers, and planetary Gear Trains whose centers may be allowed to move are included in Sec- tions 8.3.1 and 8.3.2, respectively. 8.3.1 Gear TrainS WITH FIXED GEAR CENTERS AND TRAIN VALUE Consider a compound gear that is defined as one in which two or more gears are fixed to the same shaft. Gear Trains are used to achieve large speed change. An example can be found in a garage door opener. When multiple gears are arranged in a series the overall velocity ratio is known as the train value and it is defined as D ! in ! out D ˛ 12 ˛ 23 ˛ 34 : : : ; (8.14) where ˛ ij is the velocity ratio with i denoting the driver gear and j being the driven gear. That is, ˛ ij D ! i ! j D R j R i ; in which R i is the radius of the pitch circle of gear i , for example. Example 8.3 Figure 8.4 shows a Gear Train, in which all gear centers are attached to a fixed reference or fixed frame, with the following properties: 8.3. Gear TrainS 147 Gear 1: N 1 D 10 teeth, and P d D 10, Gear 2: D 2 D 2:5 in, Gear 3: N 3 D 15 teeth, Gear 4: D 4 D 3:0 in, and P d D 10, Gear 5: D 5 D 1:5 in, and P d D 10, and Gear 6: N 6 D 30 teeth. Determine the rotational velocity of gear 6 as gear 1 drives at 2000 rpm, ccw. Figure 8.4: Gear Train with fixed centers. Solution: For gear 1, D 1 D N 1 =P d D 10=10 in D 1:0 in.
eBook - PDFPlant & Equipment NQF3 SB
TVET FIRST
- B Quail, B Els, C Letsoalo, J van Zyl, K Kasselman K Nketiah(Authors)
- 2013(Publication Date)
- Macmillan(Publisher)
Module 7 132 Module 7: Transmissions in machinery Transmissions in machinery Overview At the end of this module, you will be able to: • explain transmissions in engines and motors and the necessity of more than one gear/speed option • explain and determine drive ratios • distinguish between belt drives, chain drives, reduction gearboxes, fluid couplings, torque converters and diesel-electric drives • describe the merits, limitations and applications of each • explain the concept of mechanical sympathy when selecting and engaging gears • identify and assemble different gearbox parts in correct positions and explain their functions • demonstrate how to select gears. Unit 7 .1: The transmission system The transmission system transmits torque and rotation from a power source such as an engine to a driven member such as the wheels of a vehicle. All power sources, engines, motors and equipment with rotating parts, have a maximum rpm at which they can turn. Anything higher than this limit will cause the engine or rotating part to break down. However, by using a system of gears , the transmission system reduces the rpm of the engine by a required ratio to drive the wheels. This enables the wheels of the vehicle to turn at a slower speed than the engine actually produces. The importance of having more than one gear Gears play a major role in controlling speed in plant machinery, trucks, cars, buses, motor bikes and even geared cycles. There are several types of gears including: • ring and pinion • spiral gear • hypoid gear • hydraulic gears • reduction gears. Transmission: The part of a vehicle or machine that connects the power source to the driven part, e.g. connecting the engine of a vehicle to the wheels RPM: Revolutions per minute. The number of times something turns in one minute Gears: The component in a transmission system that transmits rotational force from one object to another Words & Terms
- Jonathan Wickert, Kemper Lewis, Jonathan Wickert(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
372 Summary I n this chapter, we discussed the topics of motion and power transmission in machinery in the context of geartrains and belt drives. The important quantities introduced in this chapter, common symbols representing them and their units are summarized in Table 8.2, and Table 8.3 reviews the key equations used. The motion of geartrains and belt or chain drives encompasses mechanical components, forces and torques, and energy and power. Gearsets, simple geartrains, compound geartrains, planetary geartrains, and belt and chain drives are used to transmit power, to change the rotation speed of a shaft, and to modify the torque applied to a shaft. More broadly, geartrains and belt and chain drives are examples of mechanisms commonly encountered in mechanical engineering. Mechanisms are combinations of gears, sheaves, belts, chains, links, shafts, bearings, springs, cams, lead screws, and other building-block components that can be assembled to convert one type of motion into another. Thousands of recipes for various mechanisms are available in printed and online mechanical engineering resources with applications including robotics, engines, automatic-feed mechanisms, medical devices, conveyor systems, safety latches, ratchets, and self-deploying aerospace structures. Quantity Conventional Symbols Conventional Units Velocity v mm/s, m/s Angle u deg, rad Angular velocity v rpm, rps, deg/s, rad/s Torque T N ? m Work W J Instantaneous power P W Diametral pitch p teeth/cm Module m mm Number of teeth N } Velocity ratio VR } Torque ratio TR } Form factor n } Table 8.2 Quantities, Symbols, and Units That Arise when Analyzing Motion and Power- Transmission Machinery Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
- Ganapathy Nagarajan(Author)
- 2024(Publication Date)
- CRC Press(Publisher)
2.1 Introduction A combination of two or more gears is made to mesh with each other to transmit power from one shaft to another. Such a combination is called Gear Train or train of toothed wheels. The nature of the train wheel used depends upon the velocity ratio required and the relative position of the axes of shafts. A Gear Train may consist of spur, helical or bevel gears. 2.2 Nomenclature of gears The following terms are illustrated in Fig. 2.1. Figure 2.1 Terms used in gears 1. Pitch circle: It is an imaginary circle which by rolling action would give the same motion as the actual gear. 2 Gear Trains Gear Trains 43 2. Pitch circle diameter: It is the diameter of the pitch circle. The size of the gear is usually speci昀ed by the pitch circle diameter. It is also known as pitch diameter. 3. Pitch point: It is a common point of contact between two pitch circles. 4. Pitch surface: It is the surface of the rolling discs which the meshing gears have replaced at the pitch circle. 5. Pressure angle or angle of obliquity: It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point. It is usually denoted by α. The standard pressure angles are 14.5° and 20°. 6. Addendum: It is the radial distance of a tooth from the pitch circle to the top of the tooth. 7. Dedendum: It is the radial distance of a tooth from the pitch circle to the bottom of the tooth. 8. Addendum circle: It is the circle drawn through the top of the teeth and is concentric with the pitch circle. 9. Dedendum circle: It is the circle drawn through the bottom of the teeth. It is also called root circle. 10. Circular pitch: It is the distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth. It is usually denoted by pc. 2.2.1 Types of Gear Trains Following are the different types of Gear Trains: 1.
eBook - ePub- Damir T. Jelaska(Author)
- 2012(Publication Date)
- Wiley(Publisher)
Chapter 6 Planetary Gear Trains6.1 Introduction
6.1.1 Fundamentals of Planetary Gear Trains
Mechanisms with gears (or rarely – with friction wheels) where one axis is movable are called planetary mechanisms . The simplest, rude planetary gear mechanism, Figure 6.1 , consists of gear 1, gear 2 and carrier V (carrying gear 2). Obviously, rotary motion of gear 1 causes two rotary motions: rotation of gear 2 around its own axis and its rotation together with carrier V, around the axis of gear 1. Those motions are similar to a planet's motion around its own axis and around the sun. Therefore gear 2 is termed as a planet gear (henceforth, planet ), central gear 1 is termed as a sun gear and planet carrier V is henceforth simply termed as a carrier . Any gear having immovable axes is generally termed as a central gear , and besides the sun one having external toothing, there is another one having internal toothing, which is termed as an annulus gear (Figure 6.1b ).Figure 6.1 Rude planetary mechanisms: (a) central gear with external toothing, (b) central gear with internal toothingSchemes of planetary Gear Trains are always presented in axial plane, like those in Figure 6.1 . They consist of sun gears, annulus gears, planet gears, carriers, shafts, bearings and couplings. In order to better understand the schemes of trains in further reading, the schemes of those elements are presented in Table 6.1 .Table 6.1 Schemes of PGT elements.The axis around which the central gears and carrier rotate or can rotate is termed the main axis, while members able to rotate around the main axis and thus receive or give rotary motion, that is the torque, are called the main members
eBook - PDF- Harold Josephs, Ronald Huston(Authors)
- 2002(Publication Date)
- CRC Press(Publisher)
We begin our discussion in the next section with a brief review of the fundamental concepts of gearing and of conjugate action (uniform motion transmission). In subsequent sections, we discuss gear tooth geometry, gear nomenclature, gearing kinematics, and Gear Trains. Section 17.16 has a glossary of commonly used gearing terms. 17.2 Preliminary and Fundamental Concepts: Rolling Wheels The transmission of motion and forces is commonly called power transmission . With gears, power transmission almost always occurs between rotating shafts. For the most part, these shafts are parallel (as with spur and helical gears), but they may also be intersecting (as with bevel and spiral bevel gears) or even nonparallel and nonintersecting (as with hypoid and worm gears). In the sequel, we will develop our analysis with parallel shaft gears and specifically with spur gears. The analysis of other types of gears is fundamentally the same but somewhat more detailed due to their more complex geometries. 574 Dynamics of Mechanical Systems For parallel shaft gears, we may consider the motion transmitted between the gears to be the same as that transmitted between rolling disks or rolling wheels as depicted in Figure 17.2.1. Generally, these wheels have different diameters. The smaller wheel is usually called the pinion and the larger the gear . Also, the disk providing the motion or forces is often called the driver , while the wheel receiving the motion or forces is called the follower . Consider again the end view of the rolling wheels as in Figure 17.2.2. Let the wheels be called A and B with centers O A and O B and radii r A and r B as shown. Let C be the contact point between A and B . Then, from elementary rolling analysis (see Section 4.11), if there is no slipping between A and B then we have: (17.2.1) where ω A and ω B are the angular speeds of A and B . Equation (17.2.1) shows that the angular speed ratio ω A / ω B is inversely equal to the radius ratio r B / r A .
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