A gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another, with some gear ratio performing a mechanical advantage. They are used to increase or decrease the speed or torque of the output shaft. Lightweight design for planetary gear transmissions. The effort force is applied to the driver and the load is applied to the follower. That means that if you connect the purple gear to a motor spinning at 100 revolutions per minute rpm, the green gear will turn at a rate of 500 rpm and. We could make a clock with a 600 tooth gear and 10 tooth pinion as an example and still get a 60 to 1 ratio. In this case, the planet gears have 12 teeth, the sun gear has 18 and the ring gear has 42 teeth. The input gear has 20 teeth and the output gear has 100 teeth. The are a number of reasons that the gear train consists of 2 different modules as well as using an extra 1st wheel in the train. The speed ratio of compound gear train is obtained by multiplying the equations. You can calculate the gear ratio by using the number of teeth of the driving gear a. This text will not deal with the stress analysis aspects of gear design.
If the ring gear is held stationary and the sun gear is used as the input, the planet carrier will be the output. Transmission or movement ratio can be expressed as. That gear train mainly used for multiple speed reduction in between long distance. This relationship between the tooth ratio and the gear ratio is very important. Plane t a r y gear tra i n s consis t o f the follo w i n g. To understand gear ratio we suggest you first read. Gear trains theory of machines engineering reference with. Gear ratio is ratio of the rotational speeds of two or more mating gears. Gear ratio you can think of gear ratio as a multiplier on speedand a divider on torque. The kinematic coefficient is the rate at which a gear rotates with respect to the input gear.
Circumferential velocities in a complex gear train have 3. In mechanical engineering, a gear ratio is a direct measure of the ratio of the rotational speeds of two or more interlocking gears. Pdf gear ratios for compound gear trains of minimum weight. A gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another, with some gear ratio performing a mechanical advantage epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear key facts. For the love of physics walter lewin may 16, 2011 duration. The benefits of knowing the gear ratio is that you can use that to your mechanical advantage. Gear trains theory of machines engineering reference. The compound gear train is defined as one or more gear mounted in same shaft.
Relations between size and gear ratio in spur and planetary gear trains 635 2 equivalent load the load in a mechatronic application is usually a combination of inertial and friction. In our example, we would find the gear ratio by dividing the thirty teeth of the driven gear by the seven teeth of our new driver. The attached pdf is the gear train of something i am working on right building at the moment. A simple gear can change magnitude and line of action of an effort force. When drawn with a compass they have the same centre. The analysis of the gear train is relatively simple, but the result may be unexpected.
The advantage of epicyclic gear train is that, it can get very high or very low velocity ratio compared to simple gear trains and compound gear trains. There is a tradeoff between speed and torque, which is rotational power. You can continue this process along a train of many gears to find a. On the left, two boxes labeled ratios, will turn yellow, this where you type in the nominal diameters of the gears. The speed ratio of the gear train is defined as the ratio between speed of the driver to speed of the driven. This is the lowest gear ratio attainable with an epicyclic gear train. Thus, they differ from an ordinary train by having a moving axis or axes.
In this train, the smaller gears are onefifth the size of the larger gears. In the first three types of gear trains, the axes of the shafts over which the gears are mounted are fixed relative to each other. In this article we will discuss gear ratio calculations for various gear train. Suppose an epicyclic gear train has 2 gears gear a and gear b and an arm arm c. Example 2 a compound epicyclic gear train overdrive has sun, small planet and large planet gears with 21, 15 and 24 teeth respectively. This means that the driver gear has to turn about 4. In order to achieve the above objective, methodology of design used is explained in next point. The epicyclic gear train is useful for transmitting highvelocity ratio with a gear of moderate size and in less space. L where a gear a and the arm c have a common axis at o 1 about which they can rotate. You can continue this process along a train of many gears to find a ratio for the whole train. In this video, we have discussed how to tackle questions related to gear train, how to make the necessary table and reach the desired conclusion.
Pdf relations between size and gear ratio in spur and planetary. Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. To determine a gear ratio, divide the driven gear by. Motor angular displacement and load angular displacement and their derivatives are related by the gear ratio n. For the gear train shown below, determine the train value, output speed, output direction, output torque, and output power. A pair of meshed gears is the basic form of a singlestage gear train. An idler gear does not affect the gear ratio velocity ratio between the driver gear and the driven gear. In this article we will discuss how to calculate gear ratio, speed and torque for various gear train. For every rotation of the 45tooth gear, the 15tooth gear must rotate 3 times. That means that if you connect the purple gear to a motor spinning at 100 revolutions per minute rpm, the green gear will turn at a rate of 500 rpm and the red gear will turn at a rate of 2,500 rpm. In an epicyclic gear train, the axes of the shafts, over which the gears are mounted, move relative to a fixed axis. A gear ratio is the ratio between the driver gear the one being powered and the driven gear the one connected to the driver gear ratios are expressed as fractions and can be written a number of ways.
In other words, the gear ratio, or speed ratio, is inversely proportional to the radius of the pitch circle and the number of teeth of the input gear. The gear ratio is the ratio of the number of turns the output shaft makes when the input shaft turns once. A gear train can be analyzed using the principle of virtual work to show that its torque ratio, which is the ratio of its output torque to its input torque, is equal to the gear. The respective speed ratio is, compound gear train. Simple gear train a simple gear train uses two gears. The current equivalent emd ratio for new locomotives began with gp50 is 70. The gear train shown below has a higher gear ratio. Show students how the gear ratio can be expressed as a fraction. An automobile transmission is an excellent example of how this principle is put to use in controlling vehicle motion. A complete gear train design will necessarily involve considerations of strength of materials and the complicated stress states to which gear teeth are subjected. The gear b meshes with gear a and has its axis on the arm o 2, about which the gear b can. Thus, it is not difficult to get the velocity ratio of the gear train in figure 76b. Relations between size and gear ratio researchgate.
Gears c and b represent a compound gear as they appear fixed together. Bevel gears can be used to change the direction of drive in a gear system by. Gears are cut to exhibit a 25 pressure angle and the module must be 3 mm throughout the train. The 600 tooth gear with teeth similar in shape to our example would be 60 inches in diameter. In epicyclic gear train, different types of gear are used like spur gear, helical gear, bevel gear and many more. Following are the different types of gear trains, depending upon the arrangement of wheels. Design of machinery an introduction to the synthesis and. It is also uncommon to see gear ratios larger than 10 to 1 for regular spur gears. Additionally, for the reverted compound gear train, applicability of the solution obtained is evaluated for the special case in which the interstage speed ratios are. To determine a gear ratio, divide the driven gear by the driving gear. With the gear mate open, select the axis of the top gear and middle gear. In figure 76b a compound ordinary train is seen to be one in which two or more gears may rotate about a single axis. We can find the ratio of any two gears if we know the number of teeth on each of the gears. When a simple gear train has three meshed gears, the intermediate gear between the driver gear and the driven gear is called an idler gear.
Planetary gearboxes are used frequently to match the inertias, lower the motor speed, boost the torque, and at the same time provide a sturdy. Design a gear train that is composed of spur gears that has a gear ratio of 29. Sharing is caring 1 1sharegear ratio is the ratio of output and input number of teeth on a shaft. It allows us to find a gear ratio without actually having to build a gear train and turn the gears. Jan 17, 2018 for the love of physics walter lewin may 16, 2011 duration. Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer, or planet, gears or pinions, revolving about a central sun gear or sun wheel. Determining compound gear ratios multiple stages when a gear train has multiple stages, the gear ratio for the overall gearing system is the product of the individual stages. Typically, the planet gears are mounted on a movable arm or carrier, which itself may rotate relative to the sun gear. Article pdf available january 2004 with 7,439 reads. Khk offers for free the gear technical data book in pdf format. They find the gear ratio for trains of simple gears. Oct 16, 2019 note that neither of these are equal to the gear ratio for the entire train, 4.
N1, n2, n3 speed of gears 1 driver, gear 2 idler, gear 3 driven respectively. Planetary gear trains are extensively used for the power transmission and are the most critical component. For example, for the gear at left the blue gears are 7 and 21 teeth, while the green gears are 9 and 30 teeth. Outline the objective of this paper is to calculate and compare the volume, weight and efficiency of three basic planetary gear trans. The characteristics of a gear ratio upshift is shown in fig. It will take two revolutions of the small gear to produce one revolution of the larger gear. Now for the middle gear and the output gear, select their axes and type in 60mm and 125 mm for their ratios. An example is a gear box that modifies the torque speed characteristic of a prime mover to match that of the load, and comprises gears, shafts, bearings, and seals. A good example is seen as the main mechanism for a hand drill.
In other words, the gear ratio is the ratio between the number of teeth on two gears that are meshed together, or two sprockets connected with a common roller chain, or the circumferences of two pulleys connected with a drive belt. Figure 76a shows a simple ordinary train in which there is only one gear for each axis. As a general rule, when dealing with two gears, if the drive gear the one directly receiving rotational force from the engine, motor, etc. Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes. The gear that is turned by the driver gear is called the driven gear. Gear ratio is the ratio of output and input number of teeth on a shaft. A gear train can be analyzed using the principle of virtual work to show that its torque ratio, which is the ratio of its output torque to. Types of gear train simple, compound, reverted, epicyclic. Jun 07, 2017 in this video, we have discussed how to tackle questions related to gear train, how to make the necessary table and reach the desired conclusion. Ordinary gear trains have axes, relative to the frame, for all gears comprising the train. Since gears 2 and 3 are mounted on one shaft b, therefore n2. A gear ratio is the ratio of the number of rotations of a driver gear to the number of rotations of a driven gear.
Simple, compound and epicyclic are types of gear train used in modern industry. Epicyclic gear train problems and solutions pdf best of all, they are entirely free to find, use and download, so there is no cost or stress at all. Introduction to gear trainsintroduction to gear trains. T1, t2, t3 number of teeth of gears 1 driver, gear 2 idler, gear 3 driven respectively. Relations between size and gear ratio in spur and planetary gear trains. Determine the following if the engine drives the input planet carrier at 4000 revmin. This book is very useful for learning about gears and gearing. Two gears fixed together in this way rotate together and at the same rpm.
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