Gear trains page 2 of 23 since the speed ratio or velocity ratio of gear train is the ratio of the speed of the driver to the speed of the driven or follower and ratio of speeds of any pair of gears in. The speed ratio of compound gear train is obtained by multiplying the equations. Types of gear trains following are the different types of gear trains, depending upon the arrangement of wheels. Gear trains mechanical engineering mcq questions and. The kinematic coefficient is the rate at which a gear rotates with respect to the input gear. Simple gear train a simple gear train uses two gears, which. To create large gear ratio, gears are connected together to form gear trains. So we get n1, n2, n3 speed of gears 1 driver, gear 2 idler, gear 3 driven respectively.
Simple gear trains, compound gear trains for large speed reduction, epicyclic gear trains algebraic and tabular methods of finding velocity ratio of epicyclic gea. Design of machinery an introduction to the synthesis and. Since gears 2 and 3 are mounted on one shaft b, therefore n2. A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission of rotation from one gear to the next. The epicyclic gear trains are used in the back gear of lathe, differential gears of the automobiles, hoists, pulley blocks, wrist watches etc. Introduction to gear trainsintroduction to gear trains. The reason bicycles are easier to cycle up a hill when the gears are changed is due to what is called gear ratio velocity ratio. The nature of the train used depends upon the velocity ratio required and the relative position of the axes of shafts. Notes on the epicyclic gear train solution techniques with application to tandem bicycling new approach. For a simple gear train, velocity ratio is the ratio of published on 06 aug 15. Each time the shaft spins one revolution, the gear moves one tooth forward. Compound gear trains are used when the velocity ratio is outside of the 0. 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. The input gear has 20 teeth and the output gear has 100 teeth.
If you want to create a high gear ratio, nothing beats theworm gear. Gear box ratio the ratio of the gear box is defined as 2 1 n n output speed input speed g. Applicable to all types of trains and a wide range of velocity ratios. Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. In all the questions the driver is on the left the. Gears general gearing arrangement designaerospace llc. 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. Notes on mechanical advantage, velocity ratio and efficiency. L where a gear a and the arm c have a common axis at o 1 about which they can rotate. Velocity ratios and gear trains for the gear train shown below, determine the train value, output speed, output direction, output torque, and output power. The diagram below shows a simple gear train where a is the driver gear, and b is the driven gear. An idler gear does not affect the gear ratio velocity ratio between the driver gear and the driven gear. Simple gear trains, compound gear trains for large speed reduction, epicyclic gear trains algebraic and tabular methods of finding velocity ratio of epicyclic gear trains. Gear ratio can be worked out in the form of numbers and examples are shown below.
Thus, we infer that the velocity ratio of a pair of gears is the inverse ratio of their number of teeth. The following two methods may be used for finding out the velocity ratio of an epicyclic gear train. Mechanical advantage, velocity ratio and efficiency. Gear trains theory of machines engineering reference with. A gear train may consist of spur, bevel or spiral gears. With the gear mate open, select the axis of the top gear and middle gear. Types of gear train simple, compound, reverted, epicyclic. It is the ratio of the speed of the driver gears to the speed of the driven gears. When gears are meshed in gear train, one of the gears is drive input and the.
Torque generated by driven gear gear ratio x torque generated by driver. The gear b meshes with gear a and has its axis on the arm o 2, about which the gear b can rotate. Vr w p wg rg rp train value when more than two gears are in mesh, the term train value tv refers to the ratio of the input speed for the first gear in the train to the output speed for the last gear in the train. 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. To determine a gear ratio, divide the driven gear by. In many cases, one of these inputs will be zero velocity, i. The gear that is turned by the driver gear is called the driven gear. As velocity ratio or ideal mechanical advantage is a simple ratio of two distances, it also does not have the unit. What is the difference between gear ratio and velocity. Note that a zero velocity input to the arm merely makes a conventional train out of the epicyclic train as shown in figure 932a.
For climbs the back gear might be changed to 26, a ratio of 2. Design a gear train that is composed of spur gears that has a gear ratio of 29. Gear trains theory of machines engineering reference. Torque and efficiency the power transmitted by a torque t nm applied to a shaft rotating at n revmin is. For the ordinary gear trains in figure 76a, we have 714 these equations can be combined to give the velocity ratio of the first gear in the train to the last gear. Velocity ratio and efficiency of simple machines duration. This gives an answer of 240rpm working out rpms revolutions per minute in the example shown, the driver gear is smaller than the driven gear. Divide 60 teeth by 30 teeth to find the velocity ratio1. Now for the middle gear and the output gear, select their axes and type in 60mm and 125 mm for their ratios.
Vr number of teeth on the driver gear divided by the number of teeth on the driven gear. It will take two revolutions of the small gear to produce one revolution of the larger gear. Home category mechanical engineering mcq questions and answers theory of machines 2 previous. The stationary gear sun gear or ring gear can be referred to as the central gear. Sharing is caring 1 1sharegear ratio is the ratio of output and input number of teeth on a shaft. In this paper, graph theory is used for the study of epicyclic gear trains or planet gear trains e. 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. 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. In all the questions the driver is on the left the first gear wheel.
To facilitate the application of this concept, only one train in a compound epicyclic train is regarded as basic. Types of gear train and velocity ratio calculation techminy. Types of gear train from typeandlist published date. An example compound gear train is shown in figure 3. Following are the different types of gear trains, depending upon the arrangement of wheels. Simple gear train a simple gear train uses two gears.
N is usually in revmin but the ratio is the same whatever units of speed are used. Show students how the gear ratio can be expressed as a fraction. Velocity ratio for epicyclic train velocity ratio of epicyclic gear train is the ratio of the speed of the driver to the speed of the driven or follower. Basic concept about gear train, speed ratio and train value duration. Machine components designed to manage forces and movement in this way are called mechanisms. Velocity ratio or speed ratio the speed ratio of the gear train is defined as the ratio between speed of the driver to speed of the driven. A large external gear is called the ring gear or annulus. Synthesis of epicyclic gear trains using the velocity. A pgt has been represented by its functional schematic, structural and kinematic graph. They find the gear ratio for trains of simple gears. The following two methods may be used for finding out velocity ratio of an epicyclic gear train. Assume, the motion transmit between gear 1 to gear 3 through idler gear 2.
On the left, two boxes labeled ratios, will turn yellow, this where you type in the nominal diameters of the gears. What is velocity ratio in simple gear train theory of. Pdf notes on the epicyclic gear train solution techniques. Vr driverdriven to calculate the speed of the driven gear multiply the speed of the driver gear by the velocity ratio. Relations between size and gear ratio researchgate. The ratio speed of any pair of gear is the inverse of the teeth. An orthographic view of the gear train showing the power. A compound gear is a gear where 2 or more gears are rigidly attached, such that they rotate at the same speed. 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. Velocity ratio of simple machine is the ratio of distance travelled by the effort to the distance travelled by theload in the machine. Gear ratios or velocity ratios, vr are calculated using the same principle as for simple gear trains, i. In an epicyclic gear train, the axes of the shafts, over which the gears are mounted, move relative to a fixed axis. We can find the ratio of any two gears if we know the number of teeth on each of the gears. Adapted to high speed applications where noise is not a concern.
The following two methods may be used for finding out velocity ratio of. One is the reciprocal of the other detailed answer. For example, for the gear at left the blue gears are 7 and 21 teeth, while the green gears are 9 and 30 teeth. The angular speed of the planet carrier can be found since we know the. The epicyclic gear train is useful for transmitting high velocity ratio with a gear of moderate size and in less space. The device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force.
The driver gear or pulley is the one connected to the power e. 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. The general rule is small to large gear means divide the velocity ratio3. What is velocity ratio in simple gear train theory of machines 2. Epicyclic gear train gear machines free 30day trial. To determine a gear ratio, divide the driven gear by the driving gear. A method of synthesizing compound epicyclic trains is developed using the concept of a velocity ratio spectrum. In this article we will discuss gear ratio calculations for various gear train. In a worm gear, a threaded shaft engages the teeth on a gear. Planetary kinematics note that point 1 on the planet gear is stationary zero velocity due to noslip assumption note that point 2 on the planet gear has the same velocity as point 2 on the sun gear also due to noslip assumption, which is given by. The epicyclic gear train is useful for transmitting highvelocity ratio with a gear of moderate size and in less space. However, the velocity ratio for each pair of gears must then be multiplied together to calculate the total velocity ratio of the gear train.
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