Thus, we infer that the velocity ratio of a pair of gears is the inverse ratio of their number of teeth. As velocity ratio or ideal mechanical advantage is a simple ratio of two distances, it also does not have the unit. The driver gear or pulley is the one connected to the power e. Pdf gear ratios for compound gear trains of minimum weight. Download objective type questions of theory of machines pdf visit our pdf store. In this article we will discuss gear ratio calculations for various gear train. In epicyclic gear train, different types of gear are used like spur gear, helical gear, bevel gear and many more.
It allows us to find a gear ratio without actually having to build a gear train and turn the gears. The train value of a gear train is competitive exam india. In this paper, graph theory is used for the study of epicyclic gear trains or planet gear trains e. 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. The input gear has 20 teeth and the output gear has 100 teeth. A hypocycloidal crank mechanism with a suntoplanet gear ratio d velocity while. 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. That is their purpose, to provide a timevarying output function in response to a constant velocity input. Epicyclic gear trains egts are commonly used in automatic transmission mechanisms to achieve a set of desired velocity ratios.
The diagram below shows a simple gear train where a is the driver gear, and b is the driven gear. The speed ratio of compound gear train is obtained by multiplying the equations. Structure and analysis of planetary gear trains prof. What is velocity ratio in simple gear train theory of.
The gear that is turned by the driver gear is called the driven gear. Mechanical advantage, velocity ratio and efficiency. Velocity ratio of gear drive in the case of involute profiles, all points of contact occur on the same straight line ab. Gear termi nology this is one of the easiest guides on gears. The gear ratio of a gear train, also known as its speed ratio, is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. Gear ratio is ratio of the rotational speeds of two or more mating gears. An epicyclic gear train consists of two gears mounted so that the center of one gear revolves. Compound gear trains involve several pairs of meshing gears. Velocity ratios are calculated by dividing the driver gear by the driven gear. Synthesis of epicyclic gear trains using the velocity. Introduction to gear trainsintroduction to gear trains. Design of machinery an introduction to the synthesis and.
Types of gear train and velocity ratio calculation techminy. When two or more gears mesh together the arrangement is called a gear set or a gear train. Simple gear train a simple gear train uses two gears. Mechanical analysis gear trains city, university of london. Since gears 2 and 3 are mounted on one shaft b, therefore n2. 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 made equal throughout the gear train. Bicycles normally have a large gear wheel which has a pedal attached and a selection of gear wheels of different sizes, on the back wheel. Understand gear trains and how to calculate ratios. A pgt has been represented by its functional schematic, structural and kinematic graph. A very good example is a bicycle which has gears that make it easier to cycle, especially up hills.
Gear ratio velocity ratio 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. 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. The gear ratio of an epicyclic gearing system is somewhat nonintuitive. Types of gear trains following are the different types of gear trains, depending upon the.
Zoltan levai received 9 february 1968 abstract both compound and internal or external planet gears are considered as well as the paired planet gears. Sharing is caring 1 1sharegear ratio is the ratio of output and input number of teeth on a shaft. A method of synthesizing compound epicyclic trains is developed using the concept of a velocity ratio spectrum. Velocity ratio and efficiency of simple machines duration. Calculations will be made to obtain the output gears angular velocity as well as the center distance between shafts. Of course, the velocity ratio of noncircular gears is not constant. For a simple gear train, velocity ratio is the ratio of published on 06 aug 15. To overcome the problem slippage as in belt drives, gear is used which produce a positive drive with uniform angular velocity. Velocity ratio of simple machine is the ratio of distance travelled by the effort to the distance travelled by theload in the machine. This type of transmission are used by skoda,toyota, lexus, etc epicyclic gearing planetry gearing.
The kinematic coefficient is the rate at which a gear rotates with respect to the input gear. The characteristics of a gear ratio upshift is shown in fig. Such a combination is called gear train or train of toothed wheels. In order to achieve the above objective, methodology of design used is explained in next point. Types of gear train simple, compound, reverted, epicyclic. Let, ta number of teeth on gear a, and tb number of teeth on gear b. Basic concept about gear train, speed ratio and train value duration. The following two methods may be used for finding out the velocity ratio of an epicyclic gear train. Gear ratios or velocity ratios, vr are calculated using the same principle as for simple gear trains. Simple compound gear train n n n n t t t t r nn nn rr rr 26 tttt 16 15 14 15 14 12 23 34 45 56 4 23 4 5 34 56. 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. Types of gear train and velocity ratio calculation.
Velocity ratio of gears pdf title velocity ratio of gears pdf precision gear manufacturer spur gears, bevel miter gears, worm, anti backlash gears manufactured by sdpsi. The velocity ratio of an epicyclic gear train is determined by the following methods. The epicyclic gear trains are useful for transmitting high velocity ratios with gears of moderate size in a comparatively lesser space. We can find the ratio of any two gears if we know the number of teeth on each of the gears. Teaching planetary gear trains with the aid of nomographs. However, simple gears with only 5 teeth tend to run a bit rough, so your best bet is to make or obtain gears with 10 and 24 teeth. This relationship between the tooth ratio and the gear ratio is very important.
Determine the following if the engine drives the input planet carrier at 4000 revmin. All normal to the tooth profiles at the point of contact coincide with the line ab thus these profiles transmit uniform rotarycoincide with the line ab, thus these profiles transmit uniform rotary. R is the angular speed of the arm, equal to the input angular speed. The nature of the train used depends upon the velocity ratio required and the relative position of the axes of shafts. Developing the gear ratio formula sae international. For a compound epicyclic train, the number of equations is considerably increased. It is stated that the simple planetary gear train consisting. The velocity ratios selected for a transmission are tailored for vehicle.
Tabular method consider an epicyclic gear train as shown in fig. Figure 1 shows an epicyclic gear mechanism employing the ravigneaux gear set as the ratio change gear train where the rotating and band clutches are designed as c and b, respectively. 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. A gear train may consist of spur, bevel or spiral gears. The gear ratio can be calculated directly from the numbers of teeth on the gears in t. Following are the different types of gear trains, depending upon the arrangement of wheels. Velocity ratios of epicyclic gear train the following two methods may be used for finding out the velocity ratio of an epicyclic gear train. Vr driverdriven to calculate the speed of the driven gear multiply the speed of the driver gear by the velocity ratio. An idler gear does not affect the gear ratio velocity ratio between the driver gear and the driven gear. Example 2 a compound epicyclic gear train overdrive has sun, small planet and large planet gears with 21, 15 and 24 teeth respectively. The epicyclic gear train is useful for transmitting high velocity ratio with a gear of moderate size and in less space. Their instantaneous velocity ratio is defined by equation 6. The gear wheel transmitted motion between one shaft to another shaft, so the multiple set of gear transmit motion from single main gear to various revolving parts is known as gear train. In this planetary gears sets are placed in series to provide transmission.
To facilitate the application of this concept, only one train in a compound epicyclic train is regarded as basic. It require small area during the power transmission and to obtain large speed reduction. Show students how the gear ratio can be expressed as a fraction. Sdpsi is a well known manufacturer of high precision standard and custom gears for a wide range of applications. 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. Gear ratio can be worked out in the form of numbers and examples are shown below. 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. Design a gear train that is composed of spur gears that has a gear ratio of 29. Velocity ratio of epicyclic gear train velocity ratio.