In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference manage between a gear with internal teeth and a gear with exterior teeth on a concentric orbit. The circulation of the spur equipment occurs in analogy to the orbiting of the planets in the solar program. This is how planetary gears acquired their name.
The components of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In nearly all cases the casing is fixed. The driving sun pinion is usually in the center of the ring equipment, and is coaxially organized in relation to the output. The sun pinion is usually attached to a clamping system in order to give the mechanical link with the engine shaft. During operation, the planetary gears, which are mounted on a planetary carrier, roll between the sun pinion and the band equipment. The planetary carrier as well represents the result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The quantity of teeth has no effect on the transmission ratio of the gearbox. The quantity of planets can also vary. As the quantity of planetary gears improves, the distribution of the load increases and therefore the torque which can be transmitted. Increasing the number of tooth engagements as well reduces the rolling electrical power. Since only area of the total output has to be transmitted as rolling vitality, a planetary equipment is extremely efficient. The benefit of a planetary equipment compared to a single spur gear is based on this load distribution. It is therefore possible to transmit great torques wit
h high efficiency with a concise design using planetary gears.
Provided that the ring gear has a frequent size, different ratios can be realized by varying the quantity of teeth of the sun gear and the amount of the teeth of the planetary gears. Small the sun equipment, the higher the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely tiny above and below these ratios. Bigger ratios can be obtained by connecting a variety of planetary stages in series in the same ring gear. In cases like this, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a ring gear that is not fixed but is driven in any direction of rotation. It is also possible to fix the drive shaft so that you can pick up the torque via the band equipment. Planetary gearboxes have grown to be extremely important in many areas of mechanical engineering.
They have become particularly well established in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Huge transmission ratios may also easily be performed with planetary gearboxes. Because of their positive properties and compact style, the gearboxes have many potential uses in industrial applications.
The benefits of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency due to low rolling power
Nearly unlimited transmission ratio options due to combo of several planet stages
Appropriate as planetary switching gear because of fixing this or that the main gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for an array of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears arrangement from manual gear container are replaced with more compact and more trustworthy sun and planetary type of gears arrangement as well as the manual clutch from manual electricity train is substituted with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The thought of epicyclic gear box is extracted from the solar system which is known as to the perfect arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) settings which is obtained by fixing of sun and planetary gears in line with the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which looks like a ring and also have angular trim teethes at its inner surface ,and is located in outermost location in en epicyclic gearbox, the internal teethes of ring equipment is in regular mesh at outer level with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is put in the center of the epicyclic gearbox; sunlight gear is in regular mesh at inner point with the planetary gears and is usually connected with the input shaft of the epicyclic equipment box.
One or more sunlight gears works extremely well for obtaining different output.
3. Planet gears- They are small gears found in between band and sun equipment , the teethes of the planet gears are in regular mesh with the sun and the ring gear at both inner and outer tips respectively.
The axis of the planet gears are mounted on the planet carrier which is carrying the output shaft of the epicyclic gearbox.
The earth gears can rotate about their axis and also can revolve between the ring and sunlight gear just like our solar system.
4. Planet carrier- This is a carrier fastened with the axis of the earth gears and is accountable for final transmission of the outcome to the productivity shaft.
The planet gears rotate over the carrier and the revolution of the planetary gears causes rotation of the carrier.
5. Brake or clutch band- These devices used to fix the annular gear, sunlight gear and planetary equipment and is manipulated by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the actual fact the fixing the gears i.e. sun gear, planetary gears and annular equipment is done to get the needed torque or rate output. As fixing any of the above triggers the variation in equipment ratios from great torque to high swiftness. So let’s observe how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle which helps the automobile to go from its initial state and is obtained by fixing the annular gear which in turn causes the earth carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the automobile to attain higher speed throughout a drive, these ratios are obtained by fixing the sun gear which makes the earth carrier the driven member and annular the driving a vehicle member as a way to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which reverses the direction of the vehicle, this gear is attained by fixing the earth gear carrier which makes the annular gear the motivated member and the sun gear the driver member.
Note- More velocity or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears can be built relatively tiny as the power is distributed over a variety of meshes. This effects in a low capacity to fat ratio and, as well as lower pitch collection velocity, leads to improved efficiency. The small gear diameters produce lower moments of inertia, significantly minimizing acceleration and deceleration torque when beginning and braking.
The coaxial design permits smaller and for that reason more cost-effective foundations, enabling building costs to be kept low or entire generator sets to be integrated in containers.
The reasons why epicyclic gearing is utilized have been covered in this magazine, so we’ll expand on this issue in only a few places. Let’s begin by examining an essential aspect of any project: cost. Epicyclic gearing is normally less costly, when tooled properly. Being an would not consider making a 100-piece lot of gears on an N/C milling machine with a form cutter or ball end mill, one should certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To preserve carriers within sensible manufacturing costs they must be created from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another factor. Epicyclic gear pieces are used because they are smaller than offset equipment sets because the load is usually shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. As well, when configured properly, epicyclic gear sets are more efficient. The next example illustrates these benefits. Let’s presume that we’re designing a high-speed gearbox to satisfy the following requirements:
• A turbine gives 6,000 hp at 16,000 RPM to the input shaft.
• The end result from the gearbox must travel a generator at 900 RPM.
• The design life is usually to be 10,000 hours.
With these requirements in mind, let’s look at three conceivable solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the original gear set and splits the two-stage lowering into two branches, and the third calls for using a two-level planetary or star epicyclic. In this situation, we chose the superstar. Let’s examine each one of these in greater detail, seeking at their ratios and resulting weights.
The first solution-a single branch, two-stage helical gear set-has two identical ratios, produced from taking the square root of the final ratio (7.70). Along the way of reviewing this option we realize its size and fat is very large. To lessen the weight we after that explore the possibility of earning two branches of a similar arrangement, as seen in the second alternatives. This cuts tooth loading and minimizes both size and pounds considerably . We finally arrive at our third remedy, which is the two-stage star epicyclic. With three planets this gear train reduces tooth loading drastically from the first approach, and a relatively smaller amount from choice two (check out “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a big part of what makes them so useful, yet these very characteristics could make building them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our objective is to make it easy so that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking for how relative speeds work in conjunction with different arrangements. In the star set up the carrier is fixed, and the relative speeds of sunlight, planet, and band are simply determined by the speed of one member and the number of teeth in each gear.
In a planetary arrangement the ring gear is set, and planets orbit the sun while rotating on the planet shaft. In this arrangement the relative speeds of sunlight and planets are dependant on the quantity of teeth in each gear and the quickness of the carrier.
Things get a lttle bit trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. It is therefore imperative to constantly calculate the quickness of sunlight, planet, and ring in accordance with the carrier. Remember that even in a solar set up where the sunshine is fixed it has a speed romance with the planet-it isn’t zero RPM at the mesh.
Torque Splits
When considering torque splits one assumes the torque to be divided among the planets similarly, but this might not be considered a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” quantity of planets. This amount in epicyclic sets constructed with two or three planets is in most cases equal to the actual number of planets. When more than three planets are applied, however, the effective quantity of planets is generally less than some of the number of planets.
Let’s look at torque splits regarding fixed support and floating support of the customers. With set support, all associates are reinforced in bearings. The centers of sunlight, band, and carrier will never be coincident because of manufacturing tolerances. Due to this fewer planets happen to be simultaneously in mesh, resulting in a lower effective number of planets posting the strain. With floating support, one or two participants are allowed a small amount of radial flexibility or float, which allows the sun, ring, and carrier to get a position where their centers happen to be coincident. This float could possibly be less than .001-.002 ins. With floating support three planets will always be in mesh, producing a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that needs to be made when making epicyclic gears. Primary we should translate RPM into mesh velocities and determine the number of load app cycles per device of time for each member. The first rung on the ladder in this determination is certainly to calculate the speeds of every of the members relative to the carrier. For example, if the sun gear is rotating at +1700 RPM and the carrier is certainly rotating at +400 RPM the swiftness of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that acceleration and the amounts of teeth in each of the gears. The usage of indications to signify clockwise and counter-clockwise rotation is certainly important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative acceleration between the two members can be +1700-(-400), or +2100 RPM.
The second step is to determine the quantity of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will always be equal to the number of planets. The planets, even so, will experience only 1 bi-directional load program per relative revolution. It meshes with sunlight and ring, but the load is usually on reverse sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the planet is known as an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load app.
As noted previously mentioned, the torque on the epicyclic customers is divided among the planets. In analyzing the stress and life of the users we must look at the resultant loading at each mesh. We discover the idea of torque per mesh to always be relatively confusing in epicyclic gear evaluation and prefer to look at the tangential load at each mesh. For instance, in searching at the tangential load at the sun-planet mesh, we consider the torque on the sun gear and divide it by the successful amount of planets and the working pitch radius. This tangential load, combined with the peripheral speed, is used to compute the power transmitted at each mesh and, adjusted by the load cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, inserting one planet ready between sun and ring fixes the angular position of sunlight to the ring. The next planet(s) is now able to be assembled just in discreet locations where the sun and ring could be simultaneously engaged. The “least mesh angle” from the primary planet that will accommodate simultaneous mesh of the next planet is equal to 360° divided by the sum of the numbers of teeth in sunlight and the ring. Hence, in order to assemble added planets, they must always be spaced at multiples of this least mesh position. If one wishes to have equivalent spacing of the planets in a straightforward epicyclic set, planets may be spaced equally when the sum of the number of teeth in sunlight and ring is usually divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the set coupling of the planets brings another degree of complexity, and right planet spacing may require match marking of the teeth.
With multiple elements in mesh, losses should be considered at each mesh so that you can measure the efficiency of the unit. Ability transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic pieces, the total ability transmitted through the sun-world mesh and ring-planet mesh may be less than input electric power. This is one of the reasons that simple planetary epicyclic sets are better than other reducer arrangements. In contrast, for most coupled epicyclic pieces total vitality transmitted internally through each mesh may be greater than input power.
What of electric power at the mesh? For simple and compound epicyclic models, calculate pitch brand velocities and tangential loads to compute vitality at each mesh. Ideals can be obtained from the planet torque relative acceleration, and the operating pitch diameters with sun and band. Coupled epicyclic models present more complex issues. Elements of two epicyclic sets could be coupled 36 different ways using one source, one productivity, and one reaction. Some arrangements split the power, while some recirculate power internally. For these types of epicyclic models, tangential loads at each mesh can only be decided through the application of free-body diagrams. Also, the components of two epicyclic pieces can be coupled nine various ways in a string, using one type, one productivity, and two reactions. Let’s look at some examples.
In the “split-electric power” coupled set displayed in Figure 7, 85 percent of the transmitted electricity flows to band gear #1 and 15 percent to ring gear #2. The result is that coupled gear set could be more compact than series coupled pieces because the vitality is split between the two factors. When coupling epicyclic units in a string, 0 percent of the energy will end up being transmitted through each placed.
Our next example depicts a arranged with “electric power recirculation.” This gear set comes about when torque gets locked in the system in a way similar to what occurs in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the horsepower at each mesh within the loop raises as speed increases. Therefore, this set will encounter much higher electricity losses at each mesh, leading to substantially lower unit efficiency .
Number 9 depicts a free-body diagram of a great epicyclic arrangement that experience electric power recirculation. A cursory research of this free-body diagram explains the 60 percent productivity of the recirculating establish shown in Figure 8. Because the planets are rigidly coupled jointly, the summation of forces on the two gears must the same zero. The induce at the sun gear mesh effects from the torque suggestions to sunlight gear. The power at the second ring gear mesh effects from the productivity torque on the ring equipment. The ratio being 41.1:1, output torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the drive on the next planet will be about 14 times the force on the first world at sunlight gear mesh. Therefore, for the summation of forces to equate to zero, the tangential load at the first band gear should be approximately 13 occasions the tangential load at the sun gear. If we assume the pitch series velocities to end up being the same at sunlight mesh and band mesh, the energy loss at the ring mesh will be roughly 13 times greater than the power loss at sunlight mesh .