In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference work between a gear with internal teeth and a gear with exterior teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar system. This is one way planetary gears obtained their name.
The parts of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In the majority of cases the housing is fixed. The generating sun pinion is in the heart of the ring equipment, and is coaxially organized with regards to the output. Sunlight pinion is usually attached to a clamping system to be able to give the mechanical link with the electric motor shaft. During procedure, the planetary gears, which will be attached on a planetary carrier, roll between the sunlight pinion and the band equipment. The planetary carrier likewise represents the output shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the required torque. The number of teeth has no effect on the transmission ratio of the gearbox. The number of planets can also vary. As the quantity of planetary gears heightens, the distribution of the strain increases and therefore the torque that can be transmitted. Increasing the number of tooth engagements as well reduces the rolling power. Since only the main total end result has to be transmitted as rolling electrical power, a planetary equipment is extremely efficient. The advantage of a planetary equipment compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit large torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear includes a continuous size, different ratios can be realized by different the number of teeth of the sun gear and the amount of teeth of the planetary gears. The smaller the sun gear, the higher the ratio. Technically, a meaningful ratio selection for a planetary stage is approx. 3:1 to 10:1, since the planetary gears and sunlight gear are extremely tiny above and below these ratios. Bigger ratios can be acquired by connecting a number of planetary phases in series in the same band gear. In cases like this, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a ring gear that’s not set but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft in order to grab the torque via the ring equipment. Planetary gearboxes have grown to be extremely important in lots of regions of mechanical engineering.
They have become particularly well established in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. High transmission ratios can also easily be achieved with planetary gearboxes. Because of the positive properties and small design and style, the gearboxes have a large number of potential uses in industrial applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency because of low rolling power
Nearly unlimited transmission ratio options because of combo of several planet stages
Ideal as planetary switching gear because of fixing this or that the main gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a wide variety of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears arrangement from manual gear container are replaced with an increase of compact and more reliable sun and planetary kind of gears arrangement and also the manual clutch from manual ability train is replaced with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The idea of epicyclic gear box is extracted from the solar system which is known as to an ideal arrangement of objects.
The epicyclic gearbox usually includes the P N R D S (Parking, Neutral, Reverse, Drive, Sport) settings which is obtained by fixing of sun and planetary gears in line with the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a kind of gear which appears like a ring and also have angular trim teethes at its inner surface ,and is put in outermost situation in en epicyclic gearbox, the inner teethes of ring gear is in frequent mesh at outer level with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It’s the equipment with angular lower teethes and is put in the center of the epicyclic gearbox; sunlight gear is in regular mesh at inner level with the planetary gears and is connected with the type shaft of the epicyclic equipment box.
One or more sunshine gears works extremely well for obtaining different output.
3. Planet gears- They are small gears used in between band and sun gear , the teethes of the planet gears are in frequent mesh with sunlight and the ring gear at both inner and outer items respectively.
The axis of the earth gears are attached to the earth carrier which is carrying the output shaft of the epicyclic gearbox.
The earth gears can rotate about their axis and in addition can revolve between your ring and the sun gear just like our solar system.
4. Planet carrier- It is a carrier attached with the axis of the planet gears and is in charge of final tranny of the outcome to the output shaft.
The earth 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 repair the annular gear, sunshine gear and planetary equipment and is managed by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the fact the fixing any of the gears i.electronic. sun equipment, planetary gears and annular equipment is done to obtain the needed torque or rate output. As fixing the above triggers the variation in gear ratios from substantial torque to high speed. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the automobile to go from its initial state and is obtained by fixing the annular gear which in turn causes the planet carrier to rotate with the power supplied to the sun gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the automobile to achieve higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the driven member and annular the travelling member so as to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which reverses the direction of the automobile, this gear is achieved by fixing the planet gear carrier which makes the annular gear the powered member and the sun gear the driver member.
Note- More quickness or torque ratios can be achieved by increasing the number planet and sun gear in epicyclic gear box.
High-speed epicyclic gears could be built relatively little as the power is distributed over a lot of meshes. This benefits in a low power to pounds ratio and, together with lower pitch series velocity, brings about improved efficiency. The small gear diameters produce lower moments of inertia, significantly lowering acceleration and deceleration torque when starting and braking.
The coaxial design permits smaller and therefore more cost-effective foundations, enabling building costs to be kept low or entire generator sets to be integrated in containers.
Why epicyclic gearing is used have already been covered in this magazine, so we’ll expand on this issue in only a few places. Let’s get started by examining a crucial aspect of any project: price. Epicyclic gearing is normally less costly, when tooled properly. Being an wouldn’t normally consider making a 100-piece lot of gears on an N/C milling equipment with a form cutter or ball end mill, you need to certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To continue to keep carriers within affordable manufacturing costs they should be made from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another factor. Epicyclic gear sets are used because they are smaller than offset equipment sets because the load is normally shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear sets are more efficient. The next example illustrates these benefits. Let’s believe that we’re creating a high-speed gearbox to satisfy the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the insight shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design your life is to be 10,000 hours.
With these requirements in mind, let’s look at three possible solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the initial gear establish and splits the two-stage decrease into two branches, and the third calls for utilizing a two-stage planetary or star epicyclic. In this situation, we chose the star. Let’s examine each of these in greater detail, looking 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 base of the final ratio (7.70). In the process of reviewing this remedy we find its size and pounds is very large. To lessen the weight we in that case explore the possibility of making two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and minimizes both size and excess weight considerably . We finally arrive at our third alternative, which may be the two-stage celebrity epicyclic. With three planets this equipment train minimizes tooth loading significantly from the primary approach, and a somewhat smaller amount from alternative two (look at “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a huge part of what makes them so useful, yet these very characteristics can make designing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our aim is to create it easy so that you can understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s start by looking at how relative speeds do the job together with different plans. In the star set up the carrier is set, and the relative speeds of sunlight, planet, and band are simply dependant on the speed of one member and the amount of teeth in each gear.
In a planetary arrangement the ring gear is set, and planets orbit sunlight while rotating on the planet shaft. In this set up the relative speeds of the sun and planets are dependant on the number of teeth in each gear and the quickness of the carrier.
Things get a little trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to often calculate the speed of sunlight, planet, and ring in accordance with the carrier. Remember that possibly in a solar arrangement where the sunlight is fixed it includes 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 may well not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” amount of planets. This amount in epicyclic sets constructed with two or three planets is in most cases equal to using the amount of planets. When a lot more than three planets are applied, however, the effective amount of planets is often less than some of the number of planets.
Let’s look by torque splits in terms of set support and floating support of the associates. With set support, all participants are reinforced in bearings. The centers of sunlight, ring, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets happen to be simultaneously in mesh, producing a lower effective number of planets posting the strain. With floating support, a couple of members are allowed a tiny amount of radial liberty or float, that allows the sun, band, and carrier to seek a position where their centers will be coincident. This float could be as little as .001-.002 in .. With floating support three planets will always be in mesh, producing a higher effective number of planets posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that needs to be made when making epicyclic gears. 1st we must translate RPM into mesh velocities and determine the number of load software cycles per unit of time for every single member. The first step in this determination is normally to calculate the speeds of each of the members relative to the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier can be rotating at +400 RPM the speed of the sun gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that swiftness and the amounts of teeth in each of the gears. The use of signs to represent clockwise and counter-clockwise rotation is important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative swiftness between the two participants is definitely +1700-(-400), or +2100 RPM.
The next step is to decide the quantity of load application cycles. Since the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will always be equal to the amount of planets. The planets, however, will experience only one bi-directional load request per relative revolution. It meshes with the sun and ring, but the load is normally on opposite sides of the teeth, resulting in one fully reversed stress cycle. Thus the earth is known as an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load application.
As noted previously mentioned, the torque on the epicyclic members is divided among the planets. In examining the stress and your life of the people we must look at the resultant loading at each mesh. We find the idea of torque per mesh to become somewhat confusing in epicyclic equipment analysis and prefer to check out the tangential load at each mesh. For instance, in searching at the tangential load at the sun-world mesh, we have the torque on the sun equipment and divide it by the successful amount of planets and the functioning pitch radius. This tangential load, combined with peripheral speed, is utilized to compute the energy transmitted at each mesh and, adjusted by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that need addressing. For example, putting one planet in a position between sun and ring fixes the angular position of the sun to the ring. The next planet(s) is now able to be assembled simply in discreet locations where in fact the sun and ring can be concurrently engaged. The “least mesh angle” from the initially planet that will accommodate simultaneous mesh of another planet is add up to 360° divided by the sum of the numbers of teeth in the sun and the ring. Hence, to be able to assemble extra planets, they must end up being spaced at multiples of the least mesh angle. If one desires to have equal spacing of the planets in a straightforward epicyclic set, planets may be spaced similarly when the sum of the amount of teeth in the sun and ring is definitely divisible by the number of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets gives another level of complexity, and correct planet spacing may necessitate match marking of teeth.
With multiple parts in mesh, losses ought to be considered at each mesh as a way to measure the efficiency of the machine. Electrical power transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic models, the total vitality transmitted through the sun-planet mesh and ring-planet mesh may be significantly less than input ability. This is one of the reasons that easy planetary epicyclic pieces are more efficient than other reducer plans. In contrast, for many coupled epicyclic models total ability transmitted internally through each mesh could be higher than input power.
What of electrical power at the mesh? For simple and compound epicyclic units, calculate pitch line velocities and tangential loads to compute electrical power at each mesh. Values can be acquired from the earth torque relative swiftness, and the working pitch diameters with sun and ring. Coupled epicyclic sets present more technical issues. Components of two epicyclic models could be coupled 36 various ways using one type, one productivity, and one response. Some arrangements split the power, although some recirculate electrical power internally. For these types of epicyclic models, tangential loads at each mesh can only just be determined through the utilization of free-body diagrams. Additionally, the factors of two epicyclic sets can be coupled nine various ways in a series, using one type, one end result, and two reactions. Let’s look at a few examples.
In the “split-electricity” coupled set shown in Figure 7, 85 percent of the transmitted ability flows to band gear #1 and 15 percent to ring gear #2. The effect is that this coupled gear set could be scaled-down than series coupled pieces because the vitality is split between the two components. When coupling epicyclic models in a series, 0 percent of the power will always be transmitted through each establish.
Our next example depicts a established with “electrical power recirculation.” This equipment set happens when torque gets locked in the machine in a way similar to what takes place in a “four-square” test process of vehicle travel axles. With the torque locked in the machine, the horsepower at each mesh within the loop improves as speed increases. As a result, this set will knowledge much higher ability losses at each mesh, leading to substantially lower unit efficiency .
Figure 9 depicts a free-body diagram of a great epicyclic arrangement that experiences electrical power recirculation. A cursory examination of this free-human body diagram explains the 60 percent proficiency of the recirculating collection displayed in Figure 8. Since the planets happen to be rigidly coupled along, the summation of forces on both gears must the same zero. The force at the sun gear mesh outcomes from the torque input to the sun gear. The induce at the second ring gear mesh benefits from the output torque on the band equipment. The ratio being 41.1:1, outcome torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the induce on the second planet will be approximately 14 times the pressure on the first planet at the sun gear mesh. As a result, for the summation of forces to mean zero, the tangential load at the first band gear must be approximately 13 occasions the tangential load at the sun gear. If we believe the pitch range velocities to be the same at the sun mesh and ring mesh, the power loss at the band mesh will be roughly 13 times greater than the power loss at the sun mesh .