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epicyclic gearbox

In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference operate between a gear with internal teeth and a gear with external teeth on a concentric orbit. The circulation of the spur equipment takes place in analogy to the orbiting of the planets in the solar system. This is one way planetary gears acquired their name.
The components of a planetary gear train could 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 generating sun pinion is definitely in the center of the ring gear, and is coaxially arranged in relation to the output. The sun pinion is usually mounted on a clamping system to be able to give the mechanical link with the motor shaft. During operation, the planetary gears, which are attached on a planetary carrier, roll between your sunlight pinion and the band equipment. The planetary carrier likewise represents the productivity shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the required torque. The quantity of teeth has no effect on the transmission ratio of the gearbox. The quantity of planets can also vary. As the number of planetary gears enhances, the distribution of the load increases and then the torque that can be transmitted. Increasing the quantity of tooth engagements likewise reduces the rolling ability. Since only area of the total productivity should be transmitted as rolling electrical power, a planetary equipment is extremely efficient. The advantage of a planetary equipment compared to a single spur gear is based on this load distribution. Hence, it is possible to transmit large torques wit
h high efficiency with a concise design using planetary gears.
So long as the ring gear includes a constant size, different ratios can be realized by various the number of teeth of the sun gear and the number of teeth of the planetary gears. Small the sun equipment, the higher the ratio. Technically, a meaningful ratio selection for a planetary stage is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely tiny above and below these ratios. Larger ratios can be acquired by connecting a lot of planetary levels in series in the same band gear. In this case, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a band gear that is not fixed but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft so that you can grab the torque via the ring gear. Planetary gearboxes have grown to be extremely important in many regions of mechanical engineering.
They have grown to be particularly well established in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Substantial transmission ratios can also easily be achieved with planetary gearboxes. Because of the positive properties and compact design and style, the gearboxes have many potential uses in professional applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency due to low rolling power
Practically unlimited transmission ratio options due to combination of several planet stages
Appropriate as planetary switching gear due to fixing this or that section of the gearbox
Chance for 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 package are replaced with an increase of compact and more efficient sun and planetary type of gears arrangement as well as the manual clutch from manual power train is replaced with hydro coupled clutch or torque convertor which made the transmitting automatic.
The thought of epicyclic gear box is taken from the solar system which is considered to the perfect arrangement of objects.
The epicyclic gearbox usually comes with 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.
Components of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which looks like a ring and have angular cut teethes at its interior surface ,and is positioned in outermost job in en epicyclic gearbox, the internal teethes of ring equipment is in constant mesh at outer level with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It is the gear with angular cut teethes and is placed in the center of the epicyclic gearbox; sunlight gear is in continuous mesh at inner stage with the planetary gears and is certainly connected with the insight shaft of the epicyclic equipment box.
One or more sun gears can be utilised for achieving different output.
3. Planet gears- These are small gears used in between ring and sun equipment , the teethes of the planet gears are in constant mesh with sunlight and the ring gear at both inner and outer things respectively.
The axis of the earth gears are mounted on the planet carrier which is carrying the output shaft of the epicyclic gearbox.
The planet gears can rotate about their axis and in addition can revolve between your ring and sunlight gear just like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the earth gears and is accountable for final tranny of the productivity 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- The device used to fix the annular gear, sunlight gear and planetary gear and is managed by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the fact the fixing the gears i.e. sun equipment, planetary gears and annular gear is done to obtain the needed torque or velocity output. As fixing the above causes the variation in equipment ratios from excessive torque to high rate. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the vehicle to move from its initial state and is obtained by fixing the annular gear which causes the earth 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 vehicle to achieve higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the driven member and annular the driving a car member so as to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which in turn reverses the direction of the vehicle, this gear is attained by fixing the earth gear carrier which makes the annular gear the powered member and sunlight gear the driver member.
Note- More speed or torque ratios may be accomplished by increasing the number planet and sun gear in epicyclic gear package.
High-speed epicyclic gears could be built relatively tiny as the power is distributed over a number of meshes. This results in a low capacity to weight ratio and, together with lower pitch brand velocity, leads to improved efficiency. The small equipment 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.
Why epicyclic gearing is utilized have been covered in this magazine, so we’ll expand on the topic in just a few places. Let’s start by examining an essential facet of any
project: price. Epicyclic gearing is normally less costly, when tooled properly. Just as one would not consider making a 100-piece lot of gears on an N/C milling equipment with an application 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 acceptable manufacturing costs they should be made from castings and tooled on single-purpose equipment with multiple cutters concurrently removing material.
Size is another element. Epicyclic gear models are used because they are smaller than offset gear sets because the load is usually shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear pieces are more efficient. The following example illustrates these rewards. Let’s presume that we’re building a high-speed gearbox to gratify the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the insight shaft.
• The output from the gearbox must travel a generator at 900 RPM.
• The design life is usually to be 10,000 hours.
With these requirements at heart, let’s look at three feasible solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the initial gear collection and splits the two-stage reduction into two branches, and the third calls for by using a two-stage planetary or star epicyclic. In this instance, we chose the star. 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 base of the final ratio (7.70). In the process of reviewing this option we recognize its size and fat is very large. To reduce the weight we after that explore the possibility of earning two branches of an identical arrangement, as observed in the second solutions. This cuts tooth loading and minimizes both size and excess weight considerably . We finally reach our third remedy, which is the two-stage superstar epicyclic. With three planets this equipment train reduces tooth loading drastically from the primary approach, and a somewhat smaller amount from solution two (look at “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a huge part of why is them so useful, yet these very characteristics can make developing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our target is to make it easy that you can understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds function together with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply dependant on the speed of 1 member and the number of teeth in each gear.
In a planetary arrangement the ring gear is fixed, and planets orbit sunlight while rotating on earth shaft. In this arrangement the relative speeds of the sun and planets are determined by the number of teeth in each equipment and the swiftness of the carrier.
Things get a lttle bit trickier when working with coupled epicyclic gears, since relative speeds may not be intuitive. It is therefore imperative to always calculate the speed of sunlight, planet, and ring in accordance with the carrier. Remember that actually in a solar set up where the sunshine is fixed it has a speed relationship with the planet-it is not zero RPM at the mesh.
Torque Splits
When contemplating torque splits one assumes the torque to be divided among the planets equally, but this might not exactly be considered a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” number of planets. This amount in epicyclic sets constructed with two or three planets is generally equal to the actual quantity of planets. When more than three planets are used, however, the effective amount of planets is at all times less than you see, the number of planets.
Let’s look for torque splits when it comes to fixed support and floating support of the participants. With fixed support, all participants are supported in bearings. The centers of the sun, ring, and carrier will not be coincident because of manufacturing tolerances. Due to this fewer planets are simultaneously in mesh, producing a lower effective quantity of planets posting the strain. With floating support, a couple of customers are allowed a small amount of radial freedom or float, that allows the sun, band, and carrier to get a position where their centers happen to be coincident. This float could be less than .001-.002 ins. With floating support three planets will be in mesh, producing a higher effective number of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that should be made when designing epicyclic gears. Initial we must translate RPM into mesh velocities and determine the quantity of load application cycles per product of time for each member. The first step in this determination is usually 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 is usually rotating at +400 RPM the quickness of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that rate and the numbers of teeth in each one of the gears. The usage of indications to symbolize 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 rate between the two customers is +1700-(-400), or +2100 RPM.
The second step is to determine the amount of load application cycles. Since the sun and ring gears mesh with multiple planets, the amount of load cycles per revolution relative to the carrier will become equal to the number of planets. The planets, on the other hand, will experience only 1 bi-directional load request per relative revolution. It meshes with the sun and ring, however the load is on contrary sides of the teeth, resulting in one fully reversed tension cycle. Thus the earth is known as an idler, and the allowable stress must be reduced 30 percent from the value for a unidirectional load app.
As noted above, the torque on the epicyclic people is divided among the planets. In examining the stress and life of the members we must consider the resultant loading at each mesh. We discover the idea of torque per mesh to end up being relatively confusing in epicyclic equipment evaluation and prefer to look at the tangential load at each mesh. For example, in looking at the tangential load at the sun-planet mesh, we take the torque on sunlight equipment and divide it by the powerful quantity of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is used to compute the energy transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there can also be assembly complications that need addressing. For example, putting one planet ready between sun and ring fixes the angular placement of sunlight to the ring. The next planet(s) can now be assembled simply in discreet locations where the sun and band can be concurrently involved. The “least mesh angle” from the initial planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the amounts of teeth in the sun and the ring. Hence, to be able to assemble additional planets, they must always be spaced at multiples of this least mesh position.
If one wants 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 certainly divisible by the number of planets to an integer. The same rules apply in a compound epicyclic, but the fixed coupling of the planets contributes another degree of complexity, and right planet spacing may necessitate match marking of teeth.
With multiple elements in mesh, losses should be considered at each mesh as a way to evaluate the efficiency of the machine. Electricity transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic sets, the total vitality transmitted through the sun-planet mesh and ring-world mesh may be less than input electrical power. This is among the reasons that easy planetary epicyclic units are better than other reducer plans. In contrast, for many coupled epicyclic sets total ability transmitted internally through each mesh may be higher than input power.
What of electricity at the mesh? For simple and compound epicyclic sets, calculate pitch range velocities and tangential loads to compute power at each mesh. Values can be acquired from the planet torque relative swiftness, and the operating pitch diameters with sunshine and ring. Coupled epicyclic pieces present more complex issues. Components of two epicyclic units can be coupled 36 different ways using one insight, one result, and one response. Some plans split the power, while some recirculate electrical power internally. For these types of epicyclic units, tangential loads at each mesh can only just be motivated through the utilization of free-body diagrams. Also, the elements of two epicyclic sets could be coupled nine various ways in a string, using one input, one output, and two reactions. Let’s look at some examples.
In the “split-power” 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 result is that coupled gear set could be smaller sized than series coupled sets because the power is split between your two components. When coupling epicyclic pieces in a string, 0 percent of the energy will be transmitted through each establish.
Our next example depicts a set with “vitality recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what takes place in a “four-square” test process of vehicle drive axles. With the torque locked in the machine, the hp at each mesh within the loop raises as speed increases. Therefore, this set will experience much higher ability losses at each mesh, resulting in considerably lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that experience electrical power recirculation. A cursory analysis of this free-human body diagram explains the 60 percent performance of the recirculating placed proven in Figure 8. Because the planets are rigidly coupled with each other, the summation of forces on both gears must the same zero. The drive at the sun gear mesh benefits from the torque suggestions to sunlight gear. The push at the next ring gear mesh benefits from the output torque on the band gear. The ratio being 41.1:1, result torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the pressure on the second planet will be approximately 14 times the induce on the first planet at sunlight gear mesh. Consequently, for the summation of forces to mean zero, the tangential load at the first ring gear must be approximately 13 instances the tangential load at the sun gear. If we believe the pitch collection velocities to always be the same at sunlight mesh and ring mesh, the power loss at the band mesh will be around 13 times higher than the energy loss at sunlight mesh .


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