epicyclic gearbox

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 external teeth on a concentric orbit. The circulation of the spur gear takes place in analogy to the orbiting of the planets in the solar program. This is one way planetary gears obtained their name.
The elements of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In nearly all cases the casing is fixed. The traveling sun pinion is in the heart of the ring equipment, and is coaxially organized with regards to the output. Sunlight pinion is usually mounted on a clamping system in order to offer the mechanical link with the motor shaft. During operation, the planetary gears, which happen to be mounted on a planetary carrier, roll between your sun pinion and the band gear. The planetary carrier likewise represents the outcome shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The quantity of teeth has no effect on the transmitting ratio of the gearbox. The number of planets can also vary. As the number of planetary gears raises, the distribution of the strain increases and then the torque that can be transmitted. Increasing the number of tooth engagements as well reduces the rolling electricity. Since only part of the total result should be transmitted as rolling vitality, a planetary gear is extremely efficient. The advantage of a planetary equipment compared to an individual spur gear is based on this load distribution. Hence, it is possible to transmit huge torques wit
h high efficiency with a concise design and style using planetary gears.
So long as the ring gear has a regular size, different ratios could be realized by various the quantity of teeth of sunlight gear and the amount of teeth of the planetary gears. Small the sun gear, the greater the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, since the planetary gears and sunlight gear are extremely tiny above and below these ratios. Higher ratios can be obtained by connecting a couple of planetary levels in series in the same band gear. In this instance, we speak of 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 any direction of rotation. Additionally it is possible to repair the drive shaft in order to grab the torque via the band equipment. Planetary gearboxes have become extremely important in many areas 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. Substantial transmission ratios may also easily be performed with planetary gearboxes. Because of the positive properties and compact style, the gearboxes have a large number of potential uses in industrial applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency because of low rolling power
Almost unlimited transmission ratio options due to blend of several planet stages
Suited as planetary switching gear because of fixing this or that section of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears set up from manual gear field are replaced with an increase of compact and more trustworthy sun and planetary type of gears arrangement plus the manual clutch from manual power train is replaced with hydro coupled clutch or torque convertor which in turn made the transmission automatic.
The idea of epicyclic gear box is taken 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, Drive, Sport) modes which is obtained by fixing of sun and planetary gears according to the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a type of gear which looks like a ring and also have angular lower teethes at its inner surface ,and is put in outermost job in en epicyclic gearbox, the inner teethes of ring equipment is in constant mesh at outer level with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is positioned in the center of the epicyclic gearbox; the sun gear is in regular mesh at inner level with the planetary gears and is certainly connected with the source shaft of the epicyclic equipment box.
One or more sun gears works extremely well for reaching different output.
3. Planet gears- They are small gears used in between band and sun equipment , the teethes of the earth gears are in constant mesh with sunlight and the ring equipment at both inner and outer items respectively.
The axis of the planet gears are attached to 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 the ring and the sun gear just like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the planet gears and is accountable for final tranny of the end result to the result 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 repair the annular gear, sunlight gear and planetary gear and is managed by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the fact the fixing the gears i.electronic. sun gear, planetary gears and annular equipment is done to obtain the expected torque or acceleration output. As fixing the above triggers the variation in gear ratios from high torque to high rate. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle which helps the automobile to move from its initial state and is obtained by fixing the annular gear which in turn causes the planet carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the automobile to achieve higher speed throughout a travel, these ratios are obtained by fixing the sun gear which makes the planet carrier the influenced 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 in turn reverses the direction of the automobile, this gear is attained by fixing the earth gear carrier which makes the annular gear the driven member and the sun gear the driver member.
Note- More quickness or torque ratios may be accomplished by increasing the quantity planet and sun equipment in epicyclic gear container.
High-speed epicyclic gears could be built relatively small as the power is distributed over a lot of meshes. This results in a low power to excess weight ratio and, as well as lower pitch series velocity, brings about improved efficiency. The tiny gear diameters produce lower moments of inertia, significantly reducing 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 used have already been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s get started by examining a significant facet of any project: cost. Epicyclic gearing is generally less costly, when tooled properly. Just as one would not consider making a 100-piece large amount of gears on an N/C milling machine with an application cutter or ball end mill, one should not really consider making a 100-piece lot of epicyclic carriers on an N/C mill. To continue to keep carriers within realistic manufacturing costs they must be made from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another issue. Epicyclic gear sets are used because they are smaller than offset gear sets since the load can be shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Also, when configured properly, epicyclic gear units are more efficient. The next example illustrates these rewards. Let’s assume that we’re designing a high-speed gearbox to gratify the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the suggestions shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design your life is usually to be 10,000 hours.
With these requirements at heart, let’s look at three practical solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear arranged and splits the two-stage lowering into two branches, and the 3rd calls for by using a two-level planetary or superstar epicyclic. In this situation, we chose the star. Let’s examine each one 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, derived from taking the square base of the final ratio (7.70). Along the way of reviewing this solution we find its size and pounds is very large. To reduce the weight we then explore the possibility of earning two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and reduces both size and excess weight considerably . We finally reach our third solution, which is the two-stage star epicyclic. With three planets this equipment train minimizes tooth loading significantly from the primary approach, and a relatively smaller amount from alternative two (see “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a big part of what makes them so useful, however these very characteristics can make developing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our target is to make it easy that you should understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking at how relative speeds job in conjunction with different arrangements. In the star set up the carrier is set, and the relative speeds of sunlight, planet, and ring are simply determined by the speed of one member and the number of teeth in each gear.
In a planetary arrangement the band gear is set, and planets orbit sunlight while rotating on the planet shaft. In this arrangement the relative speeds of sunlight and planets are determined by the number of teeth in each gear and the speed of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. It is therefore imperative to usually calculate the speed of the sun, planet, and ring relative to the carrier. Remember that actually in a solar set up where the sun 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 exactly be 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 designed with two or three planets is in most cases equal to the actual number of planets. When more than three planets are utilized, however, the effective amount of planets is usually less than some of the number of planets.
Let’s look by torque splits with regards to set support and floating support of the customers. With fixed support, all participants are reinforced in bearings. The centers of sunlight, ring, and carrier will never be coincident because of manufacturing tolerances. For that reason fewer planets are simultaneously in mesh, producing a lower effective amount of planets posting the strain. With floating support, one or two people are allowed a little amount of radial independence or float, that allows the sun, ring, and carrier to seek a position where their centers happen to be coincident. This float could be as little as .001-.002 ins. With floating support three planets will always be in mesh, resulting in a higher effective number of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that needs to be made when designing epicyclic gears. 1st we should translate RPM into mesh velocities and determine the number of load software cycles per device of time for each and every member. The first step in this determination can be to calculate the speeds of each of the members in accordance with the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is normally rotating at +400 RPM the rate of the sun gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that swiftness and the numbers of teeth in each of the gears. The utilization of symptoms to stand for 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 quickness between the two participants is certainly +1700-(-400), or +2100 RPM.
The next step is to determine the amount of load application cycles. Since the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will become equal to the quantity of planets. The planets, even so, will experience only 1 bi-directional load request per relative revolution. It meshes with the sun and ring, but the load is normally on opposing sides of one’s teeth, leading to one fully reversed anxiety cycle. Thus the earth is considered an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load software.
As noted over, the torque on the epicyclic participants is divided among the planets. In examining the stress and your life of the associates we must look at the resultant loading at each mesh. We discover the concept of torque per mesh to always be relatively confusing in epicyclic equipment analysis and prefer to check out the tangential load at each mesh. For instance, in seeking at the tangential load at the sun-world mesh, we consider the torque on sunlight gear and divide it by the effective amount of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the power transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of each component.
Furthermore to these issues there can also be assembly complications that require addressing. For example, placing one planet ready between sun and ring fixes the angular posture of the sun to the ring. The next planet(s) can now be assembled only in discreet locations where in fact the sun and band can be simultaneously engaged. The “least mesh angle” from the initially planet that will support simultaneous mesh of the next planet is equal to 360° divided by the sum of the amounts of teeth in sunlight and the ring. Therefore, so as to assemble extra planets, they must always be spaced at multiples of the least mesh position. If one wants to have equivalent spacing of the planets in a straightforward epicyclic set, planets could be spaced similarly when the sum of the number of teeth in sunlight and band is normally divisible by the amount of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets contributes another level of complexity, and appropriate planet spacing may necessitate match marking of the teeth.
With multiple components in mesh, losses ought to be considered at each mesh as a way to evaluate the efficiency of the unit. Vitality transmitted at each mesh, not input power, can be used to compute power reduction. For simple epicyclic models, the total power transmitted through the sun-planet mesh and ring-world mesh may be less than input electric power. This is one of the reasons that easy planetary epicyclic pieces are more efficient than other reducer plans. In contrast, for most coupled epicyclic models total power transmitted internally through each mesh may be greater than input power.
What of power at the mesh? For basic and compound epicyclic units, calculate pitch collection velocities and tangential loads to compute electricity at each mesh. Ideals can be acquired from the planet torque relative rate, and the working pitch diameters with sun and band. Coupled epicyclic sets present more technical issues. Elements of two epicyclic units could be coupled 36 various ways using one type, one result, and one reaction. Some arrangements split the power, while some recirculate electrical power internally. For these kind of epicyclic pieces, tangential loads at each mesh can only just be identified through the application of free-body diagrams. On top of that, the elements of two epicyclic sets can be coupled nine different ways in a series, using one input, one outcome, and two reactions. Let’s look at some examples.
In the “split-electrical power” coupled set shown in Figure 7, 85 percent of the transmitted electric power flows to ring gear #1 and 15 percent to ring gear #2. The result is that coupled gear set can be smaller than series coupled pieces because the ability is split between the two components. When coupling epicyclic pieces in a series, 0 percent of the energy will be transmitted through each establish.
Our next case in point depicts a established with “electrical power 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 procedure for vehicle travel axles. With the torque locked in the machine, the hp at each mesh within the loop heightens as speed increases. Therefore, this set will experience much higher ability losses at each mesh, leading to drastically lower unit efficiency .
Figure 9 depicts a free-body diagram of a great epicyclic arrangement that activities vitality recirculation. A cursory analysis of this free-human body diagram clarifies the 60 percent proficiency of the recirculating collection demonstrated in Figure 8. Since the planets will be rigidly coupled collectively, the summation of forces on both gears must equal zero. The force at the sun gear mesh benefits from the torque input to the sun gear. The push at the second ring gear mesh outcomes from the result torque on the band gear. The ratio being 41.1:1, productivity torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the pressure on the second planet will be roughly 14 times the pressure on the first planet at sunlight gear mesh. For this reason, for the summation of forces to equate to zero, the tangential load at the first band gear must be approximately 13 circumstances the tangential load at sunlight gear. If we believe the pitch brand velocities to become the same at the sun mesh and ring mesh, the power loss at the ring mesh will be about 13 times higher than the power loss at the sun mesh .