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 system. This is how planetary gears obtained their name.
The components of a planetary gear train could be split into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In the majority of cases the housing is fixed. The traveling sun pinion is certainly in the heart of the ring equipment, and is coaxially organized with regards to the output. The sun pinion is usually mounted on a clamping system in order to offer the mechanical connection to the electric motor shaft. During procedure, the planetary gears, which happen to be attached on a planetary carrier, roll between the sunlight pinion and the ring gear. The planetary carrier as well represents the outcome shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The quantity of teeth has no effect on the transmission ratio of the gearbox. The amount of planets may also vary. As the amount of planetary gears boosts, the distribution of the strain increases and therefore the torque that can be transmitted. Raising the amount of tooth engagements as well reduces the rolling electricity. Since only portion of the total output must be transmitted as rolling vitality, a planetary equipment is extremely efficient. The advantage of a planetary gear compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit high torques wit
h high efficiency with a compact design and style using planetary gears.
So long as the ring gear has a constant size, different ratios can be realized by various the quantity of teeth of the sun gear and the number of pearly whites of the planetary gears. The smaller the sun gear, the higher the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, since the planetary gears and the sun gear are extremely small above and below these ratios. Higher ratios can be acquired by connecting a variety of planetary levels 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 is not fixed but is driven in virtually any direction of rotation. Additionally it is possible to repair the drive shaft to be able to grab the torque via the ring gear. Planetary gearboxes have grown to be extremely important in many areas of mechanical engineering.
They have become particularly more developed in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Great transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and small design, the gearboxes have a large number of 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
Practically unlimited transmission ratio options due to combination of several planet stages
Appropriate as planetary switching gear due to fixing this or that area of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for an array of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears set up from manual gear box are replaced with more compact and more trustworthy 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 tranny automatic.
The idea of epicyclic gear box is taken 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) 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 cut teethes at its inner surface ,and is positioned in outermost placement in en epicyclic gearbox, the inner teethes of ring gear is in regular mesh at outer point with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is placed in the middle of the epicyclic gearbox; sunlight gear is in continuous mesh at inner point with the planetary gears and is connected with the input shaft of the epicyclic equipment box.
One or more sunshine gears can be utilised for attaining different output.
3. Planet gears- They are small gears used in between band and sun gear , the teethes of the earth gears are in continuous mesh with the sun and the ring gear at both the inner and outer details respectively.
The axis of the earth gears are mounted on 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- 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 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 fix the annular gear, sun gear and planetary equipment and is handled by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the fact the fixing the gears i.e. sun gear, planetary gears and annular gear is done to get the needed torque or speed output. As fixing any of the above causes the variation in equipment ratios from substantial torque to high quickness. 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 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 the sun gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the automobile to realize higher speed during a drive, these ratios are obtained by fixing sunlight gear which in turn makes the planet carrier the motivated member and annular the traveling 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 swiftness or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear box.
High-speed epicyclic gears can 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, together with lower pitch collection velocity, brings about improved efficiency. The small equipment diameters produce lower occasions of inertia, significantly minimizing 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 employed have already been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s commence by examining an essential facet of any project: cost. Epicyclic gearing is generally less expensive, when tooled properly. Being an wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling equipment with a form cutter or ball end mill, one should not really consider making a 100-piece lot of epicyclic carriers on an N/C mill. To preserve carriers within realistic manufacturing costs they should be created from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another element. Epicyclic gear models are used because they’re smaller than offset equipment sets since the load is normally shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Also, when configured effectively, epicyclic gear units are more efficient. The next example illustrates these rewards. Let’s presume that we’re designing a high-speed gearbox to meet the following requirements:
• A turbine gives 6,000 hp at 16,000 RPM to the input shaft.
• The output from the gearbox must drive 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 a single branch, two-stage helical gear set. Another solution takes the initial gear established and splits the two-stage reduction into two branches, and the third calls for by using a two-level planetary or star epicyclic. In this instance, we chose the superstar. Let’s examine each of these in greater detail, searching 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 solution we notice its size and weight 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 alternatives. This cuts tooth loading and minimizes both size and weight considerably . We finally arrive at our third answer, which is the two-stage celebrity epicyclic. With three planets this equipment train decreases tooth loading considerably from the primary approach, and a somewhat smaller amount from remedy 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, but these very characteristics can make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to create it easy for you to understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking by how relative speeds job together with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and band are simply determined by the speed of one member and the amount of teeth in each gear.
In a planetary arrangement the band gear is fixed, and planets orbit the sun 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 equipment and the acceleration of the carrier.
Things get a bit trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to generally calculate the velocity 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 marriage with the planet-it is not zero RPM at the mesh.
Torque Splits
When considering torque splits one assumes the torque to be divided among the planets equally, but this may not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” quantity of planets. This number in epicyclic sets designed with several planets is in most cases equal to the actual quantity of planets. When more than three planets are used, however, the effective quantity of planets is often less than you see, the number of planets.
Let’s look in torque splits when it comes to fixed support and floating support of the associates. With set support, all customers are backed in bearings. The centers of sunlight, ring, and carrier will never be coincident due to manufacturing tolerances. For this reason fewer planets are simultaneously in mesh, resulting in a lower effective number of planets sharing the load. With floating support, a couple of associates are allowed a tiny amount of radial liberty or float, that allows the sun, band, and carrier to seek 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 posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that should be made when making epicyclic gears. Initial we should translate RPM into mesh velocities and determine the amount of load program cycles per device of time for every member. The first rung on the ladder in this determination is usually 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 definitely rotating at +400 RPM the acceleration of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that swiftness and the amounts of teeth in each of the gears. The make use of symptoms to symbolize 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 associates is usually +1700-(-400), or +2100 RPM.
The second step is to decide the number of load application cycles. Since the sun and band gears mesh with multiple planets, the number of load cycles per revolution in accordance with the carrier will 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 the sun and ring, however the load is certainly on opposite sides of one’s teeth, resulting in one fully reversed stress cycle. Thus the planet is considered an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load application.
As noted above, the torque on the epicyclic people is divided among the planets. In analyzing the stress and your life of the users we must consider the resultant loading at each mesh. We get the concept of torque per mesh to be somewhat confusing in epicyclic equipment examination 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 successful quantity of planets and the functioning pitch radius. This tangential load, combined with peripheral speed, is employed to compute the energy transmitted at each mesh and, adjusted by the load cycles per revolution, the life expectancy of each component.
Furthermore to these issues there can also be assembly complications that need addressing. For example, inserting one planet ready between sun and ring fixes the angular placement of sunlight to the ring. Another planet(s) is now able to be assembled just in discreet locations where in fact the sun and ring can be at the same time engaged. The “least mesh angle” from the primary planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the amounts of teeth in sunlight and the ring. Hence, in order to assemble additional planets, they must become spaced at multiples of the least mesh angle. If one wishes to have equal spacing of the planets in a simple epicyclic set, planets could be spaced similarly when the sum of the number of teeth in the sun and ring is certainly divisible by the amount of planets to an integer. The same rules apply in a compound epicyclic, but the set coupling of the planets provides another level of complexity, and correct planet spacing may require match marking of pearly whites.
With multiple components in mesh, losses need to be considered at each mesh in order to evaluate the efficiency of the machine. Ability transmitted at each mesh, not input power, can be used to compute power reduction. For simple epicyclic pieces, the total ability transmitted through the sun-planet mesh and ring-planet mesh may be less than input power. This is among the reasons that easy planetary epicyclic models are more efficient than other reducer plans. In contrast, for many coupled epicyclic units total vitality transmitted internally through each mesh may be greater than input power.
What of electrical power at the mesh? For straightforward and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute ability at each mesh. Values can be obtained from the earth torque relative speed, and the working pitch diameters with sun and band. Coupled epicyclic pieces present more complex issues. Components of two epicyclic sets can be coupled 36 different ways using one input, one end result, and one reaction. Some arrangements split the power, although some recirculate electric power internally. For these kind of epicyclic sets, tangential loads at each mesh can only be identified through the utilization of free-body diagrams. Also, the elements of two epicyclic sets could be coupled nine various ways in a series, using one insight, one outcome, and two reactions. Let’s look at a few examples.
In the “split-ability” coupled set demonstrated in Figure 7, 85 percent of the transmitted electrical power flows to ring gear #1 and 15 percent to ring gear #2. The result is that coupled gear set can be smaller sized than series coupled models because the power is split between the two components. When coupling epicyclic sets in a series, 0 percent of the power will end up being transmitted through each set.
Our next case in point depicts a collection with “electrical power recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what occurs in a “four-square” test process of vehicle drive axles. With the torque locked in the system, the horsepower at each mesh within the loop increases as speed increases. As a result, this set will knowledge much higher vitality losses at each mesh, resulting in drastically lower unit efficiency .
Physique 9 depicts a free-body diagram of a great epicyclic arrangement that encounters electricity recirculation. A cursory evaluation of this free-body diagram explains the 60 percent performance of the recirculating established displayed in Figure 8. Because the planets happen to be rigidly coupled at the same time, the summation of forces on both gears must equivalent zero. The pressure at the sun gear mesh benefits from the torque type to sunlight gear. The push at the second ring gear mesh effects from the productivity torque on the band equipment. The ratio being 41.1:1, output torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the induce on the next planet will be roughly 14 times the power on the first planet at sunlight gear mesh. Consequently, for the summation of forces to equate to zero, the tangential load at the first ring gear should be approximately 13 instances the tangential load at the sun gear. If we presume the pitch range velocities to end up being the same at the sun mesh and band mesh, the power loss at the ring mesh will be roughly 13 times greater than the power loss at sunlight mesh .