Within 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 external teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar program. This is how planetary gears obtained their name.
The elements 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 nearly all cases the housing is fixed. The traveling sun pinion is definitely in the center of the ring equipment, and is coaxially organized in relation to the output. Sunlight pinion is usually mounted on a clamping system in order to provide the mechanical link with the motor shaft. During procedure, the planetary gears, which will be mounted on a planetary carrier, roll between the sunlight pinion and the ring gear. The planetary carrier as well represents the end result 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 may also vary. As the amount of planetary gears increases, the distribution of the load increases and therefore the torque that can be transmitted. Raising the quantity of tooth engagements also reduces the rolling electrical power. Since only section of the total end result should be transmitted as rolling vitality, a planetary gear is extremely efficient. The advantage of a planetary gear compared to an individual spur gear is based on this load distribution. Hence, it is possible to transmit high torques wit
h high efficiency with a compact design using planetary gears.
Provided that the ring gear has a frequent size, different ratios could be realized by varying the amount of teeth of sunlight gear and the amount of teeth 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, because the planetary gears and sunlight gear are extremely small above and below these ratios. Bigger ratios can be obtained by connecting several planetary levels in series in the same ring 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’s not fixed but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft as a way to pick up the torque via the band gear. Planetary gearboxes have become extremely important in many areas 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. Great transmission ratios can also easily be performed with planetary gearboxes. Because of the positive properties and small design and 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 because of low rolling power
Almost unlimited transmission ratio options because of mixture of several planet stages
Suited as planetary switching gear due to fixing this or that area of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears arrangement from manual gear package are replaced with more compact and more trustworthy sun and planetary type of gears arrangement plus the manual clutch from manual power train is substituted with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The idea of epicyclic gear box is taken from the solar system which is considered to the perfect 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 based on 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 internal surface ,and is positioned in outermost position in en epicyclic gearbox, the interior teethes of ring gear is in frequent mesh at outer point with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular lower teethes and is positioned in the middle of the epicyclic gearbox; the sun gear is in regular mesh at inner stage with the planetary gears and is normally connected with the suggestions shaft of the epicyclic equipment box.
One or more sunshine gears can be utilised for achieving different output.
3. Planet gears- These are small gears used in between band and sun equipment , the teethes of the planet gears are in continuous mesh with the sun and the ring equipment at both the inner and outer details respectively.
The axis of the earth gears are attached to 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 your ring and sunlight gear exactly like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the planet gears and is accountable for final transmission of the 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- These devices used to repair 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 actual fact the fixing the gears i.electronic. sun equipment, planetary gears and annular equipment is done to get the required torque or rate output. As fixing the above causes the variation in gear ratios from great torque to high velocity. 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 go 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 the sun gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the automobile to achieve higher speed during a travel, these ratios are obtained by fixing the sun gear which in turn makes the earth carrier the driven member and annular the driving a car member so that you can 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 achieved by fixing the earth gear carrier which makes the annular gear the driven member and the sun gear the driver member.
Note- More swiftness 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 tiny as the energy is distributed over a couple of meshes. This results in a low power to pounds ratio and, as well as lower pitch collection velocity, causes improved efficiency. The tiny equipment diameters produce lower occasions of inertia, significantly reducing acceleration and deceleration torque when beginning 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 utilized have been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s start by examining a crucial facet of any project: cost. Epicyclic gearing is generally less costly, when tooled properly. Just as one wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling machine with a form cutter or ball end mill, one should not consider making a 100-piece lot of epicyclic carriers on an N/C mill. To hold carriers within sensible manufacturing costs they must be made from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another point. Epicyclic gear sets are used because they’re smaller than offset gear sets since the load is usually shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Also, when configured correctly, epicyclic gear pieces are more efficient. The following example illustrates these benefits. Let’s assume that we’re developing a high-speed gearbox to gratify the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the suggestions shaft.
• The output from the gearbox must drive a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements at heart, let’s look at three possible solutions, one involving a single 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 3rd calls for using a two-stage planetary or superstar 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 root of the final ratio (7.70). Along the way of reviewing this option we recognize its size and weight is very large. To lessen the weight we then explore the possibility of making two branches of an identical arrangement, as seen in the second solutions. This cuts tooth loading and reduces both size and weight considerably . We finally reach our third choice, which is the two-stage celebrity epicyclic. With three planets this equipment train reduces tooth loading substantially from the 1st approach, and a relatively smaller amount from solution two (discover “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a large part of why is them so useful, yet these very characteristics can make creating them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our aim is to create it easy that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking for how relative speeds operate in conjunction with different plans. In the star arrangement the carrier is set, and the relative speeds of the sun, 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 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 quantity of teeth in each gear and the quickness of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to generally calculate the velocity of sunlight, planet, and ring in accordance with the carrier. Remember that even in a solar set up where the sunlight is fixed it has a speed marriage 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 equally, but this may not be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” amount of planets. This number in epicyclic sets constructed with two or three planets is in most cases equal to the actual number of planets. When a lot more than three planets are utilized, however, the effective quantity of planets is usually less than some of the number of planets.
Let’s look for torque splits when it comes to fixed support and floating support of the customers. With set support, all customers are supported in bearings. The centers of the sun, ring, and carrier will never be coincident because of manufacturing tolerances. Because of this fewer planets are simultaneously in mesh, resulting in a lower effective amount of planets sharing the load. With floating support, a couple of users are allowed a small amount of radial liberty or float, which allows the sun, band, and carrier to get a posture 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 the moment let’s explore the multiple mesh factors that needs to be made when designing epicyclic gears. 1st we must translate RPM into mesh velocities and determine the quantity of load program cycles per device of time for each and every member. The first step in this determination can be to calculate the speeds of every of the members relative to the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is definitely rotating at +400 RPM the velocity of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that velocity and the amounts of teeth in each of the gears. The utilization of signals 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 quickness between the two customers is usually +1700-(-400), or +2100 RPM.
The next step is to determine the number of load application cycles. Because the sun and ring gears mesh with multiple planets, the amount of load cycles per revolution in accordance with the carrier will be equal to the quantity of planets. The planets, however, will experience only 1 bi-directional load program per relative revolution. It meshes with the sun and ring, but the load is certainly on opposite sides of the teeth, resulting in one fully reversed stress cycle. Thus the earth is known as an idler, and the allowable pressure must be reduced thirty percent from the value for a unidirectional load program.
As noted over, the torque on the epicyclic participants is divided among the planets. In analyzing the stress and lifestyle of the associates we must consider the resultant loading at each mesh. We get the concept of torque per mesh to always be somewhat confusing in epicyclic equipment evaluation and prefer to look at the tangential load at each mesh. For instance, in seeking at the tangential load at the sun-planet mesh, we have the torque on sunlight gear and divide it by the effective amount of planets and the operating pitch radius. This tangential load, combined with peripheral speed, can be used to compute the power transmitted at each mesh and, adjusted by the load cycles per revolution, the life expectancy of each component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, putting one planet ready between sun and ring fixes the angular job of the sun to the ring. Another planet(s) can now be assembled only in discreet locations where the sun and ring can be concurrently involved. The “least mesh angle” from the first planet that will accommodate 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 additional planets, they must be spaced at multiples of the least mesh position. If one desires to have equal spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the number of teeth in sunlight and band is divisible by the number of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets adds another level of complexity, and right planet spacing may require match marking of pearly whites.
With multiple elements in mesh, losses must be considered at each mesh in order to measure the efficiency of the unit. Power transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic units, the total power transmitted through the sun-planet mesh and ring-world mesh may be significantly less than input electric power. This is among the reasons that easy planetary epicyclic units are better than other reducer arrangements. In contrast, for most coupled epicyclic sets total electric power transmitted internally through each mesh may be greater than input power.
What of vitality at the mesh? For simple and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute electric power at each mesh. Ideals can be acquired from the earth torque relative swiftness, and the operating pitch diameters with sun and band. Coupled epicyclic models present more technical issues. Elements of two epicyclic pieces can be coupled 36 various ways using one insight, one end result, and one response. Some arrangements split the power, although some recirculate electric power internally. For these kinds of epicyclic units, tangential loads at each mesh can only be identified through the application of free-body diagrams. On top of that, the elements of two epicyclic models can be coupled nine various ways in a series, using one insight, one result, and two reactions. Let’s look at some examples.
In the “split-ability” coupled set demonstrated in Figure 7, 85 percent of the transmitted vitality flows to band 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 ability is split between the two components. When coupling epicyclic sets in a string, 0 percent of the power will always be transmitted through each set.
Our next example depicts a set with “electric power recirculation.” This gear set comes about when torque gets locked in the machine in a manner similar to what occurs 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 boosts as speed increases. Therefore, this set will knowledge much higher vitality losses at each mesh, resulting in significantly lower unit efficiency .
Physique 9 depicts a free-body diagram of a great epicyclic arrangement that experience power recirculation. A cursory evaluation of this free-body diagram clarifies the 60 percent efficiency of the recirculating established displayed in Figure 8. Since the planets are rigidly coupled at the same time, the summation of forces on the two gears must the same zero. The drive at sunlight gear mesh effects from the torque suggestions to the sun gear. The push at the second ring gear mesh outcomes from the result 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 force on the second planet will be approximately 14 times the induce on the first world at sunlight gear mesh. For this reason, for the summation of forces to mean zero, the tangential load at the first band gear should be approximately 13 times the tangential load at the sun gear. If we believe the pitch range velocities to be the same at sunlight mesh and ring mesh, the power loss at the band mesh will be around 13 times greater than the power loss at the sun mesh .