epicyclic gearbox

In 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 equipment takes place in analogy to the orbiting of the planets in the solar program. This is how planetary gears acquired their name.
The components 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 casing is fixed. The generating sun pinion is certainly in the center of the ring gear, and is coaxially arranged with regards to the output. Sunlight pinion is usually attached to a clamping system in order to provide the mechanical link with the electric motor shaft. During operation, the planetary gears, which happen to be mounted on a planetary carrier, roll between your sunshine pinion and the ring equipment. The planetary carrier likewise represents the end result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The number of teeth has no effect on the transmitting ratio of the gearbox. The number of planets can also vary. As the amount of planetary gears improves, the distribution of the strain increases and therefore the torque which can be transmitted. Increasing the number of tooth engagements as well reduces the rolling electric power. Since only area of the total productivity needs to be transmitted as rolling electric power, a planetary equipment is incredibly efficient. The benefit of a planetary equipment compared to a single spur gear lies in this load distribution. Hence, it is possible to transmit high torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear includes a continuous size, different ratios can be realized by various the amount of teeth of sunlight gear and the number of pearly whites of the planetary gears. Small 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 the sun gear are extremely little above and below these ratios. Bigger ratios can be obtained by connecting a couple of planetary stages in series in the same band gear. In this instance, 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 any direction of rotation. It is also possible to repair the drive shaft so that you can grab the torque via the band equipment. Planetary gearboxes have become 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. Great 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 many planetary gears
High efficiency due to low rolling power
Practically unlimited transmission ratio options because of combination of several planet stages
Suited as planetary switching gear because of fixing this or that the main gearbox
Possibility of 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 field are replaced with more compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual electrical power train is substituted with hydro coupled clutch or torque convertor which made the transmitting automatic.
The idea of epicyclic gear box is extracted from the solar system which is considered to an ideal 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 based on the need of the travel.
Components of Epicyclic Gearbox
1. Ring gear- It is a type of gear which looks like a ring and also have angular lower teethes at its inner surface ,and is positioned in outermost job in en epicyclic gearbox, the inner teethes of ring gear is in regular mesh at outer stage with the set of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It’s the equipment with angular lower teethes and is located in the center of the epicyclic gearbox; the sun gear is in frequent mesh at inner level with the planetary gears and is connected with the source shaft of the epicyclic equipment box.
One or more sunshine gears can be utilized for obtaining 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 the inner and outer tips respectively.
The axis of the earth gears are mounted on the earth carrier which is carrying the output shaft of the epicyclic gearbox.
The planet gears can rotate about their axis and also can revolve between your ring and the sun gear exactly like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the earth gears and is responsible for final transmitting of the productivity to the productivity shaft.
The planet 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, sun gear and planetary gear and is handled 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 any of the gears i.e. sun equipment, planetary gears and annular equipment is done to obtain the essential torque or rate output. As fixing the above causes the variation in gear ratios from great torque to high quickness. So let’s observe how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle which helps the vehicle 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 power supplied to sunlight 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 earth carrier the driven member and annular the driving a vehicle 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 planet gear carrier which in turn makes the annular gear the powered member and sunlight gear the driver member.
Note- More velocity or torque ratios can be achieved by increasing the number planet and sun equipment in epicyclic gear package.
High-speed epicyclic gears could be built relatively tiny as the power is distributed over a couple of meshes. This results in a low capacity to weight ratio and, as well as lower pitch collection velocity, contributes to 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 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 employed have been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s get started by examining a crucial aspect of any project: cost. Epicyclic gearing is generally less costly, when tooled properly. Being an 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, you need to not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To continue to keep carriers within fair manufacturing costs they must be made from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another point. Epicyclic gear sets are used because they are smaller than offset gear sets because the load can be shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. As well, when configured properly, epicyclic gear sets are more efficient. The next example illustrates these benefits. Let’s presume that we’re building a high-speed gearbox to fulfill the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the source shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design existence is 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. Another solution takes the original gear collection and splits the two-stage reduction into two branches, and the third calls for by using a two-stage planetary or celebrity epicyclic. In this instance, we chose the superstar. 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, produced from taking the square root of the final ratio (7.70). Along the way of reviewing this choice we notice its size and excess weight is very large. To lessen the weight we then explore the possibility of earning two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and minimizes both size and weight considerably . We finally reach our third solution, which is the two-stage star epicyclic. With three planets this gear train minimizes tooth loading drastically from the primary approach, and a relatively smaller amount from choice two (discover “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a huge part of what makes them so useful, however these very characteristics can make building them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our aim is to make it easy so that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking by how relative speeds work together with different plans. In the star arrangement the carrier is set, and the relative speeds of sunlight, 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 ring gear is set, and planets orbit the sun while rotating on earth shaft. In this arrangement the relative speeds of sunlight and planets are determined by the quantity of teeth in each equipment and the swiftness of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds may not be intuitive. Hence, it is imperative to always calculate the velocity of the sun, planet, and ring relative to the carrier. Understand that even in a solar arrangement 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 equally, but this might not exactly be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” quantity of planets. This quantity in epicyclic sets constructed with several planets is generally equal to using the amount of planets. When a lot more than three planets are employed, however, the effective amount of planets is usually less than using the number of planets.
Let’s look by torque splits regarding set support and floating support of the customers. With set support, all users are reinforced in bearings. The centers of the sun, ring, and carrier will not be coincident because of manufacturing tolerances. Because of this fewer planets are simultaneously in mesh, producing a lower effective number of planets sharing the strain. With floating support, a couple of participants are allowed a tiny amount of radial independence or float, which allows the sun, band, and carrier to seek a posture where their centers are coincident. This float could possibly be less than .001-.002 inches. With floating support three planets will be in mesh, producing a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors 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 unit of time for every member. The first step in this determination is certainly to calculate the speeds of each of the members in accordance with the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is usually rotating at +400 RPM the rate of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that velocity and the numbers of teeth in each of the gears. The utilization of signs to signify 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 speed between the two customers is +1700-(-400), or +2100 RPM.
The second step is to determine the number of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity 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 one bi-directional load application per relative revolution. It meshes with the sun and ring, however the load is usually on reverse sides of the teeth, leading to one fully reversed tension cycle. Thus the earth is known as an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load request.
As noted above, the torque on the epicyclic associates is divided among the planets. In analyzing the stress and existence of the members we must look at the resultant loading at each mesh. We discover the idea of torque per mesh to become relatively confusing in epicyclic equipment examination and prefer to look at the tangential load at each mesh. For example, in searching at the tangential load at the sun-world mesh, we have the torque on the sun gear and divide it by the effective quantity of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the power transmitted at each mesh and, altered by the strain cycles per revolution, the life expectancy of every component.
Furthermore to these issues there can also be assembly complications that require addressing. For example, putting one planet in a position between sun and ring fixes the angular job of the sun to the ring. The next planet(s) can now be assembled just in discreet locations where in fact the sun and ring could be simultaneously engaged. The “least mesh angle” from the initially planet that will accommodate simultaneous mesh of the next planet is add up to 360° divided by the sum of the numbers of teeth in the sun and the ring. Hence, so that you can assemble extra planets, they must end up being spaced at multiples of this least mesh angle. If one desires to have equal spacing of the planets in a simple epicyclic set, planets could be spaced equally when the sum of the amount of teeth in the sun and ring is normally divisible by the number of planets to an integer. The same guidelines apply in a compound epicyclic, but the set coupling of the planets contributes another level of complexity, and correct planet spacing may require match marking of pearly whites.
With multiple pieces in mesh, losses need to be considered at each mesh so as to measure the efficiency of the unit. Vitality transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic units, the total vitality transmitted through the sun-planet mesh and ring-world mesh may be less than input power. This is one of the reasons that simple planetary epicyclic models are better than other reducer plans. In contrast, for most coupled epicyclic pieces total electric power transmitted internally through each mesh could be higher than input power.
What of electrical power at the mesh? For basic and compound epicyclic units, calculate pitch series velocities and tangential loads to compute vitality at each mesh. Ideals can be acquired from the planet torque relative acceleration, and the working pitch diameters with sun and band. Coupled epicyclic pieces present more complex issues. Components of two epicyclic pieces can be coupled 36 various ways using one type, one productivity, and one reaction. Some arrangements split the power, although some recirculate power internally. For these kinds of epicyclic pieces, tangential loads at each mesh can only be motivated through the application of free-body diagrams. On top of that, the elements of two epicyclic models could be coupled nine various ways in a series, using one source, one result, and two reactions. Let’s look at a few examples.
In the “split-power” coupled set demonstrated in Figure 7, 85 percent of the transmitted electrical power flows to ring gear #1 and 15 percent to band gear #2. The result is that this coupled gear set can be smaller sized than series coupled pieces because the ability is split between the two elements. When coupling epicyclic pieces in a series, 0 percent of the power will end up being transmitted through each established.
Our next example depicts a establish with “vitality 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 procedure for vehicle travel axles. With the torque locked in the machine, the horsepower at each mesh within the loop heightens as speed increases. Therefore, this set will knowledge much higher electrical power losses at each mesh, leading to considerably lower unit efficiency .
Physique 9 depicts a free-body diagram of an epicyclic arrangement that experience electrical power recirculation. A cursory analysis of this free-body system diagram explains the 60 percent effectiveness of the recirculating establish displayed in Figure 8. Because the planets happen to be rigidly coupled with each other, the summation of forces on the two gears must the same zero. The pressure at sunlight gear mesh results from the torque type to sunlight gear. The pressure at the next ring gear mesh benefits from the productivity torque on the ring gear. The ratio being 41.1:1, end result torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the push on the next planet will be around 14 times the drive 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 situations the tangential load at the sun gear. If we presume the pitch collection velocities to become the same at sunlight mesh and band mesh, the energy loss at the ring mesh will be approximately 13 times higher than the power loss at the sun mesh .