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 exterior teeth on a concentric orbit. The circulation of the spur equipment occurs in analogy to the orbiting of the planets in the solar program. This is one way planetary gears acquired their name.
The elements of a planetary gear train could be divided 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 normally in the center of the ring equipment, and is coaxially arranged with regards to the output. Sunlight pinion is usually mounted on a clamping system to be able to give the mechanical link with the electric motor shaft. During operation, the planetary gears, which happen to be mounted on a planetary carrier, roll between the sun pinion and the ring equipment. The planetary carrier as well represents the output 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 amount of planets may also vary. As the number of planetary gears boosts, the distribution of the strain increases and therefore the torque that can be transmitted. Raising the quantity of tooth engagements as well reduces the rolling power. Since only portion of the total end result must be transmitted as rolling electrical power, a planetary equipment is incredibly efficient. The good thing about a planetary equipment compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit huge torques wit
h high efficiency with a compact design using planetary gears.
Provided that the ring gear includes a constant size, different ratios can be realized by various the number of teeth of the sun gear and the amount of pearly whites of the planetary gears. Small the sun gear, the greater 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 tiny above and below these ratios. Larger ratios can be acquired by connecting a number of planetary stages in series in the same band gear. In cases like this, 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 repair the drive shaft as a way to pick up the torque via the ring equipment. Planetary gearboxes have grown to be extremely important in lots of regions 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. Substantial transmission ratios may also easily be performed with planetary gearboxes. Because of their positive properties and compact design, the gearboxes have many potential uses in industrial applications.
The advantages 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 because of combo of several planet stages
Suited as planetary switching gear due to fixing this or that section of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a wide range of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears set up from manual gear package are replaced with more compact and more reliable sun and planetary kind of gears arrangement and also the manual clutch from manual electrical power train is changed with hydro coupled clutch or torque convertor which 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 includes the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears in line with the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a kind of gear which looks like a ring and have angular cut teethes at its internal surface ,and is positioned in outermost job in en epicyclic gearbox, the inner teethes of ring equipment is in regular mesh at outer stage with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It’s the equipment with angular lower teethes and is placed in the middle of the epicyclic gearbox; sunlight gear is in regular mesh at inner point with the planetary gears and is certainly connected with the source shaft of the epicyclic equipment box.
One or more sunshine gears can be utilized for reaching different output.
3. Planet gears- They are small gears found in between band and sun gear , the teethes of the planet gears are in continuous mesh with sunlight and the ring gear at both the inner and outer details respectively.
The axis of the earth gears are mounted on 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 the ring and sunlight gear just like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the planet gears and is accountable for final transmitting of the outcome 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 fix the annular gear, sunlight gear and planetary equipment and is controlled by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the actual fact the fixing any of the gears i.e. sun equipment, planetary gears and annular gear is done to get the necessary torque or swiftness output. As fixing the above triggers the variation in equipment ratios from huge 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 go from its initial state and is obtained by fixing the annular gear which causes the earth 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 realize higher speed throughout a drive, these ratios are obtained by fixing the sun gear which in turn makes the earth carrier the motivated 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 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 the sun gear the driver member.
Note- More swiftness or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears could be built relatively small as the power is distributed over a variety of meshes. This effects in a low capacity to pounds ratio and, as well as lower pitch brand velocity, leads to improved efficiency. The tiny equipment diameters produce lower moments of inertia, significantly minimizing 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.
The reasons why epicyclic gearing is employed have been covered in this magazine, so we’ll expand on this issue in only a few places. Let’s commence by examining a crucial facet of any project: price. Epicyclic gearing is normally 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 a form cutter or ball end mill, one should not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To preserve carriers within affordable manufacturing costs they should be made from castings and tooled on single-purpose equipment with multiple cutters concurrently removing material.
Size is another factor. Epicyclic gear units are used because they’re smaller than offset gear sets since the load can be shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Also, when configured effectively, epicyclic gear pieces are more efficient. The next example illustrates these benefits. Let’s believe that we’re creating a high-speed gearbox to meet the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the suggestions shaft.
• The productivity from the gearbox must travel a generator at 900 RPM.
• The design your life is usually to be 10,000 hours.
With these requirements in mind, let’s look at three practical solutions, one involving a single branch, two-stage helical gear set. A second solution takes the original gear placed 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 situation, we chose the superstar. Let’s examine each one 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, derived from taking the square root of the final ratio (7.70). Along the way of reviewing this choice we recognize its size and fat is very large. To lessen the weight we in that case explore the possibility of making two branches of a similar arrangement, as observed in the second alternatives. 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 minimizes tooth loading drastically from the first approach, and a somewhat smaller amount from option two (look at “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a sizable 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 goal is to make it easy for you to understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s start by looking at how relative speeds do the job in conjunction with different plans. In the star set up the carrier is set, and the relative speeds of the sun, planet, and ring are simply determined by the speed of one member and the amount of teeth in each equipment.
In a planetary arrangement the band gear is fixed, and planets orbit the sun while rotating on the planet shaft. In this set up the relative speeds of the sun and planets are determined by the amount of teeth in each equipment and the speed of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds might not exactly be intuitive. It is therefore imperative to generally calculate the swiftness of the sun, planet, and ring in accordance with the carrier. Remember that possibly in a solar arrangement where the sunlight is fixed it has a speed romantic 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 a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” quantity of planets. This quantity in epicyclic sets designed with two or three planets is in most cases equal to using the quantity of planets. When a lot more than three planets are used, however, the effective number of planets is generally less than some of the number of planets.
Let’s look in torque splits with regards to set support and floating support of the customers. With set support, all people are backed in bearings. The centers of sunlight, band, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets will be simultaneously in mesh, producing a lower effective number of planets sharing the load. With floating support, a couple of associates are allowed a little amount of radial liberty or float, which allows the sun, ring, and carrier to get a position where their centers will be coincident. This float could possibly be as little as .001-.002 ins. With floating support three planets will be in mesh, producing a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that needs to be made when making epicyclic gears. First we should translate RPM into mesh velocities and determine the quantity of load program cycles per unit of time for every member. The first step in this determination is definitely to calculate the speeds of every of the members relative to the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is normally rotating at +400 RPM the acceleration of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that rate and the amounts of teeth in each one of the gears. The make use of signs to stand for clockwise and counter-clockwise rotation is definitely 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 associates is certainly +1700-(-400), or +2100 RPM.
The second step is to determine the number of load application cycles. Because the sun and band gears mesh with multiple planets, the amount of load cycles per revolution in accordance with the carrier will end up being equal to the amount 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, but the load is certainly on opposing sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the earth is considered an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load request.
As noted previously mentioned, the torque on the epicyclic associates is divided among the planets. In examining the stress and life of the participants we must consider the resultant loading at each mesh. We discover the concept of torque per mesh to always be somewhat confusing in epicyclic gear examination and prefer to look at the tangential load at each mesh. For instance, in searching at the tangential load at the sun-world mesh, we have the torque on sunlight equipment and divide it by the successful amount of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the power transmitted at each mesh and, adjusted by the load cycles per revolution, the life expectancy of every component.
Furthermore to these issues there may also be assembly complications that need addressing. For example, putting one planet ready between sun and ring fixes the angular position of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where in fact the sun and ring can be at the same time involved. The “least mesh angle” from the primary planet that will accommodate 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. As a result, so as to assemble more planets, they must always be spaced at multiples of the least mesh position. If one wishes to have equivalent spacing of the planets in a simple epicyclic set, planets may 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 rules apply in a substance epicyclic, but the set coupling of the planets contributes another level of complexity, and proper planet spacing may require match marking of the teeth.
With multiple pieces in mesh, losses must be considered at each mesh so that you can measure the efficiency of the machine. Electrical power transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic pieces, the total electrical 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 models are better than other reducer arrangements. In contrast, for many coupled epicyclic models total ability transmitted internally through each mesh could be higher than input power.
What of electric power at the mesh? For basic and compound epicyclic sets, calculate pitch range velocities and tangential loads to compute ability at each mesh. Ideals can be obtained from the planet torque relative velocity, and the operating pitch diameters with sun and ring. Coupled epicyclic sets present more technical issues. Elements of two epicyclic models could be coupled 36 various ways using one input, one result, and one reaction. Some arrangements split the power, although some recirculate vitality internally. For these kind of epicyclic units, tangential loads at each mesh can only be determined through the utilization of free-body diagrams. Additionally, the elements of two epicyclic units could 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-ability” coupled set proven in Figure 7, 85 percent of the transmitted electrical power flows to band gear #1 and 15 percent to ring gear #2. The effect is that this coupled gear set could be smaller than series coupled units because the power is split between your two components. When coupling epicyclic pieces in a series, 0 percent of the energy will end up being transmitted through each collection.
Our next case in point depicts a set with “electric power recirculation.” This equipment set happens when torque gets locked in the machine in a manner similar to what happens in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the hp at each mesh within the loop enhances as speed increases. Therefore, this set will knowledge much higher electric power losses at each mesh, leading to substantially lower unit efficiency .
Number 9 depicts a free-body diagram of a great epicyclic arrangement that experiences electrical power recirculation. A cursory evaluation of this free-body system diagram explains the 60 percent efficiency of the recirculating established proven in Figure 8. Because the planets will be rigidly coupled at the same time, the summation of forces on the two gears must equal zero. The drive at the sun gear mesh outcomes from the torque source to the sun gear. The push at the next ring gear mesh effects from the result torque on the band gear. The ratio being 41.1:1, output torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the drive on the second planet will be roughly 14 times the induce on the first world at the sun gear mesh. Consequently, for the summation of forces to mean zero, the tangential load at the first ring gear should be approximately 13 instances the tangential load at sunlight gear. If we presume the pitch brand velocities to end up being the same at sunlight mesh and band mesh, the energy loss at the ring mesh will be around 13 times greater than the energy loss at sunlight mesh .