epicyclic gearbox

Within an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference operate between a gear with internal teeth and a gear with exterior teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar system. This is one way 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 usually in the center of the ring equipment, and is coaxially organized in relation to the output. The sun pinion is usually attached to a clamping system to be able to give the mechanical connection to the engine shaft. During procedure, the planetary gears, which are installed on a planetary carrier, roll between the sun pinion and the band gear. The planetary carrier also represents the productivity shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The amount of teeth does not have any effect on the tranny ratio of the gearbox. The amount of planets may also vary. As the quantity of planetary gears heightens, the distribution of the load increases and then the torque that can be transmitted. Raising the amount of tooth engagements also reduces the rolling vitality. Since only the main total result should be transmitted as rolling vitality, a planetary gear is extremely efficient. The good thing about a planetary gear compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a compact design using planetary gears.
So long as the ring gear has a regular size, different ratios could be realized by varying the quantity of teeth of the sun gear and the amount of tooth of the planetary gears. The smaller the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary stage 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 acquired by connecting many planetary phases 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 ring gear that is not set but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft to be able to pick up the torque via the ring gear. Planetary gearboxes have grown to be extremely important in lots of areas of mechanical engineering.
They have grown to be particularly more developed in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Large transmission ratios can also easily be achieved with planetary gearboxes. Because of their positive properties and small design and style, the gearboxes have various potential uses in commercial 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 due to blend of several planet stages
Appropriate as planetary switching gear due to fixing this or that section of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for an array of applications
Epicyclic gearbox is an automatic type gearbox where parallel shafts and gears set up from manual gear package are replaced with an increase of compact and more dependable sun and planetary kind of gears arrangement and also the manual clutch from manual electricity train is replaced with hydro coupled clutch or torque convertor which in turn made the transmission automatic.
The thought 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) settings which is obtained by fixing of sun and planetary gears in line with the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which appears like a ring and have angular cut teethes at its interior surface ,and is located in outermost location in en epicyclic gearbox, the internal teethes of ring equipment is in constant mesh at outer level with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular cut teethes and is positioned in the middle of the epicyclic gearbox; sunlight gear is in continuous mesh at inner point with the planetary gears and can be connected with the insight shaft of the epicyclic gear box.
One or more sun gears works extremely well for attaining different output.
3. Planet gears- They are small gears found in between band and sun gear , the teethes of the earth gears are in continuous mesh with the sun and the ring equipment at both inner and outer details respectively.
The axis of the planet 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 in addition can revolve between the ring and sunlight gear just like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the planet gears and is in charge of 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- These devices used to fix the annular gear, sunshine 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 based on the actual fact the fixing the gears i.electronic. sun equipment, planetary gears and annular gear is done to get the needed torque or swiftness output. As fixing any of the above triggers the variation in equipment ratios from large torque to high rate. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the automobile 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 the sun gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the automobile to attain higher speed throughout a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the motivated member and annular the traveling member so that you can achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which reverses the direction of the automobile, this gear is attained by fixing the earth gear carrier which makes the annular gear the influenced 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 can be built relatively little as the energy is distributed over many meshes. This effects in a low power to pounds ratio and, together with lower pitch series velocity, causes improved efficiency. The tiny equipment diameters produce lower occasions 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 utilized have been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s start by examining an essential aspect of any project: price. Epicyclic gearing is normally less expensive, when tooled properly. Just as one wouldn’t normally consider making a 100-piece lot of gears on an N/C milling equipment with a form cutter or ball end mill, one should certainly not consider making a 100-piece lot of epicyclic carriers on an N/C mill. To keep carriers within acceptable manufacturing costs they should be created from castings and tooled on single-purpose devices with multiple cutters at the same time removing material.
Size is another aspect. Epicyclic gear models are used because they’re smaller than offset equipment sets because the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear models are more efficient. The following example illustrates these rewards. Let’s believe 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 productivity from the gearbox must drive 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 likely solutions, one involving a single branch, two-stage helical gear set. A second solution takes the initial gear set and splits the two-stage lowering into two branches, and the 3rd calls for using a two-level planetary or star epicyclic. In this situation, we chose the star. 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, derived from taking the square base of the final ratio (7.70). In the process of reviewing this answer we recognize its size and fat is very large. To reduce the weight we after that explore the possibility of making two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and decreases both size and excess weight considerably . We finally arrive at our third remedy, which may be the two-stage superstar epicyclic. With three planets this equipment train reduces tooth loading considerably from the 1st approach, and a somewhat smaller amount from remedy two (check out “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a large part of why is them so useful, but these very characteristics could make designing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our objective is to create it easy that you can understand and use epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking at how relative speeds operate in conjunction with different arrangements. In the star set up the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply dependant on the speed of 1 member and the number of teeth in each equipment.
In a planetary arrangement the band gear is fixed, and planets orbit sunlight while rotating on the planet shaft. In this set up the relative speeds of the sun and planets are dependant on the number of teeth in each gear and the velocity of the carrier.
Things get a lttle bit trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. It is therefore imperative to often calculate the swiftness of sunlight, planet, and ring in accordance with the carrier. Remember that actually in a solar set up where the sunlight is fixed it includes 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 similarly, but this might not be considered 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 constructed with two or three planets is in most cases equal to you see, the quantity of planets. When more than three planets are utilized, however, the effective quantity of planets is generally 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 people. With fixed support, all participants are supported in bearings. The centers of sunlight, band, and carrier will never be coincident due to manufacturing tolerances. For this reason fewer planets will be simultaneously in mesh, resulting in a lower effective quantity of planets posting the load. With floating support, one or two users are allowed a small amount of radial flexibility or float, that allows the sun, ring, and carrier to get a position where their centers will be coincident. This float could be as little as .001-.002 in .. 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 considerations that needs to be made when making epicyclic gears. First we should translate RPM into mesh velocities and determine the number of load program cycles per device of time for each and every member. The first step in this determination is to calculate the speeds of every of the members relative to the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is certainly rotating at +400 RPM the quickness of the sun gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that swiftness and the amounts of teeth in each one of the gears. The make use of indications to symbolize clockwise and counter-clockwise rotation is definitely important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative acceleration between the two users can be +1700-(-400), or +2100 RPM.
The next step is to identify the amount 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 always be equal to the amount of planets. The planets, even so, will experience only 1 bi-directional load app per relative revolution. It meshes with sunlight and ring, but the load is certainly on contrary sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the planet is considered an idler, and the allowable anxiety must be reduced 30 percent from the worthiness for a unidirectional load program.
As noted over, the torque on the epicyclic members is divided among the planets. In examining 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 gear 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 take the torque on the sun equipment and divide it by the successful number of planets and the working pitch radius. This tangential load, combined with peripheral speed, is used to compute the energy transmitted at each mesh and, modified by the load cycles per revolution, the life span expectancy of each component.
In addition to these issues there can also be assembly complications that need addressing. For example, positioning one planet ready between sun and band fixes the angular location of sunlight to the ring. Another planet(s) is now able to be assembled simply in discreet locations where the sun and band can be concurrently involved. The “least mesh angle” from the 1st 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. Thus, so as to assemble more planets, they must be spaced at multiples of the least mesh position. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets may be spaced similarly when the sum of the number of teeth in sunlight and band is usually divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets provides another degree of complexity, and proper planet spacing may necessitate match marking of tooth.
With multiple parts in mesh, losses must be considered at each mesh so that you can evaluate the efficiency of the machine. Electric power transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic pieces, the total electric power transmitted through the sun-planet mesh and ring-planet mesh may be less than input electricity. This is among the reasons that easy planetary epicyclic sets are more efficient than other reducer arrangements. In contrast, for many coupled epicyclic units total vitality transmitted internally through each mesh could be greater than input power.
What of ability at the mesh? For straightforward and compound epicyclic pieces, calculate pitch collection velocities and tangential loads to compute electrical power at each mesh. Values can be obtained from the earth torque relative quickness, and the functioning pitch diameters with sunlight and ring. Coupled epicyclic sets present more technical issues. Elements of two epicyclic units could be coupled 36 different ways using one input, one result, and one response. Some plans split the power, while some recirculate electricity internally. For these kind of epicyclic units, tangential loads at each mesh can only just be decided through the use of free-body diagrams. Additionally, the components of two epicyclic sets can be coupled nine different ways in a string, using one insight, one outcome, and two reactions. Let’s look at some examples.
In the “split-electricity” coupled set proven in Figure 7, 85 percent of the transmitted electricity flows to band gear #1 and 15 percent to ring gear #2. The result is that coupled gear set could be scaled-down than series coupled units because the electrical power is split between your two factors. When coupling epicyclic units in a string, 0 percent of the energy will be transmitted through each establish.
Our next example depicts a established with “electric 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 hp at each mesh within the loop boosts as speed increases. As a result, this set will experience much higher ability losses at each mesh, resulting in drastically lower unit efficiency .
Body 9 depicts a free-body diagram of a great epicyclic arrangement that encounters ability recirculation. A cursory evaluation of this free-physique diagram clarifies the 60 percent productivity of the recirculating established demonstrated in Figure 8. Since the planets are rigidly coupled along, the summation of forces on both gears must equal zero. The drive at the sun gear mesh effects from the torque input to the sun gear. The drive at the second ring gear mesh outcomes from the result torque on the band equipment. 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 induce on the second planet will be about 14 times the pressure 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 ring gear should be approximately 13 occasions the tangential load at sunlight gear. If we assume the pitch series velocities to always be the same at the sun mesh and ring mesh, the power loss at the band mesh will be roughly 13 times greater than the energy loss at sunlight mesh .