epicyclic gearbox

Within 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 gear takes place 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 the majority of cases the housing is fixed. The generating sun pinion is definitely in the center of the ring gear, and is coaxially organized with regards to the output. The sun pinion is usually mounted on a clamping system in order to provide the mechanical link with the electric motor shaft. During operation, the planetary gears, which happen to be installed on a planetary carrier, roll between the sunshine pinion and the band equipment. The planetary carrier likewise represents the result shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The number of teeth has no effect on the tranny ratio of the gearbox. The number of planets may also vary. As the number of planetary gears boosts, the distribution of the strain increases and then the torque which can be transmitted. Increasing the quantity of tooth engagements as well reduces the rolling electrical power. Since only portion of the total output has to be transmitted as rolling power, a planetary gear is extremely efficient. The good thing about a planetary gear compared to a single spur gear lies in this load distribution. Hence, it is possible to transmit substantial torques wit
h high efficiency with a concise design using planetary gears.
So long as the ring gear has a continuous size, different ratios can be realized by varying the quantity of teeth of sunlight gear and the amount of pearly whites of the planetary gears. Small the sun equipment, the higher the ratio. Technically, a meaningful ratio selection for a planetary stage is approx. 3:1 to 10:1, since the planetary gears and the sun gear are extremely tiny above and below these ratios. Bigger ratios can be acquired by connecting a variety of planetary stages in series in the same band gear. In this instance, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that is not set but is driven in virtually any direction of rotation. It is also possible to fix the drive shaft as a way to grab the torque via the band gear. Planetary gearboxes have grown to be extremely important in many 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. Excessive transmission ratios may also easily be achieved 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 due to low rolling power
Almost unlimited transmission ratio options due to mixture of several planet stages
Ideal 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 where parallel shafts and gears arrangement from manual gear package are replaced with an increase of compact and more trustworthy sun and planetary type of gears arrangement as well as the manual clutch from manual electric power train is replaced with hydro coupled clutch or torque convertor which in turn made the transmission 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, 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- It is a type of gear which appears like a ring and also have angular lower teethes at its internal surface ,and is placed in outermost position in en epicyclic gearbox, the internal teethes of ring gear is in constant mesh at outer stage with the set of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It’s the equipment with angular slice teethes and is positioned in the center of the epicyclic gearbox; the sun gear is in regular mesh at inner point with the planetary gears and can be connected with the source shaft of the epicyclic gear box.
One or more sunshine gears can be used for achieving different output.
3. Planet gears- These are small gears used in between band and sun gear , the teethes of the planet gears are in regular mesh with the sun and the ring equipment at both the inner and outer factors respectively.
The axis of the planet 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 sunlight gear just like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the earth gears and is in charge of final transmission of the result to the result 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 fix 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 based on the fact the fixing any of the gears i.e. sun gear, planetary gears and annular equipment is done to obtain the essential torque or swiftness output. As fixing any of the above causes the variation in equipment ratios from substantial 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 move 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 sunlight gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the automobile to realize higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which in turn makes the planet carrier the driven member and annular the generating 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 automobile, this gear is attained by fixing the earth gear carrier which makes the annular gear the driven member and the sun gear the driver member.
Note- More rate or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear package.
High-speed epicyclic gears can be built relatively little as the energy is distributed over a lot of meshes. This effects in a low power to weight 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 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 utilized have been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s commence by examining an essential facet of any project: price. 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 equipment with a form cutter or ball end mill, you need to certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To continue to keep carriers within sensible manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters simultaneously removing material.
Size is another component. Epicyclic gear sets are used because they’re smaller than offset gear sets since the load is normally shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear pieces are more efficient. The next example illustrates these benefits. Let’s presume that we’re designing a high-speed gearbox to satisfy the following requirements:
• A turbine delivers 6,000 horsepower at 16,000 RPM to the suggestions shaft.
• The outcome from the gearbox must drive a generator at 900 RPM.
• The design life is to be 10,000 hours.
With these requirements at heart, let’s look at three likely solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the initial gear set and splits the two-stage decrease into two branches, and the third calls for using a two-level planetary or superstar 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, produced from taking the square base of the final ratio (7.70). In the process of reviewing this remedy we detect its size and fat is very large. To lessen the weight we in that case explore the possibility of earning two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and reduces both size and pounds considerably . We finally reach our third solution, which may be the two-stage superstar epicyclic. With three planets this gear train reduces tooth loading substantially from the primary approach, and a relatively smaller amount from remedy two (check out “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a big part of why is them so useful, however these very characteristics could make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. 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 by how relative speeds job in conjunction with different arrangements. In the star arrangement 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 ring gear is fixed, and planets orbit sunlight 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 gear and the velocity 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 at all times calculate the acceleration of sunlight, planet, and ring in accordance with the carrier. Remember that even in a solar arrangement where the sun is fixed it includes 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 may not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This quantity in epicyclic sets constructed with several planets is in most cases equal to some of the amount of planets. When 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 at torque splits with regards to set support and floating support of the people. With set support, all users are supported in bearings. The centers of the sun, ring, and carrier will never be coincident due to manufacturing tolerances. Due to this fewer planets will be simultaneously in mesh, resulting in a lower effective amount of planets sharing the load. With floating support, one or two associates are allowed a tiny amount of radial freedom or float, which allows the sun, band, and carrier to get a position where their centers will be coincident. This float could possibly be less than .001-.002 in .. With floating support three planets will always be in mesh, resulting in a higher effective number of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that should be made when designing epicyclic gears. Initially we must translate RPM into mesh velocities and determine the number of load program cycles per unit of time for every member. The first rung on the ladder in this determination can be to calculate the speeds of each of the members in accordance with the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the acceleration of the sun gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that velocity and the numbers of teeth in each of the gears. The use of indications to stand for clockwise and counter-clockwise rotation is normally 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 associates is normally +1700-(-400), or +2100 RPM.
The second step is to decide the number of load application cycles. Since the sun and ring gears mesh with multiple planets, the amount of load cycles per revolution relative to the carrier will always be equal to the amount of planets. The planets, even so, will experience only 1 bi-directional load request per relative revolution. It meshes with the sun and ring, but the load is definitely on contrary sides of one’s teeth, resulting in one fully reversed tension cycle. Thus the planet is known as an idler, and the allowable pressure must be reduced thirty percent from the worthiness for a unidirectional load application.
As noted above, 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 locate the concept of torque per mesh to be somewhat confusing in epicyclic equipment evaluation 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 consider the torque on sunlight gear and divide it by the effective amount of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the energy transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that need addressing. For example, inserting one planet in a position between sun and ring fixes the angular situation of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where in fact the sun and band could be concurrently involved. The “least mesh angle” from the initially planet that will accommodate simultaneous mesh of another planet is equal to 360° divided by the sum of the numbers of teeth in the sun and the ring. Therefore, so as to assemble further planets, they must be spaced at multiples of this least mesh angle. If one desires to have the same spacing of the planets in a straightforward epicyclic set, planets may be spaced similarly when the sum of the number of teeth in the sun and ring is divisible by the amount of planets to an integer. The same guidelines apply in a substance epicyclic, but the set coupling of the planets offers another degree of complexity, and correct planet spacing may necessitate match marking of teeth.
With multiple parts in mesh, losses must be considered at each mesh as a way to measure the efficiency of the machine. Ability transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic units, the total power transmitted through the sun-world mesh and ring-world mesh may be less than input ability. This is among the reasons that simple planetary epicyclic units are better than other reducer plans. In contrast, for most coupled epicyclic units total vitality transmitted internally through each mesh may be greater than input power.
What of vitality at the mesh? For basic and compound epicyclic pieces, calculate pitch range velocities and tangential loads to compute ability at each mesh. Values can be acquired from the earth torque relative swiftness, and the operating pitch diameters with sun and band. Coupled epicyclic pieces present more complex issues. Elements of two epicyclic sets can be coupled 36 various ways using one input, one end result, and one reaction. Some arrangements split the power, although some recirculate ability internally. For these types of epicyclic units, tangential loads at each mesh can only just be decided through the application of free-body diagrams. Also, the components of two epicyclic sets can be coupled nine different ways in a series, using one insight, one outcome, and two reactions. Let’s look at a few examples.
In the “split-vitality” coupled set proven in Figure 7, 85 percent of the transmitted ability flows to band gear #1 and 15 percent to ring gear #2. The result is that this coupled gear set can be more compact than series coupled pieces because the ability is split between the two elements. When coupling epicyclic sets in a series, 0 percent of the power will be transmitted through each established.
Our next example depicts a establish with “electrical power recirculation.” This equipment set happens when torque gets locked in the system in a manner similar to what occurs in a “four-square” test procedure for vehicle travel axles. With the torque locked in the system, the hp at each mesh within the loop heightens as speed increases. As a result, this set will knowledge much higher electrical power losses at each mesh, resulting in considerably lower unit efficiency .
Figure 9 depicts a free-body diagram of a great epicyclic arrangement that experiences electric power recirculation. A cursory research of this free-physique diagram clarifies the 60 percent efficiency of the recirculating arranged demonstrated in Figure 8. Because the planets happen to be rigidly coupled together, the summation of forces on the two gears must the same zero. The power at the sun gear mesh outcomes from the torque type to sunlight gear. The drive at the second ring gear mesh results from the result torque on the ring gear. 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 pressure on the next planet will be approximately 14 times the force on the first planet at the sun gear mesh. Consequently, for the summation of forces to equate to zero, the tangential load at the first band gear must be approximately 13 situations the tangential load at sunlight gear. If we presume the pitch line velocities to end up being the same at the sun mesh and ring mesh, the power loss at the band mesh will be around 13 times higher than the power loss at the sun mesh .