epicyclic gearbox

Within an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference run 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 how planetary gears acquired their name.
The parts 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 can be 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 present the mechanical link with the electric motor shaft. During procedure, the planetary gears, which happen to be installed on a planetary carrier, roll between your sunshine pinion and the ring equipment. The planetary carrier as well represents the output shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The quantity of teeth has no effect on the transmitting ratio of the gearbox. The amount of planets can also vary. As the quantity of planetary gears enhances, the distribution of the load increases and then the torque which can be transmitted. Increasing the number of tooth engagements as well reduces the rolling vitality. Since only portion of the total outcome has to be transmitted as rolling electric power, a planetary equipment is extremely efficient. The benefit of a planetary gear 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 concise design and style using planetary gears.
Provided that the ring gear has a continuous size, different ratios can be realized by different the amount 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 selection for a planetary stage is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely little above and below these ratios. Higher ratios can be obtained by connecting a variety of planetary levels in series in the same band gear. In this case, 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 repair the drive shaft in order to grab the torque via the ring gear. Planetary gearboxes have become extremely important in many 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. Large transmission ratios can also easily be achieved with planetary gearboxes. Because of their positive properties and compact style, the gearboxes have a large number of potential uses in industrial applications.
The advantages 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 combo of several planet stages
Suitable as planetary switching gear because of fixing this or that part of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears arrangement from manual gear box are replaced with more compact and more trustworthy sun and planetary kind of gears arrangement and also the manual clutch from manual ability train is substituted with hydro coupled clutch or torque convertor which made the transmitting 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, 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- This is a kind of gear which appears like a ring and also have angular slice teethes at its internal surface ,and is positioned in outermost location in en epicyclic gearbox, the internal teethes of ring gear is in constant mesh at outer point with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular minimize teethes and is positioned in the center of the epicyclic gearbox; the sun gear is in frequent mesh at inner level with the planetary gears and is usually connected with the insight shaft of the epicyclic equipment box.
One or more sun gears can be utilized for reaching different output.
3. Planet gears- They are small gears used in between band and sun gear , the teethes of the planet gears are in regular mesh with sunlight and the ring equipment at both the inner and outer points 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 also can revolve between the ring and the sun gear exactly like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the earth gears and is responsible for final transmitting of the outcome 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- These devices used to fix the annular gear, sunshine gear and planetary equipment 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 gear, planetary gears and annular gear is done to get the essential torque or swiftness output. As fixing the above triggers the variation in equipment ratios from large torque to high rate. 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 causes the earth carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the vehicle to achieve higher speed throughout a travel, these ratios are obtained by fixing the sun gear which makes the earth carrier the influenced member and annular the travelling 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 achieved by fixing the earth gear carrier which in turn makes the annular gear the powered member and sunlight gear the driver member.
Note- More velocity or torque ratios may be accomplished by increasing the number planet and sun equipment in epicyclic gear box.
High-speed epicyclic gears could be built relatively tiny as the energy is distributed over several meshes. This effects in a low power to fat ratio and, together with lower pitch line velocity, leads to improved efficiency. The small equipment diameters produce lower occasions of inertia, significantly reducing 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 can be used have been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s get started by examining an essential facet of any project: cost. Epicyclic gearing is normally less costly, when tooled properly. Being an wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling equipment with an application cutter or ball end mill, you need to not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To preserve carriers within reasonable manufacturing costs they must be created from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another issue. Epicyclic gear units are used because they are smaller than offset equipment sets because the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. As well, when configured properly, epicyclic gear sets are more efficient. The next example illustrates these rewards. Let’s presume that we’re creating a high-speed gearbox to satisfy the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the input shaft.
• The end result from the gearbox must drive a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements in mind, let’s look at three practical solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the original gear set and splits the two-stage decrease into two branches, and the third calls for utilizing a two-stage planetary or celebrity 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 base of the final ratio (7.70). In the process of reviewing this alternative we see its size and pounds is very large. To reduce the weight we then explore the possibility of earning two branches of an identical arrangement, as observed in the second solutions. This cuts tooth loading and reduces both size and weight considerably . We finally arrive at our third answer, which may be the two-stage superstar epicyclic. With three planets this equipment train decreases tooth loading significantly from the initially approach, and a somewhat smaller amount from solution two (observe “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a huge part of what makes them so useful, however these very characteristics can make developing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to make it easy that you should understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds operate in conjunction with different plans. In the star set up the carrier is fixed, and the relative speeds of sunlight, planet, and ring are simply dependant on the speed of 1 member and the number 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 set up the relative speeds of the sun and planets are dependant on the quantity of teeth in each equipment and the quickness 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 speed of the sun, planet, and ring in accordance with the carrier. Understand that even in a solar set up where the sunshine is fixed it includes a speed marriage with the planet-it is not 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 be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This number in epicyclic sets designed with two or three planets is in most cases equal to you see, the quantity of planets. When a lot more than three planets are utilized, however, the effective amount of planets is always less than using the number of planets.
Let’s look for torque splits with regards to fixed support and floating support of the participants. With fixed support, all people are backed in bearings. The centers of sunlight, ring, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets will be simultaneously in mesh, producing a lower effective amount of planets sharing the load. With floating support, one or two users are allowed a small amount of radial liberty or float, which allows the sun, ring, and carrier to seek a posture where their centers happen to be coincident. This float could 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 the moment let’s explore the multiple mesh considerations that needs to be made when making epicyclic gears. Initial we must translate RPM into mesh velocities and determine the quantity of load request cycles per device of time for each and every member. The first step in this determination is usually to calculate the speeds of every of the members in accordance with the carrier. For instance, if the sun equipment 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 world and ring gears can be calculated by that rate and the numbers of teeth in each one of the gears. The make use of signals to stand for clockwise and counter-clockwise rotation is important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two customers can be +1700-(-400), or +2100 RPM.
The next step is to determine the amount of load application cycles. Because the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will always be equal to the number of planets. The planets, nevertheless, will experience only 1 bi-directional load application per relative revolution. It meshes with the sun and ring, however the load is usually on contrary sides of the teeth, leading to one fully reversed stress cycle. Thus the earth is known as an idler, and the allowable anxiety must be reduced 30 percent from the worthiness for a unidirectional load application.
As noted previously mentioned, the torque on the epicyclic members is divided among the planets. In analyzing the stress and life of the users we must consider the resultant loading at each mesh. We get the concept of torque per mesh to be somewhat confusing in epicyclic equipment research and prefer to look at the tangential load at each mesh. For example, in seeking at the tangential load at the sun-world mesh, we consider the torque on sunlight gear and divide it by the powerful amount of planets and the functioning pitch radius. This tangential load, combined with peripheral speed, is employed to compute the energy transmitted at each mesh and, altered by the strain cycles per revolution, the life expectancy of every component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, positioning one planet ready between sun and ring fixes the angular posture of the sun to the ring. The next planet(s) is now able to be assembled simply in discreet locations where the sun and band could be simultaneously engaged. The “least mesh angle” from the primary planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the numbers of teeth in the sun and the ring. Hence, in order to assemble added planets, they must be spaced at multiples of the least mesh position. If one wishes to have equivalent spacing of the planets in a straightforward epicyclic set, planets could be spaced equally when the sum of the number of teeth in the sun and ring is definitely divisible by the number of planets to an integer. The same rules apply in a substance epicyclic, but the set coupling of the planets offers another level of complexity, and appropriate planet spacing may necessitate match marking of teeth.
With multiple elements in mesh, losses have to be considered at each mesh so as to evaluate the efficiency of the unit. Ability transmitted at each mesh, not input power, can be used to compute power reduction. For simple epicyclic sets, the total power transmitted through the sun-planet mesh and ring-planet mesh may be less than input vitality. This is among the reasons that easy planetary epicyclic models are more efficient than other reducer plans. In contrast, for many coupled epicyclic sets total electrical power transmitted internally through each mesh may be higher than input power.
What of power at the mesh? For basic and compound epicyclic units, calculate pitch collection velocities and tangential loads to compute power at each mesh. Values can be obtained from the planet torque relative rate, and the working pitch diameters with sun and ring. Coupled epicyclic pieces present more technical issues. Elements of two epicyclic models could be coupled 36 different ways using one source, one output, and one response. Some plans split the power, while some recirculate electrical power internally. For these types of epicyclic sets, tangential loads at each mesh can only be decided through the consumption of free-body diagrams. Additionally, the factors of two epicyclic pieces could be coupled nine various 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 shown in Figure 7, 85 percent of the transmitted power flows to band gear #1 and 15 percent to band gear #2. The result is that coupled gear set could be scaled-down than series coupled models because the electrical power is split between the two components. When coupling epicyclic units in a string, 0 percent of the power will be transmitted through each arranged.
Our next case in point depicts a set with “power recirculation.” This gear set comes about when torque gets locked in the machine in a manner 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 boosts as speed increases. Therefore, this set will experience much higher electric power losses at each mesh, leading to drastically lower unit efficiency .
Determine 9 depicts a free-body diagram of a great epicyclic arrangement that encounters power recirculation. A cursory research of this free-body system diagram clarifies the 60 percent performance of the recirculating set demonstrated in Figure 8. Since the planets are rigidly coupled along, the summation of forces on the two gears must the same zero. The push at sunlight gear mesh effects from the torque input to sunlight gear. The force at the next ring gear mesh benefits from the productivity torque on the ring 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 around 14 times the induce on the first world at sunlight gear mesh. For this reason, for the summation of forces to equate to zero, the tangential load at the first ring gear should be approximately 13 moments the tangential load at sunlight gear. If we believe the pitch series velocities to always be the same at the sun mesh and ring mesh, the energy loss at the ring mesh will be around 13 times higher than the energy loss at sunlight mesh .