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 external teeth on a concentric orbit. The circulation of the spur gear takes place in analogy to the orbiting of the planets in the solar program. This is how planetary gears acquired their name.
The parts of a planetary gear train can be split into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In nearly all cases the casing is fixed. The driving sun pinion is certainly in the heart 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 present the mechanical link with the motor shaft. During procedure, the planetary gears, which will be mounted 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 purpose of the planetary gears is to transfer the mandatory torque. The number of teeth does not have any effect on the tranny ratio of the gearbox. The number of planets can also vary. As the amount of planetary gears heightens, the distribution of the strain increases and then the torque which can be transmitted. Raising the number of tooth engagements as well reduces the rolling vitality. Since only the main total result has to be transmitted as rolling electricity, a planetary gear is extremely efficient. The advantage of a planetary gear compared to a single spur gear is based on this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a compact style using planetary gears.
So long as the ring gear includes a continuous size, different ratios can be realized by varying the amount of teeth of sunlight gear and the amount of tooth of the planetary gears. The smaller the sun gear, the greater the ratio. Technically, a meaningful ratio range for a planetary stage is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely small above and below these ratios. Larger ratios can be acquired by connecting a couple of planetary stages in series in the same ring gear. In this case, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that’s not fixed but is driven in any direction of rotation. It is also possible to repair the drive shaft in order to pick up the torque via the ring gear. Planetary gearboxes have become extremely important in many regions of mechanical engineering.
They have grown to be particularly well established in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Great transmission ratios can also easily be performed with planetary gearboxes. Because of their positive properties and small design, 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 several planetary gears
High efficiency because of low rolling power
Almost unlimited transmission ratio options because of mixture of several planet stages
Ideal as planetary switching gear because of fixing this or that area 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 where parallel shafts and gears set up from manual gear field are replaced with more compact and more reliable sun and planetary kind of gears arrangement plus the manual clutch from manual electric power train is changed with hydro coupled clutch or torque convertor which made the transmitting automatic.
The thought of epicyclic gear box is taken from the solar system which is considered to the perfect 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 according to the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a type of gear which looks like a ring and have angular slice teethes at its inner surface ,and is put in outermost placement in en epicyclic gearbox, the interior teethes of ring equipment is in continuous mesh at outer point with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It’s the equipment with angular slice teethes and is positioned in the middle of the epicyclic gearbox; the sun gear is in regular mesh at inner level with the planetary gears and is connected with the suggestions shaft of the epicyclic equipment box.
One or more sunlight gears can be used for attaining different output.
3. Planet gears- They are small gears used in between ring and sun gear , the teethes of the earth gears are in regular mesh with sunlight and the ring equipment at both inner and outer tips respectively.
The axis of the earth gears are attached to the planet carrier which is carrying the output shaft of the epicyclic gearbox.
The planet gears can rotate about their axis and in addition 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 planet gears and is accountable for final transmitting of the output 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- These devices used to repair the annular gear, sunlight gear and planetary equipment 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 the gears i.electronic. sun gear, planetary gears and annular equipment is done to get the essential torque or acceleration output. As fixing the above triggers the variation in gear ratios from great torque to high swiftness. So let’s observe 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 planet carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the automobile to attain higher speed during a travel, these ratios are obtained by fixing the sun gear which makes the planet carrier the powered member and annular the travelling member as a way 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 in turn makes the annular gear the motivated member and the sun gear the driver member.
Note- More velocity or torque ratios can be achieved by increasing the number planet and sun gear in epicyclic gear field.
High-speed epicyclic gears can be built relatively small as the power is distributed over a lot of meshes. This outcomes in a low power to excess weight ratio and, as well as lower pitch line velocity, contributes to improved efficiency. The small gear diameters produce lower occasions of inertia, significantly lowering acceleration and deceleration torque when beginning 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.
The reasons why epicyclic gearing can be used have already been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s commence by examining a significant facet of any project: expense. Epicyclic gearing is normally less costly, when tooled properly. Just as one wouldn’t normally consider making a 100-piece lot of gears on an N/C milling machine 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 hold carriers within reasonable manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another aspect. 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 smaller sized, versus countershaft gearboxes. As well, when configured effectively, epicyclic gear sets are more efficient. The next example illustrates these rewards. Let’s believe that we’re designing a high-speed gearbox to satisfy the following requirements:
• A turbine offers 6,000 horsepower at 16,000 RPM to the suggestions shaft.
• The result from the gearbox must drive a generator at 900 RPM.
• The design existence 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 placed and splits the two-stage decrease into two branches, and the third calls for using a two-stage planetary or celebrity epicyclic. In this situation, we chose the celebrity. Let’s examine each 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, derived from taking the square root of the final ratio (7.70). In the process of reviewing this alternative we find its size and weight is very large. To lessen the weight we in that case explore the possibility of earning two branches of a similar arrangement, as seen in the second solutions. This cuts tooth loading and reduces both size and pounds considerably . We finally reach our third alternative, which is the two-stage star epicyclic. With three planets this gear train decreases tooth loading significantly from the first approach, and a somewhat smaller amount from remedy two (see “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a sizable part of why is them so useful, however these very characteristics can make creating them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our goal is to create it easy for you to understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s start by looking at how relative speeds job in conjunction with different plans. In the star arrangement the carrier is set, and the relative speeds of sunlight, planet, and band are simply dependant on the speed of one member and the number of teeth in each equipment.
In a planetary arrangement the band gear is set, and planets orbit the sun while rotating on the planet shaft. In this set up the relative speeds of sunlight and planets are determined by the amount of teeth in each equipment and the quickness of the carrier.
Things get somewhat trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to usually calculate the rate of the sun, planet, and ring relative to the carrier. Remember that also in a solar arrangement where the sun is fixed it has a speed romantic relationship 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 similarly, but this may not be considered a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” quantity of planets. This number in epicyclic sets designed with two or three planets is in most cases equal to some of the amount of planets. When more than three planets are utilized, however, the effective number of planets is always less than some of the number of planets.
Let’s look by torque splits with regards to set support and floating support of the customers. With set support, all members are backed in bearings. The centers of sunlight, ring, and carrier will not be coincident due to manufacturing tolerances. For this reason fewer planets will be simultaneously in mesh, producing a lower effective quantity of planets posting the strain. With floating support, a couple of members are allowed a little amount of radial independence or float, that allows the sun, band, and carrier to seek a posture where their centers are coincident. This float could possibly be as little as .001-.002 ins. With floating support three planets will be in mesh, resulting in a higher effective number of planets sharing the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that needs to be made when making epicyclic gears. Initially we must translate RPM into mesh velocities and determine the number of load program cycles per product of time for every single member. The first step in this determination can be 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 can be rotating at +400 RPM the speed of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that swiftness and the amounts of teeth in each one of the gears. The use of symptoms to stand for 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 swiftness between the two members is definitely +1700-(-400), or +2100 RPM.
The next step is to determine the amount of load application cycles. Since the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will end up being equal to the amount of planets. The planets, even so, will experience only 1 bi-directional load software per relative revolution. It meshes with sunlight and ring, but the load is usually on opposite sides of the teeth, resulting in one fully reversed pressure cycle. Thus the planet is considered an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load application.
As noted over, the torque on the epicyclic participants is divided among the planets. In analyzing the stress and existence of the people we must look at the resultant loading at each mesh. We get the idea of torque per mesh to always be relatively confusing in epicyclic gear research and prefer to check out the tangential load at each mesh. For instance, in looking at the tangential load at the sun-world mesh, we consider the torque on sunlight equipment and divide it by the powerful amount of planets and the operating pitch radius. This tangential load, combined with peripheral speed, is utilized 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 may also be assembly complications that need addressing. For example, inserting one planet in a position between sun and band fixes the angular location of the sun to the ring. The next planet(s) can now be assembled simply in discreet locations where in fact the sun and band could be at the same time engaged. The “least mesh angle” from the initially planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the numbers of teeth in sunlight and the ring. Thus, so as to assemble extra planets, they must become spaced at multiples of this 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 amount of teeth in the sun and ring is divisible by the number of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets adds another level of complexity, and appropriate planet spacing may require match marking of tooth.
With multiple pieces in mesh, losses ought to be considered at each mesh in order to measure the efficiency of the machine. Vitality transmitted at each mesh, not input power, must be used to compute power loss. For simple epicyclic units, the total power transmitted through the sun-world mesh and ring-world mesh may be significantly less than input electric power. This is one of the reasons that simple planetary epicyclic models are more efficient than other reducer arrangements. In contrast, for many coupled epicyclic units total power transmitted internally through each mesh may be higher than input power.
What of ability at the mesh? For basic and compound epicyclic units, calculate pitch series velocities and tangential loads to compute electrical power at each mesh. Ideals can be obtained from the earth torque relative speed, and the working pitch diameters with sun and ring. Coupled epicyclic sets present more technical issues. Elements of two epicyclic models can be coupled 36 various ways using one type, one end result, and one response. Some arrangements split the power, while some recirculate electricity internally. For these kinds of epicyclic pieces, tangential loads at each mesh can only be determined through the use of free-body diagrams. On top of that, the components of two epicyclic units could be coupled nine various ways in a string, using one insight, one result, and two reactions. Let’s look at some examples.
In the “split-electrical power” coupled set demonstrated in Figure 7, 85 percent of the transmitted power flows to ring gear #1 and 15 percent to ring gear #2. The effect is that this coupled gear set can be more compact than series coupled units because the electric power is split between the two factors. When coupling epicyclic sets in a string, 0 percent of the energy will become transmitted through each arranged.
Our next case in point depicts a established with “electrical power recirculation.” This equipment set happens when torque gets locked in the system in a manner similar to what happens 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 improves as speed increases. Therefore, this set will encounter much higher power losses at each mesh, resulting in substantially lower unit efficiency .
Physique 9 depicts a free-body diagram of an epicyclic arrangement that experiences electricity recirculation. A cursory research of this free-body system diagram clarifies the 60 percent proficiency of the recirculating establish displayed in Figure 8. Since the planets will be rigidly coupled collectively, the summation of forces on both gears must equivalent zero. The force at sunlight gear mesh results from the torque type to the sun gear. The power at the next ring gear mesh results from the result torque on the ring equipment. The ratio being 41.1:1, outcome torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the power on the next planet will be around 14 times the pressure on the first planet at sunlight gear mesh. As a result, for the summation of forces to equate to zero, the tangential load at the first band gear should be approximately 13 moments the tangential load at sunlight gear. If we believe the pitch range velocities to be the same at sunlight mesh and band mesh, the energy loss at the band mesh will be roughly 13 times greater than the energy loss at the sun mesh .