epicyclic gearbox

In 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 external teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar program. This is how planetary gears acquired their name.
The components 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 casing is fixed. The driving sun pinion is usually in the center of the ring gear, and is coaxially organized in relation to the output. The sun pinion is usually attached to a clamping system in order to give the mechanical link with the electric motor shaft. During operation, the planetary gears, which happen to be attached on a planetary carrier, roll between your sun pinion and the ring equipment. The planetary carrier likewise represents the outcome shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The quantity of teeth does not have any effect on the tranny ratio of the gearbox. The quantity of planets may also vary. As the number of planetary gears raises, the distribution of the strain increases and therefore the torque which can be transmitted. Raising the number of tooth engagements also reduces the rolling electricity. Since only part of the total end result has to be transmitted as rolling electricity, a planetary equipment is extremely efficient. The good thing about a planetary gear compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit substantial torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear has a regular size, different ratios could be realized by varying the amount of teeth of the sun gear and the amount of teeth of the planetary gears. Small the sun gear, the higher 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 little above and below these ratios. Higher ratios can be obtained by connecting several planetary stages in series in the same ring 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’s not set but is driven in any direction of rotation. It is also possible to fix the drive shaft so that you can pick up the torque via the ring equipment. Planetary gearboxes have grown to be extremely important in many areas of mechanical engineering.
They have become particularly well established in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Large transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and small design and style, the gearboxes have a large number of potential uses in commercial applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency because of low rolling power
Nearly unlimited transmission ratio options because of combination of several planet stages
Appropriate as planetary switching gear due to fixing this or that part of the gearbox
Possibility of 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 arrangement from manual gear container are replaced with an increase of compact and more reputable sun and planetary kind of gears arrangement and also the manual clutch from manual electrical power train is substituted with hydro coupled clutch or torque convertor which made the transmitting automatic.
The idea of epicyclic gear box is extracted from the solar system which is known as to an ideal arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) settings which is obtained by fixing of sun and planetary gears according to the need of the travel.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a type of gear which looks like a ring and also have angular slice teethes at its inner surface ,and is placed in outermost posture in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer stage with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It is the equipment with angular lower teethes and is put in the middle of the epicyclic gearbox; sunlight gear is in regular mesh at inner stage with the planetary gears and can be connected with the source shaft of the epicyclic gear box.
One or more sunlight gears can be used for obtaining different output.
3. Planet gears- They are small gears found in between ring and sun gear , the teethes of the planet gears are in continuous mesh with the sun and the ring gear at both inner and outer items respectively.
The axis of the planet gears are attached to the earth 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 attached with the axis of the planet gears and is accountable for final transmitting of the output to the output 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 repair the annular gear, sun gear and planetary equipment and is manipulated by the brake or clutch of the vehicle.
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 equipment is done to get the necessary torque or rate output. As fixing the above causes the variation in gear ratios from substantial torque to high acceleration. 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 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 vehicle which helps the automobile to achieve higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the earth carrier the powered member and annular the driving a vehicle member to be able to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which in turn reverses the direction of the automobile, this gear is achieved 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 acceleration 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 tiny as the power is distributed over several meshes. This results in a low power to pounds ratio and, as well as lower pitch collection 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 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 is utilized have been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s begin by examining an important aspect of any project: cost. 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 equipment with an application cutter or ball end mill, one should not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To retain carriers within realistic manufacturing costs they must be made from castings and tooled on single-purpose equipment with multiple cutters at the same time removing material.
Size is another aspect. Epicyclic gear pieces 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 more compact, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s assume that we’re developing a high-speed gearbox to satisfy the following requirements:
• A turbine offers 6,000 hp at 16,000 RPM to the insight shaft.
• The productivity from the gearbox must drive a generator at 900 RPM.
• The design your life is 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 original gear established and splits the two-stage decrease into two branches, and the 3rd calls for using a two-stage planetary or celebrity epicyclic. In this situation, we chose the star. 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 root of the final ratio (7.70). In the process of reviewing this option we realize its size and pounds is very large. To reduce the weight we then explore the possibility of making two branches of a similar arrangement, as seen in the second alternatives. This cuts tooth loading and reduces both size and weight considerably . We finally arrive at our third choice, which may be the two-stage star epicyclic. With three planets this gear train reduces tooth loading drastically from the initial approach, and a somewhat smaller amount from option two (find “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a large part of what makes them so useful, yet these very characteristics can make developing them a challenge. Within 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 work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking in how relative speeds operate in conjunction with different plans. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply determined by the speed of one member and the number of teeth in each equipment.
In a planetary arrangement the ring gear is set, and planets orbit sunlight while rotating on earth shaft. In this set up the relative speeds of the sun and planets are determined by the quantity of teeth in each equipment and the quickness of the carrier.
Things get a little trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to constantly calculate the acceleration of sunlight, planet, and ring relative to the carrier. Understand that also in a solar arrangement where the sunlight is fixed it has 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 exactly be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” quantity of planets. This quantity in epicyclic sets constructed with two or three planets is generally equal to you see, the amount of planets. When a lot more than three planets are applied, 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 people. With fixed support, all users are reinforced in bearings. The centers of sunlight, band, and carrier will not be coincident due to manufacturing tolerances. Because of this fewer planets will be simultaneously in mesh, resulting in a lower effective number of planets posting the strain. With floating support, one or two people are allowed a tiny amount of radial flexibility or float, which allows the sun, ring, and carrier to get a position where their centers are coincident. This float could 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 this time let’s explore the multiple mesh factors that should be made when making epicyclic gears. Primary we must translate RPM into mesh velocities and determine the number of load request cycles per device of time for every single member. The first step in this determination is certainly to calculate the speeds of every of the members in accordance with the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is rotating at +400 RPM the rate of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that acceleration and the numbers of teeth in each of the gears. The utilization of signals to stand for clockwise and counter-clockwise rotation can be 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 participants is normally +1700-(-400), or +2100 RPM.
The second step is to decide the quantity of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will be equal to the quantity of planets. The planets, nevertheless, will experience only 1 bi-directional load program per relative revolution. It meshes with sunlight and ring, but the load can be on contrary sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the planet is known as an idler, and the allowable tension must be reduced 30 percent from the value for a unidirectional load software.
As noted over, the torque on the epicyclic customers is divided among the planets. In analyzing the stress and life of the users we must consider the resultant loading at each mesh. We locate the concept of torque per mesh to be relatively confusing in epicyclic gear evaluation and prefer to look at the tangential load at each mesh. For example, in seeking at the tangential load at the sun-planet mesh, we take the torque on the sun gear and divide it by the successful amount of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the energy transmitted at each mesh and, altered by the load cycles per revolution, the life expectancy of every component.
In addition to these issues there can also be assembly complications that require addressing. For example, putting one planet ready between sun and band fixes the angular location of sunlight to the ring. Another planet(s) can now be assembled only in discreet locations where in fact the sun and ring could be concurrently engaged. The “least mesh angle” from the 1st planet that will support simultaneous mesh of the next planet is equal to 360° divided by the sum of the numbers of teeth in sunlight and the ring. As a result, to be able to assemble more planets, they must be spaced at multiples of the least mesh angle. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the number of teeth in sunlight and band is usually divisible by the number of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets offers another level of complexity, and correct planet spacing may require match marking of tooth.
With multiple elements in mesh, losses should be considered at each mesh so as to evaluate the efficiency of the unit. Power transmitted at each mesh, not input power, must be used to compute power loss. For simple epicyclic pieces, the total power transmitted through the sun-planet mesh and ring-planet mesh may be significantly less than input vitality. This is one of the reasons that simple planetary epicyclic sets are better than other reducer arrangements. In contrast, for many coupled epicyclic models total electricity transmitted internally through each mesh may be greater than input power.
What of electric power at the mesh? For simple and compound epicyclic sets, calculate pitch collection velocities and tangential loads to compute electricity at each mesh. Values can be obtained from the earth torque relative quickness, and the working pitch diameters with sunlight and band. Coupled epicyclic units present more technical issues. Elements of two epicyclic pieces can be coupled 36 different ways using one input, one output, and one reaction. Some arrangements split the power, while some recirculate ability internally. For these kinds of epicyclic models, tangential loads at each mesh can only just be established through the use of free-body diagrams. Additionally, the elements of two epicyclic models could be coupled nine various ways in a series, using one source, one end result, and two reactions. Let’s look at a few examples.
In the “split-electric power” coupled set proven in Figure 7, 85 percent of the transmitted vitality flows to ring gear #1 and 15 percent to band gear #2. The effect is that this coupled gear set can be more compact than series coupled models because the electrical power is split between the two elements. When coupling epicyclic pieces in a series, 0 percent of the power will become transmitted through each established.
Our next example depicts a arranged with “ability recirculation.” This gear set happens when torque gets locked in the machine in a way 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. As a result, this set will encounter much higher electrical power losses at each mesh, leading to substantially lower unit efficiency .
Body 9 depicts a free-body diagram of an epicyclic arrangement that encounters power recirculation. A cursory evaluation of this free-body diagram explains the 60 percent productivity of the recirculating collection demonstrated in Figure 8. Since the planets happen to be rigidly coupled jointly, the summation of forces on the two gears must the same zero. The induce at the sun gear mesh results from the torque insight to the sun gear. The power at the next ring gear mesh results from the output torque on the ring gear. The ratio being 41.1:1, productivity torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the power on the next planet will be around 14 times the force on the first world at sunlight gear mesh. For that reason, for the summation of forces to mean zero, the tangential load at the first band gear should be approximately 13 moments the tangential load at the sun gear. If we presume the pitch line velocities to become the same at the sun mesh and band mesh, the energy loss at the band mesh will be roughly 13 times higher than the power loss at the sun mesh .


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