In 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 external teeth on a concentric orbit. The circulation of the spur equipment 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 driving sun pinion can be in the heart of the ring equipment, and is coaxially arranged in relation to the output. The sun pinion is usually attached to a clamping system in order to present the mechanical link with the motor shaft. During operation, the planetary gears, which happen to be attached on a planetary carrier, roll between the sun pinion and the ring equipment. The planetary carrier likewise represents the productivity shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The number of teeth does not have any effect on the transmission ratio of the gearbox. The number of planets may also vary. As the number of planetary gears boosts, the distribution of the load increases and therefore the torque which can be transmitted. Raising the amount of tooth engagements likewise reduces the rolling ability. Since only section of the total outcome needs to be transmitted as rolling ability, a planetary gear is extremely efficient. The advantage of a planetary gear compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit great torques wit
h high efficiency with a compact style using planetary gears.
So long as the ring gear includes a frequent size, different ratios can be realized by varying the amount of teeth of sunlight gear and the amount of tooth of the planetary gears. Small the sun gear, the higher the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely tiny above and below these ratios. Larger ratios can be obtained by connecting many planetary stages in series in the same ring gear. In this case, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a band gear that is not set but is driven in any direction of rotation. It is also possible to fix the drive shaft to be able to grab the torque via the ring equipment. Planetary gearboxes have grown to be extremely important in many areas 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. Excessive transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and compact design and style, the gearboxes have a large number of potential uses in professional applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency due to low rolling power
Nearly unlimited transmission ratio options due to combination of several planet stages
Ideal as planetary switching gear due to fixing this or that section of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a wide selection of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears arrangement from manual gear field are replaced with more compact and more efficient sun and planetary type of gears arrangement and also the manual clutch from manual electric power train is substituted with hydro coupled clutch or torque convertor which made the transmission automatic.
The idea of epicyclic gear box is taken from the solar system which is known as to the perfect arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears according to 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 minimize teethes at its inner surface ,and is positioned in outermost position in en epicyclic gearbox, the inner teethes of ring gear is in regular mesh at outer stage with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the gear with angular trim teethes and is put in the center of the epicyclic gearbox; sunlight gear is in regular mesh at inner stage with the planetary gears and is normally connected with the input shaft of the epicyclic gear box.
One or more sunshine gears can be utilized for achieving different output.
3. Planet gears- They are small gears used in between ring and sun equipment , the teethes of the planet gears are in regular mesh with the sun and the ring gear at both inner and outer details respectively.
The axis of the earth gears are mounted on 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 your ring and the sun gear just like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the earth gears and is in charge of final transmission of the productivity to the output 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, sun gear and planetary equipment and is controlled 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 equipment, planetary gears and annular equipment is done to obtain the necessary torque or acceleration output. As fixing the above causes the variation in equipment ratios from excessive torque to high quickness. So let’s observe how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle which helps the automobile to move from its initial state and is obtained by fixing the annular gear which causes the planet carrier to rotate with the power supplied to sunlight gear.
Second gear ratio
This gives high speed ratios to the vehicle which helps the automobile to achieve higher speed during a drive, these ratios are obtained by fixing sunlight gear which in turn makes the earth carrier the motivated member and annular the driving 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 vehicle, this gear is achieved by fixing the earth gear carrier which in turn makes the annular gear the influenced member and the sun gear the driver member.
Note- More swiftness or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears can be built relatively small as the power is distributed over many meshes. This outcomes in a low capacity to fat ratio and, together with lower pitch collection velocity, contributes to improved efficiency. The small 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.
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 begin by examining an important aspect of any project: cost. Epicyclic gearing is normally less costly, when tooled properly. Just as one 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, one should not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To retain carriers within acceptable manufacturing costs they must be created from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another element. Epicyclic gear sets are used because they’re smaller than offset gear sets since the load is shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. As well, when configured effectively, epicyclic gear units are more efficient. The next example illustrates these rewards. Let’s assume that we’re creating a high-speed gearbox to fulfill the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the insight shaft.
• The output 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 conceivable solutions, one involving a single branch, two-stage helical gear set. Another solution takes the initial gear collection and splits the two-stage lowering into two branches, and the third calls for using a two-level 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). Along the way of reviewing this choice we notice its size and fat is very large. To reduce the weight we after that explore the possibility of making two branches of a similar arrangement, as seen in the second solutions. This cuts tooth loading and minimizes both size and weight considerably . We finally reach our third answer, which may be the two-stage star epicyclic. With three planets this gear train decreases tooth loading significantly from the initially approach, and a somewhat smaller amount from choice two (find “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a large part of why is them so useful, however these very characteristics can make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to make it easy that you can understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking in how relative speeds work 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 1 member and the amount of teeth in each equipment.
In a planetary arrangement the ring gear is set, and planets orbit the sun while rotating on earth shaft. In this arrangement the relative speeds of the sun and planets are determined by the quantity of teeth in each equipment and the speed of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds might not exactly be intuitive. It is therefore imperative to constantly calculate the swiftness of the sun, planet, and ring relative to the carrier. Understand that actually 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 may not 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 designed with several planets is in most cases equal to you see, the number of planets. When a lot more than three planets are applied, however, the effective quantity of planets is at all times less than some of the number of planets.
Let’s look for torque splits regarding fixed support and floating support of the people. With set support, all people are supported in bearings. The centers of sunlight, ring, and carrier will not be coincident because of manufacturing tolerances. Due to this fewer planets will be simultaneously in mesh, resulting in a lower effective quantity of planets posting the load. With floating support, a couple of associates are allowed a tiny amount of radial liberty or float, which allows the sun, band, and carrier to seek a position where their centers happen to be coincident. This float could be less than .001-.002 in .. With floating support three planets will always be in mesh, producing a higher effective number of planets posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that should be made when making epicyclic gears. First we must translate RPM into mesh velocities and determine the amount of load application cycles per product of time for each and every member. The first step in this determination is normally to calculate the speeds of each of the members relative to the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is definitely rotating at +400 RPM the acceleration of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that quickness and the numbers of teeth in each one of the gears. The utilization of signs to signify clockwise and counter-clockwise rotation is normally 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 customers is usually +1700-(-400), or +2100 RPM.
The second step is to identify the number of load application cycles. Because the sun and band gears mesh with multiple planets, the number of load cycles per revolution relative to the carrier will become equal to the number 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 is certainly on opposite sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the planet is considered an idler, and the allowable tension must be reduced 30 percent from the value for a unidirectional load program.
As noted previously mentioned, the torque on the epicyclic members is divided among the planets. In analyzing the stress and existence of the people we must consider the resultant loading at each mesh. We get the concept of torque per mesh to become somewhat 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-planet mesh, we take the torque on the sun gear and divide it by the powerful amount of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the energy transmitted at each mesh and, adjusted 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, inserting one planet in a position between sun and band fixes the angular placement of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where the sun and ring could be at the same time engaged. The “least mesh angle” from the initial planet that will support simultaneous mesh of the next planet is add up to 360° divided by the sum of the numbers of teeth in sunlight and the ring. Thus, to be able to assemble additional planets, they must be spaced at multiples of the least mesh angle. If one wishes to have equivalent spacing of the planets in a simple epicyclic set, planets could be spaced similarly when the sum of the amount of teeth in sunlight and ring is usually divisible by the amount of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets offers another level of complexity, and right planet spacing may require match marking of the teeth.
With multiple pieces in mesh, losses need to be considered at each mesh so that you can evaluate the efficiency of the unit. Electric power transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic sets, the total vitality transmitted through the sun-planet mesh and ring-world mesh may be less than input vitality. This is one of the reasons that simple planetary epicyclic units are more efficient than other reducer plans. In contrast, for many coupled epicyclic pieces total electricity transmitted internally through each mesh may be greater than input power.
What of electricity at the mesh? For basic and compound epicyclic units, calculate pitch range velocities and tangential loads to compute ability at each mesh. Values can be obtained from the planet torque relative quickness, and the working pitch diameters with sunshine and ring. Coupled epicyclic units present more complex issues. Elements of two epicyclic sets can be coupled 36 various ways using one suggestions, one result, and one reaction. Some plans split the power, although some recirculate vitality internally. For these kinds of epicyclic pieces, tangential loads at each mesh can only be motivated through the usage of free-body diagrams. Additionally, the components of two epicyclic pieces could be coupled nine different ways in a series, using one insight, one outcome, and two reactions. Let’s look at some examples.
In the “split-electric power” coupled set displayed in Figure 7, 85 percent of the transmitted electrical power flows to ring gear #1 and 15 percent to band gear #2. The result is that coupled gear set could be small than series coupled models because the electric power is split between the two components. When coupling epicyclic sets in a series, 0 percent of the power will end up being transmitted through each collection.
Our next case in point depicts a collection with “power recirculation.” This gear set comes about when torque gets locked in the machine in a way similar to what occurs in a “four-square” test process of vehicle travel axles. With the torque locked in the machine, the hp at each mesh within the loop increases as speed increases. As a result, this set will knowledge much higher electric power losses at each mesh, resulting in substantially lower unit efficiency .
Determine 9 depicts a free-body diagram of an epicyclic arrangement that activities electrical power recirculation. A cursory research of this free-physique diagram explains the 60 percent proficiency of the recirculating established proven in Figure 8. Because the planets happen to be rigidly coupled at the same time, the summation of forces on the two gears must equivalent zero. The pressure at the sun gear mesh benefits from the torque insight to sunlight gear. The drive at the second ring gear mesh benefits from the output torque on the band equipment. 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 drive on the second planet will be approximately 14 times the push on the first planet at sunlight gear mesh. For this reason, for the summation of forces to mean zero, the tangential load at the first band gear must be approximately 13 instances the tangential load at sunlight gear. If we believe the pitch collection velocities to end up being the same at sunlight mesh and band mesh, the energy loss at the ring mesh will be about 13 times higher than the energy loss at the sun mesh .