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 equipment occurs in analogy to the orbiting of the planets in the solar system. This is how planetary gears obtained their name.
The pieces of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In nearly all cases the housing is fixed. The generating sun pinion can be in the heart of the ring gear, and is coaxially organized in relation to the output. The sun pinion is usually mounted on a clamping system in order to offer the mechanical connection to the 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 also represents the outcome shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the required torque. The number of teeth has no effect on the transmitting ratio of the gearbox. The number of planets can also vary. As the quantity of planetary gears boosts, the distribution of the strain increases and then the torque which can be transmitted. Raising the number of tooth engagements also reduces the rolling electricity. Since only portion of the total productivity needs to be transmitted as rolling vitality, a planetary gear is incredibly efficient. The benefit of a planetary equipment compared to an individual spur gear lies in this load distribution. Hence, it is possible to transmit substantial torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear has a constant size, different ratios can be realized by varying the quantity of teeth of the sun gear and the amount of tooth of the planetary gears. The smaller 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 sunlight gear are extremely little above and below these ratios. Higher ratios can be acquired by connecting many planetary stages in series in the same band 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 fixed but is driven in virtually any direction of rotation. It is also possible to fix the drive shaft in order to pick up the torque via the ring gear. Planetary gearboxes have grown to be extremely important in many areas of mechanical engineering.
They have become particularly more developed in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. High transmission ratios can also easily be performed with planetary gearboxes. Because of their positive properties and small design, the gearboxes have many potential uses in commercial applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency due to low rolling power
Nearly unlimited transmission ratio options due to combo of several planet stages
Suitable as planetary switching gear due to fixing this or that the main gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a wide range of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears set up from manual gear container are replaced with an increase of compact and more reputable 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 thought 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, Drive, Sport) modes which is obtained by fixing of sun and planetary gears in line with the need of the travel.
The different parts of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which appears like a ring and also have angular cut teethes at its internal surface ,and is located in outermost situation in en epicyclic gearbox, the inner teethes of ring equipment is in constant mesh at outer point with the group of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It is the equipment with angular cut teethes and is put in the center of the epicyclic gearbox; sunlight gear is in frequent mesh at inner level with the planetary gears and is definitely connected with the type shaft of the epicyclic gear box.
One or more sun gears can be used for achieving different output.
3. Planet gears- They are small gears found in between ring and sun gear , the teethes of the planet gears are in regular mesh with sunlight and the ring gear at both the inner and outer things respectively.
The axis of the planet 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 the ring and the sun gear exactly 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 tranny of the outcome to the outcome 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- The device used to fix the annular gear, sunshine gear and planetary gear and is handled by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the actual fact the fixing the gears i.e. sun equipment, planetary gears and annular equipment is done to obtain the required torque or swiftness output. As fixing any of the above triggers the variation in equipment ratios from high torque to high velocity. So let’s see 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 in turn causes the earth carrier to rotate with the power supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the vehicle to achieve higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the motivated member and annular the travelling member in order 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 attained by fixing the earth gear carrier which makes the annular gear the powered member and the sun gear the driver member.
Note- More speed or torque ratios can be achieved by increasing the quantity planet and sun equipment in epicyclic gear container.
High-speed epicyclic gears can be built relatively small as the power is distributed over several meshes. This results in a low capacity to fat ratio and, together with lower pitch range velocity, brings about improved efficiency. The tiny gear diameters produce lower moments of inertia, significantly reducing acceleration and deceleration torque when beginning 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 already been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s start by examining an important facet of any project: cost. Epicyclic gearing is generally less expensive, when tooled properly. Just as one wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling machine with an application cutter or ball end mill, you need to not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To maintain carriers within realistic manufacturing costs they should be made from castings and tooled on single-purpose machines with multiple cutters simultaneously removing material.
Size is another point. Epicyclic gear units are used because they are smaller than offset equipment sets since the load can be shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured effectively, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s presume that we’re building a high-speed gearbox to fulfill the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the type shaft.
• The end result from the gearbox must travel a generator at 900 RPM.
• The design your life is to be 10,000 hours.
With these requirements at heart, 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 reduction into two branches, and the third calls for using a two-level planetary or star epicyclic. In this situation, we chose the star. Let’s examine each 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 choice we recognize its size and pounds is very large. To reduce the weight we in that case explore the possibility of making two branches of a similar arrangement, as observed in the second alternatives. This cuts tooth loading and decreases both size and excess weight considerably . We finally arrive at our third choice, which is the two-stage superstar epicyclic. With three planets this gear train decreases tooth loading significantly from the 1st approach, and a somewhat smaller amount from answer two (look at “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a big part of what makes them so useful, however these very characteristics could make designing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our objective is to create it easy for you to understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking by how relative speeds work in conjunction with different arrangements. In the star set up the carrier is fixed, and the relative speeds of the sun, planet, and band are simply determined by the speed of one member and the amount of teeth in each equipment.
In a planetary arrangement the band gear is set, and planets orbit sunlight while rotating on earth shaft. In this arrangement the relative speeds of the sun and planets are determined by the number of teeth in each gear and the velocity of the carrier.
Things get a lttle bit trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to always calculate the rate of the sun, planet, and ring in accordance with the carrier. Understand that also in a solar set up where the sunlight is fixed it includes a speed romance 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 well not be a valid assumption. Member support and the amount 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 generally equal to you see, the quantity of planets. When more than three planets are applied, however, the effective amount of planets is often less than using the number of planets.
Let’s look by torque splits regarding set support and floating support of the users. With fixed support, all members are supported 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, producing a lower effective number of planets sharing the strain. With floating support, one or two users are allowed a little amount of radial freedom or float, that allows the sun, ring, and carrier to seek a posture where their centers are coincident. This float could possibly be less than .001-.002 in .. With floating support three planets will always be in mesh, producing a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that needs to be made when designing epicyclic gears. Initially we should translate RPM into mesh velocities and determine the number of load request cycles per product of time for 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 gear is rotating at +1700 RPM and the carrier can be 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 can be calculated by that rate and the numbers of teeth in each of the gears. The make use of indicators to signify clockwise and counter-clockwise rotation is important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two customers is definitely +1700-(-400), or +2100 RPM.
The second step is to determine the amount of load application cycles. Since the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will become equal to the amount of planets. The planets, on the other hand, will experience only 1 bi-directional load request per relative revolution. It meshes with the sun and ring, but the load is on opposite sides of one’s teeth, leading to one fully reversed anxiety cycle. Thus the planet is considered an idler, and the allowable stress must be reduced 30 percent from the value for a unidirectional load request.
As noted previously mentioned, the torque on the epicyclic members is divided among the planets. In analyzing the stress and your life of the customers we must look at the resultant loading at each mesh. We find the concept of torque per mesh to always be somewhat confusing in epicyclic equipment research and prefer to check out the tangential load at each mesh. For example, in seeking at the tangential load at the sun-planet mesh, we take the torque on sunlight gear and divide it by the successful number of planets and the operating pitch radius. This tangential load, combined with peripheral speed, is employed to compute the power transmitted at each mesh and, modified by the strain cycles per revolution, the life expectancy of every component.
In addition to these issues there can also be assembly complications that need addressing. For example, putting one planet in a position between sun and ring fixes the angular job of the sun to the ring. The next planet(s) is now able to be assembled just in discreet locations where in fact the sun and band could be at the same time engaged. The “least mesh angle” from the 1st planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the numbers of teeth in sunlight and the ring. Therefore, as a way to assemble added planets, they must end up being spaced at multiples of the least mesh angle. If one wants 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 the sun and ring is usually divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets gives another level of complexity, and appropriate planet spacing may necessitate match marking of tooth.
With multiple pieces in mesh, losses must be considered at each mesh so as to evaluate the efficiency of the machine. Electric power transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic pieces, the total electric power transmitted through the sun-planet mesh and ring-planet mesh may be significantly less than input electric power. This is among the reasons that simple planetary epicyclic units are more efficient than other reducer arrangements. In contrast, for many coupled epicyclic sets total ability transmitted internally through each mesh may be greater than input power.
What of electrical power at the mesh? For basic and compound epicyclic models, calculate pitch line velocities and tangential loads to compute electric power at each mesh. Ideals can be obtained from the earth torque relative velocity, and the operating pitch diameters with sunlight and band. Coupled epicyclic pieces present more complex issues. Elements of two epicyclic sets could be coupled 36 different ways using one suggestions, one productivity, and one reaction. Some arrangements split the power, although some recirculate electricity internally. For these kind of epicyclic models, tangential loads at each mesh can only just be established through the utilization of free-body diagrams. Also, the components of two epicyclic sets can be coupled nine different ways in a string, using one type, one outcome, and two reactions. Let’s look at a few examples.
In the “split-power” coupled set demonstrated in Figure 7, 85 percent of the transmitted electrical power flows to band gear #1 and 15 percent to band gear #2. The effect is that coupled gear set could be small than series coupled pieces because the power is split between the two factors. When coupling epicyclic models in a series, 0 percent of the energy will be transmitted through each arranged.
Our next case in point depicts a established with “ability recirculation.” This gear set happens when torque gets locked in the system in a way similar to what takes place in a “four-square” test process of vehicle travel axles. With the torque locked in the machine, the horsepower at each mesh within the loop enhances as speed increases. Consequently, this set will experience much higher power losses at each mesh, resulting in substantially lower unit efficiency .
Body 9 depicts a free-body diagram of an epicyclic arrangement that experiences electrical power recirculation. A cursory research of this free-human body diagram explains the 60 percent efficiency of the recirculating placed shown in Figure 8. Since the planets will be rigidly coupled with each other, the summation of forces on both gears must equal zero. The force at sunlight gear mesh results from the torque suggestions to sunlight gear. The drive at the second ring gear mesh effects from the outcome torque on the band gear. 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 push on the next planet will be roughly 14 times the pressure on the first world at sunlight gear mesh. Consequently, for the summation of forces to mean zero, the tangential load at the first band gear must be approximately 13 times the tangential load at sunlight gear. If we assume the pitch range velocities to end up being the same at the sun mesh and ring mesh, the power loss at the ring mesh will be around 13 times higher than the power loss at sunlight mesh .