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 one way planetary gears obtained their name.
The components of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In nearly all cases the casing is fixed. The traveling sun pinion is certainly in the center of the ring gear, and is coaxially arranged with regards to the output. The sun pinion is usually attached to a clamping system to be able to give the mechanical link with the engine shaft. During procedure, the planetary gears, which will be mounted on a planetary carrier, roll between your sunshine pinion and the band equipment. The planetary carrier as well represents the end result 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 number of planets may also vary. As the number of planetary gears boosts, the distribution of the strain increases and therefore the torque which can be transmitted. Increasing the amount of tooth engagements as well reduces the rolling ability. Since only portion of the total end result should be transmitted as rolling ability, a planetary gear is incredibly efficient. The advantage of a planetary gear compared to a single spur gear lies in this load distribution. It is therefore possible to transmit great torques wit
h high efficiency with a compact design using planetary gears.
Provided that the ring gear includes a continuous size, different ratios can be realized by varying the quantity of teeth of the sun gear and the number of tooth of the planetary gears. The smaller the sun equipment, the higher the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely little above and below these ratios. Bigger ratios can be obtained by connecting a lot of planetary phases in series in the same band gear. In cases like this, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a ring gear that’s not fixed but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft to be able to grab the torque via the band gear. Planetary gearboxes have become extremely important in lots of regions of mechanical engineering.
They have grown to be particularly well established in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Substantial transmission ratios can also easily be performed with planetary gearboxes. Because of the positive properties and small style, the gearboxes have various potential uses in industrial applications.
The features 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 due to blend of several planet stages
Suited 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 variety of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears arrangement from manual gear box are replaced with more compact and more efficient sun and planetary kind 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 tranny 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 in line with the need of the travel.
Components of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which appears like a ring and have angular slice teethes at its inner surface ,and is placed in outermost situation in en epicyclic gearbox, the interior teethes of ring equipment is in continuous mesh at outer point with the set of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is placed in the middle of the epicyclic gearbox; sunlight gear is in frequent mesh at inner point with the planetary gears and is definitely connected with the type shaft of the epicyclic gear box.
One or more sunlight gears can be used for reaching different output.
3. Planet gears- These are small gears found in between ring and sun gear , the teethes of the planet gears are in regular mesh with the sun and the ring equipment at both the inner and outer items respectively.
The axis of the earth gears are mounted on the earth carrier which is carrying the output shaft of the epicyclic gearbox.
The planet gears can rotate about their axis and also can revolve between your ring and sunlight gear exactly like our solar system.
4. Planet carrier- It is a carrier attached with the axis of the earth gears and is in charge of final transmission of the end result to the productivity 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 gear and is managed 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 any of the gears i.electronic. sun gear, planetary gears and annular gear is done to obtain the needed torque or velocity output. As fixing any of the above triggers the variation in gear ratios from great torque to high swiftness. So let’s see 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 in turn causes the planet carrier to rotate with the energy supplied to the sun gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the vehicle to realize higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the earth carrier the driven member and annular the generating member so as 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 sunlight gear the driver member.
Note- More swiftness or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear package.
High-speed epicyclic gears can be built relatively tiny as the energy is distributed over several meshes. This effects in a low power to pounds ratio and, together with lower pitch series velocity, brings about improved efficiency. The small gear diameters produce lower moments 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.
Why epicyclic gearing can be used have been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s get started by examining an essential aspect of any project: price. Epicyclic gearing is normally less costly, 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 preserve carriers within fair 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 sets are used because they’re smaller than offset gear sets since the load can be shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear units are more efficient. The next example illustrates these rewards. Let’s presume that we’re creating a high-speed gearbox to gratify the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the type shaft.
• The output from the gearbox must drive a generator at 900 RPM.
• The design 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. A second solution takes the original gear collection and splits the two-stage decrease into two branches, and the third calls for using a two-level planetary or star epicyclic. In this instance, we chose the celebrity. Let’s examine each of these in greater detail, seeking 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 base of the final ratio (7.70). Along the way of reviewing this choice we realize its size and pounds is very large. To lessen the weight we then explore the possibility of earning two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third option, which is the two-stage star epicyclic. With three planets this equipment train minimizes tooth loading significantly from the initially approach, and a relatively smaller amount from solution two (observe “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a sizable part of why is them so useful, however these very characteristics could make developing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our aim is to create it easy so that you can understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking by how relative speeds do the job in conjunction with different arrangements. In the star set up the carrier is set, and the relative speeds of the sun, planet, and ring are simply determined by the speed of one member and the amount of teeth in each gear.
In a planetary arrangement the ring gear is fixed, and planets orbit the sun while rotating on earth shaft. In this set up the relative speeds of the sun and planets are determined by the number of teeth in each gear and the acceleration of the carrier.
Things get a lttle bit trickier when working with coupled epicyclic gears, since relative speeds may not be intuitive. It is therefore imperative to usually calculate the velocity 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 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 equally, but this may well 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 constructed with several planets is in most cases equal to the actual quantity of planets. When more than three planets are used, however, the effective number of planets is generally less than using the number of planets.
Let’s look in torque splits when it comes to set support and floating support of the users. With set support, all users are reinforced in bearings. The centers of the sun, 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 quantity of planets sharing the strain. With floating support, a couple of associates are allowed a tiny amount of radial freedom or float, which allows the sun, band, and carrier to get a posture where their centers are coincident. This float could be less than .001-.002 in .. With floating support three planets will always be in mesh, resulting in a higher effective amount of planets posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that should be made when designing epicyclic gears. 1st we must translate RPM into mesh velocities and determine the number of load software cycles per device of time for every single member. The first step in this determination is to calculate the speeds of each of the members relative to the carrier. For example, if the sun gear is rotating at +1700 RPM and the carrier can be rotating at +400 RPM the velocity of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that acceleration and the numbers of teeth in each of the gears. The utilization of symptoms to symbolize 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 speed between the two associates is certainly +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 amount of load cycles per revolution in accordance with the carrier will become equal to the number of planets. The planets, however, will experience only 1 bi-directional load program per relative revolution. It meshes with sunlight and ring, however the load is certainly on contrary sides of one’s teeth, resulting in one fully reversed tension cycle. Thus the planet is known as an idler, and the allowable pressure 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 examining the stress and your life of the members we must look at the resultant loading at each mesh. We find the idea of torque per mesh to end up being relatively confusing in epicyclic equipment research and prefer to look at the tangential load at each mesh. For example, in searching at the tangential load at the sun-world mesh, we consider the torque on the sun equipment and divide it by the successful quantity of planets and the working pitch radius. This tangential load, combined with peripheral speed, can be used to compute the power transmitted at each mesh and, altered by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there can also be assembly complications that require addressing. For example, placing one planet ready between sun and band fixes the angular location of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where in fact the sun and ring could be concurrently 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 amounts of teeth in sunlight and the ring. Therefore, as a way to assemble additional planets, they must become spaced at multiples of this least mesh angle. If one desires to have equivalent spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the amount of teeth in the sun and ring is usually divisible by the amount of planets to an integer. The same rules apply in a compound epicyclic, but the fixed coupling of the planets adds another degree of complexity, and right planet spacing may necessitate match marking of pearly whites.
With multiple pieces in mesh, losses should be considered at each mesh so as to measure the efficiency of the unit. Electricity transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic pieces, the total vitality transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input electric power. This is one of the reasons that easy planetary epicyclic pieces are more efficient than other reducer plans. In contrast, for most coupled epicyclic sets total electrical power transmitted internally through each mesh could be higher than input power.
What of ability at the mesh? For basic and compound epicyclic pieces, calculate pitch range velocities and tangential loads to compute electric power at each mesh. Ideals can be acquired from the earth torque relative acceleration, and the functioning pitch diameters with sun and band. Coupled epicyclic pieces present more technical issues. Elements of two epicyclic sets could be coupled 36 various ways using one suggestions, one result, and one reaction. Some arrangements split the power, although some recirculate power internally. For these kinds of epicyclic sets, tangential loads at each mesh can only be motivated through the use of free-body diagrams. Also, the components of two epicyclic sets can be coupled nine various ways in a string, using one suggestions, one output, and two reactions. Let’s look at some examples.
In the “split-electrical power” coupled set shown in Figure 7, 85 percent of the transmitted electrical 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 sets because the electrical power is split between the two elements. When coupling epicyclic models in a string, 0 percent of the energy will become transmitted through each set.
Our next example depicts a collection with “power recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what happens in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the horsepower at each mesh within the loop enhances as speed increases. Consequently, this set will encounter much higher electrical power losses at each mesh, leading to significantly lower unit efficiency .
Number 9 depicts a free-body diagram of an epicyclic arrangement that encounters power recirculation. A cursory research of this free-body diagram clarifies the 60 percent effectiveness of the recirculating collection proven in Figure 8. Because the planets happen to be rigidly coupled together, the summation of forces on the two gears must the same zero. The power at sunlight gear mesh results from the torque input to sunlight gear. The drive at the second ring gear mesh outcomes from the productivity torque on the band equipment. The ratio being 41.1:1, result torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the pressure on the second planet will be around 14 times the force on the first planet at the sun gear mesh. For that reason, for the summation of forces to equate to zero, the tangential load at the first ring gear must be approximately 13 occasions the tangential load at the sun gear. If we assume the pitch series velocities to be the same at sunlight mesh and band mesh, the power loss at the ring mesh will be roughly 13 times higher than the power loss at the sun mesh .