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 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 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 is certainly in the heart of the ring equipment, and is coaxially organized in relation to the output. Sunlight pinion is usually mounted on a clamping system to be able to offer the mechanical link with the engine shaft. During procedure, the planetary gears, which happen to be mounted on a planetary carrier, roll between your sunlight pinion and the band gear. The planetary carrier also represents the productivity 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 transmission ratio of the gearbox. The number of planets may also vary. As the number of planetary gears improves, the distribution of the strain increases and therefore the torque that can be transmitted. Increasing the number of tooth engagements likewise reduces the rolling vitality. Since only area of the total outcome needs to be transmitted as rolling ability, a planetary gear is incredibly efficient. The advantage of a planetary equipment compared to a single 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.
So long as the ring gear has a continuous size, different ratios can be realized by different the quantity of teeth of sunlight gear and the number of tooth of the planetary gears. The smaller the sun gear, the higher the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, since the planetary gears and the sun gear are extremely small above and below these ratios. Higher ratios can be obtained by connecting a variety of planetary levels in series in the same ring gear. In this instance, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a ring gear that is not fixed but is driven in virtually any direction of rotation. It is also possible to repair the drive shaft so as to grab the torque via the ring equipment. Planetary gearboxes have become extremely important in many regions 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. High transmission ratios may also easily be performed with planetary gearboxes. Because of their positive properties and small design and style, the gearboxes have many potential uses in professional applications.
The advantages 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 combination of several planet stages
Suited as planetary switching gear due to fixing this or that section of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears set up from manual gear field are replaced with more compact and more dependable sun and planetary kind of gears arrangement as well as the manual clutch from manual ability train is replaced with hydro coupled clutch or torque convertor which made the tranny automatic.
The thought of epicyclic gear box is taken 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) modes which is obtained by fixing of sun and planetary gears based on the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- It is a type of gear which looks like a ring and have angular lower teethes at its inner surface ,and is located in outermost placement in en epicyclic gearbox, the internal teethes of ring gear is in constant mesh at outer level with the set of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It is the gear with angular lower teethes and is positioned in the middle of the epicyclic gearbox; sunlight gear is in frequent mesh at inner stage with the planetary gears and is definitely connected with the input shaft of the epicyclic equipment box.
One or more sunlight gears can be utilised for achieving different output.
3. Planet gears- These are small gears used in between ring and sun gear , the teethes of the planet gears are in regular mesh with the sun and the ring gear at both the inner and outer items respectively.
The axis of the earth gears are attached to the planet 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 fastened with the axis of the earth gears and is responsible for final transmission of the result to the outcome 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 gear and is manipulated by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the actual fact the fixing the gears i.electronic. sun gear, planetary gears and annular gear is done to obtain the required torque or velocity output. As fixing any of the above triggers the variation in equipment ratios from great torque to high acceleration. 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 go from its initial state and is obtained by fixing the annular gear which causes the earth carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the vehicle to realize higher speed throughout a drive, these ratios are obtained by fixing the sun gear which makes the planet carrier the driven 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 reverses the direction of the vehicle, this gear is achieved by fixing the earth gear carrier which in turn makes the annular gear the motivated member and sunlight gear the driver member.
Note- More quickness or torque ratios may be accomplished by increasing the number planet and sun equipment in epicyclic gear box.
High-speed epicyclic gears can be built relatively tiny as the power is distributed over a lot of meshes. This benefits in a low power to fat ratio and, together with lower pitch series velocity, causes improved efficiency. The small gear diameters produce lower occasions of inertia, significantly reducing 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 is employed have already been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s begin by examining a significant facet of any project: expense. Epicyclic gearing is generally less costly, when tooled properly. Being an 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, one should not really consider making a 100-piece lot of epicyclic carriers on an N/C mill. To maintain carriers within acceptable 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 element. Epicyclic gear sets are used because they’re smaller than offset gear sets because the load can be shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Also, when configured correctly, 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 source shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design existence is to be 10,000 hours.
With these requirements in mind, let’s look at three feasible solutions, one involving a single branch, two-stage helical gear set. Another solution takes the initial gear set and splits the two-stage reduction into two branches, and the third calls for utilizing a two-level planetary or superstar epicyclic. In this instance, 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, produced from taking the square base of the final ratio (7.70). Along the way of reviewing this solution we notice its size and weight is very large. To reduce the weight we then explore the possibility of earning two branches of an identical arrangement, as seen in the second solutions. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third solution, which is the two-stage superstar epicyclic. With three planets this gear train minimizes tooth loading substantially from the initial approach, and a somewhat smaller amount from choice two (discover “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a sizable part of what makes them so useful, however these very characteristics can make designing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our goal is to create it easy that you can understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s start by looking by 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 dependant on 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 the sun while rotating on the planet shaft. In this set up the relative speeds of sunlight and planets are dependant on the number of teeth in each equipment and the rate of the carrier.
Things get somewhat trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to always calculate the quickness of the sun, planet, and ring relative to the carrier. Remember that actually in a solar arrangement where the sun is fixed it has a speed relationship with the planet-it isn’t zero RPM at the mesh.
Torque Splits
When considering torque splits one assumes the torque to be divided among the planets similarly, but this might not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This amount in epicyclic sets constructed with several planets is generally equal to you see, the number of planets. When a lot more than three planets are utilized, however, the effective number of planets is often less than using the number of planets.
Let’s look in torque splits with regards to fixed support and floating support of the customers. With fixed support, all customers are supported in bearings. The centers of the sun, ring, 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 members are allowed a little amount of radial liberty or float, which allows the sun, band, and carrier to seek a position where their centers will be coincident. This float could possibly be less than .001-.002 inches. With floating support three planets will always be in mesh, resulting in a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that should be made when designing epicyclic gears. Primary we must translate RPM into mesh velocities and determine the quantity of load app cycles per device of time for every single member. The first rung on the ladder in this determination is usually 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 acceleration of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that velocity and the amounts of teeth in each one of the gears. The usage of signals to stand for clockwise and counter-clockwise rotation can be important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative speed between the two people is certainly +1700-(-400), or +2100 RPM.
The second step is to determine the quantity of load application cycles. Since the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will end up being equal to the amount of planets. The planets, nevertheless, will experience only 1 bi-directional load program per relative revolution. It meshes with sunlight and ring, however the load is normally on contrary sides of the teeth, leading to one fully reversed stress cycle. Thus the planet is known as an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load software.
As noted previously mentioned, the torque on the epicyclic users is divided among the planets. In examining the stress and lifestyle of the members we must look at the resultant loading at each mesh. We get the concept of torque per mesh to become somewhat confusing in epicyclic gear examination and prefer to check out the tangential load at each mesh. For instance, in seeking at the tangential load at the sun-planet mesh, we consider the torque on sunlight equipment and divide it by the successful quantity of planets and the working pitch radius. This tangential load, combined with peripheral speed, is employed to compute the power transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of each 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 placement of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where in fact the sun and ring can be concurrently engaged. The “least mesh angle” from the 1st 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, so that you can assemble extra planets, they must always be spaced at multiples of this least mesh angle. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets could be spaced similarly when the sum of the number of teeth in the sun and ring is definitely divisible by the amount of planets to an integer. The same guidelines apply in a compound epicyclic, but the fixed coupling of the planets adds another level of complexity, and correct planet spacing may necessitate match marking of the teeth.
With multiple components in mesh, losses need to be considered at each mesh in order to evaluate the efficiency of the unit. Ability transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic units, the total vitality transmitted through the sun-world mesh and ring-planet mesh may be less than input power. This is among the reasons that simple planetary epicyclic pieces are better than other reducer plans. In contrast, for many coupled epicyclic pieces total electric power transmitted internally through each mesh may be higher than input power.
What of electrical power at the mesh? For basic and compound epicyclic sets, calculate pitch line velocities and tangential loads to compute vitality at each mesh. Ideals can be obtained from the earth torque relative swiftness, and the operating pitch diameters with sunshine and ring. Coupled epicyclic pieces present more complex issues. Elements of two epicyclic sets can be coupled 36 various ways using one insight, one result, and one response. Some arrangements split the power, although some recirculate ability internally. For these kinds of epicyclic pieces, tangential loads at each mesh can only be determined through the utilization of free-body diagrams. Also, the factors of two epicyclic units could be coupled nine different ways in a string, using one insight, one end result, and two reactions. Let’s look at a few examples.
In the “split-power” coupled set displayed in Figure 7, 85 percent of the transmitted electric power flows to ring gear #1 and 15 percent to ring gear #2. The result is that this coupled gear set can be smaller than series coupled sets because the ability is split between the two factors. When coupling epicyclic units in a series, 0 percent of the power will be transmitted through each placed.
Our next example depicts a establish with “electricity recirculation.” This gear set comes about when torque gets locked in the machine 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 raises as speed increases. Therefore, this set will encounter much higher vitality losses at each mesh, resulting in considerably lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that experiences power recirculation. A cursory research of this free-physique diagram explains the 60 percent effectiveness of the recirculating collection proven in Figure 8. Since the planets will be rigidly coupled at the same time, the summation of forces on the two gears must equivalent zero. The force at the sun gear mesh effects from the torque source to sunlight gear. The force at the second ring gear mesh results from the outcome 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 force on the next planet will be around 14 times the drive on the first world at sunlight 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 times the tangential load at the sun gear. If we assume the pitch range velocities to end up being the same at sunlight mesh and band mesh, the power loss at the ring mesh will be approximately 13 times greater than the energy loss at sunlight mesh .


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