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 external 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 traveling sun pinion is normally in the center of the ring equipment, and is coaxially arranged with regards to the output. The sun pinion is usually attached to a clamping system in order to provide the mechanical connection to the engine shaft. During operation, the planetary gears, which will be attached on a planetary carrier, roll between the sunlight pinion and the ring equipment. The planetary carrier also represents the productivity shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The number of teeth has no effect on the tranny ratio of the gearbox. The quantity of planets may also vary. As the number of planetary gears increases, the distribution of the load increases and therefore the torque that can be transmitted. Raising the number of tooth engagements also reduces the rolling electricity. Since only part of the total output needs to be transmitted as rolling power, a planetary gear is extremely efficient. The benefit of a planetary gear compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit high torques wit
h high efficiency with a compact design using planetary gears.
Provided that the ring gear has a regular size, different ratios can be realized by varying the quantity of teeth of sunlight gear and the number of the teeth 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, since the planetary gears and the sun gear are extremely small above and below these ratios. Higher ratios can be obtained by connecting many planetary phases in series in the same band gear. In this instance, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that’s not fixed but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft so that you can pick up the torque via the band equipment. Planetary gearboxes have grown to be extremely important in many 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. Excessive transmission ratios can also easily be achieved with planetary gearboxes. Because of their positive properties and small design, the gearboxes have many potential uses in industrial applications.
The features 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 mixture of several planet stages
Appropriate as planetary switching gear because of fixing this or that section of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a wide selection of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears set up from manual gear container are replaced with more compact and more trusted sun and planetary kind of gears arrangement as well as the manual clutch from manual electricity 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- It is a kind of gear which appears like a ring and have angular minimize teethes at its interior surface ,and is placed in outermost position in en epicyclic gearbox, the inner teethes of ring gear is in regular mesh at outer point with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the equipment with angular cut teethes and is put in the center of the epicyclic gearbox; the sun gear is in constant mesh at inner level with the planetary gears and can be connected with the type shaft of the epicyclic equipment box.
One or more sunshine gears can be utilised 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 sunlight and the ring equipment at both inner and outer points 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 in addition can revolve between the ring and sunlight gear exactly 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 tranny of the result to the productivity 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, sunlight gear and planetary equipment and is managed 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.electronic. sun gear, planetary gears and annular equipment is done to obtain the expected torque or velocity output. As fixing any of the above causes the variation in gear ratios from excessive torque to high quickness. 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 planet carrier to rotate with the power supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the vehicle to attain higher speed throughout a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the motivated member and annular the driving a vehicle member so that you can 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 attained by fixing the earth gear carrier which in turn makes the annular gear the driven member and sunlight gear the driver member.
Note- More rate or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears could be built relatively little as the energy is distributed over several meshes. This outcomes 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.
Why epicyclic gearing is employed have been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s get started by examining an essential aspect of any project: price. Epicyclic gearing is generally less expensive, 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 really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To keep carriers within acceptable manufacturing costs they must be created from castings and tooled on single-purpose machines with multiple cutters simultaneously removing material.
Size is another component. Epicyclic gear pieces 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. Also, when configured effectively, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s assume that we’re designing a high-speed gearbox to fulfill the following requirements:
• A turbine delivers 6,000 horsepower at 16,000 RPM to the input shaft.
• The end result from the gearbox must drive a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements in mind, let’s look at three possible solutions, one involving a single branch, two-stage helical gear set. A second solution takes the original gear arranged and splits the two-stage decrease into two branches, and the third calls for using a two-level planetary or superstar epicyclic. In this instance, we chose the celebrity. 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 answer we detect its size and weight is very large. To reduce the weight we then explore the possibility of making two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and minimizes both size and fat considerably . We finally reach our third choice, which is the two-stage star epicyclic. With three planets this equipment train minimizes tooth loading drastically from the 1st approach, and a relatively smaller amount from option two (check out “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a huge part of why is them so useful, yet these very characteristics could make creating them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to create it easy for you to understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s get started by looking in how relative speeds work in conjunction with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of sunlight, planet, and ring are simply dependant on the speed of 1 member and the amount of teeth in each gear.
In a planetary arrangement the band gear is set, and planets orbit the sun while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are dependant on the number of teeth in each gear and the acceleration of the carrier.
Things get somewhat trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to constantly calculate the velocity of the sun, planet, and ring in accordance with the carrier. Understand that actually in a solar arrangement where the sunshine is fixed it includes a speed relationship with the planet-it isn’t zero RPM at the mesh.
Torque Splits
When contemplating 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 number in epicyclic sets constructed with two or three planets is in most cases equal to you see, the amount of planets. When more than three planets are applied, however, the effective amount of planets is usually less than the actual number of planets.
Let’s look by torque splits regarding set support and floating support of the participants. With set support, all customers are backed in bearings. The centers of the sun, band, and carrier will not be coincident due to manufacturing tolerances. Due to this fewer planets happen to be simultaneously in mesh, producing a lower effective amount of planets posting the load. With floating support, one or two users are allowed a tiny amount of radial flexibility or float, that allows the sun, ring, and carrier to get a posture where their centers happen to be coincident. This float could be less than .001-.002 in .. With floating support three planets will 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 making epicyclic gears. Initial we should translate RPM into mesh velocities and determine the number of load program cycles per product of time for every single member. The first step in this determination is normally to calculate the speeds of each of the members in accordance with the carrier. For example, if the sun gear is rotating at +1700 RPM and the carrier is 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 velocity and the amounts of teeth in each one of the gears. The use of indicators to signify clockwise and counter-clockwise rotation is usually important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative rate between the two users is normally +1700-(-400), or +2100 RPM.
The second step is to determine the number of load application cycles. Since the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will become equal to the quantity of planets. The planets, on the other hand, will experience only 1 bi-directional load application per relative revolution. It meshes with the sun and ring, however the load is definitely on opposing sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the earth is considered an idler, and the allowable pressure must be reduced 30 percent from the value for a unidirectional load software.
As noted previously mentioned, the torque on the epicyclic members 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 locate the concept of torque per mesh to become somewhat confusing in epicyclic equipment examination and prefer to look at the tangential load at each mesh. For instance, in looking at the tangential load at the sun-world mesh, we consider the torque on the sun gear and divide it by the effective quantity of planets and the working pitch radius. This tangential load, combined with the peripheral speed, can be used 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 ring fixes the angular situation of sunlight to the ring. Another planet(s) can now be assembled only in discreet locations where the sun and ring can be at the same time engaged. The “least mesh angle” from the first planet that will support simultaneous mesh of the next planet is equal to 360° divided by the sum of the numbers of teeth in the sun and the ring. Thus, in order to assemble added planets, they must be spaced at multiples of the least mesh position. If one wishes to have equal 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 ring is usually divisible by the amount of planets to an integer. The same guidelines apply in a compound epicyclic, but the set coupling of the planets offers another level of complexity, and right planet spacing may require match marking of pearly whites.
With multiple components in mesh, losses must be considered at each mesh to be able to evaluate the efficiency of the unit. Electric power transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic units, the total ability transmitted through the sun-world mesh and ring-world mesh may be significantly less than input electrical power. This is one of the reasons that easy planetary epicyclic models are better than other reducer arrangements. In contrast, for most coupled epicyclic models total vitality transmitted internally through each mesh may be higher than input power.
What of vitality at the mesh? For simple and compound epicyclic pieces, calculate pitch range velocities and tangential loads to compute electric power at each mesh. Values can be obtained from the earth torque relative velocity, and the operating pitch diameters with sun and band. Coupled epicyclic units present more complex issues. Elements of two epicyclic units can be coupled 36 different ways using one source, one result, and one response. Some plans split the power, although some recirculate electric power internally. For these kind of epicyclic models, tangential loads at each mesh can only be established through the consumption of free-body diagrams. Also, the components of two epicyclic units can be coupled nine various ways in a string, using one input, one end result, and two reactions. Let’s look at some examples.
In the “split-electric 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 this coupled gear set could be small than series coupled sets because the electricity is split between your two elements. When coupling epicyclic sets in a series, 0 percent of the power will end up being transmitted through each set.
Our next example depicts a arranged with “electric power 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 procedure for vehicle drive axles. With the torque locked in the machine, the hp at each mesh within the loop enhances as speed increases. Therefore, this set will knowledge much higher vitality losses at each mesh, leading to considerably lower unit efficiency .
Number 9 depicts a free-body diagram of an epicyclic arrangement that encounters electric power recirculation. A cursory research of this free-body system diagram clarifies the 60 percent productivity of the recirculating set demonstrated in Figure 8. Since the planets happen to be rigidly coupled jointly, the summation of forces on both gears must equal zero. The power at sunlight gear mesh benefits from the torque input to sunlight gear. The drive at the next ring gear mesh outcomes from the productivity torque on the ring gear. The ratio being 41.1:1, outcome 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 roughly 14 times the force 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 band gear must be approximately 13 situations the tangential load at the sun gear. If we assume the pitch line velocities to become the same at sunlight mesh and band mesh, the power loss at the ring mesh will be around 13 times greater than the energy loss at the sun mesh .