In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference manage between a gear with internal teeth and a gear with external teeth on a concentric orbit. The circulation of the spur equipment takes place in analogy to the orbiting of the planets in the solar system. This is how planetary gears acquired their name.
The elements of a planetary gear train could be divided into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In the majority of cases the casing is fixed. The generating sun pinion is usually in the center of the ring equipment, and is coaxially arranged in relation to the output. Sunlight pinion is usually attached to a clamping system to be able to present the mechanical link with the electric motor shaft. During procedure, the planetary gears, which happen to be attached on a planetary carrier, roll between your sun pinion and the band 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 does not have any effect on the tranny ratio of the gearbox. The amount of planets can also vary. As the quantity of planetary gears raises, the distribution of the load increases and then the torque that can be transmitted. Increasing the quantity of tooth engagements as well reduces the rolling ability. Since only portion of the total result needs to be transmitted as rolling electricity, a planetary gear is incredibly efficient. The advantage of a planetary equipment compared to an individual spur gear lies in this load distribution. Hence, it is possible to transmit huge torques wit
h high efficiency with a concise design using planetary gears.
Provided that the ring gear includes a constant size, different ratios can be realized by different the amount of teeth of sunlight gear and the number of teeth of the planetary gears. The smaller 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 sunlight gear are extremely small above and below these ratios. Larger ratios can be acquired by connecting a couple of planetary levels in series in the same ring gear. In this case, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a ring gear that’s not set but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft so that you can pick up the torque via the ring gear. Planetary gearboxes have become extremely important in lots of 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. High transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and compact style, the gearboxes have many potential uses in industrial 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
Practically unlimited transmission ratio options because of combination of several planet stages
Suited 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 variety of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears arrangement from manual gear package are replaced with more compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual vitality train is substituted with hydro coupled clutch or torque convertor which in turn made the transmission automatic.
The idea 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) settings which is obtained by fixing of sun and planetary gears in line with the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a kind of gear which appears like a ring and have angular minimize teethes at its internal surface ,and is put in outermost situation in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer level with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It’s the equipment with angular minimize teethes and is located in the middle of the epicyclic gearbox; the sun gear is in regular mesh at inner stage with the planetary gears and is definitely connected with the source shaft of the epicyclic gear box.
One or more sunlight gears works extremely well for obtaining different output.
3. Planet gears- These are small gears found in between ring and sun gear , the teethes of the earth gears are in constant mesh with the sun and the ring equipment at both the inner and outer items respectively.
The axis of the planet gears are attached to the earth 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 sunlight gear exactly like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the planet gears and is in charge of final transmitting of the output to the result 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 repair the annular gear, sun gear and planetary gear and is managed by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the actual fact the fixing any of the gears i.e. sun gear, planetary gears and annular gear is done to get the expected torque or quickness output. As fixing the above triggers the variation in gear ratios from substantial 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 the sun gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the vehicle to achieve higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the planet carrier the influenced member and annular the driving a car 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 vehicle, this gear is attained by fixing the planet gear carrier which in turn makes the annular gear the influenced member and the sun gear the driver member.
Note- More quickness or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear container.
High-speed epicyclic gears could be built relatively tiny as the power is distributed over a variety of meshes. This results in a low capacity to weight ratio and, together with lower pitch line velocity, contributes to improved efficiency. The tiny equipment diameters produce lower moments of inertia, significantly reducing acceleration and deceleration torque when starting 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 is utilized have been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s start by examining a significant aspect of any project: expense. Epicyclic gearing is normally less costly, when tooled properly. Being an wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling equipment with an application cutter or ball end mill, one should certainly not 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 at the same time removing material.
Size is another aspect. Epicyclic gear units are used because they are smaller than offset equipment sets since the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Also, when configured properly, epicyclic gear pieces are more efficient. The next example illustrates these rewards. Let’s believe that we’re designing a high-speed gearbox to fulfill the following requirements:
• A turbine offers 6,000 horsepower at 16,000 RPM to the suggestions shaft.
• The output 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 practical solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the original gear collection and splits the two-stage reduction into two branches, and the third calls for utilizing a two-stage planetary or superstar epicyclic. In this instance, 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, produced from taking the square root of the final ratio (7.70). Along the way of reviewing this answer we recognize its size and weight is very large. To reduce the weight we in that case explore the possibility of earning two branches of an identical arrangement, as seen in the second solutions. This cuts tooth loading and reduces both size and weight considerably . We finally arrive at our third choice, which may be the two-stage superstar epicyclic. With three planets this equipment train reduces tooth loading drastically from the first approach, and a somewhat smaller amount from answer two (see “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 designing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our objective is to make it easy so that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds function together with different plans. In the star arrangement the carrier is set, and the relative speeds of the sun, planet, and band are simply determined by the speed of 1 member and the number 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 arrangement the relative speeds of sunlight and planets are dependant on the quantity of teeth in each gear and the speed of the carrier.
Things get a little trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. Hence, it is imperative to usually calculate the speed of sunlight, planet, and ring in accordance with the carrier. Remember that also in a solar arrangement where the sunshine is fixed it includes a speed romantic 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 similarly, but this may well 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 two or three planets is in most cases equal to some of the quantity of planets. When more than three planets are employed, however, the effective number of planets is always less than some of the number of planets.
Let’s look in torque splits in terms of set support and floating support of the people. With fixed support, all participants are reinforced in bearings. The centers of the sun, band, and carrier will not be coincident due to manufacturing tolerances. For this reason fewer planets are simultaneously in mesh, resulting in a lower effective quantity of planets sharing the strain. With floating support, one or two people are allowed a tiny amount of radial independence or float, that allows the sun, ring, and carrier to get a posture where their centers are coincident. This float could possibly be as little as .001-.002 in .. With floating support three planets will be in mesh, resulting in a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that should be made when designing epicyclic gears. 1st we should translate RPM into mesh velocities and determine the quantity of load app cycles per unit of time for each member. The first step in this determination is to calculate the speeds of every of the members in accordance with the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is normally rotating at +400 RPM the rate of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that rate and the amounts of teeth in each one of the gears. The make use of symptoms to represent 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 participants is certainly +1700-(-400), or +2100 RPM.
The second step is to identify the quantity of load application cycles. Since the sun and band gears mesh with multiple planets, the amount of load cycles per revolution in accordance with the carrier will become equal to the amount of planets. The planets, even so, will experience only one bi-directional load software per relative revolution. It meshes with sunlight and ring, but the load is normally on reverse sides of one’s teeth, resulting in one fully reversed anxiety cycle. Thus the earth is known as an idler, and the allowable stress must be reduced thirty percent from the value for a unidirectional load request.
As noted above, the torque on the epicyclic users is divided among the planets. In analyzing the stress and existence of the participants we must consider the resultant loading at each mesh. We find the concept of torque per mesh to become relatively confusing in epicyclic equipment evaluation and prefer to look at the tangential load at each mesh. For instance, in looking at the tangential load at the sun-planet mesh, we consider the torque on the sun equipment and divide it by the powerful amount of planets and the functioning pitch radius. This tangential load, combined with peripheral speed, can be used to compute the energy transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of every component.
In addition to these issues there can also be assembly complications that require addressing. For example, positioning one planet in a position between sun and band fixes the angular location of the sun to the ring. The next planet(s) is now able to be assembled only in discreet locations where the sun and band can be simultaneously involved. The “least mesh angle” from the primary planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the numbers of teeth in sunlight and the ring. Thus, so as to assemble additional planets, they must end up being spaced at multiples of the least mesh angle. If one wants to have equivalent spacing of the planets in a straightforward epicyclic set, planets may be spaced equally when the sum of the amount of teeth in the sun and ring can be divisible by the number of planets to an integer. The same guidelines apply in a compound epicyclic, but the fixed coupling of the planets gives another level of complexity, and correct planet spacing may require match marking of pearly whites.
With multiple parts in mesh, losses should be considered at each mesh to be able to evaluate the efficiency of the machine. Vitality transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic sets, the total electrical power transmitted through the sun-planet mesh and ring-planet mesh may be significantly less than input vitality. This is among the reasons that easy planetary epicyclic sets are better than other reducer arrangements. In contrast, for many coupled epicyclic units total power transmitted internally through each mesh could be greater than input power.
What of ability at the mesh? For basic and compound epicyclic units, calculate pitch line velocities and tangential loads to compute electricity at each mesh. Values can be obtained from the planet torque relative acceleration, and the operating pitch diameters with sun and ring. Coupled epicyclic pieces present more complex issues. Components of two epicyclic pieces can be coupled 36 various ways using one insight, one productivity, and one reaction. Some plans split the power, while some recirculate electrical power internally. For these types of epicyclic units, tangential loads at each mesh can only be motivated through the utilization of free-body diagrams. On top of that, the factors of two epicyclic pieces can be coupled nine different ways in a series, using one type, one outcome, and two reactions. Let’s look at a few examples.
In the “split-electrical power” coupled set shown in Figure 7, 85 percent of the transmitted electricity flows to band gear #1 and 15 percent to ring gear #2. The effect is that this coupled gear set could be small than series coupled units because the electricity is split between your two components. When coupling epicyclic models in a series, 0 percent of the power will become transmitted through each establish.
Our next example depicts a set with “electric power recirculation.” This equipment set happens when torque gets locked in the system in a way similar to what happens in a “four-square” test procedure for vehicle travel axles. With the torque locked in the system, the horsepower at each mesh within the loop enhances as speed increases. As a result, this set will encounter much higher ability losses at each mesh, leading to considerably lower unit efficiency .
Number 9 depicts a free-body diagram of an epicyclic arrangement that experiences electricity recirculation. A cursory analysis of this free-body diagram clarifies the 60 percent efficiency of the recirculating collection demonstrated in Figure 8. Since the planets happen to be rigidly coupled collectively, the summation of forces on both gears must the same zero. The drive at sunlight gear mesh results from the torque suggestions to the sun gear. The induce at the next ring gear mesh results from the result torque on the band 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 push on the second planet will be about 14 times the induce on the first world at the sun gear mesh. Therefore, for the summation of forces to equate to zero, the tangential load at the first ring gear should be approximately 13 circumstances the tangential load at sunlight gear. If we believe the pitch brand velocities to become the same at the sun mesh and band mesh, the power loss at the ring mesh will be around 13 times greater than the energy loss at sunlight mesh .