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 gear occurs in analogy to the orbiting of the planets in the solar system. This is one way planetary gears acquired their name.
The pieces 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 nearly all cases the housing is fixed. The traveling sun pinion is certainly 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 to be able to present the mechanical link with the motor shaft. During operation, the planetary gears, which are mounted on a planetary carrier, roll between your sun pinion and the band gear. The planetary carrier as well represents the outcome shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The number of teeth does not have any effect on the transmitting ratio of the gearbox. The number of planets can also vary. As the amount of planetary gears increases, the distribution of the strain increases and then the torque that can be transmitted. Increasing the quantity of tooth engagements as well reduces the rolling electricity. Since only the main total output has to be transmitted as rolling power, a planetary equipment is incredibly efficient. The good thing about a planetary equipment compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear includes a frequent size, different ratios could be realized by various the number of teeth of the sun gear and the number of teeth of the planetary gears. Small the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, since the planetary gears and sunlight gear are extremely little above and below these ratios. Bigger ratios can be obtained by connecting many planetary levels in series in the same ring gear. In this case, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a band gear that is not set but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft as a way to pick up the torque via the band gear. Planetary gearboxes have grown to be extremely important in many areas of mechanical engineering.
They have become particularly well established in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Huge transmission ratios can also easily be achieved with planetary gearboxes. Because of their positive properties and small style, 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 combo of several planet stages
Suited as planetary switching gear because of fixing this or that the main 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 where parallel shafts and gears arrangement from manual gear container are replaced with an increase of compact and more reliable sun and planetary kind of gears arrangement plus the manual clutch from manual ability train is replaced with hydro coupled clutch or torque convertor which made the tranny automatic.
The idea of epicyclic gear box is extracted from the solar system which is known as to the perfect arrangement of objects.
The epicyclic gearbox usually includes the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears according to the need of the travel.
The different parts of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which looks like a ring and have angular minimize teethes at its inner surface ,and is put in outermost position in en epicyclic gearbox, the internal teethes of ring equipment is in constant mesh at outer level with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the gear with angular cut teethes and is positioned in the center of the epicyclic gearbox; the sun gear is in regular mesh at inner level with the planetary gears and is normally connected with the suggestions 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 earth gears are in frequent mesh with sunlight and the ring gear at both the inner and outer factors 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 your ring and the sun gear exactly like our solar system.
4. Planet carrier- It is a carrier attached with the axis of the planet gears and is responsible for final tranny of the output 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 fix the annular gear, sunlight gear and planetary gear and is controlled by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the fact the fixing any of the gears i.electronic. sun equipment, planetary gears and annular gear is done to get the expected torque or velocity output. As fixing the above causes the variation in equipment ratios from huge torque to high rate. 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 gives high speed ratios to the automobile which helps the automobile to attain higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the driven 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 automobile, this gear is achieved by fixing the earth gear carrier which makes the annular gear the powered member and the sun gear the driver member.
Note- More rate or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear box.
High-speed epicyclic gears can be built relatively tiny as the power is distributed over several meshes. This outcomes in a low power to pounds ratio and, together with lower pitch brand velocity, leads to improved efficiency. The tiny equipment diameters produce lower moments of inertia, significantly minimizing 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.
The reasons why epicyclic gearing can be used have already been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s start by examining an important facet of any project: expense. Epicyclic gearing is normally less costly, when tooled properly. Just as one would not consider making a 100-piece lot 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 preserve carriers within realistic manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another issue. Epicyclic gear sets are used because they are smaller than offset equipment sets since the load is certainly shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear pieces are more efficient. The next example illustrates these rewards. Let’s believe that we’re designing a high-speed gearbox to satisfy the following requirements:
• A turbine delivers 6,000 hp at 16,000 RPM to the type shaft.
• The productivity from the gearbox must travel a generator at 900 RPM.
• The design your life is to be 10,000 hours.
With these requirements in mind, let’s look at three likely solutions, one involving a single branch, two-stage helical gear set. A second solution takes the original gear placed and splits the two-stage lowering into two branches, and the 3rd calls for by using a two-stage planetary or celebrity epicyclic. In this instance, we chose the star. Let’s examine each one 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, derived from taking the square base of the final ratio (7.70). Along the way of reviewing this solution we find its size and pounds is very large. To lessen the weight we after that explore the possibility of making two branches of an identical arrangement, as seen in the second solutions. This cuts tooth loading and minimizes both size and weight considerably . We finally reach our third answer, which may be the two-stage star epicyclic. With three planets this equipment train minimizes tooth loading substantially from the first approach, and a relatively smaller amount from answer two (check out “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a large part of what makes them so useful, however these very characteristics could make building them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to create it easy so that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s get started by looking at how relative speeds function together with different arrangements. In the star set up the carrier is set, and the relative speeds of sunlight, planet, and band are simply dependant on the speed of 1 member and the amount of teeth in each equipment.
In a planetary arrangement the ring gear is set, and planets orbit sunlight 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 a little trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. It is therefore imperative to at all times calculate the swiftness of the sun, planet, and ring relative to the carrier. Understand that possibly in a solar set up where the sunshine is fixed it has a speed romantic 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 may not be considered a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” number of planets. This amount in epicyclic sets designed with several planets is in most cases equal to the actual quantity of planets. When more than three planets are utilized, however, the effective quantity of planets is constantly less than some of the number of planets.
Let’s look by torque splits with regards to fixed support and floating support of the people. With set support, all members 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 happen to be simultaneously in mesh, producing a lower effective number of planets sharing the load. With floating support, one or two users are allowed a tiny amount of radial liberty or float, that allows the sun, band, and carrier to seek a posture where their centers are coincident. This float could be as little as .001-.002 inches. 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 considerations that should be made when designing epicyclic gears. First we must translate RPM into mesh velocities and determine the amount of load software cycles per unit of time for each and every member. The first step in this determination is usually to calculate the speeds of every of the members in accordance with the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is usually rotating at +400 RPM the quickness of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that speed and the numbers of teeth in each of the gears. The make use of indicators to stand for clockwise and counter-clockwise rotation is certainly important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative quickness between the two members is usually +1700-(-400), or +2100 RPM.
The next step is to identify the quantity of load application cycles. Since 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 amount of planets. The planets, however, will experience only 1 bi-directional load app per relative revolution. It meshes with the sun and ring, but the load is definitely on reverse sides of one’s teeth, resulting in one fully reversed stress cycle. Thus the planet is known as an idler, and the allowable stress must be reduced 30 percent from the value for a unidirectional load program.
As noted over, the torque on the epicyclic people is divided among the planets. In examining the stress and life of the customers we must consider the resultant loading at each mesh. We discover the concept of torque per mesh to always be somewhat confusing in epicyclic gear research and prefer to check out the tangential load at each mesh. For example, in searching at the tangential load at the sun-planet mesh, we take the torque on sunlight equipment and divide it by the powerful quantity of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is used to compute the power transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of each component.
Furthermore to these issues there can also be assembly complications that need addressing. For example, inserting one planet in a position between sun and band fixes the angular posture of the sun to the ring. The next planet(s) is now able to be assembled only in discreet locations where in fact the sun and band can be concurrently 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 the sun and the ring. Hence, as a way to assemble more planets, they must always be spaced at multiples of the least mesh angle. If one desires to have the same spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the amount of teeth in sunlight and band is certainly divisible by the number of planets to an integer. The same rules apply in a compound epicyclic, but the fixed coupling of the planets brings another degree of complexity, and proper planet spacing may necessitate match marking of the teeth.
With multiple components in mesh, losses ought to be considered at each mesh as a way to measure the efficiency of the unit. Electric power transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic units, the total ability transmitted through the sun-planet mesh and ring-world mesh may be less than input electricity. This is one of the reasons that easy planetary epicyclic pieces are better than other reducer arrangements. In contrast, for most coupled epicyclic sets total vitality transmitted internally through each mesh may be greater than input power.
What of power at the mesh? For basic and compound epicyclic models, calculate pitch brand velocities and tangential loads to compute power at each mesh. Values can be obtained from the earth torque relative acceleration, and the operating pitch diameters with sun and band. Coupled epicyclic sets present more complex issues. Components of two epicyclic units could be coupled 36 various ways using one source, one productivity, and one response. Some plans split the power, although some recirculate vitality internally. For these types of epicyclic models, tangential loads at each mesh can only just be determined through the application of free-body diagrams. On top of that, the factors of two epicyclic sets could be coupled nine different ways in a series, using one source, one outcome, and two reactions. Let’s look at some examples.
In the “split-vitality” coupled set displayed in Figure 7, 85 percent of the transmitted power flows to ring gear #1 and 15 percent to band gear #2. The effect is that coupled gear set could be smaller than series coupled units because the electricity is split between the two components. When coupling epicyclic sets in a string, 0 percent of the energy will be transmitted through each establish.
Our next case in point depicts a placed with “power recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what occurs in a “four-square” test procedure for vehicle travel axles. With the torque locked in the machine, the hp at each mesh within the loop boosts as speed increases. As a result, this set will encounter much higher power losses at each mesh, leading to considerably lower unit efficiency .
Number 9 depicts a free-body diagram of an epicyclic arrangement that encounters ability recirculation. A cursory examination of this free-human body diagram explains the 60 percent efficiency of the recirculating arranged shown in Figure 8. Since the planets happen to be rigidly coupled along, the summation of forces on both gears must the same zero. The force at sunlight gear mesh results from the torque input to the sun gear. The force at the next ring gear mesh results from the outcome torque on the ring gear. The ratio being 41.1:1, output 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 power on the first planet at the sun gear mesh. For this reason, for the summation of forces to mean zero, the tangential load at the first ring gear should be approximately 13 circumstances the tangential load at the sun gear. If we believe the pitch line velocities to always be the same at sunlight mesh and ring mesh, the power loss at the ring mesh will be approximately 13 times higher than the power loss at sunlight mesh .