epicyclic gearbox

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 program. This is one way planetary gears obtained their name.
The components of a planetary gear train could be split 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 gear, and is coaxially organized with regards to the output. Sunlight pinion is usually mounted on a clamping system to be able to give the mechanical link with the electric motor shaft. During operation, the planetary gears, which will be installed on a planetary carrier, roll between your sunshine pinion and the band equipment. The planetary carrier also represents the outcome shaft of the gearbox.
The sole purpose of 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 quantity of planets may also vary. As the quantity of planetary gears increases, the distribution of the strain increases and then the torque which can be transmitted. Raising the number of tooth engagements also reduces the rolling electric power. Since only part of the total result should be transmitted as rolling electric power, a planetary equipment is extremely efficient. The good thing about a planetary equipment compared to an individual spur gear is based on this load distribution. Hence, it is possible to transmit substantial torques wit
h high efficiency with a compact design using planetary gears.
Provided that the ring gear has a regular size, different ratios could be realized by various the number of teeth of the sun gear and the number of pearly whites of the planetary gears. Small the sun gear, the greater the ratio. Technically, a meaningful ratio range for a planetary stage is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely little above and below these ratios. Higher ratios can be obtained by connecting several planetary stages in series in the same ring 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 set but is driven in virtually any direction of rotation. It is also possible to fix the drive shaft so that you can pick up the torque via the band 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 should be transmitted with favorable mass inertia ratio adaptation. Large 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 commercial applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency because of low rolling power
Almost unlimited transmission ratio options because of combo of several planet stages
Appropriate as planetary switching gear due to fixing this or that part of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox is an automatic type gearbox where parallel shafts and gears arrangement from manual gear container are replaced with an increase of compact and more trusted sun and planetary kind of gears arrangement plus the manual clutch from manual electrical power train is changed with hydro coupled clutch or torque convertor which made the transmitting automatic.
The thought of epicyclic gear box is extracted from the solar system which is considered to an ideal arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) settings 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 type of gear which looks like a ring and have angular cut teethes at its inner surface ,and is placed in outermost posture in en epicyclic gearbox, the interior teethes of ring equipment is in continuous mesh at outer stage with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It is the equipment with angular minimize teethes and is placed in the middle of the epicyclic gearbox; sunlight gear is in constant mesh at inner point with the planetary gears and can be connected with the type shaft of the epicyclic gear box.
One or more sunlight gears can be used for obtaining different output.
3. Planet gears- These are small gears found in between band and sun gear , the teethes of the planet gears are in continuous mesh with the sun and the ring gear at both 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 also can revolve between the ring and sunlight gear exactly like our solar system.
4. Planet carrier- This is a carrier fastened with the axis of the planet gears and is accountable for final transmitting of the outcome 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, sunshine gear and planetary gear and is manipulated 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 any of the gears i.electronic. sun equipment, planetary gears and annular equipment is done to get the required torque or velocity output. As fixing any of the above causes the variation in gear ratios from large torque to high acceleration. So let’s observe how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile 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 sunlight gear.
Second gear ratio
This gives high speed ratios to the automobile which helps the automobile to realize higher speed throughout a travel, these ratios are obtained by fixing the sun gear which makes the planet carrier the driven 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 achieved by fixing the earth gear carrier which in turn makes the annular gear the powered member and sunlight gear the driver member.
Note- More rate or torque ratios may be accomplished by increasing the quantity planet and sun equipment in epicyclic gear container.
High-speed epicyclic gears can be built relatively tiny as the energy is distributed over several meshes. This benefits in a low power to pounds ratio and, as well as lower pitch brand velocity, brings about improved efficiency. The small equipment diameters produce lower occasions 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 the topic in simply a few places. Let’s commence by examining a significant facet of any project: expense. Epicyclic gearing is normally less costly, when tooled properly. Being an would not consider making a 100-piece large amount of gears on an N/C milling equipment with an application cutter or ball end mill, you need to certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To keep carriers within fair manufacturing costs they should be made from castings and tooled on single-purpose equipment with multiple cutters concurrently removing material.
Size is another factor. Epicyclic gear pieces are used because they’re 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 sets are more efficient. The following example illustrates these benefits. Let’s assume that we’re developing a high-speed gearbox to gratify the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the input shaft.
• The productivity from the gearbox must travel a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements at heart, let’s look at three feasible 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 3rd calls for by using a two-stage planetary or star epicyclic. In this instance, we chose the superstar. Let’s examine each one 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, derived from taking the square root of the final ratio (7.70). In the process of reviewing this option we realize its size and pounds is very large. To reduce the weight we then explore the possibility of making two branches of a similar arrangement, as seen in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third choice, which may be the two-stage superstar epicyclic. With three planets this gear train reduces tooth loading drastically from the initial approach, and a relatively smaller amount from option two (observe “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a sizable part of what makes them so useful, yet these very characteristics could make designing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our objective is to create it easy so that you can understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking at how relative speeds operate in conjunction with different plans. In the star set up the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply dependant on the speed of one member and the number of teeth in each equipment.
In a planetary arrangement the ring gear is set, and planets orbit sunlight while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are determined by the amount of teeth in each equipment and the swiftness of the carrier.
Things get somewhat trickier whenever using coupled epicyclic gears, since relative speeds might not be intuitive. Hence, it is imperative to always calculate the acceleration of sunlight, planet, and ring in accordance with the carrier. Understand that even in a solar arrangement where the sunlight is fixed it has a speed romantic 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” number of planets. This quantity in epicyclic sets constructed with two or three planets is generally equal to the actual amount of planets. When a lot more than three planets are used, however, the effective number of planets is often less than the actual number of planets.
Let’s look in torque splits with regards to set support and floating support of the members. With fixed support, all users are reinforced in bearings. The centers of the sun, band, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets will be simultaneously in mesh, resulting in a lower effective number of planets posting the load. With floating support, one or two users are allowed a little amount of radial flexibility or float, which allows the sun, ring, and carrier to get a posture where their centers happen to be coincident. This float could possibly be as little as .001-.002 ins. With floating support three planets will be in mesh, producing a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that needs to be made when designing epicyclic gears. Primary we should translate RPM into mesh velocities and determine the number of load request cycles per device of time for every single member. The first step in this determination can be to calculate the speeds of every of the members relative to the carrier. For example, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the velocity of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that acceleration and the numbers of teeth in each of the gears. The use 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 acceleration between the two associates is normally +1700-(-400), or +2100 RPM.
The next step is to decide the quantity of load application cycles. Since the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will be equal to the quantity of planets. The planets, however, 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, leading to one fully reversed anxiety 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 software.
As noted over, the torque on the epicyclic participants is divided among the planets. In examining the stress and your life of the users we must consider the resultant loading at each mesh. We locate the concept of torque per mesh to be relatively confusing in epicyclic equipment evaluation and prefer to look at the tangential load at each mesh. For example, in seeking at the tangential load at the sun-world mesh, we have the torque on sunlight equipment and divide it by the successful quantity of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the energy transmitted at each mesh and, altered by the strain cycles per revolution, the life span expectancy of every component.
In addition to these issues there can also be assembly complications that need addressing. For example, placing one planet ready between sun and band fixes the angular position of sunlight to the ring. Another planet(s) is now able to be assembled only in discreet locations where in fact the sun and band could be concurrently engaged. The “least mesh angle” from the 1st planet that will accommodate simultaneous mesh of the next planet is equal to 360° divided by the sum of the amounts of teeth in the sun and the ring. As a result, in order to assemble more planets, they must always be spaced at multiples of the least mesh position. If one wants to have the same 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 band is normally divisible by the number of planets to an integer. The same rules apply in a compound epicyclic, but the set coupling of the planets brings another level of complexity, and appropriate planet spacing may require match marking of teeth.
With multiple elements in mesh, losses should be considered at each mesh so as to evaluate the efficiency of the unit. Power transmitted at each mesh, not input power, must be used to compute power loss. For simple epicyclic pieces, the total ability transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input electricity. This is among the reasons that simple planetary epicyclic sets are better than other reducer arrangements. In contrast, for most coupled epicyclic models total electrical power transmitted internally through each mesh may be higher than input power.
What of electric power at the mesh? For simple and compound epicyclic pieces, calculate pitch collection velocities and tangential loads to compute electric power at each mesh. Values can be obtained from the earth torque relative acceleration, and the operating pitch diameters with sunlight and band. Coupled epicyclic sets present more technical issues. Elements of two epicyclic pieces could be coupled 36 different ways using one input, one output, and one response. Some arrangements split the power, while some recirculate ability internally. For these types of epicyclic models, tangential loads at each mesh can only just be established through the utilization of free-body diagrams. On top of that, the elements of two epicyclic models could be coupled nine various ways in a string, using one source, one end result, and two reactions. Let’s look at a few examples.
In the “split-power” coupled set proven in Figure 7, 85 percent of the transmitted vitality flows to band gear #1 and 15 percent to band gear #2. The result is that this coupled gear set can be smaller sized than series coupled units because the power is split between the two elements. When coupling epicyclic models in a string, 0 percent of the energy will become transmitted through each established.
Our next example depicts a arranged with “ability recirculation.” This gear set happens when torque gets locked in the machine in a manner similar to what happens in a “four-square” test process of vehicle drive axles. With the torque locked in the system, the hp 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 considerably lower unit efficiency .
Body 9 depicts a free-body diagram of a great epicyclic arrangement that encounters power recirculation. A cursory evaluation of this free-body diagram explains the 60 percent productivity of the recirculating arranged demonstrated in Figure 8. Since the planets will be rigidly coupled jointly, the summation of forces on the two gears must the same zero. The induce at sunlight gear mesh effects from the torque source to the sun gear. The power at the next ring gear mesh effects 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 big difference of, say, 3:1, the push on the next planet will be about 14 times the force on the first world at the sun gear mesh. For that reason, for the summation of forces to mean zero, the tangential load at the first band gear should be approximately 13 occasions the tangential load at the sun gear. If we presume the pitch line velocities to become the same at the sun mesh and band mesh, the energy loss at the band mesh will be roughly 13 times higher than the power loss at the sun mesh .


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