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 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 how planetary gears obtained their name.
The components 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 definitely in the heart of the ring equipment, and is coaxially arranged with regards to the output. The sun pinion is usually mounted on a clamping system to be able to provide the mechanical connection to the electric motor shaft. During operation, the planetary gears, which happen to be mounted on a planetary carrier, roll between the sunlight pinion and the band equipment. The planetary carrier likewise represents the output shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the required torque. The number of teeth does not have any effect on the transmitting ratio of the gearbox. The quantity of planets may also vary. As the quantity of planetary gears boosts, the distribution of the load increases and then the torque that can be transmitted. Increasing the amount of tooth engagements as well reduces the rolling ability. Since only the main total outcome has to be transmitted as rolling electric power, a planetary gear is extremely efficient. The good thing about a planetary equipment compared to a single spur gear is based on this load distribution. Hence, it is possible to transmit high torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear has a continuous size, different ratios could be realized by varying the number of teeth of sunlight gear and the number of pearly whites of the planetary gears. The smaller the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely tiny above and below these ratios. Higher ratios can be acquired by connecting several planetary stages 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. Additionally it is possible to fix the drive shaft to be able to grab the torque via the ring gear. Planetary gearboxes have grown to be extremely important in many regions of mechanical engineering.
They have grown to be particularly more developed in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Huge transmission ratios may also easily be performed with planetary gearboxes. Because of the positive properties and compact design and style, the gearboxes have various potential uses in industrial applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency because of low rolling power
Almost unlimited transmission ratio options because of mixture of several planet stages
Appropriate as planetary switching gear due to fixing this or that portion of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears arrangement from manual gear field are replaced with an increase of compact and more reputable sun and planetary kind of gears arrangement and also the manual clutch from manual electric power train is changed with hydro coupled clutch or torque convertor which in turn 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) settings which is obtained by fixing of sun and planetary gears according to the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a type of gear which appears like a ring and have angular lower teethes at its inner surface ,and is placed in outermost location in en epicyclic gearbox, the internal teethes of ring equipment is in constant mesh at outer level with the set of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the equipment with angular trim teethes and is put in the middle of the epicyclic gearbox; the sun gear is in constant mesh at inner point with the planetary gears and is usually connected with the source shaft of the epicyclic equipment box.
One or more sunshine gears works extremely well for achieving different output.
3. Planet gears- They 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 equipment at both the inner and outer details respectively.
The axis of the planet gears are mounted on the planet carrier which is carrying the output shaft of the epicyclic gearbox.
The planet 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- It is a carrier fastened with the axis of the planet gears and is in charge of final transmitting 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- These devices 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 based on the fact the fixing the gears i.e. sun equipment, planetary gears and annular equipment is done to get the required torque or speed output. As fixing any of the above triggers the variation in equipment ratios from huge torque to high velocity. So let’s see 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 causes the planet carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the automobile to realize higher speed throughout a drive, these ratios are obtained by fixing the sun gear which in turn makes the earth carrier the driven member and annular the driving member so as to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which reverses the direction of the automobile, this gear is achieved 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 can be achieved by increasing the quantity planet and sun gear in epicyclic gear package.
High-speed epicyclic gears could be built relatively tiny as the power is distributed over a lot of meshes. This outcomes in a low power to pounds ratio and, together with lower pitch line velocity, causes improved efficiency. The small 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.
Why epicyclic gearing is utilized have already been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s commence by examining an important facet of any project: expense. Epicyclic gearing is generally less expensive, when tooled properly. Being an would not consider making a 100-piece large amount of gears on an N/C milling machine with a form 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 continue to keep carriers within reasonable manufacturing costs they should be made from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another point. Epicyclic gear pieces are used because they're smaller than offset equipment sets since the load is definitely shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Also, when configured correctly, epicyclic gear units are more efficient. The next example illustrates these rewards. Let’s believe that we’re creating a high-speed gearbox to satisfy the following requirements:
• A turbine provides 6,000 horsepower at 16,000 RPM to the input shaft.
• The outcome from the gearbox must travel a generator at 900 RPM.
• The design life is usually to be 10,000 hours.
With these requirements at heart, let’s look at three possible solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear established and splits the two-stage decrease into two branches, and the 3rd calls for using a two-stage planetary or superstar epicyclic. In this instance, we chose the superstar. 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, derived from taking the square base of the final ratio (7.70). Along the way of reviewing this alternative we notice its size and fat is very large. To reduce the weight we in that case explore the possibility of making two branches of a similar arrangement, as seen in the second solutions. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third answer, which is the two-stage superstar epicyclic. With three planets this equipment train reduces tooth loading considerably from the primary approach, and a somewhat smaller amount from remedy two (find “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a sizable part of why is them so useful, but these very characteristics could make building them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our target is to make it easy that you can understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s get started by looking by how relative speeds operate in conjunction with different plans. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and band are simply determined by the speed of one member and the amount of teeth in each gear.
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 the sun and planets are determined by the amount of teeth in each gear and the acceleration of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. It is therefore imperative to at all times calculate the quickness of sunlight, planet, and ring relative to the carrier. Remember that also in a solar arrangement where the sunlight is fixed it includes 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 equally, but this might not be 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 constructed with several planets is in most cases equal to you see, the amount of planets. When a lot more than three planets are applied, however, the effective number of planets is usually less than the actual number of planets.
Let’s look at torque splits with regards to set support and floating support of the customers. With set support, all associates are supported in bearings. The centers of sunlight, 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 amount of planets sharing the load. With floating support, one or two associates are allowed a small amount of radial freedom or float, which allows the sun, band, and carrier to seek a position 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 amount of planets sharing the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that needs to be made when designing epicyclic gears. 1st we must translate RPM into mesh velocities and determine the amount of load program cycles per product of time for every member. The first step in this determination is normally 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 certainly rotating at +400 RPM the swiftness of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that quickness and the numbers of teeth in each one of the gears. The use of signals to stand for clockwise and counter-clockwise rotation is definitely 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 can be +1700-(-400), or +2100 RPM.
The second step is to determine the number of load application cycles. Because the sun and ring gears mesh with multiple planets, the number 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 application per relative revolution. It meshes with the sun and ring, however the load is definitely on reverse sides of one's teeth, resulting in one fully reversed tension cycle. Thus the earth is known as an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load application.
As noted over, the torque on the epicyclic members is divided among the planets. In analyzing the stress and lifestyle of the users we must consider the resultant loading at each mesh. We discover the concept of torque per mesh to always be somewhat confusing in epicyclic equipment evaluation and prefer to check out the tangential load at each mesh. For instance, in looking at the tangential load at the sun-world mesh, we take the torque on sunlight equipment and divide it by the effective quantity of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the power transmitted at each mesh and, modified by the load cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that need addressing. For example, putting one planet in a position between sun and band fixes the angular job of sunlight to the ring. Another planet(s) is now able to be assembled just in discreet locations where the sun and band can be concurrently engaged. The “least mesh angle” from the initially planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the numbers of teeth in the sun and the ring. Therefore, in order to assemble further planets, they must end up being spaced at multiples of this least mesh position. If one wants to have equal spacing of the planets in a straightforward epicyclic set, planets could be spaced similarly when the sum of the number of teeth in the sun and band is divisible by the number of planets to an integer. The same guidelines apply in a compound epicyclic, but the set coupling of the planets provides another degree of complexity, and proper planet spacing may necessitate match marking of pearly whites.
With multiple pieces in mesh, losses need to be considered at each mesh as a way to evaluate the efficiency of the machine. Power transmitted at each mesh, not input power, must be used to compute power loss. For simple epicyclic units, the total ability transmitted through the sun-world mesh and ring-planet mesh may be less than input electric power. This is among the reasons that easy planetary epicyclic units are more efficient than other reducer plans. In contrast, for many coupled epicyclic units total electricity transmitted internally through each mesh may be higher than input power.
What of vitality at the mesh? For straightforward and compound epicyclic pieces, calculate pitch brand velocities and tangential loads to compute ability at each mesh. Ideals can be acquired from the planet torque relative swiftness, and the functioning pitch diameters with sun and band. Coupled epicyclic pieces present more technical issues. Elements of two epicyclic pieces can be coupled 36 different ways using one input, one outcome, and one reaction. Some arrangements split the power, although some recirculate power internally. For these types of epicyclic pieces, tangential loads at each mesh can only just be established through the application of free-body diagrams. Additionally, the components of two epicyclic models can be coupled nine various ways in a series, using one type, one productivity, and two reactions. Let’s look at some examples.
In the “split-vitality” coupled set displayed in Figure 7, 85 percent of the transmitted ability flows to ring gear #1 and 15 percent to ring gear #2. The effect is that this coupled gear set can be more compact than series coupled units because the ability is split between the two elements. When coupling epicyclic units in a series, 0 percent of the energy will be transmitted through each placed.
Our next example depicts a collection with “electrical power recirculation.” This gear set happens when torque gets locked in the machine in a way similar to what happens in a “four-square” test procedure for vehicle drive axles. With the torque locked in the system, the horsepower at each mesh within the loop heightens as speed increases. Therefore, this set will knowledge much higher electricity losses at each mesh, resulting in drastically lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that encounters power recirculation. A cursory research of this free-body diagram clarifies the 60 percent performance of the recirculating established shown in Figure 8. Because the planets are rigidly coupled together, the summation of forces on the two gears must the same zero. The pressure at the sun gear mesh results from the torque type to the sun gear. The drive at the next ring gear mesh results from the productivity torque on the ring equipment. The ratio being 41.1:1, output torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the pressure on the second planet will be approximately 14 times the push on the first planet at sunlight gear mesh. Consequently, for the summation of forces to mean zero, the tangential load at the first band gear should be approximately 13 times the tangential load at the sun gear. If we presume the pitch series velocities to always be the same at sunlight mesh and ring mesh, the power loss at the band mesh will be about 13 times higher than the energy loss at the sun mesh .