epicyclic gearbox

Within an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference operate between a gear with internal teeth and a gear with exterior teeth on a concentric orbit. The circulation of the spur equipment occurs in analogy to the orbiting of the planets in the solar program. This is how 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 actually a ring gear. In the majority of cases the casing is fixed. The traveling sun pinion is normally in the center of the ring equipment, and is coaxially organized with regards to the output. The sun pinion is usually mounted on a clamping system in order to offer the mechanical link with the engine shaft. During procedure, the planetary gears, which will be installed on a planetary carrier, roll between the sunshine pinion and the band equipment. The planetary carrier as well represents the productivity shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The number of teeth has no effect on the transmission ratio of the gearbox. The amount of planets may also vary. As the quantity of planetary gears raises, the distribution of the load increases and therefore the torque which can be transmitted. Raising the number of tooth engagements likewise reduces the rolling ability. Since only section of the total end result needs to be transmitted as rolling electrical power, a planetary equipment is extremely efficient. The advantage of a planetary gear compared to a single spur gear is based on this load distribution. Hence, it is possible to transmit great torques wit
h high efficiency with a compact style using planetary gears.
So long as the ring gear includes a constant size, different ratios can be realized by various the amount of teeth of sunlight gear and the amount 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 the sun gear are extremely tiny above and below these ratios. Higher ratios can be acquired by connecting a lot of planetary stages in series in the same band gear. In this instance, we speak of 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 any direction of rotation. Additionally it is possible to fix the drive shaft so that you can pick up the torque via the ring equipment. Planetary gearboxes have become extremely important in lots of areas of mechanical engineering.
They have become particularly more developed in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Large transmission ratios may also easily be achieved with planetary gearboxes. Because of the positive properties and compact design and style, the gearboxes have a large number of potential uses in commercial applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency because of low rolling power
Practically unlimited transmission ratio options because of combination of several planet stages
Appropriate as planetary switching gear due to fixing this or that section of the 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 set up from manual gear field are replaced with an increase of compact and more dependable sun and planetary type of gears arrangement as well as the manual clutch from manual electrical power train is substituted with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The thought of epicyclic gear box is taken 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, Drive, Sport) settings which is obtained by fixing of sun and planetary gears based on the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which looks like a ring and also have angular trim teethes at its internal surface ,and is located in outermost location in en epicyclic gearbox, the interior teethes of ring gear is in regular mesh at outer point 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 put in the center of the epicyclic gearbox; sunlight gear is in frequent mesh at inner point with the planetary gears and can be connected with the type shaft of the epicyclic equipment box.
One or more sunshine gears can be utilized for achieving different output.
3. Planet gears- They are small gears found in between ring and sun equipment , the teethes of the earth gears are in constant mesh with sunlight and the ring equipment at both the inner and outer details respectively.
The axis of the planet gears are attached to 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- This is a carrier attached with the axis of the planet gears and is responsible for final transmitting of the result to the productivity 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- These devices used to fix the annular gear, sunshine 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 founded on the fact the fixing any of the gears i.e. sun gear, planetary gears and annular equipment is done to get the required torque or swiftness output. As fixing any of the above triggers the variation in gear ratios from substantial torque to high swiftness. 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 energy supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the vehicle to realize higher speed throughout a travel, these ratios are obtained by fixing the sun gear which in turn makes the earth carrier the powered member and annular the travelling member in order 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 planet gear carrier which in turn makes the annular gear the influenced member and sunlight gear the driver member.
Note- More swiftness or torque ratios may be accomplished by increasing the quantity planet and sun equipment in epicyclic gear package.
High-speed epicyclic gears could be built relatively small as the energy is distributed over many meshes. This effects in a low capacity to fat ratio and, as well as lower pitch line velocity, causes improved efficiency. The small equipment diameters produce lower occasions of inertia, significantly minimizing 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 employed have been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s commence by examining an essential facet of any project: cost. Epicyclic gearing is generally less costly, when tooled properly. Just as one wouldn’t normally consider making a 100-piece lot of gears on an N/C milling equipment with a form 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 hold carriers within acceptable manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another element. Epicyclic gear models are used because they’re smaller than offset equipment sets since the load is usually shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. As well, when configured correctly, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s assume that we’re creating a high-speed gearbox to fulfill the following requirements:
• A turbine provides 6,000 hp at 16,000 RPM to the input shaft.
• The output from the gearbox must drive 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 practical solutions, one involving a single branch, two-stage helical gear set. Another solution takes the initial gear establish and splits the two-stage reduction into two branches, and the third calls for by using a two-stage planetary or superstar epicyclic. In this situation, 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 answer we detect its size and fat is very large. To reduce the weight we in that case explore the possibility of earning two branches of a similar arrangement, as observed in the second alternatives. This cuts tooth loading and reduces both size and pounds considerably . We finally arrive at our third alternative, which may be the two-stage celebrity epicyclic. With three planets this equipment train reduces tooth loading drastically from the 1st approach, and a somewhat smaller amount from alternative two (see “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a big part of what makes them so useful, however these very characteristics could make designing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our aim is to make it easy that you can understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking for how relative speeds operate together with different plans. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply determined by the speed of 1 member and the number of teeth in each gear.
In a planetary arrangement the band gear is set, and planets orbit sunlight while rotating on the planet shaft. In this arrangement the relative speeds of the sun and planets are determined by the quantity of teeth in each gear and the quickness of the carrier.
Things get a lttle bit trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. Hence, it is imperative to usually calculate the velocity of sunlight, planet, and ring relative to the carrier. Remember that actually in a solar set up where the sunshine is fixed it has a speed marriage 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 might not be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” amount of planets. This number in epicyclic sets constructed with two or three planets is generally equal to you see, the amount of planets. When more than three planets are applied, however, the effective amount of planets is generally less than using the number of planets.
Let’s look at torque splits regarding set support and floating support of the participants. With set support, all users are supported in bearings. The centers of sunlight, band, and carrier will not be coincident because of manufacturing tolerances. For that reason fewer planets are simultaneously in mesh, producing a lower effective quantity of planets sharing the load. With floating support, one or two people are allowed a small amount of radial independence or float, which allows the sun, band, and carrier to seek a position where their centers will be 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 posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh considerations that needs to be made when making epicyclic gears. 1st we should translate RPM into mesh velocities and determine the quantity of load program cycles per device of time for each member. The first step in this determination is certainly to calculate the speeds of every of the members relative to the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is certainly rotating at +400 RPM the speed 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 velocity and the amounts of teeth in each one of the gears. The use of symptoms to signify clockwise and counter-clockwise rotation is important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two associates can be +1700-(-400), or +2100 RPM.
The next step is to determine the number of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will always be equal to the quantity of planets. The planets, nevertheless, will experience only one bi-directional load software per relative revolution. It meshes with sunlight and ring, however the load is certainly on opposing sides of one’s teeth, leading to one fully reversed tension cycle. Thus the earth is considered an idler, and the allowable anxiety must be reduced 30 percent from the worthiness for a unidirectional load app.
As noted previously mentioned, the torque on the epicyclic associates is divided among the planets. In analyzing the stress and lifestyle of the users we must consider the resultant loading at each mesh. We get the idea of torque per mesh to be relatively confusing in epicyclic equipment examination and prefer to look at the tangential load at each mesh. For instance, in seeking at the tangential load at the sun-world mesh, we take the torque on sunlight gear and divide it by the successful amount of planets and the working pitch radius. This tangential load, combined with peripheral speed, is utilized to compute the energy transmitted at each mesh and, adjusted by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there can also be assembly complications that need addressing. For example, positioning one planet in a position between sun and ring fixes the angular placement of sunlight to the ring. Another planet(s) is now able to be assembled only in discreet locations where the sun and ring could be concurrently engaged. The “least mesh angle” from the initial planet that will support simultaneous mesh of the next planet is add up to 360° divided by the sum of the numbers of teeth in the sun and the ring. As a result, in order to assemble additional planets, they must be spaced at multiples of this least mesh position. If one wants to have equivalent spacing of the planets in a simple epicyclic set, planets could be spaced similarly when the sum of the amount of teeth in the sun and ring is normally divisible by the number of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets offers another degree of complexity, and appropriate planet spacing may necessitate match marking of pearly whites.
With multiple components in mesh, losses must be considered at each mesh so that you can evaluate the efficiency of the machine. Electricity transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic models, the total power transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input vitality. This is one of the reasons that easy planetary epicyclic sets are better than other reducer arrangements. In contrast, for many coupled epicyclic models total power transmitted internally through each mesh could be greater than input power.
What of electric power at the mesh? For basic and compound epicyclic pieces, calculate pitch line velocities and tangential loads to compute electricity at each mesh. Values can be acquired from the planet torque relative quickness, and the working pitch diameters with sunlight and ring. Coupled epicyclic models present more technical issues. Components of two epicyclic models can be coupled 36 different ways using one insight, one result, and one reaction. Some plans split the power, while some recirculate power internally. For these kind of epicyclic pieces, tangential loads at each mesh can only just be decided through the utilization of free-body diagrams. Also, the elements of two epicyclic models can be coupled nine various ways in a string, using one insight, one result, and two reactions. Let’s look at a few examples.
In the “split-electrical power” coupled set demonstrated in Figure 7, 85 percent of the transmitted electricity flows to ring gear #1 and 15 percent to ring gear #2. The result is that coupled gear set could be more compact than series coupled models because the vitality is split between the two factors. When coupling epicyclic units in a string, 0 percent of the power will end up being transmitted through each arranged.
Our next example depicts a arranged with “electricity 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 process of vehicle travel axles. With the torque locked in the system, the hp at each mesh within the loop improves as speed increases. Therefore, this set will knowledge much higher electrical power losses at each mesh, resulting in drastically lower unit efficiency .
Shape 9 depicts a free-body diagram of an epicyclic arrangement that activities vitality recirculation. A cursory analysis of this free-body system diagram clarifies the 60 percent performance of the recirculating established demonstrated in Figure 8. Since the planets are rigidly coupled with each other, the summation of forces on the two gears must equivalent zero. The pressure at the sun gear mesh effects from the torque insight to the sun gear. The pressure at the next ring gear mesh outcomes from the productivity torque on the band equipment. The ratio being 41.1:1, result torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the power on the second planet will be roughly 14 times the drive on the first planet at the sun gear mesh. Consequently, for the summation of forces to equate to zero, the tangential load at the first band gear should be approximately 13 times the tangential load at sunlight gear. If we assume the pitch series velocities to be 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 the sun mesh .