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 takes place in analogy to the orbiting of the planets in the solar program. This is one way planetary gears obtained their name.
The elements 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 housing is fixed. The traveling sun pinion is normally in the heart of the ring gear, and is coaxially organized in relation to the output. Sunlight pinion is usually attached to a clamping system to be able to present the mechanical connection to the motor shaft. During operation, the planetary gears, which happen to be installed on a planetary carrier, roll between your sunlight pinion and the band gear. The planetary carrier also represents the end result 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 tranny ratio of the gearbox. The quantity of planets may also vary. As the quantity of planetary gears improves, the distribution of the load increases and then the torque which can be transmitted. Raising the quantity of tooth engagements as well reduces the rolling electricity. Since only the main total output must be transmitted as rolling ability, a planetary gear is extremely efficient. The good thing about a planetary gear compared to a single spur gear is based on this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a compact style using planetary gears.
So long as the ring gear includes a regular size, different ratios could be realized by various the quantity of teeth of the sun gear and the amount of teeth of the planetary gears. The smaller the sun gear, 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 little above and below these ratios. Larger ratios can be obtained by connecting several planetary phases in series in the same band 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 as a way to grab the torque via the band gear. Planetary gearboxes have grown to be extremely important in lots of 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. Large transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and small design and style, the gearboxes have many potential uses in professional 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
Practically unlimited transmission ratio options due to combo of several planet stages
Ideal as planetary switching gear due to fixing this or that area of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a broad range of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears set up from manual gear field are replaced with more compact and more reputable sun and planetary kind of gears arrangement plus the manual clutch from manual electrical power train is replaced with hydro coupled clutch or torque convertor which made the transmission automatic.
The idea of epicyclic gear box is taken from the solar system which is considered to the perfect arrangement of objects.
The epicyclic gearbox usually includes the P N R D S (Parking, Neutral, Reverse, Drive, 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- This is a type of gear which looks like a ring and have angular minimize teethes at its internal surface ,and is put in outermost location in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer point with the set of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It is the equipment with angular trim teethes and is located in the middle of the epicyclic gearbox; the sun gear is in continuous mesh at inner point with the planetary gears and can be connected with the source shaft of the epicyclic equipment box.
One or more sunlight gears can be used 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 constant mesh with the sun and the ring equipment at both inner and outer details respectively.
The axis of the earth gears are mounted on the planet carrier which is carrying the output shaft of the epicyclic gearbox.
The earth gears can rotate about their axis and also 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 accountable for final transmission of the outcome 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- These devices used to repair the annular gear, sunshine 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 equipment, planetary gears and annular equipment is done to obtain the necessary torque or quickness output. As fixing any of the above triggers the variation in gear ratios from large torque to high velocity. 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 the sun gear.
Second gear ratio
This gives high speed ratios to the vehicle which helps the vehicle to attain higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the planet carrier the driven member and annular the driving a car member so as to 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 attained by fixing the planet gear carrier which in turn makes the annular gear the driven member and the sun gear the driver member.
Note- More acceleration or torque ratios may be accomplished by increasing the number planet and sun equipment in epicyclic gear field.
High-speed epicyclic gears could be built relatively small as the power is distributed over a lot of meshes. This outcomes in a low power to weight ratio and, as well as lower pitch range velocity, brings about improved efficiency. The tiny equipment diameters produce lower occasions of inertia, significantly lowering acceleration and deceleration torque when starting 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 is employed have already been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s begin by examining a significant aspect of any project: expense. Epicyclic gearing is normally less expensive, when tooled properly. Just as one 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 lot of epicyclic carriers on an N/C mill. To maintain carriers within sensible manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another component. Epicyclic gear models are used because they’re smaller than offset equipment sets because the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. As well, 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 meet the following requirements:
• A turbine offers 6,000 horsepower at 16,000 RPM to the input shaft.
• The outcome from the gearbox must drive a generator at 900 RPM.
• The design existence is usually to be 10,000 hours.
With these requirements in mind, let’s look at three conceivable solutions, one involving a single branch, two-stage helical gear set. A second solution takes the initial gear placed and splits the two-stage lowering into two branches, and the 3rd calls for by using a two-level planetary or star epicyclic. In this situation, we chose the star. Let’s examine each 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 base of the final ratio (7.70). Along the way of reviewing this answer we see its size and excess weight is very large. To lessen the weight we after that explore the possibility of making two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and decreases both size and excess weight considerably . We finally arrive at our third alternative, which may be the two-stage superstar epicyclic. With three planets this equipment train reduces tooth loading substantially from the initially approach, and a relatively smaller amount from answer 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 developing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our objective is to create it easy 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 function together with different arrangements. In the star set up the carrier is set, and the relative speeds of the sun, planet, and ring are simply determined by the speed of 1 member and the amount of teeth in each equipment.
In a planetary arrangement the band gear is set, and planets orbit the sun while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are determined by the number of teeth in each equipment and the speed of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to generally calculate the speed of sunlight, planet, and ring relative to the carrier. Remember that possibly in a solar set up where the sunlight is fixed it has a speed relationship with the planet-it is not zero RPM at the mesh.
Torque Splits
When contemplating torque splits one assumes the torque to be divided among the planets similarly, but this might not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This number in epicyclic sets constructed with several planets is generally equal to the actual quantity of planets. When a lot more than three planets are employed, however, the effective number of planets is usually less than you see, the number of planets.
Let’s look at torque splits in conditions of set support and floating support of the participants. With fixed support, all members are supported in bearings. The centers of sunlight, ring, and carrier will not be coincident due to manufacturing tolerances. Due to this fewer planets are simultaneously in mesh, resulting in a lower effective amount of planets posting the load. With floating support, a couple of participants are allowed a small amount of radial flexibility or float, which allows the sun, band, and carrier to seek a posture where their centers are coincident. This float could be as little as .001-.002 ins. With floating support three planets will always be in mesh, producing a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that needs to be made when designing epicyclic gears. Initial we should translate RPM into mesh velocities and determine the amount of load app cycles per unit of time for each member. The first step in this determination is certainly to calculate the speeds of each 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 rate of the sun 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 usage of indicators to represent clockwise and counter-clockwise rotation can be important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative rate between the two users is certainly +1700-(-400), or +2100 RPM.
The second 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 relative to the carrier will become equal to the amount of planets. The planets, on the other hand, will experience only one bi-directional load software per relative revolution. It meshes with the sun and ring, but the load can be on contrary sides of the teeth, leading to one fully reversed pressure cycle. Thus the earth is considered an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load software.
As noted above, the torque on the epicyclic associates is divided among the planets. In examining the stress and your life of the associates we must consider the resultant loading at each mesh. We get the idea of torque per mesh to be somewhat confusing in epicyclic gear examination 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 have the torque on the sun equipment and divide it by the powerful number of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the energy transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of each component.
In addition to these issues there may also be assembly complications that need addressing. For example, inserting one planet in a position between sun and band fixes the angular situation of sunlight to the ring. Another planet(s) is now able to be assembled just in discreet locations where the sun and band could be concurrently involved. The “least mesh angle” from the initially planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the amounts of teeth in sunlight and the ring. Therefore, in order to assemble further planets, they must be spaced at multiples of this least mesh position. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets may be spaced similarly when the sum of the amount of teeth in sunlight and band is normally divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets provides another level of complexity, and appropriate planet spacing may necessitate match marking of pearly whites.
With multiple components in mesh, losses have to be considered at each mesh so as to measure the efficiency of the unit. Power transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic sets, the total electric 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 plans. In contrast, for most coupled epicyclic units total electricity transmitted internally through each mesh could be higher than input power.
What of vitality at the mesh? For straightforward and compound epicyclic pieces, calculate pitch collection velocities and tangential loads to compute electricity at each mesh. Values can be obtained from the earth torque relative quickness, and the operating pitch diameters with sunshine and band. Coupled epicyclic sets present more complex issues. Components of two epicyclic sets could be coupled 36 various ways using one input, one end result, and one reaction. Some plans split the power, although some recirculate vitality internally. For these kind of epicyclic pieces, tangential loads at each mesh can only be established through the consumption of free-body diagrams. On top of that, the elements of two epicyclic sets could be coupled nine different ways in a series, using one insight, one result, and two reactions. Let’s look at some examples.
In the “split-ability” coupled set shown in Figure 7, 85 percent of the transmitted electricity flows to ring gear #1 and 15 percent to ring gear #2. The effect is that coupled gear set can be more compact than series coupled sets because the electric power is split between your two factors. When coupling epicyclic units in a series, 0 percent of the power will become transmitted through each arranged.
Our next example depicts a placed with “vitality 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 hp at each mesh within the loop heightens as speed increases. Therefore, this set will encounter much higher power losses at each mesh, resulting in substantially lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that encounters electric power recirculation. A cursory analysis of this free-physique diagram clarifies the 60 percent proficiency of the recirculating established proven in Figure 8. Because the planets are rigidly coupled along, the summation of forces on the two gears must equivalent zero. The force at sunlight gear mesh results from the torque insight to the sun gear. The power at the second ring gear mesh effects from the result torque on the band equipment. The ratio being 41.1:1, end result torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the force on the second planet will be roughly 14 times the power on the first world at the sun gear mesh. Therefore, for the summation of forces to mean zero, the tangential load at the first band gear must be approximately 13 instances the tangential load at sunlight gear. If we assume the pitch brand velocities to become the same at the sun mesh and ring mesh, the power loss at the ring mesh will be approximately 13 times higher than the power loss at sunlight mesh .