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 takes place in analogy to the orbiting of the planets in the solar system. This is one way planetary gears obtained their name.
The parts 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 nearly all cases the housing is fixed. The generating sun pinion is in the heart of the ring gear, and is coaxially arranged in relation to the output. Sunlight pinion is usually attached to a clamping system to be able to offer the mechanical link with the electric motor shaft. During procedure, the planetary gears, which happen to be mounted on a planetary carrier, roll between the sunlight pinion and the band equipment. The planetary carrier also represents the output shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The amount of teeth has no effect on the transmitting ratio of the gearbox. The number of planets may also vary. As the amount of planetary gears boosts, the distribution of the load increases and therefore the torque that can be transmitted. Increasing the number of tooth engagements likewise reduces the rolling ability. Since only section of the total result must be transmitted as rolling electrical power, a planetary gear is extremely efficient. The good thing about a planetary gear compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit large torques wit
h high efficiency with a concise style using planetary gears.
Provided that the ring gear includes a regular size, different ratios can be realized by different the number of teeth of the sun gear and the amount of pearly whites of the planetary gears. The smaller the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary stage is approx. 3:1 to 10:1, since the planetary gears and sunlight gear are extremely little above and below these ratios. Larger ratios can be obtained by connecting a lot of planetary phases in series in the same band gear. In cases like this, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that is not fixed but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft in order to grab the torque via the ring equipment. Planetary gearboxes have become extremely important in lots of regions of mechanical engineering.
They have become particularly well established in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Great transmission ratios may also easily be performed with planetary gearboxes. Because of the positive properties and small style, the gearboxes have many 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 due to low rolling power
Nearly unlimited transmission ratio options because of blend 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 an array of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears set up from manual gear field are replaced with an increase of compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual ability train is changed with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The idea of epicyclic gear box is taken 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, Drive, Sport) modes which is obtained by fixing of sun and planetary gears in line with the need of the travel.
The different parts of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which appears like a ring and have angular lower teethes at its inner surface ,and is positioned in outermost placement in en epicyclic gearbox, the internal teethes of ring equipment is in frequent mesh at outer point with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It’s the gear with angular slice teethes and is put in the middle of the epicyclic gearbox; sunlight gear is in continuous mesh at inner point with the planetary gears and is certainly connected with the source shaft of the epicyclic equipment box.
One or more sunshine gears can be used for obtaining different output.
3. Planet gears- They are small gears found in between ring and sun equipment , the teethes of the earth gears are in frequent mesh with sunlight and the ring gear at both inner and outer details respectively.
The axis of the earth gears are attached to the planet 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 the ring and sunlight gear exactly like our solar system.
4. Planet carrier- It is a carrier attached with the axis of the earth gears and is responsible for final transmitting of the end result to the output 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, sunlight gear and planetary equipment and is handled 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 gear, planetary gears and annular gear is done to get the required torque or acceleration output. As fixing any of the above causes the variation in equipment ratios from huge torque to high speed. So let’s observe 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 power supplied to the sun gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the automobile to realize higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the influenced 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 attained by fixing the planet gear carrier which in turn makes the annular gear the powered member and the sun gear the driver member.
Note- More acceleration or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear box.
High-speed epicyclic gears can be built relatively little as the power is distributed over a number of meshes. This outcomes in a low power to weight ratio and, together with lower pitch brand velocity, brings about improved efficiency. The small equipment diameters produce lower occasions of inertia, significantly reducing 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 used have already been covered in this magazine, so we’ll expand on the topic in just a few places. Let’s begin by examining a significant aspect of any project: expense. Epicyclic gearing is generally less costly, when tooled properly. Being an wouldn’t normally consider making a 100-piece large amount of gears on an N/C milling machine with a form cutter or ball end mill, you need to not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To maintain carriers within reasonable manufacturing costs they must be created from castings and tooled on single-purpose devices with multiple cutters concurrently removing material.
Size is another point. Epicyclic gear sets are used because they’re smaller than offset gear sets since the load is definitely shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Likewise, when configured properly, epicyclic gear units are more efficient. The following example illustrates these rewards. Let’s assume that we’re designing a high-speed gearbox to meet the following requirements:
• A turbine provides 6,000 horsepower at 16,000 RPM to the insight shaft.
• The outcome from the gearbox must drive a generator at 900 RPM.
• The design your life is usually to be 10,000 hours.
With these requirements in mind, let’s look at three feasible solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the original gear collection and splits the two-stage lowering into two branches, and the third calls for utilizing a two-stage planetary or star epicyclic. In this situation, 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). In the process of reviewing this remedy we recognize its size and excess weight is very large. To reduce the weight we then explore the possibility of earning two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally reach our third solution, which is the two-stage celebrity epicyclic. With three planets this equipment train minimizes tooth loading significantly from the initial approach, and a somewhat smaller amount from alternative two (see “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a sizable part of what makes them so useful, however these very characteristics can make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our aim is to create it easy that you should understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking for how relative speeds function together with different plans. In the star set up the carrier is set, and the relative speeds of the sun, planet, and band 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 sunlight while rotating on earth shaft. In this arrangement the relative speeds of sunlight and planets are dependant on the amount of teeth in each gear and the swiftness of the carrier.
Things get a bit trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. It is therefore imperative to often calculate the rate of the sun, planet, and ring in accordance with the carrier. Understand that also in a solar set up where the sunshine 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 may not be a valid assumption. Member support and the amount 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 some of the number of planets. When more than three planets are applied, however, the effective number of planets is often less than you see, the number of planets.
Let’s look at torque splits in conditions of set support and floating support of the customers. With set support, all members are reinforced in bearings. The centers of sunlight, band, and carrier will not be coincident because of manufacturing tolerances. For this reason fewer planets happen to be simultaneously in mesh, producing a lower effective number of planets posting the load. With floating support, a couple of people are allowed a small amount of radial liberty or float, that allows the sun, ring, and carrier to get a posture where their centers are coincident. This float could be less than .001-.002 inches. With floating support three planets will be in mesh, producing a higher effective number of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that needs to be made when making epicyclic gears. Initially we should translate RPM into mesh velocities and determine the number of load app 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 relative to the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is usually rotating at +400 RPM the acceleration of sunlight gear relative to the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that rate and the amounts of teeth in each one of the gears. The utilization of indications to represent 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 swiftness between the two associates is +1700-(-400), or +2100 RPM.
The second step is to determine the number of load application cycles. Since the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will end up being equal to the quantity of planets. The planets, even so, 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 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 above, the torque on the epicyclic people is divided among the planets. In examining the stress and your life of the people we must consider the resultant loading at each mesh. We get the concept of torque per mesh to end up being somewhat confusing in epicyclic equipment analysis and prefer to check out the tangential load at each mesh. For example, in looking at the tangential load at the sun-planet mesh, we consider the torque on the sun equipment and divide it by the successful quantity of planets and the functioning pitch radius. This tangential load, combined with peripheral speed, is employed to compute the power transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of every component.
In addition to these issues there may also be assembly complications that require addressing. For example, positioning one planet in a position between sun and ring fixes the angular job of the sun to the ring. Another planet(s) can now be assembled just in discreet locations where the sun and ring can be simultaneously engaged. The “least mesh angle” from the 1st planet that will support 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. Therefore, to be able to assemble further planets, they must become spaced at multiples of the least mesh position. If one desires to have equal spacing of the planets in a straightforward epicyclic set, planets may be spaced equally when the sum of the amount of teeth in sunlight and ring is definitely divisible by the number of planets to an integer. The same rules apply in a substance epicyclic, but the set coupling of the planets adds another degree of complexity, and proper planet spacing may necessitate match marking of teeth.
With multiple parts in mesh, losses should be considered at each mesh so as to evaluate the efficiency of the unit. Electricity transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic models, the total vitality transmitted through the sun-world mesh and ring-world mesh may be less than input electric power. This is one of the reasons that easy planetary epicyclic pieces are more efficient than other reducer plans. In contrast, for many coupled epicyclic pieces total power transmitted internally through each mesh could be higher than input power.
What of electrical power at the mesh? For basic and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute electricity at each mesh. Ideals can be acquired from the earth torque relative rate, and the operating pitch diameters with sunlight and ring. Coupled epicyclic models present more complex issues. Components of two epicyclic models could be coupled 36 various ways using one input, one end result, and one reaction. Some plans split the power, although some recirculate electricity internally. For these kind of epicyclic pieces, tangential loads at each mesh can only just be motivated through the application of free-body diagrams. On top of that, the factors of two epicyclic units can be coupled nine various ways in a series, using one suggestions, one outcome, and two reactions. Let’s look at some examples.
In the “split-electricity” coupled set demonstrated in Figure 7, 85 percent of the transmitted electric power flows to band gear #1 and 15 percent to band gear #2. The effect is that coupled gear set could be scaled-down than series coupled units because the ability is split between the two elements. When coupling epicyclic sets in a series, 0 percent of the energy will always be transmitted through each arranged.
Our next example depicts a established with “electricity recirculation.” This equipment set comes about when torque gets locked in the system in a way 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 heightens as speed increases. Therefore, this set will knowledge much higher power losses at each mesh, leading to substantially lower unit efficiency .
Shape 9 depicts a free-body diagram of an epicyclic arrangement that activities electricity recirculation. A cursory examination of this free-body system diagram explains the 60 percent proficiency of the recirculating established proven in Figure 8. Since the planets are rigidly coupled along, the summation of forces on both gears must equal zero. The drive at sunlight gear mesh results from the torque insight to sunlight gear. The force at the next ring gear mesh effects from the output torque on the ring gear. The ratio being 41.1:1, productivity torque is 41.1 times input torque. Adjusting for a pitch radius big difference of, say, 3:1, the induce on the next planet will be about 14 times the pressure on the first world at the sun gear mesh. For this reason, for the summation of forces to equate to zero, the tangential load at the first ring gear should be approximately 13 times the tangential load at sunlight gear. If we presume the pitch collection velocities to end up being the same at sunlight mesh and ring mesh, the energy loss at the ring mesh will be around 13 times greater than the energy loss at the sun mesh .
