Within 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 system. This is how planetary gears obtained their name.
The pieces 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 driving sun pinion is usually in the center of the ring equipment, and is coaxially arranged with regards to the output. The sun pinion is usually attached to a clamping system in order to offer the mechanical connection to the motor shaft. During operation, the planetary gears, which will be mounted on a planetary carrier, roll between the sunshine pinion and the band gear. The planetary carrier likewise represents the productivity 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 transmitting ratio of the gearbox. The amount of planets can also vary. As the number of planetary gears increases, the distribution of the load increases and therefore the torque which can be transmitted. Increasing the quantity of tooth engagements as well reduces the rolling ability. Since only the main total output needs to be transmitted as rolling ability, a planetary equipment is incredibly efficient. The advantage of a planetary gear compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a concise design and style using planetary gears.
So long as the ring gear has a continuous size, different ratios can be realized by different the amount of teeth of the sun gear and the number of teeth 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, 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 ring gear. In cases like this, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a band gear that’s not fixed but is driven in virtually any direction of rotation. It is also possible to fix the drive shaft so as to grab the torque via the band gear. Planetary gearboxes have become extremely important in many areas of mechanical engineering.
They have become particularly more developed in areas where high output levels and fast speeds must be transmitted with favorable mass inertia ratio adaptation. Substantial transmission ratios can also easily be performed with planetary gearboxes. Because of the positive properties and compact style, the gearboxes have various potential uses in professional applications.
The features 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 due to combo of several planet stages
Suited as planetary switching gear due to fixing this or that section of the gearbox
Chance for 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 arrangement from manual gear box are replaced with an increase of compact and more trusted sun and planetary kind of gears arrangement plus the manual clutch from manual ability train is substituted with hydro coupled clutch or torque convertor which in turn made the tranny automatic.
The thought 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, Travel, 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- It is a kind of gear which appears like a ring and also have angular cut teethes at its internal surface ,and is put in outermost job in en epicyclic gearbox, the interior teethes of ring equipment is in frequent mesh at outer point with the set of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the equipment with angular cut teethes and is located in the middle of the epicyclic gearbox; sunlight gear is in constant mesh at inner stage with the planetary gears and is certainly connected with the type shaft of the epicyclic gear box.
One or more sunshine gears can be used for obtaining different output.
3. Planet gears- These are small gears used in between ring and sun gear , the teethes of the earth gears are in frequent mesh with the sun and the ring gear at both the inner and outer things 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 just like our solar system.
4. Planet carrier- This is a carrier fastened with the axis of the earth gears and is in charge of final transmitting of the outcome to the outcome 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- 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 founded on the fact the fixing the gears i.e. sun gear, planetary gears and annular equipment is done to get the required torque or quickness output. As fixing the above causes the variation in gear ratios from huge torque to high quickness. So let’s observe how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the vehicle to move 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 gives high speed ratios to the automobile which helps the vehicle to achieve higher speed throughout a travel, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the driven member and annular the generating 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 earth gear carrier which in turn makes the annular gear the powered member and sunlight gear the driver member.
Note- More speed or torque ratios may be accomplished by increasing the number planet and sun equipment in epicyclic gear box.
High-speed epicyclic gears can be built relatively tiny as the energy is distributed over a lot of meshes. This results in a low power to weight ratio and, together with lower pitch collection velocity, brings about improved efficiency. The tiny 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.
The reasons why epicyclic gearing is used have been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s commence by examining an essential aspect of any project: cost. Epicyclic gearing is generally less expensive, when tooled properly. Just as one 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, you need to certainly not consider making a 100-piece lot of epicyclic carriers on an N/C mill. To continue to keep carriers within acceptable manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another point. Epicyclic gear units are used because they are 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. As well, when configured properly, epicyclic gear models are more efficient. The next example illustrates these rewards. Let’s believe that we’re designing a high-speed gearbox to fulfill the following requirements:
• A turbine offers 6,000 hp at 16,000 RPM to the source shaft.
• The output from the gearbox must drive a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements in mind, let’s look at three conceivable solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear arranged and splits the two-stage decrease into two branches, and the third calls for utilizing a two-level planetary or star epicyclic. In this instance, we chose the star. 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 remedy 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 seen in the second alternatives. This cuts tooth loading and reduces both size and excess weight considerably . We finally reach our third choice, which is the two-stage celebrity epicyclic. With three planets this gear train reduces tooth loading substantially from the primary approach, and a relatively smaller amount from remedy two (see “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a large part of what makes them so useful, but these very characteristics can make developing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our aim is to make it easy so that you can understand and use epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking by 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 dependant on the speed of 1 member and the amount of teeth in each equipment.
In a planetary arrangement the ring gear is fixed, and planets orbit sunlight while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are dependant on the quantity of teeth in each gear and the rate of the carrier.
Things get a lttle bit trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to generally calculate the swiftness of sunlight, planet, and ring in accordance with the carrier. Remember that actually in a solar arrangement where the sunshine is fixed it includes a speed marriage 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 exactly be considered 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 several planets is in most cases equal to you see, the amount of planets. When more than three planets are employed, however, the effective number of planets is often less than the actual number of planets.
Let’s look for torque splits in conditions of set support and floating support of the members. With set support, all members are reinforced in bearings. The centers of the sun, ring, and carrier will not be coincident due to manufacturing tolerances. For this reason fewer planets happen to be simultaneously in mesh, resulting in a lower effective number of planets sharing the strain. With floating support, a couple of users are allowed a small amount of radial liberty or float, that allows the sun, ring, and carrier to get a position where their centers happen to be coincident. This float could possibly be less than .001-.002 in .. With floating support three planets will be in mesh, producing a higher effective amount of planets posting 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 quantity of load application cycles per product of time for every member. The first rung on the ladder in this determination is normally to calculate the speeds of every of the members relative to the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is rotating at +400 RPM the velocity of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that velocity and the numbers of teeth in each one of the gears. The use of indications to represent 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 speed between the two customers is normally +1700-(-400), or +2100 RPM.
The next step is to determine the number 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, even so, will experience only 1 bi-directional load software per relative revolution. It meshes with the sun and ring, however the load is on opposing sides of the teeth, leading to one fully reversed stress cycle. Thus the planet is known as an idler, and the allowable pressure must be reduced thirty percent from the value for a unidirectional load application.
As noted above, the torque on the epicyclic members is divided among the planets. In analyzing the stress and your life of the participants we must consider the resultant loading at each mesh. We locate the concept of torque per mesh to end up being somewhat confusing in epicyclic gear analysis and prefer to look at the tangential load at each mesh. For instance, in looking at the tangential load at the sun-world mesh, we consider the torque on the sun gear and divide it by the successful number of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the power transmitted at each mesh and, adjusted by the strain cycles per revolution, the life span expectancy of each 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 band fixes the angular job of the sun to the ring. The next planet(s) can now be assembled only in discreet locations where the sun and ring could be simultaneously 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 numbers of teeth in sunlight and the ring. Hence, so that you can assemble additional planets, they must be spaced at multiples of the least mesh position. If one wishes to have the same 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 ring is definitely divisible by the amount of planets to an integer. The same rules apply in a compound epicyclic, but the fixed coupling of the planets contributes another level of complexity, and proper planet spacing may require match marking of tooth.
With multiple parts in mesh, losses have to 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 pieces, the total electrical power transmitted through the sun-planet mesh and ring-world mesh may be significantly less than input electrical power. This is among the reasons that simple planetary epicyclic sets are better than other reducer plans. In contrast, for most coupled epicyclic units total power transmitted internally through each mesh may be greater than input power.
What of electrical power at the mesh? For straightforward and compound epicyclic units, calculate pitch range velocities and tangential loads to compute electric power at each mesh. Ideals can be acquired from the planet torque relative acceleration, and the functioning pitch diameters with sunshine and band. Coupled epicyclic pieces present more complex issues. Components of two epicyclic sets could be coupled 36 various ways using one suggestions, one result, and one response. Some plans split the power, although some recirculate vitality internally. For these types of epicyclic sets, tangential loads at each mesh can only just be identified through the utilization of free-body diagrams. On top of that, the factors of two epicyclic pieces can be coupled nine different ways in a string, using one input, one result, and two reactions. Let’s look at some examples.
In the “split-ability” coupled set displayed in Figure 7, 85 percent of the transmitted ability flows to band gear #1 and 15 percent to ring gear #2. The result is that this coupled gear set could be small than series coupled models because the power is split between your two factors. When coupling epicyclic pieces in a string, 0 percent of the energy will always be transmitted through each arranged.
Our next example depicts a establish with “power recirculation.” This gear set happens 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 machine, the hp at each mesh within the loop enhances as speed increases. Consequently, this set will knowledge much higher power losses at each mesh, leading to significantly lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that encounters electricity recirculation. A cursory examination of this free-body diagram explains the 60 percent effectiveness of the recirculating placed proven in Figure 8. Since the planets are rigidly coupled at the same time, the summation of forces on both gears must the same zero. The power at the sun gear mesh benefits from the torque source to sunlight gear. The drive at the next ring gear mesh effects from the outcome torque on the band 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 force on the next planet will be about 14 times the drive on the first planet at sunlight 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 believe the pitch line velocities to be the same at sunlight mesh and band mesh, the energy loss at the band mesh will be approximately 13 times higher than the energy loss at the sun mesh .