Within 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 exterior teeth on a concentric orbit. The circulation of the spur equipment takes place in analogy to the orbiting of the planets in the solar system. This is one way planetary gears acquired their name.
The elements of a planetary gear train can 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 driving sun pinion is in the center of the ring gear, and is coaxially organized in relation to the output. The sun pinion is usually mounted on a clamping system in order to give the mechanical connection to the motor shaft. During operation, the planetary gears, which will be installed on a planetary carrier, roll between the sun pinion and the band equipment. The planetary carrier also represents the result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The quantity of teeth has no effect on the transmission ratio of the gearbox. The number of planets can also vary. As the number of planetary gears heightens, the distribution of the load increases and therefore the torque which can be transmitted. Increasing the number of tooth engagements likewise reduces the rolling electrical power. Since only section of the total output must be transmitted as rolling power, a planetary equipment is incredibly efficient. The advantage of a planetary gear compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit substantial torques wit
h high efficiency with a concise design using planetary gears.
Provided that the ring gear has a constant size, different ratios could be realized by various the quantity of teeth of the sun gear and the amount of tooth of the planetary gears. Small the sun gear, the higher 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 little above and below these ratios. Bigger ratios can be acquired by connecting a variety of planetary levels 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 band gear that’s not set but is driven in any direction of rotation. It is also possible to repair the drive shaft so that you can grab the torque via the band gear. Planetary gearboxes have become 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. Excessive transmission ratios can also easily be achieved with planetary gearboxes. Because of their positive properties and small style, the gearboxes have many potential uses in commercial applications.
The benefits of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency due to low rolling power
Practically unlimited transmission ratio options due to combination of several planet stages
Ideal as planetary switching gear because of fixing this or that area of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for an array of applications
Epicyclic gearbox is an automatic type gearbox where parallel shafts and gears set up from manual gear container are replaced with an increase of compact and more trustworthy sun and planetary type of gears arrangement as well as the manual clutch from manual power train is replaced with hydro coupled clutch or torque convertor which made the transmission 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 includes the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears in line with the need of the travel.
Components of Epicyclic Gearbox
1. Ring gear- This is a type of gear which looks like a ring and have angular slice teethes at its internal surface ,and is put in outermost position in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer stage with the group of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is placed in the center of the epicyclic gearbox; sunlight gear is in frequent mesh at inner level with the planetary gears and is normally connected with the type shaft of the epicyclic gear box.
One or more sunlight gears can be used for attaining different output.
3. Planet gears- These are small gears found in between band and sun equipment , the teethes of the earth gears are in constant 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 earth carrier which is carrying the output shaft of the epicyclic gearbox.
The earth gears can rotate about their axis and also can revolve between the ring and sunlight gear exactly like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the earth gears and is accountable for final transmission of the productivity to the end 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, sun gear and planetary equipment and is manipulated by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the fact the fixing any of the gears i.electronic. sun gear, planetary gears and annular gear is done to obtain the needed torque or swiftness output. As fixing the above causes the variation in gear ratios from substantial torque to high swiftness. 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 in turn causes the planet carrier to rotate with the energy supplied to the sun gear.
Second gear ratio
This gives high speed ratios to the vehicle which helps the vehicle to attain higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the earth carrier the influenced member and annular the driving a vehicle member in order 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 vehicle, this gear is achieved by fixing the earth gear carrier which makes the annular gear the motivated member and the sun gear the driver member.
Note- More speed or torque ratios can be achieved by increasing the number planet and sun gear in epicyclic gear box.
High-speed epicyclic gears can be built relatively small as the energy is distributed over a number of meshes. This effects in a low capacity to weight ratio and, together with lower pitch series velocity, leads to improved efficiency. The tiny gear diameters produce lower occasions of inertia, significantly lowering 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.
The reasons why epicyclic gearing is used have been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s begin by examining an essential facet of any project: price. Epicyclic gearing is normally less expensive, when tooled properly. Just as one would not consider making a 100-piece lot of gears on an N/C milling equipment with a form cutter or ball end mill, one should not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To maintain carriers within sensible manufacturing costs they must be created from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another element. Epicyclic gear sets are used because they are smaller than offset gear sets because the load is shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Likewise, when configured properly, epicyclic gear sets are more efficient. The following example illustrates these benefits. Let’s assume that we’re designing a high-speed gearbox to meet the following requirements:
• A turbine delivers 6,000 hp at 16,000 RPM to the type shaft.
• The result from the gearbox must drive a generator at 900 RPM.
• The design lifestyle is to be 10,000 hours.
With these requirements in mind, let’s look at three likely solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the original gear set and splits the two-stage reduction into two branches, and the 3rd calls for by using a two-level planetary or celebrity epicyclic. In this situation, we chose the celebrity. 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, produced from taking the square root of the final ratio (7.70). In the process of reviewing this solution we detect its size and excess weight is very large. To lessen the weight we after that explore the possibility of earning two branches of an identical arrangement, as observed in the second solutions. This cuts tooth loading and decreases both size and excess weight considerably . We finally reach our third alternative, which may be the two-stage celebrity epicyclic. With three planets this gear train decreases tooth loading drastically from the initial approach, and a relatively smaller amount from solution two (observe “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a huge part of why is them so useful, however these very characteristics could make creating them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to create it easy that you should understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s commence by looking for how relative speeds job together with different arrangements. In the star arrangement the carrier is set, and the relative speeds of sunlight, planet, and ring are simply dependant on the speed of 1 member and the number of teeth in each equipment.
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 sunlight and planets are determined by the number of teeth in each equipment and the velocity 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 often calculate the acceleration of the sun, planet, and ring in accordance with the carrier. Understand that even in a solar set up where the sun is fixed it has a speed relationship with the planet-it is not zero RPM at the mesh.
Torque Splits
When considering torque splits one assumes the torque to be divided among the planets similarly, but this may not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” quantity of planets. This quantity in epicyclic sets designed with two or three planets is generally equal to the actual quantity of planets. When more than three planets are used, however, the effective quantity of planets is at all times less than using the number of planets.
Let’s look by torque splits when it comes to set support and floating support of the people. With set support, all users are backed in bearings. The centers of the sun, band, and carrier will never be coincident because of manufacturing tolerances. For this reason fewer planets are simultaneously in mesh, resulting in a lower effective quantity of planets sharing the strain. With floating support, a couple of members are allowed a tiny amount of radial liberty or float, which allows the sun, ring, and carrier to get a posture where their centers will be coincident. This float could be less than .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 should be made when making epicyclic gears. Primary we should translate RPM into mesh velocities and determine the number of load application cycles per device of time for each and every member. The first rung on the ladder in this determination is usually to calculate the speeds of each of the members relative to the carrier. For instance, if the sun equipment is rotating at +1700 RPM and the carrier is definitely rotating at +400 RPM the speed of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears can be calculated by that velocity and the amounts of teeth in each of the gears. The utilization of indications to symbolize clockwise and counter-clockwise rotation is normally important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two members is usually +1700-(-400), or +2100 RPM.
The next step is to identify the quantity of load application cycles. Because the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will be equal to the number of planets. The planets, however, will experience only 1 bi-directional load request per relative revolution. It meshes with sunlight and ring, but the load is on opposite sides of the teeth, resulting in one fully reversed stress cycle. Thus the planet is considered an idler, and the allowable pressure must be reduced 30 percent from the worthiness for a unidirectional load app.
As noted above, the torque on the epicyclic people is divided among the planets. In examining the stress and life of the associates we must look at the resultant loading at each mesh. We locate the idea of torque per mesh to become relatively confusing in epicyclic gear analysis and prefer to look at the tangential load at each mesh. For example, in searching at the tangential load at the sun-planet mesh, we consider the torque on sunlight gear and divide it by the powerful number of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is utilized to compute the energy transmitted at each mesh and, adjusted by the load 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 ready between sun and ring fixes the angular placement of the sun to the ring. The next planet(s) can now be assembled simply in discreet locations where the sun and ring could be simultaneously engaged. The “least mesh angle” from the 1st planet that will accommodate 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. Hence, as a way to assemble extra planets, they must be spaced at multiples of the least mesh angle. If one wishes to have the same spacing of the planets in a straightforward epicyclic set, planets may be spaced equally when the sum of the number of teeth in the sun and band is certainly divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the fixed coupling of the planets offers another level of complexity, and correct planet spacing may require match marking of teeth.
With multiple components in mesh, losses must be considered at each mesh so as to measure the efficiency of the machine. Ability transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic sets, the total electric power transmitted through the sun-planet mesh and ring-world mesh may be significantly less than input vitality. This is one of the reasons that simple planetary epicyclic models are better than other reducer plans. In contrast, for most coupled epicyclic sets total electrical power transmitted internally through each mesh may be higher than input power.
What of electricity at the mesh? For basic and compound epicyclic models, calculate pitch range velocities and tangential loads to compute electrical power at each mesh. Values can be obtained from the earth torque relative rate, and the operating pitch diameters with sunlight and band. Coupled epicyclic models present more complex issues. Components of two epicyclic units can be coupled 36 various ways using one type, one end result, and one response. Some plans split the power, while some recirculate ability internally. For these kind of epicyclic models, tangential loads at each mesh can only just be decided through the use of free-body diagrams. Also, the elements of two epicyclic units could be coupled nine different ways in a string, using one insight, one result, and two reactions. Let’s look at a few examples.
In the “split-electricity” coupled set proven in Figure 7, 85 percent of the transmitted electric power flows to band gear #1 and 15 percent to band gear #2. The result is that coupled gear set can be smaller than series coupled sets because the electrical power is split between the two factors. When coupling epicyclic sets in a series, 0 percent of the power will become transmitted through each established.
Our next case in point depicts a arranged with “electricity recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what occurs in a “four-square” test process of vehicle travel axles. With the torque locked in the machine, the hp at each mesh within the loop improves as speed increases. As a result, this set will encounter much higher electrical power losses at each mesh, resulting in considerably lower unit efficiency .
Shape 9 depicts a free-body diagram of a great epicyclic arrangement that experience ability recirculation. A cursory analysis of this free-physique diagram explains the 60 percent efficiency of the recirculating placed proven in Figure 8. Since the planets happen to be rigidly coupled along, the summation of forces on the two gears must equal zero. The power at sunlight gear mesh effects from the torque insight to sunlight gear. The push at the second ring gear mesh benefits from the end result torque on the band equipment. The ratio being 41.1:1, outcome torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the power on the next planet will be about 14 times the force on the first planet 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 must be approximately 13 instances the tangential load at sunlight gear. If we believe the pitch range velocities to be the same at the sun mesh and band mesh, the energy loss at the ring mesh will be around 13 times greater than the power loss at the sun mesh .