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 external teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar program. This is how planetary gears obtained their name.
The pieces of a planetary gear train can be split into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In nearly all cases the casing is fixed. The generating sun pinion is normally in the center of the ring equipment, and is coaxially arranged with regards to the output. The sun pinion is usually mounted on a clamping system to be able to provide the mechanical connection to the motor shaft. During procedure, the planetary gears, which happen to be attached on a planetary carrier, roll between your sunshine pinion and the ring gear. The planetary carrier likewise represents the output shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The amount of teeth does not have any effect on the transmitting ratio of the gearbox. The amount of planets can also vary. As the amount of planetary gears raises, the distribution of the strain increases and then the torque which can be transmitted. Raising the quantity of tooth engagements likewise reduces the rolling vitality. Since only part of the total outcome should be transmitted as rolling electricity, a planetary gear is incredibly efficient. The advantage of a planetary gear compared to an individual spur gear lies in this load distribution. Hence, it is possible to transmit substantial torques wit
h high efficiency with a concise design using planetary gears.
So long as the ring gear includes a regular size, different ratios could be realized by various the amount of teeth of sunlight gear and the number of tooth of the planetary gears. The smaller the sun equipment, the higher the ratio. Technically, a meaningful ratio selection 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. Larger ratios can be obtained by connecting many planetary levels in series in the same ring gear. In this instance, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a band gear that is not fixed but is driven in virtually any direction of rotation. It is also possible to repair the drive shaft as a way to grab the torque via the ring equipment. Planetary gearboxes have grown to be extremely important in lots of 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. Great transmission ratios may also easily be achieved with planetary gearboxes. Because of the positive properties and small design, the gearboxes have various potential uses in professional applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency because of low rolling power
Almost unlimited transmission ratio options because of blend of several planet stages
Suitable as planetary switching gear because of fixing this or that area of the gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a wide selection of applications
Epicyclic gearbox is an automatic type gearbox where parallel shafts and gears set up from manual gear package are replaced with an increase of compact and more reliable sun and planetary kind of gears arrangement and also the manual clutch from manual electrical power train is changed with hydro coupled clutch or torque convertor which in turn made the tranny automatic.
The idea of epicyclic gear box is taken from the solar system which is known as to an ideal arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears based on the need of the travel.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a type of gear which looks like a ring and have angular minimize teethes at its interior 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 ,additionally it is known as annular ring.
2. Sun gear- It’s the equipment with angular trim teethes and is placed in the middle of the epicyclic gearbox; the sun gear is in constant mesh at inner level with the planetary gears and is normally connected with the source shaft of the epicyclic equipment box.
One or more sun gears can be used for reaching different output.
3. Planet gears- These are small gears used in between band and sun gear , the teethes of the planet gears are in continuous mesh with sunlight and the ring equipment at both the inner and outer items respectively.
The axis of the earth gears are attached to the earth carrier which is carrying the output shaft of the epicyclic gearbox.
The planet 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- It is a carrier attached with the axis of the earth gears and is responsible for final transmitting of the result 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- These devices used to repair the annular gear, sun gear and planetary gear and is handled 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.electronic. sun equipment, planetary gears and annular gear is done to get the expected torque or speed output. As fixing the above causes the variation in gear ratios from substantial torque to high rate. 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 causes the planet carrier to rotate with the power supplied to sunlight gear.
Second gear ratio
This provides high speed ratios to the vehicle which helps the vehicle to achieve higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the motivated member and annular the generating member to be able 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 driven member and sunlight gear the driver member.
Note- More quickness or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear container.
High-speed epicyclic gears can be built relatively little as the energy is distributed over many meshes. This outcomes in a low power to pounds ratio and, as well as lower pitch line velocity, causes improved efficiency. The tiny gear diameters produce lower occasions of inertia, significantly reducing acceleration and deceleration torque when beginning 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 just a few places. Let’s get started by examining an important facet of any project: expense. Epicyclic gearing is generally less expensive, when tooled properly. Just as one wouldn’t normally 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 not really consider making a 100-piece lot of epicyclic carriers on an N/C mill. To retain carriers within reasonable manufacturing costs they must be made from castings and tooled on single-purpose devices with multiple cutters at the same time removing material.
Size is another issue. Epicyclic gear models are used because they are smaller than offset equipment sets since the load is normally shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured effectively, epicyclic gear pieces are more efficient. The next example illustrates these rewards. Let’s assume that we’re building a high-speed gearbox to gratify the following requirements:
• A turbine offers 6,000 horsepower 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 at heart, let’s look at three likely solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the initial gear placed and splits the two-stage decrease into two branches, and the 3rd calls for by using a two-stage planetary or superstar epicyclic. In this instance, we chose the celebrity. 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, produced from taking the square base of the final ratio (7.70). In the process of reviewing this answer we detect its size and pounds is very large. To lessen the weight we then explore the possibility of making two branches of an identical arrangement, as seen in the second alternatives. This cuts tooth loading and decreases both size and weight considerably . We finally reach our third solution, which is the two-stage superstar epicyclic. With three planets this gear train minimizes tooth loading substantially from the primary approach, and a somewhat smaller amount from option two (find “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a large part of what makes them so useful, but these very characteristics can make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our target is to create it easy that you should understand and use epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking in how relative speeds do the job in conjunction with different plans. In the star set up the carrier is fixed, and the relative speeds of sunlight, planet, and ring are simply determined by the speed of 1 member and the number of teeth in each equipment.
In a planetary arrangement the band gear is fixed, and planets orbit sunlight while rotating on the planet shaft. In this set up the relative speeds of the sun and planets are determined by the amount of teeth in each gear and the acceleration of the carrier.
Things get a little trickier when working with coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to always calculate the acceleration of the sun, planet, and ring in accordance with the carrier. Understand that possibly in a solar arrangement where the sunlight is fixed it has a speed romantic relationship with the planet-it isn’t zero RPM at the mesh.
Torque Splits
When contemplating 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” number of planets. This quantity in epicyclic sets designed with several planets is in most cases equal to some of the amount of planets. When a lot more than three planets are used, however, the effective number of planets is constantly less than the actual number of planets.
Let’s look for torque splits with regards to set support and floating support of the associates. With fixed support, all users are backed in bearings. The centers of the sun, ring, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets will be simultaneously in mesh, producing a lower effective amount of planets sharing the strain. With floating support, a couple of people are allowed a tiny amount of radial independence or float, that allows the sun, ring, and carrier to get a position where their centers will be coincident. This float could be less than .001-.002 inches. With floating support three planets will be in mesh, resulting in 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 designing epicyclic gears. Initially we should translate RPM into mesh velocities and determine the quantity of load software cycles per unit of time for each and every member. The first step in this determination is definitely to calculate the speeds of every of the members in accordance with the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is definitely 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 velocity and the numbers of teeth in each one of the gears. The utilization of indicators to stand for clockwise and counter-clockwise rotation is definitely 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 participants is usually +1700-(-400), or +2100 RPM.
The next step is to identify the amount of load application cycles. Since the sun and band gears mesh with multiple planets, the amount of load cycles per revolution relative to the carrier will end up being equal to the quantity of planets. The planets, nevertheless, will experience only one bi-directional load software per relative revolution. It meshes with the sun and ring, however the load is normally on opposite sides of one’s teeth, resulting in one fully reversed anxiety cycle. Thus the planet is considered an idler, and the allowable anxiety must be reduced 30 percent from the value for a unidirectional load software.
As noted over, the torque on the epicyclic associates is divided among the planets. In analyzing the stress and lifestyle of the customers we must look at the resultant loading at each mesh. We get the concept of torque per mesh to end up being relatively confusing in epicyclic equipment examination 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 take the torque on sunlight equipment and divide it by the effective quantity of planets and the operating pitch radius. This tangential load, combined with peripheral speed, can be used to compute the energy transmitted at each mesh and, altered by the strain cycles per revolution, the life expectancy of each component.
In addition to these issues there may also be assembly complications that require addressing. For example, putting one planet ready between sun and band fixes the angular posture of sunlight to the ring. The next planet(s) is now able to be assembled only in discreet locations where in fact the sun and band could be at the same time involved. The “least mesh angle” from the initially planet that will support simultaneous mesh of the next planet is add up to 360° divided by the sum of the amounts of teeth in sunlight and the ring. Therefore, as a way to assemble extra planets, they must become spaced at multiples of the least mesh angle. If one wants to have the same spacing of the planets in a straightforward epicyclic set, planets may be spaced similarly when the sum of the amount of teeth in sunlight and band is normally divisible by the number of planets to an integer. The same guidelines apply in a compound epicyclic, but the fixed coupling of the planets provides another degree of complexity, and correct planet spacing may necessitate match marking of tooth.
With multiple parts in mesh, losses must be considered at each mesh as a way to measure the efficiency of the unit. Electric power transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic models, the total electric power transmitted through the sun-planet mesh and ring-world mesh may be less than input power. This is among the reasons that simple planetary epicyclic pieces are better than other reducer plans. In contrast, for many coupled epicyclic models total electricity transmitted internally through each mesh could be greater than input power.
What of power at the mesh? For straightforward and compound epicyclic units, calculate pitch series velocities and tangential loads to compute electricity at each mesh. Values can be acquired from the earth torque relative velocity, and the functioning pitch diameters with sunshine and ring. Coupled epicyclic units present more technical issues. Elements of two epicyclic pieces could be coupled 36 different ways using one suggestions, one end result, and one reaction. Some plans split the power, while some recirculate ability internally. For these kind of epicyclic units, tangential loads at each mesh can only just be determined through the consumption of free-body diagrams. Additionally, the elements of two epicyclic models can be coupled nine various ways in a series, using one insight, one end result, and two reactions. Let’s look at a few examples.
In the “split-power” 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 effect is that this coupled gear set can be smaller than series coupled units because the electricity is split between your two components. 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 establish with “power recirculation.” This equipment set happens when torque gets locked in the machine in a manner similar to what happens in a “four-square” test procedure for vehicle drive axles. With the torque locked in the machine, the hp at each mesh within the loop heightens as speed increases. As a result, this set will experience much higher electrical power losses at each mesh, leading to significantly lower unit efficiency .
Determine 9 depicts a free-body diagram of a great epicyclic arrangement that encounters power recirculation. A cursory evaluation of this free-body system diagram clarifies the 60 percent performance of the recirculating collection displayed in Figure 8. Since the planets happen to be rigidly coupled collectively, the summation of forces on both gears must equal zero. The power at the sun gear mesh outcomes from the torque insight to sunlight gear. The pressure at the next ring gear mesh outcomes from the outcome torque on the band equipment. The ratio being 41.1:1, productivity torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the push on the next planet will be roughly 14 times the induce on the first planet at the sun gear mesh. For that reason, for the summation of forces to mean zero, the tangential load at the first ring gear should be approximately 13 circumstances the tangential load at the sun gear. If we believe the pitch range velocities to become the same at the sun mesh and ring mesh, the power loss at the ring mesh will be around 13 times higher than the energy loss at the sun mesh .