epicyclic gearbox

In 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 equipment occurs in analogy to the orbiting of the planets in the solar system. This is how planetary gears obtained their name.
The components of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In the majority of cases the housing is fixed. The generating sun pinion is in the heart of the ring equipment, and is coaxially arranged in relation to the output. Sunlight pinion is usually attached to a clamping system in order to give the mechanical link with the motor shaft. During procedure, the planetary gears, which are mounted on a planetary carrier, roll between your sunshine pinion and the band gear. The planetary carrier as well represents the end result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The quantity of teeth has no effect on the tranny ratio of the gearbox. The amount of planets may also vary. As the amount of planetary gears enhances, the distribution of the strain increases and then the torque which can be transmitted. Raising the quantity of tooth engagements also reduces the rolling electricity. Since only portion of the total outcome should be transmitted as rolling electric power, a planetary gear is incredibly efficient. The good thing about a planetary equipment compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit huge torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear has a regular size, different ratios can be realized by different the amount of teeth of sunlight gear and the number of tooth of the planetary gears. Small the sun gear, the higher the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, since the planetary gears and the sun gear are extremely tiny above and below these ratios. Larger ratios can be obtained by connecting a variety of planetary phases in series in the same ring 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 virtually any direction of rotation. It is also possible to fix the drive shaft as a way to pick up 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 well established in areas where high output levels and fast speeds should be transmitted with favorable mass inertia ratio adaptation. Great transmission ratios can also easily be performed with planetary gearboxes. Because of their positive properties and compact design, 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 several planetary gears
High efficiency due to low rolling power
Almost unlimited transmission ratio options because of mixture of several planet stages
Suited as planetary switching gear due to fixing this or that the main gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox can be an automatic type gearbox in which parallel shafts and gears set up from manual gear field are replaced with an increase of compact and more reputable sun and planetary kind of gears arrangement as well as the manual clutch from manual electric power train is changed with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The idea of epicyclic gear box is extracted from the solar system which is known as to an ideal 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 appears like a ring and also have angular cut teethes at its inner surface ,and is located in outermost job in en epicyclic gearbox, the internal teethes of ring gear is in frequent mesh at outer point with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It’s the equipment with angular lower teethes and is placed in the center of the epicyclic gearbox; sunlight gear is in regular mesh at inner point with the planetary gears and is connected with the suggestions shaft of the epicyclic equipment box.
One or more sunlight gears can be utilized for attaining different output.
3. Planet gears- They are small gears found in between band and sun gear , the teethes of the planet gears are in regular 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 earth gears can rotate about their axis and also can revolve between your ring and the sun gear just like our solar system.
4. Planet carrier- It is a carrier attached with the axis of the earth gears and is in charge of final transmitting of the end 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- The device used to fix the annular gear, sun 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 fact the fixing the gears i.e. sun gear, planetary gears and annular equipment is done to obtain the needed torque or acceleration output. As fixing the above causes the variation in equipment ratios from great torque to high velocity. 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 go from its initial state and is obtained by fixing the annular gear which in turn causes the earth 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 realize higher speed during a travel, these ratios are obtained by fixing the sun gear which makes the earth carrier the powered member and annular the driving a vehicle member so that you can 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 achieved by fixing the earth gear carrier which in turn makes the annular gear the influenced member and sunlight gear the driver member.
Note- More acceleration or torque ratios can be achieved by increasing the quantity planet and sun equipment in epicyclic gear field.
High-speed epicyclic gears could be built relatively small as the power is distributed over many meshes. This outcomes in a low capacity to fat ratio and, together with lower pitch collection velocity, brings about improved efficiency. The small gear diameters produce lower moments of inertia, significantly minimizing 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.
Why epicyclic gearing is used have already been covered in this magazine, so we’ll expand on this issue in just a few places. Let’s start by examining a crucial aspect of any project: price. Epicyclic gearing is normally less costly, when tooled properly. Just as one wouldn’t normally consider making a 100-piece lot of gears on an N/C milling machine 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 hold carriers within sensible manufacturing costs they must be made from castings and tooled on single-purpose equipment with multiple cutters simultaneously removing material.
Size is another aspect. Epicyclic gear units are used because they’re smaller than offset gear sets because the load can be shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. As well, when configured effectively, epicyclic gear pieces are more efficient. The following example illustrates these rewards. Let’s believe that we’re building a high-speed gearbox to gratify the following requirements:
• A turbine provides 6,000 horsepower at 16,000 RPM to the source shaft.
• The productivity from the gearbox must travel a generator at 900 RPM.
• The design lifestyle is to be 10,000 hours.
With these requirements in mind, let’s look at three practical solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear established and splits the two-stage decrease into two branches, and the third calls for utilizing a two-level planetary or superstar epicyclic. In this instance, we chose the celebrity. Let’s examine each one 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 root of the final ratio (7.70). Along the way of reviewing this remedy we notice its size and fat is very large. To lessen the weight we after that explore the possibility of earning two branches of an identical arrangement, as seen in the second alternatives. This cuts tooth loading and minimizes both size and pounds considerably . We finally reach our third answer, which is the two-stage superstar epicyclic. With three planets this gear train reduces tooth loading drastically from the first approach, and a relatively smaller amount from answer two (find “methodology” at end, and Figure 6).
The unique design and style 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 factors. Our objective is to make it easy for you to understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s commence by looking at how relative speeds work in conjunction with different plans. In the star arrangement the carrier is set, and the relative speeds of the sun, planet, and band are simply dependant on the speed of one member and the amount of teeth in each gear.
In a planetary arrangement the band gear is set, and planets orbit sunlight while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are determined by the amount of teeth in each gear and the swiftness of the carrier.
Things get a little trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. Hence, it is imperative to generally calculate the velocity of sunlight, planet, and ring relative to the carrier. Remember that possibly in a solar set up where the sun is fixed it includes a speed romance 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 might not exactly be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” amount of planets. This number in epicyclic sets designed with several planets is in most cases equal to using the quantity of planets. When a lot more than three planets are used, however, the effective amount of planets is at all times less than some of the number of planets.
Let’s look at torque splits when it comes to fixed support and floating support of the customers. With fixed support, all people are backed in bearings. The centers of sunlight, band, and carrier will never be coincident due to manufacturing tolerances. Due to this fewer planets will be simultaneously in mesh, producing a lower effective amount of planets sharing the strain. With floating support, a couple of users are allowed a little amount of radial flexibility or float, which allows the sun, band, and carrier to seek a position where their centers are coincident. This float could 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 considerations that should be made when designing epicyclic gears. Initial we should translate RPM into mesh velocities and determine the amount of load software cycles per product of time for each member. The first rung on the ladder in this determination is normally 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 usually rotating at +400 RPM the quickness of sunlight gear relative to the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that speed and the amounts of teeth in each of the gears. The make use of signals 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 speed between the two people is definitely +1700-(-400), or +2100 RPM.
The next step is to determine the quantity of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will become equal to the quantity of planets. The planets, nevertheless, will experience only 1 bi-directional load application per relative revolution. It meshes with sunlight and ring, however the load can be on opposite sides of one’s teeth, leading to one fully reversed pressure cycle. Thus the earth is considered an idler, and the allowable tension must be reduced 30 percent from the value for a unidirectional load program.
As noted previously mentioned, the torque on the epicyclic members is divided among the planets. In analyzing the stress and your life of the members we must look at the resultant loading at each mesh. We discover the concept of torque per mesh to become somewhat confusing in epicyclic equipment analysis and prefer to check out the tangential load at each mesh. For instance, in looking at the tangential load at the sun-planet mesh, we have the torque on the sun gear and divide it by the successful quantity of planets and the operating pitch radius. This tangential load, combined with peripheral speed, is used to compute the power transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of each component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, putting one planet ready between sun and ring fixes the angular location of the sun to the ring. Another planet(s) can now be assembled simply in discreet locations where in fact the sun and band could be at the same time involved. The “least mesh angle” from the 1st planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the amounts of teeth in the sun and the ring. Therefore, so that you can assemble more planets, they must end up being spaced at multiples of the least mesh angle. If one wishes to have equivalent spacing of the planets in a straightforward epicyclic set, planets could be spaced similarly when the sum of the number of teeth in sunlight and ring is definitely divisible by the amount of planets to an integer. The same guidelines apply in a compound epicyclic, but the fixed coupling of the planets contributes another level of complexity, and correct planet spacing may require match marking of pearly whites.
With multiple parts in mesh, losses need to be considered at each mesh so that you can measure the efficiency of the unit. Ability transmitted at each mesh, not input power, can be used to compute power reduction. For simple epicyclic models, the total vitality transmitted through the sun-world mesh and ring-world mesh may be less than input electrical power. This is among the reasons that simple planetary epicyclic units are better than other reducer arrangements. In contrast, for most coupled epicyclic sets total electricity transmitted internally through each mesh could be higher than input power.
What of electricity at the mesh? For basic and compound epicyclic pieces, calculate pitch series velocities and tangential loads to compute power at each mesh. Ideals can be obtained from the planet torque relative speed, and the operating pitch diameters with sunlight and band. Coupled epicyclic sets present more complex issues. Elements of two epicyclic models can be coupled 36 various ways using one insight, one productivity, and one response. Some arrangements split the power, although some recirculate electrical power internally. For these kind of epicyclic pieces, tangential loads at each mesh can only just be established through the use of free-body diagrams. Also, the components of two epicyclic models can be coupled nine various ways in a series, using one type, one productivity, and two reactions. Let’s look at a few examples.
In the “split-ability” coupled set shown in Figure 7, 85 percent of the transmitted ability flows to ring gear #1 and 15 percent to ring gear #2. The effect is that coupled gear set can be scaled-down than series coupled pieces because the power is split between the two factors. When coupling epicyclic pieces in a string, 0 percent of the power will always be transmitted through each arranged.
Our next case in point depicts a establish with “electric power recirculation.” This equipment set happens when torque gets locked in the machine in a manner similar to what takes place in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the horsepower at each mesh within the loop boosts as speed increases. Therefore, this set will encounter much higher electric power losses at each mesh, resulting in substantially lower unit efficiency .
Shape 9 depicts a free-body diagram of a great epicyclic arrangement that encounters electric power recirculation. A cursory research of this free-body system diagram clarifies the 60 percent effectiveness of the recirculating collection displayed in Figure 8. Since the planets will be rigidly coupled jointly, the summation of forces on the two gears must equivalent zero. The force at the sun gear mesh results from the torque insight 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, output torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the force on the second planet will be about 14 times the power on the first planet at sunlight gear mesh. Therefore, for the summation of forces to equate to zero, the tangential load at the first band gear must be approximately 13 instances the tangential load at sunlight gear. If we believe the pitch line velocities to always be the same at sunlight mesh and ring mesh, the energy loss at the band mesh will be approximately 13 times greater than the power loss at sunlight mesh .