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 program. This is how planetary gears obtained their name.
The pieces 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 driving sun pinion is certainly in the center of the ring equipment, and is coaxially organized with regards to the output. Sunlight pinion is usually mounted on a clamping system in order to give the mechanical link with the electric motor shaft. During operation, the planetary gears, which happen to be installed on a planetary carrier, roll between your sun pinion and the band equipment. The planetary carrier as well represents the outcome shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the required torque. The amount of teeth has no effect on the tranny ratio of the gearbox. The number of planets can also vary. As the number of planetary gears enhances, the distribution of the load increases and therefore the torque that can be transmitted. Increasing the amount of tooth engagements also reduces the rolling ability. Since only part of the total productivity must be transmitted as rolling electrical power, a planetary gear 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 substantial torques wit
h high efficiency with a compact design and style using planetary gears.
Provided that the ring gear includes a frequent size, different ratios can be realized by varying the amount of teeth of the sun gear and the number of the teeth of the planetary gears. The smaller the sun gear, the greater the ratio. Technically, a meaningful ratio selection 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. Bigger ratios can be acquired by connecting a couple of planetary stages 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 ring gear that is not set but is driven in virtually any direction of rotation. Additionally it is possible to repair the drive shaft so that you can pick up the torque via the band equipment. 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 must 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 design and style, the gearboxes have various potential uses in commercial applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency due to low rolling power
Practically unlimited transmission ratio options because of blend of several planet stages
Suitable as planetary switching gear because of fixing this or that portion of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a broad range of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears arrangement from manual gear package are replaced with an increase of compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual power train is substituted with hydro coupled clutch or torque convertor which in turn made the tranny 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, Travel, Sport) modes which is obtained by fixing of sun and planetary gears in line with the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- It is a type of gear which appears like a ring and also have angular cut teethes at its inner surface ,and is placed in outermost posture in en epicyclic gearbox, the internal teethes of ring gear is in constant mesh at outer level with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the equipment with angular lower teethes and is located in the center of the epicyclic gearbox; sunlight gear is in regular mesh at inner level with the planetary gears and is normally connected with the input shaft of the epicyclic equipment box.
One or more sunlight gears can be utilised for obtaining different output.
3. Planet gears- They are small gears found in between ring and sun equipment , the teethes of the planet gears are in continuous mesh with sunlight and the ring equipment at both the inner and outer tips respectively.
The axis of the earth gears are mounted on 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 your ring and sunlight gear just like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the planet gears and is accountable for final transmission of the end result to the productivity 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- These devices used to repair the annular gear, sunshine gear and planetary gear and is manipulated by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the fact the fixing any of the gears i.e. sun equipment, planetary gears and annular equipment is done to get the needed torque or rate output. As fixing the above causes the variation in equipment ratios from large torque to high acceleration. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle which helps the automobile 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 vehicle which helps the automobile to achieve higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the planet carrier the driven member and annular the driving 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 vehicle, this gear is attained by fixing the planet gear carrier which in turn makes the annular gear the influenced member and the sun gear the driver member.
Note- More velocity 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 tiny as the energy is distributed over a number of meshes. This effects in a low capacity to weight ratio and, as well as lower pitch line velocity, brings about improved efficiency. The tiny gear diameters produce lower moments of inertia, significantly reducing 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.
The reasons why epicyclic gearing can be used have been covered in this magazine, so we’ll expand on this issue in simply a few places. Let’s commence by examining a crucial facet of any project: cost. Epicyclic gearing is normally less costly, when tooled properly. Being an would not consider making a 100-piece large amount of gears on an N/C milling equipment with an application 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 preserve carriers within fair manufacturing costs they should be made from castings and tooled on single-purpose devices with multiple cutters concurrently removing material.
Size is another aspect. 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. Also, when configured correctly, epicyclic gear units are more efficient. The following example illustrates these rewards. Let’s assume that we’re building a high-speed gearbox to meet the following requirements:
• A turbine provides 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 usually to be 10,000 hours.
With these requirements in mind, let’s look at three likely solutions, one involving a single branch, two-stage helical gear set. Another solution takes the original gear establish and splits the two-stage lowering into two branches, and the third calls for using a two-stage planetary or star epicyclic. In this instance, 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). Along the way of reviewing this solution we detect its size and fat is very large. To lessen the weight we in that case explore the possibility of earning two branches of a similar arrangement, as observed in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third answer, which may be the two-stage superstar epicyclic. With three planets this equipment train minimizes tooth loading drastically from the first approach, and a relatively smaller amount from option two (look at “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, yet these very characteristics can 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 so that you can understand and use epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking in how relative speeds function together with different plans. In the star set up the carrier is fixed, and the relative speeds of sunlight, planet, and band 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 arrangement the relative speeds of sunlight and planets are determined by the quantity of teeth in each gear and the acceleration of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds might not exactly be intuitive. Hence, it is imperative to at all times calculate the swiftness of the sun, planet, and ring in accordance with the carrier. Remember that even in a solar arrangement 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 equally, but this may well not be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This amount in epicyclic sets designed with two or three planets is in most cases equal to you see, the amount of planets. When a lot more than three planets are employed, however, the effective amount of planets is at all times less than some of the number of planets.
Let’s look for torque splits in conditions of fixed support and floating support of the participants. With set support, all customers are reinforced in bearings. The centers of sunlight, band, and carrier will not be coincident because of manufacturing tolerances. Due to this fewer planets are simultaneously in mesh, producing a lower effective amount of planets sharing the strain. With floating support, a couple of customers are allowed a small amount of radial liberty or float, that allows the sun, band, and carrier to get a position where their centers are coincident. This float could possibly be as little as .001-.002 ins. With floating support three planets will always be in mesh, producing a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that needs to be made when designing epicyclic gears. Primary we must translate RPM into mesh velocities and determine the number of load software cycles per device of time for every member. The first step in this determination is normally to calculate the speeds of every of the members relative to the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is rotating at +400 RPM the acceleration of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that acceleration and the amounts of teeth in each one of the gears. The use of signs to represent clockwise and counter-clockwise rotation is important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative quickness between the two participants is normally +1700-(-400), or +2100 RPM.
The second step is to identify the quantity of load application cycles. Since the sun and ring gears mesh with multiple planets, the number of load cycles per revolution in accordance with the carrier will become equal to the number of planets. The planets, on the other hand, will experience only one bi-directional load software per relative revolution. It meshes with sunlight and ring, but the load is usually on opposite sides of the teeth, resulting in one fully reversed stress cycle. Thus the planet is known as an idler, and the allowable anxiety must be reduced 30 percent from the worthiness for a unidirectional load request.
As noted above, the torque on the epicyclic participants is divided among the planets. In analyzing the stress and your life of the customers we must look at the resultant loading at each mesh. We find the concept of torque per mesh to be somewhat confusing in epicyclic gear research and prefer to look at the tangential load at each mesh. For instance, in seeking at the tangential load at the sun-world mesh, we have the torque on sunlight gear and divide it by the successful amount of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the energy transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there can also be assembly complications that need addressing. For example, putting one planet in a position between sun and ring fixes the angular location of the sun to the ring. The next planet(s) can now be assembled simply in discreet locations where the sun and ring can be concurrently engaged. The “least mesh angle” from the 1st 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 the sun and the ring. Therefore, as a way to assemble extra planets, they must become spaced at multiples of the least mesh position. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets could be spaced equally when the sum of the amount of teeth in sunlight and ring is divisible by the number of planets to an integer. The same rules apply in a compound epicyclic, but the set coupling of the planets provides another level of complexity, and appropriate planet spacing may necessitate match marking of the teeth.
With multiple components in mesh, losses must be considered at each mesh so that you can measure the efficiency of the machine. Vitality transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic pieces, the total ability transmitted through the sun-world mesh and ring-planet mesh may be less than input vitality. This is among the reasons that easy planetary epicyclic pieces are better than other reducer arrangements. In contrast, for most coupled epicyclic models total ability transmitted internally through each mesh could be higher than input power.
What of ability at the mesh? For simple and compound epicyclic units, calculate pitch range velocities and tangential loads to compute power at each mesh. Values can be obtained from the earth torque relative swiftness, and the functioning pitch diameters with sunlight and ring. Coupled epicyclic units present more complex issues. Components of two epicyclic models could be coupled 36 different ways using one suggestions, one outcome, and one response. Some plans split the power, although some recirculate ability internally. For these types of epicyclic units, tangential loads at each mesh can only just be motivated through the use of free-body diagrams. On top of that, the elements of two epicyclic models can be coupled nine various ways in a series, using one suggestions, one outcome, and two reactions. Let’s look at a few examples.
In the “split-vitality” coupled set proven in Figure 7, 85 percent of the transmitted power flows to band gear #1 and 15 percent to ring gear #2. The result is that this coupled gear set can be more compact than series coupled pieces because the power is split between the two elements. When coupling epicyclic models in a string, 0 percent of the power will be transmitted through each placed.
Our next case in point depicts a arranged with “electric power recirculation.” This gear set happens when torque gets locked in the machine in a way similar to what takes place 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 increases as speed increases. Therefore, this set will encounter much higher vitality losses at each mesh, leading to drastically lower unit efficiency .
Number 9 depicts a free-body diagram of an epicyclic arrangement that activities electrical power recirculation. A cursory evaluation of this free-body system diagram clarifies the 60 percent efficiency of the recirculating establish proven in Figure 8. Because 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 outcomes from the torque suggestions to the sun gear. The push at the second ring gear mesh effects from the productivity torque on the ring equipment. 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 force on the next planet will be around 14 times the force on the first planet at the sun gear mesh. Consequently, for the summation of forces to mean zero, the tangential load at the first band gear should be approximately 13 instances the tangential load at the sun gear. If we presume the pitch line velocities to end up being the same at the sun mesh and band mesh, the power loss at the ring mesh will be roughly 13 times greater than the energy loss at the sun mesh .