epicyclic gearbox

In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference manage 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 can be divided 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 generating sun pinion is definitely in the heart of the ring gear, and is coaxially arranged with regards to the output. Sunlight pinion is usually mounted on a clamping system in order to provide the mechanical connection to the motor shaft. During operation, the planetary gears, which happen to be mounted on a planetary carrier, roll between the sunlight pinion and the band equipment. The planetary carrier also represents the output shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The amount of teeth has no effect on the tranny ratio of the gearbox. The amount of planets can also vary. As the number of planetary gears boosts, the distribution of the load increases and therefore the torque that can be transmitted. Raising the number of tooth engagements also reduces the rolling vitality. Since only the main total end result must be transmitted as rolling vitality, a planetary gear is incredibly efficient. The benefit of a planetary equipment compared to a single spur gear lies in this load distribution. It is therefore possible to transmit high torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear includes a continuous size, different ratios could be realized by various the quantity of teeth of sunlight gear and the number of tooth of the planetary gears. Small the sun equipment, the higher the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, because the planetary gears and sunlight gear are extremely little above and below these ratios. Larger ratios can be acquired by connecting several planetary levels in series in the same band gear. In this instance, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a ring gear that is not fixed but is driven in any direction of rotation. Additionally it is possible to fix the drive shaft in order to pick up the torque via the ring gear. Planetary gearboxes have become extremely important in lots of areas 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. Large transmission ratios may also easily be performed with planetary gearboxes. Because of their positive properties and small design and style, the gearboxes have a large number of potential uses in commercial applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency because of low rolling power
Practically unlimited transmission ratio options due to mixture of several planet stages
Suitable as planetary switching gear due to fixing this or that part of the gearbox
Possibility of 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 arrangement from manual gear container are replaced with an increase of compact and more reliable sun and planetary type of gears arrangement plus the manual clutch from manual power train is replaced with hydro coupled clutch or torque convertor which in turn made the transmission automatic.
The thought of epicyclic gear box is extracted from the solar system which is considered to the perfect arrangement of objects.
The epicyclic gearbox usually comes with 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 travel.
The different parts of Epicyclic Gearbox
1. Ring gear- It is a type of gear which appears like a ring and also have angular lower teethes at its interior surface ,and is put in outermost posture in en epicyclic gearbox, the internal teethes of ring gear is in regular mesh at outer point with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It’s the equipment with angular lower teethes and is placed in the middle of the epicyclic gearbox; the sun gear is in frequent mesh at inner stage with the planetary gears and can be connected with the input shaft of the epicyclic equipment box.
One or more sunshine gears can be utilised for achieving different output.
3. Planet gears- They are small gears found in between band and sun gear , the teethes of the earth gears are in constant mesh with the sun and the ring equipment at both the inner and outer things respectively.
The axis of the planet 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 the sun gear exactly like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the planet gears and is responsible for final transmission 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- The device used to fix the annular gear, sun gear and planetary equipment and is handled by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is based on the actual fact the fixing any of the gears i.e. sun gear, planetary gears and annular gear is done to get the required torque or speed output. As fixing any of the above causes the variation in equipment ratios from great torque to high quickness. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the automobile 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 automobile which helps the vehicle 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 travelling member in order 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 makes the annular gear the driven member and the sun gear the driver member.
Note- More speed or torque ratios may be accomplished by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears can be built relatively tiny as the power is distributed over a couple of meshes. This outcomes in a low power to excess weight ratio and, together with lower pitch collection velocity, causes improved efficiency. The tiny gear diameters produce lower moments of inertia, significantly minimizing 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.
Why epicyclic gearing is utilized have already been covered in this magazine, so we’ll expand on the topic in just a few places. Let’s commence by examining a crucial facet 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, one should certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To maintain carriers within reasonable manufacturing costs they should be created from castings and tooled on single-purpose devices with multiple cutters simultaneously removing material.
Size is another component. Epicyclic gear models are used because they are smaller than offset gear sets since the load is usually shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Also, when configured correctly, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s believe that we’re developing a high-speed gearbox to meet the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the type shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design life is to be 10,000 hours.
With these requirements in mind, let’s look at three possible solutions, one involving a single branch, two-stage helical gear set. A second solution takes the original gear placed and splits the two-stage decrease into two branches, and the 3rd calls for by using a two-level planetary or superstar epicyclic. In this instance, we chose the star. Let’s examine each one of these in greater detail, seeking 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 option we find its size and excess weight is very large. To lessen the weight we in that case explore the possibility of making 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 arrive at our third answer, which is the two-stage star epicyclic. With three planets this equipment train reduces tooth loading significantly from the 1st approach, and a somewhat smaller amount from remedy two (observe “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a big part of why is them so useful, however these very characteristics could make developing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our goal is to create it easy that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds job together with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply determined by the speed of 1 member and the amount of teeth in each gear.
In a planetary arrangement the ring 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 gear and the velocity of the carrier.
Things get a lttle bit trickier whenever using coupled epicyclic gears, since relative speeds may not be intuitive. It is therefore imperative to constantly calculate the velocity of sunlight, planet, and ring relative to the carrier. Understand that possibly in a solar arrangement where the sun is fixed it includes a speed marriage 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 might not exactly be considered a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” quantity of planets. This number in epicyclic sets constructed with two or three planets is generally equal to some of the amount of planets. When a lot more than three planets are used, however, the effective quantity of planets is usually less than using the number of planets.
Let’s look for torque splits when it comes to fixed support and floating support of the associates. With set support, all customers are supported in bearings. The centers of sunlight, band, and carrier will never be coincident due to manufacturing tolerances. For that reason fewer planets are simultaneously in mesh, resulting in a lower effective amount of planets sharing the strain. With floating support, one or two associates are allowed a small amount of radial flexibility or float, that allows the sun, band, and carrier to seek a posture where their centers will be coincident. This float could possibly be as little as .001-.002 inches. With floating support three planets will always be in mesh, resulting in a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that should be made when making epicyclic gears. Initially we must translate RPM into mesh velocities and determine the number of load request cycles per unit of time for every member. The first rung on the ladder in this determination is usually to calculate the speeds of every of the members relative to the carrier. For example, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the acceleration of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that acceleration and the amounts of teeth in each of the gears. The use of signals to symbolize clockwise and counter-clockwise rotation is certainly important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two customers 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 quantity of load cycles per revolution relative to the carrier will end up being equal to the amount of planets. The planets, however, will experience only one bi-directional load program per relative revolution. It meshes with the sun and ring, but the load is on opposing sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the planet is known as an idler, and the allowable tension must be reduced thirty percent from the value for a unidirectional load application.
As noted above, the torque on the epicyclic people 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 discover the concept of torque per mesh to end up being somewhat confusing in epicyclic equipment evaluation and prefer to check out the tangential load at each mesh. For example, in looking at the tangential load at the sun-world mesh, we have the torque on sunlight gear and divide it by the effective number of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the power 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 need addressing. For example, positioning one planet in a position between sun and ring fixes the angular situation of sunlight to the ring. The next planet(s) can now be assembled just in discreet locations where the sun and ring can be concurrently engaged. The “least mesh angle” from the first planet that will support simultaneous mesh of another planet is equal 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 always be spaced at multiples of this least mesh angle. If one wishes to have equal spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the amount of teeth in the sun and band is certainly 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 degree of complexity, and right planet spacing may require match marking of pearly whites.
With multiple elements in mesh, losses ought to be considered at each mesh so as to measure the efficiency of the machine. Power transmitted at each mesh, not input power, can be used to compute power reduction. For simple epicyclic units, the total electric power transmitted through the sun-planet mesh and ring-planet mesh may be less than input power. This is one of the reasons that easy planetary epicyclic units are more efficient than other reducer arrangements. In contrast, for many coupled epicyclic units total electrical power transmitted internally through each mesh could be greater than input power.
What of vitality at the mesh? For basic and compound epicyclic models, calculate pitch collection velocities and tangential loads to compute ability at each mesh. Ideals can be obtained from the earth torque relative swiftness, and the working pitch diameters with sunlight and ring. Coupled epicyclic pieces present more technical issues. Components of two epicyclic sets can be coupled 36 different ways using one suggestions, one output, and one reaction. Some plans split the power, although some recirculate electric power internally. For these kinds of epicyclic models, tangential loads at each mesh can only just be determined through the application of free-body diagrams. On top of that, the elements of two epicyclic sets can be coupled nine different ways in a string, using one source, one output, and two reactions. Let’s look at some examples.
In the “split-electric power” coupled set demonstrated in Figure 7, 85 percent of the transmitted vitality flows to ring gear #1 and 15 percent to band gear #2. The effect is that this coupled gear set can be scaled-down than series coupled models because the ability is split between your two factors. When coupling epicyclic pieces in a string, 0 percent of the power will end up being transmitted through each set.
Our next example depicts a established with “electricity recirculation.” This equipment set happens when torque gets locked in the machine in a manner similar to what occurs in a “four-square” test procedure for vehicle travel axles. With the torque locked in the machine, the hp at each mesh within the loop increases as speed increases. As a result, this set will knowledge much higher vitality losses at each mesh, resulting in substantially lower unit efficiency .
Shape 9 depicts a free-body diagram of a great epicyclic arrangement that encounters ability recirculation. A cursory analysis of this free-body diagram clarifies the 60 percent performance of the recirculating placed demonstrated in Figure 8. Because the planets are rigidly coupled jointly, the summation of forces on both gears must the same zero. The force at sunlight gear mesh outcomes from the torque source to the sun gear. The force at the second ring gear mesh outcomes 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 drive on the next planet will be approximately 14 times the pressure on the first world at the sun gear mesh. Consequently, for the summation of forces to equate to zero, the tangential load at the first ring gear should be approximately 13 times the tangential load at the sun gear. If we assume the pitch line velocities to end up being the same at sunlight mesh and band mesh, the power loss at the band mesh will be roughly 13 times greater than the power loss at the sun mesh .