epicyclic gearbox

In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference work 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 acquired their name.
The pieces 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 generating sun pinion is in the center 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 connection to the engine shaft. During operation, the planetary gears, which will be attached on a planetary carrier, roll between the sunlight pinion and the band equipment. The planetary carrier as well represents the result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The quantity of teeth does not have any effect on the transmission ratio of the gearbox. The amount of planets may also vary. As the number of planetary gears heightens, the distribution of the load increases and then the torque that can be transmitted. Increasing the number of tooth engagements as well reduces the rolling power. Since only part of the total result has to be transmitted as rolling ability, a planetary equipment is incredibly efficient. The good thing about a planetary gear compared to a single spur gear is based on this load distribution. Hence, it is possible to transmit large torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear includes a frequent size, different ratios could be realized by varying the amount of teeth of the sun gear and the number of pearly whites of the planetary gears. Small the sun gear, 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 sunlight gear are extremely tiny above and below these ratios. Larger ratios can be obtained by connecting several planetary stages in series in the same ring gear. In cases like this, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a ring gear that’s not fixed but is driven in virtually any direction of rotation. Additionally it is possible to repair the drive shaft in order to grab the torque via the ring equipment. Planetary gearboxes have become extremely important in many 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. Large transmission ratios can also easily be achieved with planetary gearboxes. Because of the positive properties and small style, the gearboxes have a large number of potential uses in industrial 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
Nearly unlimited transmission ratio options due to combo of several planet stages
Suited as planetary switching gear because of fixing this or that part of the gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears set up from manual gear field are replaced with more compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual electric 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 considered to the perfect arrangement of objects.
The epicyclic gearbox usually includes the P N R D S (Parking, Neutral, Reverse, Drive, Sport) modes 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 looks like a ring and also have angular slice teethes at its internal surface ,and is placed in outermost posture in en epicyclic gearbox, the inner teethes of ring gear is in constant mesh at outer point with the group of planetary gears ,it is also known as annular ring.
2. Sun gear- It’s the gear with angular minimize teethes and is put in the center of the epicyclic gearbox; sunlight gear is in constant mesh at inner point with the planetary gears and can be connected with the suggestions shaft of the epicyclic equipment box.
One or more sun gears can be utilised for attaining different output.
3. Planet gears- They are small gears used in between ring and sun equipment , the teethes of the earth gears are in frequent mesh with the sun and the ring gear at both the inner and outer factors respectively.
The axis of the planet 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 planet gears and is accountable for final transmission of the productivity to the end result 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- The device used to repair the annular gear, sunlight 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 based on the fact the fixing any of the gears i.electronic. sun gear, planetary gears and annular equipment is done to obtain the needed torque or quickness output. As fixing any of the above causes the variation in gear ratios from excessive 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 automobile to go from its initial state and is obtained by fixing the annular gear which causes the planet carrier to rotate with the energy supplied to sunlight gear.
Second gear ratio
This gives high speed ratios to the vehicle which helps the vehicle to realize higher speed throughout a travel, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the motivated member and annular the driving 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 vehicle, this gear is achieved by fixing the earth gear carrier which in turn makes the annular gear the motivated member and sunlight gear the driver member.
Note- More acceleration or torque ratios may be accomplished by increasing the number planet and sun gear in epicyclic gear package.
High-speed epicyclic gears could be built relatively small as the power is distributed over a lot of meshes. This effects in a low capacity to excess weight ratio and, as well as lower pitch collection 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.
Why epicyclic gearing is used have been covered in this magazine, so we’ll expand on this issue in only a few places. Let’s begin by examining a significant aspect of any project: cost. Epicyclic gearing is normally less expensive, when tooled properly. Being an would not consider making a 100-piece lot of gears on an N/C milling equipment with a form cutter or ball end mill, you need to not really consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To preserve carriers within affordable manufacturing costs they must be made from castings and tooled on single-purpose equipment with multiple cutters at the same time removing material.
Size is another factor. Epicyclic gear units are used because they’re smaller than offset gear sets because the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured properly, epicyclic gear sets are more efficient. The next example illustrates these benefits. Let’s assume that we’re developing a high-speed gearbox to satisfy the following requirements:
• A turbine gives 6,000 hp at 16,000 RPM to the source shaft.
• The productivity from the gearbox must drive a generator at 900 RPM.
• The design existence is usually to be 10,000 hours.
With these requirements at heart, let’s look at three feasible solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear establish and splits the two-stage lowering into two branches, and the 3rd calls for using a two-level planetary or celebrity epicyclic. In this instance, we chose the superstar. 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 base of the final ratio (7.70). In the process of reviewing this solution we realize its size and fat is very large. To reduce the weight we after that explore the possibility of making two branches of a similar arrangement, as seen in the second alternatives. This cuts tooth loading and reduces both size and fat considerably . We finally arrive at our third alternative, which is the two-stage superstar epicyclic. With three planets this equipment train minimizes tooth loading significantly from the primary approach, and a somewhat smaller amount from choice two (observe “methodology” at end, and Figure 6).
The unique design characteristics of epicyclic gears are a large part of what makes them so useful, but these very characteristics can make designing them a challenge. In 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 work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking for how relative speeds operate in conjunction with different arrangements. In the star set up 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 gear.
In a planetary arrangement the band gear is set, and planets orbit the sun 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 rate of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to at all times calculate the velocity of the sun, planet, and ring relative to the carrier. Remember that possibly in a solar set up where the sun is fixed it has a speed marriage with the planet-it is not zero RPM at the mesh.
Torque Splits
When contemplating torque splits one assumes the torque to be divided among the planets equally, but this may well not be a valid assumption. Member support and the number of planets determine the torque split represented by an “effective” number of planets. This number in epicyclic sets designed with two or three planets is in most cases equal to some of the number of planets. When a lot more than three planets are applied, however, the effective quantity of planets is generally less than the actual number of planets.
Let’s look at torque splits regarding set support and floating support of the participants. With fixed support, all customers are backed in bearings. The centers of sunlight, ring, and carrier will not be coincident because of manufacturing tolerances. For that reason fewer planets happen to be simultaneously in mesh, resulting in a lower effective number of planets sharing the load. With floating support, one or two members are allowed a tiny amount of radial freedom or float, that allows the sun, ring, and carrier to get a position where their centers are coincident. This float could be as little as .001-.002 ins. With floating support three planets will always be in mesh, producing a higher effective quantity of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors 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 unit of time for each and every member. The first rung on the ladder in this determination is certainly to calculate the speeds of each of the members relative to the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the speed of sunlight gear relative to 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 utilization of signals to signify 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 normally +1700-(-400), or +2100 RPM.
The next step is to determine the number of load application cycles. Since the sun and band gears mesh with multiple planets, the number of load cycles per revolution relative to the carrier will always be equal to the number of planets. The planets, however, will experience only 1 bi-directional load program per relative revolution. It meshes with sunlight and ring, however the load can be on opposing sides of the teeth, resulting in one fully reversed tension cycle. Thus the earth is considered an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load app.
As noted over, the torque on the epicyclic customers is divided among the planets. In analyzing the stress and life of the participants we must look at the resultant loading at each mesh. We locate the idea of torque per mesh to become relatively confusing in epicyclic equipment analysis and prefer to look at the tangential load at each mesh. For instance, in searching at the tangential load at the sun-planet mesh, we have the torque on the sun gear and divide it by the successful number of planets and the working pitch radius. This tangential load, combined with the peripheral speed, is utilized to compute the energy transmitted at each mesh and, modified by the strain cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, placing one planet ready between sun and band fixes the angular position of the sun to the ring. Another planet(s) can now be assembled simply in discreet locations where the sun and band can be simultaneously engaged. The “least mesh angle” from the initially planet that will accommodate simultaneous mesh of the next planet is equal to 360° divided by the sum of the numbers of teeth in sunlight and the ring. As a result, so that you can assemble more planets, they must be spaced at multiples of this least mesh position. If one wants to have equal spacing of the planets in a straightforward epicyclic set, planets could be spaced similarly when the sum of the amount of teeth in sunlight and band is usually divisible by the amount of planets to an integer. The same rules apply in a compound epicyclic, but the set coupling of the planets contributes another level of complexity, and right planet spacing may necessitate match marking of teeth.
With multiple components in mesh, losses should be considered at each mesh so that you can evaluate the efficiency of the unit. Power transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic pieces, the total electrical power transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input electrical power. This is among the reasons that easy planetary epicyclic pieces are more efficient than other reducer plans. In contrast, for many coupled epicyclic pieces total electrical power transmitted internally through each mesh may be greater than input power.
What of electric power at the mesh? For straightforward and compound epicyclic sets, calculate pitch collection velocities and tangential loads to compute electrical power at each mesh. Values can be acquired from the earth torque relative rate, and the working pitch diameters with sun and ring. Coupled epicyclic models present more technical issues. Elements of two epicyclic sets could be coupled 36 various ways using one source, one output, and one response. Some plans split the power, while some recirculate electric power internally. For these kind of epicyclic pieces, tangential loads at each mesh can only be motivated through the use of free-body diagrams. On top of that, the components of two epicyclic pieces can be coupled nine different ways in a series, using one source, one result, and two reactions. Let’s look at some examples.
In the “split-vitality” coupled set shown in Figure 7, 85 percent of the transmitted electric power flows to ring gear #1 and 15 percent to ring gear #2. The effect is that coupled gear set can be more compact than series coupled models because the electrical power is split between your two elements. When coupling epicyclic models in a series, 0 percent of the power will be transmitted through each set.
Our next case in point depicts a arranged with “electrical power recirculation.” This equipment set comes about when torque gets locked in the machine in a way similar to what occurs in a “four-square” test process of vehicle drive axles. With the torque locked in the system, the hp at each mesh within the loop improves as speed increases. Therefore, this set will experience much higher vitality losses at each mesh, resulting in substantially lower unit efficiency .
Determine 9 depicts a free-body diagram of an epicyclic arrangement that experience vitality recirculation. A cursory examination of this free-physique diagram explains the 60 percent effectiveness of the recirculating arranged demonstrated in Figure 8. Since the planets happen to be rigidly coupled together, the summation of forces on both gears must equal zero. The induce at the sun gear mesh outcomes from the torque insight to the sun gear. The power at the second ring gear mesh benefits from the end result torque on the ring gear. The ratio being 41.1:1, end result torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the pressure on the second planet will be roughly 14 times the push 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 band gear must be approximately 13 occasions the tangential load at sunlight gear. If we assume the pitch line velocities to be the same at sunlight mesh and ring mesh, the power loss at the ring mesh will be roughly 13 times greater than the energy loss at the sun mesh .