epicyclic gearbox

In 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 external teeth on a concentric orbit. The circulation of the spur equipment takes place in analogy to the orbiting of the planets in the solar system. This is one way planetary gears acquired their name.
The elements of a planetary gear train could be split into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In the majority of cases the housing is fixed. The traveling sun pinion can be in the heart of the ring gear, and is coaxially organized in relation to the output. Sunlight pinion is usually attached to a clamping system in order to present the mechanical link with the electric motor shaft. During operation, the planetary gears, which are mounted on a planetary carrier, roll between the sunlight pinion and the ring equipment. The planetary carrier also represents the outcome shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The number of teeth has no effect on the tranny ratio of the gearbox. The number of planets may also vary. As the number of planetary gears enhances, the distribution of the strain increases and therefore the torque that can be transmitted. Raising the amount of tooth engagements also reduces the rolling electricity. Since only portion of the total result needs to be transmitted as rolling power, a planetary equipment is extremely efficient. The good thing about a planetary gear compared to a single spur gear is based on 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 has a constant size, different ratios could be realized by different the quantity of teeth of the sun gear and the amount of pearly whites of the planetary gears. Small the sun gear, the greater the ratio. Technically, a meaningful ratio range for a planetary level is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely small above and below these ratios. Higher ratios can be acquired by connecting several planetary phases in series in the same band gear. In this case, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a ring gear that’s not set but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft to be able to pick up the torque via the ring gear. Planetary gearboxes have become extremely important in lots of regions 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 can 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 features 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 due to combination of several planet stages
Ideal as planetary switching gear due to 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 can be an automatic type gearbox in which parallel shafts and gears arrangement from manual gear field are replaced with more compact and more trusted sun and planetary kind of gears arrangement plus the manual clutch from manual vitality train is replaced with hydro coupled clutch or torque convertor which made the transmission 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) settings which is obtained by fixing of sun and planetary gears according to the need of the travel.
Components of Epicyclic Gearbox
1. Ring gear- It is a type of gear which appears like a ring and have angular slice teethes at its internal surface ,and is placed in outermost posture in en epicyclic gearbox, the interior teethes of ring equipment is in frequent mesh at outer point with the set of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It is the equipment with angular minimize teethes and is located in the center of the epicyclic gearbox; sunlight gear is in frequent mesh at inner point with the planetary gears and can be connected with the suggestions shaft of the epicyclic gear box.
One or more sunshine gears can be utilised for achieving different output.
3. Planet gears- They are small gears found in between ring 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 factors 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 also can revolve between your ring and the sun gear exactly like our solar system.
4. Planet carrier- This is a carrier fastened with the axis of the planet gears and is in charge of final transmission of the output to the 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 fix the annular gear, sunshine gear and planetary gear and is controlled 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 the gears i.e. sun gear, planetary gears and annular gear is done to obtain the necessary torque or swiftness output. As fixing any of the above causes the variation in equipment ratios from high 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 move 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 automobile to realize higher speed throughout a travel, these ratios are obtained by fixing the sun gear which in turn makes the earth carrier the powered 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 achieved by fixing the planet gear carrier which makes the annular gear the influenced member and the sun gear the driver member.
Note- More acceleration or torque ratios may be accomplished by increasing the number planet and sun equipment in epicyclic gear package.
High-speed epicyclic gears could be built relatively small as the power is distributed over several meshes. This results in a low capacity to excess weight ratio and, together with lower pitch series velocity, contributes to improved efficiency. The tiny equipment diameters produce lower occasions of inertia, significantly lowering 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 can be used have already been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s start by examining a significant aspect of any project: price. Epicyclic gearing is normally less costly, when tooled properly. Being an would not consider making a 100-piece lot of gears on an N/C milling machine with a form cutter or ball end mill, one should not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To keep carriers within realistic manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters simultaneously removing material.
Size is another aspect. Epicyclic gear sets 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 more compact, versus countershaft gearboxes. Also, when configured correctly, epicyclic gear units are more efficient. The following example illustrates these rewards. Let’s believe that we’re developing a high-speed gearbox to fulfill the following requirements:
• A turbine delivers 6,000 hp at 16,000 RPM to the insight 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 in mind, let’s look at three possible solutions, one involving a single branch, two-stage helical gear set. Another solution takes the original gear established and splits the two-stage reduction into two branches, and the 3rd calls for utilizing a two-level planetary or celebrity epicyclic. In this situation, 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, derived from taking the square root of the final ratio (7.70). Along the way of reviewing this choice we notice its size and excess weight is very large. To reduce the weight we in that case explore the possibility of making two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and reduces both size and fat considerably . We finally arrive at our third option, which may be the two-stage celebrity epicyclic. With three planets this equipment train decreases tooth loading considerably from the initial approach, and a somewhat smaller amount from answer two (observe “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a huge part of why is them so useful, however these very characteristics could make developing them a challenge. In 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 style characteristics.
Relative Speeds
Let’s get started by looking at how relative speeds job together with different arrangements. In the star arrangement the carrier is set, and the relative speeds of the sun, planet, and ring are simply dependant on the speed of one member and the amount of teeth in each gear.
In a planetary arrangement the ring gear is set, and planets orbit the sun while rotating on earth shaft. In this set up the relative speeds of sunlight and planets are dependant on the number of teeth in each equipment and the velocity of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds may not be intuitive. It is therefore imperative to generally calculate the velocity of sunlight, planet, and ring relative to the carrier. Understand that actually in a solar arrangement where the sun is fixed it includes a speed relationship 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 might not exactly be considered a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” amount of planets. This number in epicyclic sets constructed with several planets is generally equal to you see, the quantity of planets. When a lot more than three planets are employed, however, the effective amount of planets is at all times less than using the number of planets.
Let’s look in torque splits in conditions of fixed support and floating support of the members. With set support, all customers are supported in bearings. The centers of sunlight, band, and carrier will not be coincident due to manufacturing tolerances. For that reason fewer planets are simultaneously in mesh, resulting in a lower effective quantity of planets sharing the load. With floating support, one or two customers are allowed a little amount of radial liberty or float, which allows the sun, band, and carrier to seek a posture where their centers happen to be coincident. This float could possibly be as little as .001-.002 in .. With floating support three planets will always be in mesh, resulting in a higher effective number of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh considerations that needs to be made when designing epicyclic gears. 1st we must translate RPM into mesh velocities and determine the amount of load request cycles per product of time for every member. The first rung on the ladder in this determination is to calculate the speeds of each of the members in accordance with the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the quickness of the sun gear in accordance with the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that quickness and the numbers of teeth in each of the gears. The make use of signals to represent 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 quickness between the two people is normally +1700-(-400), or +2100 RPM.
The next step is to decide the number of load application cycles. Because the sun and ring gears mesh with multiple planets, the number of load cycles per revolution in accordance with the carrier will be equal to the amount of planets. The planets, however, will experience only one bi-directional load request per relative revolution. It meshes with sunlight and ring, but the load can be on opposing sides of the teeth, leading to one fully reversed tension cycle. Thus the earth is considered an idler, and the allowable tension must be reduced 30 percent from the value for a unidirectional load request.
As noted above, the torque on the epicyclic users is divided among the planets. In examining the stress and existence of the associates we must consider the resultant loading at each mesh. We locate the idea of torque per mesh to be somewhat confusing in epicyclic equipment research and prefer to check out the tangential load at each mesh. For example, in seeking at the tangential load at the sun-planet mesh, we have the torque on the sun gear and divide it by the powerful amount of planets and the functioning pitch radius. This tangential load, combined with the peripheral speed, is utilized to compute the power transmitted at each mesh and, adjusted by the load cycles per revolution, the life expectancy of every component.
In addition to these issues there can also be assembly complications that need addressing. For example, positioning one planet in a position 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 ring can be concurrently engaged. The “least mesh angle” from the 1st planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the numbers of teeth in the sun and the ring. As a result, to be able to assemble more planets, they must be spaced at multiples of this least mesh position. If one wishes to have equal spacing of the planets in a simple epicyclic set, planets could be spaced equally when the sum of the number of teeth in the sun and band can be divisible by the amount of planets to an integer. The same rules apply in a substance epicyclic, but the set coupling of the planets offers another level of complexity, and proper planet spacing may require match marking of pearly whites.
With multiple pieces in mesh, losses need to be considered at each mesh to be able to evaluate the efficiency of the machine. Power transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic sets, the total power transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input electricity. This is among 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 higher than input power.
What of ability at the mesh? For basic and compound epicyclic pieces, calculate pitch collection velocities and tangential loads to compute power at each mesh. Ideals can be obtained from the earth torque relative quickness, and the working pitch diameters with sunlight and band. Coupled epicyclic sets present more complex issues. Components of two epicyclic units can be coupled 36 various ways using one input, one output, and one response. Some arrangements split the power, although some recirculate electric power internally. For these kinds of epicyclic pieces, tangential loads at each mesh can only be established through the use of free-body diagrams. On top of that, the factors of two epicyclic units could be coupled nine different ways in a series, using one source, one output, and two reactions. Let’s look at some examples.
In the “split-ability” coupled set shown in Figure 7, 85 percent of the transmitted vitality flows to ring gear #1 and 15 percent to band gear #2. The result is that this coupled gear set can be small than series coupled sets because the electrical power is split between the two elements. When coupling epicyclic pieces in a string, 0 percent of the energy will always be transmitted through each set.
Our next example depicts a collection with “ability 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 system, the hp at each mesh within the loop boosts as speed increases. Consequently, this set will knowledge much higher vitality losses at each mesh, resulting in drastically lower unit efficiency .
Body 9 depicts a free-body diagram of an epicyclic arrangement that experiences ability recirculation. A cursory analysis of this free-physique diagram clarifies the 60 percent efficiency of the recirculating arranged demonstrated in Figure 8. Because the planets will be rigidly coupled at the same time, the summation of forces on the two gears must equivalent zero. The pressure at sunlight gear mesh benefits from the torque source to the sun gear. The induce at the second ring gear mesh results from the 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 big difference of, say, 3:1, the force on the second planet will be around 14 times the push on the first world at sunlight gear mesh. Consequently, for the summation of forces to equate to zero, the tangential load at the first ring gear must be approximately 13 moments the tangential load at sunlight gear. If we presume the pitch line velocities to always be the same at the sun mesh and band mesh, the power loss at the band mesh will be about 13 times higher than the power loss at sunlight mesh .