epicyclic gearbox

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 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 acquired their name.
The components 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 definitely in the heart of the ring gear, and is coaxially organized in relation to the output. The sun pinion is usually attached to a clamping system in order to provide the mechanical connection to the motor shaft. During procedure, the planetary gears, which will be installed on a planetary carrier, roll between your sunshine pinion and the band gear. The planetary carrier also represents the outcome shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The number of teeth does not have any effect on the tranny ratio of the gearbox. The quantity of planets can also vary. As the amount of planetary gears heightens, the distribution of the load increases and then the torque which can be transmitted. Increasing the amount of tooth engagements likewise reduces the rolling electric power. Since only section of the total output has to be transmitted as rolling ability, a planetary gear is extremely efficient. The advantage of a planetary gear compared to a single spur gear lies in this load distribution. Hence, it is possible to transmit substantial torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear has a regular size, different ratios could be realized by different the amount of teeth of sunlight gear and the number of tooth of the planetary gears. The smaller the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary stage is approx. 3:1 to 10:1, since the planetary gears and the sun gear are extremely little above and below these ratios. Higher ratios can be obtained by connecting a variety of planetary phases in series in the same ring gear. In this case, 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 any direction of rotation. Additionally it is possible to fix the drive shaft to be able to grab the torque via the band gear. Planetary gearboxes have become extremely important in many areas 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. Huge transmission ratios can also easily be achieved with planetary gearboxes. Because of the positive properties and small design and style, the gearboxes have various potential uses in professional applications.
The features of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to many planetary gears
High efficiency due to low rolling power
Nearly unlimited transmission ratio options due to mixture of several planet stages
Appropriate 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 an array of applications
Epicyclic gearbox is an automatic type gearbox in which parallel shafts and gears arrangement from manual gear field are replaced with an increase of compact and more trusted sun and planetary type of gears arrangement as well as the manual clutch from manual electricity train is substituted with hydro coupled clutch or torque convertor which in turn made the tranny automatic.
The thought of epicyclic gear box is extracted from the solar system which is considered to an ideal 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 based on the need of the travel.
Components of Epicyclic Gearbox
1. Ring gear- This is a type of gear which appears like a ring and also have angular lower teethes at its interior surface ,and is located in outermost location in en epicyclic gearbox, the interior teethes of ring gear is in constant mesh at outer point with the set of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is put in the center of the epicyclic gearbox; the sun gear is in constant mesh at inner level with the planetary gears and is usually connected with the insight shaft of the epicyclic gear box.
One or more sun gears can be utilised for achieving different output.
3. Planet gears- These 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 equipment at both inner and outer tips 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 your ring and the sun gear exactly like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the earth gears and is in charge of final transmission of the output 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, sun gear and planetary gear 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 fact the fixing the gears i.electronic. sun gear, planetary gears and annular equipment is done to obtain the expected torque or velocity output. As fixing the above causes the variation in gear ratios from large torque to high rate. 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 planet 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 attain higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the driven member and annular the driving member in order to 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 planet gear carrier which in turn makes the annular gear the influenced member and sunlight gear the driver member.
Note- More velocity or torque ratios can be achieved by increasing the number planet and sun equipment in epicyclic gear package.
High-speed epicyclic gears can be built relatively little as the energy is distributed over a number of meshes. This results in a low power to weight ratio and, together with lower pitch collection velocity, contributes to improved efficiency. The small 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 utilized have already been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s begin by examining an essential aspect of any project: cost. Epicyclic gearing is generally less expensive, when tooled properly. Just as one wouldn’t normally consider making a 100-piece lot of gears on an N/C milling equipment 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 maintain carriers within fair manufacturing costs they must be created from castings and tooled on single-purpose machines with multiple cutters at the same time removing material.
Size is another component. Epicyclic gear pieces are used because they are smaller than offset equipment sets because the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured correctly, epicyclic gear units are more efficient. The following example illustrates these benefits. Let’s assume that we’re designing a high-speed gearbox to satisfy the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the input shaft.
• The result from the gearbox must drive a generator at 900 RPM.
• The design existence is 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 arranged and splits the two-stage lowering into two branches, and the 3rd calls for utilizing a two-level planetary or superstar epicyclic. In this instance, we chose the celebrity. Let’s examine each 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, derived from taking the square base of the final ratio (7.70). In the process of reviewing this remedy we notice its size and excess weight is very large. To reduce the weight we then explore the possibility of earning two branches of a similar arrangement, as seen in the second solutions. This cuts tooth loading and minimizes both size and pounds considerably . We finally arrive at our third remedy, which may be the two-stage star epicyclic. With three planets this equipment train reduces tooth loading considerably from the initial approach, and a relatively smaller amount from solution two (observe “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a big part of why is them so useful, yet these very characteristics could make building them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our target is to create it easy so that you can understand and use epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking for how relative speeds function together with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of sunlight, planet, and band are simply dependant on the speed of 1 member and the number of teeth in each gear.
In a planetary arrangement the ring gear is set, and planets orbit sunlight while rotating on earth shaft. In this arrangement the relative speeds of sunlight and planets are dependant on the quantity of teeth in each gear and the acceleration of the carrier.
Things get somewhat trickier whenever using coupled epicyclic gears, since relative speeds might not be intuitive. Hence, it is imperative to usually calculate the velocity of sunlight, planet, and ring relative to the carrier. Understand that actually in a solar set up where the sun is fixed it includes a speed romance 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 be considered 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 constructed with several planets is generally equal to you see, the number of planets. When more than three planets are applied, however, the effective quantity of planets is always less than the actual number of planets.
Let’s look by torque splits in terms of fixed support and floating support of the people. With fixed support, all customers are supported in bearings. The centers of the sun, ring, and carrier will not be coincident because of manufacturing tolerances. For this reason fewer planets happen to be simultaneously in mesh, resulting in a lower effective amount of planets posting the strain. With floating support, one or two members are allowed a tiny amount of radial independence or float, that allows the sun, band, and carrier to seek a posture where their centers happen to be coincident. This float could be less than .001-.002 in .. With floating support three planets will always be in mesh, resulting in a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that should be made when designing epicyclic gears. Initial we must translate RPM into mesh velocities and determine the amount of load application cycles per device of time for each and every member. The first rung on the ladder in this determination is normally to calculate the speeds of each of the members in accordance with the carrier. For example, if the sun equipment is rotating at +1700 RPM and the carrier is definitely rotating at +400 RPM the speed of the sun gear relative to 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 utilization of indications 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 acceleration between the two members is usually +1700-(-400), or +2100 RPM.
The next step is to identify the amount of load application cycles. Since the sun and ring gears mesh with multiple planets, the number of load cycles per revolution relative to the carrier will be equal to the quantity of planets. The planets, however, will experience only one bi-directional load program per relative revolution. It meshes with sunlight and ring, however the load is usually on opposite sides of the teeth, leading to one fully reversed tension cycle. Thus the planet is known as an idler, and the allowable anxiety must be reduced 30 percent from the value for a unidirectional load software.
As noted above, the torque on the epicyclic members is divided among the planets. In analyzing the stress and existence of the users we must look at the resultant loading at each mesh. We get the idea of torque per mesh to become relatively confusing in epicyclic equipment evaluation 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 consider the torque on the sun gear and divide it by the effective quantity of planets and the operating pitch radius. This tangential load, combined with peripheral speed, is utilized to compute the energy transmitted at each mesh and, altered by the strain cycles per revolution, the life span expectancy of each component.
In addition to these issues there can also be assembly complications that require addressing. For example, positioning one planet in a position between sun and band fixes the angular situation of sunlight to the ring. The next planet(s) is now able to be assembled simply in discreet locations where the sun and band could be concurrently engaged. The “least mesh angle” from the 1st 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. Therefore, in order to assemble extra planets, they must become spaced at multiples of this least mesh angle. If one wants to have the same 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 band 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 provides another degree of complexity, and appropriate planet spacing may necessitate match marking of teeth.
With multiple parts in mesh, losses need to be considered at each mesh so as to evaluate the efficiency of the unit. Ability transmitted at each mesh, not input power, must be used to compute power reduction. For simple epicyclic units, the total ability transmitted through the sun-world mesh and ring-planet mesh may be less than input vitality. This is one of the reasons that easy planetary epicyclic sets are more efficient than other reducer plans. In contrast, for most coupled epicyclic sets total electrical power transmitted internally through each mesh may be greater than input power.
What of vitality at the mesh? For simple and compound epicyclic models, calculate pitch brand velocities and tangential loads to compute electrical power at each mesh. Values can be acquired from the earth torque relative swiftness, and the functioning pitch diameters with sunshine and band. Coupled epicyclic models present more complex issues. Components of two epicyclic sets can be coupled 36 different ways using one type, one outcome, and one response. Some plans split the power, while some recirculate electric power internally. For these types of epicyclic pieces, tangential loads at each mesh can only just be established through the usage of free-body diagrams. Also, the components of two epicyclic pieces can be coupled nine various ways in a string, using one suggestions, one result, and two reactions. Let’s look at a few examples.
In the “split-electrical power” coupled set shown in Figure 7, 85 percent of the transmitted ability flows to ring gear #1 and 15 percent to band gear #2. The result is that coupled gear set can be more compact than series coupled pieces because the electricity is split between your two factors. When coupling epicyclic units in a string, 0 percent of the power will be transmitted through each set.
Our next example depicts a collection with “vitality recirculation.” This gear set comes about when torque gets locked in the system in a way similar to what occurs in a “four-square” test procedure for vehicle drive axles. With the torque locked in the machine, the horsepower at each mesh within the loop raises as speed increases. As a result, this set will experience much higher vitality losses at each mesh, resulting in significantly lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that activities ability recirculation. A cursory examination of this free-physique diagram clarifies the 60 percent productivity of the recirculating establish shown in Figure 8. Since the planets happen to be rigidly coupled collectively, the summation of forces on both gears must the same zero. The pressure at sunlight gear mesh benefits from the torque insight to sunlight gear. The induce at the second ring gear mesh results from the productivity torque on the ring equipment. The ratio being 41.1:1, outcome torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the pressure on the next planet will be approximately 14 times the push on the first planet at sunlight 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 circumstances the tangential load at the sun gear. If we believe the pitch range velocities to be the same at the sun mesh and ring mesh, the power loss at the band mesh will be about 13 times higher than the power loss at the sun mesh .