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 occurs in analogy to the orbiting of the planets in the solar program. This is one way planetary gears obtained their name.
The components of a planetary gear train can be divided into four main constituents.
The housing with integrated internal teeth is actually a ring gear. In nearly all cases the housing is fixed. The traveling sun pinion is in the heart of the ring gear, and is coaxially organized with regards to the output. The sun pinion is usually attached to a clamping system in order to give the mechanical link with the engine shaft. During procedure, the planetary gears, which happen to be installed on a planetary carrier, roll between the sunlight pinion and the band gear. The planetary carrier also represents the end result shaft of the gearbox.
The sole reason for the planetary gears is to transfer the mandatory torque. The amount of teeth does not have any effect on the tranny ratio of the gearbox. The number of planets may also vary. As the quantity of planetary gears improves, the distribution of the strain increases and then the torque which can be transmitted. Raising the number of tooth engagements as well reduces the rolling ability. Since only area of the total output must be transmitted as rolling power, a planetary gear is incredibly efficient. The advantage of a planetary equipment compared to a single spur gear lies in this load distribution. Hence, it is possible to transmit great torques wit
h high efficiency with a concise style using planetary gears.
So long as the ring gear includes a continuous size, different ratios could be realized by varying the number of teeth of the sun gear and the number of tooth 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, since the planetary gears and the sun gear are extremely little above and below these ratios. Bigger ratios can be obtained by connecting many planetary phases in series in the same ring gear. In cases like this, we talk about multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that is not set but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft so as to grab the torque via the band equipment. Planetary gearboxes have grown to be extremely important in lots of areas 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. Great transmission ratios may also easily be achieved with planetary gearboxes. Because of the positive properties and small design, the gearboxes have many 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
Almost unlimited transmission ratio options due to mixture of several planet stages
Suited as planetary switching gear because of fixing this or that the main gearbox
Chance for use as overriding gearbox
Favorable volume output
Suitability for an array of applications
Epicyclic gearbox is an automatic type gearbox where parallel shafts and gears set up from manual gear field are replaced with more compact and more reliable sun and planetary kind of gears arrangement plus the manual clutch from manual electric power train is replaced with hydro coupled clutch or torque convertor which in turn made the tranny automatic.
The thought of epicyclic gear box is taken 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, Travel, Sport) settings which is obtained by fixing of sun and planetary gears based on the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- It is a kind of gear which appears like a ring and have angular cut teethes at its inner surface ,and is positioned in outermost placement in en epicyclic gearbox, the inner teethes of ring equipment is in frequent mesh at outer point with the group of planetary gears ,additionally it is referred to as annular ring.
2. Sun gear- It is the gear with angular slice teethes and is placed in the center of the epicyclic gearbox; sunlight gear is in frequent mesh at inner stage with the planetary gears and is connected with the input shaft of the epicyclic equipment box.
One or more sun gears can be used for attaining different output.
3. Planet gears- These are small gears used in between ring and sun equipment , the teethes of the earth gears are in continuous mesh with the sun and the ring equipment at both the inner and outer items 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 the 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 accountable for final tranny of the end result to the outcome 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 equipment and is controlled by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the actual fact the fixing any of the gears i.e. sun equipment, planetary gears and annular equipment is done to get the needed torque or velocity output. As fixing any of the above causes the variation in gear ratios from high torque to high velocity. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the automobile which helps the vehicle 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 power supplied to the sun gear.
Second gear ratio
This gives high speed ratios to the vehicle which helps the automobile to achieve higher speed during a drive, these ratios are obtained by fixing sunlight gear which in turn makes the planet carrier the powered member and annular the driving a vehicle member to be able 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 vehicle, this gear is achieved by fixing the earth gear carrier which makes the annular gear the driven member and sunlight gear the driver member.
Note- More quickness or torque ratios may be accomplished by increasing the number planet and sun gear in epicyclic gear container.
High-speed epicyclic gears can be built relatively small as the power is distributed over a lot of meshes. This effects in a low capacity to pounds ratio and, as well as lower pitch brand velocity, brings about improved efficiency. The small gear diameters produce lower moments of inertia, significantly lowering 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 used have already been covered in this magazine, so we’ll expand on the topic in only a few places. Let’s get started by examining an important aspect of any project: cost. Epicyclic gearing is normally less costly, when tooled properly. Being an wouldn’t normally 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 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 devices with multiple cutters at the same time removing material.
Size is another component. Epicyclic gear sets are used because they’re smaller than offset equipment sets because the load is normally shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured effectively, epicyclic gear sets are more efficient. The next example illustrates these rewards. Let’s presume that we’re designing a high-speed gearbox to meet the following requirements:
• A turbine delivers 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 existence is to be 10,000 hours.
With these requirements at heart, let’s look at three conceivable solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear placed and splits the two-stage reduction into two branches, and the 3rd calls for using a two-stage planetary or star epicyclic. In this instance, we chose the celebrity. 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 remedy we notice its size and excess weight is very large. To lessen the weight we then explore the possibility of making two branches of a similar arrangement, as seen in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally reach our third solution, which may be the two-stage celebrity epicyclic. With three planets this equipment train reduces tooth loading substantially from the initial approach, and a relatively smaller amount from choice two (check out “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 can make building them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our target is to create it easy for you to understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s get started by looking for how relative speeds job in conjunction with different arrangements. In the star arrangement the carrier is set, 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 equipment.
In a planetary arrangement the band gear is set, and planets orbit the sun while rotating on the planet shaft. In this set up the relative speeds of sunlight and planets are determined by the number of teeth in each gear and the rate of the carrier.
Things get somewhat trickier when working with coupled epicyclic gears, since relative speeds might not be intuitive. It is therefore imperative to constantly calculate the quickness of sunlight, planet, and ring relative to the carrier. Remember that even in a solar arrangement where the sunlight is fixed it includes a speed romantic 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 may not be 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 designed with several planets is generally equal to the actual number of planets. When more than three planets are used, however, the effective quantity of planets is at all times less than using the number of planets.
Let’s look in torque splits in terms of fixed support and floating support of the associates. With fixed support, all users are backed in bearings. The centers of the sun, ring, and carrier will not be coincident because of 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 participants are allowed a small amount of radial flexibility or float, which allows the sun, ring, and carrier to seek a posture where their centers are coincident. This float could possibly be as little as .001-.002 ins. With floating support three planets will be in mesh, producing a higher effective amount of planets sharing the load.
Multiple Mesh Considerations
At this time let’s explore the multiple mesh factors that needs to be made when making epicyclic gears. 1st we must translate RPM into mesh velocities and determine the quantity of load app cycles per unit 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 gear is rotating at +1700 RPM and the carrier is usually rotating at +400 RPM the rate of the sun gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that velocity and the numbers of teeth in each of the gears. The utilization of indicators to represent clockwise and counter-clockwise rotation can be important here. If the sun is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative swiftness between the two participants is definitely +1700-(-400), or +2100 RPM.
The second step is to decide the amount 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 become equal to the number of planets. The planets, however, will experience only 1 bi-directional load request per relative revolution. It meshes with the sun and ring, however the load is normally on opposing sides of the teeth, resulting in one fully reversed anxiety cycle. Thus the planet is considered an idler, and the allowable stress must be reduced thirty percent from the worthiness for a unidirectional load request.
As noted over, the torque on the epicyclic customers is divided among the planets. In examining the stress and your life of the members we must look at the resultant loading at each mesh. We discover the idea of torque per mesh to always be somewhat confusing in epicyclic equipment analysis and prefer to check out the tangential load at each mesh. For example, in searching at the tangential load at the sun-world mesh, we take the torque on the sun gear and divide it by the powerful quantity of planets and the working pitch radius. This tangential load, combined with peripheral speed, can be used to compute the power transmitted at each mesh and, adjusted by the load 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, inserting one planet in a position between sun and band fixes the angular situation of the sun to the ring. Another planet(s) is now able to be assembled just in discreet locations where in fact the sun and band could be at the same time engaged. The “least mesh angle” from the initially planet that will support simultaneous mesh of the next planet is equal 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 end up being spaced at multiples of this least mesh angle. If one wants to have equivalent spacing of the planets in a straightforward epicyclic set, planets could be spaced similarly when the sum of the amount of teeth in the sun and band is divisible by the number of planets to an integer. The same rules apply in a compound epicyclic, but the fixed coupling of the planets contributes another level of complexity, and proper planet spacing may require match marking of the teeth.
With multiple parts in mesh, losses need to be considered at each mesh to be able to measure the efficiency of the unit. Electric power transmitted at each mesh, not input power, must be used to compute power loss. For simple epicyclic pieces, the total vitality transmitted through the sun-world mesh and ring-world mesh may be less than input ability. This is among the reasons that easy planetary epicyclic units are better than other reducer plans. In contrast, for most coupled epicyclic pieces total vitality transmitted internally through each mesh could be greater than input power.
What of electricity at the mesh? For basic and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute ability at each mesh. Values can be acquired from the earth torque relative speed, and the operating pitch diameters with sunshine and band. Coupled epicyclic models present more complex issues. Elements of two epicyclic units can be coupled 36 various ways using one suggestions, one productivity, and one response. Some plans split the power, while some recirculate ability internally. For these kind of epicyclic pieces, tangential loads at each mesh can only be determined through the use of free-body diagrams. On top of that, the components of two epicyclic units can be coupled nine different ways in a string, using one input, one end result, and two reactions. Let’s look at some examples.
In the “split-electric power” coupled set displayed in Figure 7, 85 percent of the transmitted ability flows to ring gear #1 and 15 percent to ring gear #2. The result is that this coupled gear set could be small than series coupled units because the power is split between the two elements. When coupling epicyclic sets in a series, 0 percent of the energy will always be transmitted through each set.
Our next case in point depicts a establish with “vitality recirculation.” This gear set comes about when torque gets locked in the system in a manner similar to what occurs in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the horsepower at each mesh within the loop increases as speed increases. As a result, this set will experience much higher electrical power losses at each mesh, resulting in considerably lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that experience ability recirculation. A cursory evaluation of this free-physique diagram clarifies the 60 percent effectiveness of the recirculating collection shown in Figure 8. Because the planets are rigidly coupled jointly, the summation of forces on the two gears must equal zero. The force at sunlight gear mesh results from the torque type to the sun gear. The power at the next ring gear mesh effects from the outcome 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 drive on the second planet will be approximately 14 times the drive on the first world at the sun gear mesh. As a result, 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 assume the pitch collection velocities to become the same at the sun mesh and ring mesh, the power loss at the band mesh will be approximately 13 times higher than the power loss at the sun mesh .