epicyclic gearbox

Within 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 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 obtained their name.
The parts of a planetary gear train can be divided 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 driving sun pinion is definitely in the center of the ring gear, and is coaxially arranged in relation to the output. Sunlight pinion is usually attached to a clamping system in order to offer the mechanical link with the engine shaft. During operation, the planetary gears, which will be attached on a planetary carrier, roll between the sunshine pinion and the ring gear. The planetary carrier likewise represents the productivity shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The amount of teeth has no effect on the transmitting ratio of the gearbox. The number of planets can also vary. As the quantity of planetary gears raises, the distribution of the load increases and then the torque which can be transmitted. Raising the quantity of tooth engagements as well reduces the rolling ability. Since only area of the total result needs to be transmitted as rolling power, a planetary gear is extremely efficient. The benefit of a planetary equipment compared to an individual spur gear is based on this load distribution. It is therefore possible to transmit substantial torques wit
h high efficiency with a compact design and style using planetary gears.
So long as the ring gear includes 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 higher the ratio. Technically, a meaningful ratio range for a planetary stage is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely tiny above and below these ratios. Larger ratios can be acquired by connecting several planetary phases in series in the same band gear. In this instance, we talk about 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 any direction of rotation. It is also possible to fix the drive shaft so as to grab the torque via the ring gear. Planetary gearboxes have become extremely important in lots of regions of mechanical engineering.
They have become particularly well established 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 achieved with planetary gearboxes. Because of their positive properties and small design, the gearboxes have many potential uses in professional 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 blend of several planet stages
Ideal as planetary switching gear because of 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 is an automatic type gearbox where parallel shafts and gears set up from manual gear box are replaced with an increase of compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual vitality train is replaced with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The idea of epicyclic gear box is extracted from the solar system which is known as to the perfect arrangement of objects.
The epicyclic gearbox usually comes with the P N R D S (Parking, Neutral, Reverse, Travel, Sport) modes which is obtained by fixing of sun and planetary gears based on the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a type of gear which appears like a ring and have angular trim teethes at its inner surface ,and is located in outermost location in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer point with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the gear with angular minimize teethes and is located in the center of the epicyclic gearbox; the sun gear is in continuous mesh at inner point with the planetary gears and is usually connected with the suggestions shaft of the epicyclic equipment box.
One or more sunlight gears can be used 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 constant mesh with the sun and the ring equipment at both 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 your ring and sunlight gear just like our solar system.
4. Planet carrier- This is a carrier attached with the axis of the planet gears and is responsible for final transmission of the end result to the output 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, sunlight gear and planetary equipment and is manipulated by the brake or clutch of the vehicle.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the fact the fixing the gears i.e. sun gear, planetary gears and annular gear is done to obtain the expected torque or rate output. As fixing any of the above triggers the variation in gear ratios from excessive torque to high swiftness. So let’s observe 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 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 makes the planet carrier the powered member and annular the generating 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 planet gear carrier which makes the annular gear the powered member and sunlight gear the driver member.
Note- More velocity or torque ratios can be achieved by increasing the number planet and sun gear in epicyclic gear container.
High-speed epicyclic gears can be built relatively tiny as the energy is distributed over a lot of meshes. This outcomes in a low capacity to excess weight ratio and, together with lower pitch range velocity, brings about improved efficiency. The small gear diameters produce lower moments 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.
The reasons why epicyclic gearing is utilized have been covered in this magazine, so we’ll expand on the topic in just a few places. Let’s begin by examining a significant aspect of any project: price. Epicyclic gearing is generally less costly, 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 consider making a 100-piece lot of epicyclic carriers on an N/C mill. To continue to keep carriers within acceptable manufacturing costs they must be made from castings and tooled on single-purpose devices with multiple cutters simultaneously removing material.
Size is another issue. Epicyclic gear sets are used because they are smaller than offset equipment sets since the load is shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. Likewise, when configured effectively, epicyclic gear models are more efficient. The next example illustrates these rewards. Let’s presume that we’re developing a high-speed gearbox to fulfill the following requirements:
• A turbine delivers 6,000 horsepower at 16,000 RPM to the insight shaft.
• The outcome from the gearbox must travel a generator at 900 RPM.
• The design lifestyle is usually to be 10,000 hours.
With these requirements in mind, let’s look at three feasible solutions, one involving a single branch, two-stage helical gear set. Another solution takes the initial gear collection and splits the two-stage reduction into two branches, and the 3rd calls for utilizing a two-level planetary or star 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, produced from taking the square root of the final ratio (7.70). In the process of reviewing this alternative we detect its size and pounds is very large. To reduce the weight we after that explore the possibility of making two branches of an identical arrangement, as observed in the second alternatives. This cuts tooth loading and minimizes both size and fat considerably . We finally arrive at our third alternative, which is the two-stage star epicyclic. With three planets this gear train reduces tooth loading substantially from the primary approach, and a somewhat smaller amount from solution two (observe “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a huge part of what makes them so useful, yet these very characteristics could make designing them a challenge. In the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our objective is to create it easy for you to understand and work with epicyclic gearing’s unique style characteristics.
Relative Speeds
Let’s begin by looking for how relative speeds operate together with different arrangements. In the star set up the carrier is set, and the relative speeds of sunlight, planet, and ring are simply determined by the speed of 1 member and the number of teeth in each equipment.
In a planetary arrangement the band gear is fixed, and planets orbit sunlight while rotating on earth shaft. In this arrangement the relative speeds of sunlight and planets are dependant on the number of teeth in each gear and the swiftness of the carrier.
Things get a bit trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. It is therefore imperative to usually calculate the acceleration of the sun, planet, and ring relative to the carrier. Remember that actually in a solar set up where the sun is fixed it includes a speed relationship with the planet-it isn’t zero RPM at the mesh.
Torque Splits
When considering torque splits one assumes the torque to be divided among the planets similarly, but this might not be 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 designed with several planets is in most cases equal to you see, the quantity of planets. When a lot more than three planets are employed, however, the effective amount of planets is constantly less than you see, the number of planets.
Let’s look at torque splits when it comes to set support and floating support of the participants. With set support, all members are supported 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 posting the load. 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 get a position where their centers happen to be coincident. This float could be as little as .001-.002 inches. 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 the moment let’s explore the multiple mesh factors that should be made when making epicyclic gears. Primary we must translate RPM into mesh velocities and determine the quantity of load software cycles per product of time for each 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 example, if the sun gear is rotating at +1700 RPM and the carrier is certainly rotating at +400 RPM the rate of sunlight gear in accordance with the carrier is +1300 RPM, and the speeds of world and ring gears could be calculated by that velocity and the numbers of teeth in each one of the gears. The usage of signals to symbolize 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 swiftness between the two people can be +1700-(-400), or +2100 RPM.
The next step is to determine the quantity of load application cycles. Since the sun and ring gears mesh with multiple planets, the amount of load cycles per revolution relative to the carrier will become equal to the number of planets. The planets, however, will experience only one bi-directional load app per relative revolution. It meshes with the sun and ring, however the load is usually on reverse sides of the teeth, resulting in one fully reversed anxiety cycle. Thus the planet is known as an idler, and the allowable anxiety must be reduced thirty percent from the value for a unidirectional load app.
As noted over, the torque on the epicyclic users is divided among the planets. In examining the stress and your life of the people we must look at the resultant loading at each mesh. We find the idea of torque per mesh to become relatively confusing in epicyclic gear evaluation and prefer to look at the tangential load at each mesh. For example, in looking at the tangential load at the sun-planet mesh, we have the torque on the sun gear and divide it by the effective quantity 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, adjusted by the strain cycles per revolution, the life expectancy of each component.
Furthermore to these issues there can also be assembly complications that require addressing. For example, placing one planet in a position between sun and ring fixes the angular posture of the sun to the ring. The next planet(s) is now able to be assembled only in discreet locations where the sun and band could be at the same time involved. 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 numbers of teeth in the sun and the ring. Therefore, to be able to assemble further planets, they must end up being spaced at multiples of the least mesh position. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets could be spaced similarly when the sum of the amount 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 brings another level of complexity, and right planet spacing may require match marking of teeth.
With multiple elements in mesh, losses have to be considered at each mesh as a way to evaluate the efficiency of the machine. Power transmitted at each mesh, not input power, can be used to compute power damage. For simple epicyclic models, the total vitality transmitted through the sun-world mesh and ring-planet mesh may be significantly less than input electrical power. This is one of the reasons that simple planetary epicyclic sets are better than other reducer plans. In contrast, for many coupled epicyclic sets total electrical power transmitted internally through each mesh could be higher than input power.
What of power at the mesh? For simple and compound epicyclic pieces, calculate pitch line velocities and tangential loads to compute electrical power at each mesh. Values can be obtained from the earth torque relative speed, and the operating pitch diameters with sunshine and ring. Coupled epicyclic models present more technical issues. Components of two epicyclic units could be coupled 36 various ways using one source, one output, and one reaction. Some plans split the power, while some recirculate ability internally. For these kinds of epicyclic sets, tangential loads at each mesh can only just be motivated through the utilization of free-body diagrams. On top of that, the factors of two epicyclic sets can be coupled nine various ways in a series, using one suggestions, one end result, and two reactions. Let’s look at some examples.
In the “split-electrical power” coupled set proven in Figure 7, 85 percent of the transmitted power flows to ring gear #1 and 15 percent to ring gear #2. The result is that coupled gear set can be scaled-down than series coupled sets because the vitality is split between the two factors. When coupling epicyclic units in a series, 0 percent of the power will become transmitted through each arranged.
Our next case in point depicts a establish with “electrical power recirculation.” This gear set comes about when torque gets locked in the machine in a way similar to what takes place in a “four-square” test procedure for vehicle drive axles. With the torque locked in the system, the horsepower at each mesh within the loop improves as speed increases. Therefore, this set will encounter much higher power losses at each mesh, resulting in significantly lower unit efficiency .
Figure 9 depicts a free-body diagram of an epicyclic arrangement that experience vitality recirculation. A cursory analysis of this free-physique diagram clarifies the 60 percent proficiency of the recirculating arranged 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 power at the sun gear mesh benefits from the torque insight to the sun gear. The force at the second ring gear mesh outcomes from the output torque on the ring equipment. The ratio being 41.1:1, productivity torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the power on the next planet will be around 14 times the drive on the first planet at sunlight gear mesh. Therefore, for the summation of forces to equate to zero, the tangential load at the first ring gear must be approximately 13 circumstances the tangential load at the sun gear. If we assume the pitch series velocities to become the same at sunlight mesh and band mesh, the energy loss at the band mesh will be approximately 13 times higher than the energy loss at sunlight mesh .