In an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference operate between a gear with internal teeth and a gear with exterior teeth on a concentric orbit. The circulation of the spur gear occurs in analogy to the orbiting of the planets in the solar program. This is one way planetary gears acquired their name.
The elements of a planetary gear train could 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 usually 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 electric motor shaft. During operation, the planetary gears, which will be mounted on a planetary carrier, roll between your sunlight pinion and the ring gear. The planetary carrier as well represents the output shaft of the gearbox.
The sole reason for the planetary gears is to transfer the required torque. The number of teeth does not have any effect on the transmitting ratio of the gearbox. The quantity of planets can also vary. As the amount of planetary gears raises, the distribution of the strain increases and therefore the torque that can be transmitted. Raising the number of tooth engagements also reduces the rolling vitality. Since only area of the total outcome must be transmitted as rolling ability, a planetary equipment is incredibly efficient. The benefit of a planetary equipment compared to a single spur gear lies in this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a concise design and style using planetary gears.
So long as the ring gear has a continuous size, different ratios can be realized by various the amount of teeth of sunlight gear and the number of the teeth of the planetary gears. Small the sun equipment, the greater the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, because the planetary gears and the sun gear are extremely tiny above and below these ratios. Higher ratios can be obtained by connecting a variety of 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 can be overlaid by having a band gear that’s not set but is driven in virtually any direction of rotation. Additionally it is possible to fix the drive shaft as a way to pick up 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 must be transmitted with favorable mass inertia ratio adaptation. Great transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and small design, the gearboxes have many potential uses in commercial applications.
The advantages 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 combination of several planet stages
Ideal as planetary switching gear because of fixing this or that the main gearbox
Possibility of use as overriding gearbox
Favorable volume output
Suitability for a variety of applications
Epicyclic gearbox can be an automatic type gearbox where parallel shafts and gears arrangement from manual gear box are replaced with an increase of compact and more trustworthy sun and planetary kind of gears arrangement as well as the manual clutch from manual electrical power train is substituted with hydro coupled clutch or torque convertor which made the transmission automatic.
The thought 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 based on the need of the drive.
Components of Epicyclic Gearbox
1. Ring gear- This is a type of gear which looks like a ring and have angular minimize teethes at its interior surface ,and is positioned in outermost job in en epicyclic gearbox, the inner teethes of ring equipment is in continuous mesh at outer level with the set of planetary gears ,it is also known as annular ring.
2. Sun gear- It is the gear with angular minimize teethes and is located in the middle of the epicyclic gearbox; the sun gear is in continuous mesh at inner stage with the planetary gears and is normally connected with the source shaft of the epicyclic gear box.
One or more sunlight gears can be used for achieving different output.
3. Planet gears- They are small gears found in between band and sun gear , the teethes of the planet gears are in constant mesh with the sun and the ring gear 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 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 attached with the axis of the earth gears and is accountable for final transmission of the productivity 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, sunlight gear and planetary gear and is controlled by the brake or clutch of the automobile.
Working of Epicyclic Gearbox
The working principle of the epicyclic gearbox is founded on the fact the fixing the gears i.electronic. sun gear, planetary gears and annular equipment is done to obtain the expected torque or speed output. As fixing any of the above causes the variation in gear ratios from huge 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 vehicle to go 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 provides high speed ratios to the automobile which helps the automobile to achieve higher speed during a travel, these ratios are obtained by fixing sunlight gear which makes the planet carrier the motivated member and annular the travelling member in order 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 planet gear carrier which in turn makes the annular gear the powered member and the sun gear the driver member.
Note- More speed or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear box.
High-speed epicyclic gears can be built relatively little as the power is distributed over a number of meshes. This benefits in a low power to fat ratio and, as well as lower pitch range velocity, contributes to improved efficiency. The tiny equipment diameters produce lower moments of inertia, significantly minimizing 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.
The reasons why epicyclic gearing is used 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: price. Epicyclic gearing is generally less expensive, when tooled properly. Being an would not consider making a 100-piece lot of gears on an N/C milling machine with an application cutter or ball end mill, you need to not consider making a 100-piece lot of epicyclic carriers on an N/C mill. To hold carriers within reasonable manufacturing costs they must be made from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another point. Epicyclic gear pieces are used because they are smaller than offset gear sets since the load is certainly shared among the planed gears. This makes them lighter and more compact, versus countershaft gearboxes. Likewise, when configured effectively, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s presume that we’re creating a high-speed gearbox to meet the following requirements:
• A turbine offers 6,000 hp at 16,000 RPM to the suggestions shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design life is to be 10,000 hours.
With these requirements in mind, let’s look at three conceivable solutions, one involving an individual branch, two-stage helical gear set. Another solution takes the initial gear set and splits the two-stage decrease into two branches, and the third calls for by using a two-level planetary or celebrity epicyclic. In this instance, we chose the celebrity. Let’s examine each one 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). Along the way of reviewing this option we see its size and fat is very large. To reduce the weight we then explore the possibility of earning two branches of a similar arrangement, as observed in the second solutions. This cuts tooth loading and decreases both size and weight considerably . We finally reach our third alternative, which may be the two-stage superstar epicyclic. With three planets this equipment train decreases tooth loading drastically from the 1st 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 sizable part of what makes them so useful, yet these very characteristics can make creating them a challenge. Within 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 design characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds work in conjunction with different arrangements. In the star arrangement the carrier is set, and the relative speeds of sunlight, planet, and band are simply determined by the speed of 1 member and the amount of teeth in each equipment.
In a planetary arrangement the ring gear is fixed, and planets orbit sunlight while rotating on the planet shaft. In this set up the relative speeds of sunlight and planets are determined by the quantity of teeth in each equipment and the velocity of the carrier.
Things get somewhat trickier whenever using coupled epicyclic gears, since relative speeds may not be intuitive. It is therefore imperative to at all times calculate the speed of sunlight, planet, and ring in accordance with the carrier. Remember that actually in a solar set up where the sun is fixed it has a speed relationship 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 might not exactly be a valid assumption. Member support and the amount of planets determine the torque split represented by an “effective” number of planets. This amount in epicyclic sets constructed with two or three 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 number of planets is usually less than you see, the number of planets.
Let’s look for torque splits in conditions of set support and floating support of the people. With fixed support, all members are supported in bearings. The centers of sunlight, band, and carrier will never be coincident due to manufacturing tolerances. Because of this fewer planets are simultaneously in mesh, resulting in a lower effective number of planets posting the strain. With floating support, one or two people are allowed a tiny amount of radial liberty or float, which allows the sun, ring, and carrier to seek a posture where their centers will be coincident. This float could be less than .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 considerations that should be made when designing epicyclic gears. First we should translate RPM into mesh velocities and determine the quantity of load program cycles per device of time for each and every member. The first step in this determination is certainly 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 rotating at +400 RPM the speed of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears could be calculated by that rate and the amounts of teeth in each one of the gears. The usage of signals to represent clockwise and counter-clockwise rotation is usually important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative swiftness between the two customers is usually +1700-(-400), or +2100 RPM.
The next step is to decide the quantity of load application cycles. Since the sun and band gears mesh with multiple planets, the quantity of load cycles per revolution relative to the carrier will always be equal to the amount of planets. The planets, nevertheless, will experience only one bi-directional load software per relative revolution. It meshes with the sun and ring, but the load is on opposite sides of one’s teeth, resulting in one fully reversed stress cycle. Thus the planet is considered an idler, and the allowable tension must be reduced 30 percent from the worthiness for a unidirectional load software.
As noted previously mentioned, the torque on the epicyclic associates is divided among the planets. In examining the stress and existence of the participants we must consider the resultant loading at each mesh. We discover the idea of torque per mesh to always be somewhat confusing in epicyclic gear analysis 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 number 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, modified by the strain cycles per revolution, the life expectancy of each component.
Furthermore to these issues there may also be assembly complications that require addressing. For example, placing one planet in a position between sun and band fixes the angular job of sunlight to the ring. The next planet(s) can now be assembled only in discreet locations where in fact the sun and ring can be at the same time engaged. The “least mesh angle” from the first planet that will support simultaneous mesh of another planet is add up to 360° divided by the sum of the amounts of teeth in sunlight and the ring. As a result, so as to assemble extra planets, they must end up being spaced at multiples of this least mesh angle. If one wishes 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 the sun and ring is normally divisible by the amount of planets to an integer. The same guidelines apply in a compound epicyclic, but the set coupling of the planets brings another degree of complexity, and proper planet spacing may necessitate match marking of pearly whites.
With multiple elements in mesh, losses have to be considered at each mesh as a way to evaluate the efficiency of the unit. Ability transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic units, the total electricity transmitted through the sun-planet mesh and ring-world mesh may be significantly less than input electricity. This is among the reasons that easy planetary epicyclic units are better than other reducer arrangements. In contrast, for many coupled epicyclic sets total electrical power transmitted internally through each mesh could be higher than input power.
What of electrical power at the mesh? For simple and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute electricity at each mesh. Values can be obtained from the earth torque relative velocity, and the operating pitch diameters with sunlight and ring. Coupled epicyclic pieces present more complex issues. Elements of two epicyclic sets can be coupled 36 various ways using one type, one productivity, and one reaction. Some plans split the power, although some recirculate vitality internally. For these types of epicyclic sets, tangential loads at each mesh can only just be decided through the application of free-body diagrams. Also, the elements of two epicyclic pieces could be coupled nine different ways in a string, 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 electricity flows to band gear #1 and 15 percent to ring gear #2. The result is that coupled gear set can be more compact than series coupled sets because the electric power is split between your two components. When coupling epicyclic pieces in a series, 0 percent of the energy will become transmitted through each establish.
Our next example depicts a set with “electrical power recirculation.” This gear set comes about when torque gets locked in the machine in a way similar to what happens in a “four-square” test procedure for vehicle drive axles. With the torque locked in the machine, the hp at each mesh within the loop heightens as speed increases. As a result, this set will encounter much higher power losses at each mesh, resulting in substantially lower unit efficiency .
Shape 9 depicts a free-body diagram of a great epicyclic arrangement that experiences power recirculation. A cursory analysis of this free-body diagram explains the 60 percent proficiency of the recirculating establish shown in Figure 8. Since the planets happen to be rigidly coupled at the same time, the summation of forces on the two gears must equal zero. The force at sunlight gear mesh outcomes from the torque input to sunlight gear. The power at the second ring gear mesh benefits from the result torque on the ring gear. The ratio being 41.1:1, result torque is 41.1 times input torque. Adjusting for a pitch radius difference of, say, 3:1, the force on the second planet will be about 14 times the induce 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 situations the tangential load at the sun gear. If we presume the pitch line velocities to be the same at sunlight mesh and ring mesh, the power loss at the band mesh will be around 13 times greater than the energy loss at sunlight mesh .