epicyclic gearbox

Within an epicyclic or planetary gear train, several spur gears distributed evenly around the circumference manage 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 obtained their name.
The pieces of a planetary gear train could be divided into four main constituents.
The housing with integrated internal teeth is known as a ring gear. In the majority of cases the casing is fixed. The traveling sun pinion is in the center of the ring gear, and is coaxially arranged with regards to the output. Sunlight pinion is usually mounted on a clamping system in order to provide the mechanical connection to the motor shaft. During operation, the planetary gears, which happen to be attached on a planetary carrier, roll between your sunlight pinion and the band equipment. The planetary carrier as well represents the output shaft of the gearbox.
The sole purpose of 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 can also vary. As the quantity of planetary gears raises, the distribution of the load increases and then the torque that can be transmitted. Increasing the number of tooth engagements also reduces the rolling vitality. Since only area of the total output must be transmitted as rolling ability, a planetary gear is incredibly efficient. The advantage of a planetary equipment compared to an individual spur gear lies in this load distribution. It is therefore possible to transmit high torques wit
h high efficiency with a concise design using planetary gears.
Provided that the ring gear includes a constant size, different ratios could be realized by various the amount of teeth of sunlight gear and the amount of teeth of the planetary gears. Small the sun equipment, the higher the ratio. Technically, a meaningful ratio selection for a planetary level is approx. 3:1 to 10:1, since the planetary gears and sunlight gear are extremely small above and below these ratios. Larger ratios can be acquired by connecting a variety of planetary phases in series in the same ring gear. In this instance, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques can be overlaid by having a ring gear that is not set but is driven in any direction of rotation. Additionally it is possible to repair the drive shaft so that you can 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 must be transmitted with favorable mass inertia ratio adaptation. Large transmission ratios may also easily be achieved with planetary gearboxes. Because of their positive properties and small design and style, 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
Practically unlimited transmission ratio options because of mixture of several planet stages
Suitable as planetary switching gear due to fixing this or that part of the gearbox
Possibility of 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 container are replaced with an increase of compact and more efficient sun and planetary type of gears arrangement plus the manual clutch from manual ability train is changed 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 known as 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 in line with the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- This is a type of gear which appears like a ring and have angular lower teethes at its internal surface ,and is put in outermost posture in en epicyclic gearbox, the inner teethes of ring gear is in continuous mesh at outer point with the set of planetary gears ,it is also referred to as annular ring.
2. Sun gear- It’s the equipment with angular minimize teethes and is placed in the middle of the epicyclic gearbox; the sun gear is in frequent mesh at inner stage with the planetary gears and can be connected with the source shaft of the epicyclic equipment box.
One or more sunlight gears can be utilised for obtaining different output.
3. Planet gears- These are small gears found in between ring and sun gear , the teethes of the earth gears are in frequent mesh with the sun and the ring equipment at both the inner and outer items 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 exactly like our solar system.
4. Planet carrier- It is a carrier fastened with the axis of the earth gears and is responsible for final transmitting of the output to the end result shaft.
The earth 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 equipment 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 actual fact the fixing the gears i.e. sun gear, planetary gears and annular gear is done to get the essential torque or swiftness output. As fixing the above triggers the variation in gear ratios from excessive torque to high swiftness. 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 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 gives high speed ratios to the vehicle which helps the vehicle to achieve higher speed throughout a drive, these ratios are obtained by fixing sunlight gear which makes the earth carrier the driven member and annular the driving a vehicle member as a way to achieve high speed ratios.
Reverse gear ratio
This gear reverses the direction of the output shaft which 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 the sun gear the driver member.
Note- More quickness or torque ratios can be achieved by increasing the quantity planet and sun gear in epicyclic gear field.
High-speed epicyclic gears could be built relatively little as the energy is distributed over a couple of meshes. This outcomes in a low power to weight ratio and, together with lower pitch collection velocity, causes improved efficiency. The tiny equipment diameters produce lower moments of inertia, significantly reducing 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 used have been covered in this magazine, so we’ll expand on the topic in just a few places. Let’s commence by examining a significant facet of any project: cost. Epicyclic gearing is generally less expensive, when tooled properly. Just as one would not consider making a 100-piece large amount of gears on an N/C milling equipment with an application cutter or ball end mill, one should certainly not consider making a 100-piece large amount of epicyclic carriers on an N/C mill. To hold carriers within reasonable manufacturing costs they should 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 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. Also, when configured correctly, epicyclic gear sets are more efficient. The following example illustrates these rewards. Let’s presume that we’re designing a high-speed gearbox to meet the following requirements:
• A turbine gives 6,000 horsepower at 16,000 RPM to the type shaft.
• The output from the gearbox must travel a generator at 900 RPM.
• The design your life is to be 10,000 hours.
With these requirements in mind, let’s look at three possible solutions, one involving an individual branch, two-stage helical gear set. A second solution takes the original gear placed and splits the two-stage reduction into two branches, and the 3rd calls for by using a two-level planetary or superstar epicyclic. In this situation, we chose the star. Let’s examine each one of these in greater detail, searching 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 base of the final ratio (7.70). Along the way of reviewing this remedy we realize its size and weight is very large. To reduce the weight we in that case explore the possibility of earning two branches of an identical arrangement, as seen in the second solutions. This cuts tooth loading and decreases both size and excess weight considerably . We finally arrive at our third solution, which may be the two-stage star epicyclic. With three planets this equipment train minimizes tooth loading drastically from the 1st approach, and a somewhat smaller amount from remedy two (observe “methodology” at end, and Figure 6).
The unique design and style characteristics of epicyclic gears are a sizable part of why is them so useful, however these very characteristics can make designing them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing considerations. Our goal is to create it easy so that you can understand and work with epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s begin by looking by how relative speeds job together with different plans. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and ring are simply determined by 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 amount of teeth in each equipment and the velocity of the carrier.
Things get a little trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to usually calculate the velocity of sunlight, planet, and ring in accordance with the carrier. Remember that possibly in a solar set up where the sun is fixed it includes a speed romantic relationship 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 may well 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 constructed with two or three planets is generally equal to some of the amount of planets. When a lot more than three planets are used, however, the effective number of planets is usually less than using the number of planets.
Let’s look for torque splits in conditions of set support and floating support of the associates. With set support, all customers are reinforced in bearings. The centers of the sun, band, and carrier will not be coincident due to manufacturing tolerances. For this reason fewer planets happen to be simultaneously in mesh, resulting in a lower effective amount of planets sharing the strain. With floating support, one or two people are allowed a tiny amount of radial independence or float, that allows the sun, band, and carrier to get a posture where their centers are coincident. This float could possibly be less than .001-.002 inches. With floating support three planets will be in mesh, resulting in a higher effective quantity of planets posting the load.
Multiple Mesh Considerations
At the moment let’s explore the multiple mesh factors that should be made when making epicyclic gears. Initial we must translate RPM into mesh velocities and determine the number of load app cycles per product of time for each member. The first rung on the ladder in this determination is usually to calculate the speeds of every of the members in accordance with the carrier. For instance, if the sun equipment 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 planet and ring gears could be calculated by that acceleration and the amounts of teeth in each one of the gears. The usage of indications 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 velocity between the two participants can be +1700-(-400), or +2100 RPM.
The second step is to identify the amount of load application cycles. Because the sun and ring gears mesh with multiple planets, the quantity of load cycles per revolution in accordance with the carrier will end up being equal to the amount of planets. The planets, however, will experience only one bi-directional load program per relative revolution. It meshes with sunlight and ring, but the load is normally on reverse sides of one’s teeth, resulting in one fully reversed pressure cycle. Thus the earth is known as an idler, and the allowable pressure must be reduced thirty percent from the value for a unidirectional load application.
As noted above, the torque on the epicyclic people is divided among the planets. In analyzing the stress and lifestyle of the customers we must consider the resultant loading at each mesh. We discover the concept of torque per mesh to become relatively confusing in epicyclic equipment analysis and prefer to look at the tangential load at each mesh. For example, in looking at the tangential load at the sun-world mesh, we have the torque on sunlight gear and divide it by the effective number of planets and the operating pitch radius. This tangential load, combined with the peripheral speed, is employed to compute the energy transmitted at each mesh and, altered by the load cycles per revolution, the life span expectancy of every component.
Furthermore to these issues there may also be assembly complications that need addressing. For example, positioning one planet in a position between sun and band fixes the angular situation 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 can be concurrently engaged. The “least mesh angle” from the first planet that will support simultaneous mesh of another planet is equal to 360° divided by the sum of the amounts of teeth in sunlight and the ring. Thus, as a way to assemble additional planets, they must always be spaced at multiples of the least mesh angle. If one wishes to have equal spacing of the planets in a straightforward epicyclic set, planets may be spaced equally when the sum of the amount of teeth in the sun and band is certainly divisible by the amount of planets to an integer. The same guidelines apply in a substance epicyclic, but the fixed coupling of the planets brings another degree of complexity, and right planet spacing may necessitate match marking of pearly whites.
With multiple parts in mesh, losses should be considered at each mesh in order to evaluate the efficiency of the machine. Ability transmitted at each mesh, not input power, can be used to compute power loss. For simple epicyclic units, the total electric power transmitted through the sun-planet mesh and ring-planet mesh may be less than input vitality. This is one of the reasons that easy planetary epicyclic pieces are better 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 vitality at the mesh? For basic and compound epicyclic sets, calculate pitch collection velocities and tangential loads to compute electricity at each mesh. Values can be obtained from the earth torque relative swiftness, and the operating pitch diameters with sunlight and ring. Coupled epicyclic pieces present more complex issues. Components of two epicyclic pieces can be coupled 36 different ways using one insight, one output, and one reaction. Some plans split the power, while some recirculate electric power internally. For these types of epicyclic models, tangential loads at each mesh can only just be motivated through the use of free-body diagrams. On top of that, the factors of two epicyclic models could be coupled nine different ways in a series, using one source, one outcome, 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 band gear #1 and 15 percent to ring gear #2. The effect is that coupled gear set can be scaled-down than series coupled units because the electricity is split between your two components. When coupling epicyclic models in a series, 0 percent of the power will become transmitted through each set.
Our next example depicts a arranged with “electricity recirculation.” This equipment set happens when torque gets locked in the machine in a manner similar to what happens in a “four-square” test procedure for vehicle travel 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 vitality losses at each mesh, leading to considerably lower unit efficiency .
Shape 9 depicts a free-body diagram of an epicyclic arrangement that experiences ability recirculation. A cursory examination of this free-body diagram clarifies the 60 percent efficiency of the recirculating collection 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 induce at sunlight gear mesh results from the torque type to sunlight gear. The force at the next ring gear mesh results from the end result torque on the band 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 approximately 14 times the force 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 should be approximately 13 situations the tangential load at sunlight gear. If we believe the pitch series velocities to become the same at sunlight mesh and band mesh, the power loss at the band mesh will be roughly 13 times greater than the energy loss at sunlight mesh .