In 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 equipment occurs in analogy to the orbiting of the planets in the solar program. 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 housing is fixed. The traveling sun pinion can be in the heart of the ring gear, and is coaxially organized in relation to the output. The sun pinion is usually mounted on a clamping system to be able to offer the mechanical link with the engine shaft. During operation, the planetary gears, which happen to be attached on a planetary carrier, roll between your sunlight pinion and the ring gear. The planetary carrier likewise represents the output shaft of the gearbox.
The sole purpose of the planetary gears is to transfer the mandatory torque. The number of teeth does not have any effect on the transmission ratio of the gearbox. The amount of planets may also vary. As the amount of planetary gears improves, the distribution of the load increases and then the torque which can be transmitted. Increasing the amount of tooth engagements also reduces the rolling electrical power. Since only part of the total result needs to be transmitted as rolling ability, a planetary gear is extremely efficient. The advantage of a planetary equipment compared to a single spur gear is based on this load distribution. It is therefore possible to transmit excessive torques wit
h high efficiency with a compact style using planetary gears.
Provided that the ring gear has a regular size, different ratios could be realized by various the quantity of teeth of sunlight gear and the amount of the teeth 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, because the planetary gears and sunlight gear are extremely tiny above and below these ratios. Higher ratios can be acquired by connecting many planetary stages in series in the same band gear. In cases like this, we speak of multi-stage gearboxes.
With planetary gearboxes the speeds and torques could be overlaid by having a band gear that is not fixed but is driven in virtually any direction of rotation. Additionally it is possible to repair the drive shaft so as to grab the torque via the ring gear. Planetary gearboxes have grown to be 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. Great transmission ratios may also easily be performed with planetary gearboxes. Because of their positive properties and compact style, the gearboxes have various potential uses in commercial applications.
The advantages of planetary gearboxes:
Coaxial arrangement of input shaft and output shaft
Load distribution to several planetary gears
High efficiency due to low rolling power
Practically unlimited transmission ratio options due to mixture of several planet stages
Suitable as planetary switching gear due to 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 arrangement from manual gear package are replaced with an increase of compact and more trustworthy sun and planetary type of gears arrangement and also the manual clutch from manual electrical power train is replaced with hydro coupled clutch or torque convertor which in turn made the transmitting automatic.
The thought of epicyclic gear box is extracted from the solar system which is known as to an ideal arrangement of objects.
The epicyclic gearbox usually includes the P N R D S (Parking, Neutral, Reverse, Drive, Sport) modes which is obtained by fixing of sun and planetary gears according to the need of the drive.
The different parts of Epicyclic Gearbox
1. Ring gear- This is a kind of gear which looks like a ring and have angular cut teethes at its internal surface ,and is placed in outermost position in en epicyclic gearbox, the internal teethes of ring gear is in frequent mesh at outer point with the group of planetary gears ,additionally it is known as annular ring.
2. Sun gear- It is the equipment with angular slice teethes and is put in the middle of the epicyclic gearbox; sunlight gear is in frequent mesh at inner stage with the planetary gears and is normally connected with the insight shaft of the epicyclic gear box.
One or more sunlight gears can be used for reaching different output.
3. Planet gears- These are small gears used in between band and sun gear , the teethes of the earth gears are in constant mesh with the sun and the ring gear at both inner and outer things 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 sunlight gear exactly 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 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- The device used to repair the annular gear, sun gear and planetary gear and is managed 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.e. sun equipment, planetary gears and annular equipment is done to obtain the required torque or acceleration output. As fixing any of the above causes the variation in gear ratios from excessive torque to high velocity. So let’s see how these ratios are obtained
First gear ratio
This provide high torque ratios to the vehicle 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 sunlight gear.
Second gear ratio
This provides high speed ratios to the automobile which helps the vehicle to realize higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the influenced member and annular the driving a car 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 sunlight gear the driver member.
Note- More speed or torque ratios can be achieved by increasing the number planet and sun equipment in epicyclic gear field.
High-speed epicyclic gears could be built relatively tiny as the power is distributed over a number of meshes. This results in a low capacity to pounds ratio and, as well as lower pitch range velocity, causes 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 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 can be used have already been covered in this magazine, so we’ll expand on the topic in simply a few places. Let’s start by examining an important facet of any project: expense. Epicyclic gearing is generally less costly, when tooled properly. Being an 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, you need to not really consider making a 100-piece lot of epicyclic carriers on an N/C mill. To continue to keep carriers within reasonable manufacturing costs they should be created from castings and tooled on single-purpose machines with multiple cutters concurrently removing material.
Size is another element. Epicyclic gear units are used because they’re smaller than offset equipment sets because the load is definitely shared among the planed gears. This makes them lighter and smaller sized, versus countershaft gearboxes. As well, when configured properly, epicyclic gear models are more efficient. The following example illustrates these benefits. Let’s assume that we’re developing a high-speed gearbox to fulfill the following requirements:
• A turbine offers 6,000 horsepower at 16,000 RPM to the input shaft.
• The result from the gearbox must travel a generator at 900 RPM.
• The design existence is usually to be 10,000 hours.
With these requirements in mind, let’s look at three conceivable solutions, one involving a single branch, two-stage helical gear set. A second solution takes the original gear set and splits the two-stage lowering into two branches, and the 3rd calls for by using a two-level planetary or superstar epicyclic. In this situation, 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 choice we find its size and pounds is very large. To reduce the weight we after that explore the possibility of making two branches of a similar arrangement, as observed in the second alternatives. This cuts tooth loading and reduces both size and pounds considerably . We finally reach our third solution, which is the two-stage superstar epicyclic. With three planets this equipment train minimizes tooth loading considerably from the primary approach, and a somewhat smaller amount from remedy two (check out “methodology” at end, and Figure 6).
The unique style characteristics of epicyclic gears are a sizable part of why is them so useful, but these very characteristics can make creating them a challenge. Within the next sections we’ll explore relative speeds, torque splits, and meshing factors. Our objective is to make it easy so that you can understand and use epicyclic gearing’s unique design characteristics.
Relative Speeds
Let’s start by looking at how relative speeds job together with different arrangements. In the star arrangement the carrier is fixed, and the relative speeds of the sun, planet, and band are simply dependant on the speed of one member and the number 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 arrangement the relative speeds of the sun and planets are determined by the number of teeth in each gear and the swiftness of the carrier.
Things get somewhat trickier whenever using coupled epicyclic gears, since relative speeds may well not be intuitive. Hence, it is imperative to generally calculate the speed of the sun, planet, and ring relative to the carrier. Remember that also in a solar set up where the sunshine is fixed it has a speed 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 number of planets determine the torque split represented by an “effective” amount of planets. This number in epicyclic sets designed with several planets is in most cases equal to you see, the quantity of planets. When more than three planets are applied, however, the effective number of planets is often less than using the number of planets.
Let’s look in torque splits regarding fixed support and floating support of the members. With fixed support, all members are backed in bearings. The centers of the sun, ring, and carrier will never be coincident due to manufacturing tolerances. For this reason fewer planets are simultaneously in mesh, resulting in a lower effective quantity of planets posting the strain. With floating support, one or two members are allowed a little amount of radial flexibility or float, which allows the sun, ring, and carrier to get a posture 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 this time 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 number of load application cycles per device of time for each member. The first step in this determination is certainly to calculate the speeds of each of the members relative to the carrier. For instance, if the sun gear is rotating at +1700 RPM and the carrier is rotating at +400 RPM the rate of sunlight gear relative to the carrier is +1300 RPM, and the speeds of planet and ring gears can be calculated by that speed and the amounts of teeth in each one of the gears. The make use of indications to signify clockwise and counter-clockwise rotation is definitely important here. If sunlight is rotating at +1700 RPM (clockwise) and the carrier is rotating -400 RPM (counter-clockwise), the relative velocity between the two associates is usually +1700-(-400), or +2100 RPM.
The second step is to determine the amount of load application cycles. Since the sun and band gears mesh with multiple planets, the amount of load cycles per revolution in accordance with the carrier will always be equal to the quantity of planets. The planets, however, will experience only one bi-directional load software per relative revolution. It meshes with sunlight and ring, however the load is on reverse sides of the teeth, leading to one fully reversed pressure cycle. Thus the earth is known as an idler, and the allowable stress must be reduced 30 percent from the value for a unidirectional load app.
As noted over, the torque on the epicyclic associates is divided among the planets. In examining the stress and lifestyle of the users we must look at the resultant loading at each mesh. We discover the idea of torque per mesh to become somewhat confusing in epicyclic gear research 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 take the torque on sunlight equipment and divide it by the successful amount of planets and the working pitch radius. This tangential load, combined with the peripheral speed, can be used to compute the energy 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 need addressing. For example, inserting one planet in a position between sun and band fixes the angular placement of the sun to the ring. Another planet(s) is now able to be assembled just in discreet locations where the sun and band could be simultaneously involved. The “least mesh angle” from the first 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. Thus, in order to assemble extra planets, they must end up being spaced at multiples of this least mesh position. If one wishes to have the same spacing of the planets in a simple epicyclic set, planets may be spaced equally when the sum of the number of teeth in sunlight and band is normally divisible by the amount of planets to an integer. The same guidelines apply in a substance epicyclic, but the set coupling of the planets brings another level of complexity, and appropriate planet spacing may require match marking of pearly whites.
With multiple pieces in mesh, losses ought to be considered at each mesh as a way to evaluate the efficiency of the machine. Electric power transmitted at each mesh, not input power, must be used to compute power damage. For simple epicyclic pieces, the total power transmitted through the sun-world mesh and ring-world mesh may be less than input electrical power. This is among the reasons that easy planetary epicyclic models are more efficient than other reducer plans. In contrast, for many coupled epicyclic units total vitality transmitted internally through each mesh could be higher than input power.
What of electricity at the mesh? For straightforward and compound epicyclic sets, calculate pitch series velocities and tangential loads to compute vitality at each mesh. Ideals can be obtained from the planet torque relative acceleration, and the functioning pitch diameters with sunlight and ring. Coupled epicyclic sets present more complex issues. Components of two epicyclic sets can be coupled 36 different ways using one insight, one productivity, and one response. Some arrangements split the power, while some recirculate vitality internally. For these kinds of epicyclic units, tangential loads at each mesh can only just be decided through the utilization of free-body diagrams. Additionally, the elements of two epicyclic sets can be coupled nine various ways in a string, using one source, one end result, and two reactions. Let’s look at a few examples.
In the “split-ability” coupled set shown in Figure 7, 85 percent of the transmitted electrical power flows to ring gear #1 and 15 percent to ring gear #2. The effect is that coupled gear set could be smaller sized than series coupled sets because the power is split between the two elements. When coupling epicyclic sets in a series, 0 percent of the power will always be transmitted through each arranged.
Our next case in point depicts a placed with “electrical power recirculation.” This gear set happens when torque gets locked in the system in a way similar to what happens in a “four-square” test process of vehicle travel axles. With the torque locked in the system, the hp at each mesh within the loop raises as speed increases. Consequently, this set will encounter much higher power losses at each mesh, leading to significantly lower unit efficiency .
Physique 9 depicts a free-body diagram of a great epicyclic arrangement that encounters ability recirculation. A cursory analysis of this free-physique diagram explains the 60 percent performance of the recirculating placed shown in Figure 8. Since the planets will be rigidly coupled jointly, the summation of forces on the two gears must the same zero. The drive at sunlight gear mesh effects from the torque insight to the sun gear. The pressure at the second ring gear mesh outcomes from the output torque on the ring gear. 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 force on the second planet will be approximately 14 times the pressure on the first planet at sunlight gear mesh. Therefore, for the summation of forces to mean zero, the tangential load at the first band gear must be approximately 13 times the tangential load at sunlight gear. If we presume the pitch line velocities to become the same at sunlight mesh and ring mesh, the power loss at the ring mesh will be approximately 13 times greater than the energy loss at sunlight mesh .