We finally arrive at our third solution, which is the two-stage star epicyclic. This cuts tooth loading and reduces both size and weight considerably (see Figure 5). To reduce the weight we then explore the possibility of making two branches of a similar arrangement, as seen in the second solutions. (See Figure 4.) In the process of reviewing this solution we notice its size and weight is very large. 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). Let’s examine each of these in greater detail, looking at their ratios and resulting weights. A second solution takes the original gear set and splits the two-stage reduction into two branches, and the third calls for using a two-stage planetary or star epicyclic. With these requirements in mind, let’s look at three possible solutions, one involving a single branch, two-stage helical gear set. 3: Solar, with ratios between 1.2:1 and 1.7:1 The design life is to be 10,000 hours.The output from the gearbox must drive a generator at 900 RPM.A turbine delivers 6,000 horsepower at 16,000 RPM to the input shaft.Let’s assume that we’re designing a high-speed gearbox to satisfy the following requirements: The following example illustrates these benefits. Also, when configured properly, epicyclic gear sets are more efficient. This makes them lighter and more compact, versus countershaft gearboxes. Epicyclic gear sets are used because they are smaller than offset gear sets since the load is shared among the planed gears. To keep carriers within reasonable manufacturing costs they should be made from castings and tooled on single-purpose machines with multiple cutters simultaneously removing material. Just as one would not consider making a 100-piece lot of gears on an N/C milling machine with a form cutter or ball end mill, one should not consider making a 100-piece lot of epicyclic carriers on an N/C mill. Epicyclic gearing is generally less expensive, when tooled properly. Let’s begin by examining an important aspect of any project: cost. The reasons why epicyclic gearing is used have been covered in this magazine, so we’ll expand on the topic in just a few places. 2: Star, with ratios between -2:1 and -11:1 Why Epicyclic Gearing? Solar, with ratios between 1.2:1 and 1.7:1 (see Figure 3) Fig.Star, with ratios between -2:1 and -11:1 (see Figure 2).Planetary, with ratios between 3:1 and 12:1 (see Figure 1).There are several possibilities for epicyclic arrangements: Finally, the ring is the internal gear that meshes with the planets.Įpicyclic gear systems can be divided into three types: simple planetary epicyclic compound epicyclic and coupled epicyclic sets. As the carrier rotates, planets rotate on planet gear shafts while orbiting the sun. The sun is the center gear, meshing with the planets, while the carrier houses the planet gear shaft. Epicyclic gears consist of several components: sun, carrier, planets, and rings. Let’s begin by examining some basic terminology. 1: Planetary, with ratios between 3:1 and 12:1 Types and Arrangements Finally we’ll discuss “dos and don’ts” and share some design tips and pitfalls associated with epicyclic gears. Next we’ll look at what’s unique to epicyclic gears, including relative speeds, torque splits, and multiple mesh considerations. We will begin by defining types and arrangements and then discuss why epicyclic gear sets are used. As such, this article aims to provide assistance and guidelines for people designing epicyclic gear trains for the first time-and perhaps, if you will, ease their degree of suffering. Epicyclic gearing requires a step-by-step process to make it work, and some of the steps are not necessarily intuitive. As more and more of these engineers reach retirement age younger engineers must pick up where they left off, and for many epicyclic gearing is an area where they lack experience. Recent articles in Gear Solutions have discussed epicyclic gearing, but often in the context of experienced engineers.
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