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Planetary Gear

Feb 05, 2018

Planetary gear

This entry by the "popular science" Encyclopedia of science entry preparation and application of the project review.

Planetary gears are gear systems whose axes of rotation also rotate about the axis of the other gears in addition to being able to rotate around their own axes of rotation as the fixed-axis gears do. The rotation around one's own axis is called "rotation," and the rotation around the axes of other gears is called "revolution." It is named after the planets in the solar system.

Chinese name planetary gear English name planetary gear Features Small size, light weight, large speed ratio, high efficiency Applications Aviation, ships, cars, cranes, etc.

table of Contents

1 Introduction

2 structure

3 working principle and characteristics

▪ Transmission combination

▪ Movement characteristics

4 characteristics type

5 application

Profile Editor

Planetary gear means the axis of rotation is not fixed, and is mounted on a pivotable bracket (blue) (the black part is the housing and the yellow is the bearing). In addition to being able to rotate about their own axis of rotation (BB) like a fixed-axis gear, the planet gears (green) have their axes of rotation shifted with the axis of the blue gear (called the planet carrier) about the axis of the other gear (AA) Turn. The rotation around one's own axis is called "rotation," and the rotation around the axes of other gears is called "revolution." It is named after the planets in the solar system.

Planetary gear planetary gear according to the number of planetary gear sets installed into different groups, divided into single-row planetary and double planetary row.

Figure 1. Spindle gear

Figure 1. Spindle gear

Planetary gears have many unique advantages over plain gears. The most notable feature is the power split when power is transmitted and the input and output shafts are on the same horizontal line. Therefore, the planetary gear drive has now been widely used in various mechanical transmission system reducer, gearbox and transmission. Especially because of its characteristics of "high load, large transmission ratio", it is widely used in aircraft and vehicles (especially heavy vehicles). [1] Planetary gears also play a large role in the transmission of torque to the engine. Due to the characteristics of the engine speed torque and road driving demand is very different, the engine power to be properly assigned to the drive wheel, you can use the planetary gear of the above characteristics to be converted. Automatic transmission in the car, but also the use of these characteristics of the planetary gear, the clutches and brakes to change the relative motion of the various components to obtain a different gear ratio.

However, due to the complex structure and working status of the planetary gear, the vibration and noise problems are also prominent, which can easily lead to failure phenomena such as gear tooth pitting corrosion, tooth root cracking and even gear tooth or shaft rupture, thus affecting the operation accuracy of the equipment. Transmission efficiency and service life.

Figure 2. Double row planetary gear

Figure 2. Double row planetary gear

Structure composition editor

Simple (single row) planetary gear mechanism is the basis of variable speed mechanism, usually automatic transmission speed change mechanism consists of two or more than three rows of planetary gear mechanism. The simple planetary gear mechanism includes a sun gear, a plurality of planet gears and a gear ring, wherein the planet gears are supported by a fixed shaft of the planet carrier allowing the planet gears to rotate on the support shaft. Planetary gears and adjacent sun gear, ring gear is always in the state of regular engagement, usually using helical gears to improve the work of stability.

In the simple planetary gear mechanism, the sun gear is located in the center of the planetary gear mechanism. The sun gear and the planetary gear are often meshed, and the two external gears mesh with each other in opposite rotation directions. Just as the sun is in the center of the solar system, the sun wheel is named for its location. In addition to being able to revolve around the planet carrier support shaft, in some cases, the planet wheels will also rotate around the sun gear center axis under the driving of the planet carrier. It is like the rotation of the earth and the revolution around the sun, When this happens, it is called the role of planetary gear mechanism transmission. In the entire planetary gear mechanism, such as the existence of planetary gear rotation, while the planets are stationary, this approach is similar to the parallel shaft-type transmission called fixed-axis transmission. Ring gear is the internal gear, it is often engaged with the planetary gear, the internal gear and external gear meshing between the two rotating in the same direction. The number of planetary gears depends on the transmission design load, usually three or four, the greater the number of bear the greater load.

A simple planetary gear mechanism is commonly referred to as a three-member mechanism and three members are a sun gear, a planet carrier, and a ring gear, respectively. The three components to determine the relationship between the movement, under normal circumstances first need to fix one of the components, and then determine who is the active part, and determine the speed and direction of rotation of the active parts, the results of the passive parts speed, direction of rotation to determine It's

Figure 3. Planetary gear structure diagram

Figure 3. Planetary gear structure diagram

Working principle and features editor

Drive combination

In the planetary gear-containing gear system, the transmission principle and Dingzhou gear different. Because of the planet carrier, there are three rotating shafts that allow power in / out. You can also use clutches or brakes to limit the rotation of one of the shafts when needed, leaving only the two shafts for transmission. Therefore, the relationship between the intermeshing gears can be various combinations:

(1) power input from the sun gear, output from the outer ring gear, the planet carrier locked by institutions;

(2) power input from the sun gear, output from the planet carrier, external gear locked;

(3) power input from the planet carrier, output from the sun gear, external gear locked;

Figure 4. Planetary gears

Figure 4. Planetary gears

(4) power input from the planet carrier, output from the outer ring gear, the sun gear locked;

(5) power input from the external gear, from the planet carrier output, the sun gear locked;

(6) Power input from external gear, output from sun gear, planet carrier locked;

(7) The two motions are input from the sun gear and outer ring gear, respectively, and are output from the planet carrier after being synthesized.

(8) The two power inputs are input from the planet carrier and the sun gear, respectively, and are output from the external gear ring after being synthesized.

(9) The two power inputs from the planet carrier and the outer ring gear, respectively, from the sun gear output after synthesis;

(10) Power input from the sun gear, two-way output from the ring gear and planet carrier;

(11) power input from the planet carrier, two-way output from the sun gear and outer ring gear;

(12) Power external gear input, two-way output from the sun gear and planet carrier.

Movement characteristics

According to the above combination, the movement characteristics of a simple planetary gear mechanism can be summarized as follows:

(1) When the carrier is the active part, the driven part runs at over speed.

(2) When the planet carrier is the follower, the planet carrier must be lower than the speed of the active element.

(3) When the planet carrier is fixed, the driving part and the driven part rotate in the opposite direction.

(4) When the sun gear is the active part, the speed of the driven part will inevitably decrease.

(5) If the planet carrier is a passive component, its rotation direction is the same as that of the active component.

(6) If the planet carrier is the active part, the passive part will rotate in the same direction.

(7) In a simple planetary gear mechanism, the sun gear has the fewest number of teeth, and the carrier has the largest number of equivalent teeth. The number of gear teeth is in the middle. (Note: The number of equivalent teeth of the carrier = tens of ring gear teeth of the sun gear.)

(8) If any two elements in the planetary gear mechanism rotate in the same direction with the same speed, the speed and direction of the third element must be the same as those of the former two, that is, the mechanism is locked and becomes the direct gear. (This is a very important feature.)

(9) With only one active part and two other parts not fixed, this is neutral.

Feature type edit

Planetary gear in the structure of the following characteristics:

(1) The sun gear, planet carrier, and ring gear are all concentric, that is, rotate about a common axis. This enables cancellation of countershafts and intermediate gears such as those used for manual transmissions;

(2) All the gears are always engaged with each other, there is no need to slip gears when shifting gears, so the friction and wear are small and the service life is longer;

(3) The structure is simple and compact, its load is distributed to a large number of teeth, the intensity is big;

(4) Multiple transmission ratios are available.

Application editor

Planetary gear system in a variety of machinery has been widely used, mainly in the following areas:

Figure 5. Large transmission planetary gear train

Figure 5. Large transmission planetary gear train

(1) to achieve a large gear ratio transmission

In the planetary gear system shown on the right, if the number of teeth of each wheel is z1 = 100, z2 = 101, z2 '= 100, and z3 = 99, the transmission ratio of the input member H to the output member 1 = 100. Visible, according to need planetary gear system can get a large transmission ratio.

(2) to achieve a compact high-power transmission

Planetary gears can use several evenly distributed planetary wheels to transmit motion and power simultaneously. These planetary wheels due to revolution and centrifugal forces generated by centrifugal force between the tooth profile of the radial component can be balanced with each other, so the spindle force is small, the transmission power. In addition, because it uses the internal gear, take full advantage of the transmission space, and the input and output shaft in a straight line, so the whole gear train space than the same conditions under the ordinary fixed-axis gear train is much smaller. This wheel train is particularly suitable for aircraft.

Figure 6. Addition mechanism

Figure 6. Addition mechanism

(3) to achieve the synthesis of exercise

The synthesis of the motion is to combine the two input motions into one output motion. The degree of freedom of the differential gear train is equal to 2, and the motion of the other member can be determined only after a given movement of any two members is given. The use of differential gear this feature can be synthesized motion.

The simplest motorized synthetic wheel train is shown on the right. The rotational speed of carrier H is a combination of the rotational speeds of wheel 1 and wheel 3. Therefore, this gear train can be used as addition mechanism. When the planet carrier H, sun gear 1 or 3 as a motive force, the gear train can be used as a deceleration mechanism.

This feature of differential gear train for motion synthesis is widely used in machine tools, computational mechanisms and compensation adjustment devices.

Figure 7. Rear axle differential

Figure 7. Rear axle differential

(4) to achieve the decomposition of movement

The differential gear train can also disassemble the rotation of one prime mover member into different rotations of the other two slave basic members. The figure on the left shows the schematic diagram of the rear axle differential of the automobile. In the figure, the members 5 and 4 form a fixed-shaft gear train, and the wheel 4 is fixedly connected to the planet carrier H, and planet wheels 2 and 2 'are mounted on the H. The gears 1, 2, 2 ', 3 and the planet carrier H form a differential gear train which breaks down the movement of the engine to the gear 5 into different motions of the sun gears 1.