Planetary Gear Increase Speed
Planetary gear speed increase is the main transmission mode of wind turbine gearbox with speed increase, has the feature of large speed increase ratio, high bearing capacity, small volume, light weight, and the same axis shafts both of input and output, with these it is quietly suitable for the speed increase of wind turbine. This course introduces the principle and structure of planetary gearbox.
Transmission principle and structure of planetary gear
Figure 1 is a schematic diagram of a planetary gear mechanism, consisting of a plurality of cylindrical gears. It consists of one ring gear (internal gear), three planetary gears (external gear), one sun gear (external gear), and a planet carrier. The sun gear and the ring gear are one axis; the axes of the three planet wheels are fixed on the planet carrier, and the axis of the planet carrier coincides with the sun axis wheel. The planetary gear and the ring gear are internal meshing transmissions; meanwhile the planetary gears and the sun gear are externally meshed. The planetary gears can rotate around their own axes, and also can rotate along the planet carrier axis along with the planet carrier. The planetary gears have both rotation and revolution.
Planetary gears
Figure1—Planetary gears

The structure and composition of a single-stage planetary gearbox model are described below through five sets of pictures. Each set of pictures has two figures showing the structure and composition of the parts from two angles.

Figure 2 is a structural view of the planet carrier in the shape of a disk with three axes fixed on the disk and distributed at 120 degrees, parallel to each other. The rotating shaft of the planet carrier is installed in the bearing, and the other end of the rotating shaft is a low-speed shaft flange, which is connected to the main shaft of the wind turbine hub.

Planetary carrier
Figure2—Planetary carrier
Three planet gears are mounted to the three planet gear shafts of the planet carrier, showing in figure 3 below. Each planet gear is free to rotate about its own axis.
Planetary gear
Figure3—Planetary gear
Install the planet carrier through the bearing into the front terminal cover (planetary gear base) of the planetary gear box, and install the ring gear on the inner ring of the front terminal cover. With the internal teeth, it can mesh well with the planetary gears, when the planet carrier rotates. The planetary gears roll along the scallops inside the ring gear. Seeing figure 4 below, where the terminal cap is cut in 1/4.
planetary gear and ring gear
Figure4— planetary gear and ring gear
The shaft of the sun gear is a high-speed output shaft. Place the sun gear in the middle of the planet gears to mesh the teeth of the sun gear well with the teeth of all planet gears, as shown in figure 5.
Planetary gear components
Figure5—Planetary gear components
The rear end cover is closed to the front end cover, and a bearing is provided in the middle of the rear end cover for mounting the sun gear shaft (high speed output shaft). A single-stage planetary gearbox model is assembled, seeing figure 6.
Planetary gearbox
Figure 6—Planetary gearbox

The ratio I like this structure with planetary gears above is:

      I=1+ Z2/Z1

Z1——sun gear number,Z2——ring gears numbers。

In this example, the planetary gearbox has a variation ratio of 4, and when the low speed shaft rotates for 1 week, the high speed shaft rotates for 4 weeks. Due to the limitation of the gear structure, the single-stage planetary gear ratio of this transmission mode is suitable below 8.

Let's watch the single-stage planetary gear running animation to show different parts in different colors for clear demonstration of running status. On the left is the running animation of the planetary gearbox; on the right is the running animation of the planetary gear train, and the two animations run synchronously. In the animation on the right, the long yellow-orange arrow is the turning pointer of the planet carrier. The light purple short arrow is the turning pointer of the sun gear. The two pointers demonstrate the operation and transformation ratio of the gear train more clearly.

Note: Since the frame rate of the browser animation is much lower than the original frequency of the animation, the sun wheel reverse illusion will appear, and the animation download can be restored to the real state by playing with other animation players on the computer.
Single-stage planetary gear running animation
Single-stage planetary gear speed increasers are often used in semi-direct drive wind turbines.
Main form of speed increasing gearbox with planetary gears for wind turbine

The following describes several types of speed increaser based on planetary gear transmission. For the gear transmission schematic symbol, see the gearbox (1) of the wind turbine. In the introduction, the gear ratio is calculated according to the reducer.

Single stage planetary gear transmission

Compared with ordinary cylindrical gear speed increasers, planetary gear speed increasers are small in size and light in weight, but require high manufacturing precision and complicated structure, and are widely used in power transmissions requiring compact structure.

Gear ratio range   i=2.8~12.5

First-class planetary two-stage cylindrical gear transmission

The small size, the low speed shaft is the planetary gear transmission, which makes the power split, and the internal engagement is reasonably applied. The last stage is a parallel shaft spur gear transmission, which can reasonably allocate the speed increase ratio and improve the transmission efficiency. Gear ratio range   i=20~80

Secondary planetary gear transmission

A large gear ratio is available, and other features are the same as single-stage planetary gears.
Gear ratio range   i=24~160

Secondary planetary primary spur gear transmission

High speed ratio and small size.

The low speed shaft of the wind turbine speed increasing gearbox is tubular hollow, passing through the gear box, one end is connected to the main shaft of the wind turbine, and the other end is connected to the outer end of the other side of the gear box. The through hole of the rotating shaft is the mechanical driving device of the pitching mechanism. Or channels of power lines, signal lines, oil pipes, etc.

Figure 7 is a diagram showing the internal structure of the gearbox downloaded from the Internet. The output of the first stage planetary gear mechanism is connected to the carrier of the second stage planetary gear mechanism. The output of the second stage planetary gear mechanism uses a large diameter gear to drive the pinion to continue to increase speed. All gears use helical gears to make the transmission smoother. Appropriate design can get more than 100 times ratio, but too high speed-increasing ratio will reduce the transmission efficiency.

Multi-stage gear speed increasing mechanism
Figure 7 - Multi-stage gear speed increasing mechanism
Figure 8 is a photo of two wind turbine gearboxes downloaded from the internet.
Wind Turbine Gearbox
Figure 8 - Wind Turbine Gearbox
Other gearboxes for wind turbines
In the wind turbine, there are also yaw drive motors and pitch drive motors, which are driven by the gearbox to reduce the speed and drive the relevant system. Figure 9 is a picture reproduced from internet, on the left side is a yaw drive motor, the lower part is a planetary gear reduction box, and the output shaft is equipped with a yaw pinion. The picture on the right below is the pitch drive motor, the lower part is the planetary gear reduction box, and the output shaft is equipped with pitch gears. In fact, there is no big difference between them, only the output torque, output speed, installation method, and driving power.
Yaw driving motor and pitch driving motor
Figure 9—Yaw driving motor and pitch driving motor
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