Compared with planetary gear transmission and fixed shaft transmission, planetary gear transmission has many unique characteristics:

1)    Small size, light weight, compact structure and large transmission torque.

Due to its reasonable application of internal meshing gear pairs, the structure is relatively compact. At the same time, because its multiple planetary gears share the load around the central wheel to form a power split, so that each gear receives less load, so the gears can be small size. In addition, the accommodating volume of the internal meshing gear itself is fully utilized in structure, and its outer outline size is further reduced, making it small in size and light in weight, and the power split structure improves the bearing capacity. According to relevant literature, under the same load of transmission, the outer dimension and weight of planetary gear transmission are about 1/2 to 1/5 of that of ordinary fixed shaft gears.

2)    Input and output coaxial.

Due to its structural characteristics, the planetary gear transmission can realize the coaxial input and output, that is, the output shaft and the input shaft are on the same axis, so that the power transmission does not change the position of the power axis, which is conducive to reducing the space occupied by the entire system.

3)    It is easy to realize the speed change of small volume.

Since the planetary gear has three basic components, such as the sun gear, the inner gear, and the planet carrier, if one of them is fixed, the speed ratio is determined, that is, the same set of gear trains, and three different speed ratios can be achieved without adding other gears.

4)    High transmission efficiency.

Due to the symmetry of the planetary gear transmission structure, that is, it has several evenly distributed planetary wheels, so that the reaction forces acting on the central wheel and the bearing of the rotating piece can balance each other, which is beneficial to improve the transmission efficiency. In the case of appropriate and reasonable structural arrangement, its efficiency value can reach 0.97~0.99.

5)    The transmission ratio is large.

The combination and decomposition of motion can be realized. As long as the type of planetary gear transmission and the tooth matching scheme are properly selected, a large transmission ratio can be obtained with fewer gears, and the structure can be kept compact even when the transmission ratio is large. The advantages of light weight and small size.

6)    Smooth movement, strong shock and vibration resistance.

Due to the use of several planetary gears with the same structure, which are evenly distributed around the center wheel, the inertial forces of the planetary gear and the planetary carrier can be balanced with each other. Strong and reliable.

In a word, planetary gear transmission has the characteristics of small weight, small volume, large speed ratio, large transmission torque and high efficiency. In addition to the above advantageous features, planetary gears also have the following problems in the application process.

1)    The structure is more complicated.

Compared with the fixed-axis gear transmission, the planetary gear transmission structure is more complex, and the planet carrier, planetary gear, planetary wheel shaft, planetary gear bearing and other components are added.

2)    High heat dissipation requirements.

Due to the small size and small heat dissipation area, reasonable design of heat dissipation is required to avoid excessive oil temperature. At the same time, due to the rotation of the planet carrier or the rotation of the internal gear, due to the centrifugal force, the gear oil is easy to form an oil ring in the circumferential direction, so that the center The reduction of the lubricating oil of the sun gear will affect the lubrication of the sun gear, and adding too much lubricating oil will increase the oil churning loss, so this is a contradiction. Reasonable lubrication without excessive churning losses.

3)    High cost.

Because the planetary gear transmission structure is more complex, there are many parts and components, and the assembly is also complicated, so its cost is high. Especially the inner gear ring, due to the structural characteristics of the inner gear ring, its gear making process cannot adopt the high-efficiency gear hobbing and other processes commonly used in external cylindrical gears. It is an internal helical gear. The use of helical insertion requires a special helical guide rail or a CNC gear shaper, and the efficiency is relatively low. The equipment and tooling investment in the early stage of tooth pulling or tooth turning are very high, and the cost is much higher than that of ordinary external cylindrical gears.

4)    NVH is difficult. Due to the characteristics of the internal gear ring, it cannot finalize the tooth surface of the gear by grinding and other processes to achieve a higher precision, and it is also impossible to micro-modify the tooth surface of the gear through the gear, so that the gear meshing cannot achieve a more ideal. It is more difficult to improve its NVH level.

Summary: Due to the structural characteristics of planetary gear transmission, it has its own advantages and disadvantages. There is no perfect thing in the world. Everything has two sides. The same is true for planetary gears. The application in new energy is also based on its advantages and disadvantages. Or the specific needs of the product make full use of its advantages, make a balance between its advantages and disadvantages, and bring value to the vehicle and customers.