High-speed power units such as electric motors and internal combustion engines require a process of speed reduction and torque increase at the working end of the power unit. A reducer is the power transmission mechanism that achieves this process.
Let's first look at an animated demonstration of planetary gears.
Overview of planetary gear reducers
Planetary gear reducers are a widely used industrial product. They are small in size, lightweight, have high load-bearing capacity, long service life, smooth operation, and low noise. They feature power splitting and unique multi-tooth meshing characteristics. Maximum input power can reach 104kW . They are suitable for industries such as hoisting and transportation, engineering machinery, metallurgy, mining, petrochemicals, construction machinery, light industry and textiles, medical equipment, instrumentation, automobiles, shipbuilding, weaponry, and aerospace. New products in the planetary series include: WGN fixed-axis transmission reducer, WN master-slave gear transmission reducer, and flexible load-sharing reducer with small tooth difference.
Planetary gear reducers are a new type of gear reducer with wide applicability. The internal gears are made of 20CvMnT carburized, quenched, and ground gears. The entire unit features small size, high output torque, large speed ratio, high efficiency, and reliable performance.
Related concepts
Number of stages: The number of sets of planetary gears. Since one set of planetary gears may not be sufficient for a large transmission ratio, sometimes two or three sets are needed to meet the user's requirements. Increasing the number of planetary gears increases the length of a two- or three- stage speed reducer and reduces its efficiency.
Backlash: With the output end fixed, the input end is rotated clockwise and counterclockwise to produce ±2% of the rated torque . A slight angular displacement occurs at the input end of the reducer; this displacement is the backlash. The unit is " minutes , " which is one-sixtieth of a degree. It is also sometimes called backlash.
Structure of planetary gear reducers
The main transmission structure of a planetary gear reducer consists of planetary gears, a sun gear, and an external gear ring.
Due to their structure, planetary gear reducers have a minimum single-stage reduction of 3 and a maximum of generally no more than 10. Common reduction ratios are 3 , 4 , 5 , 6 , 8 , and 10. The number of gear reducer stages generally does not exceed 3 , but some custom-made gear reducers with large reduction ratios have 4 stages.
Below are structural diagrams of several planetary gear reducers.
Working principle of planetary gear reducer
1. The ring gear is fixed, the sun gear is the driving gear, and the planet carrier is the driven gear .
As can be seen from Figure 1 , this combination is a speed reduction transmission, and the transmission ratio is usually 2.5 to 5 , with the same direction of rotation.
2. The ring gear is fixed, the planet carrier is the driving gear, and the sun gear is the driven gear .
As can be seen from Figure 2 , this combination is a speed-increasing transmission, with a transmission ratio typically between 0.2 and 0.4 , and the direction of rotation is the same.
3. The sun gear is fixed, the ring gear is the driving gear, and the planet carrier is the driven gear .
As can be seen from Figure 3 , this combination is a speed-reducing transmission, with a transmission ratio typically between 1.25 and 1.67 , and the direction of rotation is the same.
4. The sun gear is fixed, the planet carrier is the driving force, and the ring gear is the driven force .
As can be seen from the demonstration, this combination is a speed-increasing transmission, with a transmission ratio typically between 0.6 and 0.8 , and the direction of rotation is the same.
5. The planetary carrier is fixed, the sun gear is the driving gear, and the ring gear is the driven gear .
The demonstration shows that this combination is a speed-reducing transmission, with a transmission ratio typically between 1.5 and 4 , and the directions are opposite.
6. The planetary carrier is fixed, the ring gear is the driving gear, and the sun gear is the driven gear .
The demonstration shows that this combination is a speed-increasing transmission, with a transmission ratio typically between 0.25 and 0.67 , and the directions of rotation are opposite.
7. The case of combining any two of the three components into one .
The motion is as follows when the planetary carrier and ring gear are combined as one unit as the driving element, and the sun gear as the driven element, or when the sun gear and planetary carrier are combined as one unit as the driving element, and the ring gear as the driven element. In this combination, there is no relative motion between the planetary gears; they operate as a single unit with a transmission ratio of 1:1 and the same direction of rotation. This combination is commonly used in automobiles to form direct drive gears.
8. Of the three components , one is active, and the other two are free.
The analysis shows that the other two components do not have a definite rotational speed output. The sixth combination, due to its large speed increase and the opposing directions of the active and passive components, is generally not used in automobiles. The remaining seven combinations are more commonly used.
