Text/Civil
If you usually pay attention to the automotive industry, then you must have seen the name "planetary gear set" on various press conferences, press releases, and technical stickers, in fact, for ordinary consumers, it is a bunch of gears combined together, and will not pay attention to it, but there is no shortage of consumers who want to learn more about it before buying a car or technical control that loves car knowledge, then the planetary gear set as a common infrastructure is worth learning.
About the definition of planetary gear: Planetary gear is a gear system that can rotate around its own axis of rotation like a fixed-axis gear, and at the same time the rotation shaft rotates with the planetary frame around the axis of other gears. When rotating around its own axis, it is regarded as "rotation", and rotating around other gear axes is regarded as "rotation", similar to the movement of the planets in the solar system, so it is called "planetary gear".
Composition of the planetary gear set:
The picture above is a structural diagram of a planetary gear set, in which the yellow part is the sun wheel, the dark green part is the ring of gear, and the gray part is the planetary frame. Each of these three components can be connected to three power outputs or inputs. If either of them is fixed, the other two are equivalent to ordinary gear bites. If two of them are fixed, the entire planetary gear is locked.
At the same time, note that the planetary gear in the light green part is not connected to any input/output mechanism, it has been rotating freely, otherwise the entire planetary gear set cannot be rotated. The power connected is the planetary frame, after the planetary frame is fixed, the planetary gear only rotates, not around the sun wheel.
Characteristics of the planetary gear set: Through the different definitions of the three components of the sun wheel, planetary frame and gear ring, the differential speed, deceleration (growth rate), reversal and other functions can be realized. The ordinary gear drive system has only two ports, namely the active gear and the driven gear.
Transmission mode of planetary gear set:
1. The outer ring of gears is fixed, and the sun wheel and the planetary frame rotate in the same direction. The sun wheel is a high-speed axis, and the planetary frame is a low-speed axis. The gear ratio of this transmission ranges between 3:1 and 12:1.
2. The planetary frame is fixed, and the sun wheel and the inner gear ring rotate in reverse. The sun wheel is a high-speed shaft, and the outer ring gear connection shaft is a low-speed shaft. The gear ratio of this transmission is between 2:1 and 11:1.
3. The sun wheel is fixed, and the planetary frame and the outer gear ring rotate in the same direction. The inner ring connection shaft is a high-speed shaft, and the planetary frame is a low-speed shaft. The gear ratio of this transmission ranges between 1.1:1 and 1.7:1.
The application of planetary gear sets in the automotive industry is still relatively extensive, such as the AT gearbox is the combination of multiple planetary gear sets, and the power split (Power Split, referred to as PS) in the hybrid system is a common hybrid structure. The earliest application was Toyota's THS hybrid system.
Let's take the knowledge of the planetary gear set to see its principle:
The core component of the THS hybrid system is a planetary gear set that Toyota calls a "power distributor." The engine is connected to the outer ring of the planetary gear set, and when the engine rotates, the planetary gear merges with the sun wheel and the outer ring of gear to push the two to rotate in the same direction.
Through the design of the sun wheel and the outer gear ring, Toyota distributes 72% of the torque to the outer gear ring and transmits 28% of the torque to the sun wheel. The outer ring is connected to the differential via a reduction gear and then to the wheels driving the vehicle forward. The sun wheel is connected to the MG1 motor, the engine drives the planetary frame, and the planetary gear drives the sun wheel, making the MG1 motor rotate.
The engine drives the vehicle with 72% torque and 28% torque pushes the MG1 motor to generate electricity. When a certain speed is required, the ECU calculates the speed of the outer ring gear and then determines what speed the engine needs to reach and how much speed the MG1 motor needs.
The MG2 motor is connected to the outer ring gear of the power distributor. The MG2 motor complements the torque from the engine. The equivalent of 28% of the torque is returned to the wheel end through the electrical circuit, and the outer ring gear and the MG2 motor together drive the vehicle through the reduction gear and differential.
The whole system is not complicated, but it can be seen that Toyota's use of planetary gear sets is still very unique. The applied models also achieved good sales due to low fuel consumption.
summary:
The planetary gear set is composed of planetary gears, sun wheels, planetary frames, and outer gear rings, which can realize differential speed, deceleration (growth rate), reversal and other functions. The application of the automotive industry is widespread, including AT gearboxes, etc., and the core of Toyota's THS hybrid system is the power distributor formed by the planetary gear set, which can achieve a variety of power modes and improve the fuel economy and smoothness of the car.