In mechanical equipment, in order to obtain a larger transmission ratio, or speed change and reversing, it is often necessary to use multiple pairs of gears for transmission, such as machine tools, gearboxes and differentials used in automobiles, and gear reducers widely used in engineering. etc. This kind of transmission system composed of multiple pairs of gears is called a gear train, or a gear train for short.
According to whether the axis position of each gear is fixed during transmission, the gear train is divided into two basic types: fixed axis gear train and planetary gear train. The geometric axis positions of all gears are fixed during transmission, and this kind of gear train is called fixed axis gear train.
During transmission, the geometric axis of gear g rotates around the common axis of gears a, b and member H, and such a gear train becomes a planetary gear train. According to the different degrees of freedom, the planetary gear train can be divided into epicyclic gear train and differential gear train. An epicyclic gear train has one degree of freedom and a planetary gear train has two degrees of freedom.
1. Transmission ratio of the wheel train
The ratio of the speed of the driving wheel at the beginning of the wheel train to the driven wheel at the end is called the transmission ratio of the wheel train, and i represents the size of the rotation angle.
In the formula, n1—the speed of the driving wheel 1, r/min; nk——the speed of the driven wheel, r/min;
2. The role of the gear train
2.1 Realize the transmission of motion and power between two axes that are far apart
In gear transmission, when the distance between the main and driven shafts is relatively long, if only one pair of gears is used for transmission, the size of the gears will inevitably be large. Like this, the structural size and the weight of both increasing machine, waste material again and manufacture installation is all inconvenient. If the gear train composed of two pairs of gears is used instead for transmission, the gear size can be much smaller, and the manufacturing and installation are also more convenient.
How Shifting Bicycle Gears Work
2.2 Realize shunt transmission
By using the gear train, one driving shaft can drive several driven shafts to rotate at the same time to obtain various required speeds.
2.3 Realize variable speed transmission
When the speed of the driving shaft is constant, the driven shaft can obtain various working speeds by using the gear train. This kind of transmission is called variable speed transmission. Many machines, such as automobiles, machine tools, and cranes, require variable speed drives.
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▲Gear transmission
2.4 Obtain a larger transmission ratio
A large transmission ratio can be obtained by using a fixed-axis gear train or a planetary gear train.
If a fixed-axis gear train is used to obtain a large transmission ratio, multi-stage gear transmission is required, resulting in a complex and bulky structure of the transmission device. With the planetary gear train, only a few gears are needed to obtain a large transmission ratio. Since the planetary gear system uses multiple planetary gears to share the load, and often uses internal meshing transmission, the space in the middle of the internal gear is used reasonably, and the input shaft and output shaft are on the same axis, which not only greatly increases the load-carrying capacity of the planetary reducer. improved, and the radial dimension is very compact. Under the condition of the same power and transmission ratio, the volume and weight of the planetary reducer are only 1/2~1/3 of the gear train reducer with fixed shaft.
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2.5 Realize the synthesis and decomposition of motion
In machinery, a differential planetary gear train with two degrees of freedom is used to realize the synthesis and decomposition of motion. This is the unique function of the planetary gear train.
Motion synthesis: The differential gear train has two degrees of freedom, and only when the motion of any two of the three basic components is given, the motion of the third basic component can be determined. That is to say, the motion of the third basic component is the synthesis of the motions of the other two basic components.
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▲Bevel gear differential gear train (motion synthesis)
Motion decomposition: Using the differential gear train, the rotation of one basic component can also be decomposed into the rotation of the other two basic components according to the required ratio.
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▲Automobile differential (motion decomposition)
Finally, let's take a look at the tall
3D demonstration animation of the working principle of the high-speed rail gear coupling
The birth of a gear, I did not expect the machining process to be so complicated
