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Transmission in mechanical design

Updated:24-06-2020
Summary:

The transmission is used to change the speed and torque […]

The transmission is used to change the speed and torque from the engine. It can change the transmission ratio of the output shaft and the input shaft in a fixed or stepwise manner, also known as a gearbox. The transmission is composed of a variable speed transmission mechanism and a control mechanism, and some automobiles also have a power output mechanism. Most of the transmission mechanisms are driven by ordinary gears, and some are driven by planetary gears. If the speed of the transmission output shaft can be continuously changed, it is called a continuously variable transmission, otherwise it is called a stepless transmission.
How the transmission works
The mechanical transmission mainly uses the principle of speed reduction of gear transmission. Simply put, there are multiple sets of gear pairs with different transmission ratios in the gearbox, and the shifting behavior of the car when driving is to make the different gear pairs in the gearbox work through the control mechanism. For example, at low speeds, let the gear pair with a large transmission ratio work, and at high speed, let the gear pair with a small transmission ratio work.
The two tower-shaped pulleys are respectively fixed on the shafts I and II, and the transmission belt can be shifted in three different positions on the pulley. Since the diameter ratios of the two tower-shaped pulleys at different stages are different, when the shaft I rotates at a fixed speed, the shaft II can get three different speeds by changing the position of the belt. Most of this type of transmission uses flat belt transmission, and V belt transmission can also be used. Its advantages are smooth transmission and simple structure. However, the large size makes it inconvenient to shift.

Slip gear transmission
The sliding gear can be moved on the shaft, and the torque transmitted by it is transmitted to the shaft. It is connected by a sliding key or a spline. The gears are engaged to realize the speed change. This type of transmission is convenient for shifting, compact in structure, high in transmission efficiency, and widely used, but helical gears cannot be used.
Clutch gear transmission
Helical gears or herringbone gears can be used to make the transmission smooth. If a friction clutch is used, the speed can be changed during operation. The disadvantage is that the gears are in a state of constant meshing, they wear out faster, and the clutch occupies more space.
2.2 CVT
In order to adapt to changes in working conditions, some machines often need to continuously change their working speed, which requires the use of a continuously variable transmission. There are many types of continuously variable transmissions, including mechanical, electric, electromagnetic and hydraulic. The mechanical continuously variable transmission has the advantages of simple structure, good transmission performance, strong applicability, convenient maintenance and high efficiency, so it is widely used.
Pros and cons of continuously variable transmission
Advantages: simple structure, slipping between the transmission elements during overload can avoid damage to the machine; the transmission is stable and no noise; it is easy to smoothly and continuously change the speed, etc.;
Disadvantages: accurate transmission ratio cannot be guaranteed; transmission efficiency is low; external dimensions are large; speed range is small

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