In mechanical design, the knowledge of gear transmission occupies an important position. Gear transmission is a mechanical transmission that transfers power and motion by using the teeth of two gears to mesh with each other. Among all mechanical transmissions, gear transmission is the most widely used, which can be used to transmit the motion and power between two shafts that are not far away from each other.
The following introduces the knowledge related to gear transmission, so that it can be flexibly used in design.
Features of gear transmission:
High efficiency. Among the commonly used mechanical transmissions, the gear transmission efficiency is the highest, and the closed transmission efficiency is 96%~99%, which has great economic significance for high-power transmission;
Compact structure, less space than belt and chain drives;
Stable transmission ratio is often the basic requirement for transmission performance. Gear transmission has been widely used, precisely because of its characteristics;
The gear transmission with reliable operation and long service life, correct and reasonable design and manufacture, and good use and maintenance, is very reliable, and its service life can be as long as ten or twenty years, which is incomparable to other mechanical transmissions. This is particularly important for vehicles and machines working in mines;
However, the manufacturing and installation accuracy of gear transmission is high, the price is expensive, and it is not suitable for occasions with excessive transmission distance.
Gear transmission can be divided into cylindrical gear transmission, bevel gear transmission, non-circular gear transmission, rack transmission and worm transmission according to the shape of the gear.
Cylindrical gear drive
A gear transmission used to transmit power and motion between parallel shafts. According to the relative relationship between gear teeth and gear axis, cylindrical gear transmission can be divided into three types: straight cylindrical gear transmission, helical cylindrical gear transmission and herringbone cylindrical gear transmission.
The transmission power and speed of cylindrical gear drive can be applied in a wide range, with power ranging from less than one thousandth of a watt to 100000 kilowatts and speed ranging from very low to 300 meters per second.
The meshing characteristics can be seen from the formation process of the tooth profile surface. When the involute straight cylindrical gear is engaged, the contact line of the tooth profile surface is a straight line parallel to the axis. During the meshing process, the entire tooth width enters and exits the mesh at the same time. The force on the gear teeth is also suddenly added or removed, so the transmission stability is poor, and the impact and noise are large.
Bevel gear drive
Bevel gear transmission is a gear transmission composed of a pair of bevel gears between intersecting shafts, also known as bevel gear transmission. Bevel gear transmission can be divided into straight bevel gear transmission, helical bevel gear transmission and curved bevel gear transmission according to the shape of tooth line, of which straight teeth and curved teeth are widely used.
Non-circular gear drive
It refers to a gear transmission in which the pitch surface of at least one gear is not a rotating surface.
Rack drive
The transmission structure of gear and rack. The rack is divided into straight rack and helical rack, which are used with straight cylindrical gear and helical cylindrical gear respectively; The tooth profile of a rack is a straight line rather than an involute (plane for the tooth surface), which is equivalent to a cylindrical gear with an infinitely large dividing circle radius.
worm drive
It is a kind of transmission that transfers motion and power between two spatially interlaced axes. The included angle between two axes can be any value, usually 90 °.
Worm drive is composed of worm and worm gear. Generally, the worm is the driving part. Worms and threads have the same right and left rotation, which are called right and left worm respectively. If there is only one helix on the worm, it is called a single headed worm. That is, if the worm rotates once, the worm gear rotates over one tooth. If there are two helix lines on the worm, it is called a double headed worm. That is, if the worm rotates once, the worm gear rotates over two teeth.
According to the tooth profile curve of gear teeth, it can be divided into involute gear transmission, cycloidal gear transmission and circular arc gear transmission. A transmission consisting of more than two gears is called a gear train. Gear transmission can be divided into ordinary gear transmission and planetary gear transmission according to whether there is axial motion gear in the gear train. The gear with axial motion in the gear train is called planetary gear.
