& lt 1 & gt； Straight cylindrical gear transmission;
& lt2> helical cylindrical gear drive;
& lt3> herringbone gear transmission;
& lt4> bevel gear drive;
& lt5> staggered shaft helical gear drive.
2 According to the working conditions of gears, it can be divided into:
& lt 1 & gt； Open gear transmission, gear exposure, can not guarantee good lubrication;
& lt2> semi-open gear transmission, the gear is immersed in the oil pool, with a protective cover, but not closed;
& lt3> Closed gear transmission, gears, shafts and bearings are all installed in a closed box, which has good lubrication conditions, dust and sand are not easy to enter, and the installation is accurate.
(3) Gear transmission can be classified according to the relative position of its axis.
(4) Gear transmission can be divided into cylindrical gear transmission, bevel gear transmission, non-circular gear transmission, rack transmission and worm transmission according to gear shape.
(5) 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 device 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 are gears with shaft motion in the gear train, and the gears with shaft motion in the gear train are called planetary gears. Gear transmission can be divided into closed, open and semi-open transmission according to its working conditions. Sealing the transmission in a rigid box shell and ensuring good lubrication is called closed transmission, which is widely used, especially for high-speed gear transmission. Open drive is exposed, so good lubrication cannot be guaranteed. It is only used for low-speed or unimportant drives. Semi-open transmission is in between.
The meshing law requires that the instantaneous transmission ratio i= the angular velocity of the driving wheel/the angular velocity of the driven wheel =ω 1/ω2 = constant in the process of gear meshing, which is guaranteed by the tooth profile. Fig. 2 shows that two meshing tooth profiles E 1 and E2 are in contact at any point k, and the common normal N 1N2 passing through the point k and forming the two tooth profiles intersects the connecting line O 1O2 at point C. The condition that the two tooth profiles keep in contact when meshing is that the tooth profile E 1 is at point K VK/kloc. The perpendicular lines from O 1 and O2 to N 1N2 intersect at N 1 and N2 respectively. The above formula shows that the tooth profiles of two wheels must meet the following conditions: no matter where the tooth profiles of two wheels contact, the common normal of the contact point must pass through the fixed point C node on the connecting line. This is the basic law of tooth profile meshing of circular gears. There are many curves that can satisfy this rule. In fact, we should consider the requirements of manufacturing, installation and bearing capacity. Generally, only involute, cycloid and arc curve are used as the working tooth profile of gears, and most of them are involute tooth profiles.
For involute gears, the base circle radii of wheel 1 and wheel 2 in Figure 2 are rb 1 and rb2, respectively. The straight line N 1N2 is the internal common tangent of two base circles, that is, the common normal of any contact point of two tooth profiles coincides with it. Because the two base circles have only one internal common tangent in one direction, the common normal of any contact point passes through the fixed point C, which shows that the involute conforms to the basic law of tooth profile meshing.
Two circles drawn through node C with O 1 and O2 as the center are called pitch circles. Wheel 1 pitch radius, involute gear with 2 pitch radius has the following characteristics: ①N 1N2 is the locus of contact points of two tooth profiles, which is called meshing line and is a straight line. ② The intersection point c is the common tangent tt of two circles, and the angle α′ formed by it and the meshing line N 1N2 is called the meshing angle, which is constant. (3) The pressure between tooth surfaces always follows the direction of the common normal N 1N2 of the contact point, so the pressure direction between tooth surfaces of involute gears is constant when transmitting power. ④ The transmission ratio is inversely proportional to the radius of the base circle of two wheels. After the gear is made, the base circle is determined, so even if the center distance deviates from the design, it will not affect the transmission ratio. This characteristic is called separability of transmission, which is very beneficial to the processing, assembly and maintenance of gears. ⑤ There is no slip between the tooth surfaces of the two tooth profiles when only node C contacts, and there is slip between the tooth surfaces when other points contact, and the further away from the node, the greater the slip. ⑥ Because the involute gear can mesh with the rack with straight tooth profile, it can be generated and machined with a straight tooth profile cutter, which is easy to manufacture and has high machining accuracy.
Coincidence is an important parameter affecting gear continuous transmission. As shown in Figure 2, the meshing of gear teeth begins with the contact between the tooth root of the driving wheel and the tooth crest of the driven wheel, that is, the intersection point A between the tooth crest circle of the driven wheel and the meshing line is the starting point of meshing. With the rotation of wheel 1, wheel 2 is pushed to rotate, and the contact point moves along the meshing line. When the contact point moves to the intersection e of 1 tooth top circle and meshing line (dotted line position in the figure), the tooth profile meshing ends and the two tooth profiles begin to separate. Point e is the meshing termination point, which is the actual meshing line length. If the first pair of teeth still contact at point D before point E and the last pair of teeth contact at point A, the transmission is continuous; If the first pair of teeth have left the point E and the last pair of teeth have not yet entered the meshing, then the transmission is interrupted. Considering the influence of manufacturing and installation errors and gear deformation, ε≥ 1. 1 ~ 1.4 is often required in practice. The greater the coincidence degree, the smoother the transmission. The above refers to the end coincidence degree of cylindrical gears, and helical cylindrical gears also have longitudinal coincidence degree.
The condition that a pair of gears can mesh correctly is that they must have equal modulus and equal pressure angle.