What are the characteristics of helical gear transmission compared to spur gear transmission?Why are the modulus and pressure angle of helical gears divided into normal and end faces?Why take the normal surface parameter as the standard value?
(1) Compared with spur gear transmission, the main advantages of helical gear transmission are: ① Good meshing performance.In the helical gear transmission, the contact line of the gear teeth is a straight line inclined to the gear axis, and the gear teeth start to mesh and disengage gradually, so the transmission is stable and the noise is low. At the same time, this meshing method also reduces the manufacturing error. impact on transmission. ②The degree of coincidence is large.In this way, the load of each pair of gear teeth is reduced, so that the bearing capacity of the gear is relatively improved, the service life of the gear is prolonged, and the transmission is stable. ③The minimum number of teeth of helical standard gears without undercut is less than that of straight gears. Therefore, a more compact mechanism can be obtained by adopting helical gear transmission.Compared with spur gear transmission, the main disadvantages of helical gear transmission are: Due to the existence of the helix angle, the axial thrust Fa will be generated during transmission, and it will increase with the increase of the helix angle.
(2) Since the tooth surface of the helical gear is an involute helical surface, the tooth profile of the end surface and the normal surface tooth profile perpendicular to the helical direction are different, so its parameters are divided into end surface parameters and normal surface parameters.
(3) When manufacturing helical gears, rack-type tools or disc gear milling cutters are often used to process gears. When cutting teeth, the tool feeds in the direction of the helical line of the gear teeth, so it is necessary to follow the normal parameters of the gears. Select the tool.Therefore, the parameters on the normal surface of the helical gear (module, index circle, pressure angle, tooth tip height coefficient, etc.) are specified as standard values in the project.