XNUMX. Basic parameters of worm gear reducer:
Module m, pressure angle, worm diameter coefficient q, lead angle, number of worm heads, number of worm gear teeth, tooth tip height coefficient (take 1) and head clearance coefficient (take 0.2).Among them, the modulus m and pressure angle refer to the modulus and pressure angle of the worm shaft surface, that is, the modulus and pressure angle of the worm wheel shaft surface, and both are standard values; the worm diameter coefficient q is the diameter of the worm index circle and its modulus The ratio of the number m.
XNUMX. The calculation of geometric dimensions is basically the same as that of cylindrical gears. Several issues to be noted are:
Worm lead angle () is the included angle between the tangent of the spiral line on the worm index cylinder and the end surface of the worm. The relationship with the screw helix angle is that the helix angle of the worm wheel is large, the transmission efficiency is high, and when it is less than the equivalent between meshing teeth When the angle is rubbed, the mechanism is self-locking.
The introduction of the worm diameter coefficient q is to limit the number of worm gear hobs and standardize the worm index circle diameter. When m is fixed, q is large, the stiffness and strength of the worm shaft increase accordingly; when q is small, the lead The angle increases, and the transmission efficiency increases accordingly.
The recommended number of worm heads is 1, 2, 4, 6. When the value is small, the transmission ratio is large and self-locking; when the value is large, the transmission efficiency is high.
Unlike cylindrical gear transmission, the transmission ratio of the worm and worm gear mechanism is not equal, but the center distance of the worm and worm gear mechanism is not equal, but rather.
The determination method of worm wheel steering in worm gear drive can be determined according to the direction and direction at the meshing point K (parallel to the tangent line of the helix) and the velocity vector triangle should be drawn perpendicular to the axis of the worm wheel; Grip the worm in the right hand and use the four-finger thumb" to determine.
Third, the conditions for the correct meshing of worm gears and worms
1. The modulus and pressure angle of the worm and the worm wheel in the middle plane are equal respectively, that is, the end face modulus of the worm wheel is equal to the axial face modulus of the worm and is a standard value; the end face pressure angle of the worm wheel should be equal to the axial face pressure angle of the worm and is Standard value, namely == m, ==
2. When the staggered angle of the worm wheel and worm is equal to, it must be ensured, and the spiral direction of the worm wheel and the worm must be the same.
Fourth, the characteristics of worm gear and worm mechanism can get a large transmission ratio, which is more compact than the cross-axis helical gear mechanism
The meshing tooth surfaces of the two wheels are in line contact, and its load-bearing capacity is much higher than that of the cross-axis helical gear mechanism
Worm drive is equivalent to spiral drive, which is a multi-tooth meshing drive, so the transmission is stable and the noise is small
Self-locking.When the lead angle of the worm is less than the equivalent friction angle between the meshing gear teeth, the mechanism has self-locking properties and can achieve reverse self-locking, that is, only the worm can drive the worm, but not the worm.Such as the self-locking worm mechanism used in its heavy machinery, its reverse self-locking can play a role in safety protection.
The transmission efficiency is low and the wear is serious.When the worm gear is engaged in the transmission, the relative sliding speed between the meshing gear teeth is large, so the friction loss is large and the efficiency is low.On the other hand, the relative sliding speed causes serious wear and heat generation on the tooth surface. In order to dissipate heat and reduce wear, more expensive materials with good anti-friction and anti-wear properties and good lubricating devices are often used, so the cost is high. The axial force of the worm is large.
Worm gear mechanisms are often used to transmit the motion and power between two interleaved shafts.The worm wheel and the worm are equivalent to the gear and the rack in the middle plane, and the worm and the screw are similar in shape.