Difference between worm gear and helical gear

The worm gear cooperates with the worm to realize the transmission, which is called the worm gear transmission pair.

(1) The rotation axis of the worm gear is perpendicular to the optional axis of the worm, at 90 degrees, and a large transmission ratio can be obtained, which is more compact than the staggered-axis helical gear mechanism, and the meshing tooth surfaces of the two wheels are in line contact, so its bearing capacity is greatly high. on the staggered axis helical gear mechanism;

(2) The worm drive is equivalent to a screw drive, which is a multi-tooth meshing drive, so the drive is stable and the noise is small.

(3) When the lead angle of the worm is less than the equivalent friction angle between the meshing gear teeth, the mechanism is self-locking and can realize 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.

(4) However, the worm gear 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. .And the axial force of the worm is large.

The helical gear cooperates with the helical gear to realize the transmission, and there are parallel shafts and staggered shafts, that is, the input shaft and the output shaft are parallel or staggered at a certain angle.

(1) The helical gear can also achieve a large transmission ratio through multi-stage combination, but the single-stage transmission is generally not as good as the worm gear.

(2) Both the speed-up and the deceleration can be used, and the transmission is stable. The axial force generated by the helical gear transmission must be considered in the design and application.

(3) Under the condition that the transmission is relatively large, the diameter of the index circles of the two wheels can be approximately equal by properly selecting the helix angle of the two wheels, so as to be close to the same strength.

(4) Due to the greater relative sliding between the meshing gear teeth along the tooth length direction in the staggered shaft helical gear transmission, the mechanical efficiency of the transmission is low, but it is not low compared with the worm gear.

(5) There is point contact between the meshing tooth surfaces of the two gears of the staggered shaft helical gear. In staggered helical gear drives, axial forces are also generated.

(6) For the staggered shaft helical gear transmission, the helix angles of the two wheels are not necessarily equal, so their end face modulus and end face pressure angle are not necessarily equal respectively, which is different from the parallel shaft helical gear transmission.

The applications are as follows:

(1) Staggered shaft helical gear transmission is not suitable for high-speed and high-power transmission, and is usually only used in instruments or auxiliary transmissions with small loads. Parallel shaft helical gears are widely used.

(2) Worm gear and worm mechanism are often used in occasions where the two axes are vertically staggered, the transmission ratio is large, the transmission power is not large or intermittent work.