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During the transmission process, the meshing of the helical gear is point contact, and the meshing of the worm gear is line contact. Whether different meshing conditions have different transmission efficiencies needs to be clarified.
In fact, the bearing friction loss and the splash loss cause the power loss is not large, generally take 23 = 095096. For the design of the partial rotary electric device is negligible, because the transmission member is slower and will not be affected. The main power loss of the worm gear pair is the meshing friction loss, that is, the influence of 1 is the largest, and the calculation of 1 in the mechanical design is the same as that of the spiral pair, which is: 1=tgtg(v) where the helix angle on the worm index circle is v Equivalent friction angle, v=arctgfv worm helical gear transmission can be used to calculate the meshing friction loss of the above formula, there is no clear theoretical basis, because it is a special transmission type between the helical gear and the worm gear.
The mechanical principle literature only describes the low efficiency of the helical gear transmission (relative to the spur gear or the helical gear of the two-axis parallel drive) but no specific data. Some data shows the meshing efficiency of the helical gear when the two axes are staggered at 90°. It varies with the helix angle of the tooth between 069075, but the data does not provide the exact transmission for the special type of meshing of the worm and the helical gear. Efficiency, only the calculation method is similar to the worm gear pair.
To determine the efficiency of the two different transmission types, we adopted a test comparison method. It can be seen from the test results that the QX efficiency of the worm helical gear is nearly double that of the QB1 using the worm gear pair, and the difference is more significant. Intuitively, the former should have higher efficiency, otherwise it is more difficult to obtain Tc with single-phase 004kW motor, max=150Nm. Of course, the above test does not consider the difference in the material of the transmission, but at least some problems can be explained.
22About the assembly characteristics of the worm helical gear The axial displacement of the driven gear helical gear does not have a great influence on the transmission performance when the transmission member is engaged, that is, the central plane position of the worm shaft support hole does not need to be strictly controlled in the main casing processing, and even The non-perpendicularity requirements with the follower shaft are also loose. It is also not necessary to excessively require the axial displacement and the amount of swaying of the helical gear in the assembly of the transmission member sleeve.
In addition, in the worm gear transmission, the general assembly procedure is that the worm shaft portion is assembled after the worm wheel shaft sleeve, and the worm helical gear shown can first assemble the worm shaft sleeve (including the disc spring, the bearing, etc.). This feature is necessary for the multi-turn stroke motion extraction position.
The above two points will bring convenience to product assembly and parts manufacturing to some extent. The worm gear and worm gear pair is not only unable to be assembled as easily because of the curved shape of the worm gear tooth width, that is, the throat diameter of the tooth tip, and the center plane position of the worm is also much higher.
3 The strength problem of the worm helical gear transmission In practice, we found that the helical gear tooth surface damage or partial damage in the two worm helical gear meshing pairs. One example is that when the foreign prototype is studied, it is found that the torque output helical gear tooth surface has an indentation and is more obvious at the two end positions of the proximity switch. In another case, the ZA3 multi-turn electric device of our company has a broken gear in the stroke control movement.
Through analysis, we found the cause of the damage: (1) Since the worm helical gear transmission type is similar to the worm gear pair, the load condition of the worm gear pair strength calculation method can be analyzed (only the tooth surface fatigue strength is discussed). In fact, the calculation formula of the worm gear tooth surface contact fatigue strength is also based on the calculation method of the helical gear.
In the case where the output torque is the same and the geometric parameters are also substantially the same, the tooth surface contact strength of the worm gear pair is indeed better because the pressure is relatively small. For example, QB1 product's secondary worm gear m=125, Z2=70, d2=875mm, foreign QX prototype secondary helical gear m=2, Z2=40, d2=80mm. The former has been put on the market for several years, there is no gear tooth damage at present. The feedback information, while the latter is obviously indented due to the large force at the switch position, of course, the materials of the two also have some differences.
(2) The ZA3 travel helical gear has a broken tooth phenomenon, mainly because the gear is located on the high speed shaft, and the sliding speed of the worm is higher during operation.
At this time, if the center distance error is large and the gear modulus is small, and the lubrication condition is not ideal, the tooth tooth damage may occur. This has been corrected in the design of the DDM series.
4 Conclusions In the mechanical design theory, the characteristics of the helical gear meshing have been discussed, and the problem of the special type worm helical gear in the use of the valve electric device has verified the theory. Through research, we believe that the transmission type is used on the valve electric device: when it is used as power transmission: (1) It can only be used for small part of the rotary product, and its output torque should not exceed 300Nm; (2) When conditions permit Try to increase the size of d2 to improve its stress; (3) choose a reasonable helical gear material.
In the high-speed shaft transmission movement should pay attention to: (1) to ensure good lubrication conditions; (2) the helical gear support shaft should have rolling bearings; (3) should control the center distance between the helical gear and the worm; (4) the modulus m should not be less than 15; (5) As far as space permits, increase the number of teeth to reduce the number of teeth engagement (generally has little effect on the stroke accuracy).
Analysis of the contradiction of the electric equipment of the new worm gear valve
2The characteristics of the worm helical gear transmission (1) can obtain higher transmission efficiency, which is very important for small electric devices powered by micro motors; (2) can obtain looser assembly conditions and ideal parts Processing technology.