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The contact spot of the gear pair is re-examined with the coloring method. The contact spot on the tooth length is about 50, and the tooth height is 40 to 45. This bonding surface meets the requirements of the standard contact spot of the 8-stage gear. We re-examine the gear tooth thickness and the length of the common normal line. The results are all around the midline of each tolerance zone, which fully meets the requirements. The gear center distance is re-examined and the result is 818.97mm. Although it meets the drawing requirements, it is smaller than the theoretical center distance.
The theoretical calculation of the meshing backlash of the gear pair can be seen from the above measurement results: the backlash of the gear pair is below the minimum specified value, for which we calculate the gear side clearance. The crankshaft gear Z is found by the table. The limit value of the circumferential limit is: fpt1=-0.192mm. The intermediate gear Z2 is found by the table. The limit value of the circumferential section is fpt2=-0.168mm. The minimum minor backlash value of the gear pair: jn=0.228mm It can be seen that the minimum limit clearance of 0.22mm specified in the drawings is only based on the deviation of the tooth thickness, and does not consider the influence of various comprehensive errors in processing and assembly.
Gear pair meshing backlash error analysis When considering the comprehensive factor, the measurement result is compared with the minimum deviation value verification formula: the backlash required for normal lubrication can be obtained according to the lubrication condition and the gear line speed (m/s). . Jnb: is the backlash required to consider the gear drive temperature change.
A is the gear center distance. [1(t1-20)-2(t2-20)] is the difference in length caused by the temperature change of the gear and the case material. In the above example, the difference between the linear expansion coefficient of the gear material (42CrMoA) and the gear-related housing material (20 steel) is extremely small, so jnb≈0. So jna, jnb are the minimum limit values ​​for ensuring the meshing backlash of the gear, and gear machining , assembly has nothing to do.
2fasinn is the amount of backlash change caused by the center distance error. It can be seen from the formula that the change of the center distance Δfa increases the influence of the backlash by a multiple. This error is one of the important factors affecting the size of the backlash. The measured center distance value in the above example is 818.97mm, which is 0.03mm away from the theoretical center distance of 819mm, thus affecting the backlash value.
Since the measured center distance is changed in a small direction, the backlash must be reduced. Fpb1, fpb2 is the base limit deviation of gear 1 and gear 2; F is the tooth tolerance; fx, fy is the axis non-parallelism tolerance (x direction, y direction); k value is the gear pitch error, tooth direction The comprehensive reflection of the error of the error, the non-parallelism of the axis and the like, these three errors are similar to the shape error and position error of the tooth profile. Reflected on the side gap is the contact area size, that is, the contact accuracy of the tooth length and the tooth height.
In addition to the four errors of the above calculation formula, there is an error that the diameter of the gear index circle and the center of the gear rotation are not completely coincident. The cumulative error of the circumference caused by such misalignment cannot be checked in a single gear measurement, as shown in the figure. This eccentricity inevitably causes periodic changes in the backlash, resulting in uneven backlash size. The herringbone gear structure is as shown. The crankshaft gear positioning size is 620H7h6, the minimum clearance is 0, the maximum clearance is 0.114mm. The intermediate gear positioning size is 194H7R6, the maximum clearance is 0.042mm, and the maximum interference is 0.33mm. Seen from the cooperation of the two gears and the shaft The main problem of the concentricity of the crankshaft gear rotation should be solved.
Assembling method of gear meshing backlash According to the above analysis, we perform the internal control index on the maximum factor center distance tolerance affecting the backlash, that is, the deviation takes the value of "". If the assembly still fails to meet the requirements, the normal intermediate gear shaft can also be replaced with an eccentric shaft. The eccentricity is 0.5mm, and the center distance of the gear mesh is finely adjusted by the eccentricity of the shaft to finally ensure the backlash requirement.
If the backlash is not uniform, the following measures can be taken: First, in the gear assembly, check the consistency of the 620H7h6 positioning hole in the four directions; secondly, adjust the mounting reference and the mounting reference when hobbing to make it consistent. That is to say, the outer circle is found in the assembly and processing, and the runout is not more than 0.03mm. Through the calculation and analysis of the gear gap of the diesel engine gear and the actual test, it is proved that the method can ensure the high quality meshing of the gear well. According to the commonality of the gear transmission, the method of adjusting the gear meshing backlash can also be applied to other products with higher requirements on the gear transmission.
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