| 摘要(英) |
Because the loads acting on the contact tooth pairs and the cranks of the cycloid planetary gear drives with tooth number difference (abbr. TND) of one are very large, and the contact ratio is reduced with flank modification, the load capicity cannot be enhanced effectively. Therefore the design concept by using TND of two is proposed in the study to give a possibility to improve the loaded contact characteristics.
The cycloid disk with TND of two can be regarded as combination of two sam base cycloid profile rotated against each other with an pitch angle. Therefore the analysis model of the cycloid planetary gear reducers with TND of two can be expaned from the model with TND of one. With reguarding odd and even numbered tooth pairs, the gear meshing analysis and the loaded tooth contact analysis (LTCA) model of the cycloid profile with TND of two can be established based on the developed mathematic model and the related analysis models of the cycloid profile with TND of one. The LTCA approach in the study is based on the influence coefficient method with consideration of bearing stiffness.
In this parper, the influences of the design parameters, i.e., the pin raidus and the eccentricity, on the loaded contact characterisitcs, such as the flank profile, the contact ratio, the shared loads and the contact stresses. Based on the analysis results, appropriate design parameters are determined for the following analysis: (1) the effect of the bearing stiffness of the loaded tooth contact characteristics, and (2) comparative analysis with the conventional drives with TND of one on the loaded contact charateristics.
The results from the influence analysis of parameters show that the cycloid drive with TND of two having smaller pins and a larger eccentricity owns a larger contact ratio and reduced shared loads. The eccentricity affects the variation of the load sharing stronger than the pin radius, not only because of the tooth profile, but also because of the transmission angle. A larger eccentricity can lower the shared load and the contact stress, but smaller pins reduce shared load and increase larger contact stress sightly.
The influence of the bearing stiffness, as the results show, causes the contact of the tooth pairs occuring earlier than the condtion without considering the bearing stiffness, because of additional displacements with three degrees of freedom. The maximum load sharing is enlarged because the displacement is closer to the front part of tooth pair due to the transmission angle. Moreover, the variation of the shared load on flank with considersing bearing stiffness performs in cyclic jumping type, but the period duration is reduced as a half due to the change of odd and even numbered tooth pair change. Even so the condition of bearing stiffness is not impact on the bearing load.
The comparative analysis results with TND of one show that the maximum sharing load in the case of TND of two can be reduced 35% relative to TND of one, and is distributed more soomthly. On the other hand, the maximum contact stress for TND of two can be enlarged 25% with respect to TND of one. But the contact stress for TND of two still remains at the end of contact, and the contact stress concentration occurs due to the edge effect of the tip corner. Furthmore, the radial bearing load in the case of TND of two can reduce 50% relative to the case of TND of one. But the lowered radial force is still much smaller than the circumferential force. The radial bearing force reduce just 5% relative to TND of one.
From the analysis results of this paper, the cycliod planetary gear drives with TND of two can effectively increase the contact ratio and reduce the maximum load sharing and the maximum contact stress. However, it can not efficiently reduce the bearing load on the crankshaft.
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