Contact Strength of a Skew Conical Involute Gear Drive in Approximate Line Contact
| Autor: | Szu-han Wu, 吳思漢 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Of all the different types of gears, conical gears as the special type of general spatial gearing makes them not only suitable for parallel axis transmission, but also for cases with intersecting or skew axes. However, one of the weak spots of conical gears is less surface durability in spatial applications due to point contact problems, although transmission accuracy is not correspondingly sensitive to assembly error. From the viewpoint of design, this study suggested two concepts to increase the surface durability of conical gears. Skew conical gear drives can be designed as gear pairs, with either “profile-shifted transmission”, or “approximate line contact”. The profile-shifted transmission can give us the possibility to adjust the contact position of a conical gear pair for better tooth contact bearing just only through changing certain gearing or assembly data. On the other hand, an approximate line contact drive has a contact ellipse with a large major-to-minor-axis ratio, which allows it to overcome the weakness of conical gear drives for application in power transmission. This gearing design approach is characterized by reduced edge contact sensitivity and increased surface durability. The edge contact sensitivity that can arise with this kind of gear drive due to assembly or manufacturing errors is evaluated by analyzing the value of the shift of the line of action caused by such errors. The surface durability is evaluated by calculating the Hertz stress. Some guidelines are developed based on the analysis of the influence of the gearing parameters on the edge contact sensitivity and the surface durability made possible using this design approach for conical gear drives in the approximate line contact. An efficient approach for loaded tooth contact analysis (LTCA) of conical gear drives is developed. Two new models are developed for the meshing and contact stress anslyses. This approach differs from conventional TCA methods in that the meshing analysis is based on the line of action characteristic of involute gearing. A numerical method is applied to calculate the contact stress. The non-Hertzian contact problem is solved giving due consideration to the influences of the tooth contact deformation and tooth bending deflection. The approach is not only suitable for application for cases of non-Hertzian contact, but also for practical cases, such as in gear drives with end-relief. A practical example is given to demonstrate the feasibility of the approximate line contact design. The LTCA results of the example are also compared with those of solved by the finite element method (FEM) to which they are in good consistence. Finally, a back-to-back testing equipment was developed for testing the surface fatigue strength of a skew conical gear drive. The objective of the tests was to determine the limited service life (number of load cycles) of the skew conical gear drive in approximate line contact for tooth pitting fatigue failure under several load levels. Three test gear pairs (S45C, hardening and tempering, but no case hardening) with different applied torques were tested: 200 Nm, 300 Nm, and 350 Nm. The results indicated that the surface durability of the approximate line contact design is indeed increased. Furthermore, the kinds of gear surface failures for the test were pitting, cold scuffing, and wear. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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