The Influence of the Initial Contour Parameters on the Contact Ratio of Involute Gearings

Previously, GOST 13755–81 specified a unified standard initial contour, i.e. the tool rack teeth profile. The rolling method was dominant; a family of surfaces was enveloped by tools in the process of form-generation of involute gears. The effectiveness of such standardization was enhanced by the widespread large-scale and mass production. Recently, changes in the nature and technology of production have led to a significant expansion of possible standard initial contours and their parameters. In many cases, manufacturers reject the enveloping method as well as the involute engagement in general. However, the contour parameters are still the foundation of the standard Cylindrical Involute External Gearing. Calculation of Geometry. Thus, even with the complete rejection of the initial contour, its effect on the gearing quality, namely on the contact ratio, remains unchanged. The transverse contact ratio is the ratio of the length of the engagement line segment to the normal pitch equal to the pitch of the base circumference of the pinion. In this study, dependencies of the transverse contact ratio on the number of pinion teeth, speed ratio, pressure angle and addendum coefficient are obtained. The results obtained can be used to select the initial contour parameters that provide the required traverse contact ratio, making the enveloping method and the initial contour (tool rack) redundant. It is established that the optimum transverse contact ratio equals 2. However, to compensate for manufacturing and assembly errors, the values of the number of pinion teeth, speed ratio, pressure angle and addendum coefficient should be selected so as to slightly exceed the above-mentioned transverse contact ratio.

References

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