Conjugation Criterion for Making Clearance of the Meshed Helical Surfaces¹

The meshing clearance of the helical surfaces under the condition of conjugation is studied in depth in this paper, which is significant to industrial practice as well as scholastic field. A general conjugation criterion for making clearance of the meshed helical surfaces is clearly defined for the first time, which states that the rotation angle of return stroke caused by clearance for all the points in the tooth surface must be identical. Based on this criterion, it is shown that the commonly adopted uniform clearance is not reasonable for all the meshed helical surfaces. For traditional involute helical surfaces, it is intrinsically correct to adopt the uniform clearance. However, for the helical surfaces with complex transverse tooth profiles, such as those applied to the twin screw compressors, it is unreasonable and harmful to do so due to violation of the conjugation criterion, leading to a severe local contact in the tooth surfaces and higher noise level and, hence, damaging the performance of the helical surfaces in application. As a general principle, the “uniform rotation angle” clearance distribution is a unique one, satisfying the conjugation criterion.