Contact Ratio Analysis of N-lobed Involute Modified Noncircular Bevel Gears

Noncircular bevel gears (NBGs) is a kind of spatial transmission mechanism that can be used to transmit motion and power with a variable transmission ratio between two intersecting axes. Being directed against N-lobed involute NBGs with less tooth number, the varying-coefficient-profile-shift-modification method has been presented. The equations of the modified addendum and dedendum curves are deduced. Meanwhile, the 3D models of NBGs are obtained by the modified shaper cutter. Given that the contacting line of NBGs is no longer fixed spherical curve, a novel evaluating method for the continuous transmission is proposed. By dividing the rotating angle of the driving gear when the tooth profile is meshing with an angle of the following gear pair which is about to getting into meshing, the contact ratio is obtained. As an example, the meshing process of 3-lobed 9-teeth and 4-lobed 12-teeth NBGs are analyzed, and the contact ratio of the modified NBGs meshing is calculated. This method for analyzing the contact ratio is also suitable for other kinds of gears.