To obtain gear meshing surfaces with good contact characteristics

multi-point contact gears with ladder shape of teeth is proposed based on the principle of conjugate curves. Four-point contact gears with ladder shape of teeth is taken as an example to present the design of basic tooth profiles and tooth surface design of hob. Basic tooth profiles are divided into two sections

non-working profiles and working profiles containing convex part and concave part. A circular arc and a parabolic curve are adopted as working tooth profiles to generate the upper meshing surface and the lower meshing surface respectively. Non-working tooth profiles contain a transition profile and a dedendum profile. Two circular arcs are adopted for non-working profiles. According to basic tooth profiles and gear meshing theory

the equations of the hob’s working

transition and dedendum surfaces are derived and solved by a developed program. The exactitude solid model of the hob is set up. The hob was manufactured and applied for generating gears. The four-point contact gear drive with ladder shape of teeth is acquired and the gear box prototype was assembled. The contact pattern of the gear drive is detected. Results show that the gears satisfy the design requirement. The paper is an extension of the principle of conjugate curve. The research method is suitable for other multi-point contact gears with ladder shape of teeth.