Noncircular gear of a stepless transmission mechanism

Circular gear is a kind of special gear parts, its pitch curve is not circular, so the speed ratio of non-circular gear will change at any time when transmitting power, so it is often used in the mechanism of variable transmission ratio. Noncircular gear transmission, like circular gear transmission, has excellent characteristics of compact mechanism and reliable transmission. However, the application of noncircular gear is affected due to the difficulty of design and machining. The design of non-circular gear mainly includes tooth profile matching design, tooth root transition curve design and tooth side clearance design, and the design theory is complex. Although many domestic literatures have introduced the transmission theory and design of non-circular gear, there are few literatures about the design of non-circular gear backlash. For example, written in the 1980s-1990s, it is a classic monograph on non-circular gear transmission in China, focusing on the derivation of theoretical formula, without introducing the design of non-circular gear backlash. The new research on non-circular gear design in China introduces the use of numerical calculation software and modeling software to design non-circular gear, but there is no design of backlash. The accurate model of non-circular gear without backlash can not be used for high-precision machining such as wire cutting, powder metallurgy and 3D printing. Because of the influence of manufacturing error, assembly error and thermal expansion, the non-circular gear without backlash will be jammed. For the design of tooth root transition curve of non-circular gear, only through the simulation diagram of gear shaping, the design results are clearly displayed, but the design and calculation principles are not elaborated in detail.

The complex profile of non-circular gear makes its machining difficult. Now the commonly used gear shaping and hobbing processing methods can not reach the grinding accuracy, and can not be applied in high-speed and high-precision transmission; High precision wire cutting machine can achieve error less than or equal to 0.003 mm, RA 0.2 μ However, it needs designers to provide accurate non-circular gear profile curve, and drawing accurate profile needs theoretical calculation. It is still a great challenge for mechanical designers to design pitch curve, tooth profile, tooth root transition curve and tooth side clearance. To sum up, the use of modern design methods to achieve accurate transmission design of non-circular gear, and then meet the requirements of high-precision machining, is still worth exploring and improving.

On the basis of previous studies, the design of non-circular gear is further explored. The accurate transmission design of non-circular gear of a stepless transmission mechanism is carried out by using MATLAB programming. An accurate design method of non-circular gear backlash is proposed, and the design method of tooth root transition curve and avoiding undercutting as well as the position transformation principle of gear shaper cutter are introduced in detail; Finally, the design is verified by wire cutting prototype, hoping to provide a reference for the majority of mechanical designers.