Abstract:  In order to solve the problem of improving the contact ratio of non-circular gears with composite tooth profiles, the design method of non-circular gears with composite tooth profiles was studied. Firstly, a design method for composite non-circular gears with increased tooth height coefficient, reduced curve pressure angle, and negative displacement was proposed. The design of high contact ratio composite tooth profiles for variable involute incomplete variable cycloid tooth profiles was carried out, and the non-circular cylindrical gears with high contact ratio was designed. Then, the variation law of tooth height coefficient, modification coefficient, and pitch curve pressure angle on the contact ratio degree of non-circular gear involute profile and variable involute incomplete variable cycloid composite profile was analyzed, and two types of non-circular gear composites with increased contact ratio were manufactured. Finally, the tooth backlash of non gears with increased tooth height coefficient and reduced curve pressure angle was measured and compared with the standard involute tooth profile tooth backlash. The measurement tests on the transmission ratio of non-circular gears with large composite tooth profiles were conducted, and the comparative analysis of their load-bearing capacity (the driving gear was fixed, and a torque of 15 N·m was added to the driven gear) was simulated. The research results show that the tooth backlash of non-circular gears with composite tooth profiles (reducing the curve pressure angle by 0.106mm and increasing the tooth height coefficient by 0.107mm) is significantly smaller than that of non-circular gears with involute tooth profiles (0.173mm). The experimental transmission ratio of non-circular gears with large composite tooth profile is consistent with the theoretical simulation transmission ratio; the design method of high contact ratio tooth profile with reduced curve pressure angle has the best load-bearing capacity (maximum stress value 157.5 MPa), while the design method of high contact ratio tooth profile with increased tooth height coefficient has the worst load-bearing capacity (maximum stress value 213.2 MPa). It indicates that the composite tooth profile non-circular gear design method of increasing the tooth height coefficient and reducing the pressure angle of the pitch curve is effective for increasing the high contact ratio of non-circular gears.
Key words: high contact ratio composite tooth profile; involute tooth profile non-circular gear; tooth height coefficient; displacement coefficient; pitch curve pressure angle; variable involute-variable cycloid; tooth backlash