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Loaded transmission error is an important parameter in evaluating the meshing performance of gears. The smaller the fluctuant amplitude of the loaded transmission error is, the better the meshing performance is. In view of the insufficient research on loaded transmission error of internal spur gears, software Romax is used to establish models of internal short tooth spur gear pairs in this research. The influence of tooth profile and gear helix modification parameters on fluctuant amplitude of loaded transmission error is studied, and some influence laws of the modification parameter on the fluctuant amplitude are obtained. A modification optimization method for internal short tooth spur gear pairs is investigated using the particle swarm algorithm. The research results lay a foundation for improving the meshing performance of internal short tooth spur gears.

The contact ratio is an important performance index in the design of gear transmission, and it directly affects the load-bearing capacity and transmission stability of herringbone gears. The requirements of contact ratio must be met when designing gear pairs. Firstly, the stiffness excitation and meshing impact excitation of herringbone gear system are introduced, and a bending-torsion-axis coupling model of a pair of herringbone gear transmission system is established by means of lumped-mass method. Then, the influence of contact ratio on time-varying meshing stiffness and meshing impact force is analyzed. Finally, the influence of contact ratio on the dynamic meshing performance of herringbone gear pairs is studied. The results show that when the contact ratio increases from 2.72 to 3.08, the peak-to-peak value of time-varying meshing stiffness is reduced from 4.653 3×10~8 N/mm to 3.229 9×10~8 N/mm, and the maximum meshing impact force is reduced from 2.23×10~3 N to 1.92×10~3 N, and dynamic meshing force curve of the gear pair becomes smooth, and the dynamic load factor is also reduced from 1.23 to 1.18. It is concluded that the increase of contact ratio can achieve the effect of system vibration reduction, noise reduction and transmission stability.

The gear modification is an important technique to improve gear transmission performance. A new topological modification method with circular tooth profilein gear cutter and tooth drum-shaped is put forward. Based on the gear meshing theory and the tooth contact analysis（TCA） technology,the modification parameters for helical gear are designed,and error sensitivity is studied,that is,the effects of helix angle and pressure angle errors on the transmission error and contact trace. The study shows thats gear with the proposed topological modification is insensitive to the helix angle and pressure angle errors,and it has good performance without edge contact. The result provides a theoretical foundation for the modification of helical gear.

Gear modification is an important technique to improve its transmission performance. The herringbone gears are combined with star gear transmissions to form a herringbone star gear transmission,and its modeling method of modified tooth surface as well as computing method of loaded transmission error are researched. With the target of the minimum amplitude of loaded transmission error,the gear modifications are optimized for the sun-star meshing gear pair and the star-ring meshing gear pair respectively. The modifications from optimization are redistributed,and the rationality of the redistribution is verified by the means of TCA and LTCA techniques. The research results provides a theoretical basis for the modification design of a star gear train.