Study On Theory Of 2K-H Pin And Cycloid Planetary Transmission Performance

The one-tooth-difference 2K-H cycloid-needle planetary transmission mechanism is used extensively for continuous adjustment of the seat back angle on various automobiles. The mechanism provides both the angle-adjusting function and the self-locking function. It also features a compact structure, ease of operation, a small adjusting moment, a high precision of adjustment, and the adaptability to being motor-driven.For the purpose of seat back angle adjustment, the transmission mechanism must have both properties of a small adjusting moment and a large self-locking moment. The two requirements, however, in general conflict with each other and a balance between the driving or adjusting performance and the self-locking performance has to be carefully achieved. The dissertation is devoted to build an accurate mathematical model that describes the dependence of the positive and the negative output moments on the kinematic parameters of the transmission mechanism. Such a model provides a theoretical basis to design optimization in order to maximize the adjusting performance while maintaining self-locking performance.A new definition of the backlash between gear teeth is proposed for the first time. The backlash is defined as the minimum distance between the teeth of a pair of gears in the direction of their common normal. Based on this definition, a method is presented for calculating the backlashes and the geometrical angles for theoretically modified tooth profiles and for tooth profiles fabricated by CNC machines. It is used for calculating actual the number of teeth at meshing. The method is tested with simulations of meshing states and is used to investigate the effects of tooth profile modifications and machining steps on the performance meshing.Based on the mechanical analysis of the 2K-H cycloid-needle planetary transmission mechanism, a model for the meshing state with backlash is proposed. The model, which takes into account of the friction between tooth profiles and the friction at bearings and elastic deformation of meshing teeth profile and the weights of accessories, corrects the linear relationship of force and deformation between meshing teeth profile, relates the output moment with input moment and kinematic parameters. The model is verified by comparing with static measurements on the angle-adjusting mechanism.A mathematical model of the instantaneous and average efficiencies of the conversion mechanism of the original 2K-H epicycle gear train is proposed, and is used for calculating the mechanical efficiency of both the positive and the negative transmissions. The calculated efficiencies of the conversion mechanism of the angle adjustor are in good agreement with experimental measurements. The output moments inferred from the efficiency model are consistent with the direct calculations using the method proposed in 2.The effects of various factors on the performances of the transmission mechanism are analyzed using the models proposed in 2 and 3. Effective measures to increase the self-locking moment and/or to reduce the adjusting moment are presented. A new method of tooth profile modification, i.e., modifying teeth according to the meshing position, is proposed and is used to improve the self-locking performance of a rotary-handle angle-adjusting mechanism for automobile seat backs.A MATLAB software package that integrates all work mentioned above is developed. The package is used for the design of the 2K-H cycloid-needle planetary transmission mechanism. It calculates the adjusting moment, the self-locking moment, tooth backlashes, and void angles from known kinematic parameters. The package provides a basis for further design optimization such as the optimization of kinematic parameters and the optimization of the tooth profile modification.