Research On Key Problems Of High-Speed-Ratio Planetary Gear Transmissions

More and more transmissions in mechatronic systems, such as coal mining machines and wind turbines, wind turbine gear transmission, shield machine cutter drive, are required to achieve high power density with high speed ratios as well as a low number of gears. Three kinds of high-speed-ratio planetary gear, including NGWN(Ⅰ)、NGWN(Ⅱ) and NN, will be discussed in this paper. Their range of speed ratio is as follows: 20~100、50~500、8~30. Compared to common planetary gears with several stages and a high number of gears, high-speed-ratio planetary gears with a shorter transmission chain and a low number of gears can provide a higher reliability and a longer operation life for mechatronic systems. But their efficiency is low and a large amount of heat is generated when these three kinds of high-speed-ratio planetary gear transmit high power. Besides, their performance is sensitive to manufacturing errors. And these problems have hindered their widespread application.This topic is the important component of the national major basic research program of China. Focusing on these problems of high-speed-ratio of planetary gear transmissions, the main research work of this paper is as follows.①Low-loss gears are used to improve the efficiency of these high-speed-ratio planetary gear transmissions. The methods to achieve the low-loss gears are optimizing modification coefficients and addendum coefficients simultaneously in order to equalize approach-contact ratio and recess-contact ratio. The efficiency is improved obviously after adopting this optimization method.②The sensitivity of the load sharing performance to manufacturing errors is analyzed in the view of load sharing characteristics. A load sharing model, which includes position errors of planet bearings and tooth profile errors of planets, is built up to obtain the load sharing characteristics of NN, NGWN(Ⅰ) and NGWN(Ⅱ). Results indicate that the load sharing performance of NGWN(Ⅰ) and NGWN(Ⅱ) is more sensitive to position errors of planet bearing than that of PPG. The load sharing performance of NGWN(Ⅰ) and NN is more sensitive to tooth profile errors of planets than that of NGWN( Ⅱ). But the sensitivity of load sharing performance to manufacturing errors can be lowered by floating of ring gears and using flexible planet pins. By taking load sharing measures of floating of ring gears and using flexible planet pins, NN has the best load sharing performance among the three kinds of high-speed-ratio planetary gear transmissions, and NGWN(Ⅱ) has better load sharing performance compared with NGWN(Ⅰ).③For the problem of excessive heat generation, thermal elastohydrodynamic lubrication gear model is built up to analyze the lubrication condition when these three kinds of high-speed-ratio planetary gear transmissions transmit power of 300 k W. After the analysis, the following conclusion is made: The temperature rise of NGWN(Ⅱ) is bigger than that of NGWN(Ⅰ) and NN has the smallest temperature rise among the three kinds of planetary gears. The oil film of NGWN(Ⅱ) is thiner than that of NGWN(Ⅰ) and NN has the thickest oil fim among the three kinds of planetary gears. When asymmetric gears are used in these three kinds of high-speed-ratio planetary gear, the temperature rise is decreased obviously and the thickness of oil fim is increased obviously.