航天器用超低黏度齿轮泵轻量化设计

Lightweight design of gear pumps with ultra low viscosity medium used in spacecraft

为追求航天器用超低黏度介质齿轮泵较好的容积率和较低的发射成本,该文在创建容积率和新重合度公式的基础上,采用最优化设计方法,通过泵的单位排量体积或单位排量质量最小化,实现了90%的最小容积率和质量最轻化,分析了结构参数对优化结果的影响。结果表明:采用齿顶重合度优化设计后的根切重合度为–0.3429,不能保证连续传动要求;压力角、轴半径、齿条刀具齿顶圆角半径和过渡区起始角对优化结果,分别有6.07%、7.8%、2.9%和6.4%的影响,总体上影响不大;径向、轴向间隙的影响很大,并具有0.04、0.07 mm的影响转折点,该转折点为径向、轴向间隙的取值上限提供了依据。初次针对航天用齿轮泵的优化设计尝试,阐明了超低黏度介质同样适用于齿轮泵。该研究可为提高其他行业用超低黏度液压泵的研发提供参考。

For higher volumetric efficiency and lower launch cost of gear pumps with ultra low viscosity working medium used in spacecraft. In this paper, the volumetric efficiency formula of gear pumps was firstly derived from the two main leakages of axial gap and radial gap, At the same time, a new contact ratio factor formula appropriate for undercut gear and standard gear was proposed by the estimation of limited meshing point in driven gear or driving gear. When the undercut point of driven gear was being meshed, if the corresponding meshing pressure angle of driving gear was less than the addendum pressure angle, which showed that the addendum point of driving gear couldn＇t be meshed, the contact ratio of gear pair should be calculated by the undercut point position of driven gear; conversely, it showed that the undercut point of driven gear couldn＇t be meshed, the contact ratio should be calculated by the addendum point position of driving gear. Secondly, based on the newly created volumetric efficiency formula and contact ratio factor formula, and the optimal design method theory, with the 2 key parameters i.e. the minimum allowable volumetric efficiency of 90% and the ultra low viscosity value of 0.00018 Pa·s, the optimization design model was established, which took the minimum unit displacement volume being equivalent to the pump weight as the optimization goal. By the optimization of basis parameters of gear pairs including modulus, tooth number, addendum coefficient, pressure angle and displacement factor, the volumetric efficiency decline problem was consequently solved, and the minimum space launch cost of pump weight was guaranteed. Thirdly, the effects of structural parameters of gear pumps on the optimization result were analyzed. All optimization results showed that if the usual addendum contact ratio factor formula of driving gear was used for calculating contact ratio factor in the optimization design model, with the optimized basis gear parameters, the actual contact ratio factor was –0.3429, which was not reliable for undercut gear, and the continuous gear transmission also couldn＇t be guaranteed, so only the newly created contact ratio factor formula was reliable; the influence degrees of the pump parameters including pressure angle, shaft radius, tip radius of rack cutter, and starting angle of transition region on the optimization result were respectively 6.07%, 7.8%, 2.9% and 6.4%. On the whole, these parameters had little influence on the optimization result; especially, the free space was endowed to the structure design to reduce the radial force. But the influences of radial gap and axial gap on the optimization result were very large, and unexpectedly, there was no optimal solution with the axial gap value of 0.06 mm, so the upper limit values of radial gap and axial gap could be determined by the influence turning points. For example, the upper limit value of axial gap was 0.04 mm, and the upper limit value of radial gap was 0.07 mm. For other pump parameters, there were such turning points. For example, the upper limit value of shaft radius was 13 mm, and the upper limit value of starting angle of transition region was 180°. As a whole, the designed pump shape had a small axial size and a large radial size. Finally, the first attempt of the optimal gear pump design for spacecraft clarified that the ultra low viscosity medium was also applicable to gear pumps, and catered to the development of Chinese aerospace industry. The study provides a demonstration of the optimal design method for other hydraulic pumps with ultra low viscosity medium as well.