【作者】 王丽丽；

【导师】 路长厚；

【作者基本信息】 山东大学 ， 机械电子工程， 2012， 博士

【摘要】 滑动轴承在高速、超高速条件下,固液交界面上的剪应力会超过某个极限值而导致在固体表面发生滑移现象,同时润滑油膜极易破裂形成空穴。界面滑移和空穴现象的存在对滑动轴承的润滑性能具有重要影响,甚至可能导致润滑失效。因此,界面滑移和空穴特性的研究,对滑动轴承的高速发展具有重要意义。首先,建立了基于极限剪应力的周向和轴向二维滑移模型。为了在滑移模型中建立更为准确的周向和轴向剪应力关系,定义了剪应力夹角的概念。全面考虑了轴和轴瓦表面可能产生滑移的情况,分别研究了产生界面滑移的四种状态,给出了相应的滑移速度分布图,并分别推导了四种滑移状态的基本方程。对油膜完整区域与润滑油弹性模量的有关计算项进行了分析,建立了基于改进的Elrod算法的空穴计算模型,得到了求解油膜压力的优化算法。该算法将基于JFO边界条件的描述完整油膜区和空穴区的润滑方程进行了统一,使JFO边界条件更加精确的应用于轴承空穴理论的计算。基于二维滑移模型和改进的Elrod空穴算法,在四种滑移状态下分别推导出了考虑空穴效应的理论计算模型以及差分求解公式。考虑空穴效应的滑移计算模型既全面考虑了可能发生滑移的情况,又将Elrod算法中对完整油膜区的广义雷诺方程的求解方法进行了优化,不但更贴近滑动轴承实际工况,而且提高了计算效率。其次,采用“目标速度跟踪法”对界面滑移现象进行了实验研究。轴承采用有机玻璃材质,在进油口添加着色剂,利用高速摄像机拍摄流线并计算出平均速度,通过理论与实验结果的对比发现了周向和轴向界面滑移的存在。根据实验测得的周向最小滑移速度与转速和供油压力关系曲面,计算出高粘度和低粘度润滑介质时轴瓦和轴表面的极限剪应力,并发现滑移速度随着供油压力的提高而提高。运用实验测得的极限剪应力,从理论上研究了极限剪应力和界面滑移现象对螺旋油楔滑动轴承性能的影响。研究了轴承的结构、偏心率、螺旋角、转速和极限剪应力对滑移程度的影响。结果表明滑移首先发生在极限剪应力大、油膜间隙小和油膜的封油面区域,滑移现象的存在使油膜压力、承载力、摩擦阻力和温升有所降低,而端泄量则有所提高,并且轴瓦和轴表面的滑移区域和滑移程度互相影响。为了提高轴承承载力并降低温升,提出了利用滑移现象的组合滑移表面径向滑动轴承。基于修正的SLM模型,推导出了考虑界面滑移的雷诺方程。与普通轴承相比,组合滑移表面径向滑动轴承的油膜压力、承载力和端泄量较高,而偏位角、摩擦阻力和温升较低。然后,利用理论和实验相结合的方法研究了润滑油粘度对空穴特性和端泄量的影响。采集了高粘度和低粘度润滑介质条件下螺旋油楔滑动轴承在不同转速和供油压力的空穴图像,并测量了滑动轴承的端泄量,通过理论和实验对比研究了两种润滑介质条件下轴承的空穴形状、油膜破裂位置以及再形成位置、油膜破裂面积和端泄量等。求得高粘度和低粘度润滑介质条件下油膜再形成位置与转速和供油压力的关系。两种不同粘度润滑油的实验结果对比表明,低粘度油的空穴面积比高粘度油明显减小而端泄量明显提高。实验结果与利用改进的Elrod算法计算获得的结果变化趋势一致,并且油膜破裂情况基本吻合。基于JFO边界条件建立了考虑空穴效应和界面滑移的轴承动特性计算模型,揭示了不同偏心率、螺旋角、供油压力和转速时,界面滑移和空穴效应对油膜压力、承载力、摩擦阻力、端泄量、平均温升、刚度系数和阻尼系数的影响。结果表明,考虑界面滑移时采用JFO边界条件计算获得的油膜压力、承载力、摩擦阻力、端泄量、刚度系数和阻尼系数比采用Reynolds边界条件时都有所提高,而平均温升降低和油膜的破裂延缓。最后,采用热电偶和红外测温仪分别测量了润滑油的平均温升和轴瓦内表面温度。结果表明,低粘度润滑条件下的温升比高粘度油润滑条件下的温升明显降低,采用低粘度润滑介质可以有效解决高速机床长期存在的温升问题。更多还原

【Abstract】 With the application of journal bearing in high speed and super-high speed conditions, wall slip can occur when shear stress exceeds the critical shear stress at the solid-liquid interface, the oil film is easy to crack and becomes cavitation. The presence of wall slip and cavitation has a great effect on the lubrication characteristics of journal bearing, and possibly leads to the lubrication failure. Therefore, the wall slip and cavitation characteristics of journal bearing have been investigated, which has an important significance for the development of high speed journal bearings.Firstly, the two-dimensional slip model is established based on critical shear stress model, in which the circumferential and axial wall slip of sleeve surface and axial surface is considered. The shear stress angle is used to compute the circumferential and axial shear stress component in slip model. Considering the slip states in the sleeve surface and axial surface comprehensively, the four slip states are studied, the slip velocity profiles of four slip states are given, and the theoretical model of four slip states are established.In full film region, the related items with lubricant bulk modulus are analyzed, the cavitation model is established based on modified Elrod cavitation model, which is benefit for the calculation process of oil film pressure. The generalized equation that integrates the full film region and cavitation region based on JFO boundary condition is derived, which makes the JFO boundary condition more precisely to be applied in the computation of cavitation theory.The theoretical model of four slip states and the formulas of finite differential method are established considering cavitation mechanism based on the two-dimensional slip model and modified Elrod cavitation model. The model not only considers the four slip states but also optimizes the solution of generalized Reynolds equation in full film region compared with Elrod method, which is consistent with the actual work condition and increases the computation efficiency.Secondly, the wall slip is studied experimentally by the method of target speed tracking method. The material of spiral oil wedge journal bearing is synthetic glass in experiment, the coloured dyestuff is added into the lubricant from the inlet holes, the fluid flow of lubricant is taken using the high speed camera, the average speed is computed, and the circumferential and axial wall slip is found by the difference of theoretical results and experimental results. According to the figures of minimum circumferential slip velocity with the rotating speed and supply pressure in experiment, the critical shear stresses of sleeve surface and axis surface are obtained for high viscosity lubricant and low viscosity lubricant. It is found by experiment that the slip velocity increases with the increase of input pressure.Using the critical shear stresses of sleeve surface and axis surface that are obtained in experiment, the influence of critical shear stress and wall slip on the characteristics of spiral oil wedge journal bearing is studied. The influence of the bearing structure, eccentricity, spiral angle, rotating speed and critical shear stress on slip degree is studied. The results show that wall slip occurs first in the large shear stress, the small clearance of oil film and the envelop zone. Wall slip can cause the decrease of oil film pressure, carrying capacity, friction drag and temperature rise, but produces the increase of end leakage rate. The slip position and area influence each other in the sleeve surface and axial surface.In order to improve the carrying capacity and reduce the temperature rise in journal bearing, a combined surface radial sleeve bearing using the interfacial slip technique is discussed. An extended Reynolds equation is derived based on the modified slip length model considering wall slip. Comparing with the general journal bearing, the pressure, load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly, but the attitude angle, friction drag, temperature rise of the combined bearing can be decreased.Thirdly, the influence of lubricant viscosity on the cavitation characteristics and end leakage rate is studied by theory and experiment. The pictures of spiral oil wedge journal bearings under different rotating speeds and supply pressures for high viscosity lubricant and low viscosity lubricant are taken, the end leakage rate of the journal bearing is measured, and the cavitation shape, oil film rupture location, oil film reformation location, rupture area of oil film and end leakage rate are studied by theory and experiment. The relations of oil film reformation location with the rotating speed and supply pressure are obtained for high viscosity lubricant and low viscosity lubricant in experiment. The cavitaiton area decreases and end leakage rate increases for low viscosity lubricant compared with high viscosity lubricant. The modified Elrod calculation results are in general consistent with the experimental results.The dynamic characteristic model is established based on JFO boundary condition considering cavitation effect and wall slip. The influence of wall slip and cavitation effect on pressure, carrying capacity, friction drag, end leakage rate, temperature rise, stiffness and damping coefficients for different eccentricities, spiral angles, input pressures and rotating speeds is studied. The oil film pressure, carrying capacity, friction drag, end leakage rate, stiffness and damping coefficients are larger, temperature rise is lower and the oil film rupture delays using JFO boundary condition compared with Reynolds boundary condition when the wall slip is considered.Finally, the temperature rise and the bush inner surface temperature are measured by thermocouple and infrared thermometer, separately. The results show that the temperature rise decreases for low viscosity lubricant compared with high viscosity lubricant, so the application of low viscosity lubrication can solve the temperature rise in high speed machine tools.更多还原