- 學位論文
磁油動壓頸軸承之穩定性分析
Stability Analysis for a Ferrofluid-Based Hydrodynamic Journal Bearing
摘要
摘要 磨損是主要造成機械結構和零件使用壽命縮短的原因，因此為了降低摩擦、減少磨損、提高機械使用效率、延長零件壽命，在機械結構中加入潤滑介質是最常用的方法而流體軸承能夠提供的有效潤滑和散熱效果同時具被良好的抗振能力及承載能力。相比於其他軸承，流體動壓軸承成本較低，且設計系統較為簡單，且流體動壓軸承依靠潤滑介質較大的黏度而具有更好的抗振能力及承載能力、低噪音、壽命相較於滾珠軸承長且不需要高壓壓力幫浦等之優點，而磁流體軸承在磁場的作用下可以改變磁流體黏度以提高流體軸承的承載能力並改善潤滑效果。本文希望透過將磁流體當作潤滑介質並設置外部磁場，達到控制磁流體之黏滯特性來改善流體動壓軸承的缺點，提升傳統流體動壓軸承之性能來改變液體動壓軸承之油振發生頻率。 本文建立一組流體動壓軸承轉子測試平台並針對磁流體動壓軸承的穩態特性進行研究，利用雷諾邊界條件與有限寬軸承壓力函數的解析法，得到了磁流體軸承潤滑膜的壓力分佈、承載力分佈、軸承姿態角等穩態特性參數，並考慮在有一外加磁場強度影響的狀況下，將對磁流體的黏度方程式進行修正，得到磁流體的黏度溫度、黏度壓力之特性，並探討了磁場對磁流體動壓軸承系統剛度的影響。藉由分析了磁場、溫度和軸承參數對於軸承特性的影響，建立磁流體動壓軸承的物理及數學模型。藉由分析不同磁路方向，對油軸承油漩、油振等實驗之影響。由油軸承之全頻譜串聯圖中觀察軸承發生油漩之穩定門檻轉速中可知，因為磁場可改變磁流體之黏滯係數，提高軸承潤滑液剛度提升可以改變流體引發的油漩或油振不穩定發生之頻率。實驗結果顯示，均勻磁場所獲得之效果為最優，可有效提升本測試平台之旋轉油軸承的油漩或油振不穩定門檻發生之轉速由原始之3024轉提高到4480轉赫茲；磁流體動壓軸承在外部磁場的作用下可以減少在低轉速時轉子對定子之間的乾摩擦，實驗顯示在外部磁場1200高斯作用下，磁流體動壓軸承降低了約5μm的振動量。
並列摘要
Abstract Wear is the main cause of reduced mechanical structure and part life, in order to reduce friction, wear, improve mechanical efficiency and extend the life of parts, adding lubricant is the most commonly used methods in the mechanism. Fluid bearings provided effective lubrication and cooling effects also had good anti-vibration capacity and carrying capacity. Hydrodynamic bearing had the advantages of low cost, design system is simple, better vibration resistance and load-bearing capacity, low noise, long life and does not require high-pressure pressure pump, etc. Ferrofluid bearing can changed the viscosity in the magnetic field also improved the fluid bearing capacity and lubrication. In this paper, the ferrofluid as a lubrication medium and set the external magnetic field. By increasing the ferrofluid viscosity to improve the shortcomings of hydrodynamic bearings and changed the frequency of oil whirl or whip. In this paper, established a set of hydrodynamic bearing rotor test platform and studied for the steady-state characteristics of hydrodynamic bearings. From the experiment we know when changing the viscosity of the ferrofluid, bearing stiffness and the frequency of oil whirl or whip can be increased. Experiment result shows, the best results obtained in a uniform magnetic field. Oil whirl instability threshold speed from the original 3024 rpm to 4480 rpm Hz. Ferrofluid hydrodynamic bearings can reduce dry friction in the magnetic field, the hydrodynamic bearing reduced the amount of vibration about 5μm in the magnetic field 1200 Gauss.