Design And Performance Research On The Flexure Pivot Tilting Pad Journal Bearings

As with the development of modern industrial needs, because of the excellent stability characteristics, the tilting pad bearings that being applicated in the high speed and high precision rotors are more and more widely, the stability characteristics is because that the pad can automatically adjust the angle with the shaft speed and load fluctuations and obtain a suitable oil wedge. However, the tilting-pad bearing has many disadvantages, such as complex structure, high processing requirements and prone to error accumulation, its pivots are easy to wear, even produce pad flutter. Complex assembly structures restrict its application in small or micro-rotors, thus we require a new innovative design of the tilting-pad bearings.Flexible hinge is usually used in precision instruments, due to the structure of the available micro-angular distortion and its self-response characteristics of elastic material, then it can eliminate backlash and friction in the transmission process, which can obtain high resolution, compact mechanical structure and stiffness, also quick response.Based on flexible hinge properties, this paper designed and manufactured the flexure-pivot tilting pad bearings by EDM wire cutting method, we obtain the stability characteristics similar to the tilting pad bearings but with a simpler structure at the same time. The bearings has reducing the number of parts, reducing production costs, stable design, without error accumulation, no pad flutter, contact stress-free and good stability. Especially at high speed, ultra high speed small or micro rotor systems, the advantage is more obvious. For this reason, this paper studied its lubrication design and the static and dynamic characteristics. Main research contents are as follows.Firstly, as the key parts of the bearing structure, this paper analysed the flexure hinge by the infinitesimal method and Castigliano’s theorem. Comparing the thickness and length of different types of flexible hinge on the effect of structural stiffness, the thickness is obtained greatest impact. Established the lubricated Reynolds equation and expression of oil film thickness about the flexure-pivot tilting pad bearings. this paper also solved Reynolds equation by using the finite difference method and overrelaxation iterative method, with Newton iteration method calculated the static characteristics while the bearing is in balance. This paper compared static performance, such as bearing displacement angle, pad titling angle coefficient, bearing capacity coefficient and flow coefficients, power consumption and temperature raise, changed with shaft rotational speed and eccentricity. Under certain conditions, we obtained the static performance parameters of the bearing. Also compared the bearing static performance with different rotational stiffness. The rotational stiffness within 1000-2000 N-m/rad can be used as the flexible hinge.design of the bearing.Secondly, combined with rotational stiffness of the bearing supports, by using the same frequency perturbation analysis method, this paper obtained the caculation method of reduced stiffness and damping coefficient about the bearing, studied the effect on the dynamic performance of the bearing about eccentricity, shaft speed, rotational stiffness and excitation frequency ratio. This paper also had a discussion on the stability of the bearing and gained the dynamic performance and good stability.Lastly, by using Euler’s method we calculated the centre nonlinear orbit and pad displacement of different thickness under unbalanced load, The nonlinear orbit was a circle, and the circle center was the balance position without unbalanced load. The unload pad disturbance was more obvious than the loaded. The smaller the thickness was, the time to be stable cost less, which proved the stability of the bearings on the other hand.With the lubrication calculation, the flexure-pivot tilting pad bearings showed a good static and dynamic performance, which can provide some guidance for the applications of the bearings, at the same time, the integration design broadens the idea for small or micro-rotor bearings, which has good practical significance.