Active Controlled Hydrostatic Bearings for a New Generation of Machines

Abstract

This paper presents a revolutionary approach of using a fluid-lubricated bearing for both traditional functions (load support, damping, and heat removal) and to actively control the rotor dynamics of rotating machinery. We will discuss how its use in the design of next generation turbomachinery can yield dramatic benefits. This includes an increase in efficiency, operational life, fault diagnostic, and reductions in machine size, weight, and cost. With the use of hydrostatic instead of hydrodynamic lubrication, traditional lubricants can be replaced by fluids more friendly to the process and environment. In this paper a comparison between the new hydrostatic bearing (Bently ServoFluid™ Control Bearing) and active magnetic bearings (AMB) will be presented. The Bently ServoFluid™ Control Bearing is an active controlled externally pressurized (a hybrid hydrostatic) bearing using fluid restoring force to compensate for rotor-related forces. It has the positive features of rolling element, fluid film and magnetic bearings with fewer negative attributes. The fluid restoring forces provide static and dynamic motion control similar to magnetic bearings, but with significantly larger compensation forces and with higher stiffness control. This revolutionary approach enables machinery owners to identify, understand and compensate for rotor system forces, an improvement over simply using vibration (motion) information for machinery diagnostics. This allows more complete diagnostics and prognostics of machine health. The bearing can be used to apply known perturbation forces to the rotor. Perturbation forces enable the determination of rotor system stiffness, and subsequent changes, thus improving machinery diagnostics. It can also provide information, such as the mechanical parameters governing the motion, system linearity, and stability margins for more accurate modeling of machines. Test results will be included to show experimentally determined transfer functions of each of the control loop elements, and predicted rotor forces. A typical root locus plot will be shown demonstrating how the characteristics change with bearing stiffness. Prototype machines, with both low viscosity fluid (water) and typical viscous fluid (T-10 turbine oil), have been built, tested, and successfully operated.

Controllable Sliding Bearings and Controllable Lubrication Principles—An Overview

“…For example, oil or water lubricated bearings are normally connected to servo-valves and hydraulic servo-systems [13][14][15], while gas or air lubricated bearings use piezoelectric actuators and pneumatic systems [16][17][18]. Direct and indirect actions of control forces onto the rotating shaft can occur either via bearing housing and bushing [19][20][21][22][23][24][25][26][27][28][29] or via bearing clearance [13][14][15][16][17][18]27].…”

“…For example, oil or water lubricated bearings are normally connected to servo-valves and hydraulic servo-systems [13][14][15], while gas or air lubricated bearings use piezoelectric actuators and pneumatic systems [16][17][18]. Direct and indirect actions of control forces onto the rotating shaft can occur either via bearing housing and bushing [19][20][21][22][23][24][25][26][27][28][29] or via bearing clearance [13][14][15][16][17][18]27]. The control actions influence fundamentally four parameters: either the bearing gap function h(θ) [21][22][23][24][25][26] and its gradient dh/dθ [23][24][25], or the fluid viscosity µ [30][31][32], or the fluid film pressure field p(θ) [13][14][15][16][17][18]27].…”

On the future of controllable fluid film bearings

“…Examples of case (I) can be found in [2][3][4][5] using magnetic and piezoelectric pushers and in [6][7][8] using hydraulic actuators. Examples of case (II) can be found in variable impedance bearings [9], actively controlled bearing surface profiles or simply deformable bushes [10], active journal bearings with flexible sleeves [11,12], active lubricated bearings [13][14][15], or pressurized bearings [16,17] among others. Emphasis will be given in the case of active lubricated bearings, which allows the design and control of fluid film bearings under different lubrication regimes, namely hydrodynamic, thermo-hydrodynamic, elasto-hydrodynamic and thermo-elasto-hydrodynamic.…”

“…Multirecess journal bearings with two pair of active pockets are also another kind of controllable fluid film bearing [16,23]. In terms of industrial application, the importance of hybrid journal bearings as potential application as load support elements in high-speed turbomachinery and machine tool spindles has steadily grown over the past years.…”

“…magnetic bearings [1], piezoelectric bearing pushers [2][3][4][5], hydraulic actuator journal bearings [6][7][8], variable impedance bearings [9], actively controlled bearing surface profiles or simply deformable bushes [10], active journal bearings with flexible sleeves [11,12], active lubricated bearings [13][14][15], or pressurized bearings [16,17] among others. The rapid development of these new mechatronic devices shows that the relative maturity of many "traditional technologies" implies little or no potential for significant improvements of machine performance.…”