Exploring integral controllers in actively-lubricated tilting-pad journal bearings

Abstract

Active tilting-pad journal bearings with radial oil injection combine good stability properties of conventional tilting-pad journal bearings with the capability of improving their dynamic properties even more by control techniques. The main contribution of this work is the experimental investigation of integral controllers for feedback-controlled lubrication with the aim of: a) presetting the static journal center and consequently exploring the changes of bearing dynamic properties; b) obtaining an integral controller capable of re-positioning the static journal eccentricity for matching equilibria under conventional hydrodynamic and feedback-controlled lubrication regimes. A novel application is proposed, that tries to build “non-invasive perturbation forces” and uses the active fluid film forces of the bearing as a “calibrated shaker”.

Active tilting-pad journal bearings supporting flexible rotors: Part I – The hybrid lubrication

“…Depending on the servovalve's spool position, the high pressurized oil can be permanently injected by different pad combinations, leading to a change of the journal equilibrium position within the "x-y" plane and hence on the bearing dynamic properties. For horizontal machines, injecting from bottom pads has shown to produce a vertical bearing softening [40] and to reduce the system response amplitude [25]. In general terms, the higher the supply pressure the easier it is to change the journal equilibrium position.…”

“…In general terms, the higher the supply pressure the easier it is to change the journal equilibrium position. By using feedback signals, this regime can be aided by integral controllers to attain or maintain a predefined equilibrium, especially when servovalve dynamics are unequal [25]. The Active Lubrication Regime: if the control signals driving the servovalves are defined by a control law, then the hydrostatic fluid-film force exerted over the journal can be actively-controlled.…”

“…This avoids calculating the PID parameters by heuristic means or by tuning them on site after the bearing is manufactured. Works related to control design for active TPJBs can be found in [20,21,22,23,24,25,26]. In the industry, the majority of the critical machines feature flexible rotors which make them worth analysing when supported by active TPJBs, in the same way as when they are supported by conventional TPJBs [27,28,29,30,31,32].…”

Feedback-controlled lubrication for reducing the lateral vibration of flexible rotors supported by tilting-pad journal bearings

“…It can be stated that there are roughly two ways of reducing the lateral vibrations of a rotor-bearing system, the first one by changing its equilibrium position, and a second one by affecting the bearing properties around the equilibrium. A previous work [15] on the same flexible rotor system was focused on exploring the reduction on the system lateral response by changing the journal equilibrium position via an integral controller. The second way for reducing the system lateral vibrations can be reached by implementing the feedbackcontrolled lubrication regime based on proportionalderivative (PD) controllers.…”

Experimental identification of dynamic coefficients of lightly loaded tilting-pad bearings under several lubrication regimes

“…However, since the servovalves' dynamic properties are slightly different, the journal cannot be strictly moved upward or downward without the aid of an I-controller 33 . When the servovalve spool is kept centred there is still some hydrostatic effect detectable as a consequence of leakage flow through servovalve ports.…”