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Research Papers: Hydrodynamic Lubrication

On the Controllability and Observability of Actively Lubricated Journal Bearings With Pads Featuring Different Nozzle-Pivot Configurations

[+] Author and Article Information
Jorge G. Salazar

Department of Mechanical Engineering,
Technical University of Denmark,
2800 Kgs. Lyngby, Denmark
e-mail: jgsal@mek.dtu.dk

Ilmar F. Santos

Department of Mechanical Engineering,
Technical University of Denmark,
2800 Kgs. Lyngby, Denmark
e-mail: ifs@mek.dtu.dk

1Present address: Department of Mechanical Engineering, University of La Frontera, Temuco 4780000, Chile.

2Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received October 1, 2015; final manuscript received February 5, 2016; published online October 10, 2016. Assoc. Editor: Daejong Kim.

J. Tribol 139(3), 031702 (Oct 10, 2016) (17 pages) Paper No: TRIB-15-1356; doi: 10.1115/1.4033053 History: Received October 01, 2015; Revised February 05, 2016

The fundamental properties of an actively lubricated bearing (ALB) from a control viewpoint are investigated, i.e., the stability, controllability and observability. The ALB involves the addition of an oil injection system to the standard tilting-pad journal bearing (TPJB) to introduce constantly and/or actively high pressurized oil into the rotor-pad gap through, commonly, a single radial nozzle. For the work goal, a four degrees-of-freedom (DOFs) ALB system linking the mechanical with the hydraulic dynamics is presented and studied, comprising: (i) the vertical journal movement, (ii) the pad tilt angle, (iii) the vertical pad movement—due to the pivot flexibility, and (iv) the controllable force as the hydraulic DOF. The test rig consists of a rigid rotor supported by a single rocker-pivoted rigid pad. A thorough parametric study is carried out by investigating the effects of: (a) nozzle-pivot offset, (b) pivot flexibility, and (c) bearing loading on these control basics in order to determine the pad with the best control characteristics. Different nozzle-pivot offsets can be set by varying the positioning of either the injection nozzle or the pivot line. The influence of the pivot compliance on the bearing dynamics is assessed by benchmarking the results obtained with the flexible pivot against the rigid pivot. Three different bearing loads are studied. According to the results, the proposed configurations, especially the offset-pivot pad with slight offsets, improve the bearing control characteristics by introducing an extra mechanism to access the system states. The loading condition modifies the stability, controllability, and observability, while the pivot flexibility highly affects the ALB dynamics.

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Figures

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Fig. 1

Scheme of a simplified ALB consisting of: a passive lubrication system, ⑤ low pressure pump + ③ sprinklers; an active lubrication system, ① high pressure pump + ② servovalve + ④ injection nozzles. Both lube systems are connected to the same ⑥ reservoir.

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Fig. 2

Sketched view of the pad-injector section. ①: pad, ②: pivot, ③: injector, ④: housing body, ⑤: o-ring seal, and ⑥: nozzle conical inlet wall.

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Fig. 3

Different tilting pads with pressurized oil injection nozzle: (a) offset-nozzle pad, Θnozzle<0.5, Θpivot=0.5, (b) centered-nozzle pad, Θnozzle=Θpivot=0.5, (c) offset-pivot pad, Θnozzle=0.5, Θpivot>0.5, and (d) comparison of an offset-nozzle pad with a centered-nozzle pad

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Fig. 4

Three DOFs rigid rotor-single rigid pad system. Pad with rocker-pivot and injection nozzle. ξ: vertical journal movement; θ: pad tilt angle; and η: pad vertical displacement.

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Fig. 5

Sensors placement for DOFs measuring: (a) measuring of journal displacement ξ, (b) measuring of pad tilt angle θ and pad vertical displacement η, and (c) measuring of controllable forcefc

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Fig. 6

Root locus plot for the system under 1400 N

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Fig. 7

ALB test rig with centered-nozzle pad. ①: servovalve, ②: AC motor, ③: electromagnetic shaker, ④: rotor, ⑤: levered arm, ⑥: load cell, and ⑦: displacement sensor (not seen).

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Fig. 8

Comparison of theoretical (Theo) against experimental (Exp) FRFs of the system with pad #C under different loading conditions. Journal displacement as output variable, y1=ξ.

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Fig. 9

Theoretical FRFs for all pads. Bearing applied load of 1400 N. △: pad #N2, □: pad #N1, ◯ : pad #C, ⋄: pad #P1, and ▽: pad #P2. Solid line (–): flexible pivot and dashed line (- -): rigid pivot.

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Fig. 10

Comparison of pressure profiles and their circumferential centroids for the centered-nozzle pad. (a) Hydrodynamic pressure profile, (b) hydrodynamic + constant hydrostatic pressure profile, and (c) variable hydrostatic pressure profile. Injector placed at origin. Circumferential injector limits ± 1.7 deg.

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Fig. 11

Stiffness and damping force coefficients for the ALB with different pads obtained under the studied operational condition. Bearing load of 1400 N; single pad configuration and flexible pivot.

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Fig. 12

Calibration function for the hydraulic system under the studied operational conditions. Controllable force fc as a function of control signal u. ◇: 700 N of bearing load, κH = 95 N/V. ◯: 1400 N of bearing load, κH = 80 N/V. □: 2800 N of bearing load, κH = 70 N/V.

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Fig. 13

Theoretical FRFs. Bearing applied load of 700 N. △: pad #N2, □: pad #N1, ◯: pad #C, ◇: pad #P1, ▽: pad #P2. Solid line (–): flexible pivot and dashed line (- -): rigid pivot.

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Fig. 14

Theoretical FRFs. Bearing applied load of 2800 N. △: pad #N2, □: pad #N1, ◯: pad #C, ◇: pad #P1, ▽: pad #P2. Solid line (–): flexible pivot and dashed line (- -): rigid pivot.

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