Oil-free Bearings Research Articles

Rotordynamics of a rotor supported by foil bearings under various housing excitation

Proton Exchange Membrane (PEM) Fuel cell Systems(FCS) are rapid-growing technology in transportation systems. In such applications, a motor-driven oil-free air compressor is one of the critical auxiliary subsystems. Foil bearings are the perfect choice as oil-free bearings for the compressors due to high rotordynamics stability and shock-resistance. The platform of a motor-driven oil-free compressor can also be used as an electric turbocharger for traditional internal combustion engines. All electromechanical subsystems for electric vehicles must satisfy vibration endurance requirements following ISO 16750–3:2012, characterized by certain g-loading at specific frequencies. For the compressor to satisfy ISO 16750 requirement, detailed rotordynamics simulations with externally excited compressor housing under certain g-loading are essential to design the foil bearings considering the static and dynamic loads to the bearing and rotordynamics stability. The main objectives of the current research are 1) to develop a four degree of freedom (4-DOF) dynamic model of the rotor supported by foil bearings under external excitation to the compressor, 2) to simulate linear and non-linear rotordynamics of the compressor rotor supported by two radial foil bearings, and 3) to provide appropriate design guideline such as bump stiffness and axial length of the foil bearings. The simulations show that the rotor is stable for both under single frequency excitation and simultaneous excitations of all the frequencies in ISO 17650 standard. 4-DOF modal analyses were applied to identify natural mode of the system under the housing excitation.

A review on recent advancements in an automotive turbocharger rotor system supported on the ball bearings, oil film and oil-free bearings

A review on recent advancements in an automotive turbocharger rotor system supported on the ball bearings, oil film and oil-free bearings

Position Sensorless Drive With Online Parameters Estimation for Magnetic Suspension Centrifugal Compressor

With the advantages of a high power-to-weight ratio and oil-free bearings, a magnetically Suspension centrifugal compressor (MSCC) equipped with active magnetic bearings (AMB) operates more efficiently than traditional mechanical compressors over a wide speed range by precisely controlling a high-speed permanent-magnet synchronous motor (PMSM). However, owing to the harsh working environment, the motor parameters, including the resistor, inductance and flux linkage, vary significantly. This degrades the rotor position observer performance, which is crucial for controlling a high-speed PMSM. Hence, this article proposes an improved sensorless control method combined with novel motor parameter identification. First, an improved position sliding mode observer using a novel super-twisting algorithm (STA) is designed to achieve higher precision and better transient performance. Second, the influence of parameter mismatch is analyzed. To overcome the problems of rank deficiency and system matrix uncertainties, a novel identification strategy based on recursive total least squares excitatory and inhibitory learning (RTLS EXIN) is developed to identify inductance and resistance in two-time scales. Meanwhile, the back electromotive force (EMF) in static coordinates is employed to estimate the flux linkage. Third, the results are adopted to update the control parameters immediately. Finally, the proposed method is tested on an MSCC prototype experimental platform, and the results verify its validity and feasibility.

Анализ развития безмасляных подшипниковых систем быстроходных компрессорных и энергетических агрегатов роторного типа для мобильных условий эксплуатации

The article considers an analysis of prospects for the use of oil-free bearings for working conditions in rotary units of autonomous mobile installations. The analysis made it possible to establish the current level of development of oil-free bearing technologies, the existing limitations of their use in units of autonomous mobile installations and urgent problems, the solution of which requires research and further improvement of the designs of bearing units.

Tribological characterisation of polymer composites for hydropower bearings: Experimentally developed versus commercial materials

To mitigate the effects of downstream lubricant spillage from hydroelectric power plants, environmentally friendly lubricants are required. For the sustainable operation of oil-free bearings, the development of high performance bearing materials is crucial. In this study, the tribological performance of PPS and UHMWPE-based composites, incorporating various reinforcements, such as graphene oxide, is evaluated and compared with five commercial materials. Experiments were performed under different lubricating conditions; Dry, water, and using a glycerol-based environmentally adaptive lubricant (EAL). The use of water inhibited an adequate transfer film, which increased wear for most materials. EAL lubrication showed a significant reduction in friction (up to 98%) when compared to dry conditions. The experimentally developed PPS composite provided superior tribological properties, especially under water-lubricated conditions.

Theoretical and Experimental Investigation of a Small-Scale, High-Speed, and Oil-Free Radial Anode Off-Gas Recirculation Fan for Solid Oxide Fuel Cell Systems

Abstract The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel recirculation fan for a 10 kWe solid oxide fuel cell (SOFC). The fan uses oil-free bearings, more specifically herringbone-grooved journal and spiral-grooved thrust gas bearings. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal point of 168 krpm, the measured inlet mass flow rate is 4.9 kgh–1, the total-to-total pressure rise 55 mbar, the isentropic total-to-total efficiency 55%, and the power 18.3 W. This paper compares the experimental data toward a computational fluid dynamic simulation of the full fan impeller and volute suggesting an excellent correlation at the nominal point which validates the numerical approach. However, the heat flows crossing the fan fluid domain have an increased effect at off-design conditions; thus, the experimental results need careful consideration. The fan backface leakage has negligible impact on the measurements.

Investigation of Structural Conformity in a Three-Pad Adaptive Air Foil Bearing With Regard to Active Control of Radial Clearance

Abstract Various solutions for the design of oil-free bearings are discussed in the literature. Adding hydrodynamic preload to the foil bearings by profiling the inner bore of the bearing is one of the most frequently investigated methods for improving the bearing stability and damping character of the entire system. However, this approach leads to a reduced load capacity and thus to an increased lift-off speed of the foil bearings. Observations of this kind lead to the presentation of various solutions for active bearing contour adjustment, which benefits from different profiles of the lubricant film. Most of these concepts use piezoelectric stack actuators to generate the required alternating force, although the influence of the stiffness of adaptive elements on bearing performance is not fully discussed in the literature. The focus of this study is on the investigation of structural conformity, i.e., the harmonization of stiffness with respect to the requirements for shape control and load capacity of an adaptive air foil bearing (AAFB). The result may be a basis for the consideration of additional degrees of freedom in any concept with shape control as the main design framework in interaction between the lubricant and compliant structure in an air foil bearing from both static and dynamic points of view.

300 마력급 터보 압축기용 자기베어링의 설계 및 평가

Recently, the international community is making steady efforts to reduce energy consumption to counter climate change and reduce CO₂ emissions. In view of this trend, there is a high interest in oil-free turbo compressors that are highly efficient in replacing conventional screw compressors and do not generate waste oil in the compressor field. In accordance with this trend, in the field of compressors, there is a high interest in oil-free turbo compressors which can replace existing screw compressors, have high efficiency and do not generate waste oil. In the case of an oil-free turbo compressor, magnetic bearings tend to be applied in a large amount, which has a high rotational stability at high speed and a load capacity capable of coping with a large axial thrust. In this study, magnetic bearings were designed to apply to a compressor of 300-HP and 50,000 rpm, and a rotor in the compressor were designed by direct drive method by applying a permanent magnet synchronous motor. After fabricating a 300-HP compressor with magnetic bearings, the motoring test under the no-load condition without impellers was performed up to 51,000 rpm to evaluate the structural stability against the centrifugal force of the rotating shaft. In addition, the rotational stability was evaluated by motoring test up to 50,000 rpm under the load condition with impellers. Based on the experimental results, it is presented that the hybrid magnetic bearings are suitable oil-free bearings capable of stably supporting turbo compressors.

Oil-Free Automotive Turbochargers: Drag Friction and On-Engine Performance Comparisons to Oil-Lubricated Commercial Turbochargers

Oil-free bearings for automotive turbochargers (TCs) offer unique advantages eliminating oil-related catastrophic TC failures (oil coking, severe bearing wear/seizure, and significant oil leakage, for example), while increasing overall system reliability and reducing maintenance costs. The main objective of the current investigation is to advance the technology of the gas foil bearings (GFBs) for automotive TCs by demonstrating their reliability, durability, and static/dynamic force characteristics desirable in extreme speed and temperature conditions. The paper compares drag friction and on-engine performances of an oil-free TC supported on GFBs against an oil-lubricated commercial production TC with identical compressor and turbine wheels. Extensive coastdown and fast acceleration TC rotor speed tests are conducted in a cold air-driven high-speed test cell. Rotor speed coastdown tests demonstrate that the differences in the identified rotational viscous drag coefficients and drag torques between the oil-free and production TCs are quite similar. In addition, rotor acceleration tests show that the acceleration torque of the oil-free TC rotor, when airborne, is larger than the production TC rotor due to the large mass and moment of inertia of the oil-free TC rotor even though air has lower viscosity than the TC lubricant oil. Separate experiments of the oil-free TC installed on a diesel engine demonstrate the reliable dynamic-forced performance and superior rotor dynamic stability of the oil-free TC over the oil-lubricated TC. The post on-engine test inspection of the oil-free TC test hardware reveals no evidence of significant surface wear between the rotor and bearings, as well as no dimensional changes in the rotor outer surfaces and bearing top foil inner surfaces. The present experimental characterization and verified robustness of the oil-free TC system continue to extend the GFB knowledge database.

Oil-free bearing development for high-speed turbomachinery in distributed energy systems – dynamic and environmental evaluation

AbstractModern distributed energy systems, which are used to provide an alternative to or an enhancement of traditional electric power systems, require small size highspeed rotor turbomachinery to be developed. The existing conventional oil-lubricated bearings reveal performance limits at high revolutions as far as stability and power loss of the bearing are concerned. Non-conventional, oil-free bearings lubricated with the machine working medium could be a remedy to this issue. This approach includes a correct design of the machine flow structure and an accurate selection of the bearing type. Chosen aspects of the theoretical and experimental investigations of oil-free bearings and supports; including magnetic, tilting pad, pressurized aerostatic and hydrostatic bearings as well as some applications of oil-free bearing technology for highspeed turbomachinery; are described in the paper.

Design of magnetic bearings for turbo refrigerant compressors

Magnetic bearings are oil-free bearings that are widely employed in turbo machineries such as turbo refrigerant compressors in order to eliminate lubrication systems, avoid contamination, and increase efficiency. We have developed a 145 refrigerant ton (RT)-class turbo refrigerant compressor using homopolar-type radial hybrid magnetic bearings (HMBs) and thrust magnetic bearings. The thrust magnetic bearing comprises a thrust HMB and a permanent magnet that generate downward forces to overcome high upward thrust forces of 2000 N at 21 000 rpm. A test rig and controller for the compressor with magnetic bearings were fabricated, and rotordynamics such as the unbalance response and axial displacement were investigated. Rotordynamics analyses using the finite element method predicted that the 1st bending mode is located at a high frequency with sufficient margin from the operating speeds. Further, the zero-to-peak displacement caused by the unbalanced response was sufficiently small. The rotor was stably supported with few vibrations across the entire range of the operational speeds. Our results demonstrate that the advantages of oil-free bearings can be easily exploited in turbo machineries such as turbo refrigerant compressors by adopting HMBs.

Theoretical and Experimental Investigations of Oil-Free Bearings and their Application in Diagnostics of High-Speed Turbomachinery

In order to reduce the risk of failures, the optimal design selection from the viewpoint of machine reliability must be conducted. Therefore, one should analyze thoroughly the dynamics of the rotor-bearing-casing system in the whole operating range of the machine. The rotating system presented in the paper is supported in non-conventional bearings. The actual study consists in the investigation of new coating materials in the bearing design and the improvement in rotating system dynamics to increase the total efficiency, maintain the cleanness of the working medium and ensure operation of bearings in wide temperature ranges. Despite many advantages, air-foil bearings meet problems of friction and wear in critical moments of their operation, furthermore their complete theoretical model is difficult to establish. Different modeling theories of such bearing dynamic characteristics are shortly described. The current tendency in numerical and experimental methods for diagnostics of rotor support systems of low power rotating machinery is outlined.

Oil-Free Bearings and Seals for Centrifugal Hydrogen Compressor

Oil-Free Bearings and Seals for Centrifugal Hydrogen Compressor

Experimental investigation of a direct driven radial compressor for domestic heat pumps

The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a.

Assessment of Tribological Coatings for Foil Bearing Applications

A critical component in oil-free gas foil bearings is the tribological coating system that must be used on the journal/runner and the foil pads to ensure reliable operation during transient periods and start-stop cycles. The objective of this investigation was to evaluate the performance characteristics of potential coatings for use in foil bearing applications. Tribological tests were performed using a single foil thrust bearing pad in contact with a rotating flat disk at room temperature. The coatings consisted of a tungsten disulfide-based solid lubricant (Korolon™900), hydrogenated diamond-like carbon film (H-DLC), and thin dense chrome plating deposited by the Electrolyzing™process. The results demonstrated an excellent performance for the foil pads coated with the tungsten disulfide-based solid lubricant tested against either chrome-plated or H-DLC-coated disks. The very low friction that was expected for H-DLC, however, was not observed and the tungsten disulfide-based coating dominated the tribological behavior. It is concluded that the best coating system for foil bearing applications consists of placing the soft solid lubricant coating on the foil pad and the hard, wear-resistant coating on the disk. Other combinations provide high coefficients of friction and liftoff speeds and result in high levels of wear. This phenomenon is explained using the quasi-hydrodynamic theory of powder lubrication.

Gas Bearings (Oil Free Bearings)

Gas Bearings (Oil Free Bearings)

ヘリウム冷凍機におけるコールドコンプレッサの役割と期待

Since around 1970, cryogenic systems have required the use of cold compressors. The requirement appeared for two reasons, The first was reduce the pressure of liquid helium with the intention of realizing the stable operation of large superconducting magnets with the best superconducting ability by decreasing operating temperature. The other was to improve the reliability of helium refrigerator compressors by introducing a turbo-compressor with oil-free bearings. This paper describes the circumstances and particular development of cold compressors, requirements related to helium refrigeration systems and cold compressors and future prospects.

Materials for small, oil-free bearings : Hobart S. White. Materials & methods, v. 45, Apr. 1957, p. 135–139

Materials for small, oil-free bearings : Hobart S. White. Materials & methods, v. 45, Apr. 1957, p. 135–139

Small oil-free bearings : Hobart S. White. Journal of Research, National Bureau of Standards, v. 57, Oct. 1956, p. 185–204

Small oil-free bearings : Hobart S. White. Journal of Research, National Bureau of Standards, v. 57, Oct. 1956, p. 185–204

Small oil-free bearings

An investigation was made of materials that may be suitable for use as oil-free bearings in aircraft clocks and similar instruments between —55° and +70° C, to replace lubricated jewels that do not give satisfactory operation at subzero temperatures because of congealing of the oil. Another advantage of an oil-free instrument is the freedom from cleaning and oiling periodically during shelf storage. Materials included in the investigation were plastics, plastics with fillers, impregnated metals, and impregnated carbon. Friction tests were made with an inclined-plane type of static-friction apparatus, and with shafts rotating in loaded journal bearings, at temperatures from —55° to +70° C. With bearings of typical materials stored on steel shafts, the effect of shelf storage on static friction was investigated. Wear tests were made with loaded bearings on %-inch-diameter rotating shafts made of different types of steel. With oscillating ^-inch-diameter shafts and 1,000-gram loads, wear data were obtained on bearings of the more promising materials. Using an endstone wear testing machine, wear data were obtained for end-thrust bearings made of typical bearing materials. The performance of oil-free bearings in 18 timepieces was investigated.