Patent Application
20060078239
1. Dimofte, F., “Wave Journal Bearing with Compressible Lubricant; Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing,” STLE Tribology Trans. Vol. 38, 1, pp.153-160, (1995).
U.S. Patent Documents:
Statement of Federal Sponsored Research/Development:
Federal founds were use in certain testing of the wave bearings.
1. Field of the Invention
The present invention concerns journal and thrust fluid film bearings which include a wave surface to optimize load capacity, thermal stability, and dynamic behavior for varying operating conditions.
2. Description of Related Art
High speed, high performance machines need stable, low friction bearings in order to operate smoothly and efficiently. Current standard journal bearings suffer from instabilities that can severely hinder operation of such machinery.
The electronics industry has provided numerous new developments for high speed bearings, used, for example, in hard disc drives, laser printers, and other electronic equipment where speeds in excess of 10,000 rpm are needed. These bearings typically use a gas, specifically air, as a lubricant.
Tempest and Dimofte in U.S. Pat. No. 5,593,230 disclose an air bearing having a non-circular form, which when developed into a normally flat plane has a shallow sinusoidal contour having three peaks, “wave peaks.” Each peak is arranged 120° to an adjacent peak. The top peak is formed with a groove which enhances dynamic stability of the bearing.
Tempest and Dimofte in U.S. Pat. No. 6,024,493 disclose an air bearing which includes a static shaft wherein the shaft has a sinusoidal wave form, and a rotary polygon mirror device incorporating the air bearing.
Murabe and Komura in U.S. Pat. No. 6,428,211 disclose a hydrodynamic gas bearing structure comprising a shaft with notches, “space enlarging portions,” located about the circumference of the shaft at equal distances. These notches are used to supply fluid to the bearing.
Hayakawa, et al., in U. S. Pat. No. 6,402,385 disclose a dynamic pressure bearing that includes a rotary shaft and a centered oil-retaining bearing with pockets in the internal surface of the bearing to increase the pressure of the lubricating oil between the shaft and the oil-retaining bearing, for use in high rotational precision equipment, such as magnetic disc drives, polygon mirror rotary drives (laser printers), and the like.
Such bearings as described in the prior art have not been shown to perform in applications where high temperatures in addition to high speed may be encountered. In particular, gas turbine engine manufacturers are seeking engine main shaft bearings capable of operating up to temperatures of 700° F. and 4 million DN (where DN is the speed parameter, the product of bearing bore diameter in mm and shaft rotative speed in rpm). Such operating conditions are beyond the capability of conventional ball and roller bearings. Under even less severe conditions, ball and roller bearings become unreliable, with reduced life cycle, increased maintenance problems and costs, and increased safety concerns.
Conventional circular journal bearings are disadvantaged in high performance applications due to tendencies to promote shaft instabilities at high speeds and low load conditions. More recently, non-circular types of journal bearings which provide more stability have been developed; some are disclosed, for example, in U.S. Pat. Nos. 5,593,230; 6,024,493; and 6,428,211.
Gas lubricated journal wave bearings without any supply of lubricant are disclosed and have been described, in Dimofte, F., “Wave Journal Bearing with Compressible Lubricant-Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing,” STLE Tribology Transactions, Vol. 38(1), pp. 153-160 (1995).
The journal wave bearing is a journal bearing which features a non-circular or wave configuration on the bearing sleeve. (Ref. 1) There is a slight, but precise variation in the circular profile such that a wave profile is circumscribed on the diameter of the stationary part, having an amplitude equal to a fraction of the bearing clearance. The rotating member has a circular configuration.
The journal wave bearing has several unique advantages when compared to either the plain journal bearing or other types of non-circular journal bearings such as a lobed, fixed pad, or tilting pad. The plain journal bearing has the highest load capacity, but shafts supported in it are subject to instabilities known as fractional frequency, whirl which can lead to failures. The occurrence of fractional frequency whirl makes journal plain bearings unsuitable for lightly loaded, high speed applications. Non-circular types of journal bearings can provide stable shaft operation and their use is obligatory in applications where “shaft whirl” is a problem. The journal wave bearing has two advantages over other known types of non-circular journal bearings: it has the highest load capacity of all the types of non-circular journal bearings, and it is the least expensive bearing to fabricate.
Journal wave bearing technology has been demonstrated with compressible fluid (gas) lubrication. With gas lubrication, the bearing is typically surrounded by the gas so that supplying the bearing with lubricant is not a problem; it does not require any sophisticated design features. The surrounding gas at the bearing edges is absorbed into the bearing where the distance between the shaft and the sleeve is large and it is exhausted where the shaft and sleeve surfaces are very close to each other.
There remained a need: to combine the wave shape advantages to raise the performance of the pressurized gas journal bearings; to extend the performance of the liquid lubricated journal bearings beyond their current limits by including the wave shape; to develop new, simple, and efficient thrust bearings that use the wave shape; and to open another avenue for developing active control and smart bearings based on wave bearing technology. All these create methods of operating high performance rotating machinery at higher speeds, higher temperatures, and higher efficiency, with extremely precise rotation and reliable performance. The present invention meets this need.
The object of this invention is to provide bearings having a wave surface on the stationary bearing part while the rotating member has a plain configuration. In particular the present invention provides a pressurized gas journal bearing having a wave surface that adds an improved hydrodynamic effect when the shaft rotates, in conjunction with the pressure supplied externally. The shaft can rotate in both directions. The bearing load capacity, stiffness, and stability can be significantly improved as compared to either a pressurized plain bearing or an aerodynamic wave bearing. The present invention also provides a liquid lubricated journal wave bearing having a wave surface circumscribed on the diameter of the stationary part. The position of the waves and the lubricant supply ports position is optimized for the specific application. Any liquid, such as, for example, cryogenics, mineral and synthetic hydrocarbon oils, fuels, water, polyphenylethers (PPE), and perfluoropolyethers (PFPE), can be used. The bearing can run at any temperature at which the lubricant remains stable. Another object of the present invention is to provide a bidirectional double thrust wave bearing consisting of an axial disk located between a pair of thrust plates. In addition, the present invention provides a mono-directional singular thrust wave bearing consisting of an axial disk that faces a thrust plate. Either the disk or the thrust plate rotates. The stationary part of this bearing (either the thrust plate or the disk) has a wave surface incorporated into its active face. The interaction of the stationary wave surface and the plain running surface generates hydrodynamic pressures that allow the bearing to carry thrust loads. These thrust wave bearings can be lubricated with any gas or liquid and can run at any temperature (assuming lubricant stability). Finally, this invention provides wave bearings with an elastic stationary part. The elastic part has a wave surface that can be distorted to adapt the bearing performance to the applied loads and speeds. The distortions are made by actuators (as an “Active/Passive Control Fluid Film Bearing”) or by the hydrodynamic pressures between the stationary and rotating parts (as a “Smart Bearing”).
A pressurized gas journal wave bearing 10 according to the present invention is illustrated in
The bearing sleeve 15 has a wave surface 18 circumscribed on its inner diameter. If the shaft is stationary and the sleeve is rotating, the wave profile is circumscribed on the shaft diameter (not illustrated). The profile of the wave surface 18 shows a “mean circle” 19. The radius 20 of the mean circle 19 is also the radius of the bearing sleeve. The wave surface has a starting point 22. The wave has an amplitude 25 which is the distance from the mean circle 19 to the maximum outside point of the wave 26. The position of the wave relative to the applied load direction 90 is defined by the wave position angle 30. The wave surface has a plurality of waves (three are illustrated here). The wave surface 18 is made either through a manufacturing process (such as grinding, lapping, honing, pressing, etc) or through elastic deformation of the sleeve 15 when it is mounted in its housing.
The bearing is supplied with gas (air) through holes 35 which can be designed with either inherent or orifice restrictors. In
The shaft has a radius 55 and an axis of rotation 57. Without a load, the axis of rotation 57 will be in the center of the bearing sleeve 11. When a load 90 is applied, the shaft axis 57 moves in an offset position. The distance 12 between the center of the sleeve 11 and the axis of the shaft 57 is the “eccentricity.” The difference between the bearing sleeve radius 20 and the shaft radius 55 is the bearing radial clearance. The ratio of the wave amplitude 25 to the radial clearance is the “wave amplitude ratio.”
In most machinery, loads are built up as the shaft is rotating. At rest the load applied to the bearings is the weight of the rotating part only. Therefore, the gas (air) supplied through the holes 35 is enough to levitate a “non rotating” shaft 50. When the shaft starts rotating the pressure around the shaft is amplified by the hydrodynamic effect of the plurality of convergent regions of the fluid film thickness between the shaft surface 58 and the wave surface 18. According to the present invention, in
The sleeve 18 and the shaft 50 are made from: solid ceramic materials such as silicon nitride or silicon carbide; solid hard alloys with superficial coatings (such as physical vapor deposition, PVD, or diamond like carbon, DLC, coatings); or metallic materials with plasma spray ceramic coatings.
The pressurized wave bearing can be used (for example) in any high precision machinery, such as high precision tools, centrifuges, and inspection machines, as well as in small or medium sized turbo-machinery, compressors, fans, air-breathing machines, and auxiliary power units.
A journal wave bearing lubricated with liquids 10 according to the present invention, is illustrated in
The bearing sleeve 15 has a wave 18 circumscribed on its inner surface. If the shaft is stationary and the sleeve rotates the wave surface is circumscribed instead on the shaft (not illustrated). The profile of the wave surface 18 shows a mean circle 19. The radius 20 of the mean circle 19 is also the radius of the bearing sleeve. The wave surface has a starting point 22. The wave has an amplitude 25 which is the distance from the mean circle 19 to the maximum outside point of the wave profile 26. The position of the wave surface relative to the applied load direction 90 is defined by the wave position angle 30. The value for this position angle 30 is optimize for the specific application and can be in a range from 0 to 60 degrees. The wave surface has a plurality of waves (three, for example, are illustrated). The wave surface 18 is produced either through a manufacturing process (such as grinding, lapping, honing, pressing, etc) or through elastic deformation of the sleeve 15 when it is mounted in its housing.
The bearing is supplied with a liquid lubricant through a plurality of holes 135 (only three are illustrated), one for each wave. These holes 135 feed the supply pockets with lubricant 136, as seen in
The shaft has a radius 55 and an axis of rotation 57. Without a load the axis of rotation 57 will be in the center of the bearing sleeve 11. When a load 90 is applied, the shaft axis 57 moves to an offset position. The distance 12 between the center of the sleeve 11 and the axis of the shaft 57 is the eccentricity. The difference between the bearing sleeve radius 20 and the shaft radius 55 is the bearing radial clearance. The ratio of the wave amplitude 25 to the radial clearance is the wave amplitude ratio.
When the shaft starts rotating, hills of pressure are created between the shaft 50 and the sleeve 15 due to the hydrodynamic effect of the plurality of convergent regions of the fluid film thickness between the shaft surface 58 and the wave profile 18. According to the present invention, in
According to the present invention, wave journal bearings are appropriate for use when the rotating bearing part, either the bearing sleeve or the shaft, deforms under the applied load. A bearing with a rotating elastic sleeve is illustrated in
To preserve the wave bearing performance, the bearing geometry must be unchanged during the wave bearing's life. The shaft and the sleeve is made from hard materials, with a hardness greater than 60 HRc. Any steels and alloys that can be hardened or case-hardened greater than 60 HRc may be used.
Coatings (such as physical vapor deposition, PVD, or diamond like carbon, DLC, coatings) are applied to both shaft and sleeve surfaces to avoid damage to the wave bearing surfaces when the bearing starts and stops, and to make the wave bearing less sensitive to lubricant interruption.
The wave bearing, according to the present invention, can be used in heavily loaded applications with specific loads up to 24 MPa (3500 PSI). The wave bearing is also very appropriate for use in any medium-sized loaded application with specific loads up to 5.5 MPa (800 PSI) where stable motion is requested at all loads. Journal wave bearings, according to the present invention, are appropriate for either mono-directional or bi-directional journal rotation. The wave bearings have stiffness and damping properties that can be adjusted to the needs of the machinery in which they are being used. In particular, their damping characteristics are useful to attenuate the noise and vibration level of any machinery and particularly in mechanical aero and terrestrial transmissions. Their thermal stability makes the wave bearings very suitable for high temperature application. When lubricated with polyphenylethers (PPE) and perfluoropolyethers (PFPE) the wave bearing runs at temperatures over 350° C. (662° F.).
A bidirectional thrust wave bearing 200 lubricated with a fluid (gas or liquid) according to the present invention is illustrated in
A thrust plate 204 is illustrated in
According to the present invention, a gas thrust wave bearing could be also supplied with pressurized gas through holes with restrictors as illustrated in
When a liquid lubricant is used, according to the present invention, the thrust plates 204 could have radial grooves 260 at the start of each wave, as illustrated if
According to the present invention, both the disk 206 and the thrust plates 204 are made from hard materials. For gas lubricated thrust bearings the disk and the thrust plate are made from: solid ceramic materials such silicon nitride or silicon carbide; solid hard alloys with a superficial coating (such as physical vapor deposition, PVD, or diamond like carbon, DLC coatings) on the active faces 210 and 240; or hard stainless steels with plasma spray ceramic coatings on the active faces 210 and 240. For liquid lubricated thrust bearings, steels and alloys that can be hardened or case-hardened over 60 HRc can be used. Coatings (such as physical vapor deposition, PVD, or diamond like carbon, DLC, coatings) are applied on the active faces 210 and 240 to avoid damage to the bearing surfaces when the bearing starts and stops and to make the bearing less sensitive to lubricant interruption.
A controllable journal wave bearing 300, according to the present invention, is illustrated in
According to the present invention, the amplitude 25 of the wave is controlled by the actuators 320. Any type of actuator can be used, for example, mechanical, electromagnetic, piezoelectric, hydraulic, or pneumatic. The actuators are connected to an active or passive control system that adjusts the wave amplitude 25 to shaft speed, shaft vibration level, and load. Enlarging the wave amplitude 25 causes the bearing to run stably and increases the bearing stiffness. Under heavy loads the bearing is stable and the wave amplitude should be diminished to approach the plain journal bearing geometry; the bearing can then carry a heavy load better than any type of fluid film bearing.
The bearing 300 is lubricated with a liquid lubricant. Both oils and fuels are can be used. The lubricant is supplied to the bearing through holes 135 and pockets 136 shown in
Both the shaft 50 and the elastic shell 315 are made from hard materials, with hardness over 60 HRc. Any steels and alloys that can be hardened or case-hardened over 60 HRc can be used. Coatings (such as physical vapor deposition, PVD, or diamond like carbon, DLC, coatings) are applied to both shaft and elastic shell surfaces to avoid damage to the controllable bearing surfaces when the bearing starts and stops, and to make the controllable bearing less sensitive to lubricant interruption.
According to the present invention, the controllable bearing 300 can be used in high performance rotating machinery which needs high precision rotation, or safe rotation with levels of vibration under fixed limits. Rotating machinery which is heavily loaded but starts and stops under low loads will benefit from the use of the controllable wave bearing 300.
According to the present invention, a self-acting (smart) wave bearing 400 is illustrated in
If a vertical load is applied to the shaft, the pressure in the fluid film opposite the load increases and distorts the shape of the elastic shell in that region.
According to the present invention, if the vertical load increases to the maximum load 90″ that the smart bearing 400 can carry, the amplitude 25″ of the bottom wave goes to zero, approaching a shape similar to that of a plain bearing on the bottom side, as illustrated in FIG. 6C. The elastic shell 410 superimposed over the mean circle in the bottom side of the smart bearing allows the bearing to carry a higher maximum load than a rigid wave bearing.
According to the present invention, any fluid (gas or liquid) can be used to lubricate the smart bearing. The smart bearing runs very stably dynamically and thermally at any speeds and loads and can carry a maximum load greater than any fluid film bearing including a plain journal bearing. The mart bearing can approach a shape similar to the plain bearing in the region that carries the load as the load increases (see
Both the elastic shell and the shaft are from a hard metallic alloy. Coatings (such as physical vapor deposition, PVD, or diamond like carbon, DLC, coatings) are applied to both shaft and elastic shell surfaces to avoid damage to the controllable bearing surfaces when the bearing starts and stops, and to make the smart bearing less sensitive to lubricant interruption.
