Abstract
A low-vibration floating metal bearing includes a slide bearing. The slide bearing includes oil supply holes formed at six isogonal positions in an isotropic manner with respect to an axial center, and a substantially circular bearing hole having a surface on which at least six regions with different fluid lubrication conditions are formed by inner machining so as to be continuously disposed at isogonal positions in an isotropic manner with isotropic distance with respect to an axial center. Each of the regions with different fluid lubrication conditions forms a narrow flow path that is substantially convex in cross section and extends in an axial center direction in an oil flow path by changing the amount of clearance between the surface of the substantially circular bearing hole and the surface of a substantially circular axis.
Claims
1. A low-vibration floating metal bearing comprising a slide bearing, the slide bearing comprising: oil supply holes formed at six isogonal positions in an isotropic manner with respect to an axial center; and a substantially circular bearing hole having a surface on which at least six regions with different fluid lubrication conditions are formed by inner machining so as to be continuously disposed at isogonal positions in the isotropic manner with isotropic distance with respect to an axial center, wherein each of the regions with different fluid lubrication conditions forms a narrow flow path that is substantially convex in cross section and extends in an axial center direction in an oil flow path by changing the amount of clearance between the surface of the substantially circular bearing hole and a surface of a substantially circular axis, and the narrow flow path causes a change in oil pressure to give a self-centering effect and suppress occurrence of noise from a low rotational speed range to a high rotational speed range.
2. The low-vibration floating metal bearing according to claim 1, wherein each of the regions with different fluid lubrication conditions is a region changing the amount of the clearance so as to moderately connect between the narrow flow path that is substantially convex in cross section and extends in an axial center direction and a wide flow path that is substantial concave in cross section and extends in an outer circumferential direction.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic diagram illustrating a floating metal bearing according to the present invention.
(2) FIG. 2 is a diagram illustrating a roundness result (1) of an inner surface shape of a bearing hole according to the present invention.
(3) FIG. 3 is a diagram illustrating a roundness result (2) of an inner surface shape of the bearing hole according to the present invention.
(4) FIG. 4 is a diagram illustrating a roundness result (3) of an inner surface shape of the bearing hole according to the present invention.
(5) FIG. 5 is a diagram illustrating a roundness result (4) of an inner surface shape of the bearing hole according to the present invention.
(6) FIG. 6 is a diagram illustrating a roundness result (5) of an inner surface shape of the bearing hole according to the present invention.
(7) FIG. 7 is a schematic diagram illustrating a basic idea for vibration reduction;
(8) FIG. 8 is a graph of a Stribeck curve illustrating a lubricated state according to the present invention.
(9) FIG. 9 is a diagram illustrating a centering function according to the present invention.
DETAILED DESCRIPTION
(10) The largest feature of the present invention resides in applying surface treatment repeatedly to between a narrow flow path and a wide flow path by changing the amount of clearance between the surface of a shaft and an inner surface of a bearing hole 40.
(11) FIG. 1 is a diagram schematically illustrating a low-vibration floating metal 10 according to the present invention: FIG. 1(a) is a perspective view; and FIG. 1(b) is a plan view and a single cross-section view.
(12) As illustrated in FIG. 1, the low-vibration floating metal 10 may have an outline similar to that of the normal floating metals. The low-vibration floating metal 10 has a plurality of oil supply holes 30 provided in an isogonal and isotropic manner in the center of the outer peripheral edge. Alternatively, the low-vibration floating metal 10 may have on a periphery thereof an oil supply groove (not illustrated) with the oil holes 30. FIG. 1 illustrates six oil supply holes 30, but the number of the oil supply holes 30 is not limited to six. There is no particular limitation on the number of the oil supply holes 30 as far as the advantage of the inner diameter surface shape of the bearing hole 40 as the essence of the present invention can be produced. In addition, the number of the oil supply holes 30 does not depend on the cross section area of the oil supply holes 30 or any other factor.
(13) FIGS. 2 to 6 illustrate the results of measurement of inner roundness of the bearing hole 40 according to the present invention. FIG. 2 illustrates the measurement result of roundness of the center of the outer peripheral edge. Specifically, FIG. 2 illustrates the measurement result of roundness at a position 4.13 mm inward from one end surface.
(14) FIG. 3 illustrates the measurement result of an end surface and its vicinity. Specifically, FIG. 3 illustrates the measurement result at a position 0.88 mm inward from one end surface. The roundness of the other end surface is almost the same as that illustrated in FIG. 3 and thus is omitted.
(15) In all the measurements of FIGS. 2 to 6, the measurement magnification used is 2000 times.
(16) Of line illustrated in FIGS. 2 and 6, the innermost circle represents the maximum height as defined in JIS B7451 and the outermost circle represents the maximum depth. The circle between the innermost and outermost circles represents the average value of roundness. The roundness from the maximum height to the maximum depth is 4.87 m in FIG. 2 and 3.83 m near the end surface illustrated in FIG. 3. The metal bearing used for obtaining the experimental data has six oil supply holes 30. However, the number of the oil supply holes is not limited to this as described above.
(17) FIG. 4 illustrates the result of pursuit of roundness, indicating a roundness of 1.28 m. As compared to the other drawings, the roundness in FIG. 4 is apparently higher. However, it has been revealed by measurement with a vibration meter that there is no special tendency to attenuate vibrations.
(18) FIG. 5 represents intentionally prepared data to know the state with a disordered roundness. The roundness illustrated in FIG. 5 is at a defective level not meeting criteria for quality assurance of general products. However, it was found that the roundness illustrated in FIG. 5 had less influence of a problem such as vibrations or noise on deviation of roundness.
(19) FIG. 6 illustrates roundness in the case where dynamic pressure generating points are provided at 120 degrees each to form a triangular shape as the largest isogonal and isotropic divisions. In this case, occurrence of vibrations can be suppressed as in the case described above.
(20) With regard to the number of divisions, it has been revealed that the hexagonal shape contributes to suppression of occurrence of vibrations.
(21) FIG. 8 is a schematic diagram illustrating a basic idea for vibration reduction. FIG. 8(a) illustrates the number of vibrations (G) in the vertical axis and arithmetic average roughness (Ra) in the horizontal axis. In the upper part of the graph, a circular mark shifts horizontally to indicate that improvement of surface roughness does not have influence on vibrations resulting in noise. The left-side surface roughness is Ra 0.06, and the right-side surface roughness is around Ra 0.4.
(22) On the other hand, with regard to changes in the vertical axis on the left side of the graph, that is, increases or decreases in vibrations, it is understood that vibrations decrease as the circular shape with a high roundness changes to a more polygonal shape.
(23) FIG. 8(b) illustrates a phenomenon that vibrations increase as the circular shape has higher roundness. The circular shape has a roundness of 0.8 m or less on the upper left side, and has a roundness of 2.5 to 4 m at the lower right side.
(24) In FIG. 7, a graph of a general Stribeck curve is used to describe the lubricated state of the low-vibration floating metal bearing 10 according to the present invention. The solid line drawn in the graph of FIG. 7 is a Stribeck curve generally used to describe the lubricated state between two relatively moving surfaces. The dashed-dotted line drawn in the graph illustrates the lubricated state of the low-vibration floating metal bearing 10 according to the present invention. This line is a virtual curve based on the experimental results.
(25) The low-vibration floating metal bearing 10 according to the present invention makes it possible to reduce vibrations. Thus, it is considered that, by decreasing fluid friction due to vibrations, friction resistance can also be reduced by the decrease. Therefore, S2 indicates the presence of the decrease. It is also considered that, as an effect of the present invention described later, the centering property (self-centering function) can be produced. The dynamic pressure due to a working fluid associated with the rotation acts on the entire circular periphery of the bearing. Thus, it is considered that the shift from boundary lubrication region A at the stoppage to mixed lubrication region B and fluid lubrication region C takes place in a low rotational speed range. The presence of friction decrease at the initial stage of the rotation due to the centering effect is indicated as S1.
(26) FIG. 9 is a diagram illustrating a centering property (self-centering function) as an advantage of the present invention. FIG. 9(a) illustrates distribution of pressure generated from Reynolds equation in wedge-shaped clearance. In FIG. 9(b), when the pressure distribution is placed at the circular periphery edge portion, the pressure generated from the rotation acts equally. This brings about an effect of uniformly suppressing vibrations by the pressure constantly acting toward the center. The effect is produced by the centering function associated with the advantage of the present invention.
