Abstract
The invention relates to a bearing assembly having a back-up bearing (2), which has an outer ring (4) arranged in a housing construction (12) in a flexible manner. The flexibility has angle-dependent extreme values, namely at least one minimum and at least one maximum. According to the invention, this bearing assembly is characterized in that, within 360° with respect to the circumference of the outer ring (4), there are more than two angles at which there is at least one local extreme value of the flexibility of the outer ring (4).
Claims
1. A bearing assembly comprising a backup bearing that comprises a flexible outer ring arranged in a housing construction, a flexibility of the flexible outer ring has angle-dependent extreme values with at least one minimum and at least one maximum, and within 360°, there are more than two angles at which an at least local extreme value of flexibility of the outer ring is given with respect to a circumference of the outer ring, further comprising on the circumference of the outer ring, an asymmetrical angle partitioning between circumferential sections of increased flexibility and angle sections of reduced flexibility.
2. The bearing assembly according to claim 1, further comprising between the outer ring and the housing construction, a spring and damping element that supports the outer ring with angle-dependent flexibility with respect to the housing construction.
3. The bearing assembly according to claim 1, wherein exactly two of the minimum points and two of the maximum points of flexibility are given.
4. The bearing assembly according to claim 1, wherein the two minimum points and the two maximum points are equal in magnitude to each other.
5. The bearing assembly according to claim 4, wherein the outer ring is supported on exactly two sections of the circumference thereof opposite each other on the housing construction.
6. The bearing assembly according to claim 1, wherein exactly three of the minimum points and three of the maximum points of flexibility are given.
7. The bearing assembly according to claim 1, wherein the maximum of flexibility differs by at least 5% from the minimum of flexibility.
8. The bearing assembly according to claim 1, wherein the backup bearing is constructed as a ball bearing, at least one of the parameters of pressure angle, osculation, or wall thickness of a bearing ring is dependent on angle.
9. The bearing assembly according to claim 1, wherein the backup bearing has an oscillation amplitude (A) dependent on an excitation frequency (F) or excitation direction with at least two maximum points.
10. A bearing assembly comprising a backup bearing that comprises a flexible outer ring arranged in a housing construction, a flexibility of the flexible outer ring has angle-dependent extreme values with at least one minimum and at least one maximum, and within 360°, there are more than two angles at which an at least local extreme value of flexibility of the outer ring is given with respect to a circumference of the outer ring, further comprising a second backup bearing having spring and damping properties that differ from spring and damping properties of the first backup bearing.
11. The bearing assembly according to claim 10, wherein the two backup bearings have different resonance frequencies.
12. The bearing assembly according to claim 10, wherein the first backup bearing has multiple extreme points of flexibility on the circumference, having a number that deviates from a number of extreme points of flexibility of the second backup bearing.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Several embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Shown are, partially in schematic view:
(2) FIG. 1 in a diagram, the angle dependency of the radial stiffness of a backup bearing,
(3) FIG. 2 a first embodiment of a damped backup bearing,
(4) FIG. 3 a second embodiment of a damped backup bearing,
(5) FIG. 4 a third embodiment of a damped backup bearing,
(6) FIG. 5 a fourth embodiment of a damped backup bearing,
(7) FIG. 6 a fifth embodiment of a damped backup bearing,
(8) FIG. 7 in a diagram, the dependency of an oscillation amplitude of a backup bearing according to the invention on an excitation frequency acting on the backup bearing, compared with the resonance behavior of a conventional bearing assembly,
(9) FIG. 8 a first cross section of a backup bearing with angle-dependent bearing geometry,
(10) FIG. 9 a second cross section of a backup bearing with angle-dependent bearing geometry,
(11) FIG. 10 a third cross section of a backup bearing with angle-dependent bearing geometry,
(12) FIG. 11 a bearing assembly with magnetic bearing as a main bearing, as well as several different backup bearings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(13) In the diagram according to FIG. 1, one possible angle dependency of the radial stiffness S of a backup bearing constructed according to the invention is shown. The shown curve that has the shape of a harmonic oscillation, covers an angle φ from 0° to 360°, i.e., the full circumference of the backup bearing. Through measures that will be explained using examples below, it is ensured that the radial stiffness S has two minimum and two maximum points with respect to the entire circumference of the backup bearing, wherein, in the shown case, the two minimum and two maximum points each have an identical amplitude relative to each other and each extreme value is spaced apart 90° from the next extreme value. The variation of stiffness S of the outer ring of the backup bearing on its circumference is implemented, for example, just by the shape of the outer ring. Here, for example, a backup bearing outer ring with uniform wall thickness can be inserted into a cylindrical hole of a housing holding the backup bearing.
(14) The backup bearing, whose radial stiffness S is shown in FIG. 1, can basically be formed as a sliding bearing, rolling bearing, or sliding/rolling bearing. For the case that it is shaped as a rolling bearing, it can be, for example, a roller bearing or a ball bearing. In the last case, the rolling bearing is advantageously formed as a two-row angular contact ball bearing, in particular, in an X or O arrangement. The uniformity of the flexibility on the circumference of the backup bearing can involve at least partially an angle-dependent pressure angle, an angle-dependent osculation between the rolling bodies and tracks, or a combination of angle-dependent pressure angle and angle-dependent osculation, as will be explained in more detail with reference to FIGS. 8 to 10. Alternatively or additionally, flexible and/or damping elements can be arranged outside of the outer ring of the backup bearing within the bearing assembly comprising the backup bearing. In all of the embodiments, the maximum of radial flexibility of the backup bearing differs advantageously by at least 5%, for example, at least 10%, at least 25% or at least 50%, from the minimum of flexibility.
(15) The embodiment according to FIG. 2 shows a bearing assembly designated overall with the reference symbol 1, which comprises a backup bearing 2 and a housing construction 12 only indicated in the figure, and has, in principle, the properties explained with reference to FIG. 1 just like the embodiments according to FIGS. 3 to 6.
(16) The backup bearing 2 according to FIG. 2 is provided as a safety device for supporting a shaft 3 that is supported in normal operation by a not-shown magnetic bearing. Components of the backup bearing 2 are an outer ring 4 and a plurality of rolling bodies 5, namely balls. Deviating from the simplified diagram according to FIG. 2, the rolling bodies 5 do not roll directly on the shaft 3, but instead on a not-shown inner ring of the backup bearing 2 which is set apart from the shaft 3, during normal operation, by a small gap. Only if the magnetic bearing fails does the shaft 3 fall into and engage the inner ring, so that the backup bearing 2 comes into operation. The rolling bodies 5 are arranged without a cage between the inner ring and the outer ring 4 of the backup bearing 2. The backup bearing 2—more precisely: its outer ring 4—is supported only on two circumferential sections on the housing construction 12. A gap shown in FIG. 2 only for a clearer illustration is actually not present between the outer ring 4 and two support regions 6 of the housing construction 12. Instead, as long as the magnetic bearing is operating without errors, all of the components of the backup bearing 2 are still, while the shaft 3, as already explained, has at least a minimal distance to the backup bearing 2.
(17) The two support regions 6 of the bearing assembly 1 according to FIG. 2 have no or only very minimal flexibility in the radial direction. The circumferential regions of the outer ring 4 in which this contacts the support regions 6, in particular, is pressed into the housing construction 12, correspond to the two maximum points of radial stiffness S according to FIG. 1. In contrast, the circumferential regions between the two support regions 6 form the minimum points of radial stiffness S of the outer ring 4. The radial stiffness S is to be understood as a spring constant and represents the reciprocal of the radial flexibility. In addition to the radial support, the backup bearing 2 according to FIG. 2 can also be supported in the axial direction with respect to the rotational axis of the shaft 3, wherein, in this case, also the axial stiffness of the bearing assembly 1 can be dependent on angle.
(18) The embodiment according to FIG. 3 differs from the embodiment according to FIG. 2 initially in that the backup bearing 2 is embedded in the housing construction 12 on its entire circumference. In addition, in the embodiment sketched in FIG. 3, three circumferential sections 7 of increased radial flexibility and three circumferential sections 8 of reduced radial flexibility given. The radial flexibility is produced here, on one hand, from the properties of a corrugated ribbon 9, generally called a spring and damping element, which is mounted between the outer ring 4 and the housing construction 12, and, on the other hand, from the space available to the corrugated ribbon 9 within the different circumferential sections 7, 8. While the corrugated ribbon 9 takes up a wide space within the circumferential sections 7, only a relatively narrow gap between the outer ring 4 and the housing construction 12 is available to the corrugated ribbon 9 in the circumferential sections 8, which leads to a comparatively high radial stiffness S.
(19) Each circumferential section 7, 8 extends across an angle that differs from each angle that one of the other circumferential sections 7, 8 takes up. The bearing assembly 1 according to FIG. 3 does not have point or mirror symmetry, wherein the production of resonance in the function takeover by the backup bearing 2 is counteracted.
(20) The bearing assembly sketched in FIG. 4 manages without separate spring and/or damping elements, as the embodiment according to FIG. 2 has, wherein, nevertheless, a pronounced angle dependency of radial stiffness S, as shown in FIG. 1, is given. The outer ring 4 of the backup bearing 2 according to FIG. 4 has a non-uniform wall thickness on its circumference and merely contacts narrow circumferential sections on the housing construction 12. The hole in the housing construction 12, in which the outer ring 4 is inserted, is cylindrical. The inner circumference of the outer ring 4 is also cylindrical. In a not-shown way, in those circumferential sections in which the outer ring 4 is spaced apart from the housing construction 12, there is a damping means, for example, an elastomer or a metal foam. Likewise, in a not-shown way, an anti-rotational lock can be realized between the outer ring 4 of the backup bearing 2 constructed as a rolling bearing and the housing construction 12.
(21) FIG. 5 shows an embodiment in which the outer ring 4 and the housing construction 12 have a symmetric construction. In the gap of constant width between the outer ring 4 and the housing construction 12, in this case, there is a section of a relatively stiff corrugated ribbon 9 and a section of a comparatively soft corrugated ribbon 10, that is, another spring and damping element. The circumference of the backup bearing 2 is essentially taken up by the different sections of corrugated ribbons 9, 10. The two transition regions between the corrugated ribbon 9 and the corrugated ribbon 10 can be shaped such that a local maximum of radial stiffness S of the backup bearing 2 occurs in each of these transition regions. The stiffer corrugated ribbon 9 is preferably installed, as shown in FIG. 5, in the lower region of the bearing assembly 1, so that the weight forces acting on the shaft 3 also can be received in this region.
(22) In the embodiment according to FIG. 6, in two narrow circumferential sections, the radial stiffness of the bearing assembly 1 is greatly increased by two blocks 11, in particular, made from metal, supporting the outer ring 4. In the other circumferential sections between the blocks 11 there is, in contrast, a corrugated ribbon 9 between the outer ring 4 and the housing construction 12. Deviating from the illustration according to FIG. 6, different properties can be arranged in these two circumferential sections, also sections of corrugated ribbons 9, 10, as sketched in FIG. 5.
(23) FIG. 7 shows a schematic comparison between properties of a bearing assembly 1 constructed according to the invention on one hand and a conventional bearing assembly with elastic properties on the other hand. The basic dependency of an oscillation amplitude A on an excitation frequency F is shown, wherein the behavior of a bearing assembly 1 according to the invention, as sketched, for example, in FIGS. 2 to 6, is shown by a solid line and the behavior of a conventional bearing assembly is shown by a dotted line for comparison.
(24) In a typical, conventional bearing assembly, the oscillation amplitude has, at a certain excitation frequency, the resonance frequency R, a greatly pronounced maximum. Due to the oscillation-reducing shape of the bearing assembly 1, this maximum is prevented in each of the embodiments according to FIGS. 2 to 6. Instead, as can be seen in FIG. 7, several, relatively low maximum points of oscillation amplitude A are formed. Thus, there is no greatly pronounced resonance in the bearing assembly 1 during the entire runout of the shaft 3 supported by the backup bearing 2 after the failure of the magnetic bearing.
(25) FIGS. 8 to 10 each show an embodiment of a backup bearing 2 that has an angle-dependent bearing geometry, wherein, in each of the three cases, the osculation and/or the pressure angle varies along the circumference of the backup bearing 2. In each case, in the left half of the figure there is a first cross section that relates to a first angle position, defined as the 0° position, and is equal in all cases. On the right, in each figure, for comparison a second cross section is shown that relates to a second angle position, for example, the 45° position or the 90° position.
(26) In the backup bearing 2 shown in FIG. 8, the outer ring 4 and inner ring 13 have the same osculation. The radius of the track on the outer ring 4 corresponds in the shown cross section to the radius of the track on the inner ring 13. In the 0° position (left), the pressure angle is zero; the backup bearing 2 is thus a pure radial bearing. In contrast, in the second angle position (right), the pressure angle is significantly greater than zero. In this angle region, the rolling bodies 5 thus also transmit axial forces to a significant extent in addition to radial forces. The spring behavior differs significantly in the two shown angle regions. In particular, in the region in which the pressure angle is not zero, if the backup bearing 2 is loaded in the radial direction, a force component is also generated in the axial direction. The regions of different pressure angle transition continuously one into the other, wherein the difference between a minimum pressure angle and an enlarged pressure angle is shown exaggerated in FIG. 8.
(27) In contrast to the embodiment according to FIG. 8, in the embodiment according to FIG. 9, the pressure angle does not vary, but instead the osculation along the circumference of the backup bearing 2 varies. While in the first angle region both the track of the outer ring 4 and also the track of the inner ring 13 is curved relatively slightly in comparison to the radius of the rolling bodies 5, this relates only to the inner ring 13 in the second angle region. For the outer ring 4, in contrast, the radius of curvature of the track is significantly closer to the radius of curvature of the balls 5, that is, tighter osculation (closer to 100%). The tighter osculation ensures that the balls 5 are less spring-like under the effect of a radial force than for other osculation values.
(28) The embodiment according to FIG. 10 combines features of the embodiments according to FIGS. 8 and 9. As can be seen from the comparison of the two cross sections, in the second angle position of the backup bearing 2, both the pressure angle and also the osculation change relative to the first angle position. In each of the embodiments according to FIGS. 8 to 10, the inner ring 13 has along its entire circumference a constant cross-sectional geometry, while the cross-sectional geometry of the outer ring 4 is dependent on angle. Likewise, only the geometry of the inner ring 13 or the geometry of both rings 4, 13 could be dependent on angle.
(29) In FIG. 11, a bearing assembly 1 is sketched that has, in addition to a first backup bearing 2, a second backup bearing 14 that is provided for holding the same shaft 3 that is otherwise supported by means of a magnetic bearing 15. While the right backup bearing 2 in the arrangement according to FIG. 11 has a spring and damping element 9 corresponding to one of the previously explained construction possibilities, in the second backup bearing 14, other elastic properties are given. Each of the backup bearings 2, 14 has a specific resonance behavior. In particular, the number of resonance frequencies of the first backup bearing 2 differs from the number of resonance frequencies of the second backup bearing 14. Here, no resonance frequency of the first backup bearing 2 is identical to any resonance frequency of the second backup bearing 14. Each of the backup bearings 2, 14 has a flexibility in the radial direction that is dependent on angle. Here, it is assumed that a force vector normal to the rotational axis of the backup bearing 2, 14 acts from the shaft 3 toward the outside. Then angle at which the first backup bearing 2 has local or absolute extreme values of flexibility differ from the angles at which the second backup bearing 14 has local or absolute extreme values of flexibility.
(30) In this way, two different backup bearings 2, 14 are provided that greatly differ from each other, especially with respect to their oscillation behavior, and thus overall provide a significant contribution to the most oscillation favorable properties of the bearing assembly 1.
LIST OF REFERENCE NUMBERS
(31) 1 Bearing assembly
(32) 2 Backup bearing
(33) 3 Shaft
(34) 4 Outer ring
(35) 5 Rolling body
(36) 6 Support region
(37) 7 Circumferential section
(38) 8 Circumferential section
(39) 9 Corrugated ribbon
(40) 10 Corrugated ribbon
(41) 11 Block
(42) 12 Housing construction
(43) 13 Inner ring
(44) 14 Backup bearing
(45) 15 Magnetic bearing
(46) A Oscillation amplitude
(47) F Excitation frequency
(48) R Resonance frequency
(49) S Stiffness
(50) φ Angle
