05/056898

04/11/1972

07/21/1970

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Brown-Boveri-Sulzer Turbomachinery, Ltd. (Zurich, CH)

384/304

F16C17/06; F16C17/10; F16C17/00; F16C17/04; F16C17/06

308/160,168

Geoghegan, Edgar W.

Susko, Frank

What is claimed is

1. A thrust bearing comprising

2. A thrust bearing as set forth in claim 1 wherein each said bar has one limited abutment member in the middle zone of one radially oriented side bearing on one adjacent rocker and a pair of limited abutment members on the opposite side bearing on another adjacent rocker.

3. A thrust bearing as set forth in claim 2 wherein said abutment members are protuberances projecting from said bars.

4. A thrust bearing as set forth in claim 1 wherein each rocker has one protuberance in the middle zone of one radially oriented side bearing on an adjacent bar and a pair of protuberances on the opposite side bearing on another adjacent bar.

5. A thrust bearing as set forth in claim 4 wherein said protuberances are slightly barrelled in shape and abut mating abutment surface on said bars.

6. A thrust bearing as set forth in claim 5 wherein at least one of said mating abutment surfaces is barrelled in identical manner and direction as a corresponding protuberance to provide surface contact.

7. In combination with a bearing housing and a shaft having a collar thereon; a thrust bearing mounted in said housing coaxially of said collar, said bearing including a plurality of annularly spaced bearing segments opposite said collar, a plurality of supporting bars, a joint between each of said bars and a respective one of said bearing segments for pivotally mounting said bearing segment on said bar in a zone of lubricant wedge pressure center a plurality of rockers, each said rocker being positioned between a pair of said bars and having a surface at two opposite ends thereof pivotally mounting an end of each of said pair of bars thereon, and a joint means between each of said rockers and said bearing housing including at least one radially oriented roller for pivotally mounting said rockers in the middle zone thereof on said bearing housing and tangentially of said collar, each supporting bar having one limited abutment member in the middle of one radially oriented side bearing on one of said rockers and two limited abutment members on the opposite side bearing on an adjacent rocker whereby each supporting bar has a three point bearing on said rockers.

8. The combination as set forth in claim 7 further including a second of said thrust bearings on the opposite side of said collar.

9. The combination as set forth in claim 7 wherein said bearing housing and said shaft have parallel axes and wherein the mating contact surfaces of said bars and said rockers are located in a plane perpendicular to said axes of said bearing housing and said shaft.

10. The combination as set forth in claim 9 wherein each said roller contacts said respective rocker on an axis perpendicular to said axis of said shaft and located in said plane of said mating contact surfaces of said bore and said rockers.

11. A thrust bearing comprising

12. A thrust bearing comprising

13. A thrust bearing as set forth in claim 12 wherein said protuberances are slightly barrelled in shape and abut mating abutment surfaces on said bar.

14. A thrust bearing as set forth in claim 12 wherein at least one of said mating abutment surfaces is barrelled in identical manner and direction as a corresponding protuberance to provide surface contact.

Thrust bearings have been known in which a thrust collar fixedly mounted on a shaft has slid on the bearing surfaces on a number of bearing segments which have been grouped in annular array around the shaft. These bearing segments have been pivotally mounted to a limited extent in order to allow for alignment relative to the positions of the thrust collar bearing surfaces and to the resultant lubricant wedge therebetween. To this end, each of the bearing segments have been supported on a supporting bar by means of a joint in the zone of the lubricant wedge pressure center while each supporting bar has had at least one support surface on an approximately radially oriented side bearing on a corresponding mating surface on one side of a rocker which has been common to a pair of such supporting bars.

These thrust bearings have generally had the individual rockers or all the rockers supported in a bearing housing with more or less blunted radially orientated edges which have been disposed on the side of the rocker opposite from the side of which the bars have been supported on the rocker. However, such rockers have had an instable equilibrium. That is, while equilibrium has been obtainable in the position in which the component of the bearing pressure of the bars extends through the bearing center of the edge, any slight pivoting of the rocker from this position of equilibrium results in deflection forces which in crease with an increasing magnitude of deflection. Equilibrium can, therefore, be restored only by external effects. Further, experience has shown that such rockers have become locked in the deflected position in the event of a fault due to deflection of the shaft axis relative to the housing axis. As a result, the supporting structure of the rockers and bars together with the bearing segments can be returned into the normal position only after the bearing has been relieved of the load.

Thrust bearings have also been known in which the supporting positions of the rockers on the bearing housing and the mating supporting surfaces at the ends of the rocker on which the bars are supported have been disposed in a plane which is perpendicular to the axes of the bearing housing and shaft when the relative position of the bearing housing and shaft have been parallel. In such systems, the supporting positions have been formed by the spherical end surfaces of bolts set into the bearing housing. Such spherical surfaces permit the rockers to execute tilting motions to each side so that the motions of the rocker system have not been confined to the tangential direction. For this reason, however, the supporting structure of these bearings can nevertheless perform motions which cause self-locking of the bearing in deflected positions.

Accordingly it is an object of the invention to prevent self-locking of the bearing elements of a thrust bearing.

It is another object of the invention to limit the motions of the individual elements of the supporting structure and of the bearing segments relative to each other in a thrust bearing to prevent the appearance of any instable form of equilibrium while clearly defining the direction of motion and excluding all other motions.

It is another object of the invention to statically define the positions at which the individual parts of a thrust bearing bear upon each other to prevent tilting motions in the event of over dimensioning.

Briefly, the invention provides a thrust bearing which utilizes the common application of three characteristics which prevent self-locking of the bearing when deflected relative to the bearing housing. The thrust bearing which is constructed of bearing elements, supporting bars and rockers in a relation similar to that above first mounts each rocker on at least one radially directed roller in a tangentially pivotal manner in the middle zone of the bearing housing. Further, each bar is provided on one radially orientated side with one limited abutment member in the middle zone and on the opposite side with two limited abutment members so that each bar bears at three points on adjacent rockers. Also, the axes of inclination between the rollers and the rockers and the mating support surfaces on the ends of the rockers are disposed in a plane which is perpendicular to the axes of the bearing housing and shaft when the housing and shaft are axially parallel to each other.

The three-point method of support of the bars on the rockers is obtained by providing each bar with one protruberance in the middle zone on one radially orientated abutment side and with two protruberances on the oppositely disposed abutment side. Alternatively, the same effect can be obtained by providing each rocker with one protruberance on one radially orientated abutment side in the middle zone and with two protruberances on oppositely disposed abutment side. In either instance, the limited abutment members may also be lightly barrelled. For example, it is possible for a mating abutment surface which bears on a barrelled abutment surface to be equally barrelled in the same direction to produce a limited surface contact.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a cross-sectional view taken on line I of FIG. 2 of a shaft bearing according to the invention;

FIG. 2 illustrates a longitudinal section through the shaft and bearing taken along line II in FIG. ;

FIG. 3 illustrates a developed cross-sectional view through the bars and rockers of the thrust bearing taken along the curved line III of FIG. 1;

FIG. 4a illustrates a view of a rocker bearing system on an enlarged scale according to the invention;

FIG. 4b illustrates a fragmentary view of the rocker taken on line IV ₆ -IV ₆ of FIG. 4a;

FIGS. 5a to 5c illustrates a developed view of the axis of the bar and rockers on half the bearing circumference between the highest and lowest point of the collar during a deflection of the shaft;

FIG. 6 illustrates a view of a rocker and two bars with the thrust collar inclined in accordance with FIG. 5;

FIG. 7 illustrates a view towards the shaft collar of a bar with limited supporting members;

FIG. 8 illustrates a view towards the bearing housing of a rocker with limited supporting members;

FIG. 9 illustrates a meshing of the bevel gear surfaces of bar and rocker;

FIG. 10 illustrates a view of the supporting surfaces of a bar and rocker having rounded edges according to the invention; and

FIG. 11 illustrates a view of a bar and rocker utilizing a bevel tooth and a meshing tooth gap according to the invention.

Referring to FIGS. 1 and 2, a rotatable shaft 2 is axially supported in a bearing housing 1 by means of a thrust collar 3 with the shaft 2 and thrust collar 3 being in accurate coaxial alignment with each other. The shaft 2 and thrust collar 3 may be constructed integrally or may be joined in a suitable manner from two parts. A thrust bearing which journals the collar 3 in the housing 1 includes a double system of ten bearing segments 10 - 29 each, as well as 10 supporting bars 30 - 49 each, and 10 rockers 50 69 in order to transmit the thrust forces of the shaft 2 via the collar 3 to the bearing housing 1.

Referring to FIGS. 1, 2 and 3, the bearing segments 10 - 29 are each supported on one associated supporting bar 30 - 49 by means of a joint 4 which provides all-round movability to a limited extent. The all-round movability of the bearing segments 10 - 29 is necessary in order to define a lubricant wedge between the thrust collar 3 and the sliding surfaces of the bearing segments 10 - 29; the lubricant wedge corresponding to the physical properties of the lubricant, the applied loading and the rotational speed. The two supporting bars 30 - 49 of adjacent bearing segments 10 - 29 are supported at the inwardly facing radially oriented sides 71 by supporting surfaces 72 which rest on a corresponding mating supporting surface 73 on one axially orientated side 74 each of a common rocker 50 - 69. The middle zone of the rockers 50 - 69, in turn, is supported on a base surface 89 of a cylindrical annular groove 70 of the bearing housing 1 so as to be pivotable or inclinable by means of a joint 5 to a small extent in the tangential direction.

Referring to FIGS. 2 and 3, the joint 4 between each bearing segment and the supporting bar is provided with a supporting plate 78 of hard metal inserted into a bore of the bearing segment and a journal 79 also constructed of hard metal which is inserted into a bore of the bar and extends into the oppositely disposed bore of the bearing segment to abut against the plate 78 by means of a rounded end as shown. In this way, the bearing segment is pivotable or inclinable to a small extent in a universal manner relative to the bar but is retained in the radial axial and tangential directions Further, the plate 78 contacts the journal 79 at a point located in an imaginary cylinder 9.

Referring to FIG. 2, the bearing segments 10 - 29 bear on the cylinder internal walls 91, 92 of the annular groove 70 on two oppositely disposed sides 90 with a slight clearance. The position of the bearing segments 10 - 29 within the bearing is thus defined to the extent that such segments can be inclined only to a limited extent universally and can be displaced in the axial direction. The absolute magnitude of the limited freedom of movement depends on the deviation between the axes of the shaft 2 and the bearing housing 1 which occurs during installation and arise subsequently under the operating loads. In most cases, the angular deviations, even in bearings for large machines, will be substantially or far less than 5 mm. per 1 m. or below the limit of one degree of arc.

The rockers 50 - 69 are also placed into the annular grooves 70 with the clearance of the rockers 50 - 69 between the walls 91, 92 of each annular groove 70 being so dimensioned as to provide only a limited freedom of movement in the same way as for the bars 30 - 49.

Referring to FIG. 4, each rocker 50 - 69 is provided with a radial groove 93 into which a pair of rollers 94 are placed to transmit the axial thrust of the shaft 2 to the housing 1. The rollers 94 pivotally support the rocker 50-69 on an axis of the joint 5 which lies in a common plane 84 with the axes of the remaining joints 5. Furthermore, a pin 95 is inserted in the bearing housing 1 to engage in a bore 96 of the rocker located between the rollers 94. This pin 95 which is of a diameter equal to the diameter of the bore 95 is provided with a spherical periphery 95' where the pin 95 is received in the rocker. The spherical periphery 95' is of a diameter equal to the bore diameter and the mid-point is situated in the plane 84 (FIG. 4b) so that the rocker is tangentially located in the annular groove 70 while being capable of executing angular motions to a limited extent in the tangential direction through the rollers 94.

The supporting surfaces 72 of the bars 30 - 49 and the mating supporting surfaces 73 of the rockers 50 - 69, as well as the supporting positions of the bearing segments 10 - 29 on the bars 30 - 49 and of the rockers on the base surface 89 of the groove 70 and the bearing segments themselves are so disposed and dimensioned as to permit the formation of lubricant wedges between the sliding surfaces of the bearing segments 10 - 29 and thrust collar 3. The sliding surfaces of the collar 3 are thus able to slide on the lubricant wedges without physical contact with the bearing segments 10 - 29. Also, the axis 6 of the shaft 2 is identical with the axis of the bearing housing 1 so that the bearing elements on one side of the thrust collar 3 are positioned accurately symmetrically to those of the other side of the collar 3 in relation to the central plane 97 of the thrust collar 3. In addition, the supporting surfaces 72 and mating supporting surfaces 73 of the respective bars and rockers are disposed in common planes 77 while the centers of the joints 4, 5 of the bars and rockers are disposed on a central cylinder 9 of the cylindrical annular grooves 70. The planes 77 are coincident with the planes 84 so that each roller contacts the respective rocker on an axis perpendicular to the axis of the shaft while being located in the same plane of the mating contact surfaces of the bars and rockers.

Referring to FIG. 5, in operation, if the position or shape of the shaft be changed, for example, due to flexure by the shaft dead weight or by a rotor weight or due to external eccentric loadings or thermal changes and the like, the shaft axis 6 may incline relative to the axis of the housing 1 and, in appropriate cases, may be displaced transversely to the position of the bearing center 99. This causes the thrust collar 3 to be inclined through a small angle relative to the shaft axis 6 with the axial distances between the sliding surfaces of the collar 3 and the base surface 89 of the grooves 70 varying in the same manner. That is, the axial distances will increase on one bearing side and will be reduced on the other bearing side.

The pattern formed by the bars 30 - 49 and rockers 50 - 69 in section with the cylinder surface 9 (FIG. 2) in the inclined position of the axis of the shaft 2 relative to the housing axis 6, in the interests of simplification is illustrated as a straight line although strictly speaking the line of intersection between the plane 77 and the cylinder 9 being an oblique section through a cylinder, would yield an ellipse and in developed form would yield a sinusoidal line. HOwever, the deviation from a straight line is so small that no noticeable falsification of the results is produced. Also, in the interest of clarify, the vertical deviations of the bearing segments 10 - 29 from their symmetrical normal position are shown in greatly exaggerated form relative to any deviation which could actually occur. Only negligeable, secondary deviations will therefore occur in the end result.

FIG. 5 is based on an inclination of the shaft 2 and of the thrust collar 3 in which the joints 4 of the bars 30 and 35 being on diametrically opposite sides of the bearing experience the greatest axial deviations (namely the amount h) to one or the other side of the original position, i.e. from the plane 84. For reasons of geometry, the new locations of the pivoting points 100 - 105 of the bars 30 - 35 are provided on one side of the axis of symmetry 7 -- 7 with the following ordinates:

Pivoting Point Ordinate 100 -h 101 -h cos 36° 102 -h cos 72° 103 +h cos 72° 104 +h cos 36° 105 +h

A precisely symmetrical pattern is obtained on the opposite side of the axis of symmetry 7 -- 7 The line 8 in FIG. 5b represents the intersection of the axial plane 8--8 which is perpendicular to the axial plane 7--7 of symmetry with the cylinder 9.

Referring to FIG. 6 wherein a pair of adjacent bars 34, 35 and a common rocker 54 are shown for purposes of clarity, the deviations of the bars 34, 35 and the angular relationships between the bars 34, 35 and rocker 54 are more clearly shown.

Referring to FIGS. 5a, 5b and 5c, the bars and rockers form respective lines 30-35 and 50-54, such that, as shown, for reasons of geometry the line is centrally symmetrical relative to the pivoting point of the rocker 52. The the event of a relative change of angle of the axes of the shaft 2 and bearing housing 1 within the limitations of the technically permissible changes of form, the inclination of the segment rim on one side as well as the inclination of the segment rim on the other side of the thrust collar 30 can vary within the position of the groove base 89 having to be modified. Accordingly, and because of the adjustability described hereinabove, the individual segments will support equal parts of the overall axial thrust of the shaft 2 even when these segments are in the modified position.

It has initially been assumed that if the axis of the shaft 2 is positioned at an angle relative to the bearing axis the point of intersection of the axis will still remain at position 99 so that no lateral displacement of the thrust collar is involved. However, if the original position 99 is also displaced transversely to the housing axis, for example, due to an unfavorable arrangement (for example, of the radial bearings), it is possible for the plane thrust collar 3 to be radially displaced within the adjusted bearing surfaces without any resistance.

The fact that the relative angular displacement between shaft 2 and bearing housing 1 takes place only within narrow limits (for example, less than 1 degree of arc) is taken as a self-evident condition for the operation of the bearing described herein. In practice, only those angular deviations which are substantially below the aforementioned limit may be considered permissible for reasons of elasticity; however, such deviations are still sufficiently large to cause bearing damage unless special precautions are taken. Within the limits thus defined the simplifications will have no further effect on the result.

Referring to FIG. 7, in order to obtain a three-point support of the bars 30 - 49 on the rockers 50 - 69, the abutment surfaces at the radially oriented sides 71 of the bars 30 - 49 are substantially reduced by recessing so that two supporting members 83 remain on one side 71 while one supporting member 82 remains on the opposite side 71. The surface of these supporting members 82, 83 is limited to the extent that the plane of the bar 30 - 49 can easily adapt to the mating supporting surfaces 73 of the rockers which support the bars.

Referring to FIG. 8, the rockers 50 - 69 can alternatively be provided with three limited supporting members 87, 88 respectively, as above instead of the bars 30 - 49. In such a case, the rockers will adapt to the corresponding bar abutment planes.

At least one of the limited supporting members can be constructed in slightly barrelled form with the mating supporting member barrelled in the opposite sense to produce a surface contact between the two supporting members. This surface contact will also simultaneously secure the tangential distance between a rocker and the bar supported thereon. The tangential location of the rockers at the same time also locates the tangential position of the bars.

Referring to FIGS. 7, 8 and 9, the bars 30 - 49 and the rockers 50 - 69 may also be provided with supporting surfaces 72, 73, respectively of the three-point support, the profile of which is constructed in the form of a gearwheel flank. In such a case, when in the normal middle condition, the adjacent bars and rockers contact along contact axes located on the abutment surfaces 72, 73, respectively, which contact axes 110, 111 are located in respective pitch circles 90, 98, and in an axial plane 116. If the bars and rockers are deflected due to the shaft 2 assuming an angular position, the contact axes 110, 111 will remain in the axial plane 116 if a suitable flank profile is provided since the effective length of the lever arm of one bar and of the rocker supported thereon remain equal among themselves under all conditions of deflection from the central axis 84. The gearwheel flanks of the support surfaces 72, 73 thus use only a limited part of the tooth flank for physical contact even with the largest deflections from the central position.

Referring to FIG. 10, the three-point supporting surfaces of the bars and rockers can also be provided with a greater or lesser rounding having of the edges on the lateral surfaces 71 or 74 as such provides approximately the same effect as the strictly accurate shape complying with a gearwheel flank profile as described with respect to FIG. 9.

REferring to FIG. 11, wherein like reference characters indicate like parts as above, if the relative axial distance between the bars and rockers are to be strictly located, the flanks of the supporting surfaces 72, 73 are formed by the flanks of a complete tooth 118 or of a complete tooth gap 119. The distances between the gearwheel axes are always strictly and accurately maintained within the very small angles obtained by shaft deflections which are likely to occur so that all bars and all rockers of a supporting rim 30 - 39 and 50 - 59 or 40 - 49 and 60 - 69 remain within the specified pitch.