WO2014164689A2

WO2014164689A2 - Load sensing bearing assembly

Info

Publication number: WO2014164689A2
Application number: PCT/US2014/023227
Authority: WO
Inventors: Matthew G. WILMER; Christopher S. Marks; Todd A. BARR
Original assignee: Timken Co
Current assignee: Timken Co
Priority date: 2013-03-12
Filing date: 2014-03-11
Publication date: 2014-10-09
Anticipated expiration: 2015-09-12
Also published as: WO2014164689A3

Abstract

A load sensing bearing assembly (10) comprises an inner race (12), an outer race (16), and a plurality of rolling elements (24). A cavity (20) is formed behind a raceway (14, 18) of one of the races, and a strain gage (22) is installed in the cavity to measure forces applied to the bearing assembly. A stop (30) is formed inside the cavity with an end (34) of the stop designed not to engage a support structure (S) of the bearing assembly under normal bearing load conditions. The stop engages the support structure when an applied load on the bearing assembly exceeds a predetermined load to prevent excessive flexing of the assembly, such that the strain gage may continue to provide accurate measurements of the load on the bearing assembly after the overload condition ends.

Description

LOAD SENSING BEARING ASSEMBLY

BACKGROUND

[0001] This invention relates to the sensing of loads imposed on bearings; and, more particularly, to a load sensing bearing assembly having protection for load sensors associated with the assembly when the assembly is subjected to a particularly heavy load.

[0002] For many industrial machinery applications, there is a need to better understand the loads applied to the machinery's bearings to improve and optimize the design of the bearings used and to increase their useful life. Previous methods of measuring bearing loads have included cutting a section out of the bearing to locally w^reaken the bearing structure. Sensors such as thin foil strain gages used to measure the loads applied to the bearing are then installed in this region. The reasoning for installing the gages in these areas is that when a roller passes over the weakened bearing section, a strain is induced into the strain gage sufficient for the strain gage to accurately measure it. It has been found that this approach works well in those applications where the bearing load in fairly constant. Examples of bearing designs having weakened sections are found in U.S. patents 6,687,623 B2, 6,490,935 which is assigned to the same assignee as the present application, and 5,952,587.

[0003] In those applications where a bearing overload may occasionally occur, the weakened bearing section and the associated strain gage installed have been found to plastically deform. Plastic deformation may degrade a strain gage's measuring capabilities such that future measurements made by it are either inaccurate or nonexistant (i.e., the strain gage has failed). Accordingly, in these applications, some type of protection is needed in order to preserve the functional integrity of the strain gage during these overload events and enable it to continue to make accurate measurements of applied loads after the overload situation passes.

SUMMARY

[0004] The present disclosure is directed to a load sensing bearing assembly which incorporates physical stops in a weakened area of the assembly where a strain gage is positioned. In one preferred embodiment, a cavity is formed behind a raceway of one of the races and a strain gage measuring forces applied to the bearing assembly is installed in the cavity. A stop is formed inside the cavity. The length of the stop is such that its end will not engage a support structure for the bearing assembly under normal bearing load conditions. However, when an applied load on the bearing assembly exceeds a predetermined load value, the end of the stop engages the support structure. The engagement now prevents excessive flexing of the weakened area created by the cavity and damage to the strain gage installed in the cavity so the strain gage wil continue to provide accurate meaurements of the load imposed on the bearing assembly after the overload condition ends.

[0005] The stop is formed either by a continuous annular stop or the stop can be comprised of arcuate segments. Either way, the stop is integrally formed with a side of a ring on which the cavity is formed so to project from that side of the ring. Provision of the stop allows for an alternate load path to be temporarily provided to the bearing assembly under overload conditions so that the bearing assembly and strain gage are not damaged.

[0006] hi a second embodiment, two concentric, spaced stops are provided. Again, the stops are continuous annular stops, or they may be comprised of arcuate segments. Again, the stops are integrally formed with a side of a ring on which the cavity is formed so to project from that side of the ring. As before, the stops provide a temporary, alternate load path under overload conditions so to effectively stiffen the bearing stracture while leaving the strain gage area sufficiently flexible that accurate measurements of the load applied to the bearing assembly continues to be made.

[0007] The stop or stops can be implemented with either the inner race or outer race of the bearing assembly. In either application, once the stop (or stops) make contact with (engage) the support stracture for the bearing assembly, the path of the load applied to the bearing assembly changes from being solely through rings formed at the end of the race, to being through both the rings and the stops.

[0008] Other features will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the invention are achieved as set forth in the illustrative embodiments shown in the drawings which form a part of the specification.

[0010] Fig. 1 is a sectional view of a first embodiment of a load bearing assembly of the present invention having overload protection.

9 [0011] Fig. 2 is a perspective view, in section, of a bearing inner ring with an integrally formed annular stop.

[0012] Fig. 3 is a perspective view of the complete inner ring with the stop.

[0013] Fig. 4 illustrates the load path through the inner ring during normal bearing load conditions.

[0014] Fig. 5 illustrates a temporary, alternate load path through the ring during an overload condition.

[0015] Fig. 6 is a view similar to that of Fig. 2 but in which the stop comprises arcuate segments.

[0016] Fig. 7 is a view similar to Fig. 6 but showing a local sensor sector section adjoining the inner diameter of the inner ring.

[0017] Fig. 7A is also a perspective view similar to Fig. 7 illustrating another embodiment of the invention where the contacting gap surfaces are within the bearing section.

[0018] Fig. 8 is a sectional view similar to Fig. 1, but for another embodiment of the present invention including two stops.

[0019] Fig. 9 is a perspective view, in section, of an inner ring of the bearing assembly with the annular stops.

[0020] Fig. 10 is a perspective view of the complete inner ring with the two stops.

[0021] Fig. 1 1 illustrates the load path through the inner ring during normal bearing load conditions.

[0022] Fig. 12 illustrates a temporary, alternate load path during an overload condition.

[0023] Fig. 13 is a perspective view, in section, of an outer ring of the bearing assembly with an annular stop.

[0024] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. [0025] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

DETAILED DESCRIPTION

[0026] The following detailed description illustrates the invention by way of example and not by way of limitation. This description clearly enables one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. Additionally, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in tlie following description or illusti ated in the drawings. Tlie invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it will be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0027] The following description of the preferred embodiment of the invention is not intended to limit the scope of the invention to this preferred embodiment, but rather to enable any skilled in the art to make and use the invention.

[0028] Referring to the drawings, a bearing assembly of the present invention is indicated generally 10. The bearing assembly, to which a load is applied, includes an inner ring 12 on which a bearing inner race 14 is formed, and an outer ring 16 (see Fig. 13) on which a bearing outer race 18 is formed. Bearing assembly 10 further includes a plurality of rolling elements 24 (see Fig. 8) which for the embodiment shown would be tapered roller bearings.

[0029] As shown in Fig. 1, for example, on the underside of inner ring 12, a cavity 20 is formed. The cavity comprises a channel extending annularly about the inner face of inner ring 12. Now, when inner ring 12 is installed adjacent a support structure S for bearing assembly 10, there is gap formed between the bottom of the channel forming the cavity and the support structure. Support structure S is, for example, a shaft on which the bearing assembly is installed. This means that the underside of inner ring 12 is unsupported and a flexible section 21 is formed on the ring due to the reduced thickness of the ring in the area of the cavity. When loads are applied to the bearing assembly, flexible section 21 will, to some extent, move or flex radially inwardly (downwardly as shown in Figs. 1, 4, and 5). The amount of this movement is a function of the load applied to assembly 10 at a particular time.

[0030] At least one strain gage 22 is installed on the inner wall of cavity 16 as shown in the drawings. The strain gage is, for example, adhesively mounted to the inner ring 12. Strain gage 22 is a thin film resistor type strain gage of the type well-known in the art and used to measure loads applied to bearing assembly 10. The strain gage is therefore not described in detail. Those skilled in the art will appreciate, however, that a plurality of strain gages 22 are typically installed about the inner circumference of inner ring 12 formed by cavity 20.

Outputs from the strain gages are directed to external apparatus (not shown) that converts the outputs into real time load data. Formation of cavity 20 is advantageous because, due to the resulting weakness in bearing assembly 10, the bearing assembly will exhibit a greater deflection in response to an applied load than it otherwise would, thereby increasing the sensitivity of measurements made by the strain gages 22.

[0031] As previously noted, a disadvantage of this construction of assembly 10 is that when applied loads to the assembly exceed a predetermined load, flexible section 21 of inner ring 12 may deflect so far that the strain gage is damaged or fails. If this occurs, then the applied loads are no longer effectively measured.

[0032] To prevent this, and as shown in the drawings, a stop 30 is formed inside cavity 20. As shown in Figs. 2 and 3, stop 30 is formed as a continuous annular stop. However, as shown in Figs. 6 and 7, stop 30 is comprised of a series of arcuate segments 32 formed about the cavity. Regardless of the construction, stop 30 is integrally formed with a side of the ring 12 on which cavity 20 is formed so to project radially inw ardly from that side of the ring.

[0033] The length or height of stop 30 is such that its free end 34 will not engage support structure S of bearing assembly 10 under normal bearing load conditions. This is as shown in Fig. 4. As shown by the arrows in Fig. 4, when a load is applied to the bearing assembly, the load is transferred from bearing race 14 through the outer ends of inner ring 12 to support structure S. At this time, the end 34 of stop 30 is spaced from the support structure by a gap G; even though unsupported section 21 of ring 12 flexes in response to application of the load. The width of gap G is, for example, approximately 0.003 inches. [0034] However, when an applied load on the bearing assembly exceeds a predetermined load value, deflection of section 21 of race 14 pushes stop 30 inwardly until the end 34 of the stop engages the support structure. Now, as shown by the arrows in Fig. 5, the load path changes from that shown in Fig. 4 to a temporary alternate path. That is, the load is not only transferred through the ends of ring 12, but also through stop 30 to support staicture S. The support to bearing assembly 10, now aided by stop 30, limits the amount of flexing of section 21 of ring 12 and prevents plastic deformation of the strain gages sufficient to permanently damage them. The result then is that the strain gages continue to function properly once the overload condition ends.

[0035] Once the applied load is reduced to less than the predetermined value, the amount of flexing of flexible section 21 decreases, and stop 30 draws away from support structure S. Since the engagement of stop 30 with the support structure prevented excessive flexing of the weakened area of bearing assembly 10 created by cavity 20, the strain gages 22 will continue to provide accurate meaurements of the load on the bearing assembly.

[0036] A variation of the construction previously described is shown in Fig. 7. Here, an inner ring 12 has an inner wall 40 extending about the underside of the ring. Wall 40 abuts against support structure S when bearing assembly 10 is installed in place. Cavity 20 is formed over a sector of inside wall 40 as shown in the drawing. Stop 30, which is comprised of arcuate segments 32, has an end 34 which is spaced from the support structure S by a gap similar to the gap shown in Fig. 4. In this embodiment, when an overload condition occurs, flexing of section 14 pushes end 34 of stop segments 30 against the support structure S. In the temporary force flow path now created, the path is as shown in Fig. 5 in that the force is transferred to support structure S.

[0037] Another variation of the construction is shown in Fig. 7A and has an inner ring 12 with an inner wall 40 extending continuously about the underside of the ring without any break. Wall 40 abuts against support structure S when bearing assembly 10 is installed in place. Cavity 20 is formed inside wall 40 as shown in Fig. 7A. Stop 30, which is comprised of arcuate segments 32, has an end 34 which is spaced from the inner surface of wall 40 by a gap similar to the gap shown in Fig. 4. In this embodiment, when an overload condition occurs, flexing of section 14 pushes end 34 of stop segments 32 against the inside face of wall 40. In the temporary force flow path now created, the path is as shown in Fig. 5 except that the force is transferred to support structure S through wall 40. [0038] Referring to Figs. 8-12, another embodiment of the invention is for a bearing assembly indicated generally as 100 which includes an inner ring 112 on which a bearing inner race 1 14 is formed, and an outer ring (not shown) on which a bearing outer race is formed. Bearing assembly 100 also includes a plurality of rolling elements 24.

[0039] On the underside of inner ring 1 12, a cavity 120 is formed which again comprises a channel extending annularly about the inner face of inner ring 1 12. As with the previously described embodiment, when inner ring 1 12 is installed adjacent to a support structure S for the bearing assembly a gap formed between the bottom of the channel forming the cavity and the support structure so that the underside of inner ring 112 is unsupported. Due to the reduced thickness of the ring in the area in which the cavity is formed, an unsupported, flexible section 121 is formed on ring 1 12. When loads are applied to the bearing assembly, flexible section 121 , like section 21, will move or flex radially inwardly with the amount of movement being a function of the load applied to assembly 100 that time.

[0040] At least one strain gage 22, and typically a plurality of strain gages, is installed on the inner wall of cavity 120. This is as shown in Fig. 8.

[0041] In this embodiment, to prevent excessive flexing when loads applied to bearing assembly 100 exceed a predetermined load value, two stops 130 and 230 are formed inside cavity 120. As in the previous embodiment, stops 130 and 230 can be formed as continuous annular stops, or as a series of arcuate segments spaced around the cavity. In either construction, stops 130 and 230 are integrally formed with the side of the ring 1 12 on which cavity 120 is fomied so to project radially inwardly from the side of the ring. The stops extend generally parallel to each other as shown in the drawings.

[0042] The length or height of stops 130 and 230 are such that their free ends 134 and 234 will not engage support structure S of bearing assembly 100 under normal bearing load conditions. In this situation, the load path through bearing assembly 100 is as shown in Fig. 11 with the applied load being transferred from bearing race 114 through the ends of inner ring 1 12 to support structure S. Ends 134 of stop 130 and 234 of stop 230 are spaced from support structure S at this time by the gap G which is again, for example, approximately 0.003 inches. [0043] When the applied load exceeds the predetermined load value, deflection of race 1 14 pushes the stops 130 and 230 inwardly until the respective end 134 and 234 of the stops engages support structure S. Now, the temporary load path shown by the arrows in Fig. 12 is created in which the load is not only transferred through the ends of ring 112, but also through stops 130 and 230 to support structure S. Support of bearing assembly 100 is now aided by stops 130 and 230 limiting the amount of flexing of unsupported section 121 of ring 1 12 to prevent plastic deformation of the strain gages sufficient to permanently damage them.

[0044] Once the applied load is reduced to less than the predetermined value, the amount of flexing of surface 121 decreases, and stops 130 and 230 draw away from support structure S. Because the stops prevented excessive flexing of the weakened area of bearing assembly 100, strain gages 22, as before, will continue to provide accurate meaurements of the load on the bearing assembly after the overload event ends.

[0045] While the above description has been with respect to an inner ring 12 or 112, the present invention can also be implemented on outer ring 16 of bearing assembly 10. As shown in Fig. 13, a cavity 45 is formed on the outer surface of outer ring 16 which results in an unsupported, weakened section 23 that flexes in response to the load imposed on the bearing assembly. In this construction, a stop 50 is formed inside cavity 45 and can be either a continuous annular stop or comprised of a series of arcuate segments. Regardless of the construction, stop 50 is integrally formed with a side of the ring 16 on which cavity 45 is formed and projects radially outwardly from that side of the ring.

[0046] The length or height of stop 50 is such that its free end 54 does not engage support structure S of the bearing assembly under normal bearing load conditions with the load path then being similar to that shown in Fig. 4. When the applied load exceeds a predetermined load value, deflection of section 23 of race 18 pushes stop 50 outwardly until its end 54 engages support structure S. The load path is now changed to the temporary alternate path similar to that shown in Fig. 5. As in the other described embodiments, support of the bearing assembly is aided by stop 50 limiting the amount of flexing of unsupported section 23 of ring 16 and preventing permanent plastic deformation to the strain gages. Accordingly, they will again continue to function properly after the overload condition is over.

[0047] Finally, while the bearings used in assemblies 10 and 100 are preferably tapered roller bearings, other bearings including cylindrical bearings, ball bearings, spherical or needle bearings, and radial and thrust bearings can also be used in the bearing assembly without departing from the scope of the invention.

[0048] Various features and advantages of the invention are set forth in the following claims.

Claims

CLAIMS What is claimed is:

1. A load sensing bearing assembly comprising:

an inner ring, an outer ring, and a plurality of rolling elements;

a cavity formed behind a raceway of one of the rings;

a strain gage installed in the cavity to measure forces applied to the bearing assembly; and

a stop formed inside the cavity and having an end, the stop having a length such that a gap is formed between the end of the stop and a support structure of the bearing assembly when an applied load on the bearing assembly is less than a predetermined load, and such that the end engages the support structure when the applied load on the bearing assembly exceeds the predetermined load.

2. The load sensing bearing assembly of claim 1, wherein the stop is a first stop and further including a second stop formed inside the cavity and having an end, the second stop having a length such that a gap is formed between an end of the stop and the support structure of the bearing assembly when the applied load on the bearing assembly is less than the predetermined load, and such that the end engages the support structure when the applied load on the bearing assembly exceeds the predetermined load.

3. The load sensing bearing assembly of claim 1 , wherein the cavity is formed on the inner ring.

4. The load sensing bearing assembly of claim 1, wherein the cavity is formed on the outer ring.

5. The load sensing bearing assembly of claim 3, wherein the support structure is a shaft on which the bearing assembly is installed.

6. The load sensing bearing assembly of claim 4, wherein the support structure is a housing in which the bearing assembly is installed.

7. The load sensing bearing assembly of claim 1, wherein the bearing is a tapered roller bearing.

8. The load sensing bearing assembly of claim 1, wherein the bearing is one of a cylindrical bearing, a ball bearing, a spherical bearing, a needle bearing, a radial bearing, or a thrust bearing.

9. The load sensing bearing assembly of claim 1, wherein the stop comprises an annular ring projecting from a surface of the cavity.

10. The load sensing bearing assembly of claim 9, wherein the annular ring comprises a plurality of ring segments.

1 1. The load sensing bearing assembly of claim 2, wherein the first stop and the second stop each comprise an annular ring projecting from a surface of the cavity, each of the annular rings being spaced from each other and extending substantially parallel to each other.

12. The load sensing bearing assembly of claim 11, wherein each annular ring comprises a plurality of ring segments.

13. The load sensing bearing assembly of claim 1 , wherein the cavity and the stop covers a sector of the ring and not an entire circumference thereof.

14. The load sensing bearing assembly of claim 1, wherein the stops prevent excessive flexing of the assembly and damage to the strain gage, such that the strain gage may continue to provide accurate meaurements of the load on the bearing assembly.

15. A load sensing bearing assembly comprising:

an inner ring, an outer ring, and a plurality of rolling elements ;

a cavity formed behind a raceway of one of the rings;

a stop formed inside the cavity,

wherein an applied load is transferred along a normal path when the applied load on the bearing assembly is less than a predetermined load and is transferred along an alternate path when the applied load on the bearing assembly is greater than the predetermined load.

16. The load sensing bearing assembly of claim 15, wherein the normal path of the applied load is transferred through an outer end of the ring formed with the cavity.

17. The load sensing bearing assembly of claim 15, wherein the alternate path of the applied load is transferred at least partially through the stop.

18. The load sensing bearing assembly of claim 1 , wherein the alternate path of the applied load is transferred through the stop and an outer end of the ring formed with the cavity.

19. The load sensing bearing assembly of claim 15, wherein the ring formed with the cavity has an inner wall extending continuously about an underside of the ring without any breaks.

20. The load sensing bearing assembly of claim 19, wherein the stop is spaced from an opposing inner surface of the inner wall when the applied load on the bearing assembly is less than the predetermined load, and wherein the stop engages the opposing inner surface of the inner wall when the applied load on the bearing assembly is greater than the predetermined load.