Rolling bearing and a travel unit including rolling bearings

Abstract

A rolling bearing includes rolling elements between an outer race and an inner race, a resin seal ring covering an opening of at least one end of a bearing space, and a filter covering an oil hole defined in the resin seal ring for capturing foreign matter contained in lubricating oil. The filter and the resin seal ring are integrated by insert molding and are made of the same material. An annular lip portion, which is separate from the resin seal ring, is in contact with the outer race. An engaged portion on a radially inner side of the resin seal ring is engaged in a recess defined in the inner race such that, during thermal expansion of the resin seal ring, the engaged portion is engaged such that the resin seal ring is movable in a radial direction relative to the inner race.

Claims

1. A rolling bearing comprising: an outer race, an inner race, rolling elements mounted between the outer race and the inner race, and a seal ring covering at least an opening of a bearing space defined between the outer race and the inner race at one end of the bearing space, wherein the seal ring includes an oil passage hole, and a filter covering the oil passage hole and being configured to catch foreign objects contained in lubricating oil, wherein the seal ring comprises at least an engaged portion kept in engagement with the inner race, and a wall portion extending radially outwardly from the engaged portion, wherein the engaged portion is received in a recess defined in the inner race, so as to keep the seal ring in engagement with the inner race such that the seal ring is radially movable relative to the inner race when the seal ring is thermally expanded, and wherein the seal ring is in engagement with the inner race so as to be circumferentially immovable relative to the inner race.

2. The rolling bearing of claim 1, wherein the engaged portion comprises: at least one projection at a radially inner portion of the wall portion, wherein the recess is at least one circumferentially extending seal groove defined in the inner race, and wherein the at least one projection is received in the at least one circumferentially extending seal groove, so as to keep the seal ring in engagement with the inner race such that the seal ring is radially movable relative to the inner race when the seal ring is thermally expanded.

3. The rolling bearing of claim 2, wherein: the rolling bearing is a tapered roller bearing, and the at least one circumferentially extending seal groove opens to a radially outer surface of a large-diameter flange of the inner race.

4. The rolling bearing of claim 2, wherein the rolling bearing is one of a deep groove ball bearing, a cylindrical roller bearing and a self-aligning roller bearing, and wherein the at least one circumferentially extending seal groove opens to a radially outer surface of the inner race at one end of the inner race.

5. The rolling bearing of claim 2, wherein the at least one projection comprises inner and outer projections, wherein the inner projection is located closer to the rolling elements than the outer projection is, and wherein the at least one circumferentially extending seal groove comprises an inner seal groove in which the inner projection is received, and an outer seal groove in which the outer projection is received.

6. The rolling bearing of claim 5, wherein a portion of the inner projection received in the inner seal groove is shorter than a portion of the outer projection received in the outer seal groove.

7. The rolling bearing of claim 2, wherein the at least one projection includes an axially extending engaging protrusion, and wherein the at least one circumferentially extending seal groove includes an engaging recess in which the axially extending engaging protrusion is received, so as to restrict movements of the seal ring in one or both of a radial direction and a circumferential direction.

8. The rolling bearing of claim 1, wherein the filter is a mesh member made of at least one of a resin and a metal.

9. The rolling bearing of claim 8, wherein the mesh member has a mesh size of 0.3 mm to 0.7 mm.

10. A rolling bearing comprising: an outer race, an inner race, rolling elements mounted between the outer race and the inner race, and a seal ring covering at least an opening of a bearing space defined between the outer race and the inner race at one end of the bearing space, wherein the seal ring includes an oil passage hole, and a filter covering the oil passage hole and being configured to catch foreign objects contained in lubricating oil, wherein the seal ring is made of a resin, wherein the filter is formed integrally with the seal ring by insert molding, wherein the filter is made of a material having a linear expansion coefficient which is equal to or larger than a linear expansion coefficient of the material forming the seal ring, wherein the seal ring includes an engaged portion at a radially inner end of the seal ring, the engaged portion including an inner projection and an outer projection, the inner projection being located closer to the rolling elements than the outer projection is, and wherein the inner race has an inner seal groove in which the inner projection is received, and an outer seal groove in which the outer projection is received such that the seal ring is radially movable relative to the inner race when the seal ring is thermally expanded.

11. The rolling bearing of claim 10, wherein the filter is a mesh member made of at least one of a resin and a metal.

12. The rolling bearing of claim 11, wherein the mesh member has a mesh size of 0.3 mm to 0.7 mm.

13. A travel unit comprising: a driving source, a power transmission mechanism for transmitting a rotation of the driving source to a drive wheel, and at least one rolling bearing through which the drive wheel is supported on an axle, the at least one rolling bearing comprising: an outer race, an inner race, rolling elements mounted between the outer race and the inner race, and a seal ring covering at least an opening of a bearing space defined between the outer race and the inner race at one end of the bearing space, wherein the seal ring includes an oil passage hole, and a filter covering the oil passage hole and being configured to catch foreign objects contained in lubricating oil for lubricating the power transmission mechanism and the at least one rolling bearing, wherein the seal ring is made of a resin, wherein the filter is formed integrally with the seal ring by insert molding, wherein the filter is made of a material having a linear expansion coefficient which is equal to or larger than a linear expansion coefficient of the material forming the seal ring, wherein the driving source, the power transmission mechanism and the at least one rolling bearing are coaxial with each other, wherein the opening of the bearing space is an oil flow passage defined on one of two sides of the at least one rolling bearing located closer to the power transmission mechanism through which the lubricating oil is to flow from the power transmission mechanism toward the at least one rolling bearing, wherein the seal ring includes an engaged portion at a radially inner end of the seal ring, the engaged portion including an inner projection and an outer projection, the inner projection being located closer to the rolling elements than the outer projection is, and wherein the inner race has an inner seal groove in which the inner projection is received, and an outer seal groove in which the outer projection is received such that the seal ring is radially movable relative to the inner race when the seal ring is thermally expanded.

14. The travel unit of claim 13, wherein the power transmission mechanism is a speed reducer including a planetary gear mechanism.

15. The travel unit of claim 13, wherein the at least one rolling bearing comprises a plurality of rolling bearings juxtaposed to each other in an axial direction, and wherein the bearing space is defined by a first of the plurality of rolling bearings located closest to the power transmission mechanism at one of two ends of the first of the plurality of rolling bearings located closest to the power transmission mechanism.

16. The travel unit of claim 15, further comprising a rotation sensor mounted on a second of the plurality of rolling bearings located furthest from the power transmission mechanism at one of two ends of the second of the plurality of rolling bearings located furthest from the power transmission mechanism.

17. A travel unit comprising: a driving source, a power transmission mechanism for transmitting a rotation of the driving source to a drive wheel, and at least one rolling bearing through which the drive wheel is supported on an axle, wherein the driving source, the power transmission mechanism and the at least one rolling bearing are coaxial with each other, wherein lubricating oil for lubricating the power transmission mechanism is also for lubricating the at least one rolling bearing, the at least one rolling bearing comprising: an outer race, an inner race, rolling elements mounted between the outer race and the inner race, and a seal ring covering at least an opening of a bearing space defined between the outer race and the inner race at one end of the bearing space, wherein the seal ring includes an oil passage hole, and a filter covering the oil passage hole and being configured to catch foreign objects contained in the lubricating oil, wherein the seal ring comprises at least an engaged portion kept in engagement with the inner race, and a wall portion extending radially outwardly from the engaged portion, wherein the engaged portion is received in a recess defined in the inner race, so as to keep the seal ring in engagement with the inner race such that the seal ring is radially movable relative to the inner race when the seal ring is thermally expanded, wherein the opening of the bearing space is an oil flow passage defined on one of two sides of the at least one rolling bearing located closer to the power transmission mechanism through which the lubricating oil is to flow from the power transmission mechanism toward the at least one rolling bearing, and wherein the seal ring is in engagement with the inner race so as to be circumferentially immovable relative to the inner race.

18. The travel unit of claim 17, wherein the power transmission mechanism is a speed reducer including a planetary gear mechanism.

19. The travel unit of claim 17, wherein the at least one rolling bearing comprises a plurality of rolling bearings juxtaposed to each other in an axial direction, and wherein the bearing space is defined by a first of the plurality of rolling bearings located closest to the power transmission mechanism at one of two ends of the first of the plurality of rolling bearings located closest to the power transmission mechanism.

20. The travel unit of claim 19, further comprising a rotation sensor mounted on a second of the plurality of rolling bearings located furthest from the power transmission mechanism at one of two ends of the second of the plurality of rolling bearings located furthest from the power transmission mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partial enlarged sectional view of an embodiment of the present invention.

(2) FIGS. 2(a) and 2(b) are partial enlarged views of FIG. 1.

(3) FIGS. 3(a) and 3(b) are a partial enlarged side view and a partial enlarged plan view of a seal ring, respectively.

(4) FIGS. 4(a) and 4(b) are perspective views of the seal ring.

(5) FIG. 5 is a partial enlarged sectional view of a second embodiment of the present invention.

(6) FIG. 6 is a partial enlarged view of FIG. 5 in which a dimension adjusting member is inserted.

(7) FIG. 7 is a partial enlarged sectional view of a third embodiment of the present invention.

(8) FIG. 8 is a partial enlarged sectional view of a fourth embodiment of the present invention.

(9) FIG. 9 is a partial enlarged sectional view of a fifth embodiment of the present invention.

(10) FIGS. 10(a) and 10(b) show the mesh size of filters.

(11) FIG. 11(a) is a graph showing the relationship between the size of impressions and the rate at which the bearing lifespan decreases; and

(12) FIG. 11(b) is a graph showing the relationship between the mesh size and the size of impressions.

(13) FIG. 12 is an enlarged vertical sectional view of a portion of a travel unit including rolling bearings of the first embodiment.

(14) FIG. 13 is an enlarged vertical sectional view of a portion of a travel unit including rolling bearings of a sixth embodiment according to the present invention.

(15) FIG. 14 is a vertical sectional view of a travel unit embodying this invention.

(16) FIG. 15 is a vertical sectional view of a conventional travel unit.

(17) FIG. 16 shows an entire dump truck for use in mines.

DETAILED DESCRIPTION OF THE INVENTION

(18) Now referring to the drawings, the embodiments of the invention are described. FIGS. 1 and 2 show partial enlarged sectional views of the rolling bearing 10 according to the present invention, and FIGS. 3 and 4 show the details of a seal ring 20 of the rolling bearing 10.

(19) The rolling bearing 10 is mounted in the travel unit 4 of a dump truck (construction machine) 1 used in mines, shown in FIG. 16, together with the power transmission mechanism T. This dump truck 1 includes a chassis 2 supporting the deck and the cab, and a plurality of drive wheels (tires) 3. The travel unit 4 drives the drive wheels 3.

(20) As shown in FIG. 14, the travel unit 4 includes a travel motor 5 as a driving source, and a shaft 6 connected to the rotary shaft of the travel motor 5. The power transmission mechanism T, which is a speed reducer, is mounted around the shaft 6 at its distal end.

(21) A spindle 7, which is a stationary axle, is mounted around the shaft 6. A wheel body 9 is mounted around the spindle through two of the rolling bearings 10. The rotation of the wheel body 9 is transmitted to the drive wheel 3 through a rim 8.

(22) The speed reducer of this travel unit 4 is made up of two planetary gear mechanisms 50, i.e. a first planetary gear mechanism 50a and a second planetary gear mechanism 50b. The rotation of the shaft 6 is reduced by the two planetary gear mechanisms 50a and 50b and transmitted to the wheel body 9. But the speed reducer may be made up of a different planetary gear mechanism or mechanisms, or may be one other than a planetary gear mechanism or mechanisms.

(23) In this travel unit 4, the two rolling bearings 10 are tapered roller bearings arranged parallel to each other between the spindle 7 and the wheel body 9. FIG. 12 is an enlarged vertical sectional view of the portion of the travel unit 4 where there are these rolling bearings 10.

(24) The drive wheel 3 is supported by the spindle through the parallel-arranged tapered roller bearings. In this type of construction machines, tapered roller bearings are frequently used as rolling bearings 10, because tapered roller bearings can support larger radial loads.

(25) As shown in FIG. 12, the rolling bearings 10 each include an outer race 11 having a raceway 11a, an inner race 12 having a raceway 12a, rolling elements 13 or tapered rollers disposed between the raceways 11a and 12a. The rolling elements 13 are retained in position in the circumferential direction by a retainer 14.

(26) The rolling bearings 10 are arranged parallel to each other such that their small-diameter ends face each other. Thus, the rolling bearings 10 are each arranged such that the distance between the raceways 11a and 12a of the outer and inner races 11 and 12 decreases toward the other rolling bearing 10.

(27) A preload is applied to the rolling elements 13 by pressing the inner race 12 of each rolling bearing toward the other rolling bearing, relative to the outer race 11. For this purpose, a bearing presser member 17 shown in FIG. 14 is pressed against the spindle 7 by tightening bolts 17a, thereby axially pressing the respective inner races 12 toward each other by the bearing presser member 17 and another opposite bearing presser member 18, respectively.

(28) The power transmission mechanism T and the rolling bearings 10 are lubricated by common lubricating oil. That is, the power transmission mechanism T and the rolling bearings 10 have their at least lower portions submerged in oil stored in the casing of the travel unit 4 to a certain level. The component parts of the power transmission mechanism T and the rolling bearings 10 are thus lubricated.

(29) The inner races 12 are non-rotatable because the inner races 12 are fixed to the non-rotatable axle (spindle 7). The outer races 11 are rotatable together with a rotary housing H which may be integral with, or otherwise rotatable together with, the wheel body 9 of the drive wheel 3.

(30) The space in the casing between the power transmission mechanism T and the rolling bearing 10 located nearer to the power transmission mechanism serves as an oil flow passage through which the oil in the casing, which is used to lubricate both the power transmission mechanism T and the rolling bearings 10, flows therebetween.

(31) In this embodiment, since there are the two rolling bearings 10 arranged parallel to each other in the axial direction, the oil flow passage is defined by the opening of the rolling bearing 10 on the side of the power transmission mechanism T, i.e. one of the openings of the bearing space defined between the outer race 11 and the inner race 12 of this rolling bearing 10 that faces the power transmission mechanism T. FIGS. 1 and 2 show portions of the rolling bearing 10 on the side of the power transmission mechanism T, in which the opening on the left is the opening facing the power transmission mechanism T.

(32) A seal member S is mounted to the rolling bearing 10 on the side of the power transmission mechanism T. As shown in FIGS. 4(a) and 4(b), the seal member S covers the opening of the bearing space of the rolling bearing 10 on the side of the power transmission mechanism T that faces the power transmission mechanism T.

(33) If necessary, another similar seal member S may be mounted to the rolling bearing 10 remote from the power transmission mechanism T to cover its opening remote from the power transmission mechanism T.

(34) As shown in FIG. 1, the seal member S includes a seal ring 20 (seal ring body) having an L-shaped section and including an engaged portion 21 brought into engagement with the inner race 12, a wall portion 25 extending radially outwardly from the engaged portion 21, and a labyrinth seal forming portion 26 extending from the wall portion 25.

(35) The seal ring 20 is made of a resin, and has filters 23 integrally formed by insert-molding of the same resin forming the seal ring 20 to cover oil passage holes 22 formed in the wall portion 25 of the seal ring 20 (i.e., the filters 23 and the seal ring 20 together constitute an insert-molded unit).

(36) The filters 23 are formed substantially at the center of the respective oil passage holes 22 with respect to the length direction of the holes 22 (thickness direction of the body of the seal ring 20) with their peripheral edges embedded in the resin forming the walls of the oil passage holes 22 of the body of the seal ring 20.

(37) Since the filters 23 and the seal ring 20 are made of the same resin, the filters 23 and the seal ring 20 have the same thermal expansion rate. Thus, when the seal ring 20 is thermally expanded due to a rise in temperature of lubricating oil in the rolling bearing 10, the filters 23 are expanded to the same degree as the seal ring 20. This prevents breakage of the mesh of the filters 23 or formation of holes in the filters.

(38) The filters 23 and the seal ring 20 are made of a polyamide resin in the embodiment, but they may be made of any other resin, such as polyacetal (POM), polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), polyimide (PI) or polyetherimide (PEI). The filters 23 and the seal ring 20 may also be made of any of these resins reinforced with glass fiber, e.g. glass fiber-reinforced polyamide (PA) 46 or glass fiber-reinforced polyamide (PA) 66.

(39) The content of glass fiber in such glass fiber-reinforced resin is determined to an optimum range taking into consideration the shrinkage rate of the resin and the required strength, e.g. within the range of 15-35%, preferably 25-30%. Generally speaking, the higher the glass fiber content, the smaller the shrinkage rate and thus the easier it is to control dimensions after molding. On the other hand, the lower the glass fiber content, the lower the strength of the resin and thus the easier the resin is deformed. When the glass fiber content is 25-30%, an optimum balance is achieved between the shrinkage rate and the strength.

(40) The filters 23 and the seal ring 20 may be made of a resin reinforced with not glass fiber but carbon fiber, polyethylene fiber, aramid fiber, etc.

(41) In the embodiment, the filters 23 and the seal ring 20 are formed by insert-molding of the same material. But the filters 23 may be made of a material different from the material forming the seal ring 20 and having a linear expansion coefficient substantially equal to or larger than the linear expansion coefficient of the material forming the seal ring 20.

(42) In this arrangement too, when the seal ring 20 is thermally expanded, since the filters 23 are expanded to substantially the same degree as or to a greater degree than the seal ring 20, the filter 23 are never stretched excessively, and thus never damaged.

(43) If there is no possibility of damage to the filters when the seal ring 20 is thermally expanded, the filters 23 and the seal ring 20 may be individually made of any desired materials without the need to take into consideration their linear expansion coefficients.

(44) The engaged portion 21 of the seal ring 20, which is provided at the radially inner portion of the seal ring 20, is engaged in circumferentially extending seal grooves (recesses) 30 formed in the inner race 12 such that the seal ring 20 can move radially relative to the inner race 12 when the seal ring 20 is thermally expanded.

(45) As shown in FIGS. 3(a) and 3(b), the oil passage holes 22 of this embodiment have the shape of rectangular elongated holes as seen from one side of the bearing, and are circumferentially spaced apart from each other. The number and the shape of the oil passage holes 22, as well as the distances therebetween, are not limited. For example, the holes 22 may have a shape other than rectangles as seen from one side of the bearing. For example, the holes 22 may be circular arc-shaped elongated holes as seen from one side of the bearing.

(46) The filters 23, made of resin, may be of a network structure with a mesh size of about 0.1 to 1 mm. In the embodiment, the filters 23 are of a network structure with a mesh size of 0.5 mm. The mesh size of the filters 23 should be adjusted according to the diameters of foreign objects which it is desired to catch with the filters 23. The optimum mesh size range within which the bearing lifespan is maximized will be described later.

(47) The labyrinth seal forming portion 26 is a cylindrical member extending axially inwardly from the radially outer edge of the wall portion 25 such that the distal end of this cylindrical member faces the end surface of the outer race 11 with a minute gap left therebetween. The radially outer surface of the cylindrical member faces the radially inner surface of the housing H, which retains the outer race 11 so as to be rotatable together with the outer race, with a minute gap left between the cylindrical member and the housing H. A labyrinth seal is defined by the minute gaps between the labyrinth seal forming portion 26 and the end surface of the outer race 11 and between the labyrinth seal forming portion 26 and the radially inner surface of the rotatable housing H.

(48) Oil can flow into the rolling bearing 10 through the labyrinth seal. But harmful foreign objects cannot pass therethrough because the gaps forming the labyrinth seal are sufficiently small. In FIG. 1, the minute gaps forming the labyrinth seal are larger than the actual minute gaps so that the minute gaps can be seen clearly.

(49) The labyrinth seal forming portion 26 is not limited to a cylindrical member but may be any other annular member having a central axis. For example, the labyrinth seal forming portion may have a tapered inner or outer surface. For example, this annular member may have a conical surface radially and gradually expanding in one axial direction on the side of the labyrinth seal. With this arrangement, it is more difficult for oil and foreign objects to enter the bearing through the labyrinth seal.

(50) Now the engaged portion 21 and the seal grooves 30 are described in detail. As shown in FIGS. 2(a) to 4(b), the engaged portion 21 of the seal ring 20 includes radially inwardly extending projections 24 at the radially inner portion of the wall portion 25.

(51) The projections 24 include inner projections 24a located nearer to the rolling elements 13 and outer projections 24b located remote from the rolling elements 13. The seal grooves 30 include an inner seal groove 30a in which the inner projections 24a are engaged, and an outer seal groove 30b in which the outer projections 24b are engaged.

(52) With the projections 24 engaged in the seal grooves 30, the seal ring 20 is held in position so as to be radially movable relative to the inner race 12 when the seal ring is thermally expanded.

(53) The seal ring 20 can be reliably kept in engagement with the inner race 12 by the axially spaced apart projections 24a and 24b.

(54) Before the temperature of the oil for lubricating the rolling bearings 10 rises (i.e. in a steady state), the depth h1 of the portions of the inner projections 24a inserted in the inner seal groove 30a is shallower than the depth h2 of the portions of the outer projections 24b inserted in the outer seal groove 30b as shown in FIG. 2(a).

(55) With this arrangement, when pushing the seal ring 20 into the opening of the bearing space and fixing it in position, the inner projections 24a, which are located deeper in the bearing, can be easily fitted in the inner seal groove 30a due to their elastic deformation or thermal deformation when the seal ring is pushed into the bearing space.

(56) Since the depth h2 of the portions of the outer projections 24b inserted in the outer seal groove 30b is relatively deep, even when, as shown in FIG. 2(b), the seal ring 20 is thermally expanded markedly radially outwardly due to a rise in temperature, the outer projections 24b still remain engaged in the outer seal groove 30b. Thus, even in this expanded state, the seal ring 20 can be kept in engagement with the inner race 12, thus preventing entry of harmful foreign objects into the rolling bearing 10.

(57) In particular, the height h2 of the portions of the outer projections 24b inserted in the outer seal groove 30b is determined such that no gap is present between the seal ring 20 and the inner race 12 through which harmful foreign objects can enter the rolling bearing 10 when the rolling bearing 10 is heated to the maximum expected temperature and thus the seal ring 20 is expanded to a maximum (see FIG. 2(b)).

(58) Therefore, within the expected temperature range, the outer projections 24a are always kept engaged in the outer seal groove 30b, preventing formation of a gap between the seal ring and the inner race which allows passage of harmful foreign objects.

(59) In this embodiment, as shown in FIGS. 3(a)-4(b), the inner projections 24a are arranged to alternate with the outer projections 24b in the circumferential direction.

(60) With this arrangement, when pushing the seal ring 20 into the opening of the bearing space and fixing it in position, the outer projections 24b are less likely to block the view of any of the inner projections 24a. This makes it possible to visually confirm that all the inner projections 24a, which are located deeper in the bearing, are fitted in the inner seal groove 30a. In this regard, FIGS. 1-2(b) show sectional views taken along line II-II of FIG. 3(b) to show the positional relationship between the inner and outer projections 24a and 24b as well as their respective heights.

(61) In this embodiment, the inner projections 24a and the outer projections 24b are arranged in the circumferential direction such that the former do not overlap with the latter as viewed from the axial direction. That is, the circumferential ends of the respective inner projections 24a are located at the same circumferential positions as the corresponding circumferential ends of the circumferentially adjacent outer projections 24b.

(62) But instead, the inner projections 24a and the outer projections 24b may be arranged in the circumferential direction such that the former partially overlaps with the latter as viewed from the axial direction.

(63) In this embodiment, as shown in FIG. 2(a), an axial gap w1 is present between the portions of the outer projections 24b inserted in the outer seal groove 30b and an end wall of the outer seal groove 30b. That is, the outer seal groove 30b has an axial width larger than the width of the outer projections 24b by the width of the axial gap w1. The outer projections 24b are thus axially movable in the outer seal groove 30b within the range of the axial gap w1.

(64) Since the outer projections 24b are axially movable in the outer seal groove 30b, when the seal ring 20 is thermally expanded, the outer projections 24b are smoothly movable in the radial direction without being restricted by the inner wall of the outer seal groove 30b. This prevents radially outward tensile force from acting on the seal ring 20 when the seal ring is thermally expanded, which in turn prevents damage to the filters 23.

(65) The outer seal groove 30b opens to the end surface of the inner race 12 as shown in FIG. 2(a). An axle is fixedly fitted in the radially inner surface of the inner race 12. The axle has a shoulder A configured to abut the end surface of the inner race 12 when the axle is fixedly fitted in the inner race. Thus, after fitting the outer projections 24b in the outer seal groove 30b, it is possible to close the opening of the outer seal groove 30b at the end face of the inner race with the shoulder A of the axle.

(66) The opening of the outer seal groove 30b at the end surface of the inner race 12 thus makes it easier to fit the outer projections into the outer seal groove. By closing the opening at the end surface with the shoulder A of the axle, the shoulder A prevents the outer projections 24b from coming out of the outer seal groove 30b.

(67) The operation of the seal ring 20 is now described. While the travel unit 4 is being used, oil is partly splashed from the power transmission mechanism T against the side of the rolling bearing 10 due to rotation of the power transmission mechanism T and the rolling bearing 10.

(68) Since the seal ring 20 is fitted to the opening of the bearing space of the rolling bearing 10 facing the power transmission mechanism T, oil is splashed against the seal ring 20. Oil that has splashed against the seal ring 20 partially collides against the filters 23 of the oil passage holes 22.

(69) Oil that has collided against the filters 23 passes through the mesh of the filters 23, but foreign objects contained in the oil and larger than the mesh size of the filters 23 are caught by the filters 23. The filters 23, which are integral with the seal ring 20, thus catch any harmful foreign objects contained in oil passing through the opening (the above mentioned oil flow passage) at the one axial end of the bearing space of the rolling bearing 10. The oil that has passed through the filters 23 flows into the bearing space and lubricates the rolling bearing 10. This arrangement prevents harmful foreign objects discharged from the power transmission mechanism T from entering the rolling bearing 10.

(70) If the filters 23 are clogged with foreign objects, the entire seal ring 20 can be replaced with a new seal ring 20

(71) This embodiment is directed to a rolling bearing 10 in a travel unit 4 for use in large-sized construction machines. The rolling bearing 10 is used with the outer race 11 as a rotary member and the inner race 12 as a stationary member. Since the seal ring 20 is kept in engagement with the stationary inner race 12, the filters 23 cannot move circumferentially about the axis of the bearing, so that foreign objects caught by the filters 23 are less likely to fly away.

(72) The type of the rolling bearing 10 to which the seal ring 20 is mounted is not limited. For example, this rolling bearing 10 may e.g. be a tapered roller bearing, in which tapered rollers are used as the rolling elements, a deep groove ball bearing, in which balls are used as the rolling elements 13, or a cylindrical roller bearing, in which cylindrical rollers are used as the rolling elements 13.

(73) FIG. 5 shows the second embodiment of the present invention. This embodiment includes a lip portion 41 provided at the radially outer portion of the seal ring 20 and in abutment with the outer race 11. The lip portion 41 is an annular rubber member 40 separate from and fixed to the seal ring 20. Otherwise, this embodiment is structurally similar to the first embodiment. Thus, description is made mainly of what differs from the first embodiment.

(74) In this embodiment, as shown in FIG. 5, the seal member S has a seal ring 20 (seal ring body) including an engaged portion 21 kept in engagement with the inner race 12 of the rolling bearing 10, a wall portion 25 extending radially outwardly from the engaged portion 21, and a lip mounting portion 27, provided at the radially outer portion of the wall portion.

(75) As shown in FIG. 5, the annular member 40 is fixed to the lip mounting portion 27 of the seal ring 20. The annular member 40 is made of rubber and is softer than the seal ring 20, which is made of e.g. polyamide resin. The annular member 40 is fixedly fitted around the lip mounting portion 27, and is closely pressed against the lip mounting portion 27 due to its elasticity. If the annular member 40 is made of a synthetic rubber, the synthetic rubber may be nitrile rubber, acrylic rubber, urethane rubber or fluororubber.

(76) The annular member 40, which is fixed to the lip mounting portion 27, constitutes the lip portion 41, which abuts the outer race 11. The lip portion 41 includes an abutment portion 41d provided at a distal end thereof and configured to abut the outer race 11. Even when seal ring 20 is thermally expanded, the lip portion 41 is kept in abutment with the outer race 11 due to its elasticity.

(77) Since the seal ring 20, which is fixed to the inner race 12, is made of a harder material than the annular member 40, which constitutes the lip portion 41, the seal ring is less likely to be deformed under external force. Thus, the filters 23 can be rigidly fixed to the less deformable seal ring 20. Only the annular member 40, which constitutes the lip portion 41 and which is softer and thus more susceptible to damage, is replaceable. This increases the lifespan of the seal member S as well as the bearing including the seal member S.

(78) Since the annular member 40, which constitutes the lip portion 41, is a separate member from the seal ring 20 fixed to the inner race 12, it is also possible to adjust the position of the annular member 40 in the width direction of the bearing, relative to the seal ring 20. This adjustment is made e.g. by, as shown in FIG. 6, inserting a dimension adjusting member 28 between the axially outer end surface 40a of the annular member 40 and the inner end surface 27a of the lip mounting portion 27. A plurality of such dimension adjusting members 28 in the form of plate-shaped members (shims) having different thicknesses from each other may be prepared so that the dimension of the annular member 40 is easily adjustable.

(79) By adjusting the position of the annular member 40 relative to the seal ring 20, it is possible to easily adjust the interference of the lip portion of the seal member S. This makes it possible to readjust the interference of the lip portion 41 when the lip portion 41 becomes worn, and also makes it possible to use the same seal ring 20 and annular member 40 in different bearings which are different in model number and thus have different widths.

(80) The seal ring 20 and the annular member 40, which are separate members from each other, may be rotationally fixed together by means of an adhesive or by an anti-rotation mechanism, thereby preventing wear of these members due to relative slip therebetween and thus reduced sealability. If the annular member 40 is adhesively fixed to the seal ring 20, an ordinary adhesive may be used, or they may be fixed together by vulcanization. Preferably, the axially outer end surface of the annular member 40 is adhesively bonded to the inner end surface 27a of the lip mounting portion 27, and further the inner peripheral surface 40b of the annular member 40 is adhesively bonded to the outer peripheral surface 27b of the lip mounting portion 27.

(81) Preferably, the annular member 40 is not only radially adhesively bonded to the seal ring, but is fitted on the seal ring with an interference fit to more reliably prevent slip in the rotational direction. But if an anti-rotation mechanism is used instead of an adhesive, the annular member is replaceable more easily.

(82) FIG. 7 shows the third embodiment, in which the engaged portion 21 of the seal ring 20 and one of the seal grooves 30 of the inner race 12 are provided with an engaging means 29 for restricting radial movement of the seal ring 20.

(83) As shown in FIG. 7, the engaging means 29 includes engaging protrusions 29a provided on the engaged portion 21, and engaging recesses 29b formed in the one of the seal grooves 30.

(84) The engaging protrusions 29a are provided on the respective outer projections 24b of the engaged portion 21 so as to extend axially from their intermediate portions with respect to their protruding directions. The engaging recesses 29b are formed in the inner wall of the outer seal groove 30b so as to be axially recessed from the inner wall such that the engaging protrusions 29a can be inserted in the respective engaging recesses 29b.

(85) The length of the engaging recesses 29b in the radial direction of the bearing is longer by w2 than the length of the engaging protrusions 29a in the radial direction of the bearing. Thus, with the engaging protrusions 29a engaged in the engaging recesses 29b, the engaging protrusions 29a can move in the radial direction of the bearing in the engaging recesses 29b.

(86) In this embodiment, the length of the engaging recesses 29b in the circumferential direction of the bearing is equal to the length of the engaging protrusions 29a in the circumferential direction of the bearing. But the length of the engaging recesses 29b in the circumferential direction may be slightly longer than the circumferential length of the engaging protrusions 29a so that the engaging protrusions 29a can move in the engaging recesses 29b in the circumferential direction of the bearing.

(87) With the engaged portion 21 of the seal ring 20 received in the seal groove 30 of the inner race 12, since the engaging protrusions 29a of the seal ring 20 are received in the respective engaging recesses 29b formed in the seal groove 30, the seal ring 20 is prevented from moving in the radial direction of the bearing by more than a predetermined distance. Its movement in the circumferential direction is also restricted.

(88) Thus, the engaging means prevents radial movement of the seal ring 20 by more than a predetermined distance when the seal ring 20 is thermally expanded (especially if the seal ring 20 is thermally expanded radially outwardly from a cold state), and also prevents rotation of the seal ring 20 relative to the inner race 12.

(89) Since the length of the engaging recesses 29b in the radial direction of the bearing is slightly longer than the length of the engaging protrusions 29a in the radial direction of the bearing, even if the seal ring 20 is hot when the seal ring 20 is mounted on the bearing, the engaging protrusions 29a can be smoothly fitted in the engaging recesses 29b.

(90) FIG. 8 shows the fourth embodiment of the present invention. In this embodiment, the annular member 40 constituting the lip portion 41 has a positioning step 41c on the radially inner surface thereof. The step 41c engages a step 27c formed on the lip mounting portion 27 of the seal ring 20, thus axially positioning the annular member 40 relative to the seal ring 20.

(91) In this embodiment, as well as in the other embodiments, a seal ring fitting portion 31 of the engaged portion 21 between the inner projections 24a and the outer projections 24b is press-fitted, with an interference fit, on a fitting portion 32 of the inner race between the inner seal groove 30a and the outer seal groove 30b. The fitting portion 31 is press-fitted on the fitting portion 32 with a predetermined interference fit by fitting the resin seal ring 20 onto the inner race 12 after thermally expanding the seal ring 20. Since the seal ring 20 is fitted with an interference fit, its sealability improves.

(92) FIG. 9 shows the fifth embodiment of the invention. In this embodiment, the lip-mounting portion 27 of the seal ring 20 has a section of a Japanese character .

(93) Since the lip mounting portion 27 has a -shaped section, the seal ring 20 can protect the annular member 40 from external force applied to the seal ring 20. Since the lip mounting portion 27 has a -shaped section, if an adhesive or a filler is used to fix the annular member 40 in position, the adhesive or filler also serves to prevent leakage.

(94) In any of the embodiments, the filters 23 may be made of synthetic resin such as polyamide, or may be made of a metal such as stainless steel. If the filters 23 are made of a synthetic resin, they are lightweight and resistant to rust. If the filters 23 are made of a metal, they are resistant to hard foreign matter such as metal and thus more durable.

(95) In any of these embodiments, the network member forming the filters 23 has preferably a mesh size of 0.3 to 0.7 mm, more preferably 0.5 mm. The mesh size herein used refers to the size of the openings of the network structure, and is shown by dimension w3 in FIGS. 10(a) and 10(b).

(96) If this mesh size is too large, large foreign objects can pass through the filters 23 into the bearing. Such large foreign objects could form such large impressions on the raceways and the rolling surfaces of the bearing that could affect the lifespan of the bearing. Conversely, if the mesh size is too small, the mesh may be clogged with foreign matter, thus making it impossible to supply lubricating oil into the bearing.

(97) An endurance test (experiment) was conducted to assess the relationship between the size of impressions formed on the raceways and rolling surfaces of the bearing and the lifespan of the bearing. The test results revealed that impressions not larger than a certain size do not affect the lifespan of the bearing. Another experiment was conducted to assess the relationship between the mesh size and the size of impressions formed by foreign objects that have passed through the mesh of the filters.

(98) FIGS. 11(a) and 11(b) show the results of the respective experiments. In particular, FIG. 11(a) shows the relationship between the size of impressions formed on the raceways and the rolling surfaces of the bearing and the rate at which the lifespan of the bearing has decreased due to the formation of the impressions. FIG. 11(b) shows the relationship between the mesh size and the size of impressions formed by foreign objects that have passed through the mesh of the filters.

(99) In the experiments, as the rolling bearing, a tapered roller bearing was used having the main dimensions (inner diameter, outer diameter and width) of 30 mm62 mm17.25 mm, and the bearing was operated at the rotational speed (of the shaft) of 2000 min.sup.1 with a radial load of 17.65 kN and an axial load of 1.47 kN.

(100) The experiment results revealed that the lifespan of the bearing suddenly decreased when the size of impressions formed on the raceways and rolling surfaces of the bearing exceeds 1 mm. The experiment results also revealed that the mesh size has to be 0.5 mm or smaller in order to prevent passage of foreign objects that could form impressions exceeding 1 mm. Thus, for longer lifespan of the bearing, the mesh size should be 0.5 mm or smaller. If the filter size is 0.7 mm or smaller, impressions are 1.3 mm or smaller. If impressions are 1.3 mm or smaller, the reduction rate of the lifespan of the bearing can be suppressed to an acceptable level (0.6 of the lifespan of the bearing when the bearing is free of impressions). In order to prevent clogging, the mesh size is preferably 0.3 mm or larger.

(101) FIG. 13 shows the sixth embodiment of the invention. FIG. 13 is an enlarged vertical sectional view of a portion of a travel unit 4 embodying the present invention. This travel unit 4 is also used as a drive train on a dump truck 1 for use in mines (construction machine). Except the portion shown in FIG. 13, this embodiment is substantially identical to the structure shown in FIG. 14 and other figures. Thus description of this embodiment is made mainly of what differs from the other embodiments, and some of the features that have already been described are not described here.

(102) The travel unit 4 includes, as shown in FIG. 14, which is directed to the other embodiments, a travel motor as a driving source 5, a power transmission mechanism T through which the rotation of the driving source 5 is transmitted to the drive wheel 3, and two rolling bearings 10 through which the drive wheel 3 is supported by the axle such that the motor 5, the transmission mechanism T and the rolling bearings 10 are coaxial with each other. The power transmission mechanism T is a speed reducer including a planetary gear mechanism 50 similar to the one of the other embodiments.

(103) The rolling bearings 10 each include an outer race 11 having a raceway 11a, an inner race 12 having a raceway 12a, rolling elements 13 disposed between the raceways 11a and 12a, and a retainer circumferentially retaining the rolling elements 13.

(104) The two rolling bearings 10 of this embodiment are tapered roller bearings (which means that the rolling elements 13 are tapered rollers) which are juxtaposed to each other in the axial direction. The drive wheel 3 is supported on the axle through the tapered roller bearings 10.

(105) The inner race 12 of each bearing 10 is fitted on the axle (spindle 7), which is stationary, and thus is non-rotatable. The outer race 11 is rotationally fixed to the rotary housing H, and thus is rotatable together with the housing H. The rotary housing H is integral with the body 9 of the drive wheel 3, or fixed thereto so as to be rotatable together with the wheel body 9. (The spindle 7 and the wheel body 9 are shown in FIG. 14.)

(106) An oil flow passage is formed on one side of one of the rolling bearings 10 facing the power transmission mechanism T through which oil flows from the power transmission mechanism T into the rolling bearing 10. A seal ring 20 covers the opening of the internal space of the rolling bearing 10 facing the power transmission mechanism T, and thus covers the oil flow passage. This opening is annular in shape extending along the raceways 11a and 12a of the outer and inner races 11 and 12. The seal ring 20, which covers this opening, is also annular in shape.

(107) The seal ring 20 is formed of a synthetic resin, and is mounted between a large-diameter flange 12b of the inner race 12 and the large-diameter end of the radially inner surface of the outer race 11.

(108) In this embodiment, the outer race 11 is rotated and the inner race 12 is kept stationary. The seal ring 20 is fixed by fitting to the rotary outer race 11.

(109) As shown in FIG. 13, the seal ring 20 includes an engaged portion 21 kept in engagement with the outer race 11, a wall portion 25 radially inwardly extending from the engaged portion 21, and a cylindrical labyrinth seal forming portion 26 extending from the wall portion 25 to face the radially outer surface of the inner race 12.

(110) The engaged portion 21 is a cylindrical member fixedly fitted in a seal groove 11b formed in the radially inner surface of the outer race 11 at its large-diameter end.

(111) A circumferentially extending projection 24 is formed on the radially outer surface of the engaged portion 21 and is detachably engaged in a circumferentially extending recess 11c formed in the seal groove 11b. The seal ring 20, which is mounted in the opening of the bearing space, can be dismounted from the bearing by applying an external force to the seal ring 20 in the axially outward direction (toward the power transmission mechanism T) until the projection 24 disengages from the recess 11c.

(112) The radially inner surface of the labyrinth seal forming portion 26 is slightly larger in diameter than the portion of the radially outer surface of the inner race 12 facing the radially inner surface of the labyrinth seal forming portion 26, defining a minute gap therebetween through which oil can pass but harmful foreign matter cannot.

(113) The wall portion 25 of the seal ring 20 is formed with a plurality of oil passage holes 22 extending axially through the wall portion 25. The oil passage holes 22 are, as viewed from one side of the bearing, circular arc-shaped elongated holes circumferentially spaced apart from, and circumferentially aligned with, each other.

(114) Filters 23 cover the respective oil passage holes 22. In this embodiment, the seal ring 20 is made of a resin, and the filters 23 are formed by insert molding of the same kind of resin forming the seal ring 20 so as to be integral with the seal ring 20.

(115) The filters 23 are formed substantially at the center of the respective oil passage holes 22 with respect to the length direction of the holes 22 (thickness direction of the seal ring 20) with their peripheral edges embedded in the resin forming the walls of the oil passage holes 22 of the seal ring 20.

(116) In this embodiment too, since the filters 23 and the seal ring 20 are made of the same kind of resin, the filters 23 and the seal ring 20 have the same thermal expansion rate. Thus, when the seal ring 20 is thermally expanded due to a rise in temperature of lubricating oil in the rolling bearing 10, the filters 23 are expanded to the same degree as the seal ring 20. This prevents breakage of the mesh of the filters 23 or formation of holes in the filters.

(117) In this embodiment too, the filters 23 and the seal ring 20 are made of e.g. polyamide resin. But they may be made of a different resin.

(118) The filters 23 may be fixed to the surface of the wall portion 25 facing the rolling elements 13 by means of e.g. an adhesive. With this arrangement, a space is defined in each oil passage hole 22 on the side of the filter 23 facing the power transmission mechanism T (planetary gear mechanism 50). This space serves as a space in which foreign matter collects.

(119) The filters 23 may be made of a material other than a resin, such as metal or non-woven fabric. The material forming the filters and their mesh size are determined based on the diameter range of foreign matter to be caught by the filters.

(120) The travel unit 4 of this embodiment includes a rotation sensor 60. As shown in FIG. 13, the rotation sensor 60 is mounted on the rolling bearing 10 remote from the power transmission mechanism T at its end remote from the power transmission mechanism T. If the travel unit is mounted on a construction machine, the rotation sensor 60 can be used to obtain information on the rotation of the wheel body 9 so that this information can be used for ABS control or traction control.

(121) The rotation sensor 60 includes a pulsar ring, as an encoder 61, fixed to the rotary bearing race, i.e. the outer race 11, and a sensor case 64 carrying a sensor unit 62 in the form of a magnetic sensor of a back-magnet type and fixed to the stationary bearing race, i.e. the inner race 12.

(122) Since rolling bearings used e.g. in drive trains of various construction machines are relatively large in diameter, by using a rotation sensor 60 of the back-magnet type as described above, the sensor performance stabilizes. But the rotation sensor 60 is not limited to a magnetic sensor of the back-magnet type.

(123) The sensor case 64, in which the sensor unit 62 is mounted, is fixed to a ring member 65 fitted on the radially outer surface of the inner race 12. Thus, the sensor case 64 is fixed to the inner race 12 through the ring member 65.

(124) The ring member 65 is made up of two diametrically opposed semicircular split portions. By connecting the ends of one of the two semicircular portions to the respective ends of the other semicircular portion, the ring member 65 is fixedly press-fitted on the inner race 12.

(125) In this state, a circumferentially extending protrusion 65a formed on the radially inner surface of the ring member 65 is engaged in a circumferentially extending groove 12d formed in the radially outer surface of the inner race 12.

(126) An input/output line 63 connected to a circuit board mounted on the sensor unit 62 extends through the sensor case 64 and a hole 66 formed in the ring member 65 to the outside of the rolling bearing 10.

(127) The encoder 61 is fixedly fitted in a circumferential groove 11d formed in the radially inner surface of the outer race 11 at its large-diameter end.

(128) Since the rotation sensor 60 is provided on the bearing at its position most remote from the power transmission mechanism T, it is possible to minimize the amount of foreign matter that enters the rolling bearings 10 and then reaches the rotation sensor 60. Foreign matter thus least influences the performance of the rotation sensor 60.

(129) If the filters 23 are clogged with foreign matter, it is possible to replace the seal ring 20 with a new one.

(130) As with the other embodiments, the rolling bearings 10 are tapered roller bearings in this embodiment. But the rolling bearings 10 are not limited to tapered roller bearings. For example, they may be deep groove ball bearings, in which balls, as the rolling elements 13, are mounted between an outer race 11 and an inner race 12 and retained by a retainer, or may be cylindrical roller bearings or self-aligning roller bearings, in which cylindrical rollers or spherical rollers, as the rolling elements 13, are mounted between an outer race 11 and an inner race 12 and retained by a retainer. One of the two bearings 10 may be omitted too.

(131) In this embodiment, the seal ring 20 is opposed to the outer race 11 or the inner race 12 with a minute gap left therebetween. But instead, the seal ring 20 may be brought into contact with both the outer race 11 and the inner race 12.