Of the rotational support sections of various kinds of machinery, radial roller bearings such as the radial roller bearing 1 illustrated in FIG. 23 are assembled in portions where large radial loads are applied. This radial roller bearing 1 is constructed such that a plurality of rollers 6 that are provided between a cylindrical shaped outer-ring raceway 3, which is formed around the inner circumferential surface of an outer-diameter side member 2, and a cylindrical shaped inner-ring raceway 5, which is formed around the outer circumferential surface of a shaft 4 that is located on the inner-diameter side, are supported by a cage 7 so as to be able to roll freely. As combinations of an outer-diameter side member 2 and shaft 4, there is a combination of a housing, which does not rotate even during operation, and a rotating shaft, and a combination of a gear or roller, which rotates during operation, and a support shaft thereof. In this specification, radial needle bearings that use needles are also included as a radial roller bearing.
As illustrated in FIG. 24, the cage 7 is completely constructed into a cylindrical shape using a synthetic resin material. The cage 7 has a pair of circular ring shaped rim sections 8 that are arranged concentric with each other and separated from each other in the axial direction, and has a plurality of column sections 9 that are arranged intermittently in the circumferential direction and span between the rim sections 8. The portions that are surrounded on four sides by adjacent column sections 9 in the circumferential direction and the rim sections 8 form pockets 10 for supporting the rollers 6 so as to be able to roll freely. With the rollers 6 held inside the pockets 10 so as to be able to roll freely, this kind of cage 7 is provided between the inner circumferential surface of the outer-diameter side member 2 and the outer circumferential surface of the shaft 4 so as to be able to rotate relative to the outer-diameter side member 2 and shaft 4. This cage 7 rotates with respect to the outer-diameter side member 2 and shaft 4 together with the revolving motion of the rollers 6.
When assembling the radial roller bearing 1, in order to arrange the cage 7 around the inner-ring raceway 5, the cage 7 is inserted from the end section of the shaft 4, and moved in the axial direction until it surrounds the inner-ring raceway 5. Incidentally, in this case, of the outer circumferential surface of the shaft 4, when there is an obstacle such as an outward-facing flange section or the like that has an outer diameter dimension that is greater than the inner diameter dimension of the cage 7 in the middle portion in the axial direction between the end section of the shaft 4 and the inner-ring raceway 5, this obstacle is in the way, and it may not be possible to move the cage 7 to a position surrounding the inner-ring raceway 5.
Therefore, as a cage that is capable of eliminating this kind of trouble, there is a cage (split cage) having a non-continuous section in one location in the circumferential direction 1 such as disclosed in GB 1,352,909 (A), JP 2-089814 (A), and JP 54-111242 (U). FIG. 25 illustrates the cage 7a that is disclosed in GB 1,352,909 (A). This cage 7a is made of a synthetic resin and has a non-continuous section 11 at one location in the circumferential direction. Moreover, the end sections 12a, 12b that are separated by this non-continuous section 11 fit together with an uneven fit by way of fitting sections 13.
One set each, of an outer-diameter side fitting pieces 14a, 14b and inner-diameter side fitting pieces 15a, 15b that form fitting sections 13 is formed on each of the end sections 12a, 12b. More specifically, of one end section 12a, an outer-diameter side fitting piece 14a is formed on one half section in the axial direction of the outer-diameter side half section, and an inner-diameter side fitting piece 15a is formed on the other half section in the axial direction of the inner-diameter side half section. Moreover, of the other end section 12b, an outer-diameter side fitting piece 14b is formed on the other half section in the axial direction of the outer-diameter side half section, and an inner-diameter side fitting piece 15b is formed on the one half section in the axial direction of the inner-diameter side half section. Together with fitting the pair of outer-diameter side fitting pieces 14a, 14b and pair of inner-diameter side fitting pieces 15a, 15b together in the axial direction on the outer-diameter side half section and inner-diameter side half section of the fitting section 13, the outer-diameter side fitting pieces 14a, 14b and inner-diameter side fitting pieces 15a, 15b are fitted together in the radial direction on the one half section in the axial direction and the other half section in the axial direction of the fitting section 13. In the example in FIG. 25, the state in which the end sections 12a, 12b are not fitted together is illustrated, however, when the cage 7a is assembled in the radial roller bearing, the width of the non-continuous section 11 becomes narrow, and end sections 12a, 12b fit together.
Concave sections 16a, 16b are formed in the circumferential surface of the pair of rim sections 8a, 8b. More specifically, on the outer circumferential surface of one rim section 8a, concave sections 16a that are recessed inward in the radial direction are formed at portions that are aligned in the axial direction with the pockets 10, and on the inner circumferential surface of the other rim section 8b, concave sections 16b that are recessed outward in the radial direction are formed at portions that are aligned in the axial direction with the pockets 10.
This kind of cage 7a is formed by so-called axial draw molding in which synthetic resin is injected inside the cavity of an axial draw mold (mold tool) that is formed by a pair of split molds (mold tool elements), after which these split molds are separated in the axial direction. Therefore, when compared with the case of using radial draw molding, in which the mold is a complex mold which comprises a pair of mold elements that move in the axial direction and a plurality of mold elements that move in the radial direction, the manufacturing cost of the cage 7a is kept low in the axial draw molding. This axial draw molding is performed by moving a pair of split molds in the axial direction, so when removing the split molds, it is possible to prevent damage such as plastic deformation or bleaching from occurring in the stopper sections that are provided on the edge sections of the openings of the pockets for preventing the rollers from dropping out. Therefore, axial draw molding is preferably used in cases where the volume of the stopper sections is so large that so-called unreasonable removal work in which the mold elements are removed to the outer-diameter side by pressing and elastically expanding the stopper sections is difficult, or in cases where column sections are arranged in portion further on the outside in the radial direction than the pitch circle diameter of the rollers such that it is difficult to remove the mold elements to the outside in the radial direction.
In either case, in the case of the cage 7a, it is possible to expand the width of the non-continuous section 11 in the circumferential direction due to the elastic deformation of the cage 7a. Therefore, by expanding the width of this non-continuous section 11 wider than the outer-diameter dimension of the shaft 4 around which the cage 7a is assembled, it becomes possible to assemble the cage 7a around the shaft 4 by passing the shaft 4 through the non-continuous section 11 (between the end sections 12a, 12b). Moreover, even in the case where there is an obstacle in the middle portion in the axial direction between the end section of the shaft 4 and the inner-ring raceway 5, the cage 7a can be assembled by elastically expanding cage 7a enough to ride over the obstacle, and moving the cage 7a in the axial direction to where it surrounds the shaft 4.
Incidentally, in the case of the cage 7a having conventional construction, the end sections 12a, 12b that are both sides of the non-continuous section 11 fit together by way of the fitting sections 13 not only so that there is not relative displacement in the axial direction, but also so that there is no relative displacement in the radial direction. Therefore, during operation of the radial roller bearing, expansion of the diameter of the cage due to centrifugal force is prevented. Moreover, in this case, the outer-diameter side fitting pieces 14a, 14b and the inner-diameter side fitting pieces 15b, 15a are pressed in the radial direction, so it becomes easy for wear of these outer-diameter side fitting pieces 14a, 14b and inner-diameter side fitting pieces 15b, 15a to advance, and in the worst case, there is a possibility the pieces might break.
Moreover, during operation, the outer-diameter side fitting pieces 14a, 14b and inner-diameter side fitting pieces 15b, 15a are pressed in the radial direction, so the force required to cause relative displacement in the circumferential direction of the end sections 12a, 12b becomes large. Therefore, in the case when assembled in a radial roller bearing that is assembled in manual transmission or the like, there is the possibility of a problem in that the width of the non-continuous section 11 cannot be expanded or contracted smoothly, and thus it becomes impossible to sufficiently prevent fretting wear.
Construction in which the end section that are provided on both sides of the non-continuous section can displace relative to each other in the radial direction can be achieved comparatively easily by radial draw molding that is performed by using mold elements that move in the radial direction. However, as described above, in radial draw molding, the number of parts of the mold that is used in injection molding increases, so there is a problem in that the manufacturing cost increases.
Improvement examples of the construction of a fitting section are disclosed in JP 2-089814 (A) and JP 54-111242 (U), however, even in the construction in these cases, there is the possibility that the same problems as those in the construction disclosed in GB 1,352,909 (A) will occur. The related literature above is incorporated in this specification by reference.