Roller thrust bearing cage and manufacturing method thereof

A cage includes cage pockets for retaining rollers at plural positions along a circumferential direction of an annular plate. A projection extending in thickness direction of the cage is formed at a central part in the circumferential direction on an inner face of the cage pocket to pivotally support the roller. The projection is provided with a chamfered portion (non-contact portion) formed by chamfering an edge in the thickness direction, and a flat portion (contact portion) that is brought into contact with an opposing central portion in the thickness direction on a roller end face of the roller seated in o the cage pocket. The flat portion has a flat length almost equivalent to a displaceable distance of the cage in the thickness direction thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to roller bearing cages such as needle roller thrust bearings etc. More specifically, the invention relates to roller bearing cages such as needle roller thrust bearings etc. that are used in an automatic transmission of automobile, a compressor of a vehicle air conditioner or the like.

2. Description of the Related Art

Trend for low fuel consumption of automobile in recent years has increased demands for further weight saving and further reduction of rotational torque to the roller thrust bearings that are mounted in various parts such as automatic transmission in the vehicle more and more. For weight saving, a cage made of resin has been proposed. For reduction of rotational torque, there has been proposed a cage in which projections are formed at central parts in the circumferential direction on opposite inner faces of the cage pocket over the thickness direction of the cage (width direction of assembly) to pivotally support a roller by contacting with circumferential central portions on and faces of the roller on inner and outer circumferential sides (See Japanese Patent Publication No. JP 2004-211824A). In the cage disclosed in JP 2004-211824A, by providing the projections in opposite inner faces of the cage pocket, the reduction of rotational torque can be accomplished because contact area between the opposite inner faces and the end faces of the roller is reduced. However, in such the cage, due to limitation in machining shape of punching die for the cage pocket, the projections must extends over the thickness direction of the cage. Accordingly, a linear contact area between the projections and the end faces of the roller in the thickness direction is increased, and contact portions are exposed to a large difference in contact speeds in the thickness direction. As a result, in such the structure, abnormal wear (drilling wear) can easily occur on the inner faces of the cage pocket. As the cage disclosed in JP 2004-211824A is made of metal, the thickness of the cage can be made relatively thin, so that the length of the linear contact of the projection can be made small. However, if the cage is made of resin for saving weight, the thickness of the cage is increased in order to secure strength of the cage and also, due to limitation in shape to provide draft for releasing resin formation mold, the projection must be made to extend more in the thickness direction of the cage as compared with the metal cage. Accordingly, the difference in the contact speeds between the projection and the end face of the roller is further increased, and the drilling wear as discussed above becomes more considerable.

SUMMARY OF THE INVENTION

One of the problems to be solved in the present invention is to obtain weight saving and reduction in rotational torque in a roller thrust bearing while suppressing drilling wear as described foregoing in either cases that the cage is made of metal or resin. In particular, in a case that the thickness of the cage must be large because the cage is made of resin, or the like, the invention provides a roller bearing cage that can contribute to further weight saving and reduction in rotational torque of the roller bearing while having significant effect on suppressing the drilling wear.

The invention provides a roller bearing cage comprising:

a cage main body formed with an annular plate; and

a plurality of cage pockets opened so as to be arranged along a circumferential direction on the cage main body for retaining rollers having flat end faces;

wherein a projection to pivotally support an end face of the corresponding roller is projected at a central portion in the circumferential direction on a radial inner face of each cage pocket,

the projection extends in a thickness direction of the cage main body, and includes a contact portion that is brought into a contact with a central portion or a vicinity thereof on the end face of the roller, and a non-contact portion that is adjacent to the contact portion in the thickness direction and that is not brought into contact with the end face of the roller.

In the cage according to the invention, in order to secure large load capacity to the roller seated in the cage pocket, the roller having flat end faces is retained, and in order to reduce frictional resistance by contact between the inner faces of the cage pocket and the end faces of the roller, a projection is formed at least at the circumferential central part on the inner face of the cage pocket (namely, circumferential side face of the cage pocket). The projection has a shape extending in the thickness direction to secure draft for releasing the cage from the formation mold. More specifically, the projection extends in the thickness direction at the circumferential central portion and a flat portion formed in the central part of the projection linearly extends in the thickness direction. By such the structure, if non-contact portion is not formed, the contact area between the projection on the inner face of the cage pocket and the end face of the roller would be formed linearly in the thickness direction causing circumferential speed difference. In such a state, a drilling wear can easily occur.

Under foregoing circumstances, according to the invention, the projection includes a contact portion that is brought into a contact with a central portion or a vicinity thereof on the end face of the roller, and a non-contact portion that is adjacent to the contact portion in the thickness direction and that is not brought into contact with the end face of the roller. Therefore, the projection is configured to reduce the contact area between the projection and the roller end face. As a result, according to the invention, the drilling wear due to the liner contact between the inner face of the cage pocket and the roller end face is reduced and it is possible to obtain a reduction in rotational torque. Further, according to the invention, in a case that the cage is made of resin for weight saving, even if the cage thickness is made thick to secure the cage strength and the projection is made long in the thickness direction of the cage, only the contact portion formed in a part of the projection is brought into linear contact with the roller end face. Accordingly it is possible to reduce or suppress the drilling wear and to obtain simultaneously the weight saving and reduction in rotational torque of the bearing in which the cage of the invention is mounted for low fuel consumption of an automobile.

Further, in a case that a semi-circle projection is formed on the inner face of the cage pocket to pivotally support the central portion on the roller end face by almost point contact, the difference in the circumferential speeds does not occur at the contact area between the projection and the roller end face. However, if the cage is moved in the thickness direction thereof, the projection and the central portion on the roller end face are offset to each other and non-contact therebetween occurs and the projection cannot pivotally support the roller. On the other hand, according to the invention, the flat portion may have a flat length that is at least almost equivalent to a displaceable distance of the cage in the thickness direction. By such the construction, even if the cage is moved in the thickness direction, the contact portion assuredly keeps a state that the contact potion is always brought into contact with the central portion on the roller end face, so that the roller in motion is pivotally supported and its smooth rotational motion is maintained.

The non-contact portion may include a chamfered portion formed on an edge of the projection in the thickness direction of the cage. The contact portion may include a flat portion having a flat face in the thickness direction of the cage in a central part of the projection. A pair of the chamfered portions may be formed on the opposite edges of the projection in the thickness direction of the cage.

The cage of the invention may be a needle roller bearing cage or a roller bearing cage other than needle roller bearing. The cage of the invention does not limit type of the bearing to which the cage is applied as far as the bearing is provided with a cage. The cage may be made of resin or may be made of metal. If the cage is made of resins the thickness of the cage becomes relatively large. Therefore, the invention is specifically suitable for sufficiently suppressing the drilling wear in such the resin cage. If the cage is made of metal, although the cage thickness is relatively small, the invention is also suitable for suppressing the drilling wear by providing the non-contact portion in a part of the projection.

Second aspect of the invention is provided with a manufacturing method of a roller bearing cage including a cage main body formed with an annular plate; and a plurality of cage pockets opened so as to be arranged along a circumferential direction on the cage main body for retaining rollers having flat end faces, comprising the steps of:

punching an annular plate from a metal;

forming a plurality of cage pockets on the annular plate;

pressing an edge of one of the cage pockets in a thickness direction of the annular plate on a side face of the cage pocket with a press jig having a pressing face of a predetermined shape to form a chamfered portion.

By such a manufacturing method of a roller bearing cage, a cage having the above-described construction and advantages can be obtained.

According to the invention, the drilling wear due to a contact between the inner face of the cage pocket and the roller end face is reduced and it is possible to obtain weight saving and reduction in rotational torque in the cage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the description will be made on the roller bearing cages according to the embodiments of the invention. Although the roller bearing cages of the embodiments are applied to needle roller bearing cages, the invention is applicable other types of roller bearing cages.

FIGS. 1 through 4show the cage of Embodiment 1.FIG. 1is a partial plan view showing a roller bearing cage,FIG. 2is an enlarged plan view showing a vicinity of a cage pocket inFIG. 1,FIG. 3is a sectional view taken on line III-III ofFIG. 2, andFIG. 4is an explanatory view showing a displaceable amount in a thickness direction of the cage.

A cage10according to Embodiment 1 as shown inFIG. 1includes a ring plate11having an annular shape and formed of a resin, on which cage pockets12for retaining rollers are formed at plural positions along circumferential direction. The cage pockets12are opened and arranged in a radial manner around the center of the cage at a constant pitch of a predetermined angle. Each cage pocket12is formed in a rectangular shape elongated slightly in the radial direction from the center of the cage in accordance with the roller length, and houses a roller13having flat end races to obtain a large load capacity. Resin material for the ring plate11is not specifically limited if it is suitable in terms of the cage performance and cage strength etc. For example, the cage may be constituted by a material in which polyamide 66, polyamide 46, polyphenylene sulfide, thermoplastic polyimide or the like is served as matrix, and glass fiber, carbon fiber, aramid fiber or the like may be added in the matrix to improve the strength. Polyamide 66 is particularly suitable for material of the cage because it has excellent properties such as tensile strength and bending stiffness and has small coefficient of linear expansion.

A roller retaining portion (not-shown) for preventing the roller13from running off on a circumferential inner face12aof the cage pocket12. Projections14are formed on opposite radial inner faces12ato reduce frictional resistance by contact between the inner faces12aand end faces13aof the roller13.

Embodiment 1 is generally characterized by the shape of the projections14. Referring toFIGS. 2 and 3, the shape of one of the projections14will be described in detail below. The projection14has a shape projecting into the cage pocket12at a central part in the circumferential direction on the inner surface12aof the cage pocket12over a thickness direction (height direction) of the cage10. The projection14has a curved surface shape such as semi-circle or semi-ellipse, so that the projection14is brought into a point contact with a circumferential central portion13bon the roller end face13a. The projection14extends in the thickness direction of the cage10between opposite edges of the inner surface12aof the cage pocket12. Opposite edges of the projection14are chamfered, so that a sectional shape of the projection14is constituted by chamfered portions (non-contact portions)14aon the opposite edges and a flat portion (contact portion)14bin the center part. In other words, the chamfered portions14aare formed adjacent to the flat portion14bin the thickness direction. Sectional shape of the chamfered portions14ais not limited to straight, and it may be formed with a curved shape such as rounded shape. Chamfering angle of the chamfered portions14ais not specifically limited. In a case that the cage10is formed by a conventional method such as injection molding, the opposite edges of the projection14may be formed in chamfered shapes serving as draft. Therefore, the cage10after formed can be easily drawn from the resin formation mold. The chamfered portions14aof the projection14forms non-contact portions that do not contact with the end face13aof the roller13. Although the non-contact portions are formed in a chamfered shape (rounded or tapered shape) in Embodiment 1, the non-contact portions may include a shape formed in a stepped manner with respect to the flat portion14b. The non-contact portions may have a shape so as not to contact with the end face13aof the roller13, however, the shape of the chamfered portions14ais preferable to serve as draft for being released from the mold after resin formation. By adjusting the chamfering angle of the chamfered portions14a, a preferable draft for being released from the mold can be obtained.

The flat portion14bconstitutes a maximum projected part of the projection14into the cage pocket12so as to pivotally support the roller13which is seated in the cage pocket12by contacting with a central portion13cin the thickness direction of the cage10on the end face13aof the roller13. The flat portion14bof the projection14constitutes a contact portion that is brought into contact with a region including the central portion13con the end face13aof the roller13so as to be in parallel with each other. Although the shape of the contact portion is constituted by a shape that is flat and in parallel with the end face13aof the roller13in Embodiment 1, the contact portion may contain a slightly rounded shape at boundaries to the chamfered portions14aso as to form continuity therebetween. It is preferable to avoid unnecessary frictional contact with the end face13aof the roller13at the boundaries by forming continuity in shape change between the flat portion14band the chamfered portions14a.

Referring toFIG. 4, the flat portion14bis described more in detailed. In a case that the cage10of Embodiment 1 is mounted between an outer peripheral housing member and an inner peripheral side shaft member as a roller thrust bearing without race ring or a roller thrust bearing with race ring, it is assumed that the cage10is displaceable at a distance L0in the thickness direction. In other words, the cage10is displaceable up to a first displacement position P1shown with chain line on one side in the thickness direction, on the other hand, the cage10is displaceable up to a second displacement position P2shown with chain double dashed line on the other side in the thickness direction. The distance between the positions P1and P2makes L0. The flat portion14bhas a flat length L1that is at least almost equivalent to the above-described displaceable distance L0in the thickness direction of the cage10. Preferably, the flat portion14bhas a flat length L1that is slightly longer than the above-described displaceable distance L0in the thickness direction of the cage10. Preferably, the flat length L1of the flat portion14bshould be made as short as possible, so as to reduce frictional resistance by contact to the roller end face13aand to reduce difference in circumferential speeds at the contact portion between the flat portion14band the roller end face13a. In a case that the cage10is not displaced in the thickness direction, the flat length of the flat portion14bshould be made with a small length close to zero preferably. Namely, the projection14is preferably brought into almost point contact, while not pure point contact, to the central portion13cin the thickness direction of the cage10on the end face13aof the roller13. However, the cage10is normally displaced in the thickness direction, the flat length L1of the flat portion14bis made almost equivalent to the displaceable distance L0of the cage10in the thickness direction thereof in Embodiment 1

Accordingly, in the cage10of Embodiment 1, in a case that the cage10is displaced to the first displacement position P1on one side in the thickness direction, an end of the flat portion14bof the projection14that is located on the other side in the thickness direction corresponds to the central portion13cin the thickness direction on the roller end face13a, whereas, in a case that the cage10is displaced to the second displacement position P2on the other side in the thickness direction, another end of the flat portion14bof the projection14that is located on one side in the thickness direction corresponds to the central portion13cin the thickness direction on the roller end face13a. As a result, the flat portion14ccan be in contact with the central portion13cin the thickness direction on the roller end face13ain any case that the cage10is displaced at any position in the thickness direction. Hence, the flat portion14bassuredly keeps a state that the flat portion147bis always brought into contact with the central portion13cin the thickness direction on the roller end face13a, so that the roller13in motion is pivotally supported and its smooth rotational motion is maintained.

In the cage10having the above described construction, the flat portion14bto contact with the central portion13cof the roller end face13aat a part of the projection14and the flat length of the flat portion14bis formed to as to be at least almost equivalent to the displaceable distance in the thickness direction of the cage10. Hence only the part of the projection14is brought into linear contact with the central portion13cin the thickness direction of the cage10on the roller end face13a, so that a drilling wear is much reduced by reducing the area of the linear contact.

Further, in the cage10, even if the cage10is made of resin and its thickness becomes relatively large, only the flat portion14bthat is the part of the projection14is brought into linear contact with the roller end face13a. Hence, the drilling wear is suppressed and it is possible to reduce a rotational torque to be required.

FIGS. 5 through 8Dshow the cage according to Embodiment 2.FIG. 5is a plan view showing a roller bearing cage,FIG. 6is an enlarged plan view showing a vicinity of a cage pocket inFIG. 5,FIG. 7is a sectional view taken on line VII-VII ofFIG. 6,FIGS. 8A through 8Cshow a process forming chamfered portions of the cage ofFIG. 5, andFIG. 8Dshows a modification of the process forming the chamfered portions of the cage.

Referring toFIGS. 5 through 7, the cage10shown in these drawings includes a ring plate11formed from a metal like light alloy etc. or a steel plate by punching. The ring plate11has a W-shaped section in the radial direction and plurality of roller retaining cage pockets12are formed in a radial manner around the center of the cage10. The cage pockets12are opened and formed simultaneously at the forming of the ring plate11by punching. Further, a roller retaining portion12bis formed on a circumferential inner face12a. On a radial inner face12a, a projection14is formed similarly to Embodiment 1.

Similarly to Embodiment 1, the projection14has a shape projecting into the cage pocket12at a central part in the circumferential direction on the inner surface12aof the cage pocket12over a thickness direction of the cage10. Opposite edges of the projection14in the thickness direction are chamfered, so that a sectional shape of the projection14is constituted by chamfered portions (non-contact portions)14aon the opposite edges and a flat portion (contact portion)14bthat is flat in the thickness direction. The flat portion14bis constituted to pivotally support a roller13which is seated in the cage pocket12by contacting with a central portion13cin the thickness direction on an end face13aof the roller13.

The flat portion14bof the projection14has a flat length L1that is at least almost equivalent to a displaceable distance L0in the thickness direction of the cage10. Accordingly, in a case that the cage10is displaced to the first displacement position on one side in the thickness direction, or in a case that the cage10is displaced to the second displacement position on the other side in the thickness direction, the flat portion14bcorresponds to the central portion13cin the thickness direction on the roller end face13a. As a result, the flat portion14ccan be in contact with the central portion13cin the thickness direction on the roller end face13ain any case that the cage10is displaced at any position in the thickness direction.

In the cage10according to the above-described Embodiment 2, similarly to Embodiment 1, only the part of the projection14is brought into linear contact with the central portion13cin the thickness direction of the cage10on the roller end face13a, so that a drilling wear is much reduced by reducing the area of the linear contact.

The chamfered portions14amay be formed by pressing an radial inner face of the cage pocket12formed by punching with an annular press jig15that is provided with a pressing face15ahaving an angle corresponding to an chamfering angle of the chamfered portions14a. In other words, as shown inFIG. 8A, the cage10and the press jig15are disposed in an opposite manner, and then opposite edges of the projection14in the thickness direction of the cage10are pressed with the press jig15. Thus, the chamfered portions14aare formed on the opposite edges of the projection14of the cage10as shown inFIG. 8C. The flat portion14bis formed simultaneously to the formation of the chamfered portions14a.

Incidentally, as shown inFIG. 8D, a pair of the press jigs15may be disposed in an opposite manner interposing the cage10, and the opposite edges of the projection14in the thickness direction may be simultaneously pressed with the press jigs15, so that the chamfered portions14aand the flat portion14bare simultaneously formed.

The invention is not limited by the foregoing embodiments. The invention should include various changes or modification within the scope of the claims.