Ball bearing

Abstract

To suppress collapse of the shape of a holder when molding the holding and when inserting a ball into a pocket, while suppressing deformation of the holder due to centrifugal force.SOLUTION: In a ball bearing used under an environment where a dmn value, defined by the following formula, is 900,000 or larger: dmn={(D+d) / 2}×n, where D is an outer diameter (mm) of an outward member 4, d is an inner diameter (mm) of an inward member 3, and n is a rotational speed (min-1), a holder 10 for holding balls 5 is a crown-type holder comprising an annular base part 11 and a plurality of pockets 20 formed along a circumferential direction on one axial side of the base part 11, where a minimum axial thickness t of the base part 11 at a bottom part 22 on the other axial side of the pockets 20 satisfies the following relation: 0.06Da≤t≤0.22Da, where Da is a diameter of the balls 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball bearing that can be used for high-speed rotation. [Background technology]

[0002] For example, many bearings are used in devices equipped with electric motors in automobiles, construction machinery, and other vehicles, as well as in various industrial machines. The bearings used in these devices are generally used under high-speed conditions compared to bearings used to support shafts in general equipment. In recent years, particularly in electric vehicles, there has been a trend to increase the rotational speed and make the motors smaller and lighter in order to increase the output density of the motor as a means of improving fuel efficiency and driving performance. As the maximum rotational speed of bearings increases with the speed of electric motors, the centrifugal force acting on the internal components of the bearings also increases. In recent years, drive units called "e-Axles" that integrate a drive motor, transmission, speed increaser / reduction gear, etc. have become widespread. As output increases, motor speeds are also increasing. The bearings that support the rotating shaft of the motor in an "e-Axle" have an inner ring bore diameter d of 20 mm ≤ d ≤ 40 mm or less, and are generally used at higher rotation speeds than bearings in other equipment.

[0003] In ball bearings that use balls as rolling elements, a crown-type cage may be used as the cage for holding the balls. A crown-type cage has an annular base and multiple pockets arranged circumferentially around the base. The pockets are arranged in parallel on one axial side of the cage relative to the base. Each pocket penetrates the cage in the radial direction, opens to one axial side, and has a pair of claws on both circumferential sides of the opening of each pocket to hold the balls.

[0004] In the case of ball bearings using crown cages, there is a concern that as the rotation speed of the bearing increases, the centrifugal force of the cage pockets will cause the claws to deform toward the outer diameter, resulting in the balls being trapped. For this reason, for example, in Patent Document 1, a metal deformation prevention member is attached to the opening side of the pocket to suppress deformation of the claws on both sides of the pocket. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-285506 Summary of the Invention [Problem to be solved by the invention]

[0006] Attaching a deformation prevention member as in Patent Document 1 increases the number of parts and complicates the structure of the cage, resulting in problems such as higher costs. To address this issue, one possible measure would be to increase the rigidity of the cage by, for example, increasing the thickness of the bottom of the pockets in the cage, i.e., the axial thickness of the base at the bottom of the pocket, compared to conventional methods, thereby suppressing deformation due to centrifugal force.

[0007] However, if the rigidity of the pocket is increased too much, the shape of the toe is likely to be distorted when the balls are inserted into the pocket or when the member is removed from the molding die during molding of the cage.

[0008] Therefore, an object of the present invention is to suppress deformation of the cage due to centrifugal force, while suppressing deformation of the cage when the cage is molded and when balls are inserted into the pockets. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a bearing comprising an inner member, an outer member, balls arranged between the inner member and the outer member, and a cage that holds the balls, dmn={(D+d) / 2}×n D: outer diameter of the outer member (mm) d: inner diameter of the inner member (mm) n: rotation speed (min -1 ) In a ball bearing used in an environment where the dmn value defined by is 900,000 or more, the cage is a crown-type cage having an annular base and a plurality of pockets formed along the circumferential direction on one axial side of the base to hold the balls, and the minimum axial thickness t of the base at the bottom of the other axial side of the pockets is set to be: 0.06Da≦t≦0.22Da A ball bearing was used (Configuration 1).

[0010] In configuration 1, an axial distance H between an edge on one axial end side of a connecting portion connecting the circumferentially adjacent pockets and an edge on the other axial end side of the base portion is, with respect to a pocket diameter HP defined by the diameter of the pocket, H≦t+HP / 2 A configuration in which the following can be adopted (Configuration 2).

[0011] In configuration 1 or 2, a relationship between a cross-sectional area S of the base portion in an axial cross section that passes through the bottom portion and includes an axis of the base portion and a cross-sectional area S' of the base portion in an axial cross section that passes through a circumferential center of a connecting portion that connects the circumferentially adjacent pockets and includes the axis of the base portion, S <S’ A configuration in which the above is true can be adopted (Configuration 3).

[0012] In the configuration 1, or in an embodiment in which either or both of the configurations 2 and 3 are added to the configuration 1, a configuration can be adopted in which the material of the cage contains engineering plastic (configuration 4).

[0013] In configuration 4, the material of the cage may contain carbon fiber or glass fiber as a reinforcing material (configuration 5).

[0014] A bearing device can be adopted in which a ball bearing of configuration 1 or a configuration in which one or more elements selected from configurations 2 to 5 are added to configuration 1, and the ball bearing supports a rotating shaft of a drive motor, reducer, or speed increaser for an electric transport device. [Effects of the Invention]

[0015] According to this invention, deformation of the cage due to centrifugal force can be suppressed, while deformation of the cage during molding of the cage and during insertion of balls into the pockets can be suppressed. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a front view showing an embodiment of the present invention. [Figure 2] II-II cross section of Figure 1 [Figure 3] Cross-sectional view showing balls held in the cage [Figure 4] IV-IV cross section of Figure 3 [Figure 5] VV cross section of Figure 3 [Figure 6] A graph showing the relationship between cage pocket bottom thickness / ball diameter and clearance between the cage and raceway [Figure 7] Graph showing the relationship between cage pocket bottom thickness / ball diameter and cage shape collapse safety factor DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described with reference to the drawings. A rolling bearing 1 of this embodiment is used to support the rotating shaft of a drive motor equipped in an electric transport device such as an electric vehicle, or the rotating shaft of a reducer or speed increaser equipped in such an electric transport device.

[0018] As shown in Figures 1 and 2, rolling bearing 1 (hereinafter simply referred to as bearing 1) is a ball bearing comprising an inner member 3 and an outer member 4 constituting a raceway, an inner raceway groove 3a having an arc-shaped cross section formed in the inner member 3, an outer raceway groove 4a having an arc-shaped cross section formed in the outer member 4, a plurality of rolling elements 5 arranged between the inner raceway groove 3a and the outer raceway groove 4a, and a cage 10 that holds the rolling elements 5, and the inner ring bore diameter d satisfies 20 mm ≦ d ≦ 40 mm.

[0019] Here, balls (steel balls) are used as the rolling elements 5, and will hereinafter be referred to as balls 5. In addition, in this embodiment, the inner raceway groove 3a and the outer raceway groove 4a each have an arc-shaped cross section of a single radius in any longitudinal cross section including the axis. Hereinafter, the direction along the bearing center line c of the bearing 1 will be referred to as the "bearing axial direction" or simply the "axial direction," the direction perpendicular to the axial direction will be referred to as the "bearing radial direction" or simply the "radial direction," and the circumferential direction around the bearing center line c will be referred to as the "bearing circumferential direction" or simply the "circumferential direction."

[0020] The inner member 3 (referred to as the inner ring 3 in this embodiment) has an inner diameter portion 3b to which a rotating shaft (not shown) is fixed, and rotates circumferentially together with the rotating shaft. The outer member 4 (referred to as the outer ring 4 in this embodiment) has an outer diameter portion 4b to which a fixing member for a housing, gear, or other member (not shown) is attached. In this way, the bearing 1 supports the rotating shaft rotatably relative to the fixing member. Examples of the rotating shaft referred to here include the rotating shaft of a drive motor equipped in an electric transportation device such as an electric vehicle, or the rotating shaft of a reducer or speed increaser equipped in such an electric transportation device. The bearing center axis of the bearing 1 and the rotation center axis of the rotating shaft are set coaxially.

[0021] When the bearing 1 is assembled, a lubricant such as grease is sealed inside the bearing's internal space. In addition, a seal member (not shown) is attached to the opening at the axial end of the bearing's internal space. The seal members may be provided at both axial ends of the bearing's internal space, or, depending on the specifications, may be provided only at one end in the axial direction, or no seal member may be provided at all.

[0022] The cage 10 is a crown-shaped cage molded from engineering plastic. Examples of engineering plastic include materials containing polyether ether ketone resin and polyphenylene sulfide resin. By constructing the cage 10 from a material containing engineering plastic, the amount of deformation of the components when centrifugal force is applied can be reduced. Even if the cage 10 is constructed from a material that does not contain engineering plastic, it is desirable to use a resin material that is resistant to centrifugal deformation, such as a material containing polyamide resin. However, the material and type of the cage 10 can be changed as appropriate depending on the specifications of the bearing 1. If the material of the cage 10 contains carbon fiber, glass fiber, or the like as a reinforcing material, the amount of deformation of the components when centrifugal force is applied can be further reduced.

[0023] As shown in FIGS. 2 to 5, the cage 10 includes an annular base 11 and a plurality of retaining portions (retaining claws) 12 that protrude from the base 11 in the axial direction. The side from which the retaining portions 12 protrude is referred to as the first axial side, and the opposite side is referred to as the second axial side. The outer diameter surface of the cage 10 is a curved surface (cylindrical surface) without any steps. The space between the base 11 and the circumferentially adjacent retaining portions 12, 12 forms a pocket 20 that holds the balls 5 in the circumferential direction. That is, a plurality of pockets 20 are arranged side by side in the circumferential direction on one axial side of the base 11. The outer diameter surface and inner diameter surface of the cage 10 are connected at the pockets 20. The tips of the retaining portions 12 form claws 14, and the pairs of claws 14, 14 that sandwich the pocket 20 are curved in directions that approach each other. The balls 5 are held in the pockets 20 and revolve between the inner raceway groove 3a and the outer raceway groove 4a.

[0024] The pocket 20 is surrounded by the inner surfaces of the retaining portions 12, 12 on both circumferential sides of the bearing, sandwiching the pocket center a0, and the inner surface on one axial side of the base portion 11, and these inner surfaces hold the balls 5. These surfaces that hold the balls 5 are called the pocket surface 21. The pocket surface 21 is spherical over its entire area, facing the spherical outer surfaces of the balls 5.

[0025] In the cross section shown in Figure 3, that is, in a cross section (called a circumferential cross section) that is perpendicular to the bearing radial line passing through the pocket center a0 at the pocket center a0, the pocket surface 21 is formed by an arc around the pocket center a0. The diameter of this arc is HP. The diameter HP of the pocket surface in the circumferential cross section is usually set larger than the diameter Da of the balls 5. Note that in Figure 3, for ease of understanding, the cross section of the cage 10, which is originally cylindrical, in a plan view is expanded laterally and depicted as a plane.

[0026] In the cross section shown in Figure 4, that is, a cross section that passes through the pocket center a0 and includes the bearing center line c (referred to as an axial cross section), the diameter of the arc of the pocket surface 21 is also HP. Furthermore, in the cross section shown in Figure 1, that is, a cross section that passes through the pocket center a0 and is perpendicular to the bearing center line c (referred to as an orthogonal-axial cross section), the diameter of the arc of the pocket surface 21 is also HP. However, if a recess such as an oil reservoir is provided on the pocket surface 21, the location of that recess is excluded. Hereinafter, the diameter HP of the pocket surface 21 will be referred to as the pocket diameter HP.

[0027] Bearing 1 is D: bearing outer diameter (outer diameter of outer ring 4) (mm), d: bearing inner diameter (inner diameter of inner ring 3) (mm), n: rotation speed (min -1 ), dmn={(D+d) / 2}×n It is assumed that the bearing will be used in a high-speed rotation environment with a dmn value of 900,000 or more, as specified in the JIS. The dmn value is a value specified by multiplying the bearing inner ring rotation speed by the ball pitch circle diameter.

[0028] Here, the minimum thickness t of the base 11 in the axial direction at the bottom 22 on the other axial side of the pocket 20 (hereinafter referred to as the bottom thickness t) is, relative to the diameter Da of the ball 5, 0.06Da≦t≦0.22Da (condition 1) This increases the ring rigidity of the cage 10 and suppresses deformation of the tip of the retaining portion 12 due to centrifugal force, preventing the balls 5 from being trapped. This makes it possible to use the bearing 1 under high-speed conditions where the dmn value is 900,000 or more at the maximum rotational speed in the operating environment.

[0029] 3 and 4, the bottom thickness t is the thickness of the thinnest part in the axial direction at the bottom 22 on the other axial side of the pocket 20, i.e., the thickness of the member in the axial direction at the point where the axial thickness of the base 11 is smallest. The bottom 22 is the position (see reference symbol 22) that is closest to the other axial side in the circumferential cross section shown in Fig. 3, and is also the position (see reference symbol 22) that is closest to the other axial side in the axial cross section shown in Fig. 4.

[0030] If the ring rigidity of the cage 10 is too high, excessive stress may be generated at the tip of the retaining portion 12 when the balls 5 are inserted into the pockets 20, which may cause the shape of the pawls 14 to collapse. For this reason, it is desirable that the rigidity of the tip of the retaining portion 12 is low. Therefore, in order to reduce the rigidity of the tip of the retaining portion 12, the axial distance H (see Figures 3 and 4) between the edge on one axial end side of the connecting portion 15 connecting the circumferentially adjacent pockets 20, 20 and the edge on the other axial end side of the base portion 11 is set to: H≦t+HP / 2 (condition 2) It is even more desirable to

[0031] In the embodiment, the base 11 is thinned by forming a recess 13 that opens to the other axial side surface of the connecting portion 15. This prevents an increase in the weight of the cage 10 due to an increase in the ring rigidity of the cage 10.

[0032] FIG. 6 shows the results of examining the relationship between the ratio of the bottom thickness t of the pocket 20 of the cage 10 to the diameter Da of the balls 5 and whether or not entrapment of the balls 5 occurs.

[0033] The experimental example in FIG. 6 is a verification result when a single-row deep-groove ball bearing of type 6005 is adopted as the size of the cage 10 and the dmn value is 900,000. As shown in FIG. 6, when the ratio of the bottom wall thickness t of the pocket 20 of the cage 10 to the diameter Da of the ball is 6% or more, it is possible to prevent the occurrence of the holding of the ball 5 even at dmn 900,000. Similar results can be expected for other types of single-row deep-groove ball bearings.

[0034] Further, due to the centrifugal force accompanying the high-speed rotation of the bearing 1, the cage 10 is deformed, and the maximum stress occurs near the bottom 22 of the pocket 20. Generally, in a resin product, the welded part has a tendency to have a lower strength because the orientation of the reinforcing fibers is disturbed compared to the non-welded part. Therefore, when the position of the maximum stress generated by the deformation of the member accompanying the centrifugal force overlaps with the welded part, there is a concern that the reliability of the cage may decrease. For this reason, the welding position of the cage 10 is preferably located at the connecting part 15 between the adjacent pockets 20 in the circumferential direction, avoiding the bottom 22 of the pocket 20.

[0035] Also, in the relationship between the cross-sectional area S of the base 11 in the cross-section shown in FIG. 4, that is, the axial cross-section (cross-section IV-IV in FIG. 3) passing through the bottom 22 of the pocket 20 and including the axis of the base 11 (axis of the bearing 1), and the cross-sectional area S' of the base 11 in the cross-section shown in FIG. 5, that is, the axial cross-section (cross-section V-V in FIG. 3) passing through the circumferential center 16 (see FIG. 3) of the connecting part 15 connecting the adjacent pockets 20, 20 in the circumferential direction and including the axis of the base 11 (axis of the bearing 1), S < S' ··· (Condition 3) It is preferably set to this. This is because when S < S', it is easier to position the welding position at the connecting part 15. The measurement of the cross-sectional area S and the cross-sectional area S' can be achieved by cutting the cage cross-section and using an image measuring instrument.

[0036] It is desirable that this Condition 3 holds not only in the axial cross-section (cross-section V-V in FIG. 3) passing through the circumferential center 16 of the connecting part 15, but also in the cross-section passing through any point between the circumferential ends 17, 17 (see FIG. 3) of the connecting part 15, which is the node of the connecting part 15 and the holding part 12.

[0037] As mentioned above, if the bottom thickness t of pocket 11 is increased in order to increase the ring rigidity of cage 10, the stress on claws 14 increases when balls 5 are installed in pocket 20, raising the risk of claws 14 losing their shape. Figure 7 shows the results of an investigation into whether or not cage 10 loses its shape when balls 5 are installed in pocket 20.

[0038] The experimental example in Figure 7 also uses a single-row deep groove ball bearing 6005 type for the size of cage 10. As shown in Figure 7, if the bottom thickness t of pocket 20 relative to the diameter Da of ball 5 is 22% or less, a safety factor of 1 or more can be ensured against deformation of cage 10. A safety factor of 1 or more can reliably prevent deformation of cage 10 during molding and bearing assembly. Similar results can be expected with other types of single-row deep groove ball bearings.

[0039] As described above, by adopting condition 1 in a crown type resin cage used in a ball bearing, it is possible to prevent the balls 5 from being trapped by centrifugal deformation in an operating environment with a dmn value of 900,000 or more, and to prevent the toe shape from collapsing when molding the cage 10 and when inserting the balls 5 into the pockets 20. Furthermore, by adding condition 2 or condition 3, or both, further improvements in effectiveness can be expected.

[0040] Although the shaft to which the bearing 1 of the present invention is attached has been given as an example in the form of a rotating shaft of a drive motor equipped in an electric vehicle or other electric transport device, or a rotating shaft of a reducer or speed-up gear equipped in such electric transport device, the bearing 1 of the present invention can also be applied to supporting parts of rotating shafts in various other types of transport device, industrial machinery, etc. For example, the bearing can be applied to shafts in power transmission paths in various types of transport device, rotating parts of constant velocity joints, propeller shafts, turbochargers, transmissions, and wheel bearings, or supporting parts of rotating shafts in various machine tools, generators, etc. Furthermore, as in this embodiment, the inner member 3 may be configured as an inner ring or a shaft. Furthermore, as in this embodiment, the outer member 4 may be configured as an outer ring or a housing.

[0041] Furthermore, the bearing 1 of the present invention can be applied to not only the deep groove ball bearing of this embodiment, but also angular contact ball bearings and other ball bearings in general that use balls 5 as rolling elements.

[0042] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0043] 1. Bearings (ball bearings) 3 Inner member (inner ring) 3a Inner raceway groove 4 Outer member (outer ring) 4a Outer raceway groove 5 balls (rolling elements) 10 Cage 11 Base 12 Holding part 13 Recess 14 Claws 15 Connecting part 16 Circumferential center 20 pockets 22 Bottom

Claims

1. The bearing comprises an inner member (3), an outer member (4), balls (5) disposed between the inner member (3) and the outer member (4), and a cage (10) for holding the balls (5), dmn={(D+d) / 2}×n D: outer diameter of the outer member (4) (mm) d: inner diameter of the inner member (3) (mm) n: rotation speed (min －１ ) In a ball bearing used in an environment where the dmn value specified in is 900,000 or more, The cage (10) is a crown-type cage having an annular base (11) and a plurality of pockets (20) formed along the circumferential direction on one axial side of the base (11) to hold the balls (5), and the minimum axial thickness t of the base (11) at a bottom (22) on the other axial side of the pockets (20) is set to be: 0.06Da≦t≦0.22Da Ball bearings.

2. The axial distance H between the edge of one axial end of the connecting portion (15) connecting the circumferentially adjacent pockets (20) and the edge of the other axial end of the base portion (11) is, relative to the pocket diameter HP defined by the diameter of the pocket (20), H≦t+HP / 2 2. The ball bearing according to claim 1, wherein:

3. In relation to a cross-sectional area S of the base (11) in an axial cross section that passes through the bottom (22) and includes the axis of the base (11), and a cross-sectional area S' of the base (11) in an axial cross section that passes through a circumferential center (16) of a connecting portion (15) that connects the circumferentially adjacent pockets (20, 20) and includes the axis of the base (11), S<S' 2. The ball bearing according to claim 1, wherein:

4. 2. The ball bearing according to claim 1, wherein the material of the cage (10) includes an engineering plastic.

5. 5. A ball bearing according to claim 4, wherein the material of the cage (10) contains carbon fiber or glass fiber as a reinforcing material.

6. A bearing device using the ball bearing according to any one of claims 1 to 5, in which a rotating shaft of a drive motor, a reducer, or a speed increaser for an electric transport device is supported by the ball bearing.

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