WO2023008313A1

WO2023008313A1 - Ball bearing

Info

Publication number: WO2023008313A1
Application number: PCT/JP2022/028375
Authority: WO
Inventors: 武仁櫻井; 翔平深間; 悠介鈴木; 吉稀竹田
Original assignee: Ntn株式会社
Priority date: 2021-07-27
Filing date: 2022-07-21
Publication date: 2023-02-02
Also published as: KR20240038746A; JP2023018262A; CN117751250A

Abstract

A ball bearing (1) comprises inner and outer bearing rings (2, 3), a plurality of ceramic balls (4) which are interposed therebetween, and a cap member (6) which suppresses inflow of lubricating oil from the outside of the bearing to the inside (7) of the bearing. A gap in the inside of the bearing during operation of the ball bearing (1) is set to a value greater than 0 μm at 80°C and higher. The kinetic viscosity at 100°C of the lubricating oil supplied to the inside (7) of the bearing is not more than 7.0 mm2/s. Thus, it is possible to both improve low torque properties of and prevent damage to a ball bearing which supports a rotation shaft included in a vehicle driving motor or in a transmission that is connected to a vehicle driving motor.

Description

ball bearing

This invention relates to ball bearings.

In general, automobiles such as electric vehicles (EV) and electric hybrid vehicles (HV) and vehicles for industrial machinery are equipped with a drive system including a drive motor and a transmission. Ball bearings, which are superior in low-torque properties, are employed as bearings for supporting the rotating shafts of the drive motors or transmissions. The balls and the inner and outer races, which are the constituent elements of the ball bearing, are generally made of steel, and are subjected to various heat treatments and surface modification treatments for damage prevention as necessary. In addition, in order to prevent early damage to the bearing caused by foreign matter such as gear wear powder entering the bearing, or to enclose grease inside the bearing as an initial lubricant, caps such as seals and shields are applied to the ball bearings. Installation of components is being carried out.

A typical contact seal has a ring-shaped seal lip made of an elastic material such as rubber. A mating part such as a bearing ring or a slinger that rotates relative to the seal in the circumferential direction as the bearing rotates is formed with a seal sliding surface that slides in the circumferential direction on the seal lip. The seal lip and the seal sliding surface are in sliding contact all around, microscopically accompanied by a solid contact area. The drag resistance (seal torque) of the seal lip contributes to the temperature rise of the bearing torque and ball bearings. In addition, since the inside of the bearing is closed off from the outside by the seal, the pressure difference between the inside and the outside of the bearing causes the seal lip to press against the seal sliding surface, causing an adsorption effect, which may increase the seal torque. For these reasons, general contact seals have limitations in high-speed operation of ball bearings.

On the other hand, if a non-contact seal or shield is used as the cap member, it is possible to eliminate the seal torque, but the size of the non-contact gap between the seal member and the mating part must be adjusted to prevent the intrusion of foreign matter of a specified particle size. Error management is difficult.

On the other hand, the sealed ball bearing disclosed in Patent Document 1 has a plurality of protrusions in which the seal lips are arranged in the circumferential direction, and the plurality of protrusions are located between adjacent protrusions in the circumferential direction. The seal lip and the seal sliding surface are lubricated by a lubricating oil film that is dragged through the gap between the protrusion and the seal sliding surface as the bearing rotates. It is designed to The sealed ball bearing disclosed in Patent Document 1 can cope with high-speed operation while preventing the intrusion of foreign matter of a predetermined particle size that may cause early damage to the bearing. Torque can be significantly reduced.

WO2016/143786

However, the demand for reducing CO ₂ emissions will continue to increase in the future, and there is a need to improve the energy-saving driving performance of vehicles, as well as to further advance the use of electric vehicles. For this reason, drive motors and transmissions tend to employ low-viscosity lubricating oil in order to suppress torque loss. In recent years, the use of lubricating oils with a kinematic viscosity of 27 mm ² /s or less at 40° C. and 7.0 mm ² /s or less at 100° C. is increasing. Supplying such low-viscosity lubricating oil to ball bearings in drive motors and transmissions is effective in reducing agitation resistance inside the bearings. There is a growing concern that the oil film will run out and seizure will occur.

In addition, if the ball bearing is provided with a cap member such as a seal or shield that suppresses the inflow of lubricating oil into the bearing, it is effective in reducing stirring resistance. concerns will increase.

Also, when a ball bearing is incorporated into a drive motor or a transmission connected thereto, a potential difference is generated between the shaft and the housing where the ball bearing intervenes, causing electrolytic corrosion in the elastic contact area between the steel ball and bearing ring. There is also a possibility that the usage environment will be such that

In view of the background described above, the problem to be solved by the present invention is to improve the low torque property of a ball bearing that supports a rotating shaft included in a vehicle driving motor or a transmission connected to a vehicle driving motor and prevent damage to the ball bearing. It is to make prevention compatible.

In order to achieve the above object, the present invention provides a ball bearing for supporting a rotating shaft included in a vehicle driving motor or a transmission connected to the vehicle driving motor, and includes an inner bearing ring and an outer bearing ring. a bearing ring, a plurality of balls interposed between the inner and outer bearing rings, a retainer that holds the plurality of balls, and a cap member that suppresses the inflow of lubricating oil from the outside of the bearing into the inside of the bearing; The ball is made of a material different from steel, and the internal bearing clearance during operation is set to a value greater than 0 μm at 80°C or higher, and the kinematic viscosity of the lubricating oil supplied to the bearing at 100°C is 7. 0 mm ² /s or less was adopted.

As described above, in a ball bearing that supports a rotating shaft included in a vehicle driving motor or a transmission connected to a vehicle driving motor, if balls made of a material other than steel are used, the balls will not be able to function during high-speed operation. Even if the oil film runs out in the elastic contact area of the bearing ring, the balls and the bearing ring, which are made of different materials, do not adhere to each other, and the seizure resistance is improved compared to steel balls. Further, if the bearing internal clearance during operation at 80° C. or higher is set to a value larger than 0 μm, it is possible to avoid early damage due to negative operating clearance during high-speed rotation. For these reasons, it is possible to prevent damage to the balls and bearing rings even when using a low-viscosity lubricating oil or diluting the lubricating oil. On top of that, by supplying a low-viscosity lubricating oil having a kinematic viscosity of 7.0 mm ² /s or less at 100° C. under the condition that the inflow of the lubricating oil is suppressed by the cap member, the stirring resistance can be satisfactorily reduced. can reduce the bearing torque. In this way, it is possible to achieve both improvement in low-torque property and damage prevention of the ball bearing that supports the rotating shaft of a vehicle driving motor or the like.

Here, the vehicle drive motor in the present invention refers to an electrical device that converts electrical energy and outputs rotation that serves as a vehicle drive source, and an electrical device that converts input rotation into electrical energy during regenerative braking of the vehicle. It means what corresponds to at least one.

In addition, the transmission in the present invention means a device that converts the input rotational speed and transmits it to the output side, and a continuously variable transmission that can continuously change the speed conversion ratio (reduction ratio, gear ratio), The concept includes a fixed-ratio transmission in which the speed conversion ratio is fixed, and the fixed-ratio transmission includes what is called a speed reducer or a speed increaser that has only one type of speed conversion ratio. included.

In addition, the value of kinematic viscosity in this invention is the value in the measurement in accordance with the "kinematic viscosity test method" specified in JIS K 2283: 2000 "Crude oil and petroleum products-kinematic viscosity test method and viscosity index calculation method". means.

It is preferable that the ball is made of ceramics. Since the ceramic ball is an insulator, electrolytic corrosion does not occur in the elastic contact area. Furthermore, the use of ceramic balls reduces the loss (elastic hysteresis, differential slip) in the elastic contact area between the ball and raceway compared to steel balls. can be reduced.

It is preferable that the cross-sectional shape of the raceway grooves of the inner and outer races is arcuate with a diameter not greater than 1.1 times the diameter of the ball. Such an arc shape is suitable for reducing the bearing torque while suppressing the surface pressure in the elastic contact area between the ball and the bearing ring.

The cap member is attached to one of the inner and outer races, and the cap member is a seal that slides in the circumferential direction on a seal sliding surface provided on the other of the inner and outer races. The sealing lip has a plurality of protrusions arranged in the circumferential direction, and the plurality of protrusions communicate between the protrusions adjacent in the circumferential direction to the inside and the outside of the bearing. A gap is formed, and the seal lip and the seal sliding surface are brought into a fluid lubrication state by an oil film of lubricating oil that is dragged from the gap between the protrusion and the seal sliding surface as the bearing rotates. should be provided in By doing so, it is possible to achieve high-speed operation and low seal torque comparable to non-contact seals while suppressing the intrusion of foreign matter of a predetermined particle size and the inflow of lubricating oil, which may lead to early failure of the ball bearing, by the cap member. can be done.

Also, the retainer may be a crown-shaped retainer made of synthetic resin. Such a retainer is lighter and more self-lubricating than a corrugated retainer made of steel plate, and is therefore suitable for reducing bearing torque.

In this invention, synthetic resin is a concept that includes fiber reinforced resin. Preferably, the synthetic resin comprises a fiber-reinforced polyamide resin or a fiber-reinforced polyphenylene sulfide resin. By doing so, the crown retainer has good deformation resistance against centrifugal force, and is suitable for high-speed rotation.

Also, grease is enclosed as an initial lubricant inside the bearing, and the amount of the grease enclosed is preferably 5 to 20% by volume of the total space volume of the bearing. By doing so, it is possible to suppress the agitation resistance of the grease while suppressing insufficient lubrication in the initial stage of operation of the ball bearing.

At least one of nitrile rubber, acrylic rubber, fluororubber, cold-rolled steel plate, and stainless steel plate may be used as the material of the cap member. By doing so, the cap member can be manufactured from a material commonly used as a material for seals and shields.

The balls are preferably made of nitride ceramics. Nitride-based ceramics are suitable because they are generally excellent in mechanical properties such as light weight, high strength, and high toughness.

According to the present invention, by adopting the above configuration, it is possible to achieve both improvement in low torque and prevention of damage to a ball bearing that supports a rotary shaft included in a vehicle drive motor or a transmission connected to a vehicle drive motor. can.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the ball bearing which concerns on 1st embodiment of this invention Schematic diagram showing an example of use of the ball bearing in Fig. 1 Partially enlarged cross-sectional view taken along line III-III in FIG. Bar graph showing calculated results of bearing torque Bar graph showing bearing torque test results Bar graph showing different calculation results for bearing torque Sectional drawing which shows the ball bearing which concerns on 2nd embodiment of this invention

A sealed bearing according to a first embodiment as an example of the present invention will be described with reference to FIGS. 1 to 6 of the accompanying drawings.

This ball bearing 1 shown in FIG. , a retainer 5 for holding the plurality of balls 4, and cap members 6 attached to both sides of one of the inner and outer bearing rings 3. As shown in FIG.

This ball bearing 1 is a double-sealed deep groove ball bearing.

In the following description, the direction along the bearing center axis (not shown, hereinafter the same) of the ball bearing 1 will be referred to as the "axial direction". A direction orthogonal to the axial direction is called a “radial direction”. Also, the direction along the circumference around the center axis of the bearing is referred to as the "circumferential direction". In FIG. 1, the bearing center axis is the center axis of the inner bearing ring 2 which is the rotating ring. FIG. 1 shows a cross section of an imaginary plane containing the bearing central axis. The axial direction corresponds to the horizontal direction in FIG. 1, and the radial direction corresponds to the vertical direction in FIGS.

The inner bearing ring 2 is made of a steel annular member having a raceway groove 2a that contacts the balls 4 on the outer peripheral side. The inner bearing ring 2 is fitted to the rotating shaft S at its inner circumference. The outer bearing ring 3 consists of a steel annular member having a raceway groove 3a in contact with the balls on the inner peripheral side. The outer bearing ring 3 is attached to a member such as a housing, a gear, or the like that bears the load from the rotating shaft.

The rotating shaft S is included in a vehicle driving motor or a transmission connected to the vehicle driving motor. They are the input shaft for input, the output shaft for rotational output, and the intermediate transmission shaft.

2, a vehicle driving motor 20, a transmission 30 connected to the vehicle driving motor ₂₀ , and rotation shafts S20, _S31 , S32 included in the vehicle driving motor ₂₀ or the transmission 30 are supported. An example of a rotation transmission device including a ball bearing 1 is shown. The illustrated rotation transmission device is incorporated in a vehicle drive system. The transmission 30 includes a plurality of rotating shafts S ₃₁ to S ₃₃ , gears G1 to G3 provided on each of these rotating shafts S ₃₁ to S ₃₃ , and a plurality of ball bearings 1 supporting the rotating shafts S ₃₁ to S ₃₂ . and The rotating shaft _S31 and the rotating shaft S20 of the vehicle drive motor ₂₀ rotate together. The rotating shaft _S33 is supported by a plurality of tapered roller bearings.

When the vehicle driving motor ₂₀ serves as a drive source, the transmission 30 serves as a gear reducer that reduces the rotation input from the rotation shaft S20 to the rotation shaft _S31 and outputs the rotation from the rotation shaft _S33 . When the vehicle drive motor 20 serves as a regenerative brake, the transmission 30 serves as a gear speed increaser that speeds up the rotation input to the rotating shaft _S33 from the traveling wheel side and outputs it from the rotating shaft _S31 .

The bearing internal clearance during operation of the ball bearing 1 shown in FIG. 2 is set to a value greater than 0 μm at 80° C. or higher. Here, the bearing internal clearance refers to the amount of movement when one of the inner and outer bearing rings is fixed and the other is moved. When the other is moved in the radial direction, it is called the radial internal clearance, and when it is moved in the axial direction, it is called the axial internal clearance. During operation of the rotation transmission device, if the temperature of all the ball bearings 1 is 80° C. or higher, both the radial internal clearance and the axial internal clearance of the ball bearing 1 continue to exceed 0 μm.

The ball 4 shown in FIG. 1 consists of a spherical rolling element that revolves while rotating between the inner and outer raceway grooves 2a and 3a. The ball 4 is made of a material different from steel. Nitride-based ceramics (Si ₃ N ₄ ) is used as the material. As a material for forming the balls 4, it is possible to employ ceramics other than nitrides.

The cross-sectional shape of each of the inner and outer raceway grooves 2a, 3a corresponds to the generatrix shape of each of the raceway grooves 2a, 3a on the imaginary plane shown in FIG. The cross-sectional shape of the raceway groove 2a is arcuate with a diameter not greater than 1.1 times the diameter of the ball 4 . The cross-sectional shape of the raceway groove 3a is also arcuate with a diameter not greater than 1.1 times the diameter of the ball 4 .

The retainer 5 consists of an annular bearing component that keeps a plurality of balls 4 interposed between the inner and outer raceway grooves 2a, 3a at a predetermined circumferential interval. The cage 5 in the illustrated example is a corrugated cage formed by coupling a pair of steel plate corrugated press parts.

The cap member 6 separates the outside of the ball bearing 1 and the inside 7 of the bearing. The bearing interior 7 is an annular space formed over the entire circumference between the inner and

outer races

2 and 3 .

　Lubricating oil (not shown) is supplied to the ball bearing 1 from the outside of the bearing. Examples of the lubricating method include a splashing method in which lubricating oil is applied to the ball bearing 1 and an oil bath method in which the lower portion of the ball bearing 1 is immersed in lubricating oil.

Grease G (indicated by a dot pattern in FIG. 1) is enclosed in the bearing interior 7 as an initial lubricant.

The cap member 6 prevents foreign matter from entering the bearing interior 7 from the outside of the bearing, lubricating oil supplied to the ball bearing 1 from the outside of the bearing flowing into the bearing interior 7, and grease G from leaking to the outside of the bearing. Suppress. The cap member 6 does not liquid-tightly seal the bearing interior 7 from the bearing exterior.

A seal groove 3b for holding the cap member 6 is formed in one of the inner and outer races 3. The cap member 6 is attached to the bearing ring 3 by press-fitting the peripheral portion on the bearing ring 3 side into the seal groove 3b.

The illustrated cap member 6 has a metal core 8 made of a metal plate and a seal lip 9 made of an elastic material. The cored bar 8 is made of a pressed part. Examples of the elastic material include a vulcanized rubber material, an elastomer equivalent to a rubber material, and the like. Examples of rubber materials include nitrile rubber (NBR), acrylic rubber (ACM), and fluororubber (FKM). Moreover, as said metal plate, a cold-rolled steel plate and a stainless steel plate are mentioned, for example.

A seal sliding surface 2 b that slides on the seal lip 9 in the circumferential direction is formed on the inner and outer bearing rings 2 opposite to the inner and outer bearing rings 3 . The seal sliding surface 2b has a cylindrical surface along the circumferential direction.

As shown in FIGS. 1 and 3, the seal lip 9 has a plurality of protrusions 9a arranged in the circumferential direction. These plurality of protrusions 9a create gaps 10 between adjacent protrusions 9a in the circumferential direction that communicate with the inside 7 of the bearing and the outside. The seal lip 9 and the seal sliding surface 2b are provided so as to be fluidly lubricated by an oil film of lubricating oil (indicated by dots in FIG. 3) drawn between the seal lip 9 and the seal sliding surface 2b.

The cap member 6 allows lubricating oil to flow between the inside 7 of the bearing and the outside through a gap 10 that can prevent foreign matter of a predetermined particle size from entering. Therefore, a thick oil film is formed due to the wedge effect when lubricating oil is dragged between the protrusion 9a and the seal sliding surface 2b as the bearing rotates. When the peripheral speed of the relative rotation between the seal lip 9 and the seal sliding surface 2b (the direction of the arrow A in FIG. 3 is assumed) reaches a predetermined value, each projection 9a and the seal sliding surface 2b form an oil film. are completely separated from each other, the seal lip 9 and the seal sliding surface 2b are completely separated to form a fluid lubricating state, and this fluid lubricating state continues even at a higher peripheral speed. For this reason, the seal torque in the ball bearing 1 is reduced to the same level as when a non-contact seal is employed at a predetermined circumferential speed or higher, for example, 0.2 m/s or higher.

Since the cap member 6 is disclosed in Patent Document 1, detailed description thereof will be omitted. The protrusions 9a may be arranged at uniform intervals over the entire circumferential direction. A groove extending in the circumferential direction may be formed in at least one portion of the protrusion 9a. The projecting portion 9a may be shaped to form a wedge-shaped gap with the seal sliding surface 2b, which becomes smaller on the projecting portion 9a side. The protrusion 9a may extend in a direction perpendicular to the circumferential direction, and may have an R shape that gradually approaches the seal sliding surface 2b toward the center of the width of the protrusion 9a in the circumferential direction. The height and pitch of the protrusions 9a may be set so as to have the effect of preventing the entry of foreign matter having a particle size exceeding 0.05 mm, which may cause early damage to the ball bearing 1. For example, the height of the protrusions 9a may be set to zero. It may be set to 0.05 mm or more, or may be set to 0.05 mm or less.

The lubricating oil supplied to the inside of the bearing 7 has a kinematic viscosity of 7.0 mm ² /s or less at 100°C.

After the operation of the ball bearing 1 is started, lubricating oil supplied from the outside of the bearing relatively early flows into the bearing interior 7 through the gap 10 between the cap member 6 and the seal sliding surface 2b. Therefore, if the amount necessary for initial lubrication is ensured, the smaller the amount of grease G enclosed, the more effective it is in reducing the bearing torque. In order to achieve both the purpose of initial lubrication and the suppression of bearing torque, the amount of grease G enclosed is set to 5 to 20% by volume of the total space volume of the bearing. Here, the total space volume of the bearing means that the bearing interior 7 (sealed space) surrounded by the cap members 6 provided at both axial ends of the inner and outer bearing rings 2 and 3, respectively, includes the balls 4 and the cage 5. is the space volume in which the ball bearing 1 is stopped.

The ball bearing 1 is as described above, and the bearing torque can be reduced by making the balls 4 made of nitride ceramics (Si ₃ N ₄ ). That is, the density of nitride ceramics (Si ₃ N ₄ ) is 3.304 g/cm ³ while the density of bearing steel (SUJ2) is 7.8 g/cm ³ . The longitudinal elastic modulus of the nitride ceramics is 315 GPa, while the longitudinal elastic modulus of the bearing steel is 210 GPa. The Poisson's ratio of the nitride ceramics is 0.25, while the Poisson's ratio of the bearing steel is 0.3. The thermal expansion coefficient of the nitride ceramics is 3.2 (×10 ⁻⁶ /° C.), while the thermal expansion coefficient of the bearing steel is 12.5 (×10 ⁻⁶ /° C.). is. The thermal conductivity of the nitride ceramics is 0.07 Cal/cm·s·°C, while the thermal conductivity of the bearing steel is 0.1 to 0.12 Cal/cm·s·°C. is. As is clear from these numerical comparisons, ceramic balls generally have a larger longitudinal elastic modulus and higher rigidity than steel balls. Elastic hysteresis and differential slip are reduced, resulting in reduced bearing torque.

Also, the ceramic ball 4 shown in FIG. 1 does not conduct electricity as compared to the steel ball. Therefore, electrolytic corrosion of the ball bearing 1 can also be prevented.

Also, the ceramic balls 4 and the steel bearing rings 2 and 3 are made of different materials, so they do not weld. Therefore, the seizure resistance in the elastic contact area between the ball 4 and the bearing rings 2, 3 is superior to steel balls.

Also, the ceramic ball 4 has higher rigidity than the steel ball.

Calculation results of the bearing torque for the ball 4 made of nitride ceramics (Si ₃ N ₄ ) and the ball made of steel (SUJ2 subjected to standard heat treatment) as a comparative example are shown below. It is shown in FIG. This calculation was performed for ball bearing model numbers: 6806, 6006, and 6306, respectively. The conditions for this calculation were bearing rotation speed: 5000 min ⁻¹ , radial load Fr: 730 N (20% of static load rating Cor of type 6806), axial load Fa: 0 N, lubricating oil: ISO viscosity VG10.

As is clear from Fig. 4, in the calculation results for any model number, the bearing torque was smaller when ceramic balls were used. As a result, ceramic balls have a lighter specific gravity than steel balls, so they are less affected by centrifugal force when the bearing rotates. It is believed that this is because differential slip, spin, rolling viscous resistance, and elastic hysteresis loss are reduced, which works advantageously.

In addition, by providing the cap member 6, the amount of lubricating oil flowing into the bearing interior 7 is reduced, the stirring resistance is also reduced, and damage to the bearing due to foreign matter can be prevented and the bearing torque can be reduced.

Here, since the cap member 6 provided in the ball bearing 1 shown in FIG. A test was conducted to measure the bearing torque in the case of an open bearing (with no seal) as a comparative example. The test results are shown in FIG. This test was carried out on ball bearing model number 6308, respectively. The test conditions were as follows: bearing rotational speed: 754 min ⁻¹ , radial load Fr: 754 N, axial load Fa: 0 N, lubricating oil: CVT fluid, lubrication method: oil bath (oil level intersects the lowest ball) and bottom.

As is clear from FIG. 5, the bearing torque was clearly smaller in the ball bearing provided with the non-contact seal as the cap member than in the open bearing. This result is considered to be because the amount of lubricating oil flowing into the bearing is suppressed by the cap member, and torque loss due to agitation of the lubricating oil inside the bearing works advantageously.

In particular, the cap member 6 of the ball bearing 1 shown in FIG. 1 exhibits low torque performance comparable to that of non-contact type seals and shields, so it prevents the entry of foreign matter with a predetermined particle diameter that causes early damage. , it is suitable for suppressing the inflow of lubricating oil.

Table 1 summarizes the advantages and disadvantages of open bearings with steel balls, bearings with contact seals with steel balls, and ball bearing 1 shown in FIG.

A lubricating oil having a kinematic viscosity of 7.0 mm ² /s or less at 100° C. is suitable for suppressing the shear resistance of the lubricating oil and reducing the bearing torque. The shear resistance is approximately determined by the following formula 1.
Formula 1: F = η · (u / h) · s
Here, F: shear resistance, η: oil viscosity coefficient, u: fluid velocity, h: oil film thickness, s: sliding area. When the kinematic viscosity of the lubricating oil decreases, the oil viscosity coefficient η and the oil film thickness h decrease, so the shear resistance F decreases.

In addition, since the cross-sectional shape of the inner and outer raceway grooves 2a, 3a is circular with a diameter not more than 1.1 times the diameter of the ball 4, the elastic contact area between the ball 4 and the bearing rings 2, 3 It is possible to reduce the bearing torque while suppressing the surface pressure of the bearing.

The bearing torque was calculated with various groove diameters of the inner and outer raceway grooves. The calculation result is shown in FIG. This calculation was performed for the model number of the ball bearing: 6006. The calculation conditions were bearing rotation speed: 5000 min ⁻¹ , radial load Fr: 730 N, axial load Fa: 0 N, lubricating oil: ISO viscosity VG10 (JIS K2001:1993). The diameter of the ball is constant.

As is clear from FIG. 6, it is clear that the bearing torque tends to decrease as the groove diameters of the inner and outer raceway grooves are increased. This is thought to be because the area of the elastic contact area becomes smaller as the difference in curvature between the ball and the raceway groove becomes larger, which is advantageous in suppressing the loss here.

However, according to past records, the load applied to the bearings in vehicle transmissions is about 35% of the dynamic load rating for both radial load and axial load. In this case, if the groove diameter of the inner and outer raceway grooves exceeds 1.1 times the ball diameter, the surface pressure in the elastic contact area will exceed 4200 MPa, which is the standard for static load rating. According to past records, the radial load is about 50% of the rated dynamic load, and the axial load is about 30%. In this case, if the groove diameter of the inner and outer raceway grooves exceeds 1.08 times the ball diameter, the surface pressure in the elastic contact area will exceed 4200 MPa, which is the standard for static load rating. Considering these facts, it is considered preferable to set the groove diameter of the inner and outer raceway grooves to 1.1 times or less the diameter of the ball in order to achieve both damage prevention and low torque.

Thus, the ball bearing 1 shown in FIGS. 1 to 3 supports the rotation shafts S ₂₀ , S ₃₁ , S ₃₂ included in the vehicle drive motor 20 or the transmission 30 connected to the vehicle drive motor 20. By providing the balls 4 made of a material different from steel, which is the material of the inner and outer bearing rings 2, 3, oil film breakage occurs in the elastic contact area between the balls 4 and the bearing rings 2, 3 during high-speed operation. Even if seizure occurs, the ball 4 and bearing rings 2 and 3, which are made of different materials, will not be welded together, improving seizure resistance. In addition, since the ball bearing 1 is set to have a bearing internal clearance larger than 0 μm during operation at 80° C. or higher, early damage due to negative operating clearance during high-speed rotation can be avoided. For these reasons, the ball bearing 1 can prevent damage to the balls 4 and the bearing rings 2 and 3 even if a low-viscosity lubricating oil is used or the lubricating oil is diluted. In addition, the ball bearing 1 is supplied with a low-viscosity lubricating oil having a kinematic viscosity of 7.0 mm ² /s or less at 100° C. under the condition that the inflow of the lubricating oil is suppressed by the cap member 6. The bearing torque can be reduced by satisfactorily reducing the resistance. In this way, the ball bearing 1 that supports the rotating shaft S ₂₀ of the vehicle driving motor 20 and the like can both improve the low torque property and prevent damage.

Also, in the ball bearing 1, since the balls 4 are made of ceramics, the balls 4 become insulators, and electrolytic corrosion does not occur in the elastic contact areas between the balls 4 and the bearing rings 2 and 3. Furthermore, when the ball 4 made of ceramics is used, the loss (elastic hysteresis, differential slip) in the elastic contact area between the ball 4 and the bearing rings 2, 3 is reduced compared to when the ball made of steel is used. Also from this, the ball bearing 1 can reduce the bearing torque.

Further, in the ball bearing 1, the cross-sectional shape of the raceway grooves 2a, 3a of the inner and outer bearing rings 2, 3, respectively, is arcuate with a diameter not greater than 1.1 times the diameter of the ball 4. It is possible to reduce the bearing torque while suppressing the surface pressure in the elastic contact areas between the balls 4 and the bearing rings 2 and 3 to avoid adverse effects on the life of the bearing.

Further, the ball bearing 1 is provided with the cap member 6 that realizes fluid lubrication of the seal lip 9 with respect to the seal sliding surface 2b. While the inflow is suppressed by the cap member 6, high-speed operation and low seal torque comparable to those of the non-contact seal can be realized.

Further, the ball bearing 1 is filled with grease G as an initial lubricant in the bearing interior 7, and the amount of the grease G filled is 5 to 20% by volume of the total space volume of the bearing. It is possible to suppress the stirring resistance of the grease G while suppressing insufficient lubrication of the grease G.

At least one of nitrile rubber, acrylic rubber, fluororubber, cold-rolled steel plate, and stainless steel plate is used as the material of the cap member 6, so that the ball bearing 1 is generally used as a material for seals and shields. The cap member 6 can be manufactured from a material suitable for the purpose.

In addition, since the ball 4 is made of nitride-based ceramics, the ball 4 has comprehensively excellent mechanical properties such as light weight, high strength, and high toughness, so it is suitable for high-speed rotation.

In the first embodiment, the retainer 5 is a corrugated retainer, but the retainer may be of another type. As an example, FIG. 7 shows a ball bearing 40 according to the second embodiment. It should be noted that only the points of difference from the first embodiment will be described here.

The inner and outer bearing rings 41 and the inner and outer bearing rings 42 of the ball bearing 40 are shielded. The retainer 43 is a crown-shaped retainer made of synthetic resin. The synthetic resin consists of fiber-reinforced polyamide resin or fiber-reinforced polyphenylene sulfide resin.

A shield groove 41a is formed in one bearing ring 41, and a cap member 44 is attached thereto. A full circumference groove 42 a is formed in the other inner and outer races 42 to form a labyrinth clearance with the cap member 44 .

The cap member 44 is a non-contact shield made of cold-rolled steel plate or stainless steel plate.

Lubricating oil is splashed onto the ball bearing 40 from the right side of the drawing. This inflow of lubricating oil can be effectively suppressed only by providing a cap member 44 on the right side of the ball bearing 40 in the drawing.

Since the ball bearing 40 is provided with a crown-shaped retainer 43 made of synthetic resin, the retainer 43 is lighter and more self-lubricating than a corrugated retainer made of steel plate, which is suitable for reducing bearing torque. is.

Since the synthetic resin of the ball bearing 40 is fiber-reinforced polyamide resin or fiber-reinforced polyphenylene sulfide resin, the retainer 43 has excellent deformation resistance against centrifugal force and is suitable for high-speed rotation.

The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. Therefore, the scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the meaning and scope of equivalents of the scope of the claims.

1, 40

Ball bearings

2, 3, 41, 42 Raceway rings 2a, 3a Raceway groove 2b Seal sliding surface 4

Balls

5, 43

Cage

6, 44 Cap member 7 Bearing interior 8 Core metal 9 Seal lip 9a Projection 10 Gap ₂₀ vehicle drive motor 30 transmissions S, S20, _S31 , _S32 rotating shaft

Claims

A ball bearing that supports a rotating shaft included in a vehicle drive motor or a transmission connected to a vehicle drive motor,
An inner bearing ring, an outer bearing ring, a plurality of balls interposed between the inner and outer bearing rings, a retainer that retains the plurality of balls, and an inflow of lubricating oil from the outside of the bearing into the inside of the bearing. and a cap member that suppresses
The ball is made of a material different from steel,
The bearing internal clearance during operation is set to a value greater than 0 μm at 80°C or higher.
A ball bearing, wherein the kinematic viscosity of lubricating oil supplied to the inside of the bearing at 100°C is 7.0 mm 2 /s or less.
The ball bearing according to claim 1, wherein the balls are made of ceramics.
　The ball bearing according to claim 1 or 2, wherein the raceway grooves of the inner and outer races each have an arcuate cross-sectional shape defined by a diameter equal to or less than 1.1 times the diameter of the ball.
The cap member is attached to one of the inner and outer bearing rings,
the cap member has a seal lip that slides in the circumferential direction against a seal sliding surface provided on the other of the inner and outer bearing rings;
The seal lip has a plurality of protrusions arranged in a circumferential direction, and the plurality of protrusions create a gap communicating between the inside and the outside of the bearing between adjacent protrusions in the circumferential direction, Further, the seal lip and the seal sliding surface are provided in a state of fluid lubrication by an oil film of lubricating oil that is dragged between the protrusion and the seal sliding surface through the gap as the bearing rotates. A ball bearing according to any one of claims 1 to 3.
The ball bearing according to any one of claims 1 to 4, wherein the retainer is a crown-shaped retainer made of synthetic resin.
The ball bearing according to claim 5, wherein the synthetic resin is fiber-reinforced polyamide resin or fiber-reinforced polyphenylene sulfide resin.
The ball bearing according to any one of claims 1 to 6, wherein grease is enclosed as an initial lubricant inside the bearing, and the amount of the grease enclosed is 5 to 20% by volume of the total space volume of the bearing.
The ball bearing according to any one of claims 1 to 7, wherein at least one of nitrile rubber, acrylic rubber, fluororubber, cold-rolled steel plate and stainless steel plate is used as the material of the cap member.
The ball bearing according to claim 2, wherein the balls are made of nitride ceramics.