CN117751250A

CN117751250A - Ball bearing

Info

Publication number: CN117751250A
Application number: CN202280052208.0A
Authority: CN
Inventors: 樱井武仁; 深间翔平; 铃木悠介; 竹田吉稀
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 2021-07-27
Filing date: 2022-07-21
Publication date: 2024-03-22
Also published as: WO2023008313A1; KR20240038746A; JP2023018262A

Abstract

The ball bearing (1) is provided with: inner and outer bearing rings (2, 3);a plurality of ceramic balls (4) interposed between the inner and outer bearing rings (2, 3); and a cover member (6) that suppresses inflow of lubricating oil from the outside of the bearing to the inside of the bearing (7). The internal bearing play during operation of the ball bearing (1) is set to a value greater than 0 [ mu ] m at 80 ℃ or higher. The kinematic viscosity at 100℃of the lubricating oil supplied to the bearing interior (7) was 7.0mm ² And/s or less. Accordingly, the low torque performance of the ball bearing supporting the rotary shaft included in the vehicle driving motor or the transmission connected to the vehicle driving motor is improved and the damage is prevented.

Description

Ball bearing

Technical Field

The present invention relates to ball bearings.

Background

In general, automobiles such as Electric Vehicles (EVs) and electric Hybrid Vehicles (HVs) and industrial vehicles are provided with a drive system including a drive motor and a transmission. As a bearing for supporting the rotation shaft of the drive motor or transmission, a ball bearing excellent in low torque is used. The balls and inner and outer bearing rings, which are the constituent elements of the ball bearing, are generally made of steel, and various heat treatments and surface modification treatments for preventing damage are performed as needed. In addition, in order to prevent foreign matter such as gear wear powder from entering the bearing and early damaging the bearing, or in order to seal grease as an initial lubricant in the bearing, a cover member such as a seal or a shroud is attached to the ball bearing.

A typical contact seal has a seal lip formed in an annular shape from an elastic material such as rubber. A seal sliding surface that slides in the circumferential direction with respect to the seal lip is formed on an object member such as a bearing ring or an oil slinger that rotates in the circumferential direction with respect to the seal along with rotation of the bearing. The seal lip and the seal sliding surface are in sliding contact over the entire circumference, microscopically accompanied by a solid contact area. Drag resistance (sealing torque) of the seal lip is one cause of rise in bearing torque and temperature of the ball bearing. Further, since the bearing interior is sealed from the outside by the seal, there is a case where a pressure difference between the bearing interior and the outside causes an adsorption action in which the seal lip is pressed against the seal sliding surface, and the seal torque increases. Because of this, there is a limit to high-speed operation of the ball bearing in the case of a usual contact seal.

On the other hand, when a noncontact seal or a shield is used as the lid member, the seal torque can be eliminated, but it is difficult to manage various errors that can prevent invasion of foreign matter of a predetermined particle size for the size of the noncontact gap between the seal member and the target member.

In contrast, the sealed ball bearing disclosed in patent document 1 is provided with: the seal lip has a plurality of protrusions arranged in the circumferential direction, the plurality of protrusions generating gaps which pass between the protrusions adjacent to each other in the circumferential direction and communicate with the inside and outside of the bearing, and the seal lip and the seal sliding surface are brought into a fluid lubrication state by an oil film of lubricating oil which is carried in from the gaps between the protrusions and the seal sliding surface as the bearing rotates. The seal ball bearing of patent document 1 can prevent invasion of foreign matter of a predetermined particle diameter, which causes early breakage of the bearing, and cope with high-speed operation, and can make a fluid lubrication state between the seal lip and the seal sliding surface, thereby significantly reducing the seal torque.

Patent document 1 International publication No. 2016/143786

However, CO ₂ The emission control requirements of the vehicle will become more stringent in the future, and the electric drive of the vehicle will be further advanced, so that the energy-saving running performance of the vehicle will be improved. Therefore, there is a tendency to use a low-viscosity lubricating oil for the drive motor and the transmission to suppress torque loss. In recent years, the kinematic viscosity at 40℃was 27mm ² A kinematic viscosity at 100℃of 7.0mm or less ² The case of lubricating oil of/s or less increases. When such a low-viscosity lubricating oil is supplied to the ball bearings provided in the drive motor and the transmission, stirring resistance inside the bearings is effectively reduced, but on the other hand, there is an increased possibility that oil film interruption occurs in the elastic contact region between the balls and the bearing rings during high-speed rotation, and the oil film is engaged (japanese: accessory ku kono).

In addition, if a ball bearing is equipped with a cover member such as a seal or a shroud that suppresses inflow of lubricating oil into the bearing, stirring resistance is effectively reduced, but on the other hand, in the case of low-viscosity lubricating oil in recent years, the possibility of the above-described seizure is further increased.

In addition, when a ball bearing is assembled to a drive motor or a transmission connected thereto, a potential difference may occur between a shaft and a housing via the ball bearing, and thus, there is a possibility that an environment in which electric erosion occurs in an elastic contact region between a steel ball and a bearing ring may be used.

Disclosure of Invention

In view of the above-described background, an object of the present invention is to achieve both improvement in low torque performance and prevention of damage of a ball bearing supporting a rotary shaft included in a vehicle driving motor or a transmission connected to the vehicle driving motor.

In order to achieve the above object, the present invention provides a ball bearing for supporting a rotary shaft included in a vehicle driving motor or a transmission connected to the vehicle driving motor, comprising: 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 a cover member for suppressing inflow of the lubricating oil from the outside of the bearing to the inside of the bearing, wherein the balls are made of a material other than steel, and the internal clearance of the bearing during operation is set to a value of more than 0 μm at 80 ℃ or more, and the kinematic viscosity of the lubricating oil supplied to the inside of the bearing at 100 ℃ is 7.0mm ² And/s or less.

As described above, when a ball made of a material different from steel is used for the ball bearing for supporting the rotary shaft included in the vehicle drive motor or the transmission connected to the vehicle drive motor, even if oil film interruption occurs in the elastic contact area between the ball and the bearing ring during high-speed operation, the ball and the bearing ring made of different materials do not adhere (japanese: dissolution), and seizure resistance is improved as compared with the ball made of steel. In addition, if the internal play of the bearing during operation at 80 ℃ or higher is set to a value greater than 0 μm, early damage caused by the negative running play during high-speed rotation can be avoided. Because of this, even if low-viscosity lubricating oil or thinning of the lubricating oil is used, damage to the balls and the bearing rings can be prevented. On the basis of this, under the condition that inflow of lubricating oil is suppressed by the cover member, the kinematic viscosity at 100℃is 7.0mm ² A low viscosity lubricating oil of not more than/s, whereby stirring resistance can be reduced well and reduction of bearing torque can be achieved. In this way, the low torque performance of the ball bearing supporting the rotation shaft of the motor for driving the vehicle and the like can be improved and damage can be prevented.

Here, the vehicle driving motor according to the present invention is a vehicle driving motor corresponding to at least one of an electric device that converts electric energy to output rotation that becomes a driving source of a vehicle, and an electric device that converts input rotation into electric energy at the time of regenerative braking of the vehicle.

The transmission according to the present invention is a device for converting an input rotational speed and transmitting the converted rotational speed to an output side, and includes a continuously variable transmission device in which a speed conversion ratio (reduction ratio, gear ratio) is continuously variable, and a fixed ratio transmission device in which a speed conversion ratio is fixed, and includes a device called a speed reducer or a speed increaser in which only one of the speed conversion ratios is included.

The value of the kinematic viscosity in the present invention is a value obtained by measuring "kinematic viscosity test method" specified in "crude oil and petroleum product-kinematic viscosity test method and viscosity index calculation method" according to JIS K2283:2000 ".

Preferably, the balls are made of ceramic. The ceramic balls are insulators, and no electrolytic corrosion occurs in the elastic contact area. Further, if the ceramic balls are used, the loss (elastic hysteresis and differential sliding) in the elastic contact area between the balls and the bearing ring is reduced as compared with the steel balls, and therefore, the bearing torque can be reduced.

The cross-sectional shape of the track groove of each of the inner and outer bearing rings is preferably an arc shape defined by a diameter equal to or less than 1.1 times the diameter of the ball. Such an arc shape is suitable for suppressing the surface pressure of the elastic contact area between the ball and the bearing ring and reducing the bearing torque.

Preferably, the cover member is attached to one of the inner and outer bearing rings, the cover member includes a seal lip that slides in a circumferential direction with respect to a seal sliding surface provided on the other of the inner and outer bearing rings, and the seal lip includes a plurality of protrusions arranged in the circumferential direction, the plurality of protrusions being provided: gaps are formed between the circumferentially adjacent projecting portions, which communicate with the inside and outside of the bearing, and the sealing lip and the sealing sliding surface are brought into a fluid lubrication state by an oil film of lubricating oil carried from the gaps to between the projecting portions and the sealing sliding surface as the bearing rotates. In this way, it is possible to prevent the entry of foreign matter of a predetermined particle diameter and the inflow of lubricating oil, which would cause early breakage of the ball bearing, by the cover member, and to realize high-speed operation and low sealing torque, which are not inferior to those of the non-contact seal.

The holder is preferably a crown-type holder made of synthetic resin. Such a retainer is lightweight and excellent in self-lubricating property as compared with a wave-shaped retainer made of a steel plate, and is therefore suitable for realizing reduction in bearing torque.

In the present invention, the synthetic resin is a concept including a fiber reinforced resin. The synthetic resin is preferably composed of a fiber-reinforced polyamide resin or a fiber-reinforced polyphenylene sulfide resin. In this way, the crown holder has good resistance to deformation by centrifugal force, and is therefore suitable for high-speed rotation.

In addition, it is preferable that grease is enclosed in the bearing as an initial lubricant, and the enclosed amount of the grease is 5 to 20% by volume of the total volume of the bearing. In this way, the insufficient lubrication at the initial stage of the ball bearing operation can be suppressed, and the stirring resistance of the grease can be suppressed.

It is preferable to use at least one of nitrile rubber, acrylic rubber, fluororubber, cold-rolled steel sheet and stainless steel sheet as the material of the cover member. In this way, the cover member can be manufactured from a common material as the material of the seal and the cover.

Preferably, the balls are made of nitride-based ceramics. Nitride-based ceramics are suitable because they are lightweight, have high strength, and have excellent mechanical properties such as high toughness.

The present invention can achieve both improvement in low torque performance and prevention of damage by employing the above-described structure, in which the ball bearing supports a rotary shaft included in a vehicle driving motor or a transmission connected to the vehicle driving motor.

Drawings

Fig. 1 is a cross-sectional view showing a ball bearing according to a first embodiment of the present invention.

Fig. 2 is a schematic diagram showing a use example of the ball bearing of fig. 1.

Fig. 3 is an enlarged partial cross-sectional view of line III-III of fig. 1.

Fig. 4 is a bar chart showing the calculation result of the bearing torque.

Fig. 5 is a bar graph showing test results of bearing torque.

Fig. 6 is a bar graph showing other calculation results of the bearing torque.

Fig. 7 is a cross-sectional view showing a ball bearing according to a second embodiment of the present invention.

Detailed Description

A sealed bearing according to a first embodiment of the present invention will be described with reference to fig. 1 to 6 of the drawings.

The ball bearing 1 shown in fig. 1 is constituted by: an inner bearing ring 2; an outer bearing ring 3; a plurality of balls 4 interposed between the inner bearing ring 2 and the outer bearing ring 3; a cage 5 that holds the plurality of balls 4; and cover members 6 mounted on both sides of one bearing ring 3 among the inner and outer bearing rings.

The ball bearing 1 is a double-seal deep groove ball bearing.

Hereinafter, a direction along a bearing center axis (not shown) of the ball bearing 1 will be referred to as an "axial direction". The direction perpendicular to the axial direction is referred to as a "radial direction". In addition, a direction along a circumference around the bearing center axis is referred to as a "circumferential direction". In fig. 1, the bearing center axis is the center axis of the inner bearing ring 2 as a rotating ring. Fig. 1 shows a section of an imaginary plane containing the central axis of the bearing. The axial direction corresponds to the left-right direction in fig. 1, and the radial direction corresponds to the up-down direction in fig. 1 and 3.

The inner bearing ring 2 is formed of a steel annular member having a raceway groove 2a on the outer peripheral side thereof, which contacts the balls 4. The inner bearing ring 2 is fitted to the rotation shaft S at its inner periphery. The outer bearing ring 3 is formed of a steel annular member having a track groove 3a on the inner peripheral side thereof, which is in contact with the balls. The outer bearing ring 3 is attached to a member that receives a load from the rotation shaft, such as a housing or a gear.

The rotation shaft S is included in a vehicle driving motor or a transmission connected to the vehicle driving motor, and is, for example, a motor shaft serving as a rotation center of a rotor provided in the vehicle driving motor, an input shaft provided in the transmission for rotation input, an output shaft for rotation output, and an intermediate transmission shaft.

Fig. 2 shows an example of a rotation transmission device provided with: a vehicle driving motor 20; a transmission 30 connected to the vehicle driving motor 20; and a ball bearing 1 for rotating shaft S included in motor 20 or transmission 30 for driving the vehicle ₂₀ 、S ₃₁ 、S ₃₂ And supporting. The rotation transmitting device illustrated in the drawing is assembled to a drive system of a vehicle. The transmission 30 includes: a plurality of rotation shafts S ₃₁ ～S ₃₃ The method comprises the steps of carrying out a first treatment on the surface of the Gears G1 to G3 provided on the respective rotation shafts S ₃₁ ～S ₃₃ The method comprises the steps of carrying out a first treatment on the surface of the And a plurality of ball bearings 1 supporting the rotation shaft S ₃₁ ～S ₃₂ . Rotation axis S ₃₁ And a rotation shaft S of the vehicle driving motor 20 ₂₀ And integrally rotating. Rotation axis S ₃₃ Is supported by a plurality of tapered roller bearings.

When the vehicle driving motor 20 is a driving source, the transmission 30 is driven from the rotation shaft S ₂₀ Input to the rotary shaft S ₃₁ Is decelerated from the rotation of the rotation shaft S ₃₃ An output gear reducer. When the vehicle driving motor 20 is a regenerative brake, the transmission 30 is configured to input the regenerative brake from the traveling wheel side to the rotation shaft S ₃₃ Is accelerated from the rotation axis S ₃₁ And an output gear speed increaser.

The internal bearing play in the operation of the ball bearing 1 shown in fig. 2 is set to a value of more than 0 μm at 80 ℃. Here, the bearing internal play refers to a movement amount in a case where one of the inner and outer bearing rings is moved in a state where the other is fixed. The case of moving the other in the radial direction is referred to as a radial internal play, and the case of moving in the axial direction is referred to as an axial internal play. When the rotation transmission device is operated, if the ball bearings 1 are all at 80 ℃ or higher, the state in which either the radial internal play or the axial internal play of the ball bearings 1 exceeds 0 μm is continued.

The ball 4 shown in fig. 1 is composed of spherical rolling elements that revolve while rotating between the inner and outer raceway grooves 2a, 3 a. The balls 4 are composed of a material other than steel. Nitride ceramics (Si ₃ N ₄ ) As a material thereof. Ceramics other than nitride may be used as the material constituting the ball 4.

The cross-sectional shape of each of the inner and outer rail grooves 2a, 3a corresponds to the shape of each of the generatrix of the rail grooves 2a, 3a on the virtual plane shown in fig. 1. The cross-sectional shape of the track groove 2a is an arc shape defined by a diameter 1.1 times or less the diameter of the ball 4. The cross-sectional shape of the track groove 3a is also an arc shape defined by a diameter 1.1 times or less the diameter of the ball 4.

The cage 5 is constituted by an annular bearing member that holds a plurality of balls 4 interposed between the inner and outer raceway grooves 2a, 3a at predetermined circumferential intervals. The holder 5 illustrated in the drawing is a wave-shaped holder formed by joining a pair of wave-shaped pressing members made of steel plate.

The cover member 6 divides a bearing outer portion and a bearing inner portion 7 which are the circumferences of the ball bearings 1. The bearing inner portion 7 is an annular space formed between the inner and outer bearing rings 2, 3 over the entire circumference.

Lubricating oil (not shown) is supplied to the ball bearing 1 from outside the bearing. Examples of the lubrication method include a pouring method of pouring a lubricant into the ball bearing 1 and an oil bath method of immersing the lower portion of the ball bearing 1 in the lubricant.

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

The cover member 6 suppresses the following: foreign matter intrudes into the bearing interior 7 from the outside of the bearing, lubricating oil supplied from the outside of the bearing to the ball bearing 1 flows into the bearing interior 7, and grease G leaks out of the bearing. The cover member 6 does not seal the bearing inner portion 7 from the bearing outer portion in a fluid-tight manner.

One bearing ring 3 of the inner and outer bearing rings is formed with a seal groove 3b holding the cover member 6. The cover member 6 is attached to the bearing ring 3 by pressing the peripheral edge portion on the bearing ring 3 side into the seal groove 3b.

The cover member 6 of the illustrated example has a core 8 formed of a metal plate, and a seal lip 9 formed of an elastic material. The core bar 8 is constituted by a pressed part. Examples of the elastic material include a vulcanization-molded rubber material, an elastomer equivalent to the rubber material, and the like. Examples of the rubber material include nitrile rubber (NBR), acrylic rubber (ACM), and Fluororubber (FKM). Examples of the metal sheet include a cold-rolled steel sheet and a stainless steel sheet.

In the other bearing ring 2 of the inner and outer bearing rings opposite to the one bearing ring 3, a seal sliding surface 2b that slides in the circumferential direction with respect to the seal lip 9 is formed. The seal sliding surface 2b is cylindrical in shape along the circumferential direction.

As shown in fig. 1 and 3, the seal lip 9 has a plurality of protrusions 9a arranged in the circumferential direction. The plurality of protrusions 9a are provided as: gaps 10 are formed between the circumferentially adjacent protruding portions 9a to communicate with the bearing inner portion 7 and the outside, and the sealing lip 9 and the sealing sliding surface 2b are brought into a fluid lubrication state by an oil film of lubricating oil (shown by dot patterns in fig. 3) carried in between the protruding portions 9a and the sealing sliding surface 2b from the gaps 10 in accordance with the bearing rotation of the ball bearing 1.

The cover member 6 allows the lubricant to flow between the bearing inner portion 7 and the outside through the slit 10 which prevents the intrusion of foreign matter having a predetermined particle diameter. Therefore, the oil film is formed thicker by the wedge effect when the lubricating oil is brought between the protrusion 9a and the seal sliding surface 2b with the rotation of the bearing. When the circumferential velocity of the relative rotation between the seal lip 9 and the seal sliding surface 2b (in fig. 3, the direction of the shear head a is assumed) reaches a predetermined magnitude, the respective protrusions 9a and the seal sliding surface 2b are completely separated by the oil film, and the seal lip 9 and the seal sliding surface 2b are brought into a completely separated fluid lubrication state which continues at a circumferential velocity equal to or higher than this. Therefore, the sealing torque in the ball bearing 1 is reduced to be equal to or higher than the predetermined peripheral speed, for example, 0.2m/s or higher than the case where the noncontact seal is used.

The cover member 6 is disclosed in patent document 1, and thus a detailed description thereof is omitted. The protrusions 9a may be arranged at uniform intervals throughout the entire circumference. A groove extending in the circumferential direction may be formed at least one portion of the protruding portion 9a. The protrusion 9a may have a wedge-like slit formed between the seal sliding surface 2b and the protrusion 9a side. The protrusion 9a may have an R shape extending in a direction perpendicular to the circumferential direction and gradually approaching the seal sliding surface 2b toward the center of the circumferential width of the protrusion 9a. The height and pitch of the protruding portions 9a may be set to prevent the intrusion of foreign matter having a particle diameter exceeding 0.05mm, which causes early breakage of the ball bearing 1, and may be set to, for example, 0.05mm or more or 0.05mm or less.

The kinematic viscosity at 100℃of the lubricating oil supplied to the bearing interior 7 was 7.0mm ² And/s or less.

After the start of the operation of the ball bearing 1, the lubricating oil supplied from the outside of the bearing flows into the bearing interior 7 from the gap 10 between the cover member 6 and the seal sliding surface 2b earlier. Therefore, if the amount required for initial lubrication is ensured, the smaller the sealed amount of the grease G, the more effective the reduction of the bearing torque. In order to achieve both the initial lubrication purpose and the suppression of the bearing torque, the sealing amount of the grease G is set to 5 to 20% by volume of the total space volume of the bearing. Here, the total bearing space volume is obtained by subtracting the volume of the space in which the balls 4 and the retainer 5 revolve from the bearing interior 7 (sealed space) enclosed by the cover members 6 provided at the both axial ends of the inner and outer bearing rings 2, 3, respectively, and thus refers to the space volume in the state where the ball bearing 1 is stopped.

As described above, in the ball bearing 1, the balls 4 are made of nitride-based ceramic (Si ₃ N ₄ ) And the bearing torque can be reduced. Namely, nitride-based ceramics (Si ₃ N ₄ ) Has a density of 3.304g/cm ³ While the density of the bearing steel (SUJ 2) was 7.8g/cm ³ . The nitride-based ceramic had a longitudinal elastic modulus of 315GPa, and the bearing steel had a longitudinal elastic modulus of 210GPa. The poisson ratio of the nitride-based ceramic was 0.25, and the poisson ratio of the bearing steel was 0.3. In addition, the thermal expansion coefficient of the nitride-based ceramic is 3.2 (×10) ^－6 Per c), whereas the coefficient of thermal expansion of the bearing steel is 12.5 (×10) ^－6 /(deg.C). The nitride-based ceramic has a thermal conductivity of 0.07Cal/cm·s·DEG C, and the bearing steel has a thermal conductivity of 0.1 to 0.12Cal/cm·s·DEG C. As is clear from the comparison of the above values, in general, since the ceramic balls have a larger longitudinal elastic modulus and higher rigidity than the steel balls, the elastic hysteresis and differential sliding in the elastic contact area between the balls 4 and the bearing rings 2 and 3 are reduced, and the bearing torque is reduced.

The ceramic ball 4 shown in fig. 1 is not conductive as compared with a steel ball. Therefore, the ball bearing 1 can also be prevented from being corroded.

The ceramic ball 4 and the steel bearing rings 2 and 3 are made of different materials, and therefore, they are not adhered to each other. Therefore, the seizure resistance of the elastic contact area between the ball 4 and the bearing rings 2, 3 is excellent as compared with the steel ball.

The ceramic ball 4 has higher rigidity than the steel ball.

Fig. 4 shows a nitride-based ceramic (Si ₃ N ₄ ) The results of calculation of the bearing torque were obtained in the case of the ball 4 produced and in the case of the ball produced from steel (steel subjected to standard heat treatment for SUJ 2) as a comparative example. Respectively aiming at the types of the ball bearings: 6806. 6006, 6306. The calculation condition is the bearing rotation speed: 5000min ^－1 Radial load Fr:730N (model 6806 rated static load)20% of load Cor), axial load Fa:0N, lubricating oil: ISO viscosity VG10.

As can be seen from fig. 4, in the calculation results of any model, the bearing torque using the ceramic balls was small. This result is considered to be because the ceramic balls have a smaller specific gravity than the steel balls, and therefore the influence of centrifugal force during rotation of the bearing is reduced, and the longitudinal elastic modulus is increased and the poisson ratio is reduced, and therefore differential sliding, rotation, rolling viscous resistance, and elastic hysteresis loss are reduced.

Further, by providing the cover member 6, the inflow amount of the lubricating oil into the bearing interior 7 is reduced, and the stirring resistance is also reduced, so that it is possible to prevent damage to the bearing due to foreign matter and reduce the bearing torque.

Here, since the cover member 6 included in the ball bearing 1 shown in fig. 1 has a sealing torque equal to or higher than the non-contact seal at a predetermined peripheral speed, a test for measuring the bearing torque was performed in the case of the ball bearing 1 (with a seal) including the non-contact seal as the cover member and in the case of the open bearing (without a seal) as the comparative example. The results of this test are shown in fig. 5. The test was performed separately for ball bearing model 6308. The test conditions were bearing rotational speed: 754min ^－1 Radial load Fr:754N, axial load Fa:0N, lubricating oil: CVT fluid, lubrication method: oil bath (height at which the oil level crosses the lowermost ball).

As is clear from fig. 5, the ball bearing having the noncontact seal as the cover member is significantly smaller than the open bearing with respect to the bearing torque. This is considered to be because the inflow of the lubricating oil into the bearing is suppressed by the cover member, and the torque loss in the bearing due to the stirring of the lubricating oil is reduced.

In particular, the cover member 6 of the ball bearing 1 shown in fig. 1 exhibits low torque performance comparable to a non-contact seal and a shield, and is therefore suitable for preventing invasion of foreign matter of a predetermined particle size, which causes early damage, and for suppressing inflow of lubricating oil.

The advantages and disadvantages of the open bearing provided with the steel ball, the bearing provided with the steel ball and the contact seal, and the ball bearing 1 shown in fig. 1 are summarized in terms of the score table, as shown in table 1.

TABLE 1

Bearing specification

High speed rotatability

Low torque performance

Resistance to electrolytic corrosion

Foreign matter life

Seizure resistance

Rigidity of

Steel ball/open

△

〇

×

△

Steel ball contact seal

×

〇

△

Ball bearing 1

◎

○

In addition, the kinematic viscosity at 100℃was 7.0mm ² The lubricating oil of/s or less is suitable for suppressing the shearing resistance of the lubricating oil to achieve reduction of bearing torque. The shear resistance is generally obtained by the following equation 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 becomes small, the oil viscosity coefficient η and the oil film thickness h become small, so the shear resistance F becomes small.

The cross-sectional shape of the inner and outer raceway grooves 2a, 3a is an arc shape defined by a diameter equal to or smaller than 1.1 times the diameter of the ball 4, whereby the bearing torque can be reduced while suppressing the surface pressure in the elastic contact area between the ball 4 and the bearing rings 2, 3.

The bearing torque is calculated by variously changing the groove diameters of the inner and outer raceway grooves. The result of this calculation is shown in fig. 6. For the type of ball bearing: 6006 performs the calculation separately. The calculation condition is the bearing rotation speed: 5000min ^－1 Radial load Fr:730N, axial load Fa:0N, lubricating oil: ISO viscosity VG10 (JIS K2001:1993). The diameter of the ball is constant.

As is apparent from fig. 6, the bearing torque tends to decrease as the groove diameter of the inner and outer raceway grooves increases. This is considered to be because the larger the difference in curvature between the ball and the track groove is, the smaller the area of the elastic contact region is, contributing to the suppression of loss in this case.

However, the load received by the bearing provided in the transmission of the vehicle is about 35% of the rated dynamic load in terms of the radial load and the axial load according to the past results and the like. In this case, if the groove diameter of the inner and outer raceway grooves exceeds 1.1 times the diameter of the balls, the surface pressure of the elastic contact region exceeds 4200MPa, which is a reference for the rated static load. In addition, the load received by the bearing provided in the speed increaser/decreaser serving as a regenerative braking system of the vehicle is about 50% of the rated dynamic load in terms of the past results, 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 diameter of the balls, the surface pressure of the elastic contact region exceeds 4200MPa, which is a reference for the rated static load. In view of the above, it is considered that the groove diameter of the inner and outer raceway grooves is preferably 1.1 times or less the diameter of the balls in order to prevent damage and reduce torque.

In this way, the ball bearing 1 shown in fig. 1 to 3 rotates the shaft S included in the vehicle driving motor 20 or the transmission 30 connected to the vehicle driving motor 20 ₂₀ 、S ₃₁ 、S ₃₂ The bearing is supported by the ball 4 made of a material different from steel which is the material of the inner and outer bearing rings 2, 3, so that even if the oil film is broken in the elastic contact area between the ball 4 and the bearing rings 2, 3 during high-speed operation, the ball 4 and the bearing rings 2, 3 made of different materials are not adhered, and the seizure resistance is improved. Further, since the internal bearing play of the ball bearing 1 is set to a value of more than 0 μm when operating at 80 ℃ or higher, early damage caused by the negative operating play can be avoided when rotating at high speed. Because of this, even if low-viscosity lubricating oil or thinning of the lubricating oil is used in the ball bearing 1, damage to the balls 4 and the bearing rings 2 and 3 can be prevented. On the other hand, the ball bearing 1 has a kinematic viscosity of 7.0mm when supplied with a lubricant oil at 100℃under the condition that the inflow of the lubricant oil is suppressed by the cover member 6 ² A low viscosity lubricating oil of not more than/s, whereby stirring resistance can be reduced well and reduction of bearing torque can be achieved. In this way, the rotary shaft S of the vehicle driving motor 20 and the like is supported ₂₀ The ball bearing 1 can be used for bothImproving low torque and preventing damage.

In addition, the ball bearing 1 is made of ceramic by the balls 4, and the balls 4 serve as insulators, so that no electrolytic corrosion occurs in the elastic contact area between the balls 4 and the bearing rings 2, 3. Further, when the balls 4 made of ceramic are used, the loss (elastic hysteresis and differential sliding) in the elastic contact area between the balls 4 and the bearing rings 2 and 3 is reduced as compared with the case of using balls made of steel, and therefore, the ball bearing 1 can reduce the bearing torque due to these.

In addition, since the cross-sectional shapes of the track grooves 2a and 3a of the inner and outer bearing rings 2 and 3 of the ball bearing 1 are circular arcs defined by diameters equal to or smaller than 1.1 times the diameter of the ball 4, respectively, it is possible to prevent adverse effects on bearing life by suppressing the surface pressure of the elastic contact areas between the ball 4 and the bearing rings 2 and 3, and to reduce bearing torque.

Further, by providing the cover member 6 for realizing the fluid lubrication of the seal lip 9 against the seal sliding surface 2b, the ball bearing 1 can suppress the invasion of foreign matter of a predetermined particle diameter and the inflow of lubricating oil, which would cause early breakage of the ball bearing 1, by the cover member 6, and realize high-speed operation and low sealing torque, which are not inferior to those of the noncontact seal.

In addition, the ball bearing 1 has the grease G enclosed in the bearing interior 7 as an initial lubricant in an amount of 5 to 20% by volume of the total space volume of the bearing, whereby insufficient lubrication at the initial stage of operation of the ball bearing 1 can be suppressed and stirring resistance of the grease G can be suppressed.

In addition, the ball bearing 1 uses at least one of nitrile rubber, acrylic rubber, fluororubber, cold-rolled steel sheet, and stainless steel sheet as the material of the cover member 6, so that the cover member 6 can be manufactured using a usual material as the material of the seal and the boot.

The balls 4 are made of nitride-based ceramics, and are excellent in combination of mechanical properties such as light weight, high strength, and high toughness, and therefore are suitable for high-speed rotation.

In the first embodiment, the holder 5 is provided as a wave-shaped holder, but the holder may be of other forms. As an example, fig. 7 shows a ball bearing 40 according to a second embodiment. Further, only the differences from the first embodiment will be described here.

One bearing ring 41 of the inner and outer bearing rings of the ball bearing 40 and the other bearing ring 42 of the inner and outer bearing rings correspond to the bearing ring with the shield. The holder 43 is constituted by a crown-type holder formed of synthetic resin. The synthetic resin is composed of a fiber-reinforced polyamide resin or a fiber-reinforced polyphenylene sulfide resin.

A shroud groove 41a is formed in one bearing ring 41, and a cover member 44 is attached thereto. The other bearing ring 42 of the inner and outer bearing rings is formed with an entire circumferential groove 42a forming a labyrinth gap between the bearing ring 42 and the cover member 44.

The cover member 44 is constituted by a non-contact type shield formed of a cold-rolled steel sheet or a stainless steel sheet.

The ball bearing 40 is sprayed with lubricating oil from the right side in the drawing. The inflow of the lubricating oil can be effectively suppressed only by providing the cover member 44 on the right side in the drawing of the ball bearing 40.

Since the ball bearing 40 includes the crown-shaped retainer 43 made of synthetic resin, the ball bearing is a lightweight retainer 43 having excellent self-lubricating properties as compared with a wave-shaped retainer made of steel plate, and is suitable for realizing reduction of bearing torque.

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

The presently disclosed embodiments are considered in all respects as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Description of the reference numerals

1. 40 … ball bearings; 2. 3, 41, 42 … bearing rings; 2a, 3a … track grooves; 2b … sealing the sliding surface; 4 … balls; 5. 43 … retainer; 6. 44 … cover member; 7 … bearing interiors; 8 … core; 9 …A sealing lip; 9a … projections; 10 … slit; 20 … vehicle drive motor; 30 … transmission; s, S ₂₀ 、S ₃₁ 、S ₃₂ … axis of rotation.

Claims

1. A ball bearing for supporting a rotary shaft included in a motor for driving a vehicle or a transmission connected to the motor for driving the vehicle, characterized in that,

the device is provided with: an inner bearing ring; an outer bearing ring; a plurality of balls interposed between the inner bearing ring and the outer bearing ring; a retainer that retains the plurality of balls; and a cover member for inhibiting the inflow of lubricating oil from the outside of the bearing to the inside of the bearing,

the balls are composed of a material other than steel,

the internal play of the bearing during operation is set to a value of more than 0 μm at 80 ℃ or higher,

the kinematic viscosity at 100℃of the lubricating oil supplied to the inside of the bearing was 7.0mm ² And/s or less.

2. The ball bearing of claim 1, wherein the ball bearing is configured to rotate about a rotational axis,

the balls are composed of ceramic.

3. Ball bearing according to claim 1 or 2, characterized in that,

the cross-sectional shape of the track groove of each of the inner bearing ring and the outer bearing ring is circular arc-shaped defined by a diameter 1.1 times or less the diameter of the ball.

4. A ball bearing according to any one of claim 1 to 3,

the cover member is mounted to one of the inboard bearing ring and the outboard bearing ring,

the cover member has a seal lip that slides in a circumferential direction with respect to a seal sliding surface provided at the other of the inner bearing ring and the outer bearing ring,

the seal lip has a plurality of protrusions arranged in a circumferential direction, the plurality of protrusions being provided as: gaps are formed between the circumferentially adjacent projecting portions, which communicate with the inside and outside of the bearing, and the sealing lip and the sealing sliding surface are brought into a fluid lubrication state by an oil film of lubricating oil carried from the gaps to between the projecting portions and the sealing sliding surface as the bearing rotates.

5. The ball bearing according to any one of claims 1 to 4, wherein,

the retainer is constituted by a crown-type retainer formed by synthetic resin.

6. The ball bearing of claim 5, wherein the ball bearing is configured to rotate about a rotational axis,

the synthetic resin is composed of a fiber-reinforced polyamide resin or a fiber-reinforced polyphenylene sulfide resin.

7. The ball bearing according to any one of claims 1 to 6, wherein,

the bearing is internally filled with grease as an initial lubricant, wherein the filling amount of the grease is 5-20% by volume of the total space volume of the bearing.

8. 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 sheet, and stainless steel sheet is used as a material of the cover member.

9. The ball bearing of claim 2, wherein the ball bearing is configured to rotate about a rotational axis,

the ball is made of nitride-based ceramic.