JP2015045397A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a rolling bearing that is used while being immersed in an ambient fluid.SOLUTION: A rolling bearing includes: an inner race 2; an outer race 4; multiple rolling elements 6 disposed between a raceway surface 2a of the inner race 2 and a raceway surface 4a of the outer race 4; and a holder 8 having a pocket 10 for storing the rolling elements 6. The rolling bearing is used in an environment being immersed in an ambient fluid. A groove 14 is provided at an inner periphery of the holder 8 in a circumferential direction, and a hole 12 which penetrates from the groove 14 to an outer peripheral surface of the holder 8 is provided.

Description

  The present invention relates to a rolling bearing and is not intended to be limited, but can be used for a rolling bearing used in a cryogenic fluid, for example. Here, the cryogenic fluid refers to a fluid in a temperature range of approximately 1K to 100K, and corresponds to liquid hydrogen, liquid oxygen, and the like.

  Bearings for rocket engine turbo pumps are used in an environment of extremely low temperature and high speed. That is, the liquid propellant handled by the turbo pump of the rocket engine is a so-called cryogenic fluid such as liquid hydrogen at about −253 ° C. or liquid oxygen at about −183 ° C. The liquid hydrogen turbo pump sucks cryogenic liquid hydrogen from the tank of the rocket and works to increase the pressure to about 300 atmospheres. The liquid oxygen turbopump plays a role of pressurizing cryogenic liquid oxygen to 180 atm or higher and feeding it into the combustion chamber of the engine.

  Since the turbo pump bearing supports the impeller shaft, the turbo pump bearing is used in a state where it is substantially 100% immersed in such a cryogenic fluid, and the cryogenic fluid also flows inside the bearing. Therefore, since a general oil lubrication cannot be employed in a turbo pump bearing, a cage having a solid lubricity has been developed to ensure lubricity.

  However, since a large hoop stress acts on the cage due to high-speed rotation, some reinforcement is required. The following is a conventional technique for securing the cage strength. Patent Document 1 (Japanese Patent Publication No. 2-20854) describes a bearing holder made of a composite material reinforced with glass fiber. Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-332899) discloses an electroless nickel composite plating film in which a cage is formed of a metal and the surface thereof includes nickel tetrafluoride ethylene resin powder as a main component. A solid lubricated rolling bearing is provided.

Japanese Patent Publication No. 2-20854 JP 2004-332899 A

  Since the bearing for a turbo pump of a rocket engine is used at a high speed, the hoop stress acting on the cage increases. For this reason, reliability of the cage strength is required. In the prior art, the cage itself is structurally reinforced, but the influence of the surrounding fluid is not considered.

  Therefore, an object of the present invention is to improve the reliability of the cage strength by utilizing the characteristics of the surrounding fluid for the rolling bearing used in a state immersed in the surrounding fluid.

Since the bearing is immersed in the surrounding fluid, the present invention positively utilizes the influence of the surrounding fluid that was not considered in the oil lubricated bearing when the surrounding fluid is a cryogenic fluid. This solved the problem.
Specifically, a cryogenic fluid used as a liquid propellant for a rocket is pressurized by a turbo pump to a considerably high pressure. In order to improve the reliability of the cage strength with respect to the prior art, it is necessary to pay attention to the fact that it exhibits different characteristics from oil-lubricated bearings because it is immersed in such a high-pressure ambient fluid. It is necessary to consider the shape of the cage so that it works effectively in terms of strength.

That is, the present invention includes an inner ring, an outer ring, a plurality of rolling elements interposed between a raceway surface of the inner ring and a raceway surface of the outer ring, and a cage having a pocket for accommodating the rolling elements, In a rolling bearing used in an environment immersed in a cage, a circumferential groove is provided on the inner circumference of the cage, and a hole penetrating from the groove to the outer circumferential surface of the cage is provided.

A substantially uniform pressure acts on the cage surface due to the effect of hydrostatic pressure, and the inner circumferential surface of the cage has a smaller surface area than the outer circumferential surface. As described above, since the surface area is different between the inner peripheral surface and the outer peripheral surface of the cage, the resultant force of the pressure acting on the outer peripheral surface is smaller than the resultant force of the pressure acting on the inner peripheral surface, and the force for contracting the cage Will occur. This force suppresses expansion of the cage during high-speed rotation and reduces hoop stress. However, there is a limit to increasing the difference in surface area between the inner and outer peripheral surfaces of the cage. Therefore, by utilizing the effect of the surrounding fluid, increasing the force in the direction of compressing the cage by increasing the outer diameter surface of the cage or reducing the inner diameter surface further increases the reliability of the cage strength. .

  According to the present invention, when the bearing immersed in the surrounding fluid rotates, the surrounding fluid is affected by the centrifugal force and flows from the inner diameter side to the outer diameter side through the hole provided in the cage. On the other hand, since the clearance (inner ring guide clearance) between the cage on the inner diameter side of the cage and the inner ring is narrowed, a structure in which ambient fluid does not easily flow is obtained. As a result, the pressure in the two grooves is reduced, the pressure difference between the inner diameter side and the outer diameter side of the cage becomes significant, and the force in the direction in which the cage is compressed increases. Accordingly, expansion of the cage is suppressed, and hoop stress is reduced.

(A) is a longitudinal cross-sectional view of a rolling bearing, (B) is the elements on larger scale of FIG. 1 (A). It is a cross-sectional view of the cage passing through the through hole. It is the partial expanded view which looked at the retainer from the inner diameter side. (A) and (B) are side views of a cage. (A) (B) is sectional drawing similar to FIG. 1 (A) which removed the outer ring | wheel of the rolling bearing. (A) is sectional drawing similar to FIG. 1 (A) which removed the outer ring | wheel of the rolling bearing, (B) is the elements on larger scale which show the time of normal temperature, (C) is the elements on larger scale which show at the time of cryogenic temperature.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking as an example a case where the present invention is applied to an angular ball bearing for a turbo pump.

  As shown in FIG. 1A, the angular ball bearing includes an inner ring 2, an outer ring 4, rolling elements 6, and a cage 8. A radial ball bearing having a nominal contact angle of more than 0 ° and 45 ° or less is called an angular contact ball bearing, and this type of single-row and double-row bearing excluding 3-point contact and 4-point contact is abbreviated as an angular ball bearing. The contact angle refers to an angle formed between a plane perpendicular to the center axis of the bearing (radial plane) and a line of action of a combined force of rolling element loads (force acting on the contact portion between the rolling elements and the raceway). In FIG. 1A, the contact angle is represented by the symbol α.

  For example, the material of the inner ring 2 and the outer ring 4 and the rolling element 6 is martensitic stainless steel. Alternatively, ceramics can be used for the rolling elements 6. Further, PTFE sputter coating may be applied to the raceway surface 2 a of the inner ring 2, the raceway surface 4 a of the outer ring 4, and the surfaces of the rolling elements 6. PTFE rolls to the rolling contact portion and performs a lubricating action.

  The inner ring 2 has a raceway surface 2 a on the outer periphery, the outer ring 4 has a raceway surface 4 a on the inner periphery, and a rolling element 6 is interposed between the raceway surface 2 a of the inner ring 2 and the raceway surface 4 a of the outer ring 4. . The inner ring 2 has shoulders 2b on both sides of the raceway surface 2a, and the cage 8 is guided by both shoulders 2b of the inner ring 2 (inner ring guide).

  The outer ring 4 is a so-called shoulder outer ring, and has a shoulder 4b on the contact angle side (right side in FIG. 1A), and the opposite shoulder is dropped to form a counterbore 4c.

  The cage 8 is a window-shaped resin cage, and has a plurality of pockets 10 arranged at predetermined intervals in the circumferential direction as shown in FIG. 2, and each pocket 10 penetrates the cage 8 in the radial direction. It has a cylindrical surface shape. When the surrounding fluid is a cryogenic fluid, a solid lubricant may be applied to the cage 8. Although it can select and employ | adopt from well-known solid lubricants, PTFE type synthetic resin is preferable in light of the use track record. In a turbo pump bearing that is immersed in a cryogenic fluid such as liquid hydrogen or liquid oxygen, the oil freezes and cannot be used as a lubricant, so a solid lubricant is employed.

  As shown in FIG. 3, two circumferential grooves 14 are formed on the inner periphery of the cage 8 with the pocket 10 interposed therebetween. The circumferential grooves 14 are arranged on both sides of the pocket 10 when viewed in the axial direction of the cage 8. As can be seen from FIG. 1B, through holes 12 extending in the radial direction from the bottom surface of each circumferential groove 14 to the outer peripheral surface of the cage 8 are provided. The positions of the through holes 12 are preferably equidistant in the circumferential direction and near the middle of adjacent pockets 10. As a result, in the illustrated example, the number of holes 12 is the same as the number of pockets 10.

  Since there is a difference in diameter between the inner peripheral surface and the outer peripheral surface of the cage 8, a difference in surface area occurs, and in the environment where hydrostatic pressure acts on the cage, the resultant force of the pressure received by the cage 8 from the surrounding fluid is The outer diameter side is larger than the inner diameter side. As a result, a force in the diameter reducing direction acts on the cage 8 to narrow the clearance between the inner peripheral surface of the cage 8 and the shoulder 2b of the inner ring 2, and fluid does not easily flow. In addition, the fluid flows out to the outer diameter side through the through hole 12 by the action of the centrifugal force accompanying the rotation of the bearing. Therefore, the internal pressure of the circumferential groove 14 is reduced. In this way, the force in the diameter reducing direction acts on the cage 8 more than the force in the compression direction of the conventional cage due to only the area difference between the inner circumferential surface and the outer circumferential surface of the cage. The force in the diameter reducing direction counteracts the hoop stress acting in the diameter expanding direction of the cage 8 and functions to suppress the hoop stress.

  Suppression of the hoop stress can be promoted by more effectively generating the above-described phenomenon of pressure increase on the outer diameter side and pressure decrease on the inner diameter side of the cage 8. Hereinafter, a specific configuration for that purpose will be described.

  As shown in FIG. 4, a plurality of stirring elements 8 b are provided on the side surface 8 a of the cage 8. Each stirring element 8b may be, for example, in the form of a plate-like protrusion protruding from the side surface 8a of the cage 8, or in the form of a groove formed in the side surface 8a. In short, it is only necessary that the flow of fluid from the inner diameter side to the outer diameter side of the cage 8 can be generated by the action of the centrifugal force accompanying the rotation of the cage 8. By doing so, the fluid in the vicinity of the side surface 8a of the cage 8 is positively moved to the outer diameter side to increase the pressure on the outer diameter side of the cage 8. A specific shape of such a stirring element 8b includes a radial shape (FIG. 4A) or a spiral shape (FIG. 4B). In the case of the spiral-shaped stirring element 8b, the counterclockwise direction of FIG. 4B is set to cause a fluid flow from the inner diameter side to the outer diameter side of the cage 8 as the cage 8 rotates. Make the direction of rotation.

  5 (A) and 5 (B) show a case where the through hole 12 has a uniform inner diameter in the longitudinal direction and a through hole in which the inner diameter gradually increases from the inner diameter side to the outer diameter side of the cage 8. Comparison is made with the case of 12a. In the latter case, the fluid flow in the through hole 12a by centrifugal force is promoted, and the inner diameter side of the cage 8 is further depressurized.

  Further, as shown in FIG. 6, an annular protruding edge is provided at the end of the shoulder 2b of the inner ring 2 that guides the cage 8, and a gap is provided between the side surface 8a of the cage 8 and the inner wall surface 2c of the annular protruding edge. Provide. The clearance is not shown.

  When the bearing is assembled, that is, at room temperature, as shown in FIG. 6B, a “positive” clearance exists between the inner diameter of the cage 8 and the outer diameter of the annular protrusion of the inner ring 2. , Enabling assembly.

  At the time of operation, that is, at an extremely low temperature, the linear expansion coefficient of the synthetic resin cage 8 is larger than the linear expansion coefficient of the metal inner ring 2, so that the inner diameter of the cage 8 is the inner ring 2 as shown in FIG. It becomes smaller than the outer diameter of the annular projecting edge. Accordingly, the cage 8 fits between the annular projecting edges of the inner ring 2, and a clearance is provided between the side surface 8a of the retainer 8 and the inner wall surface 2c of the annular projecting edge. This clearance is also not shown. As a result, it becomes difficult for fluid to flow into the inner diameter side of the cage 8, and the inner diameter side of the cage 8 is further depressurized.

  The effects of the above-described embodiment are summarized as follows.

  The rolling bearing according to the embodiment includes an inner ring 2, an outer ring 4, a plurality of rolling elements 6 interposed between the raceway surface 2 a of the inner ring 2 and the raceway surface 4 a of the outer ring 4, and a pocket 10 that accommodates the rolling element 6. It is based on a rolling bearing that is used in an environment immersed in an ambient fluid. And the groove | channel 14 of the circumferential direction is provided in the inner periphery of the holder | retainer 8, and the hole 12 penetrated from the groove | channel 14 to the outer peripheral surface of the holder | retainer 8 is provided.

By arranging the grooves 14 on both sides of the pocket 10 when viewed in the axial direction of the cage 8, the groove 14 has the effect of guiding the surrounding fluid from the inner diameter side to the outer diameter side of the cage 8 through the grooves 14 and the holes 12. It is exhibited in a balanced manner on both axial sides of the vessel 8.

It is preferable in terms of rotational balance of the cage 8 that the holes 12 are equally distributed in the circumferential direction of the cage 8 and the same number as the pockets 10 of the cage 8.

The hole 12 is preferably arranged in the middle of the adjacent pockets 10. Since the periphery of the pocket 10 is thin in order to form a pocket, a reduction in strength of the cage 8 can be avoided by providing the hole 12 in a portion between the pocket 10 and the pocket 10.

  By providing the stirring element 8 b on the side surface 8 a of the cage 8, a fluid flow from the inner diameter side to the outer diameter side of the cage 8 is generated by the action of centrifugal force accompanying the rotation of the cage 8, and the cage 8 The fluid in the vicinity of the side surface 8a can be positively moved to the outer diameter side to increase the pressure on the outer diameter side of the cage 8. The stirring elements 8b can be arranged in a radial or spiral shape, for example in the form of grooves or protrusions.

  If the inner diameter of the hole 12 is gradually increased toward the outer diameter of the cage 8, the flow of fluid in the through hole 12 a due to centrifugal force is promoted, and the inner diameter side of the cage 8 is further depressurized.

  By providing an annular projecting edge on the outer periphery of the end of the inner ring 2 and providing a clearance between the side surface 8b of the retainer 8 and the inner wall surface 2c of the annular projecting edge, the cage 8 and the inner ring 2 are operated during operation, that is, at extremely low temperatures. , The inner diameter of the cage 8 becomes smaller than the outer diameter of the annular projecting edge of the inner ring 2, and the retainer 8 fits between the annular projecting edges of the inner ring 2. As a result, it becomes difficult for fluid to flow into the inner diameter side of the cage 8, and the inner diameter side of the cage 8 is further depressurized.

When the ambient fluid is a cryogenic fluid, the oil freezes and cannot be used as a lubricant. Therefore, PTFE synthetic resin or other solid lubricant may be applied to the cage 8.
Further, the PTFE sputter coating may be applied to the raceway surface 2a of the inner ring 2, the raceway surface 4a of the outer ring 4, and the surface of the rolling element 6. By adopting such a configuration, PTFE is rolled to the rolling contact portion. To lubricate.

  The material of the inner ring 2, the outer ring 4, and the rolling element 6 can be made of martensitic stainless steel. Alternatively, if the material of the rolling element 6 is ceramics, the density of the ceramics is approximately 40% compared to steel, so that it is less susceptible to centrifugal force and is advantageous as a rolling element material for turbo pump bearings that rotate at high speed. It is.

  The surrounding fluid may be oil, in which case the rolling bearing is operated under oil lubrication. In other words, since the rolling bearing can be used even for applications involving cryogenic fluids, it can naturally be used even under oil lubrication.

  The rolling bearing of the embodiment can be used for a turbo pump of a rocket engine except that the surrounding fluid is oil. The turbo pump rolling bearing is highly reliable in terms of cage strength.

Although the embodiments of the present invention have been described based on the embodiments illustrated in the drawings, the present invention can be implemented with various modifications without departing from the scope of the claims.

2 inner ring 2a raceway surface 2b shoulder 2c inner wall surface of annular projecting edge 4 outer ring 4a raceway surface 4b counter bore 6 rolling element 8 cage 8a side surface 8b stirring element 10 pocket 12 through hole 14 circumferential groove

Claims (9)

In an environment immersed in an ambient fluid, comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the raceway surface of the inner ring and the raceway surface of the outer ring, and a cage having a pocket for accommodating the rolling elements. In the rolling bearing used,
The rolling bearing which provided the groove | channel of the circumferential direction in the inner periphery of the said holder | retainer, and provided the hole penetrated from the said groove | channel to the outer peripheral surface of the said holder | retainer. The rolling bearing according to claim 1, wherein the groove is located on both sides of the pocket when viewed in the axial direction of the cage. The rolling bearing according to claim 1, wherein the hole is located between adjacent pockets.   The rolling bearing according to any one of claims 1 to 3, wherein a stirring element in the form of a groove or a protrusion is provided on a side surface of the cage.   The rolling bearing according to any one of claims 1 to 4, wherein an inner diameter of the hole gradually increases toward an outer diameter of the cage.   The rolling bearing according to any one of claims 1 to 5, wherein an annular projecting edge is provided on an outer periphery of an end portion of the inner ring, and a gap is provided between a side surface of the cage and an inner wall surface of the annular projecting edge.   The rolling bearing according to any one of claims 1 to 6, wherein the surrounding fluid is a cryogenic fluid, and a solid lubricant is applied to the cage.   The rolling bearing according to any one of claims 1 to 7, wherein a PTFE sputter coating is applied to a raceway surface of the inner ring, a raceway surface of the outer ring, and a surface of the rolling element.   The rolling bearing according to any one of claims 1 to 8, which is used for a turbo pump of a rocket engine.

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