Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
  • F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
  • F16C19/14—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for both radial and axial load
  • F16C19/18—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for both radial and axial load with two or more rows of balls
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
  • F16C33/30—Parts of ball or roller bearings
  • F16C33/66—Special parts or details in view of lubrication
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
  • F16C33/72—Sealings
  • F16C33/76—Sealings of ball or roller bearings
  • F16C33/78—Sealings of ball or roller bearings with a diaphragm, disc, or ring, with or without resilient members
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/32—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings
  • F16J15/3204—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings with at least one lip
  • F16J15/3232—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings with at least one lip having two or more lips

Definitions

• This disclosure relates to a seal structure and a hub unit bearing.
• Hub unit bearings are equipped with a seal structure at the opening of the internal space between the inner surface of the outer ring and the outer surface of the hub to prevent the intrusion of muddy water and other foreign matter from the outside.
• JP 2022-155415 A discloses a seal structure in which the opening of the internal space of the hub unit bearing is sealed by having multiple seal lips slide against the lip sliding surfaces.
• single row rolling bearings, double row rolling bearings and other bearings may also be provided with a seal structure at the opening of the internal space.
• a seal structure may be provided at the boundary between the external space and the internal space.
• the seal structure comprises at least one seal lip, at least one lip sliding surface, and grease, and the at least one seal lip and the at least one lip sliding surface slide against each other via an oil film of the grease.
• the average height difference between the bottom and the opening edge of the multiple recesses is 1 ⁇ m or more and 10 ⁇ m or less.
• the ratio of the total opening area of the multiple recesses to the fixed area of the at least one lip sliding surface is 30% or more and less than 100%.
• the ratio can be preferably 30% or more and 90% or less, and more preferably 30% or more and 80% or less.
• At least a portion of the opening edge of the recess can be raised above a reference surface of the lip sliding surface where the recess is not formed.
• the seal structure according to one aspect of the present disclosure can reduce the seal torque.
• FIG. 7A to 7I are plan views showing nine examples of the opening shape of the recess.
• 8A and 8B are diagrams showing two examples in which a plurality of recesses are regularly arranged on the circumferential surface.
• 9A to 9C are diagrams showing three examples in which a plurality of recesses are regularly arranged on the axial side surface.
• 10A and 10B are diagrams showing two examples in which a plurality of recesses are arranged so that the proportion of the total opening area of the plurality of recesses to a fixed area of the lip sliding contact surface is large.
• FIG. 11 is a view corresponding to FIG. 4 and illustrating a seal structure according to a second example of an embodiment of the present disclosure.
• FIG. 12 is a schematic diagram showing a state in which cavitation occurs in the seal structure of the second example.
• FIG. 13 is a view corresponding to FIG. 12 and illustrating a seal structure according to a third example of an embodiment of the present disclosure.
• the seal structure 3 of this example is a machine element having a function of preventing the intrusion of muddy water or the like from the outside into the internal space 2, and can be applied to bearings such as the hub unit bearing 1, single row rolling bearings, double row rolling bearings, or various rotating machines. Note that, although not limited thereto, the following description refers to an example in which the seal structure 3 is applied to a seal structure that blocks an axially inner opening of the internal space 2 of an inner ring rotating type hub unit bearing 1 for a driving wheel, as shown in FIG.
• the rotating elements are formed from one of the inner member or outer member, and the non-rotating elements are formed from the other of the inner member or outer member.
• the device to which the seal structure 3 is applied has a structure in which rotating elements and non-rotating elements are arranged axially, the rotating elements are formed from a member on one axial side, and the non-rotating elements are formed from a member on the other axial side.
• At least one lip sliding surface 24 is formed on the circumferential surface and/or side surface of the other element that faces the seal lip 23, or is provided on a separate member that is supported and fixed to the circumferential surface and/or side surface of the other element.
• the lip sliding surface 24 is composed of a circumferential surface facing in the radial direction and/or a side surface facing in the axial direction.
• the lip sliding surface 24 preferably has good surface properties to ensure sliding with the seal lip 23.
• the separate member is preferably made of a metal plate with rust-resistant properties such as a ferritic stainless steel plate (SUS430) or an austenitic stainless steel plate (SUS304).
• SUS430 ferritic stainless steel plate
• SUS304 austenitic stainless steel plate
• At least one of the lip sliding surfaces 24 is characterized in that it has a plurality of recesses 35. That is, when the seal structure 3 has a plurality of seal lips 23, at least one of the seal lips 23 slides against the lip sliding surface 24 having a plurality of recesses 35 via an oil film of the grease 25. All of the lip sliding surfaces 24 corresponding to the plurality of seal lips 23 may have a plurality of recesses 35, or only a portion of the lip sliding surfaces 24 may have a plurality of recesses 35.
• the number of the seal lips 23 and the number of the lip sliding surfaces 24 are appropriately determined depending on the purpose and required performance of the device to which the seal structure 3 is applied, the arrangement of the seal structure 3 in the device, and the like.
• the lip sliding surfaces 24 when there are a plurality of lip sliding surfaces 24 corresponding to a plurality of seal lips 23, which lip sliding surface 24 is to have a plurality of recesses 35 is also appropriately determined depending on the purpose and required performance of the device.
• the multiple recesses 35 function to reduce the pressure of the oil film of the grease 25 passing through the recesses 35, and to increase the pressure of the oil film of the grease 25 at the position of the opening edge (ridge) on the forward side of the recess 35 in the direction of travel of the seal lip 23.
• the pressure of the oil film in the recess 35 falls below the cavitation pressure, cavitation occurs within the recess 35, and air bubbles 45 are generated in the oil film.
• the configuration (shape, size, number, etc.) of the multiple recesses 35 is appropriately set within a range in which the function of generating cavitation is achieved, depending on the application and required performance of the bearing or rotating machine to which the seal structure 3 of one embodiment of the present disclosure is applied.
• the configuration of the multiple recesses 35 is managed by the average height difference between the bottom and the opening edge of the multiple recesses 35, and the proportion of the total opening area of the multiple recesses to a certain area of the at least one lip sliding surface.
• the average height difference between the bottom and the opening edge of the multiple recesses 35 is 1 ⁇ m or more and 10 ⁇ m or less.
• the ratio of the total opening area of the multiple recesses 35 to the fixed area of at least one lip sliding surface 24 is 30% or more and less than 100%.
• seal structure 3 of this example we will explain the specific structure of the seal structure 3 of this example, with reference to an example in which the seal structure 3 is applied to an inner ring rotating type seal structure that blocks the axially inner opening of the internal space 2 of a hub unit bearing 1 for a driving wheel, and we will also explain the mechanism by which the apparent viscosity of the grease 25 decreases.
• the seal structure 3 of this example has at least one seal lip 23 and at least one lip sliding surface 24.
• the number of seal lips 23 is set appropriately depending on the application of the device to which the seal structure 3 is applied, and is not limited to this, but is preferably between one and three. Depending on the device to which the seal structure 3 is applied, if the number of seal lips 23 is more than three, the seal torque may increase. However, in the present disclosure, it is not prohibited to have four or more seal lips 23.
• one lip sliding surface 24 with which the single seal lip 23 slides has multiple recesses 35.
• all of the multiple lip sliding surfaces 24 with which the multiple seal lips 23 slide can be configured to have multiple recesses 35, or only some of the multiple lip sliding surfaces 24 can be configured to have multiple recesses 35.
• At least one seal lip 23 may be either a radial lip that slides against a radially facing circumferential surface, i.e., the outer or inner circumferential surface, or a thrust lip that slides against a side surface that faces in the axial direction.
• at least one seal lip 23 is configured as a radial lip
• at least one lip sliding surface 24 is configured as a radially facing circumferential surface
• at least one seal lip 23 is configured as a thrust lip
• at least one lip sliding surface 24 is configured as a side surface that faces in the axial direction.
• At least one seal lip 23 is composed of three seal lips 23a to 23c
• at least one lip sliding surface 24 is composed of three lip sliding surfaces 24a to 24c. Furthermore, all three lip sliding surfaces 24a to 24c have multiple recesses 35. Note that Figures 1 and 2 show the shapes of the seal lips 23a to 23c in their free states.
• seal lips 23a to 23c are provided on the seal member 29 of the seal ring 26.
• seal ring 26 is provided with a core metal 28.
• the core 28 is made of a metal plate such as a mild steel plate, and has a roughly L-shaped cross section.
• the core metal 28 comprises a fixed tube portion 30 having a cylindrical shape that is fitted and fixed to the axially inner end of the outer member 5, and a fixed circular ring portion 31 in the form of an inward flange that extends radially inward from the axially outer end of the fixed tube portion 30.
• the fixed ring portion 31 has a generally crank-shaped cross section.
• the seal lip 23c located furthest from the internal space 2 has its base end connected to the portion of the seal base 32 that covers the axially inner side of the fixed ring portion 31, and extends radially outward as it moves axially inward.
• the seal lip 23c is composed of a thrust lip.
• the axially inner end of the seal lip 23c, which is its tip, is in sliding contact with the lip sliding surface 24c.
• Such a seal lip 23c is called a side lip, and mainly prevents foreign matter from entering the internal space 2 from the external space.
• the lip sliding surfaces 24a to 24c can be provided on the outer peripheral surface of the inner member 6 or on a separate member supported and fixed to the inner member 6.
• the lip sliding surfaces 24a to 24c are composed of a reference surface 36 where no recesses 35 are formed, and a number of recesses 35 formed on the reference surface 36.
• the reference surface 36 is composed of a cylindrical surface centered on the central axis of the inner member 6 or the separate member, and when the lip sliding surfaces 24a to 24c are composed of side surfaces facing in the axial direction, the reference surface 36 is composed of a plane perpendicular to the central axis of the inner member 6 or the separate member.
• all three lip sliding surfaces 24a-24c correspond to the separate member and are provided on a slinger 27 that is fitted and fixed to the inner member 6. That is, the seal structure 3 in this example is composed of the seal lips 23a-23c that constitute the seal ring 26 and the lip sliding surfaces 24a-24c that constitute the slinger 27. The seal ring 26 and the slinger 27 constitute a combined seal ring.
• the slinger 27 has a rotating cylinder portion 33 and a rotating ring portion 34.
• the rotating cylinder portion 33 has a cylindrical shape and is fitted and fixed to the outside of the inner ring 17.
• the rotating cylinder portion 33 has, on its outer circumferential surface, a lip sliding surface 24a against which the seal lip 23a slides, and a lip sliding surface 24b against which the seal lip 23b slides. That is, the outer circumferential surface of the rotating cylinder portion 33 is configured as a cylindrical surface macroscopically (macroscopically), but due to the presence of multiple recesses 35 provided on the lip sliding surface 24a and the lip sliding surface 24b, it is configured as a non-cylindrical surface microscopically (microscopically).
• the rotating ring portion 34 has a disk shape and extends radially outward from the axially inner end of the rotating cylinder portion 33.
• the rotating ring portion 34 has a lip sliding surface 24c on its axially outer side against which the seal lip 23c slides. That is, the axially outer side of the rotating ring portion 34 is configured to be flat from a macroscopic perspective, but due to the presence of multiple recesses 35 provided on the lip sliding surface 24c, it is configured to be non-flat from a microscopic perspective.
• the lip sliding surfaces 24a to 24c refer to the range against which the seal lips 23a to 23c may slide, including the parts that may not be in sliding contact at the start of use but will be in sliding contact after a certain period of time has passed.
• the lip sliding surfaces 24a to 24c refer to the parts against which the seal lips 23a to 23c may slide at any time during the use of the hub unit bearing 1.
• the lip sliding surface 24a and the lip sliding surface 24b have a plurality of recesses 35 on a cylindrical reference surface 36.
• the lip sliding surface 24c has a plurality of recesses 35 on a planar reference surface 36.
• a recess 35 is provided on the entire outer peripheral surface of the rotating cylinder portion 33, including the lip sliding surface 24a and the lip sliding surface 24b.
• a recess 35 is provided on the entire axial outer surface of the rotating annular portion 34, including the lip sliding surface 24c.
• Each of the recesses 35 is composed of a depression 37 recessed below the reference surface 36 of the lip sliding surfaces 24a to 24c, and an opening edge (ridge) around it.
• the opening edge of the recess 35 exists at the same height as the reference surface 36.
• the recess 35 may have a raised portion as an optional component that is provided around the recess 35 and is raised above the reference surface 36. In this case, the opening edge of the recess 35 exists at the apex of the raised portion, which is at a higher height than the reference surface 36.
• the surface properties of the lip sliding surface 24 having multiple recesses 35 are controlled by the average height difference (H) between the bottom and the opening edge of the multiple recesses 35, and the proportion of the total opening area of the multiple recesses 35 to the fixed area of the lip sliding surface 24 having multiple recesses 35.
• the average value of the height difference (H) between the bottom and the opening edge is 1 ⁇ m or more and 10 ⁇ m or less, and preferably 2 ⁇ m or more and 5 ⁇ m or less. If the average value of the height difference (H) is less than 1 ⁇ m, the pressure of the oil film of the grease 25 cannot be sufficiently reduced at the position of the depression 37 of the recess 35, cavitation does not occur in the depression 37, and the viscosity of the grease 25 cannot be reduced. If the average value of the height difference (H) is greater than 10 ⁇ m, problems such as longer processing time may occur.
• the method for determining the height difference (H) of the recesses 35 and its average value is not particularly limited, and can be determined by any method. For example, it can be determined as follows. First, the lip sliding surfaces 24 (in this example, each of the three lip sliding surfaces 24a to 24c) are scanned with a surface roughness meter to measure the roughness curve of the lip sliding surfaces 24. After measuring the roughness curve of the lip sliding surfaces 24, the height difference (H) (see Figure 4) between the bottom and the opening edge of each recess 35 is determined. In other words, for each recess 35, the height difference between the bottom, which is the deepest part of the recess 37, and the opening edge is determined. In this example, the height difference between the bottom of the recess 37 and the reference surface 36 is determined.
• the average value of the height difference (H) for all the existing recesses 35 is calculated for each lip sliding surface (in this example, each of the three lip sliding surfaces 24a to 24c). If each of the multiple lip sliding surfaces 24 has multiple recesses 35, the average value of the height difference (H) can be the same for all lip sliding surfaces 24, or can be different for each lip sliding surface 24. In this case, the surface properties of the multiple lip sliding surfaces 24, each of which has multiple recesses 35, can be managed by the average value of the height difference (H) of the recesses 35 for the entire multiple lip sliding surfaces 24.
• the ratio of the opening area of the multiple recesses 35 to the fixed area S of the lip sliding surface 24 is 30% or more and less than 100%.
• the ratio is preferably 30% or more and 90% or less, and more preferably 30% or more and 80% or less. If the ratio is less than 30%, the amount of bubbles 45 generated by cavitation will be small, and problems may arise such as the viscosity of the grease 25 not being able to be sufficiently reduced.
• the width of the narrowest part of the opening of the recess 35 can be any width as long as it is possible to generate cavitation within the recess 35, but it is preferable that the width is greater than the height difference (H) of the recess 35.
• the width of the narrowest part of the opening of the recess 35 can be preferably greater than or equal to 30 ⁇ m and less than or equal to 100 ⁇ m.
• the width of the narrowest part of the opening of the recess 35 can also be less than the height difference (H) of the recess 35.
• the arrangement of the multiple recesses 35 is not particularly limited, and can be any arrangement, so long as it is possible to regulate the average value of the height difference (H) within a predetermined range and to regulate the ratio within a predetermined range.
• the multiple recesses 35 can be arranged regularly or irregularly. In any case, it is preferable that the multiple recesses 35 are formed so that the effect of reducing the viscosity of the grease 25 due to the occurrence of cavitation is approximately the same regardless of the circumferential position.
• the recesses 35 can be arranged so that they are located at the intersections of a square lattice when viewed from the axial direction, as shown in Figure 9 (A).
• the recesses 35 can be arranged so that they are located at the intersections of an equilateral triangular lattice when viewed from the axial direction, as shown in Figure 9 (B).
• the pitch (P) which is the distance between the centers of adjacent recesses 35, can be 50 ⁇ m or more and 80 ⁇ m or less.
• the sliding diameter which is the diameter of the portion where the seal lip 23 slides, is ⁇ 60 mm
• the number of recesses 35 will be 2300 or more and 3768 or less.
• multiple recesses 35 when multiple recesses 35 are arranged regularly on the side surface facing the axial direction, they can be arranged at multiple locations at equal radial intervals and at a fixed angle in the circumferential direction, as shown in Figure 9 (C).
• multiple types of recesses 35 each having a circular opening shape and different diameters can be combined and arranged. This allows the ratio of the total opening area of the multiple recesses 35 to the fixed area of the lip sliding surface 24 to be large, specifically, about 90% or more (effectively less than 100%).
• each of the multiple recesses 35 has a circular opening shape with the same diameter.
• the recesses 35 provided on the outer peripheral surface of the rotating cylinder portion 33, including the lip sliding surface 24a and the lip sliding surface 24b, are arranged so as to be located at the intersections of a square lattice when viewed from the radial direction.
• the recesses 35 provided on the axial outer surface of the rotating annular portion 34, including the lip sliding surface 24c, are arranged so as to be located at the intersections of a square lattice when viewed from the axial direction.
• the method for forming the recesses 35 is not particularly limited, and they can be formed by, for example, shot peening, laser processing, embossing transfer, etching, etc.
• Grease 25 is applied to the seal lip 23 to reduce the seal torque.
• the grease 25 is usually a seal grease that does not cause swelling or hardening of elastic materials (sealing materials) such as rubber and thermoplastic elastomers.
• the grease 25 is applied to the inner peripheral surfaces of each of the seal lips 23a to 23c. Therefore, the grease 25 lubricates the sliding portions between the seal lips 23a to 23c and the lip sliding surfaces 24a to 24c.
• the base oil of the grease 25 is accumulated in the annular interlip space 38a formed in the portion surrounded by the seal lip 23a, the seal lip 23b, and the outer peripheral surface of the fixed cylindrical portion 30.
• an annular interlip space 38b is also formed in the portion surrounded by the seal lip 23b, the seal lip 23c, and the axial outer surface of the rotating annular portion 34.
• the base oil of the grease 25 can be composed of, but is not limited to, mineral oil, synthetic hydrocarbon oil, or a mixture of mineral oil and synthetic hydrocarbon oil.
• the grease 25 can be made of, but is not limited to, a urea-based grease containing a urea compound as a thickener.
• the use of urea-based grease makes it easier to repel water, and has the effect of preventing water from entering from the outside.
• the consistency of the grease 25 can be 200 or more and 300 or less. If the consistency of the grease 25 is less than 200, the grease 25 becomes too hard, and there is a possibility that the lubrication of the sliding portion between the seal lips 23a to 23c and the lip sliding surfaces 24a to 24c will deteriorate. If the consistency of the grease 25 is 300 or more, the grease 25 becomes too soft, and there is a possibility that the grease 25 will leak to the outside from the sliding portion between the seal lips 23a to 23c and the lip sliding surfaces 24a to 24c.
• the lip sliding surface 24 (24a to 24c) is provided with multiple recesses 35, so the pressure of the oil film of the grease 25 is low at the position of the recess 37 of the recess 35 as shown in Figure 6, and is high at the position of the opening edge (ridge) on the front side (left side in Figure 6) of the recess 35 in the direction of movement of the seal lip 23 (23a to 23c). Then, when the pressure of the oil film at the position of the recess 37 falls below the cavitation pressure, cavitation occurs in the recess 37, and air bubbles 45 are generated inside the recess 37.
• the height difference of the recesses 35 and the proportion of the recesses 35 in the lip sliding surface 24 are regulated to values that make it easy for cavitation to occur.
• the average height difference between the bottom and the opening edge of the multiple recesses 35 is 1 ⁇ m or more and 10 ⁇ m or less, so the variation in the height difference of the recesses 35 is suppressed and the height difference of the recesses 35 is kept within a range that is likely to cause cavitation. Therefore, air bubbles 45 can be effectively generated in the oil film, and the effect of reducing the seal torque can be sufficiently obtained.
• the ratio of the total opening area of the recesses 35 to the fixed area of the lip sliding surface 24 (24a to 24c) is 30% or more and 100% or less, so the amount of air bubbles 45 generated can be ensured. Therefore, the effect of reducing the sealing torque can be sufficiently obtained.
• the hub unit bearing 1 to which the seal structure 3 of this example is applied will be described using an example of an inner ring rotating hub unit bearing for a driving wheel.
• the hub unit bearing 1 is provided with two seal structures that close the openings on both axial sides of the internal space 2 to prevent leakage of the bearing grease (not shown) sealed in the internal space 2 and to prevent foreign matter such as muddy water from entering the internal space 2.
• the seal structure 3 of this example can be applied to both of the two seal structures, or to only one of the two seal structures.
• the seal structure to which the seal structure 3 of this example is applied is determined according to the performance required of the hub unit bearing 1, etc.
• the seal structure 3 of this example is applied only to the seal structure that closes the axially inner opening of the internal space 2, and is not applied to the seal structure 4 that closes the axially outer opening of the internal space 2.
• the seal structure 3 of this example can also be applied to the seal structure that closes the axially outer opening of the internal space 2.
• the hub unit bearing 1 of this example further comprises an outer member 5, an inner member 6, and a number of rolling elements 7a and 7b.
• the left side of Figs. 1, 2, and 5, which is located on the outer side in the width direction of the vehicle when the hub unit bearing 1 is assembled to the vehicle, is referred to as the axial outer side
• the right side of Figs. 1, 2, and 5, which is located on the center side in the width direction of the vehicle when the hub unit bearing 1 is assembled to the vehicle is referred to as the axial inner side.
• each of the mounting holes 15 is a screw hole
• the braking rotor and the wheel are fixed to the rotating flange 12 by inserting the pilot portion 13 into the central hole provided in the center of each of them, and screwing a hub bolt that has passed through a through hole in the braking rotor and a through hole in the wheel into the mounting hole 15 from the outside in the axial direction.
• each of the mounting holes 15 is configured as a cylindrical hole. Therefore, the stud 16 is press-fitted into each of the mounting holes 15 with a serration.
• the spline hole 14 is an element into which the tip of the drive shaft, which is rotated and driven by an engine or electric motor as a drive source, is splined.
• the inner member 6 is rotated and driven by the drive shaft, which in turn rotates and drives the wheels and braking rotors that are fixedly connected to the rotating flange 12 of the inner member 6.
• the inner member 6 is composed of a hub that combines an inner ring 17 and a hub wheel 18.
• the inner ring 17 is made of a hard metal such as bearing steel and has a circular ring shape.
• the inner ring 17 has an inner ring raceway 11b on the axially inner side on its outer circumferential surface.
• the hub ring 18 is made of a hard metal such as medium carbon steel.
• the hub ring 18 has an inner ring raceway 11a on the axially outer side, a rotating flange 12, a pilot portion 13, and a spline hole 14.
• the hub ring 18 has a small diameter step 19, located axially inward of the axially outer inner ring raceway 11a, that has a smaller outer diameter than the adjacent axially outer portion.
• the hub ring 18 has a step surface 20, facing axially inward, at the axially outer end of the small diameter step 19.
• the inner ring 17 is fitted tightly onto the small diameter step 19 of the hub wheel 18, and its axially outer end face abuts against the step surface 20 of the hub wheel 18. This causes the hub wheel 18 and the inner ring 17 to be fixed together.
• the hub ring 18 and the inner ring 17 can also be fixed together by clamping the inner ring 17 from both axial sides between the stepped surface of the hub ring 18 and a crimped portion provided on the axially inner end of the hub ring 18, or a nut screwed onto the axially inner end of the hub ring 18.
• the inner member 6 can also be constructed by fitting and fixing two inner rings having inner ring raceways 11a, 11b on their respective outer peripheral surfaces to a shaft member having a rotating flange 12, a pilot portion 13, and a spline hole 14. Also, if the inner member 6 does not have a rotating flange 12 and a pilot portion 13, the inner member 6 can be constructed by two inner rings having inner ring raceways 11a, 11b on their respective outer peripheral surfaces.
• each of the rolling elements 7a and 7b is made up of a ball.
• the pitch circle diameter of the rolling elements in the axially outer row and the pitch circle diameter of the rolling elements in the axially inner row may have different structures. Additionally or alternatively, the diameter (ball diameter) of the rolling elements 7a in the axially outer row and the diameter (ball diameter) of the rolling elements 7b in the axially inner row may be different from each other. Also, tapered rollers may be used instead of balls for the rolling elements 7a and 7b.
• Each of the rolling elements 7a and 7b is made of an iron alloy such as bearing steel or ceramics.
• the bearing grease sealed in the internal space 2 lubricates the rolling contact areas between the rolling surfaces of the rolling elements 7a, 7b and the outer ring raceways 8a, 8b and the inner ring raceways 11a, 11b.
• the bearing grease may be, for example, a grease containing a hydrocarbon oil, such as a mineral oil or a synthetic hydrocarbon oil, as a base oil, but is not limited thereto.
• the bearing grease may contain, as a thickener, a metal soap such as lithium soap, urea, a fluorine compound, bentonite, or the like.
• the bearing grease may contain additives such as an antioxidant, a rust inhibitor, and an extreme pressure agent, as necessary.
• the seal structure 3 of this example is applied to the seal structure that closes the axially inner opening of the internal space 2. Therefore, in the hub unit bearing 1 of this example, when the seal lips 23a-23c and lip sliding surfaces 24a-24c that make up the axially inner seal structure 3 slide across the oil film of grease (seal grease) 25 while the vehicle is running, cavitation occurs in multiple recesses 35, reducing the viscosity of the grease 25 and decreasing the shear resistance of the grease 25, making it possible to reduce the seal torque.
• the seal structure 4 that closes the axially outer opening of the internal space 2 is also in a fluid lubricated state when the vehicle is running, and the seal lips 39a-39c and the lip sliding surfaces 40a-40c slide against each other via an oil film of the seal grease 41.
• the seal structure 4 includes a seal ring 42 with seal lips 39a to 39c.
• the seal ring 42 is fixed to the outer member 5.
• the seal ring 42 is composed of a core metal 43 and a seal member 44 having seal lips 39a to 39c.
• the lip sliding surfaces 40a to 40c are not provided with multiple recesses 35.
• the hub unit bearing 1 of this example can also have multiple recesses 35 similar to the seal structure 3 on any of the lip sliding surfaces 40a to 40c.
• Seal grease 41 is applied to seal lips 39a to 39c to reduce the seal torque.
• the seal grease 41 may have the same composition as grease (seal grease) 25, or may have a different composition.
• the structure of the recess 35a provided on the lip sliding surface 24 (24a to 24c) has been changed from the structure of the recess 35 in the first example.
• the recess 35a in this example has a recessed portion 37 and a raised portion 46 that is provided around the recess 35a and is raised above the reference surface 36.
• the raised portions 46 can be formed on the opening edges of all recesses 35a, or can be formed only on the opening edges of some of the recesses 35a. Also, the raised portions 46 can be formed all around the opening edges of the recesses 35a, or can be formed only on some of them. In this example, the raised portions 46 are formed on the opening edges of all recesses 35a. Also, each raised portion 46 is formed all around the recess 35a.
• the average height difference (H) between the bottom and the top of the raised portion 46, which is the opening edge is 1 ⁇ m or more and 10 ⁇ m or less, preferably 1 ⁇ m or more and 5 ⁇ m or less.
• the height difference between the bottom, which is the deepest part of recess 37, and the top of the raised portion 46 located on one side of recess 37 in the sliding direction of seal lips 23a to 23c is a1
• the height difference between the bottom of recess 37 and the top of the raised portion 46 located on the other side of recess 37 in the sliding direction of seal lips 23a to 23c is a2
• the height difference of recess 35 is calculated ⁇ (a1 + a2)/2 ⁇ .
• the average value of the height differences (H) for all recesses 35a present on lip sliding surfaces 24a to 24c is calculated.
• the ratio of the total opening area of the multiple recesses 35a to the fixed area of the lip sliding surfaces 24a to 24c is set to 30% or more and 100% or less.
• the method for processing the recess 35a is not particularly limited as long as the raised portion 46 can be formed.
• the recess 35a can be formed by shot peening or laser processing, for example.
• the pressure of the oil film of the grease 25 is low at the position of the recess 37 of the recess 35a, and is high at the position of the opening edge on the front side of the recess 35a (left side in Figure 12) in the direction of movement of the seal lips 23a to 23c. Then, when the pressure of the oil film at the position of the recess 37 falls below the cavitation pressure, cavitation occurs in the recess 37, and air bubbles 45 are generated inside the recess 37.

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• Mechanical Engineering (AREA)
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  • 2025-01-16 JP JP2025533067A patent/JPWO2025154760A1/ja active Pending
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