SEALING STRUCTURE

Abstract

A sealing structure having a circular pillar-shaped shaft that has an annular groove, which is continuous in a circumferential direction, on an outer circumferential surface, a housing having a shaft hole into which the shaft is inserted, a seal ring which seals a gap between the shaft and the housing, and a backup ring disposed on the low-pressure side of the seal ring inside the annular groove, wherein: there is a tapered surface on the low-pressure side of the groove bottom of the annular groove; a taper angle .sub. is 15 to 50; the backup ring has a tapered surface ; and a taper angle .sub. is larger than the taper angle .sub..

Claims

1. A sealed structure comprising: a column-shaped shaft having a circumferentially continuing annular groove in its outer peripheral surface; a housing having a shaft hole through which the shaft is inserted; a sealing ring made of elastic rubber which is disposed within the annular groove and is configured to seal a gap between the shaft and the housing in the shaft hole; and a backup ring made of a hard material which is disposed on a low pressure side of the sealing ring within the annular groove and is configured to prevent the sealing ring from protruding out of the annular groove due to pressure from a high pressure side; wherein: a groove bottom of the annular groove has, on its low pressure side, a tapered surface where a distance to the housing is gradually reduced from the high pressure side toward the low pressure side, and the tapered surface has a taper angle .sub. of 15 to 50, the backup ring has a tapered surface which faces the tapered surface , a taper angle .sub. of the tapered surface is larger than the taper angle .sub., and an annular edge portion on the high pressure side of the tapered surface is configured to be slidable in a state of line contact with the tapered surface , and when in a cross-section through which an axis .sub. of the shaft passes, a length of the backup ring in a direction parallel to the axis .sub. is denoted by La, a length in a direction perpendicular thereto is denoted by Lb, a length of the tapered surface in the annular groove in a direction parallel to the axis .sub. is denoted by Lc, and a distance between the groove bottom of the annular groove and the housing is denoted by Ld, following formulas are satisfied:
La0.5 mm,
La/Lb>,
Ld>Lb, and
Ld{(LcLa)/tan(90.sub.)}Lb.

2. The sealing structure according to claim 1, wherein an internal diameter of the backup ring is larger than a cross-sectional diameter up to the groove bottom of the annular groove (limited to a portion except the tapered surface ).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic cross-sectional view showing a sealing structure 1 in a preferred embodiment of the invention.

[0026] FIG. 2 is a schematic perspective view of a sealing ring before being disposed within an annular groove.

[0027] FIG. 3 is a schematic perspective view of a backup ring before being disposed within the annular groove.

[0028] FIG. 4 is a schematic cross-sectional view of the backup ring.

[0029] FIG. 5 is a schematic cross-sectional view of a conventional sealing structure in a state in which the pressure difference between the high pressure side (H) and the low pressure side (L) is zero or small.

[0030] FIG. 6 is a schematic cross-sectional view of the conventional sealing structure in a state in which the pressure difference between the high pressure side (H) and the low pressure side (L) is large.

[0031] FIG. 7 is a schematic cross-sectional view of another conventional sealing structure.

DESCRIPTION OF EMBODIMENTS

[0032] The sealing structure of the invention is a structure including a shaft and a housing, and configured to seal a gap therebetween with a sealing ring. The shaft and the housing may relatively move (by at least one of rotation and reciprocation) or be both static.

[0033] The shaft and the housing are in principle disposed so that a cross-section perpendicular to the longitudinal direction of the shaft and a cross-section perpendicular to the longitudinal direction of a shaft hole of the housing form concentric circles. However, eccentricity may occur due to relative movement of the shaft and the housing. The gap between the shaft and the housing can be sealed even if such eccentricity occurs.

[0034] In the sealing structure of the invention, one side of the shaft in its longitudinal direction is high pressure side (High) and the other side is low pressure side (Low). However, a state in which there is no pressure difference between both sides may be included.

[0035] The high pressure side (High) may be sealed with high pressure fluid such as gas or liquid, whereas the low pressure side (Low) may be sealed with atmospheric air. Alternatively, both sides may be sealed with fluid.

[0036] Examples to which the sealing structure of the invention as described above is preferably applicable may include sealing portions of high pressure hydrogen tanks or piping in fuel cells, injector portions in direct injection engines, cylinders for use in constructing machines, cylinders for use in general machines, and shock absorbers.

[0037] The sealing structure of the invention is described using drawings.

[0038] FIG. 1 is a schematic cross-sectional view showing a sealing structure 1 in a preferred embodiment of the invention. More precisely, FIG. 1 is a schematic view of a cross-section through which an axis wo of a shaft 20 passes.

[0039] As shown in FIG. 1, the sealing structure 1 of the invention has a housing 10, the shaft 20, a sealing ring 30, and a backup ring 40.

<Housing>

[0040] The housing 10 included in the sealing structure 1 of the invention is now described.

[0041] The housing 10 has a shaft hole 101 through which the shaft 20 is inserted. Then, the shaft hole 101 is of a type in which the shaft 20 having a columnar shape is fitted into the shaft hole 101 with a slight gap S formed therebetween. Therefore, a cross-section in a direction perpendicular to the longitudinal direction of the shaft hole 101 is circular in shape and the circle has a slightly larger diameter than that of a cross-section of the shaft 20.

[0042] A line connecting centers of circular cross-sections of the shaft hole 101 substantially coincides with the axis wo of the shaft 20 to be described later.

[0043] The material and the like of the housing 10 are not particularly limited as long as it has a certain strength. Examples of the material of the housing 10 include metal, ceramic, and plastic.

<Shaft>

[0044] The shaft 20 included in the sealing structure 1 of the invention is now described.

[0045] The shaft 20 has a columnar shape. Therefore, cross-sections perpendicular to the longitudinal direction of the shaft 20 are circular in shape and a line connecting their centers is the axis .sub.. The shaft 20 may rotate about the axis Wo or move in a direction parallel to the axis .sub. (longitudinal direction).

[0046] As described above, the axis .sub. substantially coincides with the line connecting the centers of the circular cross-sections of the shaft hole 101 in the direction perpendicular to its longitudinal direction.

[0047] Further, as shown in FIG. 1, the shaft 20 has a circumferentially continuing annular groove 22 in its outer peripheral surface 201.

[0048] The depth and the width of the annular groove 22 differ depending on the size and elasticity of the sealing ring 30 to be used.

[0049] A groove bottom 221 of the annular groove 22 may be formed parallel to the axis .sub. as shown in FIG. 1 but may not be parallel. The groove bottom 221 has, on its low pressure side (Low), a tapered surface where the distance to the housing 10 is gradually reduced from the high pressure side (High) toward the low pressure side (Low). The tapered surface is preferably planar as shown in FIG. 1 (linear in FIG. 1).

[0050] The tapered surface has a taper angle .sub. of 15 to 50, preferably 20 to 40, and more preferably 25 to 35.

[0051] When the taper angle is within the above-defined ranges, the sealing structure of the invention has high sealing performance.

[0052] The taper angle .sub. of the tapered surface shall mean an angle formed between the tapered surface and the axis .sub. in a cross-section as in FIG. 1 through which the axis .sub. of the shaft 20 passes.

[0053] The length of the tapered surface in the annular groove 22 in a direction parallel to the axis .sub. is denoted by Lc.

[0054] The distance from the groove bottom 221 (the portion except the tapered surface ) to the housing 10 in a direction perpendicular to the axis .sub. is denoted by Ld. In a case where the groove bottom 221 (the portion except the tapered surface ) is not parallel to the axis .sub., an average value of the distance from the groove bottom 221 (the portion except the tapered surface ) to the housing 10 is used as Ld.

<Sealing Ring>

[0055] The sealing ring 30 included in the sealing structure 1 of the invention is now described.

[0056] The sealing ring 30 is disposed within the annular groove 22 and is configured to seal the gap S formed between the shaft 20 and the housing 10 in the shaft hole 101.

[0057] The sealing ring 30 before being disposed within the annular groove 22 has a ring shape as shown in FIG. 2, and a cross-section taken along line X-X is, for example, circular in shape as shown by a dotted line in FIG. 1. The sealing ring 30 is made of elastic rubber. Therefore, when disposed within the annular groove 22, the sealing ring 30 is sandwiched between the groove bottom 221 and the housing 10 to be deformed into a shape, for example, as shown by a solid line in FIG. 1.

[0058] The sealing ring 30 shown in FIG. 1 and FIG. 2 has a circular cross-sectional shape but may have another shape.

[0059] The sealing ring 30 has a ring shape as shown in FIG. 2 and its centerline C substantially coincides with the axis .sub. of the shaft 20. In other words, the sealing ring 30 and the shaft 20 are in principle disposed so as to form concentric circles.

[0060] The sealing ring 30 is made of elastic rubber and its material may be NBR, VMQ, EPDM, FKM, or HNBR.

<Backup Ring>

[0061] The backup ring 40 included in the sealing structure 1 of the invention is now described.

[0062] The backup ring 40 is disposed on the low pressure side (Low) of the sealing ring 30 within the annular groove 22.

[0063] The backup ring 40 plays a role in preventing the sealing ring 30 from protruding out of the annular groove 22 due to pressure from the high pressure side (High).

[0064] In order to play such a role, the backup ring 40 needs to be made of a hard material having hardness not less than a certain value. Specifically, the backup ring 40 is preferably made of PA, PEEK, POM, PPS, or PTFE, and more preferably PA6 or PEEK.

[0065] The backup ring 40 has a ring shape as shown in FIG. 3, its centerline D substantially coincides with the axis wo of the shaft 20, and its cross-section taken along line Y-Y has, as shown in FIG. 1 and FIG. 4, a quadrangular shape, the shape having a tapered surface as one of its four sides.

[0066] The backup ring 40 is disposed so that the tapered surface faces the tapered surface which is a part of the groove bottom 221. The tapered surface is preferably planar as shown in FIG. 1 and FIG. 4 (linear in FIG. 1 and FIG. 4). The taper angle .sub. of the tapered surface is larger than the taper angle .sub.. In this case, an annular edge portion on the high pressure side (High) of the tapered surface is made slidable in the state of line contact with the tapered surface .

[0067] The taper angle .sub. of the tapered surface shall mean, as shown in FIG. 4, an angle (.sub.90) formed between the tapered surface and the centerline D of the backup ring 40 before being disposed within the annular groove 22.

[0068] The cross-section of the backup ring 40 has, as shown in FIG. 1 and FIG. 4, a quadrangular shape, and in a case where a surface facing the housing 10 (corresponding to the outer peripheral surface of the ring-shaped backup ring 40) is disposed so as to be parallel to the housing 10 as shown in FIG. 1, a surface on the side closer to the sealing ring 30 and/or a surface on the side farther away from the sealing ring 30 which is opposite to the surface is preferably perpendicular to the axis .sub. and the centerline D.

[0069] The length of the surface in a direction perpendicular to the axis .sub. in FIG. 1 is not less than a certain value, and is preferably at least one-fifth as long as that of the surface in the direction perpendicular to the axis .sub..

[0070] The backup ring 40 has a ring shape as shown in FIG. 3 and its centerline D substantially coincides with the centerline C of the sealing ring 30.

[0071] The backup ring 40 may have the shape of an endless ring or an open-ended ring, a part of which is cut away. The cutting direction is not particularly limited and cutting may be made, for example, at a right angle to the circumferential direction but bias cutting which is cutting diagonally to the circumferential direction is preferably performed. When the bias cutting is performed, the sealing line is easily kept even if the diameter of the backup ring 40 is increased.

[0072] In a cross-section through which the axis .sub. of the shaft 20 as shown in FIG. 1 or the centerline D of the backup ring 40 as shown in FIG. 4 passes, the length of the backup ring 40 in a direction parallel to the axis .sub. and the centerline D is denoted by La, and the length of the backup ring 40 in a direction perpendicular to the axis .sub. and the centerline D is denoted by Lb.

[0073] La satisfies La0.5 mm.

[0074] La is preferably 0.9 mm or more, and more preferably 1.0 mm or more.

[0075] La is preferably up to 3.1 mm and may be up to 1.1 mm.

[0076] When La is within the above-defined ranges, the backup ring 40 has a high strength.

[0077] La/Lb> is satisfied.

[0078] La/Lb is preferably 0.6 or more, and preferably 0.8 or more.

[0079] La/Lb is preferably up to 3.0, and preferably up to 1.5.

[0080] When La/Lb is within the above-defined ranges, the backup ring 40 is less likely to topple down in the annular groove 22, thus preventing buckling from occurring.

[0081] Lb satisfies Ld>Lb.

[0082] In this case, when the backup ring 40 is disposed within the annular groove 22, the annular edge portion comes into contact with the tapered surface . The shaft 20 is less likely to have scratches when the backup ring 40 is disposed within the annular groove 22, and the backup ring 40 is less likely to be compressed in a direction perpendicular to the axis .sub.. The backup ring 40 is more easily attached to the annular groove 22.

[0083] Further, Ld{(LcLa)/tan(90.sub.)}Lb is satisfied.

[0084] In this case, in a state in which the annular edge portion of the backup ring 40 is in contact with the tapered surface and the surface of the backup ring 40 is closely attached to the housing 10, a slight gap is formed between the surface of the backup ring 40 on the side farther away from the sealing ring 30 and a surface 223 facing it in the annular groove 22, and the gap can follow during groove deformation under applied pressure.

[0085] In the sealing structure 1 of the invention, the internal diameter of the backup ring 40 is preferably larger than the cross-sectional diameter up to the groove bottom 221 of the annular groove 22 (limited to the portion except the tapered surface ). In this case, the backup ring 40 is easily disposed within the annular groove 22, and the annular edge portion on the high pressure side (High) of the tapered surface easily slides on the low pressure side in the state of line contact with the tapered surface .

[0086] The internal diameter of the backup ring 40 is equal to the shortest distance between the centerline D and a point closest to the centerline D in the backup ring 40, i.e., the tip of the annular edge portion .

[0087] The cross-sectional diameter up to the groove bottom 221 of the annular groove 22 (limited to the portion except the tapered surface ) (diameter on a cross-section perpendicular to the axis .sub.) means the shortest distance between the groove bottom 221 (limited to the portion except the tapered surface ) and the axis .sub. in FIG. 1. In a case where the groove bottom 221 (the portion except the tapered surface ) is not parallel to the axis .sub., the cross-sectional diameter shall mean an average value of the distance from the groove bottom 221 (the portion except the tapered surface ) to the axis .sub..

[0088] In the sealing structure of the invention as described above, when the pressure difference between the high pressure side (High) and the low pressure side (Low) is increased, the sealing ring 30 is pressed on the low pressure side (Low). The backup ring 40 is thus pressed on the low pressure side (Low) to move to the low pressure side (Low). Then, the surface of the backup ring 40 slides in the state of surface contact with the inner peripheral surface of the shaft hole 101 of the housing 10, and the annular edge portion of the backup ring 40 slides substantially in the state of line contact with the tapered surface . The more the low pressure side (Low) is approached, the more the distance between the housing 10 and the tapered surface is reduced. Therefore, the more the backup ring 40 moves to the low pressure side (Low), the more the amount of compression made by the housing 10 and the tapered surface is increased. Therefore, formation of the gap between the backup ring 40 and the housing 10 can be suppressed to prevent a part of the sealing ring 30 from protruding into the gap between the backup ring 40 and the housing 10.

[0089] In a case where the shaft 20 is made eccentric, the distance between the shaft 20 and the housing 10 is the smallest at a point in the circumferential direction and is the largest at a position 180 away from the above point. Therefore, when seen on a cross-section through which the axis passes, the backup ring 40 apparently moves in the longitudinal direction of the shaft 20 but the whole of the backup ring 40 does not move parallel to the longitudinal direction of the shaft 20.

[0090] Actually, when the shaft 20 is made eccentric, the backup ring 40 is deformed so as to tilt with respect to the axis .sub. of the shaft 20, and the backup ring 40 apparently moves parallel to the axis .sub. when seen on the cross-section through which the axis .sub. passes.

[0091] This application claims priority based on Japanese Patent Application No. 2021-184846 filed on Nov. 12, 2021, the entire disclosure of which is incorporated herein by reference.

REFERENCE SIGNS LIST

[0092] 1 sealing structure of the invention [0093] 10 housing [0094] 101 shaft hole [0095] 20 shaft [0096] 201 outer peripheral surface [0097] 22 annular groove [0098] 221 groove bottom [0099] 223 outer peripheral side surface of the annular groove [0100] 30 sealing ring [0101] 40 backup ring [0102] 60 shaft [0103] 70 housing [0104] 71 annular groove [0105] 71a tapered surface [0106] 75 annular groove [0107] 100 sealing ring [0108] 120 inner peripheral edge [0109] 150 sealing ring [0110] 200 backup ring [0111] 300 backup ring