Tube and shock absorber

A tube having sealing ring grooves formed by a sequential rotational process and a shock absorber including the tube, in which durability of a sealing ring fitted in each of the sealing ring grooves is enhanced. An inclination angle (θ1) formed with respect to a plane (PL1) perpendicular to an axis of a separator tube by a side surface of the sealing ring groove, which is located on an opening end side of the separator tube, is set to 8° or more. With this, a maximum tensile stress to be applied to an O-ring can be reduced to be smaller than a maximum tensile stress in a case of using a backup ring. As a result, the durability of the O-ring can be set equivalent to or enhanced to be higher than durability in the case of using the backup ring.

TECHNICAL FIELD

The present invention relates to a tube and a shock absorber.

BACKGROUND ART

As a shock absorber to be built into a suspension system for vehicles, there is known a shock absorber including a separator tube arranged between a cylinder and an outer tube. For example, in a shock absorber disclosed in Patent Literature 1, the separator tube is fitted to an outer periphery of the cylinder, and a space between both radially shrunk end portions of the separator tube and the cylinder is sealed by sealing rings. Further, sealing ring grooves (housings) each having a substantially quadrangular shape in cross-section and extending in a circumferential direction are formed along an inner periphery of both the end portions of the separator tube. The sealing ring grooves can be formed, for example, by a beading process to be executed on the separator tube having a cylindrical shape.

Incidentally, the beading process refers to a sequential rotational process to be executed through rotation and revolution of a roller die. Thus, a material of the end portions of the separator tube is caused to plastically flow both in the circumferential direction and an axial direction. As a result, acute raised portions are formed along the circumferential direction at groove corners of each of the sealing ring grooves. In this case, the acute raised portions are ignorable when a gap (clearance) between the cylinder and the separator tube is substantially zero. However, in consideration of assembly efficiency, a predetermined gap is secured between the cylinder and the separator tube. Thus, when the shock absorber is in such a state that an internal pressure repeatedly varies intensively on a compression side or a decompression side, the sealing rings are repeatedly protruded slightly from the sealing ring grooves and restored thereto. In this configuration, when backup rings are not used, the slightly protruded portions of the sealing rings repeatedly slide against the acute raised portions. As a result, the sealing rings may be damaged.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The present invention has been made in view of the circumstances as described above, and has an object to enhance durability of sealing rings fitted into sealing ring grooves in a tube having sealing ring grooves formed by a sequential rotational process, and in a shock absorber including the tube.

Solution to Problem

In order to achieve the object described above, according to one embodiment of the present invention, there is provided a tube, including a sealing ring groove formed along an inner periphery on an end portion side of the tube, the sealing ring groove being formed into a substantially quadrangular shape in cross-section to have a bottom surface and a pair of side surfaces facing each other across a sealing ring, at least one of the pair of side surfaces forming an inclination angle of 5° or more with respect to a plane perpendicular to an axis of the tube.

In order to achieve the object described above, according to one embodiment of the present invention, there is provided a shock absorber to be mounted between two members movable relative to each other, the shock absorber including: a cylinder having a working fluid sealed therein; a piston inserted into the cylinder; a piston rod coupled to the piston so as to extend to an outside of the cylinder; an outer tube arranged at an outer periphery of the cylinder; a separator tube provided to surround the outer periphery of the cylinder, the separator tube having a cylindrical side wall forming an annular passage communicating to an inside of the cylinder; a reservoir formed on an outside of the separator tube between the cylinder and the outer tube, the reservoir having the working fluid and a gas sealed therein; and a damping force generating mechanism arranged on an outside of the outer tube, in which the separator tube has a sealing ring groove formed so as to extend in a circumferential direction of the separator tube along an inner periphery of an end portion side of the separator tube, and in which an inclination angle formed with respect to a plane perpendicular to an axis of the separator tube by one of a pair of side surfaces of the sealing ring groove facing each other across a sealing ring, which is located on an opening end side of the separator tube, is larger than an inclination angle formed by another one of the pair of side surfaces, which is located on an opposite side to the opening end side of the separator tube.

Advantageous Effects of Invention

According to the one embodiment of the present invention, the durability of the sealing rings fitted into the sealing ring grooves can be enhanced in the tube having the sealing ring grooves formed by the sequential rotational process, and in the shock absorber including the tube.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, description is made of an embodiment of the present invention. First, description is made of a damping force adjustable hydraulic shock absorber1(hereinafter referred to as “shock absorber1”) of this embodiment. Note that, for the sake of convenience of description, the up-and-down direction inFIG. 1is defined as an up-and-down direction of the shock absorber1. As illustrated inFIG. 1, the shock absorber1has a double tube structure including an outer tube2and a cylinder3, and a separator tube4(tube) is provided to surround an outer periphery of the cylinder3. Further, a reservoir5that is an annular space is formed at an outer portion of the separator tube4between the outer tube2and the cylinder3.

A piston6is inserted into the cylinder3in a slidable manner. The piston6is fixed to one end of a piston rod8with a nut7, and partitions an inside of the cylinder3into a first chamber3A and a second chamber3B. The piston rod8extends to an outside of the cylinder3through a rod guide9and an oil seal10that are mounted to the outer tube2and an upper end portion of the cylinder3. The piston6includes oil passages11and12configured to communicate the first chamber3A and the second chamber3B to each other. On a surface of the piston6on the first chamber3A side, there is arranged a check valve13configured to allow liquid oil to flow only from the second chamber3B side to the first chamber3A side through the oil passage11. Further, on a surface of the piston6on the second chamber3B side, there is arranged a disc valve14configured to open when a pressure of the liquid oil on the first chamber3A side reaches a predetermined pressure, to thereby relieve the liquid oil on the first chamber3A side to the second chamber3B side through the oil passage12.

The shock absorber1includes a base valve15arranged at a lower end portion of the cylinder3to partition the second chamber3B and the reservoir5from each other. The base valve15includes oil passages16and17configured to communicate the second chamber3B and the reservoir5to each other. Further, the base valve15includes a check valve18configured to allow the liquid oil to flow only from the reservoir5side to the second chamber3B side through the oil passage16. Further, the base valve15includes a disc valve19configured to open when a pressure of the liquid oil on the second chamber3B side reaches a predetermined pressure, to thereby relieve the liquid oil on the second chamber3B side to the reservoir5side through the oil passage17. Note that, the liquid oil is sealed as a working fluid inside the cylinder3, and the liquid oil and a gas are sealed inside the reservoir5.

The separator tube4includes sealing ring grooves22and22(housings) that extend in a circumferential direction along inner peripheries21and21of both end portions20and20and allow O-rings23and23(sealing rings) to be fitted to the sealing ring grooves22and22. When those O-rings23and23at both the end portions20and20of the separator tube4are brought into close contact with outer peripheries of the cylinder3, an annular oil passage24is formed between the cylinder3and the separator tube4. The annular oil passage24is communicated to the first chamber3A through an oil passage25formed at the upper end portion of the cylinder3. Further, a radially small opening26is formed at a lower end portion of the separator tube4. Still further, a radially large opening27arranged correspondingly to the opening26is formed through the outer tube2, and a damping force generating mechanism28is mounted to the opening27of the outer tube2.

The damping force generating mechanism28includes a cylindrical case29fitted to the opening27. A solenoid valve31is fixed to the case29with a nut32. The solenoid valve31mainly includes a main damping valve30of a pilot type (back pressure type) and a pressure control valve configured to control a valve opening pressure of the main damping valve30with a solenoid. The solenoid valve31is connected to the opening26, and generates a damping force by controlling the flow of the liquid oil to the reservoir5through the opening26.

The main damping valve30includes a disc valve33and a back pressure chamber34formed on a back surface side of the disc valve33. When receiving a pressure of the liquid oil on the opening26side, the disc valve33is deflected and opened to function as a main valve for allowing the liquid oil on the opening26side to flow to the reservoir5side. The back pressure chamber34applies an internal pressure on the back surface side of the disc valve33in a valve closing direction of the disc valve33. Further, an auxiliary passage36is connected to the opening26through a fixed orifice35. The auxiliary passage36is communicated to the back pressure chamber34through a passage36A.

FIG. 2is a sectional view taken along an axial plane of the separator tube4(plane including a center axis C1), specifically, a sectional view for illustrating one end portion20of the separator tube4. Note that, the one end portion20and another end portion20of the separator tube4are vertically symmetrical to each other inFIG. 1. Description is herein made only of the one end portion20of the separator tube4, and description of the another end portion20is omitted. The one end portion20and the another end portion20of the separator tube4described in this embodiment are vertically symmetrical to each other, but backup seals may be arranged in front and rear of the sealing ring groove only at the another end portion20. Further, the sealing ring groove of the another end portion20may be formed into a shape different from that of the one end portion. Note that, each of the end portions20of the separator tube4, which has the sealing ring groove22formed along the inner periphery21by a beading process (sequential rotational process), is radially shrunk in advance by a swaging process.

As illustrated inFIG. 3, the sealing ring groove22is formed into a substantially quadrangular shape in cross-section to have a bottom surface71and a pair of side surfaces72and73facing each other across the O-ring23(refer toFIG. 1). Of the pair of side surfaces72and73, the side surface72located on an opening end20A side of the end portion20of the separator tube4(left side inFIG. 2andFIG. 3) is opened to the opening end20A side, and is inclined at an inclination angle θ1with respect to a plane perpendicular to the axis of the separator tube4(one plane PL1including a straight line orthogonal to the center axis C1). As described later, this inclination angle θ1is set to 5° or more, specifically, to 20° in this embodiment.

Meanwhile, an inclination angle θ2(not shown) formed with respect to the plane PL1perpendicular to the axis by the side surface73located on an opposite side to the side surface72(right side inFIG. 2andFIG. 3) is set to range from 0° to 5° in accordance with the housing shapes specified by JIS B 2401. In other words, the inclination angle θ1formed with respect to the plane PL1perpendicular to the axis by the side surface72located on the opening end20A side is larger than the inclination angle θ2formed with respect to the plane PL1perpendicular to the axis by the side surface73located on the opposite side (θ1>θ2). In still other words, the side surface72and the side surface73are asymmetrical with respect to the plane PL1perpendicular to the axis, and in addition, the sealing ring groove22is asymmetrical with respect to the plane PL1perpendicular to the axis.

Further, in the sealing ring groove22, groove corners, that is, connecting portions between opening ends of the sealing ring groove22and the inner periphery21are rounded. Of the round portion of the groove corner on the side surface72side and the round portion of the groove corner on the side surface73side of the sealing ring groove22, the round portion of the groove corner on the side surface72side is hereinafter defined as a groove corner round portion R. Note that, the groove corner round portion R and the groove corner round portion on the side surface73side of the sealing ring groove22conform to housing groove corner round portions specified by JIS B 2401. Further, the sealing ring groove22has a rounded housing groove bottom specified by JIS B 2401. Still further, a gap (clearance for securing assembly efficiency) specified by JIS B 2401 is secured between the cylinder2(refer toFIG. 1) and each of the inner peripheries20of the separator tube4.

Next, with reference toFIG. 4, description is made of a beading apparatus41configured to execute the beading process (sequential rotational process) so as to form the sealing ring groove22along the inner periphery21of the end portion20of the separator tube4. Note that, although both the end portions20and20of the separator tube4are processed simultaneously by a pair of the beading apparatus41, only one of the beading apparatus41corresponding to the one end portion20of the separator tube4is illustrated. Further, for the sake of convenience of description, the up-and-down direction and the right-and-left direction inFIG. 4are defined as an up-and-down direction and a right-and-left direction of the beading apparatus41. Note that, both the end portions20and20of the separator tube4need not necessarily be processed simultaneously by the pair of the beading apparatus41, and both the end portions may be alternately processed by using a single beading apparatus.

The beading apparatus41includes a hollow-shaft roller die42to be inserted on the inner periphery21side of the end portion20of the separator tube4, and an outer die43to be fitted to an outer periphery of the end portion20of the separator tube4. As illustrated inFIG. 5, the roller die42includes an annular projecting portion44formed so as to extend in the circumferential direction along an outer periphery of the roller die42. The projecting portion44is arranged at an intermediate position of the roller die42, specifically, an intermediate position in the direction of a center axis C2of the roller die42(right-and-left direction inFIG. 5), and is formed into a substantially quadrangular shape in cross-section taken along an axial plane of the roller die42.

Further, a side surface75of the projecting portion44corresponding to the side surface72located on the opening end20A side of the separator tube4out of the pair of side surfaces72and73of the sealing ring groove22, that is, the side surface75located on a side forming the side surface72is inclined at the inclination angle θ1with respect to a plane perpendicular to the axis of the roller die42(one plane PL2including a straight line orthogonal to the center axis C2) with a slope toward a side surface76located on the opposite side so as to correspond to the inclination angle θ1of the side surface72of the sealing ring groove22. Note that, the roller die42includes a flange portion45formed to have an interval from the side surface75of the projecting portion44in the direction of the center axis C2(left direction inFIG. 5).

As illustrated inFIG. 4, the beading apparatus41includes a rotary drive mechanism47configured to drive and rotate the roller die42about the center axis C2(refer toFIG. 5). The rotary drive mechanism47includes a die support portion48configured to support the roller die42, and a servo motor (not shown) serving as a drive source. The die support portion48includes a base portion50formed into a substantially columnar shape, a first shaft portion51having an outer periphery to which an inner periphery of the roller die42is fitted, and a second shaft portion53to be connected to a regulating member52. An outer periphery of the base portion50of the die support portion48is supported by a pair of bearings54arranged to have an interval in the direction of the center axis (right-and-left direction inFIG. 4) so that the die support portion48is rotatable about the center axis. Note that, the pair of bearings54is housed in a bearing case55having a substantially cylindrical shape, and a flange portion55A of the bearing case55is fixed to a boss portion56A of a motor base56with bolts.

The die support portion48has a hole57opened in a left end surface of the base portion50so that the die support portion48is connected to a rotor shaft (not shown) of the servo motor to be inserted into the hole57to allow power transmission therebetween. Further, in the die support portion48, a flange portion58is formed at a right end portion of the base portion50so that the bearing54on the right side is held in abutment against a left end surface of the flange portion58. In addition, the flange portion45of the roller die42is held in abutment against, an inner peripheral side of a right end surface of the flange portion58. With this, leftward movement of the roller die42relative to the die support portion48is regulated. In addition, rightward movement of the roller die42relative to the die support portion43is regulated by the regulating member52that is held in abutment against a right end surface thereof. With this, the roller die42is positioned in an axial line direction with respect to the outer die43.

Note that, a left end portion of the roller die42is fitted into an annular recessed portion59formed in the right end surface of the base portion50. Further, in the die support portion48, a distal end portion of the first shaft portion51is fitted into a hole60formed in an end surface of the regulating member52. As illustrated inFIG. 4, the outer die43is formed into an annular shape, and the roller die42is inserted on its inner peripheral side. Further, the outer die43is mounted to an outer die-support plate62through intermediation of a bearing61. With this, the outer die43is rotatable about a center axis of the outer die43. In addition, the outer die43has a recessed portion63corresponding to the projecting portion44of the roller die42.

At a part on an inner side of the outer die43and on a right side with respect to the recessed portion63, there is formed a relief portion65configured to avoid interference with a tapered portion64of the separator tube4. Further, at a part on the inner side of the outer die43and on a left side with respect to the recessed portion63, there is formed an abutment portion66having an inner diameter smaller than an inner diameter of a reference inner peripheral surface43A of the outer die43. The opening end20A of the end portion20of the separator tube4is held in abutment against a right end surface of the abutment portion66. With this, in the separator tube4, flow of a material at the time of the beading process can be regulated. Note that, under a state immediately after completion of the bearing process, a raised portion67formed at the end portion20of the separator tube4is fitted in the recessed portion63of the outer die43. Thus, the separator tube4cannot be released from the outer die43.

Therefore, the outer die43is configured to be divided into four in total, specifically, two in the direction of the center axis (right-and-left direction inFIG. 4) and two in a radial direction (up-and-down direction inFIG. 4), thereby being capable of releasing the separator tube4from the die. Note that, the reference symbol68inFIG. 4represents a bearing presser fixed, to the outer die43with bolts, which is configured to fix an inner ring of the bearing61to the outer die43. Further, the reference symbol69represents another bearing presser fixed to the outer die-support plate62with bolts, which is configured to fix an outer ring of the bearing61to the outer die-support plate62. In addition, the reference symbol70represents a base plate to which the outer die-support plate62is mounted through intermediation of a pair of linear guides.

When a sealing ring groove22′ of a related-art separator tube4′ that is formed to be symmetrical with respect to the plane PL1perpendicular to the axis illustrated inFIG. 6, specifically, a sealing ring groove22′ in which inclination angles of a side surface72′ and a side surface73′ with respect to the plane PL1perpendicular to the axis are each set to range from 0° to 5° in accordance with the housing shapes specified by JIS B 2401 is processed by using the beading apparatus41described above, acute raised portions40and40are formed at both groove corners of the sealing ring groove22′. This is because the separator tube4′ is held by a die, and hence the flow of a material of the separator tube4′ is hindered, at the time of the sequential rotational process. Note that, inFIG. 6, the reference symbol42′ represents a related-art roller die, and the reference symbol44′ represents a projecting portion of the roller die42′.

Thus, in the shock absorber1under the state illustrated inFIG. 1, an internal pressure in the first chamber3A of the cylinder3fluctuates in conjunction with the slide of the piston6, which causes the O-ring23to be repeatedly protruded slightly from the sealing ring groove22′ and restored thereto. In this configuration, when a backup ring is not used, the slightly protruded portion of the O-ring23repeatedly slides against, the acute raised portions40and40. As a result, the O-ring23may be damaged. In addition, the acute raised portions40and40are more liable to be formed as a groove width of the sealing ring groove22′ is smaller.

As a countermeasure, in this embodiment, the sealing ring groove22of the separator tube4was formed to be asymmetrical with respect to the plane PL1perpendicular to the axis. Specifically, as illustrated inFIG. 2andFIG. 3, of the pair of side surfaces72and73of the sealing ring groove22, the side surface12located on the opening end20A side of the separator tube4was inclined at the inclination angle θ1of 5° or more with respect to the plane PL1perpendicular to the axis of the separator tube4. With this, the material of the separator tube4around the projecting portion44of the roller die42is allowed to more smoothly plastically flow at the time of the sequential rotational process. Thus, formation of the acute raised portion40(refer toFIG. 6) can be suppressed at least at the groove corner on the side surface72side of the side surface72and the side surface73of the sealing ring groove22.

Next,FIG. 7is a graph for showing results of tests using a finite element method, specifically, showing a relationship between the inclination angles θ1of the side surface72of the sealing ring groove22with respect to the plane PL1perpendicular to the axis (hereinafter referred to as “inclination angles θ1”) and maximum tensile stresses (MPa) to be applied to the O-ring23(Material: NBR-90) fitted to the sealing ring groove22under a state in which an internal pressure of the separator tube4is 20 MPa. Note that, a test result of a maximum tensile stress applied to the O-ring23fitted to the related-art sealing ring groove22′ (refer toFIG. 6) in a case of using the backup ring was approximately 110 MPa, which was larger than a maximum tensile stress applied to the O-ring23fitted to the sealing ring groove22of the separator tube4of this embodiment. In other words, durability of the O-ring23fitted to the related-art sealing ring groove22′ was lower than that of the O-ring23of this embodiment. Further,FIG. 8is another graph for showing a relationship between the inclination angles θ1and deformation amounts (mm) of an end portion of the O-ring23.

With reference toFIG. 7, it is understood that the maximum tensile stress applied to the O-ring23tends to be larger as a radius of curvature of the groove corner round portion R of the sealing ring groove22is smaller when the inclination angle θ1ranges from 0° to 20°. This is presumably because, in the range where the inclination angle θ1is 20° or less, as the radius of curvature of the groove corner round portion R becomes smaller, the stress is applied intensively to a part (recessed portion) of the O-ring23, which is to be deformed in conformity with the groove corner round portion R.

Further, with reference toFIG. 7, it is understood that, when the inclination angle θ1is a certain angle or larger, the maximum tensile stress applied to the O-ring23is less influenced by the groove corner round portion R and is stably maintained to be small. Meanwhile, with reference toFIG. 8, it is understood that the deformation amount is once decreased when the inclination angle θ1exceeds 30°, and that the deformation amount is increased as the inclination angle θ1becomes even larger. Specifically, as understood fromFIG. 9, when the inclination angles θ1are 10° and 30°, entry leading edge positions of the O-ring23entering a gap between the cylinder3and the separator tube4are substantially the same as each other. Meanwhile, when the inclination angle θ1exceeds 40°, the entry leading edge position of the O-ring23is retreated, and when the inclination angle θ1is 60°, the entry leading edge position of the O-ring23is further retreated. In other words, a deformation mode starts to vary approximately when the inclination angle θ1exceeds 30°. When the deformation mode varies, the leading edge position to enter the gap between the cylinder3and the separator tube4is retreated. As a result, an unnecessary space is formed to increase an axial length, which causes upsizing of the entire cylinder device. In this way, the increase in inclination angle θ1does not cause problems with the maximum tensile stress. However, the variation of the deformation mode causes the upsizing of the cylinder device, and hence it is desired that a maximum value of the inclination angle θ1be 30° or less.

Meanwhile, it is desired that, in the sealing ring groove22, the groove corner, specifically, the radius of curvature of the round portion R of the connecting portion between the opening end of the sealing ring groove22and the inner periphery21be 0.2 mm or more and 1.0 mm or less. This is because, as demonstrated by the results shown inFIG. 7, when the radius of curvature of the R is 0.05 mm, the maximum tensile stress is maintained to be large until the inclination angle θ1reaches 20°. When the radius of curvature of the R is 0.05 mm or less, a degree of sandwiching the O-ring23between the cylinder3and the separator tube4is high, and hence the O-ring23is significantly influenced at the time of entering the narrow gap between the cylinder3and the separator tube4. Further, when the radius of curvature of the R is increased, the influence on the maximum tensile stress does not vary. However, the deformation mode varies. Thus, for the reason described above, it is desired that the radius of curvature of the R be 1.0 mm or less.

Further, with reference toFIG. 7andFIG. 8, it is understood that, in the range where the inclination angle θ1is 50° or more, the maximum tensile stress to be applied to the O-ring23is substantially uniform when the radius of curvature of the groove corner round portion R ranges from 0.05 mm to 1.0 mm, and hence is not influenced by the groove corner round portion R. However, although the maximum tensile stress to be applied to the O-ring23can be reduced by setting a large inclination angle θ1, as understood also with reference toFIG. 9, the groove width of the sealing ring groove22becomes larger as the inclination angle θ1is set larger. As a result, there arise structural design problems such as a need to extend the end portion20of the separator tube4in the direction of the center axis. In that case, a volume of the separator tube4may not be sufficiently secured. As a countermeasure, when an axial length of the separator tube4and the cylinder3are extended, there arises a problem in that the axial length of the entire shock absorber1is increased to cause the upsizing as a result. In addition, as the inclination angle θ1becomes larger, the deformation amount of the end portion of the O-ring23is increased. As a result, a degree of deflection of the O-ring23is increased to cause deterioration in durability of the O-ring23. In other words, the groove width of the sealing ring groove22is increased, and the leading edge position to enter the gap between the cylinder3and the separator tube4is retreated so that an axial gap is formed. Thus, the separator tube4is extended in the axial direction along with the increase in inclination angle θ1. As a result, the cylinder device is upsized. Thus, it is desired that the maximum value of the inclination angle θ1be 30° or less so that the deformation mode does not vary.

As a countermeasure, in this embodiment, as the inclination angle θ1of the sealing ring groove22capable of securing high durability of the O-ring23without causing the structural design problems, the inclination angle θ1of 5° or more, specifically, the inclination angle θ1of 20° that was less than 30° at which the deformation mode started to vary was employed.

Next, detailed description is made of the reason why the inclination angle θ1was set to 5° or more. InFIG. 10, there are shown results of tests of varying the inclination angle θ1in the range of from 2° to 10° to confirm whether or not the acute raised portion40was formed at the groove corner of the sealing ring groove22at the time of the sequential rotational process. When the inclination angle θ1was 3° or less, the acute raised portion40was formed, and hence the evaluation of “×” was given. When the inclination angle θ1was 4°, the acute raised portion40was scarcely formed but a small raised portion was found when touching the groove corner, and hence the evaluation of “Δ” was given. When the inclination angle θ1exceeded 5°, no raised portion was found even when touching the groove corner, and hence the evaluation of “o” was given. Those test results demonstrate that the formation of the acute raised portion40was suppressed by setting the inclination angle θ1to 5° or more. Further, in order to secure stable product quality, it is desired that a tolerance of formation of the sealing ring groove22by the sequential rotational process be ±2.5°. Thus, it is more desired that the inclination angle θ1be 8° or more.

According to this embodiment, in the separator tube4(tube) having the sealing ring groove22formed along the inner periphery21of the end portion20by the sequential rotational process with the beading apparatus41, and in the shock absorber1including the separator tube4, the sealing ring groove22was formed to be asymmetrical with respect to the plane PL1perpendicular to the axis of the separator tube4. The inclination angle θ1formed with respect to the plane PL1perpendicular to the axis by the side surface72located on the opening end20A side of the separator tube4out of the pair of side surface72and side surface73facing each other across the O-ring23(sealing ring) in the sealing ring groove22was set to 8° or more, specifically, the inclination angle θ1was set to 20°. With this, at the time of the sequential rotational process, the acute raised portion40is not formed at the groove corner of the sealing ring groove22. As a result, a step of removing the acute raised portion40can be omitted, and streamlining of manufacturing steps for not only the separator tube4but also the shock absorber1can be achieved. Further, the maximum tensile stress to be applied to the O-ring23can be reduced to be significantly smaller than the maximum tensile stress in the case of using the backup ring. Thus, the durability of the O-ring23can be set equivalent to or enhanced to be higher than the durability in the case of using the backup ring. As a result, the backup ring can be omitted, and hence manufacturing cost of the shock absorber1can be significantly reduced. In addition, assembly efficiency is enhanced, and hence productivity can be enhanced.

Note that, although the O-ring is used as the sealing ring in the example described above in this embodiment, the present invention is not limited thereto. The present invention is applicable also to sealing rings such as a square ring having a rectangular shape in cross-section and a lip ring having a V-shape in cross-section.

REFERENCE SIGNS LIST