Method for manufacturing a fluid pressure cylinder

Abstract

To inexpensively provide a fluid pressure cylinder having a structure for sealing burrs on the inner peripheral side of a tube generated by friction welding.SOLUTION: Most of the cylinder end 20 has a diameter slightly smaller than the inner diameter of the tube 10, but a large-diameter portion 21 having the same diameter as the outer diameter of the tube 10 is formed at the friction-welded portion. Further, a cylindrical protruding portion 22 having a diameter smaller than the inner diameter of the tube 10 is formed from the end surface of the large diameter portion 21. When the tube 10 and the cylinder end 20 are joined together, a space 30 is formed between the inner peripheral surface of the tube 10 and the peripheral surface of the cylinder end 20 by the length of the protruding portion 22. An inner burr IB is formed from an end 31 of the space 30 on the cylinder end 20 side. Therefore, the inner burr IB is naturally accommodated inside the space 30 at the time of formation. After the joining of the tube 10 and the cylinder end 20 is completed, an O-ring 40 is fitted into the space 30 as a seal member.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a structure of a hydraulic cylinder manufactured by friction pressure welding, a jig used for manufacturing the hydraulic cylinder, and a manufacturing method thereof.

Background Art

[0002] Conventionally, when manufacturing a cylinder tube of a hydraulic cylinder, a disk-shaped member is held in alignment with one end of a cylindrical member, and the boundary portion is welded while rotating each member. However, when welding is performed in this manner, the welding location is only on the outside of the cylinder tube and the cylindrical member, and there is a limit to the range welded with respect to the thickness of the member. In particular, as the cylinder becomes larger and the cylindrical member becomes thicker, the ratio of the joint portion to the cross-section decreases.

[0003] In addition, when joining members by welding, if the management of welding quality is not thorough, it may cause working fluid leakage from the welded portion. However, if a precise inspection of the welded portion is performed for this purpose, there is a problem that the manufacturing cost increases.

[0004] Therefore, friction pressure welding is used as a joining method that can join the entire cross-section of a cylindrical member and suppress the occurrence of poor welding. Friction pressure welding is a method of joining by generating frictional heat by rotating one of two members at high speed while keeping the other member stationary in a state where the two members are in contact, heating the members to a high temperature by this frictional heat, and then pressing the members against each other at high pressure (upset pressurization) after stopping the rotation.

[0005] When joining a cylindrical member by friction pressure welding, burrs extruded by high pressure are generated on both the outer peripheral side and the inner peripheral side. Since the inside of the hydraulic cylinder separates the working fluid chambers on the extension side and the shortening side by sliding while the packing fitted to the piston is in close contact, if burrs are generated, there is a risk of damaging the packing. Also, when the burrs peel off from the inner peripheral surface during the operation of the cylinder, there is a risk of damaging the entire flow path of the working fluid. Therefore, it is desirable to remove burrs during the cylinder manufacturing process, but burrs on the inner circumference of the cylinder tube are difficult to remove because they are generated far from the opening and extend over the entire circumference.

[0006] Therefore, the fluid pressure cylinder disclosed in Patent Document 1 has a space formed in a disc-shaped member to contain burrs generated on the inner circumference of the cylinder, and further includes a flange portion (reference numeral 101 in Figure 2 of Patent Document 1) to cover this space. The flange portion is sized to create a gap between it and the inner circumferential surface of the cylindrical member, but since this gap is narrow (0.5 mm to 1 mm), it prevents burrs larger than the gap from entering the hydraulic fluid chamber. Furthermore, if no gap is formed, frictional heat will be generated in the flange due to the high-speed rotation during joining, which can lead to the formation of unexpected gaps through which burrs can pass, resulting in defective products.

[0007] In addition, Patent Document 2 discloses a hydraulic cylinder equipped with a structure that seals the burr containment space by bringing tapered surfaces into contact with each other. Simply put, during rotation, the tapered surfaces are separated, but during upset pressure, the tapered sections come closer together due to the amount of clearance, causing the tapered surfaces to also come closer together and eventually come into contact. As a result, the space where the burrs are contained is sealed, and the burrs are contained. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Utility Model Publication No. 4-87064 [Patent Document 2] Japanese Patent Publication No. 2017-72160 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] In the case of the flange portion disclosed in Patent Document 1, a gap is formed between it and the inner circumferential surface of the cylinder, so there is a possibility that burrs smaller than the gap may enter the hydraulic fluid chamber. On the other hand, in the case of the cylinder disclosed in Patent Document 2, the tapered surfaces formed on the tube and the lid portion are in close contact with each other, so it is possible to contain the burrs. However, in the case of such a structure, ensuring a sealed state requires high-precision machining of the tapered surface with high dimensional accuracy, and furthermore, precise alignment of the axis during upset pressurization and uniform pressurization of the entire circumference, which results in high processing costs.

[0010] In view of these circumstances, the present invention aims to provide a fluid pressure cylinder equipped with a structure for sealing burrs on the inner circumference of a tube generated by friction welding at a low cost, and also aims to provide a jig used in the manufacture of the fluid pressure cylinder and a method for manufacturing the fluid pressure cylinder using the jig. [Means for solving the problem]

[0011] The first invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, wherein a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxially with the tube and protruding into the tube, and a space is formed between the inner circumferential surface of the tube and the circumferential surface of the projection to accommodate internal burrs generated by friction welding, and this space is sealed by a sealing member.

[0012] The second invention is a fluid pressure cylinder characterized in that the diameter of the protrusion and the inner diameter of the tube are set such that the width between the protrusion and the inner circumferential surface of the tube described in the first invention is smaller than the cross-sectional width of the sealing member in an undeformed state.

[0013] The third invention is a fluid pressure cylinder characterized in that the axial length of the protrusion described in the first invention is longer than the sum of the axial length of the burr formed in the space and the axial cross-sectional width of the sealing member.

[0014] The fourth invention is a fluid pressure cylinder characterized in that a stepped portion is formed on the circumferential surface of the protruding portion described in the first invention, protruding radially outward from the protruding portion.

[0015] The fifth invention is a fluid pressure cylinder characterized in that, as the stepped portion described in the fourth invention, a first stepped portion is formed on the circumferential surface of the tip portion of the protruding portion.

[0016] The sixth invention is a fluid pressure cylinder, characterized in that the invention described in the fourth or fifth invention has a second step formed on the circumferential surface on the base side of the protruding portion as the step portion.

[0017] The seventh invention is a fluid pressure cylinder characterized in that the stepped portion described in the fourth invention is formed over the entire circumference of the protruding portion.

[0018] The eighth invention is a fluid pressure cylinder characterized in that the stepped portion described in the fourth invention is tapered.

[0019] The ninth invention is a fluid pressure cylinder characterized in that, within the range in which the space is formed on the inner circumferential surface of the tube described in the first invention, a stepped portion is formed that protrudes toward the center.

[0020] The tenth invention is a fluid pressure cylinder characterized in that, as the stepped portion described in the ninth invention, a third stepped portion is formed on the inner circumferential surface of the tube at a position that overlaps with the tip of the protruding portion when viewed from the radial direction.

[0021] The eleventh invention is a fluid pressure cylinder, wherein, in the invention described in the ninth or tenth invention, as the stepped portion, a fourth stepped portion is formed on the inner peripheral surface of the tube at the end on the cylinder end side and on the axially central side of the position where the inner burr is formed.

[0022] The twelfth invention is a fluid pressure cylinder, wherein the space described in the first invention is filled with a curable filler throughout the entire area.

[0023] The thirteenth invention is a fluid pressure cylinder, wherein a groove is formed on the surface of the cylinder end described in the first invention facing the inside of the tube so as to surround the protruding portion.

[0024] The fourteenth invention is a jig for temporarily placing a seal member for sealing the space of a fluid pressure cylinder, in which a tube and a cylinder end are joined by friction pressure welding, and a cylindrical protruding portion protruding into the tube is provided coaxially with the tube on the surface of the cylinder end facing the inside of the tube, and a space for accommodating an inner burr generated by friction pressure welding is formed between the inner peripheral surface of the tube and the peripheral surface of the protruding portion. The jig includes a handle longer than the axial length of the tube and a seal holding portion for holding the seal member. The seal holding portion is fixed to one end of the handle, and a shape holding portion for keeping the shape of the seal member circular when viewed from the axial direction is provided at a portion opposite to the portion where the handle is fixed with the seal holding portion sandwiched therebetween.

[0025] The fifteenth invention is a seal member insertion jig for inserting a seal member into a space in a fluid pressure cylinder, where a tube and a cylinder end are joined by friction welding, and a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxial with the tube and protruding into the tube, and a space for accommodating internal burrs generated by friction welding is formed between the inner circumferential surface of the tube and the circumferential surface of the projection, while holding the seal member in place so as not to fall out, comprising: a handle made of a round bar that is longer than the axial length of the tube; a pipe that is longer than the axial length of the tube and shorter than the handle, and has an inner diameter that allows the handle to be fitted and rotated; and half of the projection The sealing member insertion jig comprises: a retaining portion having a length greater than or equal to the diameter and less than or equal to the radius of the inner circumferential surface of the tube, and having a surface shaped to conform to the end face of the protrusion; and an insertion portion having a length greater than or equal to the radius of the protrusion and less than or equal to the radius of the inner circumferential surface of the tube, with a tip portion having a shape that allows it to enter the space, and having a length greater than or equal to the length from the end face of the protrusion to the location in the space where the sealing member is to be placed; one of the retaining portion and the insertion portion is fixed to one end of the handle, the other is fixed to one end of the pipe, the handle is fitted into the pipe, and the retaining portion and the insertion portion are rotatable relative to each other about the handle as an axis.

[0026] The sixteenth invention is a sealing member insertion jig characterized in that the retaining portion described in the fifteenth invention is fixed to the handle, the insertion portion is fixed to the pipe, and when the handle is fitted into the pipe, the retaining portion and the insertion portion are relatively displaceable along the axial direction of the handle.

[0027] The seventeenth invention relates to a method for manufacturing a fluid pressure cylinder, wherein a tube and a cylinder end are joined by friction welding, a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxially with the tube and protruding into the tube, an annular gap is formed between the inner surface of the tube and the outer surface of the projection to accommodate internal burrs generated by friction welding, and the annular gap is sealed by a sealing member, comprising: a preparation step of preparing the cylinder end, wherein the axial length of the projection is formed to be longer than the sum of the axial length of the internal burrs generated by friction welding and the axial length of the sealing member; a friction welding step of coaxially friction welding the tube and the cylinder end to form an annular gap between the inner surface of the tube and the outer surface of the projection to accommodate the internal burrs and to which the sealing member can be mounted; and a sealing member insertion step of mounting the sealing member into the annular gap to seal the internal burrs in the annular gap. The eighteenth invention relates to a method for manufacturing a fluid pressure cylinder, wherein a tube and a cylinder end are joined by friction welding, a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxially with the tube and protruding into the tube, an annular gap is formed between the inner surface of the tube and the outer surface of the projection to accommodate internal burrs generated by friction welding, and the annular gap is sealed by a sealing member, comprising: a preparation step of preparing the cylinder end, wherein the axial length of the projection is formed to be longer than the sum of the axial length of the internal burrs generated by friction welding and the axial length of the sealing member; and a friction welding step of coaxially friction welding the tube and the cylinder end to form an annular gap between the inner surface of the tube and the outer surface of the projection to accommodate the internal burrs and to which the sealing member can be mounted. [Effects of the Invention]

[0028] According to the present invention, a fluid pressure cylinder equipped with a structure for sealing burrs on the inner circumference of a tube generated by friction welding can be provided at low cost. Furthermore, a jig used in the manufacture of the fluid pressure cylinder and a method for manufacturing the fluid pressure cylinder using the jig can also be provided. [Brief explanation of the drawing]

[0029] [Figure 1] This is a longitudinal cross-sectional view of a hydraulic cylinder according to the first embodiment. [Figure 2] This figure shows the friction welding process of a hydraulic cylinder according to the first embodiment. [Figure 3] This figure shows the friction welding process of a hydraulic cylinder according to the first embodiment. [Figure 4] This figure shows the friction welding process of a hydraulic cylinder according to the first embodiment. [Figure 5] This is a magnified view of section A shown in Figure 1. [Figure 6] (a) Front view and (b) Side view showing the first jig. [Figure 7] (a) Front view and (b) Side view showing the second jig. [Figure 8] (a) Front view and (b) Side view showing the third jig. [Figure 9] (a) Front view and (b) Side view when the second jig is attached to the third jig. [Figure 10] This diagram shows the procedure for fitting the O-ring according to the first embodiment. [Figure 11] This diagram shows the procedure for fitting the O-ring according to the first embodiment. [Figure 12] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the second embodiment. [Figure 13] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the second embodiment. [Figure 14] This is an enlarged view of the portion corresponding to part A in Figure 1, showing a modified example of the second embodiment. [Figure 15] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the third embodiment. [Figure 16] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the third embodiment. [Figure 17] This is an enlarged view of the portion corresponding to part A in Figure 1, showing a modified example of the third embodiment. [Figure 18] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the fourth embodiment. [Figure 19] This is an enlarged view of the portion corresponding to part A in Figure 1, according to the fifth embodiment. [Modes for carrying out the invention]

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals, and redundant explanations are omitted. It should be noted that the drawings are schematic. Therefore, the relationship and ratios between thickness and planar dimensions may differ from those in reality, and there may be differences in dimensional relationships and ratios between drawings. Furthermore, the embodiments shown below illustrate devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the material, shape, structure, markings, etc., of the components. In the following embodiments, a hydraulic cylinder, which is an example of a fluid pressure cylinder, is described as being fixed with its axial direction aligned with the left-right direction, with the cylinder end located on the left side and the tube on the right side.

[0031] <First Embodiment> (Overall structure of a hydraulic cylinder) First, the overall structure of the hydraulic cylinder will be explained with reference to Figure 1. The hydraulic cylinder 1 has a cylinder end 20, which acts as a cap, friction-pressed to one axial end of a cylindrical member, a tube 10. Although not shown in the illustration, a cylinder rod equipped with a piston is inserted, and a cylinder head, through which the cylinder rod passes, is bolted to the other end of the tube 10. Since the present invention relates to the structure around the joint between the tube 10 and the cylinder end 20, the following description will omit explanations of parts other than the area around the joint between the tube 10 and the cylinder end 20, which are joined by friction welding.

[0032] (Structure of the cylinder end) Next, the structure of the cylinder end 20 will be described with reference to Figure 2. Most of the cylinder end 20 has a diameter slightly smaller than the outer diameter of the tube 10, but the end on the tube 10 side, which is the friction-pressure contact portion, has a large-diameter portion 21 that is the same diameter as the outer diameter of the tube 10. Furthermore, a cylindrical projection 22, which has a diameter smaller than the inner diameter of the tube 10, is formed on the surface of the large-diameter portion 21 facing the inside of the tube 10, at a position coaxial with the other parts. When the cylinder end 20 is joined to the tube 10, the tube 10 and the cylinder end 20 become coaxial, and therefore the projection 22 and the tube 10 also become coaxial.

[0033] The diameter of the protruding portion 22 is such that the width of the space 30 formed between it and the inner circumferential surface of the tube 10, which will be described later, is narrower than the cross-sectional width of the O-ring 40, which is a sealing member. Furthermore, the axial length of the protrusion 22 is longer than the sum of the axial width of the inner burr IB (explained later) and the cross-sectional width of the O-ring 40.

[0034] (Friction welding process) Next, the friction welding process between the tube 10 and the cylinder end 20 will be described with reference to Figures 2 to 5. As shown in Figure 2, in the friction welding process, the tube 10 is first fixed and the cylinder end 20 is rotated at high speed. Then, as shown in Figure 3, the large-diameter portion 21 of the rapidly rotating cylinder end 20 is brought into contact with the tube 10, generating frictional heat at the contact portion TP. At this time, the protruding portion 22 rotates without contacting the tube 10.

[0035] When the contact area TP reaches a temperature suitable for joining due to frictional heat, the rotation of the cylinder end 20 is stopped, as shown in Figure 4, and upset pressure is applied to strongly press it against the tube 10. Upset pressurization causes the tube 10 and the large-diameter portion 21 of the cylinder end 20 to join, but parts of the tube 10 and cylinder end 20 are pushed radially inward and outward, forming an outer burr OB and an inner burr IB with an umbrella-shaped cross-section containing impurities, as shown in Figure 5.

[0036] (Structure of the burr-filled section) Next, with reference to Figure 5, the structure of the encapsulation portion of the internal burr IB will be described. When the tube 10 and the cylinder end 20 are joined, a space 30 equal to the length of the protrusion 22 is formed between the inner circumferential surface of the tube 10 and the circumferential surface of the cylinder end 20. Furthermore, an internal burr IB is formed from the end 31 on the cylinder end 20 side of the space 30. Therefore, the internal burr IB is naturally contained within the space 30 during its formation.

[0037] After the tube 10 and the cylinder end 20 are joined, an O-ring 40 is fitted into the space 30 as a sealing member. The O-ring 40 has a larger cross-sectional width than the space 30, and when fitted, it deforms to tightly adhere to the inner circumferential surface of the tube 10 and the circumferential surface of the protrusion 22, sealing the space 30 and containing the inner burr IB. After that, the friction welding is completed by removing the outer burr OB.

[0038] After removing the outer burr OB, the cylinder head is bolted to the end of the tube 10 opposite to the cylinder end 20, and piping is installed to complete the hydraulic cylinder 1. Subsequently, the hydraulic cylinder 1 is attached to industrial machinery, etc., and filled with hydraulic fluid. When the hydraulic cylinder 1 is put into use, an operating hydraulic force is applied to the O-ring 40, intermittently pressing it against the end 31. This pressure prevents the O-ring 40 from falling off. In addition, a small amount of hydraulic fluid leaks from the O-ring 40 into the space 30, so after a certain amount of time has passed since the hydraulic cylinder was put into operation, the inside of the space 30 is also filled with hydraulic fluid.

[0039] (Structure of manufacturing jigs) Next, with reference to Figures 6 to 9, a jig for fitting the O-ring 40, which is a sealing member, into the space 30 will be described. Note that the line BB in Figure 6 shows the cross-section of the first jig 50 in Figure 10, and the line CC in Figure 9 shows the cross-section of the second jig 60 in Figure 11.

[0040] The first jig 50 is a jig for temporarily placing the sealing member, and is used to move the O-ring 40 to the fitting position while holding it, and to temporarily place it. The second jig 60 and the third jig 70, when combined, form a jig for inserting the sealing member. The second jig 60 is equipped with a retaining part to prevent the O-ring 40, which is temporarily placed in the fitting position, from coming off the protruding part 22 during fitting, and the third jig 70 is equipped with an insertion part for fitting the O-ring 40 to a predetermined position in the space 30.

[0041] As shown in Figure 6, the first jig 50 has a rod-shaped handle 51 with a disc-shaped seal holding part 52 at its tip, which has approximately the same diameter as the inner diameter of the tube 10. A groove 53 with approximately the same diameter as the outer diameter of the protrusion 22 is formed on one surface of the seal retaining portion 52. The groove 53 guides the seal retaining portion 52 so that the protrusion 22 fits into it and the O-ring 40 is positioned in the correct location. Furthermore, the surface of the seal holding portion 52 where the groove 53 is formed is provided with a shape-retaining portion 54 to maintain the circular shape of the O-ring 40. The shape-retaining portion 54 is formed along the entire circumference of the groove 53, with the center side protruding in the axial direction and having a radially outward oblique surface. Therefore, the shape-retaining portion 54 contacts the inner circumference of the O-ring 40, maintaining the O-ring 40 in a circular shape.

[0042] The handle 51 is fixed at one end to the center of the seal holding portion 52 on the side opposite to the side on which the shape holding portion 54 is provided. The handle 51 is formed to be longer than the tube 10 so that when the O-ring 40 is fitted into the space 30, the entire first jig 50 is not housed inside the tube 10.

[0043] As shown in Figure 7, the second jig 60 is equipped with a flat retaining portion 62 at the tip of a round bar handle 61. The retaining portion 62 has a rectangular wide surface, and one side opposite to the side to which the handle 61 is fixed is formed in an arc shape with a diameter larger than the outer diameter of the protrusion 22 and smaller than the inner diameter of the tube 10.

[0044] As shown in Figure 8, the third jig 70 has a pipe-shaped handle 71 that is longer than the tube 10 and shorter than the handle 61 of the second jig. At the tip of this handle 71 is an insertion portion 72, which is a plate with a protrusion 73 formed thereon so that its longitudinal cross-section is L-shaped. The protrusion 73 is formed in a range between a circular arc that is larger in diameter than the radius of the projection 22 but smaller in diameter than the tube 10, and a circular arc that is approximately the same diameter as the tube 10, so that it can enter the space 30. Furthermore, the protrusion 73 protrudes from the surface of the insertion portion by a length greater than the distance from the end face of the projection 22 to the location of the O-ring 40 in the space 30. The inner diameter of the handle 71 of the third jig 70 is approximately equal to the diameter of the handle 61 of the second jig. When the handle 61 of the second jig 60 is inserted into the handle 71 of the third jig 70, the insertion part 72 integrates with the retaining part 62, as shown in Figure 9, so as to cover a portion of it.

[0045] By integrating the second jig 60 and the third jig 70, the third jig 70 can rotate relative to the retaining part 62 with the handle 61 as its axis of rotation. Furthermore, the third jig 70 can also be displaced relative to the retaining part 62 along the axial direction of the handle 61.

[0046] (Instructions for installing the O-ring) Next, with reference to Figures 10 and 11, a method for manufacturing a hydraulic cylinder 1 in which the O-ring 40 is fitted into the space 30 using the first jig 50, the second jig 60, and the third jig 70 will be described. First, grease is applied to the seal holding portion 52 of the first jig 50, and the O-ring 40 is attached and held in place while maintaining its circular shape. Then, the first jig 50 is inserted from the cylinder head side of the tube 10, and a temporary sealing member placement step is performed in which the O-ring 40 is positioned in the opening of the space 30. After placement, the O-ring 40 is peeled off the seal holding part 52 by pressing and rotating the first jig, and the first jig 50 is pulled out from inside the tube 10.

[0047] Next, the second jig 60 is inserted into the tube 10. At this time, the handle 71 of the third jig 70 may be fitted onto the handle 61 of the second jig 60 beforehand. Then, the second jig 60 is pushed in until the retaining part 62 contacts the tip surface of the protruding part 22. With the retaining part 62 in contact with the tip surface of the protruding part 22, the sealing member insertion process is performed by fitting the O-ring 40 into the space using the third jig 70. Then, by rotating the third jig 70 around the handle 71 as an axis and performing this process all the way around, the fitting of the O-ring 40 into the space 30 is completed.

[0048] <Second Embodiment> A second embodiment of the present invention will be described with reference to Figures 12 and 13. In the following descriptions of each embodiment, only the differences from the first embodiment will be explained, and similar parts will be omitted.

[0049] In this embodiment, the cylinder end 20 has a first stage portion 23 formed on the circumferential surface of the tip of the projection 22, projecting radially outward. The first stage portion 23 is formed between the tip of the projection 22 (Figure 12) and the position where the end of the burr is formed (Figure 13). When manufacturing the tube, additional material is added to compensate for the length (extrusion allowance) that is reduced due to the formation of the burr during friction welding.

[0050] The protruding portion 22 may also be shaped to have a first step portion 23 on the tip side and a second step portion 24 on the large diameter portion 21 side. Furthermore, although the first stage portion 23 in Figures 12 and 13 was a radial projection, the first stage portion 23 does not necessarily have to have such a structure when applied to the present invention. For example, as shown in Figure 14, the structure may be such that the first stage portion 23 is formed on the tip side, the second stage portion 24 is formed on the base side, and a groove for fitting the O-ring 40 is formed in the projection portion 22.

[0051] (Effects of the second embodiment) The formation of the first stage portion 23 on the protruding portion 22 restricts the movement of the O-ring 40 fitted into the space 30. Therefore, if the first stage portion 23 is formed on the tip side of the protruding portion 22, it provides an anti-dislodgement effect, and if it is formed on the cylinder end side, it prevents excessive pushing. By preventing the O-ring 40 from coming off, the ability to contain the internal burr IB is improved. Also, the O-ring 40 is susceptible to pressure from the hydraulic fluid pressure inside the tube 10, and there is a risk that it may come into contact with the burr and be damaged or cut. Therefore, by forming the first stage portion 23 on the cylinder end side, damage to the O-ring 40 can be prevented.

[0052] Furthermore, the first stage portion 23 and the second stage portion 24 do not necessarily need to be formed continuously over the entire circumferential surface of the protruding portion 22; a portion of the circumference may be removed, or they may be formed at predetermined intervals on the circumferential surface. In that case, fitting and replacing the O-ring 40 becomes easier.

[0053] <Third Embodiment> A third embodiment of the present invention will be described with reference to Figures 15 and 16. In this embodiment, the tube 10 has a third stage portion 11 that protrudes radially toward the center within the range in which the space 30 is formed on the inner circumferential surface.

[0054] Furthermore, the fourth stage portion 12 may be formed on the end side of the tube 10, on the axial side of the position where the internal burr IB is formed. This corresponds to the second stage portion 24 in the second embodiment and restricts the movement of the O-ring 40 so that it does not directly contact the internal burr IB.

[0055] Furthermore, as shown in Figure 15, the third stage portion 11 only needs to be formed at any position within the range 13 that overlaps with the tip of the protruding portion 22 when viewed from the radial direction, and this position can be changed according to the size and shape of the O-ring 40. Furthermore, the tube 10 may have a structure that includes both a third stage 11 and a fourth stage 12.

[0056] In this embodiment, the third stage 11 was formed to protrude toward the axial side, but the tube 10 does not necessarily have to have such a structure when applying the present invention. For example, the third stage may be formed by machining a tapered shape as shown in Figure 17. Alternatively, a groove as shown in Figure 14 may be formed on the side of the tube 10.

[0057] (Effects of the third embodiment) The third stage 11 is formed on the tube 10 side, and it has the same effect as the first stage 23 and second stage 24 described in the second embodiment.

[0058] <Fourth Embodiment> A fourth embodiment of the present invention will be described with reference to Figure 18. Unlike embodiments 1 to 3, the hydraulic cylinder 1 according to this embodiment does not have an O-ring 40 fitted into the space 30 after friction welding. Instead, the inside of the space 30 is filled with a curable filler 41.

[0059] The curable filler 41 filling the space 30 is a resin that hardens upon drying, and integrates with the inner burr IB within the space 30. This prevents the inner burr IB from falling off, and thus prevents metal particles from entering the hydraulic fluid.

[0060] (Effects of the fourth embodiment) Furthermore, the side of the hardened curable filler 41 that is exposed inside the tube 10 has a flat shape and a uniform thickness. Therefore, partial detachment is less likely to occur than with the internal burr IB, and it is rare for small pieces or particles of the hardened filler to mix into the hydraulic fluid. Even if some of the filler peels off, damage to the inside of the tube 10 can be prevented by adjusting the components of the hardening filler to a material softer than the inner burr IB. Furthermore, since the internal burr IB does not come into direct contact with the working fluid, deterioration of the internal burr IB can be prevented, and its detachment can also be prevented.

[0061] <Fifth Embodiment> Next, a fifth embodiment of the present invention will be described with reference to Figure 19. In this embodiment, the cylinder end 20 has a groove 25 formed in the large-diameter portion 21. Due to the formation of the groove 25, a space 30 is expanded inside the cylinder end 20 after friction pressure welding.

[0062] (Effects of the fifth embodiment) The groove 25 expands the space 30, making it possible to form a portion on the large-diameter portion 21 side that is equal to the wall thickness of the tube. Furthermore, as the cylinder end side of the space 30 moves toward the large-diameter portion 21, a region that is flush with the inner circumferential surface of the tube 10 is formed, so the burr formation portion becomes flush. Due to the factors described above, the tube 10 and the cylinder end 20 reach approximately the same temperature during the heating process, making it easier to set the joining conditions and resulting in a good joining state. [Explanation of Symbols]

[0063] 1... Hydraulic cylinder, 10... Tube, 11... Third stage, 20... Cylinder end, 21... Large diameter section, 22... Protruding section, 23... First stage, 30... Space, 40... O-ring, 41... Curable filler, 50... First jig, 60... Second jig, 70... Third jig, TP... Contact section, OB... Outer burr, IB... Inner burr

Claims

1. A method for manufacturing a fluid pressure cylinder, wherein a tube and a cylinder end are joined by friction welding, a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxial with the tube and protruding into the tube, an annular gap is formed between the inner circumferential surface of the tube and the outer circumferential surface of the projection to accommodate internal burrs generated by friction welding, and the annular gap is sealed by a sealing member, A preparation step of preparing the cylinder end, wherein the axial length of the protruding portion is formed to be longer than the sum of the axial length of the internal burr generated by friction welding and the axial length of the sealing member, A friction welding step in which the tube and the cylinder end are coaxially friction-pressed together, and an annular gap is formed between the inner circumferential surface of the tube and the outer circumferential surface of the protrusion, which accommodates the inner burr and allows the sealing member to be attached. The process includes inserting the sealing member into the annular gap to seal the internal burr in the annular gap, A method for manufacturing a fluid pressure cylinder, characterized in that, in the sealing member insertion step, the sealing member is brought into close contact with the inner circumferential surface of the tube and the outer circumferential surface of the protruding portion.

2. A method for manufacturing a fluid pressure cylinder, wherein a tube and a cylinder end are joined by friction welding, a cylindrical projection is formed on the surface of the cylinder end facing the inside of the tube, coaxial with the tube and protruding into the tube, an annular gap is formed between the inner circumferential surface of the tube and the outer circumferential surface of the projection to accommodate internal burrs generated by friction welding, and the annular gap is sealed by a sealing member, A preparation step of preparing the cylinder end, wherein the axial length of the protruding portion is formed to be longer than the sum of the axial length of the internal burr generated by friction welding and the axial length of the sealing member, A method for manufacturing a fluid pressure cylinder, comprising a friction welding step of coaxially friction-welding the tube and the cylinder end, thereby forming an annular gap between the inner circumferential surface of the tube and the outer circumferential surface of the protrusion, which accommodates the inner burr and allows for the installation of the sealing member that is in close contact with the inner circumferential surface of the tube and the outer circumferential surface of the protrusion.

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