Tube provided with branch tube, shock absorber, and method for making them

1. A method for making a shock absorber, the shock absorber comprising:

a cylinder sealingly containing hydraulic fluid;

a piston inserted in the cylinder;

a piston rod coupled with the piston and extending to an exterior of the cylinder;

an outer tube externally disposed around the cylinder;

a separator tube externally disposed around the cylinder and including a cylindrical sidewall that defines an annular passage in communication with an interior of the cylinder;

a reservoir formed between the cylinder and the outer tube outside the separator tube, the reservoir sealingly containing the hydraulic fluid and gas; and

a substantially cylindrical branch tube integrally formed on the cylindrical sidewall of the separator tube, and protruding radially outwardly while defining a passage in communication with the annular passage,

wherein the shock absorber is configured to be mounted between relatively movable two members, the method comprising:

forming a prepared hole on the cylindrical sidewall of the separator tube;

causing a portion of the cylindrical sidewall of the separator tube that surrounds the prepared hole to protrude radially outwardly to form the substantially cylindrical branch tube by burring processing; and

pressing a first side and a second side of a proximal portion of the substantially cylindrical branch tube in a circumferential direction or an axial direction of the cylindrical sidewall of the separator tube from an interior to concave an inner circumferential surface radially outwardly to form at least a portion of a first recess spaced apart from the substantially cylindrical branch tube and at least a portion of a second recess spaced apart from the substantially cylindrical branch tube.

2. The method for making the shock absorber according to claim 1 , wherein

by the pressing, a compression stress by a plastic flow is generated at the first side and the second side of the proximal portion of the substantially cylindrical branch tube,

by the burring processing, a residual stress generated at the proximal portion of the substantially cylindrical branch tube is changed in a compression direction.

3. The method for making the shock absorber according to claim 1 , wherein

in the pressing step, protrusions, which protrude radially outwardly, are formed on outer circumferential surfaces of the first side and the second side of the proximal portion of the substantially cylindrical branch tube which correspond to the first recess and the second recess.

4. The method for making the shock absorber according to claim 1 , wherein

each of the first recess and the second recess has a substantially semicircular shape which surrounds the proximal portion of the substantially cylindrical branch tube.

5. The method for making a shock absorber according to claim 1 , wherein

a burring punch used in the pressing step includes a substantially cylindrical branch tube formation portion having a distal end which is rounded, and an emboss formation portion that is integrally formed at a proximal end of the substantially cylindrical branch tube formation portion and extends in a diametrical direction, and

during the burring processing, the pressing is performed, in which the emboss formation portion of the burring punch abuts against the inner circumferential surface to form the first recess and the second recess.

6. The method for making the shock absorber according to claim 1 , wherein the pressing step is performed after the burring processing.

7. A shock absorber comprising:

a cylinder sealingly containing hydraulic fluid;

a piston inserted in the cylinder;

a piston rod coupled with the piston and extending to an exterior of the cylinder;

an outer tube externally disposed around the cylinder;

a separator tube externally disposed around the cylinder and having a cylindrical sidewall that defines an annular passage in communication with an interior of the cylinder;

a reservoir formed between the cylinder and the outer tube outside the separator tube, the reservoir sealingly containing the hydraulic fluid and gas; and

a substantially cylindrical branch tube integrally formed on the cylindrical sidewall of the separator tube, and protruding radially outwardly while defining a passage in communication with the annular passage,

wherein the shock absorber is configured to be mounted between relatively movable two members, and

wherein the substantially cylindrical branch tube is formed by causing the cylindrical sidewall of the separator tube to protrude radially outwardly, recesses are formed at both sides of a proximal portion of the substantially cylindrical branch tube in a circumferential direction of the cylindrical sidewall of the separator tube by pressing the cylindrical sidewall of the separator tube from an interior thereof to concave an inner circumferential surface radially outwardly, and at least a portion of the recesses are spaced apart from the substantially cylindrical branch tube.

8. The shock absorber according to claim 7 , wherein

the separator tube has protrusions protruding radially outwardly which are formed on outer circumferential surfaces of both sides of the proximal portion of the substantially cylindrical branch tube which correspond to the recesses.

9. The shock absorber according to claim 8 , wherein

each of the recesses has a substantially semicircular shape which surrounds the proximal portion of the substantially cylindrical branch tube.

10. A method for making a shock absorber, the shock absorber comprising:

a cylinder sealingly containing hydraulic fluid;

a piston inserted in the cylinder;

a piston rod coupled with the piston and extending to an exterior of the cylinder;

an outer tube externally disposed around the cylinder;

a separator tube externally disposed around the cylinder and including a cylindrical sidewall that defines an annular passage in communication with an interior of the cylinder;

a reservoir formed between the cylinder and the outer tube outside the separator tube, the reservoir sealingly containing the hydraulic fluid and gas; and

a substantially cylindrical branch tube integrally formed on the cylindrical sidewall of the separator tube, and protruding radially outwardly while defining a passage in communication with the annular passage,

wherein the shock absorber is configured to be mounted between relatively movable two members,

the method comprising:

forming a prepared hole on the cylindrical sidewall of the separator tube;

causing a portion of the cylindrical sidewall of the separator tube that surrounds the prepared hole to protrude radially outwardly to form the substantially cylindrical branch tube by burring processing; and

pressing a vicinity of a proximal portion of the substantially cylindrical branch tube from an inner circumferential surface or an outer circumferential surface to change a residual stress generated at the proximal portion of the substantially cylindrical branch tube by the burring processing in a compression direction to generate a plastic strain to form a press processing portion spaced apart from the substantially cylindrical branch tube.

11. The method for making the shock absorber according to claim 10 , wherein the pressing step includes pressing at least one side of the proximal portion of the substantially cylindrical branch tube along an axial direction of the separator tube.

12. The method for making the shock absorber according to claim 10 , wherein the pressing step includes pressing both sides of the proximal portion of the substantially cylindrical branch tube in a circumferential direction of the cylindrical sidewall of the separator tube.

13. The method for making the shock absorber according to claim 12 , wherein

in the pressing step, recesses are formed at both sides of the proximal portion of the substantially cylindrical branch tube by concaving the inner circumferential surface radially outwardly.

14. The method for making the shock absorber according to claim 13 , wherein

each of the recesses has a substantially semicircular shape which surrounds the proximal portion of the substantially cylindrical branch tube.

15. The method for making the shock absorber according to claim 10 , wherein the pressing step is performed during the burring processing.

16. The method for making the shock absorber according to claim 10 , wherein the pressing step includes pressing the proximal portion of the substantially cylindrical branch tube from an interior thereof.

17. The method for making the shock absorber according to claim 16 , wherein

in the pressing step, recesses are formed at both sides of the proximal portion of the substantially cylindrical branch tube in a circumferential direction of the cylindrical sidewall of the separator tube by concaving the inner circumferential surface radially outwardly.

18. The method for making the shock absorber according to claim 17 , wherein

in the pressing step, protrusions, which protrude radially outwardly, are formed on outer circumferential surfaces of both sides of the proximal portion of the substantially cylindrical branch tube which correspond to the recesses.

19. The method for making the shock absorber according to claim 10 , wherein

a burring punch used in the pressing step includes a substantially cylindrical branch tube formation portion having a distal end which is rounded, and an emboss formation portion that is integrally formed at a proximal end of the substantially cylindrical branch tube formation portion and extends in a diametrical direction, and

during the burring processing, the residual stress is changed, in which the emboss formation portion of the burring punch abuts against the inner circumferential surface to press the inner circumferential surface.

20. The method for making the shock absorber according to claim 10 , wherein the pressing step is performed after the burring processing.