Patent Application
20120131797
1. Field of the Invention
The present invention relates to a processing method of a tube body wherein thickness of an end portion of the tube body is reduced by plastic working so as to finish in a predetermined dimension, a manufacturing method of a cylinder device using the processing method, and the cylinder device manufactured by the same.
2. Description of the Related Art
For example, as regards a hydraulic damper (shock absorber) of a twin tube type, as shown in
In this type of hydraulic damper, the rod guide 4 and the oil seal 5 are fitted into the open end of the outer cylinder 2 and prevented from falling off with a bended segment 2a which is an end portion of the outer cylinder 2 being bended inside in a radial direction. Further, at the end portion of the outer cylinder 2, a cap 7 for receiving a bump stopper 9 is installed in such a condition that the cap 7 is pressed-in to the outer periphery of the outer cylinder 2. The cap 7 is provided with a plurality of (for example, three) projections 7a on the inner bottom side thereof so as to fix in an axial direction by abutting the projections 7a to the bended segment 2a.
Here, as regards the end portion of the outer cylinder 2 described hereinabove, its internal diameter side is applicable as a fitting portion of the rod guide 4 and the oil seal 5 while its external diameter side is applicable as a press-fitting portion of the cap 7. Accordingly, not only dimensions of those internal and external diameters, but also concentricity, circularity, etc. of the end portion of the outer cylinder 2 should be highly precise. Further, in order not to damage the oil seal 5 in assembly, it is required for the inner surface of the end portion of the outer cylinder 2 to maintain well-conditioned surface roughness. Still further, to smoothly perform bending of the bended segment 2a, it is desirable that thickness of the end portion of the outer cylinder 2 is as thin as possible. Especially, in case of a hydraulic damper for a strut suspension, thickness of the outer cylinder 2 will be relatively large, whereby it is required to make the end portion of the outer cylinder 2 thinner.
As discussed above, the external diameter of the outer cylinder 2 is used as the press-fitting portion of the cap 7 thereby being necessary to retain a predetermined dimension for the external diameter. Accordingly, as regards the hydraulic damper for the strut suspension, the end portion of the outer cylinder 2 is made to be thin normally by cutting the inner surface of the end portion of the outer cylinder 2 to form a multi-stepped portion. Specifically, as shown in
However, highly precise work will be needed to perform conventional methods in which the end portion of the outer cylinder 2 is processed by cutting work, so that it inevitably requires considerable time and man-hour, resulting in increase of work cost. Further, there is a risk that chips or burrs produced by the cutting work adhere to the inner surface of the outer cylinder 2, and then enter as foreign materials (contamination) into the hydraulic damper. Here, the purpose of finishing the end portion of the outer cylinder 2 to form the multi-stepped portion as discussed above is to minimize strength reduction caused by thinning as much as possible.
Based on the above, finishing the end portion of the outer cylinder 2 through plastic working has been well examined. For example, US Patent Application Publication 2005/0011245 A1 (hereinafter reference 1), a counterpart application of Japanese Patent Application Unexamined Publication No. 2003-225725, discloses the following processing method: a mandrel is inserted into a base tube; and an end portion of the base tube is attached to the mandrel by performing a parallel swaging work with a die. With this method, the end portion of the base tube is processed with ironing through the parallel swaging work by squeezing thereof between the mandrel and the die. Accordingly, it is possible to make the end portion of the outer cylinder 2 to be thin formation while maintaining precise dimension and well surface roughness.
However, according to the processing method of the reference 1, it would be necessary to obtain a predetermined area reduction rate through a single parallel swaging work. Thus, in case of obtaining the predetermined area reduction rate with respect to the hydraulic damper for the strut suspension in which to have a relatively thick outer cylinder (tube body), molding force necessary for the parallel swaging work needs to go over a buckling load of the base tube, being virtually incapable of molding such a hydraulic damper. Further, since the ironing is performed while squeezing the end portion of the base tube, the external diameter of the end portion of the outer cylinder 2 will be narrowed, whereby a design change may be required for sheathing parts such as the cap 7 to be pressed in or sheathing the end portion of the outer cylinder 2.
The present invention has been made in light of the above problem, and it is an object of the present invention to provide a processing method of a tube body, a manufacturing method of a cylinder device and the cylinder device thereof being able to process an end portion of the tube body in a high degree of accuracy without depending on cutting work which generates chips or burrs when processing an inner periphery of the tube body.
In order to achieve the object described above, according to a first aspect of the present invention, there is provided a processing method of a tube body comprising the steps of: a tube-expanding step wherein a base tube is partially retained with a chuck unit having a rotational function, and a mandrel is pressed in to an end portion of the base tube so as to expand the end portion of the base tube; and a rotation ironing step wherein the chuck unit rotates the base tube together with the mandrel, a roller die is pressed against an outer-periphery surface of the end portion of the base tube and the roller die is moved with respect to the base tube and in an axial direction thereof so as to deform an inner-periphery surface of the end portion of the base tube into a shape corresponding to an external shape of the mandrel.
According to a second aspect of the present invention, there is provided a manufacturing method of a cylinder device comprising the steps of: a manufacturing step of manufacturing a cylinder by the processing method of a tube body according to claim 1; an assembling step of assembling interior parts including a piston, a piston rod and a rod guide into the cylinder; and a curling process of curling a tip end portion of the cylinder so as to prevent the interior parts from falling off.
According to a third aspect of the present invention, there is provided a cylinder device comprising: a cylinder; a rod adapted to be compressed into or extended from one end of the cylinder; a rod guide inserted into the one end of the cylinder so as to support the rod; and a curled portion formed by curling a tip end portion of the cylinder so as to prevent the rod guide from falling off from the cylinder, wherein the cylinder is formed by pressing a mandrel into an end portion of a base tube, and pressing a roller die against the base tube so as to deform an inner-periphery surface of the end portion of the base tube along an outer-periphery surface of the mandrel.
According to a fourth aspect of the present invention, there is provided a cylinder device comprising: a rod adapted to be compressed into or extended from one end of the cylinder; a rod guide inserted into the one end of the cylinder so as to support the rod; and a curled portion formed by curling a tip end portion of the cylinder so as to prevent the rod guide from falling off from the cylinder, wherein a thickness reduction rate of the one end of the cylinder is 50% or less.
With the present invention based on the above, it is possible to accurately process the end portion of the tube body without depending on any types of cutting work generating chips or burrs in process of the inner periphery of the tube body.
FIG. 9C′ and FIG. 9E′ are cross-sectional views sequentially showing a processing method of the tube body according to the second embodiment of the present invention, wherein: FIG. 9C′ shows an initial stage of a rotation ironing process; and FIG. 9E′ shows a final stage of the rotation ironing process;
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
To perform a processing method of the present invention, as shown in
The mandrel 11 is provided with, as well shown in
Hereinafter, embodiments of the processing method of the present invention will be described according to figures. First, as shown in
Next, as shown in
Following the tube expanding process described above, as shown in
The pair of roller dies 22/22 will stop its shift when reaching to the maximum diameter portion 13 of the mandrel 11, and then, as shown in
The outer cylinder 2 finished through the above process has its inner surface of the end portion, as shown in
Hereinbelow, assembling processes of the rod guide 4, etc. and a curling process are explained with reference to
First, the inner cylinder 1 sub-assembled with the bottom valve BV is inserted into the outer cylinder 2, and then the piston rod 3 installed with the piston 8 and the piston valve PV is inserted into the inner cylinder 1. Next, the rod guide 4 sub-assembled with all kinds of seals or a guide bushing is inserted into the piston rod 3 so as to fit the rod guide 4 to the piston rod 3. At this time the oil seal 5 is also inserted. If necessary, oil or gas can be enclosed.
Second, while abutting a roller 30 over the tip end portion of the outer cylinder 2, the outer cylinder 2 is rotated so as to perform a full-curling process. Here, it is not necessary to perform the full-curling process as shown in figures, but another processes can be applied such as: an oscillating curl process producing a full-curling by rotating inclined dies and abutting the dies over the end surface of the outer cylinder 2; or a process producing partial curling portions by partially caulking the outer cylinder 2, may be 4 portions, in a circumferential direction. That is, as long as the parts such as the rod guide 4 are not pulled out from the outer cylinder 2, any methods (curling the tip end portion of the outer cylinder 2 inside) can be applied. Here, thickness of the second diameter expanding portion 2B is considerably reduced whereby the second diameter expanding portion 2B is hardened due to advancement of a structural denseness; however, it does not affect facilitation of the curling process. Especially, in the oscillating curl process, advancement of the structural denseness hereinabove described is prominent; however, by performing the above-described oscillating curl process in a full circumference, the full-curling can be performed in such a manner as to squash the structurally dense portions (hardened portions) in an axial direction. Accordingly, bending of the bended segment 2a (
In general vehicle shock absorbers (cylinder devices), it is usual to use a tube having thickness approximately between 2.5 mm to 3.5 mm. Considering such a tube, and supposing a thickness reduction rate of a cylinder as more than 30%, it is still possible to obtain the high strength tube without cracks with the oscillating curl process in a full circumference. Further, necessary removing force of a sealing means including rod guides or seals in a vehicle shock absorber is 25 kN in general. In the above case of the oscillating curl process, the removing force more than 25 kN can be obtained.
Further, the following result has been verified by experiments: 1) removing force of 42 kN can be obtained in case that thickness is 2.5 mm and a thickness reduction rate is 35%; 2) removing force of 60 kN can be obtained in case that thickness is 2.9 mm and a thickness reduction rate is 41%; and removing force of 65 kN can be obtained in case that thickness is 3.2 mm and a thickness reduction rate is 47%. Here, if the thickness reduction rate is too high, it is possible to get materials too hardened thereby occurring cracks. Based on this result, the upper limit of the thickness reduction rate should be set approximately 50%.
The first diameter expanding portion 2A functioning as the fitting portion of the rod guide 4 is secured with enough thickness, whereby strength deterioration thereof is limited, and there is no problem for strength with respect to the outer cylinder 2. On the other hand, the external diameter of the outer cylinder 2 is finished to have a evenly flat surface with the outer periphery of the general portion of the base tube 10, the cap 7 conventionally applied can be used as it is. See
In the above first embodiment, the mandrel 11 with two steps made by the first forming portion 14 and the second forming portion 15 having different diameters was applied, but the number of the steps provided at the nose of the mandrel 11 is optional. If desired for thinner tubes, only one step may be applied, or if desired for more thick tube, three steps or more can be applied.
Further, in the embodiments hereinabove described, the pair of the roller dies 22/22 facing toward each other is used for the rotation ironing process; however, the number of the roller die 22 to be provided is also optional. Three roller dies 22 may be applied. Here, in case three roller dies 22 or more are applied, those roller dies 22 should be evenly arranged around the base tube 10. In addition, the present invention is applicable with a planetary ball die instead of the roller die.
In the first embodiment, the roller dies 22/22 are shifted along the base tube; however, the present invention is not limited thereto. Instead, the base tube itself may be shifted without shifting the roller dies 22/22 in an axial direction.
Still further, in the first embodiment, shift of the rotating shaft of the roller dies 22/22 in a radial direction is restricted while the roller dies 22/22 shift in an axial direction. The inner surface of the base tube 10 is thus processed to form the outer shape of the mandrel 11, and the outer diameter of the base tube 10 is formed evenly. The present invention is not limited to the above structure, but for example, as shown with a long dashed short dashed line in
In case that the reduction rate of the tube thickness is modified and if the outer diameter of the base tube 10 needs to be even, cutting work may be performed on the outer periphery of the base tube 10 (cutting process). In this case, a tool bit 23 (hereinafter described in details) as shown in
Furthermore, the reduction rate of the tube thickness can be also modified by a method shown in
Next, a processing method of a tube body in a second embodiment will be described with reference to
In the second embodiment, as the same with the process shown in
Next, as shown in FIG. 9C′, the mandrel 11 is pressed into the tip end portion of the base tube 10 retained by the chuck 21. The press-in of the mandrel 11 is performed until the end portion of the base tube 10 is abutted to the diameter expanding portion 16A (abutting portion 13A) Accordingly, the inner surface of the end portion of the base tube 10 is to be expanded into a stepped formation by the first and second forming portions 14/15 of the mandrel 11 (tube-expanding process). The base tube 10 will be rotated through operation of the chuck unit 20 at a predetermined speed.
Following the tube-expanding process, the pair of roller dies 22/22 is each shifted toward each other and then abut to a portion adjacent to the end portion of the base tube 10. Through this abutment, each of the roller dies 22/22 will roll over the outer periphery of the base tube 10 rotated and shift in parallel toward the tip end portion of the base tube 10. See
In
In case that low-cost welded tubes are used, it is possible that sizes thereof may not be constant so that processes of the end portion of the base tube 10 may be hampered in the first embodiment. However, in the second embodiment, even if the sizes of the base tube 10 are each different, the processes can be adjusted by cutting the thin padding portion 24. Accordingly, tubes with less accuracy can be applied. The other functional effects are the same with the first embodiment, whereby detail explanation will be omitted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-94307 | Mar 2007 | JP | national |
| 2008-38918 | Feb 2008 | JP | national |
This is a continuation of application Ser. No. 12/078,228, filed Mar. 28, 2008. The present application claims priority based on Japanese Patent Applications No. 2007-94307, filed Mar. 30, 2007 and No. 2008-38918 filed Feb. 20, 2008, the entirety of which being incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12078228 | Mar 2008 | US |
| Child | 13305430 | US |
