JPH11270677A - Cylinder device, and manufacture of piston rod used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold the sliding surfaces of a piston rod and sealing member in between in an always lubricated condition even in case a nitride film and oxide film are formed on the periphery of the piston rod. SOLUTION: A nitride film is formed on the outside surface of a metal member as a base for a piston rod 4, and thereon an oxide film 7 is formed. The surface of this oxide film 7 is over the whole length subjected to a buff polishing process in the circumferential direction, and thereby a number of transverse grooves 8 are formed in the film 7. This is subjected to an axial direction buff polishing process approx. over the whole length, and thereby a number of longitudinal grooves 9 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder device such as a gas spring used for opening and closing a back door and the like of a wagon car, and a method of manufacturing a piston rod used therefor.

[0002]

2. Description of the Related Art In general, as a cylinder device, a gas spring described in, for example, Japanese Utility Model Laid-Open Publication No. Sho 56-108036 (hereinafter referred to as a first prior art) is known.
The gas spring has a cylindrical tube in which compressed gas is sealed together with an oil liquid, a piston slidably provided in the tube, and a piston defining two gas chambers in the tube. A piston rod provided on the piston and having the other end protruding out of the tube via a rod guide provided on the tube; and a piston rod provided on the rod guide and in sliding contact with the outer periphery of the piston rod. And a seal member for preventing fluid in the tube from leaking to the outside.

[0003] The gas spring according to the first prior art is applied to, for example, a back door of a wagon car, and is mounted on a vehicle body side and a back door side.
When the door is closed, the piston rod is extended and retracted with respect to the cylinder.

The extension of such a piston rod,
When the piston rod moves in and out of the cylinder in response to the contraction operation, each gas chamber in the cylinder expands and contracts, thereby generating a repulsive force (spring force) in each gas chamber. At this time, a damping force (buffering effect) is generated by flowing the compressed gas between the gas chambers through an orifice or the like provided in the piston.

[0005] Here, a space is formed below the seal member provided between the cylinder and the piston rod for storing an oil liquid between the cylinder and the outer peripheral side of the piston rod. When a part of the oil liquid (oil film) adhered to the piston rod in the cylinder is scraped off by the seal member during the expansion and contraction operation, the scraped oil liquid is temporarily removed in the space. It is stored (captured).

[0006] The oil stored in the space prevents the pressurized gas in the cylinder from leaking.
In the extension stroke of the piston rod, a state in which the oil liquid is previously attached to the piston rod in the space and the oil liquid is contained between the sliding surfaces of the piston rod and the seal member, that is, a state of so-called "wet contact" Thus, the piston rod is slid with respect to the seal member, and the sliding resistance between the sliding surfaces is reduced to obtain good sliding characteristics.

A second prior art is disclosed in Japanese Utility Model Application Laid-open No.
A gas spring described in Japanese Patent No. 72945 is known. In the second prior art, a first seal member is provided between a cylinder and a piston rod, and the first seal member directly receives gas pressure from a compressed gas, and a pressure between the cylinder and the piston rod is increased. A second seal member is disposed between the first seal member and the air side opposite to the gas chambers in the cylinder with the first seal member interposed therebetween.
An oil reservoir space for filling the oil liquid is formed on the outer peripheral side of the piston rod between the seal members.

[0008] In this case, when the piston rod slides with respect to the first seal member in the process of reducing the piston rod, the oil liquid can be previously attached to the piston rod in the oil reservoir space, This also allows the piston rod to slide in a "wet contact" state with respect to the seal member, as in the first prior art, and provides good sliding characteristics.

[0009]

In the first prior art described above, when the piston rod is kept in contact with the outside air for a long time while the piston rod is extended from the cylinder, the piston rod is not extended. The oil film (extremely thin film) on the outer peripheral surface may evaporate in the atmosphere. Therefore, when the next reduction stroke is performed in this state, the piston rod is reduced into the cylinder in a state in which almost no oil liquid is contained between the sliding surfaces of the piston rod and the seal member, that is, in a so-called “dry contact” state. Move it.

[0010] As a result, the sliding resistance between the piston rod and the seal member becomes extremely large, and the seal member is worn out or damaged at an early stage, and the life of the seal member is shortened. is there.

On the other hand, in the second prior art, a second seal member is provided above (atmospheric side) a first seal member which directly receives gas pressure in a cylinder, and an oil liquid is provided between the seal members. Is formed, the piston rod can be slid in the state of "wet contact" with the first seal member by the oil liquid in the oil reservoir space even in the reduction stroke. Thus, the problem of the first related art can be solved.

However, in such a conventional technique,
It is necessary to newly provide a second seal member and the like in addition to the first seal member, which increases the number of parts,
There is a problem that the entire structure and the like are complicated.

It has also been studied to improve the corrosion resistance and wear resistance of the piston rod by subjecting the surface of the piston rod to hard chrome plating or the like. Since a plurality of fine “cracks” called channel cracks are formed on the surface of the hard chromium plating layer, a part of the oil liquid in the cylinder retained on the seal member side is partially filled with the hard chrome. The gas spring oozes out to the sliding surface between the seal member and the piston rod through the “crack” of the plating so as not to affect the life of the gas spring.

Thus, the sliding surface between the seal member and the piston rod can be always kept in a lubricated state regardless of whether the piston rod extends or contracts. Therefore, in this case, there is an advantage that it is not necessary to specially provide the second seal member and the like as described in the second related art, and the entire structure can be simplified.

On the other hand, in recent years, in order to enhance the corrosion resistance and abrasion resistance of the piston rod in consideration of environmental considerations, the outer peripheral surface of the piston rod has been replaced with hard chromium plating, and gas nitrocarburizing has been performed. A method of protecting the sliding (outer peripheral) surface of the piston rod by performing a treatment and an oxidation treatment is being studied.

However, the piston rod which has been subjected to the gas nitrocarburizing treatment and the oxidation treatment does not have any "cracks" generated when the hard chromium plating treatment is performed. For this reason, the seepage amount (supply amount) of the oil liquid from the cylinder to the sliding surface between the seal member and the piston rod is significantly reduced. As a result, there is a problem that the sliding resistance between the sliding surfaces increases, which also causes the seal member to be worn and damaged early.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention provides a method of forming a seal member and a piston rod even when a piston rod subjected to a gas soft nitriding treatment and an oxidation treatment is used. A cylinder device and a piston rod used for the same that can maintain the lubrication state between the sliding surfaces at all times to greatly reduce the sliding resistance between the sliding surfaces and greatly extend the life of the seal member and the like. The purpose of the present invention is to provide a manufacturing method.

[0018]

In order to solve the above-mentioned problems, the present invention provides a tubular tube in which an oil liquid is sealed, a piston slidably provided in the tube, A piston rod having one end connected to the piston and the other end projecting out of the tube via a rod guide provided in the tube, and a piston rod provided in the rod guide and slidably contacting the outer periphery of the piston rod; The present invention is applied to a cylinder device including a seal member for sealing between a rod guide and preventing leakage of oil in the tube to the outside.

A feature of the structure adopted by the first aspect of the present invention is that the piston rod has a cylindrical metal body, a nitride film provided on the outer surface of the metal body, and a piston film formed on the outer surface of the nitride film. A cylinder device comprising: an oxide film provided; and a circumferential lateral groove and an axial longitudinal groove formed on an outer surface of the oxide film.

With this configuration, the piston rod can cover the outer surface of the metal body with the nitride film, and can cover the surface of the nitride film with the oxide film. Corrosion resistance and abrasion resistance can be improved.

Further, since the piston rod has a circumferential lateral groove and an axial longitudinal groove formed on the surface of the oxide film, when the cylinder device is used in an inverted state, one of the oil liquid in the cylinder is removed. The portion can be guided to the sliding contact surface between the piston rod and the seal member through the lateral groove and the vertical groove, and the sliding contact surface can be always kept in a lubricated state.

According to the second aspect of the present invention, the lateral groove is provided over substantially the entire length of the outer periphery of the piston rod, and the vertical groove faces at least the seal member when the piston rod reaches the most extended position. Provided at the site.

With this configuration, when the piston rod is extended to the maximum extension position, the piston rod is provided with the vertical groove and the horizontal groove at a portion facing the seal member, so that the oil liquid in the cylinder is Can be guided to the sliding contact surface between the piston rod and the seal member through the vertical groove and the horizontal groove. Thus, when the piston rod is reduced from the most extended position, the sliding contact surface between the seal member and the piston rod can be maintained in a lubricated state.

According to the third aspect of the present invention, the oxide film has a circumferential surface roughness Ra of 0.06 to 0.15 μm, and an axial surface roughness Ra of 0.03 to 0.5 μm. 07 μm
It is.

With this configuration, a part of the oil liquid in the tube can be satisfactorily guided to the sliding contact surface between the piston rod and the seal member through the horizontal groove and the vertical groove.

Further, according to the invention of claim 4, a cylindrical tube in which an oil liquid is sealed, a piston slidably provided in the tube, one end connected to the piston, and the other end connected to the piston. A piston rod protruding out of the tube through a rod guide provided on the tube, and slidingly contacting the outer periphery of the piston rod provided on the rod guide to seal between the piston rod and the rod guide, The present invention is applied to a method for manufacturing a piston rod used for a cylinder device including a seal member for preventing oil liquid in a tube from leaking to the outside.

In the manufacturing method according to the present invention, a gas nitrocarburizing process is performed on an outer surface of the piston rod to form a nitride film, and a nitrocarburizing process is performed on the outer surface of the nitrocarburized piston rod. An oxide film forming step of forming an oxide film, and thereafter, a circumferential buff polishing step of forming a circumferential lateral groove on the surface of the oxide film by circumferential buff polishing, and a surface of the oxide film by axial buff polishing. One of the axial buffing steps for forming a longitudinal groove in the axial direction is performed first, and the other step is performed later.

With this configuration, a nitride film can be formed on the outer periphery of the piston rod in the gas nitrocarburizing process, and an oxide film can be formed on the surface of the nitride film in the oxide film process. In the circumferential buffing step, a number of lateral grooves can be easily formed in the oxide film in the circumferential direction by subjecting the surface of the oxide film to buffing in the circumferential direction. In the axial buffing step,
By subjecting the surface of the oxide film to buffing in the axial direction, a large number of longitudinal grooves can be easily formed in the oxide film in the axial direction.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cylinder device according to an embodiment of the present invention will be described below with reference to an example in which the cylinder device is applied to an inverted (spring end of a tube is directed downward) gas spring.

FIGS. 1 to 6 show a first embodiment of the present invention. In the figure, reference numeral 1 denotes a tube having a closed cylindrical shape, in which a pressurized gas and a certain amount of an oil liquid 2 are placed.
Are sealed, and the oil liquid 2 is sealed by a seal member 11 described later. As shown in FIG. 2, the tube 1 is formed with an annular stopper 1A which is located at the lower end side and engages with a piston 3 which will be described later. It regulates.

Reference numeral 3 denotes a piston slidably provided in the tube 1. The piston 3 defines two gas chambers A and B in the tube 1 above and below. The piston 3 has an orifice passage 3A communicating between the gas chambers A and B.

Reference numeral 4 denotes a piston rod. The upper end of the piston rod 4 is provided integrally with the piston 3, and the lower end of the other end of the piston rod 4 extends outside the tube 1 via a rod guide 10 described later. It is protruding.

As shown in FIGS. 3 to 6, the piston rod 4 has a metal body 5 formed in a columnar shape and a nitride film 6 formed on the outer surface of the metal body 5 over the entire circumference. When,
An oxide film 7 formed over the entire surface of the nitride film 6 and slidably in contact with a lip 11A of a seal member 11 described later.
, Formed in the surface of the oxide film 7 over the entire length in the circumferential direction, and the axial vertical grooves 9, 9 formed in the surface of the oxide film 7 over the entire length. , ....

The horizontal grooves 8 and the vertical grooves 9 are configured to guide a part of the oil liquid 2 in the tube 1 to a sliding surface between the oxide film 7 and the lip portion 11A of the seal member 11. The oxide film 7 on which the lateral grooves 8 and the longitudinal grooves 9 are formed has a circumferential surface roughness Ra of 0.06 to 0.15 μm.
m, and the surface roughness Ra in the axial direction is 0.03-0.
It is preferably about 07 μm.

Reference numeral 10 denotes a rod guide provided on the open end side (lower end side) of the tube 1. The rod guide 10 is formed as a short-axis cylindrical body, and its outer peripheral side is formed inside the open end side of the tube 1. It is fitted around. The rod guide 10 penetrates the piston rod 4 through a small gap on its inner peripheral side, and guides the piston rod 4 movably in the axial direction (up and down) of the tube 1.

Reference numeral 11 denotes a seal member provided between the tube 1 and the piston rod 4.
As shown in FIG. 2, the outer peripheral side is fitted on the inner peripheral surface of the tube 1, and the inner peripheral side is a lip portion 11 </ b> A which is in sliding contact with the surface of the oxide film 7 of the piston rod 4 with an interference. The lip portion 11A of the seal member 11 seals the gap between the lip portion 11A and the oxide film 7 of the piston rod 4 in a liquid-tight manner, so that leakage of the oil liquid 2 in the tube 1 to the outside is minimized. ing.

The gas spring according to the present embodiment has the above-described configuration. When the gas spring is mounted on, for example, a back door of a wagon car, the mounting bracket 12 provided on the upper end side of the tube 1 is used. Is mounted on the body side of the wagon car, and the mounting bracket 13 provided on the lower end side of the piston rod 4 is mounted on the back door side.

When the back door is opened and closed, the gas spring body rotates, and the piston rod 4 is further extended and contracted with respect to the tube 1. Further, when the back door is closed, the protruding end of the piston rod 4 is in a state of inverting downward, but when the back door is opened, the protruding end of the piston rod 4 is in an upright state.

When the piston 3 moves (slids) in the tube 1 in accordance with the extension and contraction of the piston rod 4 when the back door is opened and closed, the gas chambers A and B in the tube 1 expand and contract. The gas chambers A and B generate a repulsive force (spring force). At this time, a damping force is generated by the pressurized gas flowing between the gas chambers A and B via the orifice passage 3A of the piston 3.

Next, a method of manufacturing the piston rod 4 used for the gas spring will be described.

First, in the nitrocarburizing process, a gas nitrocarburizing process is performed on the outer periphery of the metal body 5 to form a nitride film 6 on the outer surface of the metal body 5 with a thickness of, for example, about 20 μm (FIG. 3). ).

Next, in the oxide film forming step, the outer periphery of the metal body 5 on which the nitride film 6 is formed is subjected to an oxidation treatment,
An oxide film 7 is formed on the surface of the nitride film 6 with a thickness of, for example, about 1 μm (FIG. 4).

Next, in the circumferential buffing step, the oxide film 7 is removed.
A large number of lateral grooves 8 are formed by buffing the surface over substantially the entire length thereof in the circumferential direction (FIG. 5). Here, the abrasive used for the buff polishing preferably has a maximum particle diameter of the abrasive powder of, for example, about 36 to 46 μm. When this abrasive is used, the surface roughness Ra of the oxide film 7 in the circumferential direction (hereinafter, referred to as circumferential surface roughness Ra) can be formed to about 0.06 to 0.15 μm. .

Further, in the axial buffing step, the oxide film 7 on which the lateral grooves 8 are formed is subjected to axial buffing over substantially the entire length thereof, so that a large number of vertical grooves 9, 9, and 9 are formed.
Are formed (FIG. 6). Also, in this axial buffing step, the surface roughness Ra (hereinafter referred to as axial surface roughness Ra) of the oxide film 7 in the axial direction is obtained by using the same abrasive as the above-mentioned circumferential buffing. 0.03-0.07
It can be formed to about μm.

In the above manufacturing method, the axial buffing step is performed first and then the axial buffing step, but the axial buffing step and the circumferential buffing step are performed later. You may.

Thus, in the present embodiment, the metal body 5 of the piston rod 4 can be double-coated (protected) by the nitride film 6 and the oxide film 7, and the wear resistance and corrosion resistance of the metal body 5 can be improved. Can be increased, and environmental considerations can be made.

Further, by mounting the gas spring so that the gas spring is turned upside down when the back door is closed, a part of the oil liquid 2 in the tube 1 is transferred to each of the horizontal grooves 8 and the vertical grooves 9 formed in the oxide film 7. Thus, the sliding contact surface between the piston rod 4 and the lip portion 11A of the seal member 11 can be brought into contact with each other in a “wet contact” state with the oil liquid 2.

Then, the surface roughness R in the circumferential direction of the oxide film 7 is next determined.
In order to investigate the influence of a and the surface roughness Ra in the axial direction on the sliding characteristics between the piston rod 4 and the seal member 11, experiments were conducted on Examples 1 and 2 of the embodiment and Comparative Examples 1 to 4. And the experimental results shown in Table 1 were obtained.

In this experiment, the piston rod 4 was set to 50,000 at a cycle of 0.17 Hz (100 mm / s).
After the extension and contraction operations were performed up to the maximum, the sliding resistance between the piston rod 4 and the seal member 11 was measured. The sliding resistance was calculated as the difference between the two gas pressures by measuring the gas pressure in the gas chamber A when the piston rod 4 expanded and contracted.

[0050]

[Table 1]

First, in Example 1, a nitrocarburizing step, an oxide film forming step, a circumferential buffing step and an axial buffing step were respectively performed to obtain a circumferential surface roughness Ra of the oxide film.
Was set to 0.12 μm, and the surface roughness Ra in the axial direction was set to 0.06 μm. Thus, in Example 1, the sliding resistance between the piston rod and the seal member 11 became 85N.

In the second embodiment, the same steps as in the first embodiment are performed, and the surface roughness Ra of the oxide film in the circumferential direction is set to 0.1.
10 μm and the axial surface roughness Ra were set to 0.04 μm. Thereby, in Example 2, the sliding resistance between the piston rod and the seal member 11 became 65N.

On the other hand, in Comparative Example 1, the nitrocarburizing step and the oxide film forming step were performed as in Examples 1 and 2, but the circumferential buffing step and the axial buffing step were omitted. .

Thus, in Comparative Example 1, as shown in Table 1, both the circumferential surface roughness Ra and the axial surface roughness Ra of the oxide film showed larger values than those of Examples 1 and 2. Was. In Comparative Example 1, the sliding resistance value was found to be about 3 to 4 times as large as those in Examples 1 and 2, and it was determined to be unacceptable.

In Comparative Examples 2 to 4, the nitrocarburizing step, the oxide film forming step, and the circumferential buffing step were performed as in Examples 1 and 2, but the axial polishing step was omitted. I have.

Thus, in Comparative Examples 2 to 4, as shown in Table 1, the circumferential surface roughness Ra of the oxide film was set to be smaller than or similar to those of Examples 1 and 2. However, the surface roughness Ra in the axial direction showed a larger value than those in Examples 1 and 2. Also in Comparative Examples 2 to 4, the sliding resistance value was found to be about 1.5 to 2 times as large as those in Examples 1 and 2, and it was determined to be unacceptable.

Therefore, according to the present embodiment, by providing the horizontal groove 8 and the vertical groove 9 in the oxide film 7 of the piston rod 4, oil can be stored in each groove, and the piston rod 4 and the sealing member A stable oil film can be formed between the sliding surfaces of the eleventh lip and the lip part 11A, and the sliding resistance between the two can be reduced.

As a result, the durability of the seal member 11 is improved.
The wear resistance and the like can be increased to extend the life and the like, and the piston rod 4 subjected to the gas nitrocarburizing treatment and the oxidation treatment can be easily applied to the gas spring. Further, "dry contact" as described in the first prior art can be reliably prevented, and it is not necessary to additionally provide a second seal member or the like as described in the second prior art. , The overall structure and the like can be simplified.

Next, FIG. 7 shows a second embodiment of the present invention. In this embodiment, the same reference numerals are given to the same components as those in the first embodiment, and the description will be given. It shall be omitted. However, a feature of this embodiment is that a piston rod 21 is provided instead of the piston rod 4 described in the first embodiment, and the surface of the oxide film 22 provided on the piston rod 21 has .. Are formed over substantially the entire length, and the oxide film 2 is formed.
.. Are provided with axial longitudinal grooves 24, 24,... Only at a portion facing the seal member 11 when the piston rod 21 reaches the most extended position.

Here, the piston rod 21 is substantially the same as the piston rod 4 described in the first embodiment, and includes a metal body, a nitride film (none of which is shown), an oxide film 22, and a lateral groove 2.
3 and the vertical groove 24. The lateral groove 23 of the piston rod 21 is formed on the surface of the oxide film 22 over substantially the entire length.

However, the vertical groove 24 is different from that of the first embodiment in that the vertical groove 24 is formed only in a portion accommodated in the tube 1 when the piston rod 21 is extended to the maximum extension position. I have.

Next, a method of manufacturing the piston rod 21 according to the present embodiment will be described. In the present embodiment, a nitrocarburizing process for subjecting the metal body of the piston rod 21 to nitrocarburizing, An oxide film forming step of forming an oxide film 22 on the outer surface of the formed metal body, and buffing in the circumferential direction on the surface of the oxide film 22 to form each lateral groove 23
The process up to the circumferential buffing step of forming the same is the same as that of the first embodiment.

However, in the axial buffing step according to the present embodiment, the axial groove is buffed only at the portion accommodated in the tube 1 when the piston rod 21 is at the most extended position, so that each longitudinal groove is formed. 24 in that
This is different from that of the first embodiment.

Then, the circumferential surface roughness Ra and the axial surface roughness Ra of the oxide film 22
An experiment was conducted based on Example 3 and Comparative Example 5 of the embodiment to investigate the effect on the sliding characteristics between the seal member 11 and the sealing member 11, and the experimental results shown in Table 2 could be obtained. Was.

In this experiment, the piston rod 21 was extended and contracted at a cycle of 0.17 Hz (100 mm / s) at the full stroke (from the maximum extension to the minimum contraction) of the piston rod. Further, the sliding resistance shown in Table 2 was calculated by using the same method as in the experiment described in the first embodiment.

[0066]

[Table 2]

First, in Example 3, a soft nitriding step, an oxide film forming step, a circumferential buffing step, and an axial buffing step were respectively performed to obtain a circumferential surface roughness Ra of the oxide film.
Was set to 0.11 μm, and the axial surface roughness Ra was set to 0.04 μm.

On the other hand, in Comparative Example 5, the nitrocarburizing step, the oxide film forming step, and the circumferential buff polishing step were performed as in Example 3, but the axial polishing step was omitted. In the circumferential buffing step according to Comparative Example 5, the circumferential surface roughness Ra of the oxide film 22 was set to 0.05 μm, but the axial surface roughness Ra showed a large value of 0.08 μm. .

As a result, when the piston rod according to Comparative Example 5 was used, as shown in Table 2, the sliding resistance value was increased while the piston rod was extended and contracted from the first few times to ten times. It was 100 N and 80 N, and it was found that almost the same sliding characteristics as the piston rod according to the third embodiment could be obtained.

However, in the case of Comparative Example 5, the sliding resistance between the piston rod and the seal member 11 increased as the piston rod continued to extend and contract, and after a durability test of 50,000 times, It was found that peeling occurred in the seal member 11 and the gas reaction force of the gas spring was reduced.

On the other hand, when the piston rod according to Example 3 was used, even after the durability test of 50,000 times,
It was found that the seal member 11 did not cause any abnormalities such as peeling, and that the function of the seal member 11 could be sufficiently exerted, and the seal member 11 could suppress a reduction in the gas reaction force of the gas spring.

Thus, also in the present embodiment configured as described above, when the piston rod 21 is extended to the maximum extension position, a part of the oil liquid 2 in the tube 1 is partially oxidized.
2 can be guided between the lip portion 11A of the seal member 11 and the oxide film 22 of the piston rod 21 through the horizontal groove 23 and the vertical groove 24, and the same operation and effect as those of the first embodiment can be obtained. be able to.

Particularly, in this embodiment, the piston rod 2
It can be suitably used for hoods, back doors, etc. of automobiles, which are often used for one full stroke. Further, since the vertical groove 24 is formed only partially on the upper end side of the piston rod 21 among the horizontal groove 23 and the vertical groove 24, the vertical groove 24 is formed in the axial buffing step of forming the vertical groove 24. Work can be saved when performing
Overall workability and the like can be improved.

In the second embodiment, the vertical grooves 2
4 has been described as being formed on the entire part accommodated in the tube 1 when the piston rod 21 has been extended to the most extended position, but the present invention is not limited to this, and the vertical groove 24 is formed when the piston rod 21 is fully extended. A configuration in which the lip portion 11A of the seal member 11 slides when extended to the position may be provided only.

In each of the above embodiments, the gas spring is applied in an upright state. Alternatively, the gas spring may be applied in an upright state.

Further, in each of the above embodiments, the gas spring is applied to the door opening device for the back door. However, the present invention is not limited to this, and the present invention is not limited to this.
The present invention may be applied to a rear window, a door opening device other than an automobile, and the like.

Further, in each of the above embodiments, a gas spring is described as an example of a cylinder device. However, the present invention is not limited to this, and is widely applied to other cylinder devices including, for example, a hydraulic shock absorber. Things.

[0078]

As described above in detail, according to the present invention, a nitride film is provided on an outer surface of a metal body constituting a piston rod, and an oxide film is formed on an outer surface of the nitride film. Is formed, the wear resistance and corrosion resistance of the metal body can be improved, and environmental considerations can be achieved. Further, since the outer surface of the oxide film has a configuration in which a circumferential horizontal groove and an axial vertical groove are formed, a part of the oil liquid in the tube is formed between the piston rod and the seal member through the horizontal groove and the vertical groove. The oil liquid can be stored in each groove by being guided between the sliding contact surfaces, and the sliding resistance between the sliding contact surfaces can be reduced.

As a result, the durability and the wear resistance of the sealing member can be enhanced, and the life can be extended, and the piston rod subjected to the gas nitrocarburizing treatment and the oxidation treatment can be easily applied to the gas spring. be able to. Further, "dry contact" as described in the first prior art can be reliably prevented, and it is not necessary to additionally provide a second seal member or the like as described in the second prior art. , The overall structure and the like can be simplified.

Also, as in the second aspect of the present invention, the lateral groove is provided over substantially the entire length of the outer periphery of the piston rod, and the vertical groove is formed at least at a portion facing the seal member when the piston rod is at the most extended position. Even if it is configured to provide,
When the piston rod is extended to the maximum extension position,
A part of the oil liquid in the tube can be guided between the seal member and the piston rod through the horizontal groove and the vertical groove, and substantially the same effect as the first aspect of the invention can be obtained.

Further, according to the third aspect of the invention, the surface roughness Ra of the oxide film in the circumferential direction is set to about 0.06 to 0.15 μm, and the surface roughness Ra in the axial direction is set to 0.03 to 0.15 μm. ~ 0.
Since the configuration is set to about 07 μm, a part of the oil liquid in the tube can be satisfactorily guided between the sliding contact surfaces between the piston rod and the seal member through the horizontal groove and the vertical groove, and the stable contact between the sliding contact surfaces can be achieved. Oil film can be formed. Thereby, the durability, wear resistance, and the like of the seal member can be further increased.

Further, since the lateral grooves are formed by buffing in the circumferential direction and the vertical grooves are formed by buffing in the axial direction, a large number of lateral grooves and a large number of vertical grooves can be easily formed by these buffing. Thus, the overall workability at the time of forming the horizontal groove and the vertical groove can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a gas spring according to a first embodiment of the present invention.

FIG. 2 is an enlarged partial cross-sectional view showing a piston rod, a seal member, and the like in FIG.

FIG. 3 is a partially enlarged view of a piston rod that has been subjected to a soft nitriding process of forming a nitride film on the outer surface of a metal body.

FIG. 4 is a partially enlarged view of a piston rod which has been subjected to an oxide film forming step of forming an oxide film on a surface of a nitride film.

FIG. 5 is a partially enlarged view of a piston rod that has been subjected to a circumferential buffing step of forming a lateral groove by performing circumferential buffing on the surface of an oxide film.

FIG. 6 is a partially enlarged view of a piston rod that has been subjected to an axial buffing step of forming a longitudinal groove by subjecting the surface of an oxide film having a longitudinal groove to axial buffing.

FIG. 7 is a partial sectional view showing a piston rod, a seal member, and the like of a gas spring according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tube 2 Oil liquid 3 Piston 4,21 Piston rod 5 Metal body 6 Nitride film 7,22 Oxide film 8,23 Horizontal groove 9,24 Vertical groove 11 Seal member

Claims (4)

[Claims] 1. A tubular tube in which an oil liquid is sealed, a piston slidably provided in the tube,
A piston rod having one end connected to the piston and the other end projecting out of the tube via a rod guide provided in the tube, and a piston rod provided in the rod guide and slidably contacting the outer periphery of the piston rod; In a cylinder device comprising a seal member for sealing between a rod guide and preventing leakage of the oil liquid in the tube to the outside, the piston rod has a cylindrical metal body, and an outer portion of the metal body. A nitride film provided on the surface, an oxide film provided on the outer surface of the nitride film, and circumferential lateral grooves and axial longitudinal grooves formed on the outer surface of the oxide film. And the cylinder device. 2. The lateral groove is provided over substantially the entire outer circumference of the piston rod, and the vertical groove is provided at least at a portion facing the seal member when the piston rod is at a maximum extension position. The cylinder device according to claim 1. 3. The oxide film has a circumferential surface roughness Ra of 0.06 to 0.15 μm, and an axial surface roughness Ra.
The cylinder device according to claim 1 or 2, wherein the diameter is 0.03 to 0.07 µm. 4. A tubular tube in which an oil liquid is sealed, a piston slidably provided in the tube,
A piston rod having one end connected to the piston and the other end projecting out of the tube via a rod guide provided in the tube, and a piston rod provided in the rod guide and slidably contacting the outer periphery of the piston rod; A method for manufacturing a piston rod used for a cylinder device comprising: a seal member that seals between a rod guide and an oil liquid in the tube to prevent leakage of the oil liquid to the outside; Subject to soft nitriding
A nitrocarburizing process for forming a nitride film, and an oxidized film forming process for forming an oxidized film on the outer surface of the piston rod subjected to the nitrocarburized process are performed. One of the circumferential buffing step of forming a circumferential transverse groove on the surface and the axial buffing step of forming an axial longitudinal groove on the surface of the oxide film by axial buffing are performed first. And a method of manufacturing a piston rod used in a cylinder device, wherein the other step is performed later.