WO2004092609A1

WO2004092609A1 - Length adjustable gas spring

Info

Publication number: WO2004092609A1
Application number: PCT/KR2004/000424
Authority: WO
Inventors: Eui Hyup Chung
Original assignee: Samhyup Co. Ltd
Priority date: 2003-03-03
Filing date: 2004-02-27
Publication date: 2004-10-28
Also published as: KR20040078296A; KR100519624B1

Abstract

The present invention relates to a length adjustable gas spring and in particular to an improved length adjustable gas spring. In a piston integral structure, a push bar is installed in an inner upper side of a cylinder and is engaged with a gas movement path pipe. A valve body is assembled with a push bar. A circular gas movement path hole is formed in a center portion so that a lower side of the gas movement path pipe is inserted into an inner center portion of a piston rod part through the center of the piston part. A hypocenter, straight advancing degree, and surface illumination intensity of an outer surface of a cylinder are enhanced based on cemented carbide.

Description

LENGTH ADJUSTABLE GAS SPRING

Technical Field

[1] The present invention relates to a length adjustable gas spring and in particular to an improved length adjustable gas spring. In a piston integral structure, a push bar is installed in an inner upper side of a cylinder and is engaged with a gas movement path pipe. A valve body is assembled with a push bar. A circular gas movement path hole is formed in a center portion so that a lower side of the gas movement path pipe is inserted into an inner center portion of a piston rod part through the center of the piston part. A hypocenter, straight advancing degree, and surface illumination intensity of an outer surface of a cylinder are enhanced based on cemented carbide. In the spindle support of the outer container, a lower side of the outer container includes a curved part inwardly rolled in a circular shape, and two or more protrusions inwardly formed, so that the curved part of the lower side of the outer container is fixed with the protrusion without welding the spindle support. A thermal contraction tube is pressure- coated on the cylinder, the piston rod part ands the outer surface of the outer container for thereby achieving a single cylinder structure having various colors, so that it is possible to enhance a product innovation, quality enhancement, low cost and productivity.

Background Art

[2] The conventional length adjustable gas spring is formed in a multi-cylinder structure having an inner cylinder 44a and an outer cylinder 10a. Many parts are installed in the interior of the outer cylinder 10a. The piston 80a is formed of a synthetic resin or metal and includes a circular metal rod shaped cylinder 30a engaged by a riveting work. The cylindrical metal piston rod 30a is processed by a surface polishing process for removing small dents, etc. A chrome coating is performed for preventing corrosion. The piston 80a and the piston rod 30a are connected by a riveting work. In the upper slanted part 12a of the outer cylinder 10a, the outer surface of the outer cylinder 10a except for the slanted part 12a is bent in a horizontal direction during the process that it is formed based on a pressure of the axial pipe mold by a power press. In addition, the dimension of the outer diameter is not uniform. The hypocenter and straight degree of the outer diameter surface of the outer cylinder 10a are improved through the polishing process. The outer surface of the polished outer cylinder is plated by chrome for thereby preventing corrosion. The spindle support 50a is welded to the lower side of the outer container 20a by a welding work. A powder painting or electro-deposition painting is performed with respect to the surfaces for thereby preventing the outer diameter surface of the outer container from being oxidized.

[3] The polishing work and a surface work of a chrome coating and painting in the conventional gas spring parts are known to largely affect the environment and the workers. Very skillful workers are needed because the polishing work, coating work and painting work need a precious work and high accuracy. Work time is increased due to complicated work processes. Therefore, the fabrication costs of the parts are increased.

[4] The length adjustable gas spring is a very important key element adapted to adjust the seating height of chairs. In the conventional art, the length adjustable gas spring is formed in a dual cylinder structure formed of an outer cylinder 10a and an inner cylinder 44a and has very precious parts. The above construction will be described with reference to the accompanying drawings.

[5] Figure 1 is a vertical cross sectional view illustrating a conventional length adjustable gas spring Figure 2 is a cross sectional view illustrating a valve assembly in a conventional length adjustable gas spring and Figure 3 is a cross sectional view illustrating a piston assembly in a conventional length adjustable gas spring

[6] As shown in Figure 1, in the conventional length adjustable gas spring there is provided an outer cylinder 10a. A piston rod 30a is installed in a lower side of the outer container 20a into which the outer cylinder is inserted. The surface of the outer cylinder 10a is polished and coated with chrome. The push bar 14a is fixed to the upper side of the outer cylinder 10a by a push support bar 16a. The lower end of the push bar contacts with a gas opening and closing pin 100a. The gas opening and closing pin 100a is installed in such a manner that it is moved up and down in the valve assembly 40a assembled in the outer cylinder 10a.

[7] The spindle support 50a is fixed to a lower side of the outer container 20a by a welding method. The piston rod 30a is fixed through the spindle support 50a, and the outer surface of the outer container is powder-painted or painted by an electro- deposition method, so that oxidation is prevented. A tapered slanted part 12a is formed in the upper side of the outer cylinder 10a. The inner cylinder 44a is inserted into the outer cylinder 10a. A trust bearing 60a and a vibration resistance rubber 62a are installed on the spindle support 50a. The lower side of the piston rod 30a is detachably engaged with the spindle support 50a by a clip 70a. The surface of the piston rod 30a is polished and coated with chrome for thereby preventing oxidation.

[8] Figure 2 is a cross sectional view illustrating a conventional valve assembly 40a.

The valve assembly 40a is formed in a circular column shape and includes a valve inner hole 41a formed in the center wherein the gas opening and closing pin 100a is inserted into the valve inner hole 41a, and an O-ring is inserted into an O-ring groove 43a for achieving a sealing state.

[9] A space part 46a is formed in the inner center of the valve assembly 40a for the flow of gas. At least two O-rings 45a are installed in the space part 46a for achieving a sealing state. An inner holder 47a is installed in the space part 46a for achieving a certain distance with the O-ring 45a and a smooth sliding operation of the gas opening and closing pin 100a. Small holes are formed in one side of the inner holder 47a and communicate with the gas path hole 42a. As shown in Figure 1, the slide member 52a is installed between the outer cylinder 10a and the container 20a for thereby achieving a slide movement of the outer cylinder 10a.

[10] The piston 80a installed in the upper side of the piston rod 30a will be described with reference to Figure 3. The piston 80a and the piston rod 30a are separated from each other. A certain metal rod is polished and coated with chrome for thereby fabricating the piston rod 30a. The piston 80a is inserted into the upper side of the piston rod 30a, and the upper side of the piston rod 30a is fixed by a riveting work. Multiple O-rings 82a are inserted into the inner and outer sides of the piston 80a for the sealing of gas. A rod guide 83a is assembled to an inner lower side of the outer cylinder 10a, and a rod seal 84a is assembled to the upper side of the rod guide for sealing the outer cylinder 10a.

[11] The piston 80a is engaged using the ring 88a and a two-step washer 85a. The two- step washer 85a supports the lower side of the piston 80a.

[12] In Figure 3, the arrow represents a state that the gas is moved from the chamber C to the chamber A.

[13] As shown in Figure 1, in the conventional length adjustable gas spring when the push bar 14a installed in the upper most portion of the outer cylinder 10a is pushed, the push bar 14a pushes the gas opening and closing pin 100a, so that a small diameter part 102a positioned at the center of the gas opening and closing pin 100a is downwardly moved, whereby the space 46a and the chamber A communicate with each other. Since the space part 46a communicates with the gas path hole 42a, the gas of the chamber C is quickly moved to the chamber A. Since the pressure of the chamber C is larger than the pressure of the chamber A, the piston 80a is moved. Since the lower side of the piston rod 30a is fixed to the spindle support 50a of the outer container 20a, the outer cylinder 10a is upwardly moved based on a reaction.

[14] When the force pressing the push bar 14a is removed, the small diameter part of the gas opening and closing pin 100a is upwardly moved, and the space part 46a and the chamber A are disconnected, so that the upward movement of the outer cylinder 10a is stopped. Disclosure of Invention

Technical Solution

[15] Accordingly, it is an object of the present invention to provide a length adjustable gas spring capable of overcoming the problems encountered in the conventional art.

[16] It is another object of the present invention to provide a length adjustable gas spring In the present invention, a single cylinder structure formed of one cylinder 30 is provided using a gas movement path pipe 70. The number of elements assembled in the interior of the cylinder 30 is minimized. The piston assembly 90 is formed of a piston part 81, and a piston rod part 91 and is integrally formed as a single piece by a metal casting or synthetic resin injection molding A spindle support 130 is fixed between a curved part 123 inwardly formed from a lower side of the outer container 120 and an inner protrusion 122 without a welding method. The outer diameter surface 32 of the cylinder 30 passes through a cylindrical cemented carbide mold for thereby enhancing a precise hypocenter and straight degree and surface illumination intensity. In addition, the outer surfaces of the cylinder 30, the piston rod part 91 and the outer container are coated with thermal contraction tubes 32-1, 95-1 and 124-1 having various colors as compared with a conventional art in which the polishing chrome coating and painting processes are performed with respect to the above surfaces for thereby implementing a length adjustable gas spring having a structure of single cylinder 30. The product innovation is implemented. It is possible to enhance the quality and to decrease the manufacturing cost and to increase the productivity.

[17] To achieve the above objects, there is provided a length adjustable gas spring

There are provided an outer container, and a cylinder installed in the interior of the outer container. The piston assembly formed of an integral piston part and piston rod is provided in the interior of the cylinder. A gas movement path pipe is provided. An outer diameter surface of the cylinder is finished of a cylindrical cemented carbide mold for thereby achieving a hypocenter and straight degree. A spindle support of the outer container is fixed between the curved part of the lower part of the outer container and the protrusion of the upper side of the curved part. A thermal contraction tube is pressure-coated onto the outer diameter surfaces of the cylinder, the piston rod part and the outer container. Therefore, it is possible to fabricate the products having various colors in their outer diameter surfaces for thereby achieving a product renovation and cost down of the products as compared to the conventional art in which only the single color product is fabricated.

Description of Drawings [18] The preferred embodiments of the present invention will be described with reference to the accompanying drawings. [19] Figure 1 is a vertical cross sectional view illustrating a conventional length adjustable gas spring; [20] Figure 2 is a cross sectional view illustrating a valve assembly in a conventional length adjustable gas spring; [21] Figure 3 is a cross sectional view illustrating a piston assembly in a conventional length adjustable gas spring; [22] Figure 4 is a vertical cross sectional view illustrating a length adjustable gas spring according to the present invention; [23] Figure 5 is a view illustrating a state that a cylinder of a length adjustable gas spring according to the present invention is upwardly moved; [24] Figure 6 is a detailed view illustrating a cylinder according to the present invention; [25] Figure 7 is an upper detailed view illustrating a cylinder according to the present invention; [26] Figure 8 is a detailed view illustrating a push bar according to the present invention; [27] Figure 9 is a detailed view illustrating a valve seal according to the present invention; [28] Figure 10 is a detailed view illustrating a push support according to the present invention; [29] Figure 11 is a detailed view illustrating a gas movement path pipe according to the present invention; [30] Figure 12 is a detailed view illustrating a piston assembly according to the present invention; [31] Figure 13 is a detailed view illustrating a piston part of a piston assembly installed in a cylinder according to the present invention; [32] Figure 14 is a detailed view illustrating an outer container according to the present invention; and

[33] Figure 15 is another detailed view illustrating an outer container according to the present invention.

Best Mode

[34] The preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[35] Figure 1 is a vertical cross sectional view illustrating a conventional length adjustable gas spring Figure 2 is a cross sectional view illustrating a valve assembly in a conventional length adjustable gas spring Figure 3 is a cross sectional view illustrating a piston assembly in a conventional length adjustable gas spring Figure 4 is a vertical cross sectional view illustrating a length adjustable gas spring according to the present invention, Figure 5 is a view illustrating a state that a cylinder of a length adjustable gas spring according to the present invention is upwardly moved, Figure 6 is a detailed view illustrating a cylinder according to the present invention, Figure 7 is an upper detailed view illustrating a cylinder according to the present invention, Figure 8 is a detailed view illustrating a push bar according to the present invention, Figure 9 is a detailed view illustrating a valve seal according to the present invention, Figure 10 is a detailed view illustrating a push support according to the present invention, Figure 11 is a detailed view illustrating a gas movement path pipe according to the present invention, Figure 12 is a detailed view illustrating a piston assembly according to the present invention, Figure 13 is a detailed view illustrating a piston part of a piston assembly installed in a cylinder according to the present invention, Figure 14 is a detailed view illustrating an outer container according to the present invention, and Figure 15 is another detailed view illustrating an outer container according to the present invention.

[36] In the present invention, there are provided a cylinder 30, a slanted part 31, an outer diameter surface 32, an adhering layer 32-1, a thermal contraction tube 32-2, a cylinder inner surface 33, a boundary surface 34, an end part inner surface 35, a slanted surface 36, a push bar 40, a small diameter part surface 41, a slanted surface 42, a large diameter part surface 43, a center groove part inner surface 44, a center groove 45, a gas movement hole 46, a push support 50, a center through hole 51, a center groove 52, an outer groove 53, an O-ring 54, a valve seal 60, an inner surface seal lip 61, a corner seal lip 62, an upper inner through hole 63, a center groove 64, a gas movement path pipe 70, a gas movement path 71, an upper end part 72, a lower part 73, a metal bar 74, a piston part 81, an inner shoulder groove 82, an outer groove 83, an O-ring 84, a support member 85, an inner groove 86, an O-ring 87, a piston assembly 90, a piston rod part 91, a center inner groove 92, an inner diameter surface 93, a boundary surface 94, an outer diameter surface 95, an adhering layer 95-1, a thermal contraction tube 95-2, a lower part 96, a groove 97, a gas movement hole 98, a rod seal 100, a metal core 101, a rod guide 110, an outer container 120, an inner protrusion 121, an inner protrusion 122, a curved part 123, an outer diameter surface

124, an adhering layer 124-1, a thermal contraction tube 124-2, an outer surface white layer 124a, an outer surface nitride spreading layer 124b, an inner diameter surface

125, an inner surface white layer 125a, an inner surface nitride spreading player 125b, a spindle support 130, an outer part 131, a center hole 132, a slide member 140, a vibration resistance rubber 150, a clip 160, an outer container metal thickness T, a X- chamber X, and a Y-chamber Y.

[37] The construction of the length adjustable gas spring according to the present invention will be described in detail with reference to the accompanying drawings as shown on Figure 4 and Figure 5..

[38] In the length adjustable gas spring according to the present invention, there is provided a cylindrical outer container 120 of which the upper and lower sides are open. A cylindrical cylinder 30 is installed in the opened upper side and interior of the outer container 120 and is moved up and down with respect to the outer container 120 and is formed in a single structure acting as a piston, wherein the upper side of the same is open, and the lower side has through holes in the center portion of the same. A slide member 140 is tightly inserted into the opened upper inner rim of the outer container 120 and is adapted to support the cylinder 30 to be smoothly moved up and down. A spindle support 130 is fixedly inserted into an opened lower side of the outer container 120 and has a center hole 132. A piston assembly 90 is installed in the interior of the cylinder 30 and supports the cylinder 30 when it moves up and down and has a center inner groove 92 (space) so that the gas movement path pipe 70 is moved and a gas movement hole 98 formed in the upper side so that gas moves. A push support 50 is formed in the opened upper inner side of the cylinder 30 and operates as a plug and has a groove in the lateral surface intermediate rim and a through hole formed in the center portion. A valve seal 60 is inserted to the inner side of the push support 50 and prevents the gas of the interior of the cylinder 30 from being leaked to the outside and has a through hole in the center portion and is formed of a rubber and elastic member in a circular shape. A synthetic resin push bar 40 has an upper end inserted into the center through holes of the push support 50 and the valve seal 60 and protruded from the upper outer side of the cylinder 30, and a lower end formed in a circular shape and has a certain step wherein an insertion groove is formed in the lower center portion of the push bar 40, and a gas movement hole 46 passing through the outer surface of one side of the insertion groove. A synthetic resin or metallic gas movement path pipe 70 is fixedly inserted into the insertion groove formed at the center of the intermediate part from the lower side of the push bar 40 and is formed in a longitudinal pipe shape wherein a space is formed in the interior of the same so that a metallic bar 74 is inserted thereinto, and the gas movement path pipe 70 is inserted into the center inner groove 92 extended to the center interior of the piston assembly 90. A rubber or elastic rod seal 100 is formed in the opened lower inner side of the cylinder 30. A rod guide 110 is provided in the lower side of the rod seal 100. A vibration resistance rubber 150 is provided in the upper side of the spindle support 130 and releases the impact of the cylinder 30 that moves up and down. A clip 160 is fixed to the groove 97 of the lower part 96 of the piston assembly 90, which passing through the lower center through hole of the cylinder 30 and the center hole 132 of the spindle support 130 of the lower side of the outer container 120.

[39] As shown in Figures 6 and 7, the cylinder 30 includes a slanted part 31 formed in the upper side and engaged with the upper layer of the chair, an outer diameter surface 32 of the cylinder 30 forming an outer surface of the cylinder 30, an end part surface 35 in which the inner diameter of the lower side surface of the cylinder 30 is larger than the inner diameter of the cylinder inner surface 33, a boundary surface 34 formed in a shape of slanted step between the lower end part inner surface and the cylinder inner surface 33, a slanted surface 36 easily bent vertically in order to prevent the elements provided inside of the cylinder 30 from being escaped to the outside, a metallic core 101 formed of a through hole formed in the lower center of the cylinder 30 and installed in the boundary surface 34 in the lower side of the cylinder, a rod seal 100 into which the metallic core 101 is inserted, and a rod guide 110 formed between the metallic core 101 and the cylinder lower most part. The metallic core 101 is adapted to prevent the rod seal 100 and the rod guide 110 from being moved in the direction of the inner side of the cylinder by a high gas pressure being injected into the interior of the cylinder.

[40] In the upper side slanted part 12a of the outer cylinder 10a of the conventional length adjustable gas spring the outer diameter surface of the outer cylinder 10a is horizontally bent by a pressurizing force of the axial pipe mold while it is formed by the vertical pressurizing force of the axial pipe mold by the power press that is operated in the upward and downward directions, and so the outer dimensions of the outer cylinder 10a are not uniformed and bent. The outer diameter surfaces are thinly abraded due to the non-uniform outer dimensions and outer diameter surfaces when the entire outer surfaces of the outer cylinder 10a are abraded.. Therefore, it is needed to correct the hypocenter and straight degree of the outer diameter surface of the outer cylinder 10a. The entire outer diameter surfaces are coated with chrome. In the chrome coating processes with respect to the outer diameter surfaces of the outer cylinder 10a, the rough surfaces, the pinholes formed in the outer diameter surfaces and the scratches that are formed due to the abrasion work with respect to the outer diameter surfaces may cause an unbalanced illumination intensity and non-uniform coating state in the coating surfaces of chrome. The rough surfaces of the outer diameter surfaces coated with chrome are processed by chrome coating work and are processed by the puffing polishing process two or three times for thereby achieving a proper illumination intensity. [41] F wever, in the present invention, the outer diameter surface 32 of the cylinder 30 bent in the horizontal direction while the upper side slanted part 31 is formed by a vertical pressurizing force of the axial pipe mold by a power press is improved using a cylindrical cemented carbide mold. A cylindrical inner through hole having a precise hypocenter is formed in the interior of the same. The inner diameter of the inner through hole is slightly smaller than the outer diameter of the pipe before the upper side slanted part 31 is formed. The size of the inner diameter is the same as the outer diameter of the cylinder 30. The length of the cylindrical mold is 10%~40% of the entire length of the cylinder 30. The length of the same is preferably 20% of the entire length. The surface illumination intensity of the inner through hole of the cemented carbide mold is very high. When it is viewed under sunlight, it has very high luster like the surface of mirror. The entire surfaces of the outer diameter surface 32 of the cylinder 30 are coated with cemented carbide mold through the inner through hole. Therefore, the outer diameter surface 32 of the cylinder 30 has precise hypocenter degree. A precise straight degree of the cylinder is achieved based on a proper length of cemented carbide mold. The surface illumination intensity of the outer diameter surface 32 of the cylinder is largely enhanced based on a high inner surface illumination intensity of the inner through hole of the cemented carbide mold. The tissue of the outer diameter surface 32 of the cylinder 30 is densely formed. Therefore, the cylinder 30 is passed through the interior of the cemented carbide mold, so that it is possible to achieve the outer diameter surface 32 of the cylinder 30 having a precise hypocenter and straight degree and an enhanced surface illumination intensity.

[42] The synthetic resin adhesive is applied onto the entire surfaces of the outer diameter surface 32 of the cylinder 30 for thereby forming a thin adhering layer 32-1. The entire portions of the outer diameter surface 32 and the adhering layer 32-1 of the cylinder are pressure-coated with a thermal contraction tube 32-2 formed of a thin film by heating the same for thereby achieving a high strength, abrasion resistance, corrosion resistance and various colors based on the use of engineering plastic. Therefore, it is possible to prevent oxidation and achieve various colors based on a customer's demand. The thermal contraction tube is a hard thin film tube formed of an engineering plastic having a high strength, an excellent abrasion resistance, oil resistance property, oxidation resistance, etc. When a proper temperature is applied to the tube, it is contracted by about 10% through 50%. The thickness of the thermal contraction tube 32-2 is properly 0.01mm ~ 0.5mm.

[43] In a contraction method, there is provided a temperature that does not affect rubber gas sealant, oil, etc. used for the length adjustable gas spring In addition, it is passed through heat or oven at a proper temperature range so that the thermal contraction tube is properly contracted. Therefore, the thermal contraction tube is contracted at a uniform thickness over the entire portions of the outer diameter of the cylinder 30. It is possible to achieve perfect oxidation prevention and various colors with respect to the outer diameter surface 32 of the cylinder 30.

[44] As shown in Figure 8, the push bar 40 is a circular bar made of a synthetic resin material and formed based on a molding injection method. The push bar 40 includes a small diameter part surface 41 forming an upper side, a large diameter part surface 43 formed in a lower side of the small diameter part and having a circular shape gradually formed in the direction of the lower side and having a certain step, a circular slanted surface 42 having a boundary between the large diameter part surface 43 and the small diameter part surface 41, a center groove 45 having a center groove part inner surface 44 (space) from the lower side of the large diameter part surface 43 to the upper center part wherein the upper end of the gas movement path pipe 70 is inserted and adhered, and a gas movement hole 46 that passes through the center groove part surface 44 of the inner side of the center groove 45 and the circular shaped slanted surface 42 and formed in such a manner that the gas of the Y chamber (Y) flows toward the X chamber (X) through the gas movement path pipe 70 and the center groove 45.

[45] As shown in Figure 9, the valve seal 60 is a seal formed of a circular rubber and elastic inserted to an inner side in the interior of the push support 50. The valve seal 60 includes an upper side inner through hole 63 formed in the upper side, a circular center groove 64 having an inner diameter of the lower side larger than the upper side inner through hole 63, an inner surface seal lip 61 having at least more than one seal lip wherein the small diameter part surface 41 of the push bar 40 passes through the interior of the same, so that the gas of the cylinder 30 is not leaked to the outside during the up and down movement, and a right angle seal lip 62 formed by the inner surface of the center groove 64 and the end surface of the lower side.

[46] When the push bar 40 is upwardly moved by the gas pressures of the interior of the cylinder 30, the circular slanted surface 42 of the push bar 40 contacts with the corner seal lip 62 of the valve seal 60, so that the gas movement between the gas movement hole 46 and the X chamber (X) is stopped.

[47] As shown in Figure 10, the push support 50 is formed in an upper side of the cylinder 30 and is formed in a cylindrical shape. The push support 50 includes an upper side center through hole 51 protruded to the outside of the upper side of the cylinder 30 wherein the small diameter part surface 41 of the push bar 40 passing through the inner through hole 63 of the upper side of the valve seal 60 passes through the center through hole 51, a center hole 52 having a large inner diameter wherein the lower side of the same is formed in the lower side of the center through hole 51, and the valve seal 60 is inserted, and an outer hole 53 formed in one side of the lateral surface part wherein the gas sealing O-ring 54 is inserted thereinto.

[48] As shown in Figure 11, the gas movement path pipe 70 includes a gas movement path 71 formed of a circular longitudinal pipe having an outer diameter of 2.5mm~10mm wherein the gas movement path 71 has an inner diameter of 1.0mm~8.0mm in the interior, an upper side end part 72 inserted into the center groove 45 of the lower side of the push bar 40 and fixedly adhered to the center groove part inner surface 44, a lower side part 73 inserted into the center inner groove 92 that passes through the gas sealing O-ring 87 of the center part of the upper side of the piston part 81 and extending to the inner center of the lower side of the piston rod part 91, and a straight metallic bar 74 inserted into the interior of the gas movement path 71 for preventing the same from being easily bent in the case that it is made of synthetic resin.

[49] As shown in Figure 12, the piston assembly 90 is installed in the cylinder 30 and has a center inner groove 92 (space) at the intermediate part so that the gas movement path pipe 70 is moved up and down in the interior, wherein the upper side of the same is opened, and the lower side of the same is closed, and the lower side of the same passes through the center through hole of the spindle support 130 of the lower side of the outer container 120 and is fixed by the clip 160.

[50] There is provided a piston part 81 having an upper side having the same diameter as the inner diameter of the cylinder 30 and adapted to prevent the cylinder 30 from being moved up in such a manner that the lower side of the cylinder 30 contacts with the piston part 81 when the cylinder 30 moves up. In the piston assembly 90 that is extended toward the lower side of the piston part 81 and is formed in a cylindrical shape, the piston assembly 90 has a diameter smaller than the piston part 81 and a lower side passing through the lower through hole of the cylinder 30 and the center hole 132 of the spindle support 130 and has a lower side part 96 having a groove 97 in one lower side. The piston assembly 90 is formed as a single piece by a die casting injection or synthetic resin injection based on mold. The above construction will be described in detail.

[51] An outer groove 83 is formed in a lateral surface of the piston part 81 wherein a gas sealing O-ring 87 formed of an elastic member is formed between the X-chamber (X) and the Y chamber (Y) for thereby achieving a gas sealing function. An inner step groove 82 is formed in one side of the rum of the center through hole of the upper side of the piston part 81 wherein a support member 81 is mounted thereon for preventing another O-ring 84 from being escaped. An inner groove 86 is formed in a lower side of the inner step groove 82 wherein the gas movement path pipe 70 passes through, and another O-ring 84 having a gas sealing function is inserted. A center inner groove 92 has a certain length longer than the up and down stroke distance of the piston rod part 91 wherein the gas movement path pipe 70 passes through the inner side of another O- ring 84 of the center of the upper side of the piston part 81 and is inserted toward the lower side of the center part of the interior of the piston rod part 91. A gas movement hole 98 is formed at a boundary between the piston part 81 and the piston rod part 91 of the piston assembly 90 and passes from the center inner groove 92 of the upper side of the piston rod part 91 to the outer diameter surface 95 of the piston rod part 91 so that the gas is moved from the X chamber (X) to the Y chamber (Y). A lower side 96 of the piston assembly 90 is inserted into the center hole 132 of the spindle support 130. A boundary support 94 contacts with the upper surface of the spindle support 130 and has a right angle step between the upper side part and the lower side part 96 capable of achieving a smooth rotation of the piston assembly 90. A groove 97 is formed in a lower side of the lower side part 96 wherein the clip 160 is inserted thereinto. [52] The rod seal 100 and the rod guide 110 formed in the lower side of the cylinder 30 are inserted into the interior of the cylinder 30 through the lower side part 96 of the piston assembly 90. A vibration resistance rubber 150 is inserted into the outer lower side of the cylinder for thereby absorbing impact of the cylinder 30.

[53] In the conventional length adjustable gas spring the piston 80a and the piston rod

30a are separately formed. Pinholes, scratches, etc formed on the outer diameter surface of the piston rod formed of a metallic rod are processed by a polishing method for thereby minimizing the pinholes, scratches, etc. The surfaces are coated with chrome for preventing oxidation of the polished surfaces. The pinholes, scratches, etc. formed on the outer diameter surfaces during the chrome coating process and the rough surfaces due to the polishing process may cause the unbalance of the density of the chrome coating and a non-uniform coating state in micro portions, so that the surfaces are rough. In order to enhance the rough surfaces, the outer diameter surfaces coated with chrome are puffing-processed by 2 or 3 times for thereby enhancing the density of the surface. The piston rod passes through the center of the rod seal for thereby minimizing the damage of the seal lip of the rod seal during the up and down movement, so that it is possible to enhance the gas sealing property and durability.

[54] In the present invention, in the case that the piston assembly 90 formed of the piston part 81 and the piston rod part 91 is formed by die casting method using metal based on the mold, the piston assembly 90 is formed of a cylindrical inner through hole formed by a cylindrical cemented carbide mold and having a precise hypocenter degree. The inner diameter of the inner through hole is slightly smaller than the outer diameter of the piston rod part 91 or is the same as the outer diameter of the piston rod part 91. The length of the cylindrical mold is preferably 20%~40% of the entire length of the piston rod part 91. The most preferred length is 30% of the entire length. The inner surface illumination intensity of the inner through hole of the cemented carbide mold is very high, so that a high luster like mirror is obtained when it is viewed by sunlight. The outer diameter surface 95 of the piston rod part 91 is pressure-inserted into the inner through hole based on the cemented carbide mold and then is pulled out, so that the outer diameter surface 95 of the piston rod part 91 has a precise hypocenter based on the hypocenter degree of the inner through hole based on the cemented carbide mold. In addition, a precise straight property of the piston rod part 91 is obtained based on a proper length of the cemented carbide mold. The surface illumination intensity of the outer diameter surface 95 of the piston rod part 91 is largely enhanced. When the cemented carbide mold is pressure-inserted into the outer diameter surface 95, the constituent state of the outer diameter surface 95 of the piston rod part 91 becomes dense, so that the piston rod part 91 is formed of an outer diameter surface 95 having a precise hypocenter degree, straight degree and enhanced surface illumination intensity. The synthetic resin adhesive is applied onto the entire portions of the outer diameter surface 95 of the piston rod part 91 for thereby forming a thin film adhering layer 95-1. The entire portions of the outer diameter surface 95 and the adhering layer 95-1 of the piston rod part 91 are pressure-coated by providing a proper heat to a thermal contraction tube formed of a thin film having a high strength, abrasion resistance, and corrosion resistance formed of an engineering plastic with respect to the entire outer portions of the adhering layer 95-1, so that it is possible to fully recover the small pinholes and scratches formed on the outer diameter surface of the piston rod part 91 using the thermal contraction tube 95-2 during the oxidation prevention and injection molding processes. When the piston rod part 91 moves up and down through the center of the rod seal 100, it is possible to enhance a gas sealing property and durability between the rod seal 100 and the outer diameter surface 95 of the piston rod part 91. Here, the thermal contraction tube is a thin film tube formed of an engineering plastic having a high strength, abrasion resistance, corrosion resistance, etc. When a proper temperature is applied to the tube, it is contacted by about 10%~50%, and the thickness of the thermal contraction tube 95-2 is preferably 0.01mm~0.5mm. In the contraction method, the thermal contraction tube is passed through heat or oven at a certain temperature range, so that the thermal contraction tube is contracted and adhered onto the outer diameter surface of the piston rod part 91 with a certain thickness. Therefore, it is possible to implement a perfect oxidation prevention and gas sealing property with respect to the outer diameter surface 95 of the piston rod part 91. Here, since the piston part 81 is installed in the interior of the cylinder 30 filled with nitride gas that is inert gas. [55] In the present invention, in the piston assembly 90 formed of the integral piston part 81 and the piston rod part 91 as a single piece, in the case that is formed of a synthetic resin by a synthetic resin injection based on the mold, the the piston rod part 91 is finished using a cemented carbide mold of a cylindrical shape formed of a cemented carbide and has a cylindrical inner through hole having a precise hypocenter degree. The inner diameter of the inner through hole is slightly smaller than the outer diameter of the piston rod part 91 or is the same as the outer diameter of the piston rod part 91. The length of the cylindrical mold is 20%~40% of the entire length of the piston rod part 91, and a preferred length of the same is 30% of the same. The inner surface intensity luminance of the inner through hole of the cemented carbide mold is very high and has a luster like mirror when viewing the same under sunlight. The cemented carbide mold preheated to a proper temperature so that the synthetic resin forming the piston rod part 91 is thermally deformed, is pressure-inserted into the inner through hole of the cemented carbide mold and is pulled out. Therefore, the outer diameter surface 95 of the piston rod part 91 has a precise hypocenter based on the hypocenter of the cylindrical construction of the inner through hole of the cemented carbide mold. A precise straight degree of the piston rod part 91 is obtained based on a proper length of the cemented carbide mold. A surface intensity luminance of the outer diameter surface 95 of the piston rod part 91 is largely enhanced based on the high inner surface luminance of the inner through hole of the cemented carbide mold. When pressure-inserting the outer diameter surface 95 based on the cemented carbide mold, the constituent state of the outer diameter surface 95 of the piston rod part 91 has dense. Therefore, the piston rod part 91 has the outer diameter surface 95 having a precise hypocenter, straight degree and enhanced surface intensity luminance. [56] An adhesive of the synthetic resin is applied to the entire portions of the outer diameter surface 95 of the piston rod part 91 for thereby forming a thin film adhering layer 95-1. A thermal contraction tube is pressure-coated into the entire portions of the outer diameter surface 95 and the adhering layer 95-1 of the piston rod part 91 by providing a proper heat to the thermal contraction tube formed of a thin film having a high strength, abrasion resistance, and corrosion resistance using an engineering plastic with respect to the entire outer portions of the adhering layer 95-1. The pin holes and scratches formed on the outer diameter surface 95 of the piston rod part 91 during the injection mold process of the piston assembly 90 are recovered by the thermal contraction tube 52-2. When the piston rod part 91 moves up and down through the center of the rod seal 100, a gas sealing property and durability between the rod seal 100 and the outer surface 95 of the piston rod part 91 are achieved. The thermal contraction tube is a hard thin film tube formed of an engineering plastic having a high strength, abrasion resistance, oil resistance property, oxidation resistance, etc. When a proper temperature is applied to the tube, it is contracted by 10%~50%. The thickness of the thermal contraction tube 95-2 is preferably 0.01mm~0.5mm. In the contraction method, the thermal contraction tube 95-2 is passed at a proper contraction temperature and is passed through heat, or oven within a proper temperature range so that the synthetic resin of the piston rod part 91 is not thermally deformed. Therefore, the thermal contraction tube is contacted on the outer diameter surface 95 of the piston rod part 91 with a proper thickness. A gas sealing force and durability are enhanced between the rod seal 100 and the outer diameter surface 95 of the piston rod part 91.

[57] As shown in Figure 14, in the outer cylinder 120, the slide member 140 formed of the synthetic resin is pressure-inserted into the inner surface of the opened upper side of the outer container 120. One or more inner side protrusion 121 is formed in an upper inner rim for preventing an escape of the slide member 140. A curved part 123 is bent at its lower end part in the inner direction. An inner protrusion 122 is formed in the upper side of the curved part 123 at the left and right sides and is extended in the inner direction of the outer container 120. A spindle support 130 formed between the curved part 123 and the inner protrusion 122. The spindle support 130 is formed of the outer side part 131 having a center hole 132 in the interior.

[58] In the surface process of the outer container 120, in the conventional art, the oxidation and corrosion are prevented by painting the outer diameter surfaces. In the surface process of the outer container 120, an adhesive of the synthetic resin is coated onto the entire portions of the outer diameter surface 124 of the outer container 120, and a thin film adhering layer 124-1 is formed. A thermal contraction tube is pressure- coated onto the entire portions of the outer diameter surface 124 of the outer container 120 and the adhering layer 124-1 by providing heat with respect to the thermal contraction tube formed of a thin film, so that it is possible to achieve a high strength, abrasion resistance and corrosion resistance and various colors with respect to the outer entire portions of the adhering layer 124-1 using an engineering plastic. Therefore, it is possible to achieve perfect oxidation prevention and various colors. The thermal contraction tube is a hard thin film tube formed of an engineering plastic having a high strength, oil resistance property, oxidation resistance, etc. When a proper temperature is applied to the tube, it is contracted by 10%~50%, and the thickness of the thermal contraction tube 124-2 is preferably 0.01mm~0.5mm. In the contraction method, it is passed through heat, or oven at a proper temperature range within which the thermal contraction tube is contracted. Therefore, the thermal contraction tube is contracted onto the outer diameter surface 124 of the outer container 120 with a certain thickness. It is possible to achieve perfect oxidation prevention and various colors with respect to the outer surfaces 124 of the outer container 120 for thereby fabricating the outer container 120.

[59] Figure 15 is a view illustrating another surface process of the outer container 120.

The outer container 120 is formed of a hard white layer 124a in an outer surface and a white layer 125 a in an inner surface formed of iron and nitride compound in the inner and outer diameter surfaces within a range of 4-10 micron by processing nitride heat treatment with respect to the inner diameter surface 125 and the outer diameter surface 124 of the outer container 120. The outer surface nitride spreading layer 124b and the inner surface nitride spreading layer 125b including nitride are formed from 100-200 microns from the white layer, so that the oxidation and corrosion prevention is enhanced, and the strength of the steel of the outer container 120 is largely enhanced. The metal thickness T of the outer container 120 is 1.25~2.5times of the sum of the thickness of the nitride layer from the inner and outer diameter surfaces. A nitride heat treatment is performed with respect to the outer container 120 having a metal thickness T of 0.8mm~ 1.6mm, so that the inner and outer surfaces of the outer container 120 are prevented from oxidation. A supporting strength of the outer container 120 with respect to external impact is largely enhanced.

[60] In the up and down movement process, when the push bar 40 is pressed in a state that the gas in the interior of the cylinder has a certain pressure, the circular slanted surface 42 of the push bar 40 is moved in the direction 'a', and a space is formed between the lower corner seal lip 62 of the valve seal 60 and the circular slanted surface 42. Therefore, the gas in the Y chamber (Y) is moved into the center inner groove 92 of the piston rod part 91 through the upper gas movement hole 98 and is moved upwardly along the gas movement path 71 of the gas movement path pipe 70 and is moved into the X chamber (X) through the gas movement hole 46 of the push bar 40. Therefore, the lower end of the piston assembly 90 is fixed to the spindle support 130 by the clip 160, so that the cylinder 30 is moved up in the direction 'b' by reaction (Figure 5). At this time, the upper layer of the chair engaged to the slanted part 31 of the cylinder 30 is moved up, so that the height of the chair is moved up.

[61] In the case that the length of the gas spring is decreased, the operation reverse to the above operation is performed.

[62] When an external force applying to the push bar 40 is removed, the push bar 40 is moved in the direction 'b' by the gas pressure in the X chamber (X) of the cylinder 30, and the circular slanted surface 42 of the push bar 40 closely contacts with the lower corner seal lip 62 of the valve seal 60, so that the moving path of the gas is disconnected. The gas movement between the X chamber (X) and the chamber (Y) is stopped. The operation of the piston assembly 90 is stopped. The movement of the cylinder 30 in the direction 'b' is stopped.

[63] The above described routines are repeatedly performed in the present invention.

Industrial Applicability [64] As described above, the present invention is implemented based on a single cylinder structure. The gas movement path pipe is installed inside the cylinder and the piston assembly. The present invention relates to a piston integral structure formed of an integral piston part and the piston rod part. The straight outer diameter surface of the cylinder is passed through the outer surface of the cylinder into the interior of the cylindrical cemented carbide mold, so that it is possible to achieve a precise hypocenter of the outer diameter surface of the cylinder, and the straight degree and enhanced surface intensity luminance. The spindle support of the outer container has a curved part dent in a circular shape in the lower side of the outer container, and at least two protrusions are inwardly formed in the upper side. A spindle support is engaged between the curved part of the lower side of the outer container and the protrusion without welding The thermal contraction tube is pressure-coated onto the outer portions of the cylinder, the piston rod part and the outer container, so that it is possible to fabricate the products based on the customer's various demands in such a manner that the outer diameter surfaces have various colors as compared to the conventional art in which only limited color are possible. In the conventional art, wastewater pollution and environment pollution problems occurs during the polishing coating and painting processes. F wever, in the present invention, an environment friendly method is adapted using the thermal contraction tube, so that it is possible to implement a product renovation and to significantly decrease the manufacturing cost of the product. An international competitive power is enhanced with the length adjustable gas spring according to the present invention.

[65] As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.

Claims

[1] A length adjustable gas spring comprising: an outer container 120 of which upper and lower sides are open; a cylindrical cylinder 30 inserted into the portions of the opened upper and lower sides of the outer container and moved up and down with respect to the outer container wherein an upper side of the same is open, and a lower side of the same has a through hole; a slide member 140 pressure-inserted into the inner side of the opened upper rim of the outer container 120 and adapted to support the cylinder 30 so that the cylinder 30 is smoothly moved up and down; a spindle support 130 fixedly inserted into the opened lower side of the outer container 120 and having a center hole 132 in the center portion of the same; a piston assembly 90 installed in the interior of the cylinder 30 and adapted to support the cylinder when the cylinder is moved up and down, wherein the piston assembly 90 includes a center inner groove 92 so that the gas movement path pipe 70 is moved, and a gas movement hole 98 formed in one upper side, so that the gas moves therein; a push support 50 formed in the opened upper inner side of the cylinder 30 and adapted to operate as plug and having a groove in the intermediate rim of the lateral surface and a through hole in the center portion of the same; a valve seal 60 inserted to the inner side of the push support 50 and adapted to prevent gas of the interior of the cylinder 30 from being leaked to the outside and having a through hole in the center portion of the same, wherein said valve seal

60 is made of rubber and elastic member in a circular shape; a synthetic push bar 40 protruded in the direction of the upper outer portions of the cylinder in a state that the upper side of the push bar 40 is inserted into the center through holes of the push support 50 and the valve seal 60, and the lower side of the push bar 40 is formed in a circular shape, wherein the push bar 40 has a certain step, an insertion groove in the center portion of the lower side, and a gas movement hole 46 passing up to one side of the insertion groove; a synthetic resin or metallic gas movement path pipe 70 fixedly inserted into the insertion groove formed in the center portion of the intermediate part in the lower side of the push bar 40, wherein said gas movement path pipe 70 is formed in a pipe shape and includes a space part for receiving the metal bar 74 thereinto and is inserted into the center inner groove 92 extended toward the center inner portion of the piston assembly 90; a rubber and elastic rod seal 100 formed in the opened lower inner side of the cylinder 30; a rod guide 110 formed in a lower side of the rod seal 100; a vibration resistance rubber 150 provided in an upper side of the spindle support

130 for releasing an impact of the cylinder 30 that is moved up and down; and

A clip 160 is fixed to the groove 97 of the lower part 96 of the piston assembly

90, which passing through the lower center through hole of the cylinder 30 and the center hole 132 of the spindle support 130 of the lower side of the outer container 120.

[2] The spring of claim 1, wherein said cylinder 30 includes: a slanted part 31 of an upper part engaged with an upper layer of a chair; an outer diameter surface 32 of the cylinder 30 forming an outer surface of the cylinder 30; an end inner surface 35 in which an inner diameter of the lower side surface of the cylinder is larger than an inner diameter of the cylinder inner surface 33; a boundary surface 34 formed of a slanted step between the inner surface 35 of the lower end part and the cylinder inner surface 33; a slanted surface 36 easily bent at a right angle for preventing the elements formed inside of the cylinder 30 from being escaped to the outside; and a through hole formed in the center of the lower side of the cylinder.

[3] The spring of claim 2, wherein said outer diameter surface 32 of the cylinder 30 includes: a thin film adhering layer 32- 1 formed by applying an adhesive formed of a synthetic resin onto the entire portions of the outer diameter surface 32; and a thermal contraction tube 32-2 formed of an engineering plastic having a high strength, abrasion resistance, and corrosion resistance and various colors, wherein said thermal contraction tube is pressure-coated onto the entire portions of the adhering layer 32- 1 and the outer diameter surfaces 32 of the cylinder 30 and has a thickness of 0.01mm~0.5mm.

[4] he spring of claim 2, wherein said outer diameter surface 32 of the cylinder

30 is finished by passing through a cylindrical cemented carbide mold for thereby achieving a precise hypocenter, straight degree and surface intensity luminance. [5] The spring of claim 1, wherein said push bar 40 includes: a small diameter part surface 41 formed of a synthetic resin in a mold injected circular bar shape and forming an upper side part; a large diameter part surface 43 formed in a lower side of the small diameter part surface and has a circular shape formed gradually larger in the direction of the lower side of the same and having a certain step; a circular slanted surface 42 having a boundary between the large diameter part surface 43 and the small diameter part surface 41; a center groove 45 in which an upper end part of the gas movement path pipe 70 is inserted and adhered, and a center groove part inner surface 44 (space) is formed from the lower side of the large diameter part surface 43 to one side of the upper center portion; and a gas movement hole 46 passing through the center groove part inner surface 44 of the interior of the center groove 45 and the circular slanted surface 42, so that the gas of the Y chamber (Y) is moved to the X chamber (X) through the gas movement path pipe 70 and the center groove 45.

[6] The spring of claim 1, wherein said valve seal 60 is a circular rubber and elastic seal inserted to the interior of the push support 50 and includes: an upper inner through hole 63 formed in an upper side; a circular space shaped center groove 64 of which a lower side has an inner diameter larger than the upper inner through hole 63; an inner surface seal lip 61 having at least one seal lip having a sealing function for preventing the gas of the cylinder from being discharged to the outside during the operation of the cylinder wherein the small diameter part surface 41 of the push bar 40 passes through the interior of the same; and a right angle corner seal lip 62 formed by the inner surface and the lower side end surface of the center groove 64.

[7] The spring of claim 1, wherein said push support 50 is formed in an upper side of the cylinder 30 in a cylindrical shape having a function of a plug and includes: a center through hole 51 of the upper side part protruded from the upper side of the cylinder wherein the small diameter part surface 41 of the push bar 40 passing through the upper side inner through hole 63 of the valve seal 60 passes through the upper side of the same; a large diameter center groove 52 of which a lower side is formed in a lower side of the center through hole 51, wherein the valve seal 60 is inserted; and an outer groove 53 formed in one side of the lateral surface part wherein the gas sealing O-ring 54 is inserted thereinto.

[8] The spring of claim 1, wherein said gas movement path pipe 70 includes: a gas movement path 71 formed in a shape of circular longitudinal pipe having an outer diameter of 2.5mm~10mm wherein the gas movement path 71 has an inner diameter of 1.0mm~8.0mm; an upper side end part 72 inserted into the center groove 45 of the lower side of the push bar 40 and fixedly adhered to the center groove part inner surface 44; a lower side part 73 inserted into the center inner groove 92 passing through the interior of the gas sealing O-ring 87 of the center portion of the upper side of the piston part 81 and extended up to the inner center of the lower side of the piston rod part 91; and a straight line metallic bar 74 inserted into the interior of the gas movement path

71.

[9] The spring of claim 1, wherein said piston assembly 90 is installed in the cylinder 30, wherein a center inner groove (space) 92 is formed at the intermediate portion so that the gas movement path pipe 70 is moved up and down in the interior, and the upper side is opened, and the lower side is closed, and the lower side is fixed by the clip 160 through the center through hole of the spindle support 130 of the lower side of the outer container; and wherein the piston rod part 91 includes a piston part 81 having an upper side with the same diameter as the inner diameter of the cylinder 30 and supporting the cylinder 30 so that the lower side of the cylinder contacts and is prevented from being moved up when the cylinder 30 is moved up, and a piston rod part 91 extended to the lower side of the piston part 81 and formed in a cylindrical shape wherein the piston rod part 91 has a diameter smaller than the diameter of the piston part 81, and the lower side of the same passes through the lower through hole of the cylinder 30 and the center hole 132 of the spindle support 130 of the outer container and there is provided a lower side part 96 having a groove 97 in a lower side; and wherein an outer groove 83 is formed in a lateral side of the piston part 81 wherein the gas sealing O-ring 87 formed of an elastic member having a gas sealing function between the X chamber (X) and the Y chamber (Y) is inserted thereinto; and an inner step groove 82 is formed in one side of the rum of the center through hole of the upper side of the piston part 81 wherein the support member 85 is mounted thereon for preventing another O-ring 84 from being escaped; and an inner groove 86 is formed in a lower side of the inner step groove 82, and the gas movement path pipe 70 passes through, and another O- ring 84 having a gas sealing function is inserted thereinto; and a center inner groove 92 has a certain length longer than the up and down stroke distance of the piston rod part 91 wherein the gas movement path pipe 70 passes through the inner side of another O-ring 84 of the center of the upper side of the piston part 81 and is inserted up to the lower side of the center part of the interior of the piston rod part 91; and a gas movement hole 98 is formed at a boundary between the piston part 81 of the piston assembly 90 and the piston rod part 91 and passes through from the center inner groove 92 of the upper side of the piston rod part 91 to the outer diameter surface 95 of the piston rod part 91 so that the gas is moved from the X chamber (X) to the Y chamber (Y); and a lower side part 96 of the piston assembly 90 is formed to be inserted into the center hole 132 of the spindle support 130; and a boundary surface 94 contacts with an upper surface of the spindle support 130 and has a right angle step of the lower side part 96 with the upper side part having a function that the piston assembly 90 is smoothly rotated; and a groove 97 is formed in the lower side of the lower side part 96 wherein the clip 160 is inserted. [10] The spring of claim 9, wherein the piston assembly 90 is formed by a die casting injection or synthetic resin injection molding based on the mold using a metallic or synthetic resin material and is integrally formed of the piston part 81 and the piston rod part 91 as a single piece. [11] The spring of claim 9, wherein said outer diameter surface 95 of the piston rod part 91 includes: a thin film adhering layer 95-1 formed by coating an adhesive formed of synthetic resin onto the entire portions of the outer diameter surface 95; and a thin film thermal contraction tube 95-2 formed of an engineering plastic having a high strength, good abrasion resistance property, and good corrosion resistance property and formed in such a manner that the entire portions of the outer surfaces 95 of the adhering layer 95-1 and the piston rod part 91 wherein said thin film has a thickness of 0.01mm~0.5mm. [12] The spring of claim 9, wherein said outer diameter surface 95 of the piston rod part 91 is finished by inserting and pulling out a cylindrical cemented carbide mold for thereby achieving a precise hypocenter, straight property and surface intensity luminance. [13] The spring of claim 1, wherein said outer container 120 in which a slide member

140 formed of a synthetic resin is pressure-inserted into the inner surface of the opened upper side of the outer container 120, includes: one or more inner protrusions 121 formed in the inner rim of the upper side for preventing an escape of the slide member 140; a curved part 123 of which a lower end portion is inwardly bent; an inner protrusion 122 formed in an upper side of the curved part 123 and inwardly formed at left and right sides symmetrically by at least two; and a spindle support 130 formed between the curved part 123 and the inner protrusion 122, wherein said spindle support 130 includes an outer part 131 having a center hole 132 in the interior. [14] The spring of claim 13, wherein said outer container 120 includes: a thin film adhering layer 124-1 formed by coating an adhesive formed of a synthetic resin onto the entire portions of the outer diameter surface 124; and a thin film thermal contraction tube 124-2 formed of an engineering plastic having a high strength, good abrasion resistance, and good corrosion resistance wherein it is pressure-coated onto the entire portions of the outer diameter surfaces 124 of the adhering layer 124-1 and the outer container 120. [15] The spring of claim 13, wherein said outer container 120 is formed of a hard white layer 124a in an outer surface and a white layer 125 a in an inner surface formed of iron and nitride compound in the inner and outer diameter surfaces within a range of 4-10 micron by processing nitride heat treatment with respect to the inner diameter surface 125 and the outer diameter surface 124 of the outer container 120; and the outer surface nitride spreading layer 124b and the inner surface nitride spreading layer 125b including nitride are formed from 100-200 microns from the white layer, so that the oxidation and corrosion prevention is enhanced, and the strength of the steel of the outer container 120 is largely enhanced; and the metal thickness T of the outer container 120 is 1.25-2.5 times of the sum of the thickness of the nitride layer from the inner and outer diameter surfaces; and the outer container 120 has a metal thickness T of 0.8mm~ 1.6mm. [16] In an operation method of a length adjustable gas spring an improved operation method of a length adjustable gas spring comprising: a routine in which when a push bar 40 is pressed in a state that a gas having a certain pressure is filled in a cylinder 30, the circular slanted surface 42 of the push bar 40 is moved in the direction 'a', and a space is formed between the lower corner seal lip 62 of the valve seal 60 and the circular slanted surface 42, and the gas in the Y chamber (Y) is moved into the center inner groove 92 of the piston rod part 91 through the gas movement hole 98 of the upper side of the piston rod part 91 and is moved along the gas movement path 71 of the gas movement path pipe 70 and is moved into the X chamber (X) through the gas movement hole 46 of the push bar 40, so that since the lower end of the piston assembly 90 is fixed to the spindle support 130 by a clip 160, the cylinder 30 is moved up in the direction 'b' by a reaction, and on the contrary, in the case that the length of the gas spring is decreased, the sequence reverse to the above sequence is performed, namely, when the force pushing the push bar 40 is removed, the push bar 40 is moved in the direction 'b' by a gas pressure of the X chamber (X) of the cylinder 30, and therefore, the circular slanted surface 42 of the push bar 40 is closely contacted with the corner seal lip 62 of the lower side of the valve seal 60, so that the gas movement path is disconnected, and the gas movement between the X chamber (X) and the Y chamber (Y) is stopped, and the operation of the piston assembly 90 is stopped, and the upward movement of the cylinder 30 in the direction 'b' is stopped.