Abstract:
A pressure container has a steel pipe and an end plate that is formed with a joint portion by allowing its tapered surface to touch a tapered surface of an opening end of the steel pipe so as to block the opening end. The steel pipe has a flange portion which can be cut at the opening end of the steel pipe, and the joint portion is allowed to touch the flange portion. The flange portion is pressed against the opening end along an axial direction so as to touch the end plate, and while the end plate is being pressed against the steel pipe along the axial direction, an electric current is applied so that welding is carried out.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-242565, filed Aug. 23, 2004, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a pressure container and a pressure accumulating/buffer apparatus such as an accumulator which are used in an automobile and an industrial machine, and particularly relates to them where a welded portion between an end plate and a body portion is uniform.  
         [0004]     2. Description of the Related Art  
         [0005]     Accumulators (pressure accumulating/buffer apparatus) are used in hydraulic circuits and shock absorbers of hydraulic control apparatuses. In the accumulators, insides of pressure containers are generally divided into gas chambers and oil chambers by bellows, and pressure fluctuation in oil flowing into the oil chambers are buffered by the swell/shrink function of gas in the gas chambers due to expansion/shirinkage of the bellows (see Jpn. Pat. Appln. KOKAI Publication Nos. 2001-116002, 2001-116003 and 2003-120601). The accumulators are widely used as apparatuses, that effectively suppress pulsation generated in the coil flowing in the hydraulic circuits, for example, in automobiles and industrial machines.  
         [0006]     In order to form pressure containers, it is necessary to joint a contour member to a cover body that closes the contour member with large strength. For example, resistance welding can be used in a pressure container with small thickness (2 mm or less), for example.  FIGS. 5 and 6  are diagrams illustrating examples of such pressure containers. That is to say, a pressure container  10  has a steel pipe (contour member)  11 , and an end plate  12  that covers an opening of the steel pipe  11 . In  FIG. 5, 13  and  14  designate electrodes.  
         [0007]     In the case where the resistance welding is carried out, an outside surface of the steel pipe  11  is clamped by a double-split electrode  13 , an outside surface of the end plate  12  is inserted into the steel pipe  11  from an end side so as to come in contact with its inner wall surface, and the electrode  14  is brought into contact with the outside surface of the steel pipe  11 . Meanwhile, the electrode  14  is allowed to touch an upper surface of the end plate  12 . While a load is applied to between the electrodes  13  and  14 , an electric current is allowed to flow in the electrode  13 , the steel pipe  11 , the end plate  12  and the electrode  14 , so that the inner wall surface of the steel pipe  11  and the outside surface of the end plate  12  are resistance-welded.  
         [0008]     On the other hand, in a pressure container with large thickness (2 mm or more) shown in  FIG. 7 , the outer peripheral surface is jointed by Co2 welding, TIG welding and the like (see F in  FIG. 7 ).  FIG. 7  is a diagram illustrating one example of the accumulator. That is to say, an accumulator  20  has a cylindrical shell (contour member)  21 , a first end plate (cover body)  22  which is fitted into one opening of the shell  21 , and a second end plate (cover body)  23  which is fitted into the other opening. The first end plate  22  is formed with a through hole  22   a , and the through hole  22   a  is blocked by a gas sealing stopper  22   b  airtightly. Further, the second end plate  23  is formed with a port  23   a , and the port  23   a  is connected to the hydraulic circuit or the like so that oil freely goes in and out the port  23   a.    
         [0009]     On a lower surface of the first end plate  22  in  FIG. 7 , a disc-shaped bellows cap  25  is provided via a metallic bellows  24  so as to be slidably along an axial direction of the shell  21 .  26  in  FIG. 7  designates a guide attached to an outer peripheral portion of the bellows cap  25 . The guide  26  has a function that assists the sliding of the bellows cap  25 . A space formed by the first end plate  22 , the metallic bellows  24  and the bellows cap  25  is a gas chamber G, and nitrogen gas or the like is sealed thereinto. Further, an oil chamber L is formed between the second end plate  23  and the bellows cap  25 .  
         [0010]     The above-mentioned method of jointing the pressure container has the following problem. That is to say, in the resistance welding, since the steel pipe is clamped by the double-split electrode, uniform contact and a strong clamping force cannot be obtained, and thus this method can be used only for thin steel pipes with thickness of up to about 2 mm. Further, in the case of the thick steel pipes, in order to obtain the strength of the welded portion by CO2 welding, TIG welding and the like of the outer peripheral surface, the steel pipes become large and heavy.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     It is an object of the present invention to form a joint portion having sufficient strength of a welded portion by obtaining large welding load and uniform contact in resistance welding even when a thick member is used and a large welding current is electrified.  
         [0012]     The present invention provides a pressure container comprising: a cylindrical contour member; and a cover body which is formed with a joint portion by allowing its side wall portion to touch an inner wall portion of an opening end of the contour member and blocks the opening end, wherein the contour member has a flange portion which can be cut at the opening end, and the joint portion is allowed to touch the flange portion, the flange portion is pressed against the opening end along an axial direction so as to touch the cover body, and while the cover body is being pressed against the contour member along the axial direction, an electric current is applied so that welding is carried out.  
         [0013]     The present invention also provides a pressure accumulating/buffer apparatus comprising: a pressure container; and an air chamber into which gas can be sealed and a liquid chamber into which a liquid can flow that are provided in the pressure container, wherein the pressure container has a cylindrical contour member and a cover body which is formed with a joint portion by allowing its side wall portion to touch an inner wall portion of an opening end of the contour member and blocks the opening end, the contour member has a flange portion which can be cut at the opening end, and the joint portion is allowed to touch the flange portion, the flange portion is pressed against the opening end along an axial direction so as to touch the cover body, and while the cover body is being pressed against the contour member along the axial direction, an electric current is applied so that welding is carried out.  
         [0014]     According to the present invention, even when a thick member is used and a large welding current is electrified, large welding load and uniform contact is obtained in the resistance welding so that the joint portion having sufficient strength of the welded portion can be formed.  
         [0015]     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0016]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0017]      FIG. 1  is a longitudinal section illustrating an accumulator according to one embodiment of the present invention;  
         [0018]      FIG. 2  is a longitudinal section typically illustrating a joint portion between a steel pipe and an end plate in the accumulator;  
         [0019]      FIG. 3  is a longitudinal section typically illustrating the joint portion between the steel pipe and the end plate in the accumulator;  
         [0020]      FIG. 4  is a vertical, sectional view of the end plate, which is deformed in a specific way in the accmulator;  
         [0021]      FIG. 5  is a longitudinal section illustrating one example of a method of jointing a shell member and a cover body in a pressure container to be used in a conventional accumulator;  
         [0022]      FIG. 6  is a longitudinal section illustrating the pressure container; and  
         [0023]      FIG. 7  is a longitudinal section illustrating a conventional accumulator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]      FIG. 1  is a longitudinal section illustrating an accumulator (pressure accumulating/buffer apparatus)  30  according to one embodiment of the present invention, and  FIG. 2  is a longitudinal section typically illustrating a joint portion Q between a steel pipe  40  and an end plate  50  incorporated into the accumulator  30 . G in  FIG. 1  designates a gas chamber (air chamber), and L designates an oil chamber (liquid chamber).  
         [0025]     The accumulator  30  has the steel pipe (contour member)  40  which has a cylindrical shape with a bottom, an end plate (cover body)  50  which is fitted into an opening of the steel pipe  40 , and a bellows mechanism  60  housed in the steel pipe  40 . The steep pipe  40  and the end plate  50  compose the pressure container, and a tapered surface  41   c , mentioned later, of the steep pipe  40  and a tapered surface  51   d , mentioned later, of the end plate  50  are jointed by resistance welding so that the joint portion Q is formed.  
         [0026]     The steel pipe  40  is formed by joining a pipe portion  41  integrally with a bottom portion  42 . The bottom portion  42  is formed with a through hole  42   a . The through hole  42   a  is blocked airtightly by a gas sealing stopper  43 . Further, a cover  44  is attached to an outer portion of the through hole  42   a .  41   a  in  FIG. 1  designates an inner wall surface of the pipe portion  41 ,  41   b  designates an outer wall surface, and  41   c  designates a tapered surface formed on the inner wall surface  41   a . Further, an alternate long and two short dashes line  45  in  FIG. 1  designates a flange portion which can be cut.  
         [0027]     The end plate  50  has an end plate main body  51  formed into a disc shape, a port portion  52  which is provided to a center of the end plate main body  51  and has a through hole therein, and a cylindrical member (cylindrical body)  53  which is jointed to an upper surface  51   a , mentioned later, of the end plate main body  51 .  
         [0028]     The end plate main body  51  is arranged so that the upper surface  51   a  is inside of the steel pipe  40  and the lower surface  51   b  is outside of the steel pipe  40 . Further, a tapered surface  51   d  is formed from a side surface  51   c  to the upper surface  51   a . The tapered surface  51   d  is provided with a ring-shaped part  54  made of rubber or resin, and it prevents sputter from entering the gas chamber G at the time of welding.  
         [0029]     The bellows mechanism  60  has a metallic bellows  61  formed into a cylindrical shape, a bellows cap  62 , a seal function member  64 , and a guide  64 . The bellows cap  62  has a disc shape and is mounted to one opening end of the metallic bellows  61 . The seal function member  63  is mounted to a central concave portion  62   a  of the bellows cap  62  and is made of a rubber material. The guide  64  is mounted to an outer peripheral portion  62   b  of the bellows cap  62 . Further, since the guide  64  slides along an inner peripheral surface of the pipe portion  41 , the bellows cap  62  can move smoothly.  
         [0030]     The other opening end of the metallic bellows  61  is mounted airtightly to the upper surface  51   a  of the end plate main body  51 . The seal function member  63  is arranged so that a lower surface  63   a  of the metallic bellows  61  in the most shrunk state touches an upper surface  53   a  of the cylindrical member  53 .  
         [0031]     In the accumulator  30  having such a constitution, when the pressure of pressure oil introduced into the oil chamber L via the through hole  52   a  of the port portion  52  exceeds gas pressure in the gas chamber G, the metallic bellows  61  expands so that the gas in the gas chamber G shrinks. On the other hand, when the pressure of the pressure oil in the oil chamber L is less than the gas pressure in the gas chamber G, the metallic bellows  61  shrinks so that the gas in the gas chamber G swells. A pressure fluctuation in the pressure oil in a hydraulic circuit is buffered by swell/shrink function of the gas in the gas chamber G, so that pulsation of the pressure oil is suppressed.  
         [0032]     The steps of manufacturing the accumulator  30  are explained below. Firstly, the cylindrical member  53  is welded to the upper surface  51   a  of the end plate main body  51 . After the metallic bellows  61  and the bellows cap  62  are welded, they are welded to the upper surface  51   a  to the end plate main body  51 .  
         [0033]     As shown in  FIGS. 2 and 3 , the end plate main body  51  and the steel pipe  41  are resistance-welded. That is to say, the tapered surface  41   c  of the pipe portion  41  is allowed to butt with the tapered surface  51   d  of the end plate man body  51 . The lower surface  51   b  of the end plate main body  51  is pressed by a first electrode  70  of a resistance welding machine (not shown) to a direction of arrow D in  FIG. 2 , and the flange portion  45  of the pipe portion  41  is pressed by a second electrode  71  to a direction of arrow U in  FIG. 2 . It is desirable that the second electrode  71  has a ring shape. The use of the ring-shaped electrode can prevent unnecessary discharge to the flange portion  45 . That is to say, the tapered surface  41   c  and the tapered surface  51   d  are pressurized. Electricity is turned on between the first electrode  70  and the second electrode  71 , so that the resistance welding is carried out. As a result, the tapered surface  41   c  and the tapered surface  51   d  are melted so as to be welded, and the joint portion Q is formed. The flange portion  45  is cut as the need arises.  
         [0034]     When the resistance welding is carried out, a foreign matter intrusion preventing cap K is attached to the port portion  52  so as to prevent foreign matter from intruding.  
         [0035]     The resistance welding can be carried out satisfactorily by applying large welding load. The steel pipe  40  is, therefore, welded to the end plate  50  satisfactorily, and a sealed state of the pressure container becomes secure and firm.  
         [0036]     According to the accumulator  30  in the embodiment, even in the case where a steel pipe with thickness of, for example, 2 mm or more is resistance-welded to a mirror plate by applying large welding current (for example, 300 kA or more), large welding load can be applied via the flange portion  45 , so that uniform contact can be obtained. As a result, the pressure container having sufficient strength of the welded portion can be formed.  
         [0037]     Further, since the electrodes do not have to be split into two and thus discharge to the members from the electrodes can be prevented, the surfaces of the members such as the steel pipe and the end plate do not get rough.  
         [0038]     In the embodiment described above, the end-plate main body  51  has a tapered surface  51   d . Instead, the end-plate main body  51  may have an edge part  54  as shown in  FIG. 4 . The pipe portion  41  may have its tapered surface  41   c  abutting on the edge part  54 . Thus, the same advantage can be attained as in the structure of  FIG. 2 .  
         [0039]     The present invention is not limited to the above embodiment. For example, the above example explains the pressure container for the accumulator, but the present invention can be applied also to pressure containers to be used for applications of a gas spring and gas stay. Further, the pressure container where the end plate is provided to one side is explained, but it goes without saying that the present invention can be applied similarly to the case where the end plates are provided to both the ends, respectively. It goes without saying that the present invention can be carried out variously without departing from the scope of the gist.  
         [0040]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.