Patent Publication Number: US-2009229680-A1

Title: Plug Structure of a Coupler

Description:
TECHNICAL FIELD 
     This invention relates to a plug structure of a coupler consisting of a socket and a plug which are detachably fitted and connected together, which can be connected accurately by a simple operation in a case where liquid or other material is shifted from a container to a container on the main body side or where a container itself is replaced and which can maintain a sealed state when an excessive force is applied in the connected state. More particularly, this invention relates to a plug structure of this type which is suitable for use as a plug of a cartridge type container of a methanol fuel cell. 
     BACKGROUND ART 
     There are cases where it is necessary to supplement liquid such as a liquid material which decreases as a machine or instrument is driven or used and, in such cases, liquid such as a liquid material is supplemented by connecting a cartridge container to a container provided on the side of the machine or instrument, or by replacing a container provided on the side of the main body of the machine or instrument with another container. 
     For simplifying such connection or replacement of containers, various types of couplers are used and, in this case, a plug is provided on the cartridge container. 
     For example, in Japanese patent Application Laid-open Publication No. 2003-172487 discloses, as shown in  FIG. 5 , a connecting device constituting a coupler which consists of a plug P having a main flow path and a subsidiary flow path and a socket S having a main flow path and a subsidiary flow path and capable of being fitted with the plug and communicating with the main flow path and subsidiary flow path of the plug. 
     In this connecting device constituting the coupler, the socket S has a main flow path  2   a  formed in the outer periphery of a valve pusher  2  fixed to a holder  1 , a subsidiary flow path  2   b  formed on the outside of the main flow path  2   a , and valves  3   a  and  3   b  for closing the flow paths  2   a  and  2   b . The valves  3   a  and  3   b  are pushed against their valve seats by urging force of springs  4   a  and  4   b  to close the main flow path  2   a  and the subsidiary flow path  2   b.    
     On the other hand, the plug P has a main flow path  6   a  formed on the outer periphery of a valve main body  6  which is slidably supported on a valve holder  5 , a subsidiary flow path  6   b  formed on the outside of the main flow path  6   a  and valves  7   a  and  7   b  for closing the flow paths  6   a  and  6   b . The valves  6   a  and  6   b  are pushed against their valve seats by urging force of springs  8   a  and  8   b  to close the main flow paths  6   a  and the subsidiary flow path  6   b.    
     When these socket S and the plug P are connected together, the subsidiary valve  3   b  of the socket S first abuts against the subsidiary valve  7   b  of the plug P and these subsidiary valves are moved in a direction in which they are spaced away against the urging force of the springs  4   b  and  8   b  and the subsidiary flow paths  2   b  and  6   b  communicate with each other. 
     As the connection of the socket S with the plug P proceeds, the main valve  3   a  of the socket S is pushed by the end surface of an inner cylinder of the plug P and thereby is withdrawn against the spring  4   a  to cause the valve to part away from the valve seat of the valve pusher  2  and open the main flow path  2   a  of the valve pusher  2 . Also, a surface of the end portion of the valve pusher on the side of the socket S abuts against a surface of a valve member provided on the plug main body  6  to push the valve main body  6  against the urging force of the spring  8   a  and thereby cause the valve main body to withdraw and open the main valve  7   a  on the side of the plug P for communication with the main flow path  6   a.    
     By this structure, as the subsidiary flow path is communicated, a gas is supplied from a gas supply source to the container and an inner bag is dwindled by the gas pressure whereby liquid in the inner bag can be supplied out of the container through the main flow path on the plug side to the main flow path on the socket side. 
     DISCLOSURE OF THE INVENTION 
     In a case where, for example, such connecting device constituting a coupler is used as a coupler for supplementing a fuel of a methanol fuel cell or a coupler for supplementing by replacing a container with another container, super engineering plastics such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK) and liquid crystal polymer (LCP) and general use engineering plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polyacetal (POM) are often used from standpoints of formability and stability of the product. These materials, however, are hard and inferior in elasticity and, therefore, are liable to be damaged when an excessive force is applied in the connected state. It is particularly a problem that where such damage will take place cannot be expected. 
     It is therefore desired to develop a plug of a coupler which can be connected accurately and stably by a simple operation which, when an excessive force exceeding a normal range of use is applied in the connected state, can maintain a sealed state and can be used safely even if the plug is broken. 
     This invention has been made in view of the problem of the prior art. It is an object of the invention to provide a plug structure which can be connected accurately and stably by a simple operation and can maintain a sealed state when an excessive force exceeding a normal range of use is applied and the plug is broken. 
     It is also an object of the invention to provide a plug structure which can release a certain magnitude of bending force and a range of use of the plug thereby can be broadened. 
     In the first aspect of the invention for overcoming the problem of the prior art, there is provided a plug structure of a coupler consisting of a socket and a plug which are detachably fitted and connected together, said plug structure comprising: 
     a plug main body of the plug; 
     a projecting connecting portion provided in the plug main body and being fitted to the socket; 
     a valve seat provided in the plug main body; 
     a valve provided in the plug main body and the projecting connecting portion, said valve having a valve head which is urged to the valve seat for sealing; and 
     means for enabling maintenance of sealing between the valve seat and the valve head even when at least a part of the projecting connecting portion is broken and separated from the main body. 
     According to this plug structure of a coupler, since a projecting connecting portion which is fitted to the socket is provided in the plug main body, a valve seat is provided in the plug main body and a valve is provided in the plug main body and the projecting connecting portion, said valve having a valve head which is urged to the valve seat for sealing, and means is provided for enabling maintenance of sealing between the valve seat and the valve head even when at least a part of the projecting connecting portion is broken and separated from the main body, even if the projecting connecting portion is broken, the sealed state can be maintained and the plug can be used safely. 
     By this plug structure, the plug can be connected accurately and stably by a simple operation when methanol in a container is supplied to a methanol fuel cell or a container itself is replaced and, when an excessive force exceeding a normal range of use is applied and the plug is thereby broken, the sealed state can be maintained and the plug can be used safely. 
     In the second aspect of the invention, there is provided a plug structure of a coupler as defined in the first aspect wherein a base portion of the projecting connecting portion being fitted to the socket is formed as a breaking starting portion on the side of the plug. 
     According to the plug structure of a coupler of this aspect, since a base portion of the projecting connecting portion being fitted to the socket is formed as a breaking starting portion on the side of the plug, the base portion of the projecting connecting portion can be determined as the breaking starting portion and the sealed state can be maintained easily and an erroneous operation after breaking can be prevented. 
     In the third aspect of the invention, there is provided a plug structure of a coupler as defined in the second aspect wherein the breaking starting portion on the side of the plug is made by a recess formed in the entire periphery or a part of the periphery of a middle portion of the projecting connecting portion. 
     According to this aspect of the invention, since the breaking starting portion on the side of the plug is made by a recess formed in the entire periphery or a part of the periphery of a middle portion of the projecting connecting portion, even when breaking does not start from the base portion of the projecting connecting portion, breaking will start from the recess formed in the entire periphery or a part of the periphery of the middle portion whereby a breaking portion can be determined and the sealed state can be maintained more easily and an erroneous operation after breaking can be prevented. 
     In the fourth aspect of the invention, there is provided a plug structure of a coupler as defined in any of the first to third aspect wherein the plug main body and the projecting connecting portion consist of two divided portions. 
     According to this aspect, since the plug main body and the projecting connecting portion consist of two divided portion, a portion where the plug main body and the projecting connecting portion are separated can be determined at the dividing portion whereby application of an excessive force can be prevented and the sealed state can be maintained by the remaining portion and an erroneous operation can be prevented. 
     In the fifth aspect of the invention, there is provided a plug structure of a coupler as defined in the fourth aspect wherein the plug main body and the projecting connecting portion which are two divided portions are detachably fitted and connected to each other. 
     According to this aspect, since the plug main body and the projecting connecting portion which are two divided portions are detachably fitted and connected to each other, a separating force can be adjusted by the connecting force. 
     In the sixth aspect of the invention, there is provided a plug structure of a coupler as defined in the fourth or fifth aspect wherein a base portion of the projecting connecting portion is formed in a substantially spherical surface which can be moved in pivotal motion. 
     According to this aspect of the invention, since a base portion of the projecting connecting portion is formed in a substantially spherical surface which can be moved in pivotal motion, when force is applied to the projecting connecting portion, a part of the force can be released by causing the base portion to move in a pivotal motion whereby the range of use can be broadened. 
     In the seventh aspect of the invention, there is provided a plug structure of a coupler as defined in any of the first to sixth aspects wherein the valve is made of two divided portions of the valve head and a portion having at least a valve stem on the outside of a valve head and the dividing surface of the valve stem is formed in a substantially spherical surface which can be moved in a pivotal motion. 
     According to this aspect of the invention, since the valve is made of two divided portions of the valve head and a portion having at least a valve stem on the outside of the valve head and the dividing surface of the valve stem is formed in a substantially spherical surface which can be moved in a pivotal motion, when force is applied to the valve, a part of the force can be released by the dividing structure of the valve head and the valve stem and a part of the force can be released also by the pivotal motion of the dividing surface of the valve whereby the range of use can be broadened. By further combining this structure with the structure by which the projecting connecting portion can be moved in a pivotal motion, a structure like a universal joint can be realized and a further excessive force can be absorbed whereby the range of use in which the sealed state can be maintained can be further broadened. 
     In the eighth aspect of the invention, there is provided a plug structure of a coupler as defined in any of the first to seventh aspects wherein a breaking starting portion on the side of the valve is formed in the valve and a breaking starting portion on the side of the valve provided in the base portion or the middle portion of the projecting connecting portion, or a dividing surface between the plug main body and the projecting connecting portion is provided outside of the breaking starting portion on the valve side or a dividing surface between a valve head and a portion having at least a valve stem thereby to prevent an erroneous operation of the valve head when the projecting connecting portion is broken and separated. 
     According to this aspect of the invention, since a breaking starting portion on the side of the valve is formed in the valve and the breaking starting portion on the side of the valve provided in the base portion or the middle portion, or a dividing surface between the plug main body and the projecting connecting portion is provided outside of the breaking starting portion on the valve side or the dividing surface between the valve head and the portion having at least the valve stem thereby to prevent an erroneous operation of the valve head when the projecting connecting portion is broken and separated, when breaking and separation due to an excessive force take place, the valve main body is located always inside and, therefore, opening of the valve will not take place whereby the sealed state can be maintained and an erroneous operation can be prevented. 
     In the ninth aspect of the invention, there is provided a plug structure of a coupler as defined in any of the first to eighth aspects wherein a gripping portion is provided in a dividing surface between the plug main body and the projecting connecting portion for enabling taking out of the projecting connecting portion after breaking and separating of the projecting connecting portion. 
     According to this aspect of the invention, since a gripping portion is provided in a dividing surface between the plug main body and the projecting connecting portion for enabling taking out of the projecting connecting portion after breaking and separating of the projecting connecting portion, even if the projecting connecting portion remains on the side of the socket in the fitted and connected state, the remaining portion can be taken out easily by gripping portion and the socket can be fitted and connected with another plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  are a vertical sectional view showing an embodiment of a plug structure of a coupler according to the invention with a socket and a vertical sectional view of a broken state of the plug structure. 
         FIG. 2  are a vertical sectional view showing a plug structure of a coupler of the invention with a suitable valve and a vertical sectional view of detached state of the plug structure. 
         FIG. 3  are a vertical sectional view showing another embodiment of a plug structure of a coupler of the invention with a socket and a vertical sectional view of a detached state of the plug structure. 
         FIG. 4  are a vertical sectional view showing an embodiment of a plug structure of a coupler of the invention with a socket, a vertical sectional view of the plug structure used in a pivotal movement and a vertical sectional view of the plug structure in a detached state. 
         FIG. 5  is a vertical sectional view of a prior art connecting device. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the accompanying drawings. 
       FIG. 1  are a vertical sectional view showing an embodiment of a plug structure of a coupler according to the invention with a socket and a vertical sectional view of a broken state of the plug structure. 
     Description will first be made about a basic structure of a coupler  10  to which the plug structure of a coupler of the present invention is applied. The coupler  10  is composed of a socket S 10  and a plug P 10  which is fitted and connected with the socket S 10 . The socket S 10  is provided, for example, on the side of a main body of a methanol fuel cell and the plug P 10  is provided on the side of a cartridge as a methanol container for communicating each other to supplement fuel to the fuel cell main body or to replace the cartridge itself. 
     As a material of a main part of the socket S 10  which is fitted and connected with the plug P 10  of the coupler  10  can be used metal materials such as stainless steel (SUS) or non-metal materials such as polypropylene (PP), polyphenylene sulfide (PPS), high-density polyethylene (HDPE) and polystyrene (PS). Super engineering plastics having methanol-proof property such as polyether ether ketone (PEEK) and liquid crystal polymer (LCP) and general use engineering plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polyacetal (POM) can also be used as preferable materials. 
     The following description will be made on the basis of vertical direction of the drawings but it does not restrict actual direction of mounting of the coupler to the main body in any way and, therefore, mounting of the coupler may be made in any direction. 
     The socket S 10  of this coupler  10  to which the plug P 10  is fitted and connected has a socket member  11  of a generally cylindrical shape having an inner space which constitutes a valve chamber. This socket member  11  is mounted and fixed to a recessed mounting opening formed in the main body of the fuel cell. 
     A valve seat member  12  is connected to the central opening of this socket member  11  and a conical surface formed on the upper surface of the valve seat member  12  constitutes a valve seat  12   a . A cylindrical valve guide  12   b  projecting downwardly in the central portion thereof is formed integrally with the valve seat  12   a.    
     A valve main body  13  is mounted above the valve seat member  12  in the valve chamber of the socket member  11 . The valve main body  13  has a valve head  13   a  in a generally disk shape of a large diameter, a valve stem  13   b  in a columnar shape of a small diameter projecting downwardly in the central portion and a guide portion  13   c  projecting upwardly in the central portion. These portions  13   a ,  13   b  and  13   c  are formed integrally and the valve stem  13   b  is reciprocably mounted in the valve guide  12   b . The valve head  13   a  of the valve main body  13  is formed in its lower end portion with an O-ring groove  13   d  in which an O-ring  14  is mounted. The valve stem  13   b  and the guide portion  13   c  provided in the upper and lower end portions of the central portion are formed in their side surfaces with a plurality of grooves which constitute flow paths  15 . Through these flow paths  15 , the valve chamber in which the valve main body  12  is located communicates with the fuel cell main body located above and the valve chamber communicates also with a plug connecting portion located below in which the plug is connected. 
     A compression helical spring  16  is provided outside of the valve head  13   a  with its lower end being in abutting engagement with the valve head  13   a  and with its upper end being pressed by a spring holder  16   a  fixed to the upper end portion of the socket member  11 . The guide portion  13   c  of the valve main body  13  is mounted in the central opening formed in the spring holder  16   a.    
     By this arrangement, the valve main body  13  is constantly urged downwardly and, by pressing the O-ring  14  mounted in the O-ring groove  13   d  against the valve seat  12   a  and thereby achieving sealing, the valve is closed whereas by causing the O-ring  14  to space away against the force of the compression helical spring  16 , the valve is opened. 
     Below the valve seat member  12  is provided rubber holder  17  as an elastic holder in a manner to cover the valve stem  13   b  which reciprocates through the valve guide  12   b . The flange portion of the rubber holder  17  abuts against the valve seat member  12  and the central opening of the rubber holder  17  abuts against the outer periphery of the valve guide  12   b  with the inside portion of the central opening constituting a flow path. A bellows portion is formed in a manner to project downwardly from the central opening which bellows portion stretches and shrink in a vertical direction to secure a flow path  18  in the inside in the sealed state. 
     A cylindrical housing  19  constituting a plug connection space for connecting the plug P 10  is provided outside of the rubber holder  17  and below the socket member  11  so that the socket member  11 , the rubber holder  17  and the housing  19  are connected integrally together. 
     In the socket S 10  constructed in this manner, the valve can be automatically opened and closed by operation of the valve stem  13   b  of the valve main body  13  in accordance with connection with the plug P 10 . 
     As a material of a main part of the plug P 10  which is fitted and connected with the socket S 10  of the coupler  10  can be used, in the same manner as in the socket S 10 , metal materials such as stainless steel (SUS) or non-metal materials such as polypropylene (PP), polyphenylene sulfide (PPS), high-density polyethylene (HDPE) and polystyrene (PS). Super engineering plastics having methanol-proof property such as polyether ether ketone (PEEK) and liquid crystal polymer (LCP) and general use engineering plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polyacetal (POM) can also be used as preferable materials. 
     As shown in  FIG. 1 , this plug P 10  is mounted on an outer periphery of a tip end portion of a nozzle N of an inner container containing methanol which is a fuel of a fuel cell and is held by a holding cap C which is screwed onto an outer container which protects the inner container. The plug P 10  has a plug main body  31  having a generally cylindrical shape of three stages. An upper end portion  31   a  is of the smallest diameter and a lower end portion  31   c  following a middle portion  31   b  is of the largest diameter. 
     In this plug main body  31  is formed a projecting connecting portion  32  of a generally cylindrical shape having the smallest diameter. The projecting connecting portion  32  projects from the tip end portion of the plug main body  31  and is mounted in the housing  19  forming the plug connecting space of the socket S 10 . In the tip end portion of the projecting connecting portion  32  is formed a seal recess  32   a  in which the lower end portion of the rubber holder  17  of the socket S 10  is inserted and connected. The central opening of the projecting connecting portion  32  is of a magnitude to enable insertion of the valve stem  13   b  of the socket S 10 . 
     The middle portion  31   b  having a middle diameter of the pug main body  31  is formed in the inside thereof with a generally conical surface which constitutes a valve seat  33 . 
     In the cylindrical portion of the lower end portion  31   c  of the plug main body  31  is inserted, along the inner periphery thereof, the nozzle N of the inner container via an O-ring  34 . The plug main body  31  is attached to the container by pressing a stepped portion between the middle portion  31   b  and the lower portion  31   c  with the holding cap C which is screwed onto the nozzle of outer container housing the inner container. 
     In the inside of the plug main body  31  is provided a valve main body  35  having a valve head  35   a  formed in the middle portion which is of a generally disk shape having a large diameter. With this valve head  35   a  are integrally formed a valve stem  35   b  having a small diameter and projecting in the central portion of the upper end portion of the plug main body  31 , and a guide portion  35   c  having a large diameter and projecting in the central portion of the lower end portion of the plug main body  31 . The valve stem  35   b  projecting in the central portion of the upper end portion is located in the projecting connecting portion  32  in a manner to reciprocate within the projecting connecting portion  32 . 
     In the upper end portion of the valve head  35   a  of the valve main body  35  is formed an O-ring groove  35   d  opposite to the valve seat  33  and an O-ring  36  is mounted in the O-ring groove  35   d.    
     The valve stem  35   b  and the guide portion  35   c  which project from the valve head  35   a  in the upper and lower central portions are formed with a plurality of grooves which form flow paths. These flow paths communicate through the guide portion  35   c  below with the inner container and communicate through the valve stem  35   b  above with the socket S 10  to be fitted and connected. 
     For guiding reciprocating motion of the valve main body  35 , a valve holder  38  of a generally cylindrical shape is provided surrounding the outside of the guide portion  35   c . A flange portion of the valve holder  38  is in abutting engagement with the lower surface of the valve seat  33  of the middle portion  31   b  of the plug main body  31  and the lower surface of the flange portion is in abutting engagement with the O-ring  34  of the inner container and is screwed onto an inner screw portion of the middle portion  31   b.    
     A compression helical spring  39  is mounted on the outer periphery of the guide portion  35   c  of the valve main body  35  with its upper end being in abutting engagement with the valve head  35   a  and with its lower end being held by a middle projecting portion of the valve holder  38 . 
     By this arrangement, the valve main body  35  is urged constantly upwardly and, by pressing the O-ring  36  mounted in the O-ring groove  35   d  of the valve head  35   a  for sealing, the valve is closed whereas, by causing the O-ring  36  to space away against the force of the compression helical spring  39 , the valve is opened. 
     A flow-path opening  38   a  is formed in a lower side wall of the valve holder  38  so that the flow path communicates with the inner container. 
     In the plug P 10  constructed in this manner, the valve is automatically opened and closed by operation of the valve stem  35   b  of the valve main body  35  in accordance with connection with the socket S 10 . 
     For discriminating the socket S 10  from other sockets and discriminating the plug P 10  from other plugs so that, for example, a socket and a plug for a specific liquid concentration only can be fitted and connected with each other, the socket S 10  and the plug P 10  of this coupler  10  are provided with a key and a key slot as discrimination means. A key is provided in either of the socket S 10  and the plug P 10  and a key slot is provided in the other and, by fitting the socket S 10  with the plug P 10 , a socket and a plug which cannot be fitted with each other can be discriminated. 
     In this coupler  10 , as shown in  FIG. 1 , a key  51  is provided on the outer peripheral surface of the projecting connecting portion  32  of the plug main body  31  of the plug P 10 . The key  51  is provided, for example, in two diagonal positions (only one is shown in  FIG. 1 ). 
     A key slot  52  which is fitted with the key  51  is provided in the inner periphery of a lower end portion of the housing  19  of the socket S 10  as a slot corresponding to the location of the key  51 . 
     Therefore, by fitting the key  51  of the plug P 10  with the key slot  52  formed in the socket S 10 , the socket S 10  and the plug P 10  can be discriminated. 
     By selecting positions of the key  51  and the key slot  52  not only at diagonal positions (180 degree different positions) but also at other different angular positions or changing shapes of the key and the key slot such as width and depth thereof and combining the changed shapes so as to prevent fitting of a socket or plug of a large size with a plug or socket of a small size, many types of sockets and plugs can be discriminated. 
     In this coupler  10 , an unillustrated connection holding means for maintaining the connection of the socket S 10  and the plug P 10  is provided. As this connection holding means, for example, one side of the connection holding means is formed as a receiving member in which an engaging member is received and the other side of the connection holding means is formed as the engaging member made of, e.g., an elastic material. The engaging member is inserted in and detached from the receiving member in a manner to override a portion of the receiving member in straight direction. The engaging member is received in and connected to the receiving member by flexing the engaging member made of an elastic material and is released by pulling it out of the receiving member. The connection holding means may be made not only of separate members but may be a structure utilizing elasticity of material of the socket S 10  and the plug P 10 . 
     In this coupler  10 , in a case where the projecting connecting portion of the plug P 10  is broken off by application of an excessive force exceeding a normal range of use in the state in which the socket S 10  is fitted and connected with the plug P 10 , the valve stem  35   b  of the valve main body  35  disposed inside of the projecting connecting portion is left in a projecting state. Since the valve can be opened by this valve stem  35   b  and, as a result, methanol in the container may be leaked out. 
     To cope with this problem, in a plug structure  70  of this coupler, while the plug main body  31  is made integrally with the projecting connecting portion  32 , a recessed portion which constitutes a breaking starting portion  71  on the plug side for determining a breaking portion is formed in the entire periphery of a base portion of the projecting connecting portion  32 . Thus, by making this recessed portion thinner than other portion, breaking occurs in this portion first. 
     The recessed portion formed as the breaking starting portion  71  on the plug side may be made not only in the entire periphery but also in a part of the periphery of the base portion so long as it will weaken strength of such portion. If the projecting connecting portion  32  projects from the central portion of the plug main body  31  without forming a recess, the root portion of the projecting connecting portion  32  is the weakest portion, so that this root portion may be used as the breaking starting portion  71  on the plug side. 
     In this plug structure  70 , a recessed portion constituting a breaking starting portion  72  on the valve side is formed in the entire periphery of a portion between the valve head  35   a  of the valve main body  35  and the valve stem  35   b  projecting upward. By making this portion thinner than other portion, breaking will start in this portion first. 
     The recessed portion formed as the breaking starting portion  72  on the valve side may be made not only in the entire periphery but also in a part of the periphery of this portion so long as it will weaken strength of such portion. 
     The positions of the breaking starting portion  71  on the plug side and the breaking starting portion  72  on the valve side are so set that the breaking starting portion  72  on the valve side is positioned below (inside) the breaking starting portion  71  on the plug side so that the valve stem  35   b  which remains in the broken state will be positioned inside of the projecting connecting portion  32  which remain in the broken state. 
     By this arrangement, an operation such as pushing of the valve stem  35   b  of the valve main body  35  with a finger can be prevented and the sealed state of the valve thereby can be maintained. 
     In this plug structure  70 , a gripping portion  73  is formed in a portion outside (upper side) of the breaking starting portion  71  on the plug side of the projecting connecting portion  32  for taking out the broken off projecting connecting portion  32  from the socket S 10 . 
     By this arrangement, as shown in  FIG. 1(   b ), when the projecting connecting portion  32  remains in a broken state in the socket S 10  in the fitted and connected state, the projecting connecting portion  32  can be taken out easily by means of the gripping portion  73 . 
     The projecting portion formed as the gripping portion  73  may be made either in the entire periphery or plural positions in the periphery of the projecting connecting portion  32  so long as the broken off portion can be taken out. A recess may be formed instead of the projection. 
     According to this plug structure  70  of the coupler, even when the projecting connecting portion  32  is broken by application of an excessive bending force, the function of the valve can be maintained to maintain the sealed state whereby leakage of contents of the container can be prevented and the coupler can be used safely. 
     Thus, a predetermined plug can be accurately selected and connected for supplying methanol in a container to a methanol fuel cell or replacing a container itself and, when a plug of a coupler is damaged by application of an excessive force, the sealed state can be maintained and the coupler can be used safely. 
     According to the invention, the breaking starting portion  72  on the valve side is provided outside of the valve head  35   a  which is sealed with the valve seat  33  of the valve main body  35  and this breaking staring portion  72  on the valve side is formed by a recessed portion in the entire periphery or a part of the periphery and, therefore, a broken off portion can be determined at a predetermined position by means of the breaking starting portion  72  on the valve side and, therefore, the sealed state can be maintained easily and an erroneous operation after breaking can be prevented. 
     For facilitating breaking off at the breaking starting portions  71  and  72 , a material among the above described materials which is easily breakable may be advantageously used. Glass fiber may, for example, be included in the material to facilitate breaking further. A suitable amount of addition of glass fiber is 20-60 weight % and, more preferably, 30 weight % or over. 
     By causing the material to have tensile strain of 3% or below, preferably 2% or below by using such material, the material can be made easily breakable. 
     A configuration of a valve which is suitable for use in the plug structure of a coupler of the present invention will now be described with reference to  FIG. 2 . 
     In a plug structure  70 A, the valve is substituted by a valve of a divided structure. The same components as the above described plug structure  70  are designated by the same reference characters and description thereof will be omitted. 
     In this plug structure  70 A, a valve head  35   a  of a valve main body  35  located inside of a plug main body  31  and a projecting connecting portion  32  is divided from a valve stem  35   b  which projects from the valve head  35   a . A connecting projection  74   a  is formed in the upper end portion of the valve head  35   a  and a connecting recess  74   b  is formed in the lower end portion of the projecting connecting portion  32  for connecting each other. 
     The plug main body  31  and the projecting connecting portion  32  are formed integrally as described above and a recessed portion is formed in the entire periphery of a base portion of the projecting connecting portion  32  as a breaking starting portion  71  on the plug side for determining a breaking portion so that, by making this portion thinner than other portion, breaking will occur in this portion first. 
     Positions of the dividing position (connecting position) between the valve head  35   a  and the valve stem  35   b  and the breaking starting portion  71  on the plug side are so set that the positions of the connecting projection  74   a  and the connecting recess  74   b  which are the dividing position on the valve side is positioned below (inside) the breaking starting portion  71  on the plug side so that the valve head  35   a  which remains in the broken state will be positioned inside of the projecting connecting portion  32  which remain in the broken state. 
     In this valve structure  70 A, by forming the valve main body  35  by dividing structure of the valve head  35   a  and the valve stem  35   b , the valve can be operated in the same manner as in the valve head of an integral structure through the connecting projection  74   a  and the connecting recess  74   b  in case where the valve is opened against the force of a compression helical spring  39 . 
     On the other hand, when an excessive force exceeding a normal range of use is applied to the plug P 10 , breaking occurs first in the breaking starting portion  71  formed between the plug main body  31  and the base portion of the projecting connecting portion  32  and, as a result, the valve stem  35   b  on the upper side is separated with the broken off projecting connecting portion  32  and the sealed state can be maintained with the remaining valve head  35   a.    
     At this time, the projecting connecting portion  32  to which the excessive force is applied is broken off but application of an excessive force to the valve main body  35  is prevented by virtue of a gap between the connecting projection  74   a  of the valve head  35   a  and the connecting recess  74   b  of the valve stem  35   b  whereby the upper side valve stem  35   b  only is separated and the sealed state can be maintained easily with the valve head  35   a.    
     According to this plug structure  70 A, the valve head  35   a  and the valve stem  35   b  outside of the valve head  35   a  are formed in a divided structure, even when the plug main body  31  and the projecting connecting portion  32  are damaged or broken off due to application of an excessive force, the separating position between the valve main body  35   a  and the valve stem  35   b  can be set at a predetermined dividing position and application of the excessive force to the valve side can also be prevented. Moreover, the sealed state can be accurately maintained with the remaining valve head  35   a  and an erroneous operation can be prevented. 
     The dividing structure of the valve may be such that the valve is divided in more portions so long as the valve seat  33  and the valve head  35   a  which is sealed with the valve seat  33  can remain in the plug P 10 . 
     In this plug structure  70 A also, a gripping portion  73  projecting in the outer peripheral side for taking out the broken off projecting connecting portion  32  from the socket S 10  is provided on the outside (upper side) of the breaking starting portion  71  on the plug side in the projecting connecting portion  32 . 
     By this arrangement, as shown in  FIG. 2(   b ), even when the broken off projecting connecting portion  32  is left in the socket S 10  in the fitted and connected state, it can be taken out easily by means of the gripping portion  73 . 
     According to this plug structure  70 A of the coupler also, even when the projecting connecting portion  32  is broken by application of an excessive bending force, the function of the valve can be maintained to maintain the sealed state whereby leakage of contents of the container can be prevented and the coupler can be used safely. 
     Thus, a predetermined plug can be accurately selected and connected for supplying methanol in a container to a methanol fuel cell or replacing a container itself and, when a plug of a coupler is damaged by application of an excessive force, the sealed state can be maintained and the coupler can be used safely. 
     Another embodiment of the plug structure of a coupler according to the invention will be described with reference to  FIG. 3 . 
     In this plug structure  70 B of a coupler, a dividing structure of the valve and a dividing structure of the plug are added to the plug structure  70  described above. 
     In this plug structure  70 B, a projecting connecting portion  32  projecting from the central portion of the plug main body  31  is divided from a plug main body  31 . The plug main body  31  is formed in its upper end portion with a fitting recess  75   a  having an engaging portion  76   a  formed in an upper inner peripheral portion thereof while the projecting connecting portion  32  is formed in its lower end portion with a fitting projection  75   b  having an engaging portion  76   b  formed in the lower outer peripheral portion thereof. 
     The fitting recess  75   a  and the engaging portion  76   a  of the plug main body  31  and the fitting projection  75   b  and the engaging portion  76   b  of the projecting connecting portion  32  which are fitted and connected to the fitting recess  75   a  and the engaging portion  76   a  cannot be disengaged from each other by application of force necessary for a normal connecting operation of the coupler  10  but are separated from each other by application of a large force exceeding a normal range of use and thereby the projecting connecting portion  32  is detached from the plug main body  31 . 
     The dividing structure on the valve side is of the same construction as that of the plug structure  70 A described above. 
     Positions of the dividing structure (fitting position) between the plug main body  31  and the projecting connecting portion  32  and the dividing structure (connecting position) of the valve head  35   a  and the valve stem  35   b  of the valve main body  35  are so arranged that the position of the connecting projection and recess  74   a  and  74   b  on the valve side is positioned below the position of the dividing structure (fitting position) between the plug main body  31  and the projecting connecting portion  32  of the plug main body  31  on the plug side so that the valve head  35   a  which remains in the broken state will be positioned inside of the projecting connecting portion  32  which remains in the broken state whereby an erroneous operation such as the valve is erroneously opened by touching with a finger can be prevented. 
     In this plug structure  70 B also, in the same manner as in the above described plug structures  70  and  70 A, the valve head  35   a  of the valve main body  35  can be spaced away from the valve seat  33  in the same manner as in the plug of an integral structure by operating the valve stem  35   b  against the force of the compression helical spring  39 . 
     When an excessive force exceeding a normal range of use is applied to this plug P 10 , the projecting connecting portion  32  is separated at the fitting recess and projection  75   a  and  75   b  and the engaging portions  76   a  and  76   b  of the plug main body  31  and the base portion of the projecting connecting portion  32  and, simultaneously, the upper side valve stem  35   b  is separated with the separated projecting connecting portion  32  whereas the sealed state can be maintained by the remaining valve head  35   a.    
     At this time, an excessive force is applied to the projecting connecting portion and the fitting projection  75   b  and engaging portion  76   b  are separated from the fitting recess  75   a  and engaging portion  76   a  but application of the excessive force to the plug main body  31  can be prevented as compared to a case where the projecting connecting portion  32  is broken off the plug main body  31 . 
     Accordingly, force by which the projecting connecting portion  32  is separated from the plug main body  31  can be adjusted by configurations of the fitting recess and projection  75   a  and  75   b  and the engaging portions  76   a  and  76   b.    
     Application of an excessive force to the valve main body  35  also can be prevented by the gap between the connecting projection  74   a  of the valve head  35   a  and the connecting recess  74   b  of the valve stem  35   b  whereby the upper side valve stem  35   b  only is separated and the sealed state by the valve head  35   a  can be maintained easily. 
     Therefore, according to this plug structure  70   b , since the valve head  35   a  is divided from the valve stem  35   b  outside of the valve head  35   a  and, additionally, the plug main body  31  is divided from the projecting connecting portion  32 , the plug main body  31  and the projecting connecting portion  32  can be separated by application of an excessive force and, moreover, the separating force can be set at a predetermined magnitude and the separating position can be set at the predetermined divided position. 
     By this plug structure  70 B of a coupler also, when the projecting connecting portion  32  is separated by application of an excessive force such as an excessive bending force, the function of the valve is maintained and the sealed state can be maintained whereby leakage of contents from the container can be prevented and the coupler can be used safely. 
     Thus, a predetermined plug can be accurately selected and connected for supplying methanol in a container to a methanol fuel cell or replacing a container itself and, when a plug of a coupler is damaged by application of an excessive force, the sealed state can be maintained and the coupler can be used safely. 
     Another embodiment of the plug structure of a coupler according to the invention will now be described with reference to  FIG. 4 . In this plug structure  70 C, in addition to the dividing structure between the valve and plug of the above described plug structure  70 B, the valve and the plug can be moved in a pivoting motion to some extent against force exceeding a normal range of use and the coupler can be used in this state while maintaining the sealed state. 
     In this plug structure  70 C, a plug main body  31  and a projecting connecting portion  32  projecting from the central portion of the plug main body  31  are formed as two divided portions and a recessed portion formed in the upper end portion of the plug main body  31  is formed as a pivoting connecting recess  77   a  having a substantially spherical surface whereas a pivoting connecting projection  77   b  having a substantially spherical shape projects from the lower end portion of the projecting connecting portion  32 . 
     By this arrangement, the projecting connecting portion  32  can be inclined to the central axis of the plug main body  31  by contact of the spherical surfaces of the pivoting connecting recess  77   a  and the pivoting connecting projection  77   b.    
     The valve which is disposed inside of the plug main body  31  and the projecting connecting portion  32  is formed as two divided portions of a valve head  35   a  of a valve main body  35  and a valve stem  35   b  projecting upwardly from the valve head  35   a . The upper end portion of the valve head  35   a  is formed as a contacting recess  78   a  having a substantially spherical surface and the lower end portion of the valve stem  35   b  is formed as a contacting projection  78   b  having a substantially spherical shape so that they can contact each other by contact of their spherical surfaces. 
     For preventing interference of the valve stem  35   b  with the pivoting connecting recess  77   a  of the plug main body  31  when the valve stem  35   b  is pushed down for opening the valve, a recessed portion  79  is formed and the lower surface of the recessed portion  79  is formed as a spherical surface portion  79   a  having the same radius of curvature as the pivoting connecting recess  77   a.    
     Other structure of the plug structure  70 C is the same as those of the above described plug structures  70 ,  70 A and  70 B and, therefore, overlapping description will be omitted. 
     According to the plug structure  70 C of a coupler, in the same manner as in the above described plug structures  70 ,  70 A and  70 B, the valve head  35   a  of the valve main body  31  can be spaced away from the valve seat  33  to open the valve through the contacting recess  78   a  and contacting projection  78   b  by operating the valve stem  35   b  against the force of the compression helical spring  39  in the same manner as in the plug of an integral structure. 
     When force which slightly exceeds a normal range of use is applied to this plug P 10 , the projecting connecting portion  32  is inclined to the central axis of the plug main body  31  at the pivoting connecting recess  77   a  of the plug main body  31  and the pivoting connecting projection  77   b  in the base portion of the projecting connecting portion  32  and also at the spherical surfaces of the contacting recess  78   a  of the valve head  35   a  and the contacting projection  78   b  of the valve stem  35   b  whereby the coupler can be used while the sealed state which performs the function as the coupler can be maintained. 
     When an excessive force exceeding a normal range of use and causing a damage is applied, the projecting connecting portion  32  is separated from the pivoting connecting recess  77   a  and the pivoting connecting projection  77   b  between the plug main body  31  and the projecting connecting portion  32  and, simultaneously, the upper side valve stem  35   b  is separated with the separated projecting connecting portion  32  from the contacting recess  78   a  and the contacting projection  78   b  and the sealed state can be maintained by means of the remaining valve head  35   a  located at the bottom portion of the pivoting connecting recess  77   a  whereby the valve head  35   a  cannot be touched directly with a finger. 
     At this time, the projecting connecting portion  32  to which an excessive force is applied is separated but application of an excessive force to the plug main body  31  can be prevented as compared to a case where the projecting connecting portion  32  is broken off. 
     By this plug structure  70 C of a coupler also, when an excessive force such as an excessive bending force is applied to the projecting connecting portion  32 , it can be used in an inclined state to a force of a certain degree and, when a larger force is applied, the projecting connecting portion  32  is separated but the function of the valve is maintained and the sealed state can be maintained whereby leakage of contents from the container can be prevented and the coupler can be used safely. 
     Thus, a predetermined plug can be accurately selected and connected for supplying methanol in a container to a methanol fuel cell or replacing a container itself and, when a plug of a coupler is damaged by application of an excessive force, the sealed state can be maintained and the coupler can be used safely even if the projecting connecting portion  32  is inclined or separated. 
     Further, according to this plug structure  70 C of a coupler, since the base portion of the projecting connecting portion  32  is formed as a substantially spherical surface along which the projecting connecting portion  32  can be pivoted, when an excessive force is applied to the projecting connecting portion  32 , such force can be partly released by pivoting of the base portion whereby the range of use of the coupler in the fitted and connected state can be broadened. 
     Further, according to this plug structure  70 C of a coupler, since the dividing surfaces of the valve head  35   a  and the valve stem  35   b  are formed as substantially spherical surfaces along which the valve head  35   a  and the valve stem  35   b  can pivot to each other, when an excessive force is applied to the valve, such force can be partly released by pivoting movement at the dividing surfaces whereby the range of use of the coupler in the fitted and connected state can be broadened. By combining the structure by which the projecting connecting portion  32  can be pivoted, the plug structure becomes a kind of universal joint which can absorb a further larger force whereby the sealed state can be maintained and the range of use of the coupler can be broadened. 
     In the above described embodiment, the projecting connecting portion  32  is made pivotable relative to the plug main body  31  and the valve stem  35   b  is also made pivotable relative to the valve head  35   a . Alternatively, either one of them only may be made pivotable and the other may be inclined within a range of elastic deformation so that the coupler can be used while the sealed state is maintained. 
     Although description has been omitted for avoiding duplication, in the respective embodiments described above, provision of the key and key slot as the discrimination means in the socket and the plug may be reversed, or the engaging portion and the receiving portion of the connection holding means by be reversed. 
     Description has been made by way of example about connecting a methanol container of methanol for a methanol fuel cell to a fuel cell main body. The use of the plug structure of the present invention is not limited to this but it may be used for other purposes also and it is suitable for use when many types of coupler must be discriminated. 
     INDUSTRIAL APPLICABILITY 
     This invention relates to a plug structure of a coupler consisting of a socket and a plug which are detachably fitted and connected together, which can be connected accurately by a simple operation in a case where liquid or other material from a container to a container on the main body side or where a container itself is replaced and which can maintain a sealed state when an excessive force is applied in the connected state. More particularly, this invention relates to a plug structure of this type which is suitable for use as a plug of a cartridge type container of a methanol fuel cell.