Abstract:
A power-assisted mechanism having a simple structure which can perform a power-assisted operation can be achieved in a power-assisted on/off valve including a valve stem which opens and closes a flow passage, an operational member which is positioned on an axis of the valve stem and is relatively movable with respect to the valve stem, and a power-assisted mechanism which reduces the speed and power-assists the movement of the operational member, and transfers the movement of the operational member to the stem valve. 
     The power-assisted mechanism is provided with a transmission rod which is positioned on an axis of the operational member, the transmission rod provided with a reduced-diameter portion that reduces the diameter thereof in a direction toward the valve stem; a pressing member which is interconnected with the valve stem; a pair of motion-transmission surfaces that are formed so as to face the pressing member and a housing that movably supports the pressing member, wherein a space between the pair of motion-transmission surfaces increasingly narrows toward the outer periphery thereof; and a plurality of radial-direction movable bodies that are interposed between the pair of motion-transmission surfaces and the reduced-diameter portion of the transmission rod and are in contact therewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Japanese patent application No. 2008-135107, filed on May 23, 2008 and PCT Application No. PCT/JP2009/052526, filed on Feb. 16, 2009, the disclosures of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a power-assisted on/off valve (high pressure valve) which power-assists and conveys an operational force to a valve stem that operates a valve body. 
     BACKGROUND ART 
     Various kinds of such power-assisted on/off valves are known in the art, and have been made practically viable. However, such power-assisted on/off valves were large, required extremely high-precision machining of the parts thereof, and it was difficult to obtain a stable performance in use over a long period of time. 
     Japanese Patent No. 3,392,301 discloses one embodiment of a power assisted on/off valve in the prior art. 
     SUMMARY OF INVENTION 
     Technical Problem 
     The inventor of the present invention has already proposed and patented in Japanese Patent No. 3,392,301 a power-assisted on/off valve having a simple structure and which can perform a power-assisted operation. 
     The objective of the present invention is to achieve a power-assisted on/off valve having a simpler structure and which can perform a larger power-assisted operation than that of the power-assisted on/off valve of Japanese Patent No. 3,392,301. 
     Solution to Problem 
     The present invention is characterized by a power-assisted on/off valve including a valve stem which opens and closes a flow passage; an operational member which is positioned on an axis of the valve stem and is relatively movable with respect to the valve stem; and a power-assisted mechanism which is interposed between the valve stem and the operational member, reduces the speed and power-assists the movement of the operational member, and transfers the movement of the operational member to the stem valve. The power-assisted mechanism is provided with a transmission rod which is positioned on an axis of the operational member, the transmission rod provided with a reduced-diameter portion that reduces the diameter thereof in a direction toward the valve stem; a pressing member which is interconnected with the valve stem; a pair of motion-transmission surfaces that are formed so as to face the pressing member and a housing that movably supports the pressing member, wherein a space between the pair of motion-transmission surfaces increasingly narrows toward the outer periphery thereof; and a plurality of radial-direction movable bodies that are interposed between the pair of motion-transmission surfaces and the reduced-diameter portion of the transmission rod and are in contact therewith. 
     It is possible to configure the pair of motion-transmission surfaces, the reduced-diameter portion of the transmission rod, and the plurality of radial-direction movable bodies so as to satisfy: 2&lt;D/d&lt;50, wherein D designates an amount of movement of the operational member in the axial direction thereof, and d designates an amount of movement of the valve stem in the axial direction thereof. 
     In a desirable embodiment, the operational member includes a piston body that is slidably fitted in the housing, wherein the piston body can move in a valve-closing direction by a spring pressure force so as to approach the valve stem, and the piston body can move in a valve-opening direction by air pressure so as to move away from the stem valve. 
     The motion-transmission surface on the housing can, e.g., include a surface that is orthogonal to the axis of the pressing member, wherein the motion-transmission surface on the pressing member is a conical surface. 
     Furthermore, by configuring the motion-transmission surface on the housing so as to include base surfaces of three radial grooves that are formed in radial directions in the housing, wherein the radial-direction movable bodies are fitted in the radial grooves, it is possible to configure a power-assisted mechanism using movable bodies that moves a small distance in the radial direction. 
     By configuring the motion-transmission surface on the pressing member so as to include a hard ring body that is a separate member from the pressing member, it is possible to improve durability, and it becomes possible to exchange the hard body. 
     It is practical to use steel balls as the radial-direction movable bodies. 
     As an alternative to a conical surface, it is possible for the reduced-diameter portion of the transmission rod to include part of a spherical surface or an aspherical surface. 
     Advantageous Effects of Invention 
     According to the power-assisted on/off valve of the present invention, the power-assisted mechanism is configured from a reduced-diameter portion formed on a transmission rod that is integral with an operational member, motion-transmission surfaces which face a pressing member and a housing, and a movable body that is movable in the radial direction via contact between the reduced-diameter portion and the motion-transmission surface. Accordingly, a power-assisted mechanism having a simple structure at an overall reduced cost, having a high reliability and high durability can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view showing an embodiment of the power-assisted on/off valve of the present invention in a closed-valve state. 
         FIG. 2  shows cross sectional views of only the upper portion of  FIG. 1 , showing different valve-opening (valve-closing) states of the power-assisted on/off valve. 
         FIG. 3  is a cross sectional view taken along the line shown in  FIG. 1   
         FIG. 4  is a cross sectional view taken along the line IV-IV shown in  FIG. 1 . 
         FIG. 5  shows enlarged cross sectional views showing details of a section including the motion-transmission surface of the housing, the motion-transmission surface of the pressing member, the reduced-diameter portion of the transmission rod, and a radial-direction movable body (steel ball), of the power-assisted on/off valve of  FIGS. 1 and 2 . 
         FIG. 6  is a graph showing a desirable example of the relationship between the stroke of the operational member (piston body) of the power-assisted on/off valve and the output thereof, according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The illustrated embodiment is applied to a normally-closed type of on/off valve. As shown in  FIG. 1 , a on/off valve  10  is provided with a gas cylinder head  20 , which is detachably attached to a high-pressure tank (gas cylinder, and a housing (cylinder)  30 . 
     A screw-in connecting projection  21 , which screws into the high-pressure tank, and a threaded-tap projection  22  are provided in the gas cylinder head  20 . An annular valve seat  23  is formed in the gas cylinder head  20  so that the annular valve seat  23  is positioned on a passageway portion between a flow passage  21   a  of the screw-in connecting projection  21  and a flow passage  22   a  of the threaded-tap projection  22 ; the annular valve seat  23  is centered at the central axis of the flow passage  21   a . An annular valve seat  25  that is made of a softer material than that of the annular valve seat  23  and has a high sealing capability is fixedly embedded into the annular valve seat  23 . The valve seat  25  can be formed from, e.g., PCTFE. 
     A retainer  27  is fixedly screw-engaged into the gas cylinder head  20  along a common axis with that of the flow passage  21   a  and so as to interpose a metal diaphragm  28 . A on/off valve body  24 , which approaches/retreats from the annular valve seat  23  (valve seat  25 ) with the metal diaphragm  28  interposed therebetween, is fitted into the retainer  27  in a retained state so as to slidably move therein. The metal diaphragm  28  enables the on/off valve body  24  to move while shutting out (closing the valve) the passageways of the flow passage  21   a  and the flow passage  22   a  when the on/off valve body  24  presses against the annular valve seat  23  (valve seat  25 ). The upper end (the opposite end portion to that of the annular valve seat  23 ) of  FIG. 1  of the on/off valve body  24  constitutes an external-force input end  24 A. 
     The housing  30  includes an upper housing (upper cylinder)  32  and a lower housing (lower cylinder)  33  that are connected with each other via a lock-ring  31 . The lower housing  33  is fixedly screw-engaged with the retainer  27 . The lower housing  33  (housing  30 ) is detachably mounted onto the retainer  27  (gas cylinder head  20 ). 
     A piston body (operational member)  34  is slidably fitted into the housing  30  (lower housing  33 ) in an air-tight manner via an O-ring  34 A. The piston body  34  is biased to move toward the on/off valve body  24  by a compression spring  35  that is inserted in between the piston body  34  and the upper housing  32 . A transmission rod  36  is fixed to the piston body  34  on an axis thereof, and the transmission rod  36  is slidably supported by the housing  30  (lower housing  33 ) in an air-tight manner via a slip bearing  37  and an O-ring  38 . A compression chamber  39  is defined between the piston body  34  and the lower housing  33 . Compressed air, having a desired pressure, is supplied into the compression chamber  39  via a compressed air source  40 A, a regulator  40 B, and a switching valve  40 C. 
     A pressing member  42  that is retained by a retainer ring  41  is slidably fitted into the housing  30  (lower housing  33 ) in the lower end shown in  FIG. 1 . The lower end of the pressing member  42  constitutes an output end  42 A that abuts against the external-force input end  24 A of the on/off valve body  24 . 
     A reduced-diameter portion  36 A, which has a reduced diameter in a direction toward the on/off valve body  24 , is formed at the lower end (the end toward the pressing member  42 ) of the transmission rod  36 . A motion-transmission surface  42 B and a motion-transmission surface  33 A that are spaced from each other are formed on the pressing member  42  and the lower housing  33 , respectively, so as to surround the reduced-diameter portion  36 A. The motion-transmission surface  33 A that is provided in the lower housing  33  is fixed, and the motion-transmission surface  42 B that is provided on the pressing member  42  is movable. 
     The reduced-diameter portion  36 A of the transmission rod  36 , in the illustrated embodiment, is formed as part of a spherical surface (or aspherical surface). The movable motion-transmission surface  42 B is a surface that is orthogonal to the axis of the pressing member  42  (the transmission rod  36 ). The fixed motion-transmission surface  33 A is formed as a part of a conical surface, having the same central axis as that of the pressing member  42 , that increasingly narrows the space between itself and the motion-transmission surface  42 B in a direction toward the outer periphery thereof. The motion-transmission surface  42 B, as shown in  FIGS. 3 and 4 , is formed as a base surface of three radial grooves  42 C that are formed in the pressing member  42  at equi-angular intervals. Each radial groove  42 C has a steel ball (radial-direction movable body)  43  rotatably fitted therein. The radial grooves  42 C can use an arbitrary shape such as a V-section groove  42 C(V) ( FIG. 4(A) ) or a circular-section groove  42 C(R) (FIG.  4 (B)), etc. The steel balls  43  simultaneously contact each of the reduced-diameter portion  36 A of the transmission rod  36 , and the pair of motion-transmission surfaces  33 A and  42 B. Furthermore, the motion-transmission surface  33 A is formed on a highly abrasion resistant hard ring body  33 B that is formed as a separate member from the lower housing  33 ; this hard ring body  33 B is fixed to the lower housing  33 . The transmission rod  36 , the pressing member  42  and the hard ring body  33 B are formed from, e.g., quenchable SUJ2 and SUS440C, etc. A relief recess  42 D, into which the reduced-diameter portion  36 A of the transmission rod  36  advances and retreats, is formed in the shaft portion of the pressing member  42 . 
     The on/off valve having the above-described structure is operated in the following manner. The drawing on the right end of  FIG. 2  shows a state in which the housing  30  is removed from the gas cylinder head  20 , and the piston body  34  is positioned at the downward extremity by the force of the compression spring  35 . When the piston body  34  is at the downward extremity, the reduced-diameter portion  36 A of the transmission rod  36  pushes the steel balls  43  in radial outward directions, and since the space between the motion-transmission surface  33 A and the motion-transmission surface  42 B increasingly narrows toward the outer peripheral direction, the pressing member  42  is pushed downwardly by the steel balls  43  and likewise is positioned at the downward extremity thereof. 
     Upon screw-mounting the housing  30  (lower housing  33 ) onto the retainer  27  of the gas cylinder head  20 , the output end  42 A of the pressing member  42  pushes the on/off valve body  24  downward via the external-force input end  24 A by the force of the compression spring  35 . Subsequently, the metal diaphragm  28  is seated onto the annular valve seat  23  (valve seat  25 ) and closes the passageway between the flow passage  21   a  and the flow passage  22   a  (closes the gas cylinder).  FIG. 1  shows this closed-valve state. Note that out of the two drawings in the center of  FIG. 2 , the left drawing shows a close-state with a new valve seat  25  and the right drawing shows a close-state with a valve seat  25  that has reached its wearing limit. The wearing limit (a limit amount at which a closed state can be maintained upon the valve seat  25  being worn) is set to an appropriate amount. 
     In the present embodiment, the valve-closing force via the compression spring  35  can be power-assisted and transferred to the pressing member  42  (on/off valve body  24 ). In other words, as shown in  FIG. 5 , due to the operation of the reduced-diameter portion  36 A, the motion-transmission surface  33 A, and the motion-transmission surface  42 B, since the pressing member  42  can be moved by a movement amount d which is smaller than a movement amount D of the transmission rod  36  (D&gt;d), the valve seat  25  of the on/off valve body  24  can press against and close the annular valve seat  23  with a strong force. The power-assistance ratio D/d can be freely set in accordance with the angle between the motion-transmission surface  33 A and the motion-transmission surface  42 B, and the angle of the reduced-diameter portion  36 A. Specifically, this power-assistance ratio D/d value can be set to approximately 2 through 50. In an example shown in the drawings, the D/d value changes at each stroke position and is set to 6 through 11. It is adequate for the space between the motion-transmission surface  33 A and the motion-transmission surface  42 B to smoothly decrease toward the outer periphery, so that, e.g., unlike in the examples shown in the drawing, the motion-transmission surface  33 A can be a surface that is orthogonal to the axis and the motion-transmission surface  42 B can be a conical surface, or both of the motion-transmission surface  33 A and the motion-transmission surface  42 B can be provided as conical surfaces. 
     In  FIG. 2 , ‘A’ designates the amount of movement of the piston body  36  from the valve fully-closed state (the drawing on the far left of  FIG. 2 ) to the valve-closed position (the drawing second from the left of  FIG. 2 ), ‘B’ designates the amount of movement thereof from the valve fully-closed state to the valve-seat wear limit (second drawing from the right in  FIG. 2 ), and ‘C’ designates the amount of movement from the valve-seat wear limit to the free state (the drawing on the far right of  FIG. 2 ); wherein the movement amounts of the pressing member  42  at each of these sections are designated by ‘a’, ‘b’ and ‘c’; and A&gt;a, B&gt;b and C&gt;c. 
       FIG. 6  is a graph showing an example of the stroke (mm) and output (kN) of the pressing member  42  (on/off valve body  24 ). In this example, by forming the reduced-diameter portion  36 A of the transmission rod  36  as part of a spherical surface (or aspherical surface), a substantially constant valve-closing force can be achieved from the valve fully-closed state to the valve-seat wear limit. 
     More specifically, the shape of the reduced-diameter portion  36 A of the transmission rod  36 , the spring reaction force Fs at this position, the movement amount Sp of the transmission rod  36 , and the output Fo of the pressing member  42  determine the movement amount So of the pressing member  42  based on the following expression:
 
 Fs×Sp=Fo×So  
 
Namely, when the piston body  34  (transmission rod  36 ) is moved downward from the uppermost position by a unit amount at a time, the spring reaction force is obtained at each position thereof. Furthermore, if a desired output is determined, since the amount of movement of the pressing member  42  can be obtained from the above expression, the amount of movement of the steel balls  43  in the radial direction thereof is obtained from the angle between the motion-transmission surface  33 A and the motion-transmission surface  42 B, and the shape of the reduced-diameter portion  36 A is obtained by connection tangent lines of each steel ball  43 . Note that the reduced-diameter portion  36 A of the transmission rod  36  can attain a sufficient power-assisted operation even with a simple conical surface.
 
     In order to open the valve, regulated compressed air only needs to be fed to the compression chamber  39  via the compressed air source  40 A, the regulator  40 B and the switching valve  40 C. When the force caused by the compressed air pressure exceeds the force of the compression spring  35 , since the piston body  34  and the transmission rod  36  moves upward, and the valve-closing force dissipates, the on/off valve body  24  moves in the valve-opening direction by the pressure of the high-pressure gas in the gas cylinder, and the on/off valve body  24  (metal diaphragm  28 ) moves away from the annular valve seat  23  (valve seat  25 ). As a result, the valve is opened, the compressed gas inside the gas cylinder can be drawn from the flow passage  21   a  to the flow passage  22   a  (an apparatus, which uses the high-pressure gas, that is screw-engaged onto the threaded-tap projection  22 ). 
     INDUSTRIAL APPLICABILITY 
     The power-assisted on/off valve of the present invention can be widely used, e.g., as a on/off valve of a high-pressure tank (gas cylinder). 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  On/off valve 
               20  Gas cylinder head 
               21  Screw-in projection 
               22  Threaded-tap projection 
               21   a ,  22   a  Flow passage 
               23  Annular valve seat 
               24  On/off valve body 
               24 A External-force input end 
               25  Valve seat 
               27  Retainer 
               28  Metal diaphragm 
               30  Housing 
               32  Upper housing 
               33  Lower housing 
               33 A Motion-transmission surface 
               33 B Hard ring body 
               34  Piston body (operational member) 
               34 A O-ring 
               35  Compression spring 
               36  Transmission rod 
               36 A Reduced-diameter portion 
               37  Slip bearing 
               38  O-ring 
               39  Compression chamber 
               40 A Compressed air source 
               40 B Regulator 
               40 C Switching valve 
               41  Retainer ring 
               42  Pressing member 
               42 A Output end 
               42 B Motion-transmission surface 
               42 C Radial groove 
               43  Steel ball (radial-direction movable body)