Abstract:
A pipe coupling comprising a socket having a plurality of locking balls capable of engaging a locking portion on a plug and connected to the plug with the locking balls in engagement with the locking portion. The socket includes a main cylinder having an end portion formed with an inlet to receive the plug and an outer cylinder located close to the end portion of the main cylinder and around the outer periphery thereof. The main cylinder and the outer cylinder define a gap having a tapered profile between them, and the locking balls are stored in the gap. The locking balls can project and recede from the inner periphery of the main cylinder. Further, the pipe coupling comprises a thrust cylinder slidable on the outer periphery of the main cylinder. When the locking balls engage the locking portion, the thrust cylinder prevents centrifugal movement of the locking balls.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-094517, filed Mar. 29, 2001, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pipe coupling having a socket capable of being attached to and detached from a mating plug, and more particularly, to a pipe coupling adapted to connect pipe lines for pressurized fluids. 
     2. Description of the Related Art 
     There has conventionally been developed a pipe coupling that is provided with a locking mechanism for locking a socket connected to a mating plug. Usually, the socket of the pipe coupling of this type has a series of tapered holes that are arranged at circumferential spaces near its plug inlet. A plurality of locking balls are stored in the tapered holes. Further, the socket is provided with an operating ring, which is slidable between a locked position in which the locking balls are urged radially inward and an unlocked position in which the balls can move radially outward. The operating ring is urged toward the locked position by means of a spring. On the other hand, the body of the mating plug has a locking groove that receives the locking balls. 
     When one end of the plug is in the plug inlet of the socket, the operating ring of the socket restrains the locking balls from moving centrifugally, thereby keeping the balls in engagement with the locking groove of the plug. Thereupon, the socket and the plug are locked lest they separate from each other. In separating the socket and the plug from each other, the operating ring of the socket is slid. By doing this, the locking balls of the socket are allowed to move centrifugally from the locking groove of the plug, whereupon the socket and the plug are unlocked. In the case where the socket or the plug is provided with a valve, the valve can be opened or closed automatically as the socket and the plug are connected to or separated from each other. 
     In operation, the pipe coupling constructed in this manner is subjected to a force of pressure from a fluid that flows therethrough and urges the socket and the plug to separate from each other. This force acts as a contact pressure on the respective engaging surfaces of the locking groove of the plug and the locking balls of the socket. If the pressure of the fluid is low, the force never adversely affects the pipe coupling. 
     If the fluid pressure increases, however, the aforesaid force becomes very high. If the pipe coupling is used in a high-pressure pipe line system in which the fluid pressure is as high as 35 MPa or more, for example, the contact pressure that acts on the locking balls is so high that the pressure-side edge of the locking groove of the plug body undergoes a sag (plastic deformation caused by the high contact pressure on the locking balls). In the worst case, the sag of the locking groove hinders the slide of the operating ring, thereby disabling the socket and the plug from being attached to or detached from each other. 
     In order to prevent the sag of the locking groove, the contact pressure that acts on each locking ball should be lowered by loading the socket with a large number of balls. To attain this, however, a large number of tapered holes for locking ball retention must be formed in the socket. In consequence, the space between each two adjacent tapered holes is inadequate, thus the strength of the locking ball retaining portion of the socket lowers inevitably. Thus, the number of locking balls can be increased only limitedly. 
     In consideration of the above, the assignee of the present invention proposed a pipe coupling that can satisfactorily cope with pipe lines in which a pressurized fluid circulates (Jpn. UM Appln. KOKAI Publication No. 7-12693). In this pipe coupling, a socket is provided with first and second rows of locking members (locking balls), while the outer peripheral surface of a plug is formed having first and second locking grooves. The socket and the plug can be locked together in a manner such that the locking members in each row are caused to engage their corresponding locking groove and that the movement of the locking members is restrained by means of an operating ring. With this configuration, the contact pressure that acts on the locking members can be dispersed to prevent the locking grooves of the plug body from sagging. Thus, the socket body and the plug body can be securely attached to and detached from each other. 
     Since the pipe coupling has a plurality of rows of locking members, it is inevitably long and complicated. In consequence, it cannot be easily reduced in size and weight and entails an increase in cost. 
     BRIEF SUMMARY OF THE INVENTION 
     The principal object of the present invention is to provide a small-sized, low-priced pipe coupling, capable of reducing the load that acts on each locking ball even when a compressed fluid circulates therein. 
     According to the present invention, there is provided a pipe coupling that comprises a socket. The socket has a plurality of locking balls capable of engaging a locking portion on a plug and connected to the plug with the locking balls in engagement with the locking portion of the plug. The socket further includes: a main cylinder having an outer peripheral surface, an inner peripheral surface, and an end portion formed with an inlet capable of receiving the plug; an outer cylinder located close to the end portion of the main cylinder and around the outer peripheral surface thereof with a fixed annular space defined between the outer cylinder and the outer peripheral surface, the end portion of the main cylinder and the inner end portion of the outer cylinder forming a gap having a tapered profile, each of the locking balls being stored in the gap and movable between a position in which the ball projects radially inward from the inner peripheral surface of the main cylinder and a position in which the ball is recessed from the inner peripheral surface; and a thrust cylinder slidably located in the space between the main cylinder and the outer cylinder and urged toward the end portion, the plug being adapted to be prevented from separating from the socket in a manner such that centrifugal movement of the locking balls is prevented by means of the thrust cylinder when the locking balls are situated in the projected position and in engagement with the locking portion of the plug. 
     According to this pipe coupling, the socket has no holes for holding the locking balls, and the locking balls are stored in the gap existing between the main cylinder and the outer cylinder. Although the locking balls are arranged in a row in the circumferential direction, as in the conventional case, therefore, a pressing load that acts on each locking ball can be lightened considerably, and the resulting pipe coupling can withstand high pressure fluid contained therein (e.g., internal pressure of 500 MPa). Since the locking balls are arranged in a row, moreover, the overall length of the pipe coupling can be made equal to that of a conventional one, and the combining operation for the locking balls is easy. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The other objects, features, and advantages of the invention will be more apparent from the following description, read in connection with the accompanying drawings, in which: 
     FIG. 1 is a sectional view showing a state in which a socket of a pipe coupling according to a preferred embodiment of the invention and a plug are separate from each other, the plug being formed of a molded pipe; 
     FIG. 2 is a sectional view showing the socket and the plug of FIG. 1 in a connected state; 
     FIG. 3 is a partial view of the socket of FIG. 1 showing the arrangement of the locking balls are arranged when the plug and socket are connected; 
     FIG. 4 is a sectional view taken along line A—A of FIG. 2; 
     FIGS. 5A to  5 C are views for illustrating the function of the locking balls, in which FIG. 5A shows the plug in an unlocked state, and FIGS. 5B and 5C show the plug in a locked state; 
     FIG. 6 is a sectional view showing an operating ring and a thrust cylinder of the socket shown in FIG. 1; 
     FIG. 7 is a plan view of an outer cylinder of the socket shown in FIG. 1; and 
     FIG. 8 is a sectional view similar to FIG. 1, showing a state in which a socket and a plug are separate from each other, the plug being of the conventional type. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a pipe coupling according to a preferred embodiment of the present invention shown in FIG. 1, a socket S comprises a main cylinder  1  and an inner cylinder  2  that is screwed into one end of the main cylinder and can be connected to a hose or the like. The main cylinder  1  has an inlet at its other end, that is, at the end portion on the right-hand side of FIG. 1, and can receive a plug P through this inlet. A seal member  3  for sealing the gap between the inner peripheral surface of the main cylinder  1  and the outer peripheral surface of the inner cylinder  2  is provided on the main cylinder  1 . 
     A sleeve/seal retainer  4  is slidably fitted in the main cylinder  1 . The seal retainer  4  is prevented from moving to the right of FIG. 1 when a step portion  4   a  on the outer periphery of the retainer  4  engages a step portion la on the inner peripheral surface of the main cylinder  1 . A gasket  5  for liquid-tightly sealing the plug P is fitted in the plugging-side end portion of the seal retainer  4 . Further, a seal member  6  for sealing the gap between the outer peripheral surface of the seal retainer  4  and the inner peripheral surface of the main cylinder  1  is provided on the retainer  4 . The inner peripheral surface of the gasket  5  is held by means of a spring seat  7  that is fitted in the seal retainer  4 . An urging member (coil spring)  8  for urging the seal retainer  4  to the right of FIG. 1 is interposed between the spring seat  7  and the inner cylinder  2 . The spring seat  7  has a collar  7   a . As the collar  7   a  engages a step portion  4   b  of the seal retainer  4 , the spring seat  7  is prevented from slipping out of the retainer  4 . 
     A small-diameter step portion  1   b  is formed on the outer periphery of the main cylinder  1 . The step portion  1   b  has a plurality of tapered radial holes  9  that are arranged in the circumferential direction. Each radial hole  9  is tapered centripetally. Retaining balls  10  are located individually in the holes  9  and serve as stopper means for preventing axial movement of a thrust cylinder  12  (mentioned later). To attain this, each retaining ball  10  has a diameter greater than the axial dimension of each hole  9 , and is movable between a position in which it partially projects from the inner peripheral surface of the main cylinder  1  and a position in which it is recessed from the inner peripheral surface and projects from the outer peripheral surface of main cylinder  1 . Further, the distal end portion of the main cylinder  1  on the plug-inlet side is thick-walled. The thickness of the thick-walled portion is smaller than the diameter of each of locking balls  13  (mentioned later), and its distal end face is formed as a taper  11  for holding the balls  13  in a manner mentioned later. 
     The thrust cylinder  12  is slidably located on the outer periphery of the small-diameter step portion  1   b  of the main cylinder  1 . The inner peripheral surface of the thrust cylinder  12  is formed having a groove  12   a  that allows the retaining balls  10  to move centripetally. Further, the distal end portion of the thrust cylinder  12  on the inner peripheral side is formed having a taper  12   b  that allows the locking balls  13  to move centrifugally. Furthermore, the inner peripheral surface portion between the groove  12   a  and the taper  12   b  is formed having a thrust surface  12   c  that presses the balls  13  centripetally. 
     An outer cylinder  14  is fixed on the outer peripheral portion that adjoins the small-diameter step portion  1   b . In the present embodiment, the outer cylinder  14  is fixed to the main cylinder  1  in a manner such that an internal thread  15  on the inner peripheral surface of the outer cylinder  14  is screwed on an external thread on the outer peripheral portion of the main cylinder  1 . The plugging-side end portion of the outer cylinder  14  is formed having an inner flange that has an inside diameter substantially equal to that of the distal end portion of the main cylinder  1 . The inner peripheral side edge of the inner flange is formed having a taper  16  that faces the taper  11  on the main cylinder  1 . 
     As shown in FIGS. 1 to  3 , the taper  16  forms a ball retaining portion that cooperates with the taper  11  of the main cylinder  1  to hold the locking balls  13 . The ball retaining portion includes a gap or annular groove with a tapered profile that is defined between the two opposite tapers  11  and  16  and has its width reduced centripetally. The width of the innermost peripheral portion of the annular groove is smaller than the diameter of each locking ball  13 . Since the thickness of the distal end portion of the main cylinder  1  is smaller than the diameter of each locking ball  13 , as mentioned before, moreover, the depth of the annular groove is also smaller than the diameter of each ball  13 . As shown in FIGS. 3 and 4, therefore, the locking balls  13  in the annular groove of the ball retaining portion can individually freely move in the radial direction of the main cylinder  1  between the position in which they project from the inner peripheral surface of the cylinder  1  and the position in which they are recessed from it. Preferably, the number of locking balls  13  stored in the annular groove should be decided so as to meet the following conditions. When the socket S and the plug P are separate from each other, gaps are formed between the adjacent locking balls  13  to allow the insertion of the plug P, as shown in FIG.  5 A. When the socket S and the plug P are connected, the adjacent balls  13  are pushed centripetally to be brought intimately into contact with one another by the thrust cylinder  12 , so that they engage the outer periphery of a locking portion  30 , which is formed of a taper of the plug P, thereby locking the plug P throughout its circumference, as shown in FIGS. 5B and 5C. 
     As shown in FIG. 7, the outer cylinder  14  has a plurality of slots  17  that extend in the axial direction of the socket S. As shown in FIG. 1, one end of a coupler (screw)  18 , which is attached to the thrust cylinder  12 , penetrates each slot  17  so as to be movable therein. The head portion of each coupler  18  that projects from its corresponding slot  17  of the outer cylinder  14  is coupled to an operating ring  19 , which is slidably fitted on the cylinder  14 , as shown in FIG. 6, and can be handled by an operator. Further, an urger (coil spring)  20  for urging the operating ring  19  to the right of FIG. 1 is interposed between the ring  19  and the outer cylinder  14 . The urger  20  is located between a step portion  14   a  on the outer periphery of the outer cylinder  14  and a step portion  19   a  on the inner periphery of the operating ring  19 . The urger  20  normally urges the ring  19  to the right of FIG.  1 . In FIG. 1, numeral  21  denotes a stop ring that serves to fix the outer cylinder  14  to the main cylinder  1 . 
     The following is a description of the operation for connecting the socket S and the plug P constructed in this manner. 
     When the socket S and the plug P are separate from each other (in the state shown in FIG.  1 ), the outer peripheral surface of the seal retainer  4  centrifugally pushes out the retaining balls  10 . Thereupon, the balls  10  enter the groove  12   a  in the inner peripheral surface of the thrust cylinder  12 , thereby preventing the cylinder  12  from moving in the axial direction. In this state, the couplers  18  and the operating ring  19  maintain the urger  20  in a compressed state. Further, the locking balls  13  can move centrifugally along the taper  12   b  of the thrust cylinder  12  or the taper  16  of the outer cylinder  14 . 
     If the plug P is inserted into the socket S through its inlet when the socket S is in the state of FIG. 1, an end portion of the plug pushes the locking balls  13 , whereupon the balls  13  are moved radially outward in the circumferential groove between the tapers  11  and  16 . If the end portion of the plug P is further inserted into the socket S beyond the locking balls  13 , it abuts against the gasket  5  of the seal retainer  4 . If the plug P is further pushed in, the seal retainer  4  moves to the left of FIG. 1 compressing the spring  8 , so that the retaining balls  10  are disengaged from the outer peripheral surface of the retainer  4 . Thereupon, the balls  10  move centripetally from the groove  12   a  in the inner peripheral surface of the thrust cylinder  12 , so that the cylinder  12  is allowed to move in the axial direction. The urging force of the urger  20  that acts on the operating ring  19  also acts on the cylinder  12  via the couplers  18 . Accordingly, the thrust cylinder  12 , along with the ring  19 , is urged to the right of FIG. 1, so that the taper  12   b  of the cylinder  12  urges the locking balls  13  to move centripetally. 
     When the locking balls  13  engage the taper or the locking portion  30  of the plug P, they move centripetally along the outer peripheral surface of the locking portion  30 . At the same time, the thrust cylinder  12  moves to the right of FIG.  1 . The thrust surface  12   c  on the inner peripheral surface of the thrust cylinder  12  pushes in the locking balls  13  centripetally, so that the balls  13  press the locking portion  30  of the plug P. Thereupon, the plug P is locked in the socket S to establish the connected state of the pipe coupling shown in FIG.  2 . 
     In separating the socket S and the plug P in the connected state of FIG. 2 from each other, the operating ring  19  is moved to the left of FIG. 2, resisting the urging force of the urger  20 . Instead of the thrust surface  12   c  of the thrust cylinder  12 , the taper  12   b  is located outside the locking balls  13 , while the groove  12   a  is situated outside the retaining balls  10 . Thereupon, the balls  13  are allowed to move centrifugally, so that the plug P can be easily drawn out of the socket S. If the plug P is drawn out, the seal retainer  4  is moved to the right of FIG. 2 by means of the urging force of the urging member  8 . The outer peripheral surface of the retainer  4  pushes the retaining balls  10  centrifugally into the groove  12   a  of the thrust cylinder  12 . Thereupon, the socket S is restored to the separated state of FIG.  1 . 
     In the connected state shown in FIG. 2, according to the pipe coupling described above, the locking balls  13  are intimately in contact with one another as they are held by means of the ball retaining portion of the socket S and engage the locking portion  30  of the plug P. Thus, all the locking balls  13  form a very large area of contact with the socket S and the plug P. Accordingly, a load that acts on each locking ball  13  can be made much lighter than in the conventional case, and the resulting pipe coupling can resist a high internal pressure (e.g., internal pressure of 500 MPa). Further, the internal pressure causes the plug P to disperse the centrifugal force that acts on the locking balls  13  and the thrust cylinder  12 , so that no substantial force acts locally. Since only one row of locking balls  13  extend in the circumferential direction, the overall length of the pipe coupling including the socket S can be made equal to that of the conventional pipe coupling. 
     Since the locking balls  13  are stored in one annular groove that is defined by the ball retaining portion or the tapers  11  and  16 , moreover, the combining operation can be facilitated without requiring independent storage of the locking balls in separate radial holes, which is essential in the conventional case. Since the locking balls  13  that are thus stored in the one annular groove can freely move in the annular groove, they are not constantly fixed in one position. Thus, the respective positions of engagement of the locking balls  13  with the ball retaining portion of the socket S is not fixed. Accordingly, stress on the socket can be reduced, so that its working life can be lengthened. 
     The thrust cylinder  12  and the operating ring  19  may be formed as an integral structure instead of being formed of separate members. In this case, the thrust cylinder may possibly be urged toward the plugging side by means of a coil or plate spring. Further, the urger  20  and the urging member  8  that urge the operating ring  19  and the seal retainer  4 , respectively, can be located individually in any other suitable positions than the aforesaid positions, provided that the same functions can be fulfilled. Furthermore, the plug P is not limited to the one shown in FIG. 1, which is formed of a molded pipe, and may be selected from various other structures including the conventional plug shown in FIG. 8, provided it can fulfill the function of a plug. In FIGS. 1 and 8, like numerals refer to the same members. 
     The present invention is not limited to the embodiment described above, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention. Therefore, the above-described embodiment is given by way of illustration only, and thus, is not limitative of the invention.