Patent Publication Number: US-8523242-B2

Title: Connection-structure of a flexible tube

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure for connecting a flexible or resin tube to an end portion of a metal pipe. 
     2. Description of the Related Art 
     Conventionally, there is known a connection-structure as disclosed in Japanese Unexamined Patent Publication No. 2006-090416. In this connection-structure, an end portion of the metal pipe is provided with at least two radially enlarged portions, and a seal ring is positioned in an annular groove formed between the radially enlarged portions. A flexible tube is fitted to the metal pipe such that the tip portion of the flexible tube passes over the two radially enlarged portions. 
     In the conventional structure, however, the tip portion of the flexible tube tends to expand because of an operation in which the flexible tube is connected to the metal pipe, so that a gap is formed between the flexible tube and the metal pipe, increasing the possibility for water or dust to accumulate in the gap. Due to this, the metal pipe rusts easily, and therefore, it is necessary to use material for the metal pipe that is resistant to rust, such as stainless steel, or to carry out an operation in which an outer surface of the metal pipe is painted, and so on. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to improve the tightness of the fitting between the flexible tube and the metal pipe, so that it becomes hard for water or dust to enter between the flexible tube and the metal pipe. 
     According to the present invention, there is provided a connection-structure of a flexible tube, in which the flexible tube is tightly fitted to an outer surface of an end portion of a metal pipe. The connection-structure of the flexible tube comprises an annular projection, a first radially enlarged portion, a seal ring, and a second radially enlarged portion. The annular projection is formed on the outer surface of the end portion of the metal pipe, and circumferentially extends over the whole circumference of the metal pipe. The first radially enlarged portion is formed on the tip side of the metal pipe relative to the annular projection, and defines a first annular groove with the annular projection. The seal ring is fitted into the first annular groove. The second radially enlarged portion is formed on the base side of the metal pipe relative to the annular projection, and defines a second annular groove with the annular projection. The tip portion of the flexible tube is positioned close to the maximum diameter portion of the second radially enlarged portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The object and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which: 
         FIG. 1  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a first embodiment of the present invention; 
         FIG. 2  is a cutaway side view showing an upper-half section of the metal pipe of the first embodiment; 
         FIG. 3  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a second embodiment; 
         FIG. 4  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a third embodiment; 
         FIG. 5  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a fourth embodiment; 
         FIG. 6  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a fifth embodiment; 
         FIG. 7  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a sixth embodiment; and 
         FIG. 8  is a cutaway side view showing an upper-half section of a connection-structure of a flexible tube of a seventh embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is described below with reference to the embodiments shown in the drawings. Each embodiment is a connection-structure of a flexible tube and a metal pipe, utilized in a fuel filler pipe for an automobile, through which fuel is channeled from a fuel filler opening to a fuel tank. 
       FIG. 1  shows a first embodiment, in which a metal pipe  10  horizontally extends from the left side such that an opening  11  faces the right side. A flexible or resin tube  30  horizontally extends from the right side, and is tightly fitted to an outer surface of an end portion of the metal pipe  10 . 
     An annular projection  12  is formed on the outer surface of the end portion of the metal pipe  10 . The annular projection  12  circumferentially extends over the whole circumference of the metal pipe  10 . In the embodiment, the annular projection  12  is formed using a spool processing technique. A first radially enlarged portion  14  is formed on a portion closer to the tip  13  of the metal pipe  10  relative to the annular projection  12 . The first radially enlarged portion  14  extends parallel to the annular projection  12  to define a first annular groove  15  with the annular projection  12 . The first annular groove  15  has the shape of an outward-facing open channel, in which a seal ring  16  is fitted. The seal ring  16  is an O-ring, and is made of fluorocarbon polymers, for example. 
     A second radially enlarged portion  17  is formed on the base side (i.e., a portion opposite to the tip  13 ) of the metal pipe  10  relative to the annular projection  12 . The second radially enlarged portion  17  extends parallel to the annular projection  12  to define a second annular groove  18  with the annular projection  12 . The second annular groove  18  has a greater breadth than that of the first annular groove  15 , and a seal ring is not provided. 
     The first radially enlarged portion  14  is formed using a bulging technique, and the second radially enlarged portion  17  is formed using a spool processing technique. The second radially enlarged portion  17  is bulged in comparison with portions adjacent thereto. 
     The diameter of the outer surface of the metal pipe  10  on the opposite side of the second annular groove  18  with respect to the second radially enlarged portion  23  is substantially the same as that of the second annular groove  18 . 
     As shown in  FIG. 2 , an outer surface of the first radially enlarged portion  14  is a first tapered surface  21  of which the diameter becomes smaller as the distance to the tip portion of the metal pipe  10  decreases. An outer surface on the side of the second radially enlarged portion  17  nearest to the second annular groove  18  is a second tapered surface  22  of which the diameter becomes smaller as the distance to the second annular groove  18  decreases. An outer surface of the second radially enlarged portion  17  that is on the opposite side to the second tapered surface  22  is a third tapered surface  23  that is inclined in the opposite direction of the second tapered surface  22 . The inclination angles of the second and third tapered surfaces  22 ,  23  are substantially the same, and are steeper than the first tapered surface  21 . 
     The maximum diameters of the annular projection  12 , and the first and second radially enlarged portions  14 ,  17  are substantially identical, and are slightly less than the outer diameter of the seal ring  16  fitted into the first annular groove  15 . 
     The flexible tube  30  is made of polyamide resin, fluoroplastics, olefin resin, and so on, and the inside diameter of the flexible tube  30  is slightly less than the outside diameter of the metal pipe  10 . Therefore, in a state in which the flexible tube  30  is press-fitted to the metal pipe  10 , the flexible tube  30  is in tight contact with the metal pipe  10  in a liquid-proof manner. That is, an inner surface of the flexible tube  30  is hermetic or in tight contact with the first tapered surface  21  of the first radially enlarged portion  14 , the seal ring  16 , the second annular groove  18 , the second tapered surface  22  of the second radially enlarged portion  17 , and a part of the third tapered surface  23 . The tip portion  31  of the flexible tube  30  is positioned close to the maximum diameter portion of the second radially enlarged portion  17 , and reaches an edge of the third tapered portion  23 , passing over the second tapered surface  22 . The amount by which the tip portion  31  of the flexible tube  30  protrudes from the peak of the second radially enlarged portion  17 , i.e., the boundary between the second tapered surface  22  and the third tapered surface  23 , to the third tapered surface  23 , is 0.5-5.0 mm. 
     An outer surface of the metal pipe  10  is painted for rust-prevention, but because the flexible tube  30  is tightly fitted to the end portion of the metal pipe  10 , the painted portion of the metal pipe  10  can be reduced. More concretely, on the outer surface of the metal pipe  10  a portion (A) up to the second annular groove  18 , to which the tip portion of the flexible tube  30  is fitted tightly, should be painted. A portion (B) of the second annular groove  18 , where the flexible tube  30  is separated from a surface of the groove  18 , i.e., a part close to the annular projection  12  and a wall of the side of the second annular groove  18 , may be painted depending upon the condition. Conversely, from the annular projection  12  to the tip portion  13  of the metal pipe  10  need not be painted. 
     In a connecting operation of the metal pipe  10  and the flexible tube  30 , the tip portion  13  of the metal pipe  10  is placed in line with the mouth of the flexible tube  30 , and the metal pipe  10  is gradually inserted into the flexible tube  30 . Due to this, the end portion of the flexible tube  30  is expanded by the first tapered surface  21 , and passes over the seal ring  16  and the annular projection  12 , to reach the second annular groove  18 . The metal pipe  10  is then further inserted into the flexible tube  30 , and this connecting operation is completed when the tip portion  31  reaches the position slightly over the peak  24  of the second tapered surface  22 , i.e., by 0.5-5.0 mm. 
     In this connecting operation, the metal pipe  10  may be inserted into the flexible tube  30  while an outer surface  19 , which is the base side of the metal pipe  10  relative to the second radially enlarged portion  17 , is fixed by a jig and so on. Thus, since the jig is engaged with the second radially enlarged portion  17 , the metal pipe  10  can be strongly pressed, so that the connecting operation is easy. 
     In a state in which the flexible tube  30  is connected to the metal pipe  10 , the tip portion  31  of the flexible tube  30  is positioned slightly over the peak  24  of the second tapered surface  17 , and positioned on an edge of the third tapered surface  23 . Therefore, the tip portion  31  of the flexible tube  30  is expanded by the second radially enlarged portion  17 , so that a tension force greater than that in the other portions is generated in the tip portion  31 . That is, the tip portion  31  is in tight contact with the second radially enlarged portion  17  in a liquid-proof manner, so that water, dust, and so on is prevented from entering between the metal pipe  10  and the flexible tube  30 , decreasing the possibility of material causing rust to accumulate. Therefore, the metal pipe  10  hardly rusts, and a surface area in the end portion of the metal pipe  10 , which should be painted for rust-prevention, can be reduced. 
       FIG. 3  shows a second embodiment. 
     The difference from the first embodiment is a shape of the second radially enlarged portion  41 . The inclination angle of the second tapered surface  42  of the second radially enlarged portion  41  and the inclination angle of the first tapered surface  21  are substantially the same. Further, the second radially enlarged portion  41  has a vertical surface  43 , positioned on the opposite side of the second tapered surface  42 , and the vertical surface  43  is substantially perpendicular to the outer surface of the metal pipe  10 . The tip portion  31  of the flexible tube  30  passes over the second tapered surface  42 , and reaches the upper edge of the vertical surface  43 . The other structures are identical to the first embodiment. 
     According to the second embodiment, similar effects as the first embodiment can be obtained. In addition to these effects, due to the vertical surface  43  of the second radially enlarged portion  41 , a jig becomes easily engaged with the second radially enlarged portion  41  of the metal pipe  10  in a connecting operation of the metal pipe  10  and the flexible tube  30 , and thus a pressing operation of the metal pipe  10  becomes easier than the first embodiment. 
       FIG. 4  shows a third embodiment. 
     The differences from the first and second embodiments are a second radially enlarged portion  44  and an outer surface of the metal pipe  10 . A second tapered surface  45  of the second radially enlarged portion  44  has the same inclination angle as the first tapered surface  21 , similarly to the second embodiment. Conversely, an outer surface  46  of the second radially enlarged portion  44 , opposite to the second tapered surface  45 , is a cylindrical surface having substantially the same diameter as the maximum diameter of the second radially enlarged portion  44 . The tip portion  31  of the flexible tube  30  passes over the second tapered surface  45 , and reaches an edge of the outer surface  46 . The other structures are identical to the first and second embodiments. 
     In the third embodiment, since the diameter of the base portion of the metal pipe  10  with respect to the second radially enlarged portion  44  is the same as the maximum diameter of the second radially enlarged portion  44 , the diameter of the tip portion  31  of the flexible tube  30  cannot be reduced in a state in which the tip portion  31  of the flexible tube  30  is positioned over the second radially enlarged portion  44 . Therefore, a gap cannot open up between the tip portion  31  of the flexible tube  30  and the metal pipe  10 . 
       FIG. 5  shows a fourth embodiment. 
     The fourth embodiment has a similar structure as the first embodiment. The point different from the first embodiment is that the seal ring  16  and a back-ring  47  are fitted into the first annular groove  15 . The back-ring  47  is in contact with the annular projection  12 , and the seal ring  16  is in contact with a side surface of the first radially enlarged portion  14 . The other structures are identical to the first embodiment, and the effect and operation are identical to the first embodiment. 
       FIG. 6  shows a fifth embodiment. 
     The fifth embodiment has a structure that resembles the second embodiment. The point different from the second embodiment is that the seal ring  16  and the back-ring  47  are fitted into the first annular groove  15 . The other structures are identical to the second embodiment, and the effect and operation are identical to the second embodiment. 
       FIG. 7  shows a sixth embodiment. 
     The sixth embodiment has a structure that resembles the third embodiment. The point different from the third embodiment is that the seal ring  16  and the back-ring  47  are fitted into the first annular groove  15 . The other structures are identical to the third embodiment, and the effect and operation are identical to the third embodiment. 
       FIG. 8  shows a seventh embodiment. 
     The basic structure of the seventh embodiment is the same as that of the first embodiment, but the position of the tip portion  31  of the flexible tube  30  is different. That is, although the position of the tip portion  31  of the flexible tube  30  is close to the maximum diameter portion of the second tapered surface  22 , the tip portion  31  does not reach the peak  24  of the second radially enlarged portion  17 , but is positioned on the second tapered surface  22 . The tightness of fit between the flexible tube  30  and the metal pipe  10  is inferior to the first embodiment, but superior to a conventional structure. Thus, water or dust are prevented from entering between the flexible tube  30  and the metal pipe  10 . 
     The present disclosure relates to subject matter contained in Japanese Patent Application No. 2011-038414 (filed on Feb. 24, 2011) which is expressly incorporated herein, by reference, in its entirety.