Patent Publication Number: US-7717722-B2

Title: Cable terminal and cable using the same

Description:
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2007/060139 filed May 17, 2007. 
     TECHNICAL FIELD 
     The present invention relates to a cable terminal and to a cable using the same, and particularly relates to a terminal used for a tension cable for applying high voltage on an ignition plug and to the tension cable. 
     BACKGROUND ART 
     A typical tension cable (also called as a high-tension cord) mounted on an internal combustion engine (e.g., an engine) is attached with a metallic cable terminal by a method such as crimping, in order to establish conduction between the cable and a plug terminal of an ignition plug. 
     A known exemplary arrangement of such a cable terminal includes: a pair of gripping portions for radially gripping an end of a cable body from both sides; an insertion portion curved to be substantially annular, the pair of gripping portions being respectively provided on ends of the insertion portion; and an acicular portion provided integrally with the insertion portion and the gripping portions (Patent Document 1). 
     When such a cable terminal is used, the cable terminal is brought into conduction with a core inside the cable body by thrusting the acicular portion into the cable body from an end face of the cable body, and the entirety of the cable terminal is crimped to the cable body by making the gripping portions partially cut in a coating provided on an outer circumference of the cable body with the acicular portion being thrust into the cable body. Then, by inserting the cable terminal into a plug cap while the plug cap covers a plug terminal, an end of the plug terminal is inserted into the insertion portion of the cable terminal, such that an inner surface of the insertion portion partially contacts a contact provided on an outer circumference of the plug terminal, thereby establishing conduction between the cable terminal and the plug terminal. 
     Patent Document 1: JP-A-2001-313147 
     DISCLOSURE OF THE INVENTION 
     Problems to Be Solved by the Invention 
     However, according to the arrangement of the cable terminal disclosed in the patent document 1, since the inner surface of the insertion portion merely contacts the contact provided on the outer circumference of the plug terminal, the contact of the plug terminal and the insertion portion of the cable terminal may be misaligned in terms of an insertion direction. When such a misalignment arises, the insertion portion may be located on a constricted portion provided contiguous to the contact, and favorable conduction cannot be established. 
     In order to prevent such a misalignment in terms of the insertion direction, JP-UM-A-4-8772 discloses that a connector spring is provided on the cable terminal, and that the connector spring is locked to the constricted portion of the plug terminal. 
     However, such a connector spring may not be usable, depending on a shape of the constricted portion of the plug terminal. Specifically, in an arrangement where the constricted portion is so deeply concaved that substantially no taper face is formed thereon, the connector spring having been locked thereto may not be disengaged from the constricted portion. Thus, for instance, at the time of an inspection of the ignition plug, the plug cap may not be easily detached from the plug terminal. 
     In addition, according to the arrangement of the cable terminal disclosed in the patent document 1, since the acicular portion is thrust into the cable body from its end face to be in conduction with the core, an insertion direction of the acicular portion may be deviated at the time when the cable terminal is mounted. When such a deviation arises, a sufficient contact may not be established between the acicular portion and the core, thereby entailing an instable conduction. 
     An object of the invention is to provide a cable terminal capable of reliably establishing conduction with a cable body and an ignition plug and enhancing workability, and to provide a cable using the same. 
     Means for Solving the Problems 
     A cable terminal according to an aspect of the invention is a cable terminal inserted into a plug cap for an ignition plug while being crimped to a cable body, the cable terminal including: a crimped portion crimped to the cable body; an extending piece provided integrally with the crimped portion to extend forward in an insertion direction; and a conductor contacting piece provided integrally with the crimped portion to face an end face of the cable body, in which an end of the extending piece abuts on an inner surface of the plug cap to determine a position in terms of the insertion direction, the plug cap being made of an elastic body, the extending piece is provided with a springy press piece that projects to a plug terminal of the ignition plug inserted into the plug cap and contacts an end face of the plug terminal, and the conductor contacting piece is sandwiched between a portion of an outer circumference of the plug terminal and a core exposed from the end face of the cable body, the plug terminal disposed to be in tight contact with the inner surface of the plug cap. 
     A cable according to another aspect of the invention includes: the above-described cable terminal; the cable body to which the cable terminal is crimped; and the plug cap into which the cable terminal having been crimped to the cable body and the ignition plug are inserted, the cable terminal being inserted from a first end side of the plug cap, the ignition plug being inserted from a second end side of the plug cap. 
     According to the aspect(s) of the invention, since the cable terminal includes the press piece and the conductor contacting piece, the cable terminal can contact the plug terminal in two directions perpendicular to each other, thereby favorably preventing a deviation of the insertion direction of the plug terminal. At this time, since the position of the extending piece is determined within the plug cap, a pressing force can be sufficiently applied on the end face of the plug terminal. In addition, since the conductor contacting piece is sandwiched between the outer circumference of the plug terminal and the core while being pressed by the plug terminal having been disposed within the plug cap made of an elastic body, contact between the plug terminal and the cable terminal can be favorably maintained, and reliable conduction can be established therebetween as compared with a conventional arrangement in which an acicular portion is used. Further, since no connector spring is used in order to obtain reliable conduction unlike a conventional arrangement, the plug cap can be easily attached to and detached from the ignition plug even when the ignition plug has a large constricted portion, thereby enhancing workability. 
     Preferably in the cable according to the aspect of the invention, a plug-insertion hole of the plug cap is provided with a projection that inwardly projects, and the projection is fitted into a recess provided adjacent to the plug terminal of the ignition plug in a concave-convex manner. 
     According to the aspect of the invention, since the concave-convex fitting portion is provided adjacent to the plug terminal, the position of the plug terminal can be further stabilized. Thus, conduction between the plug terminal and the cable terminal can be favorably maintained, thereby contributing to enhanced reliability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view showing a primary portion of a cable according to an exemplary embodiment of the invention. 
         FIG. 2  is a lateral view showing an end of a cable body having been stripped. 
         FIG. 3  is a lateral view showing the end of the cable body having been crimped with a cable terminal. 
         FIG. 4  is a top view showing the end of the cable body in  FIG. 3 . 
         FIG. 5  is a bottom view showing the end of the cable body in  FIG. 3 . 
         FIG. 6  is a front view showing the end of the cable body in  FIG. 3 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An exemplary embodiment of the invention will be described below with reference to the attached drawings. 
       FIG. 1  shows a cross-sectional view showing a primary portion of a tension cable  10  (cable) according to the exemplary embodiment of the invention.  FIG. 2  is a lateral view showing an end of a cable body  11  having been stripped.  FIG. 3  is a lateral view showing the end of the cable body  11  having been crimped with a cable terminal  12 .  FIGS. 4 to 6  are respectively a top view, a bottom view and a front view, each of which shows the end of the cable body in  FIG. 3 . 
     The tension cable  10  includes: a cable body  11 ; a cable terminal  12  mounted on a first end of the cable body  11 ; a plug cap  13  for covering the entirety of the cable terminal  12  together with the first end of the cable body  11 ; and a plug cover  14  for externally covering the plug cap  13 . The tension cable  10  is connected to an ignition plug  90  at the first end while being connected to an ignition coil, a suitable voltage-applying device or the like (not shown) at its second end. 
     In this exemplary embodiment, the cable body  11  includes a core  15  formed of plural carbon fibers as shown in  FIG. 2 . With this arrangement, the cable body exhibits a greater electrical resistance than a typical cable having a metal core formed of, for example, copper wires. The cable body  11 , which exhibits a greater electrical resistance as described above, can control electric noises generated when a high voltage is applied thereon, and reduce electric-wave disturbance brought to other electronic devices. In addition, insulation coating  16  of the cable body  11  is externally covered with braided shield  17  made of a metal conductor. With this arrangement, generated noises can be more reliably prevented from leaking to the outside. In order to prevent the metal conductor from coming apart, a terminal end of the braided shield  17  is covered with a suitable resin such as hot melt. 
     The cable terminal  12 , which is exemplarily made of conductive stainless, is crimped and fixed to the insulation coating  16  of the cable body  11  by use of a predetermined crimping tool or the like. More specifically, the cable terminal  12  includes: a crimped portion  18  press-attached to the insulation coating  16  by crimping; a conductor contacting piece  19  provided integrally with the crimped portion  18  so as to face an end face of the cable body  11 ; and an extending piece  20  also provided integrally with the crimped portion  18  and extended forward in an insertion direction in which the cable body  11  is inserted (i.e., a direction coinciding with the axis direction of the cable body  11 ). 
     The crimped portion  18  is provided with a serrated cut-in portion  21  that is crimped by a crimping tool to slightly cut into the insulation coating  16 . The cut-in portion  21  reliably fixes the crimped portion  18  to the insulation coating  16  after the crimped portion  18  is press-attached thereto. 
     The conductor contacting piece  19  is formed by bending the crimped portion  18  toward the center of the cable body  11 . An end of the conductor contacting piece  19  is provided with a locking piece  22  formed by bending the conductor contacting piece  19  backward in the axis direction of the cable body  11 . The locking piece  22  locks an outer end periphery of the insulation coating  16  at a position radially opposite to where the extending piece  20  is provided. 
     A face of the conductor contacting piece  19  that faces the end face of the cable body  11  is in contact with the core  15  having been exposed by stripping the insulation coating  16  around the first end of the cable body  11 . The core  15  is bent along the conductor contacting piece  19  and sandwiched between the crimped portion  18  and the insulation coating  16 . In this manner, by pressing the core  15  having been exposed at the first end of the cable body  11  to substantially the entirety of the planar portion of the conductor contacting piece  19 , a favorable contact can be established between the core  15  and the conductor contacting piece  19 , thereby establishing a reliable conduction between the core  15  and the cable terminal  12 . In addition, the conductor contacting piece  19  is in abutment with a first contact  92  formed on an outer circumference of a plug terminal  91  of the ignition plug  90 . With this arrangement, the first contact  92  and the core  15  sandwiches the conductor contacting piece  19  to establish a conduction with each other. 
     On the other hand, the extending piece  20  is integrally provided with a press piece  23  at a position spaced apart by a predetermined distance from the end face of the cable body  11 . The press piece  23  projects to the plug terminal  91  in a cantilevered manner, and a bent portion provided on a first end of the press piece  23  contacts a second contact  93  formed on an end face of the plug terminal  91 . The press piece  23 , which is a springy member, is elastically deformed to reliably contact the second contact  93  while applying a predetermined pressing force thereto. Due to the contact of the press piece  23  with the conductor contacting piece  19 , the plug  91  can be in conduction with the cable body  11  in two directions perpendicular to each other: namely, a first insertion direction in which the ignition plug  90  is inserted: and a second insertion direction (a direction perpendicular to the first insertion direction) in which the cable body  11  is inserted. 
     The plug cap  13 , which is an elastic body exemplarily made of synthetic resin (rubber), is an important component in relation to the cable terminal  12 . The plug cap  13 , which is an L-shaped member, is provided with a cable-insertion hole  24  at its first end, into which the cable body  11  crimped with the cable terminal  12  is inserted. A second end of the plug cap  13  is provided with a plug-insertion hole  25  into which the ignition plug  90  is inserted. The insertion holes  24 ,  25  are internally communicated with each other. 
     As shown in  FIG. 1 , an inner opposing surface of the plug cap  13  that faces the opening portion of the cable-insertion hole  24  provides an abutment portion  26  on which a first end of the extending piece  20  of the cable terminal  12  abuts. Since the entirety of the plug cap  13  is elastic, the extending portion  20  is slightly buried in the abutment portion  26 , thereby positioning the cable terminal  12  thereto in terms of the insertion direction. 
     A clearance defined by the opposing surface and the conductor contacting piece  19  when the cable terminal  12  is inserted thereinto is slightly smaller than an outer diameter of the plug terminal  91  on which the first and second contacts  92 ,  93  are provided. With a suitable tightening margin being provided by the clearance, the plug terminal  91  is located in the clearance. With this arrangement, the plug terminal  91  having been located in the clearance is in tight contact with the inner surface of the plug cap  13 . In addition, applied with a pressing force generated by the elastic deformation of the inner surface of the plug cap  13 , the plug terminal  91  is pressed to the conductor contacting piece  19 . Thus, the first contact  92  is reliably brought partially into contact with the conductor contacting piece  19 . 
     An inner diameter of the cable-insertion hole  24  is also set at such a value that can provide a tightening margin sufficient for the outer diameter of the cable body  11 . The cable body  11  having been inserted in the cable-insertion hole  24  is applied with a pressing force generated by elastic deformation of an inner surface of the cable-insertion hole  24 . With this arrangement, even when the plug terminal  91  located in the above-described clearance applies a force on the cable body  11  in a direction in which the cable body is disengaged from the cable-insertion hole  24 , the cable body  11  can sufficiently resist the force applied by the plug terminal  91 , whereby the contact of the plug terminal  91  with the conductor contacting piece  19  is favorably maintained. 
     A top portion of the plug-insertion hole  25  shown in  FIG. 1  (i.e., a portion in the vicinity where the plug-insertion hole  25  is communicated with the cable-insertion hole  24 ) internally and circumferentially projects toward the inside, thereby defining a projection  27  having an arc cross section. The projection  27  is fitted into a recess  94  provided adjacent to a bottom of the plug terminal  91 , thereby suitably establishing a concave-convex fitting. Elastic deformation of the projection  27  allows the plug terminal  91  to be inserted thereinto beyond the projection  27 , so that the projection  27  is fitted into the recess  94 . With this arrangement, the plug terminal  91  is stably positioned within the plug cap  13 . The recess  94  is equivalent to the constricted portion having been described in the description of the background art. The recess  94  used in the ignition plug  90  according to this exemplary embodiment has a greater constriction than an ordinary constricted portion. Thus, it is difficult to apply a conventional connector spring to the above-arranged ignition plug  90 . 
     While the projection  27  and the recess  94  are in a concave-convex fitting, the second contact  93  of the plug terminal  91  is in abutment with the press piece  23  of the cable terminal  12  and applied with a pressing force generated by elastic deformation of the press piece  23 . Even when the plug terminal  94  is applied with the above pressing force, the concave-convex fitting prevents the plug terminal  91  from being returned by the pressing force. In addition, the extending piece  20  can be prevented from being warped by a reaction force from the plug terminal  91  because: the extending piece  20  is curved to be rigid and firm as shown in  FIG. 6 ; the extending piece  20  is provided with a rib  28  for positioning the plug cap  13  and the cable terminal  12  when the plug cap  13  and the cable terminal  12  are assembled and for reinforcing the extending piece  20  as shown in  FIG. 6 ; and substantially the entirety of the extending piece  20  abuts on an inner opposing surface of the cable-insertion hole  24 . Accordingly, the contact of the second contact  93  with the press piece  23  is favorably maintained. 
     The plug-insertion hole  25  of the plug cap  13  also provides a tightening margin sufficient for an inserted portion  95  of the ignition plug  90 . With this arrangement, the plug cap  13  can be stably held on the inserted portion  95  of the ignition plug  90  via the plug-insertion hole  25  capable of covering a larger area, thereby preventing easy disengagement of the plug cap  13  from the ignition plug  90 . In addition, the concave-convex fitting portion and the vicinity of the plug terminal  91  are not required to provide a holding force, which also contributes to favorable maintenance of the contact between the plug terminal  91  and the cable terminal  12 . 
     Additionally, a plug cover  14  included in the tension cable  10  according to this exemplary embodiment is made of metal so as not to let electric noises generated within the plug cap  13  leak to the outside thereof. As shown in  FIG. 1 , the plug cover  14  includes two dividable halves respectively adapted to be opened and closed about a hinge  29  provided on a top portion of the plug cover  14 . Plural engaging portions  30  provided on an outer circumference of a second half of the plug cover  14  are engaged with a collar-shaped periphery provided along an outer circumference of a first half of the plug cover  14  ( FIG. 1  only shows the first half of the plug cover  14  and the engaging portions  30  provided on the second half of the plug cover  14 ). By engaging the engaging portions  30  therewith, the two halves are closed, so that the entirety of the plug cap  13  is housed within the plug cover  14 . 
     Further, a recessed groove  31  is provided in the vicinity of the opening portion of the plug cover  14  adjacent to the ignition plug  90 , into which a holding ring  32  formed of spring material is fitted. The holding ring  32  forcibly connects the two halves of the plug cover  14 , and maintains a favorable fitting of the plug cap  13  with the ignition plug  90 . The vicinity of the opening portion of the plug cover  14  adjacent to the cable body  11  is closed by a member such as a shrink tube  33  that bridges the plug cover  14  and the cable body  11 . 
     It should be noted that, although the best structure, method and the like for implementing the invention have been described in the above description, the invention is not limited to the above description. Specifically, while the invention has been described above with a specific embodiment(s) being particularly illustrated and mainly described, those skilled in the art may make various modifications to the above-described embodiments in terms of a shape, quantity or any other detailed configuration without departing from a scope of a technical idea and an object of the invention. 
     Thus, a shape, quantity and the like described above merely serve as exemplifying the invention for facilitating an understanding of the invention, and do not serve as any limitations on the invention, so that what is described by a name of a component for which the description of the shape, quantity and the like are partially or totally omitted is also included in the invention.