Waterproof plug

Abstract: A wire insertion hole (313) is formed through a rubber plug (310) along an axis thereof, and the rubber plug (310) has a fixing region to which a metal terminal is clamped. The fixing region includes a clamping portion (312) to be clamped by an insulation barrel of the metal terminal, and a withdrawal prevention portion (315) with an inturned portion (316) extended from a distal end of said withdrawal prevention portion (315) in overhanging relation to a barrel clamping section of said clamping portion (312). When the withdrawal prevention portion (315) tends to be elastically deformed and bent forwardly by the insulation barrel, the inturned portion (316) is pulled, and elastically flexed or deformed. The withdrawal prevention portion (315) is thus made less liable to be elastically deformed and bent forwardly. Therefore, the withdrawal prevention portion (315) is kept engaged with the barrel, and the barrel is prevented from passing past the withdrawal prevention portion (315), thus preventing the disengagement of the barrel from the clamping portion (312).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a rubber plug used in a connector required to have a waterproof effect, and also to a withdrawal prevention structure for preventing the rubber plug from being easily disengaged from a metal terminal. 2. Prior Art A conventional rubber plug of this type is shown in Fig. 1. As shown in this Figure, the rubber plug 40 is fitted on a front end portion of a sheath of a wire 41, and is fixedly clamped to the wire by a metal terminal 42, and in this condition the rubber plug is inserted into a cavity in a connector housing. The rubber plug 40 has a cylindrical shape as a whole, and has a wire insertion hole 43 extending therethrough along an axis thereof, and the wire 41 can be passed through this hole 43 in a sealed manner. Two annular seal lips 44 are formed on an outer peripheral surface of the rubber plug 40 at a rear portion thereof, and a clamping region 46 to be clamped by an insulation barrel 45 of the metal terminal 42 is provided at a front end portion of the rubber plug. The force of clamping between the rubber plug 40 and the metal terminal 42 is provided by a clamping force applied by the insulation barrel 45, and therefore the withdrawal of the rubber plug 40 can be prevented merely by increasing the clamping force. However, if the clamping force is merely increased, end edges of the insulation barrel 45 bite the rubber plug 50 to such an extent that the rubber plug 40 may be damaged if the end edge of the insulation barrel 45 is formed into a sharp edge. In such a case, the sealing property would be adversely affected. Therefore, it is not proper to merely increase the clamping force. Despite this, the above type is not provided with any withdrawal prevention means, and therefore is not satisfactory from the viewpoint of withdrawal prevention. To deal with this problem, there has been developed a rubber plug 30 shown in Fig. 2. This rubber plug 30 includes a waterproof portion 31 and a clamping portion 32, and has a tubular shape as a whole, the rubber plug 30 having an insertion hole 33 formed therethrough along its axis for passing a wire W therethrough. Two ribs 34 are formed on an outer peripheral surface of the waterproof portion 31, and can be elastically deformed into intimate contact with an inner peripheral surface of a cavity (not shown), thereby preventing water from introducing into the cavity. A metal terminal T shown in Fig. 4 is attached to the clamping portion 32, and the clamping portion 32 is smaller in outer diameter than the waterproof portion 31. A barrel B, formed at a rear end of the metal terminal T, is compressively clamped to the outer periphery of the clamping portion 32. When the barrel B is thus clamped to the clamping portion 32, the metal terminal is disposed at a right side (Fig. 2) of the rubber plug 30, and the wire W, fixedly connected to the rear end portion of the metal terminal, passes through the insertion hole 33, and extends outwardly from the rubber plug 30 to the left (Fig. 2). A flange-like withdrawal prevention portion 35 is formed on a distal end (right end in Fig. 2) of the clamping portion 32 remote from the waterproof portion 31 over an entire periphery thereof. This withdrawal prevention portion 35 serves to prevent the barrel B from being disengaged from the clamping portion 32 when inserting the rubber plug 30, together with the metal terminal, into the cavity. When the rubber plug 30 of the above construction is to be inserted into the cavity, the metal terminal mounted on the right side (Fig. 2) of the rubber plug 30 is directed toward the cavity, and then the rubber plug is inserted, together with the metal terminal, into the cavity. This inserting operation is carried out by first holding the rubber plug 30 by the fingers and by pushing the rear end of the rubber plug. If it is necessary to insert the rubber plug 30 to a deeper position in the cavity even after the rubber plug 30 is fully received in the cavity, the exposed portion of the wire W, extending outwardly from the rubber plug 30 and disposed outwardly of the cavity, is held by the fingers, and is pushed toward the cavity. At this time, the wire W is advanced, together with the metal terminal, into a deeper position in the cavity whereas the rubber plug 30 can not advance easily because of a frictional resistance between the rubber plug and an inner surface of the cavity. Therefore, there is a fear that the barrel B tends to be displaced relative to the clamping portion 32 toward the front end (right end in Fig. 2) of the rubber plug. The barrel B, if thus displaced toward the front end, abuts the withdrawal prevention portion 35 (see Fig. 3), and therefore is prevented from further displacement, thereby preventing the barrel B from being disengaged from the clamping portion 32. Thereafter, the rubber plug 30 and the metal terminal, held in a condition shown in Fig. 3, are inserted in unison into the cavity. Furthermore, there has been proposed a rubber plug 50 in Japanese Utility Model Unexamined Publication No. 62-163879 as shown in Fig. 5. In this rubber plug 50, an annular projection 52 is formed on a surface of a wire insertion hole 51 at a front end thereof, so that the inner diameter of the wire insertion hole 51 is made smaller at the projection 52 than the outer diameter of a wire 53 to be inserted into the insertion hole 51. With this arrangement, a front end of the rubber plug 50 is forcibly bulged when the wire 53 is passed therethrough, and this bulged end is engaged with an insulation barrel as shown in Fig. 6. As a result, the rubber plug 50 is prevented from withdrawal. However, in the structure shown in Fig. 2 in which the withdrawal prevention portion 35 is merely provided in a projected manner, when the frictional resistance between the rubber plug 30 and the inner surface of the cavity becomes so large that a pressing force acting from the barrel B on the withdrawal prevention portion 35 exceeds a limit value, the barrel B elastically deforms and bends the withdrawal prevention portion 35 to the right (Fig. 3). At the same time, the barrel B gradually squeezes the withdrawal prevention portion 35 to pass past the same. As a result, in some cases, the barrel B has been disengaged from the clamping portion 32, thus loosing the function of retaining the barrel B. Furthermore, the rubber plug structure shown in Fig. 5 has the following problem to be solved. Because of the provision of the annular projection on the surface of the wire insertion hole, the inner diameter of the wire insertion hole is constricted, so that the wire can not be easily passed therethrough. Therefore, the wire insertion operation is rather troublesome, and can not be carried out efficiently. The rubber plug must also meet the sealing requirement. For example, in the rubber plug 40 shown in Fig. 1, sealing engagement of the rubber plug 40 with the housing is achieved by the seal lips 44, and the plug 31 also has inner lips 47 for sealing contact with the wire. Even in the type of rubber plug having such inner lips 37, if the wire 41 is pulled, a gap develops between the inner surface of the wire insertion hole 43 and the wire 41, thus adversely affecting the sealing property. SUMMARY OF THE INVENTION The present invention has been made in view of the above problem, and an object of the invention is to provide a rubber plug, as well as a rubber plug withdrawal prevention structure, which will positively prevent withdrawal of the rubber plug and will maintain a sealing property. To achieve the above object, according to the invention there is provided a rubber plug including an insertion hole for passing a wire therethrough, and a clamping portion extending from a front end of a waterproof portion, wherein the rubber plug is secured to a metal terminal by mounting a barrel, provided at a rear end of the metal terminal connected to the wire, around the clamping portion; and the rubber plug is inserted into a cavity in a connector, with a front end thereof first introduced into the cavity, thereby achieving a waterproof effect in the cavity, wherein a withdrawal prevention portion for retaining the barrel is formed on an outer periphery of the clamping portion at a front end thereof, and projects radially outwardly; and an inturned portion extends from a distal end of the withdrawal prevention portion in overhanging relation to a barrel clamping section of the clamping portion, the inturned portion being curved along the outer periphery of the clamping portion. In the rubber plug of the invention, when a force tending to disengage the barrel and the rubber plug from each other is applied, this force tends to deform and bend the withdrawal prevention portion; however, in the invention, since the inturned portion extends from the withdrawal prevention portion, the inturned portion is subjected to a pulling force, and is deformed. At this time, a restoring force of the inturned portion acts in combination with a restoring force of the withdrawal prevention portion, and therefore the withdrawal prevention portion is less liable to be elastically deformed by the addition of the restoring force of the inturned portion. Therefore, the barrel is prevented from passing over the withdrawal prevention portion. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 3 are a cross-sectional views of conventional rubber plugs; Fig. 4 is a perspective view of a metal terminal; Figs. 5 is a cross-sectional views of another conventional rubber plug; Fig. 6 is a cross-sectional view of the conventional rubber plug of Fig. 5 in its used condition; Fig. 7 is a perspective view of a first embodiment of the invention; Fig. 8 is a side-elevational view of the first embodiment; Fig. 9 is a cross-sectional view of the first embodiment having a barrel attached thereto; Fig. 10 is a perspective view of a second embodiment of the invention; and Fig. 11 is a front-elevational view as seen from a clamping portion side in Fig. 10. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment A first preferred embodiment of the present invention will now be described with reference to Figs. 7 to 9. A rubber plug 310 of this embodiment includes a waterproof portion 311 and a clamping portion 312, and has a cylindrical shape as a whole, the rubber plug 310 having an insertion hole 313 formed therethrough along an axis thereof. A wire W is adapted to pass watertight through this insertion hole 313. The waterproof portion 311 has an outer diameter slightly smaller than an inner diameter of a cavity in a connector (not shown). Ribs 314 are formed on an outer periphery of the waterproof portion 311 over an entire periphery thereof, and when the rubber plug 310 is inserted into the cavity, these ribs 314 are elastically deformed into intimate contact with the inner peripheral surface of the cavity, thereby preventing water from intruding from the outside of the connector into the cavity. A metal terminal of a conventional construction as described above (Fig. 4) is attached to the clamping portion 312 of the rubber plug 310. The clamping portion 312 extends from a front end surface (right end surface in Figs. 8 and 9) of the waterproof portion 311 in coaxial relation thereto. The clamping portion 312 is smaller in outer diameter than the waterproof portion 311, and a U-shaped barrel B, formed at a rear end of the metal terminal, is compressively clamped to the outer periphery of the clamping portion 312. When the barrel B is thus clamped to the clamping portion 312, the metal terminal is disposed at the right side (Figs. 8 and 9) of the rubber plug 310, and the wire W, fixedly connected to the rear end portion of the metal terminal, passes through the insertion hole 313, and extends outwardly from a rear end surface (left end surface in Figs. 8 and 9) of the waterproof portion 311. A peripheral withdrawal prevention portion 315 is formed on an outer surface of a front end of the clamping portion 312 remote from the waterproof portion 311 over an entire periphery thereof, this portion 315 being directed radially outwardly into a flange-like configuration. A dimension of radial projection of this withdrawal prevention portion 315 is larger than the thickness of the barrel B. An axial thickness of the withdrawal prevention portion 315 is generally equal to its radial projection dimension. A continuous, inturned portion 316 is formed integrally with an outer peripheral portion of the withdrawal prevention portion 315 over an entire periphery thereof. The inturned portion 316 extends from the withdrawal prevention portion 315 in overhanging relation to the barrel clamping portion, is cylindrical, and is spaced a predetermined distance from the outer peripheral surface of the clamping portion 312 in concentric relation thereto. The operation of this embodiment will now be described. The rubber plug 310 of this embodiment is attached to the metal terminal by compressively clamping the barrel B to the clamping portion 312. When the rubber plug 310 is thus attached to the metal terminal, the metal terminal is disposed at the clamping portion side (that is, the right side in Figs. 8 and 9) of the rubber plug 310. When the rubber plug 310 and the metal terminal are to be mounted in the cavity, the rubber plug 310 is held by the fingers, with the metal terminal directed toward the cavity, and then they are inserted into the cavity. Therefore, the metal terminal, the clamping portion 312 of the rubber plug 310, and the waterproof portion 311 are introduced sequentially into the cavity in this order. When the waterproof portion 311 is inserted into the cavity, the ribs 314 on the outer periphery of the waterproof portion 311 are elastically deformed into contact with the inner peripheral surface of the cavity, so that a frictional resistance develops between the rubber plug 310 and the inner peripheral surface of the cavity because of an elastic restoring force of the ribs 314. Therefore, when the waterproof portion 311 begins to be inserted into the cavity, the fingers are held against the end surface of the waterproof portion 311, and the rubber plug 310 is forced into the cavity. If it is necessary to further advance the rubber plug 310 into a predetermined deeper position in the cavity even after the waterproof portion is completely inserted into the cavity, the exposed portion of the wire W, extending outwardly from the end surface of the waterproof portion 311 of the rubber plug 310 and disposed outwardly of the cavity, is held by the fingers, and is pushed to further advance the rubber plug 310 in the cavity. At this time, if although the wire W advances, together with the metal terminal, into the deeper position in the cavity, the rubber plug 310 can not advance easily because of the frictional resistance between the ribs 314 and the inner surface of the cavity, the barrel B is displaced relative to the clamping portion 312 toward the front end (right end in Figs. 8 and 9). When the barrel B is thus displaced toward the front end, the barrel B abuts against the withdrawal prevention portion 315 as shown in Fig. 9, and in this condition an axial pressing force is applied from the barrel B to the withdrawal prevention portion 315, and tends to deform and bend this portion 315 forwardly. In the rubber plug 310 of this embodiment, the withdrawal prevention portion 315 and the inturned portion 316 are both formed over the entire periphery of the clamping portion 312. Therefore, when the withdrawal prevention portion 315 tends to be elastically deformed and bent forwardly, the inturned portion 316 is pulled, and elastically flexed or deformed. At this time, the elastic restoring force of the inturned portion 316 serves as an elastic retaining force to protect the withdrawal prevention portion 315 against the pressing force applied from the barrel B. Because of the elastic retaining force possessed by the withdrawal prevention portion 315 and the elastic retaining force possessed by the inturned portion 316, the withdrawal prevention portion 315 is made less liable to be elastically deformed and bent forwardly. Therefore, the withdrawal prevention portion 315 is kept engaged with the barrel B, and the barrel B is prevented from passing past the withdrawal prevention portion 315, thus preventing the disengagement of the barrel B from the clamping portion 312. Therefore, by pushing the wire W, the rubber plug 310 can be inserted, together with the metal terminal, into the deeper position in the cavity, with the barrel B kept retained by the withdrawal prevention portion 315. Second Embodiment A second embodiment of the present invention will now be described with reference to Figs. 10 and 11. A rubber plug 320 of this embodiment differs from the first embodiment in that a withdrawal prevention portion, as well as an inturned portion, have a different configuration. Four withdrawal prevention portions 325 projecting radially outwardly are formed on an outer peripheral surface of a front end of a clamping portion 322 remote from a waterproof portion 321, and are circumferentially spaced at predetermined angles (90°) from one another. In this embodiment, the length of each withdrawal prevention portion 325 in the circumferential direction is substantially 1/8 of the outer diameter of the clamping portion 322. An inturned portion 326 extends from a distal end of each of the withdrawal prevention portion 325 in overhanging relation to the barrel clamping portion. The inturned portion 326 is equal to the withdrawal prevention portion 325 in length in the circumferential direction. The inturned portions 326 are arcuately curved, and are disposed on a circle concentric with the clamping portion 322. The operation of this embodiment will now be described. In the rubber plug 320 of this embodiment, the inturned portions 326 are arcuately curved, and are disposed on the circle concentric with the clamping portion 322. Therefore, when the withdrawal portions 325 are elastically deformed and bent forwardly, the inturned portions 326 are also elastically flexed or deformed in accordance with the deformation of the withdrawal prevention portion 326. At this time, the elastic restoring force of the inturned portion 326 serves as an elastic retaining force to protect the withdrawal prevention portion 325 against the pressing force applied from the barrel B. Because of the elastic retaining force possessed by the inturned portion 326 and the elastic retaining force possessed by the withdrawal prevention portion 325, the withdrawal prevention portion 325 will not be elastically deformed and bent forwardly by the pressing force applied from the barrel, and therefore the withdrawal prevention portions 325 retain the barrel against disengagement. The present invention is not to be limited to the embodiments described above with reference to the drawings, and for example, the following modifications fall within the scope of the present invention, and also other modifications than the following can be made within the scope of the invention. In the above embodiment, although the four withdrawal prevention portions 325 and the four inturned portions 326 are provided, the number thereof may be not more than three, or not less than five. The arrangement of the withdrawal prevention portions and the inturned portions in the circumferential direction, as well as the length thereof in the circumferential direction, may be suitably determined. In the above embodiment, although the withdrawal prevention portion as well as the inturned portion 316 is formed over the entire periphery of the clamping portion 312, there can be adopted an arrangement in which the withdrawal prevention portion is provided over the entire periphery whereas the inturned portion is interrupted at predetermined intervals in the circumferential direction. In the illustrated embodiments, although the outer peripheral surface of the wire is held in intimate contact with the inner peripheral surface of the wire insertion hole (that is, the inner peripheral surface of the fixing region) before the insulation barrel is clamped, a slight clearance may be provided between the inner peripheral surface of the wire insertion hole and the wire before the clamping if a seal is formed between the rubber plug and the sheathed wire by the inner seal lip or portion formed by the projected edge upon clamping. In this case, the wire can be easily, passed through the rubber plug while enabling the formation of seals at the inner and outer sides of the rubber plug.

Claims: A waterproof plug adapted to be inserted into a cavity of a connector, with a front end thereof first introduced into said cavity, thereby achieving a waterproof effect in said cavity, said waterproof plug comprising: an insertion hole (313) for passing a wire (W) therethrough; a clamping portion (312; 322) extending from a front end of a waterproof portion, to be clamped by a barrel (B) of a metal terminal that is provided at a rear end of said metal terminal; a withdrawal prevention portion (315; 325) for retaining said barrel, which is formed on an outer periphery of said clamping portion (312; 322) at a front end thereof so as to project radially outwardly; characterized in that said withdrawal prevention portion comprises an inturned portion (316; 326) extended from a distal end of said withdrawal prevention portion (315; 325) in overhanging relation to a barrel clamping section of said clamping portion (312; 322), said inturned portion (316; 326) being curved along the outer periphery of said clamping portion (312; 322). The rubber plug according to claim 1, wherein said withdrawal prevention portion (315), as well as said inturned portion are formed over the entire periphery of said clamping portion (312). The rubber plug according to claim 1, wherein said withdrawal prevention portion (325), as well as said inturned portion (326) are formed over part of the periphery of said clamping portion (322). The waterproof plug as claimed in claim 3, wherein said withdrawal prevention portion (325), as well as said inturned portion (326) each are circumferentially spaced at predetermined angles from each other. The waterproof plug as claimed in claim 4, wherein said predetermined angles each are 90° The waterproof plug as claimed in anyone of claims 3 to 5, wherein said withdrawal prevention portion (325), as well as said inturned portion (326) each have a length in circumferential direction being substantially 1/8 of the outer diameter of said clamping portion (322). The waterproof plug as claimed in anyone of claims 1 to 6, further comprising a plurality of inner seal lips formed on an inner peripheral surface of said wire insertion hole (313), said inner seal lips being annular and being able to watertightly contact the sheathed wire (W) in a compressed manner. The waterproof plug as claimed in anyone of claims 1 to 7, wherein said waterproof plug (310; 320) is made of rubber. A waterproof plug (310; 320) with a structure for preventing said plug from withdrawing from a metal terminal, said plug comprising: a wire insertion hole (313) formed through said waterproof plug (310; 320) along an axis thereof for passing a sheathed wire (W) therethrough; annular seal lips (314) formed on an outer peripheral surface of said waterproof plug; a clamping portion (312; 322) for being clamped by an insulation barrel (B) of a metal terminal; a withdrawal prevention portion (315; 325) disposed outwardly of said clamping portion (312; 322) for engagement with said insulation barrel (B) to thereby prevent withdrawal of said waterproof plug (310; 320); characterized in that said withdrawal prevention portion comprises an inturned portion (316; 326) extended from a distal end of said withdrawal prevention portion (315; 325) in overhanging relation to a barrel clamping section of said clamping portion (312; 322), said inturned portion (316; 326) being curved along the outer periphery of said clamping portion (312; 322).

Inventors: KATSUMA TAKATOSHI, MATSUOKA HIROYUKI, SAIJO EIJI, YAMADA SHINICHI, KATSUMA, TAKATOSHI, MATSUOKA, HIROYUKI, SAIJO, EIJI, YAMADA, SHINICHI, Katsuma, Takatoshi, c/o Sumitomo Wiring Syst. Ltd., Matsuoka, Hiroyuki, c/o Sumitomo Wiring Syst. Ltd., Saijo, Eiji, c/o Sumitomo Wiring Syst. Ltd., Yamada, Shinichi, c/o Sumitomo Wiring Syst. Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1995
Main classification: H01R13
IPC codes: H01R13