Patent Publication Number: US-6341975-B1

Title: Connector with locking arm having groove facing away from connector housing

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a connector having a locking arm. 
     2. Description of the Related Art 
     A connector with a locking arm is disclosed in Japanese Patent Application Laid-Open No. 1-112577. This prior art connector includes a connector housing, and the locking arm is formed integrally with an outer surface of the connector housing. The locking arm includes a base part erected from the outer surface of the connector housing. An arm part cantilevered is from the base part and extends along the outer surface of the connector housing. A locking projection is formed on the outer surface of the arm part, which is the surface facing away from the outer surface of the connector housing. The connector and a mating connector are connectable with each other. During this connection, the locking projection interferes with the hood of the mating connector. As a result, the locking arm flexes elastically toward the outer surface of the connector housing. When both connectors are placed in the normal fit-in state, the locking arm is restored elastically to its original state, and the locking projection is locked in the locking hole of the hood. As a result, both connectors are locked to each other in the normal fit-in state. 
     Prior art connectors have a connector housing that accommodates metal terminal fittings. The metal terminal fittings are fixed to ends of electric wires, and several such wire/connector housing assemblies are combined with each other to produce a wire harness subassembly. Wire harness subassemblies are packed in a shipping case for transport by piling them up one upon another. 
     The prior art connector with a locking arm also includes a flexure space between the locking arm and the outer surface of the connector housing. The locking arm is cantilevered and extended over the connector housing. Thus, there is a possibility that a foreign matter may penetrate into the flexure space between the locking arm and the outer surface of the connector housing. 
     The prior art wire harness subassemblies are taken out from the shipping case one by one in a place where they are assembled with other wires and connector housings to produce the wire harness. However, an electric wire of another wire harness subassembly that is still in the shipping case may penetrate into the flexure space and may be caught by the locking arm. If the wire harness subassembly is taken out forcibly from the shipping case in this state, the locking arm of the connector caught by the electric wire is subjected to a force for displacing the locking arm away from the outer surface of the connector housing, with the locking arm tilting on the base part acting as the supporting point. 
     In this event, there is a possibility that the locking arm of the conventional connector may be broken at its base part even though the displacement amount of the locking arm is not very great. 
     The present invention has been made in view of the above-described situation, and an object of the present invention is to prevent breakage of a locking arm displaced away from a connector housing. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a connector having a connector housing and a locking arm formed integrally with an outer surface of the connector housing. The locking arm includes a base part erected from the outer surface of the connector housing. An arm part is cantilevered from the base part and extends almost parallel with the outer surface of the connector housing. Thus a flexure space is defined between the outer surface of the connector housing and an inner surface of the arm part. The flexure space enables the arm part to flex elastically when the connector and a mating connector are locked to each other. In this construction, a groove is formed on the base part and the arm part, such that the groove formed on the base part extends along a direction in which the base part is erected and the groove formed on the arm part extends along a direction in which the arm part is extended. A thickness between a bottom surface of a groove of the base part and a surface thereof opposite to the bottom surface is almost equal to or larger than a thickness of the arm part. 
     Preferably, the groove of the base part is formed on a surface that receives a compression load when the locking arm is displaced in a direction away from an outer surface of the connector housing. 
     Preferably, a substantially cylindrically generated arc-shaped surface is defined on a surface of the base part that is continuous both with an inner surface of the arm part and with the outer surface of the connector housing. 
     As noted above, the prior art locking arm often is broken at its base part when the locking arm tilts away from the outer surface of the connector housing. It is believed that this breakage may occur because the base part has a great increase in the rate of strain relative to change in the tilting angle of the rear end portion of the arm part because the locking arm tilts from the connector housing, with the base part acting as the supporting point of the tilting motion of the locking arm. 
     According to the present invention, the groove is formed on both the base part and the arm part, and the thickness between a bottom surface of the groove of the base part and the rear surface thereof is almost equal to or larger than the thickness of the arm part. Thus, a portion at both sides of the groove in the base part projects in the shape of a rib. Accordingly, the base part is less flexible than the arm part and thus increase of the strain of the base part is suppressed. On the other hand, the formation of the groove allows the arm part to be more flexible than the base part. Consequently, the deformation of the arm part relaxes the tilting force applied to the base part. 
     When a tensile load is applied to the rib-shaped portion at both sides of the groove, a stress concentrates on one point and thus the outer surface of the rib-shaped portion is liable to crack and break. But, according to the first embodiment, a compression load is applied to the rib-shaped portion. Consequently, the stress is applied widely to the locking arm. Therefore, there is no fear that the locking arm is broken. 
     The rear surface of the base part that is continuous with the inner surface of the arm part and with the outer surface of the connector housing defines a generally cylindrical arc-shaped surface. Thus, the rear surface of the base part has a larger radius of curvature than a surface formed by a combination of a curved surface and a flat surface. Thus, a concentration of the stress on the rear surface of the base part is prevented, which allows the base part to have a higher breakage prevention function. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a connector of a first embodiment of the present invention. 
     FIG. 2 is a longitudinal sectional view showing the connector. 
     FIG. 3 is a sectional view taken along a line  3 — 3  of FIG.  2 . 
     FIG. 4 is a rear view showing the connector in a state in which a locking arm is broken away. 
     FIG. 5 is a sectional view showing a conventional connector. 
     FIG. 6 is a graph showing the relationship between an angle of tilting made by an arm part with a base part acting as a supporting point and a maximum strain of a locking arm. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A connector according to a first embodiment of the present invention will be described below with reference to FIGS. 1-6. 
     A connector in accordance with a first embodiment is identified by the letter A in FIGS. 1,  2  and  4 . The connector A includes a connector housing  10  made of PBT. A locking arm  11  is formed integrally with an outer surface of the connector housing  10 . The locking arm  11  includes a base part  12  erected from a front end of an outer surface  10 A of the connector housing  10 . An arm part  13  is cantilevered from the upper end of the base part  12  and extends rearwardly along the outer surface  10 A of the connector housing  10 . A locking projection  14  is formed on an outer surface  13 A of the arm part, which is the surface confronting the outer surface  10 A of the connector housing  10 . A flexure space  15  is provided between an inner surface  13 B of the arm part  13  and the outer surface  10 A of the connector housing  10 . 
     The connector A and a mating connector (not shown) can be connected with each other. During this connection, the locking projection  14  interferes with an inner peripheral surface of a hood of the mating connector. As a result, the locking arm  11  flexes elastically, such that the arm part  13  tilts on the base part  12 , which acts as the supporting point of the tilting motion of the arm part  13 . Thus, the arm part  13  approaches the outer surface  10 A of the connector housing  10 . When both connectors are placed in a normal fit-in state, the locking arm  11  is restored elastically to its original state, and the locking projection  14  is locked to a locking hole (not shown) of the hood part. As a result, both connectors are locked to each other in the normal fit-in state. 
     The connector A of the first embodiment is used with metal terminal fittings (not shown) that have been fixed to ends of electric wires (not shown). The terminal fittings then are inserted into the rear of the connector housing  10 . The connector A is combined with other connectors and wires to produce a wire harness subassembly. Then, several such wire harness subassemblies are packed in a shipping case for transport. In a wire harness-assembling place, the connector A installed on one wire harness subassembly is taken out from the shipping case. At this time, there is a possibility that an electric wire of another wire harness subassembly will penetrate into the flexure space  15  provided between the connector housing  10  and the locking arm  11  and will be caught by the arm part  13 . If the wire harness subassembly is to be forcibly taken out from the shipping case in this state, the locking arm  11  caught by the electric wire is subjected to a force that will displace the locking arm  11  in a direction away from the outer surface  10 A of the connector housing  10 . More particularly, the locking arm  11  will tilt upward on the base part  12 , with the base part  12  acting as the supporting point. In this event, there is a possibility that the locking arm of the conventional connector will be broken at its base part even though the displacement amount of the locking arm is not very great. However, the connector of the first embodiment is constructed so that the locking arm  11  can be prevented from being broken easily. The construction of the locking arm  11  will be described in detail below. 
     A vertical groove  16  is formed on the front surface  12 F of the base part  12  of the locking arm  11 , such that the groove  16  extends along the direction in which the base part  12  is erected from the connector housing  10 . The front surface  12 F on which the groove  16  is formed faces a direction opposite to the extension direction of the arm part  13 , and receives a compression load when the locking arm  11  tilts upward, namely, in a direction away from the connector housing  10 . The groove  16  is of substantially rectangular cross section, and is positioned in the center of the base part  12  in its widthwise direction. Rib-shaped portions  16 B of substantially rectangular cross section are formed, respectively, at the right and left sides of the groove  16 , such that the ribs  16 B project forward from a bottom surface  16 A of the groove  16 . The base (lower end in FIG. 2) of the front surface  12 F (outer surface) of the rib-shaped portion is continuous with and flush with the front surface  10 F of the connector housing  10 . The rise end (upper end in FIG. 2) of the front surface  12 F of the rib-shaped portion  16 B is continuous with the outer surface  13 A of the arm part  13  through a cylindrically generated arc-shaped surface  17 . Additionally, the front surface  12 F of the base part  12  is almost perpendicular to the outer surface  13 A of the arm part  13 . 
     A smallest longitudinal thickness between the bottom surface  16 A of the groove  16  of the base part  12  and the rear surface  12 R is identified by Tk in FIG.  2 . Similarly, a vertical thickness of a front region of the arm part  13 , between the base part  12  and the locking projection  14 , is identified by Ta in FIG.  2 . The dimensions Tk and Ta are set such that the thickness Tk is about 1.5 times as large as the thickness Ta. The depth Sk of the groove  16  is set to about ⅓ of a minimum thickness Tk between the bottom surface  16 A of the groove  16  and the rear surface  12 R of the base part  12 . Accordingly, the entire minimum thickness Tk+Sk of the entire base part  12  is about twice as large as the vertical thickness Ta of the arm part  13 . 
     The rear surface of the base part  12  is continuous with the inner surface of  13 B of the arm part  13  and with the outer surface  10 A of the connector housing  10 , and is formed as a substantially cylindrical generated arc-shaped surface  12 R having a uniform curvature. More specifically, the arc-shaped surface  12 R is a semicylindrical arc-shaped surface that is continuous with and substantially tangent to the inner surface  13 B of the arm part  13 . Additionally, the semicylindrical arc-shaped surface  12 R is continuous with and substantially tangent to the outer surface  10 A of the connector housing  10 . The semicylindrical arc-shaped surface  12 R substantially prevents tensile forces from being convergently applied to the rear of the base part  12  and enables an efficient dispersion of tensile forces in response to a lifting of the arm part  13 . The shortest thickness Tk of the base part  12  is the thickness between its front surface  12 F and a straight line parallel to the front surface  12 F and tangent to the cylindrically generated arc-shaped surface  12 R. 
     A groove  18  is formed on the outer surface  13 A of the arm part  13 , which is the surface of the arm part  13  that does not face the connector housing  10 , and which defines the upper side of the arm part  13  in FIG.  2 . 
     More particularly, the groove  18  extends along the extension direction (front-to-back direction) of the arm part  13 . 
     The groove  18  is of substantially rectangular cross section, and is formed in a region of the outer surface  13 A of the arm part  13  that extends substantially from the base part  12  to the locking projection  14 . Thus, the groove  18  is located in the center of the arm part  13  in its widthwise direction. The front end of a bottom surface  18 A of the groove  18  (upper surface in FIG. 2) is continuous with the bottom surface  16 A of the groove  16  of the base part  12 , with a cylindrically generated arc-shaped surface  19  extending between the surfaces  18 A and  16 A. Additionally, the bottom surface  18 A is almost perpendicular to the bottom surface  16 A. Thus the inner side surface of the groove  16  and that of the groove  18  are flush and continuous with each other. The depth Sa of the groove  18  is about ½ of the thickness Ta of the arm part  13  and almost equal to the depth Sk of the groove  16  of the base part  12 . Furthermore, the groove  16  and the groove  18  have the same width Ws. 
     The operation of the first embodiment is described below. 
     As explained above, there is a potential for the locking arm  11  to be broken at its base part  12  when the locking arm  11  is subjected to a force for displacing the locking arm  11  upward from the connector housing  10 , such that the locking arm  11  tilts on the base part  12 , and with the base part  12  acting as the supporting point of the tilting motion of the locking arm  11 . It is believed that such a breakage may occur because the base part  12  has a great increase in the rate of strain relative to change in the tilting angle of the arm part  13 . 
     According to the first embodiment, the groove  16  is formed on the base part  12  to project the rib-shaped portion  16 B forwardly from the bottom surface  16 A of the groove  16 . Further, the groove  18  is formed on the arm part  13 . Furthermore, the smallest thickness Tk between the bottom surface  16 A of the groove  16  of the base part  12  and the rear cylindrically generated arc-shaped surface  12 R is larger than the vertical thickness Ta of the arm part  13 . 
     From the viewpoint of the strength of materials, an object is less flexible if the moment of inertia of the section is greater. In the first embodiment, the thickness Tk between the bottom surface  16 A of the base part  12  and the rear surface  12 R thereof is set larger than the vertical thickness Ta of the arm part  13 . Therefore, the moment of inertia of the section of a rectangular area of the base part  12 , not including the rib-shaped portion  16 B of the base part  12 , is greater than the moment of inertia of the section of the arm part  13  not having the groove  18  formed thereon. Further, the moment of inertia of the section of the base part  12  is greater because the rib-shaped portion  16 B is projected from the bottom surface  16 A of the groove  16 . The moment of inertia of the section of the arm part  13  is smaller because the groove  18  is formed thereon. As such, the moment of inertia of the section of the base part  12  is greater than that of the arm part  13 , and, thus, the base part  12  has a higher flexure rigidity. 
     The thickness Tk of the base part  12 , measured from the rear surface  12 R to the bottom  16 A of the groove  16 , and not including the rib-shaped portion  16 B, is substantially equal to the vertical thickness Ta of the arm part  13 . Thus, sections of the base part  12  not having the rib-shaped portion  16 B formed thereon and the arm part  13  not having the groove  18  formed thereon are equal to each other in the moment of inertia of the section. However, the rib-shaped portion  16 B is formed on the base part  12 , and the groove  18  is formed on the arm part  13 . Therefore, the moment of inertia of the section of the base part  12  is greater than that of the arm part  13 . 
     As described above, in the first embodiment, the base part  12  is less flexible than the arm part  13 . Therefore, when the locking arm  11  tilts upward, namely, in a direction away from the connector housing  10 , with an electric wire caught by the front end of the arm part  13 , the arm part  13  deforms such that it curves with the inner surface  13 B being substantially convex. Thus, the force acting on the front end of the locking arm  11  to displace the locking arm  11  away from the connector housing  10  is relaxed and as a result, not applied to the base part  12 . The rigidity of the base part  12  is increased by the rib-shaped portion  16 B. Consequently, the base part  12  is hardly strained. Accordingly, breakage of the base part  12  of the locking arm  11  is prevented. 
     There is a fear that the stress is increasingly applied to the arm part  13  because the arm part  13  is more flexible than the base part  12 . However, because the arm part  13  is long in the front-to-back direction of the connector housing  10 , the stress is dispersed in a wide range of the arm part  13 . Accordingly, the stress is not locally applied to the arm part  13  and there is no possibility that the arm part  13  is broken. 
     Further, when a tensile load is applied to the rib-shaped portion during the upward tilting of the locking arm  11 , the outer surface of the rib-shaped portion is liable to crack and break. But according to the first embodiment, the rib-shaped portion  16 B is formed on the front surface  12 F to which a compression load is applied. Thus, there is no fear that the locking arm  11  is cracked and thus broken. 
     Further, the thickness Tk of the base part  12  is larger than the thickeness Ta of the arm part  13 . Thus, the rigidity of the base part  12  is increased and thereby the base part  12  is allowed to have a higher breakage prevention function. 
     Further, the rear surface  12 R of the base part  12  continuous with the inner surface  13 B of the arm part  13  and the outer surface  10 A of the connector housing  10  is formed as a cylindrically generated arc-shaped surface. Thus, the rear surface  12 R of the base part  12  has a larger radius of curvature than that of a surface formed in combination of a curved surface and a flat surface. Consequently, it is possible to prevent the stress from concentrating on the rear surface  12 R of the base part  12  and to prevent breakage of the base part  12  to a high extent. 
     FIG. 6 shows a graph indicating the result of tests conducted on the connector housing A, made of PBT, of the first embodiment and a conventional connector B (shown in FIG. 5) made of PBT. The tests were conducted on the preferred connector A to investigate the correlation between the angle of tilting made by the arm part  13 , with the base part  12  acting as the supporting point of the tilting motion of the arm part  13  and the maximum strain of the locking arm  11 . Additionally the tests were conducted on the prior art connector B to investigate the correlation between the angle of tilting made by an arm part  23 , with a base part  22  acting as the supporting point of tilting made by the arm part  23  and the maximum strain of a locking arm  21 . In the conventional connector B, the thickness of the base part  22  was almost equal to that of the arm part  23 . Further, a groove was not formed on the base part  22  and the arm part  23 . The graph indicates that supposing that the tilting angle of the arm part  12  is equal to that of the arm part  23 , the maximum strain value of the connector A of the first embodiment is smaller than that of the conventional connector B. This means that the locking arm  11  of the connector A of the first embodiment has a stress dispersion degree higher than that of the locking arm  21  of the conventional connector B. 
     The present invention is not limited to the embodiment explained by way of the above description and drawings. For example, the following embodiments are included in the technical scope of the present invention. Further, various modifications can be made without departing from the spirit and scope of the present invention. 
     In the preferred embodiment, the depth of the shallowest portion of the groove of the base part and that of the groove of the arm part are about ½ of the thickness of the base part and the arm part. But according to the present invention, the relationship between the depth of the groove and the thickness of the base part and the arm part can be set and altered as desired. 
     In the preferred embodiment, the depth of the shallowest portion of the groove of the base part is set equally to that of the groove of the arm part. But according to the present invention, both depths may be different from each other. 
     In the preferred embodiment, the curve constituting the sectional configuration of the groove as viewed along a section taken longitudinally along the locking arm is a circular curve having a uniform curvature (uniform diameter). But according to the present invention, the sectional configuration of the groove may comprise a curve whose curvature varies. 
     In the preferred embodiment, the sectional configuration of the groove as viewed along a section taken across the width of the base part includes a straight line. But according to the present invention, the sectional configuration of the groove may comprise a curve whose curvature is uniform or varies.