Abstract:
A terminal fitting ( 10 ) has a forwardly open tube ( 11 ) for receiving a male tab (T). An inner resilient contact piece ( 16; 22 ) has a base end ( 16 A;  22 A) unitary with a first wall of the tube ( 11 ) and an outer resilient contact piece ( 15; 21 ) has a base end ( 15 A;  21 A) unitary with a second wall of the tube ( 11 ). The respective base ends ( 15 A,  21 A;  16 A,  22 A) are in face-to-face contact, but a clearance ( 17; 23 ) is defined between the resilient contact pieces ( 16, 22; 15, 21 ) forward of the base ends ( 15 A,  21 A;  16 A,  22 A) prior to insertion of the male tab (T) into the tube ( 11 ). A male tab (T) can be inserted into the tube ( 11 ) and gradually closes the clearance ( 17; 23 ) from the rear end toward the front end. Thus, the support for resilient deformation shifts and stress concentrations are avoided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a terminal fitting with resilient contact pieces.  
           [0003]    2. Description of the Related Art  
           [0004]    Japanese Unexamined Utility Model Publication No. 3-55674 discloses a terminal fitting with opposite front and rear ends. A rectangular tube is formed at the front end of the terminal fitting and a resilient contact piece is in the rectangular tube. The resilient contact piece is supported at only one end and extends along forward and backward directions. A male tab inserted into the rectangular tube portion deforms the resilient contact piece. As a result, the male tab is pressed resiliently between a ceiling wall of the rectangular tube and the resilient contact piece with a specified contact pressure attributable to a restoring force accumulated in deformed the resilient contact piece.  
           [0005]    The above-described terminal fitting could be miniaturized by reducing the thickness of the resilient contact piece. However the smaller resilient contact piece might not reliably achieve the specified contact pressure.  
           [0006]    Two resilient contact pieces could be placed one over in an effort to increase the contact pressure. For example, FIG. 7 shows a terminal fitting with an upper resilient contact piece  101 A that will contact a male tab (unillustrated) and a lower resilient contact piece  101 B that will not contact the male tab. The two resilient contact pieces  101 A,  101 B are held in close contact with each other over substantially the entire length from base end portions  103 A,  103 B to extending end portions  102 A,  102 B. The extending end portion  102 A of the upper resilient contact piece  101 A is pressed by the male tab from above. Thus, both the upper and lower resilient contact pieces  101 A and  101 B are displaced resiliently down. As a result, the resilient forces accumulated in the two resilient contact pieces ensure a higher contact pressure.  
           [0007]    The upper and lower resilient contact pieces  101 A,  101 B are held in close contact with each other over substantially the entire length from the base end portions  103 A,  103 B to the extending end portions  102 A,  102 B. The two resilient contact pieces  101 A,  101 B are deformed resiliently as the male tab is inserted and are displaced down together while being held in close contact with each other. The base end portions  103 A,  103 B are the supporting points for this resilient deformation. Thus, the deformation supporting points remain unchanged in the process of resiliently displacing the resilient contact pieces  101 A,  101 B, and stress is concentrated on the deformation supporting points at the base end portions  103 A,  103 B of the resilient contact pieces  101 A,  101 B.  
           [0008]    The present invention was developed in view of the above problem and an object thereof is to prevent the concentration of a stress at resilient contact pieces.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention relates to a terminal fitting with a plurality of resilient contact pieces at least partly placed substantially one over another and extending in forward and backward directions. Base ends of the resilient contact pieces are held substantially in close contact with each other. However, a clearance is defined between at least parts of the resilient contact pieces when a male tab is unconnected. The male tab presses the resilient contact pieces during a connecting operation, and extends a close contact area between the resilient contact pieces from the base ends toward the extending ends.  
           [0010]    The resilient contact pieces deform resiliently as the male tab is connected to displace portions of the resilient contact pieces corresponding to the clearance therebetween. The ends of the resilient contact pieces that are in close contact are the supporting point about which the resilient contact pieces deform. Thus, the supporting point of the resilient deformation of the resilient contact pieces is displaced toward the extending ends as the close contact area of the resilient contact pieces is extended form the base ends toward the extending ends during the connection of the male tab. Therefore, the supporting point of the resilient deformation of the resilient contact pieces is not fixed at one position, and the concentration of stress during the resilient deformation can be avoided.  
           [0011]    A contact portion at an extending end of the resilient contact piece closest to the male tab is pressed by the male tab. Thus, the resilient contact pieces are deformed to accumulate resilient restoring forces that ensure a contact pressure between the male tab and the resilient contact pieces.  
           [0012]    The resilient contact pieces preferably are in close contact when the male tab is connected. Further, the resilient contact pieces have the clearance when the male tab is unconnected, but are held substantially in contact with each other at a position more toward the extending ends thereof than the clearance.  
           [0013]    At least one resilient contact may piece have a weakened portion formed by reducing a lateral cross section normal to the extending direction of the resilient contact piece. The resilient contact piece has a lower rigidity where the weakened portion is formed, and hence stress is distributed over the area where the weakened portion is formed when the resilient contact piece is deformed. As a result, stress acting on the supporting point of the resilient deformation of the resilient contact pieces is reduced.  
           [0014]    At least one of the resilient contact pieces is curved slightly to have a concave side facing inwardly in a free state where the male tab is not connected.  
           [0015]    A clearance narrower than the thickness of the male tab preferably is defined between a contact portion of the resilient contact piece and an opposite plate of the terminal fitting when the resilient contact pieces are in a free state.  
           [0016]    At least one resilient contact piece comprises a curved portion extending from an extending end of a substantially flat portion. The convexly curved portion faces in a resiliently deforming direction of the plurality of the resilient contact pieces.  
           [0017]    At least one of the plurality of the resilient contact pieces comprises an embossment for contact the male tab.  
           [0018]    The clearance preferably opens forwardly when the male tab is unconnected.  
           [0019]    These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description of preferred embodiments and accompanying drawings. It should be understood that even though embodiments are separately described, single features thereof may be combined to additional embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a longitudinal sectional view of a terminal fitting according to a first embodiment of the present invention showing a state immediately before a male tab is connected with a resilient contact piece.  
         [0021]    [0021]FIG. 2 is a longitudinal section of the terminal fitting showing an intermediate stage of connecting the male tab with the resilient contact piece.  
         [0022]    [0022]FIG. 3 is a longitudinal sectional view of the terminal fitting showing a state where connection of the male tab and the resilient contact piece is complete.  
         [0023]    [0023]FIG. 4 is a perspective view of resilient contact pieces of a second embodiment.  
         [0024]    [0024]FIG. 5 is a side view of resilient contact pieces of a third embodiment.  
         [0025]    [0025]FIG. 6 is a side view showing a progressed state of the resilient deformation of the resilient contact pieces.  
         [0026]    [0026]FIG. 7 is a side view of prior art resilient contact pieces. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    A terminal fitting according to a first embodiment of the invention is identified by the numeral  10  in FIGS.  1  to  3 . The terminal fitting  10  has a substantially rectangular tube  11  at the front end thereof and an unillustrated wire connection portion at the rear end of the rectangular tube  11 . The wire connection portion is crimped, bent, folded or welded into connection with an unillustrated wire or connected by insulation displacement with the wire. The terminal fitting  10  is to be inserted into a connector housing (unillustrated) and is electrically connectable with a male Tab T to be inserted into the rectangular tube  11  from the front. A leading end Ta of the male tab T is tapered to be thinner toward its tip.  
         [0028]    In the following description, a mating side with the male tab T (left side in FIGS.  1  to  3 ) is referred to as the front, and reference is made to FIGS.  1  to  3  concerning the vertical direction.  
         [0029]    The substantially rectangular tube  11  has a bottom plate  12  coupled to the wire connection portion. A pair of side plates  13  stand up from the opposite left and right sides of the bottom plate  12  and a pair of ceiling plates  14  extend in substantially normal from the upper ends of the opposite side plates  13 . The ceiling plates  14  are placed substantially one over the other.  
         [0030]    Upper and lower resilient contact pieces  15 ,  16  are formed in the substantially rectangular tube  11 . The lower resilient contact piece  15  is formed by cutting a part of the bottom plate  12  and bending the cut part obliquely up. More particularly, the lower resilient contact piece  15  defines a cantilever with a rear base end  15 A joined unitarily to the bottom plate  12 . Portions of the lower resilient contact piece  15  forward of the base end  15 A are curved slightly and have a concave side facing inwardly in a free state (see FIG. 1) where the male tab T is not connected.  
         [0031]    The upper resilient contact piece  16  has a base end  16 A that extends unitarily from a lower edge of either one of the left and right side plates  13 . The base end  16 A of the upper resilient contact piece  16  is held substantially in close contact with the upper surface of the bottom plate  12 . The upper resilient contact piece  16  further has a substantially flat portion  16 B that extends obliquely up to the front substantially along the lower resilient contact piece  15 . A curved portion  16 C extends from an extending front end of the substantially flat portion  16 B and is curved to have the convex portion facing up. A peak on the upper surface of the curved portion  16 C is embossed to project upward, thereby forming a substantially spherical contact portion  16 D to be brought into contact with the lower surface of the male tab T. A clearance narrower than the thickness of the male tab T is defined between the contact portion  16 D and the lower surface of the lower ceiling plate  14  when the resilient contact pieces  15 ,  16  are in the free unbiased state undeformed by the male tab T.  
         [0032]    The curved shape of the lower resilient contact piece  15  creates a clearance  17  between the lower surface of the substantially flat portion  16 B and the upper surface of the lower resilient contact piece  15  when the resilient contact pieces  15  and  16  are in the free state. Further, the upper edge of the extending end  15 B of the lower resilient contact piece  15  is held substantially in contact with the lower surface of the curved portion  16 C of the upper resilient contact piece  16  when the resilient contact pieces  15  and  16  are in the free state. Thus, the clearance  17  is defined between the base ends  15 A,  16 A of the two resilient contact pieces  15 ,  16  and the extending end  15 B of the lower resilient contact piece  15 . Further, the curved portion  16 C is substantially in contact with the lower resilient contact piece  15  at a portion thereof sloped obliquely up to the front and more backward than the contact portion  16 D.  
         [0033]    The male tab T is connected with the female terminal fitting  10  from the front mating side so that the lower surface of the tapered leading end Ta of the male tab T enters the rectangular tube  11  and contacts the contact portion  16 D from above. The male tab T is inserted further into the rectangular tube  11  so that the tapered leading end Ta of the male tab T presses the contact portion  16 D of the upper resilient contact piece  16  down in a deforming direction DD. Thus, the upper resilient contact piece  16  is deformed resiliently down in the deforming direction DD.  
         [0034]    A supporting point  18  of the resilient deformation of the upper resilient contact piece is displaced forward as the deformation progresses. Specifically, the front of the base end  16 A of the upper resilient contact piece  16  is the supporting point  18  of the resilient deformation at the start of the resilient deformation. Further resilient deformation presses the upper resilient contact piece  16  back in the insertion direction of the male tab T at the contact portion  16 D of the extending end thereof. As a result, the substantially flat portion  16 B buckles and curves down. Accordingly, the rear end of the substantially flat portion  16 B contacts the upper surface of the lower resilient contact piece  15  (see FIG. 2). The substantially flat portion  16 B buckles further as the deformation of the upper resilient contact piece  16  proceeds. Consequently, a substantially middle section of the flat portion closely contacts the lower resilient contact piece  15 . A close contact area between the two resilient contact pieces  15 ,  16  extends from the base ends  15 A,  16 A toward the extending ends as the resilient deformation progresses, and the clearance  17  gradually disappears from the rear end thereof.  
         [0035]    The extending end  15 B of the lower resilient contact piece  15  is pressed by the upper resilient contact piece  16  and is deformed down and made flatter as the resilient deformation of the upper resilient contact piece  16  progresses.  
         [0036]    The clearance  17  between the resilient contact pieces  15  and  16  substantially disappears when the male tab T is connected completely, and the two resilient contact pieces  15 ,  16  are held in close contact with each other over substantially the entire length of the lower resilient contact piece  15  from the base end  15 A to the extending end  15 B (see FIG. 3).  
         [0037]    Both the upper and lower resilient contact pieces  15 ,  16  are deformed resiliently in this state. Thus, a specified contact pressure is ensured between the upper resilient contact piece  16  and the male tab T by a larger resilient force, which is a sum of the resilient restoring forces of the two resilient contact pieces  15 ,  16 .  
         [0038]    The clearance  17  is defined in the resiliently deforming direction DD of the resilient contact pieces  15 ,  16  between the lower and upper resilient contact pieces  15 ,  16  when the male tab T is not connected. However, the upper resilient contact piece  16  undergoes a resilient deformation in the deforming direction DD during connection of the male tab T. This deformation. of the upper resilient contact piece  16  occurs primarily in an area corresponding to the clearance  17  between the resilient contact pieces  15 ,  16 . Additionally, the end forward end of the area of close contact between the lower and upper resilient contact pieces  15  and  16  is the supporting point for the resilient deformation of the upper resilient contact piece  16 .  
         [0039]    In this way, the supporting point  18  of the resilient deformation of the resilient contact piece  16  is displaced toward the forward mating side as the close contact area of the two resilient contact pieces  15 ,  16  extends forward from the base ends  15 A,  16 A to the extending end  15 B during the connection of the male tab T. Accordingly, the supporting point  18  of the resilient deformation of the resilient contact piece  16  is not fixed, and stress is distributed over substantially the entire flat portion  16 B of the resilient contact piece  16  during the resilient deformation, with the result that the local concentration of stress is avoided.  
         [0040]    Next, a second preferred embodiment of the present invention is described with reference to FIG. 4.  
         [0041]    A second embodiment is illustrated in FIG. 4 and has a substantially rectangular window  19  formed in the substantially flat portion  16 B of the upper resilient contact piece  16 . Portions of the upper resilient contact piece  16  at the window  19  have a smaller lateral cross section normal to the extending direction of the resilient contact piece  16  as compared to a portion where the window  19  is not formed. The resilient contact piece  16  has a lower rigidity at the window  19  and stress is distributed over the portion where the window  19  is formed during the resilient deformation of the resilient contact piece  16 . As a result, stress at a supporting point  18  of the resilient deformation of the resilient contact piece  16  is reduced. The other construction in FIG. 4 is similar to or the same as the first embodiment. Thus, no description is given on the construction, functions and effects thereof by identifying the similar or same construction by the same reference numerals.  
         [0042]    A third embodiment of the invention is illustrated in FIGS. 5 and 6. The third embodiment has a lower resilient contact piece  21  with a base end  21 A. A rear half  21 B of the lower resilient contact piece  21  forward of the base end  21 A is curved to have a concave upper surface. The lower resilient contact piece  21  also has a front extending end  21 C, and a front half  21 D of the lower resilient contact piece  21  near the front extending end  21 C is substantially flat. The third embodiment also has an upper resilient contact piece  22  with a base-end  22 A, a substantially flat portion  22 B and a base end curved portion  22 C with a concave upper surface between the base end  22 A and the substantially flat portion  22 B. The upper resilient contact piece  22  further has a front end  22 D. A clearance  23  is defined between the two resilient contact pieces  21 ,  22 . Approximately a rear half of the clearance is formed between the curved portions  21  B,  22 C and approximately a front half of the clearance  23  is formed between the flat portions  21 D,  22 B. A supporting point  24  of the resilient deformation is displaced forward when the two resilient contact pieces  21 ,  22  are deformed resiliently and the clearance  23  disappears from the rear end thereof, as shown in FIG. 6.  
         [0043]    The invention is not limited to the above described and illustrated embodiments. For example, the following embodiments are also embraced by the technical scope of the present invention as defined by the claims. Beside the following embodiments, various changes can be made without departing from the scope and spirit of the present invention as defined by the claims.  
         [0044]    Two resilient contact pieces are placed one over the other in the foregoing embodiments. However, the invention is also applicable to a case where three or more resilient contact pieces are placed substantially one over another. In this case, all the resilient contact pieces may be placed one over another with no clearance left therebetween when the male tab is connected or a clearance may be left between some resilient contact pieces.  
         [0045]    The resilient contact pieces extend forward substantially opposite from the inserting direction of the male tab being supported at only one end in the forgoing embodiments. However, the resilient contact pieces may extend backward in the same direction as the inserting direction of the male tab while being supported only at one end according to the present invention.  
         [0046]    The upper resilient contact piece is longer than the lower resilient contact piece in the foregoing embodiments. However, the upper resilient contact piece may be shorter than or substantially equal to the lower resilient contact piece according to the present invention.  
         [0047]    The extending end of the lower resilient contact piece in the foregoing embodiments is more toward the base end than the contact portion of the upper resilient contact piece. However, the extending end of the lower resilient contact piece may be more toward the extending end than the contact portion of the upper resilient contact piece while the lower resilient contact piece remains shorter than the upper resilient contact piece.  
         [0048]    In the foregoing embodiments, the two resilient contact pieces are placed substantially one over the other with no clearance left therebetween in the connected state with the male tab. However, according to the present invention, the clearance may be partly left between the two resilient contact pieces when the connection of the male tab is completed. Accordingly, the clearance may be progressively or gradually reduced during the connection or insertion of the male tab independently of whether a smaller clearance remains at the end of the connection or not.  
         [0049]    The two resilient contact pieces contact each other at a position more toward the extending ends than the clearance in the illustrated embodiments. However, the two resilient contact pieces may closely contact each other only at the base ends and the clearance may be open toward the extending front ends. In this case, the clearance may be left open toward the extending ends or the resilient contact pieces may have no clearance left therebetween when the connection of the male tab is completed.  
         [0050]    The lower resilient contact piece is formed in the foregoing embodiments by cutting the base plate of the rectangular tube and lifting the cut portion, and the upper resilient contact piece extends from the side plate. However, the upper resilient contact piece may be formed by cutting the bottom plate of the rectangular tube and lifting the cut portion, and the lower resilient contact piece may extend from the side plate. Alternatively or additionally, the base plate may be folded so as to have two or more plate layers and the two or more resilient contact pieces may be formed by suitably cutting these plate layers.  
         [0051]    The resilient contact piece is provided with the window in the second embodiment as a means for forming the weakened portion. However, the weakened portion may be formed by cutting the side edges of the resilient contact piece away to narrow its width or reduce its cross section along a direction substantially normal to the inserting direction of the male tab.  
         [0052]    The weakened portion is provided only at the upper resilient contact pieces in the foregoing second embodiment. However, the weakened portion may be at only the lower resilient contact piece or may be provided at both the upper and lower resilient contact pieces according to the present invention.