Patent Publication Number: US-11387585-B2

Title: Anti-fretting/multiple contact terminal using knurl pattern

Description:
BACKGROUND 
     Electrical contact between terminals typically relies on the creation of a high-contact force between the components providing the electrical contact. The surface area of the respective electrical contacts may be relatively large, however, due to process variations and other factors only a few electrical contact points are provided between the respective electrical contacts. Additionally, mechanical vibration between the respective components can cause fretting at the point of contact, eventually resulting in a loss of electrical contact as the conductive material is worn away at the one or two electrical contact points. To combat this problem, complex geometries associated with the electrical contacts can be utilized to ensure additional points of contact. However, the added complexity increases the time and cost associated with manufacturing the electrical contact. 
     It would be beneficial to develop an electrical contact that provides a cost effective system for increasing the number of contact points between respective terminals while maintaining electrical contact in the presence of mechanical vibration/fretting. 
     SUMMARY 
     According to some aspects, a female electrical terminal includes a securing end, a mating end located opposite the securing end along a longitudinal coupling axis, and a contact pad. The mating end further includes a housing provided with an opening configured to receive a male contact or terminal. The contact pad is positioned within the housing to contact the male terminal or contact received within the opening, wherein a surface of the contact pad includes a plurality of protrusions extending from the surface. 
     According to another aspect, a connection assembly may include a female electrical terminal and a male electrical terminal. The female electrical terminal may include a first end and a second end, the first end having an opening and a contact pad located within the first end, wherein a surface of the contact pad is knurled to provide a plurality of protrusions. The male electrical terminal includes a male contact that is received within the opening of the female electrical terminal and placed in contact with the contact pad, wherein electrical contact points are provided between one or more of the plurality of protrusions and the male contact. 
     According to another aspect, a male electrical contact includes a first surface and a second surface opposite the first surface. The first surface or the second surface may include a contact surface that includes a plurality of protrusions extending from the surface. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a terminal according to some embodiments. 
         FIG. 2  is a top view of the terminal according to some embodiments. 
         FIG. 3  is a side view of the terminal according to some embodiments. 
         FIG. 4  is a cross-sectional view of the terminal taken along line  2 - 2  shown in  FIG. 2  according to some embodiments. 
         FIG. 5  is a cross-sectional view of the terminal taken along line  3 - 3  shown in  FIG. 3  according to some embodiments. 
         FIG. 6  is a magnified view of the knurl pattern formed on the contact pad according to some embodiments. 
         FIG. 7  is a cross-sectional view of the contact pad taken along line  6 - 6  that illustrates the projections created by the recesses made in the contact pad according to some embodiments. 
         FIG. 8  is a chart illustrating height of the contact pad along a planar axis according to some embodiments. 
         FIG. 9  is an isometric view of a male electrical terminal having a male contact that includes a knurled surface according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     According to some aspects, a contact pad utilized to make electrical contact with a respective terminal may utilize a knurl pattern to increase a number of contact points between the respective terminals. In some embodiments, the knurl pattern includes a plurality of recessed indents on the contact pad, wherein the plurality of recesses formed in the contact pad cause a plurality of projections or ridges (i.e., knurl pattern) to be formed adjacent the recesses. Each of the plurality of projections provides a possible electrical contact point between the contact pad and the mating terminal. In addition, fretting of one or more of the contact points associated with the contact pad result in a new electrical contact point being created at a different projection along the contact pad. In this way, fretting does not result in a loss of electrical contact between the respective terminals. In some embodiments the plurality of recesses utilized to form the knurl pattern may have various geometries, such as a rhombus shaped recess. Furthermore, a cost-effective and simple stamping process may be utilized to form the plurality of recesses (and therefore the knurl pattern), such that the knurl pattern does not add significantly to the cost of the terminal. 
     Referring to  FIGS. 1-3  a female electrical terminal  100  is provided that includes a contact pad  130  (shown in  FIGS. 4-8 ) having a knurled surface. The female electrical terminal  100  includes a mating end  101  configured to receive a compatible male electrical terminal (e.g., blade-type contact  105 ) and a securing end  103  configured to receive and retain a wire/conductor (not shown). A longitudinal coupling axis is defined between the mating end  101  and the securing end  103 , in the direction of coupling indicated by arrow  109 . The mating end  101  includes a housing  102  comprised of a plurality of walls including first and second side walls  104 ,  108 , bottom wall  106 , and top wall  110 . The housing extends longitudinally toward the securing end  103 , and the plurality of walls define an opening  115  configured to receive and retain blade-type contact  105 . In some embodiments, the blade-type contact  105  received within the opening  115  is retained, in part, by contact force spring  116 . In some embodiments, the contact force spring  116  provides a contact force that ensures engagement between a portion of the blade-type contact  105  and the contact pad  130  located on an inner surface of the housing and having a knurled surface (described in more detail with respect to  FIGS. 4-7 , below). A spring lock  117  is positioned on bottom wall  106  utilized to lock the terminal  100  into the connector housing. The securing end  103  includes a conductor wing  112  and an insulation wing  114 . A wire (not shown) received at the securing end  103  is secured to the female electrical terminal  100  by crimping the conductor wing  112  (at a conductive or exposed length of the wire) and further secured by crimping the insulation wing  114  around a portion of the wire. The terms “top” and “bottom” are utilized to differentiate between the respective sidewalls, although it should be understood that these terms do not require that the top wall  110  being located at a location above the bottom wall  106 . Depending on the installation of the female electrical terminal  100 , the respective sidewalls may be positioned in any orientation relative to one another. 
     Referring now to  FIGS. 4 and 5 , cross-sectional views of the female electrical terminal  100  are shown according to some embodiments.  FIG. 4  is a cross-sectional view of the female electrical terminal  100  taken along line  2 - 2  shown in  FIG. 2 .  FIG. 5  is a cross-sectional view of the female electrical terminal  100  taken along line  3 - 3  shown in  FIG. 3 . 
     In the cross-sectional view shown in  FIG. 4 , the knurled contact pad  130  is located on an interior surface of top wall  110 . In some embodiments, the knurled contact pad  130  is located on a raised platform. For example, in the cross-sectional view shown in  FIG. 5 , contact pad  130  is located on a raised platform that extends into the interior of the housing  102  toward contact force spring  116 . A male electrical terminal—for example a blade-type connector such as  105  shown in  FIG. 1 —inserted into opening  115  is forced into contact with contact pad  130  by the contact force exerted by contact force spring  116 . The knurled surface of contact pad  130  ensures a plurality of contact points between the contact pad  130  and the blade-type connector  105 . In some embodiments, the knurled surface of the contact pad  130  includes a plurality of recesses or indents formed in the contact pad. As discussed in more detail below with respect to  FIGS. 6 and 7 , in some embodiments the plurality of recesses are fabricated using a press operation. Formation of each of the recesses using a press operation results in generation of a corresponding protrusion (shown in  FIG. 7 ) directed towards the contact force spring  116  that opposes the contact pad  130 . The blade-type connector  105  comes into contact with one or more of these protrusions extending from the knurled surface of contact pad  130 . Subsequent fretting caused by mechanical vibration between the contact pad  130  and the blade-type contact  105  may result in the points of contact between the blade-type contact  105  and the contact pad  130  changing from one or more first sets of protrusions to one or more second sets of protrusions. 
     In some embodiments, the contact pad  130  extends along a significant portion of the top wall  110 . For example, in some embodiments the contact pad  130  extends along at least 50% of the length of top wall  110 . In some embodiments the contact pad  130  extends along at least 75% of the length of the top wall  110 . 
     In some embodiments, contact force spring  116  is secured to an outer surface of bottom wall  106  via spring fixture  120  (shown in  FIG. 5 ) located on an exterior surface of bottom wall  106 . A first portion of the contact force spring  116  extends toward the opening  115  and then a second part extends into the opening and toward contact pad  130 . When the blade-type contact  105  is inserted into the opening, the contact force spring  116  is flexed, resulting in a contact force being generated by the contact force spring  116  that urges the blade type contact  105  into contact with the contact pad  130 . 
     Referring to  FIGS. 6 and 7 , the knurled surface of the contact pad is discussed in more detail according to some embodiments. In particular,  FIG. 6  is a magnified view of a portion of the knurled surface (portion  132 , shown in  FIG. 4 ) of contact pad  130 .  FIG. 7  is a cross-sectional view of knurled surface taken along line  6 - 6  as shown in  FIG. 6 . In some embodiments, the knurled surface is comprised of a plurality of recesses  140  formed on a surface of the contact pad  130 . In the embodiment shown in  FIG. 6 , the plurality of recesses  140  have a rhombus geometry. In other embodiments, various other geometries may be utilized to form the recesses  140 . In some embodiments, the knurled surface may include recesses having more than one size, depth, and/or geometry. Modifying one or more of the size, depth, and/or geometry of the recesses  140  may result in a modification of the plurality of protrusions  142  (shown in  FIG. 7 ) formed adjacent to the recesses  140  as a result of recess formation. In some embodiments, the recesses  140  are fabricated as part of the stamping process utilized for fabricate the contact pad  130 . In some embodiments, the knurl pattern is fabricated on the portion of contact pad  130  expected to come into contact with the male terminal. For example, in some embodiments the male terminal is a blade-type connector, wherein the width of the knurl pattern would be equal to or greater than a width of the blade-type contact  105 . 
       FIG. 7  is a cross-sectional view that illustrates a plurality of recesses  140  and corresponding plurality of protrusions  142  located adjacent each of the plurality of recesses  140 . In some embodiments, prior to the stamping process the contact pad has an essentially flat surface defined by plane P. In some embodiments, the plurality of recesses  140  are fabricated using a stamping process, which as a result of the recess fabrication generates a plurality of protrusions  142  adjacent each of the plurality of recesses  140 . The height of the plurality of protrusions  142  depend on the size, depth, and geometry of the plurality of recesses. Although the embodiment shown in  FIG. 7  includes approximately uniform depth of the plurality of recesses  140  and approximately uniform height of the plurality of protrusions  142 , in some embodiments the depth of the plurality of recesses  140  and the height of the plurality of protrusions  142  will exhibit variation. In some embodiments, variation in the height of the plurality of protrusions  142  is desirable to provide a plurality of initial contact points associated with a first plurality of protrusions located at a first height (i.e., greatest height) and a plurality of secondary contact points associated with a second plurality of protrusions. Fretting of one or more of the first plurality of protrusions first brought into contact with the male terminal results in one or more of the second plurality of protrusions being brought into contact with the male terminal. In this way, fretting of contact points does not result in a loss of electrical connection between the male terminal and the contact pad  130 . 
       FIG. 8  is a graph illustrating the height of the recesses  140  and protrusions  142  associated with the contact pad according to some embodiments. The planar surface of the contact pad  130  is assigned a reference height of zero. In some embodiments, the recesses  140  are defined by a depth of approximately negative twenty to negative forty micrometers (μm) and the protrusions  142  are defined by a height of approximately fifteen to twenty-five μm. In some embodiments, the recesses  140  having a depth that is greater than the height of the protrusions  142 . In some embodiments, this is a result of the press operation, in which a press including a plurality of protrusions is utilized to form the recesses  140 . The protrusions  142  are formed as a result of the movement of material in formation of the recesses  140 . One of the benefits of contact pad  130  is the non-uniformity associated with the heights of the plurality of protrusions  142 . For example, in the embodiment shown in  FIG. 8 , the protrusions  142  having the greatest height will create the first contact points between the contact pad  130  and the male terminal, while the protrusions having lesser heights will not (at least initially) be brought into contact with the male terminal. As the protrusions  142  having the greatest height fret and wear to the point of loss of contact with the male terminal, protrusions having lesser heights initially will be brought into contact with the male terminal. In this way, electrical contact is maintained between the contact pad  130  and the male terminal despite the presence of fretting and wear. 
       FIG. 9  is an isometric view of a blade type contact  900  that includes a knurled contact area  902  according to some embodiments. In contrast to embodiments shown—for example—in  FIGS. 4 and 5 , in the embodiment shown in  FIG. 9  the knurled surface of the male blade type connector  900  inserted into the opening associated with the female electrical terminal (not shown). In some embodiments, knurled contact area  902  includes a plurality of protrusions formed along a first surface to provide the desired knurling. In some embodiments, both a first side and a second side located opposite the first side of the blade type contact  900  may be knurled to ensure that regardless of the orientation of the blade type contact  900  the knurling will come into contact with the contact pad of the female electrical terminal. As discussed above, in some embodiments the knurled surface is created via formation of a plurality of recesses formed on the surface of the blade type connector  900 , which results in a plurality of protrusions being formed on the surface that provides the desired knurling of contact area  902 . In some embodiments, if the male blade type connector  900  includes a knurled contact area  902  then the contact pad located on the female terminal (not shown) may not include a knurled surface. That is, in some embodiments only one of the contact surfaces is knurled. In other embodiments, both the male blade type connector and the contact pad included as part of the female terminal may include knurled surfaces that interact with one another. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     According to some aspects, a female electrical terminal includes a securing end, a mating end located opposite the securing end along a longitudinal coupling axis, and a contact pad. The mating end further includes a housing provided with an opening configured to receive a male contact pad located within the housing and oriented to be brought into contact with the male contact received within the opening, wherein a surface of the contact pad includes a plurality of protrusions extending from the surface. 
     The female electrical terminal of the preceding paragraph can optionally include, additionally and/or alternatively any, one or more of the following features, configurations, and/or additional components. 
     For example, in some embodiments the plurality of protrusions may be non-uniform in height. 
     In some embodiments, one or more contact points may be formed between one or more of the plurality of protrusions and the male contact, and wherein the one or more contact points may migrate over time in response to fretting of original contact points. 
     In some embodiments, the contact pad may include a plurality of recesses. 
     In some embodiments, the plurality of protrusions may be formed in response to formation of the plurality of recesses. 
     In some embodiments, the plurality of recesses may be rhombus shaped. 
     In some embodiments, the housing may include at least a bottom wall, a top wall, and two side walls extending between the bottom wall and the top wall defining an opening for receiving the male contact, wherein the contact pad is located on an inner surface of the bottom wall or top wall. 
     In some embodiments, the female electrical terminal may further include a spring affixed to the top wall that extends into the opening within the housing, wherein the spring is placed in contact with the male contact to provide contact force between the male contact and the contact pad. 
     In some embodiments, the securing end may include a conductive wing and an insulator wing. 
     According to another aspect, a connection assembly may include a female electrical terminal and a male electrical terminal. The female electrical terminal may include a first end and a second end, the first end having an opening and a contact pad located within the first end, wherein a surface of the contact pad is knurled to provide a plurality of protrusions. The male electrical terminal includes a male contact that is received within the opening of the female electrical terminal and placed in contact with the contact pad, wherein electrical contact points are provided between one or more of the plurality of protrusions and the male contact. 
     The connection assembly of the preceding paragraph can optionally include, additionally and/or alternatively any, one or more of the following features, configurations, and/or additional components. 
     For example, in some embodiments the first end may include a housing defining the opening for receiving the male contact. 
     In some embodiments, the housing may include at least a top wall, a bottom wall, and two side walls extending between the top wall and the bottom wall, wherein the top wall, the bottom wall and the two side walls form the opening for receiving the male contact and wherein the contact pad is located on an inner surface of the bottom wall. 
     In some embodiments, the female electrical terminal may further include a spring affixed to the top wall that extends into the opening, wherein the spring provides contact force between the male contact and the contact pad. 
     In some embodiments, the plurality of protrusions may be non-uniform in height. 
     In some embodiments, the contact pad may include a plurality of recesses. 
     In some embodiments, the plurality of recesses may be rhombus-shaped. 
     According to another aspect, a male electrical contact includes a first surface and a second surface opposite the first surface. The first surface or the second surface may include a contact surface that includes a plurality of protrusions extending from the surface. 
     The male electrical contact of the preceding paragraph can optionally include, additionally and/or alternatively any, one or more of the following features, configurations, and/or additional components. 
     For example, in some embodiments, the plurality of protrusions may be non-uniform in height. 
     In another embodiment, one or more contact points may be formed between one or more of the plurality of protrusions and a contact pad associated with a female terminal. 
     In another embodiment, the contact surface may include a plurality of recesses. 
     In another embodiment, the plurality of protrusions may be formed in response to formation of the plurality of recesses.