Patent Publication Number: US-11646510-B2

Title: Shielding electrical terminal with knurling on inner contact walls

Description:
This patent application is directed to a shielding electrical terminal suitable for electrically interconnecting a shielded electrical cable, particularly a shielding electrical terminal with knurling on inner contact walls. 
     BACKGROUND 
     Electrical contact between terminals, such as the shielding electrical terminals used to terminate the shield conductors of shielded electrical cables, e.g., coaxial cable, typically relies on the creation of a contact force between the terminals. Shielding electrical terminals typically use one or several spring contacts arms to provide the contact force between the terminals. However, this arrangement usually provides a few small electrical contact points between the male and female shield terminals. Additionally, mechanical vibration between the respective components can cause fretting at the point of contact, eventually resulting in a loss or degradation, e.g., increase electrical resistance, of the electrical contact as the conductive material is worn away at the few small 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 the respective terminals while maintaining electrical contact in the presence of mechanical vibration/fretting and minimizing an air gap between the respective terminals. 
     SUMMARY 
     According to one or more aspects of the present disclosure, a shielding electrical terminal includes a securing portion configured to attach the shielding electrical terminal to an outer shield conductor of a shielded cable and a cylindrical mating portion having an inner surface configured to make electrical contact with a corresponding cylindrical shield terminal inserted within the mating portion. The inner surface defines a plurality of protrusions extending from the inner surface. 
     In one or more embodiments of the shielding electrical terminal according to the previous paragraph, the plurality of protrusions is non-uniform in height. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, the inner surface defines a knurled surface having a plurality of recesses and wherein the plurality of protrusions is arranged on perimeter edges of the plurality of recesses. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, each recess in the plurality of recesses is rhombus shaped. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, major axes of the plurality of rhombus shaped recesses are aligned generally parallel to a longitudinal axis of the shielding electrical terminal and minor axes of the plurality of rhombus shaped recesses are aligned generally perpendicular to a longitudinal axis of the shielding electrical terminal. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, an outer wall of the mating portion is continuous and does not define an aperture extending therethrough. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, an outer wall of the mating portion defines an axial slit aligned parallel to a longitudinal axis of the shielding electrical terminal. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, the mating portion and the securing portion are formed of a sheet of metal. A thickness of the sheet of metal forming the mating portion is equal to a thickness of the sheet of metal forming the securing portion. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, the mating portion is formed from a first sheet of metal and the securing portion is formed of a second sheet of metal. A thickness of the first sheet of metal is less than a thickness of the second sheet of metal. 
     In one or more embodiments of the shielding electrical terminal according to any one of the previous paragraphs, the plurality of protrusions is sized, shaped, and arranged to minimize an air gap formed between the inner surface of the mating portion and the corresponding cylindrical shield terminal inserted when inserted within the mating portion. 
     According to one or more aspects of the present disclosure, a method of forming a shielding electrical terminal is presented. The shielding electrical terminal formed by this method has a mating portion configured to make electrical contact with a corresponding cylindrical shield terminal inserted within the mating portion and a securing portion configured to attach the shielding electrical terminal to an outer shield conductor of a shielded cable. The method includes the steps of:
         a) forming a terminal preform from a first sheet of metal;   b) forming a plurality of protrusions in a surface of the terminal preform such that the plurality of protrusions extends from the surface; and   c) rolling the terminal preform into cylindrical shape, thereby forming the mating portion which has an inner surface configured to make electrical contact with a corresponding cylindrical male shield terminal inserted within the mating portion, wherein the surface is an inner surface of mating portion.       

     In one or more embodiments of the method according to the previous paragraph, plurality of protrusions is formed such that it is non-uniform in height. 
     In one or more embodiments of the method according to any one of the previous paragraphs, step b), forming a plurality of protrusions in a surface of the terminal preform such that the plurality of protrusions extends from the surface, further includes the step of:
         d) forming a plurality of recesses in the surface such that the plurality of protrusions is arranged on perimeter edges of the plurality of recesses.       

     In one or more embodiments of the method according to any one of the previous paragraphs, the plurality of protrusions and the plurality of recesses is formed using a knurling process. 
     In one or more embodiments of the method according to any one of the previous paragraphs, each recess in the plurality of recesses is rhombus shaped. The plurality of recesses is formed such that major axes of the plurality of rhombus shaped recesses are generally aligned parallel to a longitudinal axis of the shielding electrical terminal and the plurality of recesses is formed such that minor axes of the plurality of rhombus shaped recesses are aligned generally perpendicular to a longitudinal axis of the shielding electrical terminal. 
     In one or more embodiments of the method according to any one of the previous paragraphs, an outer wall of the mating portion is continuous and does not define an aperture extending therethrough. 
     In one or more embodiments of the method according to any one of the previous paragraphs, an outer wall of the mating portion defines an axial slit aligned parallel to a longitudinal axis of the shielding electrical terminal. 
     In one or more embodiments of the method according to any one of the previous paragraphs, the method further includes the step of:
         e) forming a securing portion from the first sheet of metal, wherein a thickness of the mating portion is equal to a thickness of the securing portion.       

     In one or more embodiments of the method according to any one of the previous paragraphs, the method further includes the step of:
         f) forming a securing portion from a second sheet of metal, wherein a thickness of the first sheet of metal forming the mating portion is less than a thickness of the second sheet of metal forming the securing portion.       

     In one or more embodiments of the method according to any one of the previous paragraphs, the method further includes the step of:
         g) inserting the corresponding cylindrical shield terminal within the mating portion, wherein the plurality of protrusions is sized, shaped, and arranged to minimize an air gap formed between the inner surface of the mating portion and the corresponding cylindrical shield terminal.       

    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG.  1    is a perspective view of a shielding electrical terminal and a corresponding mating shielding electrical terminal according to some embodiments; 
         FIG.  2    is a partial perspective view of the shielding electrical terminal of  FIG.  1    according to some embodiments; 
         FIG.  3    is a partial cross section view of the shielding electrical terminal of  FIG.  1    according to some embodiments; 
         FIG.  4    is a close-up view of knurling on an inner surface of the shielding electrical terminal of  FIG.  1    according to some embodiments; 
         FIG.  5    is a cross section view of the knurling of  FIG.  4    according to some embodiments; 
         FIG.  6    is a chart illustrating a height of the knurling of  FIG.  4    according to some embodiments; 
         FIG.  7    is a perspective view of a shielding electrical terminal according to some embodiments; 
         FIG.  8    is a cross section view of the shielding electrical terminal of  FIG.  7    according to some embodiments; 
         FIG.  9    is a perspective view of a shielding electrical terminal according to some embodiments; 
         FIG.  10    is an alternate perspective view of the shielding electrical terminal of  FIG.  9    rotated approximately 90 degrees about a longitudinal axis according to some embodiments; 
         FIG.  11    is a cross section view of the shielding electrical terminal of  FIG.  9    according to some embodiments; 
         FIG.  12    is a top view of a terminal preform used to form the shielding electrical terminal of  FIG.  9    according to some embodiments; 
         FIG.  13    is a schematic cross section view of the shielding electrical terminal of  FIG.  1 ,  7   , or  9  illustrating an air gap between the shielding electrical terminal of  FIG.  1 ,  7   , or  9  and a corresponding mating shielding terminal; and 
         FIG.  14    is a flow chart of a method for forming shielding electrical terminal according to some embodiments. 
     
    
    
     In the drawings, different versions of the elements of the various embodiments share the last two digits of the reference numbers. 
     DETAILED DESCRIPTION 
     A shielding electrical terminal is described herein and a method of forming such a terminal is described herein. The shielding electrical terminal is an outer shielding terminal configured to be connected to the shield conductor of one shielded cable and an inner shielding terminal that slides within the outer shielding terminal. Rather than having resilient contact arms to provide a contact force between the inner and outer shielding terminals, the outer shielding terminal has pattern of knurled features defining a plurality of protrusions and recesses on an inner surface. When the inner shielding terminal is received within the outer shielding terminal, these protrusions are in an interference fit condition with the inner shielding terminal, thereby providing a number of electrical contact points between the inner and outer shielding connectors. 
       FIGS.  1  through  5    illustrate a first example of an outer or female shielding electrical terminal, hereinafter referred to as the terminal  100 . The terminal has a securing portion  102  defining features that are configured to attach the terminal  100  to a shielded electrical cable (not shown). The terminal  100  also has a mating portion  104  that is mechanically and electrically connected to the securing portion  102 . The mating portion  104  has a hollow cylindrical shape and is configured to interconnect with a corresponding mating inner or male shielding electrical terminal  10  that is received within the mating portion  104 . The inner surface  106  of the mating portion  104  is knurled to define a plurality of recesses  108 , in the illustrated example rhombus-shaped recesses, that are surrounded by a plurality of protrusions  110  extending above the inner surface  106 . This plurality of protrusions  110  is formed by the displacement of material caused by the knurling process. The height of the protrusions  110  created by the knurling process is fairly random so that the plurality of protrusions  110  has a nonuniform height. Due to the rhombic shape of the recesses  108 , the height of the protrusions  110  above the inner surface  106  vary around the perimeter of the recesses  108  due to more material being displaced near the obtuse angled corners  112  of the recess  108  than at the acute angled corners  114  of the recess  108 . The height of the protrusions  110  above the inner surface  106  may also vary due to tolerance variations in the knurling process. The rhombus-shaped recesses  108  are arranged in offset rows and columns such that major axes of the rhombus-shaped recesses are aligned generally parallel to the longitudinal axis X of the terminal  100  and minor axes of the rhombus-shaped recesses are aligned generally perpendicular to the longitudinal axis X of the terminal  100 . As used herein “generally” parallel or perpendicular means ±10° of absolutely parallel or perpendicular. 
     When the mating terminal is received within the terminal  100 , at least a portion of the protrusions  110  on the inner surface  106  of the terminal are in an interface fit with the outer surface of the mating terminal. The highest protrusions  110  from the inner surface  106  of the terminal  100  are in mechanical and electrical contact with the outer surface of the mating terminal, thereby providing a plurality of electrical connections between the terminal  100  and the mating terminal which lowers the connection resistance and improves shielding efficiency. The protrusions  110  extend from the inner surface  106  at a height by a distance typically between 0.03 and 0.07 mm. As shown in  FIG.  13   , an air gap  12  between the terminal  100  and the mating terminal  10  is reduced to less than 0.1 mm, preferably less than 0.08 mm, more preferably less than 0.05 mm and even more preferably 0.03 mm, further improving shieling efficiency of the terminal and mating terminal connection. The protrusions  110  having different height also improve resistance of the terminal  100  to fretting corrosion since the higher protrusions  110  that may be degraded by fretting are replaced in contact of protrusions  110  that had an originally lower height than the initial protrusions  110  in contact. The recesses  108  may also serve as a repository for fretting corrosion debris so that the debris does not interfere in the electrical connection between the terminal  100  and the mating terminal. 
     Each projection in the plurality of projections  110  provides a possible electrical contact point between the mating portion  104  and the corresponding mating terminal. In addition, fretting of one or more of the contact points on the inside surface result in a new electrical contact point being created at a different projection on the inside surface since the height of the protrusions is nonuniform. In this way, fretting does not result in a loss or degradation of electrical contact between the respective terminals. Furthermore, a cost-effective and simple stamping process may be utilized to form the knurling, and hence the plurality of projections  110 , so that the formation of the plurality of projections  110  does not add significantly to the cost of the terminal. 
     In the example illustrated in  FIGS.  1 - 6   , an outer wall  116  of the mating portion is continuous, meaning that it does not define any holes, apertures, slits, slots, gaps, breaks, orifices, or openings, etc., except for the opening  118  on the end that receives the mating terminal. 
       FIG.  6    is a graph illustrating the height of the recesses  108  and protrusions in the mating portion  104  according to some embodiments. The inner surface  106  of the mating portion  104  is assigned a reference height of zero. In some embodiments, the recesses  108  are defined by a depth of approximately negative twenty to negative forty micrometers (μm) and the protrusions  110  are defined by a height of approximately fifteen to twenty-five μm. In some embodiments, the recesses  108  have a depth that is greater than the height of the protrusions  110 . In some embodiments, this is a result of the knurling process, in which a press including a patterned die is utilized to form the recesses. The protrusions  110  are formed as a result of the movement of material in formation of the recesses  108 . For example, in the embodiment shown in  FIG.  6   , the protrusions  110  having the greatest height will create the first contact points between the mating portion  104  and the corresponding mating terminal, while the protrusions  110  having lesser heights will not (at least initially) be in contact with the corresponding mating terminal. As the protrusions  110  having the greatest height fret and wear to the point of loss of contact with the mating terminal, protrusions  110  having lesser heights initially will be brought into contact with the mating terminal. In this way, electrical contact is maintained between the mating portion  104  and the corresponding mating terminal despite the occurrence of fretting and wear. It has been observed that forming the plurality of protrusions  110  on the inner surface of the mating portion protects them from being damaged by premature deformation during both the manufacturing process and shipping and handling of the terminal. 
       FIGS.  7  and  8    illustrate a second example of a shielding electrical terminal  200 . In this example the sheet metal forming the mating portion  204  is thinner than the sheet metal forming the securing portion  202  as best shown in  FIG.  8   . This provides the benefit of a lower insertion force for inserting the corresponding mating terminal within the mating portion  204  due to the lower hoop strength of the mating portion  204  provided by the thinner sheet metal while still providing attachment features in the securing portion  202 , e.g., crimping wings as shown in  FIGS.  7  and  8   , that are thick enough to securely attach the terminal to the shielded cable. The mating portion  204  defines an open-ended axial slit  220  extending parallel to the longitudinal axis X of the terminal  200  from the opening toward the securing portion  202 . This open-ended slit  220  decreases the hoop strength of the mating portion  204 , thereby reducing the mating engagement force. 
       FIGS.  9 - 11    illustrate a third example of a shielding electrical terminal  300 . In this example the mating portion  304  and the securing portion  302  are formed from a single sheet of metal and have the same thickness. The mating portion  304  defines a closed-ended slot  322  in the mating portion  304  extending parallel to the longitudinal axis X of the terminal  300 . This closed-ended slot  322  decreases the hoop strength of the mating portion  304 , thereby reducing the mating engagement force. A terminal preform  324  for the terminal  300  that is cut from the single piece of sheet metal is shown in  FIG.  12   . The terminal preform is attached to a tractor strip  326  that is used to handle the terminal preform  324  through the forming processes and later the fully formed terminal  300 . The tractor strip is then later removed from the terminal  300 . 
     While the illustrated terminals of  FIGS.  1  through  12    are arranged generally parallel or in line with the shielded cables, alternative embodiments of the terminals may be envisioned in which the terminals are generally arranged in at right angle to the cables. In yet other alternative embodiments of the terminal, the securing portion may be configured to be interconnected to conductive traces on a printed circuit board. In addition, while the example terminals illustrated in  FIGS.  1 - 12    have protrusions and recesses that define a rhombic shape, alternative embodiments may have other shaped such as square, rectangular, triangular, round, oval, etc. 
       FIG.  14    shows a flowchart of a method  400  of forming a shielding electrical terminal having a mating portion and a securing portion, such as one of the terminals described above. The method includes the steps of: 
     Step a), FORM A TERMINAL PREFORM FROM A FIRST SHEET OF METAL  402 , includes forming a terminal preform, e.g.,  324  from a first sheet of metal; 
     Step b), FORM A PLURALITY OF PROTRUSIONS IN A SURFACE OF THE TERMINAL PREFORM  404 , includes forming a plurality of protrusions  110 ,  210 ,  310  in a surface of the terminal preform, e.g.,  324  such that the plurality of protrusions extends from the surface. 
     Step c), ROLL THE TERMINAL PREFORM INTO CYLINDRICAL SHAPE  408 , includes rolling the terminal preform, e.g.,  324  into cylindrical shape, thereby forming a mating portion  104 ,  204 ,  304  which has an inner surface  106 ,  206 ,  306  configured to make electrical contact with a corresponding cylindrical male shield terminal inserted within the mating portion  104 ,  204 ,  304 ; 
     Step d), FORM A PLURALITY OF RECESSES IN THE SURFACE  406  is an optional sub-step of step b) that includes forming a plurality of recesses  108 ,  208 ,  308  in the inner surface  106 ,  206 ,  306  such that the plurality of protrusions  110 ,  210 ,  310  is arranged on perimeter edges of the plurality of recesses  108 ,  208 ,  308 ; 
     Step e) FORM A SECURING PORTION FROM THE FIRST SHEET OF METAL, WHEREIN A THICKNESS OF THE MATING PORTION IS EQUAL TO A THICKNESS OF THE SECURING PORTION  410 , is an optional step that includes forming a securing portion  302  from the first sheet of metal, wherein a thickness of the mating portion  304  is equal to a thickness of the securing portion  302 . The securing portion  302  is then attached to the mating portion  304  formed in step c); 
     Step f), FORM A SECURING PORTION FROM A SECOND SHEET OF METAL, WHEREIN A THICKNESS OF THE FIRST SHEET OF METAL FORMING THE MATING PORTION IS LESS THAN A THICKNESS OF THE SECOND SHEET OF METAL FORMING THE SECURING PORTION  412  is an optional step that includes forming a securing portion  202  from a second sheet of metal, wherein a thickness of the first sheet of metal forming the mating portion  204  is less than a thickness of the second sheet of metal forming the securing portion  202 . The securing portion  202  is then attached to the mating portion  204  formed in step c); and 
     Step g), INSERTING THE CORRESPONDING CYLINDRICAL SHIELD TERMINAL WITHIN THE MATING PORTION  414  is an optional step that includes inserting the corresponding cylindrical shield terminal  100 ,  200 ,  300  within the mating portion, wherein the plurality of protrusions  110 ,  210 ,  310  is sized, shaped, and arranged to minimize an air gap  12  formed between the inner surface  106 ,  206 ,  306  of the mating portion  104 ,  204 ,  304  and the corresponding cylindrical shield terminal  10 . 
     Accordingly, a shielding electrical terminal and a method of manufacturing such a shielding electrical terminal is provided. The terminal and the method provide the benefits over the prior art shielding terminals of improved shielding efficiency due to a lower connection resistance and reduced air gap between the terminal and the mating terminal. The terminal and the method also provide improve resistance of the terminal to fretting corrosion. The terminal and the method further provide a terminal with reduced mating force requirements to interconnect the terminal with the mating terminal, thereby improving ergonomics for the process of connecting the terminal with the mating terminal. 
     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 is not limited to the disclosed embodiment(s), but that the invention will include all embodiments falling within the scope of the appended claims.