Abstract:
A stud electrical connection method is provided that employs a stud having a patterned external surface and a nut operably secured to the stud in a radially compressive manner, wherein the patterned external surface of the stud comprises a nonconductive coating on a portion thereof. Accordingly, installation of the nut onto the stud creates an electrically conductive path between an attached conductive member and a panel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of co-pending U.S. provisional patent application Ser. No. 60/114,410, filed on Dec. 31, 1998, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to an electrical connection and more specifically to an electrical connection for an automotive vehicle employing a weld stud. 
     It is common to arc weld an enlarged circular end of a threaded metal stud onto a sheet metal body panel of an automotive vehicle. Various parts are then inserted upon the single threaded stud and an internally threaded nut is rotationally inserted onto the stud. However, the nut installation is a time-consuming process which often leads to undesirably varying fastening forces. 
     Conventional threaded weld studs have also been employed as electrical grounding points for a vehicle wire harness to an engine compartment frame or panel. Traditionally, after the stud is welded onto the panel, the vehicle is dipped into an E-coat bath to obtain a corrosion resistant coating and then a spray paint coating is robotically applied. An elastomeric or plastic cap is typically secured onto the stud during the E-coat and paint processes in order to prevent the non-conductive coatings from adhering to the otherwise electrically conductive stud. After painting, the cap is manually removed and then an electrical eyelet is inserted onto the stud. A conventional internally threaded nut is rotated onto the stud by a manually operated torque wrench to secure the eyelet. Alternately, the nut itself can be used in place of the cap during the coating processes, however, the nut must then be removed and then reinstalled after the eyelet is mounted to the stud. 
     Screws have also been used to retain an electrical eyelet to a grounding panel. Conventional eyelets require upturned tabs to prevent rotation of the eyelets during installation of nuts for the stud construction or when screws are installed. This adds extra cost and complexity to the eyelet. 
     These traditional constructions are very labor intensive, especially when multiplied by the number of ground studs used in the vehicle. Quality control and repeatability are also difficult to maintain due to under-torquing of the nut or screw, loss of nuts or screws, inadequate prevention of paint in the conductive path, and other intermittent electrical failure concerns, especially when the installation is occurring on a quickly moving vehicle assembly line. It is noteworthy that the paint and E-coat are prone to clogging the threads on these conventional nuts and thereby causing the torque wrench to reach a shut off torque prior to the desired clamp load. Cross threading also causes premature torque wrench shut off. 
     It is also known to use a pneumatic tool to swage and compress an unthreaded metal nut or sleeve over an arc welded stud in a torque-free manner. This torque-free construction employs a two-part stud, separated by a reduced diameter neck. The tool pulls off the threaded end after the nut is secured to the remaining threaded part of the stud. The nut can be unscrewed and reused. Notwithstanding, it is not believed that such a swaged nut and stud system has been used for an electrical connection or for grounding, especially where a paint prohibiting cap has not been employed. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a preferred embodiment of a stud electrical connection employs a stud having a patterned external surface and a nut operably secured to the stud in a radially compressive manner. In another aspect of the present invention, installation of the nut onto the stud creates an electrically conductive path between an attached conductive member and a panel. In a further aspect of the present invention, the stud is an electrically grounding weld stud. Yet a further aspect of the present invention creates an electrically conductive path between a stud coated by a generally nonconductive material and a conductive nut. A method of assembling an electrical system using a coated stud and a conductive member engaged onto the stud through swaging is additionally provided. 
     The stud electrical connection of the present invention is advantageous over conventional constructions in that the present invention achieves reliable electrical conductivity between a coated stud and a nut without the need for extraneous caps or rotational initial assembly steps. Thus, the present invention reduces assembly time and cost while improving electrical reliability in a very repeatable manner. Stud welding feeder reliability is also improved due to the use of longer than typical ground studs prior to severing of the tool gripping end of the stud. 
     The stud electrical connection of the present invention is further advantageous over conventional devices in that the present invention employs a low cost nut since it does not employ internal threads prior to insertion upon the stud. Engagement of the nut onto the threaded stud does not require any torque upon the nut, thereby reducing the likelihood of inadvertent fracture of the weld between the stud and adjacent panel. Anti-rotational tabs on the eyelet are also not necessary. Moreover, the nut can be unscrewed and reused. Installation of the present invention nut is significantly quicker than conventional pre-threaded nuts, since the traditional nut run-down time is not required. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an engine compartment of an automotive vehicle employing a first preferred embodiment of the stud electrical connection of the present invention; 
     FIG. 2 is an exploded perspective view showing the preferred embodiment stud electrical connection of the present invention; 
     FIG. 3 is a side elevational view showing the first preferred embodiment stud electrical connection of the present invention; 
     FIG. 4 is a partially fragmented, side elevational view showing the first preferred embodiment stud electrical connection of the present invention; 
     FIG. 5 is a fragmented side elevational view, taken within circle  5  of FIG. 4, showing a stud employed in the first preferred embodiment stud electrical connection of the present invention; 
     FIG. 6 is a fragmented cross sectional view, taken within circle  6  of FIG. 4, showing the first preferred embodiment stud electrical connection of the present invention; 
     FIG. 7 is a side elevational view showing a nut employed in a second preferred embodiment stud electrical connection of the present invention; 
     FIG. 8 is a side elevational view showing the preferred embodiment fastening tool used with the present invention stud electrical connection; 
     FIG. 9 is a partially fragmented and exploded, side elevational view showing the second preferred embodiment stud electrical connection of the present invention; and 
     FIGS. 10-13 are a series of partially fragmented, side elevational views showing the assembly sequence of the second preferred embodiment stud electrical connection of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a stud electrical connection  21  of the present invention employed in an engine compartment  23  of an automotive vehicle  25 . Stud electrical connection  21  is operable to conduct electricity from an electrical component, such as a battery  27 , direct current window wiper motor  29 , horn  31 , power distribution box  32  or the like to a conductive metal panel or frame  33  of the vehicle. 
     Referring to FIGS. 2 through 5, the first preferred embodiment of the stud electrical connection  21  includes a weld stud  51 , a nut  53 , also known as a sleeve member, and an electricity conductor  55 . Electricity conductor  55  is preferably a wire  57 , branching from a wire harness  59  (see FIG. 1) with a generally circular metal eyelet terminal  61  crimped on an end thereof. Wire  57  is made of a flexible copper inner wire surrounded by an insulative casing. 
     Stud  51  includes a circular flange  63 , extending in a lateral direction, a first threaded segment  65 , a neck  67  and a second threaded segment  69 . First threaded segment  65  has a M6.0×1.0 millimeter thread while second threaded segment  69  has a M5.0×0.8 millimeter thread. The threads define external engagement patterns on the stud. Furthermore, neck  67  has a reduced diameter and smaller lateral cross sectional area as compared to the threaded segments. Neck  67  is also provided with a 40 degree (total) angular taper x and a circumferential radius at the apex of the taper to define the reduced diameter section. Neck  67  has a breaking load of at least 500 kilograms and no more than 580 kilograms as applied in a linear manner along the longitudinal axis of stud  51 . Stud  51  is preferably made from SAE 1010 steel with a zinc finish and has a cold rolled thread. 
     The first preferred embodiment nut  53  has a circular-cylindrical section  81  and an enlarged diameter flanged section  83 . Nut  53  has a smooth and unthreaded internal aperture  85  prior to installation on stud  51 . Nut  53  is preferably made from SAE 1010 steel with a tin zinc finish for the engine compartment. 
     FIG. 7 illustrates a second preferred embodiment nut  153 . Nut  153  has an externally chamfered end  163 , a circular-cylindrical section  165 , a hexagonal wrench-receiving formation  167  and an enlarged diameter section  169 . Nut  153  also has a smooth and unthreaded aperture  171  prior to installation onto a second preferred embodiment stud  151  (see FIG.  9 ). 
     A pneumatically actuated fastening/setting tool  181  is shown in FIGS. 8-13. Tool  181  employs a piston cylinder  183  and trigger  185  to operate parts inside a nose  187 . Tool  181  uses a standard air pressure of about 85 or 100 psi to generate about 3,040-3,535 newtons of clamping force at the joint. Nose  187  of tool  181  further has a nose piece  189 , jaw case  191  and jaw  193 . 
     The sequence of fastening both preferred embodiment stud electrical connectors can be observed with reference to FIGS. 9-13. Exemplary stud  151  is fed into a collet of a weld head or gun (not shown) and the unit is cycled forward until the stud touches panel  33  thereby generating a “stud on work” signal to an electronic control unit. The weld gun subsequently lifts the stud approximately 1.2 millimeters off of the panel. A pilot arc is then generated to ionize an air gap between the proximal end of the stud and the panel. Next, the main welding current is turned on in order to generate molten material at the proximal end of the stud and at the surface of the panel. Finally, the weld gun then cycles forward to plunge the stud into the molten puddle of material. The molten weld puddle solidifies and the weld gun retracts, whereby the stud is permanently welded to the panel. 
     Next, eyelet  61  is coaxially aligned with and linearly inserted onto stud  151  whereby a hole within eyelet  61  is disposed around a first threaded segment  201  of stud  151 . Nut  153  is then linearly slid over a second segment  203  of stud  151  and onto first segment  201 . This can be observed by comparing FIGS. 9,  10  and  11 . Tool  181  is linearly inserted onto stud  151  and nut  153 . This step may be concurrent with the prior one. Referring to FIG. 11, second threaded segment  203 , acting as a mandrel, is received inside of jaw  193  while nose piece  189  and a distal end of jaw case  191  surround the cylindrical section of nut  153 . Next, jaw  193  firmly grips second threaded segment  203  while jaw case  191  linearly pushes nut  153  into desired abutting contact against eyelet  61 , creating a linear preload instead of torque. Thus, eyelet  61  is longitudinally sandwiched between an end of nut  153  and a flange  205  of stud  151 . 
     Jaw case  191  is caused to swage and radially compress the cylindrical section of nut  153  in an inward lateral manner thereby forming threads on the aperture of nut  153  (see FIG.  6 ). This advantageously causes identically matching threads and eliminates the traditional problem of cross-threading of misaligned pre-threaded nuts and studs. Moreover, the tool does not significantly apply any rotational or torquing force upon stud  151  or nut  153  during initial fastening; this preserves the secure relationship of stud  151  to panel  33  and achieves accurate tolerances and repeatable quality of fastening forces to panel  33 . 
     Finally, the comparison of FIGS. 11-13 demonstrates breaking of a neck  207  of stud  151 , wherein jaw  193  which still retains second threaded segment  203 , is linearly moved away from first threaded segment  201 . Second segment  203  is then discarded. Nut  153  can thereafter be unscrewed from stud  151  by use of a wrench. It is expected that nut  153  can be reusable infinitely as long as the threads are not stripped. 
     More specifically, the electrical grounding assembly or connector of the present invention for the second embodiment includes a grounding stud welded to a panel, such as a vehicle body panel, and a hollow collar for electrically connecting a connector to the panel. The connector includes a through-hole through which the stud passes. The collar is made of metal such as steel. The collar comprises a flange having a size larger than the through-hole of the connector and a body portion to be swaged onto the stud. In this embodiment, a tool engagement portion of a hexagonal configuration, as viewed from the top, is formed on the sides between the flange and the body portion. The tool engaging portion is engaged with a tool, such as a wrench or the like, to facilitate the rotation for removing the attached collar. The flange is not necessary if an outer diameter of the portion is larger than that of the through-hole of the connector. 
     The connector is connected to the panel in the following manner. An inner diameter of the body portion of the collar is initially formed slightly larger than an outer diameter of the stud so as to be easily inserted into the stud. Therefore, the placement of the component on the panel and the insertion of the collar into the stud can be easily done on one side of the panel. In order to swage the collar onto the stud, the body portion of the collar is supported by a nose grip of a blind rivet setting tool, or a similar tool, and the tip of the stud is held with jaws of the tool and then the tool is actuated. Despite the action of the jaws to pull out the stud, the stud is firmly welded to the panel and remains fixed since the reaction force is against the flange of the stud and not the weld. Thus, the collar body portion is swaged while the grip presses the collar against the panel so that the inner diameter of the body portion is reduced to fit into the threads of the stud. Thus, the collar is attached to the stud. This method is more completely explained in PCT Publication No. WO 94/01687 and U.K. Patent Application No. 2,274,697. 
     In particular accord with the method of this invention, the stud is welded to the panel at an early stage in the manufacturing process before the panel has been covered by a coating, such as an undercoat or paint. Subsequently, the panel including the stud, is subjected to a coating process (such as an E-coat dip or robotic spraying) and the threads of the stud become generally covered with an insulative and generally non-conductive layer. By applying the swaged nut onto the stud in accordance with the present invention, the swaging force drives the metal nut against the threads of the stud, thereby displacing and piercing the coating and providing proper electrical connection between the eyelet and stud. The cutting action of the painted threads into the sleeve or nut, clears away enough paint at the interface to create a very low resistance joint, less than 0.5 milliohms, thereby eliminating the need to cover the stud through the paint process at the assembly plant. 
     The electrical path can best be observed in FIGS. 4 and 6. When exemplary weld stud  51  is being employed as a grounding stud, the electricity will sequentially flow from the electrical component, through wire  57 , through eyelet  61 , through nut  53  (assuming that the paint coating insulates eyelet  61  from stud  51 ), into stud  51 , and to panel  33 . Although some paint or other coating may still be partially present between nut  53  and stud  51 , enough will be removed to create an acceptable electrically conductive path. 
     While various embodiments of the stud electrical connection have been disclosed, it should be appreciated that other aspects can be employed within the scope of the present invention. For example, the wire and eyelet disclosed can be replaced by other electrical conductors such as circuit boards or elongated stampings. Furthermore, the stud electrical connection can be used for non-automotive apparatuses such as household appliances, power tools or industrial machines. It is also envisioned that a traditionally pre-threaded nut and torquing action can be used with the present invention stud, although many of the advantages disclosed herein will not be achieved. The presently disclosed stud can also be mounted to a power distribution box or other electrical component instead of to a vehicle body panel; thus, electricity can flow in an opposite direction to that shown in FIG.  4 . It is envisioned that an electrical wire or conductor may be attached or soldered directly to the nut instead of employing a separate eyelet. Various materials and dimensions have been disclosed in an exemplary fashion, however, other material and dimensions may of course be employed. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of this invention.