Abstract:
The invention is a removable bolt holder for securing a terminal bolt to a power distribution box housing with the bolt positioned to accept a battery terminal and to secure the battery terminal to a bus bar, for example with a nut. The bolt holder is formed separately from the housing, preferably of a material which is more heat-resistant than the material of the housing. The bolt holder is provided with locking structure which allows a first bolt to be inserted shank first into a terminal engaging position, and which further allows a replacement bolt head to be inserted to release the locking connection with the first-inserted bolt. If the bolt is stripped or fractured during assembly the bolt can be removed from the holder without removing the holder from the housing. If the holder is damaged, the entire holder can be removed from the housing.

Description:
FIELD OF THE INVENTION 
     This invention is in the field of stud bolt terminal connections in the power distribution box of automotive vehicles. 
     BACKGROUND OF THE INVENTION 
     An electrical junction block or power distribution box is used in automotive vehicles to streamline wiring by eliminating multi-branch wiring. The power distribution box consolidates branch circuits and fuses, typically by incorporating bus bars into a housing to connect vehicle battery power to various electrical components serving the vehicle. The power distribution box often uses a stud bolt to connect a vehicle battery terminal to the bus bar. 
     In one type of conventional power distribution box, the stud bolt is molded into the plastic cover of the power distribution box. The insert molding process for joining the stud bolt to the cover, and the additional material needed, increases the manufacturing cost of the power distribution box and prevents replacement of a broken or stripped stud bolt. 
     A second type of conventional power distribution box shown in FIGS. 1 and 1A provides the stud bolt  140  as a separate component for direct attachment to a portion  100  of the power distribution box. Stud bolt holding features are molded into the plastic material of the box rather than insert molding the bolt into the box. Specifically, an open-ended, three-sided slot  100   a  is formed in the plastic wall of power distribution box housing  100 , for example during the molding process. Slot  100   a  is sized to receive a square-headed stud bolt  140  in a radially sliding fit from the side of the housing. Sidewalls  100   b  and recessed platform  100   c  in slot  100   a  define the final resting place for stud bolt  140 , engaging it in a close friction fit on three sides of the square head to prevent rotation. A bus bar  120  is subsequently assembled in essentially permanent fashion to housing  100 , with a terminal portion  120   a  lying in slot  100  over bolt  140 . An aperture  120   b  in bus bar  120  fits over the threaded shank of the stud bolt to radially secure the stud bolt in position. A battery terminal  160  is subsequently secured to terminal end  120   a  of bus bar  120  by being placed over the protruding threaded shank of the stud bolt, followed by a nut (not shown) threaded onto the bolt shank and torqued to compress terminal  160  against bus bar  120 . 
     Although the radial sliding fit of stud bolt  140  in slot  100   a  is intended to permit the removal and replacement of stud bolts stripped or broken during assembly, the essentially permanent attachment of bus bar  120  to housing  100  makes this difficult. 
     Another disadvantage with the stud bolt holding arrangement of FIGS. 1 and 1A is that the plastic material of housing  100  directly absorbs any heat created by electrical arcing at the stud bolt. Arcing is often caused by insufficient torque on the nut securing the terminal to the stud bolt and bus bar. This can result in damage to the housing itself. 
     Insufficient torque generally results from the relatively low strength offered by slot  100   a  against the tendency of stud bolt  140  to rotate as the nut is applied. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus and method for removably securing a stud bolt to the housing of a power distribution box, junction block, or similar device. In general, the invention is a separately-formed stud bolt holder adapted to be removably secured in a receptacle in the power distribution box (PDB) housing. The stud bolt holder is preferably made from material which is more heat-resistant than the material used for the PDB housing. However, the problem of potential arcing due to insufficient torque in the nut connection of a terminal to the stud bolt is greatly reduced by the greater ability of the stud bolt holder to withstand torque than stud bolt retention features molded directly into the PDB housing. 
     Because the stud bolt holder can withstand greater terminal-securing torque, the stud bolt threads are preferably sized to fracture before stripping to clearly indicate a failure to the person applying the nut. 
     In the event that the stud bolt is stripped or fractured during assembly, the stud bolt holder is configured to allow a replacement stud bolt to function as a disassembly tool. The removability of the stud bolt holder from the PDB housing makes it easier to get at a broken stud bolt for removal, and further allows the stud bolt holder itself to be replaced if damaged during assembly or by subsequent arcing at the terminal. 
     In carrying out this invention in an illustrative embodiment thereof, a stud bolt holder is sized to fit into an opening in a PDB housing under a bus bar contact plate. The holder is first inserted into the opening in the PDB housing from an underside of the housing. Latch projections in the opening mate with the exterior of the holder to removably secure the holder in the housing. The stud bolt is inserted shank first into the holder until the bolt head is locked in place by a set of resilient internal lock arms. At this point the shank extends from the holder through apertures in the bus bar and battery terminal. A nut is then threaded onto the shank and tightened with sufficient torque to secure the terminal against the bus bar in a reliable electrical connection. 
     If the stud bolt is stripped or fractured during assembly, another stud bolt can be inserted head first into the stud bolt holder until it abuts the head of the broken stud bolt. The internal lock arms in the holder are designed to be forced out of locking engagement with the broken stud bolt head by the replacement stud bolt head, such that a tap on the protruding shank of the broken stud bolt is sufficient to knock both the broken stud bolt and the replacement stud bolt out of the stud bolt holder. 
     These and other features and advantages of the invention will become apparent upon a further reading of the specification in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an assembly in which a stud bolt is secured to a PDB in a manner according to the prior art. 
     FIG. 1A is an exploded view of the components in FIG.  1 . 
     FIG. 2 is an exploded perspective view of a power distribution box and stud bolt holder according to the present invention. 
     FIG. 3 is a side elevation view, in section, of the stud bolt holder and stud bolt of FIG.  2 . 
     FIGS. 4 and 5 show the stud bolt holder of FIG. 3 being unlocked and a broken stud bolt removed using a replacement stud bolt as a disassembly tool. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, a power distribution box (PDB) assembly is illustrated. The assembly includes a molded plastic housing  10  having an upper side  12  and an underside  14 . The upper side  12  includes typical structure such as mini-fuse receptacles  16  and cavities  18  for larger fuses, relays and other known electrical components and connectors. The housing also includes a stud bolt receptacle  19  extending from underside  14  to upper side  12 . Stud bolt receptacle  19  includes a recessed shelf  22  serving as a rest or support for an electrical terminal  24  electrically connected to the ends of power supply cables  26  from a vehicle battery. Power cables  26  provide electrical power through terminal  24  to the electrical components mounted in the PDB receptacles and cavities, typically through a bus bar or similar conductor mounted in the PDB housing. 
     One such bus bar is illustrated at  30 . The bus bar is typically stamped or otherwise formed from conductive metal, with supporting male terminal blades  34 . Female-female terminals of known type (not shown) secured in the housing cavities receive male terminal blades  34  to connect the bus bar with male contacts from the electrical components. Apertures  36  located throughout the bus bar mate with locking projections of known type (not shown) in the housing to secure the bus bar in the housing. 
     It will be understood by those skilled in the art that the illustrated power distribution box and bus bar arrangement is merely a representative example, and that the stud bolt holder invention described below can be used with virtually any PDB/bus bar configuration employing a power terminal designed to be connected to the bus bar with a bolt. 
     It will also be understood that terms of orientation such as “upper side” and “underside” are used for convenient reference, and are not intended to limit the ultimate orientation of the components when assembled and placed in a vehicle. 
     The term “stud bolt” is a common term in the industry for the style of bolt illustrated, but is intended herein to encompass any bolt or stud capable of being used to secure a bus bar or similar PDB conductor to a battery terminal. 
     To power the components, and to prevent arcing, electrical terminal  24  needs to be securely connected to bus bar  30 . The bus bar accordingly includes a flat area or plate  38  adapted to receive terminal  24  in a mating electrical connection. Plate  38  and terminal  24  include aligned stud bolt apertures  42 ,  28 . When the bus bar is inserted into the housing from underside  14 , the plate  38  is pushed up through receptacle  19  to a final position substantially level with shelf  22 . Plate  38  thus provides a stable contact surface for terminal  24 . 
     Terminal  24  is next secured to bus bar plate  38  with stud bolt  44 . The illustrated stud bolt is an industry standard conductive fastener having a four-sided square head  46  with a flat top face  47  and a threaded shank  48 . Stud bolt  44  is retained in an inventive holder  50  which is used to position and hold bolt  44  within housing  10 . The holder has a body made from an electrically non-conductive, flame-retardant and heat-resistant plastic material. 
     As best shown in FIG. 3, the holder has a bolt-receiving passage or receptacle  52  extending between bolt insertion end  56  and terminal end  58 . Passage  52  is sized and shaped to closely receive square head  46  of the stud bolt in an axial sliding fit, and to prevent head  46  from rotating when a nut is threaded onto shank  48  and torqued in place. For this purpose, passage  52  is preferably square, although other shapes can be used. 
     Restraining arms  60  extend from the interior walls  54  of holder  50 , from base ends  62  integrally joining the arms to the interior walls adjacent bolt insertion end  56  of the holder, to free ends  64  near the terminal end  58  of the holder. Each arm has an intermediate portion  66  spaced from the interior wall of the holder by a gap  68 . Each arm further includes a cam surface  70  sloped or inclined from base portion  62  to free end  64  in a direction angled toward the stud bolt. Each cam surface ends in a notch or seat for receiving the top face  47  of the bolt head after the bolt head has been pushed past surface  70 . The illustrated seat is defined by two surfaces  72  and  74  extending generally at right angles to one another, although the configuration of the seat can vary according to the shape of the bolt head. 
     In the illustrated embodiment of FIG. 2, holder  50  is generally rectangular with four exterior sides and is adapted to be secured in stud bolt holder receptacle  19  in a mechanical snap-fit. For example, two opposite sides  80  of the holder are illustrated with a central groove  82  extending the length of the holder. The sides  80  include feet  84  at the bolt insertion end  56 , protruding from each corner. Remaining sides  86  have locking indentations  88 . To secure holder  50  in housing  10 , some or all of the feet  84  of the holder are gripped by the assembler. The upper, terminal end  58  of the holder is inserted into receptacle  19  at the underside  14  of the housing. Grooves  82  in the holder receive guides  20  from receptacle  19 , ensuring proper alignment and smooth, stable sliding insertion. When holder  50  is completely inserted in receptacle  19  as illustrated in FIG. 3, the holder locking indentations  88  receive the housing latch projections  23  and the holder is locked in the housing. However, the lock can be released and the holder removed from the housing by applying a firm pulling force on feet  84 . 
     Stud bolt  44  is inserted shank first through bolt insertion end  56  of the holder. Bolt head  46  contacts cam surfaces  70  of the arms  60 , forcing the arms apart toward the interior wall  54  of the holder. When the top face  47  of the bolt head reaches the seat surface  72 , the arms snap or flex back inwardly until their seat surfaces  74  contact respective sides of the bolt head. The seat surfaces  72  and  74  thereby axially and radially engage the bolt head with shank  48  extending from the terminal end of the holder. In the illustrated embodiment, each of the four sides of the bolt head is held by an arm  60 . 
     The stud bolt may be secured in holder  50  before or after the holder is secured to the PDB housing. 
     With the stud bolt fully inserted and secured in the holder, and the holder secured in the PDB housing, stud bolt shank  48  extends through aperture  42  in the bus bar plate  38  and aperture  28  in the electrical terminal  24  (FIG.  3 ). A nut  90  is then threaded onto the bolt shank to tighten terminal  24  on plate  38 , securing the parts together and establishing a reliable electrical connection. 
     The threads on shank  48  of the stud bolt are preferably selected, along with the size and material of the shank itself, to fracture before stripping in the event of over-torque. This provides a clear indication to the assembler that the terminal connection is broken or faulty, ensuring prompt replacement on the assembly line. 
     In the event of a fracture of the stud bolt shank  48 , stud bolt head  46  remains locked in holder  50 . 
     Stud bolt holder  50  is designed to permit rapid removal of a broken or stripped stud bolt from the locked position using nothing more than a replacement stud bolt as a disassembly tool. Referring to FIGS. 4 and 5, broken stud bolt  44   a  is shown being removed using a replacement stud bolt  44   b . Replacement stud bolt  44   b  is inserted head first (rather than shank first) into bolt insertion end  56  of the holder, until it abuts the face of broken stud bolt  44   a . In doing so, the head  46   b  of replacement bolt  44   b  forces arms  60  apart, thereby releasing the holder&#39;s locking connection on the broken stud bolt head  46   a . A tap or push on the end of the shank portion of broken stud bolt  44   a  is sufficient to push both the broken and replacement bolts back out of the holder through bolt insertion end  56  as best shown in FIG.  5 . Replacement stud bolt  44   b  can then be inserted shank first (rather than head first) back into the holder as shown in FIG. 3 to allow the electrical connection with the bus bar and battery terminal to be completed. 
     Although the illustrated embodiment shows the removal of a broken stud bolt from the holder being accomplished with a replacement stud bolt, it will be apparent that removal of the broken bolt could be achieved with a variety of tools. However, use of a replacement bolt as a disassembly tool is highly preferred. 
     The stud bolt holder  50  allows easy assembly of the power distribution box. Since the arms  60  and the four interior walls of passage  52  hold all four sides of the stud bolt head, the holder readily withstands the torque forces generated when tightening the nut. If the terminal  24  is poorly or incorrectly secured on the housing, arcing will melt rather than ignite the flame retardant material of the holder, which can then be easily replaced without damage to the PDB housing. If the bolt shank is stripped or broken, the bolt is easily replaced using a replacement bolt as the tool. 
     Since minor changes and modifications varied to fit particular operating requirements and environments will be understood by those skilled in the art, this invention is not considered limited to the specific examples chosen for purposes of illustration. For example, the stud bolt holder receptacle, the stud bolt holder, and the stud bolt head need not be square or rectangular as shown. The exact nature of the mechanical connection of the stud bolt holder to the PDB housing is not limited to the specific example shown, but can be achieved with a variety of cooperating structures and attachment methods known to those skilled in the art. The structure used in the holder to secure the stud bolt head can also vary provided that the stud bolt head is locked in place upon insertion, is prevented from rotating under torque from a nut, and is capable of being disengaged from the bolt head for replacement, preferably by using the head of a replacement bolt as a disassembly tool. These and other changes will be readily apparent to those skilled in the art in order to adapt the invention to a variety of power distributions box housings and bus bar conductor arrangements.