Abstract:
The present invention relates to an electrical thermostatic cord assembly and a method of manufacturing the same. The cord assembly includes an electrical subassembly, a protective cap, and a one-piece body. The electrical subassembly includes a thermally sensitive switch mechanism. The protective cap is disposed on at least a portion of the switch mechanism. The one-piece body is molded over the electrical subassembly such that a portion of the protective cap is exposed to allow the switch mechanism to respond to ambient temperature changes.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to electrically powered accessories for motor vehicles and, more particularly, to a cord for such electrically powered accessories.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various electrically powered devices are designed for use with vehicles, including automobiles, light duty trucks, and heavy duty vehicles. These devices, including cold weather starting devices such as radiant heaters, engine block heaters, fluid heaters, battery warmers, and the like, are generally fixed to the automobile and operationally connected to an appropriate component of the vehicle engine. Further, a cord is utilized to electrically connect the specified device to a power source such as an electrical outlet. Oftentimes, however, it is desirable to electrically connect the device to the power source while simultaneously having the ability to control the flow of electricity to the device based on a change in the ambient temperature. At least one system includes a thermostat within a circuit between the power source and the device. Such systems typically include the thermostat mounted to a portion of the automobile body. A first cord is run between the power source and the thermostat. A second cord is run between the thermostat and the device. Such a system can often be cumbersome, costly and difficult to assemble within an engine compartment of a vehicle.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention relates to an electrical thermostatic cord assembly comprising an electrical subassembly, a protective cap, and a one-piece body. The electrical subassembly includes a thermally sensitive switch mechanism. The protective cap is disposed on at least a portion of the switch mechanism. The one-piece body is molded over the electrical subassembly such that a portion of the protective cap is exposed to allow the switch mechanism to respond to ambient temperature changes.  
         [0004]     A further aspect of the present invention provides a method of manufacturing a thermostatic cord assembly having an integral temperature sensitive switch mechanism. The method generally includes electrically coupling a first prong, the switch mechanism and a first wire in series. A second prong is electrically coupled to a second wire and a third prong is electrically coupled to a third wire. A body is molded around a portion of each of the prongs and a portion of the switch mechanism such that the remaining portion of each of the prongs and the switch mechanism is exposed therefrom. In this manner, the switch mechanism is enabled to respond to an ambient temperature change.  
         [0005]     A yet further aspect of the present invention provides a method of manufacturing a thermostatic cord assembly. The method generally includes selecting a switch mechanism from a plurality of switch mechanisms having different characteristics where each switch mechanism is operable to close a circuit at a different temperature. Further, the method includes electrically connecting the switch mechanism to a first prong and molding a body portion around a portion of the first prong such that the remaining portion of the first prong is exposed therefrom to enable electrical connection to a power source.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a top plan view of a portion of an automobile schematically illustrating a thermostatic cord assembly according to the present invention;  
         [0009]      FIG. 2  is a perspective view of a first embodiment thermostatic cord assembly;  
         [0010]      FIG. 3  is a cross-sectional view taken through line III-III of  FIG. 2 ;  
         [0011]      FIG. 4  is a front plan view of the components of an electrical subassembly of the thermostatic cord assembly shown in  FIGS. 2 and 3 ; and  
         [0012]      FIG. 5  is a perspective view of a second embodiment thermostatic cord assembly.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0014]      FIG. 1  depicts a vehicle  10  including an engine  12  and a powered automobile accessory  14  such as an air intake heater. A thermostatic cord set  16  is electrically connected to the accessory  14  and terminates at a plug  18 . The plug  18  is mounted to a bumper or grill component  20  of the vehicle  10 . An auxiliary cord  22  includes a receptacle  24  for selectively interconnecting the thermostatic cord set  16  to a power source  26  via the plug  18 . The power source  26  includes an alternating current electrical outlet such as those generally mounted in walls of building structures.  
         [0015]      FIG. 2  depicts a first embodiment thermostatic cord set  16  including an electrical subassembly  28 , a protective cap  30 , a body  32 , a cord  34 , a neutral prong  36 , a ground prong  38  and a male connector  39 . Electrical subassembly  28  includes a hot prong  40 , a switch mechanism  42 , and a female connector  43 . The neutral prong  36  includes an insertion end  36   a  with an aperture extending therethrough and an attachment end  36   b  with a pair of crimp flanges  44 . The ground prong  38  includes an insertion end  38   a  and an attachment end  38   b  with a pair of crimp flanges  44 . The hot prong  40  includes an insertion end  40   a  with an aperture extending therethrough and an attachment end  40   b  having an attachment flange  46  (shown in  FIG. 3 ) with aperture  46   a  extending therethrough. The male connector  39  includes a male portion opposite a pair of crimp flanges  44 .  
         [0016]      FIG. 3  depicts the switch mechanism  42  fixedly attached to the hot prong  40  via a rivet  48  through aperture  46   a  in attachment flange  46 . Female connector  43  is coupled to the switch mechanism  42  with a rivet  48 . Female connector  43  includes a female receptacle receiving the male portion of the male connector  39 , as shown in  FIG. 2 . In an exemplary embodiment, the female receptacle includes a high retention, yet relatively low insertion force female disconnect receptacle such as that described in U.S. Pat. No. 5,181,866, assigned to Heyco Stamped Products, Inc., the disclosure of which is hereby incorporated by reference herein.  
         [0017]     The switch mechanism  42  includes a housing  49 , a switching member  52 , a plunger  54 , a lever  56 , a first contact  58 , a second contact  60 , and a thermally conductive membrane  62 . The housing  49  includes an annular ledge  49   a  and an external shoulder  49   b . The annular ledge  49   a  supports the switching member  52 . The lever  56  naturally biases open such that the plunger  54  applies an upward force on the switching member  52 , as illustrated in  FIG. 3 . This causes switching member  52  to deform. The switching member  52  is constructed of a material having a coefficient of thermal expansion within a predetermined range. Therefore, upon the ambient temperature decreasing to be within a predetermined range of temperatures, the switching member  52  decreases in length and becomes substantially planar. This causes the plunger  54  to apply a downward force on the lever  56 . A sufficient drop in ambient temperature, hence, causes the lever  56  to bridge the gap between the first contact  58  and second contact  60  and close the circuit therebetween. It should be appreciated that the switch mechanism  42  may be tuned to close the circuit within any desirable temperature range. For example, in one application, a switching member  52  having a first coefficient of thermal expansion may be utilized to close the circuit within a first predetermined temperature range. Alternatively, a switching member  52  having a second coefficient of thermal expansion different from the first coefficient of thermal expansion may be utilized to close the circuit within a second predetermined temperature range that is different than the first predetermined temperature range.  
         [0018]     The thermally conductive membrane  62  maintains the switching member  52  in engagement with the annular ledge  49   a  within the housing  49  of the switch mechanism  42 . In an exemplary embodiment, the thermally conductive membrane  62  includes a thin aluminum membrane. However, it should be appreciated that the thermally conductive membrane  62  may be constructed of any material sufficient to transfer changes in ambient temperature to the switching member  52 .  
         [0019]     The protective cap  30  includes a flat top portion  30   a , a cylindrical wall portion  30   b , and an external rim  30   c . The cylindrical wall portion  30   b  includes an inner shoulder engaging the external shoulder  49   b  of the housing  49  of the switch mechanism  42 . This secures the protective cap  30  thereon. As illustrated in  FIG. 3 , the body  32  of the plug  18  envelops the external rim  30   c  of the protective cap  30  to reinforce its maintenance on the switch mechanism  42 . The flat top portion  30   a  of the protective cap  30  is envisioned to be constructed of a thin thermally conductive polymer such that it serves to protect the thermally conductive membrane  62  from physical abuse, yet enables the switching member  52  to react to ambient temperature changes. It should be appreciated that while the protective cap  30  is disclosed herein as including a flat top portion  30   a  and a cylindrical wall portion  30   b , alternative protective caps  30  capable of serving the principles of the present invention are intended to be within the scope of the present invention. In an exemplary embodiment, the entire protective cap  30  is constructed via an injection molding process such that the flat top portion  30   a  is integral with the cylindrical wall portion  30   b.    
         [0020]     The body  32  is also constructed of a polymer via an injection molding process. The body  32  includes an insertion face  32   a , a central portion  32   b , and a cord portion  32   c . The body  32  includes a single structure enveloping portions of appropriate components of the plug  18 . Specifically, the insertion ends  36   a ,  38   a ,  40   a  of the neutral prong  36 , ground prong  38 , and hot prong  40  extend from the insertion face  32   a  of the body  32 . Furthermore, the flat top portion  30   a  of the protective cap  30  is exposed from the central portion  32   b  of the body  32 . This ensures the least amount of thermal insulation in the region of the switching member  52  of the switch mechanism  42 . Lastly, the cord  34  extends from the cord portion  32   c  of the body  32 . The cord  34  includes three wires  64  (as shown in  FIG. 2 ). In an exemplary embodiment the three wires  64  share a wire jacket. The three wires  64  are each crimped between the crimp flanges  44  of one of the neutral prong  36 , ground prong  38 , and male connector  39 . The cord  34  therefore is operable to transmit electricity to the automobile accessory  14 , as described above.  
         [0021]     During manufacture, a large spool of connector units  63  is unwound. As shown in  FIG. 4 , each connector unit  63  includes a neutral prong  36 , a ground prong  38 , and a male connector  39 . A first seam  66  attaches a side of the male connector  39  to one side of the ground prong  38 . A second seam  67  attaches an opposite side of the ground prong  38  to a side of the neutral prong  36 . This enables the neutral prong  36 , ground prong  38 , and male connector  39  to be detached from the spool as a connector unit  63 . It should be appreciated that an exemplary spool includes a multiplicity of connector units  63  attached together as a continuous belt.  
         [0022]     Next, a large spool of the cord  34  is unwound to a desired length and cut. An end of the cut cord  34  is stripped to expose the three separate wires  64 . The three wires  64  are inserted into the crimp flanges  44  on the male connector  39 , neutral prong  36 , and ground prong  38 . After insertion, a force is applied to crimp the crimp flanges  44  together, thereby securing the wires  64  thereto. In an exemplary embodiment, the three exposed ends of the wires  64  are simultaneously inserted into the crimp flanges  44  and secured therein. This helps reduce the processing time associated with manipulating each crimp flange  44  separately. The male connector  39  is then detached from the ground prong  38  at seam  66 . The ground prong  38  is then detached from the neutral prong  36  at seam  67 . Detachment is achieved by simply breaking the seams  66 ,  67  by hand or by machine.  
         [0023]     Next, with reference to  FIG. 3 , the hot prong  40  and female connector  43  are attached to the switch mechanism  42  to define electrical subassembly  28 . This includes providing rivets  48  through the hot prong  40 , female connector  43  and into engagement with the first  58  and second contacts  60 . This engagement is achieved using a typical riveting tool or machine as is commonly known in the art. The male portion of the male connector  39  is then inserted into the female portion of the female connector  43 . The protective cap  30  is then pressed over and secured on the thermally conductive membrane  62  of the switch mechanism  42 .  
         [0024]     The electrical subassembly  28  coupled to male connector  39 , as well as the neutral prong  36 , ground prong  38  and a portion of cord  34  are all placed within a mold cavity. The mold cavity defines the external geometry of the body  32  of the plug  18 . It is important to note that the insertion ends of the neutral prong  36 , ground prong  38 , and hot prong  40 , as well as the flat top portion  30   a  of the protective cap  30 , extend out of the mold cavity. With the aforementioned components in place, a semi-liquid polymer is injected into the mold cavity to form the body  32  of the plug  18 . Once the semi-liquid polymer cures, the plug  18  is removed from the mold cavity. Lastly, electrical connectors  65  are attached to the opposite end of the cord  34  (as shown in  FIG. 2 ). The electrical connectors  65  enable the cord  34  to be attached to the automobile accessory  14  described above.  
         [0025]     It should be appreciated that the hot prong  40 , switch mechanism  42 , female connector  43  and male connector  39  are connected in series to selectively provide power from power source  26  to accessory  14 . Furthermore, it should be appreciated that these components provide a mechanical robustness that aids in the manufacturing process described above. Because these components are rigidly connected via the rivets  48 , the electrical subassembly  28  is more capable of supporting itself within the mold cavity prior to molding the body  32 .  
         [0026]      FIG. 5  depicts an alternative embodiment of a plug  118  in accordance with the principles of the present invention. The plug  118  of the second embodiment is substantially similar to the plug  18  of the first embodiment. The plug  118  includes an electrical subassembly  128 , a protective cap  130 , a body  132 , a cord  134 , a neutral prong  136 , a ground prong  138  and a hot prong  140 . The electrical subassembly  128  includes a switch mechanism  142  and a jumper wire  147 . Similar to that described above with reference to the first embodiment, the switch mechanism  142  is electrically connected in series with the hot prong  140 . However, the hot prong  140  does not extend to and rigidly attach with a first contact (not shown) of the switch mechanism  142 . Rather, the jumper wire  147  provides the electrical connection between the hot prong  140  and the switch mechanism  142 . Furthermore, the switch mechanism  142  does not include a female connector  43  attached to the second contact (not shown). Therefore, one of wires  164  of the cord  134  directly connects to a second contact (not shown) on the switch mechanism  142 . It should be appreciated that the switch mechanism  142  is otherwise identical to the switch mechanism  42  described above in accordance with the first embodiment.  
         [0027]     The method of manufacturing the plug  118  is substantially similar to manufacturing the plug  18  described above, with an exception to the assembly of the electrical subassembly  128  and connection of male connector  39  to the electrical subassembly. Specifically, the switch mechanism  142  is connected with the hot prong  140  via the jumper wire  147 , as opposed to the rigid connection established with the rivet  48 . It is envisioned that one end of the jumper wire  147  is attached to the hot prong  140  and the opposite end of jumper wire  147  is coupled to the switch mechanism  142  using solder or a similar material. Furthermore, one of the wires  164  of the cord  134  is directly connected to an opposite side of the switch mechanism  142 , as opposed to the rigid connection established by the female connector  43  and male connector  39  of the first embodiment. This connection is also envisioned to be achieved via the use of solder or some similar material.  
         [0028]     The remainder of the manufacturing process is generally identical to that disclosed with reference to the first embodiment. The neutral prong  136 , ground prong  138 , hot prong  140 , jumper wire  147 , electrical subassembly  128  and a portion of the cord  134  are all positioned within a mold cavity. A semi-liquid polymer is then injected into the mold cavity to form the body  132 . Once the polymer cures, the plug  118  is removed from the cavity and electrical connectors  165  may be attached to the opposite end of the cord  134  in preparation for use with the vehicle accessory  14 .  
         [0029]     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without department from the spirit and scope of the invention as defined in the following claims.