Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a rotary connector, and particularly to a rotary connector having an alignment feature and/or an overcurrent protection feature. 
   2. Discussion of the Background 
   A rotary connector is used as a connector device for a flexible transmission medium that transfers electrical signals, optical signals, electric power, etc. between a stationary member and a rotating member rotating relatively to the stationary member within a limited range of rotational number. In this rotary connector, a flexible flat cable is housed in the form of a spiral connector within an annular space defined by a rotating case and a stationary case, which are combined for rotation. Alternatively, U.S. Pat. No. 5,310,356 assigned to The Furukawa Electric Co., Ltd discloses a flexible flat cable is housed in a rotary case in the form of stationary windings along the inside wall of the stationary member, then reversing direction via a U-shape turn, and continuing as rotating windings along the outside wall of the rotational member. The entire contents of U.S. Pat. No. 5,310,356 are incorporated herein by reference. Opposing ends of the flexible flat cable are connected to the rotating case and stationary case respectively, and the rotating case is allowed to rotate relatively to the stationary case as the flat cable is coiled and uncoiled simultaneously from the respective side walls of the rotary connector. 
   The rotary connector is typically required to be in a neutral position when mounted in a final assembly. The neutral position is usually a center position in the range of rotational movement of the rotary connector so that the rotary connector can be rotated the same number of rotations (i.e. angular rotational range) in both the clockwise and counterclockwise direction without damaging the flexible flat cable fixed to the stationary and rotary part of the rotary connector. That is, the neutral position allows the same number of functional rotations in either direction. In mounting the rotary connector in the steering apparatus of an automobile, for example, the steering wheel is adjusted to a straight-advance position as the neutral position connector is set into the steering apparatus. Thus, the steering wheel is free to operate the steering apparatus without causing a strain (or breaking) the flexible flat cable. 
   Because the rotary connector is provided as a subcomponent of a final assembly, such as a steering wheel assembly, the rotary connector is typically fixed in the neutral position until placed in the final assembly, where the rotary connector is made free to rotate in the assembly. Fixing in the neutral position is typically provided by a fixing pin having retaining hooks, called snap fits, that are removably mounted extending between mounting portions on the rotating and stationary cases, or by a seal that is pasted on both the cases. An example of a fixing mechanism is disclosed in U.S. Pat. No. 5,257,943, the entire content of which is incorporated herein by reference. 
   Conventional methods of fixing or sealing the rotary connector are problematic, however, in that it is difficult to verify that the connector is actually in the neutral position at the time of assembly. While the rotational and stationary part of the connector may have alignment marks that indicate the relative position of these parts when they are in the neutral position, because the rotational connector can make several complete rotations, the alignment marks may be aligned in positions other than the neutral position. Therefore, if the fixed or sealed neutral position is broken during transport of the rotary connector to the place of final assembly, for example, the neutral position cannot be found by using the alignment marks. Moreover, even if the fixed or sealed neutral position is not broken, it cannot be visually verified at final assembly that the rotary connector is actually in the alignment position corresponding to the neutral position. 
   Over current protection for the flexible flat cable has conventionally been provided by a fuse housed in a fuse box mounted on the final assembly such as a vehicle chassis. Such a fuse box is typically bulky and requires additional wiring from the rotary connector, which leads to additional material and assembly cost. Moreover, the fuse box may be accessible to an inexperienced user of the final assembly, which may lead to the wrong fuse being provided in the fuse box. Where the replaced fuse is rated lower than the proper fuse rating, premature blowing of the fuse may occur. More importantly, where the replaced fuse is rated higher than the proper fuse rating, excessive heat and even fire may result. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to mitigate any or all of the above-described problems. 
   Another object of the present invention is to provide a rotary connector that allows simple verification of a neutral position of the rotary connector. 
   Yet another object of the present invention is to provide a rotary connector having a simple and compact overcurrent protection feature. 
   These and other objects of the present invention are provided by a rotary connector. According to one aspect of the invention the rotary connector includes a first part, a second part configured to rotate relative to the first part, and an electrical cable housed within the rotary connector. A viewing window is configured to reveal a feature of the electrical cable when the rotary connector is in a neutral position. 
   In another aspect of the invention a steering wheel assembly includes a rotary connector including a first part, a second part configured to rotate relative to the first part, and an electrical cable housed within the rotary connector. A viewing window is configured to reveal a feature of the electrical cable when the rotary connector is in a neutral position. 
   In still another aspect of the invention, a method of manufacturing a rotary connector includes providing first and second parts of the rotary connector that can be rotationally coupled to one another, and providing a flexible cable that can be housed within the rotary connector when the first and second parts are rotationally coupled to one another. The flexible cable in a predetermined arrangement within the rotationally coupled first and second parts such that a feature of the flexible cable is visible from an exterior of the rotary connector when the first part is in a neutral position relative to the second part. 
   Another aspect of the invention includes a rotary connector includes a stationary case, a rotating case configured to rotate relative to the stationary case, an electrical cable housed within the rotary connector, and means for indicating a neutral position of the rotary connector. 
   Still another aspect of the invention is a method of identifying a neutral position of a rotary connector. The method includes rotating a first part of the connector relative to a second part of the connector such that through holes in the first and second part are substantially aligned to reveal an interior annular space of the rotary connector. The first and second parts of the connector are positioned such that a feature of an electrical cable housed in the interior annular space is visible to indicate a neutral position of the rotary connector. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a rotary connector in accordance with one embodiment of the present invention; 
       FIG. 2  is a partial cross-sectional view taken along line A—A of  FIG. 1 ; 
       FIG. 3  is an exploded view of the rotary connector showing the interrelation of parts included in a rotary connector assembly according to one embodiment of the present invention; 
       FIG. 4  is an illustration of a flexible flat cable assembly used with the a rotary connector in accordance with one embodiment of the present invention; 
       FIGS. 5–7  are illustrations showing various constructions of a flexible flat cable that may be used in accordance with the present invention; 
       FIGS. 8A and 8B  are front views of the rotary connector  1  that illustrate the use of viewing window and U-shaped bend  20 C to indicate a neutral position of the rotary connector, in accordance with one embodiment of the present invention; 
       FIG. 9  shows a multiple conductor flexible flat cable used in prior art rotary connectors; 
       FIG. 10  shows a single ribbon flexible flat cable used in accordance with an embodiment of the present invention; 
       FIG. 11  is a drawing of a high current capable rotary connector having an integral blade fuse in accordance with one embodiment of the present invention; 
       FIG. 12  is an enlarged drawing showing details of the blade fuse area of the rotary connector in accordance with one embodiment of the present invention; 
       FIG. 13A  is a drawing showing the configuration of a prior art bus bar assembly; 
       FIG. 13B  is a drawing showing the configuration of a bus bar assembly in accordance with an embodiment of the present invention; 
       FIG. 14  is a drawing showing a detailed configuration of a bus bar assembly having a surface mount fuse in accordance with one embodiment of the present invention; and 
       FIG. 15  is a drawing showing a detailed configuration of a bus bar assembly having a Pico fuse in accordance with one embodiment of the present. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings,  FIG. 1  is a perspective view of a rotary connector in accordance with one embodiment of the present invention, and  FIG. 2  is a partial cross-sectional view taken along line A—A of  FIG. 1 . As seen in  FIG. 1 , the rotary connector  1  includes a rotating case  10  and a stationary case  11 . The rotating case  10  includes an inner cylinder shaft portion  10 A and an upper flange  10 B. The upper flange  10 B includes a rotating junction  10 C, which provides electrical connection of a cable (not shown in  FIG. 1 ) housed in the connector to an external electrical system. In the embodiment of  FIG. 1 , the rotating junction  10 C includes wires  12 , however pins may also be used. The upper flange  10 B of the rotating case  10  further includes a through hole  10 D positioned at a predetermined radial position on the upper flange  10 B. 
   As best seen in  FIG. 2 , the stationary case  11  includes an outer cylinder wall  11 A, an upper flange  11 B and a lower flange  11 C. The upper flange  11 B is provided with a through hole  11 D. The through hole  11 D is positioned at substantially the same radial position as the through hole  10 D so that these through holes overlap one another when rotated to the same angular position. Overlapping of the through holes  10 D and  11 D creates a window  1 A that allows visual indication of a flexible flat cable within an annular space of the rotary connector  1  as will be further described below. Referring again to  FIG. 1 , the stationary case  11  includes a plurality of mounting flanges  11 E arranged at suitable positions on the outer cylinder wall  11 A for fixedly mounting the stationary case  11  on an assembly such as a vehicle-body. Also arranged on the outer cylinder wall  11 A of the case  11  is a stationary junction  11 F, which provides electrical connection of the cable housed in the rotary connector  1  to an external electrical system. In the embodiment of  FIG. 1 , the stationary junction  11 F includes wires  13 , however, pins may also be used. 
     FIG. 3  is an exploded view of the rotary connector showing the interrelation of parts included in a rotary connector assembly according to one embodiment of the present invention. As seen in this figure, the rotary connector assembly includes a rotating case  310 , a stationary case  311 , a flexible flat cable  320  and a separable stationary flange  311 C. The rotating case  310  includes a rotating junction  310 D and the stationary case  311  includes a stationary junction  311 F. As seen in  FIG. 3 , the flexible flat cable  320  includes four separate flat cables bent to form U-shapes  320 C. The stationary case  311  joins with the stationary flange  311 C along the dashed assembly line in  FIG. 3  to form an integral unit defining an annular space that the flexible flat cable  320  is contained in. The rotating case  310  is then rotationally coupled to the stationary case  311 . As with the embodiment of  FIGS. 1 and 2 , the rotating case  310  and the stationary case  311  include a rotating through hole  310 D and a stationary through hole  311 D respectively. The through hole  311 D is positioned at substantially the same radial position as the through hole  310 D so that they overlap one another when rotated to the same angular position. While not shown in  FIG. 3 , in the final assembly of the rotary connector, one end of the flexible flat cable  320  is connected to the rotating junction  310 D of the rotating case  310 , and an opposing end of the cable  320  is connected to the stationary junction  311 F of the stationary case  311 . 
     FIG. 4  is an illustration of a flexible flat cable assembly used with a rotational connector in accordance with one embodiment of the present invention. One end of the flexible flat cable  420  includes rotational junction  410 D having male pins  412 , while an opposing end of the flexible flat cable  420  includes stationary junction  411 F having male wires or pins or wires  413 . In the embodiment of  FIG. 4 , the male pins or wires  412  and  413  are suitable for connecting the flexible flat cable  420  to female electrical connectors of external wires. As with the embodiment of  FIG. 3 , the flexible flat cable  420  of  FIG.4  includes four flat wires that are housed within the annular space of the rotary connector. However, it is understood that the number of flat wires in the cable assembly may be changed depending on the electrical requirements of the assembly that the flexible flat cable is used with. Moreover, in one embodiment of the present invention, the rotary connector has a fixed number of flat wires, with a predetermined number of flat wires being electrically active based on the electrical requirements of the assembly, and remaining cables being “dummy cables” that act as spacers. 
   As seen in  FIG. 4 , the flat wires of the flexible flat cable  420  are housed such that each wire has some of its length wrapped around the inner cylinder shaft portion  10   a  of the rotating case  10  shown in  FIG. 1 , for example. Each wire of the flat cable  420  is then turned back upon itself to form a U-shape  420 C so that the remainder of the flexible flat cable length is wound inside the outer cylinder wall  11   a  of the stationary case  11  in an opposite direction. The U-shape bend  420 C of one of the flat wires of the flexible flat cable  420  acts as an indicator that the rotary cable is in a neutral position as will be further described below. 
   The flat cable of  FIGS. 3 and 4  is a flexible belt-shaped transmission medium for transmitting electrical signals, optical signals, electric power, etc. As shown in  FIG. 5 , for example, the cable  520  is an electrical transmission medium that includes a plurality of flat rectangular electrical conductors  520 A, arranged parallel to one another. In the embodiment of  FIG. 5 , an insulator  520 B, such as a polyester film, covers the conductors  520 A to electrically insulate them from one another.  FIGS. 6 and 7  show alternative constructions of a flexible flat cable that may be used in accordance with the present invention. As seen in  FIG. 6 , a cable  620  is an electrical transmission medium that includes a plurality of electrical conductors  620 A, having a circular cross section and arranged parallel to one another. An electrical insulation material  620 B covers the conductors  620 A. In  FIG. 7 , a flat cable  720  is a light transmission medium in the form of a tape fiber that includes a plurality of optical fibers  720 A for transmitting optical signals. A covering material  720 B covers the fibers  720 A and provides a flexibility to the cable. Still alternatively, the flat cable may be a combination of an electrical transmission medium and a light transmission medium, in which case the cable includes electrical conductors and optical fibers covered by an insulation material. In one embodiment of the present invention, a single conductor ribbon wire may be used for the flexible flat cable, as will be described with respect to  FIG. 10  below. 
   As noted above, viewing of the U-shaped bend of the flexible flat cable within the window provides an indication that the rotary connector is in a desired neutral position.  FIGS. 8A and 8B  are front views of a rotary connector  1  that illustrate the use of viewing window and the U-shaped bend to indicate a neutral position of the rotary connector, in accordance with one embodiment of the present invention. In  FIGS. 8A and 8B , the rotary connector  801  is positioned such that the through hole of the rotating case overlaps the through hole of the stationary case to form viewing window  801 A that allows viewing of the interior annular space of the rotary connector  801 . 
   As seen in  FIG. 8A , there is no flat cable bend visible within the viewing window  801 A, which indicates that the rotary connector  801  is not in its neutral position. That is, the rotary case is in a position relative to the stationary case, other than the neutral position. While  FIG. 8A  shows no visibility of the flexible cable  820  in the window  1 A, one of ordinary skill in the art would understand that a portion of the cable  20  other than the U-shaped bend  20 C may be visible in the viewing window  801 A. In such a situation an orientation of the cable  820  will make clear that the portion of the cable  820  in the window  801  is not the bend  820 C, and therefore, the rotary connector is not in its neutral position. However, where the rotary case is rotated relative to the stationary case such that the U-shaped bend  820 C is within the viewing window  801 A, the rotary connector  801  is in the neutral position as shown in  FIG. 8B . 
   Thus, according to the present invention, the rotating case  10  is in a neutral position relative to the stationary case  11  when the through holes  10 D and  11 D are aligned to form viewing window  1 A, and one of the U-shaped bends  20 C of the cable  20  is visible within the viewing window  1 A. In order for the alignment of the viewing window  1 A and the cable bend  20 C to correspond to the neutral position, the through holes  10 D and  11 D must be positioned in a predetermined position on the rotary connector, and the length of the flexible flat cable  20  must correspond to the positioning of the viewing window  1 A as well as the rotational range (i.e. the maximum number of turns or angular rotation) of the rotary connector. That is, where the rotary connector  1  has a rotational range of several turns, the viewing window will appear with each 360 degrees of rotation, but the length of the flexible flat cable  20  is selected such that a bend  20   c  will appear in the viewing window only when the connector is in the desired neutral position. 
   For example, in the embodiment of the present invention shown in  FIG. 3 , the flexible flat cable  320  is 805 mm long and the viewing window formed by the through holes  210 D and  311 D is located at approximately 2 o&#39;clock when referenced to a clock face, if viewed from the vehicle driver&#39;s position in the case of an automobile application. With this configuration, the rotary connector will have a rotational range of approximately +/−2.5 turns and the cable bend  320 C will appear in the viewing window at approximately 2.5 turns from each end of the functional rotational range. This identifies the functional center of the rotary connector and the neutral position. It is to be understood, however, that the present invention is not limited to this specific example, and the rotational range of the connector may be any number of turns with the desired neutral position being other than the functional center of the connector. 
   More specifically, in one embodiment of the present invention, the cable lengths L 1 , L 2 , L 3  and L 4  of the present invention have four progressively longer lengths. The cable lengths may be determined by the following calculations:
 
 L   1 =*length to make bus bar (rotor side)+(2.5)(π)( d   r )+(0.5)(π)(( d   s   −d   r )/2)+(2.5)(π)( d   s )+*length to make bus bar (stationary side).
 
 L   2 =*length to make bus bar (rotor side)+(2.75)(π)( d   r )+(0.5)(π)(( d   s   −d   r )/2)+(2.75)(π)( d   s )+*length to make bus bar (stationary side).
 
 L   3 =*length to make bus bar (rotor side)+(3)(π)( d   r )+(0.5)(π)(( d   s   −d   r )/2)+(3)(π)( d   s )+*length to make bus bar (stationary side).
 
 L   4 =*length to make bus bar (rotor side)+(3.25)(π)( d   r )+(0.5)(π)(( d   s   −d   r )/2)+(3.25)(π)( d   s )+*length to make bus bar (stationary side).
 
Where:
     *length varies due to external design factors   d r =outside diameter of rotational member   d s =inside diameter of stationary member]   

   In addition, the calculation of cable lengths may account for the thickness of the cable. Referring to  FIG. 4 , the distance from the outer circle of the cables to the stationary junction  411 F and the distance from the inner circle to the rotating junction  410 D are the “lengths to make bus bar”. These distances can vary from design to design and cannot be formulated as with the diameters. 
   Centering of the rotary connector to a neutral position will be described with respect to the rotary connector  1  shown in  FIG. 1 . Centering to the neutral position is preferably accomplished by turning the rotary case  10  in a clockwise direction. Rotation is complete when the rotary connector  1  has depleted the flat cable  20  windings along the inner wall  11   a  of the stationary case  11  and begins to pull at the junction  11 F. The pulling of the flat cable  20 , at the stationary junction  11 F is readily discernable as the operating torque of the rotary connector  1  is very low (typically &lt;0.1 Nm) and the end of travel for the flat cable  20  feels much like the rotary connector  1  has been snagged. Once the end of rotational travel has been established, the rotating case  10  is to be counter-rotated (2.5–3.0 turns in a preferred embodiment) until the through hole  10 D of the rotating case  10  aligns with the through hole  11 D of the stationary case  11 , creating a centering window  1 A. When the U-shape turn  20 C of the flat cable  20  appears in the centering window  1 A the rotary connector  1  is properly centered within its functional rotational limits, i.e. its neutral position. 
   In one embodiment of the present invention, the rotary connector may be provided with a fixing mechanism such as that described in U.S. Pat. No. 5,257,943, which is incorporated herein by reference. In accordance with the present invention however, if the fixing mechanism for fixing the rotary connector in a neutral position is broken during transport of the rotary connector to the final assembly, the neutral position can be easily found at the place of final assembly. Moreover, the fixing mechanism may be eliminated from the rotary connector to save material and assembly costs. Finally viewing the U-shaped bend at the flexible flat cable in the viewing window provides visual assurance at the final assembly that the rotary connector is actually in a neutral position. 
   In one embodiment of a rotary connector, the flexible cable within the connector may require overcurrent protection. As noted in the background section above, prior art rotary connectors provided such overcurrent protection by a fuse contained in a separate fuse box that was bulky and unsightly, and readily accessible to any user of the assembly that the rotary connector was applied to. The present inventors recognized that the need for housing the fuse in an external fuse box was due to space considerations within the rotary connector. More specifically, the present inventors discovered that the prior art use of multiple conductor flexible flat cables to provide high current capability required the use of multiple fuses to provide overcurrent protection of the cable. 
     FIG. 9  shows a multiple conductor flexible flat cable typically used in prior art rotary connectors. As seen in this figure, the prior art cable includes input bus bar  901 , input cable length  903 , input bus bar  905 , load  907 , output bus bar  909 , output cable length  911 , and output bus bar  913 . The input components,  901 ,  903  and  905  carry current to the load  907 , and the output components  909 ,  911 , and  913  carry current away from the load  907 . For example, the input components may carry high current from chassis wires of an automobile to a resistive heating coil of a heated steering wheel in an automobile, while the output components provide current to return wires in the chassis of the automobile. 
   As seen in  FIG. 9 , each of the input length  903  and the output length  911  include six conductors  915  separated from one another by insulation strips  917 . The input bus bar  905  and output bus bar  909  each provide a common electrical connection for the six conductors  915  of their respective connectors in order to provide high current to the load  907 . However, the input bus bar  901  and the output bus bar  913  provide six discrete bonding pads for chassis wires that carry current to and from the flexible flat cable. As also seen in  FIG. 9 , use of the discrete bus bars  901  and  913  require six different fuses  920  to provide overcurrent protection for each of the six current paths providing current to the load  907 . The present inventors recognized that this configuration results in inefficient use of space that prevents the overcurrent protection system of the flexible flat cable from being provided integral with the rotary connector. 
     FIG. 10  shows a single ribbon flexible flat cable used in accordance with an embodiment of the present invention. As seen in this figure, the cable includes input bus bar  1001 , input cable length  1003 , input bus bar  1005 , load  1007 , output bus bar  1009 , output cable length  1011 , and output bus bar  1013 . As with the prior art cable of  FIG. 9 , the input components,  1001 ,  1003  and  1005  carry current to the load  1007 , and the output components  1009 ,  1011 , and  1013  carry current away from the load  1007 . However, as seen in  FIG. 10 , each of the input length  1003  and the output length  1011  includes a single ribbon conductor  1015  having a relatively large width for providing high current capacity. The single ribbon conductor is preferably made of copper, but any suitable conductor may be used. The ribbon conductors  1015  are coated with an insulating material such as a mylar sheet that electrically insulates and provides a flexibility for the cable lengths. Because the cable lengths  1003  and  1011  use a single ribbon conductor, each of the bus bars  1001 ,  1005 ,  1009 , and  1013  are common electrical connection bus bars. Thus, as also seen in  FIG. 10 , a single fuse  1020  provides overcurrent protection for the flexible flat cable. The present inventors recognized that such use of a single fuse provides space efficiency that allows the overcurrent protection to be integrated within the rotary connector. 
     FIG. 11  is a picture of a high current capable rotary connector having an integral blade fuse in accordance with one embodiment of the present invention. As seen in  FIG. 11 , the rotary connector  1101  is shown without a cover to reveal the flexible flat cables housed within the annular space of the rotary connector  1101 . The rotary connector  1101  includes a rotating case and a stationary case, combined for the purpose of housing flexible flat cable(s), similar to the rotary connectors previously described with respect to  FIGS. 1 and 4 . In the embodiment of  FIG. 11 , the flexible flat cable  1120  includes four flat wires, two of which are single conductor ribbon wires ( 1103  visible in  FIG. 11 ) for providing input and output high current to the rotary connector  1101 , with the two remaining ribbon wires being multiple conductor wires ( 1105  visible in  FIG. 11 ) for providing separate current sources to the rotary cable  1101 . While the flexible flat cable  1120  of  FIG. 11  is shown to have U-shaped turns  1120 C, such a configuration is not necessary to obtaining the advantages of the overcurrent fuse provided integral to the rotary connector  1101 . For example, the flexible flat cable  1120  may be provided as a spiral, as described for prior art cables in the Background of the Invention section above. 
   The ribbon wires of the flexible cable  1120  are coated with a Mylar sheet and electrically connected with a bus-bar to the rotating and stationary mating terminations of the rotary connector. The Mylar sheet affords some structure to the flat cable and provides electrical insulation from adjacent flat cables. By design, these flat cables are incapable of handling currents exceeding a predetermined amperage (for example 8.0 Amps), so over-current protection is generally necessary. In  FIG. 11 , the over current protection is provided by a blade fuse  1107  mounted internal to the rotary connector  1101 . The blade fuse  1107  is suitably rated for the size of the copper ribbon and preferably snaps into a recess in the rotary connector  1101  so as to be completely housed within the rotary connector  1101  when the connector is fully assembled. 
     FIG. 12  is an enlarged drawing showing details of a blade fuse area of a rotary connector in accordance with one embodiment of the present invention. As seen in this figure, the electrical bus-bar of the present invention is separated into two electrically insulated parts  1203  and  1205 . Each insulated side  1203  and  1205  of the bus bar includes tangs (not shown) that protrude and provide a suitable docking feature for intermediate terminals  1209  which in turn provide a suitable docking feature the blade type fuse  1207 . The bus-bar also serves as an intermediate terminal for electrically fixing the flexible flat cable to any external wires. 
   In addition to providing a fuse contained within the rotary connector, a bus bar assembly according to the present invention provides heat sinking features that improve the over current protection for the flexible flat cable of the rotary connector.  FIG. 13A  is a drawing showing the configuration of a prior art bus bar assembly. As seen in this figure, the prior art bus bar assembly of includes a housing  1351  and six discrete bonding pads  1353  for connecting discrete wires to the bus bar assembly as described with respect to  FIG. 9  above. The bonding pads  1353  of the bus-bar assembly are fabricated using a nominal copper thickness of 0.3 mm appropriate for ultra sonic welding of the flexible flat cable and round wire to the bus bar. The present inventors have recognized that this configuration of the prior art bus bar assembly provides little ability to sink away excess heat created by high current electrical loads, thus potentially blowing the fuse prematurely. 
     FIG. 13B  is a drawing showing the configuration of a bus bar assembly in accordance with an embodiment of the present invention. As seen in this figure, the bus bar assembly includes a housing  1301 , and parts  1303  and  1305  physically separated and electrically insulated from one another. While not shown in  FIG. 13A , the parts  1303  and  1305  are electrically connected to one another by a fuse device that provides over current protection for the rotary cable assembly. As shown in  FIG. 13B , the bus-bar parts  1303  and  1305  are fabricated using extra thick copper of 0.8 mm, which sinks away some of the heat created from high electrical loads, thus avoiding premature fuse blow. Moreover, the housing  1301  of the bus bar assembly includes sink fins  1309  that sink away some of the heat created from high current electrical loads, thus avoiding premature fuse blow. While not shown in  FIG. 13B , the housing  1301  may also include a cooling pipe for heat sinking. In the embodiment of  FIG. 13B , the housing  1301  includes a wire recess  1311  for holding an input round wire, such as a chassis wire of an automobile, to the bus bar assembly, and a bus bar connector portion  1313  for connecting to a connector end of the flexible flat cable of the rotary connector. 
     FIG. 14  is a drawing showing a detailed configuration of a bus bar assembly having a surface mount fuse in accordance with one embodiment of the present invention. As with the bus bar described in  FIG. 12 , the bus bar includes a housing  1401  and electrically insulated parts  1403  and  1405 . The parts  1403  and  1405  are electrically connected by surface mount fuse  1407 . In addition, the bus bar assembly includes heating fins  1409  and increased thickness copper. The bus bar and fuse assembly also includes a round wire recess  1411  for holding an input wire to the bus bar assembly, and a bus bar connector portion  1413  for connecting to a connector end of the flexible flat cable of the rotary connector.  FIG. 15  is a drawing showing a detailed configuration of a bus bar assembly having a Pico fuse in accordance with one embodiment of the present. As with the embodiments previously described, the bus bar assembly includes a housing  1501  and electrically insulated parts  1503  and  1505 . In the embodiment of  FIG. 15 , each insulated side of the bus bar  1503  and  1505  has a hole that provides typical mounting for Pico fuse  1507 , which electrically connects the parts  1503  and  1505 . The bus bar assembly of  FIG. 15  also includes heating fins  1509  and increased thickness copper.  FIG. 15  also shows an electrical wire fixed in the wire recess  1509 , and a ribbon cable fixed to the bus bar connector portion  1511 . 
   Thus, a rotary connector of the present invention houses a fused devise for purpose protecting vulnerable flexible flat cables from over-current loading. The fused device is preferably housed within the connector in a more overall compact design of the rotary connector. Moreover, the fused device is preferably housed within the connector such a way as to not permit replacement of the fuse so that the rotary connector is provided as a replacement unit. However, an embodiment of the invention may include a fuse provided integral to the rotary connector and readily removable for replacement by any user, or by use of special purpose tooling that is generally available only to experienced maintenance persons. 
   Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Technology Category: 7