Abstract:
A bus bar module ( 10 ) includes a bus bar ( 11 ) made of a metal material integrally molded into an insulating layer ( 12 ) made from resin. The bus bar module ( 10 ) also includes a distortion absorptive section ( 15 ) for absorbing distortion resulting from difference in the thermal expansion coefficient between the bus bar ( 11 ) and the insulating layer ( 12 ). Thus, the insulating layer ( 12 ) can stretch out by a difference in expanded dimension between the insulating layer ( 12 ) and the bus bar ( 11 ) at thermal expansion. In this way, the distortion resulting from the difference in the thermal expansion coefficient between the bus bar ( 11 ) and the insulating layer ( 12 ) can be absorbed, and crack occurrence in the insulating layer ( 12 ) can be prevented.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bus bar module integrally composed of bus bar and resin insulating layer. 
     2. Description of the Related Art 
     Electric circuits used in an internal combustion engine and in other high temperature environments utilize a bus bar module. A bus bar module has a plurality of bus bars made of a metallic material that has high heat resisting properties (a copper alloy, for example). The bus bars are aligned in parallel, and a plurality of bus bars are integrated by means of insert molding with insulating layers made of resin material (epoxy resin, for example) having heat resisting properties. Thus, the insulating layers insulate the space between the individual bus bars. A bus bar module as described above, is disclosed in the Japanese Unexamined Patent Publication No. 2000-151149. 
     The thermal expansion coefficient of metal generally differs widely from the thermal expansion coefficient of resin. Thus, there is a fear that repeated cycling from room temperature conditions to high temperature conditions may cause cracks in the resin of a bus bar module that has a metallic bus bar integrated into a resin insulating layer due to the differences of the thermal expansion coefficients. 
     Accordingly, in view of the aforementioned circumstances, the present invention is originated and the subject of the present invention is to prevent the occurrence of the crack in the resin insulating layer. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a bus bar module with a bus bar made of a conductive metallic material and an integrally molded resin insulating layer. The bus bar module further includes a distortion absorptive means for absorbing a distortion that results from a difference in thermal expansion coefficients between the bus bar and insulating layer. 
     The distortion absorptive means preferably is disposed to divide the insulating layer at an appropriate position along the longitudinal direction of the bus bar. 
     The bus bar module preferably comprises an insulating layer on the surface of the bus bar. 
     The distortion absorptive means absorbs the distortion that results from a difference in thermal expansion coefficient between the bus bar and the insulating layer. Accordingly, it is possible to prevent cracks from occurring in the insulating layer. 
     The thermal expansion coefficient of resin is greater than the thermal expansion coefficient of metal. However, the distortion absorptive means at the divided position of the resin layer effectively enables the resin layer to stretch further by the difference in the thermally expanded dimension between the insulating layer and the bus bar. Hence, there would be no possibilities for a forceful deformation and an excessive stress upon the insulating layer. 
     The bus bar is partially exposed at the divided position of the insulating layer. However, since the surface of the exposed part is covered with an insulating coating, the bus bar can be maintained in an insulating condition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a schematic diagram showing a condition in use of a bus bar module in the embodiment 1. 
     FIG. 2 illustrates a partially enlarged sectional view of a bus bar module. 
     FIG. 3 illustrates a partially enlarged sectional view of a bus bar module in the embodiment 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A bus bar module in accordance with the invention is identified by the number  10  in FIGS. 1 and 2. The bus bar module  10  has a base part made of synthetic resin material having heat resisting properties and oil resisting properties. The base part is connected to a connector  20  that is contained, for example, in a cylinder head  21  of internal combustion engine. Accordingly, a portion of the connector  20  in the inside of the cylinder head  21  is exposed to a high temperature and also is smeared with dispersing oil. The bus bar module  10  extends to the outside of the cylinder head  21 , and an electrical wiring system  22  is connected with an individual bus bar  11  at an edge of the bus bar module  10 . The bus bar module  10  is arranged in an arrangement space  23  that is close to the cylinder head  21 , and accordingly the bus bar module  10  is exposed to a high temperature condition due to heat radiation from the cylinder head  21  during operation of the internal combustion engine and a normal temperature condition during the cooling down that occurs when the internal combustion engine is stopped. These extreme ranges of temperature conditions are repeated alternately. 
     The bus bar module  10  is integrated in one package by means of integral insert molding. The bus bar module  10  is composed of a plurality of bus bars  11  made up of metallic materials having electrical conductive properties, such as yellow brass and an alloy of heat resisting copper. Three bus bars  11  are shown in the illustrated embodiments, but two or more than three also may be provided. the bus bar module  10  also includes an insulating layer  12  made from a synthetic resin material having heat resisting properties, such as epoxy resin or polyphenylene sulfide (PPS). 
     Each bus bar  11  comprises a main part  11 A that stretches in a straight line. A first linking part  11 B extends nearly vertically from a base of the main part  11 A and is connected to a connector  20 . A second linking part  11 C extends nearly vertically from an edge of the main part  11 A and is connected to a an electrical wiring system  22 . The lengths of the main parts  11 A of the individual bus bars  11  are different from each other. Accordingly, the individual linking parts  11 B with the connector  20  are mutually parallel, and in addition, the individual linking parts  11 C with the electrical wiring system  22  are also mutually parallel. 
     The main parts  11 A of the bus bars  11  are parallel and the insulating layer  12  is between the neighboring main parts  11 A. The insulating layer  12  also is arranged outside the outermost main parts  11 A. More particularly, the insulating layer  12  and the main part  11 A are superimposed alternately. Furthermore, an insulating coating  13  with heat resisting properties, such as enamel coating, is provided on the entire surface of each individual bus bar  11 . This insulating coating  13  is provided on the bus bar  11  prior to insert molding, and hence before the bus bar  11  is integrated in one package with the insulating layer  12 . 
     The bus bar module  10  is provided with distortion absorptive means  14  that can absorb distortion attributable to thermal expansion resulting from the difference between the thermal expansion coefficient of the metal, which is the material for the bus bar  11 , and the thermal expansion coefficient of the synthetic resin, which is the material for the insulating layer  12 . The distortion absorptive means  14  divides the insulating layer  12  at a plural number of appropriate positions along a longitudinal direction of the main part  11 A of the bus bar  11 . In other words, the insulating layer  12  is partially removed. The distortion absorptive means  14  divides the insulating layer  12  into a plurality of separated insulating layers  12 A along the longitudinal direction of the main part  11 A, and a dividing space  15  is maintained between the mutual end faces of the separated insulating layers  12 A. The dimension in the longitudinal direction of the dividing space  15  is established based on the thermal expansion coefficient of the metal, which is the material for the bus bar  11 , the thermal expansion coefficient of the synthetic resin, which is the material for the insulating layer  12 , the longitudinal dimension of the individual separated insulating layer  12 A, and so on. The established dimension of the dividing space  15  should be greater than the difference in a dimension between the thermally expanded dimension of the bus bar  11  and the thermally expanded dimension of the separated insulating layers  12 A when the bus bar module  10  is heated up to the estimated maximum temperature. Additionally, based on the established dimension of the dividing space, the neighboring separated insulating layers  12 A are designed not to interfere with each other at thermal expansion. In this case, the surface of the exposed section of the main part  11 A in the dividing space  15  between the separated insulating layers  12 A is maintained with the insulating coating  13 . 
     The thermal expansion coefficient of synthetic resin is comparatively greater than that of metal. Accordingly, the elongation amount of the separated insulating layers  12 A made from synthetic resin is comparatively greater than the elongation amount of the corresponding region in the main part  11 A of the bus bar  11  made of metal. However, at the dividing space  15  between the insulating layers  12 , the end parts of the separated insulating layers  12 A can relatively stretch out to the main part  11 A for accommodating the difference of the expansion dimension between the bus bar  11  and the separated insulating layers  12 A. Accordingly, it is not possible to give rise to a forceful deformation and an excessive stress upon the separated insulating layer  12 A. 
     The distortion absorptive means  14  can absorb distortion that results from the difference in thermal expansion coefficient between the metal of the bus bar  11  and the thermal expansion coefficient of the synthetic resin of the insulating layer  12 . Accordingly, it is possible to prevent cracks from occurring in the insulating layer  12 . 
     Additionally, the insulating coating  13  is provided on the surface of the bus bar  11 . As a result, surfaces of the partially exposed sections of the main part  11 A in the divided position of the insulating layer  12  are covered by the insulating coating  13 . Accordingly, an insulating condition can be maintained. 
     A bus bar module in accordance with a second embodiment of the invention is identified by the numeral  30  in FIG.  3 . The bus bar module  30  has a distortion absorptive means  33  is different from the distortion absorptive means of the first embodiment. Since the other composition is identical to the first embodiment, the same numerals are put for the same composition, and the explanation regarding the structure, operation and effect is omitted here. 
     The distortion absorptive means  33  of the second embodiment comprises a part  31 B of the individual main part  31 A of each bus bar  31  that is sigmoidally or sinusoidally bent to define a plurality of S-shapes. The sigmoidally bent parts  31 B, are disposed in a selected longitudinal position along the bus bars  31 , and define curvatures that are the same among the neighboring main parts  31 A. Accordingly, the bent parts  31 B effectively nest with one another, and the thickness of the insulating layer  32 A between the neighboring main parts  31 A, as measured in the top-to-bottom direction of FIG. 3, is continuously uniform along the longitudinal direction. In addition, the outside surface of the insulating layer  32 B outside the main part  31 A is flat and parallel to the longitudinal direction of the bus bar  31 . Therefore, the thickness of the region corresponding to the sigmoidally bent part  31 B of the insulating layer  32 B is uniform in the longitudinal direction.