Abstract:
An inverter unit comprising component parts including at least an inverter and a filter which removes a high harmonic wave component from an output of said inverter, wherein said component parts are housed in an aluminum case having a bottom wall portion and a side wall portion, said filter includes a coil which is wound around a core extending straight and is arranged at a position closed to one end of said case, an end portion of said core being wound with said coil is arranged closed to an inner surface of said side wall portion of the case, and a ferromagnetic plate, which leads magnetic flux coming in and out said end portion of the core arranged closed to said wall portion of the case to the direction along the inner surface of the side wall portion of the case, is disposed between said end portion of said core and said inner surface of said side wall portion of the case.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     This invention pertains to an inverter unit for converting an output of a power source being comprised of a generator or the like driven by an internal combustion engine or the like into an AC voltage having a constant frequency.  
       BACKGROUND OF THE INVENTION  
       [0002]     There have been used an inverter unit for obtaining an AC voltage having a constant frequency (generally a commercial frequency) by using a generator driven by a prime mover such as an internal combustion engine as a power source. As shown in  FIG. 6 , an inverter unit for converting an output of an AC generator into an AC output having a constant frequency includes: an AC/DC converter CNV for converting an output of an AC generator into a DC output; an inverter INV for converting the output of the converter into an AC voltage of a constant frequency; and a filter FL. The filter FL is a low-pass filter having, for example, first and second coils L 1 , L 2  and a capacitor C 1 , and is provided for removing a high harmonic wave component from the output of the inverter INV.  
         [0003]      FIG. 7  is a schematic diagram showing an example of a structure of a conventional inverter unit  401  of this type. In  FIG. 7 , a reference numeral  402  shows a box-like case having a rectangular shaped bottom wall portion  402   a , and a side wall portion comprising side walls  402   b ,  402   c  facing to the longitudinal direction of the bottom wall portion  402   a  and side walls  402   d ,  402   e  facing to the cross direction of the bottom wall portion  402   a . In the case  402 , there are housed component parts of the inverter unit, including the converter CNV, the inverter INV and the filter FL.  
         [0004]     The first and second coils L 1 , L 2  of the filter FL are wound around first and second bobbins B 1 , B 2  mounted to first and second cores I 1 , I 2 , respectively. In order to maintain the stability of cut-off frequency of the filter with respect to the change of load current, a prismatic core being comprised of a laminated steel plate and extending straight is used as the cores I 1 , I 2  being wound with the coils L 1 , L 2 , respectively.  
         [0005]     The coils L 1 , L 2  are arranged at a position closed to the side wall portion  402   b  which is one end of the case  402  so that central axes of the coils coincide with each other, and an end portion I 1   b  of the core I 1  of the first coil L 1  and an end portion (not shown) of the core I 2  of the second coil L 2  are respectively arranged closed to the side walls  402   d ,  402   e  facing to the cross direction of the case  402 . The capacitor C 1  and the component parts of the converter CNV and the inverter INV are mounted to a printed board  403  which is arranged by the coils L 1 , L 2 .  
         [0006]     It may be possible to arrange the coils L 1 , L 2  at the central of the case  402 . However, in this case, the structure of the unit becomes complicated, an outlet of an output line from the filter becomes complex, and the cost increases because of an increase in manufacturing processes, since it becomes necessary to divide the printed board  403  into two parts.  
         [0007]     On the other hand, if the coils L 1 , L 2  are arranged on the end portion of the case  402  as shown, it is possible to simplify the structure of the unit since it is unnecessary to divide the printed board  403 . In addition, it is possible to make the outlet of the output line from the filter FL to outside easily in the case where the coils L 1 , L 2  are arranged on the end portion of the case  402 .  
         [0008]     The inverter unit of this type often provides a function as a heat sink to the case  402  in order to improve heat radiation from the converter and the inverter. Also, for preventing the weight of the inverter becoming heavy, it is desirable to use a case as light as possible. Therefore, the case  402  is generally made from aluminum which not only has good heat conductivity but also is light weight.  
         [0009]     Although it is not shown in the drawings, resin is cast into the case  402 , and at least a part of the component parts of the unit is molded by the resin, so that the inverter unit has water-resisting and earthquake-resisting characteristics. An inverter unit of this type is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 11-122932.  
         [0010]     An inverter unit shown in  FIG. 7  includes an AC/DC converter CNV for converting an AC output of a generator into a DC output because it is assumed that an AC generator is used as power source. However, the AC/DC converter may be omitted in the case where an output of a DC power source such as a storage battery and a solar battery is converted into an AC output of constant frequency.  
         [0011]     As shown in  FIG. 7 , if the coils L 1 , L 2  are disposed at the end portion of the case  402  made of aluminum, and the end portions of the cores I 1 , I 2  being wound with the coils L 1 , L 2 , respectively, are arranged closed to the inner surface of the side walls  402   d ,  402   e  of the case  402 , the magnetic flux coming in and out the end portions of the cores I 1 , I 2  flows through the side walls  402   d ,  402   e  of the case. If an AC magnetic flux flows through the side walls  402   d ,  402   d  of the case, eddy current flows at the side walls  402   d ,  402   e . Then, since magnetic flux generated by the eddy current prevents an AC magnetic flux flowing through the cores I 1 , I 2  from changing, magnetic resistance of the cores I 1 , I 2  is increased, and inductance of the coils L 1 , L 2  is decreased.  
         [0012]     Therefore, it has been necessary for the conventional inverter unit of this type to make the coils L 1 , L 2  have larger inductance than their needs, with making allowance for its possible reduction of inductance of the coils L 1 , L 2 . Thus, it was inevitable for the coils L 1 , L 2  to be large and the cost to be expensive.  
         [0013]     To avoid the reduction of inductance of the coils L 1 , L 2 , the distance between the end portions of the cores I 1 , I 2  and the inner surfaces of the side walls  402   d ,  402   e  of the case  402  may be enlarged. However, in this case, the case  402  becomes large, which causes the inverter unit to become large.  
       SUMMARY OF THE INVENTION  
       [0014]     Accordingly, it is a principal object of the present invention to provide an inverter unit adapted to have a smaller coil constituting a filter than a conventional type so as to make the unit light and smaller.  
         [0015]     The present invention is applied to an inverter unit comprising component parts including at least an inverter and a filter which removes high harmonic wave component from an output of the inverter. The component parts are housed in an aluminum box-like case having a bottom wall portion and a side wall portion. The filter includes a coil which is wound around a core extending straight and is disposed at a position closed to one end of the case, and an end portion of the core being wound with the coil is arranged closed to an inner surface of the side wall portion of the case. In the present invention, there is provided, at the end portion of the core, magnetic flux guiding member which guides magnetic flux coming in and out the end portion of the core arranged closed to the side wall portion of the case so as to direct the flux to the direction along the inner surface of the side wall portion of the case.  
         [0016]     With the inverter unit constructed as aforementioned, it is possible to decrease the magnetic flux passing through the side wall portion of the case closed to the end portion of the core and restrain eddy current flowing at the side wall portion of the case. The eddy current flowing at the side wall portion of the case is decreased, which prevents magnetic resistance from being increased and prevents inductance of the coil to be decreased. Thus, a smaller coil of the filter than the conventional type can be used, and the inverter unit can be made light and smaller.  
         [0017]     The aforementioned magnetic flux guiding member may be constructed of a ferromagnetic plate which has a surface larger than the end surface of the core and is disposed between the end portion of the core and the inner surface of the side wall portion of the case.  
         [0018]     Also, the aforementioned magnetic flux guiding member may be constructed of a protrusion which integrally protrudes from the end portion of the core arranged closed to the inner surface of the side wall portion of the case along the inner surface of the side wall portion of the case and extends toward the other side of the bottom wall portion of the case. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above and other objects and features of the invention will be apparent from the detailed description of the preferred embodiments of the invention, which are described and illustrated with reference to the accompanying drawings, in which;  
         [0020]      FIG. 1  is a schematic perspective view of the inverter unit constructed in accordance with the first embodiment of the invention;  
         [0021]      FIG. 2  is a plan view of a main part of the inverter unit shown in  FIG. 1 ;  
         [0022]      FIG. 3  is a sectional view taken along the line III-III of  FIG. 2 ;  
         [0023]      FIG. 4  is a plan view of a main part of the inverter unit constructed in accordance with the second embodiment of the invention;  
         [0024]      FIG. 5  is a sectional view taken along the line V-V of  FIG. 4 ;  
         [0025]      FIG. 6  is a circuit diagram illustrating an example of an electrical construction of the inverter unit;  
         [0026]      FIG. 7  is a schematic perspective view of a conventional inverter unit.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]     FIGS.  1  to  3  show the first embodiment of an inverter unit  1  according to the present invention. The inverter unit  1  includes, as same as the inverter unit shown in  FIG. 6 , a converter CNV, a inverter INV and a filter FL, and the filter FL is comprised of first and second coils L 1 , L 2  and a capacitor C 1 .  
         [0028]     In  FIG. 1 , a reference numeral  2  denotes a box-like case which is made of aluminum. The case  2  comprises a rectangular plate-like bottom wall portion  2   a  and a side wall portion. The side wall portion comprises a pair of side walls  2   b ,  2   c  facing to the longitudinal direction of the bottom wall portion  2   a , and a pair of side walls  2   d ,  2   e  facing to the cross direction of the bottom wall portion  2   a . In the case  2 , there are stored component parts of the inverter unit, including the converter CNV, the inverter INV and the filter FL.  
         [0029]     The first and second coils L 1 , L 2  of the filter FL are wound around first and second bobbins B 1 , B 2  mounted to first and second cores I 1 , I 2 , respectively. The first and second cores I 1 , I 2  are prismatic cores, which is constituted by laminating a predetermined number of steel plates.  
         [0030]     The coils L 1 , L 2  are arranged at a position closed to the side wall  2   b  which is on one end side of the longitudinal direction of the case  2 , so that central axes of the coils coincide with each other and are directed to the cross direction of the case, and an end portion I 1   a  of the first core I 1  and an end portion I 2   a  of the core I 2  are respectively adjacent to each other. The other end portions I 1   b , I 2   b  of the first and second core I 1 , I 2  are arranged so as to be closed to inner surfaces of a pair of the side walls  2   d ,  2   e  facing to the cross direction of the case.  
         [0031]     The capacitor C 1  and the component parts of the converter CNV and the inverter INV are mounted to a printed board  3  which is arranged on a space between the coils L 1 , L 2  and the side wall  2   c  which is on the other end side of the longitudinal direction of the case  2 .  
         [0032]     In this embodiment, a first plate  5  is arranged between the other end portion I 1   b  of the first core I 1  and the side wall  2   d  of the case opposed to the other end portion I 1   b  of the first core I 1 , and a second plate  6  is arranged between the other end portion I 2   b  of the second core I 2  and the side wall  2   d  of the case opposed to the other end portion I 2   b  of the second core I 2 . The plates  5  and  6  constitute a magnetic flux guiding member which guides magnetic flux φ coming in and out the end portions I 1   b , I 2   b  of the first and second cores so as to direct the flux to the direction along the inner surfaces of the side walls  2   d ,  2   e  of the case. The first and second plates  5 ,  6  are made of ferromagnetic material such as iron.  
         [0033]     The first plate  5  is formed so as to include a portion existing between the other end portion I 1   b  of the first core I 1  and the side wall  2   d  of the case opposed to the other end portion I 1   b  of the first core I 1  and a portion extending beyond an outer edge of an end surface of the other end of the first core I 1 . Similarly, the second plate  6  is formed so as to include a portion existing between the other end portion I 2   b  of the second core I 2  and the side wall  2   e  of the case opposed to the other end portion I 2   b  of the second core I 2  and a portion extending beyond an outline of an end surface of the other end of the second core I 2 .  
         [0034]     In the illustrated example, the first and second plates  5 ,  6  are rectangular shaped plates having a larger surface than the end surfaces of the first and second cores I 1 , I 2 , and these plates are arranged in a condition to be put between the other end portion I 1   b  of the first core I 1  and the side wall  2   d  of the case and between the other end portion I 2   b  of the second core I 2  and the side wall  2   e  of the case, respectively.  
         [0035]     As aforementioned, in the case where the first and second plates  5 ,  6  made of ferromagnetic materials and having larger surfaces than the end surfaces of the first and second cores I 1 , I 2  are arranged between the other end portion I 1   b  of the first core I 1  and the side wall  2   d  of the case opposed to the other end portion I 1   b  of the first core I 1 , and between the other end portion I 2   b  of the second core I 2  and the side wall  2   d  of the case opposed to the other end portion I 2   b  of the second core I 2 , respectively, and where the plates  5  and  6  constitute a magnetic flux guiding member which guides magnetic flux φ coming in and out the end portions I 1   b , I 2   b  of the first and second cores so as to direct the flux to the direction along the inner surfaces of the side walls  2   d ,  2   e  of the case, it is possible to decrease an amount of magnetic flux passing through the side walls of the case since it can be easier for the magnetic flux φ to flow through a magnetic path which does not penetrate the wall portion of the case  2 . Thus, eddy current flowing at the case is decreased, which can prevent magnetic resistance from being largely increased by the eddy current occurring at the case and prevent decrease in inductance of the coils which is caused by increasing magnetic resistance of the core.  
         [0036]     As described above, according to the present invention, since it is possible to prevent that inductance of the coil is largely decreased by being affected by the eddy current flowing at the case, it is unnecessary to prepare a larger coil in anticipate that the inductance of the coil is decreased; thus, the inverter unit can be made light and smaller by using a smaller coil than the conventional type.  
         [0037]      FIGS. 4 and 5  illustrate the second embodiment of the present invention. In this embodiment, protrusions  11 ,  12  are provided at the end portions I 1   b , I 2   b  of the first and second cores I 1 , I 2  opposed to a pair of the side walls  2   d ,  2   e  facing to the cross direction of the case  2 . The protrusions  11 ,  12  are integrally protruding from the end portions I 1   b , I 2   b  of the first and second cores I 1 , I 2  and extending toward the opposite side of the bottom wall portion  2   a  of the case along the inner surfaces of the side walls  2   d ,  2   e . The protrusions  11 ,  12  constitute the magnetic flux guiding member which guides the magnetic flux coming in and out the end portions of the cores so as to direct the flux to the direction along the inner surfaces of the side walls of the case.  
         [0038]     In the illustrated example, at end portions of steel plates respectively constituting the cores I 1 , I 2 , there are provided bent portions bending perpendicular to the longitudinal direction of the steel plates, which form, at the end portions I 1   b , I 2   b  of the cores I 1 , I 2 , the protrusions  11 ,  12  extending along the inner surfaces of the side walls  2   d ,  2   e  toward the other side of the bottom wall portion  2   a  of the case.  
         [0039]     In the embodiment shown in FIGS.  1  to  3 , there is provided a gap between the adjacent end portions of the bobbins B 1 , B 2  wound with the coils L 1 , L 2 , respectively. However, in the embodiment shown in  FIGS. 4 and 5 , the adjacent end portions of the bobbins B 1 , B 2  are butted without any gap. Other constructions of the embodiment shown in  FIGS. 4 and 5  are the same as the embodiment shown in  FIG. 1  to  3 .  
         [0040]     In the case where the protrusions  11 ,  12  extending and protruding toward the opposite side of the bottom wall portion  2   a  of the case are provided along the inner surfaces of the side walls  2   d ,  2   e  of the case at the end portions I 1   b , I 2   b  of the cores I 1 , I 2  as shown in  FIGS. 4 and 5 , it is possible to decrease an amount of magnetic flux passing through the side walls of the case since it can be easier for the magnetic flux φ to flow through a magnetic path which does not penetrate the side walls of the case  2 . Thus, eddy current flowing at the case  2  is decreased, which can prevent magnetic resistance of the cores I 1 , I 2  from being largely increased and prevent inductance of the coils to be decreased.  
         [0041]     Furthermore, in the case where the protrusions  11 ,  12  protruding toward the opposite side of the bottom wall portion  2   a  of the case are provided at the end portions of the cores as shown in  FIGS. 4 and 5 , it is possible to decrease an amount of magnetic flux passing to the side of the bottom wall portion  2   a  of the case and decrease an eddy-current loss by decreasing the eddy current flowing at the bottom wall portion of the case, thereby restraining a generation of heat from the case.  
         [0042]     Still, in the embodiment shown in  FIGS. 4 and 5 , it may be allowed to additionally provide protrusions protruding toward the side of the bottom wall portion  2   a  of the case from the end portions I 1   b , I 2   b  of the cores I 1 , I 2  other than the protrusions  11 ,  12  protruding toward the opposite side of the bottom wall portion  2   a  of the case from the end portions I 1   b , I 2   b  of the first and second cores I 1 , I 2 . However, if the protrusions protruding toward the side of the bottom wall portion  2   a  of the case from the end portions I 1   b , I 2   b  of the cores I 1 , I 2  are provided, it is desirable to bring the length of the protrusions protruding toward the side of the bottom wall portion shorter than the length of the protrusions protruding toward the opposite side of the bottom wall portion, and make the magnetic resistance of the magnetic path which flows the magnetic flux through the protrusions protruding toward the opposite side of the bottom wall portion  2   a  from the end portions I 1   b , I 2   b  of the cores I 1 , I 2  smaller than the magnetic resistance of the magnetic path which flows the magnetic flux through the protrusions protruding toward the side of the bottom wall portion  2   a  from the end portions I 1   b , I 2   b  of the cores I 1 , I 2 .  
         [0043]     Although the coils L 1 , L 2  are separately wound around the core I 1 , I 2 , respectively, in each embodiment described above, these coils may be wound around a common core; that is, the coils L 1 , L 2  may be placed adjacently and wound around a long core which is a unity of the cores I 1 , I 2 .  
         [0044]     Although some preferred embodiments of the invention have been described and illustrated with reference to the accompanying drawings, it will be understood by those skilled in the art that they are by way of example, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined only to the appended claims.