Patent Publication Number: US-8982570-B2

Title: Electrically conductive path device

Description:
TECHNICAL FIELD 
     The present invention relates to an electrically conductive path device including a plurality of bus bars as an electrically conductive path. 
     BACKGROUND ART 
     In recent years, hybrid vehicles are becoming more widespread. Electric vehicles have also been developed rapidly. The hybrid vehicles and the electric vehicles are mounted with a high-voltage battery, an inverter and a motor. The inverter converts direct-current (DC) power supplied from the high-voltage battery into alternating-current (AC) power which is then supplied to the motor. Specifically, the AC power is supplied to the motor via high-voltage cables. In the hybrid vehicles and the electric vehicles, since the high-voltage cables are used for an electrical connection between the inverter and the motor as described above, there is required means for preventing radiation noise from the high-voltage cables. 
     Patent Literature 1 discloses a conventional technology for preventing the radiation noise which is explained below with reference to the drawing. 
     Referring to  FIG. 5 , there is shown an inverter  1 . The inverter  1  is covered with a conductive shield cover  2 . The shield cover  2  is connected to a vehicle body  4  via a grounding wire  3  and grounded.  FIG. 5  also shows a motor  5 . The motor  5  is covered with a conductive shield cover  6 . The shield cover  6  is connected to the vehicle body  4  via a grounding wire  7  and grounded. The inverter  1  and the motor  5  are electrically connected to each other via three shield wires  8 . The shield wire  8  includes a core wire  9 , an insulation member  10  and a braid  11 . Each end of the braid  11  is connected to the shield cover  2 ,  6  via a grounding wire  12  and grounded. 
     In the above-described structure, the inverter  1  is supplied with DC power from a DC power source. The inverter  1 , with this supplied power, produces three-phase AC power by operating a semiconductor switch located inside the inverter  1 . The core wires  9  of the shield wires  8  transmit the change in voltage created by the switching operation of the semiconductor switch. 
     Since the shield wires  8  connected to the inverter  1  and to the motor  5  are provided with the braids  11 , it is possible to prevent the radiation of electro-magnetic wave from the core wires  9  to outside by connecting the braids  11  to ground at the shield covers  2  and  6 . 
     CITATION LIST 
     Patent Literature 
     PLT 1: Japanese Patent Application Publication No. H10-135681 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, in the conventional art the radiation noise is prevented using the shield wires  8 . However, it is expected that there would be increasing number of cases in which these shield wires  8  will be replaced with other electrically conductive paths. Thus, there is a need for alternative means for preventing the radiation noise. 
     In view of the above-described problem, an object of the present invention is to provide an electrically conductive path device which can prevent the radiation noise. 
     Solution to Problem 
     In order to achieve the above-mentioned object, the present invention provides, in a first aspect, an electrically conductive path device having two or three bus bars which electrically connect one object to the other object and a capacitance portion for creating stray capacitance, wherein the capacitance portion is formed between facing portions of the bus bars. 
     According to the present invention having the above-described features, when change in voltage produced at the one object is transmitted to the bus bar corresponding to a path from the one object to the other object, the change in voltage is not transmitted further to the other object but is transmitted to the bus bar corresponding to a path from the other object to the one object via the capacitance portion formed between the facing portions of the bus bars, i.e. via the stray capacity. In the present invention, the facing portions of the bus bars are formed and positioned so that facing surfaces of the facing portions of the corresponding phases have the same surface area and that the distance between the facing surfaces of the facing portions is uniform. Furthermore, the stray capacitance can be adjusted for example by adjusting the distance between the phases, by changing the surface area and/or by changing the length of the bus bars. 
     Furthermore, the present invention provides, in a second aspect, the electrically conductive path device described above, wherein the one object is an inverter, the other object is a motor of a moving body and the number of bus bars is three, and wherein the electrically conductive path device is further provided with an impedance matching portion formed at a connection end of the bus bars. 
     According to the present invention having the above-described features, when change in voltage produced by switching operation of a semiconductor located inside the inverter is transmitted to the bus bar corresponding to a path from the inverter to the motor, the change in voltage is not transmitted further to the motor but is transmitted to the bus bar corresponding to a path from the motor to the inverter via the capacitance portion formed between the facing portions of the bus bars, i.e. via the stray capacity. In addition, according to the present invention, by forming the impedance matching portions, output impedance of the inverter can be matched with input impedance of the motor. Thus, creation of a standing wave between the inverter and the motor can be avoided, thereby reducing a chance of creation of the radiating noise. Furthermore, the impedance matching portions may be formed so as to effectively prevent reflection for example by gradually decreasing or increasing the width of the impedance matching portions. 
     Furthermore, the present invention provides, in a third aspect, the electrically conductive path device described above, wherein the facing portions are covered with an insulator such that the facing portions are arranged with a predetermined space between each other, the space between the facing portions covered with the insulator may be a hollow space, a space filled with the insulator or a space into which a dielectric material is inserted. 
     According to the present invention having the above-described features, the space between the facing portions can be maintained reliably by the insulator. In addition, the capacitance can be easily adjusted. Furthermore, in the present invention, the insulator may be inserted into an overmolded or insert molded case or may be mounted inside a case made of plastic components. 
     Advantageous Effects of Invention 
     According to the first aspect of the present invention described above, the radiation noise can be prevented in the case of using the bus bars as an electrically conductive path. In this case, the stray capacitance created between the phases can be arranged larger than in the case of using the electric wires, thus the noise can be cancelled out effectively. The present invention utilizing the stray capacitance is considered as almost an ideal capacitor having an excellent frequency property. Moreover, since the present invention has a simple structure, the radiation noise can be prevented at a low cost. 
     According to the second aspect of the present invention described above, the change in voltage created at the inverter can be cancelled out and thus is prevented from being transmitted to the motor, thereby preventing insulation breakdown at the motor. In addition, according to the present invention, the output impedance of the inverter and the input impedance of the motor can be matched by providing the impedance matching portion, thereby preventing the creation of the standing wave between the inverter and the motor. Therefore, the present invention can prevent the creation of the radiation noise and/or can reduce the amount of the radiation noise. 
     According to the third aspect of the present invention described above, advantageously the distance between the respective phases can be maintained constant, and also the stray capacitance can be adjusted. Also, the present invention can provide an optimum embodiment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a schematic illustration of wiring configuration of an electrically conductive path device of the present invention according to a first embodiment; 
         FIG. 1B  shows a cross sectional view of the electrically conductive path device applied between an inverter and a motor; 
         FIG. 1C  shows a cross sectional view of an electrically conductive path device applied between a battery and the inverter; 
         FIG. 2A  shows a perspective view of a main body of electrically conductive path device according to the first embodiment applied between the inverter and the motor; 
         FIG. 2B  shows a cross sectional view of the main body of electrically conductive path device shown in  FIG. 2A ; 
         FIG. 2C  shows a perspective view of a modified example of  FIG. 2A ; 
         FIG. 2D  shows a cross sectional view of the modified example of  FIG. 2A ; 
         FIG. 3A  shows a perspective view of an impedance matching portion of the electrically conductive path device shown in  FIG. 2A ; 
         FIG. 3B  shows a perspective view of a connection structure of  FIG. 3A ; 
         FIG. 3C  shows a perspective view of a modified example of  FIG. 3A ; 
         FIG. 3D  shows a perspective view of another modified example of  FIG. 3A ; 
         FIG. 4A  shows a perspective view of a main body of electrically conductive path device of the present invention according to a second embodiment applied between the inverter and the motor; 
         FIG. 4B  shows a cross sectional view of the main body of electrically conductive path device shown in  FIG. 4A ; 
         FIG. 4C  shows a perspective view of a modified example of  FIG. 4A ; and 
         FIG. 5  is an illustration of a conventional art for preventing radiation noise. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following will explain a first embodiment of the present invention with reference to the drawings.  FIGS. 1A through 1C  show an electrically conductive path device of the present invention according to a first embodiment, in which  FIG. 1A  is a schematic illustration of wiring configuration of an electrically conductive path device of the present invention according to a first embodiment,  FIG. 1B  shows a cross sectional view of the electrically conductive path device applied between an inverter and a motor, and  FIG. 1C  shows a cross sectional view of an electrically conductive path device applied between a battery and the inverter. 
     In this exemplary embodiment, the present invention is applied to a hybrid vehicle (or, the present invention may be applied to an electric vehicle). However, the present invention is not limited to this, and the present invention may be applied to, for example, vehicles other than the hybrid or electric vehicles. Preferably, the present invention is applied to a moving body. 
     Referring to  FIG. 1 , there is shown a hybrid vehicle  21 . The hybrid vehicle  21  is driven by a combination of two power sources, an engine  22  and a motor unit  23 . A battery  25  (e.g. a battery pack) supplies power to the motor unit  23  via an inverter unit  24 . In this embodiment, the engine  22 , the motor unit  23  and the inverter unit  24  are mounted at an engine room  26  located near front wheels. The battery  25  is mounted at a rear of vehicle  27  near rear wheels. Alternatively, the battery  25  may be mounted inside a vehicle room near the engine room  26 . 
     The motor unit  23  and the inverter unit  24  are electrically connected to each other by an electrically conductive path device  28  of the present invention. The battery  25  and the inverter unit  24  are electrically connected to each other by an electrically conductive path device  29  of the present invention. The electrically conductive path device  28  functions similarly to a conventional motor cable (i.e. a high-voltage wire harness). The electrically conductive path device  29  functions similarly to a conventional underfloor cable (i.e. a high-voltage wire harness with its middle portion being wired under a vehicle floor). Alternatively, a conventional underfloor cable may be used instead of the electrically conductive path device  29 . 
     The electrically conductive path device  29  and the battery  25  are connected to each other via a junction box  30  mounted to the battery  25 . A rear end  31  of the electrically conductive path device  29  is electrically connected to the junction box  30 . Thus, a portion of the electrically conductive path device  29  adjacent the rear end  31  is wired inside the vehicle above the vehicle floor. In addition, a portion of the electrically conductive path device  29  adjacent a front end  32  of the electrically conductive path device  29  is also wired above the vehicle floor. The front end  32  of the electrically conductive path device  29  is electrically connected to the inverter unit  24 . 
     In this embodiment, the motor unit  23  includes a motor and a generator, and the inverter unit  24  includes an inverter and a converter. The motor unit  23  further includes a shield cover. The inverter unit  24  is also provided with a shield cover. The battery  25  may be a modularized Ni-MH battery or a Li-ion battery. Alternatively, an electric storage device such as a capacitor may be employed. Types and kinds of the battery  25  are not limited to the ones described above, unless they can be used in the hybrid vehicle  21  or in an electric vehicle. 
     Referring to  FIGS. 1A and 1B , the electrically conductive path device  28  is provided with three bus bars  33  which electrically connect the motor unit  23  to the inverter unit  24 , an insulator  35  and capacitance portions  34  which create stray capacitance C 1 . 
     The bus bars  33  correspond to an electrically conductive path for supplying three-phase AC power, and all of the three bus bars are formed into the same shape. The bus bars  33  are provided with facing portions  36 . These facing portions  36  of the respective bus bars  33  are arranged so that the corresponding facing portions  36  are arranged to face each other. The three bus bars  33  are formed into a suitable shape and positioned in a suitable manner so as to create the uniform stray capacitance C 1  between the three phases. Thus, the facing portions  36  are formed and positioned so that the facing surfaces of the facing portions  36  have the same surface area and that the distance between the facing surfaces of the facing portions  36  is uniform. 
     The capacitance portion  34  is formed between the facing portions  36  of the respective bus bars  33 . In this embodiment, the capacitance portion  34  includes inner covers  37  disposed between the facing portions  36  and a hollow space  38  located between the inner covers  37 . Such arrangement is described by way of example only, and it is also effective if the hollow space  38  is filled with the insulator  35  or includes a dielectric material inserted into the hollow space  38 . The inner cover  37  is formed by the insulator  35 . The stray capacitance C 1  can be adjusted by adjusting the distance between the bus bars, by changing the surface area and/or by changing the length of the bus bars  33 . 
     The insulator  35  is arranged to cover the respective bus bars  33  to ensure insulation property of the bus bars  33 . The insulator  35  is provided with a spacing portion  39  to maintain the facing portions  36  to be spaced apart from each other at a predetermined interval. 
     The three bus bars  33  are provided with an impedance matching portion arranged at a connection end located at each end of the bus bars  33 . That is, the impedance matching portion is formed at an end of a main body  40  of the electrically conductive path device described above. The impedance matching portion will be explained in more detail below. 
     In terms of the electrically conductive path device  28 , by operating a semiconductor switch (e.g. IGBT) located inside the inverter of the inverter unit  24 , change in voltage is created and transmitted to the bus bar  33  corresponding to a path from the inverter to the motor. At that time, the change in voltage is not transmitted further to the motor but is transmitted to the bus bar  33  corresponding to a path from the motor to the inverter via the capacitance portion  34  formed between the facing portions  36  of the bus bars  33 , i.e. via the stray capacitance C 1 . 
     Therefore, the electrically conductive path device  28  is arranged to effectively cancel out the noise. Due to this effect, insulation breakdown can be prevented around the motor unit  23 . 
     As will be appreciated from the foregoing, the electrically conductive path device  28  is obviously an effective technology although it is different from the radiation noise prevention technology of the conventional art which uses common-mode current. 
     In this embodiment, the inverter unit  24  is fixed directly above the motor unit  23 . That is, the inverter unit  24  and the motor unit  23  are disposed adjacent to each other. Thus, the length of the electrically conductive path device  28  is short. The inverter unit  24  is fixed directly above the motor unit  23  by the fixation legs  41 . 
     Referring to  FIGS. 1A and 1C , the electrically conductive path device  29  for electrically connecting the battery  25  to the inverter unit  24  is provided with two bus bars  42 , a capacitance portion  43  for creating stray capacitance C 2 , an insulator  44  and a tubular protective member (not shown) for covering and protecting the bus bars  42 , the capacitance portion  43  and the insulator  44 . 
     The two bus bars  42  correspond to a positive electrically conductive path and a negative electrically conductive path, respectively, and are formed into the same shape. The two bus bars  42  are arranged so that facing portions  45  of the bus bars  42  are arranged to face each other. Furthermore, the two bus bars  42  are formed into a suitable shape and positioned in a suitable manner so as to create the uniform stray capacitance C 2  between these two phases. 
     The electrically conductive path device  29  functions similarly to and has an effect similar to the electrically conductive path device  28  described above. 
     The following will explain some exemplary embodiments of an electrically conductive path device for electrically connecting the motor unit  23  to the inverter unit  24 . 
     Exemplary Embodiment 1 
     The following will explain an exemplary embodiment 1 with reference to the drawings.  FIGS. 2A through 2D  show an electrically conductive path device arranged between an inverter and a motor, in which  FIG. 2A  is a perspective view of a main body of the electrically conductive path device,  FIG. 2B  is a cross sectional view of the main body of the electrically conductive path device shown in  FIG. 2A ,  FIG. 2C  is a perspective view of a modified example of  FIG. 2A , and  FIG. 2D  is a cross sectional view of the modified example of  FIG. 2A . Furthermore,  FIG. 3A  shows a perspective view of an impedance matching portion of the electrically conductive path device shown in  FIG. 2A ,  FIG. 3B  is a perspective view of a connection structure of  FIG. 3A ,  FIGS. 3C and 3D  show perspective views of modified examples of  FIG. 3A . 
     Referring to  FIGS. 2A and 2B , a main body  40  of the electrically conducting path device  28  includes three bus bars  33 , capacitance portions  34  and an insulator  35 . There is also provided an impedance matching portion  46  formed at an end of the man body  40  as shown in  FIG. 3A . The impedance matching portion  46  and the main body  40  together constitute the electrically conductive path device  28 . 
     The bus bar  33  is formed by punching a conductive metal plate to obtain a strip, followed by bending the strip at the widthwise center into an L-shape. In the drawings there is shown a bent portion  47 , the facing portions  36  being continuously formed at both ends of the bent portion  47 . All of three bus bars  33  are formed into the same shape. These three bus bars  33  are formed and positioned such that the facing portions  36  are arranged at an equal interval with respect to each other. 
     The capacitance portion  34  is formed between the facing portions  36  of the respective bus bars  33 . Furthermore, the capacitance portions  34  are arranged so as to create the uniform stray capacitance C 1  between the phases (refer to  FIG. 1B ). The insulator  35  is arranged to cover the respective bus bars  33  to ensure insulation property of the bus bars  33 . 
     Referring to  FIG. 3A , the impedance matching portion  46  is arranged so that output impedance of the inverter is matched with input impedance of the motor. Furthermore, the impedance matching portion  46  is formed so that the width of the bus bars  33  is gradually decreased (e.g. by forming a tapered portion  48 ). The gradually changing width described above can effectively prevent reflection. 
     An end of the impedance matching portion  46  corresponds to a connection end. In terms of the connection between the inverter and the motor via the connection end, the connection end may be arranged into a shape suitable for a direct connection (not shown) or may be provided with electric wires  49  as shown in  FIG. 3B . 
     Preferably, a portion of the electric wire  49  for connection is insulated by an insulator  50  by overmolding and such. 
     The electrically conductive path device  28  is not limited to the above-described embodiment. That is, the shape of the electrically conductive path device  28  may be modified as shown in  FIGS. 2C and 2D . 
     As shown in  FIGS. 2C and 2D , a main body  51  of the electrically conductive path device includes three bus bars  52 , capacitance portions  53  and an insulator  54 . 
     The bus bar  52  is formed by punching a conductive metal plate to obtain a strip, followed by bending the strip at the widthwise center into an L-shape. In the drawing there is shown a bent portion  55 , in which facing portions  56  are continuously formed at both ends of the bent portion  55 . All of three bus bars  52  are formed into the same shape. These three bus bars  52  are formed and positioned such that the facing portions  56  are arranged at an equal interval with respect to each other. In addition, the three bus bars  52  are arranged so that the facing portions  56  have the same surface area with respect to each other. Thus, the bus bar  52  has the larger bent portion  55  and the smaller facing portion  56  compared to the bus bar  33 . 
     By changing the shape of the bus bar  52 , the stray capacitance of the main body  51  of the electrically conductive path device is adjusted. 
     In terms of the adjustment of the stray capacitance, it is effective to gradually change the interval between respective three bus bars  57  as shown in  FIG. 3C . Furthermore, as shown in  FIG. 3D , it is also effective to provide an interval adjustment portion  59  at a central portion of each of three bus bars  58 . 
     Exemplary Embodiment 2 
     The following will explain an exemplary embodiment 2 with reference to the drawings.  FIGS. 4A through 4C  show an electrically conductive path device applied between the inverter and the motor, in which  FIG. 4A  is a perspective view of a main body of the electrically conductive path device,  FIG. 4B  is a cross sectional view of the main body of the electrically conductive path device shown in  FIG. 4A , and  FIG. 4C  is a perspective view of a modified example of  FIG. 4A . 
     Referring to  FIGS. 4A and 4B , a main body  60  of the electrically conductive path device includes three bus bars  61 , capacitance portions  62  and an insulator  63 . 
     The bus bar  61  is formed by punching a conductive metal plate to obtain a strip, followed by bending the strip at the widthwise center into an L-shape. In the drawings, there are shown facing portions  64  of the bus bars  61 . The three bus bars  61  are formed and positioned such that the facing portions  64  are arranged to face each other at an equal interval with respect to each other. Thus, the three bus bars  61  form a tubular shape. 
     The capacitance portion  62  is formed between the facing portions  64  of the respective bus bars  61 . Furthermore, the capacitance portions  62  are arranged so as to create the uniform stray capacitance between the phases. In this embodiment, the capacitance portions  62  are filled with an insulator  63  (alternatively, the capacitance portion  62  may be a hollow space or may include a dielectric material inserted into the capacitance portion). The insulator  63  is arranged to cover the respective bus bars  61  to ensure insulation property of the bus bars  61 . 
     As shown in  FIG. 4C , an impedance matching portion  65  is formed at an end of the electrically conductive path device. The impedance matching portion  65  is formed so that the width of the bus bars  61  is gradually decreased (e.g. by forming a tapered portion  48 ). The gradually changing width described above can effectively prevent reflection. 
     It should be apparent that the electrically conductive path devices shown in  FIGS. 4A through 4C  function similarly to and have an effect similar to the electrically conductive path device  28  shown in  FIGS. 1A-1C ,  2 A- 2 D and  3 A- 3 D. 
     Also, it should be apparent that the present invention can be modified and practiced in various ways without departing from the spirit of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
             C 1 , C 2  stray capacitance 
               21  hybrid vehicle (moving body) 
               22  engine 
               23  motor unit 
               24  inverter unit 
               25  battery 
               26  engine room 
               27  rear of vehicle 
               28 ,  29  electrically conductive path device 
               30  junction box 
               31  rear end 
               32  front end 
               33  bus bar 
               34  capacitance portion 
               35  insulator 
               36  facing portion 
               37  inner cover 
               38  hollow space 
               39  spacing portion 
               40  main body of electrically conductive path device 
               41  fixation leg 
               42  bus bar 
               43  capacitance portion 
               44  insulator 
               45  facing portion 
               46  impedance matching portion 
               47  bent portion 
               48  tapered portion 
               49  electric wire 
               50  insulation portion 
               51  main body of electrically conductive path device 
               52  bus bar 
               53  capacitance portion 
               54  insulator 
               55  bent portion 
               56  facing portion 
               57 ,  58  bus bar 
               59  interval adjustment portion 
               60  main body of electrically conductive path device 
               61  bus bar 
               62  capacitance portion 
               63  insulator 
               64  facing portion 
               65  impedance matching portion