Patent Publication Number: US-2017370968-A1

Title: Current sensor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2016-126810, filed on Jun. 27, 2016, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to a current sensor which measures a current flowing in a conductor. 
     BACKGROUND DISCUSSION 
     Recently, hybrid vehicles or electric vehicles have been distributed, which are provided with a three-phase alternating current motor (hereinafter, simply referred to as a “motor”) and an inverter. In these vehicles, the rotation of the motor is appropriately controlled by measuring a current flowing in the motor. Each of U-phase, V-phase, and W-phase terminals of the motor is connected to the inverter through a conductor (bus bar), and the magnitude of the current flowing in each bus bar is measured by a current sensor. 
     In a current sensor disclosed in JP 2014-006116 A (Reference 1), a plurality of cores and a plurality of bus bars, which are made of a magnetic material, are configured by insert molding using molding resin. In the current sensor, in a state in which the bus bars are inserted into an internal space of the cores. A magnetic flux, which is formed around the bus bars depending on the magnitude of the current flowing in the bus bars, is detected by a detecting device, and the magnitude of the current flowing in the bus bars is obtained by arithmetic calculation based on the magnitude of the detected magnetic flux. 
     The current sensor disclosed in Reference 1 is assembled by integrating six bus bars and six cores (magnetic cores), which are separated from one another and arranged in a staggered form, with a main body made of a resin by insert molding, and then mounting a Hall device (detecting device). 
     As described above, since the opposite ends of each bus bar are connected to the motor and the inverter, respectively, it is necessary to increase positional accuracy in respect to the end portions of the bus bar, which are supported by the main body of the current sensor. In the case in which the bus bars and the main body are integrated by insert molding, an interior of the mold is typically filled with a molten resin in a state in which the opposite ends of the bus bars are held in the mold. The bus bars are continuously held in the mold until the main body is formed and extracted from the mold, and as a result, the bus bars and the main body are integrated with each other. However, in some cases, after the resin molding, the end portions of the bus bars in the main body may deviate from a position where the bus bars are held in the mold. 
     In general, a contraction degree of a resin product during the curing of the resin product is smallest at a surface of the resin product and increases toward the interior of the resin product. When the resin is contracted in the inside of the main body, the bus bars receive a stress. Therefore, it is considered that a positional deviation of the end portions of the bus bars in the main body (current sensor) after the resin molding is caused by the stress. 
     Thus, a need exists for a current sensor which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     A feature of a current sensor according to an aspect of this disclosure resides in that the current sensor includes: six or more bus bars; a core made of a magnetic material and having a base portion and seven or more arm portions which extend in a vertical direction from the base portion and are spaced apart from each other, and in which each of the bus bars is inserted into a gap formed between adjacent arm portions; and a main body configured to integrally hold the bus bars and the core in a state in which the bus bars and the core are insert-molded using polyphenylene sulfide (PPS) or polyphthalamide (PPA). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of one side of a current sensor; 
         FIG. 2  is a perspective view of the other side of the current sensor; 
         FIG. 3  is a top plan view of a main part of the current sensor; 
         FIG. 4  is a partial perspective view illustrating a positional relationship between bus bars and a core; 
         FIG. 5  is a cross-sectional view of a main part of the internal structure of the current sensor; 
         FIG. 6  is a cross-sectional view of a main part of the internal structure of a current sensor of another exemplary embodiment; and 
         FIG. 7  is a cross-sectional view of a main part of the internal structure of a current sensor of another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments disclosed here will be described in detail. 
     First Exemplary Embodiment 
     As illustrated in  FIGS. 1 to 5 , a current sensor  10  is provided with a main body  20 , bus bars  30 , a core  40 , and magnetic sensors  50 . The main body  20  is made of resin, and integrated with the bus bars  30  and the core  40  by insert molding. The current flowing in the bus bars  30  is measured using the core  40  and the magnetic sensors  50 . 
     As illustrated in  FIGS. 1 and 2 , the main body  20  has a central portion  202  where the bus bars  30  are insert-molded, and end portions  222  which are formed at the opposite sides of the central portion  202  in the longitudinal direction. The end portions  222  have a smaller thickness (in an up and down direction in  FIG. 1 ) than the central portion  202 , and the end portions  222  are formed in parallel with a front surface  204  of the main body  20  while having a level difference from the surface  204 . Mounting holes  224  are formed in the end portions  222 , respectively, to mount and fix the current sensor  10  to another member. 
     Six sensor holding holes  210  in which the magnetic sensors  50  are disposed are formed in the front surface  204  of the main body  20 . In addition, six sets (six pairs) of intermediate restriction holes  212  are formed to extend from the front surface  204  to a rear surface  206  of the main body  20  with each bus bar  30  being interposed between one pair of intermediate restriction holes  212  each of which faces the bus bar  30  from one of the inner circumferential surfaces thereof. The six sets of intermediate restriction holes  212  are arranged in parallel and in a straight line in the longitudinal direction of the main body  20 . The intermediate restriction holes  212  are an example of hole portions. As necessary, the bus bars  30  may be held at predetermined positions in the main body  20  by disposing protruding members or the like at the positions of the intermediate restriction holes  212  across the bus bar  30  interposed between each pair of intermediate restriction holes  212  when performing the insert molding using a resin. 
     The bus bars  30  have a rectangular plate shape, and are made of a metal with high conductivity, such as copper or a copper alloy. The current sensor  10  has six bus bars  30  ( 30   a  to  30   f ). One end portion  31  of each of the bus bars  30   a  to  30   f  is connected to one of U-phase, V-phase, and W-phase terminals of two three-phase alternating current motors (not illustrated), and the other end portion  32  is connected to an inverter (not illustrated). Therefore, a conducting current flows in the bus bars  30  toward the two three-phase alternating current motors. 
     The sensor main body of the current sensor  10  includes the core  40  and the magnetic sensors  50 . The core  40  is configured by stacking a plurality of magnetic bodies such as electromagnetic steel sheets. As illustrated in  FIGS. 4 and 5 , the core  40  has a base portion  41  which is provided in the longitudinal direction of the main body  20 , and seven arm portions  42  which extend in a vertical direction from the base portion  41  and are spaced apart from each other. The seven arm portions  42  of the core  40  are arranged so as to hold each of the bus bars  30   a  to  30   f  therebetween. That is, the bus bars  30  are respectively inserted into gaps  60  formed in the core  40 . 
     Each magnetic sensor  50  is a device that outputs voltage (signal) depending on a magnitude of a magnetic flux (e.g., a Hall device). As illustrated in  FIG. 5 , each magnetic sensor  50  is inserted into one of the sensor holding holes  210  (see  FIG. 1 ) of the main body  20 , and disposed in one of the gaps  60  each formed between the adjacent arm portions  42 . A circuit board  15  is fixed to the upper surface of the main body  20  and processes an output from each magnetic sensor  50 . The circuit board  15  is connected to the magnetic sensors  50  and supplies power to the magnetic sensors  50 . Signal lines  16  extend upward from the circuit board  15  to transmit a sensor output to a controller of the inverter (a circuit board on which a control circuit of the inverter is mounted). 
     The main body  20  integrally holds the bus bars  30  and the core  40  in a state of being molded with a resin. As the molding resin, polyphenylene sulfide (PPS), polyphthalamide (PPA), or the like is used. Both of the PPS and the PPA have an excellent insulation property and flame resistance. Therefore, the insulation property may be appropriately maintained in the current sensor  10  and the durability of the current sensor  10  may be improved. When comparing the PPS and the PPA, since the PPA has lower specific gravity and higher insulation property and flame resistance, the PPA may be more preferable as the molding resin of the main body  20 . 
     As illustrated in  FIG. 3 , in the main body  20 , an end surface  208  for holding the bus bars  30  protrudes in the extension direction of the bus bars  30 . That is, in the main body  20 , the end surface  208  at a side where the bus bars  30  extend has protruding portions  216  that protrude in the extension direction of the bus bars  30 . A concave portion  218  is formed between every adjacent protruding portions  216 . As the concave portion  218  is formed, a creeping distance between adjacent bus bars  30  is increased. Therefore, the adjacent bus bars  30  may be disposed in an insulated state. In addition, since the creeping distance between the adjacent bus bars  30  is increased without changing the space distance between the adjacent bus bars  30 , it is possible to compactly configure the current sensor  10 . 
       FIG. 4  is a view illustrating a relative disposition of the bus bars  30  and the core  40  by omitting the main body  20  from the current sensor  10 . The arm portions  42  of the core  40  are disposed to surround the bus bars  30  ( 30   a  to  30   f ). 
     The bus bars  30   a  to  30   c  transmit a single UVW three-phase output current, and the bus bars  30   d  to  30   f  transmit another UVW three-phase output current. As illustrated in  FIGS. 2 and 3 , the one end portions  31  of the bus bars  30  extend from the main body  20 , and the other end portions  32  thereof are bent at a right angle at a position corresponding to an end surface  214  of the main body  20 . Hole portions  33  are formed in the other end portions  32  to fix power cables of the motors, respectively. 
     As described above, the current sensor  10  is used by being connected between two three-phase alternating current motors and the inverter. When power is applied to the three-phase alternating current motors, a current flows in the bus bars  30 . When the current flows, the magnetic flux is generated around the bus bars  30 . The magnitude of the generated magnetic flux is proportional to the magnitude of the flowing current. The generated magnetic flux is collected in the core  40  having low magnetic resistance, and passes through the interior of the core  40 . Because the core  40  has the arm portions  42 , the magnetic flux passes through air in each gap  60  at tip sides of facing arm portions  42 . Because the magnetic sensor  50  is disposed in each gap  60 , the magnitude of the magnetic flux in the gap  60  is detected by the magnetic sensor  50 , and the magnitude of the current flowing through each bus bar  30  is obtained based on the magnitude of the magnetic flux. 
     Another Exemplary Embodiment 
     (1) In the current sensor  10 , seven or more bus bars  30  and a core  40  having eight or more arm portions  42  may be insert-molded in the main body  20 . In the case in which the current sensor  10  has, for example, seven bus bars  30 , six bus bars may be used for three-phase alternating current motors, and one bus bar may be used for another function. In addition, since the motors perform three-phase output, whenever a motor is added, three bus bars  30  and three arm portions  42  of the core  40  are increased. 
     (2) Although an example in which the single core  40  is insert-molded in the main body  20  has been illustrated in the first exemplary embodiment, a core  40   b  may be inserted into the main body  20  to detect a current flowing in a single bus bar  30   g,  together with an integrated core  40   b  (see  FIG. 6 ). The core  40   a  has a base portion  41 a and seven arm portions  42   a,  and bus bars  30   a  to  30   f  and magnetic sensors  51  are disposed in gaps  60  each formed between adjacent arm portions  42   a.  Meanwhile, in the core  40   b,  the bus bar  30   g  and a magnetic sensor  52  are disposed in a single gap  60 . Therefore, the current sensor  10  may detect a current, which is generated in the bus bar  30   g  by a device other than the motors, using the core  40   b  provided separately from the core  40   a.    
     (3) In the case in which three motors are connected to the current sensor  10 , for example, the core  40  inserted into the main body  20  may be disposed by being divided into an integrated core  40   c  for six phases and an integrated core  40   d  for three phases (see  FIG. 7 ). The core  40   c  has a base portion  41   c  and seven arm portions  42   c,  and bus bars  30   a  to  30   f  and magnetic sensors  53  are disposed in gaps  60  each formed between adjacent arm portions  42   c . Meanwhile, the core  40   d  has a base portion  41   d  and four arm portions  42   d,  and bus bars  30   g  to  30   i  and magnetic sensors  54  are disposed in gaps  60  each formed between adjacent arm portions  42   d.    
     The current sensor disclosed here may be widely used for a current sensor for measuring a current flowing in a bus bar. 
     A feature of a current sensor according to an aspect of this disclosure resides in that the current sensor includes: six or more bus bars; a core made of a magnetic material and having a base portion and seven or more arm portions which extend in a vertical direction from the base portion and are spaced apart from each other, and in which each of the bus bars is inserted into a gap formed between adjacent arm portions; and a main body configured to integrally hold the bus bars and the core in a state in which the bus bars and the core are insert-molded using polyphenylene sulfide (PPS) or polyphthalamide (PPA). 
     According to this configuration, the current sensor is configured by insert-molding six or more bus bars and an integrated core having seven or more arm portions using a resin. The integrated core may serve as a framework in the main body. That is, even if the resin is contracted in the main body, the influence of the contraction of the resin is reduced in the inside of the core by a holding function of the integrated core as a framework. As a result, it is possible to prevent positional deviation of the end portions of the bus bars which are disposed in the core. In addition, in the current sensor, since the integrated core is assembled by being inserted into the main body, it is possible to simply assemble the core to the current sensor. In addition, because the integrated core is used such that a dimension in the longitudinal direction of the main body may be reduced, the current sensor may be compactly configured. 
     Further, in the current sensor having the present configuration, the main body is resin-molded using polyphenylene sulfide (PPS) or polyphthalamide (PPA). Both of the PPS and the PPA have an excellent insulation property and flame resistance. Therefore, insulation property can be appropriately maintained in the current sensor and durability of the current sensor can be improved. 
     Another feature of the current sensor resides in that the main body has a protruding portion that is formed as an end portion of the main body, which holds the bus bars, protrudes in an extension direction of the bus bars. 
     In the current sensor, the bus bars are disposed in an insulated state from other adjacent bus bars. In order to establish this insulated state, it is required to ensure a predetermined creeping distance between the adjacent bus bars. According to the present configuration, the main body has a protruding portion that is formed as the end portion of the main body, which holds the bus bars, protrudes in the extension direction of the bus bars. Therefore, a concave portion is formed in an outer surface of the main body between adjacent bus bars. With the concave portion, a creeping distance between adjacent bus bars is increased. Therefore, adjacent bus bars may be disposed in an insulated state. In addition, since the creeping distance between adjacent bus bars is increased without changing a space distance between the adjacent bus bars, it is possible to compactly configure the current sensor. 
     Still another feature of the current sensor resides in that the main body has a pair of hole portions that are respectively formed at opposite sides of each of the bus bars interposed therebetween. 
     When the bus bars are integrated with the main body by resin molding, the opposite end portions of the bus bars are hold in the mold. However, even if the opposite end portions of the bus bars are held in the mold, positional accuracy of the end portions of the bus bars may not be sufficient in the main body after the molding in some cases. Therefore, in the present configuration, the main body has a pair of hole portions formed at the opposite sides of each bus bar interposed therebetween. Therefore, the main body may be resin-molded, for example, in a state in which protruding members or the like are disposed at positions of the hole portions and each the bus bars is fitted between the protruding members. As a result, since the positions of the bus bars become stable in the main body, it is possible to improve positional accuracy of the end portions of the bus bars in the current sensor. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.