Abstract:
In coreless current sensors of a coreless current sensor structure, and in a current detection method employed in the coreless current sensor structure, a coil-like portion that surrounds the outer circumference of a conductor, such as a shield plate, is formed of a connecting line connected to a terminal of a magnetic detection element.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a coreless current sensor structure, a coreless current sensor, and a current detecting method. 
       BACKGROUND ART 
       [0002]    There is known a coreless current sensor, which is a current sensor that does not contain a magnetic flux collector core. See, Japanese Laid-Open Patent Publication No. 2010-045874 (hereinafter referred to as “JP2010-045874A”). According to JP2010-045874A, a coreless current sensor 40 is used to control an inverter 41, which controls the output power of a three-phase AC motor 39. More specifically, in order to eliminate phase delays and gain errors contained in output voltages Vuv1, Vvw1 due to residual magnetic fluxes that are produced by a shield plate 53 of the coreless current sensor 40, the output voltages Vuv1, Vvw1 are corrected, and the inverter 41 is controlled based on the corrected output voltages Vuv1, Vvw1 together with command values that are input from an external source (see Abstract). 
         [0003]    The output voltages Vuv1, Vvw1 are corrected using a map 5 (see, FIGS. 2( a ) through 2( d )), which defines a relationship between command values id1, iq1 and rotational speeds ω of the rotor of the motor 39 and corrective values (gain corrective values A1, B1 and phase corrective values A2, B2) (see paragraphs [0030] through [0038]). Alternatively, the output voltages Vuv1, Vvw1 are corrected using a map 8 (FIG. 6), which defines a relationship between present positions θ[°] of the motor 39 and the corrective values (see paragraphs [0043] through [0045]). 
       SUMMARY OF INVENTION 
       [0004]    According to JP2010-045874A, as described above, maps of corrective values depending on rotational speeds ω and positions θ are used in order to reduce adverse effects (phase delays and gain errors contained in the output voltages Vuv1, Vvw1) of magnetic fluxes produced by the shield plate 53. Consequently, unless maps of the corrective values are kept, the output voltages Vuv1, Vvw1 cannot be corrected, and it is necessary to provide a sufficient memory capacity and to acquire data in advance, which imposes quite a high load. 
         [0005]    The present invention has been made in view of the above problems. It is an object of the present invention to provide a coreless current sensor structure, a coreless current sensor, and a current detecting method, which are capable of preventing a reduction (phase delay) in response due to magnetic fluxes with a simple arrangement. 
         [0006]    According to the present invention, there is provided a coreless current sensor structure comprising a magnetic detecting device for detecting a magnetic flux produced from a current path and converting the detected magnetic flux into a voltage, a shield plate disposed around the magnetic detecting device for blocking an external magnetic flux toward the magnetic detecting device, wherein an output voltage converted from a detected magnetic flux by the magnetic detecting device is converted into a current in order to detect a current flowing through the current path, and a connection line connected to terminals of the magnetic detecting device and including a coiled portion surrounding the shield plate, wherein the current is calculated based on a voltage across the magnetic detecting device. 
         [0007]    According to the present invention, the connection line connected to the terminals of the magnetic detecting device includes the coiled portion that surrounds the shield plate. When the coiled portion generates a counter-electromotive force, which depends on a change in the magnetic flux applied to the shield plate, the generated counter-electromotive force is added to the output voltage of the magnetic detecting device. 
         [0008]    If the coiled portion is disposed around the shield plate so as to produce the counter-electromotive force in order to compensate for a response delay in the output voltage from the magnetic detecting device, which is caused with respect to a change in the current flowing through the current path due to a delay of a change in the magnetic flux on the shield plate with respect to the change in the current, then the response delay in the output voltage can be compensated for by the counter-electromotive force. As a result, the response delay in the output voltage, i.e. a response reduction due to the magnetic flux (phase delay), can be compensated for with a simple arrangement. 
         [0009]    Alternatively, if the coiled portion is disposed around the shield plate in order to increase the response delay in the output voltage through use of the counter-electromotive force, then the response delay in the output voltage can be increased when necessary. 
         [0010]    The connection line, which includes the coiled portion, may further include an output line on which voltage changes depending on the voltage conversion, and the coiled portion may be coiled counterclockwise around a first specific region of the shield plate from a side of the output line proximate the magnetic detecting device and toward an output end of the output line, as the first specific region of the shield plate is viewed in a direction of the magnetic flux at the first specific region, when the magnetic detecting device outputs a positive voltage based on the generated magnetic flux produced from the current path. 
         [0011]    The connection line may further include a ground line, and the coiled portion may be coiled clockwise around a second specific region of the shield plate from a side of the ground line proximate the magnetic detecting device and toward an output end of the ground line, as the second specific region of the shield plate is viewed in a direction of the magnetic flux at the second specific region, when the magnetic detecting device outputs a positive voltage based on the generated magnetic flux produced from the current path. 
         [0012]    According to the present invention, there also is provided a coreless current sensor comprising a magnetic detecting device for detecting a magnetic flux produced from a current path and converting the detected magnetic flux into a voltage, a conductor disposed around the magnetic detecting device, and a wire for outputting an output voltage from the magnetic detecting device to an external circuit, the wire including a coiled portion disposed around the conductor, wherein the conductor is placed in a position in which the conductor generates an eddy current due to a magnetic flux produced from the current path, thereby causing a delay of a change in the magnetic flux detected by the magnetic detecting device with respect to a change in a current flowing through the current path, and the coiled portion of the wire is disposed such that a response delay in the output voltage from the magnetic detecting device, which is caused with respect to the change that occurs in the current flowing through the current path due to a delay of a change in the magnetic flux with respect to the change in the current, is compensated for by a counter-electromotive force generated in the coiled portion in a direction to oppose the change in the magnetic flux applied to the conductor. 
         [0013]    According to the present invention, even if a response delay in the output voltage from the magnetic detecting device is caused with respect to a change in the current flowing through the current path due to a delay of a change in the magnetic flux on the conductor with respect to the change in the current, the response delay is compensated for by the counter-electromotive force generated in the coiled portion. Therefore, a phase deviation (response delay) can be prevented with a simple arrangement. 
         [0014]    According to the present invention, there also is provided a current detecting method to be carried out using a coreless current sensor including a magnetic detecting device for detecting a magnetic flux produced from a current path and converting the detected magnetic flux into a voltage, a conductor disposed around the magnetic detecting device, and a wire for outputting an output voltage from the magnetic detecting device to an external circuit, the wire including a coiled portion disposed around the conductor, comprising the steps of placing the conductor in a position in which the conductor generates an eddy current due to a magnetic flux produced from the current path, thereby causing a delay of a change in the magnetic flux detected by the magnetic detecting device with respect to a change in a current flowing through the current path, generating a counter-electromotive force in the coiled portion in a direction to oppose the change in the magnetic flux applied to the conductor, and compensating for a phase deviation between the waveform of the current flowing through the current path and the waveform of an output from the magnetic detecting device by using the counter-electromotive force for the conductor, the phase deviation being caused due to the delay of the change in the magnetic flux with respect to the change in the current. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram of an electric vehicle incorporating a plurality of coreless current sensors according to an embodiment of the present invention; 
           [0016]      FIG. 2A  is a plan view showing schematically the structure of each of the coreless current sensors according to the embodiment; 
           [0017]      FIG. 2B  is a cross-sectional view taken along line IIB-IIB of  FIG. 2A , showing the structure of the coreless current sensor; 
           [0018]      FIG. 3A  is a plan view of a coreless current sensor according to a comparative example, showing the manner in which a positive current flows through a bus bar; 
           [0019]      FIG. 3B  is a cross-sectional view taken along line IIIB-IIIB of  FIG. 3A ; 
           [0020]      FIG. 4  is a view showing the manner in which an eddy current is generated in a shield plate shown in  FIGS. 3A and 3B ; 
           [0021]      FIG. 5  is a diagram showing the relationship between a current flowing through the bus bar (bus bar current), an output voltage from a magnetic detecting device (device voltage), a counter-electromotive force generated for the shield plate, and an error caused by a response delay of the device voltage with respect to the bus bar current in the comparative example; 
           [0022]      FIG. 6A  is a plan view of the coreless current sensor according to the comparative example, showing the manner in which a negative current flows through the bus bar; 
           [0023]      FIG. 6B  is a cross-sectional view taken along line VIB-VIB of  FIG. 6A ; 
           [0024]      FIG. 7  is a view showing the manner in which an eddy current is generated in the shield plate shown in  FIGS. 6A and 6B ; 
           [0025]      FIG. 8A  is a plan view of the coreless current sensor according to the present embodiment, showing the manner in which a positive current flows through a bus bar; 
           [0026]      FIG. 8B  is a cross-sectional view taken along line VIIIB-VIIIB of  FIG. 8A ; 
           [0027]      FIG. 9  is a diagram showing the relationship between the bus bar current and the device voltage according to the embodiment; 
           [0028]      FIG. 10A  is a plan view of the coreless current sensor according to the present embodiment, showing the manner in which a negative current flows through the bus bar; 
           [0029]      FIG. 10B  is a cross-sectional view taken along line XB-XB of  FIG. 10A ; 
           [0030]      FIG. 11  is a diagram showing by way of example the relationship between numbers of turns of a turn wire around the shield plate and phase deviations of a corrected device voltage; 
           [0031]      FIG. 12  is a plan view showing schematically the structure of a first modification of the coreless current sensor shown in  FIG. 2A ; 
           [0032]      FIG. 13  is a plan view showing schematically the structure of a second modification of the coreless current sensor shown in  FIG. 2A ; and 
           [0033]      FIG. 14  is a plan view showing schematically the structure of a third modification of the coreless current sensor shown in  FIG. 2A . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     1. Embodiment 
     [1-1. Arrangement of Electric Vehicle  10 ] 
       [0034]      FIG. 1  is a block diagram of an electric vehicle  10  (hereinafter referred to as a “vehicle  10 ”) incorporating therein plural coreless current sensors  20   u,    20   v,    20   w  according to an embodiment of the present invention. The coreless current sensors  20   u,    20   v,    20   w  also are referred to as “current sensors  20   u,    20   v,    20   w ”, and are collectively referred to as “coreless current sensors  20 ” or simply “current sensors  20 ”. 
         [0035]    In addition to the coreless current sensors  20 , the vehicle includes a propulsive motor  12  (hereinafter referred to as a “motor  12 ”), an inverter  14 , a battery  16 , a power supply circuit  18 , a resolver  22 , and an electronic control unit  24  (hereinafter referred to as an “ECU  24 ”). 
       [1-2. Drive System] 
       [0036]    The motor  12 , which comprises a three-phase AC brushless motor, generates a drive force F [N] (or a torque [N·m]) for the vehicle  10  based on electric power supplied from the battery  16  through the power supply circuit  18  and the inverter  14 . The motor  12  also outputs electric power (regenerated electric power Preg) [W] generated in a regenerative mode to the battery  16  and a non-illustrated auxiliary, in order to charge the battery  16  and to energize the auxiliary. 
         [0037]    The inverter  14 , which is of a three-phase full-bridge configuration, converts direct current from the battery  16  into a three-phase alternating current and supplies the three-phase alternating current to the motor  12 . The inverter  14  also supplies the battery  16  and the auxiliary with direct current, which is converted from an alternating current generated by the motor  12  in a regenerative mode. The inverter  14  includes upper switching elements  30   u,    30   v,    30   w  (hereinafter collectively referred to as “upper switching elements  30 ”) and lower switching elements  32   u,    32   v,    32   w  (hereinafter collectively referred to as “lower switching elements  32 ”), which are turned on and off according to a predetermined sequence by drive signals from the ECU  24  in order to rotate the three-phase AC motor  12 . The inverter  14  also includes inverse-parallel diodes, which are associated respectively with the upper switching elements  30  and the lower switching elements  32 . The inverse-parallel diodes are omitted from illustration in  FIG. 1 . 
         [0038]    The inverter  14  may have the same structural and operational details as those disclosed in JP2010-045874A, for example. 
       [1-3. Electric Power System] 
       [0039]    The battery  16 , which serves as an energy storage device including a plurality of battery cells, may comprise a lithium ion secondary battery, a nickel hydrogen battery, or a capacitor, for example. According to the present embodiment, the battery  16  comprises a lithium ion secondary battery. A DC/DC converter, not shown, may be connected between the inverter  14  and the battery  16 , for stepping up or stepping down an output voltage from the battery  16  or an output voltage from the motor  12 . 
         [0040]    The power supply circuit  18  includes a relay switch  34  and bus bars  36   u,    36   v,    36   w  (hereinafter collectively referred to as “bus bars  36 ”). 
         [0041]    The relay switch  34  comprises a normally open ON/OFF switch for use during normal operation (power mode or regenerative mode) of the vehicle  10 . The relay switch  34  is connected between the inverter  14  and the positive terminal of the battery  16 . 
         [0042]    The bus bars  36   u,    36   v,    36   w  comprise copper wires in the form of plates interconnecting the motor  12  and junctions  38   u,    38   v,    38   w  between the upper switching elements  30  and the lower switching elements  32 . As described above, the upper switching elements  30  and the lower switching elements  32  of the inverter  14  are turned on and off according to a predetermined sequence in order to rotate the three-phase AC motor  12 . At this time, the directions of the currents that flow through the bus bars  36  are successively reversed. 
       [1-4. Coreless Current Sensor  20 ] 
       [0043]      FIG. 2A  is a plan view showing schematically the structure of each of the coreless current sensors  20  according to the present embodiment, and  FIG. 2B  is a cross-sectional view taken along line IIB-IIB of  FIG. 2A , showing the structure of the coreless current sensor  20 . 
         [0044]    As shown in  FIGS. 2A and 2B , the current sensor  20  includes a printed circuit board  50  disposed parallel to the bus bar  36 , a magnetic detecting device  52  mounted on the printed circuit board  50 , and a shield plate  54 . The shield plate  54  has a lower surface parallel to the bus bar  36 , and left and right surfaces that lie perpendicularly to the lower surface of the shield plate  54 . 
         [0045]    The magnetic detecting device  52  detects a magnetic flux φ 1  generated by the bus bar  36  and converts the detected magnetic flux φ 1  into a voltage. In other words, the magnetic detecting device  52  outputs a voltage (hereinafter referred to as a “device voltage Ve”), which is dependent on the magnetic flux φ 1 . Since the magnetic flux φ 1  is proportional to the current flowing through the bus bar  36  (hereinafter referred to as a “bus bar current Ib”) [A], the device voltage Ve represents the bus bar current Ib. The output voltage (device voltage Ve) from the magnetic detecting device  52  is output to the ECU  24  through a printed wire  60  (connection line) that is printed on the printed circuit board  50 . The magnetic detecting device  52  may comprise, for example, a Hall device, a magnetoresistance device, or a Hall IC (Integrated Circuit) in the form of an amplifier circuit combined with a Hall device. 
         [0046]    The shield plate  54  serves to prevent disturbance noise from being applied to the magnetic detecting device  52 . The shield plate  54  surrounds the bus bar  36  in three directions (downward, leftward, and rightward directions as shown in  FIG. 2B ). The shield plate  54  is made of a magnetically permeable material such as Permalloy or the like. As shown in  FIG. 2B , when a disturbance noise NZ is generated in the direction of the magnetic detecting device  52 , the disturbance noise NZ passes through the shield plate  54  but does not reach the magnetic detecting device  52 . Therefore, the shield plate  54  is effective to protect the magnetic detecting device  52  from the disturbance noise NZ. 
         [0047]    As shown in  FIG. 2A , the printed wire  60  includes an output line  62  and a ground line  64 . The output line  62  and the ground line  64  are connected to terminals of the magnetic detecting device  52  and to input terminals of the ECU  24 . 
         [0048]    According to the present embodiment, the output line  62  includes a turn wire  66  (coiled portion) in the form of a coil that extends around the shield plate  54 . The turn wire  66  is effective to improve the output response of the current sensor  20 , to be described in detail later. The printed circuit board  50  is of a double-layer structure including through holes  68 , which keeps any overlapping portions of the turn wire  66  isolated and out of electric contact with each other. 
       [1-5. Resolver  22 ] 
       [0049]    The resolver  22  detects an electric angle θ, which is a rotation angle of an unillustrated output shaft or outer rotor of the motor  12 , and outputs it to the ECU  24 . 
       [1-6. ECU  24 ] 
       [0050]    The ECU  24  controls various components of the vehicle  10  through signal lines  70  (see  FIG. 1 ). The ECU  24  includes non-illustrated input and output parts, an operation part, and a memory part. According to the present embodiment, the ECU  24  converts output voltages (device voltages Ve) from the current sensors  20  from analog voltages into digital voltages, so that the ECU  24  can process the digital voltages as current values (bus bar currents Ib). Stated otherwise, the current sensors  20  and the ECU  24  operate jointly to make up a coreless current sensor unit  80  (coreless current sensor structure). In  FIG. 1 , the signal lines  70  that interconnect the inverter  14  and the ECU  24  are shown in simplified form, however, the signal lines  70  actually interconnect the ECU  24  with the gates of the upper switching elements  30   u,    30   v,    30   w  and the lower switching elements  32   u,    32   v,    32   w.    
       2. Operations and Advantages of the Turn Wire  66   
     [2-1. In the Absence of the Turn Wire  66 ] 
       [0051]    In order to explain the operations and advantages of the turn wire  66  according to the present embodiment, initially, operations in the absence of the turn wire  66  will be described below. When the inverter  14  is energized, directions of the currents that flow through the bus bars  36  are switched in succession, as described above. 
       (2-1-1. When the Bus Bar Current Ib Flows in a Positive Direction) 
       [0052]      FIG. 3A  is a plan view of a coreless current sensor  20   com  (hereinafter referred to as a “current sensor  20   com ”), which is free of the turn wire  66  according to a comparative example, and which shows the manner in which the bus bar current Ib flows in an upward direction (hereinafter referred to as a “positive direction”).  FIG. 3B  is a cross-sectional view taken along line IIIB-IIIB of  FIG. 3A . The current sensor  20   com  includes a printed wire  160  having an output line  162  and a ground line  164 , each of which is free of the turn wire  66 . 
         [0053]    The current sensor  20   com  operates in the following manner when the positive bus bar current Ib flows in the current sensor  20   com.  
   (a-1) Upon flowing of the positive bus bar current Ib, a magnetic field is generated around the bus bar  36  in a clockwise direction in  FIG. 3B , i.e., from the left to the right in  FIG. 3A , according to Ampere&#39;s right-hand rule, thereby producing a magnetic flux θ 1  in the shield plate  54  around the bus bar  36 .   (a-2) When the magnetic flux θ 1  is produced in the shield plate  54 , as shown in  FIG. 4 , an eddy current Ie is generated in the shield plate  54  in a direction that acts to oppose a change in the magnetic flux θ 1 .   (a-3) Due to the eddy current Ie generated in the shield plate  54 , the magnetic flux θ 1  produced in the shield plate  54  suffers a slight phase deviation from the bus bar current Ib. Therefore, the waveform of the output (device voltage Ve) from the magnetic detecting device  52 , which detects the magnetic flux θ 1 , also has a phase deviation (response delay) from the bus bar current Ib (see  FIG. 5 ). As shown in  FIG. 5 , an error e represents an error that occurs between the bus bar current Ib and the device voltage Ve as a result of the response delay.   
 
         [0057]    As described above, the coreless current sensor  20   com  according to the comparative example causes a phase delay (response delay) between the waveform of the bus bar current 
         [0058]    Ib and the waveform of the device voltage Ve. Bus bar currents Ib in U, V, and W phases, which are detected by the respective coreless current sensors  20   com,  are required in order to calculate a d-axis current Id and a q-axis current Iq for energizing the motor  12  (see, JP2010-045874A). The phase delay (response delay) between the bus bar current Ib and the device voltage Ve makes it impossible to control the motor  12  accurately, resulting in a reduction in output efficiency of the motor  12 . Such a problem is manifested in particular when the rotational speed [rpm] of the motor  12  is high. 
       (2-1-2. When the Bus Bar Current Ib Flows in a Negative Direction) 
       [0059]      FIGS. 6A and 6B  show a magnetic flux θ 1 , which is produced around the coreless current sensor  20   com  according to the comparative example, when the bus bar current Ib flows in a downward direction (hereinafter referred to as a “negative direction”) in  FIG. 6A . 
         [0060]    The current sensor  20   com  operates in the following manner when the negative bus bar current Ib flows in the current sensor  20   com.  
   (b-1) Upon flowing of the negative bus bar current Ib, a magnetic field is generated around the bus bar  36  in a counterclockwise direction in  FIG. 6B , i.e., from the right to the left as shown in  FIG. 6A , according to Ampere&#39;s right-hand rule, thereby producing a magnetic flux θ 1  in the shield plate  54  around the bus bar  36 .   (b-2) When the magnetic flux θ 1  is produced in the shield plate  54 , as shown in  FIG. 7 , an eddy current Ie is generated in the shield plate  54  in a direction that acts to oppose a change in the magnetic flux θ 1 .   (b-3) Due to the eddy current Ie generated in the shield plate  54 , the magnetic flux θ 1  produced in the shield plate  54  suffers a slight phase deviation from the bus bar current Ib. Therefore, the waveform of the output (device voltage Ve) from the magnetic detecting device  52 , which detects the magnetic flux θ 1 , also has a phase deviation (response delay) from the bus bar current Ib (see  FIG. 5 ).   
 
         [0064]    As described above, when the negative bus bar current Ib flows in the current sensor  20   com,  the coreless current sensor  20   com  also suffers from the same problems as those that occur when the positive bus bar current Ib flows in the current sensor  20   com.    
       [2-2. In the Presence of the Turn Wire  66 ] 
       [0065]    Operations in the presence of the turn wire  66  will be described below. When the inverter  14  is energized, the directions of currents that flow through the bus bars  36  are switched in succession. 
       (2-2-1. When the Bus Bar Current Ib Flows in a Positive Direction) 
       [0066]      FIGS. 8A and 8B  show magnetic fluxes (magnetic fluxes θ 1 , θ 2 ), which are produced around the current sensor  20  having the turn wire  66 , when the bus bar current Ib flows in the positive direction (the upward direction in  FIG. 8A ). 
         [0067]    The current sensor  20  operates as follows and offers the following advantages when the positive bus bar current Ib flows in the current sensor  20 .
   (c-1) Upon flowing of the positive bus bar current Ib, a magnetic field is generated around the bus bar  36  in a clockwise direction in  FIG. 8B , i.e., from the left to the right as shown in  FIG. 8A , according to Ampere&#39;s right-hand rule, thereby producing a magnetic flux θ 1  in the shield plate  54  around the bus bar  36 .   (c-2) When the magnetic flux θ 1  is produced in the shield plate  54 , as shown in  FIG. 4 , an eddy current Ie is generated in the shield plate  54  in a direction that acts to oppose a change in the magnetic flux θ 1 .   (c-3) Due to the eddy current Ie generated in the shield plate  54 , the magnetic flux θ 1  produced in the shield plate  54  suffers a slight phase deviation from the bus bar current Ib. Therefore, the waveform of the output (device voltage Ve) from the magnetic detecting device  52 , which detects the magnetic flux θ 1 , also has a phase deviation (response delay) from the bus bar current Ib (see  FIG. 5 ). Operations of the current sensor  20  up to this point are the same as those of the current sensor  20   com  according to the comparative example.   (c-4) Upon flowing of the positive bus bar current Ib, the voltage (device voltage Ve) on the output line  62  is positive, except at the instant that the polarity of the bus bar current Ib changes from negative to positive. Also, current flows from the ground line  64  toward the output line  62  of the printed wire  60 . Therefore, according to Ampere&#39;s right-hand rule, a magnetic flux θ 2  is produced around the turn wire  66  in a direction opposite to the magnetic flux θ 1  in the neighborhood of the shield plate  54  (see  FIG. 8B ).   (c-5) As the magnetic flux θ 1  in the shield plate  54  increases, a counter-electromotive force Vi is generated in the turn wire  66  in a direction (upward direction in  FIG. 8B ) that acts to oppose the increase in the magnetic flux θ 1  (in accordance with Lenz&#39;s Law).   (c-6) The direction in which the counter-electromotive force Vi is generated is the same as the direction (upward direction in  FIG. 8B ) of the magnetic flux θ 2  produced in the shield plate  54 . As a result, as shown in  FIG. 9 , the counter-electromotive force Vi is added to the output (device voltage Ve) from the magnetic detecting device  52  that detects the magnetic flux θ 1 . Thus, the waveform of the device voltage Ve, which is output to the ECU  24 , becomes closer in phase to the waveform of the bus bar current Ib, thereby reducing the phase deviation (response delay) between the bus bar current Ib and the device voltage Ve.   
 
         [0074]    As described above, the coreless current sensor  20  according to the present embodiment is capable of reducing a phase deviation (response delay) between the waveform of the bus bar current Ib and the waveform of the device voltage Ve ( FIG. 9 ). The bus bar currents Ib in U, V, and W phases, which are detected by the respective current sensors  20 , are required to calculate a d-axis current Id and a q-axis current Iq for energizing the motor  12  (see, JP2010-045874A). Consequently, the reduced phase delay (response delay) between the bus bar current Ib and the device voltage Ve makes it possible to control the motor  12  more accurately, thereby enabling the output efficiency of the motor  12  to be maintained or increased. This advantage is manifested in particular when the rotational speed [rpm] of the motor  12  is high. 
       (2-2-2. When the Bus Bar Current Ib Flows in a Negative Direction) 
       [0075]      FIGS. 10A and 10B  show magnetic fluxes (magnetic fluxes θ 1 , θ 2 ), which are produced around the current sensor  20  having the turn wire  66 , when the bus bar current Ib flows in the negative direction (the downward direction in  FIG. 10A ). 
         [0076]    The current sensor  20  operates as follows and offers the following advantages when the negative bus bar current Ib flows in the current sensor  20 .
   (d-1) Upon flowing of the negative bus bar current Ib, a magnetic field is generated around the bus bar  36  in a counterclockwise direction in  FIG. 10B , i.e., from the right to the left in  FIG. 10A , according to Ampere&#39;s right-hand rule, thereby producing a magnetic flux θ 1  in the shield plate  54  around the bus bar  36 .   (d-2) When the magnetic flux θ 1  is produced in the shield plate  54 , as shown in  FIG. 7 , an eddy current Ie is generated in the shield plate  54  in a direction that acts to oppose a change in the magnetic flux θ 1 .   (d-3) Due to the eddy current Ie generated in the shield plate  54 , the magnetic flux θ 1  produced in the shield plate  54  suffers a slight phase deviation from the bus bar current Ib. Therefore, the waveform of the output (device voltage Ve) from the magnetic detecting device  52 , which detects the magnetic flux θ 1 , also has a phase deviation (response delay) from the bus bar current Ib (see  FIG. 5 ). Operations of the current sensor  20  up to this point are the same as those of the current sensor  20   com  according to the comparative example.   (d-4) Upon flowing of the negative bus bar current Ib, the voltage (device voltage Ve) on the output line  62  is negative, except at the instant that the polarity of the bus bar current Ib changes from positive to negative. Also, current flows from the output line  62  toward the ground line  64  of the printed wire  60 . Therefore, according to Ampere&#39;s right-hand rule, a magnetic flux θ 2  is produced around the turn wire  66  in a direction opposite to the magnetic flux θ 1  in the neighborhood of the shield plate  54  (see  10 B).   (d-5) As the magnetic flux θ 1  in the shield plate  54  increases, a counter-electromotive force Vi is generated by the turn wire  66  in a direction (downward direction in  FIG. 10B ) that acts to oppose the increase in the magnetic flux θ 1  (in accordance with Lenz&#39;s law).   (d-6) The direction in which the counter-electromotive force Vi is generated is the same as the direction (downward direction in  FIG. 10B ) of the magnetic flux θ 2  produced in the shield plate  54 . As a result, as shown in  FIG. 9 , the counter-electromotive force Vi is added to the output (device voltage Ve) from the magnetic detecting device  52  that detects the magnetic flux θ 1 . Thus, the waveform of the device voltage Ve, which is output to the ECU  24 , becomes closer in phase to the waveform of the bus bar current Ib, thereby reducing the phase deviation (response delay) between the bus bar current Ib and the device voltage Ve.   
 
         [0083]    As described above, upon flowing of the negative bus bar current Ib, the coreless current sensor  20  according to the present embodiment offers the same advantages as those that are realized when the positive bus bar current Ib flows. 
       [2-3. Number of Turns of the Turn Wire  66 ] 
       [0084]    According to the present embodiment, as described above, the counter-electromotive force Vi is added to the device voltage Ve in order to reduce the phase deviation (response delay) between the bus bar current Ib and the device voltage Ve. The effect of reducing the phase deviation (response delay) can be adjusted depending on the number of turns Nt of the turn wire  66 . In  FIG. 2A , the number of turns Nt is 1. 
         [0085]      FIG. 11  is a diagram showing by way of example the relationship between the number of turns Nt of the turn wire  66  around the shield plate  54  and phase deviations Pc [deg] of the corrected device voltage Ve. In  FIG. 11 , if the number of turns Nt is zero, the phase deviation Pc is very large. As the number of turns Nt increases to 1 and 2, the phase deviation Pc becomes smaller. The phase deviation Pc is closest to zero when the number of turns Nt is 3. In the example shown in  FIG. 11 , therefore, the phase deviation Pc becomes optimum when the number of turns Nt is 3. 
       3. Advantages of the Embodiment 
       [0086]    According to the present embodiment, as described above, the counter-electromotive force Vi from the output line  62  is added to the device voltage Ve in order to compensate for the phase deviation (response delay) between the waveform of the bus bar current Ib and the waveform of the device voltage Ve. Consequently, it is possible to suppress the phase deviation (response delay) with a simple arrangement. 
       4. Modifications 
       [0087]    The present invention is not limited to the above embodiment, but may incorporate various alternative arrangements based on the disclosure of the present description. For example, the present invention may employ the following arrangements. 
         [0000]    [4-1. Objects in which the Invention may be Incorporated] 
         [0088]    According to the above embodiment, the coreless current sensor  20  is incorporated in a vehicle  10 . However, the coreless current sensor  20  may be incorporated in other objects. For example, the current sensor  20  may be incorporated in various mobile bodies such as electric trains, ships, airplanes, or the like. Alternatively, the current sensor  20  may be incorporated in machine tools or electric products. 
         [0089]    According to the above embodiment, the coreless current sensor  20  is used in an AC-based application (e.g., for energizing an AC motor  12 ). However, the coreless current sensor  20  is not limited to such an application, and may be used in applications for compensating a phase deviation (response delay) between a detected current and an output voltage. For example, the coreless current sensor  20  may be used in DC motors, so as to enable quick switching (from OFF to ON or from ON to OFF) to be detected with a high response. 
       [4-2. Shield Plate  54 ] 
       [0090]    According to the above embodiment, the shield plate  54  is of a rectangular shape with one side removed (i.e., a U shape with corners) (see  FIGS. 2A and 2B ). However, the shield plate  54  is not limited to such a shape, and may be of a curved shape (i.e., a U shape without corners), for example. 
         [0091]    According to the above embodiment, the shield plate  54  has been given as an example of a component for producing a response delay in the device voltage Ve from the magnetic detecting device  52 . However, another conductor (in particular, a conductor that facilitates generation of eddy currents) may be used to produce such a response delay. If the shield plate  54  is used, the eddy current Ie is proportional to the square of the thickness of the shield plate  54 . 
       [4-3. Turn Wire  66 ] 
       [0092]    According to the above embodiment, as shown on the right side in  FIG. 2A , the turn wire  66  is included in the output line  62  in surrounding relation to the shield plate  54 . However, as shown on the left side in  FIG. 12 , a coreless current sensor  20 A (first modification) shown in  FIG. 12  has a turn wire  66   a  included in an output line  62   a  of a printed wire  60   a,  so as to be coiled around the shield plate  54 . In  FIG. 12 , using the through holes  72 , the output line  62   a  is kept out of contact with the ground line  64 , and using the through holes  68   a,  the output line  62   a  is prevented from having overlapping portions. 
         [0093]    According to the above embodiment and the first modification shown in  FIG. 12 , the turn wires  66 ,  66   a  are included within the output lines  62 ,  62   a.  However, a coreless current sensor  20 B (second modification) shown in  FIG. 13  does not have a turn wire included within the output line  62   b  of the printed wire  60   b,  but instead, the ground line  64   a  is included within the turn wire  66   b.  As shown in  FIG. 12 , using the through holes  72   a,  the ground line  64   a  is kept out of contact with the output line  62   b.    
         [0094]    Alternatively, a coreless current sensor  20 C (third modification) shown in  FIG. 14  has a turn wire  66  in an output line  62  of a printed wire  60   c,  and has a turn wire  66   b  in a ground line  64   b.    
         [0095]    According to the above embodiment as well as the first through third modifications, on the printed circuit board  50  that lies parallel to the bus bar  36 , in both plan and cross-sectional views, the turn wire  66  is disposed on one or both of the right side or the left side of the magnetic detecting device  52 . However, the turn wire  66  is not limited to such a position. If the printed circuit board  50  is of a three-dimensional pattern, for example, the turn wire  66  may be positioned on the upper side or the lower side, or on both upper and lower sides, of the magnetic detecting device  52 , as viewed in cross-section. 
       [4-4. Other Applications] 
       [0096]    According to the above embodiment, the turn wire  66  is used to reduce a phase deviation (response delay) between the waveform of the bus bar current Ib and the waveform of the device voltage Ve. However, the turn wire  66  also is suitable for an application of increasing the phase deviation (response delay) between the waveform of the bus bar current Ib and the waveform of the device voltage Ve, e.g., an application for delaying the output of the magnetic detecting device  52  in synchronism with another output. In such an application, the turn wires  66 ,  66   a,    66   b  should be coiled in an opposite direction around the shield plate  54 .