Patent Publication Number: US-2023162894-A1

Title: Shunt resistor

Description:
TECHNICAL FIELD 
     The present invention relates to a shunt resistor for current detection. 
     BACKGROUND ART 
     Conventionally, a shunt resistor is widely used in current detecting applications. Such a shunt resistor includes a plate-shaped resistance element and plate-shaped electrodes joined to both ends of the resistance element. The resistance element is made of alloy, such as copper-nickel alloy, copper-manganese alloy, iron-chromium alloy, or nickel-chromium alloy. The electrodes are made of highly conductive metal, such as copper. 
     The shunt resistor is required to have a small temperature coefficient of resistance (TCR) in order to detect current with little temperature fluctuation. The temperature coefficient of resistance (TCR) is an index that indicates a rate of change in resistance due to temperature change. In order to improve the TCR of the shunt resistor, an alloy with a low TCR, such as Manganin (registered trademark), has been used as a material of the resistance element. 
     CITATION LIST 
     Patent Literature 
     Patent document 1: Japanese laid-open patent publication No. 2007-329421 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, there is a limit to adjusting (improving) the TCR by selecting the material of the resistance element. It is therefore an object of the present invention to provide a shunt resistor allowing for easy adjustment of TCR regardless of a material of a resistance element, i.e., capable of achieving a desired TCR. 
     Solution to Problem 
     In an embodiment, there is provided a shunt resistor comprising: a resistance element having a plate shape; and electrodes connected to both end surfaces of the resistance element, wherein the electrodes have cut portions, respectively, the cut portions extending parallel to joint portions of the resistance element and the electrodes, and each of the cut portions is located at a position where a relationship Y≤0.80X-1.36 holds, where Y is a distance from each joint portion to each cut portion, and X is a length of the joint portions in a width direction of the electrodes. 
     In an embodiment, the shunt resistor further comprises voltage detection terminals provided on voltage detecting portions located between the joint portions and the cut portions. 
     In an embodiment, a width of the electrodes at positions where the cut portions are formed is ½ or more of the length of the joint portions in the width direction of the electrodes. 
     Advantageous Effects of Invention 
     Each cut portion is formed at a position where the relationship L≤0.80X-1.36 holds, where Y is the distance from the joint portion to the cut portion, and X is the length of the joint portion in the width direction of the electrodes. The cut portions extend parallel to the joint portions. As a result, a desired TCR can he satisfied with a simple configuration. In addition, the TCR of the shunt resistor can be easily adjusted by the adjustment of the length of the cut portions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view schematically showing an embodiment of a shunt resistor; 
         FIG.  2    is a plan view of the shunt resistor shown in  FIG.  1   ; 
         FIG.  3    is a graph showing a rate of change in resistance value of the shunt resistor due to temperature change; 
         FIG.  4    is a plan view showing another embodiment of a shunt resistor; 
         FIG.  5    is a plan view showing still another embodiment of a shunt resistor; 
         FIG.  6    is a perspective view schematically showing still another embodiment of a shunt resistor; and 
         FIG.  7    is an exploded perspective view of the shunt resistor of  FIG.  6   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG.  1    is a perspective view schematically showing an embodiment of a shunt resistor  1 , and  FIG.  2    is a plan view of the shunt resistor  1  shown in  FIG.  1   . White arrows shown in  FIG.  2    indicate a direction of an electric current flowing through the shunt resistor  1 . As shown in  FIGS.  1  and  2   , the shunt resistor  1  includes a plate-shaped resistance element  5  made of an alloy having a predetermined thickness and a predetermined width, and electrodes  6  and  7  made of a highly conductive metal connected to both end surfaces  5   a  and  5   b  of the resistance element  5 . Specifically, the electrode  6  is connected to the end surface  5   a , and the electrode  7  is connected to the end surface  5   b . Configurations of the electrode  7 , which will not he particularly described, are the same as configurations of the electrode  6 . The electrodes  6  and  7  are arranged symmetrically with respect to the resistance element  5 . The width of the electrode  6  and the width of the electrode  7  are the same, and are represented by a width W 2 . A width direction of the electrodes  6  and  7  is a direction perpendicular to the current direction. An example of an alloy forming the resistance element  5  is a nickel-chromium alloy. An example of the highly conductive metal forming the electrodes  6  and  7  is copper. 
     Specifically, inner end surfaces  6   a  and  7   a  of the electrodes  6  and  7  are joined to the both end surfaces  5   a  and  5   b  of the resistance element  5 , respectively, by means of welding (for example, electron beam welding, laser beam welding, or brazing). The inner end surfaces  6   a  and  7   a  are joint surfaces joined to the resistance element  5 . Hereinafter, in this specification, the inner end surfaces  6   a  and  7   a  may be referred to as joint surfaces  6   a  and  7   a.    
     The inner end surface  6   a  of the electrode  6  and the end surface  5   a  of the resistance element  5  constitute a joint portion  8  of the resistance element  5  and the electrode  6 . The inner end surface  7   a  of the electrode  7  and the end surface  5   b  of the resistance element  5  constitute a joint portion  9  of the resistance element  5  and the electrode  7 . 
     The electrodes  6  and  7  have cut portions  11  and  12 , respectively. The cut portions  11  and  12  extend parallel to the joint portions  8  and  9  (i.e., the joint surfaces  6   a  and  7   a  and both end surfaces  5   a  and  5   b ), respectively. The cut portions  11  and  12  of this embodiment have a slit shape extending linearly. The cut portion  11  extends linearly from a side surface  6   b  of the electrode  6  toward the center of the electrode  6 , and the cut portion  12  extends linearly from a side surface  7   b  of the electrode  7  toward the center of the electrode  7 . 
     Configurations of the cut portion  12 , which will not be particularly described, are the same as those of the cut portion  11 . The cut portion  11  and the cut portion  12  are arranged symmetrically with respect to the resistance element  5 . In this embodiment, the cut portion  12  has the same width W 1  as the width of the cut portion  11 . A length of the cut portion  11  in a width direction of the electrodes  6  and  7  (i.e., a direction parallel to the joint surfaces  6   a  and  7   a  and perpendicular to the current direction) is the same as a length of the cut portion  12  in the width direction of the electrodes  6  and  7 , and both lengths are denoted by t 1 . 
     The cut portions  11  and  12  formed in the electrodes  6  and  7  causes the electric current flowing through he shunt resistor  1  to avoid the cut portions  11  and  12 . As a result, a state of the electric current flowing through the shunt resistor  1  is different from a state of electric current flowing through a shunt resistor without the cut portions. As a result, a TCR (temperature coefficient of resistance) of the shunt resistor  1  is different from a TCR (temperature coefficient of resistance) of a shunt resistor without cut portions in electrodes. 
     in this embodiment, a length of the joint portion  8  (or the joint surface  6   a  and the end surface  5   a ) in the width direction of the electrode  6  is the same as a length of the joint portion  9  (or the joint surface  7   a  and the end surface  5   b ) in the width direction of the electrode  7 . A distance from the joint portion  8  (or the joint surface  6   a ) to the cut portion  11  is the same as a distance from the joint portion  9  (or the joint surface  7   a ) to the cut portion  12 . In the present embodiment, the cut portions  11  and  12  are located such that a relationship expressed by a formula (1) Y≤0.80X-1.36 holds, where Y represents the distance from each of the joint portions  8  and  9  to each of the cut portions  11  and  12 . and X represents the length of the joint portions  8  and  9  in the width direction of the electrodes  6  and  7 . 
     The TCR of the shunt resistor  1  can be adjusted by forming the cut portions  11  and  12  at positions where the relationship of the above formula (1) holds. Specifically, when the cut portions  11  and  12  are formed at positions where the relationship of the above formula (1) is established, the TCR of the shunt resistor  1  can be adjusted by changing the length t 1  of the cut portions  11  and  12 . In other words, the temperature coefficient of resistance of the shunt resistor  1  can be adjusted by forming the cut portions  11  and  12  having an adjusted length t 1  at positions where the relationship of the above formula (1) holds. 
     Voltage detection terminals  16  and  17  are provided on surfaces of the electrodes  6  and  7 , respectively. The voltage detection terminals  16  and  17  are used for measuring a voltage generated across the resistance element  5  (i.e., generated between both end surfaces  5   a  and  5   b ). For example, a aluminum wires are coupled to the voltage detection terminals  16  and  17 , so that the voltage generated between both end surfaces of the resistance element  5  is detected. The voltage detection terminal  16  is provided on a voltage detecting portion  20  of the electrode  6 , and the voltage detection terminal  17  is provided on a voltage detecting portion  21  of the electrode  7 . The voltage detecting portion  20  is located between the joint portion  8  and the cut portion  11 , rind the voltage detecting portion  21  is located between the joint portion  9  and the cut portion  12 . 
     The voltage detection terminals  16  and  17  provided on the voltage detecting portions  20  and  21  (i.e., the voltage detecting portions  20  and  21  located in voltage detecting positions) can allow for measuring of the voltage reflecting the adjusted TCR. Specifically, the voltage of the resistance element  5  can be measured while the TCR of the shunt resistor  1  is affected by the cut portions  11  and  12 . The arrangements of the voltage detection terminals  16  and  17  adjacent to the resistance element  5  make it possible to measure the voltage that more reflects the adjusted TCR. 
       FIG.  3    is a graph showing a rate of change in a resistance value of the shunt resistor  1  due to temperature change.  FIG.  3    shows the rate of change in the resistance value of the shunt resistor  1  according to the change in temperature when the resistance element  5  is made of a nickel-chromium alloy and the electrodes  6  and  7  are made of copper. The cut portions  11  and  12  are formed at positions where the relationship of the above formula (1) holds. In  FIG.  3   , the width W 1  (see  FIG.  2   ) of the cut portions  11  and  12  is 0.1 mm, the width W 2  (see  FIG.  2   ) of the electrodes  6  and  7  is 15 mm, the width W 3  of the resistance element  5  (see  FIG.  2   ) is 7 mm, and the distance (see  FIG.  2   ) from each of the joint portions  8  and  9  (or the joint surfaces  6   a  and  7   a ) to each of the cut portions  11  and  12  is 3 mm. 
       FIG.  3    shows the rate of change in the resistance value of the shunt resistor with the temperature change when the length t 1  of the cut portions  11  and  12  is 2 mm, 2.5 mm, 3 mm, and 3.5 mm. For comparison,  FIG.  3    further shows a rate of change in a resistance value of a shunt resistor in which the cut portions  11  and  12  are not formed. Other configurations of the shunt resistor in which the cut portions  11  and  12  are not formed are the same as those of the shunt resistor  1 . 
       FIG.  3    shows that, when the cut portions  11  and  12  having the width W 1  of 0.1 mm are formed in the electrodes  6  and  7 , a ratio of the rate of change in the resistance value to an amount of change in temperature of the shunt resistor  1  is reduced. The ratio of the rate of change in the resistance value to the amount of change in temperature of the shunt resistor  1  corresponds to the temperature coefficient of resistance (TCR) of the shunt resistor  1 . Furthermore,  FIG.  3    shows that the temperature coefficient of resistance of the shunt resistor  1  depends on the length t 1  of the cut portions  11  and  12 . Specifically,  FIG.  3    shows that the adjustment of the length t 1  of the cut portions  11  and  12  when the cut portions  11  and  12  are formed at the positions where the relationship of the above formula (1) holds, i.e., the cut portions  11  and  12  having the adjusted length t 1  formed at the positions where the relationship of the above formula (1) holds, allows for the adjustment of the temperature coefficient of resistance (TCR) of the shunt resistor  1 . 
     As shown in  FIG.  3   , as the length t 1  of the cut portions  11  and  12  increases, the temperature coefficient of resistance of the shunt resistor  1  decreases. When the length t 1  is 3 mm, an absolute value of the temperature coefficient of resistance of the shunt resistor  1  is minimized. When the length t 1  is 3.5 mm, the temperature coefficient of resistance of the shunt resistor  1  has a negative slope. Therefore, by adjusting the length t 1  of the cut portions  11  and  12 , i.e., by forming the cut portions  11  and  12  having an adjusted length t 1  at the positions where the relationship of the above formula (1) holds, the temperature coefficient of resistance (TCR) of the shunt resistor  1  can be adjusted over a wide range (i.e., a desired TCR can be achieved). As a result, an optimum TCR adjustment can be achieved not only when a nickel-chromium alloy is used for the resistance element  5 , but also when various alloys are used for the resistance element  5 . According to the present embodiment, the desired temperature coefficient of resistance can be achieved with a simple structure in which the cut portions  11  and  12  having an adjusted length t 1  are formed at positions where the above formula (1) holds. 
     In this embodiment, the width W 3  of the resistance element  5  is 7 mm, and the width W 1  of the cut portions  11  and  12  is 0.1 mm. It should be noted, however, the widths W 3  and W 1  are not limited to this embodiment. The TCR of the shunt resistor  1  can be adjusted by the adjustment of the length t 1  of the cut portions  11  and  12  regardless of the magnitudes of the width W 3  and the width W 1 . When the cut portions  11  and  12  are formed at positions where the relationship of the above formula (1) holds and the cut portions  11  and  12  extend parallel to the joint portions  8  and  9 , the temperature coefficient of resistance (TCR) of the shunt resistor  1  can be adjusted easily (i.e., a desired TCR can be achieved) by adjusting the length t 1  of the cut portions  11  and  12 , i.e., by forming the cut portions  11  and  12  having an adjusted length t 1  at the positions where the relationship of the above formula (1) holds. 
     As shown in  FIG.  2   , a width W 4  of the electrode  6  (and the electrode  7 ) narrowed by the formation of the cut portion  11  (and the cut portion  12 ) is preferably ½ or more of a length X of the joint portions  8  and  9 . In other words, the width W 4  of the electrodes  6  and  7  is a width of the electrodes  6  and  7  at positions where the cut portions  11  and  12  are formed with respect to a direction perpendicular to the width direction of the electrodes  6  and  7 . The width W 4  having ½ or more of the length X allows the electrodes  6  and  7  to have sufficient mechanical strength, and can prevent a decrease in high-frequency characteristics of the shunt resistor  1  that can occur due to the decrease in the width W 4 . The results of  FIG.  3    show that, when the cut portions  11  and  12  are formed at positions where the relationship of the above formula (1) holds, the TCR can vary widely while the width W 4  is ½ or more of the length X. 
       FIG.  4    is a plan view showing another embodiment of the shunt resistor  1 . Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to  FIGS.  1  and  2   , and redundant descriptions thereof will be omitted. In this embodiment, the cut portion  12  extends from a side surface  7   c  of the electrode  7  toward the center of the electrode  7 . Side surfaces  6   c  and  7   c  shown in  FIG.  4    are opposite surfaces from the side surfaces  6   b  and  7   b.    
     In this embodiment also, when the cut portions  11  and  12  are formed at positions where the relationship of the above formula (1) holds, the temperature coefficient of resistance (TCR) of the shunt resistor  1  can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t 1  of the cut portions  11  and  12 , i.e., by forming the cut portions  11  and  12  having an adjusted length t 1  at the positions where the relationship of the above formula (1) holds. In an embodiment, the cut portion  11  may be formed so as to extend from the side surface  6   c  of the electrode  6  toward the center of the electrode  6 , and the cut portion  12  may be formed so as to extend from the side surface  7   b  of the electrode  7  to the center of the electrode  7 . 
       FIG.  5    is a plan view showing still another embodiment of the shunt resistor  1 . Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to  FIGS.  1  and  2   , and redundant descriptions thereof will be omitted. In this embodiment, the electrode  6  further has a cut portion  13 , and the electrode  7  further has a cut portion  14 . 
     The cut portions  13  and  14  extend parallel to the joint portions  8  and  9  (or the joint surfaces  6   a  and  7   a  and both end surfaces  5   a  and  5   b ), respectively. The cut portions  13  and  14  of this embodiment have a slit shape extending linearly. The cut portion  13  extends linearly from the side surface  6   c  of the electrode  6  toward the center of the electrode  6 , and the cut portion  14  extends linearly from the side surface  7   c  of the electrode  7  toward the center of the electrode  7 . The cut portion  13  is formed on an extension line of the cut portion  11 , and the cut portion  14  is formed on an extension line of the cut portion  12 . Specifically, the cut portions  13  and  14  are arranged at the same positions as the cut portions  11  and  12 , respectively, in the direction perpendicular to the width direction of the electrodes  6  and  7 . 
     Configurations of the cut portion  14 , which will not he particularly described, are the same as those of the cut portion  13 . The cut portion  13  and the cut portion  14  are arranged symmetrically with respect to the resistance element  5 . In this embodiment, the cut portion  14  has a width W 5  which is the same as a width of the cut portion  13 . A length of the cut portion  13  in the width direction of the electrodes  6  and  7  is the same as a length of the cut portion  14  in the width direction of the electrodes  6  and  7 , and both of these lengths are represented by length t 2 . 
     in this embodiment, voltage detection terminals  18  and  19  are provided on the surfaces of the electrodes  6  and  7 , respectively. The voltage detection terminal  18  is provided on a voltage detecting portion  22  of the electrode  6 , and the voltage detection terminal  19  is provided on a voltage detecting portion  23  of the electrode  7 . The voltage detecting portion  22  is located between the joint portion  8  and the cut portion  13 . The voltage detecting portion  23  is located between the joint portion  9  and the cut portion  14 . Configurations of the voltage detection terminals  18  and  19  and the voltage detecting portions  22  and  23 , which are not specifically described, are the same as those of the voltage detection terminals  16  and  17  and the voltage detecting portions  20  and  21 , respectively. 
     Also in this embodiment, when the cut portions  11 ,  12 ,  13 , and  14  are formed at positions where the relationship of the above formula (1) holds, the temperature coefficient of resistance (TCR) of the shunt resistor  1  can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t 1  of the cut portions  11  and  12  and the length t 2  of the cut portions  13  and  14 , i.e., by forming the cut portions  11 ,  12 ,  13  and  14  having adjusted lengths t 1  and t 2  at the positions where the relationship of the above formula (1) holds. The length t 1  and the length t 2  may be the same or different. The width W 1  and the width W 5  may he the same or different. Also in the present embodiment, the width W 4  of the electrodes  6  and  7  narrowed by the formation of the cut portions  11 ,  12 ,  13  and  14  is preferably ½ or more of the length X of the joint portions  8  and  9 . 
       FIG.  6    is a perspective view schematically showing still another embodiment of a shunt resistor  1 , and  FIG.  7    is an exploded perspective view of the shunt resistor  1  of  FIG.  6   . Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiments described with reference to  FIGS.  1  and  2   , and redundant descriptions thereof will be omitted. The shunt resistor  1  of this embodiment further includes a substrate  40  which is made of insulating material, and a pedestal  35 . Conductors  41  and  42  and voltage detection terminals  46  and  47  are provided on a surface of substrate  40 . White arrows shown in  FIG.  6    indicate the direction of electric current flowing through the shunt resistor  1 . The pedestal  35  has electrical contacts  36 ,  37  on its surface. 
     As shown in  FIGS.  6  and  7   , the cut portion  11  of this embodiment has a first surface  11   a  extending parallel to the joint portion  8  and a second surface  11   b  extending in a direction perpendicular to the first surface  11   a . The cut portion  12  has a first surface  12   a  extending parallel to the joint portion  9  and a second surface  12   h  extending in a direction perpendicular to the first surface  12   a . An outer end surface  6   d  of the electrode  6  and the first surface  11   a  are coupled by the second surface  11   b , and an outer end surface  7   d  of the electrode  7  and the first surface  12   a  are coupled by the second surface  12   b.    
     The electrode  6  is folded at a position between the first surface  11   a  and the joint surface  6   a , and the electrode  7  is folded at a position between the first surface  12   a  and the joint surface  7   a . The electrodes  6 ,  7  are symmetrically bent with respect to the resistance element  5 . The outer end faces  6   d  and  7   d  are in contact with the conductors  41  and  42 , respectively. With such configurations, the electric current flows from the conductor  41  through the electrode  6 , the resistance element  5 , and the electrode  7  to the conductor  42 . 
     The first surfaces  11   a ,  12   a  are in contact with the electrical contacts  36 ,  37 , respectively. The pedestal  35  further includes a plurality of conductive wires (not shown). The electrical contact  36  is coupled to the voltage detection terminal  46  via one of the plurality of conductive wires, and the electrical contact  37  is coupled to the voltage detection terminal  47  via another conductive wire. With such configurations, the voltage generated across the resistance element  5  (i.e., generated between the end surfaces  5   a  and  5   b ) can be measured via the voltage detection terminals  46  and  47 . For example, the voltage generated across the resistance element  5  is detected via aluminum wires coupled to the voltage detection terminals  46  and  47 . 
     Also in this embodiment, the electric current flows from the conductor  41  to the conductor  42  while avoiding the cut portions  11  and  12 . Therefore, as well as the embodiments described with reference to  FIGS.  1  and  2   , the temperature coefficient of resistance (TCR) of the shunt resistor  1  can be adjusted (i.e., a desired TCR can be achieved) by adjusting the length t 1  of the cut portions  11  and  12  in the width direction of the electrodes  6  and  7 , i.e., by forming the cut portions  11  and  12  having an adjusted length t 1  at the positions where the relationship of the above formula (1) holds. Also in this embodiment, the width W 4  of the electrode  6  (and the electrode  7 ) narrowed by the formation of the cut portion  11  (and the cut portion  12 ) is preferably ½ or more of the length X of the joint portions  8  and  9 . 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a shunt resistor for current detection. 
     REFERENCE SIGNS LIST 
     
         
           1  shunt resistor 
           6 ,  7  electrode 
           6   a , 7   a  inner end surface (joint surface) 
           6   b , 7   b  side surface 
           6   c , 7   c  side surface 
           6   d , 7   d  outer end surface 
           8 ,  9  joint portion 
           11 , 12 , 13 , 14  cut portion 
           11   a , 12   a  first surface 
           11   b , 12   b  second surface 
           16 , 17 , 18 , 19  voltage detection terminal 
           20 , 21 , 22 , 23  voltage detecting portion 
           35  pedestal 
           36 , 37  electrical contact 
           40  substrate 
           41 , 42  conductor 
           46 , 47  voltage detection terminal