Patent Application
20230326631
The present invention relates to a resistance alloy for use in a shunt resistor, use of a resistance ahoy in a shunt resistor, and a shunt resistor using a resistance alloy.
Resistance alloys for shunt resistors used for current detection and the like and composed of electrodes and a resistive body include copper-manganese based alloys (such as copper-manganese-nickel alloys), copper-nickel based alloys, nickel-chromium based alloys, and iron-chromium based alloys. For a resistance alloy for shunt resistors, in order to obtain high detection accuracy, copper-manganese based alloys are often used that have a low temperature coefficient of resistance (which may be hereafter referred to as “TCR”) and have a small thermal electromotive force with respect to copper. General copper-manganese based alloys (copper-manganese-nickel based alloys) include a copper-manganese-tin based alloy having a specific resistance of 29 μΩ·cm.
Consider designing a small-sized and low-resistance shunt resistor using the resistance alloy. In this case, it is necessary to increase the plate thickness to reduce resistance, which results in a decrease in processability in pressing and the like. On the other hand, if the distance between electrodes is reduced to achieve reduced resistance, the contribution of the TCR of the electrode portions to the entire shunt resistor increases. That is, the TCR of the shunt resistor as a whole (product TCR) increases.
Consider designing a small-sized and low-resistance shunt resistor using a resistance material having a low resistance value, such as a copper-nickel based alloy having a specific resistance of 20 μΩ·cm. In this case, the TCR of the resistance alloy is large, and the product TCR also becomes large. In addition, the thermal electromotive force with respect to copper is also large. Accordingly, as a resistance alloy for a shunt resistor, its uses and use conditions are limited.
Patent Literature 1: JP 2007-329421 A
Patent Literature 2: WO2016/111109 A1
In recent years, there has been a demand for using a current detection resistor for detecting large currents, such as on the order of 1000 A. To address such demand, the resistance value of shunt resistors has been progressively reduced to 100 μΩ, 50 μΩ, 25 μΩ, and 10 μΩ, for example.
Upon constructing a shunt resistor (current detection resistor) using the above resistance alloys, copper electrodes are welded to both ends of a resistive body. Copper has a high TCR of about 4,000 ppm/K (25 to 100° C.). If the shunt resistor is reduced in size or resistance, the percentage of contribution of the TCR of the copper electrodes to the resistance value of the shunt resistor increases. Consequently, the TCR of the shunt resistor increases and the current detection accuracy decreases.
Patent Literature 1 discloses techniques for adjusting the TCR by means of the shape of the resistor. However, processing the electrodes introduces the issue of an increase in the actual resistance of the resistor. Another issue is that it is difficult to perform processing or adjustment when the resistor is reduced in size.
In addition, when the shunt resistor is reduced in resistance and size, another issue is that the TCR of the resistor increases and the detection accuracy decreases. There is also the need to ensure the reliability of the current detection device.
Further, depending on the product specifications, the thickness and width of the shunt resistor may be fixed, in which case the following problems may occur.
For the following description, reference is made to
1) When the size of the electrodes of the shunt resistor is constant, if the resistance value of the shunt resistor is to be reduced, it is necessary to increase the thickness of the resistive body. However, if the plate thickness of the resistive body is large, problems may occur, such as a drooping of the cut portion or the inability to maintain a clean shape thereof when pressing (punching) or the like is performed.
2) Compared to the shunt resistor structure illustrated in
Further, as illustrated in
3) As another means for reducing the resistance value of the shunt resistor, it may be contemplated to reduce the specific resistance of the resistive body alloy the resistive body is composed of.
For example, as a resistive body alloy enabling a decrease in TCR and specific resistance, there is a Cu—7Mn—2.3Sn alloy. The specific resistance is 29 μΩ·cm, which cannot be said to be sufficiently low. As a resistance alloy having a specific resistance of 20 μΩ·cm, there is a Cu—Ni based alloy. This, however, has TCR perfbrmance of approximately 330 ppm/K, which is not very good. Additionally, the thermal electromotive force with respect to copper is large and has a large influence on current detection accuracy.
Patent Literature 2 discloses a resistance alloy composed of a Cu alloy containing Cu, no less than 6.20 mass % and no more than 7.40 mass % of Mn, and no less than 0.15 mass % and no more than 1.5 mass % of Si, the resistance alloy having a TCR absolute value no more than 15 ppm/K from 25° C. to 150° C.
This makes it possible to reduce the absolute value of the TCR in a wide temperature range. However, Patent Literature 2, while achieving a low TCR, does not disclose that specific resistance and thermal electromotive force with respect to copper are also reduced. This point will be discussed below.
It is an objective of the present invention to achieve a low specific resistance and a small thermal electromotive force with respect to copper in a resistor for current detection, such as a shunt resistor, while maintaining a low TCR.
Another objective is to provide a resistance alloy for use in such a shunt resistor.
According to an aspect of the present invention, there is provided a copper-manganese based resistance alloy for use in a current detection shunt resistor, the resistance alloy including 4.5 to 5.5 mass % of manganese, 0.05 to 0.30 mass % of silicon, 0.10 to 0.30 mass % of iron, and a balance being copper, and having a specific resistance of 15 to 25 μΩ.
A resistance alloy is characterized by a TCR less than or equal to 100×10−6/K (range of 0 to 100×10−6).
A resistance alloy according to one of the above is characterized by a thermal electromotive force with respect to copper within ±1 μV/K.
In this way, it is possible to achieve reductions in TCR and thermal electromotive force with respect to copper while reducing the value of the TCR of a shunt resistor formed with copper electrodes.
The present invention also provides use of the resistance alloy according to one of the above in a resistive body of a shunt resistor for use in a current detection device.
The present invention also provides a current detection shunt resistor comprising a resistive body and an electrode, the resistive body being formed of a resistance alloy including 4.5 to 5.5 mass % of manganese, 0.05 to 0.30 mass % of silicon, 0.10 to 0.30 mass % of iron, and a balance being copper, and having a specific resistance of 15 to 25 μΩ.
The present invention also provides a current detection shunt resistor comprising a resistive body and an electrode, the resistive body being formed of a resistance alloy including 4.5 to 5.5 mass % of manganese, 0.05 to 0.30 mass % of silicon, 0.10 to 0.30 mass % of iron, and a balance being copper, and having a specific resistance of 15 to 25 μΩ.
The present description includes the contents disclosed in JP Patent Application No. 2020-145278, based on which the present application claims priority.
By using the resistance alloy of the present invention, it is possible to achieve a low specific resistance and a small thermal electromotive force with respect to copper in a shunt resistor for use in a current detection device, while reducing the TCR thereof.
Further, by using the resistance alloy of the present invention, it is possible to ensure current detection reliability of the shunt resistor.
The inventors, by additionally including an appropriate amount of Fe in a resistance material using a Cu—Mn—Si based alloy such as described in Patent Literature 2, can achieve a low specific resistance (such as 15 to 25 μΩ·cm) while keeping a low TCR (such as less than or equal to 100×10−6/K).
Further, the composition and the like may be adjusted to have a small thermal electromotive force with respect to copper.
In the following, resistance alloys for use in shunt resistors according to the embodiments of the present invention, and a shunt resistor using the same, for example, will be described with reference to the drawings.
First, the inventors' considerations concerning the present invention will be briefly explained.
1) As the focus of the inventors, it is important to mix and use a resistance alloy that shows a negative TCR in the resistive body, to compensate for the contribution of the large positive TCR of copper used in the electrodes. However, there are few reports concerning resistance alloys having a large negative TCR.
2) While copper-nickel alloys having low TCR and excellent long-term stability are present, such alloys have a large thermal electromotive force of 40 μV/K with respect to copper. Thus, in a shunt resistor for use in a current detection device with large current flows, the detection accuracy decreases due to the Peltier effect.
3) As an example of an alloy having a negative TCR, there is a nickel-chromium based alloy. However, the nickel-chromium based alloy has a specific resistance greater than or equal to two-fold compared to copper-nickel alloys and copper-manganese alloys. Accordingly, it is difficult to achieve a reduced resistance of the shunt resistor.
In the present embodiment, a resistance alloy for a resistive body that makes it possible to achieve a low specific resistance (such as 15 to 25 μΩ·cm) is provided.
Further, the results of adjustment of the alloy composition and the like to have a low TCR (less than or equal to 100×10−6/K) and a sufficiently small thermal electromotive force with respect to copper (less than or equal to 1.0 μV/K) are indicated.
An embodiment of the present invention will be described below in concrete terms.
An alloy of the present embodiment is a resistance alloy having a low TCR, and is a quaternary alloy composed of copper-manganese-silicon-iron. The resistance alloy can be used as the resistance material of a shunt resistor.
Herein, the mass fraction of copper is shown on the axis on the upper-left side, and the mass fraction of silicon+iron is shown on the axis on the upper-right side. Meanwhile, the mass fraction of manganese is shown on the axis on the bottom side.
A representative value of manganese is 5.0 mass %. A representative value of silicon is 0.15 mass %. A representative value of iron is 0.2 mass %. The balance is copper.
As illustrated in
Next, an example of an evaluation sample manufacturing process will be briefly described:
The mass fraction of each of the alloy components in the region R is adjusted with respect to each other such that the resistance alloy has the following characteristics (appropriate conditions).
1) The specific resistance is greater than or equal to 15 μΩ·cm and less than or equal to 25 μΩ·cm.
2) The TCR with reference to 25° C. is less than or equal to 100×10−6/K (from 0 to approximately 100×10−6/K) at 100° C.
3) Thermal electromotive force with respect to copper is within +10 μV/K.
Thus, in the present invention, in order to solve the problems, a resistance alloy is provided that has a low specific resistance (about 20 μΩ·cm: in a range of 15 to 25 μΩ·cm), a low TCR (less than or equal to 100×10−6/K), and a small thermal electromotive force with respect to copper (within ±1 μV/K).
As used herein, the term “small-sized” with reference to a shunt resistor means those with a chip size of less than or equal to 6.3×3.1 mm. Also, the term “low resistance” means that the resistance of the product is 0.5 mΩ or less.
Various resistance alloys were prepared as shown below.
The compositions and characteristics of the resistance alloys are shown in Table 1.
Table 1 shows the compositions ant electrical characteristics (specific resistance, TCR, and thermal electromotive force with respect to copper) of the resistance alloys (Examples 1 and 2) according to the present embodiment and the resistance alloys including Comparative Example 1 (Cu—14Ni) and Comparative Example 2 (Cu—Mn—Sn alloy). Table 1 further includes Sample 1 to Sample 7 for the purpose of verifying and determining a composition range (content range) of the resistance alloy of the present invention.
With respect to the specific resistance of the resistance material, for the samples of Examples 1, 2, values (15 to 25 μΩ·cm) equivalent to those of Comparative Examples 1, 2, which are commercially available materials, were obtained. The thermal electromotive force with respect to copper (0 to 100° C.) is less than or equal to 0.2 μV/K, and sufficiently satisfies the appropriate condition.
By considering the data of Table 1, particularly the values of Examples 1, 2 and Samples 1 to 7, the following can be seen.
Compared to the results for Samples 1 to 3 that include neither Fe nor Si, the CuMn alloy makes it possible to achieve the appropriate conditions (characteristics requirements) with respect to the specific resistance and TCR characteristics of the present invention. However, the thermal electromotive force with respect to copper may exceed 1 μV/K. Accordingly, it is necessary to add an element that lowers the thermal electromotive force with respect to copper, without adversely affecting (increasing) the TCR.
If another element, such as Fe herein, is added to the CuMn alloy, the TCR decreases but the specific resistance tends to increase. Accordingly, in order to evaluate the effect of decreasing the TCR, it is necessary to consider both the specific resistance and the TCR.
As illustrated in
Further, in the Cu—5Mn—Fe alloys, it can be evaluated that the TCR increases (deteriorates) as the Fe composition increases. In particular, the TCR sharply increases as the Fe composition exceeds 0.5 mass % and reaches 1.0 mass %.
Note, however, that the TCR does not sharply increase as long as the Fe composition is less than 0.5 mass %, such as about 0.2 mass %.
In any of the ranges, the TCR is less than or equal to 100×10−6/K.
As will be seen from Sample 4 (Fe: 0.2 mass %), even if the amount of Fe added is small, there is the effect of greatly lowering the thermal electromotive force with respect to copper. Further, it can be seen that, from the values of Samples 2 and 4-6, by adding 0.1 to 0.3 mass % of Fe, the thermal electromotive force with respect to copper falls within the range of about ±0.5 μV/K. In addition, as will also be seen from
Thus, in the Cu—Mn alloys, if the resistance alloy has 0.10 to 0.30 mass % of iron added thereto, the thermal electromotive force with respect to copper can be kept within ±1 μV/K and the TCR less than or equal to 100×10−6/K.
If the composition of the Cu—Mn based alloy material is nearly 100% Cu, it can be expected that oxidation of Cu will become a problem. Accordingly, it is also important to suppress oxidation of Cu.
Using the evaluation element of
It can be seen from the XRD data (
This phenomenon is presumed to be based on the Cu-oxidation suppressing effect due to an Si oxide being formed on the material surface of the resistance alloy by the addition of Si.
As illustrated in
In the following, the effectiveness of the present invention is described in detail.
The present invention provides a resistance alloy for a current detection shunt resistor, the resistance alloy having 4.5 to 5.5 mass % of Mn, 0.10 to 0.30 mass % of Fe, 0.05 to 0.30 mass % of Si, and the balance being Cu.
The resistance alloy has a specific resistance in the range of 15 to 25 μΩ·cm.
Further, the resistance alloy has a TCR less than or equal to 100×10−6/K (25-100° C.).
Further, the resistance alloy has a thermal electromotive force with respect to copper within ±1 μV/K.
With such characteristics, the resistance alloy is suitable for a small-sized and low-resistance shunt resistor, and a low TCR value can also be achieved. The current detection accuracy of a current detection device using the shunt resistor is improved, and the space required for the current detection device can be reduced by a reduction in size of the shunt resistor.
Next, a second embodiment of the present invention will be described.
The shunt resistor A illustrated in
The resistive body 11 and the electrodes 15a, 15b may be joined by electron beam (EB) welding, laser beam (LB) welding, and the like. The shunt resistor A illustrated in
To confirm the effect of using the resistance alloy of the present invention in a shunt resistor product, a shunt resistor was fabricated using the resistive body of each of Example 1 and Comparative Example 2.
Table 2 compares Comparative Example 2 and Example 1, and shows size, resistance value, and TCR.
The outer size of the shunt resistor was 6.3 mm×3.1 mm, the thickness of the resistive body was 1 mm, and the rated resistance value of the shunt resistor was 0.2 mΩ.
As shown in Table 2, in the shunt resistor using the resistance alloy of Example 1, compared to when the resistance alloy of Comparative Example 2 is used, the specific resistance can be reduced, although the rated resistance value is the same. Accordingly, the length of the resistive body can be increased from 2 mm to 3 mm. Thus, the TCR can be reduced as described with reference to
In the shunt resistor according to the present embodiment, freedom of design of the shunt resistor can be ensured by using a resistive body having a relatively high specific resistance.
Further, by using the resistance alloy having a relatively high specific resistance, the contribution of the TCR of Cu used in the electrodes relative to the entire resistor can be reduced. Accordingly, a shunt resistor taking advantage of the characteristics of the resistance alloy can be provided.
Herein, in the present embodiment, the TCR of the resistance material is adjusted to be on the negative side. Thus, the TCR of the resistor to which the copper electrodes have been joined can be reduced.
For the shunt resistor A structured and dimensioned as illustrated in
Next, a third embodiment of the present invention will be described. This is an example of manufacture in which an elongated joined material comprising a resistive body and electrodes joined together is prepared and then punched and cut. In this way, it is possible to mass-produce relatively small-sized shunt resistors.
In the following, an example of such manufacturing process is described.
As illustrated in
As illustrated in
As illustrated in
The resistance value may be adjusted by the difference in thickness of the resistance material 21 and the electrode material 25a, 25b. Further, a step (Δh2) may be formed, as will be described below with reference to
Next, as illustrated in
Then, as illustrated in
Note that, as illustrated in
The shunt resistor according to the present embodiment has a specific resistance in the range of 15 to 25 μΩ·cm.
Further, the resistance alloy has a TCR less than or equal to 100×10−6/K (25-100° C.).
Further, the resistance alloy has a thermal electromotive force with respect to copper within ±1 μV/K. Further, the thermal electromotive force with respect to copper may be within ±0.5 μV/K, or even within ±0.2 μV/K.
With the above characteristics, the resistance alloy is suitable for small-sized and low-resistance shunt resistors, and a low TCR value can also be achieved. The current detection accuracy of a current detection device using the shunt resistor is improved, and the space required by the current detection device can be reduced by reduction in size of the shunt resistor.
In the foregoing embodiments, the illustrated configurations and the like are not limiting and may be modified, as appropriate, within a range in which the effects of the present invention can be obtained. Other modifications may also be made and implemented without departing from the scope of the purpose of the present invention.
The constituent elements of the present invention may be optionally selectively added or omitted, and an invention having an optionally selectively added or omitted configuration is also included in the present invention.
The present invention may be utilized as an alloy for a resistor.
All publications, patents and patent applications cited in the present description are incorporated herein by reference in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-145278 | Aug 2020 | JP | national |
This application is a 371 application of PCT/JP2021/026813 having an international filing date of Jul. 16, 2021, which claims priority to JP2020-145278 filed Aug. 31, 2020, the entire content of each of which is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/026813 | 7/16/2021 | WO |
