Patent Application
20140097933
The invention relates to a current detecting resistor, especially relating to a shunt resistor consisting of metal material that uses resistance alloy material as resistance body.
The shunt resistor is used for observing battery current of electrical charge and discharge so as to prevent the battery trouble beforehand. The shunt resistor is excellent in current detection accuracy, small in current drift, and even if a large current is applied, excessive heat is not generated. The shunt resistor is used in a field where super-low resistance value is required, and for instance, a shunt resistor of plate-shape has been proposed (refer to Japanese laid open patent publication H6-224014).
In case of detecting high frequency current, the plate-shaped resistance body shown in the patent publication, is unsuitable for detecting an accurate current, since skin effect may appear comparatively from early stage of low frequency. That is, as shown in left figure of
Even in case of making cross-section of resistance body 11 circle-shaped as shown in right figure of
The invention has been made basing on above-mentioned circumstances. Therefore object of the invention is to provide a shunt resistor, which controls influence by skin effect by high frequency current.
The shunt resistor of the invention has a rod-shaped resistance body, and a pair of main electrode of another material from the resistance body, wherein end faces of the resistance body and the main electrode are bonded. The resistance body has a hole going through in direction where main electrodes are disposed, or a high resistance part at axis portion that is highly resistive than outer part, and low resistance part that is formed in outer of the high resistance part. It is preferable that outer circumference of the resistance body is circle-shaped.
According to the invention, by installing a through hole or a high resistance part that goes through in direction of its axis inside of rod-shaped resistance body, since current doesn't flow fundamentally in the through hole or the high resistance part, fluctuation band of the current pathway can be reduced. Therefore, change of resistance value by skin effect by high frequency current can be reduced.
Left view of
Embodiments of the invention will be described below with referring to
For instance, resistance alloy material of CuMn-system or CuNi-system of non-magnetism is used for resistance body 11 (11c) of low resistance part. These materials have low resistivity and excellent temperature coefficient of resistance. For instance, resistance alloy material of NiCr-system of non-magnetism having higher resistivity than low resistance part is used for resistance rod 11b.
Further, skin depth δ where current is distributed by skin effect is expressed by,
δ=1/√{square root over (πfμσ)} (Equation 1)
provided, f: frequency, μ: permeability of the conductor, σ: conductivity of the conductor. Since magnetism material is a material that passes magnetic flux easily, permeability μ is large, and skin depth δ becomes shallow, then it is preferable to use non-magnetic material with small permeability.
As a result, as shown in
Since main electrode 12a is square pillar-shaped according to the resistor of the embodiment, the resistor has a feature that it is easy to mount by surface mounting etc. and easy to treat when manufacturing. As to structure 1 of fixing resistance body 11 and main electrode 12a,
Pressure bonding, brazing, or welding, etc. is used for fixing main electrode and resistance body. Cold pressure bonding, heat pressure bonding, friction pressure bonding, or ultrasonic pressure bonding etc. can be used for pressure bonding. Laser welding, resistance welding, spot welding, electron beam welding, or arc welding, etc. can be used for welding. (Further, these fixation methods are not limited to embodiment 1, and can be applied to all embodiments 1-5.)
As to fixing structure 2, concave portion O is formed on end face of the main electrode so as to fit to outer circumference of the resistance body for fixing it beforehand. Then end portion of resistance body 11 is fitted into concave portion O and fixed by above-mentioned fixing method.
As to fixing structure 3, convex portion T is formed on end face of the main electrode so as to fit to inner circumference of the resistance body for fixing it beforehand. Then convex portion T is fitted into the hole 11a of the resistance body and fixed by above-mentioned fixing method. According to these fixing structures 2, 3, fixing position of resistance body 11 to main electrode 12a becomes stable, then, an advantage of easy assembling is caused.
In this embodiment, pipe-shaped structure of main electrode 12b is used as well as resistance body 11. Inside diameter of the hole of main electrode 12b is almost same to outside diameter of resistance body 11. End portion of the resistance body fits into the hole of the main electrode, and fixed by above-mentioned fixation method. Moreover, it is acceptable that making inside diameter of the hole of the resistance body almost same to outside diameter of the main electrodes, and main electrodes fit into the hole of the resistance body. Also, it is possible that since main electrode has a hole at both ends, inserting cable into the hole and crushing a portion of the main electrode so as to connect the cable to the main electrode.
In the embodiments, though the resistance body has been explained as cylinder-shaped, the resistance body may be polygonal cylindrical in cross-section such as square-shaped. Moreover, the resistor doesn't have detecting electrodes in this embodiment. In this case, current can be detected at both main electrodes, such as, by welding wires on main electrodes.
In
On the other hand, in case of pipe-shaped (hollow) resistance body, it is understood that increase of inductance and resistance is controlled up to frequency of about 100 kHz. That is, it is understood that by having a through hole in rod-shaped resistance body (by making hollow structure), change of inductance and resistance is improved at higher frequency area, and use of the shunt resistor up to about one digit higher frequency area becomes possible.
In pipe-shaped resistance body, thickness of Δ mark is 1.5 mm and a little thick while × and ⋄ marks are 1 mm thickness. From
As shown in
According to the shunt resistor 10, since voltage detecting electrode 13 and detecting terminal 13a are integral, its assembly process becomes simple. Moreover, difference of fixing position of detecting terminal 13a can be controlled, and voltage detection at nearest position to resistance body 11 becomes possible.
Further, since voltage detection electrode 13 becomes a part of the electrode, it never comes off from the bonded portion, it excels in durability, and change of resistance with lapse of time becomes small. And, since there is no lapping portion of electrode and resistance body, it is pillar-shaped as a whole. And since electrode and resistance body are bonded in entire end faces of them, smooth current pathway and heat radiation route are obtained, and bonded strength is also strong.
The shunt resistor 10 has a structure that flatness parts 12f, 12f are formed at both ends of electrode 12, 12 that is columnar. The flatness part 12f has opening 14 therein. And, it forms a structure that bus bar connected with battery etc. can be connected and fixed to flatness part 12f by using bolt and nut through opening 14. Opening 14 may be a screw hole, and may fix the bus bar to flatness part 12 by screw stop. Since flatness part 12f is formed, it becomes easy to connect and to fix with bus bar or tabular metal terminal fittings.
Next, method for manufacturing the resistor 10 will be described. First, rod-shaped resistance body 11 having a hole therein going through in direction of its axis, or having a high-resistivity portion therein going through in direction of its axis, a pair of main electrode 12,12 of another material from the resistance body, and a pair of voltage detecting electrode 13,13 of another material from the main electrode, are prepared. The resistance body 11 is formed by cutting long rod-shaped material of Manganin etc. into prescribed size, to form a pillar-shaped resistance body 11 having end faces, which are cut faces, at both ends. And, a hole going through in direction of its axis, or a high-resistivity portion going through in direction of its axis, is formed. Main electrode 12 is formed to have end faces, which is cut face, at both ends, by cutting rod-shaped material such as copper into prescribed size similarly. Voltage detecting electrode 13 consisting of plate-shaped part having detecting terminal 13a protruding from the electrode, is formed by cutting sheet of copper plate into the shape. Cutting process of copper plate can use press machining, wire-discharge machining, or etching processing etc.
Next, plate-shaped voltage detecting electrode 13 is disposed between resistance body 11 and main electrode 12, and end faces of the electrode 13 are abutted and fixed between end faces of resistance body 11 and main electrode 12, so that these end faces are opposed, by above-mentioned fixation method.
Next, holes are formed at end faces of main electrodes 12,12. Depth of the hole is adjusted in proportion to area of flatness part 12f to be formed. Even though the hole may not be formed, however, by forming the hole, it becomes easy to form the flatness part 12f with press machining. And, flatness part 12f is formed by crushing the part where the hole has been formed. Opening 14 is formed in flatness part 12f. By forming flatness part 12f at position of lower side of the resistor, bottom face of the resistor becomes almost flat, and it is easy to treat when mounting.
According to above-mentioned process, since electrode and voltage detecting terminal of the resistor can be formed at a time, shunt resistor of high accuracy, of easy handling, and convenient to use can be produced by simple process.
Further, voltage detecting electrode may not be disposed at both end faces of resistance body 11, but end face of main electrode 12, 12 may be abutted and fixed to both end faces of resistance body so as to oppose each other. In this case, it is necessary that voltage detecting wiring be directly fixed to main electrodes.
The structure is that a plural of resistance body 21A, 21B, 21C, etc, each having circle-shaped cross-section, is disposed on concentric circle in a range. They are disposed to be overcrowded so as not to come in contact mutually. According to equation 1 (see paragraph 0012), it is understood that skin depth is unrelated to diameter of wire. When comparing thick wire with thin wire, since skin depth becomes constant not relating to diameter of wire but relating to frequency, in case of thick wire, big distribution of current becomes formed. On the other hand, in case of thin wire, current flows almost in whole of the section. Accordingly, since in case of thin wire diameter, resistance change by skin effect decreases, then by composing resistance body with a plural of thin diameter wires, influence of skin effect can be decreased even by using resistance body that doesn't have a through hole or a high resistance part in its central portion.
Even if not using thin diameter wire such as skin depth level, by using resistance body of double layer structure that have low resistance part of skin depth level in outer of high resistance part, similar effect can be achieved as mentioned above.
In this embodiment, by using rod-shaped resistance bodies 31A,31B,31C having a through hole therein or two-layer structure where low resistance part is disposed in outer of high resistance part, moreover decrease of change of detected voltage by skin effect can be achieved.
The invention can be suitably used for current detecting resistor consisting of metal material, which uses resistance alloy material as resistance body, especially for the resistor for usage of detecting high frequency current.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-150691 | Jul 2011 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/067283 | Jul 2012 | US |
| Child | 14102762 | US |
