JP2008281364A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current sensor, constituted in such a way as to detect DC magnetic fields corresponding to a current to be measured, on the basis of the modulation of magnetic flux due to the Villari effects, reducing the output offset due to residual magnetic fields, improving the linearity of output characteristics, and reducing hysteresis and suitable for vehicle-mounted uses. <P>SOLUTION: The current sensor is provided with a piezoelectric ring 1 formed in a ring shape; a first magnetic ring 2 formed into a ring shape; and a second magnetic ring 3 formed in a ring shape. The two magnetic rings 2 and 3 are each jointed to and integrated with the front and the back of the piezoelectric ring 1, and a wire rod is wound around the inside and the outside of the ring-like sections to form a pickup coil 4. At least one of the first and second magnetic rings 2 and 3 is provided with a gap 5, which cuts off the ring-like member. The piezoelectric ring 1 generates oscillations in the radial directions by adding a prescribed AC current between electrodes. A wire 6 through which a current to be measured I flows is positioned inside the ring-like section, to detect the strength of magnetic fields generated by the current to be measured I by the pickup coil 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a current sensor for detecting the strength of a magnetic field generated by a current to be measured by a pickup coil, and more specifically, by applying a predetermined vibration force to a magnetic material associated with a pickup coil. The present invention relates to an improvement in output characteristics in a configuration in which an inverse magnetostriction effect (biliary effect) is generated and modulated to detect a change in a magnetic field corresponding to a current to be measured.

  With respect to a current sensor that detects a direct current in a non-contact manner, there are applications that are required to be able to measure a large current and to perform measurement even in a severe environment where the temperature is relatively high. For example, in an in-vehicle application, the specification exceeds a general industrial application such as being small and robust, and having a wide operating temperature. Specifically, a current of about 50 amperes can be measured, and at least 130 ° C. in a vehicle engine room. It is necessary to be able to operate at a degree. In recent years, fuel cell vehicles and hybrid vehicles have attracted attention, and current sensors have become important components.

  As a current sensor capable of detecting a large current, for example, a sensor using a Hall element is well known. This is because the Hall element is arranged in the gap part provided in the annular magnetic core, the electric wire through which the current to be measured flows is positioned inside the annular part, and the strength of the magnetic field generated by the current to be measured is detected by the Hall element ( (Hall voltage). However, a current sensor using a Hall element has many drawbacks because it is difficult to reduce the size because of the configuration in which the Hall element is sandwiched between gap portions of the magnetic core, and difficult to use in a high-temperature environment.

Further, as can be seen in Patent Document 1 and Non-Patent Document 1, there is a proposal of a technique in which a current sensor is configured by using the Villari effect. This will be described with reference to the typical configuration example according to the present invention shown in FIG. 1, but the piezoelectric ring 1 is joined and integrated with the annular magnetic ring 2 (3), and the annular A wire rod is wound around the inside and outside of the part to form the pickup coil 4, and the pickup coil 4 detects the strength of the DC magnetic field generated by the DC current I. In order to detect the intensity of the magnetic flux crossing the pickup coil 4, that is, the strength of the DC magnetic field, it is necessary to modulate this. For this reason, the piezoelectric ring 1 is vibrated in the diametrical direction by applying a predetermined AC voltage, and the magnetic ring By applying a mechanical vibration force to 2 (3), the inverse magnetostriction effect (biliary effect) is caused to modulate the magnetic flux. Thereby, the change of the magnetic field corresponding to the current I to be measured can be detected, and the current can be detected.
JP 2006-98332 A

The Institute of Electrical Engineers of Japan Magnetics MAG-05-34 A high-current sensor using the Billari effect Takashi Tadatsu and Ichiro Hamada

  However, the current sensor using the barrier effect as seen in Non-Patent Document 1 has the following problems. Some magnetic materials have a large residual magnetization, and an output voltage (offset) is generated in the pickup coil 4 even when the measured current I is 0 even if the output due to the residual magnetic flux is 0, resulting in poor output characteristics.

  Since the magnetic ring 2 (3) has a hysteresis with respect to the magnetic characteristics, there is a problem that the influence on the output characteristics of the current sensor is inevitable, and an improvement to further reduce the hysteresis of the magnetic characteristics is required. ing.

  Further, although the output of the pickup coil 4 shows generally good linearity with respect to the current I to be measured, the region where the linearity can be obtained (the range of the current I to be measured) is narrow. Therefore, there is a demand to expand the current measurement region where linearity can be obtained.

  The present invention solves the above-mentioned problem, and its purpose is to detect a DC magnetic field corresponding to the current to be measured by modulating the magnetic flux by the billiary effect, and to reduce the output offset due to the residual magnetic flux. It is an object of the present invention to provide a current sensor that can improve linearity well and reduce hysteresis and can be preferably applied to in-vehicle applications.

  In order to achieve the above-described object, a current sensor according to the present invention is (1) a current sensor for detecting the strength of a magnetic field generated by a current to be measured by a pickup coil, and a piezoelectric ring formed in an annular shape. The first magnetic ring formed in an annular shape is joined to form one annular body, a gap for blocking the annular portion is provided in the first magnetic ring, and a wire is wound around the inside and outside of the annular body. Thus, the pickup coil is configured.

  (2) On the premise of the invention of (1) above, a second magnetic ring formed in an annular shape is joined to the piezoelectric ring, and the piezoelectric body is formed by the second magnetic ring and the first magnetic ring. It is good to comprise so that a ring may be inserted | pinched. In other words, the two magnetic rings are joined and integrated to the front and back of the piezoelectric ring. In the invention of (1), since only the piezoelectric ring expands and contracts in the radial direction, warping occurs. However, when the thermal expansion coefficients of the magnetic ring and the piezoelectric ring are different, two magnetic rings are thus obtained. By sandwiching the piezoelectric ring, the occurrence of warpage in the entire current sensor can be suppressed even if a temperature change occurs.

  (3) Furthermore, on the premise of the invention of (2) above, it is preferable to provide a gap for blocking the annular portion in the second magnetic body ring.

  (4) In addition, the current sensor includes a piezoelectric body cylinder formed in a cylindrical shape and a magnetic body cylinder formed in a cylindrical shape, and the magnetic body cylinder is provided with a gap that blocks the cylindrical portion. The magnetic cylinder and the piezoelectric cylinder may be superposed concentrically and integrally joined together, and a wire rod may be wound around the cylindrical portion to form a pickup coil.

  (5) In each of the above inventions, an adjustment member having a different magnetic permeability may be disposed in the gap portion.

  In the present invention, since a gap is provided in the magnetic ring (magnetic cylinder), the magnetic resistance can be adjusted. The magnetic resistance of the magnetic ring (magnetic cylinder) can be changed according to the width of the gap part and the material forming the part, and the generation of magnetic flux can be controlled by adjusting the magnetic resistance.

  In the current sensor according to the present invention, since the gap is provided in the magnetic ring (magnetic cylinder), the magnetic resistance can be changed and the generation of magnetic flux can be controlled. For this reason, it is possible to appropriately control the DC magnetic flux generated by the current to be measured. As a result, the offset of the output due to the residual magnetic flux can be reduced, the linearity of the output characteristics can be improved satisfactorily, the current detection band can be widened, and the hysteresis can be reduced.

  FIG. 1 shows a preferred embodiment of the present invention. In this embodiment, the current sensor includes a ring-shaped piezoelectric ring 1 and a ring-shaped first magnetic ring 2 and second magnetic ring 3, and the two magnetic rings 2 and 3 are piezoelectric. The body ring 1 is joined and integrated to the front and back, and a wire rod is wound around the inside and outside of the annular portion to form the pickup coil 4.

  At least one of the first magnetic ring 2 and the second magnetic ring 3 is provided with a gap 5 that blocks the annular portion. The formation position and the number of gaps can be arbitrarily set. The piezoelectric ring 1 is polarized and vibrates in the diameter direction by applying a predetermined alternating voltage between the electrodes. Specifically, the polarization treatment of the piezoelectric ring 1 is performed by applying a silver paste for baking on two opposing surfaces to form a conductive film (polarization electrode), and placing it in silicon oil heated to 80 to 120 ° C. Then, a process of applying a voltage of 2 to 3 kV / mm between the polarization electrodes for 20 to 60 minutes is performed for polarization.

  The electric wire 6 through which the current I to be measured flows is positioned inside the annular portion, and the strength of the magnetic field generated by the current I to be measured is detected by the pickup coil 4.

  In this case, since the electric wire 6 is positioned in the annular portion, the magnetic flux due to the current I to be measured is generated in the circulation direction with respect to the magnetic rings 2 and 3. When an AC voltage is applied to the piezoelectric ring 1, the magnetic flux density increases or decreases by a corresponding amount even when the magnetic field is constant, that is, in the state of a DC magnetic field, and the magnetic flux changes. That is, by applying a mechanical vibration force to the magnetic rings 2 and 3, an inverse magnetostriction effect (biliary effect) is caused to modulate the magnetic flux. Due to this change in magnetic flux, an electromotive force is generated in the pickup coil 4, and the output of the pickup coil 4 increases or decreases in proportion to the magnitude of the DC magnetic field, that is, the magnitude of the current I to be measured. Therefore, the change in the magnetic field corresponding to the current I to be measured can be detected, and the current can be detected.

By the way, when the gap 5 is provided for the magnetic ring 2 (3), the corresponding portion is shown in FIG.
φ = N · I / (L / μS)
It becomes. I is the current to be measured, N is the number of turns of the wire 6, L is the length of the magnetic path, and S is the cross-sectional area. Here, N · I is a magnetomotive force, and L / μS is a magnetic resistance. And the magnetic flux density B is
B = N · I / (L / μ)
It becomes. Since the magnetic resistance of the magnetic path portion and the gap 5 due to the magnetic material is in series,
L / μ = ΔL / μg + (L−ΔL) / μs
It becomes. ΔL is the length of the gap 5, μg is the permeability of the gap 5, and μs is the permeability of the magnetic material.

And the electromotive force V in the pickup coil 4 is
e = Vsinωt
E is
e = −n · S · δB / δt
So,
| ΔB | = 1 / (n · S) ∫edt
= 1 / (n · S) ∫Vsinωtdt
= V · 1 / (n · S) · 1 / (π · f)
＝ V = n · S · π · f. dB
= (N · I · n · S · π · f) / (ΔL / μg + (L−ΔL) / μs)
It becomes. From the above, it can be seen that the electromotive force V can be appropriately adjusted according to the length ΔL of the gap 5 and the material (magnetic permeability μg) of the gap 5.

  Also, a plurality of gaps 5 may be provided for the magnetic ring 2 (3). Furthermore, it is good also as a structure which arrange | positions the adjustment member from which the magnetic permeability differs in the site | part of the gap 5. FIG.

  As described above, since the current sensor according to the present invention is composed of the piezoelectric material and the magnetic material, there is no problem when used in a high temperature environment, and the operating temperature range is wide. The current detection operation utilizes magnetic flux modulation due to the barrier effect, so that the size can be reduced unlike the configuration using the Hall element, and detection without being affected by the disturbance magnetic field can be performed. In addition, since the Hall element is a semiconductor and has a weak radiation resistance, it can be said that the current sensor according to the present invention has a high radiation resistance.

  In this case, since the magnetic ring 2 is provided with the gap 5, the magnetic resistance can be adjusted, and the magnetic resistance of the magnetic ring 2 can be changed according to the width of the gap 5 part and the substance forming the part, The generation of magnetic flux can be controlled by adjusting the magnetic resistance. For this reason, it is possible to properly control the DC magnetic flux generated by the current I to be measured. As a result, the output offset due to the residual magnetic flux can be reduced, the linearity of the output characteristics can be improved satisfactorily, and the current detection band can be widened. Hysteresis can be reduced. Therefore, the current sensor according to the present invention can be preferably applied to in-vehicle applications.

  In the present embodiment, the magnetic ring is bonded to both the front and back sides of the piezoelectric ring. However, the present invention is not limited to this, and the magnetic ring may be bonded to one side of the piezoelectric ring. .

(Cylinder type configuration example of current sensor)
FIG. 3 is a perspective view showing another example of the current sensor according to the present invention. This current sensor includes a piezoelectric body 10 formed in a cylindrical shape and a magnetic body 11 formed in a cylindrical shape, and the magnetic body 11 and the piezoelectric body 10 are overlapped concentrically. The pickup coil 4 is constructed by integrally joining and winding a wire around the inside and outside of the cylindrical part. The magnetic cylinder 11 is provided with a gap 5 that blocks the cylindrical portion. The piezoelectric ring 10 vibrates in the diameter direction or the length direction of the cylindrical body by applying a predetermined alternating voltage between the electrodes. Here, the magnetic cylinder 11 is concentrically overlapped on the outside of the piezoelectric cylinder 10, but conversely, the piezoelectric cylinder 10 may be concentrically overlapped on the outside of the magnetic cylinder 11. Alternatively, the magnetic cylinder may be configured to be joined simultaneously to the inside and outside of the piezoelectric cylinder.

  In the present invention, even if the current sensor is configured in the cylindrical shape shown in FIG. 3, the operation of current detection is not changed, and the operation is the same as that of the ring type shown in FIG.

  In order to verify the effect of the present invention, the current sensor shown in FIG. 1 was prototyped and its output characteristics were evaluated. In the trial production, two configurations, a configuration (a) in which the gap 5 was provided to the magnetic ring 2 and a configuration (b) in which the gap 5 was not provided, were manufactured, and current measurement was performed on each of them. As a result, the output characteristics shown in FIGS. 4A and 4B were obtained.

  As is clear from FIGS. 4A and 4B, the output characteristic is less offset by the residual magnetic flux in the configuration (a) in which the gap 5 is provided than in the configuration (b) in which the gap 5 is not provided. It was confirmed that the hysteresis can be reduced. Furthermore, in the configuration (a) in which the gap 5 is provided, it was confirmed that the range in which the output linearity can be obtained with respect to the change in the current to be measured, that is, the measurable current region can be expanded.

  In the present invention, a large DC current can be detected in a non-contact manner and the operating temperature becomes wide. Therefore, in-vehicle applications such as hybrid vehicles and electric vehicles, and applications of large current sensors such as solar power generation, wind power generation, and fuel cells. It is effective for.

1 is a perspective view showing a preferred embodiment of a current sensor according to the present invention. It is a perspective view explaining the effect | action of the gap in a magnetic body ring. It is a perspective view which shows other embodiment of the current sensor which concerns on this invention. It is a graph which shows the output characteristic of a current sensor, (a) is an output characteristic in the structure which provided the gap, (b) is an output characteristic in the structure which does not provide a gap.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric ring 2 1st magnetic body ring 3 2nd magnetic body ring 4 Pickup coil 5 Gap 6 Electric wire 10 Piezoelectric cylinder 11 Magnetic body cylinder

Claims (5)

A current sensor for detecting the strength of a magnetic field generated by a current to be measured by a pickup coil,
Joining the annularly formed piezoelectric ring and the annularly formed first magnetic ring to form one annular body,
A gap for blocking the annular portion is provided in the first magnetic ring,
A current sensor characterized in that a wire rod is wound inside and outside the annular body to form the pickup coil.   An annular second magnetic ring is joined to the piezoelectric ring, and the piezoelectric ring is sandwiched between the second magnetic ring and the first magnetic ring. The current sensor according to 1.   The current sensor according to claim 2, wherein a gap for blocking an annular portion is provided in the second magnetic body ring. A current sensor for detecting the strength of a magnetic field generated by a current to be measured by a pickup coil, comprising a piezoelectric cylinder formed in a cylindrical shape, and a magnetic cylinder formed in a cylindrical shape,
The magnetic cylinder is provided with a gap for blocking the cylindrical part,
A current sensor characterized in that the magnetic cylinder and the piezoelectric cylinder are overlapped concentrically and integrally joined, and a wire rod is wound around the inside and outside of the cylindrical portion to form the pickup coil.   The current sensor according to any one of claims 1 to 4, wherein an adjustment member having a different magnetic permeability is disposed in the gap portion.

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