JP6732503B2 - Noise reduction shielded cable - Google Patents

Description

The present invention relates to a noise reduction shielded cable that suppresses, for example, high frequency radiation noise and high voltage surge.

Conventionally, a shielded cable is generally used as a cable through which a high-frequency communication signal or a drive current that switches at a high voltage flows, and measures against high-frequency noise are required. The following method is known as a method for dealing with a surge (high voltage noise) generated from a switching circuit such as an inverter device or a DC-DC converter device, and a power supply terminal such as a motor.

As a first example, a filter circuit including an inductor L, a capacitor C, and a resistor R is attached to an inverter device, a motor, or a cable in order to reduce a noise level of a circuit that generates a surge or a line of a part.

As a second example, in consideration of the fact that high-voltage noise is radiated or induced (electromagnetic interference) from the cable that connects the device to the load, etc., an electric wire with a heavy electromagnetic shield (electromagnetic shielding structure with high shielding performance) , Use connector or ferrite core.

FIG. 6 shows an example of a conventional general inverter/motor system. A motor 51 and an inverter 52 are connected by a three-phase cable 53, and each terminal of a shield conductor 54 of the three-phase cable 53 is a motor 51. And is connected to each metal housing of the inverter 52 and is grounded from the metal housing to the ground plane 55.

FIG. 7 shows an example of a noise reduction method using a conventional high shield component, in which a motor 61 and an inverter 62 are connected by a high shield electric wire 63 via a high shield connector 64, respectively. The inverter 62 is grounded.

FIG. 8 shows a cross section of an example of a conventional shielded cable 11, in which three insulated coated electric wires 1 to 3 are covered with an outer shield layer 12, and the outer shield layer 12 is covered with a protective layer 49. .. Each of the insulating covered electric wires 1 to 3 is composed of the inner conductor 4 and the insulating layer 5, and the air or the insulator 50 is arranged between the insulating layer 5 and the outer shield layer 12.

Further, for example, in Patent Document 1 (not shown), as an example of a conventional noise reduction method, each inductor (coil) is arranged in three lines connecting a motor and an inverter device, and each line is arranged in each line. It is described that a filter composed of a resistor and a capacitor is connected to suppress a surge.

Further, in Patent Document 2 (not shown), as an example of a conventional signal transmission cable, first and second inner magnetic field countermeasure conductors and a knitting wire for grounding are provided between a central conductor and an outer cover. It is described that the wire (external conductor) and the shield body are concentrically arranged to reduce distortion and noise of a transmission signal.

In the patent document 2, two or three cable cores are wired in an insulator, the insulator is covered with a shield, and an inner magnetic field countermeasure conductor is provided around the center conductor (inner conductor) of each cable core. It is described that the braided wires (outer conductor) are concentrically arranged.

JP, 2010-136564, A JP, 9-259656, A

However, for example, in the method of the first conventional example, the cost is increased in the filter circuit, and the power loss generated in the inductor and the resistance is large in the application where the circuit current is large, which causes the device to become large and the efficiency to decrease. There was concern that it could happen.

Further, in the above-mentioned second conventional method, by increasing or thickening the metal shielding portion of the electric wire or connector, the size, mass, and cost are increased, and the ground plane is routed. Regarding noise, there was a concern that noise could not be reduced sufficiently.

In view of the above points, the present invention, for example, in comparison with a conventional method of adding a filter circuit inside or between devices or a method of improving the shield performance of a cable, increases the cost and mass and the amount of heat generated from the circuit. An object of the present invention is to provide a noise-reducing shielded cable capable of suppressing radiation noise to an AM/FM radio or the like, high-voltage surge, etc. while suppressing.

In order to achieve the above object, a noise-reducing shielded cable of the present invention has two or more insulation-coated electric wires each having an inner conductor and an insulation coating portion covering the inner conductor and forming a plurality of cores, and insulation of each insulation-coated electric wire. It is characterized in that it comprises an enclosing conductor surrounding the covering portion and an outer shield conductor enclosing the enclosing conductor in a state of being insulated from the enclosing conductor.

With this configuration, the presence of the enclosing conductor between the inner conductor and the outer shield conductor of each insulation-covered electric wire, that is, the presence of the enclosing conductor between the inner conductor and the outer shield conductor of each insulation-covered electric wire, Capacity is reduced. Therefore, the characteristic impedance between the inner conductor and the outer shield conductor of each insulation-coated electric wire increases, and the characteristic impedance between the inner conductors of each insulation-coated electric wire relatively decreases. As a result, the common mode characteristic impedance seen from the surge current increases, and reflection is suppressed at the cable end on the motor side, for example, and the surge that occurs is reduced.

Further, under the condition that three (three-phase) insulating coated electric wires that flow symmetrical three-phase alternating current such as a three-phase motor are arranged in a positional relationship of 120° rotational symmetry, an electromagnetic field generated by an alternating current of each phase is generated. The noises cancel each other out. Therefore, compared with the conventional method of adding the filter circuit inside or between the equipment and the method of improving the shield performance of the cable, the AM/FM can suppress the increase in cost and mass and the heat generation amount from the circuit, as compared with the conventional method. Radiation noise to radio and high voltage surges are suppressed.

In the noise reduction shielded cable, it is preferable that the outer shield conductor is grounded and the surrounding conductor is not grounded.

With this configuration, since the surrounding conductor is not grounded, the capacitance between each inner conductor and the outer shield conductor is kept small.

In the noise reduction shielded cable, it is preferable that the insulation coated electric wires are arranged rotationally symmetrically in cross section.

With this configuration, for example, two insulating covered electric wires are arranged at 180° intervals, three insulating covered electric wires are arranged at 120° intervals, and four insulating covered electric wires are arranged at 90° intervals. The distance from the center of rotational symmetry to the center of each insulated wire is equal. As a result, the capacitance between the inner conductor and the outer shield conductor of each insulation-coated electric wire becomes equal, and the capacitance of each inner conductor becomes equal.

In the noise reduction shielded cable, one or more lengths of the surrounding conductors having different lengths are arranged along the axial direction of the insulation-coated electric wire so that the frequency characteristic of impedance becomes flat. It is preferable that the length of the surrounding conductor in the axial direction of the electric wire is regulated so as not to resonate so that high frequency noise and surge do not increase.

With this configuration, when high-frequency noise or surge flows through the insulated wire, the surrounding conductor is prevented from resonating at the noise or surge frequency. Further, the resonance of each surrounding conductor at the surge frequency is suppressed over almost the entire length of the long insulating covered electric wire.

According to the present invention, for example, as compared with the conventional method of adding a filter circuit inside or between devices or the method of improving the shield performance of the cable, only the surrounding conductor for each insulation covered electric wire is used to reduce the cost and mass. It is possible to suppress the radiation noise to the AM/FM radio and the like, the surge of high voltage, etc. while suppressing the increase and the amount of heat generated from the circuit.

Further, by the configuration in which the outer shield conductor is grounded and the surrounding conductor is not grounded, for example, the electrostatic capacitance between the inner conductors of the respective insulation-coated wires can be maintained large, and the effect of the above invention can be promoted.

In addition, the insulation-coated wires are arranged rotationally symmetrically in cross section, so that the capacitance between the inner conductor and outer shield conductor of each insulation-coated wire and the capacitance between the inner conductors are made uniform. Thus, the effects of the above invention can be promoted.

In addition, one or a plurality of enclosing conductors are arranged along the axial direction of the insulation-coated electric wire, and the length of the enclosing conductor in the axial direction of the electric wire is regulated to a length that does not resonate with the frequency of noise or surge flowing in the insulation-coated electric wire. With this configuration, it is possible to suppress resonance of the surrounding conductor with respect to noise and surge applied to the insulated coated electric wire, thereby promoting the effects of the above invention.

It is sectional drawing which shows 1st embodiment of the noise reduction shielded cable of this invention. (A) is a figure explaining the electrostatic capacitance of each part of the conventional shielded cable, (b) and (c), respectively, of the noise reduction shielded cable of this invention. It is a graph which compares and shows the surge voltage of this invention and each conventional shielded cable. It is sectional drawing which shows 2nd embodiment of a noise reduction shielded cable. (A) is explanatory drawing which shows the 1st example of several surrounding conductors arrange|positioned at a noise reduction shielded cable, (b) is explanatory drawing which shows the 2nd example of several surrounding conductors similarly. It is explanatory drawing which shows the conventional general inverter/motor system. It is explanatory drawing which shows an example of the noise reduction system using the conventional shield component. It is sectional drawing which shows an example of the conventional shielded cable.

FIG. 1 shows a cross section of a first embodiment of a noise reduction shielded cable of the present invention.

In this noise reduction shielded cable 10, three (three-phase) insulating covered electric wires 1 to 3 are arranged at 120° intervals in a rotationally symmetrical manner, and each insulating covered electric wire 1 to 3 is surrounded by one surrounding conductor 6. Then, the inner surface 6a of the surrounding conductor 6 is brought into contact with the outer surface 5a of the insulating covering portion (first insulating layer) 5 of each of the insulating covered electric wires 1 to 3, and the second insulating layer is provided outside the surrounding conductor 6. The (insulator) 7 is arranged, the outer shield layer (outer shield conductor) 8 is arranged outside the second insulating layer 7, and the surrounding conductor 6 is surrounded by the outer shield layer 8.

The insulation coating portions 5 of the insulation coating electric wires 1 to 3 are in contact with each other. The surrounding conductor 6 is annularly arranged around the three insulation-coated electric wires 1 to 3 with a substantially triangular cross section (rice ball shape). An outer surface 5a1 on the radially outer side (the side farther from the center S of rotational symmetry) of each insulating coating portion 5 contacts the inner surface 6a1 of each of the three curved corners (tops) 6b of the enclosing conductor 6 in a contactable or contactable manner. doing. The outer surfaces 5a2 on the radially inner side (close to the center S of rotational symmetry) of the insulating coating portions 5 are in contact with each other.

The curved corners 6b of the enclosing conductor 6 are integrally connected to the planar straight portions 6c between them. The three straight portions 6c have the same length, and the corner portions 6b have the same shape and size. The inner surface 6a2 of each straight portion 6c is in tangential contact with the outer surface 5a1 of each insulating coating portion 5.

A space 15 is formed between the inner surface 6a2 of each straight portion 6c and the outer surface 5a of the insulation coating portion 5 of the two adjacent insulation coating electric wires 1 to 3. When the outer surface 5a1 of the insulating coating 5 is close to the inner surface 6a1 of the surrounding conductor 6, the space 15 continues to a minute gap between the inner surface 6a1 and the outer surface 5a1. These spaces 15 and gaps are air layers, that is, insulators. It is also possible to place a thin insulating layer (not shown) between the inner surface 6a1 and the outer surface 5a1. The space 15 is also formed in the center of the three insulation-coated electric wires 1 to 3 (on the center S side of rotational symmetry).

The surrounding conductor 6 is formed to have an appropriate length along the axial (longitudinal) direction of each of the insulation-coated electric wires 1 to 3. The length of the surrounding conductor 6 will be described later with reference to FIG. The wall thickness of the surrounding conductor 6 is uniform over the entire circumference. The inner peripheral surface of the second insulating layer (insulator) 7 is in contact with the outer peripheral surface of the surrounding conductor 6.

The outer peripheral surface of the second insulating layer 7 contacts the inner peripheral surface of the outer shield layer (external shield conductor) 8, and the outer peripheral surface of the outer shield layer 8 contacts the inner peripheral surface of the protective layer (insulator) 9. There is. The insulating layer 7, the outer shield layer 8 and the protective layer 9 are formed along the outer peripheral shape of the enclosing conductor 6 to have a substantially triangular cross section (diaper shape).

The three insulation-coated electric wires 1 to 3 are surrounded (covered) by the enclosing conductor 6, the second insulating layer 7, the outer shield layer 8 and the protective layer 9 and are held in a rotationally symmetrical form. In this embodiment, the wall thicknesses of the surrounding conductor 6, the second insulating layer 7, and the outer shield layer 8 are substantially the same. The wall thicknesses of the surrounding conductor 6 and the outer shield layer 8 are substantially equal. The circumference of the outer shield layer 8 is longer than the circumference of the surrounding conductor 6. The surrounding conductor 6 with respect to the outer shield layer 8 can also be referred to as an inner shield layer.

Each of the insulation-coated electric wires 1 to 3 is composed of an inner conductor 4 having a circular cross section and an insulation coating part 5 having an annular cross section that covers the inner conductor 4. The distance from the rotationally symmetrical center S of each of the insulated coated electric wires 1 to each curved corner portion 6b of the surrounding conductor 6 is equal. Further, the distance from the center S to each straight portion 6c of the surrounding conductor 6 is equal.

The surrounding conductor 6 of the present embodiment is made of, for example, a braided wire in which conductive wires are braided, or a metal foil such as a copper foil or an aluminum foil. Other than that, the surrounding conductor 6 may be formed of a conductive resin containing metal powder or conductor powder, or the like. The surrounding conductor 6 may be formed in a tubular (annular) seamless shape, or may be formed by winding a conductive tape or the like in an annular shape. It is preferable that these surrounding conductors 6 can be bent (have flexibility) in the radial direction of the electric wire. The noise reduction shield cable 10 is preferably bendable in the radial direction.

As the inner conductor 4 of each of the insulation-coated electric wires 1 to 3, a single core wire made of copper, aluminum or the like, or a bundle of a plurality of element wires is used. The outer shield layer 8 is formed of a braided wire made of a conductive metal, copper foil, aluminum foil, or the like. The first and second insulating layers 5, 7 and the protective layer 9 are made of a synthetic resin material or the like.

The noise reduction shielded cable 10 described above is a three-phase cable that connects an inverter (not shown) to a motor or a generator, and includes three insulated coated electric wires 1 to 3 as main lines and an external shield for electromagnetically shielding the electric wires. A structure is provided in which the layer 8 is provided, and both ends of the outer shield layer 8 are grounded (in the case of the outer shield layer 8 not for high voltage, only one end can be grounded), and the surrounding conductor 6 is not grounded at both ends. Has become. This structure can also be called a noise reduction method or the like.

Generally (in the past), in a configuration in which a device such as an inverter device or a DC-DC converter device having a switching circuit inside is connected to a load motor or the like by a shield cable, the switching operation of the switch circuit causes As a result, switching noise with a sharp rise of the voltage waveform or high-voltage surge is generated, and it is often necessary to protect the motor against breakdown voltage and to take measures against EMC (electromagnetic interference).

In the noise reduction shielded cable 10 (see FIG. 2B) of the present embodiment, compared with the conventional shielded cable 11 (see FIG. 2A), the inner conductor 4 and the outside of each of the insulated coated electric wires 1 to 3 are external. Capacitances C'1s, C'2c, C'3s with the shield layer 8 are reduced, and capacitances C'12, C'23, C'31 between two adjacent inner conductors 4 are reduced. Is increasing. This is confirmed by the simulation result described later.

As a result, the characteristic impedance between the inner conductors 4 and the outer shield layer 8, that is, the common mode characteristic impedance becomes large, and the characteristic impedance between the adjacent inner conductors 4, that is, the normal mode characteristic impedance becomes relatively small.

These changes have the effect of reducing the common-mode noise component that causes radiation noise and reducing the surge voltage that occurs due to the switching operation in the system that connects the inverter/motor to each other (Fig. 3).

As described above, the noise reduction shielded cable 10 according to the present embodiment increases cost and mass, and increases the cost of the circuit, as compared with the conventional method of adding the filter circuit inside or between the apparatuses and the method of improving the shield performance of the cable. It is possible to suppress radiation noise to the AM/FM radio or the like, high voltage surge, etc. while suppressing the amount of heat generation.

Below, the capacitance between the inner conductor 4 and the outer shield layer 8 of each of the insulated coated electric wires 1 to 3 of the noise reduction shielded cable 10 of the present embodiment, and the static capacitance between two adjacent inner conductors 4. The simulation result of the capacitance will be described with reference to FIGS. 2A to 2C and Tables 1 and 2.

2A shows a conventional shielded cable 11, and FIGS. 2B and 2C show a noise reduction shielded cable 10 of the present embodiment.

In FIG. 2A, the capacitance between the inner conductor 4 and the outer shield layer 12 of each of the insulated coated electric wires 1 to 3 of the conventional shielded cable 11 is indicated by the symbols C1s, C2s, and C3s, and two adjacent ones are shown. Capacitances between the inner conductors 4 are indicated by symbols C12, C23, and C31.

In FIGS. 2B and 2C, the electrostatic capacitance between the inner conductor 4 and the outer shield layer 8 of each of the insulation-coated electric wires 1 to 3 of the noise reduction shielded cable 10 is represented by the symbols C′1s, C′2s, C. It is shown by '3s, and the electrostatic capacitances between two adjacent inner conductors 4 are shown by symbols C'12, C'23, C'31. In FIG. 2C, the electrostatic capacitances between the inner conductors 4 and the surrounding conductor 6 of the noise reduction shielded cable 10 are represented by the symbols C1k, C2k, C3k, and the electrostatic capacitances between the surrounding conductor 6 and the outer shield layer 8. The capacity is indicated by Cks.

Table 1 is a simulation result of each capacitance in the conventional shielded cable 11 of FIG. 2A, and Table 2 is each capacitance in the noise reduction shielded cable 10 of the embodiment of FIGS. 2B and 2C. The results of the simulation are shown in matrix form. The unit of capacitance is pF (picofarad). The capacitance in each table is a value that is not combined. The capacitance between the inner conductor 4 and the outer shield layer 8 and the capacitance between the inner conductors 4 are calculated by the combined value of the capacitances between the conductors 4 and 8.

For example, while the electrostatic capacitance C1s between the inner conductor 4 (No1) and the outer shield layer 12 of the conventional shielded cable 11 in Table 1 is 123 pF, the noise reduction shielded cable of the present embodiment in Table 2 is shown. The electrostatic capacitance C′1s between the inner conductor 4 (No1) of 10 and the outer shield layer 8 is as small as 0 pF. This result is the same for the electrostatic capacitances C'2s and C'3s between the inner conductor 4 (No2, 3) and the outer shield layer 8.

Further, for example, while the electrostatic capacitance C12 between the internal conductor 4 (No1) and the internal conductor 4 (No2) of the conventional shielded cable 11 in Table 1 is 26 pF, in the present embodiment in Table 2 The capacitance C′12 between the inner conductor 4 (No1) and the inner conductor 4 (No2) of the noise reduction shielded cable 10 is 27 pF (the capacitance between the inner conductors No1 and No. 2 in Table 2 is the enclosure conductor). 6) and a value of 123 pF, which is the electrostatic capacitance C1k between the inner conductor 4 (No1) and the surrounding conductor 6, are added, and thus it is as large as 150 pF. This result is the same for the electrostatic capacitances C'31 and C'23 between the internal conductors 4 (No1, 3) and between the internal conductors 4 (No2, 3).

In the conventional shielded cable 11 of FIG. 2A, the capacitance between the inner conductor 4 and the outer shield layer 12 is C1s=C2s=C3s, and between the inner conductors 4 (one inner conductor 4 and The capacitance (between the other inner conductors 4) is C12=C23=C31.

Further, in the noise reduction shielded cable 10 of the present embodiment of FIG. 2B, the capacitance between the inner conductor 4 and the outer shield layer 8 is C′1s=C′2s=C′3s, The capacitance between the inner conductors 4 is C'12=C'23=C'31. This is because the insulated coated electric wires 1 to 3 are arranged rotationally symmetrically. Then, C1s=C2s=C3s>C'1s=C'2s=C'3s, and C12=C23=C31<C'12=C'23=C'31.

That is, the capacitance between the inner conductor 4 and the outer shield layer 8 in the noise reduction shielded cable 10 of the present embodiment is the capacitance between the inner conductor 4 and the outer shield layer 12 in the conventional shielded cable 11. The capacitance between the inner conductors 4 in the noise reducing shielded cable 10 of the present embodiment is larger than the capacitance between the inner conductors 4 in the conventional shielded cable 11.

As described above, in the noise reduction shielded cable 10 of the present embodiment, the capacitance between each inner conductor 4 and the outer shield layer 8 is reduced as compared with the conventional shielded cable 11, and two adjacent inner conductors are used. Increasing the capacitance between the conductors 4 increases the characteristic impedance between each inner conductor 4 and the outer shield layer 8, that is, the common mode, and increases between the two adjacent inner conductors 4, that is, the normal mode. Has a relatively small characteristic impedance.

FIG. 3 shows the surge voltage of the conventional shielded cable 11 and the noise reduction shielded cable 10 of the present embodiment in comparison. The measured value of the conventional shielded cable 11 is shown by a dotted line, and the measured value of the noise reduction shielded cable 10 of the present embodiment is shown by a solid line. In FIG. 3, the horizontal axis represents time μs and the vertical axis represents voltage V. As is clear from FIG. 3, the surge voltage of the noise reduction shielded cable 10 of this embodiment is lower than the surge voltage of the conventional shielded cable 11.

That is, the enclosing conductor 6 of the noise reduction shielded cable 10 of FIG. 2B has a large characteristic impedance between the inner conductors 4 and the outer shield layer 8, that is, a large common mode characteristic impedance, or a small coupling. By relatively reducing the characteristic impedance between the inner conductors 4, that is, in the normal mode, or by increasing the coupling, the reflection at the cable end on the motor side is suppressed, and the generated surge is reduced. Further, since the coupling between the two adjacent inner conductors 4 is large, the high frequency current of each phase is more likely to return due to the two adjacent inner conductors 4, and the electromagnetic field noises generated cancel each other out. The effect of reducing radiation noise is expected.

FIG. 4 shows a second embodiment of the noise reduction shielded cable of the present invention.

This noise reduction shielded cable 20 uses two insulation-coated electric wires 21 and 22 for the three insulation-coated electric wires 1 to 3 of the embodiment of FIG. 1, and has a substantially triangular cross-section of the embodiment of FIG. It is characterized in that the cross-sectional shape is circular in contrast to the rice ball shape.

That is, the two insulation-coated electric wires 21 and 22 that are rotationally (line-wise) symmetrically arranged at intervals of 180° are surrounded by the enclosure conductor 26 having an annular cross section, and the outer surface of the insulation-coated portion 25 of each insulation-coated electric wire 21 and 22 is surrounded. The inner surface 26a of the conductor 26 is in contact with 25a.

A ring-shaped second insulating layer (insulator) 27 is arranged outside the surrounding conductor 26, and a ring-shaped outer shield layer (outer shield conductor) 28 is arranged outside the insulating layer 27. The surrounding conductor 26 and the outer shield layer 28 are insulated by the second insulating layer 27. The outer shield layer 28 is covered with a protective layer (insulator) 29 having an annular cross section.

The insulation coating portions 25 of the insulation coating electric wires 21, 22 are in contact with each other. The insulating coating portions 25 are in contact with each other on the outer surface 25a2 on the radially inner side, and the outer surface 25a1 on the outer side in the radial direction of each insulating coating portion 25, which is 180° opposite to the outer surface 25a2, is in contact with the inner surface 26a of the enclosing conductor 26. There is. Inside the surrounding conductor 26, a space 23 is formed on the side opposite to the virtual line connecting the insulation-coated electric wires 21, 22 by 90°.

The inner peripheral surface of the second insulating layer (insulator) 27 contacts the outer peripheral surface of the surrounding conductor 26, the inner peripheral surface of the outer shield layer 28 contacts the outer peripheral surface of the insulating layer 27, and the outer peripheral surface of the outer shield layer 28. The inner peripheral surface of the protective layer 29 is in contact with the surface.

The thickness of the surrounding conductor 26 of this embodiment is substantially the same as the thickness of the outer shield layer 28, and the inner and outer diameters of the surrounding conductor 26 are smaller than the inner and outer diameters of the outer shield layer 28. The two insulated coated electric wires 21 and 22 are surrounded (covered) by the enclosing conductor 26, the insulating layer 27, the outer shield layer 28, and the protective layer 29, and are held on the center side of the enclosing conductor 26.

The structures and materials of the insulation-coated electric wires 21 and 22 composed of the inner conductor 24 and the insulation coating portion 25, and the materials of the surrounding conductor 26, the outer shield layer 28, the insulating layer 27, and the protective layer 29 are generally the same as those in the embodiment of FIG. The same is true. Both ends of the outer shield layer 28 are grounded (only one end can be grounded in the case of weak current), and the surrounding conductor 26 is not grounded at both ends. The noise reduction shielded cable 20 of FIG. 4 can be used to connect, for example, a high voltage DC battery or the like.

The noise reduction shielded cable 20 of FIG. 4 also has the same effects as those of the noise reduction shielded cable 10 of FIG. That is, as compared with the conventional shielded cable 11, the capacitance between the inner conductor 24 and the outer shield layer 28 is reduced, and the capacitance between the inner conductors 24 is increased. As a result, the characteristic impedance between each inner conductor 24 and the outer shield layer 28, that is, the common mode characteristic impedance becomes large, and the characteristic impedance between the adjacent inner conductors 24, that is, the normal mode characteristic impedance becomes small.

These changes are effective in reducing the common-mode noise component that causes radiation noise in the system in which the inverter/motor is connected to each other, and also in reducing the surge voltage generated due to the switching operation.

In addition, in the embodiment of FIG. 4, the number of the insulation-coated electric wires 21 and 22 may be three instead of two as in the embodiment of FIG. 1. In this case, the insulation coating portions 25 of the three insulation-coated wires are in contact with each other, and each insulation coating portion 25 is covered with the enclosure conductor 26 having an annular cross section and is in contact with the enclosure conductor 26. An annular insulating layer 27, an outer shield layer 28, and a protective layer 29 are concentrically arranged on the outer sides, respectively.

Further, in the embodiment of FIG. 4, the conductor 26, the insulating layer 27, the outer shield layer 28, and the protective layer 29 are surrounded by an elliptical cross section along the outer surface 25a of the insulating covered portion 25 of the two insulated covered wires 21 and 22, respectively. It is also possible to form and dispose in a substantially oval shape. In this case, the contact area between the outer surface 25a of each insulating coating portion 25 and the inner surface 26a of the surrounding conductor 26 is larger than in the embodiment of FIG.

Further, in the embodiment of FIG. 4, the surrounding conductor 26, the insulating layer 27, the outer shield layer 28, and the protective layer 29 are cut along the cross-sectional length along the outer surface 25a of the insulating covered portion 25 of the three insulated covered electric wires instead of two. It is also possible to form and arrange in a circular shape or a substantially oval shape.

In addition, in each of the embodiments shown in FIGS. 1 and 4, it is possible to set the number of the insulated wires 1 to 3, 21, and 22 to four. For example, the four insulated coated electric wires (not shown) are arranged rotationally symmetrically so as to be located at each corner of the virtual square. The surrounding conductors (6, 26) are in contact with the insulating coating portions 5, 25 of the four insulating coated electric wires.

FIGS. 5A and 5B show embodiments in which the lengths of the enclosing conductors 6 and 26 in the noise reduction shielded cables 10 and 20 of the above-described embodiments are specified, respectively.

5(a) and 5(b), for the sake of convenience, the insulating covered electric wires 1 to 3, 21, 22 and the insulating layers 7, 27 and the outer shield layers 8, 28 are omitted, and the surrounding conductors 6, 26 are shown by solid lines. It is shown as numeral 36, and the protective layers 9 and 29 are shown as broken lines as numeral 39.

In the noise reduction shielded cable 30 of the embodiment of FIG. 5A, for example, a plurality of enclosing conductors (divided enclosing conductors) 36a having a length that does not resonate with the surge frequency when the surge voltage shown in FIG. It is characterized in that it is arranged in series at a size L1.

The three surrounding conductors 36a constitute one surrounding conductor 36 of the noise reduction shielded cable 30. The surrounding conductor 36 is divided into three in the longitudinal direction of the electric wire. A gap n is formed between the surrounding conductors 36a.

The surge voltage is applied to the inner conductors 4, 24 of the insulation-coated electric wires 1-3, 21, 22. At that time, the surrounding conductor 36 arranged outside the insulation-coated electric wires 1-3, 21, 22 is a surge. The length L1 of each surrounding conductor 36a is defined so as not to resonate with the frequency. The length L1 of the surrounding conductor 36a is obtained by the line length resonance formula.

For example, when the length L1 of the enclosing conductor 36a is 1 m, the resonance point (frequency) is 100 MHz+α and the surge frequency is about 10 to 20 MHz, so that all enclosing conductors have a resonance frequency of 100 MHz or less. The length L1 of 36a is specified to be 1 m or less.

In the noise reduction shielded cable 40 of the embodiment shown in FIG. 5B, a plurality of surrounding conductors (divided surrounding conductors) 36b, 36c, 36d each having a length that does not resonate with the surge frequency when a surge voltage is generated have different lengths L2. , L3, L4 are arranged in series.

The eight surrounding conductors 36b to 36d constitute one surrounding conductor 36 of the noise reduction shielded cable 40. The surrounding conductor 36 of one noise reduction shielded cable 40 is divided into eight in the longitudinal direction of the electric wire. A gap n1 is formed in an appropriate length between the surrounding conductors 36b to 36d.

In FIG. 5B, three types of enclosing conductors 36b to 36d having lengths L2 to L4 are arranged in the order of 36b, 36c, 36d, and 36c, and the arrangement pattern is repeated. The lengths L2 to L4 of the surrounding conductors 36b to 36d are defined to be 1 m or less so that the resonance frequency is 100 MHz or less, respectively, as in the case of FIG. 5A.

In addition, in the embodiment of FIG. 5B, it is possible to arrange a plurality of enclosing conductors 36b to 36d having different lengths L in the axial direction of the wire at random without regularity. The number of divisions of the enclosing conductor 36 (the number of enclosing conductors 36a to 36d) is appropriately set according to the total length of the noise reduction shield cables 30 and 40.

Further, in the noise reduction shielded cable having a short overall length, if the length of the surrounding conductor 36 is a length that does not resonate with the surge frequency, the surrounding conductor 36 is not divided and one surrounding conductor 36 reduces one noise. It is also possible to support reduced shielded cables.

The present invention is effective not only as the noise reduction shielded cables 10, 20, 30, 40, but also as a noise reduction method, a shielded cable noise reduction method, a cable usage method, and the like.

In addition, the noise reduction shielded cables 10, 20, 30, 40 of the present invention can be appropriately modified according to the conventionally known knowledge. As long as such a modification still has the configuration of the noise reduction shielded cable of the present invention, it is of course included in the scope of the present invention.

The noise reduction shielded cable of the present invention suppresses an increase in cost and mass and the amount of heat generated from the circuit as compared with, for example, a conventional method of adding a filter circuit inside or between devices or a method of improving the shield performance of the cable. However, it can be used to suppress radiation noise to AM/FM radios, high voltage surges, and the like.

1-3, 21, 22 Insulated coated electric wire 4,24 Inner conductor 5,25 Insulated coating part 6, 26, 36a to 36d Enclosing conductor 7,27 Insulating layer 8,28 External shield layer (external shield conductor)
10, 20, 30, 40 Noise reduction shielded cable L1 to L4 Length

Claims (2)

Two or more insulation-coated electric wires each having a plurality of cores, each having an inner conductor and an insulation coating portion covering the inner conductor, a surrounding conductor surrounding the insulation coating portion of each insulation-coated electric wire, and the surrounding conductor are insulated An outer shield conductor surrounding the surrounding conductor in a state ,
The outer shield conductor is grounded, the enclosure conductor is not grounded,
One or a plurality of the enclosing conductors are arranged along the axial direction of the insulating covered electric wire, and the length of the enclosing conductor in the electric wire axial direction is set to a length that does not resonate with the frequency of noise or surge applied to the insulating covered electric wire. noise reduction shielded cable characterized that you have but defined. Noise reduction shielded cable according to claim 1, wherein each of the sheathed wires are arranged in rotational symmetry in cross section.

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