JP2012129631A - High frequency noise filter for on-vehicle apparatus, wire harness, and drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently reduce high frequency noise in each of a plurality of frequency bands, such as a frequency band of medium wave broadcasting and a frequency band of FM broadcasting, while suppressing increases in the number of components used and in the number of connection points.SOLUTION: A high frequency noise filter for an on-vehicle apparatus includes: a linear conductor 13 interconnecting an upstream terminal 11 and a downstream terminal 12; a first capacitor 14 comprising a self-resonant capacitor and having one end electrically connected to a first connection point P1 on an electrical conductor and the other end capable of being grounded; and a second capacitor 15 comprising a self-resonant capacitor different in electrostatic capacity from the first capacitor and having one end electrically connected to a second connection point P2 on the electrical conductor and the other end capable of being grounded. A ringed ferrite core surrounding the electrical conductor is disposed between the connection points.

Description

  The present invention relates to a high-frequency noise filter for in-vehicle equipment, and is used, for example, to reduce high-frequency noise generated in a radio broadcast frequency band.

  For example, when receiving and listening to radio waves of medium wave broadcasting (AM (amplitude modulation) broadcasting in a frequency band of 520 kHz to 1650 kHz) with an in-vehicle radio receiver, the frequency of high-frequency electromagnetic noise generated from equipment on the vehicle is broadcast. Since it overlaps with the frequency band, this noise is received by the antenna of the in-vehicle radio receiver, noise is mixed into the received broadcast, and noise appears in the sound output from the speaker.

  Since various devices, switches, and the like that perform current switching are mounted around the engine or the like on the vehicle, these serve as noise sources and generate high-frequency electromagnetic noise. In addition, a rear defogger (condensation preventer for the rear window), a high-mount stop lamp, and the like often exist in the vicinity of the antenna for the vehicle-mounted radio.

  Accordingly, high-frequency electromagnetic noise generated by a noise source on the vehicle propagates to a load such as a rear defogger or a high-mount stop lamp via the power line. And the electromagnetic noise radiated | emitted from such a load is received by the antenna which exists in the vicinity, and mixes with the input for vehicle-mounted radios, and has a bad influence.

  Therefore, in order to reduce high-frequency noise radiation, a noise filter is generally inserted in a power supply line connected to a load such as a rear defogger through which noise propagates (Patent Document 1). The noise filter used for such an application is configured as shown in FIG. This noise filter is configured with a single capacitor as shown in FIG. 8, but since this capacitor has a residual inductance inside, this noise filter is equivalent to 1 as shown in FIG. A capacitance (capacitance) component (C) of each capacitor and a residual inductance component (L) are connected in series to form a self-resonant trap filter. In other words, the impedance of the circuit decreases near the resonance frequency. By connecting this noise filter between the power line and ground, only the high-frequency noise component near the resonance frequency is filtered and radiated electromagnetic waves (noise) ) Is reduced.

Further, as other conventional techniques related to this type of noise filter, for example, Patent Documents 2 to 4 are known.
In Patent Document 2, it is proposed to obtain a large impedance with the same size by forming a metal magnetic film on the outer peripheral surface of a ferrite used as a filter. It also suggests changing the film thickness and anisotropy of the metal magnetic material to control the frequency band.

  Patent Document 3 proposes a configuration in which a bobbin case that simultaneously accommodates a core and a connector terminal is provided in an air core portion of a coil, and the coil and the connector terminal are directly joined. Thereby, the filter portion and the connector portion are integrated, and variation in impedance characteristics is suppressed, and miniaturization and cost reduction are realized.

  In Patent Document 4, it is proposed that a noise filter using a capacitor similar to that of Patent Document 1 is built in the joint connector to reduce the amount of wiring and the number of wiring work.

JP 2006-238529 A JP-A-8-250334 JP 2009-54713 A JP 2009-146570 A

  Even when a conventional capacitor type noise filter is used, for example, electromagnetic noise can be reduced to some extent over almost the entire frequency band (520 kHz to 1650 kHz) of medium wave broadcast received by an in-vehicle radio receiver. .

  Conventionally, the frequency of electromagnetic noise generated from equipment on the vehicle and radiated from the vicinity of loads such as rear defogger and high-mount stop lamps is up to a frequency band that affects the reception of medium wave broadcasting, Electromagnetic noise generated on the vehicle did not affect a higher frequency band, for example, a low frequency band (76 MHz to 108 MHz) of FM broadcasting or analog television broadcasting.

  However, for example, in a hybrid vehicle that has been produced in recent years, both the engine and the electric motor are used as drive sources, and an inverter is mounted for controlling the electric motor. Such an inverter is a large electromagnetic noise source because it constantly switches a large current at a high speed. In addition, the frequency component of electromagnetic noise generated from the inverter may include a component that affects the low frequency band (76 MHz to 108 MHz) of FM broadcast or analog television broadcast.

  However, when the conventional noise filter as described above is used, electromagnetic noise in a high frequency band (76 MHz to 108 MHz) cannot be suppressed. For this reason, there is no problem when receiving and listening to radio waves of medium wave broadcasting with an in-vehicle radio receiver, but when receiving and listening to radio waves of FM broadcasts and analog TV broadcasts, it is affected by electromagnetic noise generated by the inverter. It will be.

  As for the noise filter, not only the above capacitor type but also various configurations and characteristics have existed conventionally. However, noise filters with high performance characteristics have a problem that the number of components constituting the filter increases and the cost of components increases, and the number of connection points increases and the manufacturing cost and the cost of installation work increase. .

  The present invention has been made in view of the above-described circumstances, and an object thereof is to suppress an increase in the number of components to be used and the number of connection points, and the frequency band of medium wave broadcasting and the frequency band of FM broadcasting. Thus, an object is to provide a high-frequency noise filter for in-vehicle devices, a wire harness, and a drive circuit capable of sufficiently reducing high-frequency noise for each of a plurality of frequency bands.

In order to achieve the above-described object, the high-frequency noise filter for on-vehicle equipment according to the present invention is characterized by the following (1) to (5).
(1) A high-frequency noise filter for in-vehicle equipment comprising a self-resonant capacitor that includes a predetermined capacitance and self-inductance equivalently,
An electrical conductor located in a section between the power source and the load, electrically connecting the power source and the load;
A first capacitor composed of the self-resonant capacitor, one end of which is electrically connected to a first connection point on the electric conductor and the other end of which can be grounded;
The first capacitor is composed of a self-resonant capacitor having a different capacitance, one end is electrically connected to a second connection point on the electric conductor, and the other end is groundable. Be provided.
(2) The high-frequency noise filter for on-vehicle equipment according to (1) above,
A magnetic material disposed on the electric conductor in a position facing the first connection point to the second connection point and having a function of generating a magnetic loss;
(3) The on-vehicle equipment high frequency noise filter according to (2) above,
A ferrite core was used as the magnetic material.
(4) The high-frequency noise filter for in-vehicle equipment according to (3) above,
The ferrite core is formed in a ring shape, and the electric conductor is disposed so as to penetrate a central portion of the ring of the ferrite core.
(5) The high-frequency noise filter for on-vehicle equipment according to (1) above,
A ferrite core formed in a ring shape can be arranged in a range from the first connection point to the second connection point of the electric conductor so that a central portion thereof is penetrated by the electric conductor.

According to the high-frequency noise filter for on-vehicle equipment having the configuration (1), it is possible to sufficiently reduce high-frequency noise for each of a relatively low frequency band and a high frequency band. That is, noise can be reduced in two different frequency bands by a combination of resonance in the first capacitor and resonance in the second capacitor.
According to the high-frequency noise filter for on-vehicle equipment having the configuration (2), electromagnetic noise can be more effectively reduced in a relatively high frequency band. When the magnetic material is not present, the noise attenuation amount tends to be small in a frequency region relatively close to the resonance frequency of the second capacitor. However, when the magnetic material is provided, the magnetic loss causes a wide frequency range. A sufficiently large noise attenuation can be obtained.
According to the on-vehicle equipment high frequency noise filter having the configuration (3), the ferrite core used as the magnetic material has a function of generating a magnetic loss in a high frequency region, so that it is more effective in a relatively high frequency band. Electromagnetic noise can be reduced.
According to the high-frequency noise filter for on-vehicle equipment having the configuration (4), the periphery of the electric conductor is covered with the ferrite core to form a closed magnetic circuit, so that electromagnetic noise can be reduced more effectively. That is, by forming a closed magnetic path, the magnetic permeability of the ferrite core increases and the magnetic loss tends to increase.
According to the high frequency noise filter for in-vehicle devices having the configuration (5) above, the high frequency noise filter for in-vehicle devices can be reduced in size.

In order to achieve the above-described object, the wire harness according to the present invention is characterized by the following (6).
(6) A wire harness including a high-frequency noise filter for in-vehicle equipment having any one of the configurations (1) to (5),
The electric conductor is constituted by a core wire of a part of the electric wires constituting the wire harness,
The core wire is electrically connected to one end of the first capacitor at a first connection point on the core wire, and is electrically connected to one end of the second capacitor at a second connection point on the core wire. To be
thing.

  According to the wire harness having the configuration (6), it is possible to sufficiently reduce high-frequency noise in each of a relatively low frequency band and a high frequency band. That is, noise can be reduced in two different frequency bands by a combination of resonance in the first capacitor and resonance in the second capacitor.

In order to achieve the above-described object, the drive circuit according to the present invention is characterized by the following (7).
(7) A drive circuit including, in a circuit configuration, a noise filter including a self-resonant capacitor that includes a predetermined capacitance and self-inductance equivalently,
Power supply,
Load,
An electrical conductor that electrically connects the power source and the load;
A first capacitor composed of the self-resonant capacitor, one end of which is electrically connected to a first connection point on the electric conductor;
A second capacitor having a capacitance different from that of the first capacitor and having one end electrically connected to a second connection point on the electric conductor;
A first ground connected to the other end of the first capacitor;
A second ground connected to the other end of the second capacitor;
Be provided.

  According to the drive circuit having the configuration (7), it is possible to sufficiently reduce high frequency noise in each of a relatively low frequency band and a high frequency band. That is, noise can be reduced in two different frequency bands by a combination of resonance in the first capacitor and resonance in the second capacitor.

  According to the present invention, high-frequency noise can be obtained for each of a plurality of frequency bands such as a frequency band for medium wave broadcasting (520 kHz to 1650 kHz) and a frequency band for FM broadcasting (76 MHz to 108 MHz) without using many components. Can be sufficiently reduced.

  The present invention has been briefly described above. Further, details of the present invention will be further clarified by reading through the modes for carrying out the invention described below with reference to the accompanying drawings.

It is a connection diagram which shows the structure of the noise filter of 1st Embodiment. FIG. 2 is an electric circuit diagram showing an equivalent circuit of the noise filter shown in FIG. 1. It is a connection diagram which shows the structure of the noise filter of 2nd Embodiment. FIG. 4 is an electric circuit diagram showing an equivalent circuit of the noise filter shown in FIG. 3. It is a perspective view which shows the external appearance of the ring type ferrite core contained in the noise filter of FIG. It is a connection diagram which shows the structure of the noise filter of 3rd Embodiment. It is a graph which compares and shows the frequency characteristic of the attenuation amount of each noise filter. It is a connection diagram which shows the structure of the capacitor | condenser type noise filter of a prior art example. It is an electric circuit diagram which shows the equivalent circuit of the noise filter of FIG. It is a connection diagram which shows the modification of the noise filter of FIG. It is a connection diagram which shows the structure of the measurement circuit used in order to measure the frequency characteristic of the attenuation amount of each noise filter. It is a graph which shows the frequency characteristic of the attenuation amount of the noise filter shown in FIG. It is a graph which shows the frequency characteristic of the attenuation amount of the noise filter shown in FIG. It is a graph which shows the characteristic decomposed | disassembled for every impedance component regarding the ring type ferrite core contained in the noise filter of FIG.

  Specific embodiments relating to the high-frequency noise filter for in-vehicle equipment of the present invention will be described below with reference to the drawings.

(First embodiment)
The configuration (connection diagram) of the noise filter 10 of the first embodiment is shown in FIG. An equivalent circuit of the noise filter 10 shown in FIG. 1 is shown in FIG. The noise filter 10 is used to suppress high-frequency electromagnetic noise generated from various devices mounted on the vehicle from being mixed into a receiver such as an in-vehicle radio and causing adverse effects such as noise sound output. Designed with the assumption of In particular, the noise filter 10 can sufficiently reduce electromagnetic noise in both of a relatively low frequency band such as a radio medium wave broadcast and a relatively high frequency band such as an FM broadcast. It is constituted as follows.

  Vehicle equipment that can be a specific noise source includes equipment that incorporates a circuit that switches large currents at high speed using electronic switches such as transistors, such as various inverters and converters, and power supplies such as power switches for various equipment. There are a switch for switching current on and off, and an electric motor that operates as a drive source of the vehicle.

  The electromagnetic noise generated by such a noise source propagates to various power supply lines existing at positions adjacent to the electromagnetic noise via a wire harness connected to the device. And electromagnetic noise is radiated | emitted from places, such as a rear defogger and a high mount stop lamp, connected to these power supply lines. Since there are many cases where an antenna for an in-vehicle radio is arranged near the rear defogger or the high-mount stop lamp, electromagnetic noise radiated from these loads is mixed into the input of the in-vehicle radio from the antenna. The electromagnetic noise mixed in the in-vehicle radio has an adverse effect on the reception status of radio waves such as radio broadcasts and is output from the speaker as noise sound.

  In order to suppress the influence of such electromagnetic noise, the noise filter 10 is connected in the vicinity of the connection portion between the load of the rear defogger and high mount stop lamp that radiates electromagnetic noise and the power supply line. Since the noise filter 10 can attenuate the electromagnetic noise propagated from the noise source onto the power supply line, the electromagnetic noise radiation from the rear defogger and the high-mount stop lamp can be suppressed.

  The noise filter 10 shown in FIG. 1 includes a linear conductor 13, a first capacitor 14, and a second capacitor 15. When the noise filter 10 is actually used, a noise filter is provided in one section on a power line (for example, + 12V line) connecting a load that radiates electromagnetic noise, for example, a rear defogger heat line and a power source that supplies power to the load. 10 is inserted (load and power supply not shown). That is, one end of the linear conductor 13 is connected to the upstream terminal 11 of the power supply line (terminal located on the power supply side as viewed from the noise filter 10), and the other end of the linear conductor 13 and the downstream terminal 12 of the power supply line. (A terminal located on the load side when viewed from the noise filter 10). The first capacitor 14 and the second capacitor 15 are connected to a ground electrode (ground such as a negative terminal of the battery) 16 via a metal part of the vehicle body. At this time, the first capacitor 14 and the second capacitor 15 may be connected to separate ground electrodes.

  As shown in FIG. 1, the upstream terminal 11 and the downstream terminal 12 of the power supply line are electrically connected via a linear conductor 13, that is, an electric wire. One end of the first capacitor 14 is connected to the first connection point P1 on the linear conductor 13, and the other end is connected to the ground electrode 16 of the on-vehicle power source. The second capacitor 15 has one end connected to the second connection point P2 on the linear conductor 13, and the other end connected to the ground electrode 16 of the on-vehicle power source. In addition, in this embodiment, although the conductor which connects between the upstream terminal 11 and the downstream terminal 12 was made into the linear thing, it is not restricted to this. Various shapes of electrical conductors can be applied, and specifically, bus bars and the like can be used as the conductors. Moreover, when connecting between the upstream terminal 11 and the downstream terminal 12 with the electric wire with which a wire harness is provided, you may use the core wire with which an electric wire is provided as the conductor. Further, for example, the following method can be considered in connecting one end of the first capacitor 14 and one end of the second capacitor 15 to the core wire as the linear conductor 13. That is, this is a technique in which a part of the outer sheath covering the core wire is peeled off, and a part of the core wire exposed from the outer sheath and a lead extending from one end of the capacitor are crimped by a crimp terminal. In addition, for example, the blade-shaped piece of the pressure contact terminal is bitten into the electric wire, and the blade-shaped piece of the pressure contact terminal is also bited into the lead extending from one end of the capacitor. The method of connecting one end of the first capacitor 14 and one end of the second capacitor 15 to the linear conductor 13 is not limited to these methods.

  An interval is provided between the first connection point P1 and the second connection point P2 so as to ensure a distance Lx. As specific examples of the distance Lx, 55 mm or 110 mm is assumed. By providing an interval between the first connection point P1 and the second connection point P2, interference between the first capacitor 14 and the second capacitor 15 can be prevented. Further, for example, a space for mounting a ferrite core can be secured. Note that securing the distance Lx is not indispensable for carrying out the present invention. Even if the distance Lx is 0, interference between the first capacitor 14 and the second capacitor 15 can be prevented.

  The first capacitor 14 can be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 2, the first capacitor 14 has an electrical characteristic equivalent to that in which a capacitor 14a and an inductor 14b are connected in series. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 14a and the inductor 14b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  In the configuration example shown in FIGS. 1 and 2, a component having a capacitance of 2.0 μF is used as the first capacitor 14 in order to attenuate electromagnetic noise in the radio frequency band (520 kHz to 1650 kHz) of radio. We are using. It should be noted that the electrostatic capacity of the first capacitor 14 can be adjusted by the length of the lead of the first capacitor 14 in attenuating electromagnetic noise in the frequency band of radio medium-wave broadcasting. The capacity is not limited to 2.0 μF. In the section from the first connection point P1 to the ground electrode 16 via the first capacitor 14, electromagnetic noise in a predetermined frequency band may be attenuated.

  The second capacitor 15 can also be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 2, the second capacitor 15 has an electrical characteristic equivalent to that in which a capacitor 15a and an inductor 15b are connected in series. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 15a and the inductor 15b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  As described above, with the noise filter 10 inserted in a section on the power supply line connecting the load and the power supply, power is supplied from the power supply to the load to drive the load. As described above, the drive circuit is configured by a circuit including the power source, the load, the linear conductor 13, the first capacitor 14, the second capacitor 15, and the ground electrode 16.

  In the configuration example shown in FIGS. 1 and 2, a second capacitor is used to attenuate electromagnetic noise in a frequency band (76 MHz to 108 MHz) including a frequency band of radio FM broadcasting and a lower band of analog television broadcasting. 15 is a component having a capacitance of 220 pF. Specific noise attenuation characteristics of the noise filter 10 shown in FIGS. 1 and 2 will be described in detail later. It should be noted that the electrostatic capacity can also be adjusted by the length of the lead of the second capacitor 15 in attenuating the electromagnetic noise in the frequency band including the radio FM broadcast frequency band and the analog TV broadcast lower band. As a result, the capacitance of the second capacitor 15 is not limited to 220 pF. In the section from the second connection point P2 through the second capacitor 15 to the ground electrode 16, electromagnetic noise in a predetermined frequency band may be attenuated.

(Second Embodiment)
The configuration (connection diagram) of the noise filter 10B of the second embodiment is shown in FIG. FIG. 4 shows an equivalent circuit of the noise filter 10B shown in FIG. This noise filter 10B is a modification of the noise filter 10 shown in FIGS. 1 and 2 and is configured to be used for the same application as the noise filter 10. In FIGS. 3 and 4, the components corresponding to those of the first embodiment are denoted by the same reference numerals.

  The noise filter 10 </ b> B shown in FIG. 3 includes a linear conductor 13, a first capacitor 14, a second capacitor 15, and a ring type ferrite core 20.

  As shown in FIG. 3, the upstream terminal 11 and the downstream terminal 12 of the power supply line are electrically connected via a linear conductor 13, that is, an electric wire. A ring-type ferrite core 20 is disposed so as to surround the linear conductor 13. In addition, in this embodiment, although the conductor which connects between the upstream terminal 11 and the downstream terminal 12 was made into the linear thing, it is not restricted to this. Various shapes of conductors can be applied. Specifically, a bus bar or the like can be used as the conductor. Moreover, when connecting between the upstream terminal 11 and the downstream terminal 12 with the electric wire with which a wire harness is provided, you may use the core wire with which an electric wire is provided as the conductor.

  The ring-type ferrite core 20 is formed in a ring shape as shown in FIG. 5, and is configured such that the linear conductor 13 passes through a through hole 20a formed in the center portion thereof. In FIG. 3, the cross section of the ring type ferrite core 20 is shown.

  The ring-type ferrite core 20 is a magnetic core used for measures against EMI (unwanted radiation). As a specific example, a nickel oxide zinc-based ferrite core having a permeability μ of about 800 is used. A general ferrite material is composed of a mixture of various metal oxide powders, and the main component is ferric oxide. What was pressed into the final shape is formed by sintering at a high temperature of 900 to 1000 ° C. The ferrite material for EMI countermeasure includes nickel oxide and zinc oxide in addition to iron, and the magnetic permeability μ of the material is determined by these ratios.

Regarding the characteristics of ferrite magnetic materials, there is an AC “complex permeability (permeability) μ”, where μ is “real part permeability μ ′” and “magnetic loss term (imaginary part permeability) μ”. " These relationships are expressed by the following equation.
μ = μ′−jμ ”(1)
Further, the relationship between the characteristic real part permeability μ ′ of the magnetic material and the opposite magnetic loss term μ ″ is expressed by the following equation.
tan σ = μ ″ / μ ′ (2)
tanσ is defined as the loss factor.

  The real part magnetic permeability μ ′ is a magnetic permeability acting in a low frequency region. For example, when a ferrite core is used when producing a coil, the same result as that obtained by winding a large number of turns with a small number of turns can be obtained by the function of the real part permeability μ ′. On the other hand, when the frequency becomes extremely high, electromagnetic induction cannot catch up and a loss occurs. This loss is the “magnetic loss term μ”. It is generally considered that electromagnetic noise is suppressed because high-frequency electromagnetic noise is converted into heat and consumed by this magnetic loss.

  In general, a ferrite material having a large magnetic permeability μ has a large “magnetic loss term μ” and is considered to have a high EMI noise suppressing effect. Further, a ferrite material having a large magnetic permeability μ can obtain an EMI noise suppressing effect even in a relatively low frequency region. In particular, since the ring-shaped ferrite material forms a closed magnetic path, the magnetic permeability μ increases and the “magnetic loss term μ ″” also increases.

  In the case of the noise filter 10B as shown in FIG. 3, it is necessary to configure the linear conductor 13 so as to pass through the through hole 20a of the ring type ferrite core 20, so that the ring as shown in FIG. When the type ferrite core 20 is used, workability when the noise filter 10B is assembled is poor. In order to improve workability, the ring-shaped ferrite core 20 having a shape as shown in FIG. 5 may be configured by combining materials previously divided into a plurality of portions. However, in that case, unless the surface accuracy of the joint surface between the divided members is increased to prevent the deterioration of the magnetic permeability μ, the ability to suppress electromagnetic noise also decreases.

  In the present embodiment, the ring-type ferrite core 20 is used to reduce electromagnetic noise in a frequency band of 30 MHz or higher. In other words, the principle that the ring-type ferrite core 20 reduces high-frequency electromagnetic noise is not the influence of the inductance according to the “magnetic permeability μ” of the magnetic material, but the influence of the aforementioned “magnetic loss term μ”. ing.

  As shown in FIG. 3, one end of the first capacitor 14 is connected to the first connection point P <b> 1 on the linear conductor 13, and the other end is connected to the ground electrode 16 of the on-vehicle power source. The second capacitor 15 has one end connected to the second connection point P2 on the linear conductor 13, and the other end connected to the ground electrode 16 of the on-vehicle power source. At this time, the first capacitor 14 and the second capacitor 15 may be connected to separate ground electrodes.

  An interval is provided between the first connection point P1 and the second connection point P2 so that a sufficient distance Lx is secured. As specific examples of the distance Lx, 55 mm or 110 mm is assumed. By providing a sufficient space between the first connection point P1 and the second connection point P2, a space for arranging the ring-type ferrite core 20 can be secured between them. Note that securing the distance Lx is not indispensable for carrying out the present invention. Even if the distance Lx is 0, interference between the first capacitor 14 and the second capacitor 15 can be prevented.

  The first capacitor 14 can be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 4, the first capacitor 14 has an electrical characteristic equivalent to that in which a capacitor 14a and an inductor 14b are connected in series. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 14a and the inductor 14b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  In the configuration example shown in FIG. 3 and FIG. 4, a component having a capacitance of 2.0 μF is used as the first capacitor 14 in order to attenuate electromagnetic noise in the radio frequency band (520 kHz to 1650 kHz) of radio. We are using. It should be noted that the electrostatic capacity of the first capacitor 14 can be adjusted by the length of the lead of the first capacitor 14 in attenuating electromagnetic noise in the frequency band of radio medium-wave broadcasting. The capacity is not limited to 2.0 μF. In the section from the first connection point P1 to the ground electrode 16 via the first capacitor 14, electromagnetic noise in a predetermined frequency band may be attenuated.

  The second capacitor 15 can also be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 4, the second capacitor 15 has an electrical characteristic equivalent to that in which a capacitor 15a and an inductor 15b are connected in series. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 15a and the inductor 15b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  In the configuration example shown in FIGS. 3 and 4, the second capacitor is used to attenuate electromagnetic noise in a frequency band (76 MHz to 108 MHz) including a frequency band of radio FM broadcasting and a lower band of analog television broadcasting. 15 is a component having a capacitance of 220 pF. It should be noted that the electrostatic capacity can also be adjusted by the length of the lead of the second capacitor 15 in attenuating the electromagnetic noise in the frequency band including the radio FM broadcast frequency band and the analog TV broadcast lower band. As a result, the capacitance of the second capacitor 15 is not limited to 220 pF. In the section from the second connection point P2 through the second capacitor 15 to the ground electrode 16, electromagnetic noise in a predetermined frequency band may be attenuated.

  The influence of the ring type ferrite core 20 shown in FIG. 3 can be handled as a circuit equivalent to a parallel resonant circuit including a resistance component 20R, an inductance component 20L, and a capacitance component 20C, as shown in FIG.

When the periphery of the electric line is covered with a ring-shaped magnetic material, the inductance increases due to electromagnetic induction. The reactance according to this inductance increases as the frequency increases, and the impedance also increases. The impedance Z is expressed by the following equation.
Z = R + jXL (3)
XL = 2πfL (4)
Where R: resistance, f: frequency, XL: reactance, L: inductance

Further, the relationship between the core impedance “| Z1 |” and the material impedance “| Z2 |” has the following relationship.
| Z1 | = (Ae / Le) N ^2. | Z2 | (5)
Ae: average cross-sectional length of core, Le: average magnetic path length of core, N: number of turns

  That is, the substantial impedance of the ring-type ferrite core 20 tends to increase as the ratio between the outer dimension and the inner diameter dimension of the ring-shaped core increases and as the length increases.

  FIG. 14 shows the impedance Z of electrical characteristics related to the influence of the ring-type ferrite core 20 used in the present embodiment, and the frequency characteristics of the resistance component R and reactance component XL (XC) included in Z. In FIG. 14, in the region where the reactance component is positive, the influence of the inductance component 20L is larger than that of the capacitance component 20C (functions as the inductive reactance XL). In the region where the reactance component is negative, the influence of the inductance component 20L is the capacitance component 20C. (Acts as capacitive reactance XC). The frequency f0 at which the reactance component becomes 0 is the resonance point, and the impedance Z at the resonance point includes only the influence of the resistance component 20R. In addition, the frequency fc at the cross point where the reactance component XL and the resistance component R coincide with each other represents a characteristic characteristic of the ring-type ferrite core 20 as a magnetic material. The frequency fc of the cross point substantially matches the frequency of the cross point at which the influence of the “real part permeability μ ′” and the influence of the “magnetic loss term μ” ”coincide.

  In the present embodiment, the characteristics of the ring-type ferrite core 20 are used particularly within a frequency range that is higher than the cross-point frequency fc and lower than the resonance point frequency f0. In other words, the impedance Z due to the influence of the ring-type ferrite core 20 is affected by the reactance component due to the resistance component 20R and the inductance component 20L, as shown in the above equation (3). Further, it can be said that the resistance component 20R is effective in suppressing EMI noise.

  As described above, with the noise filter 10B inserted in one section on the power supply line connecting the load and the power supply, power is supplied from the power supply to the load to drive the load. As described above, the drive circuit is configured by the circuit including the power source, the load, the linear conductor 13, the first capacitor 14, the second capacitor 15, the ground electrode 16, and the ring-type ferrite core 20.

(Third embodiment)
By the way, when a noise filter is to be inserted into the power line of the rear defogger, for example, a very large current flows through this load (heat wire), so it is necessary to use a thick wire (for example, a wire with a cross-sectional area of 3 mm ² ). . It is difficult to form a filter coil with such a thick electric wire. Further, even when the inductance component is formed by the ring-type ferrite core 20 as in the noise filter 10B of the second embodiment, the size of the ring-type ferrite core 20 is avoided, so that the size of the noise filter 10B is avoided. I can't. Therefore, in the noise filter 10C of the third embodiment, paying attention to the fact that a circuit element substantially including an inductance component can be inserted in the middle of a power supply line simply by passing an electric wire through the through hole 20a of the ring-type ferrite core 20, An embodiment in which the ring type ferrite core 20 is not included in the configuration of the filter 10C will be described. The configuration (connection diagram) of the noise filter 10C of the third embodiment is shown in FIG. In FIG. 6, components corresponding to those of the second embodiment are denoted by the same reference numerals.

  A noise filter 10 </ b> C illustrated in FIG. 6 includes a linear conductor 13, a first capacitor 14, and a second capacitor 15.

  As shown in FIG. 6, the upstream terminal 11 and the downstream terminal 12 of the power supply line are electrically connected via a linear conductor 13, that is, an electric wire. A ring-type ferrite core 20B is disposed so as to surround the periphery of the linear conductor 13. When assembling the ring-type ferrite core 20B to the linear conductor 13, for example, a noise filter that accommodates the linear conductor 13 inside the linear conductor 13, the first capacitor 14, and the second capacitor 15 is provided. A ring-shaped ferrite core 20B that is partially exposed from the case of 10C and is divided into two halves with respect to the exposed portion is connected to the linear conductor 13 in the through hole 20a of the ring-shaped ferrite core 20B. It is possible to assemble them so that they pass through.

  The ring-type ferrite core 20B is formed in a ring shape as shown in FIG. 5, and is configured such that the linear conductor 13 passes through the through hole 20a formed in the center portion thereof. In FIG. 6, the cross section of the ring-type ferrite core 20B is shown.

  As shown in FIG. 6, in the case of the noise filter 10C, in order to improve workability, the ring type ferrite core 20B having a shape as shown in FIG. Is preferred. However, in that case, unless the surface accuracy of the joint surface between the divided members is increased to prevent the deterioration of the magnetic permeability μ, the ability to suppress electromagnetic noise also decreases.

  As shown in FIG. 6, one end of the first capacitor 14 is connected to the first connection point P1 on the linear conductor 13, and the other end is connected to the ground electrode 16 of the on-vehicle power source. The second capacitor 15 has one end connected to the second connection point P2 on the linear conductor 13, and the other end connected to the ground electrode 16 of the on-vehicle power source. At this time, the first capacitor 14 and the second capacitor 15 may be connected to separate ground electrodes.

  An interval is provided between the first connection point P1 and the second connection point P2 so that a sufficient distance Lx is secured. As specific examples of the distance Lx, 55 mm or 110 mm is assumed. By providing a sufficient space between the first connection point P1 and the second connection point P2, it is possible to secure a space for arranging the ring-type ferrite core 20B therebetween.

  The first capacitor 14 can be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 4 (the equivalent circuit is the same in the second embodiment and the third embodiment), the first capacitor 14 is equivalent to a capacitor 14a and an inductor 14b connected in series. Has excellent electrical characteristics. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 14a and the inductor 14b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  In the configuration example shown in FIG. 6, a component having a capacitance of 2.0 μF is used as the first capacitor 14 in order to attenuate electromagnetic noise in the radio frequency band (520 kHz to 1650 kHz) of radio. Yes. It should be noted that the electrostatic capacity of the first capacitor 14 can be adjusted by the length of the lead of the first capacitor 14 in attenuating electromagnetic noise in the frequency band of radio medium-wave broadcasting. The capacity is not limited to 2.0 μF. In the section from the first connection point P1 to the ground electrode 16 via the first capacitor 14, electromagnetic noise in a predetermined frequency band may be attenuated.

  The second capacitor 15 can also be used as a self-resonant filter. That is, as shown in the equivalent circuit of FIG. 4, the second capacitor 15 has an electrical characteristic equivalent to that in which a capacitor 15a and a second capacitor 15b are connected in series. Therefore, resonance occurs at a frequency determined by the characteristics of the capacitor 15a and the inductor 15b, and the impedance becomes very small at a frequency near the resonance point. Thereby, electromagnetic noise can be attenuated in the frequency band near the resonance point.

  In the configuration example shown in FIG. 6, in order to attenuate electromagnetic noise in a frequency band (76 MHz to 108 MHz) including a frequency band of radio FM broadcasting and a lower band of analog television broadcasting, the second capacitor 15 is A component having a capacitance of 220 pF is used. It should be noted that the electrostatic capacity can also be adjusted by the length of the lead of the second capacitor 15 in attenuating the electromagnetic noise in the frequency band including the radio FM broadcast frequency band and the analog TV broadcast lower band. As a result, the capacitance of the second capacitor 15 is not limited to 220 pF. In the section from the second connection point P2 through the second capacitor 15 to the ground electrode 16, electromagnetic noise in a predetermined frequency band may be attenuated.

  The influence of the ring type ferrite core 20B shown in FIG. 6 can be treated as a circuit equivalent to a parallel resonant circuit including a resistance component 20R, an inductance component 20L, and a capacitance component 20C, as shown in FIG.

  As described above, according to the noise filter 10C of the present embodiment, the size of the noise filter 10C can be reduced by the amount that the ring ferrite core 20B is not included in the configuration.

Next, specific characteristics of the noise filters 10 and 10B will be described. Since the characteristics of the noise filter 10C are the same as those of the noise filter 10B, the description thereof is omitted.
FIG. 7 shows frequency characteristics regarding the attenuation amounts of the four types of noise filters. Characteristic curves CV1 and CV2 shown in FIG. 7 represent the characteristics of the noise filter shown in FIGS. 8 and 10, respectively. Further, characteristic curves CV3 and CV4 shown in FIG. 7 represent the characteristics of the noise filters 10 and 10B, respectively. The noise filter shown in FIG. 8 is composed of a single self-resonant capacitor. The noise filter shown in FIG. 10 is composed of a single self-resonant capacitor and a ferrite core FC arranged so as to surround the power line on the load side.

  FIG. 12 shows frequency characteristics regarding the attenuation amount of the noise filter 10 alone. Moreover, the frequency characteristic regarding the attenuation amount of the noise filter 10B alone is shown in FIG.

  The characteristics of the noise filters shown in FIGS. 7, 12, and 13 represent the results of measurement using the measurement circuit having the configuration shown in FIG. In the measurement circuit of FIG. 11, a 50Ω input resistor and a pseudo noise source are connected to the input side of the sample circuit corresponding to each noise filter, and a 50Ω resistor corresponding to the load is connected to the output side and terminated. is there. That is, how much noise level is attenuated between the input side and output side of each noise filter is measured for each frequency.

  As shown in FIG. 7, in the characteristic curve CV1 of the conventional noise filter, a sufficiently large attenuation is obtained in a relatively low frequency band corresponding to the frequency band (520 kHz to 1650 kHz) of the radio medium wave broadcast. In the high frequency band (76 MHz to 108 MHz) corresponding to the low frequency band of FM broadcast or analog television broadcast, only an attenuation of about 10 dB can be obtained. In the characteristic curve CV2 of the noise filter using the ferrite core FC, the attenuation in the high frequency band (76 MHz to 108 MHz) is increased to about 20 dB, but this level is insufficient.

  On the other hand, in the characteristic curve CV3 of the noise filter 10 shown in FIG. 7, there is a resonance point at a frequency near 100 MHz in addition to the low frequency band, and a large attenuation is obtained near the resonance point. Therefore, electromagnetic noise can be significantly suppressed in a high frequency band (76 MHz to 108 MHz) that affects the low frequency band of FM broadcast or analog television broadcast.

  However, in the characteristic curve CV3 of the noise filter 10 shown in FIG. 7, since an anti-resonance point appears in the vicinity of 40 MHz, the attenuation is limited to 25 dB or less in the frequency band of 80 MHz or less. On the other hand, in the characteristic curve CV4 of the noise filter 10B shown in FIG. 7, the occurrence of the anti-resonance point in CV3 is eliminated, and it affects the low frequency band of FM broadcasting and analog TV broadcasting over a wide frequency range. A large attenuation is obtained in the high frequency band (76 MHz to 108 MHz).

  On the other hand, when the characteristic curve CV3 in FIG. 12 representing the characteristics of the noise filter 10 is compared with the characteristic curve CV4 in FIG. 13 representing the characteristics of the noise filter 10B, the following difference can be seen. That is, the influence of the anti-resonance point (abrupt decrease in attenuation near 40 MHz) appearing in the characteristic curve CV3 is almost eliminated in the characteristic curve CV4. Therefore, not only the frequency band of radio medium-wave broadcasting (520 kHz to 1650 kHz) but also the entire high frequency band (76 MHz to 108 MHz) that affects the low frequency band of FM broadcasting and analog television broadcasting is electromagnetic. Noise can be sufficiently attenuated.

  In addition, about specific numerical values, such as the electrostatic capacitance of the 1st capacitor | condenser 14 which comprises the noise filters 10, 10B, and 10C, the electrostatic capacitance of the 2nd capacitor | condenser 15, and distance Lx, required filter The amount of attenuation can be appropriately changed according to the frequency characteristics.

  As described above, it is assumed that the high-frequency noise filter for on-vehicle equipment of the present invention is used by being inserted into a power supply line of equipment such as a rear defogger and a high-mount stop lamp that radiates electromagnetic noise on the vehicle. By implementing the present invention, not only the frequency band of radio medium wave broadcasting (520 kHz to 1650 kHz), but also the entire high frequency band (76 MHz to 108 MHz) that affects the low frequency band of FM broadcasting and analog television broadcasting. Since the electromagnetic noise can be sufficiently attenuated, it is assumed that it is mounted on a hybrid car or the like.

10, 10B, 10C Noise filter 11 Upstream terminal 12 Downstream terminal 13 Linear conductor 14 First capacitor 15 Second capacitor 14a, 15a Capacitor 14b, 15b Inductor 16 Ground electrode 20, 20B Ring type ferrite core 20a Through Hole P1 First connection point P2 Second connection point

Claims (7)

A high-frequency noise filter for in-vehicle equipment comprising a self-resonant capacitor that includes a predetermined capacitance and self-inductance equivalently,
An electrical conductor located in a section between the power source and the load, electrically connecting the power source and the load;
A first capacitor composed of the self-resonant capacitor, one end of which is electrically connected to a first connection point on the electric conductor and the other end of which can be grounded;
The first capacitor is composed of a self-resonant capacitor having a different capacitance, one end is electrically connected to a second connection point on the electric conductor, and the other end is groundable. A high frequency noise filter for on-vehicle equipment, comprising:   2. The magnetic material according to claim 1, further comprising a magnetic material disposed at a position facing the first conductor on the electric conductor in a range from the first connector to the second connector and having a function of generating a magnetic loss. High frequency noise filter for in-vehicle equipment.   The high frequency noise filter for in-vehicle equipment according to claim 2, wherein a ferrite core is used as the magnetic material.   The high frequency noise filter for in-vehicle equipment according to claim 3, wherein the ferrite core is formed in a ring shape, and the electric conductor is disposed so as to penetrate a central portion of the ring of the ferrite core.   A ferrite core formed in a ring shape can be arranged in a range from the first connection point to the second connection point of the electric conductor so that a central portion thereof is penetrated by the electric conductor. The high-frequency noise filter for on-vehicle equipment according to claim 1. It is a wire harness provided with the high frequency noise filter for vehicle equipment as described in any one of Claim 1 to 5,
The electric conductor is constituted by a core wire of a part of the electric wires constituting the wire harness,
The core wire is electrically connected to one end of the first capacitor at a first connection point on the core wire, and is electrically connected to one end of the second capacitor at a second connection point on the core wire. To be
A wire harness characterized by that. A drive circuit including a noise filter including a self-resonance type capacitor equivalently including a predetermined capacitance and self-inductance in a circuit configuration,
Power supply,
Load,
An electrical conductor that electrically connects the power source and the load;
A first capacitor composed of the self-resonant capacitor, one end of which is electrically connected to a first connection point on the electric conductor;
A second capacitor having a capacitance different from that of the first capacitor and having one end electrically connected to a second connection point on the electric conductor;
A first ground connected to the other end of the first capacitor;
A second ground connected to the other end of the second capacitor;
A noise filter circuit comprising:

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