JP2010014614A - Granular substance detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive granular substance detector of high measuring precision capable of simply detecting a granular substance. <P>SOLUTION: The granular substance detector 100 is equipped with a first plate-shaped electrode 1 of which one side is covered with an inter-electrode dielectric 4, the second electrode 2 arranged on one side of the first electrode through a space through which an exhaust gas containing a granular substance 11 flows and performing either or both of the formation of an electric field and discharge by the voltage applied across both electrodes 1 and 2, a voltage applying power supply 9, the measuring counter electrode 5 arranged on the surface of the inter-electrode dielectric 4, a characteristics measuring means 3 for measuring the electrical characteristics between the measuring counter electrode 5 and the first electrode 1, and a granular substance amount calculating means 13 for calculating the amount of the granular substance 11 collected on the surface of the inter-electrode dielectric 4 on the basis of the change quantity of the electrical characteristics measured by the characteristics measuring means 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus for detecting particulate matter contained in exhaust gas or the like of a diesel engine.

  Diesel engine exhaust gas, etc. contains particulate matter (Particulate Matter (PM), organic solvent soluble components, and soot and sulfate detected as three components), which causes air pollution. ing. In particular, if a problem occurs in a particulate matter generation source such as a diesel engine, the particulate matter in the exhaust gas released to the atmosphere increases, which has a great adverse effect on the environment. In order to prevent this, it is important to detect particulate matter in the exhaust gas and recognize problems such as diesel engines.

  Recently, in order to prevent pollution and improve the environment, a diesel particulate filter (DPF) has been incorporated into an exhaust system or the like for exhaust gas treatment. ing. This DPF is generally made of ceramic and can be used for a long period of time with high reliability. However, it cannot be said that there is no possibility that defects such as cracks are generated due to thermal degradation, and if so, particulate matter will leak even though the amount is small. In order to prevent this, it is important to detect particulate matter in the exhaust gas treated with DPF and immediately detect the occurrence of defects.

As a prior document, for example, Patent Document 1 can be cited. Patent Document 1 discloses a particulate matter detection device that measures the amount of particulate matter by charging the particulate matter by corona discharge and measuring its ionic current.
JP 60-123761 A

  However, in the method described in Patent Document 1, since the ion current charged in the particulate matter is weak, a large-scale detection circuit for detecting the weak ion current is necessary, and the apparatus becomes expensive. End up. In addition, if the exhaust gas flow rate is high, the particulate matter cannot be effectively charged, and the measured value will be smaller than the amount of particulate matter actually contained in the exhaust gas. There is room for improvement.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a particulate matter detection device that can easily detect particulate matter, is inexpensive, and has high measurement accuracy. As a result of repeated research, it was found that this problem can be solved by the following means.

  That is, according to the present invention, one electrode having a plate-like shape in which one surface is coated with a dielectric (interelectrode dielectric), and a gas containing particulate matter on one surface side of the one electrode Two electrodes that perform either or both of forming an electric field and / or discharging according to a voltage applied between the electrode and a voltage applied through one space, and a power source that applies the voltage, and Measurement counter electrode disposed on the surface of the dielectric (dielectric between electrodes), characteristic measurement means for measuring electrical characteristics between the measurement counter electrode and one electrode, and measurement by the characteristic measurement means A particulate matter detection device comprising particulate matter amount calculation means for obtaining the amount of particulate matter collected on the surface of the dielectric (interelectrode dielectric) based on the amount of change in electrical characteristics Provided.

  The particulate matter detection device according to the present invention includes a flow meter for measuring or estimating the flow rate of the gas flowing through the space, and the gas flow rate and the amount of the particulate matter that are measured or estimated by the flow meter. Based on this, it is preferable to include a particulate matter concentration calculating means for calculating the concentration of the particulate matter in the gas flowing through the space.

  In the particulate matter detection device according to the present invention, the electrical characteristics are preferably one or more electrical characteristics selected from an electrical characteristics group consisting of resistance, inductance, capacitance, and impedance.

  In the particulate matter detection device according to the present invention, the measurement counter electrode has a plurality of linear portions, and the plurality of linear portions are long and parallel to the direction perpendicular to the direction in which the gas containing the particulate matter flows. Thus, it is preferable to dispose on the surface of the dielectric (dielectric between electrodes). In this case, it is preferable that the measurement counter electrode having a plurality of linear portions has a lattice shape. In other words, in addition to the plurality of linear portions being long and parallel in the direction perpendicular to the direction in which the gas containing particulate matter flows, there may be portions that are long and parallel in the same direction as the direction in which the gas containing particulate matter flows. For example, it becomes a lattice. In these cases, it is preferable that the measuring counter electrode having a plurality of linear portions is disposed over the entire surface of the dielectric (interelectrode dielectric).

  In the particulate matter detection device according to the present invention, it is preferable that the two electrodes have a plate shape. In this case, it is preferable that the second electrode is constituted by a tube wall surface. That is, the plate-shaped body is rounded to form a tubular shape, and specifically, the entire surface or one surface of the exhaust pipe corresponds.

  In the particulate matter detection device according to the present invention, it is preferable that the two electrodes have a needle shape or a rod shape.

  In the particulate matter detection device according to the present invention, a dielectric (external electrode dielectric) covering the other surface of one electrode having a plate shape and a surface of the dielectric (external electrode dielectric) are disposed. It is preferable to provide a heater.

  In the particulate matter detection device according to the present invention, a voltage is applied between one electrode and a measurement counter electrode, and a power supply for removal is provided for oxidizing and removing particulate matter by creeping discharge. It is preferable to cause creeping discharge on the surface of the dielectric (interelectrode dielectric) coated on one surface of one electrode by application.

  In the particulate matter detection device according to the present invention, the measurement counter electrode is preferably covered with a film-like dielectric.

  The particulate matter detection device according to the present invention is a device that is installed in a flow path through which gas (exhaust gas) containing particulate matter passes and detects particulate matter contained in the gas. In the particulate matter detection device according to the present invention, a voltage is applied by a power source to cause the two electrodes to discharge, and the gas flowing in the space between the interelectrode dielectric side of the one electrode and the two electrodes The contained particulate matter is charged, or the precharged particulate matter is collected on the surface of the interelectrode dielectric covering one electrode. Then, the particulate matter is deposited on the interelectrode dielectric, and the electrical characteristics between the one electrode provided across the interelectrode dielectric on which the particulate matter is deposited and the measurement counter electrode Changes with a certain relationship to the amount of particulate matter deposited. Therefore, the particulate matter detection device according to the present invention obtains the amount of particulate matter collected on the surface of the interelectrode dielectric by knowing the amount of change in the electrical characteristics. Since it can be quantified, it is naturally possible to determine the presence or absence of particulate matter in the gas flowing through the space (whether the amount is 0 (zero)). Therefore, the particulate matter detection device according to the present invention is referred to as a detection device. In the particulate matter detection device according to the present invention, the amount of particulate matter contained in the gas flowing through the space is determined based on the amount of the particulate matter, and the gas is determined from the relationship with the flow rate of the gas flowing through the space. It is possible to calculate the concentration of particulate matter in

  As an electrical characteristic, for example, in order to detect an amount of change in impedance, it is only necessary to measure a change in current of 10 nA (nanoampere) level, although it varies depending on the measurement frequency and the magnitude of the measurement voltage. Therefore, the particulate matter detection device according to the present invention is not expensive, can easily detect particulate matter, measure the amount, and measure the concentration, and has a small measurement error. . In addition, detection of particulate matter, measurement of amount, measurement of concentration makes it possible to immediately detect the malfunction of diesel engines and the like, and the occurrence of DPF defects. Through these, the particles according to the present invention can be detected. The particulate matter detection device contributes to the reduction of particulate matter emission and contributes to the prevention of air pollution.

  In the particulate matter detection device according to the present invention, the electrical characteristics change depending on the area of the particulate matter deposited on the surface of the measurement counter electrode, and even if the physical properties of the particulate matter change, they are hardly affected. .

  In a preferred embodiment of the particulate matter detection device according to the present invention, the measurement counter electrode has a plurality of linear portions, and the plurality of linear portions are perpendicular to the direction in which the gas containing the particulate matter flows. The measurement counter electrode which is arranged on the surface of the dielectric body in parallel with the direction and has a plurality of linear portions, has a lattice shape, and additionally has a plurality of linear portions. Is disposed over the entire surface of the dielectric. According to the particulate matter detection device of the present invention having such an aspect, it is possible to improve the measurement sensitivity of the electrical characteristics and to detect the particulate matter deposited on the interelectrode dielectric without missing it. The measurement accuracy of the amount and concentration of the particulate matter is excellent.

  In the particulate matter detection device according to the present invention, as a preferred embodiment, when the two electrodes have a plate shape, in particular, it is possible to adopt an embodiment in which the two electrodes are constituted by a tube wall surface. Can be accommodated in a compact exhaust pipe.

  In a preferred embodiment, the particulate matter detection device according to the present invention includes a heater disposed on the surface of the dielectric outside the electrode, so that the electrical characteristics measured by one electrode and the measurement counter electrode are stabilized. . In addition, the particulate matter can be oxidized and removed by the heat of the heater, and the particulate matter can be repeatedly and accurately detected.

  In a preferred embodiment of the particulate matter detection device according to the present invention, the particulate matter detection device includes a power supply for removal for oxidizing and removing particulate matter by creeping discharge by applying a voltage between one electrode and the measurement counter electrode. By applying the voltage, it is possible to cause creeping discharge on the surface of the interelectrode dielectric coated on one surface of one electrode, so that the collected particulate matter is oxidized and removed by this creeping discharge. Is possible. By this oxidation removal, the particulate matter can be detected repeatedly with high accuracy.

  In the preferred embodiment of the particulate matter detection device according to the present invention, since the measurement counter electrode is covered with a film-like dielectric, deterioration due to discharge or exhaust gas hardly occurs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate, but the present invention should not be construed as being limited thereto. Various changes, modifications, improvements, and substitutions can be added based on the knowledge of those skilled in the art without departing from the scope of the present invention. For example, the drawings show preferred embodiments of the present invention, but the present invention is not limited by the modes shown in the drawings or the information shown in the drawings. In practicing or verifying the present invention, the same means as described in this specification or equivalent means can be applied, but preferred means are those described below.

  [Particulate matter detection device] First, the particulate matter detection device according to the present invention will be described focusing on the configuration, function, action and the like.

  1 and 7 are diagrams schematically showing an embodiment of a particulate matter detection device according to the present invention. FIG. 1 is a cross-sectional view showing a sensor unit, and FIG. 7 is a configuration diagram showing an electric control system. The particulate matter detection device 100 shown in FIGS. 1 and 7 includes an electrode 1 having a plate shape, two electrodes 2 having a plate shape, and an upper surface (one surface) of the one electrode 1 (in FIG. 1). Interelectrode dielectric 4 covering the electrode, a power source 9 for applying a voltage between one electrode 1 and the second electrode 2, and a plurality of linear portions disposed on the surface of the interelectrode dielectric 4 A counter electrode 5, an outer electrode dielectric 6 covering the lower surface (other surface) of one electrode 1 (in FIG. 1), a heater 7 disposed on the surface of the outer electrode dielectric 6 (lower surface in FIG. 1), A heater power supply 10 for supplying electricity to the heater 7, a sheet-like heat insulating material 8 that covers and protects the heater 7, keeps it insulated from the surroundings, and electrical characteristics between the one electrode 1 and the measurement counter electrode 5 Characteristic measuring device (means) 3 for measuring (change), and particulate matter amount calculating device for calculating the amount of particulate matter 11 It means) 13, and a particulate matter concentration calculation unit (means) 16, a flow meter 14 and the control unit 12, which calculates the concentration of particulate matter 11. In addition, the part comprised by one electrode 1, two electrodes 2, the interelectrode dielectric 4, the measurement counter electrode 5, the outer electrode dielectric 6, the heater 7, and the heat insulating material 8 shown in FIG. It is installed in the flow path through which the exhaust gas containing the substance 11 passes. These are sometimes referred to as sensor units.

  In the particulate matter detection device 100, the exhaust gas containing the particulate matter 11 from the left to the right in FIG. 1 (as indicated by arrows) covers the interelectrode dielectric 4 that covers one electrode 1 that has a plate shape. And a space between the two electrodes 2 having a plate shape. The flow rate of the exhaust gas is measured by a flow meter 14 not shown in FIG. In this state, when the power source 9 applies a DC high voltage to the second electrode 2, for example, discharge occurs, and the exhaust gas (molecules) around the second electrode 2 is separated into positive ions and negative ions, Negative ions move toward one electrode 1 to which a positive DC high voltage is applied. At this time, the particulate matter 11 contained in the exhaust gas collides with the negative ions and is negatively charged. The charged particulate matter 11 is collected and accumulated by electrostatic force on the surface of the interelectrode dielectric 4 covering the plus one electrode 1. Then, the electrical characteristics between the one electrode 1 and the measurement counter electrode 5 change depending on the degree of deposition of the particulate matter 11, so if the amount of change in the electrical characteristics is known, dust collection collects the distance between the electrodes. The amount of particulate matter (PM) deposited on the surface of the dielectric 4 is determined. Then, the PM concentration of the exhaust gas is obtained from the amount of accumulated PM.

  FIG. 8 is a graph for explaining the function of the particulate matter amount calculating device 13, and FIG. 9 is a graph for explaining the function of the particulate matter concentration calculating device 16. The change amount E1 of the electrical characteristic between one electrode 1 and the measurement counter electrode 5 is in a fixed relationship with the PM deposition amount W1 (see FIG. 8), and the change amount of the electrical characteristic by the characteristic measurement device 3 If E1 is known, the PM deposition amount W1 is obtained by the particulate matter amount calculation device 13 having a calculation function based on FIG. If the flow rate of the exhaust gas is constant, the PM deposition amount W1 has a constant relationship with the PM concentration C1 (see FIG. 9), and if the PM deposition amount W1 is known, it has a calculation function based on FIG. The PM concentration C1 is obtained by the particulate matter concentration calculation device 16. When the flow rate of the exhaust gas changes, the particulate matter concentration calculation device 16 corrects based on the flow rate obtained by the flow meter 14, and obtains the PM concentration C1 from the PM deposition amount W1.

  In the particulate matter detection device 100, the particulate matter amount calculation device 13 and the particulate matter concentration calculation device 16 are incorporated in the control device 12. The control device 12 is mainly composed of, for example, a sequencer having an electric signal input / output function, and is measured by the flow meter 14 in addition to the particulate matter amount calculating device 13 and the particulate matter concentration calculating device 16. In addition to having a function of inputting an electrical signal of the flow rate, the entire apparatus is controlled including control of the heater power supply 10 and power supply 9 and switching of processes.

  As an electrical characteristic between one electrode 1 and the measurement counter electrode 5, for example, when obtaining impedance, resistance, capacitance, and inductance can be measured using an AC power source. FIG. 10 is a diagram illustrating an equivalent circuit (RC circuit) when a voltage V is applied between one electrode 1 and the measurement counter electrode 5 using an AC power source in the state where the particulate matter 11 is present. . The total impedance of the circuit is configured only by the capacitance C0 based on the interelectrode dielectric 4 in the state where the particulate matter 11 is not present, but in the state where the particulate matter 11 is present, A capacitance C1 and a resistor R1 are added. And the electrostatic capacitance C1 and resistance R1 change under a fixed relationship with the quantity of the deposited particulate matter 11. Therefore, if the amount of change in the total impedance of the circuit is obtained, the amount of particulate matter 11 deposited can be obtained. The inductance component is considered to be almost negligible.

  In addition to the above, a change in impedance may be measured by using a constant current source and measuring a change in voltage between one electrode 1 and the measurement counter electrode 5. By measuring the change in the current flowing between the electrode 1 and the measurement counter electrode 5 and the change in the charge accumulated between the electrode 1 and the measurement counter electrode 5, the one electrode 1 and the measurement counter electrode 5 are measured. The change in impedance between the two may be measured.

  The characteristic measuring device 3 can have an appropriate configuration depending on the electrical characteristics as described above and how to obtain the change. For example, the characteristic measuring device 3 can be composed of an AC power source for applying a voltage to one electrode 1 and the measuring counter electrode 5 and a measuring device. A preferred measuring instrument is an LCR meter.

  As described above, in the particulate matter detection device according to the present invention, first, particulate matter 11 is collected from the exhaust gas and deposited on the surface of the interelectrode dielectric 4 (dust collection step). The change in electrical characteristics between the electrode 1 and the measurement counter electrode 5 is measured (measurement process), mainly through two steps, the particulate matter is detected, or the amount thereof is determined (otherwise There is a removal step of removing the particulate matter 11 described later). The one electrode 1 functions as a dust collecting electrode in the dust collecting step and serves as a measuring electrode in the measuring step. For this reason, it is necessary to switch the connection of one electrode 1 for each process (see FIG. 7). That is, in the dust collection process, one electrode 1 and the characteristic measuring device 3 are separated, and in the measurement process, the one electrode 1 and the power source 9 are separated. The control device 12 performs management and control of these processes.

  A preferable distance between the interelectrode dielectric 4 and the second electrode 2 forming a space through which exhaust gas flows is 0.5 to 50 mm, and a more preferable distance is 0.6 to 40 mm. By setting such an interval, it is possible to discharge more efficiently and collect particulate matter. If the distance between the interelectrode dielectric 4 and the second electrode 2 is shorter than 0.5 mm, the dust collection rate may decrease and the measurement accuracy may decrease. If it is longer than 50 mm, a higher voltage is required. And wasteful energy may be required.

  The power source 9 supplies a stable DC voltage or AC voltage that can generate a discharge between the first electrode 1 and the second electrode 2. As the power source 9, for example, a power source using a flyback power source circuit or the like can be employed. In this case, energy is stored in the transformer from the power supply on the input side, and the stored energy is discharged to the output side, whereby a high-voltage DC voltage can be supplied. In a flyback power supply circuit, the accumulation and release of energy to and from the transformer are controlled by a transistor or the like, and the current on the output side is rectified by a diode.

  FIG. 5 is a perspective view showing the outer electrode dielectric 6 and one electrode 1. In FIG. 5, the arrows indicate the flow direction of the exhaust gas. One electrode 1 serves as a member that collects and collects charged particulate matter 11 while performing either or both of forming an electric field and / or discharging as a counter electrode of the second electrode 2. One plate-like electrode 1 in the particulate matter detection device 100 has a generally rectangular shape as shown in FIG. 5, but in addition, a polygon such as a pentagon, a circle, an ellipse, a track shape, etc. A shape, a shape in which irregularities are formed on the outer periphery, a shape in which one or a plurality of slits are formed, and the like can be adopted.

  Although the plate-like two electrodes 2 do not show a perspective view, like the one electrode 1, they are generally rectangular. Similarly to the one electrode 1, a polygon such as a pentagon, a circle, an ellipse, a track shape, a shape in which irregularities are formed on the outer periphery, or a shape in which one or a plurality of slits are formed may be employed.

  The measurement counter electrode 5 having a plurality of linear portions is arranged so as to be longer in the direction perpendicular to the direction in which the exhaust gas flows (arrow in FIG. 1). The distance between the linear measurement counter electrodes 5 is the change in electrical characteristics between the one electrode 1 and the measurement counter electrode 5 caused by the one electrode 1 collecting the particulate matter 11. It is set within a range that can be clearly measured. For example, it is about 0.2 to 10 mm.

  FIG. 6 is a perspective view showing another aspect of the measurement counter electrode having a plurality of linear portions. In FIG. 6, the arrows indicate the flow direction of the exhaust gas. The measurement counter electrode 105 shown in FIG. 6 has a lattice shape, and there are opposing portions in two directions. In addition, the measurement counter electrode 105 is disposed over the entire surface of the interelectrode dielectric 4. In the particulate matter detection device according to the present invention, from the viewpoint of improving the measurement sensitivity and measurement accuracy of the electrical characteristics, it is not preferable that the distance between the linear measurement counter electrodes is long. It is preferable to be disposed at a position corresponding to all the spaces in which the exhaust gas flows. The measurement counter electrode 105 shown in FIG. 6 embodies such a preferred embodiment.

  Returning to the description of the particulate matter detection device 100. The shape and size of the heater 7 may be determined so that the entire particulate matter 11 collected on the surface of the interelectrode dielectric 4 can be combusted.

  The heater 7 is affected not only by the oxidation and removal of the particulate matter 11 but also by the influence of moisture such as dew condensation when measuring the change in electrical characteristics between the one electrode 1 and the measurement counter electrode 5. Used to not. For example, it is possible to prevent moisture from adhering to the one electrode 1 and the measurement counter electrode 5 by appropriately heating at the time of detecting the impedance change or discharging. The preferable heating temperature at this time is 200-300 degreeC.

  As a preferable heater power source 10, a step-down chopper type power source can be cited from the viewpoint of enabling efficient temperature control. Particularly preferred is a step-down chopper type switching power supply using a self-extinguishing type semiconductor switch. In this case, a preferable switching frequency is 20 kHz or more which is higher than the audible frequency. In order to directly affect the fuel consumption, it is desirable to make the current and power of the heater power supply smaller. A preferred heater power supply 10 has a temperature control function by calculating the temperature of the heater 7 from the voltage and current.

  The heat insulating material 8 suppresses heat radiation generated by the heater 7 and enables the heat of the heater 7 to be efficiently used for the combustion of the particulate matter 11. A preferable thickness of the heat insulating material 8 is, for example, about 100 to 1000 μm as a thickness capable of suppressing heat dissipation.

  In the particulate matter detection device 100, a voltage is applied between one electrode 1 and the measurement counter electrode 5 instead of or in combination with the heater 7 and the heater power source 10, and the inter-electrode A mode in which a power supply for removal for causing creeping discharge on the surface of the dielectric 4 can be employed. In this case, in order to cause creeping discharge including the power supply for removal, it is necessary to be able to construct an electric control circuit different from the dust collection process and the measurement process. That is, a switching circuit is provided so that the one electrode 1 and the characteristic measuring device 3, the one electrode 1 and the power source 9 are separated from each other, and the one electrode 1 and the measuring counter electrode 5 can be connected to the power supply for removal. It is necessary to keep. An AC power source or a pulse power source can be used as the power source for removal.

  In the above, one embodiment of the particulate matter detection device according to the present invention has been described. However, as another embodiment, an embodiment in which the two electrodes are formed of a tube wall surface, or two electrodes having a needle shape or a rod shape are employed. Can be mentioned. FIG. 2 is a cross-sectional view showing the particulate matter detection device 200 corresponding to the former. In FIG. 2, the tubular two electrodes 202 constitute a tube wall surface. In FIG. 2, the direction in which the exhaust gas flows is a direction from the near side to the far side. FIG. 3 is a cross-sectional view showing the particulate matter detection device 300 corresponding to the latter, and the second electrode 302 has a pointed bar shape. In the particulate matter detection device 300, the discharge is a corona discharge. The particulate matter detection devices 200 and 300 are the same in principle and action as the device configuration except for the second electrode, and the description thereof is omitted.

  Further, as another embodiment of the particulate matter detection device according to the present invention, a mode in which the measurement counter electrode is covered with a film-like dielectric material can be mentioned. FIG. 4 is a cross-sectional view showing the particulate matter detection device 400 having such an embodiment. FIG. 11 is a diagram corresponding to FIG. 10, and in the particulate matter detection device 400, the voltage between one electrode 1 and the measurement counter electrode 5 is measured using an AC power source in the state where the particulate matter 11 is present. It is a figure showing the equivalent circuit (RC circuit) when V is applied. The total impedance of the circuit is the capacitance based on the capacitance C0 based on the interelectrode dielectric 4 and the film-shaped dielectric 24 covering the measurement counter electrode (see FIG. 4) in the absence of the particulate matter 11. Although constituted by C2, in the state where the particulate matter 11 is present, the capacitance C1 and the resistance R1 of the particulate matter 11 are added. And the electrostatic capacitance C1 and resistance R1 change under a fixed relationship with the quantity of the deposited particulate matter 11. Therefore, as in the case of the particulate matter detection device 100, if the amount of change in the total impedance of the circuit is obtained, the amount of deposition of the particulate matter 11 is obtained.

  [Materials of Particulate Matter Detection Device] Next, materials forming the constituent elements of the particulate matter detection device according to the present invention will be described by taking the case of the particulate matter detection device 100 as an example.

  Preferred materials for forming the first electrode 1, the second electrode 2, and the measurement counter electrode 5 and the wiring used for connection thereof are gold, silver, copper, platinum, palladium, nickel, titanium, manganese, molybdenum, and tungsten. What contains at least 1 type selected from the group which consists of. A preferable content of these components is 20% by volume or more, and a more preferable content is 60% by volume or more. Further, stainless steel can be used as a material for forming the first electrode 1, the second electrode 2, the measurement counter electrode 5, and the wiring used for connecting them.

  Preferred materials for forming the interelectrode dielectric 4, the outer electrode dielectric 6, and the heat insulating material 8 are alumina, magnesium oxide, silicon oxide, silicon nitride, aluminum nitride, zirconia, cordierite, mullite, spinel, and aluminum-titanium. Examples thereof include a ceramic containing at least one selected from the group consisting of a series oxide, a magnesium-calcium-titanium series oxide, a barium-titanium-zinc series oxide, and a barium-titanium series oxide. A ceramic-glass composite material that can be fired at a low temperature in which a glass component is mixed with the ceramics can also be used. Such a ceramic interelectrode dielectric 4 and an outer electrode dielectric 6 are not easily destroyed even when a temperature change occurs, and are excellent in thermal shock resistance. In the case of the heat insulating material 8, it is preferable to use a porous or fiber shape. These materials are also adopted as preferable materials for the film-like dielectric 14 of the particulate matter detection device 400 shown in FIG.

  Preferred materials for forming the heater 7 are platinum, copper, nickel, titanium, manganese, tungsten, molybdenum, tungsten carbide, and the like. In particular, platinum exhibits high accuracy in the relationship between the resistance value and the temperature. By using this as the material of the heater 7, temperature control with high accuracy becomes possible.

  [Method for Producing Particulate Matter Detection Device] Next, a method for producing a particulate matter detection device according to the present invention will be described by taking as an example the case where the particulate matter detection device 100 is produced.

  First, a binder, a plasticizer, a dispersant, a solvent such as water or an organic solvent, etc., are mixed with the ceramic raw material preferable as the above-described interelectrode dielectric 4, outer electrode dielectric 6, and heat insulating material 8 as necessary. Then, a slurry-like raw material for molding is prepared. In mixing, an alumina pot and alumina cobblestone, or a monoball (ball mill) can be used. The raw materials for the interelectrode dielectric 4, the outer electrode dielectric 6, and the heat insulating material 8 may have the same composition or different compositions. It is preferable to add a foaming agent to the raw material for molding the heat insulating material 8.

  As the binder, methyl cellulose, polyvinyl alcohol, polyethylene oxide or the like can be suitably used as the aqueous binder, and polyvinyl butyral, acrylic resin, polyethylene, polypropylene or the like can be suitably used as the non-aqueous binder. . Examples of acrylic resins include (meth) acrylic resins, (meth) acrylic acid ester copolymers, acrylic acid ester-methacrylic acid ester copolymers, and the like. From the viewpoint of suppressing the generation of cracks during the subsequent forming, drying, and firing of the green sheet, the preferred addition amount of the binder is 3 to 20 parts by mass, particularly preferably 100 parts by mass of the ceramic raw material. The addition amount is 6 to 17 parts by mass.

  Preferred plasticizers are glycerin, polyethylene glycol, dibutyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate and the like. A preferable addition amount of the plasticizer is 30 to 70 parts by mass with respect to 100 parts by mass of the binder, and a particularly preferable addition amount is 45 to 55 parts by mass. When the amount is more than 70 parts by mass, the green sheet becomes too soft and may be easily deformed in the process of processing the sheet. When the amount is less than 30 parts by mass, the green sheet becomes too hard and cracks are generated only by bending. , Handling may be worse.

  Preferred dispersing agents are anionic surfactants, wax emulsions, pyridine and the like in aqueous systems, and fatty acids, phosphate esters, synthetic surfactants and the like in non-aqueous systems. The preferable addition amount of a dispersing agent is 0.5-3 mass parts with respect to 100 mass parts of ceramic raw materials, and especially preferable addition amount is 1-2 mass parts. When the amount is less than 0.5 parts by mass, the dispersibility of the ceramic raw material may be lowered, and a crack or the like may occur in the green sheet. If the amount is more than 3 parts by mass, the dispersibility of the ceramic raw material remains unchanged, and impurities during firing increase.

  Preferred organic solvents (solvents) are xylene, butanol and the like. An organic solvent may be used individually by 1 type, and may mix and use multiple. A preferable amount of the solvent added is 50 to 200 parts by mass with respect to 100 parts by mass of the ceramic raw material, and a particularly preferable amount of addition is 75 to 150 parts by mass.

  Next, the slurry-like forming raw material is stirred under a reduced pressure to defoam, and further prepared to have a predetermined viscosity. From the viewpoint of facilitating molding into a sheet shape, the preferable viscosity is 2.0 to 6.0 Pa · s as a value measured with a B-type viscometer, and the more preferable viscosity is 3.0 to 5.0 Pa · s. The particularly preferred viscosity is 3.5 to 4.5 Pa · s.

  Then, the forming raw material whose viscosity is adjusted is formed into a sheet shape, and a green sheet to be the interelectrode dielectric 4, the outer electrode dielectric 6, and the heat insulating material 8 is formed later. A preferable forming method is a doctor blade method, a press forming method, a rolling method, a calendar roll method, or the like. A preferable green sheet has a thickness of 50 to 800 μm.

  Next, on the surface of the obtained green sheet, one electrode 1, measurement counter electrode 5, heater 7, and conductor paste that becomes necessary wiring are disposed, and the green sheet is laminated to form a green laminate. obtain. For the conductive paste, a solvent such as binder and terpineol is added to the powder made of a material suitable for the electrode 1, the measuring counter electrode 5, the heater 7, and the necessary wiring as described above. It can be prepared by kneading. A suitable arrangement means for the conductive paste is a screen printing method.

  Specifically, the conductor paste is arranged by printing one electrode 1 and a conductor paste to be necessary wiring on one surface of the green sheet to be the outer electrode dielectric 6, and further interelectrode dielectric 4. And the measurement counter electrode 5 and necessary wiring are formed in a desired pattern on the surface of the green sheet to be the interelectrode dielectric 4 (the measurement counter electrode has the form shown in FIG. 6, for example). It is preferable to take it). On the other hand, on the other surface of the green sheet that will be the dielectric 6 outside the electrode, a heater 7 and a conductive paste that will be necessary wiring are printed, and a green sheet that will be the heat insulating material 8 is further laminated (see FIG. 1). The green sheets are preferably laminated while being pressurized.

  Next, the obtained green laminated body is dried at 60 to 150 ° C., and if it contains an organic binder, it is degreased at 400 to 800 ° C., and then fired at 1200 to 1600 ° C. In this way, one electrode 1, interelectrode dielectric 4, one electrode 1 and measurement counter electrode 5, outer electrode dielectric 6, heater 7, and heat insulating material 8 constituting the particulate matter detection device 100 are provided. A fired laminate comprising is obtained.

  For the second electrode 2, a commercially available thin plate made of the above-described suitable material is purchased and used and integrated with the fired laminate through a support member. As the second electrode, a laminate of ceramic and conductor paste may be used. As the support member, a sintered body made of a material suitable for the above-described interelectrode dielectric 4, outer electrode dielectric 6, and heat insulating material 8 can be used. Further, the fired laminate and the support member for the second electrode 2 may be integrated so as to form a cavity (space) through which exhaust gas containing the particulate matter 11 flows. In this case, before obtaining the fired laminate, a green sheet that forms the cavity on the interelectrode dielectric 4 (measurement counter electrode 5) side of the green laminate, a green sheet that serves as a top plate, Are further laminated, and on the inner surface (surface facing the cavity) of the green sheet serving as the top plate, the second electrode 2 and the conductor paste serving as necessary wiring are disposed later, Obtaining, drying, necessary degreasing, and firing may be performed.

  As the power source 9, the characteristic measuring device 3, and the heater power source 10, commercially available products that meet the above-described preferable specifications are purchased. A commercially available product can also be used for the flow meter 14. The power source 9 is detachably connected to the first electrode 1 and the second electrode 2, and the characteristic measuring device 3 is detachably connected to the first electrode 1 and the measurement counter electrode 5. Is connected to the heater 7. The particulate matter amount calculating device 13 and the particulate matter concentration calculating device 16 can be constructed by software in a computer such as a sequencer. The control device 12 can be constructed by software in a computer such as a sequencer and a substantial control circuit (hardware) so as to realize the operation of the particulate matter detection device 100 described above or later. As described above, the particulate matter detection device 100 can be manufactured.

  [Method of Using Particulate Matter Detection Device] Next, a method of using the particulate matter detection device according to the present invention will be described taking the case of the particulate matter detection device 100 as an example.

  First, the sensor part of the particulate matter detection device 100 is installed in, for example, an exhaust system (exhaust gas pipe) of a diesel engine, and power supply, control line connection, and the like are performed to make it usable.

  (Dust collection step) In a state where one electrode 1 is separated from the characteristic measuring device 3, for example, a high voltage of direct current is applied between the second electrode 2 and the first electrode 1 by the power source 9 to discharge the particles. The particulate matter 11 is charged to collect dust and deposited on the surface of the interelectrode dielectric 4.

  A preferable time for applying the high voltage is 0.5 to 120 seconds, and more preferably 2 to 10 seconds. If the time is shorter than 0.5 seconds, the accumulation amount (dust collection amount) of the particulate matter 11 is reduced, so that the measurement accuracy of the particulate matter amount 11 may be reduced. Therefore, it may be difficult to accurately grasp the amount of the particulate matter 11 from the subsequent detection of the amount of change in impedance.

  A preferable voltage to be supplied to the first electrode 1 and the second electrode 2 varies depending on the distance between the electrodes, but by increasing the applied voltage, the electric field is strengthened and the dust collecting power is improved. On the other hand, the voltage is preferably 10 kV or less in practice because insulation, insulation distance, and the like become problems and the apparatus becomes large.

  A preferable current due to the discharge flowing between the first electrode 1 and the second electrode 2 is 1 mA or less, and a more preferable current is 1 to 100 μA. If it is less than 1 μA, the dust collection rate may decrease.

  When the particulate matter detection device according to the present invention is used in an exhaust system of an automobile, it is desirable that the power consumption is small because it directly affects fuel consumption. Also, considering the reduction of electromagnetic noise generated and the size of the circuit that generates discharge, the preferred power consumption is 10 W or less, and the more preferred power consumption is 1 W or less.

  (Measurement Step) When the deposition of the particulate matter 11 is finished, the application of a high voltage between the two electrodes 2 and the one electrode 1 is stopped to stop the discharge, and the power source 9 is disconnected from the one electrode 1. Then, the one electrode 1 is connected to the characteristic measuring device 3 and the characteristic measuring device 3 is operated, and the amount of change in impedance between the one electrode 1 and the measuring counter electrode 5 is preferably about 1 to 60 seconds. Measure. The amount and concentration of the particulate matter 11 are determined by the amount of change in impedance.

  When the characteristic measuring device 3 is constituted by an AC power source for applying a voltage to one electrode 1 and the measuring counter electrode 5 and a measuring instrument, a preferable voltage value applied from the AC power source is 1 to 60 V, more A preferable voltage value is 2 to 30V. If the voltage is less than 1V, the detection signal is small and susceptible to noise. If the voltage is greater than 60V, the general-purpose IC may not be used. A preferable measurement frequency is 300 kHz or less.

  (Removal step) When the measurement of the amount of change in impedance between one electrode 1 and the measurement counter electrode 5 is finished, the heater 7 is operated by the heater power supply 10 and the particulate matter deposited on the surface of the interelectrode dielectric 4 11 is oxidized and removed.

  When the heater power supply 10 is a step-down chopper type switching power supply, the preferred current applied to the heater 7 is about 0.8 to 4 A, and the preferred power consumption is 48 W or less.

  A preferable time when the particulate matter 11 is removed by oxidation by the heater 7 is 1 to 600 seconds, and a particularly preferable time is 3 to 120 seconds. When the time is shorter than 1 second, the particulate matter 11 may not be oxidized and removed. When the time is longer than 600 seconds, energy may be consumed wastefully.

  A preferable temperature when the particulate matter 11 collected on the surface of the interelectrode dielectric 4 is oxidized and removed by the heater 7 is 500 to 900 ° C., and a particularly preferable temperature is 550 to 700 ° C. When the temperature is lower than 500 ° C., the particulate matter may be difficult to be removed by oxidation. When the temperature is higher than 900 ° C., the lifetime of the device may be shortened.

  As described above, a voltage is applied between the one electrode 1 and the measurement counter electrode 5 instead of or in combination with the heater 7 and the heater power source 10 to thereby provide an interelectrode dielectric. 4 is provided with a power supply for removal for causing creeping discharge, and the particulate matter 11 collected by the creeping discharge can be removed by oxidation. In this case, a preferable voltage for the creeping discharge varies depending on the thickness of the interelectrode dielectric 4, but is, for example, 2 to 15 kV. The preferred power usage is 10-30W. A preferable time for creeping discharge is 1 to 600 seconds, and a particularly preferable time is 3 to 120 seconds. When the time is shorter than 1 second, the particulate matter 11 may not be oxidized and removed. When the time is longer than 600 seconds, energy may be consumed wastefully.

  As described above, by repeating the dust collection process, the measurement process, and the removal process, it is possible to stably detect the particulate matter 11 over a long period of time. In addition, when exhaust gas from a diesel engine is used as a particulate matter detection target, when the conditions such as the rotational speed, torque, exhaust gas flow rate, temperature, etc. of the diesel engine are in a specific state, It is preferable to perform either or both of discharges. These are determined by the control device 12 (sequencer or the like) by inputting the diesel engine information as a signal to the control device 12 and providing a thermometer in the exhaust gas pipe and inputting the information to the control device 12 as a signal. It is possible to

  The particulate matter detection device according to the present invention can be suitably used as a means for detecting particulate matter contained in exhaust gas or the like of a diesel engine or a flue.

It is a figure showing typically one embodiment of the particulate matter detection device concerning the present invention, and is a sectional view showing only a sensor part. It is a figure which shows typically other embodiment of the particulate matter detection apparatus which concerns on this invention, and is sectional drawing showing only a sensor part. It is a figure which shows typically other embodiment of the particulate matter detection apparatus which concerns on this invention, and is sectional drawing showing only a sensor part. It is a figure which shows typically other embodiment of the particulate matter detection apparatus which concerns on this invention, and is sectional drawing showing only a sensor part. It is a figure showing typically one embodiment of the particulate matter detection device concerning the present invention, and is a perspective view showing dielectric outside an electrode and one electrode. It is a figure which shows typically one Embodiment of the particulate-material detection apparatus which concerns on this invention, and is a perspective view showing the other aspect of a measurement counter electrode. It is a figure showing typically one embodiment of the particulate matter detection device concerning the present invention, and is a lineblock diagram showing an electric control system. It is a graph for demonstrating the function of the particulate matter amount calculation apparatus in the particulate matter detection device according to the present invention. It is a graph for demonstrating the function of the particulate matter concentration calculation apparatus in the particulate matter detection device according to the present invention. It is a figure showing the equivalent circuit (RC circuit) in the particulate matter detection apparatus shown by FIG. It is a figure showing the equivalent circuit (RC circuit) in the particulate matter detection apparatus shown by FIG.

Explanation of symbols

1: one electrode, 2, 202, 302: second electrode, 3: characteristic measuring device, 4: interelectrode dielectric, 5,105: measurement counter electrode, 6: outer electrode dielectric, 7: heater, 8: Heat insulating material, 9: power source, 10: power source for heater, 11: particulate matter, 12: control device, 13: particulate matter amount calculating device, 14: flow meter, 16: particulate matter concentration calculating device, 24: membrane Dielectric, 100, 200, 300, 400: particulate matter detection device.

Claims (12)

One electrode having a plate-like shape in which one surface is coated with a dielectric, and one electrode disposed on the one surface side of the one electrode through a space through which a gas containing particulate matter flows Two electrodes that perform either or both of forming an electric field and / or discharging according to a voltage applied between the power source, a power source that applies the voltage, and
Measuring counter electrode disposed on the surface of the dielectric, characteristic measuring means for measuring electrical characteristics between the measuring counter electrode and the one electrode, and electricity measured by the characteristic measuring means Particulate matter amount calculation means for obtaining the amount of particulate matter collected on the surface of the dielectric based on the amount of change in the mechanical characteristics;
A particulate matter detection device comprising:   A flow meter for measuring or estimating a flow rate of the gas flowing in the space, and particles in the gas flowing in the space based on the flow rate of the gas measured or estimated by the flow meter and the amount of the particulate matter The particulate matter detection device according to claim 1, further comprising particulate matter concentration calculation means for calculating the concentration of the particulate matter.   3. The particulate matter detection device according to claim 1, wherein the electrical characteristic is one or more electrical characteristics selected from a group of electrical characteristics including resistance, inductance, capacitance, and impedance.   The measurement counter electrode has a plurality of linear portions, and the plurality of linear portions are arranged on the surface of the dielectric so as to be long in parallel to the direction in which the gas containing the particulate matter flows. The particulate matter detection device according to any one of claims 1 to 3, wherein the particulate matter detection device is provided.   The particulate matter detection device according to claim 4, wherein the measurement counter electrode having the plurality of linear portions has a lattice shape.   The particulate matter detection device according to claim 4 or 5, wherein the measurement counter electrode having the plurality of linear portions is arranged over the entire surface of the dielectric.   The particulate matter detection device according to any one of claims 1 to 6, wherein the two electrodes have a plate shape.   The particulate matter detection device according to claim 7, wherein the second electrode includes a tube wall surface.   The particulate matter detection device according to any one of claims 1 to 6, wherein the two electrodes have a needle shape or a rod shape.   The particulate matter according to any one of claims 1 to 9, further comprising: a dielectric covering the other surface of the electrode having the plate shape; and a heater disposed on the surface of the dielectric. Detection device.   A power supply is provided between the one electrode and the measurement counter electrode to remove oxidation of particulate matter by creeping discharge, and one surface of the one electrode is applied by applying the voltage. The particulate matter detection device according to any one of claims 1 to 10, wherein creeping discharge is caused on the surface of the dielectric covered with the material.   The particulate matter detection device according to any one of claims 1 to 11, wherein the measurement counter electrode is covered with a film-like dielectric.

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