WO2020090438A1 - Détecteur de microparticules - Google Patents

Détecteur de microparticules Download PDF

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Publication number
WO2020090438A1
WO2020090438A1 PCT/JP2019/040453 JP2019040453W WO2020090438A1 WO 2020090438 A1 WO2020090438 A1 WO 2020090438A1 JP 2019040453 W JP2019040453 W JP 2019040453W WO 2020090438 A1 WO2020090438 A1 WO 2020090438A1
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WIPO (PCT)
Prior art keywords
electrode
noise
collection
flow path
gas flow
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PCT/JP2019/040453
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English (en)
Japanese (ja)
Inventor
英正 奥村
和幸 水野
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日本碍子株式会社
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Publication of WO2020090438A1 publication Critical patent/WO2020090438A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/60—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrostatic variables, e.g. electrographic flaw testing

Definitions

  • the present invention relates to a particle detector.
  • the particle detector As the particle detector, a ceramic housing having a gas flow path, and a charge generation unit that adds charge generated by discharge to particles in the gas introduced into the gas flow path to form charged particles,
  • the gas flow path was provided with a collection unit that collects the charged fine particles on the downstream side of the charge generation unit, and a number measurement unit that measures the number of the fine particles based on the amount of charges of the collected charged fine particles.
  • the thing is known (for example, refer patent document 1).
  • the collection part has a collection electrode exposed in the gas flow path, and a counter electrode facing the collection electrode with the gas flow path in between.
  • the collection electrode collects the charged fine particles by using an electric field generated between the collection electrode and the counter electrode in the gas flow path by the voltage applied between the collection electrode and the counter electrode.
  • the amount of charges of the collected charged fine particles is detected as a minute current (for example, several pA).
  • the amount of electric charge of the collected charged fine particles is detected as a minute current (for example, several pA), it is easily affected by noise around the collecting electrode, which makes it difficult to detect accurately.
  • the present invention has been made to solve such a problem, and its main purpose is to improve the detection accuracy of the amount of fine particles.
  • the present invention has adopted the following means in order to achieve the above-mentioned main purpose.
  • the particle detector of the present invention is A particle detector used to detect particles in a gas, A casing having a gas flow path through which the gas passes, A charge generation unit that adds a charge generated by electric discharge to the fine particles in the gas introduced into the gas flow path to form charged fine particles, A collector provided in the gas flow path on the downstream side of the gas flow with respect to the charge generator, and having a collector electrode for collecting the charged fine particles, A noise detection electrode for detecting noise around the collection electrode, A noise component is subtracted from the particle detection signal based on a particle detection signal from the collection electrode and a noise signal from the noise detection electrode to obtain a corrected signal, and the amount of the particles is determined based on the corrected signal.
  • a computing unit for computing It is equipped with.
  • the particle detection unit subtracts the noise component from the particle detection signal based on the particle detection signal from the collection electrode and the noise signal from the noise detection electrode to obtain a corrected signal, and based on the corrected signal Calculate the quantity. Since the corrected signal is a signal that is hardly affected by noise, the accuracy of detecting the amount of particles is increased by calculating the amount of particles based on the corrected signal.
  • charge includes ions in addition to positive charges and negative charges.
  • signal may be a parameter that changes according to the amount of charged fine particles collected by the collecting electrode, and examples thereof include current.
  • amount of fine particles includes, for example, the number of fine particles, mass, surface area, and the like.
  • the noise detection electrode may be provided on the wall surface of the gas flow path of the housing. In this case, since the surface of the noise detection electrode is exposed, it is easy to detect noise.
  • the noise detection electrode may be provided on a wall surface of the gas flow path of the housing, and the surface of the noise detection electrode may be covered with a non-conductive protective layer. .. By doing so, it is possible to reliably prevent the charged fine particles from adhering to the noise detection electrode, and it becomes difficult for leakage current to flow.
  • the noise detection electrode may be embedded in the housing. Even in this case, it is possible to reliably prevent the charged fine particles from adhering to the noise detection electrode, and it becomes difficult for leakage current to flow.
  • the noise detection electrode may be provided on the downstream side of the collection electrode.
  • the noise detection electrode since the charged fine particles are collected by the collection electrode provided on the upstream side of the noise detection electrode, it is possible to prevent the charged fine particles from being collected by the noise detection electrode.
  • the surface of the noise detection electrode is covered with a protective layer or when the noise detection electrode is embedded in the housing, charged particles are not attached to the noise detection electrode. Need not be provided on the downstream side of.
  • the particle detector of the present invention may include a leakage current absorption electrode provided so as to surround the collection electrode, and the noise detection electrode may be provided inside the leakage current absorption electrode.
  • the leakage current absorption electrode absorbs the leakage current that is about to flow into the collection electrode. When such a leak current flows into the collection electrode, it affects the particle detection signal, but since it is absorbed by the leak current absorption electrode here, it is prevented that a leak current is added to the particle detection signal from the collection electrode. .. Further, since the noise detection electrode is also provided inside the leakage current absorption electrode, it is possible to prevent the leakage current from being added to the noise signal from the noise detection electrode.
  • the noise detection electrode is covered with a protective layer or if the noise detection electrode is embedded in the housing, it is difficult for the leakage current to flow to the noise detection electrode, so It does not necessarily have to be provided inside the electrode.
  • the particle detector of the present invention is provided with a removal electrode provided in the gas flow path between the charge generation section and the collection section for removing excess charge not charged to the particles to the ground. Good. In this case, since the excess charge is removed by the removal electrode, it is possible to prevent the excess charge from being collected by the collection electrode and counted in the amount of fine particles.
  • the particulate matter detector of the present invention is provided with the leakage current absorption electrode, and the noise detection electrode is provided inside the leakage current absorption electrode, and the charge generation unit and the collection unit are provided in the gas flow path.
  • the leakage current absorption electrode may be shared with the removal electrode, the removal electrode being provided between the removal electrodes and removing the excess charge not charged to the particles to the ground. In this case, since the excess charge is removed by the removal electrode, it is possible to prevent the excess charge from being collected by the collection electrode and counted in the amount of fine particles. Moreover, since the leakage current absorption electrode is shared with the removal electrode, the structure of the electrode can be simplified.
  • the removal electrode does not have a unique power source for generating an electric field on the removal electrode, and the voltage arranged around the removal electrode and the removal electrode.
  • the surplus charges may be removed to the ground by utilizing the electric field generated between the applied electrode and the electrodes.
  • the structure of the particle detector can be simplified as compared with the case where the removal electrode has its own power source for generating an electric field.
  • the voltage application electrode is a discharge electrode of the charge generation unit to which a voltage is applied by a discharge power supply, or the voltage application electrode is opposed to the collection electrode of the collection unit by a collection power supply. It may be a counter electrode to which is applied. By doing so, it is possible to use the discharge power supply or the collection power supply instead of the power supply unique to the removal electrode.
  • the arithmetic unit detects the first reference noise signal detected by the collection electrode and the noise detection electrode in a state where the gas is not passed through the gas flow path. Obtaining the amplification factor of the second reference noise signal so that it matches the second reference noise signal, and then, in a state where the gas is passed through the gas flow path, from the particle detection signal from the collection electrode,
  • the corrected signal may be obtained by subtracting an amplified signal obtained by multiplying the noise signal from the noise detection electrode by the amplification factor as the noise component. By doing so, the amplification factor can be accurately obtained without being affected by the gas.
  • the noise signal on the collection electrode and the noise signal on the noise detection electrode may have different signal magnitudes due to the difference in distance from the noise source (for example, the discharge electrode) or the difference in electrode area, These effects can be canceled by the amplification factor of the second reference noise signal.
  • Such a particle detector of the present invention has a first input terminal, a second input terminal and one output terminal, the collecting electrode is connected to the first input terminal, and the noise is input to the second input terminal.
  • a detection electrode is connected through an amplification factor adjusting unit, the arithmetic unit is connected to the output terminal, and a differential that outputs a difference between signals input to the first and second input terminals from the output terminal.
  • An amplifier circuit is provided, and the arithmetic unit of the amplification factor adjustment unit is such that the output signal from the differential amplifier circuit is in a range considered to be zero in a state where the gas is not passed through the gas flow path.
  • FIG. 3 is a perspective view of the particle detection element 20.
  • FIG. 3 is a sectional view taken along line AA of FIG.
  • FIG. 3 is a sectional view taken along line BB of FIG. CC sectional drawing of FIG. 3 is an exploded perspective view of the particle detection element 20.
  • FIG. Explanatory drawing of another example of the number detection part 60.
  • the flowchart which shows an example of a calibration. Sectional drawing when the removal electrode 44 and the guard electrode 68 are provided separately (corresponding to the BB sectional view of FIG. 2).
  • the partial cross section figure of another embodiment of particulate detection element 20 The partial cross section figure of another embodiment of particulate detection element 20.
  • FIG. 8 is an exploded perspective view of a modified example of the particle detection element 20. Sectional drawing of a modification of the particle detection element 20 (corresponding to the BB sectional view of FIG. 2).
  • FIG. 1 is an explanatory view of the particle detector 10 of the present embodiment
  • FIG. 2 is a perspective view of the particle detection element 20
  • FIG. 3 is a sectional view taken along line AA of FIG. 2
  • FIG. 4 is a sectional view taken along line BB of FIG. 5 is a sectional view taken along line CC of FIG. 2
  • FIG. 6 is an exploded perspective view of the particle detection element 20.
  • the vertical direction, the horizontal direction, and the front-back direction are as shown in FIGS. 1 and 2.
  • the particle detector 10 detects the number of particles 26 (see FIG. 5) contained in the exhaust gas flowing through the exhaust pipe 12 of the engine.
  • the particle detector 10 includes a particle detection element 20 and an accessory unit 80 including various power sources 36 and 56 and a number detection unit 60.
  • the particle detection element 20 is attached to a ring-shaped pedestal 16 fixed to the exhaust pipe 12 while being inserted into a columnar support 14.
  • the particle detection element 20 is protected by the protective cover 18.
  • the protective cover 18 has a hole (not shown) through which the exhaust gas flowing through the exhaust pipe 12 passes through a gas flow path 24 provided at the lower end 22a of the particle detection element 20.
  • the particle detection element 20 includes a housing 22, a charge generation section 30, an excess charge removal section 40, a collection section 50, and guard electrodes 68 and 92 (see FIGS. 3 and 4). And a noise detection electrode 70 and a heater electrode 78.
  • the housing 22 is a long rectangular parallelepiped that is long in a direction intersecting the axial direction of the exhaust pipe 12 (here, a direction that is substantially orthogonal).
  • the housing 22 is made of ceramic such as alumina.
  • the lower end 22a of the housing 22 is arranged inside the exhaust pipe 12, and the upper end 22b is arranged outside the exhaust pipe 12.
  • a gas flow path 24 is provided at the lower end 22 a of the housing 22.
  • Various terminals are provided on the upper end 22b of the housing 22.
  • the axial direction of the gas flow path 24 matches the axial direction of the exhaust pipe 12.
  • the gas flow path 24 extends from a rectangular gas inlet 24 a provided on the front surface of the housing 22 to a rectangular gas outlet 24 b provided on the rear surface of the housing 22. It is a continuous rectangular parallelepiped space.
  • the housing 22 includes a pair of left and right flow path walls 22c and 22d that form a gas flow path 24.
  • the charge generation unit 30 is provided on the flow passage wall 22c so that charges are generated in the gas flow passage 24 in the vicinity of the gas introduction port 24a.
  • the charge generator 30 has a discharge electrode 32 and two ground electrodes 34, 34.
  • the discharge electrode 32 is provided along the inner surface of the flow path wall 22c, and as shown in FIG. 3, has a plurality of fine protrusions around a rectangle.
  • the two ground electrodes 34, 34 are rectangular electrodes, and are embedded in the flow path wall 22c so as to be parallel to the discharge electrode 32 with a space therebetween.
  • a pulse voltage of several kV of the discharge power supply 36 (one of the accessory units 80) is applied between the discharge electrode 32 and the two ground electrodes 34, 34.
  • an air discharge is generated due to the potential difference between the electrodes.
  • the portion of the housing 22 between the discharge electrode 32 and the ground electrodes 34, 34 serves as a dielectric layer.
  • the discharge electrode 32 is connected to a discharge electrode terminal 33 (see FIGS. 2 and 6) on the upper end 22b of the housing 22, and is connected to a discharge power supply 36 via this terminal 33.
  • the two ground electrodes 34, 34 are connected to the ground electrode terminal 35 (see FIGS. 2 and 6) of the upper end 22b of the housing 22, and are connected to the discharging power supply 36 via this terminal 35. ..
  • the fine particles 26 contained in the gas enter the gas flow path 24 through the gas introduction port 24a and, when passing through the charge generation unit 30, charge 28 generated by the air discharge of the charge generation unit 30. Is added to form charged fine particles P, and the particles move backward. Further, of the generated electric charges 28, those not added to the fine particles 26 move rearward as the electric charges 28.
  • the surplus charge removal unit 40 is provided downstream of the charge generation unit 30 and upstream of the collection unit 50, as shown in FIG.
  • the surplus charge removal portion 40 has a removal electrode 44 (see FIGS. 4 and 5), but an application electrode (an electrode for generating an electric field on the removal electrode 44) is provided at a position facing the removal electrode 44. I don't have it.
  • the removal electrode 44 is provided along the inner surface of the flow path wall 22d on the right side and is exposed in the gas flow path 24.
  • the removal electrode 44 is connected to the ground via a removal electrode terminal 45 (see FIGS. 2 and 6).
  • the collection unit 50 is provided downstream of the charge generation unit 30 and the surplus charge removal unit 40 in the gas flow path 24.
  • the collecting unit 50 collects the charged fine particles P, and has a counter electrode (electric field generating electrode) 52 and a collecting electrode 54.
  • the counter electrode 52 is provided along the inner surface of the left channel wall 22c and is exposed in the gas channel 24 (see FIGS. 3 and 5).
  • the collection electrode 54 is provided along the inner surface of the right channel wall 22d and is exposed in the gas channel 24 (see FIGS. 4 and 5).
  • the counter electrode 52 and the collecting electrode 54 are arranged at positions facing each other.
  • a DC voltage V1 (a positive potential, for example, about 2 kV) is applied to the counter electrode 52 by a collection power supply 56 via a counter electrode terminal 53 (see FIGS. 2 and 6).
  • the collection electrode 54 is connected to the ground via the collection electrode terminal 55 (see FIGS. 2 and 6), the differential amplifier circuit 62 and the ammeter 64.
  • a relatively strong electric field is generated between the counter electrode 52 and the collection electrode 54 of the collection unit 50. Therefore, the charged fine particles P flowing in the gas flow path 24 are attracted to and collected by the collection electrode 54 by this relatively strong electric field. ..
  • the strength of the electric field generated by the discharge electrode 44, the distance between the removal electrode 44 and the discharge electrode 32, and the distance between the removal electrode 44 and the counter electrode 52 are determined by the collection electrode 54 without the charged fine particles P being collected by the removal electrode 44. It is set so as to be collected and the charge 28 not added to the fine particles 26 is removed by the removal electrode 44.
  • the electric mobility of the electric charge 28 is 10 times or more the electric mobility of the charged fine particles P, and the electric field necessary for collecting the electric charge is one digit or more. Therefore, such setting can be easily performed. Become.
  • the guard electrode 68 is a leakage current absorption electrode that absorbs a leakage current flowing from the counter electrode 52 through the housing 22 to the collection electrode 54.
  • the guard electrode 68 is provided on the surface of the flow path wall 22d so as to surround the collection electrode 54 as shown in FIGS. A part of the guard electrode 68 is shared with the removal electrode 44.
  • the guard electrode 68 is connected to the ground through the removal electrode terminal 45 (see FIGS. 2 and 6) together with the removal electrode 44. Note that, in FIG. 4, for the sake of convenience, the collection electrode 54 is shown as a quadrangle and the guard electrode 68 is described as having a shape surrounding the quadrangle. Since a lead-out portion for use is provided, the upper portion of the guard electrode 68 has a shape surrounding the lead-out portion.
  • the noise detection electrode 70 is an electrode that detects noise around the collection electrode 54.
  • the noise detection electrode 70 is provided along the inner surface of the flow path wall 22d of the housing 22 and is exposed in the gas flow path 24.
  • the noise detection electrode 70 is provided in the region surrounded by the guard electrode 68 (that is, inside the guard electrode 68) and on the downstream side of the collection electrode 54 as shown in FIGS. 4 to 6.
  • the number detecting unit 60 is one of the accessory units 80, and includes a differential amplifier circuit 62, an ammeter 64, and a number measuring device 66, as shown in FIG.
  • the number detecting unit 60 corresponds to the calculating unit of the present invention.
  • the collection electrode 54 is connected to the + side input terminal (first input terminal)
  • the noise detection electrode 70 is connected to the ⁇ side input terminal (second input terminal).
  • the ammeter 64 has one terminal connected to the output terminal of the differential amplifier circuit 62 and the other terminal connected to the ground.
  • the ammeter 64 measures a current based on the electric charge 28 of the charged fine particles P collected by the collecting electrode 54.
  • the number measuring device 66 is composed of a microprocessor having a well-known CPU and the like, and calculates the number of the particles 26 based on the current of the ammeter 64.
  • the heater electrode 78 is a strip-shaped heating element embedded in the housing 22. Specifically, as shown in FIGS. 2 and 6, the heater electrode 78 has the flow path wall 22c of the case 22 drawn in a zigzag manner from one heater electrode terminal 79 of the upper end 22b of the case 22. After that, wiring is provided so as to return to the other heater electrode terminal 79 on the upper end 22b of the housing 22.
  • the heater electrode 78 is connected to a power supply device (not shown) via a pair of heater electrode terminals 79, 79, and generates heat when energized by the power supply device.
  • the heater electrode 78 heats each electrode such as the housing 22, the removal electrode 44, and the collection electrode 54.
  • the particle detection element 20 is composed of six sheets S1 to S6.
  • Each of the sheets S1 to S6 is made of the same material as the case 22.
  • the sheets are referred to as a first sheet S1, a second sheet S2, ...
  • the right side surface of each of the sheets S1 to S6 is referred to as a front surface
  • the left side surface is referred to as a back surface.
  • the thickness of each of the sheets S1 to S6 may be set appropriately, and may be the same or different.
  • a heater electrode 78 is provided on the surface of the first sheet S1. One end and the other end of the heater electrode 78 are arranged above the front surface of the first sheet S1, and the heater electrode terminals 79 are provided above the back surface of the first sheet S1 through the through holes of the first sheet S1. , 79, respectively.
  • the ground electrodes 34, 34 are provided on the surface of the second sheet S2.
  • the ground electrodes 34, 34 are integrated into one wiring 34a.
  • the end of the wiring 34a is arranged above the front surface of the second sheet S2, and is provided above the back surface of the first sheet S1 through the through holes of the second sheet S2 and the first sheet S1. It is connected to the electrode terminal 35.
  • the wiring 44a of the removal electrode 44, the wiring 54a of the collection electrode 54, and the wiring 70a of the noise detection electrode 70 are provided along the vertical direction.
  • the upper ends of the wirings 44a, 54a, 70a are provided above the back surface of the first sheet S1 through the through holes of the second sheet S2 and the first sheet S1 and are provided with a removal electrode terminal 45, a collection electrode terminal 55, and noise. Each is connected to the detection electrode terminal 71.
  • the discharge electrode 32 and the counter electrode 52 are provided on the surface of the third sheet S3.
  • a gas flow path 24, that is, a rectangular parallelepiped space is provided on the lower end side of the fourth sheet S4.
  • the removal electrode 44, the collection electrode 54, the noise detection electrode 70, and the guard electrode 68 are provided on the back surface of the fifth sheet S5.
  • the removal electrode 44 integrated with the guard electrode 68 is connected to the wiring 44a of the second sheet S2 through each through hole of the fourth sheet S4 and the third sheet S3, and the removal electrode terminal 45 is connected through this wiring 44a. It is connected to the.
  • the collecting electrode 54 is connected to the wiring 54a of the second sheet S2 via the through holes of the fourth sheet S4 and the third sheet S3, and is connected to the collecting electrode terminal 55 via the wiring 54a.
  • the noise detection electrode 70 is connected to the wiring 70a of the second sheet S2 via the through holes of the fourth sheet S4 and the third sheet S3, and is connected to the noise detection electrode terminal 71 via this wiring 70a.
  • the wiring 32a of the discharge electrode 32 and the wiring 52a of the counter electrode 52 are provided on the back surface of the sixth sheet S6 along the vertical direction.
  • the lower end of the wiring 32a is connected to the discharge electrode 32 provided on the third sheet S3 through the through holes of the fourth to fifth sheets S4 to S5.
  • the lower end of the wiring 52a is connected to the counter electrode 52 provided on the third sheet S3 through the through holes of the fourth to fifth sheets S4 to S5.
  • the upper ends of the wirings 32a and 52a are connected to the discharge electrode terminal 33 and the counter electrode terminal 53 provided above the surface of the sixth sheet S6 through the through holes of the sixth sheet S6, respectively.
  • the particle detection element 20 can be manufactured using a plurality of ceramic green sheets. Specifically, each of the plurality of ceramic green sheets is provided with notches, through holes or grooves, or screen-printed with electrodes or wiring patterns, if necessary, and then laminated and fired. The notches, the through holes, and the grooves may be filled with a material (for example, an organic material) that will be burned out during firing. In this way, the particle detection element 20 is obtained. Then, the discharge electrode terminal 33 and the counter electrode terminal 53 of the particle detection element 20 are connected to the discharge power supply 36 and the collection power supply 56 of the accessory unit, respectively. Further, the ground electrode terminal 35 and the removal electrode terminal 45 of the particle detection element 20 are connected to the ground.
  • a material for example, an organic material
  • the collection electrode terminal 55 and the noise detection electrode terminal 71 are connected to the + side and ⁇ side input terminals of the differential amplifier circuit 62, respectively, and the output terminals of the differential amplifier circuit 62 are counted through the ammeter 64. Connect to device 66. Then, the heater electrode terminals 79, 79 are connected to a power supply device (not shown). By doing so, the particle detector 10 can be manufactured.
  • the fine particle detection element 20 When measuring the fine particles 26 contained in the exhaust gas of an automobile, the fine particle detection element 20 is attached to the exhaust pipe 12 of the engine as described above (see FIG. 1). As shown in FIG. 5, the fine particles 26 contained in the exhaust gas introduced into the gas flow path 24 from the gas introduction port 24a are charged with a charge 28 (here, a positive charge) generated by the discharge of the charge generation unit 30. It becomes fine particles P.
  • the charged fine particles P have a weak electric field (the electric field generated between the removal electrode 44 and the voltage application electrodes (the discharge electrode 32 and the counter electrode 52) arranged around the removal electrode 44), and the length of the removal electrode 44 is the collection electrode 54.
  • the excess charge removing section 40 which is shorter than the above, passes through as it is and reaches the collecting section 50.
  • the charges 28 not added to the particles 26 are attracted to the removal electrode 44 of the excess charge removal unit 40 even if the electric field is weak, and are discarded to the ground via the removal electrode 44.
  • the unnecessary charges 28 that have not been added to the fine particles 26 hardly reach the collection unit 50.
  • the charged fine particles P that have reached the collection unit 50 are collected by the collection electrode 54 by the collection electric field generated by the counter electrode 52.
  • a current obtained by adding a current based on the noise around the collection electrode 54 to a current based on the charge 28 of the collected charged fine particles P flows through the collection electrode 54.
  • the noise around the collection electrode 54 includes, for example, noise generated by the charge generation unit 30 and noise generated by vehicle-mounted devices such as ETC.
  • a current based on noise around the collection electrode 54 flows through the noise detection electrode 70. Since the charged fine particles P are collected by the collecting electrode 54 provided on the upstream side of the noise detection electrode 70, a current based on the charged fine particles P does not flow through the noise detection electrode 70.
  • the current flowing through the collection electrode 54 is input to the + side input terminal of the differential amplifier circuit 62, and the current flowing through the noise detection electrode 70 is input to the ⁇ side input terminal. From the output terminal of the differential amplifier circuit 62, a signal amplified after subtracting the current flowing through the noise detection electrode 70 from the current flowing through the collection electrode 54 is output to the ammeter 64. Therefore, a current (a current not including a noise component) based on the charge 28 of the charged fine particles P collected by the collecting electrode 54 flows through the ammeter 64. Then, the current is measured by the ammeter 64, and the number measuring device 66 calculates the number of the fine particles 26 based on the current.
  • the number measuring device 66 integrates (accumulates) the current value over a predetermined period to obtain the integrated value (accumulated charge amount), divides the accumulated charge amount by elementary charge, and obtains the total number of charges (collected charge number).
  • the number Nt of the fine particles 26 collected by the collecting electrode 54 is obtained by dividing the number of collected charges by the average value of the number of charges added to one fine particle 26 (average number of charges) (see below). (See formula (1)).
  • the number measuring device 66 detects this number Nt as the number of fine particles 26 in the exhaust gas.
  • Nt (accumulated charge amount) / ⁇ (elementary charge) ⁇ (average number of charges) ⁇ (1)
  • the charged particles P may not be newly collected by the collection electrode 54. Therefore, by heating the collection electrode 54 by the heater electrode 78 periodically or at the timing when the deposition amount reaches a predetermined amount, the deposit on the collection electrode 54 is heated and incinerated, and the collection electrode 54 is heated. Refresh the electrode surface.
  • the heater electrode 78 can also incinerate the fine particles 26 attached to the inner peripheral surface of the housing 22.
  • the role of the guard electrode 68 will be described.
  • the voltage V1 is applied between the counter electrode 52 and the collection electrode 54 of the collection unit 50. Since the voltage V1 is several kV, a leakage current of several tens to several hundreds pA is generated in the counter electrode 52 and the collection electrode 54 even in the case 22 made of ceramic such as alumina which is usually considered as an electric insulator. It flows from one side to the other side through the housing 22.
  • the detected current measured by the ammeter 64 when detecting the number Nt is several pA. Therefore, the leakage current affects the detection current. In this embodiment, such a leakage current is absorbed by the guard electrode 68 and is discarded to the ground.
  • the collection electrode 54 is surrounded by the guard electrode 68.
  • the noise detection electrode 70 is also surrounded by the guard electrode 68. Therefore, it is possible to prevent the leakage current from affecting the current flowing through the collection electrode 54 and the current flowing through the noise detection electrode 70.
  • the counting device 66 subtracts the noise signal (current) from the noise detection electrode 70 from the particle detection signal (current) from the collection electrode 54 and then amplifies the signal (corrected signal). ) Is used to calculate the number of fine particles. Since the corrected signal is a signal that is hardly affected by noise, the accuracy of detecting the number of particles is increased by calculating the number of particles based on the corrected signal.
  • the surface of the noise detection electrode 70 is exposed to the gas flow path 24, it is easy to detect noise.
  • the charged fine particles P are collected by the collecting electrode 54 provided on the upstream side of the noise detection electrode 70, it is possible to prevent the charged fine particles P from being collected by the noise detection electrode 70. ..
  • the leak current is absorbed by the guard electrode 68, the leak current is prevented from being added to the particle detection signal from the collection electrode 54.
  • the noise detection electrode 70 is also provided inside the guard electrode 68, it is possible to prevent a leak current from being added to the noise signal from the noise detection electrode 70. Therefore, it is possible to prevent the detection accuracy from decreasing due to the influence of the leakage current, and it is possible to improve the detection accuracy of the number of fine particles.
  • the guard electrode 68 is shared with the removal electrode 44, the structure of the electrode can be simplified.
  • the removal electrode 44 does not have its own power source for generating an electric field on the removal electrode 44, and is provided between the removal electrode 44 and the voltage application electrodes (the discharge electrode 32 and the counter electrode 52) arranged around the removal electrode 44.
  • the excess electric charge 28 is removed to the ground by using the electric field generated in the. Therefore, the structure of the particle detector 10 can be simplified as compared with the case where the removal electrode 44 has its own power source for generating an electric field.
  • the number detection unit 60 includes the amplification factor adjustment unit 61 between the ⁇ side input terminal of the differential amplifier circuit 62 and the noise detection electrode 70, as shown in FIG. 7. Good.
  • the number detection unit 60 detects the first reference noise signal detected by the collection electrode 54 when the charge generation unit 30 and the collection unit 50 are energized in a state where gas is not passing through the gas flow path 24.
  • the amplification factor of the second reference noise signal is calculated so that the second reference noise signal detected by the noise detection electrode 70 matches (calibration).
  • the number detection unit 60 adjusts the amplification factor of the amplification factor adjustment unit 61 to be the amplification factor of the second reference noise signal thus obtained, and in a state where the gas is passed through the gas flow path 24.
  • a corrected signal is obtained by subtracting a signal obtained by multiplying the current from the noise detection electrode 70 by the adjusted amplification factor from the current from the collection electrode 54, and the number of particles is calculated based on the corrected signal. You may calculate.
  • the number measuring device 66 of the number detection unit 60 performs a short circuit check of the charge generation unit 30, the surplus charge removal unit 40, and the collection unit 50 in advance before starting the calibration, and it is not shorted in any of them. To confirm.
  • the number measurement device 66 starts the calibration, first, the charge generation unit 30 and the collection unit 50 are temporarily energized (S110). In the temporary energization, the low voltage is applied when S110 is executed for the first time, but the voltage is increased stepwise so as to approach the main voltage as the number of times increases after the second time (step-up application). Subsequently, the number measuring device 66 measures the leakage current (S120).
  • the leakage current is measured by measuring the current flowing through the collecting electrode 54 with an ammeter (not shown). Subsequently, the number measuring device 66 determines whether the leakage current is less than or equal to a predetermined threshold value (S130), and if the leakage current exceeds the threshold value, it is considered that some abnormality may occur. Then, the power supply to the charge generation unit 30 and the collection unit 50 is turned off to issue a warning (S135), and the calibration is completed. The warning is given, for example, by lighting or blinking a lamp, sounding a buzzer, or explaining the situation by voice.
  • the threshold value of the leakage current is set in advance in a preliminary experiment or the like within a range in which there is no abnormality in the particle detector 10.
  • the number measuring device 66 determines whether or not the temporary energization voltage has reached the main energization voltage (voltage at the time of measuring the number of fine particles) (S140), If the voltage for the main energization has not been reached, the process returns to S110, temporary energization is performed with a voltage one step higher than the previous time, and then the processes of S120 to S140 are executed again.
  • the number measuring device 66 keeps the voltage of the main energization applied to the charge generation unit 30 and the collection unit 50, and the differential amplifier circuit 62. Is energized (S150) and the differential current is measured (S160).
  • the differential current is an output signal of the differential amplification circuit 62, and is multiplied by the amplification factor adjusted by the amplification factor adjustment unit 61 detected by the noise detection electrode 70 from the first reference noise signal detected by the collection electrode 54. It is a value obtained by subtracting the second reference noise signal.
  • the number measuring device 66 determines whether or not the differential current is substantially zero, that is, whether or not it is equal to or less than a predetermined zero point specified value (S170), and the differential current exceeds the zero point specified value. If so, the amplification factor of the amplification factor adjusting unit 61 is updated (S175), and the processes of S160 and S170 are executed again.
  • the amplification rate is set low at the first time, and is set to a gradually larger value each time the amplification rate is updated in S175.
  • the number-counting device 66 stores the amplification factor at that time in a memory (not shown) (S180), and the charge generation unit 30, the collection unit 50, and the The power supply to the differential amplifier circuit 62 is turned off (S190), and the calibration is completed. After that, the number measuring device 66 calculates the number of fine particles using the amplification factor stored in a memory (not shown).
  • the amplification factor can be obtained accurately without being affected by gas.
  • the noise signal on the collecting electrode 54 and the noise signal on the noise detecting electrode 70 are different in magnitude depending on the difference in distance between the noise generating source (for example, the discharge electrode 32) of each electrode 54, 70 and the difference in electrode area. However, even if they are different, the influences thereof can be canceled by the amplification rate of the amplification rate adjusting unit 61 set by the calibration.
  • the calibration is performed by the number measuring device 66 of the number detecting unit 60, but may be performed by another processor (for example, an engine ECU).
  • the guard electrode 68 and the removal electrode 44 are used in common, but as shown in FIG. 9 (corresponding to the DD sectional view of FIG. 2), the frame-shaped guard electrode 68 and the rectangular removal electrode are provided. 44 and 44 may be provided separately. Also in FIG. 9, the guard electrode 68 is provided so as to surround the collection electrode 54, and the noise detection electrode 70 is provided inside the guard electrode 68 and on the downstream side of the collection electrode 54. In this case, both electrodes 68 and 44 may be connected to the ground via a common wire, or may be connected to the ground via individual wires.
  • the noise detection electrode 70 is provided along the inner surface of the flow channel wall 22d, but it may be embedded in the flow channel wall 22d of the housing 22 like the noise detection electrode 170 shown in FIG.
  • the same components as those in the above-described embodiment are designated by the same reference numerals.
  • the noise detection electrode 170 does not necessarily have to be provided on the downstream side of the collection electrode 54. Further, it becomes difficult for leakage current to flow through the noise detection electrode 170. Therefore, the noise detection electrode 170 does not necessarily have to be arranged inside the guard electrode 68.
  • the distance from the surface of the noise detection electrode 170 (the lower surface in FIG. 10) to the surface of the housing 22 is preferably short.
  • the distance is preferably 0.1 mm or less, more preferably 0.01 mm or less.
  • the surface of the noise detection electrode 70 provided along the inner surface of the flow path wall 22d may be covered with a non-conductive protective layer 70b.
  • the same components as those in the above-described embodiment are designated by the same reference numerals.
  • the thickness of the protective layer 70b is preferably thin in consideration of noise detection by the noise detection electrode 70, preferably 0.1 mm or less in consideration of not disturbing the gas flow, and the thickness of the noise detection electrode 70 (for example, If considering 0.005 to 0.01 mm), 0.01 mm or less is preferable.
  • the material of the protective layer 70b ceramics such as alumina and glass such as silica are preferable from the viewpoint of heat resistance.
  • An example of the method for forming the glass protective layer 70b will be described below. That is, a plate-shaped glass (having a thickness of about 0.1 mm) larger than the noise detection electrode 70 is placed on the noise detection electrode 70, and the glass is heated to a temperature higher than the glass transition point to be softened. Thus, the protective layer 70b made of glass can be formed.
  • guard electrode 68 absorbs the leakage current flowing on the surface and discards it to the ground, but in addition to this, as shown in FIGS.
  • Guard electrodes 69, 69 may be embedded so as to surround 54 and the noise detection electrode 70 from above and below. 12 and 13, the same components as those in the above-described embodiment are designated by the same reference numerals.
  • both guard electrodes 69, 69 are provided on the surface of the fourth sheet S4 above and below the gas flow path 24, respectively.
  • the lower guard electrode 69 is connected to the removal electrode 44.
  • the upper guard electrode 69 is connected in the middle of the conductive path connecting the removal electrode 44 and the wiring 44a, and is connected to the removal electrode terminal 45 via the wiring 44a.
  • the leakage current flowing in the housing 22 is absorbed by the guard electrodes 69, 69 embedded in the housing 22 and discarded to the ground, and the leakage current flowing on the surface is absorbed in the guard electrode 68 and grounded. Thrown away Therefore, it is possible to further suppress the leakage current from affecting the current flowing through the collection electrode 54 and the current flowing through the noise detection electrode 70.
  • the guard electrode 68 is provided on the inner surface of the gas flow path 24 in the above-described embodiment, the position of the guard electrode 68 is not particularly limited to the inner surface, and any position that can absorb the leakage current can be used. I do not care.
  • part or all of the guard electrode 68 may be embedded inside the housing 22.
  • guard electrode 68 is provided in the above-described embodiment, the guard electrode 68 may be omitted if the housing 22 has high electric insulation and the leakage current is substantially zero without the guard electrode 68. ..
  • the surplus charge removing unit 40 is described as having no application electrode for generating an electric field on the removal electrode 44 or an original removal power source for applying a voltage to the application electrode.
  • an applying electrode may be provided at a position facing the removing electrode 44 (left side channel wall 22c), and a removing power source for applying a voltage to the applying electrode may be provided. In that case, the voltage applied to the removal electrode 44 is adjusted so as to collect the excess charges 28 but not the charged fine particles P.
  • the removal electrode 44 of the excess charge removal unit 40, the collection electrode 54 of the collection unit 50, the noise detection electrode 70, and the guard electrode 68 are provided on the flow path wall 22d on the right side of the housing 22, and the left side thereof is provided.
  • the counter electrode 52 of the collection unit 50 is provided on the flow channel wall 22c, the present invention is not limited to this.
  • the removal electrode 44, the collection electrode 54, the noise detection electrode 70, and the guard electrode 68 are provided on the flow path wall 22c on the left side of the housing 22, and the counter electrode 52 of the collection unit 50 is provided on the flow path wall 22d on the right side. It may be provided. ..
  • the removal electrode 44 of the excess charge removing portion 40 is provided on the right flow passage wall 22d of the housing 22, but the removal electrode connected to the ground may be provided on the left flow passage wall 22c. Good.
  • the charge generation unit 30 is configured by the discharge electrode 32 provided along the inner surface of the gas flow path 24 and the two ground electrodes 34, 34 embedded in the housing 22. Any structure may be used as long as it can generate electric charges by discharging.
  • the ground electrodes 34, 34 may be provided along the inner surface of the gas flow path 24 instead of being buried in the wall of the gas flow path 24.
  • the charge generation section may be composed of a needle electrode and a counter electrode.
  • the charge generation unit 30 is provided on the flow channel wall 22c, but instead of or in addition to this, the charge generation unit 30 may be provided on the flow channel wall 22d.
  • the counter electrode 52 is exposed to the gas flow path 24, but it is not limited to this and may be embedded in the housing 22.
  • the particulate matter detector 10 is not particularly limited to the exhaust pipe 12 of the engine, and may be any pipe as long as a gas containing particulates flows therethrough. Such a tube may be used.
  • the particle detection element 20 detects the number of particles, but it may detect the mass or surface area of the particles.
  • the mass of the fine particles can be obtained, for example, by multiplying the number of the fine particles by the average mass of the fine particles, and the relationship between the accumulated charge amount and the mass of the collected fine particles is stored in a storage device as a map in advance. It is also possible to obtain the mass of the fine particles from the accumulated charge amount using this map.
  • the surface area of the fine particles can also be determined by the same method as the mass of the fine particles.
  • the present invention can be used for a particle detector that detects particles in exhaust gas of a power machine such as an automobile.

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Abstract

L'invention concerne un détecteur de microparticules 10 qui comprend un boîtier 22, une unité de génération de charge 30, une unité de collecteur 50, une électrode de détection de bruit 70 et une unité de détection de comptage 60. Le boîtier (22) comprend un trajet d'écoulement de gaz (24). L'unité de génération de charge 30 produit des microparticules chargées P en ajoutant une charge 28 générée par décharge vers des microparticules 26 dans un gaz qui a été introduit dans le trajet d'écoulement de gaz 24. L'unité de collecteur 50 comprend une électrode de collecte 54 qui est disposée plus du côté aval du flux de gaz que l'unité de génération de charge à l'intérieur du trajet d'écoulement de gaz 24, et qui collecte les microparticules chargées P. L'électrode de détection de bruit 70 détecte le bruit de l'environnement de l'électrode de collecte 54. L'unité de détection de comptage 60 soustrait, sur la base d'un signal de détection de microparticules provenant de l'électrode de collecte 54 et d'un signal de bruit provenant de l'électrode de détection de bruit 70, une composante de bruit à partir du signal de détection de microparticules pour obtenir un signal déjà corrigé, et calcule un nombre de microparticules sur la base du signal déjà corrigé.
PCT/JP2019/040453 2018-10-31 2019-10-15 Détecteur de microparticules WO2020090438A1 (fr)

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JP2018-205612 2018-10-31

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008128739A (ja) * 2006-11-17 2008-06-05 Isuzu Motors Ltd 微小粒子の粒子数計測方法及び装置
WO2008111403A1 (fr) * 2007-03-15 2008-09-18 Ngk Insulators, Ltd. Appareil de détection de matière particulaire
JP2013029385A (ja) * 2011-07-27 2013-02-07 Sharp Corp イオン量測定装置、イオン量測定方法及びイオン発生装置
JP2016075674A (ja) * 2014-10-07 2016-05-12 日本特殊陶業株式会社 微粒子測定システム
US20170168002A1 (en) * 2015-12-11 2017-06-15 Hyundai Motor Company Particulate matter sensor and measurement method thereof
WO2018139345A1 (fr) * 2017-01-26 2018-08-02 日本碍子株式会社 Dispositif de détection du nombre de particules fines

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008128739A (ja) * 2006-11-17 2008-06-05 Isuzu Motors Ltd 微小粒子の粒子数計測方法及び装置
WO2008111403A1 (fr) * 2007-03-15 2008-09-18 Ngk Insulators, Ltd. Appareil de détection de matière particulaire
JP2013029385A (ja) * 2011-07-27 2013-02-07 Sharp Corp イオン量測定装置、イオン量測定方法及びイオン発生装置
JP2016075674A (ja) * 2014-10-07 2016-05-12 日本特殊陶業株式会社 微粒子測定システム
US20170168002A1 (en) * 2015-12-11 2017-06-15 Hyundai Motor Company Particulate matter sensor and measurement method thereof
WO2018139345A1 (fr) * 2017-01-26 2018-08-02 日本碍子株式会社 Dispositif de détection du nombre de particules fines

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