JP2015219147A - Fine particle detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine particle detection system that allows an amount of fine particle to be more correctly detected.SOLUTION: A fine particle detection system 1 comprises: an ion source 15 that generates an ion CP by an aerial discharge; a sensor unit 10 that has a first member 45 arranged around the ion source and serving as first reference potential SGND; and a signal current detection circuit 230 that detects a signal current Is flowing between the first reference potential SGND and second reference potential CGND. The ion source 15 has an electrode structure 100 that includes a discharge potential pad 113 regarded as discharge potential PV2 and different potential pads 136 and 137 regarded as different potential letting the second reference potential CGND be a reference, and the sensor unit 10 has separators 71 and 72 that enclose a structure pad unit 100K where the discharge potential pad 113 and the different potential pads 136 and 137 take a position in a radial direction and house a discharge potential terminal 73 and different potential terminals 76 and 77. One part of a surface of the sensor unit has a leak current suppressive film 78 that suppresses a leak current flowing between the discharge potential terminal 73 and the different potential terminals 76 and 77 through surfaces of the separators 71 and 72.

Description

  The present invention relates to a fine particle detection system that detects fine particles in a gas to be measured.

2. Description of the Related Art Conventionally, there has been a fine particle detection system that detects the amount of fine particles in exhaust gas of a vehicle (internal combustion engine) by generating ions by air discharge such as corona discharge, and attaching these ions to the fine particles in exhaust gas and charging them. Are known.
The sensor unit (sensor body) of such a particle detection system includes, for example, a connection terminal for a discharge electrode and other connection terminals that are connected to a lead wire having a discharge potential that causes an air discharge, as disclosed in Patent Document 1. (For example, a heater connection terminal) is held while being separated from each other by an insulating separator. In the separator, each connection terminal is in contact with a discharge electrode pad and other pads provided on the surface of the sensor unit that includes the discharge electrode and forms the ion source.

JP 2013-170914 A

The fine particle detection system described above includes a member that is a reference potential (sensor GND) of the discharge potential applied to the connection terminal for the discharge electrode and a member that is conductive to the potential of the chassis (vehicle body) (chassis GND). The sensor GND and the chassis GND are insulated from each other. This fine particle detection system detects an electric current flowing between the sensor GND and the chassis GND as a signal current while generating an air discharge between the discharge electrode having a discharge potential and the member having the sensor GND. Yes.
The chassis GND is also used as a reference potential of the heater potential applied to, for example, the heater connection terminal, and the heater potential and the chassis GND, and the discharge potential and the sensor GND constitute an independent electric circuit. .

  However, if the insulation surface of the separator is deteriorated due to water droplets adhering to the surface of the above-described insulating separator due to the influence of humidity, the discharge potential for the discharge electrode through the surface of the separator is reduced. A leakage current may flow between the connection terminal and the connection terminal for the heater that is set to the chassis GND or a heater potential based on the chassis GND. When such a leakage current flows, an error due to the leakage current occurs in the detected signal current, and the amount of fine particles cannot be detected accurately.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a fine particle detection system capable of detecting the amount of fine particles more accurately.

  One aspect thereof includes: an ion source that generates ions by air discharge; a sensor unit that is disposed around the ion source and configured as a first reference potential; the first reference potential; A fine particle detection system including a signal current detection circuit that detects a signal current flowing between a first reference potential and an insulated second reference potential, wherein the ion source is made of an insulating material and is arranged in a longitudinal direction. An insulating base having an extending shape, a discharge electrode body provided on the insulating base and applied with a discharge potential based on the first reference potential to generate the air discharge with the first member; A discharge potential pad that is electrically connected to the discharge electrode body and is formed on the surface of the insulating substrate to be the discharge potential, and is formed on the surface of the insulating substrate, and is based on the second reference potential or the reference potential. On the potential A discharge potential lead having an electrode structure including a different potential pad different from the discharge potential, the discharge potential having a discharge potential terminal at one end, and the different potential; The sensor portion is made of an insulating material, and the structure pad portion where the discharge potential pad and the different potential pad are located in the electrode structure is disposed in the longitudinal direction. The discharge potential terminal and the different potential terminal are enclosed and held in a state of being insulated from each other while being surrounded by a radial direction orthogonal to the direction, while the discharge potential terminal is used as the discharge potential pad and the different potential terminal. Are connected to the different potential pads, respectively, and the separators are electrically connected to each other, and the separator has a part of the surface through the surface of the separator and the discharge potential terminal. A particulate sensing system having a suppressing leakage current suppressing film leakage current flowing between the potential terminal.

In this fine particle detection system, the separator of the sensor unit has a leakage current suppressing film that suppresses a leakage current flowing between the discharge potential terminal and the different potential terminal through a part of the surface of the separator. Yes.
Thereby, the influence of the leakage current on the signal current flowing between the first reference potential and the second reference potential can be suppressed, and the amount of fine particles can be detected more accurately.

An example of the leakage current suppressing film is a metal film that conducts to the first reference potential. In this case, the leakage current flowing on the separator surface from the discharge potential terminal flows into the first reference potential, which is the reference potential of the discharge potential, and does not flow into the second reference potential, thus appropriately preventing fluctuations in the signal current due to the leakage current. it can.
Examples of the leakage current suppressing film include a water-repellent coating film. It is possible to suppress water droplets from adhering to the separator surface, to prevent a decrease in insulation on the separator surface, and to suppress leakage current.

The first reference potential is a reference potential of the discharge potential, and specifically, the above-described sensor GND corresponds to this. The second reference potential is insulated from the first reference potential (sensor GND). Specifically, the chassis GND described above corresponds to this.
The signal current detection circuit detects a current flowing between the first reference potential and the second reference potential as a signal current.

Further, the different potential corresponds to a second reference potential (chassis GND) or a potential based on the second reference potential (chassis GND), for example, a heater potential applied to both ends of the heater for heating the electrode structure. Note that one of the heater potentials is preferably a second reference potential (chassis GND). Further, the different potential pad may be a heater pad which is set to the heater potential and is conducted to the heater. The different potential terminal includes a heater terminal that contacts the heater pad.
Moreover, as a separator, a single separator may be used and the separator which combined several parts may be used.

Examples of the insulating material constituting the insulating base include insulating glass and ceramic. Among these, insulating ceramics having high heat resistance such as alumina, mullite, silicon nitride are preferable.
Examples of the electrode structure in which the discharge electrode body is provided on the insulating base include a structure in which the electrode structure is included in a ceramic base made of an insulating ceramic such as alumina. In addition, for example, after forming a discharge electrode body on the surface of a ceramic substrate, a discharge electrode body is provided on an insulating substrate made of a ceramic substrate and a glass coat by partially coating the discharge electrode body with a glass coat. Also included are electrode structures.

  Furthermore, in the fine particle detection system described above, the leakage current suppression film may be a fine particle detection system that is a metal film that conducts to the first reference potential.

  In this fine particle detection system, the metal film that is the leakage current suppressing film is electrically connected to the first reference potential. For this reason, when the leakage current flowing on the surface of the separator from the discharge potential terminal reaches the metal film, the leakage current flows into the first reference potential through the metal film and does not flow into the second reference potential leading to the different potential terminal. For this reason, the influence of the leakage current on the signal current can be suppressed.

  Further, in the fine particle detection system described above, in the structure pad portion, the insulating base is a plate having two main surfaces, a first main surface and a second main surface, and the discharge potential pad is The different potential pad is located on the first main surface, the different potential pad is located on the second main surface, and is spaced apart from the discharge potential pad in the longitudinal direction, and the separator is the discharge potential terminal. And a first separator that surrounds the discharge potential pad of the structure pad portion, and a second separator that is aligned with the first separator in the longitudinal direction and surrounds the different potential terminal and the different potential pad of the structure pad portion. It is preferable that the metal film is a fine particle detection system that is attached to at least a part of the surface of the second separator among the separators.

In this fine particle detection system, in the structure pad portion, the insulating base is a plate having a first main surface and a second main surface, and the discharge potential pad and the different potential pad located on each surface are in the longitudinal direction. It is separated. As a result, the creeping distance between the discharge potential pad and the different potential pad on the insulating substrate can be increased, and it is possible to suppress the occurrence of spark discharge between these pads and between the terminals connected thereto, and the surface of the insulating substrate. Leakage current flowing through can be suppressed. Furthermore, the separator includes a first separator that surrounds the discharge potential terminal and the discharge potential pad, and a second separator that surrounds the different potential terminal and the different potential pad, which are arranged in the longitudinal direction. In this way, by using the separator divided into two, it is easy to hold the insulating substrate and each terminal, and the discharge potential terminal and the different potential pad which are arranged apart from each other in the longitudinal direction can be appropriately discharged. In addition, the different potential terminal can be made conductive.
Moreover, since the metal film which is a leakage current suppression film | membrane is formed in one 2nd separator among the separators divided into two, formation of a metal film is easier than the case where a separator is integrated.

  Furthermore, in the fine particle detection system described above, the second separator is disposed on the first main surface side of the structure pad portion, and has a first outer peripheral surface facing a radially outer side orthogonal to the longitudinal direction. A main surface side member, and a second main surface side member that is disposed on the second main surface side of the structure pad portion and accommodates and holds the different potential terminal in contact with the different potential pad. The first main surface side member and the second main surface side member sandwich the structure pad portion from both sides of the first main surface side and the second main surface side, and the metal film is Of the outer peripheral surface of the first main surface side member, it is preferable that the fine particle detection system is deposited over the entire circumference at least in the longitudinal direction near the first separator.

In the fine particle detection system, the second separator further includes a first main surface side member and a second main surface side member. And the metal film which is a leakage current suppression film | membrane has adhered to the site | part near the 1st separator at least about the longitudinal direction among the outer peripheral surfaces of the 1st main surface side member of a 2nd separator over the perimeter. Thereby, the second main surface side member that accommodates the different potential terminal through the outer peripheral surface of the first main surface side member of the second separator among the leakage current flowing on the separator surface between the discharge potential terminal and the different potential terminal. It is possible to sufficiently suppress the current flowing into the.
Moreover, since the second separator is composed of two members, it is easy to provide a metal film.

  In the above-described system, no short circuit occurs between the terminals or between the terminals and the pads via the metal film. Of the first main surface of the structure pad portion, the discharge potential pad and the different potential pad do not exist at a portion facing the first main surface side member. The discharge potential terminal is accommodated in the first separator, and the different potential terminal is accommodated in the second main surface side member of the second separator, and the first main surface and the first main surface side member of the structure pad portion. This is because there are no terminals or pads in between.

  Further, in the above-described particle detection system, the leakage current suppression film may be a particle detection system that is a water-repellent coating film.

  In this fine particle detection system, the leakage current suppressing film is a water-repellent coating film. For this reason, it is possible to suppress water droplets from adhering to the separator surface due to the influence of humidity, etc., thereby preventing a decrease in the insulation property of the separator surface, and between the discharge potential terminal and the different potential terminal. The flowing leakage current can be suppressed.

  Examples of the water-repellent coating film include fluorine resins such as PTFE, PFA, and FEP, water-repellent inorganic ceramics, and glass films. Examples of the method for forming the coating film include dip coating and spray coating.

  In addition, the water-repellent coating film includes the entire surface of the separator (as described above, when the separator includes two separators, a first separator that surrounds the discharge potential terminal and a second separator that surrounds the different potential terminal. It is more preferable to provide it on the entire surface of at least one of them. In this case, the coating film can be more easily formed by using dip coating.

  Further, in any one of the fine particle detection systems described above, the electrode structure may be a fine particle detection system having a heater portion that conducts to the different potential pad and heats the electrode structure.

  In this particulate detection system, the electrode structure is heated by the heater to remove foreign matters such as water droplets and soot attached to the electrode structure, and to recover the deterioration of insulation generated in the ion source. An air discharge can be caused to generate ions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating a state where a particulate detection system is applied to an exhaust pipe of an engine mounted on a vehicle according to an embodiment. It is explanatory drawing which shows schematic structure of a circuit part among the fine particle detection systems which concern on embodiment. It is a longitudinal section of a sensor part among particulate detection systems concerning an embodiment. It is a disassembled perspective view which shows the structure of a sensor part among the fine particle detection systems which concern on embodiment. It is a perspective view showing the whole ceramic element of a sensor part among particulate detection systems concerning an embodiment. It is a disassembled perspective view which shows the structure of the ceramic element of a sensor part among the fine particle detection systems which concern on embodiment. It is explanatory drawing which showed typically the electric function and operation | movement of a sensor part, and the mode of intake and discharge | emission of exhaust gas among the fine particle detection systems which concern on embodiment. It is explanatory drawing about the 2nd separator which concerns on embodiment and applied the metal film as a leakage current suppression film | membrane. It is explanatory drawing about the 2nd separator which applied the water-repellent fluorine-type coating film as a leakage current suppression film | membrane concerning a deformation | transformation form.

(Embodiment)
Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a particulate detection system 1 according to the present embodiment (hereinafter also simply referred to as system 1) is mounted on an exhaust pipe EP of an engine ENG mounted on a vehicle AM, and exhaust gas flowing through the exhaust pipe EP. Fine particles S such as soot in the gas EG (gas to be measured) is detected. The system 1 includes a sensor unit 10, a circuit unit 190, and electric wires 165 to 168 connecting them.
The sensor unit 10 forms a sensor body in the system 1. The sensor unit 10 is fixed to the exhaust pipe EP, and a part of the tip side thereof is disposed in the exhaust pipe EP and contacts the exhaust gas EG (see FIG. 3).
The circuit unit 190 is connected to the sensor unit 10 via the electric wires 165 to 168, and has a circuit that drives the sensor unit 10 and detects a signal current Is described later.
Among the electric wires 165 to 168, the electric wires 165 and 166 are triple coaxial cables (triaxial cables), and the electric wires 167 and 168 are small-diameter single-core insulated wires. Among these, the electric wire 165 includes a discharge potential lead wire 161 as a core wire (center conductor), and the electric wire 166 includes an auxiliary potential lead wire 162 as a core wire (center conductor). The electric wire 167 includes a first heater lead wire 163 as a core wire, and the electric wire 168 includes a second heater lead wire 164 as a core wire (see FIGS. 2 and 3).

First, a schematic configuration of the circuit unit 190 in the system 1 will be described with reference to FIG. The circuit unit 190 includes a measurement control circuit 220 including a signal current detection circuit 230 and a heater energization circuit 226, an ion source power supply circuit 210, and an auxiliary electrode power supply circuit 240.
Among these, the ion source power supply circuit 210 has a first output terminal 211 having a sensor GND potential SGND and a second output terminal 212 having a discharge potential PV2. The second output terminal 212 is connected to the discharge potential lead wire 161. Specifically, the discharge potential PV2 is set to a positive high potential (for example, 1 to 2 kV) with reference to the sensor GND potential SGND. The ion source power supply circuit 210 constitutes a constant current power source that is feedback-controlled for its output current and autonomously maintains its effective value at a predetermined current value (for example, 5 μA).

  On the other hand, the auxiliary electrode power circuit 240 has an auxiliary first output terminal 241 that is set to the sensor GND potential SGND and an auxiliary second output terminal 242 that is set to the auxiliary potential PV3. The auxiliary second output terminal 242 is connected to the auxiliary potential lead 162. Specifically, the auxiliary potential PV3 is a positive DC high potential with reference to the sensor GND potential SGND, but the peak potential of the discharge potential PV2. The potential is lower than, for example, DC 100 to 200V.

  Further, the signal current detection circuit 230 forming a part of the measurement control circuit 220 is connected to the signal input terminal 231 connected to the first output terminal 211 of the ion source power supply circuit 210 that is set to the sensor GND potential SGND, and the chassis GND potential CGND. And a ground input terminal 232 to be connected. The chassis GND potential CGND and the sensor GND potential SGND are insulated from each other, and the signal current detection circuit 230 has a signal input terminal 231 (sensor GND potential SGND) and a ground input terminal 232 (chassis GND potential CGND). The signal current Is flowing between them is detected.

  The heater energization circuit 226 is a circuit for energizing a heater portion 130 of the ceramic element 100 described later by PWM control, and includes a first heater energization end 226a connected to the first heater lead wire 163, and a second heater lead. A second heater energization end 226b connected to the line 164 is provided. The second heater energization end 226b and the second heater lead wire 164 are electrically connected to the chassis GND potential CGND and become the chassis GND potential CGND. Further, the first heater energization end 226a and the first heater lead wire 163 are at a potential based on the chassis GND potential CGND.

In addition, in the circuit unit 190, the ion source power supply circuit 210 and the auxiliary electrode power supply circuit 240 are surrounded by an inner circuit case 250 having a sensor GND potential SGND. The first output terminal 211 of the ion source power circuit 210, the auxiliary first output terminal 241 of the auxiliary electrode power circuit 240, and the signal input terminal 231 of the signal current detection circuit 230 are connected to the inner circuit case 250.
In the present embodiment, the inner circuit case 250 accommodates and surrounds the ion source power circuit 210, the auxiliary electrode power circuit 240, and the secondary iron core 271B of the insulation transformer 270, and the inner circuit case 250 of the ion source power circuit 210. The first output terminal 211 and the auxiliary first output terminal 241 of the auxiliary electrode power supply circuit 240 are electrically connected to the sensor GND potential SGND. The first output terminal 211 of the ion source power circuit 210 and the auxiliary first output terminal 241 of the auxiliary electrode power circuit 240 are connected to the sensor GND potential SGND of the coaxial double outer conductors 165G and 166G of the electric wires 165 and 166, respectively. Are connected to the inner outer conductors 165G1 and 166G1.

  On the other hand, the insulation transformer 270 has an iron core 271 wound around a primary iron core 271A wound around a primary coil 272 and a secondary iron core 271B wound around a power circuit coil 273 and an auxiliary electrode power supply coil 274. It is configured separately. Among these, the primary side iron core 271A is conducted to the chassis GND potential CGND, and the secondary side iron core 271B is conducted to the sensor GND potential SGND (the first output terminal 211 of the ion source power supply circuit 210).

Further, the ion source power supply circuit 210, the auxiliary electrode power supply circuit 240, the inner circuit case 250, and the measurement control circuit 220 including the signal current detection circuit 230 and the heater energization circuit 226 have an outer circuit case having a chassis GND potential CGND. 260. Further, the ground input terminal 232 of the signal current detection circuit 230, the second heater power supply terminal 226b of the heater power supply circuit 226, and the primary iron core 271A of the insulation transformer 270 are connected to the outer circuit case 260, and the chassis GND potential CGND is Has been.
In the present embodiment, the outer circuit case 260 includes an ion source power supply circuit 210, an auxiliary electrode power supply circuit 240, an inner circuit case 250, a signal current detection circuit 230, and a heater energization circuit 226 therein. And the primary side iron core 271A of the insulation transformer 270 is accommodated and enclosed. Further, the outer circuit case 260 is electrically connected to the outer outer conductors 165G2 and 166G2 of the coaxial double outer conductors 165G and 166G of the electric wires 165 and 166, which are set to the chassis GND potential CGND.

The measurement control circuit 220 includes a regulator power source PS. The regulator power supply PS is connected to an external battery BT mounted on the vehicle AM through the power supply wiring BC, and is driven by the battery BT. Further, the GND potential of the battery BT is made common to the chassis GND potential CGND.
The measurement control circuit 220 includes a microprocessor 202 and can communicate with the control unit ECU that controls the internal combustion engine via the communication line CC. The measurement result (signal current Is) of the signal current detection circuit 230 described above. ) Or a value obtained by converting this into the amount of fine particles or the like can be transmitted to the control unit ECU.

  Part of the electric power input from the outside to the measurement control circuit 220 through the regulator power supply PS is distributed to the ion source power supply circuit 210 and the auxiliary electrode power supply circuit 240 via the isolation transformer 270. The insulating transformer 270 forms a primary coil 272 that forms part of the measurement control circuit 220, a power circuit coil 273 that forms part of the ion source power circuit 210, and a part of the auxiliary electrode power circuit 240. The auxiliary electrode power supply side coil 274 and the iron core 271 (primary side iron core 271A, secondary side iron core 271B) are insulated from each other. For this reason, while electric power can be distributed from the measurement control circuit 220 to the ion source power supply circuit 210 and the auxiliary electrode power supply circuit 240, insulation between them can be maintained.

Next, a mechanical configuration of the sensor unit 10 constituting the sensor body of the system 1 will be described with reference to a longitudinal sectional view of FIG. 3 and an exploded perspective view of FIG. In FIG. 3, the lower side in the figure is the front end side GS in the longitudinal direction HN of the sensor unit 10, and the upper side in the figure is the rear end side GK. Further, in FIG. 4, the lower side and the right side in the figure are the tip side GS of the sensor unit 10.
The sensor unit 10 has a plate shape extending in the longitudinal direction HN and includes a ceramic element 100 that generates ions by air discharge. In addition, the ceramic element 100 is held while being insulated, and is insulated from the metal shell 50 and a member coupled to the metal shell 50, the metal shell 50, etc., which are set to the sensor GND potential SGND, and is surrounded and held. A fitting 90 attached to the exhaust pipe EP and having a chassis GND potential CGND and a member coupled to the fitting 90 are provided.

Specifically, the sensor unit 10 includes a cylindrical mounting bracket 90 on its front end side GS. The mounting bracket 90 has a flange portion 91 that bulges outward in the radial direction and forms an outer hexagonal shape, and the outer periphery of the distal end portion 90s on the distal end side GS from the flange portion 91 is connected to the exhaust pipe EP. A male screw used for fixing is formed. The sensor unit 10 is attached to a metal mounting boss BO, which is separately fixed to the exhaust pipe EP, by a male screw at the distal end portion 90s of the mounting bracket 90, and is attached to the exhaust pipe EP via the mounting boss BO. It is fixed. For this reason, the mounting bracket 90 is set to the same chassis GND potential CGND as the exhaust pipe EP.
A metal-made cylindrical outer cylinder 95 is fixed to the rear end side GK of the mounting bracket 90. Specifically, the front end portion 95s of the outer cylinder 95 is fitted on the rear end portion 90k of the mounting bracket 90, and is integrated by laser welding.

Inside the mounting metal 90 in the radial direction, a cylindrical metal shell 50 and an inner cylinder 80 integrated therewith are arranged via a first insulating spacer 60 and a second insulating spacer 61 made of an insulator. . Along with these, a cylindrical sleeve 62 and an annular wire packing 63 are also arranged in the mounting bracket 90.
Specifically, the metal shell 50 has an annular flange 51 that bulges outward in the radial direction, and the inner cylinder 80 also has an annular flange 81 at the tip. And the front-end | tip part 80s of the inner cylinder 80 is externally fitted by the rear-end part 50k of the metal shell 50 so that these flange parts 51 and 81 may overlap, and it is united by laser welding. Further, the metal shell 50 and the inner cylinder 80 which are integrated with each other are provided with a first insulating spacer 60 located on the front end side GS and a second insulating spacer 61 located on the rear end side GK. It is sandwiched and arranged in the mounting bracket 90. Further, a sleeve 62 is disposed on the rear end side GK of the second insulating spacer 61. A wire packing 63 is disposed between the rear end portion 90kk of the mounting bracket 90 and the sleeve 62, and the rear end portion 90kk of the mounting bracket 90 is bent and crimped radially inward.

  In addition, a cup-shaped metal cup 52 is disposed inside the metal shell 50, and a hole is formed in the bottom of the metal cup 52, and the plate-shaped ceramic element 100 constituting the ion source 15 is inserted. Yes. Further, around the ceramic element 100, a cylindrical ceramic holder 53 made of alumina and holding the ceramic element 100 in order from the front end side GS to the rear end side GK, and a first powder formed by compressing talc powder A packed layer 54, a second powder packed layer 55, and a cylindrical ceramic sleeve 56 made of alumina are disposed. Of these, the ceramic holder 53 and the first powder filling layer 54 are located in the metal cup 52.

  Further, a caulking ring 57 is disposed between the rear end portion 50kk of the metal shell 50 and the ceramic sleeve 56, and the rear end portion 50kk of the metal shell 50 is bent inward in the radial direction and caulked. The ceramic sleeve 56 is pressed via the caulking ring 57. Thereby, the powder of the second powder filling layer 55 is compressed, the metal cup 52 and the ceramic sleeve 56 are fixed in the metal shell 50, and the ceramic element 100 is also airtightly held in the metal shell 50.

  In addition, the tip 50s of the metal shell 50 protects the ceramic element 100 from water droplets and foreign matters, and protects the exhaust gas EG around the ceramic element 100. A cylindrical inner protector 45 and an outer protector 40 are fixed, and surround the tip portion of the ceramic element 100 from the radially outer side. The inner protector 45 and the outer protector 40 are formed by fitting a large-diameter portion 47 on the rear end side GK of the inner protector 45 to the front end 50 s of the metal shell 50, and further to the outside of the rear protector 40. After the large-diameter portion 42 of the end side GK is externally fitted, each is fixed by laser welding.

In the outer protector 40, the cylindrical body portion 41 is formed with a plurality of rectangular outer introduction holes 40I on the periphery of the tip side GS for introducing the exhaust gas EG therein. The cylindrical body 46 of the inner protector 45 is formed with a plurality of triangular and round inner introduction holes 45I on the periphery of the front end side GS and the rear end side GK.
Further, a round discharge port 45O for discharging the introduced exhaust gas EG (gas to be measured) is formed at the tip portion of the inner protector 45, and the tip portion of the inner protector 45 including the discharge port 45O is formed. Projecting outward from the opening 43 at the tip of the outer protector 40.

Here, regarding the inner protector 45 and the outer protector 40, the intake and exhaust of the exhaust gas EG to the inner protector 45 and the outer protector 40 when the sensor unit 10 is used will be described with reference to FIG.
In FIG. 7, the exhaust gas EG circulates in the exhaust pipe EP from the left to the right in the drawing. When the exhaust gas EG flowing through the exhaust pipe EP passes around the outer protector 40 and the inner protector 45 of the sensor unit 10, the flow velocity rises outside the outlet 45 </ b> O of the inner protector 45, so-called venturi effect. Thus, a negative pressure is generated in the vicinity of the discharge port 45O. Then, due to this negative pressure, the intake exhaust gas EGI taken into the inner protector 45 is exhausted from the exhaust port 45O. At the same time, the exhaust gas EG around the outer introduction hole 40I of the outer protector 40 is taken into the outer protector 40 from the outer introduction hole 40I, and further into the inner protector 45 through the inner introduction hole 45I of the inner protector 45. Incorporated.
And since the intake exhaust gas EGI in the inner protector 45 is discharged from the discharge port 45O, in the inner protector 45, from the inner introduction hole 45I on the rear end side GK toward the discharge port 45O on the front end side GS. An air flow of flowing intake exhaust gas EGI is generated.

Next, returning to the description of the mechanical configuration of the sensor unit 10 with reference to FIGS. 3 and 4, the rear end side GK of the metal shell 50, that is, the rear end side GK of the ceramic sleeve 56 located in the metal shell 50. Outside, an insulating holder 70 made of an insulator is disposed inside the inner cylinder 80, and the ceramic element 100 is inserted into the insertion hole 70 c of the insulating holder 70.
Further, a first separator 71 made of an insulator is arranged on the rear end side GK of the insulating holder 70, and a second separator 72 made of the same insulator is arranged in the longitudinal direction HN on the rear end side GK. Both are accommodated inside the inner cylinder 80.
Further, the second separator 72 includes a first main surface side member 72A and a second main surface side member 72B.

  The first separator 71 has an insertion hole 71c. The ceramic element 100 is inserted into the insertion hole 71c and the discharge potential terminal 73 is accommodated. On the other hand, the second separator 72 has a first insertion hole 72c and a second insertion hole 72d. Among these, the 1st penetration hole 72c is located in 72A of 1st main surface side members. The second insertion hole 72d is formed between the first main surface side member 72A and the second main surface side member 72B. In addition, in the second insertion hole 72d, the element rear end portion 100K (see FIG. 5) of the ceramic element 100 on the rear end side GK in the longitudinal direction HN is located, and the auxiliary potential terminal 75, the first heater terminal 76, and A second heater terminal 77 is accommodated. As described later, the ceramic element 100 has a first main surface 101S1 and a second main surface 101S2 at the element rear end portion 100K (see FIG. 5). The first main surface side member 72A is disposed to face the first main surface 101S1 of the element rear end portion 100K of the ceramic element 100, and the second main surface side member 72B is disposed on the element rear end portion 100K of the ceramic element 100. It is arranged to face the second main surface 101S2.

  As shown in FIG. 8, the second insertion hole 72d is formed by a first groove 72d1 formed by the first main surface side member 72A and a second groove 72d2 formed by the second main surface side member 72B. ing. The first groove 72d1 forms a rectangular groove that accommodates approximately half of the element rear end portion 100K of the ceramic element 100 on the first main surface 101S1 side. On the other hand, the second groove 72d2 accommodates substantially half of the element rear end portion 100K of the ceramic element 100 on the second main surface 101S2 side, and connects the auxiliary potential terminal 75, the first heater terminal 76, and the second heater terminal 77 to each other. It consists of three grooves that are housed in an insulated state.

  In the insertion hole 71c of the first separator 71, the discharge potential terminal 73 is in contact with a later-described discharge potential pad 113 (see FIGS. 5 and 6) of the ceramic element 100. Further, in the second insertion hole 72 d of the second separator 72, the auxiliary potential terminal 75 is connected to the auxiliary potential pad 125 of the ceramic element 100, and the first heater terminal 76 is connected to the first heater pad 136 of the ceramic element 100. The two heater terminals 77 are in contact with the second heater pads 137 of the ceramic element 100, respectively.

  Further, the discharge potential terminal 73 is connected to one end portion 161 t of the discharge potential lead wire 161 in the first insertion hole 72 c of the second separator 72. Further, in the second insertion hole 72 d of the second separator 72, the auxiliary potential terminal 75 is connected to one end portion 162 t of the auxiliary potential lead wire 162, and the first heater terminal 76 is connected to one end portion 163 t of the first heater lead wire 163. The second heater terminal 77 is connected to one end 164t of the second heater lead 164, respectively.

  A tip end portion 82s of the sensor GND connection fitting 82 is externally fitted to the rear end portion 80k of the inner cylinder 80 and laser-welded. Further, electric wires 165 to 168 are inserted into the sensor GND connection fitting 82. Of the outer conductors 165G and 166G of the electric wires 165 and 166, the inner outer conductors 165G1 and 166G1 are electrically connected to the sensor GND connection fitting 82. As a result, the inner cylinder 80, the metal shell 50, the inner protector 45, and the outer protector 40 that are electrically connected to the sensor GND connection fitting 82 are all set to the sensor GND potential SGND (first reference potential).

Further, a fluoro rubber grommet 84 and a chassis GND connection fitting 83 are arranged in the small diameter portion 96 on the rear end side GK of the outer cylinder 95, and electric wires 165 to 168 are inserted through these. . Of the outer conductors 165G and 166G of the electric wires 165 and 166, the outer outer conductors 165G2 and 166G2 are electrically connected to the chassis GND connection fitting 83, respectively.
The chassis GND connection fitting 83 is reduced in diameter radially by caulking together with the small diameter portion 96 of the outer cylinder 95, and the grommet 84 and the chassis GND connection fitting 83 are fixed in the small diameter portion 96 of the outer cylinder 95. . As a result, the mounting bracket 90, the outer cylinder 95, and the chassis GND connection bracket 83 that are electrically connected to the exhaust pipe EP and the mounting boss BO are all set to the chassis GND potential CGND that is insulated from the sensor GND potential SGND. Further, as described above, the chassis GND potential CGND is made common with the GND potential of the battery BT (see FIG. 2) mounted on the vehicle AM.

Next, details of the structure of the ceramic element 100 will be described. As shown in FIGS. 5 and 6, the ceramic element 100 has a plate-like insulating ceramic base 101 (insulating base) made of alumina, and in this ceramic base 101, a discharge electrode body 110 and an auxiliary electrode. The electrode body 120 and the heater part 130 are embedded and integrally sintered.
More specifically, the ceramic substrate 101 has three ceramic layers 102, 103, and 104 made of alumina derived from an alumina green sheet, and two insulating coatings made of alumina formed by printing between these layers. Layers 105 and 106 are interposed. A discharge electrode body 110 is disposed between the insulating coating layer 105 and the ceramic layer 103. The auxiliary electrode body 120 is disposed between the ceramic layer 103 and the insulating coating layer 106, and the heater unit 130 is disposed between the insulating coating layer 106 and the ceramic layer 104. And these are integrated and the ceramic element 100 (electrode structure) is formed.

  In the present embodiment, the ceramic base 101 (insulating base) of the ceramic element 100 is longer than the ceramic layers 103 and 104 on the first ceramic portion 101A including the ceramic layers 103 and 104, as shown in FIG. The second ceramic portion 101B made of the ceramic layer 102, which is shortened in the direction HN, is stacked. Further, the second tip 101BS of the longitudinal direction HN tip side GS of the second ceramic portion 101B is pulled down to the longitudinal direction HN rear end side GK rather than the first tip 101AS of the first ceramic portion 101A on the longitudinal direction HN tip side GS. Yes.

In the ceramic element 100, the discharge electrode body 110 has a form extending in the longitudinal direction HN, and is electrically connected to the acicular electrode portion 112 made of platinum wire, and the acicular electrode portion 112, and one surface of the ceramic layer 103. A lead portion 111 formed by pattern printing on the 103S1 and a discharge potential pad 113 that is electrically connected to the lead portion 111 are provided.
Of the discharge electrode body 110, the lead portion 111 and the embedded portion 112A on the rear end side GK of the needle electrode portion 112 to which the lead portion 111 is connected are covered with the insulating coating layer 105 and the ceramic layer 102, Specifically, it is embedded in the ceramic substrate 101 between the ceramic layer 102 and the ceramic layer 103.
That is, the ceramic substrate 101 includes the lead portion 111 and the embedded portion 112 </ b> A of the needle electrode portion 112 in the discharge electrode body 110.

  On the other hand, the exposed portion 112B on the tip side GS of the needle-like electrode portion 112 made of platinum wire is exposed from the second tip 101BS of the second ceramic portion 101B of the ceramic base 101. Moreover, the needle-like tip 112S that is tapered on the tip side GS in the exposed portion 112B is bent so that its tip is separated from the surface 103S1 of the ceramic layer 103 by 2 to 3 mm, that is, the surface 103S1 of the ceramic layer 103. It protrudes in the air outside the ceramic base 101, apart from the air.

  The discharge potential pad 113 is formed on the first main surface 101S1 (on the surface 103S1 of the ceramic layer 103) of the ceramic substrate 101 at the substrate rear end portion 101K in the longitudinal direction HN rear end side GK. As described above, the discharge potential pad 73 is brought into contact with the discharge potential pad 113 to be conductive.

The auxiliary electrode body 120 is formed by pattern printing, and is disposed on the front end side GS of the ceramic element 100 and has a rectangular shape. The auxiliary electrode body 122 is electrically connected to the auxiliary electrode section 122 and is connected to the rear end side GK of the ceramic element 100. The auxiliary electrode lead 121 extends. The auxiliary electrode body 120 (auxiliary electrode lead portion 121, auxiliary electrode portion 122) is formed on the surface 103S2 opposite to the surface 103S1 of the ceramic layer 103, and is covered with the insulating coating layer 106. Specifically, the ceramic base 101 is embedded between the ceramic layer 103 and the ceramic layer 104.
In addition, the auxiliary electrode part 122 of the auxiliary electrode body 120 includes the inside of the first ceramic part 101A of the ceramic base 101 in the longitudinal direction HN tip side GS (ceramic layer 103 and the second tip 101BS of the second ceramic part 101B). Embedded between the ceramic layers 104).

  On the other hand, the auxiliary electrode lead portion 121 of the auxiliary electrode body 120 is electrically connected to the conductive pattern 124 formed on the one surface 104S1 of the ceramic layer 104 from the end portion 123 on the rear end side GK through the through hole 106c of the insulating coating layer 106. doing. Furthermore, the conductive pattern 124 is formed on the other surface 104S2 of the ceramic layer 104, that is, on the second main surface 101S2 at the substrate rear end portion 101K of the ceramic substrate 101 through the through hole 104h1 penetrating the ceramic layer 104. The auxiliary potential pad 125 is conducted. As described above, the auxiliary potential pad 75 is brought into contact with the auxiliary potential pad 125 to be conductive.

On the one surface 104S1 of the ceramic layer 104, a heater portion 130 is formed by pattern printing. The heater unit 130 is disposed on the front end side GS of the ceramic element 100, and the heating unit 131 that heats the ceramic element 100, and the two heating units 131 that are connected to the heating unit 131 and extend to the rear end side GK of the ceramic element 100. Heater leads 132 and 133 are provided. The heater unit 130 is formed on one surface 104S1 of the ceramic layer 104 and is covered with the insulating coating layer 106.
Further, the heater lead portions 132 and 133 are formed on the other surface 104S2 of the ceramic layer 104, that is, the base of the ceramic base 101 from the end portions 134 and 135 on the rear end side GK through the through holes 104h2 penetrating the ceramic layer 104. The first heater pad 136 and the second heater pad 137 formed on the second main surface 101S2 at the rear end 101K are electrically connected to each other. As described above, the first heater pad 136 is in contact with the first heater terminal 76, and the second heater pad 137 is in contact with the second heater terminal 77, so that they are conductive.

As described above, in the ceramic element 100 of the present embodiment, the discharge potential pad 113 is formed on the first main surface 101S1 at the base rear end portion 101K of the ceramic base 101, while the auxiliary potential pads other than the discharge potential pad 113 are formed. 125, a first heater pad 136 and a second heater pad 137 are formed on the second main surface 101S2.
Further, the discharge potential pad 113, the auxiliary potential pad 125, the first heater pad 136, and the second heater pad 137 other than the discharge potential pad 113 are spaced apart from each other in the longitudinal direction HN at the substrate rear end portion 101K of the ceramic substrate 101. Has been. Specifically, the discharge potential pad 113 is disposed closer to the distal end GS in the longitudinal direction HN than the auxiliary potential pad 125, the first heater pad 136, and the second heater pad 137. As a result, the creeping distance on the ceramic substrate 101 between the discharge potential pad 113 and the other pads 125, 136, and 137 can be increased (it can be taken longer), and sparks are generated between these pads and between terminals connected thereto. The occurrence of discharge is suppressed.

Next, detection of fine particles in the system 1 will be described.
Among the ceramic elements 100 constituting the ion source 15, the discharge electrode body 110, the auxiliary electrode body 120, and the heater unit 130 are respectively the discharge potential lead wire 161, the auxiliary potential lead wire 162, the first heater lead wire 163, and the first heater electrode 130 described above. Two heater leads 164 are connected to a circuit unit 190 (see FIGS. 1 and 2) not shown in FIG. The outer conductors 165G1 and 166G1 inside the electric wires 165 and 166 are also connected to the first output terminal 211 of the ion source power circuit 210 and the auxiliary first output terminal 241 of the auxiliary electrode power circuit 240 in the circuit unit 190, The sensor GND potential is SGND (first reference potential). The inner protector 45 disposed around the ceramic element 100 (ion source 15) is connected to the sensor GND potential SGND (first reference potential) as described above via the sensor GND connection fitting 82 and the like conducted to the sensor GND. It is said that.

  Here, a positive high voltage (e.g., from the ion source power supply circuit 210 of the circuit unit 190 to the needle electrode unit 112 of the discharge electrode body 110 through the discharge potential lead wire 161, the discharge potential terminal 73, and the discharge potential pad 113) A discharge potential PV2 (see FIGS. 2 and 6) of 1 to 2 kV is applied. Then, between the needle-like tip 112S of the exposed part 112B of the needle-like electrode part 112 and the inner protector 45 (first member) set as the sensor GND potential SGND (first reference potential), Specifically, corona discharge is generated, and ions CP (see FIG. 7) are generated around the needle-like tip 112S. As described above, the exhaust gas EG is taken into the inner protector 45 by the action of the outer protector 40 and the inner protector 45, and the intake exhaust gas from the rear end side GK toward the front end side GS in the vicinity of the ceramic element 100. EGI airflow is generated. Therefore, the generated ions CP adhere to the fine particles S in the intake exhaust gas EGI as shown in FIG. Thereby, the fine particles S become positively charged charged fine particles SC, and flow toward the discharge port 45O together with the intake exhaust gas EGI and are discharged.

  On the other hand, the auxiliary electrode unit 122 of the auxiliary electrode body 120 is supplied with a predetermined potential (for example, 100 to 100) from the auxiliary electrode power circuit 240 of the circuit unit 190 through the auxiliary potential lead 162, the auxiliary potential terminal 75, and the auxiliary potential pad 125. An auxiliary potential PV3 (see FIG. 2 and FIG. 6) of 200 V is applied. As a result, among the ions CP generated by the ion source 15, the floating ions CPF (see FIG. 7) that have not adhered to the fine particles S are transferred from the auxiliary electrode portion 122 to the inner protector 45 (collecting electrode) on the radially outer side. Give the repulsion to go. Thereby, floating ion CPF is made to adhere to each part of a collection pole (inner protector 45), and collection is assisted. Thus, the floating ions CPF can be reliably collected, and even the floating ions CPF are prevented from being discharged from the discharge port 45O.

  In the system 1, the signal current detection circuit 230 detects a signal (signal current Is) corresponding to the charge amount of the discharged ions CPH adhering to the charged fine particles SC discharged from the discharge port 45O. Thereby, the amount (concentration) of the fine particles S contained in the exhaust gas EG can be detected appropriately.

  As described above, in this embodiment, the inner protector 45 around the ceramic element 100 (ion source 15) is set to the sensor GND potential SGND, and a corona discharge is generated between the inner protector 45 and the inner protector 45. At the same time, the inner protector 45 is also used as a collecting electrode. That is, in this embodiment, the collection potential for collecting by the inner protector 45 (collection electrode) is equal to the sensor GND potential SGND.

  Further, the first heater pad 136 passes through the first heater lead 163 and the first heater terminal 76, and the second heater lead 164 and the second heater terminal 77 from the heater energization circuit 226 of the measurement control circuit 220 of the circuit unit 190. A predetermined heater energizing voltage is applied between the first heater pad 137 and the second heater pad 137. Then, the heat generating part 131 of the heater part 130 generates heat by energization, heats the ceramic element 100, and removes foreign matters such as water droplets and soot attached to the ceramic element 100. Thereby, it is possible to recover the decrease in insulation that has occurred in the ion source 15.

  Specifically, as the heater energization voltage, a voltage obtained by pulse-controlling the direct current battery voltage (DC 12 V or 24 V) of the battery BT of the vehicle AM by the heater energization circuit 226 is applied. For example, the first heater potential PVht applied to the first heater pad 136 through the first heater lead wire 163 and the first heater terminal 76 is a positive potential obtained by pulse-controlling the battery voltage (DC 12 V or 24 V). The Further, the second heater potential applied to the second heater pad 137 through the second heater lead 164 and the second heater terminal 77 is the same as the GND potential of the battery BT and the chassis GND potential CGND (second reference potential). (See FIGS. 2 and 6).

  As described above, in the system 1 of the present embodiment, the corona discharge is caused between the exposed portion 112B (needle tip portion 112S) of the discharge electrode body 110 and the inner protector 45 disposed around the ceramic element 100. Therefore, the inner protector 45 is set to the sensor GND potential SGND, and the discharge potential pad 113 is applied with the DC high potential discharge potential PV2 to the sensor GND potential SGND through the discharge potential terminal 73. The In addition, the auxiliary potential PV3 is applied to the auxiliary potential pad 125 through the auxiliary potential terminal 75. The auxiliary potential PV3 is also a potential based on the sensor GND potential SGND.

  On the other hand, the first heater potential 136 is applied to the first heater pad 136 through the first heater terminal 76, and the second heater pad 137 is set to the chassis GND potential CGND through the second heater terminal 77. These potentials applied to the heater unit 130, that is, the first heater potential PVht and the chassis GND potential CGND are the chassis GND potential CGND that is insulated from the sensor GND potential SGND or the potential based on the chassis GND potential CGND. Hereinafter, the first heater potential PVht and the chassis GND potential CGND that are different from the discharge potential PV2 are also referred to as different potentials PVht and CGND.

  Thus, in the system 1, the discharge potential PV2 applied to the discharge potential terminal 73 is based on the sensor GND potential SGND, while the first heater terminal 76 and the second heater terminal 77 (hereinafter, different potential terminals 76, 77), the different potentials PVht and CGND are based on the chassis GND potential CGND. The different potentials PVht and CGND, the discharge potential PV2 and the sensor GND potential SGND constitute an independent electric circuit. Further, the signal current detection circuit 230 detects the signal current Is flowing between the sensor GND potential SGND and the chassis GND potential SGND.

  Further, the first separator 71 and the second separator 72 (hereinafter also referred to as separators 71 and 72) are the first heater pad 136 and the second heater pad 137 (hereinafter referred to as different potential pads 136 and 137) of the ceramic element 100. And the element rear end portion 100K (structure pad portion) where the discharge potential pad 113 is located are surrounded from the radial direction. The separators 71 and 72 receive and hold the discharge potential terminal 73 and the different potential terminals 76 and 77 in a state of being insulated from each other, while the discharge potential terminal 73 is placed on the discharge potential pad 113 and the different potential terminals 76 and 77 are placed. The different potential pads 136 and 137 are brought into contact with each other to be conducted.

  However, various portions of the surface of the separators 71 and 72 (the outer surface of the separators 71 and 72, the inner peripheral surface forming the insertion hole 71c of the first separator 71, the inner peripheral surface forming the second insertion hole 72d of the second separator, etc. ), When the insulation of the surfaces of the separators 71 and 72 deteriorates due to adhesion of water droplets due to the influence of humidity, the discharge potential terminal 73 and the different potential terminals 76 and 77 through the surfaces of the separators 71 and 72. Leakage current may flow between As a path of this leakage current, for example, from the discharge potential terminal 73 through the inner peripheral surface forming the insertion hole 71c of the first separator 71 that accommodates the discharge potential terminal 73 and the surface of the first separator 71, A route that reaches the inner or outer peripheral surface of the second separator 72 and reaches the different potential terminals 76 and 77 accommodated in the second insertion hole 72d of the second separator can be considered. When such a leakage current flows, an error due to the leakage current occurs in the detected signal current Is, and the amount of the fine particles S cannot be accurately detected.

Therefore, in the system 1 of the present embodiment, as shown in FIG. 8, a different potential from the discharge potential terminal 73 to a part of the surface of the first main surface side member 72 </ b> A of the second separator 72 among the separators 71 and 72. A metal film 78 is deposited as a leakage current suppressing film that suppresses the leakage current flowing through the terminals 76 and 77. The metal film 78 is formed by depositing copper.
Specifically, the second separator 72 has an outer peripheral surface 72m that faces the radially outer side HR perpendicular to the longitudinal direction HN. In addition, the outer peripheral surface 72Am facing the radially outer side HR of the first main surface side member 72A that forms a half of the second separator 72 has an outer surface 72Ao that forms a half of the outer peripheral surface 72m of the second separator 72 and the second main surface 72Am. The inner surface 72Ai faces the surface member 72B. The central portion of the inner side surface 72Ai constitutes the first groove 72d1 of the second insertion hole 72d. Further, an outer peripheral surface 72Bm facing the radially outer side HR of the second main surface side member 72B forming the other half of the second separator 72 is an outer surface 72Bo constituting the remaining half of the outer peripheral surface 72m of the second separator 72; The inner surface 72Bi faces the first main surface side member 72A. The central portion of the inner side surface 72Bi constitutes a second groove 72d2 of the second insertion hole 72d.

In the present embodiment, a metal film 78 made of copper is deposited on a part of the outer peripheral surface 72Am of the first main surface side member 72A (see FIGS. 8A and 8B).
More specifically, the metal film 78 covers the entire circumference of a portion of the outer peripheral surface 72Am of the first main surface side member 72A that is closer to the first separator 71 in the longitudinal direction HN (downward in FIG. 8B). I wear it. However, the metal film 78 is at a position slightly pulled down from the end surface 72At near the first separator 71 in the outer peripheral surface 72Am of the first main surface side member 72A so as not to contact the first separator 71 (FIG. 8B). ), With a space above the end face 72At. Further, the metal film 78 is in contact with the inner cylinder 80 at the contact portion CT, and is electrically connected to the sensor GND potential SGND (first reference potential) through the inner cylinder 80 (see FIG. 8D).

  Of the first main surface 101S1 of the element rear end portion 100K (structure pad portion), a portion facing the inner surface 72Ai of the first main surface side member 72A has a discharge potential pad 113, an auxiliary potential pad 125, and a different potential. The potential pads 136 and 137 are not present. The discharge potential terminal 73 is accommodated in the first separator 71, and the auxiliary potential terminal 75 and the different potential terminals 76 and 77 are accommodated in the second main surface side member 72 </ b> B of the second separator 72. There are no terminals or pads between the 100K first main surface 101S1 and the first main surface side member 72A. For this reason, even if the metal film 78 is provided on the surface of the first main surface side member 72A, a short circuit through the metal film 78 does not occur between the terminals or between the terminals and the pads. That is, the metal film 78 is formed at a portion where each terminal or between the terminal and the pad is not short-circuited (see FIG. 8C). On the other hand, when the metal film is formed on the second main surface side member 72B, the auxiliary potential terminal 75 and the different potential terminals 76 and 77 to be held may be short-circuited via the metal film. A metal film is not formed on the surface 72Bm.

As described above, in the system 1 of the present embodiment, the separators 71 and 72 of the sensor unit 10 are formed on a part of the surface (the outer peripheral surface 72Am of the first main surface side member 72A of the second separator 72). , 72 has a metal film 78 as a leakage current suppressing film that suppresses a leakage current flowing between the discharge potential terminal 73 and the different potential terminals 76, 77 through the surface of.
Further, in the system 1 of the present embodiment, the metal film 78 that is the leakage current suppressing film is electrically connected to the sensor GND potential SGND. For this reason, when the leakage current that leaks from the discharge potential terminal 73 and flows on the surfaces of the separators 71 and 72 reaches the metal film 78, it flows into the sensor GND potential SGND through the metal film 78. That is, it does not flow into the chassis GND potential CGND that communicates with the different potential terminals 76 and 77. For this reason, the influence of the leakage current on the signal current Is can be suppressed.
Thus, the leakage current flowing between the discharge potential terminal 73 and the different potential terminals 76 and 77 through the surfaces of the separators 71 and 72 is suppressed, the influence of the leakage current on the signal current Is is suppressed, and the amount of fine particles is more accurately determined. Can be detected.

Furthermore, in the system 1 of the present embodiment, the ceramic base 101 has a plate shape having the first main surface 101S1 and the second main surface 101S2 at the element rear end portion 100K of the ceramic element 100, and is located on each surface. Discharge potential pad 113 and different potential pads 136 and 137 are spaced apart in the longitudinal direction HN. As a result, a creeping distance on the ceramic substrate 101 between the discharge potential pad 113 and the different potential pads 136 and 137 is gained, and the occurrence of spark discharge between these pads and between terminals connected thereto is suppressed, and ceramic Leakage current through the surface of the substrate 101 can be suppressed. Further, the separators 71 and 72 include a first separator 71 that surrounds the discharge potential terminal 73 and the discharge potential pad 113, and a second separator 72 that surrounds the different potential terminals 76 and 77 and the different potential pads 136 and 137. These are arranged in the longitudinal direction HN. Thus, by using the two separators 71 and 72, it is easy to hold the ceramic base 101 and the terminals 73, 76, and 77, and it is different from the discharge potential pad 113 that is spaced apart in the longitudinal direction HN. The discharge potential terminal 73 and the different potential terminals 76 and 77 can be appropriately conducted to the potential pads 136 and 137, respectively.
Moreover, since the metal film 78 which is a leakage current suppression film | membrane is formed in one 2nd separator 72 among the separators 71 and 72 divided into two, formation of the metal film 78 is easier than the case where a separator is integrated. is there.

Furthermore, in the system 1 of the present embodiment, the second separator 72 further includes a first main surface side member 72A and a second main surface side member 72B. And the metal film 78 which is a leakage current suppression film | membrane is formed in the site | part close | similar to the 1st separator 71 about longitudinal direction HN among the outer peripheral surfaces 72Am of the 1st main surface side member 72A of the 2nd separator 72 over the perimeter. Yes. As a result, out of the leakage current flowing on the surfaces of the separators 71 and 72 between the discharge potential terminal 73 and the different potential terminals 76 and 77, the different potential is passed through the outer peripheral surface 72 Am of the first main surface side member 72 A of the second separator 72. The amount flowing to the second main surface side member 72B that accommodates the terminals 76 and 77 can be sufficiently suppressed.
Moreover, the metal film 78 can be simply provided by comprising the 2nd separator 72 by two members.

  Furthermore, in the system 1 of the present embodiment, the ceramic element 100 has a heater portion 130 that conducts to the different potential pads 136 and 137 and heats the ceramic element 100 inside. For this reason, by heating the ceramic element 100 with the heater unit 130, foreign matters such as water droplets and soot adhered to the ceramic element 100 are removed, and the deterioration of the insulating property generated in the ion source 15 is recovered, and appropriately Ions can be generated by causing an air discharge.

(Deformation)
Next, modifications of the above-described embodiment will be described. In the system 1 of the embodiment, the sensor GND potential SGND (first reference potential) is applied to a part of the surface of the first main surface side member 72A of the second separator 72 of the separators 71 and 72 as the leakage current suppressing film. A conductive metal film 78 was formed. On the other hand, in the system 1 of the present modified embodiment, as shown in FIG. 9, the first main surface side member 72 </ b> A and the second main surface constituting the second separator 72 of the separators 71 and 72 as the leakage current suppressing film. Insulating and water-repellent fluorine-based coating films 79a and 79b are provided on the entire surface of the surface side member 72B.
Specifically, as in the embodiment, the outer peripheral surface 72Am that faces the radially outer side HR of the first main surface side member 72A is the outer main surface 72Ao that constitutes a half of the outer peripheral surface 72m of the second separator 72, and the second main surface 72Am. The inner surface 72Ai faces the surface member 72B. In this example, in addition to the outer peripheral surface 72Am, the fluorine-based coating film 79a is applied to the entire surface of the first main surface side member 72A including the inner wall of the first insertion hole 72c by dip coating.
Further, the outer peripheral surface 72Bm facing the radially outer side HR of the second main surface side member 72B is an inner surface facing the outer surface 72Bo constituting the remaining half of the outer peripheral surface 72m of the second separator 72 and the first main surface side member 72A. It consists of side surface 72Bi. In this example, the fluorine-based coating film 79b is also applied by dip coating to the entire surface of the second main surface side member 72B including the outer peripheral surface 72Bm.

  In this example, as described above, the water-repellent coating films 79a and 79b are formed on the entire surface of the first main surface side member 72A and the second main surface side member 72B by dip coating. However, by using other techniques such as spray coating, the water-repellent coating films 79a and 79b are formed on part of the surfaces of the first main surface side member 72A and the second main surface side member 72B (for example, the outer peripheral surface 72Am, 72Bm).

As described above, in the system 1 according to this modification, the leakage current suppressing films are the water-repellent coating films 79a and 79b. For this reason, it is possible to suppress the water droplets from adhering to the surfaces of the separators 71 and 72 due to the influence of humidity and the like, thereby preventing a decrease in the insulating properties of the surfaces of the separators 71 and 72 and reducing leakage current. Flow can be suppressed.
Thus, the leakage current flowing between the discharge potential terminal 73 and the different potential terminals 76 and 77 through the surfaces of the separators 71 and 72 is suppressed, the influence of the leakage current on the signal current Is is suppressed, and the amount of fine particles is more accurately determined. Can be detected.

In the above, the present invention has been described with reference to the embodiment and the modified embodiment, but the present invention is not limited to the embodiment and the modified embodiment, and can be applied with appropriate modifications without departing from the gist thereof. Needless to say.
For example, in the embodiment, the discharge potential PV2 is a positive high potential, but the discharge potential PV2 may be a negative high potential.
In the embodiment, the ceramic base 101 (insulating base) made of alumina as the ceramic element 100 (electrode structure) shows the embedded portion 112A of the discharge electrode body 110. However, in the electrode structure, The structure in which the discharge electrode body is provided on the insulating substrate is not limited to this. For example, a discharge electrode body is formed on the surface of a substrate made of an insulating ceramic such as alumina by printing or the like, and a part thereof is glass coated to form an embedded portion, whereby an insulating substrate made of a ceramic substrate and a glass coat. It is also possible to use a ceramic element (electrode structure) provided with a discharge electrode body.

EP Exhaust pipe EG Exhaust gas (measured gas)
SGND sensor GND potential (first reference potential)
CGND Chassis GND potential (second reference potential, different potential)
PV2 Discharge potential PV3 Auxiliary potential PVht First heater potential (different potential)
S Fine particle CP Ion CPF Floating ion GS Front end side GK Rear end side HN Longitudinal direction HR Radially outer side 1 Fine particle detection system 10 Sensor unit 15 Ion source 40 Outer protector 45 Inner protector (first member)
50 Metal shell 71 First separator (separator)
71c Insertion hole 72 Second separator (separator)
72A 1st main surface side member 72Am Outer peripheral surface 72B (of 1st main surface side member) 2nd main surface side member 72Bm (Outside of 2nd main surface side member) 72c 1st insertion hole 72d 2nd insertion hole 73 Discharge Potential terminal 75 Auxiliary potential terminal 76 First heater terminal (different potential terminal)
77 Second heater terminal (different potential terminal)
78 Metal film (leakage current suppression film)
79a, 79b Fluorine coating film (leakage current suppression film)
80 Inner cylinder 90 Mounting bracket 95 Outer cylinder 100 Ceramic element (electrode structure)
100K element rear end (structure pad)
101 Ceramic substrate (insulating substrate)
101S1 First main surface 101S2 Second main surface 101K Substrate rear end portion 110 Discharge electrode body 113 Discharge potential pad 120 Auxiliary electrode body 125 Auxiliary potential pad 130 Heater portion 136 First heater pad (different potential pad)
137 Second heater pad (different potential pad)
161 Discharge potential lead wire 161t (Discharge potential lead wire) one end 163 First heater lead wire (different potential lead wire)
163t (first heater lead wire) one end 164 second heater lead wire (different potential lead wire)
164t (second heater lead) one end 190 circuit unit 210 ion source power supply circuit 220 measurement control circuit 226 heater energization circuit 230 signal current detection circuit 240 auxiliary electrode power supply circuit

Claims (6)

An ion source for generating ions by air discharge, and
A sensor unit having a first member disposed around the ion source and serving as a first reference potential;
A particulate detection system comprising a signal current detection circuit that detects a signal current flowing between the first reference potential and the second reference potential that is insulated from the first reference potential,
The ion source is
An insulating base made of an insulating material and extending in the longitudinal direction;
A discharge electrode body that is provided on the insulating base and is applied with a discharge potential based on the first reference potential to generate the air discharge with the first member;
A discharge potential pad formed on the surface of the insulating substrate in conduction with the discharge electrode body and having the discharge potential; and
An electrode structure including a different potential pad formed on a surface of the insulating base and having a different potential from the discharge potential at the second reference potential or a potential based on the second reference potential;
A discharge potential lead wire having a discharge potential terminal at one end;
A different potential lead having a different potential and having a different potential terminal at one end;
The sensor part
The structure is made of an insulating material and surrounds the structure pad portion where the discharge potential pad and the different potential pad are located in the electrode structure from the radial direction orthogonal to the longitudinal direction, and the discharge potential terminal and the different potential. Having a separator that contacts and conducts the discharge potential terminal to the discharge potential pad and the different potential terminal to the different potential pad, while accommodating and holding the terminals in an insulated state;
The separator is
A particulate detection system having a leakage current suppression film that suppresses a leakage current flowing between the discharge potential terminal and the different potential terminal through a part of the surface of the separator. The particulate detection system according to claim 1,
The leakage current suppression film is
A fine particle detection system which is a metal film conducting to the first reference potential. The fine particle detection system according to claim 2,
In the structure pad portion, the insulating base is a plate having two main surfaces, a first main surface and a second main surface,
The discharge potential pad is located on the first main surface,
The different potential pad is located on the second main surface and separated from the discharge potential pad in the longitudinal direction,
The separator is
A first separator surrounding the discharge potential terminal and the discharge potential pad of the structure pad portion, and the first separator and the different potential pad of the structure pad portion arranged in the longitudinal direction. A surrounding second separator,
The metal film is
A fine particle detection system formed by adhering to at least a part of the surface of the second separator among the separators. The fine particle detection system according to claim 3,
The second separator is
A first main surface side member disposed on the first main surface side of the structure pad portion and having an outer peripheral surface facing a radially outer side perpendicular to the longitudinal direction;
A second main surface side member that is disposed on the second main surface side of the structure pad portion and accommodates and holds the different potential terminal in contact with the different potential pad;
With the first main surface side member and the second main surface side member,
The structure pad portion is sandwiched from both sides of the first main surface side and the second main surface side,
The metal film is
A fine particle detection system formed by adhering the entire outer periphery of the first main surface side member to a portion near the first separator in at least the longitudinal direction. The particulate detection system according to claim 1,
The leakage current suppression film is
A fine particle detection system that is a water-repellent coating film. The particulate detection system according to any one of claims 1 to 5,
The electrode structure is
A fine particle detection system including a heater portion that conducts to the different potential pad and heats the electrode structure.

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