JP6214119B2 - Fine particle detection system and fine particle detection method - Google Patents

Description

  The present invention relates to a fine particle detection system for detecting fine particles in a gas to be measured and a fine particle detection method in the fine particle detection system.

2. Description of the Related Art Conventionally, there is known a fine particle detection system that detects the amount of fine particles in exhaust gas by generating ions by corona discharge and charging the fine particles in exhaust gas with the ions.
In such a sensor body of a fine particle detection system, for example, as shown in Patent Document 1, an ion source that generates corona discharge is a discharge electrode to which a discharge voltage is applied (the needle of the needle-like electrode body 20 in Patent Document 1). And a metal surrounding portion (particulate charging portion 12 in Patent Document 1) that surrounds the periphery and serves as a reference potential (sensor GND). And the metal surrounding part used as this sensor GND is electrically connected to the exhaust pipe etc. of a vehicle among the sensor main bodies, and other metal parts (outer surrounding part 14 in patent document 1) used as chassis GND, and ceramic It is insulated by a manufactured insulator (the first insulating spacer 121 or the like in Patent Document 1).
The ion source driving circuit that applies a discharge voltage to the ion source (discharge electrode) operates based on the sensor GND, while the amount of fine particles (specifically, the amount of charged fine particles having ions attached to the fine particles). The signal current detection circuit that detects the magnitude of the signal current that changes according to the operation is based on the chassis GND.

JP 2013-195069 A

  By the way, when a foreign substance adheres to the above-described ceramic insulator and the insulation of the surface of the insulator is lowered, a leakage current may flow through the surface of the insulator. When such a leakage current flows, an error occurs in the detected signal current, and the amount of fine particles cannot be accurately detected.

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

  One aspect thereof is an ion source that generates ions by air discharge, an ion source power supply circuit that applies a voltage to the ion source, and the amount of charged fine particles in which the ions adhere to the fine particles in the gas to be measured. A particle detection system including a signal current detection circuit for detecting a magnitude of a changing signal current, wherein the ion source power supply circuit is a discharge voltage at which the air discharge occurs, and is lower than the discharge voltage, A non-discharge voltage that does not cause an air discharge is selected and applied to the ion source, and the discharge voltage is applied to the ion source power supply circuit during the discharge period that causes the air discharge. Ion that causes the ion source power supply circuit to apply the non-discharge voltage to the ion source during the measurement period of the non-discharge period that does not cause the air discharge other than the discharge period. Driving means; signal current acquisition means for acquiring the signal current detected by the signal current detection circuit during the discharge period; and non-discharge current detected by the signal current detection circuit during the measurement period. A fine particle detection system comprising non-discharge current acquisition means and signal current correction means for correcting the value of the signal current detected during the discharge period using the non-discharge current.

  In this particle detection system, a non-discharge voltage that does not cause air discharge is applied to the ion source during the measurement period of the non-discharge period, and the non-discharge current detected by the signal current detection circuit is acquired during this measurement period. To do. Then, the value of the signal current detected during the discharge period is corrected using this non-discharge current.

By the way, the non-discharge current is a current detected by the signal current detection circuit even though no air discharge is generated in the ion source. For example, it is considered that a leakage current flowing due to a decrease in insulating properties of the surface of each part of the ion source is detected. And it is thought that the current corresponding to this non-discharge current is also included in the signal current detected during the discharge period. The current corresponding to the non-discharge current is a current that is not the original signal current due to the fine particles (hereinafter referred to as a non-signal current), and causes an error in the detected signal current.
Therefore, by correcting the value of the signal current detected during the discharge period using the non-discharge current, the influence of the non-signal current included in the signal current is reduced, and the amount of fine particles is reduced by the corrected signal current. Can be detected more accurately.

Here, the discharge period is a period in which a discharge voltage is applied to the ion source to cause air discharge in the ion source. The non-discharge period is a period other than the discharge period, and is a period in which no air discharge is generated in the ion source. Of these non-discharge periods, the measurement period is a period during which a non-discharge voltage that is lower than the discharge voltage and does not cause air discharge is applied to the ion source, and a part or all of the non-discharge period is applicable. .
A non-discharge period may be provided so that the discharge period and the non-discharge period alternate periodically, and a part or all of the non-discharge period may be a measurement period. Alternatively, the measurement period may be provided at a rate of once in a plurality of non-discharge periods that arrive periodically.

As a correction method using the non-discharge current, in addition to the method of subtracting the non-discharge current from the signal current detected during the discharge period to obtain a corrected signal current, the non-discharge current is multiplied by a predetermined coefficient. There is a method of subtracting the value from the detected signal current to obtain a corrected signal current.
Further, as the non-discharge current used for this correction, the non-discharge current may be measured once in one measurement period, and this may be used. The value of the non-discharge current may be obtained from the measured value. Specifically, an average value of a plurality of measured values may be used. Moreover, you may use the average value of the measured value except the maximum value and the minimum value among several measured values.

  In performing such correction, it is preferable to correct the value of the signal current detected during the discharge period in consideration of the ratio of the magnitude of the non-discharge voltage to the discharge voltage. For example, in the above-described correction method, in a method using a value obtained by multiplying a non-discharge current by a predetermined coefficient, a ratio between the magnitude of the non-discharge voltage and the discharge voltage may be used as the coefficient. Specifically, a value α × Ise obtained by multiplying the non-discharge current Ise by the ratio α (= V2 / V1e) of the discharge voltage V2 to the non-discharge voltage V1e is obtained, and this is detected as the signal current Is detected during the discharge period. The value (Is−α × Ise) subtracted from is preferably used as the corrected signal current Is.

  In addition, as an ion source power supply circuit having a configuration in which a discharge voltage and a non-discharge voltage can be selected and applied to the ion source, for example, the output voltage is divided into two stages of the discharge voltage and the non-discharge voltage, or the discharge voltage and the non-discharge voltage. In addition to a power supply that can be output by switching to three or more levels of voltage including the voltage, a power supply that can continuously change the output voltage within the voltage range including the discharge voltage and the non-discharge voltage. It is done.

  Further, in the fine particle detection system described above, the signal current correction unit is estimated to be included in the signal current detected during the discharge period from the non-discharge current detected during the measurement period. Estimated non-signal current acquisition means for obtaining an estimated non-signal current; and corrected signal current acquisition means for obtaining a corrected signal current by subtracting the estimated non-signal current from the signal current detected during the discharge period. A fine particle detection system is preferable.

As described above, the non-discharge current is considered to be, for example, a leakage current detected, and the signal current detected during the discharge period also includes a non-signal current corresponding to the non-discharge current. It is thought that.
Therefore, in this particulate detection system, an estimated non-signal current is obtained from the non-discharge current, and a corrected signal current is obtained by subtracting this estimated non-signal current from the signal current detected during the discharge period.
The estimated non-signal current includes, for example, a value obtained by multiplying the above-described non-discharge current by a predetermined coefficient (such as a ratio α between the non-discharge voltage and the discharge voltage).
Thereby, the influence of the non-signal current included in the signal current can be appropriately reduced.

  Furthermore, in the fine particle detection system described above, the non-discharge voltage is 1 / α of the discharge voltage (α> 1), and the estimated non-signal current acquisition unit is configured as the estimated non-signal current. A fine particle detection system that acquires a value obtained by multiplying the non-discharge current by the α is preferable.

The magnitude of non-signal current such as leakage current is considered to be proportional to the magnitude of the applied voltage. Therefore, in this particulate detection system, a non-signal current that is α times the non-discharge current is proportional to the ratio α (= V2 / V1e) of the magnitude of the non-discharge voltage V1e and the discharge voltage V2 during the discharge period. It is estimated that the current flows and is subtracted from the signal current.
Thereby, the non-signal current included in the signal current can be appropriately corrected by a simple method.

  In another aspect, an ion source that generates ions by air discharge, an ion source power supply circuit that applies a voltage to the ion source, and the amount of charged fine particles in which the ions adhere to the fine particles in the gas to be measured. A fine particle detection method in a fine particle detection system comprising a signal current detection circuit for detecting a magnitude of a signal current that changes in response, wherein the ion source power circuit includes a discharge voltage at which the air discharge occurs, and the discharge A non-discharge voltage that is lower than the voltage and does not cause the air discharge is selected and applied to the ion source.In the discharge period that causes the air discharge, the ion source power supply circuit The ion source power supply in the measurement period among the ion source discharge driving step for applying the discharge voltage to the ion source and the non-discharge period that does not cause the air discharge other than the discharge period. An ion source non-discharge driving step for applying the non-discharge voltage to the ion source, a signal current acquisition step for acquiring the signal current detected by the signal current detection circuit during the discharge period, and the measurement A non-discharge current acquisition step for acquiring a non-discharge current detected by the signal current detection circuit in a period, and a signal for correcting the value of the signal current detected during the discharge period using the non-discharge current A particle detection method comprising a current correction step.

The particle detection method of the particle detection system includes an ion source discharge drive step, an ion source non-discharge drive step, a signal current acquisition step, a non-discharge current acquisition step, and a signal current correction step.
When detecting the fine particles in the fine particle detection system, the amount of fine particles can be detected more accurately by correcting the signal current using the non-discharge current.

It is explanatory drawing explaining the state which mounted | wore the exhaust pipe of the engine mounted in the vehicle with the particulate detection system which concerns on embodiment. It is explanatory drawing which shows schematic structure of the microparticle detection system which concerns on embodiment. It is explanatory drawing which illustrates typically the mode of taking in of fine particles, charge, and discharge in a fine particle charge part among fine particle detection systems concerning an embodiment. It is a flowchart which shows operation | movement of the microprocessor which performs the process of particle detection among the particle | grain detection systems which concern on embodiment. 6 is a timing chart illustrating a signal current correction process according to the embodiment.

Embodiments of the present invention will be described below with reference to the drawings. A particulate detection system 1 (hereinafter also simply referred to as system 1) according to the present embodiment is mounted on an exhaust pipe EP of an engine ENG mounted on a vehicle AM, and an exhaust gas EG (measured gas) that circulates in the exhaust pipe EP. Fine particles S (eg, soot) in the inside are detected (see FIG. 1). In addition, this system 1 mainly consists of the detection part 10, the circuit part 201, and the pumping pump 300 (refer FIG. 2).
The detection unit 10 is attached to an attachment part EPT in which an attachment opening EPO is perforated in the exhaust pipe EP. A part thereof (in FIG. 2, the right side (front end side) of the attachment portion EPT) is disposed in the exhaust pipe EP through the attachment opening EPO and comes into contact with the exhaust gas EG.
The circuit unit 201 is connected to the detection unit 10 via a cable 160 made of a plurality of wiring materials outside the exhaust pipe EP. The circuit unit 201 includes a circuit that drives the detection unit 10 and detects a signal current Is described later.

First, the configuration on the electric circuit of the circuit unit 201 in the system 1 will be described. The circuit unit 201 includes a measurement control circuit 220, an ion source power circuit 210, and an auxiliary electrode power 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. Specifically, the discharge potential PV2 is set to a positive high potential with respect to the sensor GND potential SGND. Thereby, the discharge voltage V2 is applied between the sensor GND potential SGND and the second output terminal 212, and in this embodiment, the magnitude is V2 = 3 kV. 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. Specifically, the auxiliary potential PV3 is a positive DC high potential with respect to the sensor GND potential SGND, but is lower than the peak potential of the discharge potential PV2, for example, a potential of DC 100 to 200V. Thereby, the auxiliary voltage V3 of DC 100 to 200 V is applied between the sensor GND potential SGND and the auxiliary second output terminal 242.

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

In addition, in the circuit unit 201, the ion source power supply circuit 210 and the auxiliary electrode power supply circuit 240 are surrounded by an inner circuit case 250 that is set to the 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 houses and surrounds the ion source power supply circuit 210, the auxiliary electrode power supply circuit 240, and the secondary iron core 271B of the insulation transformer 270, and the sensor GND wiring 165 of the cable 160. Is conducting.

  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 electrically connected to the ground potential PVE, and the secondary side iron core 271B is electrically connected to the sensor GND potential SGND (the first output terminal 211 of the ion source power supply circuit 210).

Further, the measurement control circuit 220 including the ion source power supply circuit 210, the auxiliary electrode power supply circuit 240, the inner circuit case 250, and the signal current detection circuit 230 is connected to the ground input terminal 232 of the signal current detection circuit 230 and connected to the ground potential. It is surrounded by an outer circuit case 260 made of PVE. Further, in addition to the ground input terminal 232 of the signal current detection circuit 230, the primary iron core 271 </ b> A of the isolation transformer 270 is connected to the outer circuit case 260.
In this embodiment, the outer circuit case 260 includes the ion source power supply circuit 210, the auxiliary electrode power supply circuit 240, the inner circuit case 250, the measurement control circuit 220 including the signal current detection circuit 230, and the primary of the insulation transformer 270. The side iron core 271A is accommodated and surrounded, and is electrically connected to the ground potential wiring 167 of the cable 160.

The measurement control circuit 220 includes a regulator power source PS. The regulator power supply PS is driven by an external battery BT through the power supply wiring BC.
The measurement control circuit 220 includes the microprocessor 100 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 ECU. Furthermore, a particle detection start instruction signal ST (described later) output from the ECU is input to the measurement control circuit 220 via the communication line CC. The microprocessor 100 can detect the instruction signal ST.

  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.

  The pressure feed pump 300 takes in the ambient air (air) around itself and is directed toward an ion gas injection source 11 described later through an air feed pipe 310 having tip portions inserted into the outer circuit case 260 and the inner circuit case 250. Then, clean compressed air AK is pumped.

  Next, the cable 160 will be described (see FIG. 2). Disposed in the center of the cable 160 are a discharge potential wiring 161 and an auxiliary potential wiring 162 made of copper wire, and a hollow air pipe 163 made of resin. In addition, the sensor GND wiring 165 and the ground potential wiring 167 made of a braided copper thin wire are surrounded by an insulating layer (not shown) sandwiching the periphery in the radial direction.

As described above, the circuit unit 201 is connected to the cable 160 (see FIG. 2). Specifically, the second output terminal 212 of the ion source power supply circuit 210 is connected to and connected to the discharge potential wiring 161. The auxiliary second output terminal 242 of the auxiliary electrode power supply circuit 240 is connected to and conductive with the auxiliary potential wiring 162. Further, the first output terminal 211 of the ion source power circuit 210 is connected to the auxiliary first output terminal 241 of the auxiliary electrode power circuit 240, the signal input terminal 231 of the signal current detection circuit 230, the inner circuit case 250, and the sensor GND wiring 165. The sensor GND potential SGND is made conductive. In addition, the ground input terminal 232 of the signal current detection circuit 230 is connected to and connected to the outer circuit case 260 and the ground potential wiring 167 to be the ground potential PVE.
In addition, the air supply pipe 310 of the pressure pump 300 is communicated with the air pipe 163 of the cable 160 through the inside circuit case 250.

  Next, the detection unit 10 will be described (see FIG. 2). As described above, the detection unit 10 is mounted on the mounting portion EPT having the mounting opening EPO in the exhaust pipe EP of the engine ENG, and contacts the exhaust gas EG (measured gas). The detection unit 10 is roughly composed of an ion gas ejection source 11, a fine particle charging unit 12, a first conduction member 13, a needle electrode body 20, and an auxiliary electrode body 50 in terms of its electrical functions.

  The first conducting member 13 is made of metal and has a cylindrical shape. The first conducting member 13 is externally fitted to the distal end side of the cable 160, is crimped and connected to the sensor GND wiring 165 of the cable 160, and is electrically connected to the sensor GND wiring 165. In the cable 160, the discharge potential wiring 161, the auxiliary potential wiring 162, and the air pipe 163 are held inside the first conduction member 13.

The distal end side of the discharge potential wiring 161 of the cable 160 is connected to the needle electrode body 20 in the first conductive member 13. The needle-like electrode body 20 is made of a tungsten wire and has a needle-like tip portion 22 whose tip portion is pointed like a needle.
In addition, the distal end side of the auxiliary potential wiring 162 of the cable 160 is connected to the auxiliary electrode body 50 in the first conductive member 13. The auxiliary electrode body 50 is made of a stainless steel wire, and its distal end side is bent back in a U shape, and further has an auxiliary electrode portion 53 that is pointed in a needle shape at the distal end portion.

On the other hand, the first conducting member 13 is conducted to the first output terminal 211 of the ion source power supply circuit 210 through the sensor GND wiring 165 of the cable 160 and the inner circuit case 250, and is set to the sensor GND potential SGND.
Moreover, the 1st conduction | electrical_connection member 13 surrounds the radial direction periphery of the site | part located out of the exhaust pipe EP among the acicular electrode body 20 and the auxiliary electrode body 50. FIG.

  Furthermore, the circumference of the first conducting member 13 in the radial direction is attached to the exhaust pipe EP and surrounded by an exterior member 14 that is electrically connected to the exhaust pipe EP. The exterior member 14 is electrically connected to the ground potential wiring 167 of the cable 160 and is set to the ground potential PVE.

  Further, the air pipe 163 of the cable 160 has an open end in the first conducting member 13. The compressed air AK supplied from the pressure feed pump 300 through the air pipe 310 and the air pipe 163 of the cable 160 and discharged from the air pipe 163 is further discharged to the front end side (right side in FIG. 2) discharge space DS (described later). To be pumped.

Further, a nozzle portion 31 is fitted on the distal end side (right side in FIG. 2) of the first conducting member 13. The nozzle portion 31 has a concave shape whose center is directed to the tip side, and a fine through hole is formed at the center to form a nozzle 31N.
Further, the nozzle portion 31 is also electrically connected to the first conducting member 13 and is set to the sensor GND potential SGND.

As the nozzle portion 31 is fitted on the distal end side of the first conducting member 13, a discharge space DS is formed inside them. In this discharge space DS, a needle-like distal end portion 22 of the needle-like electrode body 20 protrudes, and this needle-like distal end portion 22 is a surface on the proximal end side of the nozzle portion 31 and a concave facing surface 31T. Facing each other. Accordingly, when a high voltage is applied between the needle-shaped tip 22 and the nozzle portion 31 (opposing surface 31T), air discharge occurs, and N ₂ , O _2, etc. in the atmosphere are ionized, and positive ions (for example, N ³⁺ , O ^2+, hereinafter also referred to as ions CP). Further, the compressed air AK discharged from the air pipe 163 of the cable 160 is also supplied to the discharge space DS. For this reason, the air AR originating from the compressed air AK is ejected from the nozzle 31N of the nozzle portion 31 toward the mixed region MX (described later) on the tip side at a high speed, and the compressed air AK (air AR) ), The ions CP are also injected into the mixing region MX.

  Further, the fine particle charging unit 12 is configured on the tip side (right side in FIG. 2) of the nozzle unit 31. An intake port 33I (opening toward the downstream side of the exhaust pipe EP) and a discharge port 43O are perforated on the side surface of the fine particle charging unit 12. The fine particle charging unit 12 is also electrically connected to the nozzle unit 31 and is set to the sensor GND potential SGND.

The fine particle charging unit 12 is configured such that the inner space is narrowed in a slit shape by the collecting electrode 42 bulging inward, and on the base end side (left side in FIG. 2) from this, A columnar space is formed between the nozzle portion 31 and the nozzle portion 31.
Of the spaces in the fine particle charging unit 12, the above-described cylindrical space is referred to as a cylindrical mixed region MX1. Moreover, let the slit-shaped internal space comprised by the collection electrode 42 be the slit-shaped mixing area MX2. Then, the cylindrical mixed region MX1 and the slit-shaped mixed region MX2 are collectively referred to as a mixed region MX. Further, a cylindrical space is formed on the tip side of the collecting electrode 42, and a discharge path EX communicating with the discharge port 43O is formed. In addition, a lead-in path HK that communicates from the inlet 33I to the mixing region MX (cylindrical mixing region MX1) is formed on the proximal end side of the collecting electrode 42.

Next, the electrical functions and operations of each part of the system 1 will be described with reference to FIG. 3 in addition to FIG. FIG. 3 schematically shows the electrical function and operation of the detection unit 10 of the system 1 for easy understanding.
The acicular electrode body 20 is connected to and connected to the second output terminal 212 of the ion source power supply circuit 210 via the discharge potential wiring 161 of the cable 160, and the sensor GND potential SGND and the acicular electrode body 20 In the meantime, a discharge voltage V2 (= 3 kV) is applied.
The auxiliary electrode body 50 is connected to and connected to the auxiliary second output terminal 242 of the auxiliary electrode power supply circuit 240 via the auxiliary potential wiring 162 of the cable 160, and the sensor GND potential SGND and the auxiliary electrode body 50 are connected. The auxiliary voltage V3 of DC 100 to 200V is applied between the two.
Further, the first conductive member 13, the nozzle unit 31, and the fine particle charging unit 12 are connected to the first output terminal 211 of the ion source power supply circuit 210 and the auxiliary first power supply circuit 240 via the sensor GND wiring 165 of the cable 160. The output terminal 241, the inner circuit case 250 surrounding these circuits, and the signal input terminal 231 of the signal current detection circuit 230 are connected and conductive. These are the sensor GND potential SGND.
In addition, the exterior member 14 is connected to the outer circuit case 260 surrounding the measurement control circuit 220 including the signal current detection circuit 230 and the ground input terminal 232 of the signal current detection circuit 230 via the ground potential wiring 167 of the cable 160. Conducted. These are set to the same ground potential PVE as the exhaust pipe EP.

Therefore, as described above, when a high discharge voltage V2 is applied between the nozzle portion 31 (opposing surface 31T) that is set to the sensor GND potential SGND and the needle-like tip portion 22, an air discharge, specifically Corona discharge occurs. More specifically, a positive needle corona PC in which a corona is generated around the needle-like tip 22 serving as the positive electrode is generated. As a result, N ₂ , O _2, etc. in the atmosphere (air) forming the atmosphere is ionized and positive ions CP are generated. Part of the generated ions CP is ejected toward the mixing region MX through the nozzle 31N together with the air AR originating from the compressed air AK supplied to the discharge space DS.
In the present embodiment, the needle-like tip 22 forms a discharge electrode. Further, the nozzle portion 31 and the needle-like tip portion 22 (discharge electrode) surrounding the discharge space DS serve as the ion source 11 and the ion gas ejection source 11.

When the air AR is injected into the mixing region MX (columnar mixing region MX1) through the nozzle 31N of the nozzle portion 31, the pressure in the columnar mixing region MX1 decreases, so that the exhaust gas EG is drawn from the intake port 33I. Through HK, it is taken into the mixing area MX (columnar mixing area MX1, slit-shaped mixing area MX2). The intake exhaust gas EGI is mixed with the air AR, and is discharged from the discharge port 43O via the discharge path EX together with the air AR.
At this time, if the exhaust gas EG contains fine particles S such as soot, the fine particles S are also taken into the mixing region MX as shown in FIG. By the way, the injected air AR contains ions CP. For this reason, the fine particles S such as soot that have been taken in become positively charged fine particles SC due to the attachment of the ions CP. In this state, the fine particles S are taken in from the discharge port 43O through the mixing region MX and the discharge path EX. It is discharged together with the exhaust gas EGI and the air AR.
On the other hand, among the ions CP ejected to the mixed region MX, the floating ions CPF that have not adhered to the fine particles S receive a repulsive force from the auxiliary electrode portion 53 of the auxiliary electrode body 50, and the collection electrode is set to the sensor GND potential SGND. 42 is attached to and captured by each part of the fine particle charging unit 12 that forms 42.

As shown in FIG. 2, the discharge current Id is supplied from the second output end 212 of the ion source power supply circuit 210 to the needle-shaped tip 22 in accordance with the air discharge in the ion gas injection source 11. Most of the discharge current Id flows into the nozzle unit 31 as the power reception current Ij and flows to the first output terminal 211 of the ion source power supply circuit 210. On the other hand, the collection current Ih resulting from the charge of the floating ions CPF collected by the collection electrode 42 also flows to the first output terminal of the ion source power supply circuit 210. That is, a received collection current Ijh (= Ij + Ih) that is the sum of the received current Ij and the collected current Ih flows into the first output terminal 211 of the ion source power supply circuit 210.
However, the power collection current Ijh is smaller than the discharge current Id by a current corresponding to the charge of the discharged ions CPH attached and discharged to the charged fine particles SC. For this reason, the signal current Is corresponding to the difference between the discharge current Id and the received and collected current Ijh (discharge current Id−received and collected current Ijh) flows between the sensor GND potential SGND and the ground potential PVE to be balanced.
Therefore, the signal current Is corresponding to the charge amount of the discharged ions CPH discharged by the charged fine particles SC is detected by the signal current detection circuit 230, whereby the amount of the fine particles S in the exhaust gas EG can be detected.

As described above, in the system 1 of the present embodiment, the discharge voltage V2 is applied to the ion source 11 (the needle-like tip portion 22 of the needle-like electrode body 20) to generate corona discharge (air discharge). By detecting the signal current Is, the fine particles S in the exhaust gas EG are detected.
By the way, in the system 1, the fine particle charging unit 12 and the first conducting member 13 of the ion source 11 are set to the sensor GND potential SGND, and the exhaust pipe EP to be grounded PVE and the exterior member conducting to the exhaust pipe EP. A ceramic insulating member (not shown) is interposed between the two and 14 to insulate them.

  However, if the insulation of the surface of each part of the ion source 11 decreases due to foreign matters adhering to the insulating member, the sensor GND potential SGND that detects the signal current Is through the surface of the ion source 11 and the insulating member. And a ground potential PVE may cause a leakage current. When a current (non-signal current Ie) that is not the original signal current Is caused by the fine particles S flows between the sensor GND potential SGND and the ground potential PVE like this leakage current (see FIG. 2). An error occurs due to the non-signal current Ie being included 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, the magnitude is set to be lower than the discharge voltage V2 and does not cause air discharge during the non-discharge period T1 (measurement period T1e) in which no air discharge is generated in the ion source 11. The non-discharge voltage V1e is applied to the ion source 11, and the non-discharge current Ise detected by the signal current detection circuit 230 is acquired. Further, using this non-discharge current Ise, an estimated non-signal current Ime (estimated value of the non-signal current Ie) estimated to be included in the signal current Is during the discharge period T2 in which the air discharge is generated in the ion source 11 is used. Thus, the value of the signal current Is is corrected. Then, the amount of the fine particles S is detected from the corrected signal current Is (hereinafter also referred to as a corrected signal current Isa).
Hereinafter, regarding the correction of the signal current Is, the operation of the microprocessor 100 that executes the particle detection process in the system 1 will be described with reference to the flowchart of FIG. 4 and the timing chart of FIG.

  As shown in FIG. 4, when a key switch (not shown) of the engine ENG is turned on, the system 1 (the microprocessor 100 of the measurement control circuit 220) is activated and necessary initial settings are made in step S1. Thereafter, in step S2, the presence / absence of an instruction signal ST (see FIG. 2) for starting particle detection from the ECU is detected.

  When there is no particulate detection start instruction signal ST from the ECU (No), Step S2 is repeated, and the input of the particulate detection start instruction signal ST from the ECU is awaited. If the instruction signal ST for starting the particle detection from the ECU is detected (Yes), the process proceeds to step S3.

  In step S3, it is determined whether or not the current timing is the non-discharge period T1, that is, whether the current timing is the non-discharge period T1 at every predetermined timing or the other discharge period T2 (FIG. 5). reference). This timing is determined by a timer (not shown) of the microprocessor 100. In this embodiment, a non-discharge period T1 having a length of 100 msec arrives at a cycle of 1 second. That is, the non-discharge period T1 having a length of 100 msec and the discharge period T2 having a length of 900 msec are alternately repeated. When it is the non-discharge period T1 (Yes), the process proceeds to step S4, and when it is the discharge period T2 (No), the process proceeds to step S8.

  In step S4, the non-discharge voltage V1e that is lower than the discharge voltage V2 and does not cause an air discharge is applied to the ion source 11 over the entire period of the non-discharge period T1. That is, the entire non-discharge period T1 is a measurement period T1e in which the non-discharge voltage V1e is applied (non-discharge period T1 = measurement period T1e). Here, the non-discharge voltage V1e is 1 / α of the discharge voltage V2 (V1e = V2 / α). Specifically, V2 = 3 kV, V1e = 1 kV, and α = 3. The ion source power supply circuit 210 is configured to be able to select two voltages, a discharge voltage V2 and a non-discharge voltage V1e, as voltages to be applied to the ion source 11 based on an instruction from the microprocessor 100.

  Next, in step S5, the signal current detection circuit 230 acquires the non-discharge current Ise (n) that flows when the non-discharge voltage V1e is applied to the ion source 11. In the present embodiment, the value of the non-discharge current Ise (n) is an average value of values measured a plurality of times during one n-th non-discharge period T1 (measurement period T1e). As shown in FIG. 5, the value of the non-discharge current Ise (n) acquired in the immediately preceding non-discharge period T1 is used to correct the signal current Is (n) described below. Note that n is an integer.

  Further, in the subsequent step S6, the estimated non-signal current Ime (n) = α × Ise (n) during the discharge period T2 is calculated using the non-discharge current Ise (n) acquired in step S5. That is, as shown in FIG. 5, the latest estimated non-signal current is estimated as Ime (n) = α × Ise (n), Ime (n + 1) = α × Ise (n + 1) for each non-discharge period T1.

  Next, the process proceeds to step S7, where it is determined whether or not it is the non-discharge period T1, that is, whether or not the non-discharge period T1 continues. If the non-discharge period T1 continues (Yes), this step S7 is repeated to wait for the non-discharge period T1 to end. When the non-discharge period T1 ends (No), the process proceeds to step S13.

  In step S13, it is determined whether or not the key switch of engine ENG is turned off. If the key switch of the engine ENG is not OFF (No), the process returns to step S3, and the particle detection process is continued. On the other hand, when the key switch of the engine ENG is turned off (Yes), the particle detection process is terminated.

In step S3, when it is the discharge period T2 (No), when the process proceeds to step S8, the discharge voltage V2 is applied to the ion source 11 to generate corona discharge.
Next, in step S <b> 9, the signal current detection circuit 230 acquires the signal current Is (n) that flows when the discharge voltage V <b> 2 is applied to the ion source 11. In the present embodiment, the value of the signal current Is (n) is an average value of values measured a plurality of times during the nth discharge period T2.
Further, in the subsequent step S10, the signal current Is (n) acquired in step S9 is corrected using the estimated non-signal current Ime (n) (= α × Ise (n)) acquired in step S6. Specifically, a corrected signal current Isa (n) = (Is (n) −Ime (n)) = (Is (n) −) obtained by subtracting the estimated non-signal current Ime (n) from the signal current Is (n). α × Ise (n)) is calculated.
In step S11, the corrected signal current Isa (n) is output as a measurement result of the fine particles S to the ECU.

  Next, the process proceeds to step S12, and it is determined whether or not it is the discharge period T2, that is, whether or not the discharge period T2 is continued. If the discharge period T2 continues (Yes), this step S12 is repeated to wait for the discharge period T2 to end. When the discharge period T2 ends (No), the process proceeds to step S13.

  In step S13, as already described, it is determined whether or not the key switch of the engine ENG is turned off. If the key switch of the engine ENG is not turned off (No), the process returns to step S3 to continue the particle detection process, and if the key switch of the engine ENG is turned off (Yes). Then, the particle detection process is terminated.

As described above, in the system 1 of the present embodiment, in the non-discharge period T1 (= measurement period T1e) other than the discharge period T2 causing the air discharge, the air discharge occurs lower than the discharge voltage V2. A non-discharge voltage V1e is applied to the ion source 11, and the non-discharge current Ise (n) detected by the signal current detection circuit 230 is acquired during the non-discharge period T1. Then, the value of the signal current Is (n) detected during the discharge period T2 is corrected by using the non-discharge current Ise (n).
Thereby, the influence of the non-signal current Ie (n) included in the signal current Is (n) is reduced, and the amount of the fine particles S is corrected by the corrected signal current Is (n) (corrected signal current Isa (n)). Can be detected more accurately.

Furthermore, in the system 1 of the present embodiment, the estimated non-signal current Ime (n) estimated to be included in the signal current Is (n) detected during the discharge period T2 is obtained from the non-discharge current Ise (n). Thus, the corrected signal current Isa (n) is obtained by subtracting the estimated non-signal current Ime (n) from the signal current Is (n) detected during the discharge period T2.
Thereby, the influence of the non-signal current Ie (n) included in the signal current Is (n) can be appropriately reduced.

Furthermore, in the system 1 of the present embodiment, the ratio α (specifically, the magnitude of the non-discharge voltage V1e (specifically, V1e = 1 kV) and the discharge voltage V2 (specifically, V2 = 3 kV) In proportion to α = 3), it is estimated that a non-signal current Ie (n) that is α times the non-discharge current Ise (n) flows during the discharge period T2 (estimated non-signal current Ime (n) = α × Ise (n)), which is subtracted from the signal current Is (n).
Thereby, the non-signal current Ie (n) included in the signal current Is (n) can be appropriately corrected by a simple method.

  Further, according to the fine particle detection method used in the system 1 of the present embodiment, in detecting the fine particles, the amount of the fine particles S can be detected more accurately by correcting the signal current Is using the non-discharge current Ise. it can.

In the present embodiment, the microprocessor 100 executing steps S4 and S8 corresponds to ion source driving means.
Further, the microprocessor 100 executing step S9 corresponds to a signal current acquisition unit, and the microprocessor 100 executing step S5 corresponds to a non-discharge current acquisition unit. Further, the microprocessor 100 executing steps S6 and S10 corresponds to the signal current correction means, and among these, the microprocessor 100 executing step S6 corresponds to the estimated non-signal current acquisition means. The microprocessor 100 executing S10 corresponds to a corrected signal current acquisition unit.

In the present embodiment, the microprocessor 100 executing step S8 corresponds to an ion source discharge driving step, and the microprocessor 100 executing step S4 corresponds to an ion source non-discharge driving step.
Further, the microprocessor 100 executing step S9 corresponds to a signal current acquisition step, and the microprocessor 100 executing step S5 corresponds to a non-discharge current acquisition step. In addition, the microprocessor 100 executing steps S6 and S10 corresponds to a signal current correction step.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the entire non-discharge period T1 is the measurement period T1e for applying the non-discharge voltage V1e. However, a part of the non-discharge period T1 may be the measurement period T1e. Specifically, a part of the non-discharge period T1 (for example, the first 50 msec period of T1 = 100 msec) is set as the measurement period T1e, while the non-discharge voltage V1e is applied to the ion source 11 while non-discharge is performed. In the remaining period of the period T1, the voltage applied to the ion source 11 may be further reduced, or the voltage application may be stopped (V1e = 0V).
In the embodiment, as the non-discharge current Ise and the signal current Is, an average value of values measured a plurality of times within one measurement period T1e and the discharge period T2 is used. However, in the one measurement period T1e and the discharge period T2, The non-discharge current Ise and the signal current Is may be measured once and these values may be used. Moreover, you may use the average value of the measured value except the maximum value and the minimum value among several measured values.
Further, in the embodiment, the corona discharge is generated in the discharge space DS to generate the ions CP. However, the needle-like tip portion 22 of the needle-like electrode body 20 is placed in the mixing region MX (columnar mixing region MX1). The corona discharge is generated between the needle-shaped tip 22 and the inner surface of the fine particle charging unit 12 surrounding the mixed region MX to generate ions CP, and the ions CP are fine particles such as soot in the mixed region MX. You may make it adhere to S.

AM Vehicle ENG Engine EP Exhaust pipe EG Exhaust gas S Particle SC Charged particle CP Ion CPF Floating ion CPH Discharged ion Is Signal current Ie Non-signal current Ise Non-discharge current Ime Estimated non-signal current Isa Corrected signal current T1 Non-discharge period T1e Measurement Period T2 Discharge period 1 Particulate detection system 10 Detection unit 11 Ion gas injection source (ion source)
12 Fine Particle Charger 20 Needle-like Electrode 22 (Needle Tip) (Ion Source)
31 Nozzle (ion source)
31N Nozzle SGND Sensor GND potential PV2 Discharge potential PV3 Auxiliary potential PVE Ground potential V1e Non-discharge voltage V2 Discharge voltage V3 Auxiliary voltage MX Mixed region 42 Collection electrode 50 Auxiliary electrode body 53 (Auxiliary electrode body) Auxiliary electrode section 160 Cable AK Compression Air AR Air 300 Pressure pump 100 Microprocessor 201 Circuit unit 210 Ion source power circuit 220 Measurement control circuit 230 Signal current detection circuit 240 Auxiliary electrode power circuit S4, S8 Ion source driving means S8 Ion source discharge driving step S4 Ion source non-discharge driving Step S9 Signal current acquisition means, signal current acquisition step S5 Non-discharge current acquisition means, non-discharge current acquisition steps S6, S10 Signal current correction means, signal current correction step S6 Estimated non-signal current acquisition means S10 Corrected signal current acquisition means

Claims (4)

An ion source that generates ions by air discharge;
An ion source power supply circuit for applying a voltage to the ion source;
A particle detection system comprising: a signal current detection circuit that detects a magnitude of a signal current that varies according to the amount of charged particles in which the ions adhere to particles in a measurement gas,
The ion source power circuit is
The discharge voltage at which the air discharge occurs, and the non-discharge voltage that is lower than the discharge voltage and does not cause the air discharge, are configured to be applied to the ion source,
In the discharge period causing the air discharge, the ion source power supply circuit is applied the discharge voltage to the ion source,
Among the non-discharge periods that do not cause the air discharge other than the discharge period, the ion source power supply circuit causes the ion source power supply circuit to apply the non-discharge voltage to the ion source during the non-discharge period; and
Signal current acquisition means for acquiring the signal current detected by the signal current detection circuit during the discharge period;
Non-discharge current acquisition means for acquiring a non-discharge current detected by the signal current detection circuit during the measurement period;
A fine particle detection system comprising: a signal current correction unit that corrects the value of the signal current detected during the discharge period using the non-discharge current. The particulate detection system according to claim 1,
The signal current correction means includes
Estimated non-signal current acquisition means for obtaining an estimated non-signal current estimated to be included in the signal current detected during the discharge period from the non-discharge current detected during the measurement period;
A fine particle detection system comprising corrected signal current acquisition means for obtaining a corrected signal current by subtracting the estimated non-signal current from the signal current detected during the discharge period. The fine particle detection system according to claim 2,
The non-discharge voltage is 1 / α of the discharge voltage (α> 1),
The estimated non-signal current acquisition means includes
A particulate detection system that acquires a value obtained by multiplying the non-discharge current by the α as the estimated non-signal current. An ion source that generates ions by air discharge;
An ion source power supply circuit for applying a voltage to the ion source;
A fine particle detection method in a fine particle detection system comprising a signal current detection circuit that detects a magnitude of a signal current that changes according to the amount of charged fine particles in which the ions adhere to fine particles in a gas to be measured,
The ion source power circuit is
Select a discharge voltage at which the air discharge occurs and a non-discharge voltage lower than the discharge voltage at which the air discharge does not occur,
Configured to be applied to the ion source,
An ion source discharge driving step of causing the ion source power supply circuit to apply the discharge voltage to the ion source during a discharge period causing the air discharge;
An ion source non-discharge driving step for applying the non-discharge voltage to the ion source in the ion source power supply circuit during a measurement period among non-discharge periods that do not cause the air discharge other than the discharge period;
A signal current acquisition step of acquiring the signal current detected by the signal current detection circuit during the discharge period;
A non-discharge current acquisition step of acquiring a non-discharge current detected by the signal current detection circuit during the measurement period;
A fine particle detection method comprising: a signal current correction step of correcting the value of the signal current detected during the discharge period using the non-discharge current.

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