JP6603612B2 - Particle sensor - Google Patents

Description

  The present invention relates to a particle sensor.

  In an internal combustion engine (for example, a diesel engine), the exhaust gas may contain fine particles such as soot. The exhaust gas containing such fine particles is purified by collecting the fine particles with a filter. Moreover, the particulates accumulated in the filter are burned and removed by raising the temperature of the filter as necessary. However, when a problem such as breakage of the filter occurs, unpurified exhaust gas is directly discharged downstream of the filter. Therefore, there is a need for a particulate sensor capable of directly detecting the amount of particulates in exhaust gas and detecting the amount of particulates in exhaust gas in order to detect a filter failure.

  Such a fine particle sensor is disclosed in Patent Document 1, for example. The fine particle sensor of Patent Document 1 includes a cylindrical gas intake tube extending from the rear end side to the front end side, and a discharge portion that generates an air discharge, and the discharge electrode is disposed inside the gas intake tube. With body. The gas intake pipe is located on the rear end side of the gas intake pipe and is located on the front end side of the gas intake pipe and the gas intake port for taking in the measurement gas containing fine particles into the gas intake pipe. A gas discharge port for discharging the gas to be measured to the outside of the gas intake pipe; This fine particle sensor attaches ions generated around the discharge part by air discharge (corona discharge) to the fine particles contained in the gas to be measured taken into the gas intake pipe through the gas intake, Fine particles in the gas to be measured are detected using a signal current that flows according to the amount of attached ions.

JP 2015-129712 A

  By the way, in the fine particle sensor of Patent Document 1, ions generated around the discharge portion by air discharge are sufficiently larger than fine particles contained in the gas to be measured taken into the gas intake tube through the gas intake. Sometimes it could not be attached. Specifically, the gas inlet of the gas intake pipe is arranged at the rear end side of the gas intake pipe, and the gas outlet of the gas intake pipe is arranged at the front end side of the gas intake pipe. The gas to be measured taken into the intake pipe flows from the rear end side to the front end side of the gas intake pipe and is discharged from the gas discharge port of the gas intake pipe.

  However, the gas to be measured taken into the gas inlet pipe through the gas inlet flows linearly from the rear end side to the front end side of the gas inlet pipe. Will pass through. For this reason, the ions generated around the discharge part cannot be sufficiently brought into contact with the fine particles contained in the gas to be measured, and the ions are sufficiently adhered to the fine particles contained in the gas to be measured. There was something that could not be done.

  Moreover, since the discharge part is arrange | positioned on the ceramic base | substrate of a sensor element, in the area | region where the ceramic base | substrate exists among the circumference | surroundings of a discharge part, the generation amount of ion decreases. For this reason, it is possible to sufficiently attach ions to the fine particles contained in the gas to be measured introduced into the gas intake pipe through the gas intake located on the side where the ceramic substrate is present when viewed from the discharge part. There was something I couldn't do.

  For this reason, in the above-described fine particle sensor, the signal current that flows according to the amount of ions attached to the fine particles tends to be small, and it has been a problem to improve the sensitivity of the fine particle sensor.

  The present invention has been made in view of the current situation, and provides a particle sensor that can increase the signal current that flows in accordance with the amount of ions attached to the particle and improve the sensitivity of the particle sensor. For the purpose.

  One aspect of the present invention has a cylindrical gas intake tube extending from the rear end side to the front end side, and a discharge portion that generates an air discharge, and the discharge portion is disposed inside the gas intake tube. An electrode body, and the gas intake pipe is located on a rear end side of the gas intake pipe and takes in a gas to be measured containing fine particles into the gas intake pipe, and the gas intake pipe A gas discharge port for discharging the gas to be measured to the outside of the gas intake pipe, and ions generated around the discharge part by the air discharge are passed through the gas intake port. The fine particles in the gas to be measured are attached to the fine particles contained in the gas to be measured introduced into the gas intake pipe, and the fine particles in the gas to be measured are flowed according to the amount of the ions attached to the fine particles. In the particle sensor to detect The gas inlet is entirely located on the rear end side of the front end of the discharge part, guides the gas to be measured into the gas intake pipe, and takes the gas to be measured taken into the gas intake pipe. Is a fine particle sensor including a guide body that generates a swirling flow swirling around the discharge portion.

  In the fine particle sensor described above, the entire gas intake port of the gas intake tube is arranged on the rear end side with respect to the front end of the discharge portion of the discharge electrode body (the site that generates air discharge). The gas intake port of the gas intake pipe is disposed on the rear end side of the gas intake pipe, and the gas discharge port of the gas intake pipe is disposed on the front end side of the gas intake pipe. Therefore, the gas to be measured taken into the gas intake pipe through the gas inlet flows toward the tip side, and around the discharge part located around the discharge part of the discharge electrode body in the internal space of the gas intake pipe. It flows through the flow path to the gas discharge port of the gas intake pipe via the space. For this reason, ions generated around the discharge part by air discharge are likely to adhere to fine particles contained in the gas to be measured taken into the gas intake tube through the gas intake.

  In addition, ions generated around the discharge part due to the air discharge tend to flow toward the front end side with the flow of the gas to be measured, so the gas intake pipe is passed through the gas intake port located on the rear end side. It becomes difficult to be discharged to the outside, and ions are more likely to adhere to the fine particles.

  Moreover, in the above-described particle sensor, a guide body is provided at the gas inlet. This guide body guides the gas to be measured to the inside of the gas intake pipe so that a swirl flow is generated in which the gas to be measured taken into the gas intake pipe through the gas intake port swirls around the discharge portion. It has a form. That is, the guide body guides the gas to be measured to the inside of the gas intake pipe, and generates a swirling flow in which the gas to be measured taken into the gas intake pipe swirls around the discharge portion.

  In this way, by generating a swirling flow of the gas to be measured that swirls around the discharge part, the chance that the ions generated around the discharge part come into contact (adhesion) with the fine particles contained in the gas to be measured is increased. Since many ions can be attached to the fine particles. Thereby, the signal current which flows according to the amount of ions attached to the fine particles can be increased, and the sensitivity of the fine particle sensor can be improved.

  Furthermore, in the particulate sensor described above, the gas inlet may be a particulate sensor that is located on the rear end side with respect to the rear end of the discharge portion.

  In the above-described particulate sensor, the gas inlet of the gas intake pipe is arranged on the rear end side of the gas intake pipe, and the gas outlet of the gas intake pipe is arranged on the front end side of the gas intake pipe. Ions flow from the rear end side (gas intake port) of the gas intake pipe toward the front end side (gas exhaust port).

  On the other hand, in the fine particle sensor described above, the entire gas inlet is located on the rear end side with respect to the rear end of the discharge part. This makes it difficult for ions generated around the discharge portion due to air discharge to be discharged to the outside of the gas intake tube through the gas intake port, so that the ions easily adhere to the fine particles.

  Furthermore, in any one of the fine particle sensors, the gas intake pipe has an opening through which the gas to be measured and the ions can pass between the outside and the inside of the gas intake pipe. It is preferable to have only a gas exhaust port, and the gas exhaust port is a fine particle sensor arranged at the tip of the gas intake pipe.

  The fine particle sensor described above has only the gas inlet and the gas outlet as an opening through which the gas to be measured and ions can pass between the outside and the inside of the gas inlet pipe. Further, the gas discharge port is arranged at the tip of the gas intake pipe. Therefore, in the gas inlet pipe of the above-described particulate sensor, the entire gas inlet is located on the rear end side of the tip of the discharge part, and the gas outlet is located at the tip of the gas inlet pipe. There is no opening through which the gas to be measured and ions can be discharged to the outside from the tip of the discharge portion to the gas discharge port located at the tip of the gas intake tube.

  For this reason, the gas and ions to be measured flowing to the tip side of the gas intake pipe are discharged to the outside of the gas intake pipe until they reach the gas outlet located at the tip of the gas intake pipe. Can be prevented. As a result, it is possible to increase the chance of contact between the fine particles contained in the gas to be measured and ions inside the gas intake pipe, and it is possible to attach more ions to the fine particles.

  Further, the particle sensor according to any one of the above, further comprising a cylindrical wall portion that surrounds the periphery of the gas intake pipe in the radial direction via a gap, and the outside of the gas intake port is covered by the wall portion. A fine particle sensor is preferable.

  The fine particle sensor described above includes a cylindrical wall portion that surrounds the periphery of the gas intake pipe in the radial direction via a gap. The outside of the gas inlet (the radially outer side of the gas inlet pipe) is covered with this wall portion. That is, when the gas intake pipe is viewed in the radial direction from the outside, the gas intake is disposed at a position where it is hidden behind the wall portion and cannot be seen. For this reason, when water (water droplets) scatters from the outside of the gas intake pipe toward the gas intake port, the wall portion prevents (prevents) the water (water droplet) from entering the gas intake port. It becomes possible. This makes it difficult for the water (water droplets) to enter the gas intake pipe through the gas intake.

  Furthermore, in any one of the fine particle sensors, only an internal space of the gas intake tube is provided between the discharge portion and a cylindrical discharge peripheral portion surrounding the discharge portion of the gas intake tube. It is preferable to use an existing fine particle sensor.

  In the above particulate sensor, only the internal space of the gas intake tube exists between the discharge portion and the cylindrical discharge peripheral portion surrounding the discharge portion of the gas intake tube. That is, no other member exists between the discharge peripheral portion and the discharge portion in the radial direction of the gas intake tube. For this reason, it becomes possible to generate ions over the entire periphery (360 °) of the discharge part. This makes it easier for ions to adhere to the fine particles contained in the gas to be measured swirling around the discharge part.

  Further, in any one of the fine particle sensors, the fine particle sensor is attached to a metal vent pipe having a ground potential through which the gas to be measured flows, and the gas intake pipe is different from the ground potential. The first potential is set, and the discharge unit is set to a discharge potential different from the ground potential and the first potential, and the air discharge is generated between the gas intake pipe and the particulate sensor A fine particle sensor that detects the amount of the fine particles in the measurement gas using the signal current that flows between the first potential and the ground potential according to the amount of the ions attached to the fine particles may be used.

  The fine particle sensor described above is used by being attached to a metal vent pipe having a ground potential through which a gas to be measured flows. The discharge unit having the discharge potential generates an air discharge (for example, corona discharge) with the gas intake tube having the first potential. In this fine particle sensor, since the ions attached to the fine particles are discharged to the outside of the gas intake pipe through the gas outlet, the signal flowing between the first potential and the ground potential according to the amount of ions attached to the fine particles. The amount of fine particles in the gas to be measured is detected using an electric current. Even in such a fine particle sensor, as described above, many ions can be attached to the fine particles, so that the sensitivity of the fine particle sensor can be improved.

It is the schematic of the vehicle carrying the particulate detection system concerning an Example. It is a longitudinal cross-sectional view of the particulate sensor concerning an Example. It is another longitudinal cross-sectional view of the particulate sensor. It is a disassembled perspective view of the particulate sensor. It is a schematic diagram of a particulate detection system. It is a perspective view of the sensor element which comprises a particulate sensor. It is a disassembled perspective view of the sensor element. It is explanatory drawing of the microparticle detection system concerning an Example. It is a cross-sectional view of the protector (gas intake pipe) of the fine particle sensor. It is the C section enlarged view of FIG. It is a figure which shows the flow of the to-be-measured gas in the protector of an Example. It is a correlation diagram between the fine particle concentration and the magnitude of the signal current. It is a figure which shows the flow of the to-be-measured gas in the inside of the protector of a comparative example.

(Example)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a vehicle AM equipped with a particulate detection system 1 according to an embodiment. FIG. 2 is a longitudinal sectional view of the particle sensor 10 according to the embodiment. FIG. 3 is another longitudinal cross-sectional view of the particle sensor 10 according to the embodiment, and is a cross-sectional view taken at a position shifted by 90 ° around the axis AX. FIG. 4 is an exploded perspective view of the particle sensor 10. FIG. 5 is a schematic diagram of the particle detection system 1. However, in FIG. 5, the control device 200 included in the particle detection system 1 is mainly illustrated, and only a part of the particle sensor 10 (such as the electric wire 165) is illustrated.

  As shown in FIG. 2, the side where the protector 45 (gas intake pipe) is disposed (downward in FIG. 2) in the axial direction GH (direction in which the axis AX extends, vertical direction in FIG. 2) of the particle sensor 10. Is the front end side GS, and the side (upward in FIG. 2) from which the electric wire 165 and the like on the opposite side extends is the rear end side GK.

  As shown in FIG. 1, the particle detection system 1 (hereinafter also simply referred to as the system 1) includes a particle sensor 10 and a control device 200 that controls the particle sensor 10. The particulate sensor 10 is attached to an exhaust pipe EP (venting pipe) of an engine ENG (internal combustion engine) mounted on the vehicle AM, and particulates S such as soot in the exhaust gas EG (measured gas) flowing through the exhaust pipe EP. Is detected. Specifically, the particulate sensor 10 is fixed to a metal exhaust pipe EP, and a part of the tip side thereof is disposed in the exhaust pipe EP and exposed to the exhaust gas EG (see FIG. 2).

  The control device 200 is connected to the particle sensor 10 via electric wires 165, 167, and 168 (see FIGS. 1 and 5). Of the electric wires 165, 167, and 168, the electric wire 165 is a triple coaxial cable (triaxial cable), 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) (see FIGS. 4 and 5). Further, 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. 4 and 5).

  As illustrated in FIG. 5, the control device 200 includes an ion source power supply circuit 210 and a measurement control circuit 220. 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. 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). The ion source power supply circuit 210 outputs a discharge potential PV2 applied to a discharge electrode body 110 described later.

The measurement control circuit 220 includes a signal current detection circuit 230 and a heater energization circuit 226. Among these, the signal current detection circuit 230 has a first input terminal 231 and a second input terminal 232 that are set to the sensor GND potential SGND. The signal current detection circuit 230 detects the signal current Is flowing between the first input terminal 231 and the second input terminal 232. The sensor GND potential SGND (first potential) is higher than the chassis GND potential CGND (ground potential) by an offset voltage V _offset (specifically, 0.5 V). Therefore, the second input terminal 232 is set to a potential that is higher than the chassis GND potential CGND by an offset voltage V _offset (specifically, 0.5 V).

  The heater energization circuit 226 is a circuit that energizes a heater 130 of the sensor element 100 described later by PWM control. The heater energization circuit 226 has a first heater energization end 226 a connected to the first heater lead 163 and a second heater energization end 226 b connected to the second heater lead 164. Note that the second heater energization end 226b and the second heater lead wire 164 are electrically connected to the chassis GND potential CGND and set to the chassis GND potential CGND. The first heater energization end 226a and the first heater lead wire 163 are set to the first heater potential PVht with reference to the chassis GND potential CGND.

  The ion source power supply circuit 210 is 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 supply circuit 210 and the first 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 circuit 210 and the secondary iron core 271B of the insulation transformer 270, and is connected to the first output terminal 211 of the ion source power circuit 210. The sensor GND is set to the GND potential SGND. Further, the first output end 211 of the ion source power supply circuit 210 is electrically connected to the inner outer conductor 165G1 which is the sensor GND potential SGND among the coaxial double outer conductors 165G of the electric wire 165.

  The insulation transformer 270 is configured such that the iron core 271 is separated into a primary iron core 271A wound around the primary coil 272 and a secondary iron core 271B wound around the power circuit coil 273. Of these, the primary iron core 271A is electrically connected to the chassis GND potential CGND. On the other hand, the secondary 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 ion source power supply circuit 210, the inner circuit case 250, and the measurement control circuit 220 including the signal current detection circuit 230 and the heater energization circuit 226 are surrounded by the outer circuit case 260 that is set to the chassis GND potential CGND. . Further, the second input end 232 of the signal current detection circuit 230, the second heater energization end 226b of the heater energization circuit 226, and the primary side iron core 271A of the insulation transformer 270 are connected to the outer circuit case 260 and connected to the chassis GND. The potential is CGND.

  In this embodiment, the outer circuit case 260 includes therein an ion source power supply circuit 210, an inner circuit case 250, a measurement control circuit 220 including a signal current detection circuit 230 and a heater energization circuit 226, and an insulating transformer. 270 primary iron core 271A is accommodated and enclosed. Further, the outer circuit case 260 is electrically connected to the outer outer conductor 165G2 having the chassis GND potential CGND among the coaxial double outer conductors 165G of the electric wire 165.

  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 a control unit ECU that controls the internal combustion engine via a communication line CC. Thereby, signals such as the measurement result (the magnitude of the signal current Is) of the signal current detection circuit 230 described above can be transmitted to the control unit ECU.

  Further, 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 through the insulation transformer 270. In the isolation transformer 270, 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 an iron core 271 (primary iron core 271A, secondary The side iron cores 271B) are electrically 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, electrical insulation between them can be maintained.

Next, the particle sensor 10 will be described with reference to FIGS.
As shown in FIGS. 2 and 3, the particle sensor 10 is configured such that the axial direction GH (the direction in which the axis AX extends, the vertical direction in FIG. 2) from the rear end side (upper side in FIG. 2) to the front end side (lower side in FIG. 2). ). The fine particle sensor 10 includes a sensor element 100 that generates ions by air discharge. The sensor element 100 has a plate shape extending in the axial direction GH. In addition, the fine particle sensor 10 includes a metal shell 50 that holds the sensor element 100 while being electrically insulated from the sensor element 100 and is set to the sensor GND potential SGND. In addition, a mounting bracket 90 is provided that surrounds and holds the metallic shell 50 and is attached to the exhaust pipe EP and has a chassis GND potential CGND while ensuring electrical insulation with the metallic shell 50.

  More specifically, the fine particle sensor 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 shape hexagon. Further, the mounting bracket 90 has a cylindrical wall portion 93 that surrounds the outer periphery of a protector 45 (gas intake pipe), which will be described later, at a position closer to the distal end GS than the flange portion 91. A male screw 93b for fixing the particulate sensor 10 to the exhaust pipe EP is formed on the outer periphery of the rear end side GK in the cylindrical wall portion 93. Accordingly, the particulate sensor 10 is attached to a metal mounting boss BO separately fixed to the exhaust pipe EP using the male screw 93b of the mounting bracket 90, and is attached to the exhaust pipe EP via the mounting boss BO. Fixed. For this reason, the mounting bracket 90 is set to the same chassis GND potential CGND as the exhaust pipe EP.

  Further, 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 the rear end portion 90k of the mounting bracket 90 and the front end portion 95s of the outer cylinder 95 are laser welded. Thus, the mounting bracket 90 and the outer cylinder 95 are integrated.

  On the inner side in the radial direction of the mounting bracket 90, a cylindrical metal shell 50 and an inner cylinder 80 integrated therewith are disposed via an insulating spacer 60 made of an electrical insulating material. 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 a substantially cylindrical shape and has an annular flange portion 51 that bulges radially outward. The inner cylinder 80 is made of metal and has a cylindrical shape extending in the axial direction GH. Then, the front end portion 80s of the inner cylinder 80 is fitted on the rear end portion 50k of the main metal shell 50 so that the front end of the inner tube 80 abuts on the flange portion 51 of the main metal shell 50, and the rear end portion of the main metal shell 50 The metal shell 50 and the inner cylinder 80 are integrated with each other by laser welding the 50k and the tip 80s of the inner cylinder 80.

  Further, the flange portion 51 of the metal shell 50 is disposed in the mounting metal 90 in a state of being sandwiched between the insulating spacer 60 located on the front end side GS and the sleeve 62 located on the rear end side GK. Note that an annular packing 65 made of carbon graphite is interposed between the flange portion 51 of the metal shell 50 and the insulating spacer 60, so that the airtightness between the flange portion 51 of the metal shell 50 and the insulating spacer 60 is interposed. Is secured. In addition, an annular packing 66 made of carbon graphite is interposed between the insulating spacer 60 and the mounting bracket 90 to ensure airtightness between the insulating spacer 60 and the mounting bracket 90. 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.

  A cup-shaped metal cup 52 is disposed inside the metal shell 50. Further, a hole 52b is formed at the bottom of the metal cup 52, and the sensor element 100 is inserted into the hole 52b. Further, around the sensor element 100, a cylindrical ceramic holder 53 made of alumina and holding the sensor 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 filling layer 54, a second powder filling layer 55, and a cylindrical ceramic sleeve 56 made of alumina are disposed. Among 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 rearmost end 50 kk of the metal shell 50 and the ceramic sleeve 56. The rearmost end 50 kk of the metal shell 50 is bent and crimped radially inward, and presses the ceramic sleeve 56 via the crimping 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 sensor element 100 is also airtightly held by the metal shell 50.

  Further, a cylindrical protector 45 (gas intake pipe) made of stainless steel is fixed to the distal end portion 50s of the metal shell 50 in a manner that surrounds the distal end portion 100S of the sensor element 100 from the radially outer side. The protector 45 protects the sensor element 100 from water droplets and foreign matters, and guides the exhaust gas EG to the periphery of the distal end portion 100S of the sensor element 100. The protector 45 is fixed to the tip 50s of the metal shell 50 as follows. Specifically, the rear end portion 45k of the protector 45 is externally fitted to the front end portion 50s of the metal shell 50, and the front end portion 50s of the metal shell 50 and the rear end portion 45k of the protector 45 are laser-welded. Has been.

  On the rear end side GK of the protector 45, a plurality of gas inlets 45I are formed in a manner of being arranged at equal intervals in the circumferential direction (see FIGS. 2 and 4). Exhaust gas EG (gas to be measured) containing fine particles S is taken into the protector 45 through the gas inlet 45I. Further, a gas discharge port 45O for discharging the introduced exhaust gas EG (gas to be measured) is formed at the tip of the protector 45. The gas discharge port 45 </ b> O is a circular opening whose axis coincides with the axis AX of the particle sensor 10, and only one gas discharge port 45 </ b> O is provided at the tip of the protector 45. In addition, the rear end side cylindrical portion 45t of the protector 45 in which the gas intake port 45I is formed is surrounded by the cylindrical wall portion 93 of the mounting bracket 90 around the radial direction via an annular gap. Yes. Thereby, the outside of the gas intake port 45 </ b> I is covered with the cylindrical wall portion 93.

  Here, with reference to FIG. 8, the intake of the exhaust gas EG into the protector 45 and the discharge of the exhaust gas EG to the outside of the protector 45 when the fine particle sensor 10 is used will be described. In FIG. 8, the exhaust gas EG circulates in the exhaust pipe EP from left to right. When the exhaust gas EG flowing through the exhaust pipe EP passes around the protector 45 of the fine particle sensor 10, the flow velocity rises outside the gas exhaust port 45O of the protector 45, and due to the venturi effect, the gas exhaust port 45O is increased. Negative pressure is generated in the vicinity.

  Then, the intake exhaust gas EGI taken into the protector 45 is discharged from the gas discharge port 45O by this negative pressure. At the same time, the exhaust gas EG around the front end side cylindrical portion 45m of the protector 45 is taken into the space between the cylindrical wall portion 93 of the mounting bracket 90 and the rear end side cylindrical portion 45t of the protector 45, Further, the air is taken into the protector 45 through the gas inlet 45I of the protector 45. Since the intake exhaust gas EGI inside the protector 45 is discharged from the gas discharge port 45O to the outside of the protector 45, the protector 45 has a gas intake port 45I on the rear end side GK and a front end side GS on the inside of the protector 45. An air flow of the intake exhaust gas EGI flowing toward the gas discharge port 45O is generated.

  In this way, a part of the exhaust gas EG flowing in the exhaust pipe EP is taken into the protector 45 through the gas inlet 45I, and the exhaust gas EG (intake exhaust gas) taken into the protector 45 is also introduced. EGI) is discharged to the outside of the protector 45 through the gas discharge port 45O.

  Further, in the fine particle sensor 10 of the present embodiment, as shown in FIG. 2, at the rear end side GK of the metal shell 50 (specifically, the rear end side GK of the ceramic sleeve 56), A ring-shaped insulating holder 173 made of an electrical insulating material is disposed. The insulating holder 173 is formed with an insertion hole 173c penetrating the insulating holder 173 in the axial direction GH, and the sensor element 100 is inserted into the insertion hole 173c. Furthermore, a third insulating member 172 is disposed adjacent to the insulating holder 173 on the rear end side GK of the insulating holder 173. The third insulating member 172 is made of an electrical insulating material and has a cylindrical shape extending in the axial direction GH.

  Furthermore, a first insulating member 71 is disposed inside the third insulating member 172. The first insulating member 71 is made of an electrical insulating material and has a cylindrical shape extending in the axial direction GH. Further, a second insulating member 72 is disposed on the rear end side GK of the first insulating member 71. The second insulating member 72 is made of an electrical insulating material and has a cylindrical shape extending in the axial direction GH. A cylindrical spacer 78 extending in the axial direction GH is interposed between the first insulating member 71 and the second insulating member 72.

  The first insulating member 71 has an insertion hole 71c that penetrates itself in the axial direction GH. The sensor element 100 is inserted into the insertion hole 71c, and the discharge potential terminal member 73 is accommodated. Further, the second insulating member 72 has a first insertion hole 72c and a second insertion hole 72d that pass through the second insulating member 72 in the axial direction GH (see FIG. 4). Among these, the rear end portion 100K of the sensor element 100 is located in the second insertion hole 72d, and a first heater terminal member 76 and a second heater terminal member 77, which will be described later, are accommodated in an insulated state. ing.

  The first insulating member 71 holds the discharge potential terminal member 73 while bringing the discharge potential terminal member 73 into contact with the discharge potential pad 113 (see FIG. 6) of the sensor element 100 in the insertion hole 71c. Yes. At the same time, the first insulating member 71 electrically insulates the discharge potential terminal member 73 from the inner cylinder 80.

  Further, the second insulating member 72 holds the first heater terminal member 76 while bringing the first heater terminal member 76 into contact with the first heater pad 136 of the sensor element 100 in the second insertion hole 72d. Yes. Further, the second insulating member 72 holds the second heater terminal member 77 while bringing the second heater terminal member 77 into contact with the second heater pad 137 of the sensor element 100 in the second insertion hole 72d. Yes. At the same time, the second insulating member 72 electrically connects the first heater terminal member 76 and the second heater terminal member 77 to the sensor GND connection fitting 82 (a cylindrical member connected to the rear end portion 80k of the inner cylinder 80). Insulated.

  The discharge potential lead wire 161 is inserted into the first insertion hole 72 c of the second insulating member 72. One end portion 161 t of the discharge potential lead wire 161 is connected to the discharge potential terminal member 73. Thereby, the discharge potential terminal member 73 is set to the discharge potential PV2, and the discharge potential pad 113 connected to the discharge potential terminal member 73 is also set to the discharge potential PV2.

Further, the first heater terminal member 76 is connected to one end 163t of the first heater lead wire 163 in the second insertion hole 72d. As a result, the first heater terminal member 76 is set to the first heater potential PVht, and the first heater pad 136 connected to the first heater terminal member 76 is also set to the first heater potential PVht.
Further, the second heater terminal member 77 is connected to one end 164t of the second heater lead 164 in the second insertion hole 72d. Thus, the second heater terminal member 77 is set to the chassis GND potential CGND, and the second heater pad 137 connected to the second heater terminal member 77 is also set to the chassis GND potential CGND.

  The rear end portion 80k of the inner cylinder 80 is fitted with a tip end portion 82s of a sensor GND connection fitting 82 having a cylindrical shape and is laser-welded. The sensor GND connection fitting 82 is provided around the first insulating member 71 and the second insulating member 72 (more specifically, the third insulating member that houses and holds the first insulating member 71 and the second insulating member 72 therein). The periphery of the member 172 is surrounded. The rear end portion 82k of the sensor GND connection fitting 82 is caulked on the inner side in the radial direction, and supports the second insulating member 72 located on the inner side in the radial direction.

  Further, the outer outer conductor 165G1 of the outer conductor 165G of the electric wire 165 is electrically connected to the sensor GND connection fitting 82 through the first connection member 99. As shown in FIG. 4, the first connection member 99 includes a grip portion 99b that inserts and grips the outer conductor 165G1, and an extending portion 99c that extends from the grip portion 99b to the distal end side GS. The grip portion 99b includes a cylindrical portion 99d having a substantially cylindrical shape partially interrupted in the circumferential direction, and a pair of plate-like portions extending in parallel while being separated from a portion where the circumferential portion of the cylindrical portion 99d is interrupted. 99f. The pair of plate-like portions 99f are formed with holes through which the shaft portion 98b of the rivet 98 is inserted. Accordingly, in the state where the outer conductor 165G1 is inserted into the cylindrical portion 99d of the grip portion 99b, the shaft portion 98b of the rivet 98 inserted through the holes of the pair of plate portions 99f is crimped, and the pair of plate portions 99f. By tightening (approaching), the cylindrical portion 99d can be brought into close contact with the outer conductor 165G1 while reducing the diameter. In this way, the outer conductor 165G1 can be gripped by the grip portion 99b.

  As described above, with the outer conductor 165G1 held by the holding portion 99b, the tip 99s of the extending portion 99c of the first connection member 99 is connected to the rear end 82k of the sensor GND connection fitting 82, The external conductor 165G1 is electrically connected to the sensor GND connection fitting 82. Accordingly, the inner cylinder 80, the metal shell 50, and the protector 45 that are electrically connected to the sensor GND connection fitting 82 are all set to the sensor GND potential SGND.

  Further, a metal cylinder 85 is fitted and welded inside the small diameter portion 96 on the rear end side GK in the outer cylinder 95. Further, a fluoro rubber grommet 84 is disposed inside the cylindrical body 85, and electric wires 165, 167, 168 are inserted through the through holes of the grommet 84. An O-ring 86 is interposed between the small diameter portion 96 of the outer cylinder 95 and the cylinder 85.

  Further, of the outer conductor 165G of the electric wire 165, the outer outer conductor 165G2 is electrically connected to the outer cylinder 95 through the grip member 89 and the third connection member 87. As shown in FIG. 4, the gripping member 89 is parallel to the cylindrical portion 89d having a substantially cylindrical shape in which a part in the circumferential direction is interrupted and a portion in which a part in the circumferential direction of the cylindrical portion 89d is interrupted. And a pair of plate-like portions 89f extending in the direction. The pair of plate-like portions 89f are formed with holes through which the shaft portion 88b of the rivet 88 is inserted.

  Further, as shown in FIG. 4, the third connecting member 87 includes a flat plate-shaped contact portion 87b that contacts the plate-shaped portion 89f of the gripping member 89, and a flat plate-shaped extension that bends and extends from both ends of the contact portion 87b. It has existing portions 87c and 87d. A hole through which the shaft portion 88b of the rivet 88 is inserted is formed in the contact portion 87b. The extending portions 87 c and 87 d are portions connected to the inner peripheral surface of the outer cylinder 95.

  Accordingly, the outer conductor 165G2 is inserted into the cylindrical portion 89d of the gripping member 89, and the pair of plate-like portions 89f is in a state where the plate-like portion 89f of the gripping member 89 is in contact with the contact portion 87b of the third connecting member 87. And the shaft portion 88b of the rivet 88 inserted through the hole of the contact portion 87b and the pair of plate-shaped portions 89f are tightened (approached), thereby reducing the diameter of the cylindrical portion 89d and reducing the diameter of the outer conductor 165G2. Can be in close contact with. In this way, the external conductor 165G2 can be gripped by the gripping member 89, and the gripping member 89 can be connected (coupled) to the third connection member 87.

  The extending portions 87 c and 87 d of the third connection member 87 are connected to the inner peripheral surface of the outer cylinder 95, so that the outer conductor 165 G 2 is electrically connected to the outer cylinder 95. As a result, the outer cylinder 95, the mounting bracket 90 that conducts to the outer cylinder 95, and the exhaust pipe EP are all set to the chassis GND potential CGND that is insulated from the sensor GND potential SGND. The chassis GND potential CGND is common to the GND potential of the battery BT (see FIG. 5) mounted on the vehicle AM, as described above.

  Next, the sensor element 100 will be described in detail. As shown in FIGS. 6 and 7, the sensor element 100 has a plate shape extending in the axial direction GH and includes a ceramic base 101 made of an electrical insulating material (specifically, alumina). In the ceramic substrate 101, a discharge electrode body 110 and a heater 130 are embedded and sintered integrally.

  More specifically, the ceramic base 101 has three ceramic layers 102, 103, and 104 made of alumina derived from an alumina green sheet, and the ceramic layers 102 and 103 are made of alumina formed by printing. An insulating coating layer 105 is interposed. A discharge electrode body 110 is disposed between the ceramic layer 102 and the insulating coating layer 105. Further, an insulating coating layer 106 made of alumina formed by printing is interposed between the ceramic layer 103 and the ceramic layer 104. A heater 130 is disposed between the insulating coating layer 106 and the ceramic layer 104. And these are integrated and the sensor element 100 is formed.

  The discharge electrode body 110 has a form extending in the axial direction GH. The discharge electrode body 110 includes a needle electrode portion 112 made of a platinum wire, and a lead portion 111 that conducts to the needle electrode portion 112. The lead portion 111 is formed on the other surface 102S2 of the ceramic layer 102 by pattern printing. Further, the lead portion 111 and the buried portion 112A on the rear end side GK of the needle electrode portion 112 are buried in the ceramic base 101 (specifically, between the ceramic layer 102 and the ceramic layer 103). ing. Further, the lead portion 111 is discharged from one end 102b of the ceramic layer 102 through the through-hole conductor formed in the through-hole 102h penetrating the ceramic layer 102 from the end portion 111b on the rear end side GK. Conductive to the potential pad 113.

  On the other hand, the tip-side GS portion of the needle-like electrode portion 112 is a discharge portion 112B that is exposed to the outside of the ceramic base 101 in a form that protrudes from the tip 101S of the ceramic base 101 to the tip-side GS (see FIG. 6). ). A portion of the discharge portion 112B on the tip side GS is a tapered needle-like tip portion 112S.

  A heater 130 is formed on one surface 104S1 of the ceramic layer 104 by pattern printing. The heater 130 includes a heat generating part 131 disposed on the front end side GS of the sensor element 100, and two heater lead parts (first heater lead) that are connected to the heat generating part 131 and extend to the rear end side GK of the sensor element 100. Part 132 and a second heater lead part 133). The heater 130 is formed on one surface 104S1 of the ceramic layer 104 and is covered with an insulating coating layer 106. Accordingly, the heater 130 (the heat generating portion 131, the first heater lead portion 132, and the second heater lead portion 133) is embedded in the ceramic base 101 (specifically, between the ceramic layer 103 and the ceramic layer 104). ing.

  The first heater lead portion 132 is formed on the other surface 104S2 of the ceramic layer 104 from the end portion 134 on the rear end side GK through a through-hole conductor formed in the through-hole 104h1 penetrating the ceramic layer 104. The first heater pad 136 is electrically connected. Further, the second heater lead portion 133 is formed on the other surface 104S2 of the ceramic layer 104 from the end portion 135 on the rear end side GK through a through-hole conductor formed in the through-hole 104h2 that penetrates the ceramic layer 104. The second heater pad 137 is conducted.

Next, the electrical function and operation of the particulate detection system 1 will be described.
The discharge electrode body 110 of the sensor element 100 is connected to the ion source power supply circuit 210 of the control device 200 through the discharge potential lead wire 161 (see FIG. 5). The heater 130 is connected to the heater energization circuit 226 of the control device 200 through the first and second heater lead wires 163 and 164.

  Further, the outer conductor 165G1 inside the electric wire 165 is connected to the first output terminal 211 of the ion source power supply circuit 210 in the control device 200, and is set to the sensor GND potential SGND. Further, the protector 45 disposed around the sensor element 100 via the sensor GND connection fitting 82 and the like that are electrically connected to the external conductor 165G1 is also set to the sensor GND potential SGND.

  Here, a positive high voltage (for example, 1 to 2 kV) discharge potential PV2 is output by the ion source power supply circuit 210, and the discharge electrode is discharged through the discharge potential lead wire 161, the discharge potential terminal member 73, and the discharge potential pad 113. A discharge potential PV <b> 2 is applied to the needle electrode part 112 of the body 110. Then, air discharge (specifically, corona discharge) is performed between the discharge portion 112B of the needle electrode portion 112 and the protector 45 (reference potential member) that is set to the sensor GND potential SGND (reference potential). As a result, ions CP (positive ions) are generated around the discharge part 112B (see FIG. 8).

  As described above, the exhaust gas EG is taken into the protector 45 through the gas intake port 45I. Therefore, as shown in FIG. 8, the ions CP generated around the discharge portion 112B adhere to the fine particles S in the intake exhaust gas EGI, and become the charged fine particles SC in which the fine particles S are positively charged. As described above, since the air flow of the intake exhaust gas EGI from the rear end side GK to the front end side GS is generated inside the protector 45, the charged fine particles SC are discharged together with the intake exhaust gas EGI. It flows toward the outlet 45O and is discharged to the outside of the protector 45 through the gas discharge port 45O.

  On the other hand, among the generated ions CP, the floating ions CPF (see FIG. 8) that did not adhere to the fine particles S adhere to each part of the protector 45 (collecting electrode). Thereby, the floating ions CPF are collected by the protector 45, and the floating ions CPF can be prevented from being discharged to the outside of the protector 45 through the gas 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 gas discharge port 45O. The signal current Is flows between the sensor GND potential SGND (the potential of the protector 45 and the like) and the chassis GND potential CGND (the potential of the exhaust pipe EP and the like). Thereby, the amount (concentration) of the fine particles S contained in the exhaust gas EG can be detected.

  As described above, in this embodiment, the protector 45 arranged around the sensor element 100 is set to the sensor GND potential SGND, and a corona discharge is generated between the protector 45 and the discharge portion 112B of the discharge electrode body 110. Let Further, this protector 45 is also used as a collecting electrode for collecting floating ions CPF. In other words, in this embodiment, the collection potential for collecting the floating ions CPF by the protector 45 (collection electrode) is equal to the sensor GND potential SGND.

  Further, in the present system 1, the heater 130 is energized through the first heater pad 136 and the second heater pad 137 by the heater energization circuit 226 of the measurement control circuit 220 of the control device 200 (the first heater pad 136 and the second heater pad 136). When a predetermined heater energizing voltage is applied between the heater pads 137), the heat generating portion 131 of the heater 130 generates heat, and the sensor element 100 can be heated. Thereby, the foreign material adhering to the sensor element 100 can be removed.

  In this embodiment, a voltage obtained by pulse-controlling a 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 as the heater energization voltage. Specifically, the first heater potential PVht applied to the first heater pad 136 through the first heater lead wire 163 and the first heater terminal member 76 is the positive side obtained by pulse-controlling the battery voltage (DC 12V or 24V). Potential. Further, the second heater potential applied to the second heater pad 137 through the second heater lead wire 164 and the second heater terminal member 77 is the chassis GND potential CGND common to the GND potential of the battery BT (FIG. 5). reference).

  By the way, in the fine particle sensor 10 of the present embodiment, the entire gas inlet 45I of the protector 45 (gas intake pipe) is disposed on the rear end side GK with respect to the front end 112BS of the discharge portion 112B of the discharge electrode body 110 ( (See FIG. 8). The gas intake 45I of the protector 45 is disposed on the rear end side GK of the protector 45, and the gas discharge port 45O of the protector 45 is disposed on the front end side GS of the protector 45. Therefore, the exhaust gas EG (measured gas) taken into the protector 45 through the gas inlet 45I flows toward the tip side GS, but the discharge electrode body 110 in the inner space K of the protector 45 is provided. The discharge portion 112B passes through the discharge portion surrounding space SK (see FIG. 8). For this reason, the ions CP generated around the discharge part 112B by corona discharge (air discharge) easily adhere to the fine particles S contained in the exhaust gas EG taken into the protector 45 through the gas inlet 45I.

  Further, the ions CP generated around the discharge part 112B by the corona discharge also tend to flow toward the front end side GS along with the flow of the exhaust gas EG, and therefore are positioned on the rear end side GK of the discharge part 112B. It becomes difficult for the gas CP to be discharged to the outside of the gas intake pipe through the gas inlet 45I, and the ions CP are more easily attached to the fine particles S.

  Moreover, in the fine particle sensor 10 of the present embodiment, the entire gas inlet 45I of the protector 45 is disposed on the rear end side GK with respect to the rear end 112BK of the discharge portion 112B (see FIG. 8). As a result, the ions CP generated around the discharge part 112B by corona discharge are less likely to be discharged to the outside of the protector 45 through the gas inlet 45I, so that the ions CP easily adhere to the fine particles S.

  Further, in the fine particle sensor 10 of the present embodiment, as shown in FIGS. 9 and 10, a guide body 45 </ b> G is provided at the gas inlet 45 </ b> I of the protector 45. 9 is a cross-sectional view of the protector 45 taken at the position BB in FIG. FIG. 10 is an enlarged view of part C in FIG. The guide body 45G generates a swirl flow SF (see FIG. 11) in which the exhaust gas EG (measured gas) taken into the protector 45 through the gas intake port 45I swirls around the discharge portion 112B. In addition, the exhaust gas EG is guided to the inside of the protector 45.

  Specifically, for a part of the cylindrical side wall portion of the protector 45, a U-shape comprising two cuts extending in parallel to the circumferential direction and a cut extending in the axial direction GH connecting the two cuts. The guide body 45G is formed and the gas intake port 45I is formed by bending a portion surrounded by the cut (a portion to be the guide body 45G) and bending the portion inward in the radial direction of the protector 45 ( 9 and 10). The guide body 45G extends from the side wall portion of the protector 45 in a direction orthogonal to the axial direction GH. In this embodiment, the gas inlets 45I (guide bodies 45G) are provided at eight positions at equal intervals in the circumferential direction of the protector 45.

  Accordingly, the guide body 45G guides the exhaust gas EG to the inside of the protector 45, and generates a swirling flow SF in which the exhaust gas EG taken into the protector 45 swirls around the discharge portion 112B (see FIG. 11). Thus, by generating the swirl flow SF of the exhaust gas EG swirling around the discharge part 112B, the ions CP generated around the discharge part 112B come into contact (adhesion) with the fine particles S contained in the exhaust gas EG. Since the opportunity to do so can be increased, a large number of ions CP can be attached to the fine particles S. Thereby, the signal current Is flowing according to the amount of ions CP adhering to the fine particles S (charge amount of the discharged ions CPH) can be increased, and the sensitivity of the fine particle sensor 10 can be improved.

  Further, in the fine particle sensor 10 of the present embodiment, the internal space of the protector 45 is between the cylindrical discharge peripheral portion 45H surrounding the discharge portion 112B of the protector 45 and the discharge portion 112B of the discharge electrode body 110. Only K (discharge part surrounding space SK) exists (see FIGS. 2 and 8). That is, no other member exists between the discharge part 112B of the discharge electrode body 110 and the discharge peripheral part 45H of the protector 45. For this reason, it becomes possible to generate the ions CP over the entire periphery (360 °) of the discharge part 112B. Thereby, the ions CP easily adhere to the fine particles S contained in the exhaust gas EG (measured gas) swirling around the discharge part 112B.

  Further, in the fine particle sensor 10 of the present embodiment, the gas inlet 45I described above is provided with an opening through which the exhaust gas EG (gas to be measured) and the ions CP can pass between the outside and the inside of the protector 45 (gas intake pipe). And only the gas discharge port 45O (see FIGS. 1, 2, and 8). Further, the gas discharge port 45 </ b> O is disposed at the tip of the protector 45. Therefore, in the protector 45 of the particle sensor 10 of the present embodiment, the entire gas inlet 45I is located on the rear end side GK with respect to the tip 112BS of the discharge part 112B, and the gas discharge port 45O is located on the tip of the protector 45. In the protector 45, there is no opening through which the exhaust gas EG and the ions CP can be discharged to the outside from the tip 112BS of the discharge portion 112B to the gas discharge port 45O located at the tip of the protector 45. (See FIG. 8).

  For this reason, the exhaust gas EG and the ions CP flowing to the front end GS of the protector 45 are discharged to the outside of the protector 45 until reaching the gas discharge port 45O located at the front end of the protector 45. Can be prevented. Thereby, in the inside of the protector 45 (internal space K), the chance that the fine particles S contained in the exhaust gas EG and the ions CP come into contact can be increased, and more ions CP can be attached to the fine particles S. It becomes possible.

  As described above, in the fine particle sensor 10 of the present embodiment, more ions CP can be attached to the fine particles S inside the protector 45 (internal space K), so that the sensitivity of the fine particle sensor 10 is improved. Can do.

  In addition, as described above, the particle sensor 10 of the present embodiment has an annular shape around the radial direction of the protector 45 (specifically, the rear end side tubular portion 45t in which the gas intake port 45I of the protector 45 is formed). A cylindrical wall portion 93 is provided to surround the gap. The outside of the gas inlet 45I (the radially outer side of the protector 45) is covered with this cylindrical wall portion 93 (see FIG. 8). That is, when the protector 45 is viewed from the outside in the radial direction (a direction orthogonal to the axial direction GH), the gas intake port 45I is disposed at a position where it is hidden behind the cylindrical wall portion 93 and cannot be seen. For this reason, when water (water droplets) scatters from the outside of the protector 45 toward the gas intake port 45I, the cylindrical wall portion 93 prevents the water (water droplets) from entering the gas intake port 45I. It becomes possible. Thereby, the said water (water droplet) becomes difficult to enter the inside of the protector 45 through the gas inlet 45I.

(Sensor sensitivity comparison test)
Next, the sensitivity of the particle sensor 10 of the example and the particle sensor 310 of the comparative example were compared. The particulate sensor 310 of the comparative example is different from the particulate sensor 10 of the embodiment only in the form of the gas inlet of the protector, and the others are the same. Specifically, the protector 345 of the particulate sensor 310 of the comparative example has only a circular through-hole penetrating the side wall of the protector 345 as a gas intake at the same position as the gas intake 45I of the protector 45 of the embodiment. The guide body is not provided.

Specifically, first, the particulate sensor 10 is mounted on a test exhaust pipe (venting pipe), and an exhaust gas (measuring gas) containing particulates (specifically, soot) is caused to flow through the exhaust pipe to generate a signal. The magnitude of the signal current Is detected by the current detection circuit 230 is grasped. In this test, the concentration (pA) of the signal current Is with respect to each fine particle concentration was measured by varying the fine particle (soot) concentration (mg / m ³ ) of the exhaust gas flowing through the exhaust pipe. The measurement was performed in the same manner for the fine particle sensor 310 of the comparative example. In this test, the fine particle concentration (mg / m ³ ) of the exhaust gas flowing in the exhaust pipe is measured by a micro soot sensor manufactured by AVL.

The test results are shown in FIG. FIG. 12 is a correlation diagram between the fine particle concentration (mg / m ³ ) of the exhaust gas and the magnitude (pA) of the signal current Is. In FIG. 12, the data (measured values) of the example is plotted with a square, and the data of the comparative example is plotted with a rhombus. In FIG. 12, the regression line L1 (correlation line) obtained by the least square method for the data of the example is shown by a solid line, and the regression line L2 (correlation line) obtained by the least square method for the data of the comparative example by a broken line. Show.

  As can be seen from FIG. 12, when the exhaust gas having the same fine particle concentration flows through the exhaust pipe, the signal current Is is larger in the fine particle sensor 10 of the embodiment than in the fine particle sensor 310 of the comparative example. That is, the fine particle sensor 10 of the example is more sensitive than the fine particle sensor 310 of the comparative example. More specifically, the slope of the regression line L1 (correlation line) of the example was about 1.5 times the slope of the regression line L2 (correlation line) of the comparative example. Therefore, it can be said that the fine particle sensor 10 of the example has about 1.5 times the sensitivity as compared with the fine particle sensor 310 of the comparative example. It can be said that such a difference in sensitivity is caused by a difference in the shape of the gas inlet of the protector.

  Specifically, in the particulate sensor 310 of the comparative example, the gas inlet of the protector 345 (gas intake pipe) is a circular through hole that penetrates the side wall of the protector 345 without providing a guide body. For this reason, as shown in FIG. 13, the exhaust gas taken into the protector 345 through the gas inlet is mainly linear from the rear end side GK to the front end side GS around the discharge portion 112B. Will flow into.

  Here, FIG. 13 is a diagram simulating the flow of exhaust gas around the discharge part 112B in the internal space of the protector 345, and the protector 345 is orthogonal to the axial direction GH at a position on the tip side of the discharge part 112B. Fig. 2 shows the flow of exhaust gas at the position of the cut section. In FIG. 13, the flow direction of the exhaust gas is indicated by an arrow, and the linear flow of exhaust gas from the rear end side GK toward the front end side GS is indicated by dots (black dots).

  In the particulate sensor 310 of the comparative example, as shown in FIG. 13, the exhaust gas taken into the protector 345 through the gas intake is mainly from the rear end side GK to the front end side GS around the discharge portion 112B. Since it flows linearly toward the surface, it quickly passes around the discharge part 112B where ions are generated. For this reason, the ions generated around the discharge part 112B cannot be sufficiently brought into contact with the fine particles contained in the exhaust gas, and the ions can be sufficiently adhered to the fine particles contained in the exhaust gas. It is thought that it was not possible.

  On the other hand, in the fine particle sensor 10 of the embodiment, a guide body 45G is provided at the gas inlet 45I of the protector 45 (see FIGS. 9 and 10). The guide body 45G generates a swirl flow SF (see FIG. 11) in which the exhaust gas EG (measured gas) taken into the protector 45 through the gas inlet 45I swirls around the discharge portion 112B. As described above, the exhaust gas EG is guided into the protector 45. For this reason, as shown in FIG. 11, the flow of the exhaust gas taken into the protector 45 becomes a swirl flow SF swirling around the discharge part 112B around the discharge part 112B.

  Here, FIG. 11 is a diagram simulating the flow of exhaust gas around the discharge part 112B in the internal space of the protector 45, and the protector 45 is in a direction orthogonal to the axial direction GH at a position on the tip side of the discharge part 112B. Fig. 2 shows the flow of exhaust gas at the position of the cut section. In FIG. 11, the flow direction of the exhaust gas is indicated by arrows.

  In the fine particle sensor 10 of the embodiment, as shown in FIG. 11, by generating a swirl flow SF of exhaust gas swirling around the discharge part 112B inside the protector 45, ions generated around the discharge part 112B are generated. Can increase the chance of contact (adhesion) with the fine particles contained in the exhaust gas. For this reason, many ions can be attached to the fine particles. Accordingly, it is considered that the signal current Is flowing in accordance with the amount of ions attached to the fine particles can be increased as compared with the fine particle sensor 310 of the comparative example, and the sensitivity of the fine particle sensor 10 can be improved.

  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 sensor element 100 having the discharge electrode body 110 and the heater 130 is used as the sensor element. However, as a sensor element, in addition to the discharge electrode body 110 and the heater 130, a sensor element having an auxiliary electrode body having an auxiliary electrode portion on the distal end side may be used (see JP-A-2015-129712). . By applying an auxiliary potential having a predetermined potential (for example, a positive DC potential of 100 to 200 V) to the auxiliary electrode portion of the auxiliary electrode body, ions CP (positive ions) generated by the corona discharge described above are applied. Among these, the repulsive force toward the protector 45 (collecting electrode) on the radially outer side from the auxiliary electrode portion 122 can be applied to the floating ions CPF (see FIG. 8) that have not adhered to the fine particles S. Thereby, the floating ions CPF can be efficiently attached to each part of the collection electrode (protector 45) to assist the collection.

Moreover, in the Example, the plate-shaped ceramic laminated body which laminated | stacked the several ceramic layer in the thickness direction was illustrated as the ceramic base | substrate 101 which comprises the sensor element 100.
However, as a ceramic substrate, a ceramic substrate formed into a shape such as a rectangular column shape, a hexagonal column shape, a columnar shape, a cylindrical shape in addition to a plate shape may be used. For example, as a columnar or cylindrical ceramic substrate, a ceramic laminate in which a plurality of ceramic layers are laminated in an annual ring shape, or one or a plurality of ceramic sheets are wound in a spiral shape so that a plurality of ceramic layers are radially arranged. Examples include stacked ceramic laminates.

  In the embodiment, the cylindrical wall portion 93 located on the front end side GS of the mounting bracket 90 is inserted into the exhaust pipe EP so that the rear end of the gas intake pipe (protector 45) is formed by the cylindrical wall portion 93. It was set as the form which surrounds the outer periphery of the side cylindrical part 45t. However, the gas inlet pipe (the protector is not provided) without the cylindrical wall portion 93 surrounding the outer periphery of the rear end side cylindrical portion 45t of the protector 45 (without inserting the cylindrical wall portion 93 into the exhaust pipe EP). A cylindrical member (cylindrical wall portion) surrounding the outer periphery of 45) may be fixed to the distal end portion 50s of the metal shell 50 together with the gas intake pipe (protector 45).

1 Particle Detection System 10 Particle Sensor 45 Protector (Gas Intake Pipe)
45H Discharge peripheral portion 45I Gas inlet 45O Gas outlet 45G Guide body 50 Metal shell 80 Inner tube 90 Mounting bracket 93 Tubular wall portion 95 Outer tube 100 Sensor element 101 Ceramic substrate 110 Discharge electrode body 112 Needle electrode portion 112B Discharge portion 112BS Front end of discharge unit 112BK Rear end of discharge unit 130 Heater 200 Control device ENG Engine (Internal combustion engine)
EG Exhaust gas (measured gas)
EP exhaust pipe (venting pipe)
CGND Chassis GND potential (ground potential)
SGND sensor GND potential (first potential)
PV2 Discharge potential S Fine particle CP Ion CPF Floating ion GS Tip side (Axial tip side)
GK Rear end side (Axial rear end side)
GH Axial direction Is Signal current K Internal space SF of gas intake pipe Swirling flow

Claims (6)

A cylindrical gas intake pipe extending from the rear end side to the front end side;
A discharge part that generates an air discharge, and the discharge part is disposed inside the gas intake tube.
The gas intake pipe is located at the rear end side of the gas intake pipe, and is located at the gas intake port for taking in the gas to be measured containing fine particles into the gas intake pipe, and at the front end side of the gas intake pipe. A gas discharge port for discharging the gas to be measured to the outside of the gas intake pipe,
Ions generated around the discharge part by the air discharge are attached to the fine particles contained in the gas to be measured taken into the gas intake pipe through the gas intake, and the ions attached to the fine particles are attached. In a fine particle sensor that detects the fine particles in the gas to be measured using a signal current that flows according to the amount of ions,
The gas intake is
The whole is located on the rear end side than the front end of the discharge part,
A fine particle sensor comprising a guide body that guides the measurement gas into the gas intake pipe and generates a swirling flow in which the measurement gas taken into the gas intake pipe swirls around the discharge portion. The fine particle sensor according to claim 1,
The gas inlet is a particulate sensor, the entirety of which is located on the rear end side with respect to the rear end of the discharge part. The fine particle sensor according to claim 1 or 2,
The gas intake pipe is
As an opening through which the gas to be measured and the ions can pass between the outside and the inside of the gas intake pipe, the gas intake pipe has only the gas inlet and the gas outlet,
The gas discharge port is a fine particle sensor arranged at a tip portion of the gas intake pipe. The fine particle sensor according to any one of claims 1 to 3,
A cylindrical wall portion surrounding the gas intake pipe in the radial direction through a gap;
The particulate sensor is covered with the wall outside the gas intake. The fine particle sensor according to any one of claims 1 to 4,
A particulate sensor in which only the internal space of the gas intake tube exists between the discharge portion and a cylindrical discharge peripheral portion surrounding the discharge portion of the gas intake tube. The fine particle sensor according to any one of claims 1 to 5,
The fine particle sensor is attached to a metal vent pipe having a ground potential through which the gas to be measured flows.
The gas intake pipe has a first potential different from the ground potential;
The discharge unit is a discharge potential different from the ground potential and the first potential, and generates the air discharge between the gas intake pipe,
The fine particle sensor detects the amount of the fine particles in the gas to be measured using the signal current flowing between the first potential and the ground potential according to the amount of the ions attached to the fine particles. Particle sensor.

Images