JP2018054377A - PM sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PM sensor having higher accuracy of detection.SOLUTION: Provided is a PM sensor 1 disposed inside an exhaust tube 202 of an internal combustion engine 100 so as to extend from the tube wall to the center of tube axis. The PM sensor 1 comprises: a sensor unit 20 for detecting the amount of particulate matter containing an exhaust gas; a cylindrical inner case 11 for accommodating the sensor unit 20 and having an exhaust gas introduction opening Hin2 on the tube wall side and an exhaust gas discharge opening Hout on the tube axis center side; a cylindrical outer case 12 for accommodating the inner case 11 and having an intake opening Hin1 for taking in the exhaust gas from the exhaust passage of the exhaust tube 202 at a position closer to the tube wall side than is the discharge opening Hout; and an exhaust gas flow channel Hm formed between the inner case 11 and the outer case 12 so as to lead to the introduction opening Hin2 from the intake opening Hin1 and having, at least in part, a guidance part Hma for distributing the exhaust gas in the circumferential direction of the inner case 11 or the outer case 12.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to PM sensors.

  A PM sensor is known as a sensor for detecting the amount of particulate matter (hereinafter referred to as “PM”) contained in exhaust gas of an internal combustion engine.

  For example, the PM sensor is disposed on the downstream side of the PM filter (for example, diesel particulate filter) in the exhaust passage, and is used for determining a failure of the PM filter. Further, the PM sensor is disposed, for example, upstream of the PM filter and is used for measuring the amount of PM discharged from the internal combustion engine.

  The PM sensor includes a porous filter disposed so as to block the passage of the exhaust gas taken in, and at least a pair of electrodes facing each other with the porous filter interposed therebetween. PM contained in the exhaust gas passing through the porous filter accumulates on the upstream surface of the porous filter. The PM sensor derives the amount of PM deposited on the porous filter based on the amount of change in the capacitance of the capacitor formed by the pair of electrodes (see, for example, Patent Document 1 and Patent Document 2).

JP 2012-241643 A JP 2006-008863 A

  By the way, in order to increase the detection accuracy of the PM amount in the PM sensor, it is desired to efficiently take the exhaust gas into the PM sensor.

  Accordingly, an object of the present invention is to provide a PM sensor with high detection accuracy by efficiently incorporating exhaust gas into the PM sensor.

  The main present invention for solving the above-mentioned problems is a PM sensor disposed in an exhaust pipe of an internal combustion engine so as to go from the pipe wall toward the center of the pipe axis, and detects the amount of particulate matter contained in the exhaust gas. A sensor unit; and the sensor unit; a cylindrical inner case having the exhaust gas inlet on the tube wall side and the exhaust gas exhaust port on the tube axis center side; and the inner case; A cylindrical outer case having an intake port for taking in the exhaust gas from the exhaust passage of the exhaust pipe closer to the tube wall than the exhaust port, and the inlet port from the intake port between the inner case and the outer case And a flow path for the exhaust gas having a guide part that distributes the exhaust gas in the circumferential direction of the inner case or the outer case at least partially.

  According to the PM sensor of the present invention, the detection accuracy of the PM amount can be further increased.

The figure which shows an example of the periphery structure of PM sensor which concerns on 1st Embodiment. The figure which shows an example of the whole structure of PM sensor which concerns on 1st Embodiment. The figure which shows an example of the flow path of the exhaust gas of PM sensor which concerns on 1st Embodiment The figure which shows an example of the detailed structure of the sensor part of PM sensor which concerns on 1st Embodiment. The figure which shows an example of the detailed structure of the sensor part of PM sensor which concerns on 1st Embodiment. The figure which shows an example of the flow path of the exhaust gas of PM sensor which concerns on 2nd Embodiment

  Hereinafter, the PM sensor 1 according to an embodiment will be described in detail with reference to the drawings.

  The L axis, the W axis, and the T axis in the drawings indicate the longitudinal direction, the width direction, and the height direction of the PM sensor 1, and the directions are orthogonal to each other. The positive direction side of the L-axis corresponds to the direction from the tube wall of the exhaust pipe 202 forming the exhaust passage P toward the center of the pipe axis, and the positive direction side of the W-axis is the direction downstream of the exhaust pipe 202. It corresponds to. Hereinafter, the positive direction side in the longitudinal direction L is referred to as the “front end side” or “the tube axis center side of the exhaust pipe 202”, and the negative direction side thereof is referred to as “the base end side” or “the pipe wall side of the exhaust pipe 202”. Called.

[PM sensor peripheral configuration]
FIG. 1 is a diagram illustrating a peripheral configuration of the PM sensor 1 according to the present embodiment. FIG. 1 shows an internal combustion engine 100, an exhaust system 200, and PM sensors 1a and 1b.

  The internal combustion engine 100 is typically a diesel engine. However, it can also be applied to gasoline engines other than diesel engines.

  The exhaust system 200 includes, for example, an exhaust pipe 202 that forms an exhaust passage P, an oxidation catalyst 204, and a PM filter 206. The oxidation catalyst 204 is provided upstream of the PM filter 206 in the exhaust passage P, and decomposes and removes carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas. The PM filter 206 is typically a diesel particulate filter.

  The PM sensors 1a and 1b are typically used for derivation of the PM accumulation amount in the PM filter 206, failure determination of the PM filter 206, and the like. In the present embodiment, the PM sensor 1 a provided on the upstream side of the PM filter 206 is used for derivation of the PM accumulation amount in the PM filter 206 and the like. Further, the PM sensor 1b provided on the downstream side of the PM filter 206 is used for failure determination of the PM filter 206 and the like.

  In addition, since PM sensor 1a and 1b in this embodiment have the same structure, below, it abbreviates as "PM sensor 1" and demonstrates. However, the PM sensor 1 may be disposed only on the upstream side or the downstream side with respect to the PM filter 206.

[PM sensor configuration]
Hereinafter, the PM sensor 1 according to the present embodiment will be described in detail with reference to FIGS. 2, 3, 4A, and 4B.

  FIG. 2 is a diagram illustrating an example of the overall configuration of the PM sensor 1 according to the present embodiment. Here, FIG. 2 shows a cross-sectional shape of the PM sensor 1 cut along a virtual plane parallel to the WL plane.

  FIG. 3 is a diagram illustrating an example of the flow path Hm in the PM sensor 1 according to the present embodiment. Here, FIG. 3 shows the outer surface of the inner case 11 with the outer case 12 removed.

  4A and 4B are diagrams illustrating an example of a detailed configuration of the sensor unit 20 of the PM sensor 1 according to the present embodiment.

  An arrow Q shown in FIGS. 2, 3, and 4 </ b> B represents a flow path of exhaust gas flowing through the PM sensor 1. In FIG. 2, the exhaust gas is taken into the PM sensor 1 from the intake port Hin <b> 1 and flows in order to the flow path Hm, the introduction port Hin <b> 2, the sensor unit 20, and the exhaust port Hout.

  The PM sensor 1 includes an inner case 11, an outer case 12, a support member 13, a mounting portion 14, and a sensor portion 20.

  Here, the inner case 11 is a member that accommodates the sensor unit 20 therein, and the outer case 12 is a member that accommodates the inner case 11 therein. The inner case 11 and the outer case 12 are attached by the attachment portion 14 so as to extend from the pipe wall of the exhaust pipe 202 toward the center of the pipe axis. The inner case 11 is welded inside the mounting portion 14 and has a structure in which the proximal end side is closed.

  The inner case 11 has a bottomed cylindrical shape, for example, and is arranged so that the central axis is along the longitudinal direction L. The inner case 11 accommodates the sensor unit 20 in a cylindrical shape. Further, the inner case 11 has a shape that protrudes from the distal end of the outer case 12 toward the distal end side in the longitudinal direction L.

  On the tube wall side of the inner case 11, an introduction port Hin <b> 2 for introducing exhaust gas into the sensor unit 20 from a flow path Hm formed between the inner case 11 and the outer case 12 is formed. Specifically, the introduction port Hin <b> 2 is a through-hole that penetrates the wall portion of the inner case 11, and a plurality of the introduction ports Hin <b> 2 are formed along the circumferential direction of the cylinder of the inner case 11.

  An exhaust port Hout for exhausting the exhaust gas introduced into the sensor unit 20 is formed on the tube axis center side of the inner case 11. More specifically, the exhaust port Hout is provided as one through port having a diameter smaller than the inner diameter of the inner case 11 at the approximate center of the bottom surface position of the inner case 11 on the tube axis center side. The exhaust port Hout is configured, for example, so as to be positioned near the center of the tube axis of the exhaust pipe 202 (details will be described later) so that the intake negative pressure is applied to the intake port Hin1.

  The outer case 12 has, for example, a cylindrical shape and is arranged so that the central axis is along the longitudinal direction L. More specifically, the outer case 12 accommodates the inner case 11 so that the central axis of the inner case 11 and the central axis of the outer case 12 coincide. The inner diameter of the outer case 12 is larger than the outer diameter of the inner case 11, and the outer case 12 accommodates the inner case 11 so as to be separated from the outer surface of the inner case 11. That is, an exhaust gas flow path Hm is formed between the inner surface of the outer case 12 and the outer surface of the inner case 11.

  An intake port Hin <b> 1 for taking in the exhaust gas from the exhaust passage P is formed on the tube axis center side of the outer case 12. More specifically, the intake port Hin1 is formed with an opening in a direction intersecting the flow direction of the exhaust gas so as to communicate with the flow path Hm at the tip of the outer case 12. That is, the exhaust gas is taken into the intake port Hin1 in a state where the exhaust gas collides with the outer surface of the inner case 11 and decelerates.

  The inlet Hin1 and the flow path Hm are formed over the entire circumference of the outer case 12 in the circumferential direction of the cylinder. As a result, when the PM sensor 1 is attached to the exhaust pipe 202, the direction of the opening of the intake port Hin1 is deviated from the flow direction of the exhaust gas, and an individual difference for each PM sensor 1 occurs with respect to the exhaust gas intake amount. To prevent that.

  The intake port Hin <b> 1 of the outer case 12 is provided closer to the tube wall than the exhaust port Hout of the inner case 11. In other words, the exhaust port Hout is disposed closer to the center side of the tube axis of the exhaust pipe 202 than the intake port Hin1. Since the flow velocity of the exhaust gas flowing through the exhaust passage P is faster at the center of the tube axis than at the tube wall side of the exhaust tube 202, the intake Hind1 has an intake negative with respect to the exhaust port Hout. The pressure is applied (details will be described later).

  The flow path Hm includes a plurality of guide portions Hma that distribute exhaust gas in the circumferential direction of the inner case 11 or the outer case 12 (see FIG. 3). The guide portion Hma is unevenness formed on the outer surface of the inner case 11 or the inner surface of the outer case 12, and is formed so as to draw a spiral in this embodiment. The guide portion Hma has a role of making the pressure distribution in the circumferential direction of the flow path Hm uniform and increasing the intake amount of exhaust gas at the intake port Hin1 (details will be described later).

  The attachment portion 14 fixes the PM sensor 1 to the tube wall of the exhaust pipe 202. The attachment portion 14 is configured to include, for example, a male screw formed on the outer peripheral surface of the base end side portion of the PM sensor 1. The male screw of the mounting portion 14 is fitted into a female screw formed in the through-hole 202 a of the exhaust pipe 202 to fix the PM sensor 1 to the pipe wall of the exhaust pipe 202.

  The support member 13 supports the sensor unit 20 inside the inner case 11. For example, the support member 13 is provided on the inner peripheral surface of the cylindrical inner case 11 along the longitudinal direction L, and supports the sensor unit 20 so as to surround the entire periphery. The support member 13 is typically made of a fibrous mat having heat resistance.

  The sensor unit 20 collects PM contained in the exhaust gas and detects the amount of the PM (see FIGS. 4A and 4B).

  The sensor unit 20 according to the present embodiment includes a filter member 21, an electrode 22, and a heater 23.

  The filter member 21 collects PM in the exhaust gas taken into the inner case 11. The filter member 21 includes, for example, porous ceramics or ceramic partition walls in which fine through holes are formed, and forms a plurality of lattice-shaped cells partitioned along the longitudinal direction L. The filter member 21 is provided with partition walls so that the cells C1 with the upstream side plugged and the cells C2 with the downstream side plugged are alternately formed in a lattice pattern. In other words, the partition wall is interposed between the cell C1 whose upstream side is plugged and the cell C2 whose downstream side is plugged.

  The exhaust gas flows in from the cell C2 plugged on the downstream side, and flows through the partition wall of the filter member 21 to the cell C1 plugged on the adjacent upstream side. The PM contained in the exhaust gas is collected on the surface of the partition walls and the pores when the exhaust gas flows from the cell C2 whose downstream side is plugged into the cell C1 whose upstream side is plugged.

  A plurality of electrodes 22 (22a to 22e in FIGS. 4A and 4B) are arranged so as to face each other across the cells C1 and C2 of the filter member 21, and constitute a capacitor with the adjacent electrode 22 (hereinafter, “ Also referred to as “capacitor”). More specifically, each electrode 22 is a plate-like conductive member extending in the longitudinal direction L. Each electrode 22 is arranged in parallel so that the plate surface of the plate-like conductive member faces the plate surface of the other electrode 22 in the height direction T.

  A conductive wire (not shown) is connected to each electrode 22, and the conductive wire is drawn to a capacitance detection circuit (not shown) built in the control unit 30. And the electrostatic capacitance of a capacitor | condenser is detected in the said electrostatic capacitance detection circuit.

  The heater 23 (23a and 23b in FIGS. 4A and 4B) is, for example, a heating wire, and generates heat by energization to heat the filter member 21, thereby burning and removing PM deposited on the filter member 21 ( Hereinafter, it is also referred to as “sensor regeneration”). The heater 23 is made of a linear conductor and is inserted between the electrode 22 and the filter member 21 in a state of being embedded so as to meander in the insulating ceramic sheet.

  Conductive wires (not shown) are connected to both ends of each heater 23, and the conductive wires are drawn to a constant current power supply circuit (not shown) built in the control unit 30. The function of the heater 23 can be given to at least one electrode 22.

  The control unit 30 is, for example, a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

  The control unit 30 includes a PM amount deriving unit 30a and a sensor regeneration control unit 30b. The control unit 30 according to the present embodiment also includes a capacitance detection circuit that detects the capacitance of the capacitor and a power supply circuit that supplies a current to be passed through the heater 23.

  The PM amount deriving unit 30a estimates the PM amount contained in the exhaust gas based on the detected capacitance of the capacitor. The PM amount deriving unit 30a determines whether the amount of exhaust gas discharged from the engine 100 in the exhaust gas discharged from the engine 100 based on a change in the capacitance of the capacitor in a predetermined period (for example, a period from the end of the sensor regeneration process to the start of the next sensor regeneration). Estimate the total PM amount.

  At this time, the PM amount deriving unit 30a detects the capacitance of the capacitor based on the electric signal indicated by the capacitance detection circuit. For example, the change amount of the capacitance and the PM amount obtained in advance through experiments or the like are used. The amount of PM is estimated using a map showing the relationship. Further, the PM amount deriving unit 30a can also estimate the instantaneous PM amount in real time from the amount of change per unit time in the capacitance of the capacitor. Note that the calculation processing for detecting the PM amount from the capacitance of the capacitor is known in Japanese Patent Application Laid-Open No. 2006-008863 and the like by the present inventors, and therefore the description thereof is omitted here.

  The sensor regeneration control unit 30b energizes each heater 23 at a predetermined timing (for example, when the capacitance of the capacitor exceeds a predetermined value), and burns and removes PM deposited on the filter member 21. Then, the sensor regeneration control unit 30b continues the sensor regeneration process until the capacitance of the capacitor decreases to a predetermined capacitance that indicates complete removal of PM.

  The PM amount deriving unit 30a and the sensor regeneration control unit 30b are realized, for example, when the CPU refers to a control program or various data stored in a ROM, a RAM, or the like. However, the function is not limited to processing by software, and can of course be realized by a dedicated hardware circuit.

[PM sensor operation]
The exhaust gas discharged from the internal combustion engine 100 is processed by the oxidation catalyst 204 and the PM filter 206 and flows toward the downstream side of the exhaust passage P.

  Part of the exhaust gas flowing through the exhaust passage P flows into the PM sensor 1 via the intake port Hin1. At this time, the exhaust port Hout is disposed closer to the center side of the tube axis of the exhaust pipe 202 than the intake port Hin1, so that intake negative pressure acts on the intake port Hin1. More specifically, since the exhaust gas has a higher flow velocity toward the center of the tube axis of the exhaust pipe 202, the pressure at the intake port Hin1 is higher than the pressure at the exhaust port Hout located near the center of the tube axis of the exhaust pipe 202. Relatively negative pressure. Therefore, the exhaust gas is sucked into the intake port Hin1 and flows toward the exhaust port Hout via the sensor unit 20.

  Here, a spiral guide portion Hma is formed in the flow path Hm. Due to the shape of the guide portion Hma, at least a part of the exhaust gas spirally flows through the flow path Hm from the intake port Hin1 to the introduction port Hin2, and is distributed in the circumferential direction in the flow channel Hm. Accordingly, the pressure distribution in the circumferential direction becomes uniform in the flow path Hm, and the exhaust gas easily enters the intake port Hin1. This also makes it easier for the exhaust gas that has entered the downstream side of the outer case 12 to enter the intake port Hin1. In addition, the backflow of the exhaust gas once entering the intake port Hin1 is difficult to occur. As described above, it is possible to increase the intake amount of the exhaust gas at the intake port Hin <b> 1 and increase the introduction amount of the exhaust gas to the sensor unit 20 by the guide portion Hma.

  The exhaust gas flowing into the intake port Hin1 passes through the flow path Hm between the inner case 11 and the outer case 12, and flows into the inner case 11 from the inlet port Hin2. Thereafter, the exhaust gas flows into the cell C2 plugged on the downstream side formed in the filter member 21, and then passes through the partition wall and flows into the cell C1 plugged on the upstream side. It flows out from the exhaust port Hout. At this time, PM contained in the exhaust gas is collected in the partition wall of the cell C2, and the exhaust gas excluding the PM is discharged to the outside from the exhaust port Hout on the front end side.

  The PM amount deriving unit 30a, for example, in the exhaust gas from the internal combustion engine 100 based on the amount of change in capacitance from the capacitance of the capacitor when the sensor regeneration processing is performed by the sensor regeneration control unit 30b. Estimate the total PM amount.

  As described above, according to the PM sensor 1 according to the present embodiment, the exhaust gas is introduced when the exhaust gas is introduced into the sensor unit 20 through the flow path Hm while the amount of the exhaust gas taken into the intake port Hin1 is increased by the guide unit Hma. It has the structure which decelerates gas. Thus, by decelerating the exhaust gas when introduced into the sensor unit 20, PM contained in the exhaust gas can be reliably collected by the filter member 21, and the flow rate of the exhaust gas is changed. This can prevent the PM collection rate from fluctuating. Further, at that time, it is possible to increase the amount of PM collected by the filter member 21 by increasing the amount of exhaust gas taken into the intake port Hin1 by the guide portion Hma, substantially improving the resolution, Further, the sensitivity of the sensor can be improved, and the detection accuracy of the PM amount can be improved.

(Second Embodiment)
The PM sensor 1 according to the present embodiment is different from the first embodiment in that the guide portion Hma is formed only in a portion communicating with the intake port Hin1. Note that description of configurations common to the first embodiment is omitted.

  FIG. 5 is a diagram illustrating an example of the flow path Hm in the PM sensor 1 according to the present embodiment.

  The plurality of guide portions Hma formed in the flow path Hm according to the present embodiment distribute exhaust gas in the circumferential direction of the inner case 11 or the outer case 12, respectively, as in the first embodiment. However, the guide portion Hma according to the present embodiment is formed only in a portion communicating with the intake port Hin1. And the guide part Hma which concerns on this embodiment is formed so that a part of spiral may be drawn.

  Even with such a configuration, it is possible to make the pressure distribution in the circumferential direction uniform in the flow path Hm. As a result, similarly to the first embodiment, the amount of exhaust gas introduced into the sensor unit 20 can be further increased, and the PM amount detection accuracy can be improved.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be considered.

  In the said embodiment, the aspect formed so that a helix or a part of helix might be drawn was shown as an example of the guide part Hma. However, the guide portion Hma only needs to be able to make the pressure distribution in the circumferential direction uniform in the flow path Hm, and is formed on at least a part of the outer surface of the inner case 11 or the inner surface of the outer case 12 to surround the exhaust gas. Any shape that distributes in the direction may be used. In addition, the guide portion Hma may be configured as the shape of the inner case 11 or the outer case 12, or may be configured by attaching other members.

  Moreover, in the said embodiment, as an example of the inner case 11 and the outer case 12, the aspect which exhibits a similar cylindrical shape was shown. However, the inner case 11 and the outer case 12 may have other shapes such as an elliptical shape, and the inner case 11 and the outer case 12 may have shapes that are not similar.

  Moreover, in the said embodiment, the aspect formed in the bottom part of the front-end | tip of the inner case 11 was shown as an example of the exhaust port Hout. However, the exhaust port Hout may be formed at other positions such as the side surface on the downstream side of the inner case 11.

  Moreover, in the said embodiment, the electrostatic capacitance type sensor comprised by the filter member 21 and the electrode 22 was shown as an example of the sensor part 20. As shown in FIG. However, the sensor unit 20 may be of another type, for example, an electric resistance sensor that detects a change in resistance value by attaching PM to a resistance element.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  The PM sensor according to the present disclosure is useful as a sensor for detecting the amount of PM in the exhaust gas flowing through the exhaust passage of the internal combustion engine.

DESCRIPTION OF SYMBOLS 1 PM sensor 11 Inner case 12 Outer case 13 Support member 14 Mounting part 20 Sensor part 21 Filter member 22 Electrode 23 Heater 30 Control unit Hin1 Intake Hin2 Inlet Hm Flow path Hma Guide part Hout Exhaust outlet

Claims (6)

A PM sensor disposed in an exhaust pipe of an internal combustion engine from a pipe wall toward a pipe axis center,
A sensor unit for detecting the amount of particulate matter contained in the exhaust gas;
A cylindrical inner case that houses the sensor unit and has the exhaust gas introduction port on the tube wall side and the exhaust gas exhaust port on the tube axis center side;
A cylindrical outer case containing the inner case and having an intake port for taking the exhaust gas from the exhaust passage of the exhaust pipe closer to the tube wall than the exhaust port;
A guide portion is formed between the inner case and the outer case so as to communicate from the intake port to the introduction port and distributes the exhaust gas in the circumferential direction of the inner case or the outer case at least partially. The exhaust gas flow path;
PM sensor comprising: The PM sensor according to claim 1, wherein a plurality of the guide portions are formed along a circumferential direction of the inner case or the outer case. The PM sensor according to claim 1, wherein the guide portion is formed so as to draw a spiral or a part of the spiral along at least one of an outer surface of the inner case and an inner surface of the outer case. The inner case protrudes toward the tube axis center of the exhaust pipe from the tip of the outer case,
The PM sensor according to any one of claims 1 to 3, wherein the intake port is formed with an opening facing a front end of the outer case in a direction intersecting a flow direction of exhaust gas. The PM sensor according to any one of claims 1 to 4, wherein the intake port, the flow path, and the introduction port are disposed over the entire circumference of the inner case or the outer case. The said sensor part has a filter member which collects the particulate matter contained in exhaust gas, and at least a pair of electrodes which mutually oppose on both sides of at least one part of the said filter member. The PM sensor according to one item.

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