JP2018119887A - PM sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PM sensor capable of minimizing the chance of leaving residual PM in cells after a regenerative process.SOLUTION: The present disclosure is directed at a PM sensor comprising: a porous material configured to have an exhaust gas introduced therein through an opening and provided with cell partition walls that accumulates thereon particulate matter contained in the exhaust gas; and a heater comprising a first heat generating section disposed on the porous material in the vicinity of the opening and a second heat generating section extending from the first heat generating section toward a direction away from the opening, where the first and second heat generating sections are used to heat the porous material to reduce temperature irregularity on the porous material in a flow direction of the exhaust gas.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a PM sensor having a porous body on which PM in exhaust gas is deposited.

  Conventionally, research and development of PM sensors for detecting the amount of PM in exhaust gas have been performed. This type of PM sensor includes, for example, a wall flow type porous body. A plurality of cells are typically formed in this porous body. More specifically, the first cell whose upstream side is sealed (closed) in the exhaust gas flow direction and the second cell whose downstream side is sealed are arranged so as to be adjacent to each other with the cell partition wall interposed therebetween. The PM sensor configured as described above is disposed in the exhaust pipe of the vehicle, and when the internal combustion engine of the vehicle is started, the exhaust gas passes through the porous body. At this time, PM is deposited on the cell partition walls.

  The porous body of the PM sensor is provided with at least a pair of electrodes facing each other in a direction substantially perpendicular to the flow direction of the exhaust gas. Several cell partitions are interposed between the electrodes, and a signal correlated with the amount of deposited PM is output from the electrode pair. Based on this output signal, the ECU used with the PM sensor derives the amount of PM in the exhaust gas.

  Further, the porous body is further provided with a heater for removing PM on the cell partition walls. The heater heats the porous body under the control of the ECU or the like and burns the accumulated PM (see, for example, Patent Document 1). This process may be referred to as a reproduction process.

Japanese Patent Laid-Open No. 2006-8863

  Generally, it is required that no PM remains in the cell after the regeneration process.

  An object of the present disclosure is to provide a PM sensor capable of suppressing PM from remaining in a cell after regeneration processing.

  One form of the present disclosure is a porous body into which exhaust gas is introduced from an opening, the porous body having cell partition walls in which particulate matter contained in the exhaust gas is deposited, and the porous body A heater having a first heat generating portion disposed in proximity to the opening, and a second heat generating portion extending in a direction away from the opening with the first heat generating portion as a reference. The heat generating part and the second heat generating part are directed to a PM sensor that reduces temperature unevenness in the flow direction of exhaust gas in the porous body by heating the porous body.

  According to the present disclosure, it is possible to provide a sensor capable of suppressing PM from remaining in a cell after regeneration processing.

FIG. 1 is a diagram illustrating an example of a PM sensor according to the present disclosure. FIG. 2 is a perspective view of the sensor unit of FIG. FIG. 3 is a perspective view showing a modification of the sensor unit of FIG.

  Hereinafter, the heating device of the present disclosure will be described in detail with reference to the drawings.

<1. Definition>
Table 1 below shows the meanings of acronyms and abbreviations used in the present embodiment.

  In each figure, the x-axis is the direction (centric direction) from the outside of the exhaust pipe E of the vehicle toward the center of the exhaust pipe E, and the flow of exhaust gas in the porous body 13A of the PM sensor 1 The direction (hereinafter simply referred to as the flow direction) is indicated. More specifically, the negative direction side of the x-axis indicates the upstream side in the flow direction, and the positive direction side indicates the downstream side in the flow direction.

  In FIG. 2, the y axis indicates the row direction of the cells arranged in a matrix, and the z axis indicates the column direction.

  Hereinafter, the flow direction x, the row direction y, and the column direction z may be described.

<2. Configuration of PM sensor>
In FIG. 1, the PM sensor 1 includes a case 11 attached to the exhaust pipe E and inserted into the exhaust pipe E (that is, the exhaust gas flow path), and a sensor unit 13.

  In the present disclosure, the case 11 includes a bottomed cylindrical inner case portion 11A and a cylindrical outer case portion 11B surrounding the cylindrical outer peripheral surface of the inner case portion 11A.

  In the inner case portion 11A, the downstream end (hereinafter referred to as the tip) in the flow direction x and the vicinity thereof protrude from the outer case portion 11B to the positive direction side of the x-axis. Further, an outlet 11C that discharges exhaust gas that has passed through the inner case portion 11A into the exhaust pipe E is formed at the tip of the inner case portion 11A. Furthermore, a plurality of inlets 11D are formed at intervals along the circumferential direction on the proximal end side of the inner case portion 11A (that is, the end portion on the opposite side to the distal end). From this inlet 11D, the exhaust gas guided through the flow path 11E formed by the outer peripheral surface of the inner case portion 11A and the inner peripheral surface of the outer case portion 11B is introduced into the inner case portion 11A. In FIG. 1, for convenience, reference numeral 11D is attached only to a single entrance.

  As illustrated in FIG. 2, the sensor unit 13 includes a porous body 13A, a plurality of electrode pairs (not shown), and at least one heater 13B.

  The porous body 13A is made of, for example, ceramics and has a rectangular parallelepiped outer shape. Such a porous body 13A is attached to the inner space of the inner case portion 11A (see FIG. 1) using, for example, a ceramic fibrous mat (not shown).

  More specifically, the porous body 13A has two end surfaces S1 and S3 that face each other in the x-axis direction, and four side surfaces S5, S7, S9, and S11 that connect the two end surfaces S1 and S3. In the present disclosure, it is assumed that the end surface S1 is on the negative direction side of the x axis and the end surface S3 is on the positive direction side of the x axis.

  In the porous body 13A, a plurality of cells partitioned by lattice-like cell partition walls are formed. The plurality of cells are arranged in a matrix in a plan view from the flow direction x, and are sealed (closed) at an end portion on the upstream side in the flow direction x. In addition, the plurality of cells are closed at the end on the downstream side in the flow direction x, and the second cell opens without being plugged at the end on the downstream side in the flow direction x. Cell C2. The first cell C1 and the second cell C2 are alternately provided in both the row direction y and the column direction z.

  In the present disclosure, a plurality of openings A are formed at positions facing the plurality of inlets 11D in the y-axis or z-axis direction on at least one of the four side surfaces S5 to S11 (for example, the side surface S5). With each opening A, each inlet 11D and each first cell C1 are in fluid communication.

  In FIG. 2, for convenience of illustration, one first cell is denoted by reference symbol C <b> 1 and one second cell is denoted by reference symbol C <b> 2. In FIG. 2, the inlet 11 </ b> D is indicated by a broken line for convenience of illustration.

  With the above configuration, the exhaust gas flowing into the inner case portion 11A from the inlet 11D is introduced from the opening A into the first cell C1 of the porous body 13A. Thereafter, the introduced exhaust gas passes through the cell partition wall that partitions the first cell C1, and then escapes to the second cell C2. Thereafter, the exhaust gas flows out from the opening of the second cell C2, and is discharged from the outlet 11C of the inner case portion 11A (see FIG. 1) to the exhaust pipe E.

  In the above process, most of the PM in the exhaust gas is deposited inside the first cell C1 and on the surface of the cell partition wall. Part of the PM may enter the pores of the cell partition wall.

  The plurality of electrode pairs (not shown) are, for example, flat conductors, and are provided in the cell partition so as to face each other in the column direction z with the cells C1 and C2 arranged in the row direction y interposed therebetween, for example. Each electrode pair constitutes a capacitor and outputs a signal indicating an electrostatic capacity correlated with the amount of PM deposited on the cell partition wall to an ECU (not shown).

  Note that the electrode pair is not a main part of the present disclosure, and a known technique can be applied. Moreover, when an electrode pair is shown in FIG. 2, the visibility of the heater 13B which is the principal part of this indication falls. For this reason, illustration of an electrode pair is abbreviate | omitted.

  The ECU includes a microcomputer or the like that operates in accordance with a program stored in advance. The ECU calculates the PM amount based on the output signal of the electrode pair described above. For example, when the calculated PM amount exceeds a predetermined reference value, the first described later At least energization control of the heater 13B is performed.

  The first heater 13B includes, for example, a linear resistor, and is provided on at least one side surface of the four side surfaces S5 to S11. However, the present invention is not limited to this, and the first heater 13B may be embedded directly below at least one of the four side surfaces S5 to S11. The first heater 13B is energized under the control of the control unit 15 to heat the porous body 13A. Here, the heating temperature is a temperature at which PM deposited on the cell partition walls can be combusted.

  Essentially, one first heater 13B is sufficient. However, in the present disclosure, since the temperature of the porous body 13A is measured as described later, it is preferable that there are a plurality of the porous bodies 13A.

  More specifically, the first heater 13B includes a first heat generating part 131A, a second heat generating part 131B, and a third heat generating part 131C. Each of the heat generating portions 131A to 131C is a resistor formed by printing or the like, and is a meandering pattern meandering in the example of FIG.

  131 A of 1st heat generating parts are arrange | positioned along the opening part A in the part close | similar to the opening part A in the porous body 13A when planarly viewed from either one of the y-axis direction or the z-axis direction.

  The second heat generating portion 131B is disposed in a portion relatively distant from the opening A in the porous body 13A when viewed in plan from the same direction as described above. Specifically, the second heat generating portion 131B extends in a direction away from the opening A with respect to the first heat generating portion 131A.

  The third heat generating portion 131C is disposed so as to face the first heat generating portion 131A in the x-axis direction across the opening A in the porous body 13A when viewed in plan from the same direction as described above.

  In the following description, the meandering pitch in the first heat generating part 131A, the second heat generating part 131B, and the third heat generating part 131C is referred to as a first meandering pitch, a second meandering pitch, and a third meandering pitch. In the present disclosure, the first meandering pitch is selected to be smaller than the second meandering pitch. Further, the first meandering pitch and the third meandering pitch are appropriately selected in consideration of temperature unevenness around the opening A in the porous body 13A.

  For convenience of explanation, the characteristics (specific resistance and density) of the first heat generating portion 131A, the second heat generating portion 131B, and the third heat generating portion 131C are the same except for the meandering pitch.

<3. Action / Effect>
As described above, in order to burn the PM deposited on the cell partition walls, the first heat generating portion 131A, the second heat generating portion 131B, and the third heat generating portion 131C generate heat by the energization control to the first heater 13B, and the porous body 13A is heated. Even during such regeneration processing, exhaust gas flows from the inlet 11D. This exhaust gas takes away the heat of the opening A of the porous body 13A and its surroundings.

  As described above, since the exhaust gas takes away heat, it is assumed that the characteristics (specific resistance, density, meandering pitch) of the first heat generating portion 131A, the second heat generating portion 131B, and the third heat generating portion 131C are the same. The temperature of the opening A and the vicinity thereof (hereinafter simply referred to as the vicinity of the opening) is lower than the temperature of the downstream portion in the exhaust gas flow direction in the porous body 13A than in the vicinity of the opening. As a result, in the first cell C1, PM may not remain in the portion corresponding to the vicinity of the opening A and may remain after the regeneration process.

  However, in the present disclosure, since the first meandering pitch is selected to be smaller than the second meandering pitch, the temperature in the vicinity of the opening A of the porous body 13A is set higher than the temperature of the downstream portion. I can do it. Therefore, even if the exhaust gas takes away the heat in the vicinity of the opening A, the temperature unevenness in the flow direction of the exhaust gas in the porous body 13A can be reduced, and the vicinity of the opening A is set to a temperature at which PM can burn. I can do it. Accordingly, it is possible to provide a sensor capable of suppressing PM from remaining in the cell after the regeneration process.

  Further, in the present disclosure, in each of the cells C1 and C2, PM can be deposited also on a portion on the negative direction side of the x axis with reference to the opening A of the porous body 13A. Such PM can be burned by the third heat generating portion 131C.

<4. Addendum>
In the above description, the meandering pitch in the first heat generating part 131A, the second heat generating part 131B, and the third heat generating part 131C is the first meandering pitch, the second meandering pitch, and the third meandering pitch. However, the present invention is not limited to this, and the first heat generating portion 131A, the second heat generating portion 131B, and the third heat generating portion 131C have other characteristics (specific resistances) as long as they have the same meandering pitch as illustrated in FIG. The temperature unevenness may be reduced by adjusting the density and meandering pitch) and making the heat generation amount of the first heat generating portion 131A larger than the heat generation amount of the second heat generating portion 131B.

  In the above description, the PM sensor 1 is a so-called capacitance type, but may alternatively be an electric resistance type.

  The sensor of the present disclosure can suppress PM from remaining in the cell after regeneration processing, and is suitable for in-vehicle use.

1 PM sensor 13A Porous body 13B Heater

Claims (4)

A porous body into which exhaust gas is introduced from an opening, and having a cell partition wall in which particulate matter contained in the exhaust gas is deposited;
A heater having a first heat generating portion disposed along the opening in the porous body, and a second heat generating portion extending in a direction away from the opening with reference to the first heat generating portion; With
PM sensor which reduces the temperature nonuniformity in the flow direction of the exhaust gas in the said porous body by said 1st heat generating part and said 2nd heat generating part heating the said porous body.   2. The PM sensor according to claim 1, wherein the first heat generating portion and the second heat generating portion have a first meander pitch and a second meander pitch smaller than the first meander pitch.   The PM sensor according to claim 1, wherein the first heat generating portion has a heat generation amount larger than a heat generation amount of the second heat generating portion.   2. The PM sensor according to claim 1, wherein the heater further includes a third heat generating portion disposed in the porous body so as to face the first heat generating portion with the opening interposed therebetween.

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