JP5874196B2 - Particulate matter sensor - Google Patents

Description

  The present invention relates to a PM sensor that can detect an average amount of PM deposited in the entire DPF, and can secure a sufficient capacitance for detection.

  In a vehicle equipped with an internal combustion engine such as a diesel engine, a diesel particulate filter (hereinafter referred to as DPF) is installed in an exhaust gas exhaust flow path from the internal combustion engine to the atmosphere, and particulate matter ( Particulate Matter (hereinafter referred to as PM) is collected. The DPF is a member that temporarily collects PM in a honeycomb pore filter made of porous ceramic.

  When the amount of PM collected in the DPF (hereinafter referred to as PM accumulation amount) increases, the exhaust pressure of the internal combustion engine rises and the characteristics of the internal combustion engine deteriorate, so the process of burning the collected PM is performed. Is called. This process is called DPF regeneration. During the DPF regeneration, fuel injection for increasing the exhaust temperature is performed. When the exhaust gas temperature rises, the DPF is heated up and the PM collected in the DPF burns.

  At this time, if the amount of accumulated PM is too large, the DPF is damaged by the heat during DPF regeneration. In order to regenerate the DPF before the PM accumulation amount becomes too large, it is necessary to accurately detect the PM accumulation amount.

  As a PM sensor for detecting the PM deposition amount, there is known a sensor in which two electrodes are installed in the DPF and the PM deposition amount is detected from the capacitance of a capacitor formed by the two electrodes. In this type of PM sensor, PM, which is a mixture of a dielectric and a conductor, is deposited between the electrodes, so that the capacitance increases linearly with respect to the amount of PM deposited.

  The conventional PM sensor 91 shown in FIG. 9 has two electrodes 93 and 94 formed in a half-cylindrical shape on the outer periphery of a columnar DPF 92. When the two electrodes 93 and 94 face each other with the DPF 92 interposed therebetween, the capacitance of the capacitor formed by the two electrodes 93 and 94 changes according to the total amount of PM deposited on the DPF 92 (Patent Document 1).

  In the conventional PM sensor 101 shown in FIG. 10, one electrode 103 is installed on the outer periphery of a cylindrical DPF 102, and the other electrode 104 is installed concentrically on the inner side. The capacitance of the capacitor formed by the two electrodes 103 and 104 changes according to the amount of PM deposited on a part of the DPF 102 sandwiched between the two electrodes 103 and 104 (Patent Document 2).

JP 2010-144630 A JP 2011-012577 A

  However, generally, the DPF is accommodated in a metal housing for protecting the DPF, and this housing is attached to the vehicle body. For this reason, a capacitor is also formed between the electrode installed on the outer periphery of the DPF and the housing.

  In the PM sensor 91 of FIG. 9, since the distance between the electrodes 93 and 94 and the housing 95 is significantly shorter than the distance between the two electrodes 93 and 94, the capacitance of the capacitor formed by the electrodes 93 and 94 and the housing 95 is 2. The capacitance of the capacitor by the two electrodes 93 and 94 is significantly larger. Furthermore, the capacitance of the capacitor formed by the electrodes 93 and 94 and the housing 95 is unstable both thermally and mechanically. As a result, the circuit of the PM sensor 91 is a circuit in which the electrodes 93 and 94 and the capacitor of the housing 95 are connected in parallel to the capacitor of the two electrodes 93 and 94. If the capacitor for which the PM deposition amount is to be detected has a capacitance that is significantly larger than that and an unstable capacitor is connected in parallel, the PM deposition amount cannot be detected accurately.

  In the PM sensor 101 of FIG. 10, the capacitance of the capacitor by the two electrodes 103 and 104 is increased by reducing the distance between the outer electrode 103 and the inner electrode 104. However, for that purpose, the inner electrode 104 is disposed near the outer periphery of the DPF 102, and the PM deposition amount in a part of the DPF 102 inside the inner electrode 104 cannot be detected. If the PM deposition amount is detected only in a part of the DPF 102 outside the inner electrode 104, the detected value may deviate from the average PM deposition amount of the entire DPF 102.

  Accordingly, an object of the present invention is to provide a PM sensor that solves the above-described problems, can detect the average amount of PM deposited in the entire DPF, and can secure a sufficiently large capacitance for detection. .

This onset Ming order to achieve the above object, based on the capacitance of the capacitor formed by inserting the first electrode and the second electrode into a plurality of cells of a diesel particulate filter of the diesel particulate filter In the particulate matter sensor for detecting the amount of particulate matter deposited , the diesel particulate filter is configured such that the plurality of cells are stacked vertically and horizontally, and the plurality of cells are walls made of a porous material and vertically and horizontally have four sides. The first electrode is arranged in a line on a diagonal line passing through the vicinity of the diameter of the diesel particulate filter, or the outer periphery of the diesel particulate filter is enclosed. Arranged in a line on a diagonal line that is not near, and the side of the plurality of cells where the electrode is inserted Inserted into the first open cell whose end face is not sealed, and the second electrode is arranged in two rows across the first electrode on a diagonal passing near the diameter of the diesel particulate filter Or arranged in two rows across the first electrode on a diagonal line that is not near the outer periphery of the diesel particulate filter, and an end surface on the side where the electrode is inserted among the plurality of cells Is inserted into a second open cell that is not sealed, and the first electrode and the second electrode are the first open cell and the second open cell among the plurality of cells. And an end face on the side where the electrode is inserted are arranged in parallel with a third open cell not sealed, and the third open cell is connected to the first electrode. Arranged with the second electrode A particulate matter sensor that is adjacent to each of the said first open cell in the direction the second open cell perpendicular to the diagonal direction of.

  The present invention exhibits the following excellent effects.

  (1) The average PM deposition amount of the entire DPF can be detected.

  (2) A sufficient capacitance can be secured for detection.

It is a partial end elevation of DPF to which the present invention is applied. It is a partial sectional side view of DPF to which the present invention is applied. It is a partial end view of a DPF to which a PM sensor devised in the process leading to the present invention is attached. It is a principal part enlarged view of FIG. It is a partial end view of a DPF to which a PM sensor devised in the process leading to the present invention is attached. It is a principal part enlarged view of FIG. It is a fragmentary end view of DPF with which PM sensor of the present invention was attached. It is a perspective view of DPF with which PM sensor of the present invention was attached. It is a perspective view of the conventional PM sensor. It is a perspective view of the conventional PM sensor.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  First, the structure and function of the DPF will be described as the basis of the present invention.

  As shown in FIG. 1, the DPF 1 includes a plurality of cells 3 that are vertically and horizontally surrounded by walls 2 made of a porous material, and the end surfaces of the cells 3 are alternately sealed vertically and horizontally. In the figure, the sealing is indicated by hatching. The sealed cell 3 is called a sealed cell 3a, and the unsealed cell is called an open cell 3b. As shown in the drawing, both vertical and horizontal neighbors of the sealed cell 3a are open cells 3b, and both vertical and horizontal neighbors of the open cell 3b are sealed cells 3a. In addition, although the end surface shape of the cell 3 is a square here, it may be a shape that can be continuously arranged, such as a rectangle or a parallelogram.

  Sealing and opening are reversed between the one end face and the opposite end face. That is, in one cell 3, if one end face is sealed, the opposite end face is always open, and if one end face is open, the opposite end face is always sealed. Therefore, the same cell 3 becomes a sealed cell 3a when viewed from one side, and becomes an open cell 3b when viewed from the opposite side.

  As shown in FIG. 2, the DPF 1 is installed in the exhaust gas discharge flow path, and one end face is desired upstream and the opposite end face is desired downstream. On the upstream side, exhaust gas does not flow into the sealing cell 3a, but exhaust gas flows only into the open cell 3b. Since the open cell 3b into which the exhaust gas has flowed is sealed at the opposite end face desired downstream to become a sealed cell 3a, the exhaust gas passes through the wall 2 made of a porous material and is adjacent to the sealed cell 3a. Move to. Since the adjacent sealing cell 3a has an open end cell 3b that is open at the opposite end face desired downstream, the exhaust gas flows out from the open cell 3b. In this way, when exhaust gas passes through the wall 2, PM in the exhaust gas is adsorbed on the wall 2 made of the porous material. In FIG. 2, it is shown that the exhaust gas flowing into one open cell 3b moves to two adjacent sealing cells 3a, but actually the exhaust gas flowing into one open cell 3b is adjacent vertically and horizontally. Since it moves to the four sealing cells 3a, PM is adsorbed on the four walls 2 in the vertical and horizontal directions.

  The inventor has devised the PM sensor 4 shown in FIG. 3 in the process leading to the present invention. This PM sensor 4 is provided with first and second electrodes 5 and 6 on the DPF 1, and the amount of PM deposited on the DPF 1 is detected by the capacitance of the capacitor formed by the first and second electrodes 5 and 6. Is.

  In the PM sensor 4, the first electrode 5 is inserted into a plurality of open cells 3b arranged in a diagonal line among all the open cells 3b, and adjacent to the plurality of open cells 3b into which the first electrode 5 is inserted. Thus, the second electrode 6 is inserted into the plurality of open cells 3b arranged in a line in the diagonal direction. Since the open cells 3b are arranged alternately with the plugged cells 3a, the open cells 3b adjacent to the open cells 3b are the open cells 3b adjacent to each other by skipping the plugged cells 3a vertically and horizontally. is there.

  The electrodes 5 and 6 inserted into the open cell 3b are, for example, metal wires. The plurality of first electrodes 5 inserted into the open cells 3 b in a row are short-circuited by a short-circuit line 7. Similarly, a plurality of second electrodes 6 inserted in another row of open cells 3 b are short-circuited by another short-circuit line 8. The depth at which the electrodes 5 and 6 are inserted from the end face is arbitrary, but as the electrodes are inserted deeper, the length of the electrodes 5 and 6 becomes longer, which contributes to an increase in the electrode facing area. Therefore, for example, it is preferable that the electrodes 5 and 6 reach near the place where the opposite end face of the open cell 3b is sealed.

  The end surface into which the electrodes 5 and 6 are inserted may be the end surface desired upstream of the exhaust gas discharge passage or the end surface desired downstream, but the electrodes 5 and 6 are inserted into the same end surface.

  In the PM sensor 4 of FIG. 3, attention is paid to one electrode P0 among the plurality of first electrodes 5. The second electrode 6 closest to the electrode P0 is an electrode Q0 on a diagonal line intersecting the column formed by the first electrode 5, and when the pitch (vertical and horizontal width) of the cells 3 is d, the pair of electrodes P0 The distance between Q0 is √2d. Therefore, the electrode P0 and the electrode Q0 form a capacitor having a distance between electrodes of √2d and an electrode facing area proportional to the electrode diameter. The second electrode 6 next closest to the electrode P0 is the electrodes Q + 1 and Q-1 positioned in the immediate vicinity of the electrode Q0 on the column formed by the second electrode 6, and the distance between the electrode P0 and Q ± 1 is 2d. Become. The electrode P0 and the electrode Q ± 1 form two capacitors having a distance between the electrodes of 2d and an electrode facing area proportional to the electrode diameter. Similarly, a capacitor is formed by the electrode P0 and a plurality of second electrodes 6 that are in order from the third and subsequent electrodes. A capacitor composed of a plurality of first electrodes 5 and a plurality of second electrodes 6 formed by combining them has a distance between electrodes of √2d and a parallel structure composed of two electrode plates having a predetermined electrode facing area. It can be regarded as a plate capacitor.

  The capacitor composed of the plurality of first electrodes 5 and the plurality of second electrodes 6 has a short inter-electrode distance of √2d as compared with the conventional PM sensors 91 and 101, so that the capacitance is large. Since 6 is away from the housing, it can be expected that the influence of the housing is reduced.

  In the PM sensor 4, metal wires are inserted into the open cells 3b as the electrodes 5 and 6, and the inserted metal wires ensure durability against high temperatures during DPF regeneration and mechanical vibration during vehicle travel. Therefore, a wire diameter that is somewhat thick is necessary. Considering the thickness and clearance of the wall 2 with respect to the pitch d of the cell 3, the wire diameter is determined as thick as possible.

  In FIG. 4, the end surface of DPF1 is further expanded and shown.

  Among the open cells 3b into which the electrodes 5 and 6 are inserted, the flow of exhaust gas flowing through the wall 2 from the plugged cells 3a is indicated by arrows for the open cells 3b of the electrodes P0 and Q0. This arrow is the arrow seen from the side section of FIG. 2 as seen from the end face. However, in actuality, exhaust gas flows into one open cell 3b through four vertical and horizontal walls 2 and from four vertical and horizontal plugged cells 3a. Here, the inside of the capacitor composed of electrodes 5 and 6 (between electrode plates). It is shown only for. As described above, since PM is adsorbed on the wall 2 when exhaust gas passes through the wall 2, PM is deposited on the wall 2 between the electrodes P0 and Q0. Similarly, in general open cells R in which the electrodes 5 and 6 are not inserted, exhaust gas flows from the four vertical and horizontal plugged cells 3a and PM is deposited on the walls 2 as well.

  At this time, since the electrodes 5 and 6 are inserted in the open cells 3b of the electrodes P0 and Q0, the flow rate of the exhaust gas is restricted as compared with the general open cells R and decreases. Assuming that the PM content in the exhaust gas is uniform regardless of the location, the amount of PM flowing is smaller at locations where the flow rate is smaller. Therefore, the wall 2 of the open cell 3b of the electrodes P0 and Q0 has a smaller PM deposition amount than the wall 2 of the general open cell R. This is common to the open cell 3b in which all the electrodes 5 and 6 are inserted. Therefore, when viewed in FIG. 3, the inner wall 2 of the capacitor composed of the electrodes 5 and 6 is the wall 2 having a small amount of PM deposited as described in FIG. On the other hand, all the open cells 3b into which the electrodes 5 and 6 are not inserted are the general open cells R described with reference to FIG. .

  As a result, the PM deposition amount detected by the PM sensor 4 is smaller than the PM deposition amount in the open cell R, and smaller than the average PM deposition amount of the entire DPF 1.

  Therefore, the present inventor devised the PM sensor 9 shown in FIG. 5 by devising the electrode arrangement so that the average PM deposition amount of the entire DPF 1 can be detected.

  The PM sensor 9 shown in FIG. 5 includes a first electrode 5 inserted into a plurality of open cells 3b arranged in a diagonal line among the open cells 3b, and each open cell 3b into which the first electrode 5 is inserted. The second electrode 6 is inserted into a plurality of open cells 3b arranged in a diagonal line including the second adjacent open cell 3b. The open cell 3b adjacent to the second is an open cell 3b adjacent to each other by skipping two plugged cells 3a and one open cell 3b vertically and horizontally.

  As shown in FIG. 6, in the PM sensor 9, there is one open cell 3b in which the electrodes 5 and 6 are not inserted between the open cell 3b in which the electrode P0 is inserted and the open cell 3b in which the electrode Q0 is inserted. Exists. That is, there is an open cell 3b in which the electrodes 5 and 6 are not inserted inside the capacitor composed of the electrodes 5 and 6. This is called a detection open cell S.

  The four walls 2 surrounding the detection open cell S are walls 2 in which the flow rate of the exhaust gas is not restricted, like the four walls 2 of the general open cell R. Therefore, the same amount of PM deposition as that of the open cell R is obtained in the detection open cell S.

  As shown in FIG. 5, since there is an open cell S for detection in which the PM deposition amount is the same as that of the open cell R inside the capacitor composed of the electrodes 5 and 6, the PM deposition amount detected by the PM sensor 9 is This can be regarded as the average PM deposition amount of the entire DPF1.

  However, in the PM sensor 9 shown in FIG. 5, the distance between the electrodes of the capacitor due to the electrodes 5 and 6 is 2√2d, and the distance between the electrodes of the capacitor due to the electrodes 5 and 6 is twice that of the PM sensor 4 in FIG. Therefore, the electrostatic capacity is halved.

  Therefore, the present inventor has arrived at the present invention by further devising the electrode arrangement so that the average PM deposition amount of the entire DPF 1 can be detected and the capacitance is increased. That is, as shown in FIG. 7, in the PM sensor 10 of the present invention, the first electrode 5 is inserted into a plurality of open cells 3b arranged in a diagonal line among the open cells 3b, and the first electrode 5 is The second electrode 6 is inserted into the plurality of open cells 3b arranged in a diagonal line including the open cells 3b adjacent to each other in the vertical and horizontal directions from the inserted open cells 3b. The second electrode 6 is also inserted into the plurality of open cells 3b arranged in a diagonal line including the open cells 3b adjacent to each other in the direction opposite to the one direction from the inserted open cells 3b.

  As shown in FIG. 8, in the PM sensor 10 of the present invention, short-circuit lines 8, 7, 8 along the row of open cells 3 b in which the electrodes 5, 6 are inserted are laid along the end face of the DPF 1. The longer the length of this row (the number of cells 3), the more the number of electrodes 5 and 6 increases, which contributes to an increase in the electrode facing area. For example, when the electrodes 5 and 6 are inserted into the open cells 3b so that the rows pass near the diameter of the cylindrical DPF 1, the number of the electrodes 5 and 6 is the largest. For example, if the diameter of the DPF 1 is 200 mm and the pitch (vertical / horizontal width) d of the cells 3 is 1 mm, nearly 140 cells 3 are diagonally arranged near the diameter, so that the open cells into which the electrodes 5 and 6 are inserted are arranged. 3b is close to 140 pieces each.

  Thus, the first and second electrodes 5 and 6 inserted into the open cell 3b of the DPF 1 are short-circuited by the short-circuit lines 8, 7, and 8, respectively, and the short-circuit lines 8, 7, and 8 are connected to a detection circuit (not shown). The The short-circuit wires 8 and 8 are short-circuited. Since the detection circuit is the same as the conventional one, the description thereof is omitted.

  Hereinafter, the operation of the PM sensor 10 of the present invention will be described.

  When PM is deposited in the DPF 1 in FIG. 8, the PM deposited on the wall 2 of the cell 3 between the plurality of first electrodes 5 and the plurality of second electrodes 6 also in the portion shown in FIG. 7. The amount increases. Therefore, the capacitance of the capacitor composed of the electrodes 5 and 6 is increased.

  At this time, in the PM sensor 10 of the present invention, the plurality of open cells 3b arranged in the diagonal line with the first electrode 5 inserted are arranged in the diagonal line with the second electrode 6 inserted. A plurality of open cells 3b are adjacent to each other with two plugged cells 3a and one open cell in the vertical and horizontal directions, and at the same time arranged in a diagonal line with the second electrode 6 inserted in the opposite direction. A plurality of open cells 3b are adjacent to each other with two plugged cells 3a and one open cell. As a result, the capacitor composed of one row of the first electrodes 5 and two rows of the second electrodes 6 has a distance between the electrodes of 2√2d and a parallel structure composed of three electrode plates each having a predetermined electrode facing area. It can be regarded as a plate capacitor.

  Since the PM sensor 10 of the present invention has a capacitor composed of one row of the first electrodes 5 and two rows of the second electrodes 6, the capacitance is twice that of the PM sensor 9 of FIG. 5, and the PM of FIG. A capacitance equivalent to that of the sensor 4 can be obtained. Moreover, in the PM sensor 10, the detection open cell S exists inside the capacitor composed of the electrodes 6, 5, 6. Therefore, the detected PM accumulation amount is larger than that of the PM sensor 4 of FIG. This can be regarded as an average amount of PM deposition.

  However, the number of the electrodes 5 and 6 is 1.5 times that of the PM sensor 9 in FIG. 5, but the capacitance is twice, so that the advantage is great.

  The number of rows of electrodes 5 may be increased to form a capacitor composed of two rows of first electrodes 5 and two rows of second electrodes 6. In this case, the number of the electrodes 5 and 6 is twice that of the PM sensor 9 in FIG. 5, but the capacitance is three times, so that the advantage is great. As the number of rows of electrodes 5 and 6 increases, the capacitance increases, but the number of open cells 3b in which the flow rate of exhaust gas is restricted also increases. Therefore, the number of rows of electrodes 5 and 6 is appropriately determined. Good.

  As described above, in the PM sensor 10 of the present invention, the capacitor formed by the electrodes 5 and 6 has a significantly larger capacitance than the capacitor formed by the electrodes 93 and 94 with the DPF 92 sandwiched as in the PM sensor 91 of FIG. Become. At the same time, compared with the capacitance of the capacitor by the electrodes 5 and 6 and the housing (not shown), since the electrodes 5 and 6 are separated from the housing, the capacitance of the capacitor by the electrodes 5 and 6 is significantly larger. . Therefore, the PM accumulation amount can be accurately detected.

  Further, in the PM sensor 10 of the present invention, since the electrodes 6, 5, 6 are respectively inserted into the plurality of open cells 3b arranged in a diagonal line, the electrodes 103, 104 are arranged like the PM sensor 101 of FIG. Unlike the arrangement that is biased near the outer periphery of the DPF 62, the electrodes 5 and 6 are positioned so as not to be biased near the outer periphery of the DPF 1, and the average PM deposition amount of the entire DPF 1 can be detected. In particular, as in the present embodiment, when the rows of electrodes 6, 5, 6 are arranged along the diameter of the DPF 1, the amount of PM deposited in the range from the center of the DPF 1 to the outer periphery is detected.

  Furthermore, in the PM sensor 10 of the present invention, since the detection open cell S exists inside the capacitor composed of the electrodes 6, 5, 6, the detected PM deposition amount can be regarded as the average PM deposition amount of the entire DPF 1. .

1 Diesel particulate filter (DPF)
2 wall 3 cell 3a plugged cell 3b open cell 4 PM sensor 5 first electrode 6 second electrode 7 short circuit 8 short circuit 9 PM sensor 10 PM sensor

Claims (1)

Particulate matter sensor for detecting the amount of particulate matter deposited on the diesel particulate filter based on the capacitance of a capacitor formed by inserting a first electrode and a second electrode into a plurality of cells of the diesel particulate filter In
The diesel particulate filter is formed by stacking the plurality of cells vertically and horizontally,
The plurality of cells are surrounded by four walls vertically and horizontally with walls made of a porous material, and end faces are alternately sealed vertically and horizontally,
The first electrodes are arranged in a line on a diagonal passing near the diameter of the diesel particulate filter, or arranged in a line on a diagonal not near the outer periphery of the diesel particulate filter, and Of the plurality of cells, the end surface on the side where the electrode is inserted is inserted into the first open cell that is not sealed,
The second electrodes are arranged in two rows across the first electrode on a diagonal passing near the diameter of the diesel particulate filter, or on a diagonal not near the outer periphery of the diesel particulate filter It is arranged in two rows across the first electrode, and is inserted into a second open cell where the end face on the side where the electrode is inserted is not sealed among the plurality of cells,
The first electrode and the second electrode are arranged between the first open cell and the second open cell among the plurality of cells, and an end surface on the side where the electrode is inserted is visible. It is arranged in parallel across the third open cell that is not sealed,
The third open cell is adjacent to each of the first open cell and the second open cell in a direction orthogonal to a diagonal direction in which the first electrode and the second electrode are disposed. and particulate matter sensor, characterized in that are.