JP2012237228A - Pm sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PM sensor capable of detecting an average amount of PM deposition of the entire DPF, and capable of securing capacitance enough to be detected.SOLUTION: A DPF 1 in which a plurality of cells 3 whose four longitudinal and lateral faces are surrounded by walls 2 made of porous materials are longitudinally and laterally stacked, and end faces of the cells 3 are longitudinally and laterally plugged in an alternative manner includes first and second electrodes 5, 6. In the PM sensor 4 in which the PM deposition amount of the DPF 1 is detected based on the capacitance of the capacitor formed of the first and second electrodes 5, 6, the first electrodes 5 are inserted in a plurality of open cells 3b aligning in a diagonal line direction among open cells 3b, and the second electrodes 6 are inserted in the plurality of open cells 3b aligned in the diagonal line direction adjacent to the open cells 3b in which the first electrodes 5 are inserted.

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 51 shown in FIG. 5 has two electrodes 53 and 54 formed in a half-cylindrical shape on the outer periphery of a columnar DPF 52. When the two electrodes 53 and 54 face each other with the DPF 52 interposed therebetween, the capacitance of the capacitor formed by the two electrodes 53 and 54 changes in accordance with the total PM deposition amount of the DPF 52 (Patent Document 1).

  In the conventional PM sensor 61 shown in FIG. 6, one electrode 63 is installed on the outer periphery of a cylindrical DPF 62, and the other electrode 64 is installed concentrically on the inner side. The capacitance of the capacitor formed by the two electrodes 63 and 64 changes according to the PM deposition amount of a part of the DPF 62 sandwiched between the two electrodes 63 and 64 (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 51 of FIG. 5, since the distance between the electrodes 53 and 54 and the housing 55 is significantly shorter than the distance between the two electrodes 53 and 54, the capacitance of the capacitor by the electrodes 53 and 54 and the housing 55 is 2. It is significantly larger than the capacitance of the capacitor by the two electrodes 53 and 54. Furthermore, the capacitance of the capacitor formed by the electrodes 53 and 54 and the housing 55 is unstable both thermally and mechanically. As a result, the PM sensor 51 circuit is a circuit in which the electrodes 53 and 54 and the capacitor of the housing 55 are connected in parallel to the capacitor of the two electrodes 53 and 54. 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 61 of FIG. 6, the capacitance of the capacitor by the two electrodes 63 and 64 is increased by reducing the distance between the outer electrode 63 and the inner electrode 64. However, for that purpose, the inner electrode 64 is disposed near the outer periphery of the DPF 62, and the PM deposition amount in a part of the DPF 62 inside the inner electrode 64 cannot be detected. If the PM deposition amount is detected only in a part of the DPF 62 outside the inner electrode 64, the detected value may deviate from the average PM deposition amount of the entire DPF 62.

  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. .

  In order to achieve the above object, the PM sensor of the present invention has a plurality of cells stacked vertically and horizontally, surrounded by walls made of a porous material, and the end faces of the cells are alternately plugged vertically and horizontally. A diesel particulate filter (hereinafter referred to as a DPF) is provided with first and second electrodes, and the DPF particulate matter (hereinafter referred to as the DPF) due to the capacitance of a capacitor formed by the first and second electrodes. In the PM sensor in which the accumulation amount of PM) is detected, the first electrode is inserted into a plurality of open cells arranged in a diagonal line among cells that are not sealed (hereinafter referred to as open cells), and the first The second electrode is inserted into a plurality of open cells arranged in a line in a diagonal direction adjacent to the plurality of open cells in which the first electrode is inserted.

  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 fragmentary sectional view of DPF to which the present invention is applied. 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.

  As shown in FIG. 3, the PM sensor 4 of the present invention is provided with first and second electrodes 5 and 6 on the DPF 1, and the electrostatic capacitance of the capacitor formed by the first and second electrodes 5 and 6. The PM accumulation amount of the DPF 1 is detected by the capacity.

  In the PM sensor 4 of the present invention, 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 the plurality of open cells 3b into which the first electrode 5 is inserted. The second electrode 6 is inserted into a plurality of open cells 3b that are adjacent to each other and arranged in a diagonal line. 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.

  As shown in FIG. 4, in the PM sensor 4 of the present invention, the short-circuit lines 7 and 8 along the row of the open cells 3 b in which the electrodes 5 and 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 1st, 2nd electrodes 5 and 6 inserted in the open cell 3b of DPF1 are each short-circuited by the short circuit lines 7 and 8, and the short circuit lines 7 and 8 are connected to the detection circuit which is not shown in figure. Since the detection circuit is the same as the conventional one, the description thereof is omitted.

  Hereinafter, the operation of the PM sensor 4 of the present invention will be described.

  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 the distance between the electrode P0 and 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 each having an electrode distance of 2d and an electrode facing area proportional to the electrode length. 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.

  When PM is deposited in the DPF 1 in FIG. 4, the amount of PM deposited on the wall 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. 3. Will increase. Therefore, the capacitance of the capacitor composed of the electrodes 5 and 6 is increased.

  At this time, in the PM sensor 4 of the present invention, a plurality of open cells 3b arranged in a diagonal line with the first electrode 5 inserted therein and a plurality of cells arranged in a diagonal line with the second electrode 6 inserted therein. Since the open cell 3b is adjacent to each other with only one sealing cell 3a interposed therebetween, the capacitor between the electrodes 5 and 6 has a distance between electrodes of √2d, and sandwiches the DPF 52 like the PM sensor 51 of FIG. The capacitance is significantly larger than that of the capacitor formed by the electrodes 53 and 54. 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 4 of the present invention, since the electrodes 5 and 6 are respectively inserted into the plurality of open cells 3b arranged in a diagonal line, the electrodes 63 and 64 are formed of the DPF 62 as in the PM sensor 61 of FIG. Unlike the arrangement that is biased near the outer periphery, 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 the electrodes 5 and 6 are arranged along the diameter of the DPF 1, the PM deposition amount in the range from the center portion of the DPF 1 to the outer peripheral portion is detected.

1 Diesel particulate filter (referred to as 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

Claims (1)

A diesel particulate filter (hereinafter referred to as a DPF) in which a plurality of cells surrounded by vertical and horizontal four faces with a wall made of a porous material are stacked vertically and horizontally and end faces of the cells are alternately sealed vertically and horizontally, In the PM sensor, the second electrode is provided, and the accumulation amount of the particulate matter of the DPF (hereinafter referred to as PM) is detected by the capacitance of the capacitor formed by the first and second electrodes.
The first electrode is inserted into a plurality of open cells arranged in a diagonal line among cells that are not sealed (hereinafter referred to as open cells),
The PM sensor, wherein the second electrode is inserted into a plurality of open cells arranged in a diagonal line adjacent to the plurality of open cells in which the first electrode is inserted.