JP6036388B2 - Particulate matter measuring device - Google Patents

Description

  The present invention relates to a particulate matter measuring device, and more particularly to a particulate matter measuring device in exhaust gas discharged from an internal combustion engine.

  For example, a diesel particulate filter (hereinafter referred to as DPF) is known as a filter that collects particulate matter (hereinafter referred to as PM) in exhaust gas discharged from a diesel engine. Yes. In general, a DPF includes a large number of cells that form a lattice-shaped exhaust passage partitioned by porous ceramic partition walls, and is formed by alternately plugging the upstream side and the downstream side of these cells. The

  Since there is a limit to the amount of PM collected by the DPF, when the amount of accumulated PM reaches a predetermined amount, so-called forced regeneration is required to burn and remove the accumulated PM. Therefore, it is desired to measure the PM accumulation amount with high accuracy for the forced regeneration control.

  For example, in Patent Document 1, a pair of electrodes are inserted into a pair of cells facing each other with a measurement cell whose downstream side is plugged, and the capacitance of the capacitor formed between these electrodes is based on the capacitance of the capacitor. A PM sensor for detecting the amount of accumulated PM is disclosed.

JP 2012-241643 A

  By the way, in the above-described prior art PM sensor, as shown in FIG. 10A, the exhaust gas flowing into the measurement cell 100 passes through the four right, left, upper and lower partition walls that partition the measurement cell 100, It flows into the four adjacent cells 101-104. Therefore, PM in the exhaust gas is deposited in a substantially rectangular shape on the left and right and upper and lower partition wall surfaces of the measurement cell 100 (see FIG. 10B).

  As described above, when PM is deposited in a substantially rectangular shape on the partition wall surface of the measurement cell 100, the change in capacitance between the electrodes 10A and 10B forming the capacitor may be saturated, leading to a decrease in sensitivity.

  The present invention has been made in view of such a point, and an object thereof is to effectively suppress early saturation of a change in capacitance and to suppress a decrease in sensitivity.

  In order to achieve the above-mentioned object, the particulate matter measuring device of the present invention is provided in an exhaust passage of an internal combustion engine, and forms a plurality of cells forming a lattice-like exhaust flow path partitioned by porous partition walls. A filter in which the upstream side and the downstream side are alternately plugged, and at least one cell is a measurement cell, and a pair of opposed cells among the four cells adjacent to the measurement cell via a partition wall And a pair of electrodes respectively inserted from the non-plugged side and the pair of cells in which the electrodes are not inserted among the four cells, and block at least a part of the flow paths of the cells. And a deposit amount calculating means for calculating a deposit amount of particulate matter in the exhaust gas collected by the filter based on a capacitance between the pair of electrodes.

  Further, the closing member may be formed by embedding from the plugged side of the cell to the non-plugged side.

  Further, the closing member may be formed by plugging the non-plugged side of the cell.

  Moreover, you may block | close the non-plugging side edge part of one cell among a pair of cells in which the said electrode was inserted with the 2nd closure member.

  The filter may be disposed in the exhaust passage with the plugged side of the measurement cell facing upstream.

  In addition, a bypass passage that branches from a predetermined position of the exhaust passage, and an exhaust passage that is downstream of the bypass passage, and traps particulate matter in the exhaust that flows through the exhaust passage on the downstream side. A second filter that collects, and the filter may be disposed in the bypass passage.

  Moreover, when performing forced regeneration which burns and removes the particulate matter deposited on the filter, the pair of electrodes may function as a heater.

  According to the particulate matter measuring device of the present invention, it is possible to effectively suppress the early saturation of the capacitance change and suppress the decrease in sensitivity.

It is a typical whole block diagram which shows the measuring apparatus of the particulate matter which concerns on one Embodiment of this invention. In the particulate matter measurement device according to an embodiment of the present invention, (a) is a schematic perspective view of a DPF viewed from the exhaust downstream side, and (b) is a schematic view of a part of the DPF viewed from the exhaust downstream side. FIG. (A)-(e) is A1-A5 line longitudinal cross-sectional view of Fig.2 (a). (A)-(e) is the B1-B5 line cross-sectional view of Fig.2 (a). FIG. 6 is a schematic cross-sectional view showing a modification of the blocking member in the particulate matter measurement device according to an embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing a modification of the electrode cell in the particulate matter measurement device according to one embodiment of the present invention. It is the figure which compared PM deposited on the partition wall surface of the cell for measurement with the prior art in the particulate matter measuring device concerning one embodiment of the present invention. In the particulate matter measuring device according to one embodiment of the present invention, it is a diagram comparing the time when the change in capacitance saturates with the prior art. It is a typical whole block diagram which shows the measuring apparatus of the particulate matter which concerns on other embodiment of this invention. In the conventional PM sensor, (a) is a view showing the flow of exhaust gas flowing into the measurement cell, and (b) is a view showing PM deposited on the partition wall surface of the measurement cell.

  Hereinafter, based on FIGS. 1-4, the measuring apparatus of the particulate matter which concerns on one Embodiment of this invention is demonstrated. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b.

  Further, in the exhaust passage 12, an exhaust pipe injection device 13, an exhaust aftertreatment device 14, a DPF inlet temperature sensor 31, and a DPF outlet temperature sensor 32 are provided in this order from the exhaust upstream side.

  The exhaust pipe injection device 13 injects unburned fuel (HC) into the exhaust passage 12 in response to an instruction signal output from an electronic control unit (hereinafter, ECU) 20. In addition, when using the post injection by the multistage injection of the engine 10, this in-pipe injection device 13 may be omitted.

The DPF inlet temperature sensor 31 detects the temperature of exhaust gas flowing into the DPF 16 (hereinafter referred to as inlet temperature T _IN ). The DPF outlet temperature sensor 32 detects the temperature of exhaust gas flowing out from the DPF 16 (hereinafter referred to as outlet temperature T _OUT ). The inlet temperature T _IN and the outlet temperature T _OUT are output to the electrically connected ECU 20.

  The exhaust aftertreatment device 14 is configured by arranging an oxidation catalyst 15 and a DPF 16 in order from the exhaust upstream side in a case 14a.

  The oxidation catalyst 15 is formed, for example, by supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When the unburnt fuel (HC) is supplied by the in-pipe injection device 13 or post-injection during forced regeneration of the DPF 16, the oxidation catalyst 15 oxidizes this and raises the temperature of the exhaust gas. As a result, the DPF 16 is heated to the PM combustion temperature (for example, about 600 ° C.), and the deposited PM is burned and removed.

  The DPF 16 has, for example, a large number of cells forming a grid-like exhaust flow path partitioned by porous ceramic partition walls along the exhaust gas flow direction, and the upstream side and the downstream side of these cells are alternately arranged. It is configured by plugging. Hereinafter, based on FIGS. 2-4, the detailed structure of DPF16 of this embodiment is demonstrated.

  As shown in FIGS. 2 to 4, in the DPF 16, a plurality of cells 1 that are open on the exhaust upstream side (plugged on the exhaust downstream side) are selected for capacitance measurement (hereinafter, cell 1 is referred to as “cell 1”). Called measurement cell).

  Of the four cells 2 to 5 adjacent to the measurement cell 1 through a partition wall, the pair of cells 2 and 3 that are opposed to each other with the measurement cell 1 in between are a pair of electrodes A and B forming a capacitor. Are inserted (hereinafter, cells 2 and 3 are referred to as electrode cells).

  Further, a pair of cells 4 and 5 that face each other with the measurement cell 1 interposed therebetween and into which the electrodes A and B are not inserted are provided with a closing member 6 that closes the exhaust flow path in the cells 4 and 5 ( Hereinafter, the cells 4 and 5 are referred to as blocking cells).

  The electrodes A and B are, for example, conductive metal wires, and are inserted from the non-plugged side (exhaust downstream side) into the electrode cells 2 and 3 plugged on the exhaust upstream side to form a capacitor. . The electrode A inserted into the electrode cell 2 has a base end portion on the exhaust downstream side protruding outward, and the base end portion is connected by a connection line A1 (see FIG. 2) formed of a conductive metal member. Are connected to each other. Similarly, the electrode B inserted into the electrode cell 3 has a base end portion on the exhaust downstream side protruding outward, and a connection line B1 formed of a conductive metal member at the base end portion (FIG. 2). Are connected to each other.

  In the present embodiment, the protruding amount of the electrode A is set longer than the protruding amount of the electrode B in order to avoid contact between the connecting line A1 and the connecting line B1. In addition, these protrusion amounts do not necessarily need to make the electrode A longer, and the electrode B can be set longer.

  The closing member 6 provided in the closing cells 4 and 5 is made of, for example, ceramics made of the same material as the DPF 16. In the present embodiment, the closing member 6 covers the entire area in the closing cells 4 and 5 so as to block all the exhaust flow paths from the plugging side to the non-plugging side of the closing cells 4 and 5. It is buried (see FIGS. 3 and 4).

  In other words, the exhaust gas that has flowed into the measuring cell 1 is configured to flow into the electrode cells 2 and 3 without flowing into the blocking cells 4 and 5. Thereby, PM in the exhaust gas flowing into the measuring cell 1 is collected on the surface of the partition walls on the electrode cells 2 and 3 side, and the deposition on the partition walls on the closing cells 4 and 5 side is effectively suppressed. The

  Note that the closing member 6 does not necessarily need to be embedded in the entire area in the closing cells 4 and 5, and as shown in FIG. 5, a part of the flow path in the closing cells 4 and 5 is closed (see FIG. In the example shown, the non-plugged side may be plugged.

  Further, as shown in FIG. 6, an additional closing member 7 (second closing member) may be provided at the insertion side end of one of the electrodes A and B (electrode A in the illustrated example). In this case, not only deposition of PM on the partition wall surfaces on the blocking cells 4 and 5 side but also deposition on the partition wall surface on the electrode cell 2 side can be effectively suppressed.

  Next, returning to FIG. 1, the ECU 20 of the present embodiment will be described. The ECU 20 performs various controls such as fuel injection of the engine 10 and the exhaust pipe injection device 13, and includes a known CPU, ROM, RAM, input port, output port, and the like. Moreover, ECU20 has the electrostatic capacitance calculating part 21 and PM deposition amount estimation part 22 as a one part function element. Each of these functional elements will be described as being included in the ECU 20 which is an integral hardware, but any one of these may be provided in separate hardware.

  The capacitance calculation unit 21 calculates the capacitance C between the electrodes A and B based on the signals input from the electrodes A and B. The electrostatic capacity C is calculated by the following formula 1 where the dielectric constant ε of the medium between the electrodes A and B, the area S of the electrodes A and B, and the distance d between the electrodes A and B are calculated.

The PM accumulation amount estimation unit 22 calculates the average value of the inlet temperature T _IN detected by the DPF inlet temperature sensor 31 and the outlet temperature T _OUT detected by the DPF outlet temperature sensor 32 (hereinafter, DPF average temperature T _AVE ), static Based on the capacitance C calculated by the capacitance calculation unit 21, the PM deposition amount PM _DEP collected by the DPF 16 is estimated. For the estimation of the PM deposition amount PM _DEP , an approximate expression or a map obtained in advance by experiments can be used.

  Next, the function and effect of the particulate matter measurement device according to the present embodiment will be described.

  In the conventional PM sensor, four cells facing each other across the measurement cell are plugged only on the exhaust upstream side, and the exhaust downstream side is not plugged. Therefore, PM in the exhaust gas flowing into the measurement cell is deposited in a substantially rectangular shape on the surfaces of the four partition walls that partition the measurement cell (see FIG. 10B). Thus, when PM is deposited in a substantially rectangular shape on the partition wall surface of the measurement cell, there is a problem that the change in capacitance between the electrodes forming the capacitor is saturated at an early stage, leading to a decrease in sensitivity.

  On the other hand, in the particulate matter measuring apparatus according to the present embodiment, the blocking cells 4 and 5 are placed in the blocking cells 4 and 5 which are opposed to each other with the measuring cell 1 interposed therebetween and into which the electrodes A and B are not inserted. A closing member 6 is provided to close the exhaust flow path.

  That is, since the flow of the exhaust gas into the blocking cells 4 and 5 is blocked, the PM in the exhaust gas flowing into the measurement cell 1 becomes a partition wall on the electrode cell 2 and 3 side as shown in FIG. Collected and deposited on the surface. As a result, as shown in FIG. 8, it is possible to greatly delay the time when the change in capacitance is saturated as compared with the PM sensor of the prior art.

  Therefore, according to the particulate matter measuring device of the present embodiment, the early saturation of the capacitance change is effectively suppressed, and the decrease in sensitivity can be reliably suppressed.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, the DPF 16 has been described as being disposed in the exhaust passage 12 with the non-plugged side of the measurement cell 1 facing the upstream side of the exhaust, but the plugged side of the measurement cell 1 is on the upstream side of the exhaust. You may arrange it.

  Further, as shown in FIG. 9, a bypass passage 18 branched from the exhaust passage 12 downstream of the oxidation catalyst 15 is provided, and a measurement DPF 16 having a reduced capacity is disposed in the bypass passage 18. Also good. In this case, it is preferable to provide a large-capacity DPF 17 (second filter) in the exhaust passage 12 on the downstream side of the branch portion, and provide the bypass passage 18 with an orifice 18a for adjusting the flow rate of the exhaust gas. When forced regeneration of the measurement DPF 16 is executed, a voltage may be applied to the electrodes A and B so as to function as a heater.

DESCRIPTION OF SYMBOLS 1 Measurement cell 2, 3 Electrode cell 4, 5 Closure cell 6 Closure member 10 Engine 12 Exhaust passage 14 Exhaust aftertreatment device 16 DPF (filter)
20 ECU
21 Capacitance calculation unit (deposition amount calculation means)
22 PM accumulation amount estimation unit (deposition amount calculation means)
A and B electrodes

Claims (7)

A filter provided in the exhaust passage of the internal combustion engine and alternately plugged upstream and downstream of a plurality of cells forming a grid-like exhaust flow path partitioned by porous partition walls;
A pair of electrodes inserted into the pair of opposed cells from the non-plugged side among the four cells adjacent to the measurement cell via a partition wall, and at least one cell as a measurement cell;
Among the four cells, a blocking member that is provided in a pair of cells into which the electrode is not inserted and blocks at least a part of the flow path of the cell;
A deposit amount calculating means for calculating a deposit amount of the particulate matter in the exhaust gas collected by the filter based on a capacitance between the pair of electrodes; apparatus.   The particulate matter measuring device according to claim 1, wherein the blocking member is formed by embedding from a plugged side to a non-plugged side of a cell.   The particulate matter measuring device according to claim 1, wherein the blocking member is formed by plugging a non-plugged side of a cell.   The measurement of the particulate matter according to any one of claims 1 to 3, wherein a non-plugged side end portion of one of the pair of cells into which the electrodes are inserted is closed with a second closing member. apparatus.   The particulate matter measuring device according to any one of claims 1 to 4, wherein the filter is arranged in the exhaust passage with a plugging side of the measurement cell facing an upstream side. A bypass passage branched from a predetermined position of the exhaust passage;
A second filter that is provided in the exhaust passage downstream of the bypass passage branching position and collects particulate matter in the exhaust gas flowing in the downstream exhaust passage;
The particulate matter measuring device according to any one of claims 1 to 5, wherein the filter is disposed in the bypass passage. The particulate matter measuring device according to claim 6, wherein when performing forced regeneration for burning and removing particulate matter deposited on the filter, the pair of electrodes function as a heater.

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