JP2017191054A - Sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PM sensor that offers improved accuracy in quantitative measurement of PM.SOLUTION: A sensor includes a housing for an exhaust gas to flow in, a plurality of capturing members disposed in predetermined regions in the housing and configured to capture particulate matter in the exhaust gas flowing inside the housing, and a diffusion member 300 for diffusing the exhaust gas flowing into the housing in a predetermined region. The housing has a plurality of passage ports 14 through which the exhaust gas flows in, and the diffusion member 300 is designed to direct flows of the exhaust gas from the plurality of passage ports 14 to cause collision therebetween.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a sensor, and more particularly to a PM sensor that detects particulate matter (hereinafter referred to as “PM”) contained in exhaust gas.

  Conventionally, a capacitive PM sensor is known as a sensor that is provided in an exhaust system of an internal combustion engine and detects PM in exhaust gas discharged from the internal combustion engine (see, for example, Patent Document 1). The capacitance type PM sensor measures the amount of PM by utilizing the fact that the capacitance between the electrodes changes due to the PM deposited between a pair of electrodes arranged opposite to each other.

JP 2011-87991 A

  By the way, although a cell for depositing PM is provided between a pair of electrodes in the capacitive PM sensor, a plurality of the cells may be provided in order to measure the amount of PM with higher accuracy.

  However, if the amount of exhaust gas entering the plurality of cells varies, the amount of PM varies from cell to cell, and there is a certain limit to improving the measurement accuracy of the amount of PM.

  An object of the present invention is to provide a sensor capable of improving the measurement accuracy of the amount of PM.

The sensor according to the present invention comprises:
A casing through which exhaust gas flows;
A plurality of collection units arranged in a predetermined region in the housing and collecting particulate matter in the exhaust gas moving in the housing;
A diffusion section for diffusing the exhaust gas flowing into the housing in the predetermined region;
Is provided.

  According to the present invention, the measurement accuracy of the amount of PM can be improved.

It is a schematic block diagram which shows the exhaust system of the diesel engine to which PM sensor of this Embodiment was applied. It is a fragmentary sectional view showing PM sensor of this embodiment. It is sectional drawing which cut the inner side case part by the A line in FIG. It is the figure which looked at the fan from the passage opening side. It is an enlarged view of a wing member.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an exhaust system of a diesel engine (hereinafter simply referred to as “engine”) 100 to which the PM sensor 10 of the present embodiment is applied. The exhaust pipe 110, in order from the exhaust upstream side, an oxidation catalyst 210, DPF (Diesel particulate filter) 220, NO _X purification catalyst 230 or the like are provided. The PM sensor 10 as an example of the sensor according to the present embodiment is provided, for example, in the exhaust pipe 110 upstream of the DPF 220 or in the exhaust pipe 110 downstream of the DPF 220.

  Next, a detailed configuration of the PM sensor 10 will be described based on FIG. The PM sensor 10 includes a case member 11 inserted into the exhaust pipe 110, a pedestal part 20 for attaching the case member 11 to the exhaust pipe 110, and a sensor part 30 accommodated in the case member 11.

  The case member 11 includes a bottomed cylindrical inner case portion 11A and a cylindrical outer case portion 11B that surrounds a cylindrical outer peripheral surface of the inner case portion 11A. The inner case portion 11A corresponds to the “housing” of the present invention.

  The inner case portion 11A is formed to have a longer length in the axial direction than the outer case 11B so that the tip side protrudes from the outer case portion 11B. The length of the inner case portion 11A in the axial direction is substantially the same as the radius of the exhaust pipe 110 so that the bottom of the inner case portion 11A protrudes to the vicinity of the axial center CL of the exhaust pipe 110. In addition, although it is preferable that the bottom part of inner case part 11A protrudes to the axial center CL vicinity of the exhaust pipe 110, it is not limited to this, For example, it does not need to protrude to the axial center CL vicinity. Further, in the present embodiment, the axial sectional shapes of the inner case portion 11A and the outer case portion 11B are circular, but the axial sectional shapes of the inner case portion 11A and the outer case portion 11B are the flow paths of the exhaust pipe 110. Various cross-sectional shapes in the axial direction can be employed, such as an elliptical shape whose major axis is the direction (left and right direction in FIG. 2), a rhombus shape having a vertex in the flow direction of the exhaust pipe 110, and a polygonal shape. In the following description, the bottom side of the case member 11 is the front end side, and the side opposite to the bottom side is the base end side.

  A lead-out port 13 through which exhaust gas in the inner case portion 11A is led into the exhaust pipe 110 is provided at the bottom of the inner case portion 11A. Furthermore, a plurality of passage openings 14 are provided in the cylindrical wall portion on the proximal end side of the inner case portion 11A and arranged at intervals in the circumferential direction. The passage port 14 allows the exhaust gas in the flow path 15 defined by the outer peripheral surface of the inner case portion 11A and the inner peripheral surface of the outer case portion 11B to pass through the inner case portion 11A. At the upstream end of the flow path 15, an annular introduction port 12 is provided that is partitioned by the distal end side cylindrical wall portion of the inner case portion 11A and the distal end portion of the outer case portion 11B. Thereby, the exhaust gas flowing through the exhaust pipe 110 hits the cylindrical wall surface of the inner case part 11A protruding from the outer case part 11B, and enters the flow path 15 from the inlet 12 disposed in the vicinity of the axial center CL of the exhaust pipe 110. It is taken in smoothly. The exhaust gas flowing in the flow path 15 is taken into the inner case portion 11A from the passage port 14, passes through the sensor unit 30, and then passes through the outlet port 13 disposed in the vicinity of the axial center CL of the exhaust pipe 110 into the exhaust pipe 110. Is derived smoothly.

  Further, the inner case portion 11A is provided with a diffusion portion 300 for diffusing the exhaust gas in the inner case portion 11A. Details of the diffusion unit 300 will be described later.

  The pedestal portion 20 includes a male screw portion 21 and a nut portion 22. The male screw portion 21 is provided at the base end portion of the case member 11 and closes the base end side opening of the case member 11. The male screw portion 21 is screwed with a female screw portion of a boss portion 110 </ b> A formed in the exhaust pipe 110. The case member 11 is fixed to the exhaust pipe 110 by the male screw portion 21 being screwed with the female screw portion of the boss portion 110A. The nut portion 22 is, for example, a hex nut, and is provided at the upper end portion of the male screw portion 21. The male screw portion 21 and the nut portion 22 are formed with through holes (not shown) through which conductive wires and the like described later are inserted. Note that the method for fixing the case member 11 to the exhaust pipe 110 is not limited to the above-described screw engagement. For example, a flange having a shape along the outer shape of the exhaust pipe 110 is provided on the base end side of the case member 11. The case member 11 may be fixed to the exhaust pipe 110 by forming the flange and fixing the flange to the outer peripheral surface of the exhaust pipe 110 using a bolt or the like.

  The sensor unit 30 includes a collecting member 31, a pair of electrode plates 32, a control unit 40, and an electric heater (not shown).

  The collecting member 31 is arranged in a predetermined region below the portion corresponding to the passage port 14 in the inner case portion 11A, and a plurality of collecting members 31 that form a lattice-shaped exhaust passage surrounded by, for example, a porous ceramic partition wall. Cell C. The plurality of cells C are arranged adjacent to each other. The cell C corresponds to the “collecting part” of the present invention.

  The longitudinal direction of the cell C, that is, the flow path direction coincides with the longitudinal direction of the inner case portion 11A in which the sensor unit 30 is accommodated, and in the process of exhaust gas from the inlet port 12 to the outlet port 13, the partition wall of the cell C PM contained in the exhaust gas is collected on the surface and pores.

  The pair of electrode plates 32 are flat conductive members, for example, and are alternately stacked with the cells C sandwiched in the thickness direction. By sandwiching the cell C between a pair of electrode plates 32 arranged to face each other, the entire cell C forms a capacitor. Thus, by making the entire cell C a capacitor by the pair of flat electrode plates 32, the electrode surface area can be effectively secured, and the detectable capacitance can be increased.

  The electric heater is, for example, a heating wire, and performs so-called collection member regeneration in which PM accumulated in the cell C is burned and removed by heating the cell C by generating heat by energization.

  The control unit 40 includes a collection member regeneration control unit 41 and a PM amount estimation calculation unit 42 as functional elements, and is connected to the pair of electrode plates 32 by wires (not shown).

  The collection member regeneration control unit 41 executes collection member regeneration control for energizing the electric heater according to the capacitance Cp between the pair of electrode plates 32 detected by a capacitance detection circuit (not shown). .

  The capacitance Cp between the pair of electrode plates 32 is expressed as follows: the dielectric constant of the medium between the pair of electrode plates 32 is ε, the surface area of each electrode plate 32 is S, and the distance between each electrode plate 32 is d. It is represented by the following formula 1.

  In Equation 1, the surface area S of each electrode plate 32 is constant, and when the dielectric constant ε and the distance d change due to the PM collected in the cell C, the capacitance Cp also changes accordingly. It is known that a substantially proportional relationship is established between the capacitance Cp between the electrode plates 32 and the amount of PM deposited on the collection member 31.

When the accumulated amount of PM collected in the cell C exceeds the upper limit value, the proportional relationship between the capacitance Cp between the pair of electrode plates 32 and the accumulated amount of PM collapses, and the relationship between the pair of electrode plates 32 is lost. The estimation accuracy of the electrostatic capacity Cp is reduced. Therefore, when the electrostatic capacity Cp between the pair of electrode plates 32 reaches a predetermined electrostatic capacity upper limit threshold Cp _MAX indicating the upper limit accumulation amount of PM, the collecting member regeneration control unit 41 energizes the electric heater. The collection member regeneration control is started. This collection member regeneration control is continued until the electrostatic capacity Cp falls to a predetermined electrostatic capacity lower limit threshold Cp _min indicating complete removal of PM.

The PM amount estimation calculation unit 42 exhausts exhausted from the engine 100 based on the capacitance change amount ΔCp during the regeneration interval T _n (from the end of the collection member regeneration control to the start of the next collection member regeneration control). Estimate the total PM amount m _PMSUM . The PM amount m _PMn collected by the collecting member during the regeneration interval T _n is obtained by the following formula 2 obtained by multiplying the capacitance change amount ΔCp by the primary coefficient β.

The PM amount estimation calculation unit 42 sequentially accumulates the PM amount m _PMn between the regeneration intervals T _n calculated from Equation 2, and based on the following Equation 3, the total PM amount in the exhaust gas discharged from the engine 100 m _{Compute PMSUM} in real time.

In addition, estimation of PM amount is not restricted to said method, Various methods are employable. For example, it is possible to estimate the total PM amount or the instantaneous PM amount by referring to this map by obtaining the relationship between the capacitance Cp and the PM amount m _PM in advance by experiments or the like.

  By the way, the exhaust gas flowing in the exhaust pipe 110 enters the flow path 15 and flows into the inner case portion 11 </ b> A through the plurality of passage ports 14. For example, when the flow rate of the exhaust gas is relatively fast, the exhaust gas flowing from the plurality of passage openings 14 formed on the entire circumference of the inner case portion 11A collides with force near the center line in the inner case portion 11A. As a result, the exhaust gas is diffused and uniformly mixed in the inner case portion 11A, so that the exhaust gas flows evenly into each cell C, thereby improving the measurement accuracy of the amount of PM.

  However, when the flow rate of the exhaust gas is relatively slow, the exhaust gas that has flowed into the inner case portion 11A via the plurality of passage ports 14 gently flows in the inner case portion 11A. Do not collide near the line, or collide with relatively weak force. Therefore, the exhaust gas is less likely to be diffused in the inner case portion 11A, and it is difficult to evenly flow into each cell C.

  Accordingly, in the present embodiment, the exhaust gas in the inner case portion 11A is diffused by the diffusion portion 300 in a predetermined region on the lower side of the drawing from the passage port. As a result, the exhaust gas flows evenly into each cell C, and as a result, the measurement accuracy of the amount of PM can be improved. Details of the diffusion unit 300 will be described below. FIG. 3A is a diagram illustrating a state in which exhaust gas flows from the passage port 14 in a cross-sectional view of the inner case portion 11A taken along line A in FIG. FIG. 3B is a diagram showing a state in which exhaust gas diffuses in a predetermined region in a cross-sectional view of the inner case portion 11A taken along line A in FIG.

  The diffusing unit 300 is disposed on the upstream side of the sensor unit 30 in the movement direction of the exhaust gas in the inner case unit 11A (the direction from the top to the bottom in FIGS. 2, 3A, and 3B). As shown in FIG. 3A, the diffusion part 300 is provided in each of the passage openings 14 and has a protruding wall 301 that protrudes inside the inner case part 11 </ b> A.

  The protruding wall 301 is inclined so as to be positioned downward from the position of the upper edge 14A of the passage opening 14 in the inner case portion 11A toward the inside of the inner case portion 11A. By forming the protruding wall 301 in this way, the exhaust gas flowing into the inner case portion 11A from the flow path 15 via the passage port 14 moves in the direction of the arrow X and is below the passage port 14 of the inner case portion 11A. It is collected near the center line L in the predetermined area on the side. That is, the diffusing unit 300 moves the exhaust gas flowing from each of the plurality of passage ports 14 so as to collide with each other in the inner case portion 11A. Then, as shown in FIG. 3B, the exhaust gas entering from each passage port 14 collides in the vicinity of the center line L of the inner case portion 11A, so that the exhaust gas in the inner case portion 11A moves from the vicinity of the center line L to the arrow Y. It is spread like. The diffused exhaust gas flows evenly into each cell C (see FIG. 2) of the sensor unit 30 arranged in a predetermined region. Thereby, the measurement accuracy of the amount of PM can be improved.

  In the above embodiment, the configuration having the protruding wall 301 as the diffusing portion 300 is exemplified, but the present invention is not limited to this. For example, the diffusing unit 300 may be a conical member that tapers toward the bottom. According to this, exhaust gas can be easily collected near the center line L of the inner case portion 11A, and can be effectively diffused. Further, the diffusion unit 300 may be a mesh member. Further, the diffusing unit 300 may be configured such that a wing member such as a fan is provided at an appropriate position in the inner case unit 11A to improve the diffusibility of exhaust gas.

  Further, as shown in FIGS. 4A and 4B, the diffusion unit may be a fan 310. The fan 310 has a plurality of wing members 311 attached in the cylindrical inner case portion 11A and extending in the circumferential direction from the center of the circle. The wing member 311 is formed in a wave shape. The exhaust gas flowing into the inner case portion 11A is diffused by passing through the fan 310 portion. The fan 310 may be configured not to rotate the wing member 311 or may be configured to rotate the wing member 311.

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

  The present invention is useful as a sensor capable of improving the measurement accuracy of the amount of PM.

10 PM sensor 11A Inner case part 30 Sensor part 300 Diffusion part

Claims (4)

A casing through which exhaust gas flows;
A plurality of collection units arranged in a predetermined region in the housing and collecting particulate matter in the exhaust gas moving in the housing;
A diffusion section for diffusing the exhaust gas flowing into the housing in the predetermined region;
Comprising a sensor. The housing has a plurality of passage ports through which the exhaust gas flows,
The diffusion unit moves the exhaust gas flowing from each of the plurality of passage ports so as to collide with each other in the housing.
The sensor according to claim 1. The diffusion unit is a fan having a plurality of wing members.
The sensor according to claim 1. The diffusion unit is disposed upstream of the plurality of collection units in the movement direction of the exhaust gas.
The sensor according to any one of claims 1 to 3.

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