JP2017191050A - Sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PM sensor with self-diagnostic capability.SOLUTION: A PM sensor includes: a filter member having a plurality of cells for capturing particulate matter in an exhaust gas; a plurality of pairs of electrodes, each pair being disposed to face each other with the cells in between; an estimation unit configured to estimate the amount of the particulate matter on the basis of electrical characteristic values observed between the plurality pairs of electrodes; and a diagnostic unit configured to compare difference in the amount of the particulate matter among the plurality of pairs of electrodes with a predetermined threshold, and to diagnose the presence/absence of anomaly on the basis of a result of the comparison.SELECTED DRAWING: Figure 3A

Description

  The present disclosure relates to sensors, and more particularly to PM (particulate matter) sensors.

  Conventionally, a PM sensor that detects PM in exhaust gas discharged from an internal combustion engine is known (see, for example, Patent Document 1). In the electric resistance PM sensor described in Patent Document 1, a pair of conductive electrodes are arranged opposite to each other on the surface of an insulating substrate, and the electric resistance value is caused by the conductive PM (mainly soot component) adhering to these electrodes. The amount of PM is estimated using the change.

JP2012-83210A

  In recent years, from the viewpoint of preventing environmental pollution, an upper limit value of PM value in exhaust gas discharged from an internal combustion engine has been defined by law. In order to comply with laws and regulations, it is necessary to measure the PM value in the exhaust gas with a PM sensor and monitor the exhaust gas so that the measured PM value does not exceed the upper limit value of the PM value.

  However, if the PM sensor does not function normally due to some cause, the exhaust gas cannot be monitored properly. Therefore, in some countries, there are laws and regulations that require the PM sensor itself to be equipped with a self-diagnosis function in order to self-diagnose whether the PM sensor is functioning normally.

  An object of the present disclosure is to provide a PM sensor equipped with a self-diagnosis function.

  A sensor according to one embodiment of the present disclosure includes a filter member having a plurality of cells that collect particulate matter in exhaust gas, a plurality of pairs of electrodes that are arranged to face each other with the cells interposed therebetween, and a space between the plurality of pairs of electrodes. The estimation unit for estimating the amount of the particulate matter based on the electrical characteristic value of the above and the magnitude of the difference in the amount of the particulate matter between the plurality of pairs of electrodes and a predetermined threshold are compared, and the result of the comparison A diagnosis unit that diagnoses whether or not an abnormality has occurred, and the diagnosis unit performs the diagnosis in conjunction with the regeneration process of the filter member.

  According to the present disclosure, a PM sensor equipped with a self-diagnosis function can be provided.

It is a schematic block diagram which shows an example of the exhaust system of the diesel engine to which PM sensor of 1st Embodiment was applied. It is explanatory drawing of PM sensor of 1st Embodiment. It is explanatory drawing of the sensor part and control unit of PM sensor of 1st Embodiment. It is a disassembled perspective view of the sensor part of PM sensor of a 1st embodiment.

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

(First embodiment)
FIG. 1 is a schematic configuration diagram illustrating an example of an exhaust system of a diesel engine (hereinafter simply referred to as an engine) 100 to which the PM sensor 10 of the first embodiment is applied. In the exhaust pipe 110 of the engine 100, an oxidation catalyst 210, a DPF 220, a NOx purification catalyst 230, and the like are provided in order from the exhaust upstream side. The PM sensor 10 of the present embodiment is provided, for example, in either the exhaust pipe 110 upstream of the DPF 220 or the exhaust pipe 110 downstream of the DPF 220.

  FIG. 2 is an explanatory diagram of the PM sensor 10 according to the first embodiment. FIG. 3A is an explanatory diagram of the sensor unit 60 and the control unit 40 of the PM sensor 10 according to the first embodiment. FIG. 3B is an exploded perspective view of the sensor unit 60 of the PM sensor 10 according to the first embodiment.

  The PM sensor 10 includes a case member 11 inserted into the exhaust pipe 110, a pedestal portion 20 for attaching the case member 11 to the exhaust pipe 110, a sensor unit 60 accommodated in the case member 11, the sensor unit 60, And a control unit 40 connected thereto.

  The case member 11 is formed in a bottomed cylindrical shape with the bottom side (the lower end side in the illustrated example) closed. The length L in the cylinder axis direction of the case member 11 is formed to be substantially the same as the radius R of the exhaust pipe 110 so that the bottom cylindrical wall portion protrudes to the vicinity of the axial center CL of the exhaust pipe 110. ing. 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 of the case member 11. The case member 11 has a double-pipe structure including a cylindrical inner case portion 11A with a bottom and a cylindrical outer case portion 11B that surrounds a cylindrical outer peripheral surface of the inner case portion 11A.

  11 A of inner side case parts are formed so that the axial direction length may become longer than the outer case part 11B so that the front end side may protrude rather than the outer case part 11B. In addition, at the bottom of the inner case portion 11A, a lead-out port 13 for leading the exhaust gas in the inner case portion 11A into the exhaust pipe 110 is provided. 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 formed which is partitioned by the tip side cylindrical wall portion of the inner case portion 11 </ b> A and the tip portion of the outer case portion 11 </ b> B. The opening area _{S 12} of the inlet 12 is formed smaller than the opening area _{S 13} of the outlet _{13 (S 12 <S 13)} .

  That is, the exhaust gas flowing through the exhaust pipe 110 hits the cylindrical wall surface of the inner case portion 11A protruding from the outer case portion 11B, and smoothly enters the flow path 15 from the inlet 12 disposed in the vicinity of the axial center CL of the exhaust pipe 110. Is taken in. Further, 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 60, and then is exhausted from the outlet port 13 disposed in the vicinity of the axial center CL of the exhaust pipe 110. 110 is smoothly led out. In the PM sensor 10, the inlet 12 and the outlet 13 are arranged in the vicinity of the axial center CL where the exhaust gas flow velocity becomes the fastest in the exhaust pipe 110. As a result, the exhaust flow rate passing through the filter member 61 can be effectively increased.

  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 the female screw portion 21 of the boss portion 110 </ b> A formed in the exhaust pipe 110. The nut portion 22 is, for example, a hexagonal nut, and is fixed to the upper end portion of the male screw portion 21. The male screw portion 21 and the nut portion 22 have through holes (not shown) through which the first conductive wire 62A, the second conductive wire 63A, the third conductive wire 62B, the fourth conductive wire 63B, and the like are inserted. Is formed.

  The sensor unit 60 includes a plurality of filter layers 61 and a plurality of first electrode plates 62 and second electrode plates 63.

  The filter layer 61 functions as a filter member having a plurality of cells that collect particulate matter in the exhaust gas. The filter layer 61 is, for example, plugged alternately upstream and downstream of a plurality of cells that are partitioned by partition walls such as porous ceramics to form an exhaust passage, and these cells are arranged in parallel in one direction. It is formed in a rectangular parallelepiped shape. The PM contained in the exhaust gas flows into the cell C2 whose upstream side is plugged from the cell C1 whose downstream side is plugged, as shown by a broken line arrow in FIG. 3B. C1 partition walls (in FIG. 3B, the partition walls are omitted for the sake of clarity). In the following description, the cell flow path direction is the length direction of the sensor section 60 (arrow L in FIG. 3A), and the direction orthogonal to the cell flow path direction is the width direction of the sensor section 60 (arrow in FIG. 3A). W).

  The first electrode plate 62 and the second electrode plate 63 are, for example, plate-like conductive members, and the outer dimensions in the length direction L and the width direction W are formed substantially the same as the filter layer 61. Yes. The first electrode plate 62 and the second electrode plate 63 are alternately stacked with the filter layer 61 interposed therebetween.

  A capacitor is formed by arranging the first electrode plate 62 and the second electrode plate 63 to face each other and sandwiching the filter layer 61 between the first electrode plate 62 and the second electrode plate 63. ing. By forming a capacitor with the flat plate-like first electrode plate 62 and second electrode plate 63, it becomes possible to effectively secure the electrode surface area S and increase the absolute value of the detectable capacitance. Is possible. Further, since the inter-electrode distance d becomes the cell pitch and is made uniform, variations in the initial capacitance can be effectively suppressed.

  The first electrode plate 62 is connected to the control unit 40 via the first conductive line 62A or the third conductive line 62B. Similarly, the second electrode plate 63 is connected to the control unit 40 via the second conductive line 63A or the fourth conductive line 63B.

  The control unit 40 includes a filter regeneration control unit 41, a first PM amount estimation calculation unit 42A, a second PM amount estimation calculation unit 42B, and a diagnosis unit 43.

  The filter regeneration control unit 41 sets an electric heater (not shown) according to the capacitance between the first electrode plate 62 and the second electrode plate 63 detected by a capacitance detection circuit (not shown). Energize. The heat generated from the energized electric heater burns and removes the PM accumulated in the cell C1. Thus, the filter regeneration control unit 41 controls the filter regeneration of the filter layer 61. Instead, the filter regeneration control unit 41 directly applies a voltage to the first electrode plate 62 and the second electrode plate 63, and generates heat from the first electrode plate 62 and the second electrode plate 63. The filter regeneration of the filter layer 61 may be controlled by burning and removing the PM accumulated in the cell C1.

  The first PM amount estimation calculation unit 42A and the second PM amount estimation calculation unit 42B are discharged from the engine 100 based on the amount of change in capacitance in the regeneration interval from the end of filter regeneration to the start of the next filter regeneration. Estimate the total amount of PM in the exhaust gas. Here, the first PM amount estimation calculation unit 42A and the second PM amount estimation calculation unit 42B function as an estimation unit that estimates the amount of particulate matter based on the electrical characteristic values between a plurality of pairs of electrodes. To do.

  Below, an example of the estimation method of total PM amount is demonstrated concretely. The capacitance Cp between the electrodes is expressed by the following formula 1 where ε is the dielectric constant of the medium between the electrode plates 62 and 63, S is the surface area of the electrode plates 62 and 63, and d is the distance between the electrode plates 62 and 63. Is done.

  In Formula 1, the surface areas S of the electrode plates 62 and 63 are constant, and when the dielectric constant ε and the distance d change due to PM collected in the cell C1, the capacitance Cp also changes accordingly. It is known that a substantially proportional relationship is established between the capacitance Cp between the electrode plates 62 and 63 and the amount of PM deposited on the filter layer 61.

When the amount of PM deposited in the cell C1 exceeds the upper limit value, the proportional relationship between the capacitance Cp between the electrode plates 62 and 63 and the amount of PM deposition is lost, and the capacitance between the electrode plates 62 and 63 is lost. The estimation accuracy of Cp decreases. Therefore, when the electrostatic capacity Cp of the electrode plates 62 and 63 reaches a predetermined electrostatic capacity upper limit threshold Cp _MAX indicating the PM upper limit deposition amount, the filter regeneration control unit 41 starts filter regeneration control for energizing the electric heater. . This filter regeneration control is continued until the capacitance Cp drops to a predetermined capacitance lower limit threshold Cp _min that indicates complete removal of PM.

The PM amount estimation calculation units 42A and 42B are arranged in the exhaust gas discharged from the engine 100 based on the capacitance change amount ΔCp during the regeneration interval T _n (from the end of the filter regeneration control to the start of the next filter regeneration control). Estimate the total PM amount m _PMSUM . The PM amount m _PMn collected by the filter layer 61 during the regeneration interval T _n is obtained by the following Equation 2 obtained by multiplying the capacitance change amount ΔCp by the primary coefficient β.

The PM amount estimation calculation units 42A and 42B sequentially accumulate the PM amount m _PMn between the regeneration intervals T _n calculated from Equation 2 based on the following Equation 3 to calculate the total amount in the exhaust gas discharged from the engine 100. _Calculate PM amount m _PMSUM in real time.

In addition, estimation of PM amount is not restricted to said method, Various methods are employable. For example, a map can be created by _obtaining a relationship between the capacitance Cp and the PM amount m _PM in advance by experiments or the like, and the total PM amount or instantaneous PM amount can be estimated by referring to this map.

  The diagnosis unit 43 has a predetermined threshold value for the magnitude of the difference between the particulate matter amount estimated by the first PM amount estimation calculation unit 42A and the particulate matter amount estimated by the second PM amount estimation calculation unit 42B. A comparison is made, and whether or not an abnormality has occurred in the PM sensor 10 is diagnosed based on the comparison result. Here, the predetermined threshold value is not limited as long as it can be diagnosed whether or not an abnormality has occurred in the PM sensor 10. For example, using the PM sensor 10 in which no abnormality has occurred, the amount of particulate matter estimated by the first PM amount estimation calculation unit 42A and the amount of particulate matter estimated by the second PM amount estimation calculation unit 42B A difference distribution is obtained in advance based on experiments or the like, and a threshold is determined in advance based on the distribution. Thus, the PM sensor 10 can have a self-diagnosis function.

  The diagnosis unit 43 diagnoses whether or not an abnormality has occurred in the PM sensor 10 in conjunction with the regeneration process of the filter layer 61. In one example, immediately after the filter layer 61 is regenerated, the diagnosis unit 43 detects the particulate matter amount estimated by the first PM amount estimation calculation unit 42A and the particulate matter estimated by the second PM amount estimation calculation unit 42B. The magnitude of the difference from the quantity is compared with a predetermined threshold value. Here, immediately after the filter layer 61 is regenerated is a predetermined time after the filter layer 61 is regenerated, but as long as the particulate matter adhering to the filter layer 61 can be ignored. There is no particular restriction on the time. The diagnosis unit 43 diagnoses the PM sensor 10 immediately after the filter layer 61 is regenerated, for example, whether or not an abnormality of the PM sensor 10 due to, for example, defective combustion of particulate matter or a failure of the electric heater has occurred. Can be diagnosed.

  In one example, the diagnosis unit 43 determines that the particulate matter amount estimated by the first PM amount estimation calculation unit 42A and the particulate matter estimated by the second PM amount estimation calculation unit 42B immediately before the filter layer 61 is regenerated. The magnitude of the difference from the quantity is compared with a predetermined threshold value. Here, the time point immediately before the filter layer 61 is regenerated is a predetermined time before the time when the filter layer 61 is regenerated, but the closer the time the filter layer 61 is regenerated, the better. The diagnosis unit 43 diagnoses the PM sensor 10 immediately before the filter layer 61 is regenerated, so that, for example, the PM sensor due to non-uniformity in the way the particulate matter adheres, clogging of the filter layer 61, or the like. It is possible to diagnose whether or not ten abnormalities have occurred.

  In one example, the diagnosis unit 43 is estimated by the first PM amount estimation calculation unit 42A and the second PM amount estimation calculation unit 42B both immediately after the filter layer 61 is regenerated and immediately before the filter layer 61 is regenerated. The difference in the amount of particulate matter to be compared is compared with a predetermined threshold value. In this way, the diagnosis unit 43 can perform a more accurate diagnosis.

  In one example, the first PM amount estimation calculation unit 42A and the second PM amount estimation calculation unit 42B are the same PM amount estimation calculation unit. One PM amount estimation calculation unit functions as a first PM amount estimation calculation unit 42A at a certain point in time, and functions as a second PM amount estimation calculation unit 42B at another point in time. In this way, the configuration of the control unit 40 can be simplified.

(Other embodiments)
In the first embodiment, the control unit 40 includes a filter regeneration control unit 41, a first PM amount estimation calculation unit 42A, a second PM amount estimation calculation unit 42B, and a diagnosis unit 43. However, instead of this, at least one of the filter regeneration control unit 41, the first PM amount estimation calculation unit 42A, the second PM amount estimation calculation unit 42B, and the diagnosis unit 43 is replaced with separate hardware. May be provided.

  In the first embodiment, the PM sensor 10 estimates the total PM amount in the exhaust gas discharged from the engine 100 based on the capacitance between the first electrode plate 62 and the second electrode plate 63. doing. Instead, the PM sensor 10 detects the exhaust gas exhausted from the engine 100 based on a change in other electrical characteristic values such as an electrical resistance value between the first electrode plate 62 and the second electrode plate 63. The total PM amount in the medium may be estimated.

  As long as at least one of the first electrode plates 62 is connected to the first conductive line 62A and at least one other of the first electrode plates 62 is connected to the third conductive line 62B, the first The method of connecting the electrode plate 62 and the control unit 40 is not particularly limited. As long as at least one of the second electrode plates 63 is connected to the second conductive line 63A and at least one other of the first electrode plates 63 is connected to the fourth conductive line 63B, The connection method of the first electrode plate 63 and the control unit 40 is not particularly limited. Accordingly, the way of connection is not limited to that shown in FIG. 3A.

  The PM (particulate matter) sensor according to the present disclosure is suitable for use in a vehicle equipped with a diesel engine.

DESCRIPTION OF SYMBOLS 10 PM sensor 11 Case member 11A Inner case part 11B Outer case part 12 Inlet port 13 Outlet port 14 Passage port 15 Channel 20 Base part 21 Male screw part 22 Nut part 40 Control unit 41 Filter regeneration control part 42A 1st PM amount Estimation calculation unit 42B Second PM amount estimation calculation unit 43 Diagnosis unit 60 Sensor unit 61 Filter layer 62 First electrode plate 62A First conductive wire 62B Third conductive wire 63 Second electrode plate 63A Second conductive Line 63B Fourth conductive line

Claims (4)

A filter member having a plurality of cells for collecting particulate matter in the exhaust;
A plurality of pairs of electrodes opposed to each other across the cell;
An estimation unit for estimating the amount of particulate matter based on the electrical property value between the plurality of pairs of electrodes;
A comparison between the magnitude of the difference in the amount of the particulate matter between the plurality of pairs of electrodes and a predetermined threshold value, and a diagnostic unit that diagnoses whether an abnormality has occurred based on the result of the comparison;
With
The diagnosis unit is a sensor that executes the diagnosis in conjunction with a regeneration process of the filter member.   The sensor according to claim 1, wherein the diagnosis unit executes the diagnosis immediately before executing the regeneration process of the filter member.   The sensor according to claim 1, wherein the diagnosis unit executes the diagnosis immediately after execution of the regeneration process of the filter member.   The sensor according to claim 1, wherein the electrical characteristic value is a capacitance.

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