JP2016161541A - Sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor that can correctly obtain an amount of PM deposition.SOLUTION: The sensor comprises: a sensor unit 8 in which at least one pair of electrodes A and B forming a capacitor with the electrodes A and B arranged to oppose each other across a cell is formed in a filter member 16; estimation means 101 that estimates an amount of deposition of a particle like substance to be collected by the filter member 16 on the basis of an electrostatic capacity between the electrodes A and B; temperature detection means 102 that detects a temperature of the sensor unit 8; and a reference electrostatic capacity map 23 that is created by, preliminarily for each temperature of the sensor unit 8, obtaining the reference electrostatic capacity serving as the electrostatic capacity between the electrodes A and B when the particle like substance is not collected by the filter member 16. The estimation means 101 is configured to: obtain the reference electrostatic capacity corresponding to the temperature of the sensor unit 8 detected by the temperature detection means 102 with reference to the reference electrostatic capacity map 23; and estimate an amount of deposition of the particle like substance on the basis of a difference having the reference electrostatic capacity subtracted from the electrostatic capacity between the electrodes A and B.SELECTED DRAWING: Figure 2

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.

  As a filter for collecting PM in exhaust gas discharged from a diesel engine, for example, a diesel particulate filter (DPF) is known. 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 JP 2014-055820 A

  However, the above-described conventional PM sensor has a problem in that the amount of accumulated PM cannot be accurately obtained because the detected capacitance value changes depending on the temperature.

  Therefore, an object of the present invention is to provide a sensor that can solve the above-described problems and can accurately determine the PM deposition amount.

  The present invention has been devised to achieve the above object, and is disposed opposite to a filter member including a cell that is disposed in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas, with the cell interposed therebetween. And a sensor unit provided with at least a pair of electrodes forming a capacitor, and an estimation means for estimating the amount of particulate matter deposited on the filter member based on the capacitance between the electrodes. Temperature detection means for detecting the temperature of the sensor unit, and the pair of the particulate matter when the particulate matter is not collected in the filter member in advance for each temperature of the sensor unit. A reference capacitance map created by obtaining a reference capacitance which is a capacitance between the electrodes, and the estimation means refers to the reference capacitance map and is detected by the temperature detection means. The sensor unit A reference capacitance corresponding to the temperature is obtained, and the accumulation amount of the particulate matter is estimated based on a difference in capacitance obtained by subtracting the reference capacitance from the capacitance between the electrodes. It is a sensor.

  ADVANTAGE OF THE INVENTION According to this invention, the sensor which can obtain | require PM accumulation amount correctly can be provided.

It is a schematic block diagram which shows an example of the exhaust system of the diesel engine to which the sensor which concerns on one Embodiment of this invention was applied. (A) is the typical perspective view which looked at the sensor part from the exhaust downstream side, (b) is the typical top view which looked at a part of the sensor part from the exhaust downstream side. In this invention, it is a graph which shows an example of the temperature characteristic of the electrostatic capacitance Cp. It is a schematic block diagram which shows an example of the exhaust system of the diesel engine to which the sensor which concerns on one modification of this invention was applied.

  Hereinafter, based on an accompanying drawing, a diagnostic device concerning an embodiment of the present invention is explained. 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.

  FIG. 1 is a schematic configuration diagram illustrating an example of an exhaust system of a diesel engine to which a sensor according to the present embodiment is applied.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 that is an internal combustion engine 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.

  An exhaust pipe injection device 13 and an exhaust aftertreatment device 14 are provided in the exhaust passage 12 in 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 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.

  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 constitutes the filter member of the present invention, and includes a cell that is disposed in the exhaust passage 12 and collects PM in the exhaust. The DPF 16 has a large number of cells that form a grid-like exhaust flow path partitioned by porous ceramic partition walls along the flow direction of the exhaust gas, and the upstream side and the downstream side of these cells are alternately plugged. It is configured to stop.

  A DPF inlet temperature sensor 31 is disposed on the upstream side near the DPF 16, and a DPF outlet temperature sensor 32 is disposed on the downstream side near the DPF 16. The DPF inlet temperature sensor 31 detects the temperature of the exhaust gas flowing into the DPF 16 (hereinafter referred to as DPF inlet temperature), and constitutes the temperature detection means 102 of the present invention. The DPF outlet temperature sensor 32 detects the temperature of exhaust gas flowing out from the DPF 16 (hereinafter referred to as DPF outlet temperature). These DPF inlet temperature and DPF outlet temperature are output to the electrically connected ECU 20.

  As shown in FIG. 2, in the DPF 16, a plurality of cells 1 with the exhaust upstream side released (the exhaust downstream side plugged) are selected for capacitance measurement (hereinafter, the cell 1 is used for 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 blocking members (not shown) that block the exhaust passages in the cells 4 and 5. (Hereinafter, cells 4 and 5 are referred to as blocking cells).

  The closing member provided in the closing cells 4 and 5 is made of ceramics made of the same material as the DPF 16, for example. The blocking member is embedded in the entire region in the blocking cells 4 and 5 so as to block all the exhaust passages from the plugging cells 4 and 5 to the non-plugged side. Note that the closing member does not necessarily have to be embedded in the entire area in the closing cells 4 and 5, and blocks a part of the flow path in the closing cells 4 and 5 (for example, the non-plugged side is closed). You may provide so that it may seal.

  As described above, the DPF 16 is configured such that the exhaust gas flowing into the measurement cell 1 flows 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

  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 electrodes A inserted into the electrode cell 2 project the base end portion on the exhaust downstream side outward, and the base end portions are connected to each other by a connection line 41 formed of a conductive metal member. . Similarly, the electrodes B inserted in the electrode cell 3 project the base end portion on the exhaust downstream side outward, and the base end portions are connected to each other by a connection line 42 formed of a conductive metal member. Has been.

  In this embodiment, the protrusion amount of the electrode A from the DPF 16 is set longer than the protrusion amount of the electrode B in order to avoid contact between the connection line A1 and the connection 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. Hereinafter, the DPF 16 that is a filter member provided with a pair of electrodes A and B is referred to as a sensor unit 8.

  Next, the sensor 100 according to the present embodiment will be described.

  The sensor 100 according to the present embodiment includes the sensor unit 8 described above, and an estimation unit 101 that estimates a PM deposition amount (PM deposition amount) collected in the DPF 16 based on the capacitance between the electrodes A and B. , And a capacitance type sensor.

  The estimation unit 101 includes a capacitance calculation unit 21 and a PM accumulation amount estimation unit 22. The capacitance calculation unit 21 and the PM accumulation amount estimation unit 22 are mounted on the ECU 20. The capacitance calculating unit 21 and the PM accumulation amount estimating unit 22 may be mounted on a hardware unit other than the ECU 20.

  The electrostatic capacity calculation unit 21 calculates the electrostatic capacity Cp between the electrodes A and B. The capacitance calculating unit 21 applies a DC voltage between the electrodes A and B to measure a resistance value Rp (an internal resistance value of the capacitor) between the electrodes A and B, and also applies an AC voltage between the electrodes A and B. Applied, the impedance Z between the electrodes A and B is measured, and the capacitance Cp is calculated by the following formula 1.

  The PM accumulation amount estimation unit 22 estimates the PM accumulation amount collected by the DPF 16 based on the capacitance Cp calculated by the capacitance calculation unit 21. For the estimation of the PM deposition amount, an approximate expression or a map obtained in advance by experiments can be used. Details of the estimation of the PM accumulation amount in the PM accumulation amount estimation unit 22 will be described later.

  The sensor 100 according to the present embodiment further includes a temperature detection unit 102 that detects the temperature of the sensor unit 8 and a reference capacitance map 23.

  In the present embodiment, the temperature detection means 102 includes the DPF inlet temperature sensor 31 described above, a DPF inlet temperature sensor 31 as a temperature sensor provided in the vicinity of the DPF 16, and detection values of the DPF inlet temperature sensor 31 (here, DPF And a temperature estimation unit 25 that estimates the temperature of the sensor unit 8 based on the inlet temperature. That is, in the present embodiment, the temperature detection unit 102 is configured to estimate the temperature of the sensor unit 8 from the DPF inlet temperature. Note that the specific configuration of the temperature detection unit 102 is not limited to this, and for example, a thermocouple may be provided inside the DPF 16 to directly measure the temperature of the sensor unit 8. .

  The reference capacitance map 23 is created in advance by obtaining a reference capacitance that is a capacitance Cp between the electrodes A and B when PM is not collected in the DPF 16 for each temperature of the sensor unit 8. It represents the relationship between the temperature of the sensor unit 8 and the capacitance Cp between the electrodes A and B when PM is not collected. The reference capacitance map 23 may be obtained in advance by experiments or the like.

  The temperature estimation unit 25 and the reference capacitance map 23 are mounted on the ECU 20. The temperature estimation unit 25 and the reference capacitance map 23 may be mounted on a hardware unit other than the ECU 20.

  Further, in the present embodiment, the PM accumulation amount estimation unit 22 constituting the estimation unit 101 refers to the reference capacitance map 23, and the reference electrostatic capacity corresponding to the temperature of the sensor unit 8 detected by the temperature detection unit 102. The capacitance is obtained, and the PM deposition amount is estimated based on the difference ΔCp between the capacitances obtained by subtracting the reference capacitance from the capacitance Cp between the electrodes A and B obtained by the capacitance calculation unit 21. Configured.

  As shown in FIG. 3, the capacitance Cp between the electrodes A and B increases as the temperature of the sensor unit 8 increases, and increases as the PM deposition amount increases. In the present embodiment, the difference in capacitance obtained by subtracting the reference capacitance (capacitance Cp when PM is not collected in the DPF 16) at the current temperature of the sensor unit 8 from the measured capacitance Cp. Based on ΔCp, the PM deposition amount is estimated. As a result, the capacitance Cp can be accurately obtained regardless of the temperature.

  Further, the capacitance Cp also changes due to moisture in the DPF 16 such as when the DPF 16 gets wet. As described above, the capacitance Cp is calculated based on the measured resistance value Rp and the impedance Z, but the resistance value Rp between the electrodes A and B greatly changes due to the influence of moisture in the DPF 16, and as a result. It is considered that the capacitance Cp cannot be obtained accurately.

  Therefore, in the present embodiment, the apparatus further includes a moisture effect correction unit 24 that corrects the capacitance Cp between the electrodes A and B in accordance with the resistance value Rp between the electrodes A and B, and between the corrected electrodes A and B. The PM deposition amount estimation unit 22 is configured to estimate the PM deposition amount using the capacitance Cp.

  The moisture effect correction unit 24 uses, for example, the relationship between the resistance value Rp and the correction coefficient obtained in advance, obtains a correction coefficient corresponding to the measured resistance value Rp from the relationship, and calculates the correction coefficient as the capacitance Cp. The capacitance Cp is corrected by multiplying by the measured value. The moisture effect correction unit 24 is mounted on the ECU 20. The moisture effect correction unit 24 may be mounted on a hardware unit other than the ECU 20. By providing the moisture effect correcting unit 24, it is possible to obtain the PM deposition amount more accurately without being affected by moisture.

  As described above, in the sensor 100 according to the present embodiment, the temperature detection unit 102 that detects the temperature of the sensor unit 8 and a pair when PM is not collected in the DPF 16 for each temperature of the sensor unit 8 in advance. A reference capacitance map 23 created by obtaining a reference capacitance Cp between the electrodes A and B, and the estimation means 101 (PM deposition amount estimation unit 22) includes a reference capacitance. Referring to the capacitance map 23, a reference capacitance corresponding to the temperature of the sensor unit 8 detected by the temperature detecting means 102 is obtained, and the static capacitance obtained by subtracting the reference capacitance from the capacitance Cp between the electrodes A and B is obtained. The PM deposition amount is estimated based on the difference ΔCp in the electric capacity.

  With this configuration, it is possible to accurately estimate the PM deposition amount without being affected by the temperature of the sensor unit 8.

  In the present embodiment, the apparatus further includes a moisture effect correction unit 24 that corrects the capacitance Cp between the electrodes A and B according to the resistance value Rp between the electrodes A and B, and includes an estimation unit 101 (PM deposition amount estimation unit). 22) is configured to estimate the PM deposition amount using the corrected capacitance Cp between the electrodes A and B.

  With this configuration, it is possible to estimate the PM deposition amount more accurately without being affected by moisture in the DPF 16.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  For example, although not mentioned in the above embodiment, it is considered that not only the temperature characteristic of the material constituting the DPF 16 but also the temperature characteristic of the PM itself affects the capacitance Cp. Therefore, the estimation means 101 may be configured so that the influence due to the temperature characteristic of PM can also be compensated. For example, a correction coefficient map referred to by the measured capacitance difference ΔCp and the temperature of the sensor unit 8 is provided, and the correction coefficient obtained by the correction coefficient map is multiplied by the capacitance difference ΔCp, whereby PM Compensating for the effect of temperature characteristics is conceivable.

  In the above embodiment, the DPF 16 is 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. May be arranged toward the exhaust upstream side. Further, the closing members of the closing cells 4 and 5 may be omitted.

  Further, as shown in FIG. 4, 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, a large-capacity DPF 17 (second filter member) may be provided in the exhaust passage 12 downstream of the branch portion. 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.

8 Sensor unit 10 Engine (internal combustion engine)
12 Exhaust passage 16 DPF (filter member)
23 reference capacitance map 100 sensor 101 estimation means 102 temperature detection means A, B electrode

Claims (4)

A sensor unit provided with at least a pair of electrodes that are arranged in an exhaust passage of the internal combustion engine and collect cells in the exhaust gas, and that are arranged opposite to each other with the cell interposed therebetween, to form a capacitor; An estimation means for estimating the amount of particulate matter deposited on the filter member based on the capacitance between the electrodes, and a capacitance type sensor comprising:
Temperature detecting means for detecting the temperature of the sensor unit;
A reference capacitance map created in advance by obtaining a reference capacitance that is a capacitance between the pair of electrodes when particulate matter is not collected in the filter member for each temperature of the sensor unit. And comprising
The estimation unit refers to the reference capacitance map, obtains a reference capacitance corresponding to the temperature of the sensor unit detected by the temperature detection unit, and calculates the reference capacitance between the electrodes. A sensor configured to estimate a deposition amount of particulate matter based on a difference in capacitance subtracted from a capacitance. A water effect correction unit that corrects the capacitance between the electrodes according to the resistance value between the electrodes;
The sensor according to claim 1, wherein the estimation unit is configured to estimate a deposition amount of the particulate matter using the corrected capacitance between the electrodes. The filter member is composed of a diesel particulate filter in which the upstream side and the downstream side of the plurality of cells forming a grid-like exhaust flow path partitioned by a porous partition wall are alternately plugged.
The pair of electrodes are at least one of the cells as a measurement cell, and are inserted from a non-plugged side into a pair of opposing cells among four cells adjacent to the measurement cell via a partition. The sensor according to claim 1 or 2. The temperature detection unit includes a temperature sensor provided in the vicinity of the diesel particulate filter, and a temperature estimation unit that estimates the temperature of the sensor unit based on a detection value of the temperature sensor. Sensor.

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