JP2017040563A - Particulate matter detection sensor and method for manufacturing particulate matter detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a particulate matter detection sensor, capable of reducing the variation of sensitivity between individual sensor elements resulting from defects of an insulating base to improve detection accuracy, and the particulate matter detection sensor.SOLUTION: A particulate matter detection sensor for detecting a particulate matter in gas to be measured comprises a sensor element 1 including a pair of detection electrodes 3 and 4 having at least a part buried in an insulating base 2. When the detection part 11 is immersed in water having a conductivity of 100 μS/cm at a temperature of 25°C, a resistivity Rw in the water represented by the following formula 1 is 1.2 GΩcm or more. Rw=R1×S/D...(the formula 1), where R1 is a resistance (a unit: GΩ) between the pair of detection electrodes; S is the area (a unit: cm) of the detection electrode; and D is an electrode interval (a unit: cm) between the pair of detection electrodes.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particulate matter detection sensor for detecting a conductive particulate matter contained in a gas to be measured, and a method for manufacturing the particulate matter detection sensor.

  In order to detect the amount of particulate matter (ie, particulate matter (PM)) in exhaust gas discharged from an internal combustion engine, an electrical resistance particulate matter detection sensor is used. As an example, the particulate matter detection sensor disclosed in Patent Document 1 has an insulating substrate and a detection electrode at least partially embedded in the insulating substrate, and detects the side surface where the detection electrode is exposed. A sensor element as a surface is provided.

  On the detection surface of such a sensor element, detection electrodes having different polarities are alternately arranged with an insulating layer interposed therebetween. When an electrostatic field is formed by applying a voltage between these electrodes, the charged particulate matter is attracted and collected on the detection surface, and the electrodes become conductive. Therefore, the amount of particulate matter contained in the exhaust gas can be detected from the change in resistance value between the electrodes.

JP 2012-78130 A

  In the particulate matter detection sensor having the above-described configuration, the insulating substrate is formed by laminating a sheet material serving as an insulating layer, and the detection electrode is formed of a conductive film disposed between the layers of the sheet material. For example, the laminated body is formed into a block shape having a size to be a plurality of sensor elements, and then cut and fired to form individual sensor elements.

  However, it has been found that when a defect occurs in the insulating substrate during manufacturing of the laminate, a leak current is likely to occur due to the defect. Defects are considered to be due to poor adhesion or breakage that occurs when, for example, the sheet material constituting the insulating substrate is pressure-bonded with the conductive film interposed therebetween, but may not be detected as a decrease in insulation performance in a normal inspection process. is there. In addition, since the amount and size of defects differ for each sensor element, even if the same voltage is applied between the electrodes of the sensor element, the magnitude of the leakage current differs, and the strength of the electrostatic field formed between the electrodes also increases. It is not uniform. This tendency increases as the insulating layer becomes thinner. As a result, there is a problem that sensitivity variation increases between individual sensor elements, and detection accuracy decreases.

  The present invention has been made in view of such a problem, and a particulate matter detection sensor having high detection accuracy by suppressing sensitivity variations caused between individual elements due to defects inside an insulating substrate. And a method of manufacturing the same.

One aspect of the present invention is a particulate matter detection sensor for detecting particulate matter in a gas to be measured,
A sensor element having an insulating substrate and a pair of detection electrodes at least partially embedded in the insulating substrate;
When the sensor element immerses the detection unit including the pair of detection electrodes in water having a conductivity of 100 μS / cm at a temperature of 25 ° C., the resistivity Rw in water represented by the following formula 1 is: It is in the particulate matter detection sensor which is 1.2 GΩcm or more.
Rw = R1 × S / D (Formula 1)
In Equation 1, R1 is a resistance between the pair of detection electrodes, S is an area of the detection electrode, and D is an electrode interval between the pair of detection electrodes.

Another aspect of the present invention is a method for manufacturing a particulate matter detection sensor for detecting particulate matter contained in a gas to be measured.
While laminating a plurality of ceramic green sheets whose plastic deformation rate represented by the following formula 3 is 1% or more,
A laminating step in which a pair of conductive films are alternately arranged in the laminating direction between the plurality of ceramic green sheets to form a laminate;
And firing the laminate to obtain a sensor element having an insulating base and a pair of detection electrodes at least partially embedded in the insulating base. In the manufacturing method.
Plastic deformation rate = (H / L) × 100 (Equation 3)
However, in Formula 3, H is the amount of strain (unit: mm) from the maximum stress to fracture in the strain-stress curve of the tensile test evaluation sample, and L is the length (unit: mm) of the linear portion of the evaluation sample. mm).

  The particulate matter detection sensor focuses on the fact that the amount and size of defects generated in the insulating substrate are reflected in the resistivity Rw in water, and the resistivity Rw in water is 1.2 GΩcm or more. If so, sensor sensitivity is improved and stable detection is possible. That is, it can be considered that there is no defect that affects the sensor sensitivity, and current leakage can be suppressed even if the sensor is arranged in a gas to be measured containing moisture. Therefore, the sensitivity of the sensor element is improved, and the detection accuracy can be improved by preventing the sensitivity from being varied for each sensor element.

  In the method for manufacturing the particulate matter detection sensor, the particulate matter detection sensor having such insulating characteristics can be easily manufactured by using a ceramic green sheet having a plastic deformation rate of 1% or more. By adjusting the plastic deformation rate of the ceramic green sheet constituting the insulating substrate to 1% or more, the deformation when the sheets are bonded to each other with the conductive film interposed therebetween is facilitated, and the step is easily absorbed. Therefore, it becomes possible to prevent the occurrence of defects by suppressing sheet breakage during bonding and sheet peeling after bonding.

  As described above, according to the above aspect, it is possible to provide a particulate matter detection sensor having a small variation in sensitivity between individual elements due to defects in the insulating substrate and improving detection accuracy, and a method for manufacturing the same.

The principal part enlarged view of the sensor element of the particulate matter detection sensor in Embodiment 1. FIG. 1 is an overall perspective view showing a schematic configuration of a particulate matter detection sensor in Embodiment 1. FIG. FIG. 3 is an exploded perspective view illustrating a configuration of a sensor element of the particulate matter detection sensor according to the first embodiment. It is a figure for demonstrating the method of calculating the plastic deformation rate of a ceramic green sheet, and the whole schematic diagram of the tensile test evaluation sample. The strain-tensile stress curve figure which shows an example of the result of a tension test. The figure which shows the relationship between the plastic deformation rate of the ceramic green sheet and the resistivity in water in an Example. The figure which shows the relationship between the resistivity in water and dead mass in an Example. The figure for demonstrating the method to measure the resistivity of a sensor element in an Example, The typical side view and front view of a sensor element. The perspective view which shows the schematic structure of the container for a measurement for demonstrating the method to measure the resistivity of the sensor element in the water in an Example. The principal part enlarged view of the sensor element of the particulate matter detection sensor in a comparative example. The principal part enlarged view of the sensor element of the particulate matter detection sensor in a comparative example. BRIEF DESCRIPTION OF THE DRAWINGS The whole schematic sectional drawing of the exhaust gas purification apparatus of the internal combustion engine containing the particulate matter detection sensor for demonstrating the measuring method of a dead mass in an Example. The figure which shows the time change of the sensor output of the particulate matter detection sensor in an Example.

(Embodiment 1)
Next, an embodiment of a particulate matter detection sensor and a manufacturing method thereof will be described with reference to FIGS. The particulate matter detection sensor in this embodiment includes a stacked sensor element 1 and detects particulate matter contained in the gas to be measured. The gas to be measured is, for example, combustion exhaust gas discharged from an internal combustion engine, and includes fine particulate matter such as conductive soot. The sensor element 1 includes an insulating base 2 and a pair of detection electrodes 3 and 4 that are at least partially embedded in the insulating base 2. For example, the pair of detection electrodes 3 and 4 are arranged flush with the surface of the insulating base 2 to constitute the detection unit 11.

  As shown in FIG. 2, the insulating base 2 has a rectangular parallelepiped shape as a whole, and the detection unit 11 in which the detection electrodes 3 and 4 are exposed on the side surface on one end side in the longitudinal direction X (that is, the right end side in the figure). Is provided. Terminal electrodes 31 and 41 are disposed on the other side surface of the insulating base 2 (that is, the left end side in the drawing) and connected to the measuring unit 12. The terminal electrodes 31 and 41 are connected to the detection electrodes 3 and 4, respectively, inside the insulating substrate 2. As shown in FIG. 3, the insulating substrate 2 is configured by laminating ceramic green sheets 2a having electrical insulating properties, and conductive films 3a and 4a serving as detection electrodes 3 and 4 are interposed between the ceramic green sheets 2a. Be placed.

  As shown in FIG. 1, in the detection unit 11, detection electrodes 3 and detection electrodes 4 having different polarities are alternately arranged on the surface of the insulating substrate 2. Here, two detection electrodes 4 are arranged in parallel at substantially equal intervals between the three detection electrodes 3. The three detection electrodes 3 and the two detection electrodes 4 are electrically connected to each other inside the insulating substrate 2 to constitute opposing electrode pairs. An interelectrode insulating layer 21 is formed between the adjacent detection electrode 3 and detection electrode 4. The thickness of the interelectrode insulating layer 21, that is, the electrode interval between the pair of detection electrodes 3 and 4 is usually about 5 μm to 100 μm, for example, about 20 μm.

The sensor element 1 is configured such that the resistivity Rw in water represented by the following formula 1 is 1.2 GΩcm or more. Here, the resistivity Rw in water refers to both electrodes 3 when the detection unit 11 including a pair of detection electrodes 3 and 4 is immersed in water having a conductivity of 100 μS / cm at a temperature of 25 ° C. 4 is the resistivity.
Rw = R1 × S / D (Formula 1)
However, in Formula 1, R1 is a resistance (unit: GΩ) between the pair of detection electrodes 3 and 4, S is an area (unit: cm ² ) of the detection electrodes 3 and 4, and D is a pair of This is an electrode interval (unit: cm) between the detection electrodes 3 and 4.

  The particulate matter detection sensor captures the particulate matter between the pair of detection electrodes 3 and 4 in the detection unit 11 and detects an electrical characteristic that changes depending on the amount of the particulate matter. Therefore, the sensor element 1 needs to ensure insulation between the detection electrodes 3 and 4 and desirably has a high resistivity. In particular, if the resistivity in water is 1.2 GΩcm or more, the insulating substrate 2 is free from defects that affect the sensor sensitivity, and variations in sensor sensitivity are reduced. For this reason, for example, in the gas to be measured containing moisture like combustion exhaust gas, moisture does not enter the defect and the insulation is not lowered. In the case where the resistivity in water is less than 1.2 GΩcm, the insulation may be deteriorated when moisture enters a defect existing inside the insulating substrate 2. Thus, by using the resistivity in water as an index, sensor sensitivity can be stabilized and detection accuracy can be improved.

The sensor element 1 is configured such that the resistivity Rd in a dry state represented by the following formula 2 is 3.6 GΩcm or more. Here, the resistivity Rd in the dry state is, for example, a pair when the detection unit 11 of the sensor element 1 is heated and then allowed to cool so that no moisture exists in the insulating base 2. The resistivity between the detection electrodes 3 and 4.
Rd = R2 × S / D (Formula 2)
However, in Formula 2, R2 is the resistance (unit: GΩ) between the pair of detection electrodes 3 and 4, S is the area (unit: cm ² ) of the detection electrodes 3 and 4, and D is This is the electrode interval (unit: cm) between the pair of detection electrodes 3 and 4.

  The sensor element 1 has a high resistivity of 3.6 GΩcm or more in the dry state when the resistivity Rw in water is 1.2 GΩcm or more, and the insulation between the pair of detection electrodes 3 and 4. Can be kept in good condition. When the resistivity Rd in the dry state is less than 3.6 GΩcm, the insulating property of the insulating substrate 2 becomes insufficient and the sensor sensitivity is lowered. Even if the resistivity Rd in the dry state is 3.6 GΩcm or more, the resistivity Rw in water may not be less than 1.2 GΩcm due to the influence of defects inside the insulating substrate 2. It is not always sufficient to determine the insulating performance of the insulating base 2 based only on the resistivity Rd in the dry state.

  In such a particulate matter detection sensor, a plurality of ceramic green sheets 2a are stacked, and a pair of conductive films 3a and 4a are alternately arranged in the stacking direction between the plurality of ceramic green sheets 2a. And a firing step of firing the laminate to obtain the sensor element 1. At this time, the insulating characteristics of the sensor element 1 can be improved by using the ceramic green sheet 2a having a predetermined plastic deformation rate. Below, the manufacturing method of the sensor element 1 is explained in full detail.

  As shown in FIG. 3, the insulating substrate 2 is made of a laminate of ceramic green sheets 2a having electrical insulation. The detection electrodes 3 and 4 are respectively composed of conductive films 3a and 4a formed on the surface of the ceramic green sheet 2a. When a predetermined number of the ceramic green sheets 2a are stacked to form the insulating substrate 2, a plurality of adjacent ceramics are detected. It is sandwiched between the green sheets 2a. For the ceramic green sheet 2a, for example, a known ceramic material such as an insulating material such as alumina, magnesia, titania, mullite, or a dielectric material obtained by mixing a high dielectric constant material such as barium titanate with alumina or zirconia is used. . For the conductive films 3a and 4a, for example, a metal material such as aluminum, gold, platinum, or tungsten, a metal oxide material such as ruthenium oxide, or a known conductive material such as a perovskite-type conductive oxide material is used. Used.

Preferably, a ceramic green sheet 2a having a plastic deformation rate represented by the following formula 3 of 1% or more is used.
Plastic deformation rate = (H / L) × 100 (Equation 3)
However, in Formula 3, H is the amount of strain (unit: mm) from the maximum stress to fracture in the strain-stress curve of the tensile test evaluation sample, and L is the length (unit: mm) of the linear portion of the evaluation sample. mm).
Here, the plastic deformation rate is calculated based on the evaluation results of the tensile test shown in FIGS. For example, the tensile test is performed using the evaluation sample 10 having the dumbbell shape shown in FIG. 4 and the length of the linear portion L, and when both ends of the evaluation sample 10 are gripped and a tensile stress is applied, Measure the amount of distortion. Thus, the strain-stress curve shown in FIG. 5 is obtained, and the strain until the fracture occurs in the plastic deformation region, that is, exceeds the strain amount H1 that is the maximum stress indicated by the arrow in the figure and the strain up to the strain amount H2 at which the fracture occurs. The amount difference H2−H1 may be the distortion amount H.

  When the ceramic green sheet 2a has a plastic deformation rate of 1% or more, when the ceramic green sheets 2a are stacked with the conductive films 3a and 4a sandwiched therebetween, the ceramic green sheets 2a are formed at the periphery of the conductive films 3a and 4a. In close contact. Thereby, after lamination | stacking of the ceramic green sheet 2a, sheet | seat peeling or a piece does not arise, but an insulation characteristic can be improved. Preferably, the plastic deformation rate is in the range of 1% to 7%, and a step generated at the peripheral edge of the conductive films 3a and 4a is absorbed to improve insulation. The plastic deformation rate can be adjusted by, for example, a binder added when the ceramic green sheet 2a is manufactured, and can be adjusted to a desired plastic deformation rate according to the swelling state of the binder solution.

  In FIG. 3, two types of electrode films 3a and 4a having the same area are alternately formed on the upper surface of a plurality of rectangular ceramic green sheets 2a adjusted to a predetermined plastic deformation rate, for example, by screen printing. Is done. The electrode films 3a and 4a have a substantially symmetrical trapezoidal shape, and are arranged at the same position where the bottoms of the same length are exposed at the side edges of the ceramic green sheet 2a. Here, the sensor element 1 is configured by laminating six ceramic green sheets 2a, and terminal electrodes 31 and 41 are formed on the upper surface of the uppermost ceramic green sheet 2a by, for example, screen printing. Below that, three ceramic green sheets 2a on which an electrode film 3a to be a detection electrode 3 is formed are arranged, and two sheets in which an electrode film 4a to be a detection electrode 4 is formed between these layers. The ceramic green sheet 2a is inserted.

  The plurality of electrode films 3a are connected to each other through through-hole conductors 3c disposed in adjacent ceramic green sheets 2a, and are connected to one of the electrode films 3a to extend to the other end side of the ceramic green sheets 2a. The terminal 3 is connected to the electrode 3b. Similarly, the plurality of electrode films 4a are connected to each other through through-hole conductors 4c formed in adjacent ceramic green sheets 2a, and connected to one of the electrode films 4a to the other end side of the ceramic green sheets 2a. The terminal electrode 41 is connected by the extending extraction electrode 4b and the through-hole conductor 4c. The through-hole conductors 3c and 4c are formed by filling a through-hole formed in the ceramic green sheet 2a with a conductive material.

  The sensor element 1 is integrated by laminating the plurality of ceramic green sheets 2a, and further arranging a layer to be a heater not shown in the lowermost layer and firing it. The heater may have a known configuration in which a heater electrode having a predetermined pattern is embedded between the ceramic green sheets 2a. An intermediate layer made of the ceramic green sheet 2a can also be disposed between the heater and the upper layer constituting the detection unit 11.

  The sensor element 1 thus obtained is arranged in the exhaust passage of the internal combustion engine, and detects, for example, particulate matter in the combustion exhaust gas that has passed through a diesel particulate filter. As shown in FIG. 1, the detection unit 11 is exposed to combustion exhaust gas flowing through an exhaust passage, with a plurality of electrode pairs including detection electrodes 3 and 4 facing each other with an interelectrode insulating layer 21 interposed therebetween. At the time of detection, a predetermined voltage is applied between the detection electrodes 3 and 4 of the detection unit 11 to form an electrostatic field, and the particulate matter is attracted and deposited on the surface of the interelectrode insulating layer 21.

  In the multilayer sensor element 1, the thickness of the ceramic green sheet 2a corresponds to the layer thickness of the interelectrode insulating layer 21, that is, the electrode interval, and the ceramic green sheet 2a is thinned to shorten the electrode interval. It becomes possible to quickly detect the substance. However, since the electrode films 3a and 4a are sandwiched between the ceramic green sheets 2a and a step is formed, the ceramic green sheet 2a is peeled off or cut off at the boundary between them, particularly at the ends of the electrode films 3a and 4a. Such defects are likely to occur. If there is such a defect, leakage current is likely to occur during detection in flue gas containing moisture, and the strength of the electrostatic field formed between the electrodes varies depending on the amount and size of the defect. Even when manufactured in the above, sensitivity may vary depending on the sensor element 1.

  On the other hand, the sensor element 1 of the present embodiment is affected by moisture in the gas to be measured because both the resistivity Rw in water and the resistivity Rd in a dry state have a resistivity higher than a predetermined value. And stable detection can be performed. Therefore, the sensitivity variation of the sensor element 1 can be suppressed and the detection accuracy by the particulate matter detection sensor can be improved.

  The sensor element 1 having the above characteristics can be easily obtained by using the ceramic green sheet 2a having a predetermined plastic deformation rate. An example of a method for adjusting the plastic deformation rate of the ceramic green sheet 2a and a method for manufacturing the sensor element 1 using the method will be described below as examples.

(Example)
The sensor element 1 having the above configuration was manufactured, and the relationship between the resistivity in water and in the dry state and the plastic deformation rate of the ceramic green sheet was examined.
First, an alumina green sheet was produced as the ceramic green sheet 2a. A solvent such as ethanol was added to the alumina powder to form a slurry, and pulverized with a ball mill or the like to make the average particle size 0.5 μm or less. A necessary amount of a separately prepared binder solution was added to and mixed with the alumina slurry, and foreign matters were removed by filtering with a filter to obtain an alumina sheet forming slurry.

The binder solution was prepared by adding a binder such as polyvinyl butyral and a plasticizer such as benzylbutyl phthalate to a solvent such as ethanol and mixing them. At this time, the swelling state of the binder was adjusted according to the standing time after mixing.
The plastic deformation rate of the alumina green sheet can be adjusted by the standing time of the binder solution to be added, that is, the swelling state of the binder. When the standing time is short and the binder is not sufficiently swollen, the green sheet hardly undergoes plastic deformation. If the standing time is extended, the binder swells and the green sheet becomes plastically deformed, and the plastic deformation rate can be adjusted by the standing time. However, if the standing time is too long, the binder swells too much and the plastic deformation rate becomes small.

  Using this slurry for forming an alumina sheet, it was formed into a sheet by a doctor blade method or the like and dried to obtain an alumina green sheet. The thickness of the alumina green sheet was adjusted according to the use site. For example, the alumina green sheet used for the interelectrode insulating layer 21 was formed into a thin alumina green sheet so as to have a thickness of 20 μm after lamination and firing according to the electrode spacing (for example, 20 μm). Moreover, when forming a heater and an intermediate | middle layer, the thick alumina green sheet was shape | molded so that it might become 200 micrometers after lamination | stacking and baking, for example. When forming a thick alumina green sheet, the viscosity of the alumina sheet forming slurry may be adjusted as necessary. The thickness of the sheet can be adjusted by the blade gap in the case of a doctor blade method, for example.

The produced alumina green sheet was cut into a predetermined size, and electrode films 3a and 4a to be the detection electrodes 3 and 4 were formed into a predetermined shape by screen printing or the like. Similarly, a heater or the like was formed. These sheets were laminated in a predetermined order and pressed and pressure-bonded by a method such as uniaxial pressing or cold isostatic pressing (that is, CIP). For example, the conditions for CIP were 85 ° C. and 49 MPa.
In this way, a laminate block in which a plurality of sensor elements were integrated was produced. Next, the laminated body block was cut for each sensor element by a cutting machine or dicing, and degreased and fired (for example, 1450 ° C., 2 hours). Thereafter, the detection electrode 11 was polished to expose the detection electrodes 3 and 4, thereby obtaining the sensor element 1.

  With respect to the obtained sensor element 1, the relationship between the plastic deformation rate of the alumina green sheet, the resistivity Rw in water, and the dead mass that serves as an index of sensor sensitivity was investigated, and the results are shown in FIGS. Shown (ie, samples S1-S6). Each sample S1-S6 uses the same material alumina green sheet, and changes the swelling state of a binder, and makes plastic deformation rate 0-7%. The plastic deformation rate was calculated by preparing an evaluation sample for each of the samples S1 to S6 and measuring the amount of strain by the method shown in FIGS.

The resistivity Rw in water was calculated based on Equation 1 described above. As shown in FIGS. 8 and 9, in the detection unit 11 of the sensor element 1, when the area of the detection electrodes 3 and 4 is S and the electrode interval between the detection electrodes 3 and 4 is D, a predetermined conductivity is obtained. A measurement container 13 that contains water W (that is, conductivity at 25 ° C. of 100 μS / cm) was prepared, and the resistance R1 between the detection electrodes 3 and 4 was measured.
First, the internal heater (not shown) of the sensor element 1 was energized, and the detection unit 11 was heated at a temperature of about 800 ° C. for 2 minutes. Thus, the conductive organic matter adhering to the detection surface was removed by combustion, and then cooled to room temperature. It inserted in the container 13 for a measurement so that the detection part 11 of the sensor element 1 might become a bottom part side, and left to stand for 5 minutes in the state in which the detection part 11 was immersed in water. Next, the resistance R1 between the electrodes was measured by the measuring unit 12, and the resistivity Rw in water was calculated from the area S of the electrodes and the electrode spacing D.

  As is clear from FIGS. 6 and 7, there is a correlation between the plastic deformation rate (unit:%) of the alumina green sheet, the resistivity Rw (unit: GΩcm) in water, and the dead mass (mg). . In FIG. 6, the resistivity Rw in water increases as the plastic deformation rate increases. In particular, the increase rate is large until the plastic deformation rate is 0 to 1%. When the plastic deformation rate is 1% and the resistivity Rw reaches 1.2 GΩcm, thereafter, the increase in the resistivity Rw in water becomes gradual and becomes almost stable.

  At this time, when the surface of the detection unit 11 was observed for the sensor element 1 having a resistivity Rw in water of less than 1.2 GΩcm, as shown in FIG. 10 and FIG. Peeling B occurred. No crack A or peeling B was observed in the sensor element 1 having a resistivity Rw in water of 1.2 GΩcm or more.

  On the other hand, in FIG. 7, the sensor element 1 has an insensitive mass that decreases as the resistivity Rw in water increases, and the sensor sensitivity is improved. In particular, when the resistivity Rw in water is 1.2 GΩcm or more, the dead mass is less than 20 mg and becomes almost constant at around 17 mg. Here, the dead mass is the PM weight corresponding to the threshold value of the sensor output, and is measured by an actual machine test. As shown in FIGS. 12 and 13, the exhaust pipe 101 of the internal combustion engine E is provided with an oxidation catalyst 103 and a diesel particulate filter (ie, DPF) 102 from the upstream side, and the sensor element 1 is disposed downstream thereof. A particulate matter detection sensor S <b> 100 is provided to detect particulate matter PM that has passed through the DPF 102. Here, the PM weight discharged from the downstream end of the exhaust pipe 101 between the start of measurement and the time when the sensor output reaches a predetermined threshold value was defined as a dead mass.

  Table 1 shows the resistivity Rd (unit: GΩcm) in the dry state, the plastic deformation rate (unit:%) of the alumina green sheet, and the dead mass (unit: mg) for the sensor elements 1 of the samples S1 to S6. ). When measuring the resistivity Rd in the dry state, the detector 11 of the sensor element 1 shown in FIG. 7 is preliminarily subjected to energization processing to the built-in heater in the same manner as when measuring the resistivity Rw in water ( That is, after heating to about 800 ° C. for 2 minutes and cooling to room temperature, the measurement unit 12 measured the resistance R2 between the electrodes. Based on the measurement result R2, the electrode area S, and the electrode spacing D, the resistivity Rd in the dry state was calculated based on the above equation 2.

  As is apparent from Table 1, when the plastic deformation rate (unit:%) of the alumina green sheet is increased from 0%, the resistivity Rd (unit: GΩcm) in the dry state is more rapid than the resistivity Rw in water. To increase. In the range where the plastic deformation rate is 0.5% or more, the resistivity Rd in the dry state is 3.6 GΩcm or more which can be measured by the measuring unit 12 and generally has the insulating characteristics required for the sensor element 1. Satisfied. However, the insensitive mass representing the sensor sensitivity is, for example, that the samples S4 to S6 having a plastic deformation rate of 1.0% or more show substantially equivalent good numerical values, whereas the plastic deformation rate is 0.5%. In sample S3, the dead mass exceeds 20 mg, and the sensor sensitivity is slightly inferior. For this reason, using only the resistivity Rd in the dry state for the quality determination of the sensor element 1 causes a variation in the sensitivity of the sensor element 1.

  On the other hand, if the resistivity Rw in water is 1.2 GΩcm or more, the sensor element 1 exhibits stable and excellent insulating characteristics as described above. At the same time, the resistivity Rd in the dry state is also 3.6 GΩcm or more. The sensor element 1 exhibiting such insulating characteristics can be obtained by adjusting the plastic deformation rate of the alumina green sheet constituting the insulating base 2. When the plastic deformation rate of the alumina green sheet to be the ceramic green sheet 2a is 1% or more, the electrode films 3a and 4a are laminated when the electrode films 3a and 4a to be the detection electrodes 3 and 4 are sandwiched and bonded. The alumina green sheet is plastically deformed following the shape of the outer peripheral edge of the sheet.

  For this reason, as shown in FIG. 1, the sensor element 1 in which the adjacent alumina green sheets are in close contact with each other at the edge where the electrode films 3a and 4a are interrupted is obtained. In such a sensor element 1, no defective space is formed in the insulating base 2, so that good insulation is ensured. On the other hand, when the plastic deformation rate of the alumina green sheet is less than 1%, the alumina green sheet cannot follow the outer peripheral shape of the electrode films 3a and 4a at the time of lamination and pressure bonding, and stress concentrates on the step portion. It is presumed that the sheet is cut or the sheet is peeled off at the step portion (see, for example, FIGS. 10 and 11).

  As described above, in the particulate matter detection sensor, the detection unit 11 of the sensor element 1 is set such that the resistivity Rw in water is 1.2 GΩcm or more, or the resistivity Rd in the dry state is 3. By configuring so as to be 6 GΩcm or more, the amount of defects in the interelectrode insulating layer 21 can be suppressed. Accordingly, even when a plurality of sensor elements 1 are cut out from a block-shaped laminate and manufactured simultaneously, defects occurring inside the laminate are suppressed, so that variations in sensitivity of sensor elements due to defects are suppressed, Detection accuracy can be improved.

  The particulate matter detection sensor of the present invention is not limited to the above embodiment and the above examples, and various modifications can be made without departing from the spirit of the present invention. For example, in Embodiment 1 and Examples described above, the particulate matter contained in the combustion exhaust gas of the internal combustion engine has been described. However, the present invention can be applied to any gas to be measured that contains particulate matter. In addition, the method for manufacturing the particulate matter detection sensor is not limited to the above-described method, as long as the sensor element 1 having the insulating characteristics can be obtained.

  In addition, the sensor element 1 constituting the particulate matter detection sensor may have a configuration in which at least a part of the detection electrodes 3 and 4 is embedded in the laminated insulating base 2, and may be a ceramic green sheet or a detection purpose. The shape, size, material, and the like of the electrode and other parts can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Sensor element 11 Detection part 12 Measurement part 2 Insulating base | substrate 2a Ceramic green sheet 3, 4 Electrode for detection 3a, 4a Conductive film 31, 41 Terminal electrode

Claims (6)

A particulate matter detection sensor for detecting particulate matter contained in a gas to be measured,
A sensor element (1) having an insulating substrate (2) and a pair of detection electrodes (3, 4) at least partially embedded in the insulating substrate (2);
The sensor element (1) has the following formula 1 when the detection unit (11) including the pair of detection electrodes (3, 4) is immersed in water having a conductivity of 100 μS / cm at a temperature of 25 ° C. A particulate matter detection sensor having a resistivity Rw in water of 1.2 GΩcm or more.
Rw = R1 × S / D (Formula 1)
However, in Formula 1, R1 is the resistance (unit: GΩ) between the pair of detection electrodes, S is the area (unit: cm ² ) of the detection electrode, and D is the pair of detection electrodes. Electrode spacing (unit: cm). The particulate matter detection sensor according to claim 1, wherein the sensor element (1) has a resistivity Rd in a dry state represented by the following formula 2 of 3.6 GΩcm or more.
Rd = R2 × S / D (Formula 2)
However, in Formula 2, R2 is the resistance (unit: GΩ) between the pair of detection electrodes, S is the area (unit: cm ² ) of the detection electrode, and D is the pair of detection electrodes. Electrode spacing (unit: cm).   The particulate matter detection sensor according to claim 1 or 2, wherein an electrode interval between the pair of detection electrodes (3, 4) is 5 µm to 100 µm.   The particulate matter detection sensor according to any one of claims 1 to 3, wherein the gas to be measured is combustion exhaust gas discharged from an internal combustion engine. A manufacturing method of a particulate matter detection sensor for detecting particulate matter contained in a gas to be measured,
While laminating a plurality of ceramic green sheets (2a) whose plastic deformation rate represented by the following formula 3 is 1% or more,
A laminating step in which a pair of conductive films (3a, 4a) are alternately arranged in the laminating direction between the plurality of ceramic green sheets (2a) to form a laminate;
A sensor element (1) having an insulating base (2) and a pair of detection electrodes (3, 4) at least partially embedded in the insulating base (2) by firing the laminate. A method for producing a particulate matter detection sensor, comprising: a firing step.
Plastic deformation rate = (H / L) × 100 (Equation 3)
However, in Formula 3, H is the amount of strain (unit: mm) from the maximum stress to fracture in the strain-stress curve of the tensile test evaluation sample, and L is the length (unit: mm) of the linear portion of the evaluation sample. mm).   6. The method for manufacturing a particulate matter detection sensor according to claim 5, wherein the gas to be measured is combustion exhaust gas discharged from an internal combustion engine.

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