JP2011080926A - Particulate detecting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particulate detecting element simply constituted so as to detect the amount of conductive fine particles (particulate PM) contained in gas to be measured, suppressing the elimination of PM collected in a detection part, shortened in insensitive time, and having a highly reliable structure. <P>SOLUTION: The particulate detecting element 10 is provided, wherein a pair of detection electrodes 11 and 12 opposed to each other with a predetermined interval D are provided on the surface of an electric insulating heat-resistant substrate 13 to constitute the detection part 100 and electric resistance R<SB>X</SB>changed by the amount of the conductive fine particles collected in the detection part 100 and deposited between the detection electrodes is detected to detect the conductive fine particles in the gas to be measured. The end edges of the detection electrodes 11 and 12 are formed into inclined surfaces having an acute angle taper shape wherein the angle θ formed by the inclined surface and the electric insulating heat-resistant substrate 13 is larger than 40° but smaller than 90°, or an obtuse angle taper shape wherein the angle θ formed by the inclined surface and the electric insulating heat-resistant substrate 13 is larger than 90° but smaller than 140°. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a particulate detection sensor that is used in an exhaust system of an internal combustion engine for automobiles and is suitable for detecting the amount of carbon in a gas to be measured.

In recent years, combined with common rail fuel injection system, supercharger system, oxidation catalyst, diesel particulate filter DPF, selective catalytic reduction (SCR) system, exhaust gas recirculation (EGR) system, diesel engine, gasoline lean burn engine, etc. Reduction of environmentally hazardous substances such as nitrogen oxides NOx, particulate matter PM, unburned hydrocarbons HC, etc. contained in the combustion exhaust gas.
The DPF used in such a system generally has a honeycomb structure made of porous ceramics having excellent heat resistance and countless pores, and PM is contained in the pores existing in the porous partition walls. When trapped, PM accumulates, clogs the pores and the pressure loss increases, it is heated in the DPF by heating with a burner or heater, or by post injection that injects a small amount of fuel after the combustion explosion of the engine. The combustion exhaust gas is introduced, the DPF is heated, and PM collected in the DPF is burned and removed to be regenerated.
In order to further improve the combustion efficiency of the internal combustion engine, determination of the DPF regeneration timing, OBD (on-board diagnosis, in-vehicle fault diagnosis device) for detecting deterioration, breakage, etc. of the DPF, feedback of the internal combustion engine In control and the like, there is a need for detection means that can continuously detect the amount of PM contained in combustion exhaust gas with high accuracy.

  As a means for detecting the amount of PM in combustion exhaust gas, Patent Document 1 discloses that a pair of electrodes is formed on the surface of a substrate having heat resistance and electrical insulation, and a gap between the electrodes is used as a detection unit. Alternatively, a heating element is formed inside, and the conductive part excluding the electrode, the detection part, and the terminal part that forms the detection part on the substrate is covered with a protective layer made of an airtight and electrically insulating material, and the detection part and the protective layer A smoke density sensor is disclosed in which a heat generation density of a heating element in the vicinity of the boundary is made higher than a heat generation density of the detection unit, and a temperature of the detection unit is heated to 400 ° C. or more and 600 ° C. or less. Yes.

However, in the conventional smoke concentration sensor as disclosed in Patent Document 1, the electrical resistance between the pair of electrodes that changes due to the deposition of conductive smoke is detected by an electronic circuit, but the smoke is not deposited. In this case, since the pair of electrodes is in an insulated state, there is a dead time until the electrical resistance between the pair of electrodes gradually decreases due to the deposition of smoke and the electrical resistance can be detected by the electronic circuit.
In addition, when the smoke accumulated between the pair of electrodes is detached from the detection unit, the dead time may be further increased.
In order to use such a smoke concentration sensor for DPF failure diagnosis or DPF regeneration control, it is desirable that this dead time be as short as possible.

  Accordingly, in view of such circumstances, the present invention is a particulate detection element that detects the amount of conductive fine particles (particulate PM) contained in a gas to be measured with a simple configuration, and is collected by a detection unit. An object of the present invention is to provide a particulate detection element having a structure with a short dead time and high reliability by suppressing desorption of PM.

  In the first aspect of the invention, a pair of detection electrodes facing each other with a predetermined gap provided on the surface of the electrically insulating heat-resistant substrate is used as a detection unit, and the conductive fine particles collected by the detection unit and deposited between the detection electrodes In the particulate detection element that detects the conductive fine particles in the gas to be measured by detecting the electric resistance that varies depending on the amount of the gas, the edge of the detection electrode forms an inclined surface, and the inclined surface and the electrically insulating heat-resistant An acute angle taper with an angle greater than 40 ° and less than 90 °, or an obtuse angle taper with an angle between the inclined surface and the electrically insulating heat-resistant substrate greater than 90 ° and less than 140 °. (Claim 1).

  According to the first invention by the present inventors, according to the first invention, it becomes easy to collect PM between the electrodes, and furthermore, the PM once collected by the detection unit is hardly separated from between the detection electrodes. Become. For this reason, it was found that PM was quickly deposited between the detection electrodes, and the dead time could be shortened. When the angle is set to 40 ° or less, the PM is difficult to deposit between the detection electrodes, and when the angle is set to 140 ° or more, the detection electrode end face is separated from the scope of the present invention. It has been found that a space in which PM is not collected is formed between the electrically insulating heat-resistant substrate and the dead time becomes longer in any case.

  More desirably, as in the second aspect of the invention, the angle formed by the inclined surface and the electrically insulating heat-resistant substrate is formed in an obtuse angle taper shape of 100 ° to 125 ° (claim 2).

In 3rd invention, when the 10-point average surface roughness of the said electrically insulating heat-resistant board | substrate is set to _RZ1, and the 10-point average surface roughness of the said detection electrode is set to _RZ2 , the surface roughness of the said electrically insulating heat-resistant board | substrate. And the contrast ratio R _Z2 / R _Z1 of the surface roughness of the detection electrode is set to 3.5 or less (Claim 3).

If the contrast ratio between the surface roughness of the electrically insulating heat-resistant substrate and the surface roughness of the detection electrode is determined so as to be within the scope of the third invention by the inventors' extensive studies, it is included in the gas to be measured. PM is more likely to adhere to the surface of the electrically insulating heat-resistant substrate than the surface of the detection electrode, and it is difficult for the PM to be detached from the surface of the electrically insulating heat-resistant substrate, so that the PM is quickly removed between the detection electrodes. It was found that the dead time can be shortened because of the accumulation.
Out of the scope of the present invention, the surface roughness of the detection electrode becomes rough as the contrast ratio R _Z2 / R _Z1 between the surface roughness of the electrically insulating heat-resistant substrate and the surface roughness of the detection electrode is larger than 3.5. Or when the surface roughness of the electrically insulating heat-resistant substrate is smooth, PM becomes easier to deposit on the surface of the detection electrode than between the detection electrodes. It was found that the dead time becomes longer because it is easier to desorb from.

  In the fourth invention, the height of the detection electrode is 1 μm or more and 200 μm or less.

If the detection electrode is formed so as to fall within the scope of the fourth invention by the present inventors' earnest test, PM captured between the electrodes can be held in three dimensions, and PM from between the electrodes can be held. It has been found that the desorption time can be suppressed and the dead time can be further shortened.
When the height of the detection electrode is formed lower than 1 μm outside the scope of the present invention, PM cannot be held between the detection electrodes, and when the height of the detection electrode is formed higher than 200 μm. Since it becomes difficult for PM to penetrate deeply between the detection electrodes and easily detaches from between the detection electrodes, it has been found that the dead time becomes long.

  More preferably, as in the fifth invention, the height of the detection electrode is formed to be higher than 5 μm and lower than 150 μm.

  It has been clarified by the inventors' diligent tests that the PM is easily collected between the electrodes and the dead time is shortened by setting the height of the detection electrode within the range of the fifth invention.

  More preferably, as in the sixth invention, the height of the detection electrode is higher than 25 μm and lower than 100 μm.

  As a result of diligent tests by the present inventors, it was found that by setting the height of the detection electrode within the range of the sixth invention, PM can be easily collected between the electrodes, and the dead time is further shortened.

The expanded perspective view which shows the outline | summary of the whole particulate detection element in embodiment of this invention. The wiring example of the detection electrode in the detection part of the particulate detection element in embodiment of this invention is shown, (a) is a plane at the time of forming a comb-tooth shaped detection electrode in the direction orthogonal to the axial direction of an element FIG. 4B is a plan view when a comb-shaped detection electrode is formed in the axial direction of the element, and FIG. 4C is a plan view when the detection electrode is formed in a substantially spiral shape. It is sectional drawing which shows the characteristic of the particulate detection element which is the principal part of this invention, (a) And (b) shows the desirable range of the angle with respect to the insulating base material of the electrode end surface which is the principal part of this invention. (C) shows the desirable range of the surface roughness of the electrode with respect to the surface roughness of the insulating substrate, and (d) shows the range in which the present invention can be applied to the height of the electrode. FIG. 2 is a half sectional view showing an outline of a particulate detection sensor having a particulate detection element according to an embodiment of the present invention. The block diagram which shows the example of the exhaust gas purification apparatus which used the particulate detection sensor which has a particulate detection element in embodiment of this invention as an abnormality detection means of DPF. The characteristic view which shows the problem of the conventional particulate detection element. The characteristic view which shows the effect of the electrode end surface angle with respect to the dead time of the particulate detection element in the embodiment of the present invention. The characteristic view which shows the effect of the surface roughness ratio with respect to the dead time of the particulate detection element in the embodiment of the present invention. The characteristic view which shows the effect of the electrode height with respect to the dead time of the particulate detection element in embodiment of this invention.

The particulate detection element 10 according to the first embodiment of the present invention is, for example, a failure of a diesel particulate filter (DPF) that collects particulate matter (PM) contained in combustion exhaust discharged from a diesel internal combustion engine. In order to perform diagnosis (OBD) and DPF regeneration control, it is used in a particulate detection sensor 1 for detecting PM in combustion exhaust gas, in particular, conductive fine particles.
A feature of the particulate detection element 10 of the present invention is that PM in the gas to be measured is detected by detecting an electrical resistance that varies depending on the amount of PM deposited between a pair of opposing detection electrodes provided with a predetermined gap. By specifying the three-dimensional shape of the detection electrode in the particulate detection element, PM contained in the gas to be measured is easily collected, and the dead time of the particulate detection sensor is shortened.

The outline of the particulate detection element 10 and the particulate detection sensor 1 including the particulate detection element 10 will be described with reference to FIGS.
As shown in FIG. 1, the particulate detection element 10 is an electrically insulating heat-resistant substrate in which an electrically insulating heat-resistant material such as alumina is formed into a flat plate by a known method such as a doctor blade method, a press molding method, CIP, or HIP. 13, a detection unit 100 in which a predetermined pair of detection electrodes 11 and 12 are formed with a predetermined inter-electrode distance D therebetween, and a lead unit for electrically connecting the detection electrodes 11 and 12 to an external electrical resistance measurement unit 111 and 121 and terminal portions 112 and 122, and the insulating protective layer 14 covering the lead portions 111 and 112 excluding the detection portion 100 and the terminal portions 112 and 122.
The detection electrodes 11 and 12, which are the main part of the present invention, are characterized by a three-dimensional shape described later, and the dead time td is shortened by facilitating trapping of PM between the detection electrodes.
Further, in order to stabilize the detection electric resistance by heating the detection electrodes 11 and 12 to a predetermined temperature or to remove PM deposited on the detection unit 100 by heating, the inside or the back surface of the electrically insulating heat-resistant substrate 13 is used. It is good also as a structure which provided the heater of the omission of illustration which heats by electricity.

With reference to FIG. 2, the detection electrodes 11 and 12 which comprise the detection part 100 of the particulate detection element 10 of this invention are explained in full detail. This figure (a) shows the example at the time of forming the detection electrodes 11 and 12 in the comb-tooth shape extended in the direction orthogonal to the longitudinal axis direction of the particulate detection element 10, This figure (b) shows detection. An example in which the electrodes 11 and 12 are formed in a comb shape extending in the longitudinal axis direction of the element 10 is shown.
In either case, the end edge of the detection electrode 11 and the end edge of the detection electrode 12 are formed so as to face each other with a predetermined distance D between the electrodes.
The inter-electrode distance D can be appropriately formed in the range of 40 μm or more and 300 μm or less depending on the amount of PM present in the measurement gas to be applied. Can be demonstrated.
In the present invention, the width W of the detection electrodes 11 and 12 is not particularly limited, and can be formed with an arbitrary width.

With reference to FIG. 3, the feature of the three-dimensional shape of the detection electrodes 11 and 12 which are the principal part of this invention is demonstrated. As a first embodiment of the present invention, as shown in FIG. 3A, an angle θ formed by the edges of the detection electrodes 11 and 12 and the upper surface of the electrically insulating heat-resistant substrate 13 is larger than 40 ° and 90 °. It is formed so as to form an acute angle tapered inclined surface so as to be smaller. It has been found that when the detection electrodes 11 and 12 are formed so as to have such an angle, the dead time can be shortened as compared with the case where the inclined surfaces are not formed on the edges of the detection electrodes 11 and 12 as in the prior art. The PM floating between the detection electrodes 11 and 12 rolls around the edges of the detection electrodes 11 and 12 and easily adheres to the surface of the electrically insulating heat-resistant substrate 13, so that the gap between the electrodes D can be filled more quickly. It is presumed to be accumulated.
In the present invention, the angle θ formed with the upper surface of the electrically insulating heat-resistant substrate 13 at the edges of the detection electrodes 11 and 12 is specifically provided for providing an acutely tapered inclined surface that is larger than 40 ° and smaller than 90 °. Such a method is not particularly limited, but can be realized by the following method.
(1) When the detection electrodes 11 and 12 are formed by screen printing, the solid content ratio of the electrode forming paste is lowered, the dynamic viscosity is lowered, the vapor pressure during printing and drying is lowered, etc. By adjusting the printing conditions, the wettability with respect to the electrically insulating substrate 13 is increased, or the drying conditions are reduced.
(2) In addition to screen printing, the detection electrodes 11 and 12 can be formed by a method such as a film transfer method, a photolithography method, or a micro contact printing method. In this case, after forming the detection electrodes 11 and 12, by performing processing such as laser etching and sandblasting, an inclined surface having an acute tapered shape can be provided at the edge.

Further, as a second embodiment of the present invention, as shown in FIG. 3B, the angle θ formed between the edges of the detection electrodes 11 and 12 and the upper surface of the electrically insulating heat-resistant substrate 13 is larger than 90 °. It is formed so as to form an obtuse angle tapered inclined surface so as to be smaller than 140 °. It has been found that when the detection electrodes 11 and 12 are formed so as to have such an angle, the dead time can be further shortened as compared with the case where the inclined surfaces are not formed on the edges of the detection electrodes 11 and 12 as in the prior art. It is presumed that PM collected and deposited on the surface of the electrically insulating heat-resistant substrate 13 is difficult to desorb.
Further, it has been found that when the angle of the inclined surface formed on the edge of the detection electrodes 11 and 12 is set to 100 ° or more and 125 ° or less, PM can be more effectively collected between the detection electrodes and the dead time can be shortened.
In addition, in order to provide an obtuse angle tapered surface having an angle θ with the upper surface of the electrically insulating heat-resistant substrate 13 larger than 90 ° and smaller than 140 ° at the edge of the detection electrodes 11 and 12, as in the above case. The specific method in the present invention is not particularly limited, but can be realized by the following method.
(1) When forming the detection electrodes 11 and 12 by screen printing, contrary to the case of providing an acutely tapered inclined surface, an inorganic filler is added to the printing paste in a solid content ratio of several to several tens%, This can be realized by reducing the wettability with respect to the electrically insulating substrate 13 or increasing the drying speed to extremely reduce the fluidity during printing and drying.
In addition to (2) screen printing, the detection electrodes 11 and 12 can be formed by a method such as a film transfer method, a photolithography method, or a microcontact printing method. In this case, after forming the detection electrodes 11 and 12, by performing processing such as laser etching, sand blasting, and chemical etching, an inclined surface having an obtuse angle tapered shape can be provided at the edge.
In addition, in the photolithography method, an obtuse angle tapered inclined surface can be realized at the edge by adding an inorganic filler to the electrode paste and subjecting it to overdevelopment.

Further, as a third embodiment of the present invention, as shown in FIG. 3C, the 10-point average surface roughness R _Z1 of the electrically insulating heat-resistant substrate 13 and the 10-point average surface roughness of the detection electrodes 11 and 12 are set. In relation to the _thickness R _Z2, it is desirable that R _Z2 / R _Z1 be 3.5 or less. The 10-point average surface roughness R _Z1 of the electrically insulating heat-resistant substrate 13 is desirably 100 nm or more in order to adsorb PM on the surface. In general, the 10-point average surface roughness R _Z1 of the electrically insulating substrate 13 is 1.0 μm.
As electrically insulating 10-point average surface roughness R _Z1 heat the substrate 13 becomes more rough, chemical treatment such as chemical etching or thermal etching, honing, electrically insulating heat substrate 13 by a physical treatment such as sand blasting The detection electrode 11 is processed by chemical processing such as chemical etching or physical processing such as mirror lapping so that the surface of the detection electrode 11 or 12 is processed or the 10-point average surface roughness R _{Z2 of} the detection electrodes 11 and 12 becomes smoother. , 12 can be processed to satisfy a desired relationship.

  Furthermore, as a fourth embodiment of the present invention, as shown in FIG. 3D, it is desirable that the film thickness H of the detection electrodes 11 and 12 is 1 μm or more and 200 μm or less. According to the test described later, it is more preferable that the film thickness height H of the detection electrodes 11 and 12 is higher than 5 μm and lower than 150 μm, and the film thickness height H of the detection electrodes 11 and 12 is higher than 25 μm and 100 μm. It was found that the dead time td can be further shortened by forming it lower.

  The present invention is not limited to the above embodiment, and the effect of the present invention can be improved by combining the above embodiment. For example, the angle θ formed by the inclined surface of the edge of one of the detection electrodes 11 and 12 and the upper surface of the electrically insulating heat-resistant substrate 13 is formed in an acute taper shape that is larger than 40 ° and smaller than 90 °. The angle θ between the inclined surface of the edge of the detection electrode and the upper surface of the electrically insulating heat-resistant substrate 13 may be formed in an obtuse angle taper shape that is larger than 90 ° and smaller than 140 °.

With reference to FIG. 4, the particulate detection sensor 1 which has the particulate detection element 10 of this invention is demonstrated.
The particulate detection sensor 1 is fixed to the particulate detection element 10 inserted and fixed in the substantially cylindrical insulator 20 and the flow path wall 70 forming the gas flow path 700 to be measured, and holds the insulator 20. A housing 30 that holds the detection unit 100 of the particulate detection element 10 in a specific measurement gas, a cover body 40 that is provided on the distal end side of the housing 30 and protects the measurement unit 100 of the particulate detection element 10, A detection electrode 11 provided on the base end side, connected to the terminal portions 112 and 122 of the particulate detection element 10 via the connection fittings 113 and 123, and changes according to the amount of PM collected and deposited on the measurement unit 100. a pair of signal lines 114 and 124 for transmitting the detected electrical resistance _{R X} between 12 to the outside of the electrical resistance detecting means, which And a substantially cylindrical casing 50 that is fixed on the base end side through a sealing member 60. When a heater for heating the detection unit 100 is provided, a pair of energization lines connected to an external energization control device is connected. The cover body 40 is appropriately provided with measured gas inlet / outlet holes 410 and 411 for introducing / extracting the measured gas containing PM to / from the detection unit 100.

With reference to FIG. 5, the outline | summary of the exhaust gas purification system of the diesel engine E / G which provided the particulate detection sensor 1 of this invention is demonstrated. The diesel engine E / G is a direct injection diesel engine that is pressurized to a high pressure by a high pressure pump PMP _FL , and high pressure fuel accumulated in the common rail R is directly injected into a combustion chamber by an injector INJ.
The exhaust manifold MH _EX of the diesel engine E / G is provided with a turbine TRB that rotates using exhaust gas, and the intake manifold MH _IN is provided with a turbocharger TRB _CGR that rotates in conjunction with TRB in the turbine. ing.
The air compressed by the supercharger TRB _CGR and cooled via the intercooler CL _INT is sent to the intake manifold MH _IN . A part of the combustion exhaust discharged from the exhaust manifold MH _EX is cooled via the EGR cooler CL _EGR , and returned to the intake manifold MH _IN via the EGR valve V _EGR to improve the combustion efficiency.
The combustion exhaust discharged from the exhaust manifold MH _EX passes through the oxidation catalyst DOC to oxidize unburned hydrocarbons HC, carbon monoxide CO, and nitrogen monoxide NO, and passes through the diesel particulate filter DPF. The particulate matter PM is removed, and further, NOx is reduced to harmless N ₂ and H ₂ O by passing through a selective catalytic reduction SCR (not shown), and discharged.
At least at the outlet of the DPF, the particulate sensor 1 is mounted so that the detection unit 100 of the particulate detection element 10 of the present invention is exposed to the exhaust passage 700, and the exhaust gas is discharged into the combustion exhaust discharged from the engine E / D. The amount of PM contained is constantly monitored, and the detection result is used for DPF regeneration control and OBD (vehicle-mounted fault self-diagnosis device).

Here, with reference to FIG. 6, the problem of the conventional particulate detection element will be described. In the conventional particulate detection element, PM made of conductive carbon or the like contained in the gas to be measured is deposited between a pair of detection electrodes formed on the surface of the electrically insulating heat-resistant substrate with a predetermined gap therebetween. Then, a conduction path is formed between the detection electrodes by PM, and the electric resistance value between the electrodes gradually decreases. Therefore, the amount of PM is calculated by measuring this. FIG. 6 shows changes in the electrical resistance value between the detection electrodes when the PM amount is increased at a constant speed.
However, as shown in FIG. 6, when PM is not deposited between the detection electrodes, it is in a substantially insulated state, so the electrical resistance between the detection electrodes is several tens of MΩ or more, and accompanies PM deposition. The electric resistance value gradually decreases, but until the value becomes several MΩ or less, a detection current hardly flows and there is a dead time td in which the electric resistance value cannot be measured. If the dead time td is long, when the particulate detection element is used for OBD as described above, it may take time to detect an abnormality, and the reliability as a sensor is poor. Further, once the PM adhering between the detection electrodes is desorbed, there is a possibility that the electric resistance value increases and the dead time td becomes longer.

With reference to FIG. 7, the test result which investigated the effect with respect to dead time td of taper angle (theta) which the end surface of the detection electrodes 11 and 12 of the particulate detection element 10 of this invention and the electrically insulating heat-resistant board | substrate 13 demonstrates is demonstrated. .
In this test, the inter-electrode distance D is 40 μm, 100 μm, and 300 μm, the electrode height H is 5 μm, the 10-point average surface roughness R _Z1 of the electrically insulating heat-resistant substrate 13 is 1.0 μm, and the detection electrodes 11 and 12 The dead time td when the 10-point average surface roughness _RZ2 is 3.5 μm and the detection electrodes 11 and 12 are formed by changing the taper angle θ is measured and the result is shown in FIG.
In the conventional particulate detection element, no taper is formed on the edge of the detection electrode. Therefore, a taper angle θ of 90 ° was used as a comparative example, and a range in which the dead time td was shorter than this was determined as a range in which the effect of the present invention could be exhibited.

As shown in FIG. 7, when the electrode edge taper angle θ is formed at an acute angle, the dead time td becomes shorter than the conventional case when set in a range larger than 40 ° and smaller than 90 °. When the extreme edge taper angle θ is formed to be an obtuse angle, it has been found that the dead time td is shorter than the conventional case when it is set in a range larger than 90 ° and smaller than 140 °.
In particular, it has been found that the dead time td when the electrode edge taper angle θ is formed in the range of 95 ° to 135 ° can be made shorter than when the electrode edge taper angle θ is formed at an acute angle.
If the electrode edge taper angle θ is 40 ° or less, the dead time td becomes longer than that of the conventional case. Particularly, if the electrode edge taper angle θ is formed to be 30 ° or less, the PM holding power is remarkably lowered, and the dead time td becomes extremely long. When the electrode edge taper angle θ is formed to be 140 ° or more, a space into which PM cannot enter is formed between the edge of the detection electrodes 11 and 12 and the electrically insulating heat-resistant substrate 13, and the electric resistance between the electrodes. It was found that value detection was difficult.

Referring to FIG. 8, the relationship between the 10-point average surface roughness R _Z2 of the detection electrodes 11 and 12 of the particulate detection element 10 of the present invention and the 10-point average surface roughness R _Z1 of the electrically insulating heat-resistant substrate 13 is shown. A test result of investigating the effect on the dead time td when the regulation is performed will be described.
In this test, the inter-electrode distance D is 40 μm, 100 μm, and 300 μm, the electrode height H is 5 μm, the taper angle θ is 85 °, and the 10-point average surface roughness R _Z2 of the detection electrodes 11 and 12 is electrically insulative. The dead time td when the detection electrodes 11 and 12 are formed by changing the contrast ratio R _Z2 / R _Z1 with respect to the 10-point average surface roughness R _Z1 of the heat-resistant substrate 13 is measured, and the result is shown in FIG.
Specifically, a plurality of electrically insulating heat-resistant substrates 13 having different surface roughnesses are prepared, and the detection electrodes 11 and 12 are arranged so that the 10-point average surface roughness R _Z2 of the detection electrodes 11 and 12 is 3.5 μm. Formed and tested.
In the conventional particulate detection element, since the surface roughness of the electrically insulating heat-resistant substrate and the surface roughness of the detection electrode are not specified, the contrast ratio R _Z2 / R _Z1 (3.5) at this time is used as a comparative example. The range in which the dead time td was shorter than that of the comparative example was defined as the present example.
As shown in FIG. 8, it was found that the contrast ratio R _Z2 / R _Z1 is preferably 3.5 or less.
When the surface roughness of the electrically insulating heat-resistant substrate 13 is rougher than the surface roughness of the detection electrodes 11 and 12, that is, when the contrast ratio R _Z2 / R _Z1 is 1 or less, PM is preferentially applied to the surface of the electrically insulating heat-resistant substrate 13. However, if the surface roughness of the electrically insulating heat-resistant substrate 13 is too rough, the adhesion strength between the detection electrodes 11 and 12 may be weakened.
When the surface roughness of the electrically insulating heat-resistant substrate 13 is made smooth so that the contrast ratio R _Z2 / R _Z1 is larger than 3.5, the PM is more likely to adhere to the surface of the detection electrodes 11, 12, while the electrical insulation Since it becomes easy to detach | desorb from the surface of the heat resistant board | substrate 13, the dead time td will become long significantly.

With reference to FIG. 9, the test result investigated about the effect with respect to the dead time td of the height (film thickness) H of the detection electrodes 11 and 12 of the particulate detection element 10 of this invention is demonstrated.
In this test, the interelectrode distance D is 40 μm, 100 μm, 300 μm, the taper angle θ is 85 °, and the 10-point average surface roughness R _Z2 of the electrically insulating heat-resistant substrate 13 of the detection electrodes 11, 12 is 10-point average. the contrast ratio _R Z2 _{/ R Z1} with respect to the surface roughness _{R Z1} as 3.5, and measures the dead time td when forming the detection electrodes 11 and 12, the results are shown in Figure 9.
As shown in FIG. 9, it has been found that the height of the detection electrodes 11 and 12 is preferably 1 μm or more and 200 μm or less.

The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.
For example, in the above-described embodiment, the particulate detection sensor mounted on an internal combustion engine such as an automobile engine has been described as an example. However, the particulate detection sensor of the present invention is not limited to being mounted on a vehicle. It can also be used for particulate detection in large-scale plants such as plants.

DESCRIPTION OF SYMBOLS 1 Particulate detection sensor 10 Particulate detection element 100 Detection part 11, 12 Detection electrode 111, 121 Lead part 112, 122 Terminal part 113, 113 Connection metal fitting 114, 114 Signal line 13 Electrically insulating heat-resistant board 14 Insulating protective layer θ Detecting electrode edge taper angle D Detecting electrode distance W Detecting electrode width R _Z1 Electrical insulating heat resistant substrate 10 point average surface roughness R _Z2 Detecting electrode 10 point average surface roughness H Detecting electrode height td Dead time 20 Insulator 30 Housing 40 Cover body 50 Casing 60 Sealing member 70 Gas channel wall to be measured 700 Gas channel to be measured

JP 59-197847 A

Claims (6)

A pair of detection electrodes facing each other with a predetermined gap provided on the surface of the electrically insulating heat-resistant substrate is used as a detection unit, and the electricity varies depending on the amount of conductive fine particles collected by the detection unit and deposited between the detection electrodes. In a particulate detection element that detects resistance and detects conductive fine particles in a gas to be measured.
An edge of the detection electrode is an inclined surface, and an angle formed by the inclined surface and the electrically insulating heat-resistant substrate is greater than 40 ° and smaller than 90 °, or the inclined surface and the electrical insulating property A particulate detection element characterized in that it forms an obtuse angle taper with an angle with the heat-resistant substrate larger than 90 ° and smaller than 140 °.   The particulate detection element according to claim 1, wherein an angle formed between the inclined surface and the electrically insulating heat-resistant substrate is an obtuse angle taper of 100 ° or more and 125 ° or less. When the 10-point average surface roughness of the electrically insulating heat-resistant substrate is _RZ1, and the 10-point average surface roughness of the detection electrode is _RZ2 , the surface roughness of the electrically insulating heat-resistant substrate and the surface of the detection electrode The particulate detection element according to claim 1 or 2, wherein a contrast ratio R _Z2 / R _Z1 with roughness is 3.5 or less.   The particulate detection element according to claim 1, wherein a height of the detection electrode is 1 μm or more and 200 μm or less.   The particulate detection element according to claim 4, wherein the height of the detection electrode is higher than 5 μm and lower than 150 μm.   The particulate detection element according to claim 5, wherein the height of the detection electrode is higher than 25 μm and lower than 100 μm.

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