JP5606356B2 - Particulate matter detector - Google Patents

Description

  The present invention relates to a particulate matter detection device that detects particulate matter contained in a gas to be measured, and is particularly suitable for an exhaust purification system that purifies combustion exhaust of an internal combustion engine.

  2. Description of the Related Art Conventionally, in automobile diesel engines and the like, environmental pollutants contained in exhaust gas, particularly particulate matter (Particulate Matter; hereinafter referred to as PM as appropriate) mainly composed of soot particles and soluble organic components (SOF). In order to collect, a diesel particulate filter (hereinafter referred to as DPF as appropriate) is installed in the exhaust passage. The DPF is made of porous ceramics having excellent heat resistance, and traps PM by passing exhaust gas through a partition wall having a large number of pores.

  If the amount of collected PM exceeds the allowable amount, DPF may cause clogging and increase the negative pressure or increase the slipping of PM. It is recovering. The regeneration period generally uses the fact that the differential pressure increases with the increase in the amount of PM collected. For this reason, a differential pressure sensor is installed to detect the pressure difference upstream and downstream of the DPF. . In the regeneration process, high-temperature combustion exhaust gas is introduced into the DPF by heater heating or post injection, and PM is burned and removed.

On the other hand, as a sensor capable of directly detecting PM in exhaust gas, there is an electric resistance sensor in which a pair of conductive electrodes are formed on the surface of an insulating substrate and a heating element is formed on the back surface or inside of the substrate. Proposed. When this sensor is installed downstream of the DPF, PM passing through the DPF is detected, and the on-board diagnosis (OBD) monitors the operating state of the DPF to detect abnormalities such as cracks and breakage. It can be used for early detection.
In recent years, an extremely fine particulate material of 50 nm or less that passes through the DPF has been regarded as a problem.

  In Patent Document 1, as a particulate matter detection device for detecting such a fine particulate matter, a through-hole is formed in the particulate matter detection element body, and the inside of the wall surface forming the through-hole is covered with a dielectric. A configuration in which a pair of broken electrodes is embedded is disclosed. In this particulate matter detection element, a voltage is applied between a pair of electrodes to cause a discharge in the through-hole, and the particulate matter passing through the through-hole is charged by the discharge to electrically charge the inner wall surface of the through-hole. The particulate matter in the gas to be measured is detected by measuring the change in the electrical characteristics of the wall surface of the through-hole such as capacitance.

However, as disclosed in Patent Document 1, in the configuration in which through holes are provided so as to penetrate both side surfaces of the particulate matter detection element, the flow direction of the gas to be measured and the position of the particulate matter detection element are unavoidable. It has been found that the flow rate of the gas to be measured flowing into the through hole varies greatly depending on the relationship.
For example, the traveling direction of the gas to be measured and the opening direction of the through hole provided in the particulate matter detection element are orthogonal to each other, the flow rates of the gas to be measured flowing at both ends of the through hole are substantially equal, and a pressure difference is generated in the through hole. In such a case, there is a possibility that the gas to be measured hardly flows into the through hole in order to collect the particulate matter due to the charge of the particulate matter.
On the other hand, when the direction of travel of the gas to be measured and the opening direction of the through hole provided in the particulate matter detection element coincide, the gas to be measured having a flow rate proportional to the flow rate flows into the through hole, but the flow rate is In an early case, there is a possibility that the particulate matter collected in the through hole is blown away by the gas to be measured.

In general, in a particulate matter detection device, a portion of the particulate matter detection element that is exposed to the gas to be measured is covered with a cover having an opening in order to protect the particulate matter detection element.
Therefore, in the conventional particulate matter detection device, the opening direction of the cover body and the opening direction of the through hole are specified so that the traveling direction of the gas to be measured and the opening direction of the through hole have a predetermined positional relationship, Furthermore, when assembling the particulate matter detection device into the gas flow path to be measured, the particulate matter cannot be detected stably unless the traveling direction of the gas to be measured and the opening direction of the through hole are specified. There is a fear.

Further, when the combustion exhaust gas of the internal combustion engine is the gas to be measured, the flow velocity of the combustion exhaust gas that is the gas to be measured changes depending on the operating state of the engine.
However, in the conventional particulate matter detection device, the change in the flow rate of the gas to be measured and the change in the flow rate of the gas to be measured taken into the particulate matter detection element do not necessarily coincide with each other, and the change in the detection output is the gas to be measured. It may be difficult to distinguish whether it is due to a change in the particulate matter in it or due to a change in the flow rate of the gas to be measured.

  Furthermore, in the conventional particulate matter detection device, when the sensitivity is increased to a level at which extremely fine particulate matter that passes through the DPF can be detected, accidental trapping of particulate matter having a relatively large particle diameter, aggregates thereof, and the like. The case where the particles are collected and the case where the fine particulate matter is deposited cannot be detected separately, and the state of the DPF may be erroneously determined.

  Therefore, in view of such a situation, the present invention does not need to consider the direction of assembly of the detection element in the manufacturing process or the direction during assembly to the gas flow path to be measured. In addition to realizing stable detection regardless of the circumferential assembly angle, it is possible to prevent erroneous detection of coarse particles and stably detect extremely fine particulate matter in the measured gas flow path. The flow rate of the measurement gas taken into the detection element changes linearly in accordance with the change in the flow rate of the measurement gas, the change in the flow rate of the measurement gas and the change in the amount of particulate matter contained in the measurement gas It is an object of the present invention to provide a highly reliable particulate matter detection device that can detect and distinguish the above.

According to the first aspect of the present invention, a pair of detection electrodes are provided on an insulating substrate which is formed in a substantially flat plate shape extending in the axial direction and whose tip side is disposed in the gas to be measured, and is deposited between the detection electrodes. In a particulate matter detection device including a particulate matter detection element that measures an electrical property that varies depending on the amount of particulate matter in a measurement gas and detects the particulate matter in the measurement gas.
A plurality of through holes are formed in the outer periphery of the base end side of the cover body formed in a substantially bottomed cylindrical shape that covers the particulate matter detection element as the measurement gas introduction hole, and the cover as the measurement gas lead-out hole One or a plurality of through holes are formed in the bottom of the body, and the gas to be measured introduced into the cover body moves along the longitudinal axis direction from the proximal end side to the distal end side of the detection element. While forming the flow,
A gas flow passage to be measured extending in the axial direction is defined inside the particulate matter detection element, and a base end side of the gas flow passage to be measured is opened toward a direction orthogonal to the traveling direction of the gas to be measured. The tip end side is opened in a direction opposite to the measurement gas outlet hole, and the pair of detection electrodes is in a flow rate stable region where the flow rate of the measurement gas flowing in the measurement gas flow passage is stable. It arrange | positions in the position which opposes.

According to the first aspect of the present invention, no matter what rotational direction the cover body is assembled with respect to the gas flow path to be measured, and what the particulate matter detection element is relative to the circumferential direction of the cover body. Even if assembled at an angle, when the gas to be measured flows along the longitudinal axis direction of the particulate matter detection element, the base end of the gas passage to be measured partitioned inside the particulate matter detection element The gas to be measured is inevitably drawn into the gas passage to be measured due to the pressure difference between the side opening and the tip side opening.
Further, according to the present invention, it has been found that the change in the flow rate of the measurement gas introduced into the measurement gas ventilation passage is small due to the change in the assembly angle in the circumferential direction of the particulate matter detection element.
Therefore, stable detection can be realized regardless of the assembly angle in the circumferential direction of the particulate matter detection element without considering the directionality of the particulate matter detection element during manufacture or assembly.
Moreover, in the present invention, since the pair of detection electrodes are formed at positions facing the flow velocity stabilization region, it is possible to detect the particulate matter contained in the measurement gas under extremely stable conditions.
Furthermore, according to the present invention, it has been found that the flow rate of the measurement gas introduced into the measurement gas ventilation passage changes substantially linearly with respect to the change in the flow rate of the measurement gas.
Therefore, it becomes possible to distinguish and detect the change in the flow rate of the gas to be measured and the change in the amount of the particulate matter contained in the gas to be measured, and an extremely reliable particulate matter detection device can be realized.

  In a second aspect of the present invention, the coarse particle collecting portion is formed by extending the base end side opening of the gas flow passage to be measured and recessing the surface of the insulating substrate at a position facing the base end side opening. And

  According to the invention of claim 2, coarse particles having a relatively large particle diameter or a plurality of particles gathered among the particulate matter contained in the gas to be measured introduced into the gas flow path to be measured. Aggregated particles collide with the coarse particle collecting portion due to inertia and are collected without moving to the flow velocity stable region where the pair of detection electrodes are formed, and fine particulate matter having a particle size is classified. Then, it moves to the flow velocity stable region together with the gas to be measured and is detected by the pair of detection electrodes.

Further, as a specific shape of the detection electrode, as in the invention of claim 3, the pair of detection electrodes is formed on one surface of the inner wall defining the gas flow passage to be measured, and is formed outside. A comb-like electrode connected to a pair of detection electrode lead portions connected to the provided detection circuit and having a plurality of detection electrode detection portions alternately drawn with a certain gap may be used. As described above, the pair of detection electrodes are embedded in the insulating base and formed in a substantially flat plate shape facing each other with the gas flow passage to be measured interposed therebetween, and the respective detection electrodes You may comprise by a pair of electrode lead part for a detection which connects an electrode detection part and the detection circuit provided outside.
In any case, the flow rate of the gas to be measured introduced into the gas flow path to be measured can be stabilized regardless of the arrangement direction of the particulate matter detection element, so that the reliability is extremely easy. A high particulate matter detection device can be realized.
In addition, it is possible to improve the trapping property of the particulate matter by applying a voltage between the pair of electrodes.

The outline | summary of the particulate-material detection apparatus in the 1st Embodiment of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is an arrow plane in the cross section along AA in this figure (a). Figure. FIG. 3 is a developed perspective view showing an outline of a particulate matter detection element that is a main part of the particulate matter detection device according to the first embodiment of the present invention. The outline | summary of the conventional particulate-material detection apparatus in a comparative example is shown, (a) is a longitudinal cross-sectional view, (b) is an arrow top view in the cross section along AA in this figure (a). The expansion | deployment perspective view which shows the outline | summary of the particulate matter detection element which is the principal part of the particulate matter detection apparatus in a comparative example. The effect of the particulate matter detection device in the first embodiment of the present invention is shown, (a) is a cross-sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are orthogonal, (B) is a flow analysis diagram showing the flow of the gas to be measured in the particulate matter detection device at that time. The effect of the particulate matter detection device in the first embodiment of the present invention is shown, (a) is a cross-sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are parallel. (B) is a flow analysis figure which shows the flow of the to-be-measured gas in the particulate matter detection apparatus at that time. The effect of the particulate matter detection device in the first embodiment of the present invention is shown, (a) is a longitudinal sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are orthogonal, (B) is a flow analysis diagram in the cross section along AA in FIG. (A), (c) is a flow analysis diagram in the cross section along B-B in (a), (d) ) Is an enlarged view of the main part of FIG. The effect of the particulate matter detection device in the comparative example is shown, (a) is a cross-sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are orthogonal, (b) The flow analysis figure which shows the flow of the to-be-measured gas along the longitudinal cross-section in a particulate matter detection apparatus, (c) is a principal part enlarged view of this figure (b). The effect of the particulate matter detection device in the comparative example is shown, (a) is a cross-sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are parallel, (b), The flow analysis figure which shows the flow of the to-be-measured gas along the longitudinal cross-section in the particulate matter detection apparatus, (c) is a principal part enlarged view of this figure (b). The effect of the particulate matter detection device in the comparative example is shown, (a) is a longitudinal sectional view showing the positional relationship when the particulate matter detection element and the flow direction of the gas to be measured are orthogonal, and (b) FIG. 4A is a flow analysis diagram in a cross section along AA in FIG. 1A, FIG. 3C is a flow analysis diagram in a cross section along B-B in FIG. The principal part enlarged view of c). Together with the comparative example, the effect of the particulate matter detection device of the present invention is shown, (a) is a characteristic diagram showing the effect on the flow velocity change of the gas to be measured, (b) is the change in the mounting angle in the circumferential direction of the detection element The characteristic view which shows the effect with respect to. The outline | summary of the particulate-material detection apparatus in the 2nd Embodiment of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is an arrow plane in the cross section along AA in this figure (a). Figure. The expansion | deployment perspective view which shows the outline | summary of the particulate matter detection element which is the principal part of the particulate matter detection apparatus in the 2nd Embodiment of this invention. The outline | summary of the particulate-material detection apparatus in the 3rd Embodiment of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is an arrow plane in the cross section along AA in this figure (a). Figure. The expansion | deployment perspective view which shows the outline | summary of the particulate matter detection element which is the principal part of the particulate matter detection apparatus in the 3rd Embodiment of this invention.

With reference to FIG. 1, the outline | summary of the particulate matter detection apparatus 6 in the 1st Embodiment of this invention is demonstrated.
The particulate matter detection device 6 of the present invention is disposed in a combustion exhaust passage of an internal combustion engine, and uses the combustion exhaust as a measurement gas, and the particulate matter contained in the measurement gas is the tip of the particulate matter detection element 1. Between the detection electrodes 12 and 13 that change in accordance with the amount of particulate matter contained in the gas to be measured that is collected by the pair of detection electrodes 12 and 13 provided between the electrodes and deposited between the detection electrodes (12 and 13). 12, 13) by detecting the electrical characteristics such as resistance value and capacitance, and detecting the amount of particulate matter in the gas to be measured. Particularly, the particle size is very fine with a particle size of 50 nm or less. It is suitable for detecting particulate matter.

  The particulate matter detection device 6 according to the present embodiment is a particulate matter fixed inside the substantially cylindrical housing 5 fixed to a gas flow path to be measured (not shown) via an insulator 4 and a sealing member 40. The detection element 1 and the cover bodies 2 and 3 having a double cylinder structure that covers the portion exposed to the gas to be measured are connected to an energization control device and a detection circuit (not shown).

The innermost cover body cylinder 3 that covers the particulate matter detection element 1 is formed in a substantially bottomed cylinder shape, and has a plurality of inner cylinder side surface through-holes 301 at the outer periphery on the proximal end side of the side surface 300 as a gas to be measured. Are bored at equal intervals, and one or a plurality of inner cylinder bottom through-holes 311 are drilled in the inner cylinder bottom portion 310 as the measurement gas outlet holes.
In the present embodiment, the inner cylinder side surface through-holes 301 are drilled at six locations at equal intervals in the circumferential direction.
Therefore, the gas to be measured introduced into the cover body cylinder 3 forms a flow that moves along the longitudinal axis direction from the proximal end side to the distal end side of the particulate matter detection element 1.
At this time, since a plurality of inner cylinder side surface through-holes 301 are provided, even if rotated and assembled in the circumferential direction, the influence on the flow direction of the gas to be measured flowing in the cover body cylinder 3 is small.

Furthermore, a cover body outer cylinder 2 formed in a substantially bottomed cylinder shape so as to cover the cover body cylinder 3 is provided concentrically, and a plurality of outer cylinder side-surface penetrations are provided on the outer periphery of the side surface portion 200 of the cover body outer cylinder 2. A hole 201 is formed, and one or a plurality of outer cylinder bottom through holes 211 are formed in the outer cylinder bottom 210.
The cover body outer cylinder 2 does not directly introduce the gas to be measured into the cover body cylinder 3, but can introduce the gas to be measured into the cover body cylinder 3 by limiting the flow rate of the gas to be measured. It is possible to reduce the influence of the flow velocity of the gas to be measured, which changes according to the operating condition.

  In addition, since the outer cylinder side surface through hole 201 is provided on the distal end side and the inner cylinder side surface through hole 301 is provided on the proximal end side, the gas to be measured introduced from the outer cylinder side surface through hole 201 is transferred to the inner cylinder side surface through hole 301. Since the traveling direction of the gas to be measured changes when introduced into the gas, a part of the coarse particles having a relatively large particle size among the particulate matter contained in the gas to be measured is covered with the cover body outer cylinder 2 and the cover. The effect of classifying the particulate matter collected between the body cylinder 3 and introduced inside the cover body cylinder 3 is also exhibited.

The particulate matter detection element 1, which is the main part of the present invention, is covered on the inner side of insulating bases 10, 11, 14, and 15 formed in a substantially flat plate shape extending in a substantially axial direction using an insulating heat-resistant material such as alumina. A measurement gas ventilation path 141 for introducing measurement gas is defined.
The base end side opening 152 of the gas flow passage 141 to be measured is drawn out to one surface side located on the base end side of the portion of the particulate matter detection element 1 exposed to the gas to be measured, and the traveling direction of the gas to be measured The holes are opened in a direction orthogonal to the direction.

Further, a gas flow passage 141 to be measured is formed so as to extend to the base end side opening 152 and bend so that the traveling direction of the gas to be measured changes steeply and extends in the particulate matter detection element 1 in the axial direction. Has been.
The tip side opening 142 of the gas flow passage 141 to be measured is opened in a direction facing the inner cylinder bottom opening 311.
In addition, a coarse particle collecting portion 111 that is recessed in the counter-opening direction is formed in the counter-opening direction of the base end side opening 152.

A pair of detection electrodes 12 and 13 are formed on one surface of the inner wall that defines the gas flow passage 141 to be measured.
In the present embodiment, as shown in FIG. 4B, the detection electrodes 12 and 13 are provided with a plurality of detection electrode detection units 120 and 130 formed in a substantially strip shape, and each of them is arranged in an alternating manner. The detection electrode detection parts 120 and 130 are formed in a comb-like shape connected to the detection electrode lead parts 121 and 131.
Furthermore, the detection electrode lead parts 121 and 131 are connected to a detection circuit (not shown) provided outside.
Further, a portion where the detection electrode detection portions 120 and 130 and the detection electrode lead portions 121 and 131 are connected, a tip portion of the detection electrode detection portions 120 and 130 facing the detection electrodes 131 and 121, and detection The electrode lead portions 121 and 131 are covered with the insulating substrate 14, and only the portion where the detection electrode detection portions 120 and 130 are arranged in parallel is exposed to the gas passage 141 to be measured.
The detection electrode detectors 120 and 130 are provided at positions facing the flow rate stabilization region where the flow rate of the gas to be measured flowing through the gas flow path 141 to be measured is stable.

With reference to FIG. 2, the more specific structure and manufacturing method of the particulate matter detection element 1 which is the principal part of this invention are demonstrated.
In the present embodiment, the insulating bases 10, 11, 14, and 15 are formed in a substantially flat plate shape by a known method such as a doctor blade method or a press using an insulating heat-resistant material such as alumina.
The insulative base 15 forms a base end side opening portion forming layer, and the base end side opening portion 151 is formed at a position that becomes the base end of the portion of the substantially flat base portion 150 exposed to the gas to be measured. A hole is formed, and notches 152 and 153 for exposing the pair of detection electrode terminal portions 123 and 133 are formed on the proximal end side.

The insulating substrate 14 constitutes a measured gas ventilation path forming layer, and in order to partition the measured gas ventilation hole 141 and the distal end side opening 142, from the front end side to a position facing the measured gas introduction hole 151. Cut-out portions 143 and 144 are formed on the base end side so as to expose the pair of detection electrode terminal portions 123 and 133.
The insulating substrate 11 constitutes a collection portion forming layer, and a rectangular through hole is formed as a coarse particle collection portion 111 at a position facing the measured gas introduction hole 151 of the flat substrate portion 110.
In the present embodiment, a pair of detection electrodes 12 and 13 are formed on the surface of the insulating substrate 11 by a known method such as screen printing, plating or vapor deposition using a conductive material such as Pt.

In the present embodiment, the pair of detection electrodes 12 and 13 includes a plurality of detection electrode detectors 120 and 130 formed in a substantially flat plate shape alternately with a certain gap therebetween. One ends of the detection electrode detection portions 120 and 130 are formed in a comb-like shape connected to the detection electrode lead portions 121 and 131.
Further, detection electrode terminal portions 123 and 133 are formed on the base end sides of the detection electrode lead portions 121 and 131.
The insulating bases 10, 11, 14, 15 and the pair of detection electrodes 12, 13 are integrally laminated to constitute a sensor unit (10-15).

Further, the heater portion 16 and the insulating substrate 17 are formed by being laminated on the insulating substrate 10.
The heater section 16 includes a heating element 160 that generates heat when energized, heating element lead sections 161 and 162, and heating element terminal sections 163 and 164, and is used for thick film printing and plating. It is formed between the insulating substrate 17 and the insulating substrate 16 by a known method such as vapor deposition.
The insulating substrate 17 is formed in a substantially flat plate shape using a heat-resistant insulating material such as alumina by a known method such as a doctor blade method or pressing, and the heating element terminal portions 163 and 164 are exposed on the base end side. Notches 171 and 172 for the purpose are formed.

The sensor unit (10 to 15), the heater unit 16, and the insulating substrate 17 are laminated and sintered integrally, so that the base end side is measured inside the insulating substrate which is the main part of the present invention. Particles that define a gas flow path 141 to be measured in which a base end opening 151 that opens in a direction perpendicular to the gas traveling direction and a tip end opening 142 that faces the bottom opening 311 at the tip end are formed. The shape detection element 1 is completed.
In addition, in this embodiment, it is good also as a structure which abolished the collection part formation layer 11 and formed a pair of detection electrodes 12 and 13 in the surface of the insulating base | substrate 10. FIG. In this case, coarse particles collide with the surface of the insulating substrate 10 at the position facing the measured gas introduction hole 151 and are collected.

Furthermore, in the above-described embodiment, the notched portions 143, 144, 152, 153, 171, and 172 are provided in the insulating bases 14, 15, and 17, so that the detection electrode terminal portions 123 and 133 and the heating element terminal portion 163 are provided. However, it is also possible to adopt a configuration in which the respective electrode terminal portions are drawn out on the surfaces of the insulating bases 15 and 17 through the through-hole electrodes.
The heater section 16 generates heat when energized, the temperature of the detection electrodes 12 and 13 is kept constant, the detection conditions are stabilized, and the particulate matter deposited between the detection electrodes 12 and 13 is heated. It is used for removing.

Here, with reference to FIG. 3 and FIG. 4, as a comparative example, a particulate matter detection element 1 z having a measured gas vent hole 141 z penetrating the side surface direction of a conventional insulating substrate 14 z and the same are provided. The particulate matter detection device 6z will be described.
The particulate matter detection device 6z of the comparative example has the same configuration as that of the particulate matter detection device 6 in the first embodiment of the present invention except for the particulate matter detection element 1z, and is different from the present invention. For the sake of clarity, the same reference numerals are assigned to the same components, and the different reference symbols are assigned to the reference symbols corresponding to similar parts.
In the particulate matter detection element 1z in the comparative example, as shown in FIG. 3A, the measured gas vent hole 141z is formed in a direction penetrating both side surfaces of the insulating bases 10z, 14z, 15; As shown in FIG. 3 (b), a pair of detection electrode detection portions 120z, 130z and detection electrode lead portions 121z, 131z connecting portions 122z, 132z, a part of detection electrode lead portions 121z, 131z, and The tips of the detection electrode detection portions 120z and 130z facing the other detection electrode lead portions 131z and 121z are exposed to the gas flow path 141z to be measured.

A difference between the effect of the particulate matter detection device 6 in the first embodiment of the present invention and the effect of the particulate matter detection device 6z in the comparative example will be described with reference to FIGS.
As Example 1 of the present invention, in the particulate matter detection device 6 of the present invention, the assembly direction of the particulate matter detection element 1 is 90 ° with respect to the flow direction of the gas to be measured flowing outside the cover body outer cylinder 2. FIG. 5A shows a cross section when the base end side opening portion 152 is located at a position where the measurement target gas opens toward the downstream direction of the gas to be measured. FIG. 5B shows the flow analysis result in the longitudinal section along the line.

As shown in FIG. 5B, the gas to be measured introduced into the outer cylinder 2 through the outer cylinder side surface opening 201 is introduced into the cover body outer cylinder 2 using the outer cylinder side hole 201 as the measured gas introduction hole. 3 is introduced into the inside of the cover body cylinder 3 from the inner cylinder side surface opening 301 provided on the base end side, and further lowered along the longitudinal axis direction of the particulate matter detection element 1. Then, it is discharged to the outside through the inner cylinder bottom part opening 311 and the outer cylinder bottom part opening 211.
At this time, the gas to be measured flowing around the base end side opening portion 151 that opens in the direction orthogonal to the longitudinal axis of the particulate matter detection element 1 on the base end side of the particulate matter detection element 1, As shown in FIG. 5 (b), the gas is taken in from the proximal-side opening 151 by the pressure difference with the gas to be measured flowing around the distal-side opening 142 that opens in the direction opposite to the cylinder bottom opening 311. The gas to be measured passes through the gas flow passage 141 to be measured, and a flow toward the distal end opening 142 is formed.

On the base end side of the gas flow path 141 to be measured, the traveling direction of the gas to be measured is greatly bent, so that the coarse particulate matter having a large particle size contained in the gas to be measured collides with the collection unit 111 due to inertia. The very fine particulate matter having a particle diameter of 50 nm or less that has been collected moves in the measured gas ventilation path 141 along the flow of the measured gas.
As the gas flow path 141 to be measured moves toward the tip side, the flow velocity of the gas to be measured becomes stable, and the flow velocity is almost constant in the gas measurement stable region.

As Example 2 of the present invention, in the particulate matter detection device 6 of the present invention, the assembly direction of the particulate matter detection element 1 is 0 ° with respect to the flow direction of the gas to be measured flowing outside the cover body outer cylinder 2. FIG. 6A shows a cross section when the base end side opening portion 152 becomes a position where the base end side opening portion 152 is opened in a direction perpendicular to the flow direction of the gas to be measured. FIG. 6B shows the flow analysis result in the longitudinal section along -A.
As shown in FIG. 6B, also in Example 2, a flow from the proximal end side opening 151 toward the distal end side opening 142 is formed in the gas passage 141 to be measured. As in the first embodiment, the flow velocity of the gas to be measured is stabilized toward the tip side of the gas flow passage 141 to be measured, and the flow velocity is almost constant in the gas measurement stable region.

With reference to FIG. 7, the flow analysis result of the cross-sectional direction in Example 2 is demonstrated.
Fig.7 (a) is a longitudinal cross-sectional view which shows a flow analysis position, FIG.7 (b), (c) is the flow in the cross section along AA and BB in Fig.7 (a), respectively. An analysis result is shown and FIG.7 (d) is a principal part enlarged view of FIG.7 (c).
As shown in FIG. 7 (b), the gas to be measured introduced from the inner cylinder side surface through-hole 301 has a high flow velocity on the base end side of the particulate matter detection element 1 and flows around the cover body outer cylinder 2. A flow from the left side of the drawing, which is the upstream side of the measurement gas, to the right side, which is the downstream side, is formed. This is probably because the flow velocity and pressure of the gas to be measured introduced from the outer cylinder side surface through-hole 201 are higher toward the upstream side of the gas to be measured, so that the influence remains.
However, the gas to be measured flowing inside the cover body cylinder 3 is rectified by the inner peripheral wall of the cover body cylinder 3 and the surface of the particulate matter detection element 1, and as shown in FIG. The gas to be measured flowing inside has a flow showing a uniform flow velocity distribution from the proximal end side toward the distal end side.
Furthermore, as shown in FIGS. 7C and 7D, it can be seen that the tail flow in the measured gas ventilation path 141 is a very uniform flow from the base end side to the tip end side.

Here, the flow analysis result in the comparative example will be described.
As Comparative Example 1, in the conventional particulate matter detection device 6z, the assembly direction of the particulate matter detection element 1z is 90 ° with respect to the flow direction of the gas to be measured flowing outside the cover body outer cylinder 2. That is, FIG. 8 (a) shows a cross section when the measured gas vent hole 141z is at a position where the measured gas vent hole 141z is opened perpendicularly to the flow direction of the measured gas. FIG. 8B shows the flow analysis result in the vertical section.
As shown in FIG. 8B, the flow of the gas to be measured formed around the particulate matter detection element 1z is the same in the cover bodies 2 and 3, so that it is naturally the same as in the first embodiment. The flow of is formed.
However, in Comparative Example 1, the measured gas vent hole 141z is open in the side surface direction. For this reason, the flow speeds on both sides of the opening are almost equal, and as shown in FIG. 8C, a small flow from the base end side to the tip end side is formed in the measured gas vent hole 141z. A flow crossing the openings on both sides of the measurement gas vent 141z is hardly formed.
Therefore, in Comparative Example 1, when the gas to be measured is placed so that the flow direction of the gas to be measured and the width direction of the particulate matter detection element 1z are orthogonal to each other, the gas to be measured is in the gas to be measured vent hole 141z. It turned out that there was a possibility that it was hardly taken in.

As Comparative Example 2, in the conventional particulate matter detection device 6z, the assembly direction of the particulate matter detection element 1z is 0 ° with respect to the flow direction of the gas to be measured flowing outside the cover body outer cylinder 2. That is, FIG. 9A shows a cross section when the measured gas vent hole 141z is in a position opened in a direction parallel to the flow direction of the measured gas. FIG. 9B shows the flow analysis result in the longitudinal section along the line.
As shown in FIGS. 9B and 9C, in Comparative Example 2, the gas to be measured that has entered the gas gas passage 141z to be measured obliquely from one opening into the gas gas hole 141z to be measured, It can be seen that a large flow is formed in a direction that coincides with the flow from the other opening to the right side of the drawing, that is, the flow from the upstream side to the downstream side of the gas to be measured.

In Comparative Example 2. FIG. 10 shows the flow analysis result in the cross-sectional direction.
As shown in FIGS. 4C and 4D, it can be seen that a large flow is formed in the measured gas vent hole 141z in a direction coinciding with the flow of the measured gas from the upstream side to the downstream side.
For this reason, in Comparative Example 2, when the gas to be measured is placed so that the flow direction of the gas to be measured and the width direction of the particulate matter detection element 1z are parallel to each other, an extremely high flow velocity is generated in the gas to be measured gas vent 141z. The gas to be measured was found to flow in.

FIG. 11A shows a change in the flow rate of the gas to be measured flowing in the gas flow passage 141 to be measured of the particulate matter detection device 6 of the present invention with respect to a change in the flow rate of the gas to be measured, and the particulate matter detection device 6z of the comparative example. This shows the difference from the change in the flow rate of the gas to be measured flowing in the gas flow path 141z to be measured. In addition, the particulate matter detection element 1 and the particulate matter detection element 1z show the results of measurement under the condition that the width direction is perpendicular to the flow direction of the gas to be measured.
As shown in FIG. 1A as Example 1, in the particulate matter detection device 6 according to the present invention, when the flow velocity V (m / s) of the gas to be measured changes according to the operation state of the internal combustion engine, Following this, the inflow amount Q (mm ³ / s) of the gas to be measured introduced into the gas flow path 1 to be measured almost linearly changes, indicating that the linearity is maintained.
On the other hand, as shown in Comparative Example 1 in FIG. 6A, in the conventional particulate matter detection device 6z, when the flow rate is slow, the measurement gas hardly flows into the measurement gas vent passage 141z. When the flow rate is high, it can be seen that the flow rate of the gas to be measured introduced into the gas flow path 141z to be measured increases rapidly, and the linearity is not maintained.

With reference to FIG. 11B, the influence when the angle of the particulate matter detection element 1, 1z is changed in the circumferential direction with respect to the flow direction of the gas to be measured having a constant flow rate will be described.
As shown in FIG. 11B as Example 2, in the particulate matter detection device 6 of the present invention, even when the position where the particulate matter detection element 1 is placed rotates in the circumferential direction, the particulate matter detection device 6 is substantially constant. It turned out to be a flow rate.
As described above, according to the present invention, this is due to the difference in pressure between the pressure at the proximal end opening 151 and the pressure at the distal end opening 142 of the gas to be measured flowing around the particulate matter detection element 1. This is probably because the flow velocity in the gas passage 141 is determined.
On the other hand, as shown as Comparative Example 2 in FIG. 11B, in the conventional particulate matter detection device 6z, when the position where the particulate matter detection element 1 is placed rotates in the circumferential direction, the measurement target It was found that the flow rate of the gas to be measured introduced into the gas vent 1z changes greatly.
When the flow direction of the gas to be measured and the width direction of the particulate matter detection element 1z are orthogonal to each other, the gas to be measured hardly flows into the gas flow path 141z to be measured, and the flow direction of the gas to be measured and the particulate shape When the width direction of the substance detection element 1z is parallel, a large amount of gas to be measured is introduced into the gas flow path 141z to be measured.
Therefore, in the conventional particulate matter detection device 6z, the detection result may be unreliable at all unless the flow direction of the gas to be measured and the placement direction of the particulate matter detection element 1z are set as specific conditions. is there.

  In addition, according to the present embodiment, as shown in FIG. 1B, the plurality of detection electrode detection units 120 and 130 of the detection electrodes 12 and 13 formed in a comb shape are arranged in parallel. Since only the portion is exposed to the measured gas ventilation path 141, a voltage is applied between the detection electrodes 12 and 13, and the particulate matter contained in the measured gas passing through the measured gas ventilation path 141 is removed. When charging and collecting between the detection electrodes 12 and 13, only the region where the electric field strength between the detection electrodes 12 and 13 is uniform is exposed to the gas flow path 141 to be measured. It is possible to prevent uneven distribution of the substance and to output stably.

On the other hand, as shown in FIG. 3B, in the comparative example, a connection part 122z between a pair of detection electrode detection parts 120z and 130z formed in a comb shape and detection electrode lead parts 121z and 131z, 132z, a part of the detection electrode lead parts 121z and 131z, and the tips of the detection electrode detection parts 120z and 130z facing the other detection electrode lead parts 131z and 121z are exposed to the gas flow path 141z to be measured. Yes.
For this reason, a voltage is applied between the detection electrode detectors 120z and 130z, and the particulate matter contained in the gas to be measured passing through the gas flow path 141z to be measured is charged between the detection electrodes 12z and 13z. When it is attempted to collect, portions where the electric field concentration inevitably appears at the tips of the detection electrode connection portions 122z and 132z and the detection electrode detection portions 120z and 130z. For this reason, there is a possibility that the particulate matter contained in the gas to be measured is unevenly distributed to the portion where the electric field strength is high, and the reliability of the output result is further lowered.

From the above, when the particulate matter detection device 6 of the present invention is used, even if the angle between the flow direction of the gas to be measured and the circumferential direction of the particulate matter detection element 1 changes, the measurement is performed under almost constant conditions. A gas to be measured is introduced into the gas vent hole 141.
Therefore, unlike the conventional particulate matter detection device 6z shown as the comparative example, it is not necessary to consider the directionality of the particulate matter detection element 1z at the time of manufacture or when assembling to the measurement gas flow path. A highly reliable particulate matter detection device can be easily realized.
Further, according to the particulate matter detection device 6 of the present invention, when the amount of combustion exhaust discharged as the gas to be measured changes due to a change in the operating condition of the internal combustion engine, the particulate matter detection device 6 enters the gas to be measured gas vent 141. Since the flow rate of the measured gas to be introduced changes almost linearly, whether the detected change in the amount of particulate matter in the measured gas is due to changes in combustion conditions or abnormalities such as DPF It is also easy to judge.

In the above embodiment, FIG. 1 and the like show an example in which only one outer cylinder bottom opening 211 and one inner cylinder bottom opening 311 are formed, but the bottom 210 of the cover bodies 2 and 3, When a plurality of bottom openings 211 and 311 are provided in 310, a part of them functions as a lead-out hole for discharging the gas to be measured to the gas flow path to be measured, and the other part covers the gas to be measured. It functions as an introduction hole for taking in the inside of the bodies 2 and 3 and facilitates exchange of the gas to be measured introduced into the cover body.
In addition, when there are a plurality of outer cylinder bottom part openings 211 and inner cylinder bottom part openings 311, the flow in the cross-sectional direction of the cover bodies 2 and 3 may change, but it flows inside the cover bodies 2 and 3. Compared to the flow rate of the gas to be measured, the flow rate of the gas to be measured flowing through the gas flow path to be measured outside the covers 2 and 3 is much faster, and therefore, regardless of the number of holes drilled in the bottom of the covers 2 and 3. First, the flow of the gas to be measured formed inside the cover body cylinder 3 is directed from the proximal end side to the distal end side of the cover body 3 as a whole.
Therefore, due to the pressure difference between the proximal end opening 152 and the distal end opening 142, the measured gas ventilation path 141 inevitably enters from the proximal opening 152 to the distal opening 142. A flow toward will be formed.
For this reason, it is thought that the same effect as the said embodiment is exhibited irrespective of the number of the holes provided in the bottom part of the cover body. The same applies to the embodiments described below.

With reference to FIG. 12, FIG. 13, the particulate matter detection apparatus 6a in the 2nd Embodiment of this invention is demonstrated.
In the first embodiment, an example in which the pair of detection electrodes 12 and 13 are formed on the surface of the insulating substrate 10 or the collecting portion forming layer 11 and the air passage forming layer 14 is laminated thereon. As shown, in the present embodiment, a pair of detection electrodes 12a and 13a are formed in a comb-like shape on the surface on the back surface side of the insulating substrate 15 and laminated on the insulating base 15 as a ventilation path forming layer. The difference is that the conductive substrate 14a is formed. Even in such a configuration, the same effect as the above embodiment can be exhibited.
Further, according to the present embodiment, the structure is simplified, the number of laminated insulating bases can be reduced, and the manufacturing cost can be reduced.

With reference to FIG. 14 and FIG. 15, the particulate matter detection device 6b in the third embodiment of the present invention will be described.
In the above-described embodiment, an example in which a so-called comb-like electrode is formed on one surface of the inner peripheral wall defining the measurement gas ventilation path 141 as the pair of detection electrodes 12 and 13 has been described. , A pair of detection electrodes 12b, 13b are embedded in the insulating bases 10, 11b, 14b, 15 and are formed in a substantially flat plate shape opposed to each other with the gas passage 141 to be measured interposed therebetween. The point which comprised by part 120b, 130b is different.
According to the present embodiment, as in the above embodiment, a stable flow rate in the measured gas ventilation path 141b is obtained due to the pressure difference between the proximal end opening 152b and the distal end opening 142b of the measured gas ventilation path 141b. A gas to be measured is introduced.
In the present embodiment, a voltage is applied between the detection electrode detectors 120b and 130b, the particulate matter passing through the gas flow path 141b to be measured is charged, and adhered to the surfaces of the insulating bases 11b and 14b. Detecting the detection electrode by detecting the capacitance between the detection electrode detectors 120b and 130b, which changes according to the amount of deposition, as an electrical characteristic, or applying an alternating current between the detection electrode detectors 120b and 130b. By detecting the change in AC impedance between the parts 120b and 130b, the amount of particulate matter detected in the gas to be measured can be detected.
The surfaces of the detection electrode detectors 120b and 130b are covered with the insulating bases 11b and 14b, respectively, and the insulating bases 11b and 14b are insulated by densely sintering alumina or the like as in the above embodiment. Alternatively, the material may be made of a porous material, or may be formed to be porous so as to improve the collection property.
Alternatively, the insulating bases 11b and 14b may be formed of a dielectric, and the capacitance may be measured as an electrical characteristic.
Furthermore, instead of the insulating bases 11b and 14b, a conductive material such as zirconia may be used to detect conductivity that changes in accordance with the amount of particulate matter deposited as electrical characteristics.

DESCRIPTION OF SYMBOLS 1 Particulate matter detection element 10, 11, 14, 15 Insulating base | substrate 12, 13 Detection electrode 120, 130 Detection electrode detection part 121, 131 Detection electrode lead part 122, 132 Detection electrode connection part 123, 133 Detection Electrode terminal part 111 Coarse-grain collecting part 141 Gas passage 142 to be measured Bottom opening 151 Side opening 16 Heater 160 Heating element 161, 162 Heating element lead part 2 Cover body outer cylinder 200 Outer cylinder peripheral wall part 201 Outer cylinder peripheral wall opening Hole 210 Outer cylinder bottom part 211 Outer cylinder bottom part opening 3 Cover body cylinder 300 Inner cylinder peripheral wall part 301 Inner cylinder peripheral wall opening 310 Inner cylinder bottom part 311 Inner cylinder bottom part opening 4 Insulator 40 Sealing member 5 Housing 6 Gas sensor

JP 2009-186278 A

Claims (4)

A pair of detection electrodes is provided on an insulating substrate formed in a substantially flat plate shape extending in the axial direction, and the tip side thereof is disposed in the measurement gas, and particles in the measurement gas deposited between the detection electrodes In a particulate matter detection device comprising a particulate matter detection element that measures electrical characteristics that change depending on the amount of a substance and detects particulate matter in a gas to be measured.
As the measurement gas introduction hole, a plurality of through holes are formed in the outer periphery on the proximal end side of the cover body formed in a substantially bottomed cylindrical shape covering the particulate matter detection element,
As the measurement gas outlet hole, one or a plurality of through holes are formed in the bottom of the cover body,
The gas to be measured introduced into the cover body forms a flow that moves along the longitudinal axis direction from the proximal end side to the distal end side of the detection element, and
A gas flow path to be measured extending in the axial direction is defined inside the particulate matter detection element,
The base end side of the gas flow path to be measured is opened toward the direction orthogonal to the traveling direction of the gas to be measured,
Open the tip side in the direction facing the measured gas outlet hole,
The particulate matter detection device, wherein the pair of detection electrodes are arranged at positions facing a flow velocity stabilization region where the flow velocity of the gas to be measured flowing in the gas passage to be measured is stable.   2. The coarse particle collecting unit according to claim 1, wherein the coarse particle collecting unit is formed by extending the surface of the insulating base at a position facing the base end opening, extending to the base end opening of the gas passage to be measured. Particulate matter detection device.   The pair of detection electrodes are formed on one surface of an inner wall that defines the gas flow path to be measured, and are connected to a pair of detection electrode lead portions that are connected to a detection circuit provided outside. The particulate matter detection device according to claim 1 or 2, wherein the electrode detection unit is a comb-like electrode in which the electrode detection unit is alternately drawn with a certain gap.   The pair of detection electrodes is embedded in the insulating base and formed in a substantially flat plate shape opposed to each other with the gas flow passage to be measured interposed therebetween, and each detection electrode detection unit The particulate matter detection device according to claim 1 or 2, comprising a pair of detection electrode lead portions for connecting a detection circuit provided outside and a detection circuit.

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