JP2011033577A - Fine particle sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fine particle sensor effectively collecting fine particles such as soot from measured gas such as exhaust gas and improving a sensitivity in detecting the fine particles. <P>SOLUTION: The soot detection sensor 1 is equipped with: a detection part 27 detecting soot based on a resistance variable in accordance with a condition of soot deposition; and a cover 33 having a shielding part to block passage of the measured gas, and the cover 33 has a gas through-hole 35 allowing to pass the measured gas. Formulas (1) and (2) are satisfied; the formula (1): (A/B)×100≤40, and the formula (2): A<SP>1/2</SP>/T≥0.5, in which A represents an area of the gas through-hole 35 projected on a virtual plane of the detection part 27, B represents an area of the shielding part projected on the virtual plane, and T represents a minimum distance from an opening end of the gas through-hole 35 to the virtual plane. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a particulate sensor that detects particulate matter generated in, for example, an internal combustion engine, such as soot (particulate matter: PM) made of carbon.

  Conventionally, for example, as a device for detecting the amount of soot contained in the exhaust of a diesel engine, a particulate form for obtaining the amount of soot in the exhaust by measuring the oxygen concentration reduced by soot combustion based on an oxygen sensor A substance detection device has been proposed (see Patent Document 1).

  Similarly, in order to detect the amount of soot contained in the exhaust gas, by removing hydrocarbons and moisture from the soot adhering to the detection part by electric heating, and stabilizing the specific resistance between the electrodes, An apparatus for accurately measuring the amount of soot collected has been proposed (see Patent Document 2).

JP-A-2005-337782 JP 59-196453 A

  However, in the above-described prior art, it is difficult to efficiently collect the soot in the exhaust gas. Therefore, the sensitivity of the apparatus is low, and therefore the amount of soot (and hence the soot concentration in the exhaust gas) cannot be detected with high accuracy. There was a problem.

  The present invention has been made to solve the above-mentioned problems, and its object is to efficiently collect particulates such as soot from a gas to be measured such as exhaust gas, and to increase sensitivity when detecting the particulates. It is an object to provide a fine particle sensor capable of

  (1) According to the first aspect of the present invention, in the fine particle sensor for detecting the fine particles in the gas to be measured, the detection of the fine particles is performed based on the electrical characteristics that change as the fine particles contained in the gas to be measured reach. And a cover having a shielding unit that restricts the measurement gas from reaching the detection unit, and the cover is formed with a gas hole through which the measurement gas can pass. In addition, the gas escape hole and the detection unit are arranged so that at least a part thereof overlaps when the gas escape hole is projected on a virtual plane including the surface of the detection unit, and the gas escape hole Where A is the projected area on the virtual plane, B is the projected area of the shielding part on the virtual plane, and T is the shortest distance from the open end of the gas escape hole to the virtual plane. ,following (1), and satisfies the (2).

(A / B) × 100 ≦ 40 (1)
A ^1/2 /T≧0.5 (2)
In the present invention, a cover for restricting the measurement gas to reach the detection unit is provided, and in the cover, a gas hole through which the gas to be measured can pass is formed. When the gas escape holes are projected on a virtual plane including the surface of the detection unit, they are arranged so that at least a part thereof overlaps. In addition, the area A (the projected area A projected perpendicular to the virtual plane) where the gas escape hole is projected on the virtual plane and the area B (the perpendicular to the virtual plane) where the shielding part is projected onto the virtual plane. The relationship between the projected area B) projected onto the virtual surface and the shortest distance T from the opening end of the gas escape hole to the virtual surface is set so as to satisfy the expressions (1) and (2). The area B of the shielding part is a value including the area A of the gas escape hole.

  In the present invention, a part of the gas to be measured that hits the shielding part passes through the gas escape hole, so that the gas to be measured is concentrated in the detection part. However, if the area A of the gas escape hole is too large with respect to the area B of the shielding part, the gas to be measured does not concentrate (the gas to be measured does not collect in the gas escape hole). Yes.

  Further, if the shortest distance T from the opening end of the gas escape hole to the virtual plane is too large with respect to the area A of the gas escape hole, the flow velocity of the gas to be measured that has become faster when passing through the gas escape hole reaches the detection unit. To be late. Further, the gas to be measured after passing through the gas escape hole diffuses in a direction parallel to the surface of the detection unit. It has been confirmed from the experimental examples described later that the amount of collected fine particles at the detection unit decreases under these influences, and is thus set in the range of the formula (2).

  Therefore, in the fine particle sensor of the present invention, the flow of the gas to be measured from the sensor periphery to the detection unit can be suitably rectified, so that the ability to collect fine particles such as soot is high. In other words, since the gas flow of the gas to be measured flowing into the detector can be controlled (the gas to be measured is concentrated before the gas vent hole and the gas flow rate through the gas vent hole is increased), soot and other fine particles are efficiently captured. Can be collected. Therefore, since the sensitivity of the sensor is improved, the amount of soot (and hence the soot concentration in the gas to be measured) can be obtained with high accuracy.

  Here, the virtual plane including the surface of the detection unit refers to the detection unit when two parallel virtual planes are arranged between the gas escape hole and the detection unit and the distance between the two virtual planes is maximized. It is a virtual plane on the side in contact.

  Note that changes in electrical characteristics in the detection unit include, for example, changes in resistance and electromotive force, and changes in resistance and electromotive force can be detected as changes in sensor output (for example, voltage).

  (2) In the invention of claim 2, the detection unit is a flat plate member that detects the fine particles based on electrical characteristics that change depending on the adhesion state of the fine particles contained in the gas to be measured. Features.

  The present invention shows a flat detection unit, and the electrical characteristics of the detection unit (for example, a pair of particles) depending on the state of the fine particles adhering to the surface of the detection unit (the presence or absence of fine particles and the amount of fine particles). When electrodes are placed on the surface of the detector, the resistance between the electrodes changes). Based on this change in electrical characteristics, the presence and amount of fine particles (and the concentration of fine particles in the gas under measurement) Can be detected.

(3) In invention of Claim 3, the said shielding part is flat form, It is characterized by the above-mentioned.
As shown in FIG. 1A, the present invention shows an example in which a flat shield portion is disposed (for example, in parallel) opposite to a flat detector portion. In the figure, the area A of the gas escape hole, the area B of the shielding part (including the area A), and the position of the distance T are illustrated, but the areas A and B are on the virtual plane side (detection part side). Is the area projected from the top of the figure.

(4) The invention of claim 4 is characterized in that the detection section is surrounded by the cover.
As shown in FIG. 1B, in the present invention, for example, a rectangular tube-like cover is disposed so as to surround a flat detection portion, and a part of the cover (upper side in the figure) serves as a shielding portion. Function. In the figure, the area A of the gas escape hole, the area B of the shielding part (including the area A), and the position of the distance T are illustrated, but the areas A and B are on the virtual plane side (detection part side). Is the area projected from the top of the figure.

  Further, the shape of the cover may be cylindrical, and is illustrated in FIG. Even when the cover is cylindrical, the area B of the shielding part that functions to collect particulates such as soot can be set in the same manner as in the above-described example.

(5) The invention of claim 5 is characterized in that the maximum diameter of the gas escape hole and the shortest distance T from the opening end of the gas escape hole to the virtual plane are 0.1 mm or more.
In the present invention, since the maximum diameter of the gas escape hole and the shortest distance T are 0.1 mm or more, there is an advantage that the gap between the gas escape hole or the shielding part and the detection part is not easily blocked by the flaw. .

(A) is explanatory drawing which illustrates invention of Claim 3, (b), (c) is explanatory drawing which illustrates invention of Claim 4. It is a perspective view which shows the wrinkle detection sensor of 1st Embodiment. (A) is a top view which shows the element part of the wrinkle detection sensor of 1st Embodiment, (b) is the X-X 'sectional drawing, (c) is explanatory drawing which shows the front side of the 1st board | substrate. It is explanatory drawing which shows the electrical structure of the wrinkle detection sensor of 1st Embodiment. It is a perspective view which shows the modification of the element part of the wrinkle detection sensor of 1st Embodiment. It is explanatory drawing (Table 1) which shows the sensor parameter of Experimental example 1. FIG. It is a graph which shows the relationship between (A / B) x100 of example 1 of an experiment, and a sensor output. It is a perspective view which shows the element part of the wrinkle detection sensor of a comparative example. It is explanatory drawing (Table 2) which shows the sensor parameter of Experimental example 2. FIG. 10 is a graph showing the relationship between A ^1/2 / T and sensor output in Experimental Example 2. (A) is a top view which shows the element part of the wrinkle detection sensor of 2nd Embodiment, (b) is the Y-Y 'sectional drawing. (A) is a top view which shows the element part of the wrinkle detection sensor of 3rd Embodiment, (b) is the Z-Z 'sectional drawing. (A) is explanatory drawing which shows the wrinkle detection sensor of 4th Embodiment, (b) is explanatory drawing which shows the wrinkle detection sensor of 5th Embodiment, (c) is explanatory drawing which shows the wrinkle detection sensor of 4th Embodiment. It is.

Next, an embodiment of the fine particle sensor of the present invention will be described.
[First Embodiment]
In the present embodiment, a soot detection sensor that detects the amount of soot in the gas to be measured (and hence the soot concentration) will be described as an example of the particulate sensor.

a) First, the configuration of the wrinkle detection sensor will be described.
The soot detection sensor of the present embodiment is a resistance variable sensor that is disposed on the downstream side of a particulate filter that collects soot, for example, in an exhaust passage of a diesel engine, and detects the concentration of soot in the exhaust. is there.

  As shown in FIG. 2, the soot detection sensor 1 is provided with an element part 3 for detecting the concentration of soot on the front end side (left side in FIG. 2) exposed to exhaust, and on the rear end side (right side in FIG. 2), While holding the element part 3, it has a main body part 5 (accommodating a lead wire or the like extending from the element part 3) to fix the sensor 1 itself to an exhaust pipe or the like.

  The element part 3 is a long first substrate 7 made of alumina having electrical insulation (length 45 mm × width 3.8 mm × thickness 1.3 mm) and a length made of alumina having electrical insulation. A long substrate (length 45 mm × width (maximum) 7 mm × thickness 0.5 mm) made of a second substrate 9 having a length (length 41 mm × width 3.8 × thickness 1.0) and similarly alumina having electrical insulation properties The third substrate 11 is a sintered body laminated and integrated.

Hereinafter, each configuration will be described in detail.
As shown in FIG. 3 (c), the first substrate 7 has a pair of electrode portions 13 and 15 formed on the surface thereof, and the electrode portions 13 and 15 are disposed on the tip side (the left side in FIG. 3). Comb electrodes 17 and 19 are provided, and lead portions 21 and 23 are provided on the rear end side. The comb-teeth electrodes 17 and 19 and the substrate surface exposed between the electrodes 17 and 19 constitute a detection unit 27 that detects the amount of wrinkles (and hence the concentration of wrinkles).

  As shown in FIG. 3B, the detection unit 27 is exposed on the surface of the first substrate 7 on the side where the electrode units 13 and 15 are formed (upper side in FIG. 3). The second substrate 9 is integrally joined so as to cover the lead portions 21 and 23 of the 13 and 15. A heater 25 is built in the front end side of the first substrate 7.

  In addition, a third substrate 11 (longer than the second substrate 9) is integrally bonded to the surface of the second substrate 9, so that the front end side of the third substrate 11 has a predetermined gap 29. The upper part of the detection part 27 of the 1st board | substrate 7 is covered.

  As shown in FIG. 3A, the third substrate 11 has a base end portion (length 39.5 mm × width 3.8 mm) 31 that is the same as the width of the first and second substrates 7 and 9 on the rear end side. In addition, a cover (length 7 mm × width 7 mm) 33 wider than the base end portion 31 is provided on the distal end side.

  The cover 33 is a shielding part (specifically, a substrate that prevents passage of soot) from restricting the gas to be measured to reach the detection part 27, and is arranged in parallel with the detection part 27 so as to face the detection part 27. In addition, it is arranged so as to protrude from the detection unit 27 and in the width direction (the direction perpendicular to the longitudinal direction and thickness direction of the element unit 3: the vertical direction in FIG. 3A) and cover the entire surface of the detection unit 27. ing.

  In addition, a circular gas escape hole 35 having a diameter of 2 mm is formed in the vicinity of the center of the cover 33, and this gas escape hole 35 is disposed so as to overlap the detection unit 27 when viewed in the plate thickness direction. (See FIG. 3 (a)).

  That is, the gas escape hole 35 and the detection unit 27 are at least partly projected when the gas escape hole 35 is projected on a virtual plane including the surface of the detection unit 27 (a plane perpendicular to the vertical direction in FIG. 3B). Are arranged to overlap. The center of the gas escape hole 35 is at the center in the width direction and at a position of 3.5 mm (accordingly, the area center of the cover 33) from the tip side.

  In particular, in the present embodiment, A (projection area A) is an area where the gas escape hole 35 is projected on a virtual plane including the surface of the detection unit 27, and an area where the cover (shielding part) 33 is projected on the virtual plane. B (projection area B: hatched portion, where B is an area including A), T is the shortest distance from the opening end of the gas escape hole 35 to the virtual plane (here, the detection unit 27). It is set so as to satisfy the expressions (1) and (2).

(A / B) × 100 ≦ 40 (1)
A ^1/2 /T≧0.5 (2)
The shortest distance T is the height of the gap 29 between the first substrate 7 and the third substrate 11 formed by the thickness of the second substrate 9.

b) Next, the manufacturing method of the element part 3 which is the principal part of the wrinkle detection sensor 1 is demonstrated easily.
In addition, the number is not attached | subjected to the material in the middle of a manufacturing process.
First, for example, a heating element pattern was embedded in a laminated body formed by laminating insulating ceramic sheets made of alumina or the like to form a first sheet to be the first substrate portion 7.

Next, in order to form both electrode parts 13 and 15, for example, Pt paste was screen-printed on the surface of the first sheet.
Next, the 2nd sheet | seat which consists of alumina which becomes the 2nd board | substrate part 9 on the surface of the 2nd sheet | seat was laminated | stacked.

Next, on the surface of the second sheet, a third sheet made of, for example, alumina to be the third substrate portion 11 was laminated. The third sheet has an opening serving as a gas escape hole 35.
Here, when laminating the third sheet, there is a gap corresponding to the thickness of the second sheet on the leading end side of the third sheet and the leading end side of the first sheet. A spacer made of a disappearing material is arranged.

And after drying the laminated body of the 1st-3rd sheet | seat, it baked, for example at 1520 degreeC for 2 hours, and the element part 3 was obtained.
c) Next, an electrical configuration for operating the wrinkle detection sensor 1 will be described.

  The wrinkle detection sensor 1 of the present embodiment is a resistance change type sensor that detects a voltage corresponding to a change in resistance between both electrode portions 13 and 15, and therefore, as shown in FIG. 4, the electrodes of the wrinkle detection sensor 1 The lead parts 21 and 23 of the parts 13 and 15 are connected to a sensor control circuit 41 for operating the wrinkle detection sensor 1 and taking out the sensor output. Further, both ends of the heater 25 are connected to a heater control circuit 43 that applies a voltage to the heater 25 and controls the applied voltage.

  As the sensor control circuit 41, for example, a constant current is supplied between the electrode portions 13 and 15, and the voltage between the electrode portions 13 and 15 generated thereby (according to a change in resistance due to the amount of soot) is determined. A detection circuit can be employed. In addition, a circuit used for a known resistance change type sensor using a Wheatstone bridge circuit or the like can be employed.

  In addition, in order to control the operation of the wrinkle detection sensor 1, an electronic control device 45 having a known microcomputer as a main part is provided. The electronic control device 45 is connected to the sensor control circuit 41 and the heater control circuit 51. It is connected.

d) Next, a method for detecting the concentration of soot in the measurement gas using the soot detection sensor 1 will be described.
First, as a pretreatment, the heater 25 is energized and the soot adhering to the surface of the detection unit 27 of the soot detection sensor 1 is incinerated to clean the soot detection sensor 1.

  Next, with the exhaust of the diesel engine being supplied, the element part 3 of the soot detection sensor 1 is exposed to the exhaust at a predetermined operating temperature for a predetermined time. The predetermined operating temperature is the exhaust temperature.

  Thereby, wrinkles adhere to the surface of the detection unit 27 of the wrinkle detection sensor 1. That is, as shown by the arrow in FIG. 3B, the exhaust that has hit the surface side of the cover 33 passes through the gas escape hole 35 in a direction parallel to the surface of the detection unit 27 in the gap 29. It spreads and flows out of the element unit 3, and at this time, wrinkles adhere to the surface of the detection unit 27.

Therefore, for example, a predetermined constant current is supplied between the electrode parts 13 and 15 with the wrinkles attached to the detection part 27, and the voltage generated between the electrode parts 13 and 15 at that time is measured as a sensor output.
Here, the resistance between the electrode portions 13 and 15 to which the soot has adhered (and therefore the sensor output corresponding to the resistance) has a correlation with the amount of soot, and the amount of soot attached to the detection unit 27 is ( There is a correlation with the concentration of soot in the exhaust (if the temperature of the exhaust and the time exposed to the exhaust are constant).

  Since these correlations are stored in the memory of the electronic control unit 45 as data obtained by experiments in advance, the amount of soot is obtained from the sensor output based on this data, and the concentration of soot is obtained from the amount of soot. Can be sought.

  e) As described above, in the present embodiment, the cover 33 that prevents the gas to be measured from passing is provided so as to face the detection unit 27, and the cover 33 has the gas so that the projection area with respect to the detection unit 27 overlaps. A through hole 35 is formed. Further, the area A (projected area A) where the gas escape hole 35 is projected on the virtual plane, the area B (projected area B) where the cover 33 is projected on the virtual plane, and the open end of the gas escape hole 35 are assumed to be the virtual plane. Is set so as to satisfy the expressions (1) and (2).

  Therefore, the soot detection sensor 1 of the present embodiment can suitably rectify the flow of the gas to be measured from the periphery of the sensor to the detection unit 27, so that soot is collected as will be apparent from an experimental example described later. Therefore, it has a remarkable effect that the sensitivity of the wrinkle detection sensor 1 is improved. As a result, the amount of soot (and hence the soot concentration in the gas to be measured) can be obtained with high accuracy.

  In addition, when the maximum diameter of the gas escape hole 35 and the gap 29 between the detection unit 27 and the cover 33 are small, the gas escape hole 35 and the gap 29 are likely to be closed.

  In the present embodiment, the thickness of the cover 33 is 0.5 mm. However, the present invention is not limited to this. The same effect can be obtained up to 10 times the maximum diameter (here, the diameter) of the gas escape hole 35. . However, if the cover 33 is too thick, the tube friction when the soot passes through the gas vent hole 35 increases and the soot easily closes the gas vent hole 35. Therefore, the thickness of the cover 33 is about 0.1 to 3 mm. Is preferred.

f) A modification of the present embodiment will be shown below.
The element portion 53 of the soot detection sensor 51 shown in FIG. 5A has a rectangular cover (shielding portion) 55, and a square gas escape hole 57 is formed in the cover 55.

5B has a rectangular cover (shielding portion) 65, and a hexagonal gas escape hole 67 is formed in the cover 65. As shown in FIG.
Further, the element portion 73 of the soot detection sensor 71 shown in FIG. 5C has a rectangular cover (shielding portion) 75, and the cover 75 has five small-diameter circular gas vent holes 77 formed therein. Yes. The arrangement of the five gas escape holes 77 is axisymmetric with respect to the central axis of the element portion 73, and the total area of the five gas escape holes 77 corresponds to the area A.

The above-described wrinkle detection sensors 51, 61, 71 also have the same effects as the wrinkle detection sensor 1 of the first embodiment.
<Experimental example 1>
Next, experimental examples in which the effect of the present invention has been confirmed will be described.

In Experimental Example 1, the influence on the sensor output when the sensor parameters A and B of the calculation formula of “(A / B) × 100” are changed in the wrinkle detection sensor is examined.
In Experimental Example 1, a plurality of samples of the wrinkle detection sensor having the same element portion as in the first embodiment (Examples Nos. 1 to 18 within the scope of the present invention, Comparative Example No outside the scope of the present invention) .1-6) were prepared.

  Specifically, as shown in Table 1 of FIG. 6, the area A (hole area) of the gas escape hole and the area B (plate area) of the cover (shielding part) are set, and the A / B area ratio is changed. Various element portions were prepared. The plate area B includes the area A. However, the shortest distance T between the opening end of the gas escape hole and the detection part was constant (1 mm).

And the element part of the soot detection sensor of each sample was attached to the model gas apparatus (soot generating apparatus), and it exposed to test gas for 5 minutes on the following experimental conditions, and the soot was made to adhere to a detection part.
(Experimental conditions)
-Flow rate of supplied test gas: 1000 L / min
・ Concentration of soot contained in test gas: 150 mg / m ³
-Gas temperature: 100 ° C
・ Gas flow velocity: 2.1m / sec
Next, each wrinkle detection sensor to which wrinkles were attached was operated, and the output of the wrinkle detection sensor at that time was measured. The result is shown in FIG.

As shown in FIG. 7, it can be seen that in the range where the value of (A / B) × 100 is 40 or less, the sensor output is greatly increased compared to the case where the value is not so.
As shown in FIG. 8, when a wrinkle detection sensor having an element portion without any cover was produced and a similar experiment was performed, the sensor output was 2V.
<Experimental example 2>
Next, Experimental Example 2 will be described.

In Experimental Example 2, the influence on the sensor output when the sensor parameters A and T in the calculation formula of “A ^1/2 / T” are changed in the soot detection sensor is examined.
In Experimental Example 2, a plurality of samples of wrinkle detection sensors having the same element portion as in the first embodiment (Examples Nos. 19 to 26 within the scope of the present invention, Comparative Example No. outside the scope of the present invention) .7-13) were prepared.

Specifically, as shown in Table 2 of FIG. 9, the area (hole area) A of the gas escape hole and the shortest distance T between the open end of the gas escape hole and the detection unit were set, and A and T were changed. Various element parts were produced. However, the area B (including area A) of the cover was constant (25 mm ² ).

  Then, the element part of the soot detection sensor of each sample is attached to a model gas apparatus (soot generator), and exposed to the test gas for 5 minutes under the same experimental conditions as in Experimental Example 1 to attach soot to the detection part. It was.

Next, each wrinkle detection sensor to which wrinkles were attached was operated, and the output of the wrinkle detection sensor at that time was measured. The result is shown in FIG.
As shown in FIG. 10, it can be seen that when the value of A ^1/2 / T is in the range of 0.5 or more, the sensor output is greatly increased as compared with the case where the value is not so.
<Experimental example 3>
Next, Experimental Example 3 will be described.

In Experimental Example 3, a plurality of samples of the wrinkle detection sensor provided with the same element portion as in the first embodiment were produced.
Specifically, a sample X in which the diameter of the gas escape hole was (0.09 mm) and a sample Y in which the shortest distance T was (0.9 mm) were produced. In addition, a sample Z was prepared in which the diameter of the gas escape hole was (1.01 mm) and the shortest distance T was (1.01 mm). Other dimensions are the same as those in the first embodiment.

  Then, the element part of the soot detection sensor of each sample is attached to a model gas apparatus (soot generator), and exposed to the test gas for 5 minutes under the same experimental conditions as in Experimental Example 1 to attach soot to the detection part. It was.

As a result, in the soot detection sensor of sample X, the gas escape hole is closed with soot, and in the soot detection sensor of sample Y, the gap (the gap between the cover and the detection unit) is closed with soot. Neither the gas vent hole nor the gap was blocked by the heel.
[Second Embodiment]
Next, the second embodiment will be described, but the description of the same content as the first embodiment will be omitted.

  As shown in FIG. 11, the wrinkle detection sensor 81 of the present embodiment includes a laminated substrate 86 in which a first substrate 83 and a second substrate 85 are laminated, and the first embodiment is arranged on the distal end side of the first substrate 83. A detection unit 87 similar to the embodiment is provided.

  In addition, a metal rectangular tubular cover 91 is disposed around the multilayer substrate 86 so as to cover the entire multilayer substrate 86 until reaching the main body 89 to which the multilayer substrate 86 is fixed. One side of 91 (above FIG. 11B) is a shielding part 93.

  The shielding portion 93 is formed in parallel with the detection portion 87, and a gas escape hole 95 is formed on the distal end side of the shielding portion 93. Specifically, the gas escape hole 95 is formed so as to overlap the detection part 87 when the gas escape hole 95 itself is projected onto the detection part 87 side. A similar gas discharge hole 97 is formed on the cover 91 on the side opposite to the gas escape hole 95.

  In the present embodiment, the projected area of the gas escape hole 97 on the virtual plane (similar to the first embodiment) is A, the projected area of the shielding part 93 on the virtual plane is B, and the opening of the gas escape hole 97 is The shortest distance from the end to the virtual plane is T. Also in the present embodiment, the expressions (1) and (2) are satisfied as in the first embodiment.

Therefore, the present embodiment has the same effect as the first embodiment and has an advantage that the cover 91 (and thus the shielding portion 93) is not easily damaged because the cover 91 is cylindrical.
[Third Embodiment]
Next, the third embodiment will be described, but the description of the same contents as the first embodiment will be omitted.

The soot detection sensor of this embodiment is an electromotive force type sensor in which the electromotive force of the sensor changes according to the amount of soot.
a) First, the configuration of the wrinkle detection sensor will be described.

  As shown in FIG. 12, the element portion 103 of the wrinkle detection sensor 101 of the present embodiment is formed by stacking a sensor element substrate 105 corresponding to a first substrate, a second substrate 107 and a third substrate 109.

  Among these, the third substrate 109 is provided with a flat plate-like cover 111 (functioning as a shielding part) wider than the rear end side at the front end side thereof, as in the first embodiment. Similarly, a circular gas escape hole 113 is formed in the approximate center.

Further, the second substrate 107 functions as a spacer for forming a gap 115 of a predetermined distance T between the first substrate 105 and the third substrate 109 as in the first embodiment.
Further, the sensor element substrate 105 includes, for example, a solid electrolyte substrate (or a substrate made of a proton conductor) 117 made of an oxygen ion conductor such as zirconia, and a shielding plate 121 made of alumina or the like having a heater 119. The gaps are joined together with a gap so that a space of 123 is formed. The atmosphere introduction unit 123 is configured to communicate with the atmosphere side (the right side in FIG. 12), and the periphery on the side in contact with the exhaust is airtight so that the exhaust does not enter the atmosphere introduction unit 123.

  A pair of electrodes 125, 127 are formed on both sides of the solid electrolyte plate 117 on the front end side, with the fixed electrolyte substrate 117 interposed therebetween, thereby forming a detection unit 129. The outer electrode 125 is in contact with the exhaust, and the inner electrode 127 (in the atmosphere introduction portion 123) is in contact with the atmosphere.

Also in the present embodiment, the area A, the area B, and the shortest distance T are the same as those in the first embodiment, and the equations (1) and (2) are the same as in the first embodiment. Meet.
b) Next, the operation of the wrinkle detection sensor 101 will be described.

  In the soot detection sensor 101 having the above-described configuration, soot accumulated on the detection unit 129 is burned by the heating of the heater 119. As a result, a difference in oxygen concentration occurs between the electrodes 125 and 127 (that is, the oxygen concentration decreases around the outer electrode 125 where the soot is burned). Therefore, an electromotive force corresponding to the oxygen concentration is generated in the detection unit 125 (and therefore between the electrodes 125 and 127) (or a mixed potential due to the generated CO is generated).

Therefore, by measuring the electromotive force (or hybrid potential), the amount of soot (and hence the soot concentration) can be determined.
[Fourth Embodiment]
Next, the fourth embodiment will be described, but the description of the same contents as the first embodiment will be omitted.

The wrinkle detection sensor of this embodiment is a resistance change type sensor using a counter electrode.
As shown in FIG. 13A, the element portion 132 of the wrinkle detection sensor 131 of this embodiment includes a ceramic base 137 having a pair of ceramic substrates 133 and 135 arranged in parallel, and the ceramic substrates 133 and 135. A pair of plate-like electrodes 139 and 141 disposed inside is provided. The pair of electrodes 139 and 141 and the space 143 sandwiched between the pair of electrodes 139 and 141 constitute a detection unit 145 (gray portion in the figure). The space 143 may be filled with a porous material.

  A flat cover 147 (shaded portion in the figure) functioning as a shielding part is arranged on the side of the ceramic base 137 (the front side in the figure) so as to keep a predetermined distance from the detection part 145. Yes. Further, a gas vent hole 149 similar to that in the first embodiment is formed in the center of the cover 147.

  Here, the area A is the area of the gas escape hole 149, and the area B is the surface area of the cover 147 (including the area A). The shortest distance T (not shown) is the shortest distance from the open end of the gas escape hole 149 to the detection unit 145.

Also according to the present embodiment, the same effects as those of the first embodiment can be obtained.
[Fifth Embodiment]
Next, the fifth embodiment will be described, but the description of the same contents as the first embodiment will be omitted.

The wrinkle detection sensor of the present embodiment is a sensor applicable to an electrostatic induction wrinkle detection sensor as described in, for example, JP-T-2007-519899.
This electrostatic induction type wrinkle detection sensor is for charging a wrinkle attached to a detection unit and detecting wrinkles (wrinkle concentration or the like) based on the charged amount of the charged wrinkle.

  As shown in FIG. 13B, the wrinkle detection sensor 151 of this embodiment includes an insulator 153 and a center electrode 155 on the front end side of the sensor, and the center electrode 155 is a detection unit (gray portion in the figure). ).

  A flat cover 157 (shaded portion in the figure) functioning as a shielding part is arranged on the front side of the figure so as to keep a predetermined distance from the center electrode 155. Further, a gas escape hole 159 similar to that in the first embodiment is formed at the center front end side of the cover 157.

  Here, the area A is the area of the gas escape hole 159, and the area B is the surface area of the cover 157 (including the area A). The shortest distance T (not shown) is the shortest distance from the opening end of the gas escape hole 159 to the center electrode 155.

Also according to the present embodiment, the same effects as those of the first embodiment can be obtained.
[Sixth Embodiment]
Next, although the sixth embodiment will be described, description of the same contents as those of the first embodiment will be omitted.

The soot detection sensor of this embodiment is a sensor applicable to a discharge-type soot detection sensor as described in, for example, Japanese Patent Application Laid-Open No. 2007-327936.
This discharge type soot detection sensor detects soot (soot concentration or the like) based on the discharge voltage between the electrodes, which changes due to the presence of soot in the detector including the space between the electrodes.

  As shown in FIG. 13C, the wrinkle detection sensor 151 of this embodiment includes a heater 163, an insulator 165, a center electrode 167, and an outer electrode 169 on the front end side of the sensor. The outer electrode 169 and the space 171 (gray portion in the figure) sandwiched between the center electrode 167 and the outer electrode 169 function as the detection unit 173.

  A flat cover 175 (shaded portion in the figure) functioning as a shielding part is arranged on the front side of the figure so as to keep a predetermined distance from the detection part 173. Further, a gas escape hole 177 similar to that in the first embodiment is formed at the center front end side of the cover 175.

  Here, the area A is the area of the gas escape hole 177, and the area B is the surface area of the cover 175 (including the area A). The shortest distance T (not shown) is the shortest distance from the open end of the gas escape hole 177 to the detection unit 173.

Also according to the present embodiment, the same effects as those of the first embodiment can be obtained.
In addition, this invention is not limited to the said embodiment at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.

  (1) For example, the particulate sensor of the present invention can be applied not only to a soot detection sensor that can detect soot contained in the exhaust of an internal combustion engine, for example, but also to a sensor that detects suspended particulates in smoke in a factory or the like. .

  (2) Further, instead of the rectangular cylindrical cover as in the second embodiment, a cylindrical cover such as a cylindrical shape can also be used as shown in FIG.

1, 51, 61, 71, 81, 101, 131, 151, 161 ... Wrinkle detection sensor 3, 53, 63, 73, 103, 132 ... Element part 13, 15 ... Electrode part 25, 119, 163 ... Heater 27, 87, 145, 173 ... detecting section 29, 115 ... gap 33, 55, 65, 75, 91, 111, 147, 157, 175 ... cover 35, 57, 67, 77, 95, 113, 149, 159, 177 ... Gas escape hole 45 ... Electronic control device 93 ... Shielding part

Claims (5)

In a fine particle sensor that detects fine particles in a gas to be measured,
A detection unit that detects the fine particles based on electrical characteristics that change when the fine particles contained in the measurement gas arrive;
A cover having a shielding part that restricts the measurement gas from reaching the detection part;
With
The cover is formed with a gas hole through which the gas to be measured can pass, and the gas hole and the detection unit are projected onto a virtual plane including the surface of the detection unit. In some cases are arranged so that at least some overlap,
The area where the gas escape hole is projected onto the virtual plane is A, the area where the shielding part is projected onto the virtual plane is B, and the shortest distance from the opening end of the gas escape hole to the virtual plane is A fine particle sensor characterized by satisfying the following formulas (1) and (2) when T:
(A / B) × 100 ≦ 40 (1)
A ^1/2 /T≧0.5 (2)   2. The fine particle according to claim 1, wherein the detection unit is a flat plate member that detects the fine particle based on electrical characteristics that change depending on an adhesion state of the fine particle contained in the gas to be measured. Sensor.   The fine particle sensor according to claim 1, wherein the shielding portion has a flat plate shape.   The fine particle sensor according to claim 1, wherein the detection unit is surrounded by the cover.   5. The shortest distance T from the maximum diameter of the gas escape hole and the opening end of the gas escape hole to the virtual plane of the detection unit is 0.1 mm or more. Particle sensor.