JP2021043123A - Detector for detecting number of fine particles - Google Patents

Abstract

To increase the accuracy of detection of a detector for detecting the number of fine particles.SOLUTION: The detector for detecting the number of fine particles has a bottomed cylindrical protective cover 80 surrounding a region around a gas flow passage 24 of a detection element 20 for detecting the number of fine particles. The protective cover 80 has gas inlet ports 81 and gas exhaust ports 82. The gas inlet ports 81 are provided on an exist 24b side of the gas flow passage 24 not to face the detection element 20 but to face the spaces on both sides of the detection element 20. The gas exhaust ports 82 are provided on an entrance 24a side of the gas flow passage 24 and face the detection element 20.SELECTED DRAWING: Figure 6

Description

The present invention relates to a fine particle number detector.

As the fine particle number detector, a charge generating element provided in the gas flow path of the fine particle number detecting element generates an electric charge by corona discharge, and the fine particles in the gas to be measured are charged by the electric charge to obtain charged fine particles. Is known to be collected by a collecting electrode and the number of fine particles is measured based on the amount of electric charge of the collected charged fine particles (see, for example, Patent Document 1). Patent Document 1 describes that such a fine particle number detecting element is protected by a protective cover, and an exhaust gas flowing through an exhaust pipe through a hole provided in the protective cover is provided at the lower end of the fine particle number detecting element. It is stated that it will pass through the road. On the other hand, Patent Documents 2 and 3 disclose a fine particle amount detector provided with a protective cover.

Japanese Patent No. 6420525 U.S. Pat. No. 8225648 Japanese Unexamined Patent Publication No. 2013-160617

Although Patent Document 1 describes a protective cover that protects the fine particle number detecting element, the protective cover is not devised to improve the detection accuracy of the fine particle number. Further, the protective cover disclosed in Patent Documents 2 and 3 is applied to the fine particle amount detecting element, not applied to the fine particle number detecting element, much less to improve the detection accuracy of the fine particle number. is not it.

The present invention has been made to solve such a problem, and an object of the present invention is to improve the detection accuracy of the fine particle number detector.

The fine particle number detector of the present invention
Charges are added to the fine particles in the exhaust gas flowing in from the inlet of the gas flow path of the fine particle number detection element to form charged fine particles, and the collection target, which is either the charged fine particles or the charge not added to the fine particles, is collected. A fine particle number detector that collects particles by using an electric charge on a collection electrode provided in the gas flow path and detects the number of the fine particles based on the current flowing through the collection electrode.
A tubular protective cover provided so as to surround the gas flow path of the fine particle number detecting element, and
A gas introduction port provided on the outlet side of the gas flow path of the protective cover and facing the spaces on both sides of the fine particle number detecting element without facing the fine particle number detecting element.
A gas discharge port provided on the inlet side of the gas flow path of the protective cover and facing the fine particle number detection element, and a gas discharge port.
It is equipped with.

In this fine particle number detector, the mainstream of the exhaust gas introduced into the protective cover from the gas introduction port passes through the spaces on both sides of the fine particle number detection element and then is discharged from the gas discharge port to the outside of the protective cover. On the other hand, the side flow of the exhaust gas introduced into the protective cover from the gas introduction port passes through the gas flow path from the inlet of the gas flow path provided on the gas discharge port side, and then passes through the gas flow path, and then the gas flow path provided on the gas introduction port side. It goes out of the gas flow path from the outlet of. The flow velocity of the sidestream of the exhaust gas is lower than that of the mainstream of the exhaust gas. Here, according to the following White equation indicating the number of charges of particles due to diffusion charging, the number of charges, that is, the number of charges charged on fine particles, increases as the time increases (that is, as the gas flow velocity decreases). .. Therefore, the lower the flow velocity of the gas passing through the gas flow path, the larger the number of average charges added to each fine particle. In the present invention, as described above, since the exhaust gas flowing through the gas flow path has a low flow velocity, the number of average charges added to the fine particles in the exhaust gas flowing through the gas flow path is large. As a result, when the collection target is charged fine particles, the collection current per charged fine particle is large, so that the detection accuracy is high. Further, when the collection target is a charge (surplus charge) that is not added to the fine particles, the amount of decrease in current per charged fine particle becomes large, so that the detection accuracy becomes high. The "cylindrical shape" includes, for example, a cylinder (circular cross section), an elliptical cylinder (oval cross section), a square cylinder (polygonal cross section), and the like.

In the fine particle number detector of the present invention, the protective cover may have a drain port at a position below the side wall or at the bottom surface. In this way, even if the water contained in the exhaust gas introduced from the gas inlet is accumulated in the protective cover, the accumulated water is discharged to the outside of the protective cover through the drain port.

In the fine particle number detector of the present invention, the protective cover may be a bottomed tubular cover having a circular or elliptical cross section. In this way, the protective cover can suppress the pressure loss of the exhaust gas flowing in the exhaust pipe to a small extent.

Explanatory drawing of the fine particle number detector 10. FIG. 3 is a cross-sectional view of a structure for attaching the fine particle number detector 10 to the exhaust pipe 12. The perspective view of the fine particle number detection element 20. FIG. 3 is a sectional view taken along the line AA of FIG. BB sectional view of FIG. The perspective view which shows the internal structure of the protective cover 80. The perspective view of the protective cover 80. FIG. 6 is a sectional view taken along line DD of FIG.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view of a fine particle number detector 10 according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a structure of mounting the fine particle number detector 10 to an exhaust pipe 12, and FIG. 3 is a perspective view of the fine particle number detection element 20. FIG. 4 is a sectional view taken along the line AA of FIG. 3, and FIG. 5 is a sectional view taken along the line BB of FIG. In this embodiment, the vertical direction, the horizontal direction, and the front-rear direction are as shown in FIGS. 1 and 3.

As shown in FIG. 1, the fine particle number detector 10 detects the number of fine particles 26 (see FIG. 5) contained in the exhaust gas flowing through the exhaust pipe 12 of the engine. The fine particle number detector 10 includes a fine particle number detecting element 20, and an accessory unit 68 including various power supplies 36 and 56 and a number detecting unit 60.

As shown in FIG. 2, the fine particle number detecting element 20 is supported inside a through hole 72 that penetrates the main metal fitting 70 in the vertical direction via a supporter 74. The main metal fitting 70 is provided with a bolt portion (male screw) 70a on the outer peripheral surface, and is screwed into a nut portion (female screw) 76a of a ring-shaped boss 76 fixed to the exhaust pipe 12. As a result, the fine particle number detecting element 20 is attached to the exhaust pipe 12. A gasket 78 is mounted between the main metal fitting 70 and the boss 76. A bottomed tubular protective cover 80 is fixed to the lower end of the main metal fitting 70. The protective cover 80 is provided so as to surround the gas flow path 24 of the fine particle number detecting element 20. Therefore, the protective cover 80 prevents foreign matter from hitting the fine particle number detecting element 20 or splashing water on it. Details of the protective cover 80 will be described later.

As shown in FIG. 5, the fine particle number detecting element 20 includes a charge generating unit 30, a surplus charge removing unit 40, a collecting unit 50, and a heater electrode 66 in a housing 22.

As shown in FIG. 1, the housing 22 is a long rectangular parallelepiped that is long in a direction intersecting the central axis of the exhaust pipe 12 (here, in a direction substantially orthogonal to each other). The housing 22 is an insulator and is made of ceramic such as alumina. The lower end 22a of the housing 22 is arranged inside the exhaust pipe 12, and the upper end 22b is arranged outside the exhaust pipe 12. A gas flow path 24 is provided at the lower end 22a of the housing 22. Various terminals are provided on the upper end 22b of the housing 22.

The central axis of the gas flow path 24 substantially coincides with the central axis of the exhaust pipe 12. As shown in FIG. 3, the gas flow path 24 has a rectangular parallelepiped shape extending from a rectangular inlet 24a provided on the rear surface of the housing 22 to a rectangular outlet 24b provided on the front surface of the housing 22. It is a space. The housing 22 includes a pair of left and right flow path walls 22c and 22d that form the gas flow path 24 (see FIG. 3).

As shown in FIGS. 4 and 5, the charge generation unit 30 is provided on the flow path wall 22c so that the charge is generated in the vicinity of the inlet 24a in the gas flow path 24. The charge generation unit 30 has a discharge electrode 32 and two ground electrodes 34 and 34. The discharge electrode 32 is provided along the inner surface of the flow path wall 22c, and has a plurality of fine protrusions around the rectangle as shown in FIG. The two ground electrodes 34, 34 are rectangular electrodes, and are embedded in the flow path wall 22c at intervals so as to be parallel to the discharge electrode 32. In the charge generation unit 30, a high-frequency high voltage (periodic voltage) of the discharge power supply 36 (one of the accessory units 68) is applied between the discharge electrode 32 and the two ground electrodes 34 and 34, so that both of them are used. Air discharge occurs due to the potential difference between the electrodes. At this time, the portion of the housing 22 between the discharge electrode 32 and the ground electrodes 34, 34 serves as a dielectric layer. By this air discharge, the gas existing around the discharge electrode 32 is ionized to generate a positive charge 28. The discharge electrode 32 is connected to the discharge electrode terminal 33 (see FIG. 3) provided at the upper end 22b of the housing 22 via the wiring inside the housing 22. The discharge electrode 32 is connected to the discharge power supply 36 via the discharge electrode terminal 33. The ground electrodes 34, 34 are connected to the ground electrode terminals 35 (see FIG. 3) provided at the upper end 22b of the housing 22 via wiring in the housing 22. The ground electrodes 34 and 34 are connected to the ground (earth) via the ground electrode terminal 35.

As shown in FIG. 5, the fine particles 26 contained in the gas enter the gas flow path 24 from the inlet 24a, and when passing through the charge generation unit 30, the charge 28 generated by the aerial discharge of the charge generation unit 30 is added. After being formed into charged fine particles P, they move toward the outlet 24b. Further, among the generated charges 28, those not added to the fine particles 26 move toward the outlet 24b with the charges 28 as they are. Of the generated charges 28, those that are not added to the fine particles 26 are called surplus charges.

The surplus charge removing unit 40 is provided downstream of the charge generating unit 30 and upstream of the collecting unit 50. The excess charge removing unit 40 has a pair of removing electrodes 42, 42. One of the removal electrodes 42 is provided along the inner surface of the left flow path wall 22c and is exposed in the gas flow path 24. The other removal electrode 42 is provided along the inner surface of the right flow path wall 22d and is exposed in the gas flow path 24. The pair of removal electrodes 42, 42 are arranged at positions facing each other, and are connected to the removal electrode terminals 45 (see FIG. 3) provided at the upper end 22b of the housing 22 via wiring in the housing 22. There is. The removal electrodes 42 and 42 are connected to the ground (earth) via the removal electrode terminals 45.

The collecting unit 50 is provided downstream of the charge generating unit 30 and the excess charge removing unit 40 in the gas flow path 24. The collecting unit 50 collects the charged fine particles P, and has an electric field generating electrode 52 and a collecting electrode 54. The electric field generation electrode 52 is provided along the inner surface of the left flow path wall 22c and is exposed in the gas flow path 24. The collection electrode 54 is provided along the inner surface of the flow path wall 22d on the right side and is exposed in the gas flow path 24. The electric field generating electrode 52 and the collecting electrode 54 are arranged at positions facing each other. The electric field generating electrode 52 is connected to the electric field generating electrode terminal 53 (see FIG. 3) provided at the upper end 22b of the housing 22 via wiring in the housing 22. A DC voltage V1 (positive potential, for example, about 2 kV) is applied to the electric field generating electrode 52 via the electric field generating electrode terminal 53 by the collecting power source 56 (one of the accessory units 68). The collection electrode 54 is connected to the collection electrode terminal 55 (see FIG. 3) provided at the upper end 22b of the housing 22 via the wiring inside the housing 22, and is grounded via the collection electrode terminal 55. It is connected to the ammeter 62 connected to the ground). As a result, a relatively strong electric field is generated between the electric field generating electrode 52 and the collecting electrode 54 of the collecting unit 50. Therefore, the charged fine particles P flowing through the gas flow path 24 are attracted to the collection electrode 54 by this relatively strong electric field and collected.

Of the charges 28 generated by the charge generation unit 30, the surplus charge 28 that was not added to the fine particles 26 is attracted to the removal electrode 42 by the electric field generated between the discharge electrode 32 and the removal electrode 42, and is captured and grounded. Or it is attracted to the removal electrode 42 by the electric charge generated between the electric field generation electrode 52 and the removal electrode 42, and is captured and thrown to the ground. That is, the removal electrode 42 removes the excess electric charge 28 by using the discharge power supply 36 and the collection power supply 56, and the removal electrode 42 does not have its own power supply that generates an electric field. In this way, the surplus charge removing unit 40 suppresses that the surplus charge 28 is collected by the collection electrode 54 of the collection unit 50 and is counted in the number of fine particles 26.

The number detection unit 60 is one of the accessory units 68, and includes an ammeter 62 and a number measuring device 64 as shown in FIG. In the ammeter 62, one terminal is connected to the collection electrode 54 and the other terminal is connected to the ground. The ammeter 62 measures the current based on the charge 28 of the charged fine particles P collected on the collection electrode 54. The number measuring device 64 calculates the number of fine particles 26 based on the current of the ammeter 62.

The heater electrode 66 is embedded in the housing 22. The heater electrode 66 is a band-shaped heating element that is routed over the entire surface of the housing 22. Both ends of the heater electrode 66 are connected to heater electrode terminals 67 and 67 (see FIG. 3) provided at the upper end 22b of the housing 22, respectively. The heater electrode 66 is connected to a power feeding device (not shown) via the heater electrode terminals 67 and 67, and generates heat when energized by the power feeding device. The heater electrode 66 heats each electrode such as the housing 22, the removal electrode 42, the electric field generating electrode 52, and the collecting electrode 54.

Here, the protective cover 80 will be described in detail. 6 is a perspective view showing the internal structure of the protective cover 80 (a perspective view when FIG. 2 is cut along the CC plane), FIG. 7 is a perspective view of the protective cover 80, and FIG. 8 is a DD cross section of FIG. It is a figure.

The protective cover 80 is a bottomed and cylindrical member, that is, a cup-shaped member, and is provided so as to surround the gas flow path 24 of the fine particle number detecting element 20. Although the protective cover 80 is made of metal in this embodiment, it is not particularly limited to metal, and may be made of, for example, an insulating material. The protective cover 80 includes a gas introduction port 81, a gas discharge port 82, and a drain port 83. The gas introduction port 81 is provided on the outlet 24b side of the gas flow path 24 in the protective cover 80. A plurality of gas inlets 81 (three in this case) are arranged in a row in the vertical direction, and the rows are provided in two rows. The central axis of the gas introduction port 81 is substantially parallel to the central axis of the exhaust pipe 12. The gas introduction port 81 in the left column is provided in a region 80a that does not face the fine particle number detecting element 20 but faces the space on the left side of the fine particle number detecting element 20. The gas inlet 81 in the right column is provided in a region 80b that does not face the fine particle number detecting element 20 but faces the space on the right side of the fine particle number detecting element 20. The gas discharge port 82 is provided on the inlet 24a side of the gas flow path 24 in the protective cover 80. A plurality of gas discharge ports 82 (three in this case) are arranged in a row in the vertical direction, and the rows are provided in a region facing the fine particle number detecting element 20 (here, the inlet 24a of the gas flow path 24). ing. The central axis of the gas discharge port 82 is substantially parallel to the central axis of the exhaust pipe 12. The drainage port 83 is provided below the side wall on the gas introduction port 81 side and below the side wall on the gas discharge port 82 side of the protective cover 80, respectively. The lower surface of the fine particle number detecting element 20 floats from the bottom surface of the protective cover 80.

Next, an example of using the fine particle number detector 10 will be described. When measuring the fine particles 26 contained in the exhaust gas of an automobile, the fine particle number detecting element 20 is attached to the exhaust pipe 12 of the engine as described above (see FIG. 1).

As shown in FIG. 8, the exhaust gas flowing through the exhaust pipe 12 enters the inside of the protective cover 80 through the gas introduction port 81 of the protective cover 80. As shown by the solid arrow in FIG. 8, the mainstream of the exhaust gas that has entered the inside of the protective cover 80 from the gas introduction port 81 forming the left row passes through the space on the left side of the fine particle number detection element 20 and then the gas discharge port 82. Is discharged to the outside of the protective cover 80. As shown by the solid arrow in FIG. 8, the mainstream of the exhaust gas that has entered the inside of the protective cover 80 from the gas introduction port 81 forming the right column passes through the space on the right side of the fine particle number detection element 20 and then the gas discharge port 82. Is discharged to the outside of the protective cover 80. On the other hand, as shown by the dotted arrow in FIG. 8, the side flow of the exhaust gas is introduced after passing through the gas flow path 24 in the direction opposite to the main flow from the inlet 24a of the gas flow path 24 provided on the gas discharge port 82 side. It goes out of the gas flow path 24 from the outlet 24b of the gas flow path 24 provided on the port 81 side and joins the main stream of the exhaust gas. The flow velocity of the sidestream of the exhaust gas is lower than that of the mainstream of the exhaust gas. The flow of exhaust gas inside the protective cover 80 was confirmed by simulation. In FIG. 8, the exhaust gas introduced into the protective cover 80 from the gas introduction port 81 travels diagonally (spreads to the left and right) with respect to the central axis of the gas introduction port 81, because the exhaust gas travels diagonally (spreads to the left and right) to the outer circumference of the protective cover 80. This is because the gas is introduced into the protective cover 80 from the gas introduction port 81 after flowing along the surface. However, even if the exhaust gas is introduced into the protective cover 80 along the central axis of the gas introduction port 81, there is no particular problem.

As shown in FIG. 5, the fine particles 26 contained in the exhaust gas introduced into the housing 22 from the inlet 24a carry a charge 28 (here, a positive charge) generated by the discharge of the charge generation unit 30 to become the charged fine particles P. Become. The charged fine particles P pass through the excess charge removing unit 40 as they are and reach the collecting unit 50. On the other hand, the electric charge 28 not added to the fine particles 26 is attracted to the removal electrodes 42 and 42 of the excess charge removal unit 40 and is discarded to the ground via the removal electrodes 42 and 42. As a result, the unnecessary electric charge 28 not added to the fine particles 26 hardly reaches the collecting portion 50.

The charged fine particles P that have reached the collection unit 50 are collected by the collection electrode 54 by the collection electric field generated by the electric field generation electrode 52. Then, the current based on the electric charge 28 of the charged fine particles P collected by the collecting electrode 54 is measured by the ammeter 62, and the number measuring device 64 calculates the number of the fine particles 26 based on the current. The relationship between the current I and the amount of electric charge q is I = dq / (dt) and q = ∫Idt. The number measuring device 64 integrates (accumulates) the current values over a predetermined period to obtain the integrated value (accumulated charge amount), divides the accumulated charge amount by the elementary charge, and obtains the total number of charges (collected charge number). By dividing the number of collected charges by the average value (average number of charges) of the number of charges added to one fine particle 26, the number Nt of the fine particles 26 collected on the collection electrode 54 is obtained (below). See equation (1)). The number measuring device 64 detects this number Nt as the number of fine particles 26 in the exhaust gas.
Nt = (accumulated charge) / {(elementary charge) x (average charge number)} ... (1)

With the use of the fine particle number detecting element 20, if a large number of particles are deposited on the wall of the gas flow path 24, the insulation between the electrodes becomes insufficient, and the number of particles may not be measured normally. Therefore, the deposits on the wall of the gas flow path 24 are heated and incinerated to refresh the walls of the gas flow path 24 and the electrodes 32, 42, 52, 54 at regular intervals or when the accumulated amount reaches a predetermined amount. ..

In the fine particle number detector 10 described above, the mainstream of the exhaust gas introduced into the protective cover 80 from the gas introduction port 81 passes through the spaces on both the left and right sides of the fine particle number detection element 20 as shown by the solid line arrow in FIG. After passing through, the gas is discharged from the gas discharge port 82 to the outside of the protective cover 80. On the other hand, the side flow of the exhaust gas introduced into the protective cover 80 from the gas introduction port 81 is a gas flow path from the inlet 24a of the gas flow path 24 provided on the gas discharge port 82 side as shown by the dotted line arrow in FIG. After passing through 24, the gas flows out of the gas flow path 24 from the outlet 24b of the gas flow path 24 provided on the gas introduction port 81 side. The flow velocity of the sidestream of the exhaust gas is lower than that of the mainstream of the exhaust gas. Here, according to the above-mentioned White equation, the number of electric charges, that is, the number of electric charges charged on the fine particles, increases as the time increases (that is, as the gas flow velocity decreases). Therefore, the lower the flow velocity of the gas passing through the gas flow path 24, the larger the number of average charges added to each fine particle. In the present embodiment, as described above, since the exhaust gas flowing through the gas flow path has a low flow velocity, the number of average charges added to the fine particles in the exhaust gas flowing through the gas flow path is large. As a result, the collection current per charged fine particle becomes large, so that the detection accuracy becomes high.

Further, since the protective cover 80 has the drain port 83, even if the water contained in the exhaust gas introduced from the gas introduction port 81 collects in the protective cover 80, the accumulated water passes through the drain port 83. It is discharged to the outside of the protective cover 80. In particular, since the lower surface of the fine particle number detecting element 20 is located higher than the drain port 83, the water collected in the protective cover 80 is discharged from the drain port 83 without coming into contact with the fine particle number detecting element 20.

Further, since the protective cover 80 has a cylindrical shape (that is, a circular cross section), the pressure loss of the exhaust gas flowing in the exhaust pipe 12 can be suppressed to a small value.

It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

For example, in the above-described embodiment, the drain port 83 is provided at a position below the side wall of the protective cover 80, but the drain port 83 may be provided on the bottom surface of the protective cover 80.

In the above-described embodiment, the protective cover 80 has a tubular shape with a circular cross section, but may have a tubular shape with an elliptical cross section. Even in this way, the pressure loss of the exhaust gas flowing in the exhaust pipe 12 can be suppressed to a small value. Further, although the protective cover 80 is a bottomed tubular member, it may be a bottomless tubular member.

In the above-described embodiment, rows of three gas inlets 81 arranged in the vertical direction are provided in the regions 80a and 80b facing the left and right spaces of the fine particle number detection element 20, but the gas inlets arranged in a row are particularly provided. The number of 81 is not limited to three, and may be two or four or more. Alternatively, one gas introduction port 81 may be provided in each of the regions 80a and 80b facing the left and right spaces of the fine particle number detection element 20. The gas inlet 81 may be a round hole or a square hole. Alternatively, the gas introduction port 81 may be a slit extending in the vertical direction. Further, in the above-described embodiment, the rows of the gas introduction ports 81 are provided one by one in the regions 80a and 80b facing the left and right spaces of the fine particle number detection element 20, but a plurality of rows may be provided. Further, in the above-described embodiment, the three gas introduction ports 81 are arranged in the vertical direction, but the present invention is not particularly limited to this. For example, a plurality of gas introduction ports 81 may be provided in a zigzag pattern or randomly in the regions 80a and 80b facing the left and right spaces of the fine particle number detection element 20.

In the above-described embodiment, the central axis of the gas introduction port 81 is substantially parallel to the central axis of the exhaust pipe 12, but the central axis of the exhaust pipe 12 may be directed outward. For example, the central axis of the gas introduction port 81 may be parallel to the direction of the solid arrow indicating the mainstream of the exhaust gas passing through the gas introduction port 81 of FIG. In this way, the exhaust gas introduced from the gas introduction port 81 can easily advance in the spaces on the left and right of the fine particle number detecting element 20.

In the above-described embodiment, the case where the fine particle number detector 10 is attached to the exhaust pipe 12 of the engine has been illustrated, but the present invention is not particularly limited to the exhaust pipe 12 of the engine, as long as it is a pipe through which a gas containing fine particles flows. It can be any tube.

In the above-described embodiment, the number of fine particles is determined by setting the collection target as charged fine particles, but the number of fine particles may be obtained by using the collection target as surplus charge. For example, in the first embodiment described above, the removal electrode 42 is omitted, the voltage applied to the electric field generation electrode 52 by the collection power supply 56 is set lower than the voltage V1, and the excess charge is collected by the collection electrode 54. The charged fine particles P may be discharged from the outlet 24b without being collected by the collection electrode 54. In that case, first, the total number of charges 28 generated by the charge generation unit 30 is measured, and then, when the gas containing the fine particles 26 is passed through the gas flow path 24, the surplus charge is generated from the current flowing through the collection electrode 54. The number of fine particles can be obtained by measuring the number and subtracting the number of surplus charges from the total number of charges 28. In this case, the amount of current decrease per charged fine particle P becomes large. As a result, the value obtained by subtracting the number of surplus charges from the total number of charges 28 becomes large, so that the detection accuracy becomes high. However, in this case, it is necessary to measure both the total number of charges 28 and the number of surplus charges, the charges 28 are lighter than the fine particles 26 and the behavior is unstable, and the number of the fine particles 26 is these numbers. Considering that it is several orders of magnitude smaller than that of the above, the error can be reduced by setting the collection target as the charged fine particles P.

The present invention can be used as a fine particle number detector for detecting the number of fine particles in the exhaust gas of a power machine such as an automobile.

10 Fine particle number detector, 12 exhaust pipe, 20 fine particle number detection element, 22 housing, 22a lower end, 22b upper end, 22c, 22d flow path wall, 24 gas flow path, 24a inlet, 24b outlet, 26 fine particles, 28 charges, 30 charge generator, 32 discharge electrode, 33 discharge electrode terminal, 34 ground electrode, 35 ground electrode terminal, 36 power supply for discharge, 40 excess charge removal part, 42 removal electrode, 45 removal electrode terminal, 50 collection part, 52 electric field Generating electrode, 53 Electric field generating electrode terminal, 54 Collecting electrode, 55 Collecting electrode terminal, 56 Collecting power supply, 60 Counting detector, 62 Current meter, 64 Counting device, 66 Heater electrode, 67 Heater electrode terminal, 68 Attached unit, 70 main metal fittings, 70a bolt part, 72 through hole, 74 supporter, 76 boss, 76a nut part, 78 gasket, 80 protective cover, 80a, 80b area, 81 gas inlet, 82 gas outlet, 83 drain ..

Claims (3)

Charges are added to the fine particles in the exhaust gas flowing in from the inlet of the gas flow path of the fine particle number detection element to form charged fine particles, and the collection target, which is either the charged fine particles or the charge not added to the fine particles, is collected. A fine particle number detector that collects particles by using an electric charge on a collection electrode provided in the gas flow path and detects the number of the fine particles based on the current flowing through the collection electrode.
A tubular protective cover provided so as to surround the gas flow path of the fine particle number detecting element, and
A gas introduction port provided on the outlet side of the gas flow path of the protective cover and facing the spaces on both sides of the fine particle number detecting element without facing the fine particle number detecting element.
A gas discharge port provided on the inlet side of the gas flow path of the protective cover and facing the fine particle number detection element, and a gas discharge port.
Particle count detector equipped with. The protective cover has a drainage port at a lower position on the side wall or on the bottom surface.
The fine particle number detector according to claim 1. The protective cover is a tubular cover having a circular or oval cross section.
The fine particle number detector according to claim 1 or 2.