Patent Publication Number: US-2021172365-A1

Title: Particulate matter measuring device component

Description:
TECHNICAL FIELD 
     The present invention relates to a particulate matter measuring device component. 
     BACKGROUND ART 
     For example, Japanese Unexamined Patent Publication JP-A 2014-159783 (hereinafter, also referred to as Patent Literature 1) discloses a particulate matter measuring device component which is used for measuring an amount of particulate matters in an exhaust gas discharged from a Diesel engine. The particulate matter measuring device component disclosed in Patent Literature 1 includes a filter divided into a plurality of cells by a porous partition wall, and a pair of electrodes disposed to sandwich a cell when setting at least one cell as a measurement cell. The particulate matter measuring device component disclosed in Patent Literature 1 is configured to calculate a deposit amount of particulate matters in an exhaust gas which are trapped in the filter, based on an electrostatic capacitance between the pair of electrodes. Also, since a flow channel of the exhaust gas and the filter are formed over the entirety, they are entirely arranged on the way of an exhaust pipe. The particulate matter measuring device component is retained by a metal fitting, and the metal fitting is fixed outside the exhaust pipe. 
     SUMMARY OF INVENTION 
     A particulate matter measuring device component includes a base portion formed of ceramics and having a flow channel through which a gas flows, a filter portion formed of porous ceramics and disposed inside the flow channel so as to divide the flow channel into a plurality of divisions, and a pair of electrodes for forming an electrostatic capacitance which is disposed in the base portion so as to sandwich at least a part of the filter portion, the flow channel being located on one end side of the base portion, a retaining portion being disposed on the other end side of the base portion. 
     Another particulate matter measuring device component includes a base portion formed of ceramics and having a flow channel through which a gas flows, a filter portion formed of porous ceramics and disposed inside the flow channel so as to divide the flow channel into a plurality of divisions, and a pair of electrodes for forming an electrostatic capacitance which is disposed in the base portion so as to sandwich at least a part of the filter portion, the base portion having a length direction, when the base portion is bisected in the length direction, the flow channel being on only one bisected side of the base portion. 
     Still another particulate matter measuring device component includes a pair of base portions which are plate-shaped members formed of ceramics, the pair of base portions being apposed so that main surfaces thereof face each other, a filter portion formed of porous ceramics and disposed so as to divide a space between the pair of base portions to form a flow channel, and a pair of electrodes for forming an electrostatic capacitance which is disposed in each of the pair of base portions so as to sandwich at least a part of the filter portion, the flow channel being located on one end side of the pair of base portions, a retaining portion being disposed on the other end side of the pair of base portions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a particulate matter measuring device component; 
         FIG. 2  is a sectional view (a longitudinal sectional view) of the particulate matter measuring device component taken along the line A-A shown in  FIG. 1 ; 
         FIG. 3  is a sectional view (a horizontal sectional view) of the particulate matter measuring device component taken along the line B-B shown in  FIG. 1 ; 
         FIG. 4  is a schematic view depicting a wiring pattern of an electrode of the particulate matter measuring device component shown in  FIG. 1 ; 
         FIG. 5  is a schematic view depicting a wiring pattern of an electrode of another example of the particulate matter measuring device component; 
         FIG. 6  is a schematic view depicting a wiring pattern of an electrode of another example of the particulate matter measuring device component; 
         FIG. 7  is a schematic view depicting a wiring pattern of an electrode of another example of the particulate matter measuring device component; 
         FIG. 8  is a perspective view of another example of the particulate matter measuring device component; 
         FIG. 9  is a horizontal sectional view depicting another example of the particulate matter measuring device component; 
         FIG. 10  is a longitudinal sectional view depicting another example of the particulate matter measuring device component; 
         FIG. 11  is a longitudinal sectional view depicting another example of the particulate matter measuring device component; 
         FIG. 12  is a longitudinal sectional view depicting another example of the particulate matter measuring device component; 
         FIG. 13  is a perspective view of another example of the particulate matter measuring device component; 
         FIG. 14A  is a perspective view of another example of the particulate matter measuring device component,  FIG. 14B  is a sectional view (a longitudinal sectional view) taken along the line C-C of  FIG. 14A , and  FIG. 14C  is a sectional view (a longitudinal sectional view) taken along the line D-D of  FIG. 14A ; 
         FIGS. 15A to 15D  are schematic views depicting a method of manufacturing the particulate matter measuring device component; and 
         FIGS. 16A to 16D  are schematic views depicting another example of a method of manufacturing the particulate matter measuring device component. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a particulate matter measuring device component  100  will be described with reference to the drawings. In  FIG. 1  and the like, a Cartesian coordinate system xyz fixed and defined with respect to the particulate matter measuring device component  100  is shown. In below descriptions, the directions may be described with reference to the coordinate system. In the particulate matter measuring device component  100 , any direction may be a vertical direction or a horizontal direction, and a z-axis direction may also be referred to as the vertical direction or a height direction. Also, the description “when the particulate matter measuring device component  100  is seen from above” indicates “when seen in the z-axis direction”. 
     As shown in  FIGS. 1 to 4 , the particulate matter measuring device component  100  includes a base portion  1  having flow channels  11  formed therein, and filter portions  2  disposed inside the flow channels  11 . The particulate matter measuring device component  100  further includes a pair of electrodes  3  for forming an electrostatic capacitance which is disposed in the base portion  1 . The particulate matter measuring device component  100  is used to measure an amount of particulate matters in an exhaust gas discharged from a Diesel engine, for example. 
     The base portion  1  is a member for forming the flow channel  11  through which a gas flows. The base portion  1  is formed of insulating ceramics such as alumina, for example. The base portion  1  has one or more flow channels  11  formed therein, for example. In the particulate matter measuring device component  100  shown in  FIG. 1 , the base portion  1  has a cuboid outer shape and is formed therein with the three flow channels  11 . The base portion  1  can be set so that a height (a length in the z-axis direction) is 60 mm, a length between side surfaces having openings (a depth, a length in the y-axis direction) is 40 mm, and a length between side surfaces with no openings (a width, a length in the x-axis direction) is 10 mm. 
     The flow channel  11  extends from one side surface of the base portion  1  to an opposite side surface thereto. The flow channel  11  opens to one side surface of the base portion  1  and to an opposite side surface thereto. The three flow channels  11  are aligned in the height direction of the base portion  1 . Each of the flow channels  11  is divided into a plurality of divisions by the filter portion  2 , and one divided space is also referred to as the divided flow channel  12 . Also, the flow channel  11  (the divided flow channel  12  between the filter portions  2 ) formed as a result of the division by the filter portion  2  can be set so that a width (a length between the filter portions  2 ) is 1.2 mm and a height (an interval between a bottom surface and a ceiling surface) is 1.2 mm. The length of the flow channel  11  can be set to 40 mm, which is the same as the length of the base portion  1 . 
     The filter portion  2  is a member for trapping therein particulate matters in the gas. As shown in  FIG. 2 , the filter portion  2  is disposed inside the flow channel  11 . As shown in  FIG. 3 , in the particulate matter measuring device component  100  of the present disclosure, the filter portion  2  has a plate shape and is disposed so as to extend along the length direction of the flow channel  11 . The filter portions  2  are provided so as to divide the flow channel  11  of the base portion  1  into a plurality of regions (the divided flow channels  12 ). The particulate matter measuring device component  100  of the present disclosure includes the four filter portions  2  for one flow channel  11 . The four filter portions  2  are aligned side by side. The filter portion  2  is formed of porous ceramics. As the porous ceramics, porous alumina may be exemplified. When the filter portion  2  is formed of porous alumina, the gas to flow in the flow channel  11  can pass through the filter portion  2 . At this time, the filter portion  2  can trap (deposit) part of the particulate matters included in the gas. 
     Herein, the flow channel  11  is located on one end side of the base portion  1 , and a retaining portion  1   a  is disposed on the other end side of the base portion  1 . In other words, the base portion  1  has a height direction (the z-axis direction) perpendicular to the length direction (the y-axis direction) in which the flow channel  11  extends, and when the base portion  1  is bisected in the height direction, the flow channel  11  is on only one bisected side of the base portion  1 . In the example of  FIG. 1 , the flow channel  11  is located on a lower side of the base portion  1  in the height direction (the z-axis direction), and the retaining portion  1   a  is disposed on an upper side of the base portion  1  in the height direction (the z-axis direction). The retaining portion  1   a  is a portion for retaining the particulate matter measuring device component  100  with a metal member and the like when fixing the component to an exhaust pipe. By this configuration, it is possible to arrange only one end of the base portion  1  having the flow channels  11  and the filter portions  2  inside the exhaust pipe, and to arrange the retaining portion  1   a  outside the exhaust pipe. Then, it is possible to retain and fix the other end by a metal fitting or the like outside the exhaust pipe. As a result, since it is possible to reduce thermal stress applied between the metal fitting and (the retaining portion  1   a  of) the particulate matter measuring device component  100 , it is possible to improve reliability of the retaining (mounting) of the particulate matter measuring device component  100 , and reliability of electrical connection between the particulate matter measuring device component  100  and an external circuit. 
     Also, in the particulate matter measuring device component  100  of the present disclosure, a wall surface of the flow channel  11  of the base portion  1  is denser than a surface of the filter portion  2 . Thereby, it is possible to make it difficult for the particulate matters to be deposited on the wall surface of the flow channel  11  of the base portion  1  and to easily deposit the particulate matters on the surface of the filter portion  2 . As a result, since it is possible to easily deposit the particulate matters on the filter portion  2  in a concentrated manner, it is possible to increase linearity between a deposit amount of the particulate matters and a measured value. As a result, it is possible to improve the measuring precision of the particulate matter measuring device component  100 . 
     The configuration where the wall surface of the flow channel  11  of the base portion  1  is denser than the surface of the filter portion  2  can be checked by a following method, for example. Specifically, the wall surface of the flow channel  11  of the base portion  1  and the surface of the filter portion  2  are observed using a scanning electron microscope (SEM). Then, the obtained SEM images are subjected to image processing, so that porosities of the surfaces are obtained. As a result, it is possible to regard a surface having a less porosity as denser. The porosity of the wall surface of the flow channel  11  of the base portion  1  can be set to 3% or less, for example. The porosity of the surface of the filter portion  2  can be set to 40% to 70%, for example. In the meantime, the wall surface of the flow channel  11  described herein means an entire inner surface of the base portion  1  of the flow channel  11  which base portion faces the gas. That is, the ceiling surface and the bottom surface are included in the wall surface. 
     When the porosity of the wall surface of the flow channel  11  of the base portion  1  is set to 3% or less, it is possible to make it difficult for the particulate matters to enter the base portion  1 . As a result, since it is possible to reduce a concern that the particulate matters are attached to the electrodes  3 , it is possible to reduce a concern that the particulate matters will be attached to the electrodes  3  and the electrostatic capacitance between the electrodes  3  cannot be thus correctly measured. As a result, it is possible to further improve the measuring precision of the particulate matter measuring device component  100 . 
     The base portion  1  and the filter portion  2  are formed integrally with each other. When the base portion  1  and the filter portion  2  are formed integrally with each other, it is possible to improve the long-term reliability of the particulate matter measuring device component  100 . Specifically, in a case where the base portion  1  and the filter portion  2  are separately formed and are then joined, the peeling may occur from an interface between the base portion  1  and the filter portion  2 , for example. In particular, when a bonding material or the like is used for joining, the bonding material is deteriorated, so that the filter portion  2  may not be correctly fixed to the base portion  1 . In contrast, when the base portion  1  and the filter portion  2  are formed (fired) integrally with each other, it is possible to reduce the concern that the peeling may occur from the interface between the base portion  1  and the filter portion  2 . 
     In particular, when the base portion  1  and the filter portion  2  are formed of the same ceramics, it is possible to approximate thermal expansion coefficients of the base portion  1  and the filter portion  2 . Thereby, it is possible to improve the long-term reliability of the particulate matter measuring device component  100  under heat cycle. Here, the description “formed of the same ceramics” means that the main component (a component occupying 80 mass % or more) of the ceramic constituting the base portion  1  and the filter portion  2  is the same. 
     In the particulate matter measuring device component  100  of the present disclosure, the base portion  1  and the filter portion  2  are formed of alumina. Alumina can be manufactured at low cost and a porosity of a surface thereof can be easily adjusted, as described below. 
     The base portion  1  having a surface of which the porosity is 3% or less and the filter portion  2  having a surface of which the porosity is about 40% to 70% can be formed integrally with each other by a following method, for example. Specifically, for a portion which becomes the base portion  1 , a ceramic paste including alumina powders of 93 mass % and a resin binder of 7 mass % is used. Also, for a portion which becomes the filter portion  2 , a ceramic paste including alumina powders of 55 mass %, a pore-forming material of 38 mass % and a resin binder of 7 mass % is used. The ceramic pastes are processed into green sheets having a predetermined shape by a doctor blade method. At this time, it is possible to form the electrodes  3  for forming an electrostatic capacitance by printing a conductive paste on the green sheet. Then, the green sheets are pressurized and laminated by using a uniaxial press machine. After performing surface processing, as required, the green sheets are fired at 1500° C., so that the filter portion  2  and the base portion  1  having the above-described porosities can be formed. 
     Sizes of the filter portion  2  can be set so that a length in a width direction of the base portion  1  is 0.3 mm, a length in a thickness direction of the base portion  1  is 1.2 mm, which is the same as the interval between the bottom surface and ceiling surface of the flow channel  11 , and a length in the length direction of the base portion  1  is 40 mm. 
     The electrode  3  is a member for forming an electrostatic capacitance. As shown in  FIG. 2 , a pair of the electrodes  3  is disposed in the base portion  1  so as to sandwich the filter portion  2 . More specifically, when the plurality of flow channels  11  are provided, like the particulate matter measuring device component  100  of the present disclosure, the electrodes  3  are disposed so as to sandwich the filter portion  2  positioned in each flow channel  11 . The electrodes  3  may be disposed to span and cover a plurality of filter portions  2  or may be disposed to correspond to the filter portions  2  one by one, for example. As shown in  FIG. 2 , when the three flow channels  11  are located in the vertical direction, like the particulate matter measuring device component  100  of the present disclosure, the electrodes  3  may be positioned above the upper flow channel  11 , between the upper flow channel  11  and the midmost flow channel  11 , between the midmost flow channel  11  and the lower flow channel  11 , and below the lower flow channel  11 . The electrode  3  positioned between the upper flow channel  11  and the midmost flow channel  11  can form the electrostatic capacitance between the corresponding electrode and the electrode  3  positioned above the upper flow channel  11  and can also form the electrostatic capacitance between the corresponding electrode and the electrode  3  positioned between the midmost flow channel  11  and the lower flow channel  11 . Also, the electrode  3  positioned between the midmost flow channel  11  and the lower flow channel  11  can form the electrostatic capacitance between the electrode and the electrode  3  positioned below the lower flow channel  11 , as well. 
     The electrostatic capacitance is formed between the pair of electrodes  3  disposed so as to sandwich the filter portion  2 . When the particulate matters are trapped in the filter portion  2 , the electrostatic capacitance between the pair of electrodes  3  changes. When the change in the electrostatic capacitance is detected by an external detection device, a deposit amount of the particulate matters trapped in the filter portion  2  can be measured. 
     In the particulate matter measuring device component  100  of the present disclosure, the electrode  3  is embedded in the base portion  1 . Thereby, it is possible to reduce a concern that the electrode  3  will be corroded due to the gas. Also, since it is possible to reduce a concern that the particulate matters and the like will be attached to a surface of the electrode  3 , it is possible to improve the measuring precision of the particulate matter measuring device component  100 . Meanwhile, in the particulate matter measuring device component  100  of the present disclosure, the electrode  3  is disposed (embedded) in the base portion  1 . However, the invention is not limited thereto. Specifically, the electrode  3  may be disposed on an outer surface of the base portion  1  (a surface except the wall surface of the flow channel  11 ), for example. 
     As shown in  FIG. 4 , in the particulate matter measuring device component  100  of the present disclosure, the electrode  3  has a linear wiring pattern, for example, and is disposed so as to extend along the filter portion  2 . In this way, when the electrode  3  is disposed so as to extend along the filter portion  2 , it is possible to improve linearity between the amount of the particulate matters trapped in the filter portion  2  and the change in electrostatic capacitance between the electrodes  3 . The reason is that it is possible to reduce the change in electrostatic capacitance due to the particulate matters attached to a portion of the component (for example, the wall surface of the flow channel  11 ) except the filter portion  2  by disposing the electrode  3  so as to extend along the filter portion  2 . In the meantime, the shape of the electrode  3  as seen from above is not limited to the linear shape, and may be a circular shape or a rectangular shape, for example. 
     Also, when the electrode  3  is formed into the linear wiring pattern, it is possible to increase a resistance value, as compared to a configuration where the electrode  3  is formed to have a circular shape or a rectangular shape. For this reason, the electrode  3  can be enabled to function as a heater by applying a high voltage to the electrode. Thereby, it is possible to remove the particulate matters trapped in the filter portion  2  by heating. 
     In particular, like an example shown in  FIG. 5 , the electrode  3  has a linear wiring pattern and is disposed in a region, in which the filter portion  2  is sandwiched, of the base portion  1  and in a region, in which the filter portion  2  is not sandwiched, and as seen from above, a portion of the electrode  3  which portion is positioned in the region in which the filter portion  2  is not sandwiched may be formed to be narrower than a portion which is positioned in the region in which the filter portion  2  is sandwiched. Thereby, while securing a width of the portion of the electrode  3  which portion is positioned in the region in which the filter portion  2  is sandwiched to favorably form the electrostatic capacitance between the electrodes, it is possible to narrow a width of the portion of the electrode  3  which portion is positioned in the region in which the filter portion  2  is not sandwiched, thereby increasing the resistance value. Thereby, it is possible to enable the electrode  3  to effectively function as the electrode for forming the electrostatic capacitance and to effectively function as a heater. 
     In the examples of  FIGS. 4 and 5 , an end of the electrode  3  has a leading portion  3   a  drawn out to the base portion  1  which is positioned outside the flow channel  11  in the width direction (the x-axis direction) of the base portion  1 . A through-conductor (not shown) electrically connected by the leading portion  3   a  and drawn out to an upper surface of the base portion  1  through the base portion  1  is provided. The upper surface of the base portion  1  is provided with a terminal electrode (not shown) which is electrically connected to the through-conductor. The terminal electrode and the external detection device can be electrically connected. 
     In the examples of  FIGS. 4 and 5 , each of the pair of electrodes  3  disposed so as to sandwich the filter portion  2  has one linear wiring pattern having a meander shape where ends of portions disposed so as to extend along each of the plurality of filter portions  2  are connected in a serpentine shape. An end of one electrode is drawn to the outer surface of the base portion  1 , and each of the pair of electrodes  3  is configured as one-system wiring. In contrast, in examples of  FIGS. 6 and 7 , each of the pair of electrodes  3  has a linear wiring pattern having two meander shapes, and is configured as a two-system wiring. In the example of  FIG. 6 , the two wiring patterns are arranged side by side in the width direction (the x-axis direction) of the flow channel  11 , and in the example of  FIG. 7 , the two wiring patterns are arranged side by side in the length direction (the y-axis direction) of the flow channel  11 . Meanwhile, in  FIGS. 6 and 7 , the leading portion  3   a  is omitted. 
     In this way, when each of the pair of electrodes  3  arranged to sandwich the filter portion  2  is configured as the two-system wiring, it is possible to detect the particulate matters by the electrode  3  of one system and to remove the trapped particulate matters by the electrode  3  of the other system. For this reason, it is possible to continuously detect the particulate matters without stopping the detection of the particulate matters so as to remove the particulate matters. In the examples of  FIGS. 6 and 7 , each of the pair of electrodes  3  arranged to sandwich the filter portion  2  is configured as the two-system wiring. However, since a plurality of systems have only to be provided, the wirings of three or more systems are also possible. 
     For the electrode  3 , a metal material such as platinum, tungsten and the like may be used. Also, when the electrode  3  is formed to have a linear wiring pattern, a width may be set to 2 mm, a length may be set to 38 mm, and a thickness may be set to 30 μm, for example. 
     In the particulate matter measuring device component  100  of the present disclosure, the base portion  1  has therein the flow channel  11 . However, the invention is not limited thereto. Specifically, for example, as shown in  FIG. 8 , the component may include a pair of base portions  1  which are plate-shaped members formed of ceramics and apposed so that main surfaces thereof face each other, filter portions  2  formed of porous ceramics and disposed so as to divide a space between the pair of base portions  2  to form flow channels, and a pair of electrodes  3  for forming an electrostatic capacitance which is disposed in each of the pair of base portions so as to sandwich the filter portions  2 , wherein the flow channels  11  are located on one end side of the pair of base portions  1  and a retaining portion  1   a  is disposed on the other end side of the pair of base portions  1 . 
     In the particulate matter measuring device component  100  of the present disclosure, the space between the base portion  1  and the base portion  1  is divided by the filter portions  2 , so that the flow channels  11  (the divided flow channels  12 ) are formed. The gas is enabled to flow into the flow channel  11 , so that it is possible to trap the particulate matters with the filter portions  2 , and to measure the amount of the particulate matters by detecting a change in electrostatic capacitance between the electrodes  3 . Also in the particulate matter measuring device component  100 , it is possible to improve the measuring precision, like the above-described particulate matter measuring device component  100 . 
     More specifically, in the particulate matter measuring device component  100  shown in  FIG. 8 , the six base portions  1  are provided with the five spaces, each of which is formed between the respective base portions, with being spaced side by side in the horizontal direction (the x-axis direction), and the four filter portions  2  are disposed in each of the five spaces. The number of the base portions  1  may be two to five, or seven or more. Also, the number of the filter portions  2  may be appropriately changed. 
     The filter portions  2  are disposed in a space which is positioned on one end side of the base portions  1 , of the space between the pair of base portions  1 , so that the flow channels  11  are formed biasedly on one end side of the base portions  1 . The retaining portion  1   a  is disposed on the other end side of the base portions  1 . That is, like the disclosure shown in  FIG. 1 , the flow channels  11  are located on the lower sides of the base portions  1  in the height direction (the z-axis direction), and the retaining portion  1   a  is disposed on the upper sides of the base portions  1  in the height direction (the z-axis direction). Also, like the preceding disclosure, the retaining portion  1   a  is a portion for retaining the particulate matter measuring device component  100  with a metal member and the like when fixing the component to an exhaust pipe. Therefore, like the preceding disclosure, it is possible to arrange only one ends of the base portions  1  having the flow channels  11  and the filter portions  2  inside the exhaust pipe, and to arrange the retaining portion  1   a  outside the exhaust pipe. Then, it is possible to retain and fix the other ends by a metal fitting or the like outside the exhaust pipe. As a result, since it is possible to reduce thermal stress applied between the metal fitting and (the retaining portion  1   a  of) the particulate matter measuring device component  100 , it is possible to improve the reliability of the retaining (mounting) of the particulate matter measuring device component  100 , and the reliability of the electrical connection between the particulate matter measuring device component  100  and an external circuit. 
     In the example of  FIG. 8 , a second base portion  1   b  formed of ceramics similar to the base portion  1  is arranged in a space which is positioned on the other end side of the base portion  1 , of the space between the pair of base portions  1 . The pair of base portions  1  and the second base portion  1   b  disposed therebetween are formed integrally with each other. According to this configuration, since the retaining portion  1   a  is formed of densified ceramics, it is possible to increase the strength of the retaining portion  1   a,  to which the metal fitting is mounted, and to retain the component with a higher force by the metal fitting. Also, it is possible to suppress the exhaust gas introduced into the flow channel  11  positioned on one end side from being leaked through the other end to the outside of the exhaust pipe by the second base portion  1   b.    
     Instead of the second base portion  1   b,  a filter portion  2  which is positioned most closely to the other end of the base portion  1 , of the filter portions  2  may be configured to extend to the other end. However, it is more effective to arrange the second base portion  1   b  formed of the densified ceramics similar to the base portion  1 . 
     Also, in the example of  FIG. 8 , the second base portion  1   b  is arranged so as to be in contact with the filter portion  2  which is positioned most closely to the other end of the base portion  1 , of the filter portions  2 . However, a space may be formed between the filter portion  2  positioned most closely to the other end and the other end, and the second base portion  1   b  may be arranged therein. 
     In the particulate matter measuring device component  100  shown in  FIG. 8 , the filter portion  2  constitutes a portion of a lower wall. However, the base portion  1  which is in contact with the lower filter portion  2  may be disposed below the lower filter portion  2 , as the lower wall. In this way, since it is possible to improve the stiffness of the particulate matter measuring device component  100  and to reduce an exposed area of the filter portion  2  having relatively low strength, it is possible to suppress deformation due to the thermal stress and a damage due to an external force and to thus secure the high reliability. Also, all the wall surfaces in contact with the flow channel  11  are the filter portions  2 , so that the trapping efficiency is increased and the sensitivity is improved. 
     Also, in the particulate matter measuring device component  100  of  FIG. 1 , the end portions of the flow channels  11  are opened. However, the invention is not limited thereto. For example, like an example of  FIG. 9 , the end portions of the flow channels  11  may be partially sealed by sealing portions  4 . In particular, one end of the flow channel  11  may be partially opened and a portion of the other end which portion faces the opened one end may be sealed, and one end of the flow channel  11  may be partially sealed, and a portion of the other end which portion faces the sealed one end may be opened. 
     Thereby, since the gas to flow inside the flow channel  11  can easily pass through the filter portion  2 , it is easy to trap the particulate matters with the filter portion  2 . As a result, it is possible to improve the measurement precision of the particulate matter measuring device component  100 . Meanwhile, in  FIG. 9 , the flow of the gas is denoted with the arrow. 
     Also, for the sealing portion  4 , a resin material such as fluorine-contained resin, for example, may be used. In addition, the sealing portion  4  may be formed of the same ceramics as the filter portion  2  or the base portion  1 . Thereby, since it is possible to reduce a difference of thermal expansions of the filter portion  2  or base portion  1  and the sealing portion  4 , it is possible to improve the long-term reliability under heat cycle. 
     Also, the filter portion  2  may be formed of the ceramics and may be formed (fired) integrally with the base portion  1  and the sealing portion  4 . Thereby, it is possible to reduce a concern that the deterioration will be caused from an interface between the sealing portion  4  and the base portion  1  or between the sealing portion  4  and the filter portion  2 . 
     The particulate matter measuring device component  100  of  FIGS. 10 to 12  includes a plurality of filter portions  2  having different porous degrees from each other. Thus, this allows the particulate matter measuring device component  100  to have higher added value, such as the particulate matter measuring device component  100  capable of perceiving a distribution of particle sizes of the particulate matters and the particulate matter measuring device component  100  capable of continuously trapping the particulate matters for a long time and having a long lifetime. 
     Specifically, in the example of  FIG. 10 , the filter portions  2  have three types of filter portions  2   a,    2   b  and  2   c  formed of porous ceramics and having different pore sizes and pore diameters. In the example of  FIG. 10 , a first filter portion  2   a  having a relatively large pore diameter, a third filter portion  2   c  having a relatively small pore diameter, and a second filter portion  2   b  having an intermediate pore diameter are provided. 
     Since the plurality of filter portions  2   a,    2   b  and  2   c  having the different pore diameters is provided, the particulate matters trapped by the respective filter portions  2   a,    2   b  and  2   c  have different average particle sizes. For this reason, it is possible to perceive a distribution of particle sizes of the trapped particulate matters from the electrostatic capacitance detected by the electrodes  3  arranged to sandwich each of the plurality of filter portions  2   a,    2   b  and  2   c  having the different pore diameters, so that it is possible to guess a combustion state of an engine configured to discharge the exhaust gas containing the particulate matters and a state of the PM filter positioned upstream of the particulate matter measuring device component  100 , for example. 
     Also, in the example of  FIG. 10 , the plurality of filter portions  2   a,    2   b  and  2   c  having the different pore diameters is aligned in order of the magnitudes of the pore diameters. Specifically, in the example of  FIG. 10 , three rows of spaces (the flow channels  11 ) are aligned in the right and left direction of  FIG. 10  (the x-axis direction), where the first filter portion  2   a  is arranged in the left row, the second filter portion  2   b  is arranged in the center row, and the third filter portion  2   c  is arranged in the right row. That is, in each row, the filter portions  2  having the same pore diameter are arranged side by side in the vertical direction (the z-axis direction). According to this arrangement, it is possible to arrange the electrodes  3  side by side configured to sandwich the filter portions  2  having the same pore diameter, and to integrate the electrodes into one, like the example of  FIG. 4 . 
     The type of the magnitude of the pore diameter of the filter portion  2  is not limited to the three types, and may be two types, or four or more types. Also, in the example of  FIG. 10 , the filter portions  2  having the same pore diameter are aligned side by side in the vertical direction (the z-axis direction) but may be aligned side by side in the horizontal direction (the x-axis direction). Although the filter portions may be randomly aligned, the filter portions are preferably aligned side by side, as described above. 
     In the meantime, the pore diameter is an average pore diameter. The pore diameter may be obtained by capturing a SEM image of a surface or a section of the filter portion  2  and calculating an average pore diameter of pores in a range of the SEM image through image analysis. the SEM image in a view field of 1.0 mm×1.3 mm at 100-fold magnification of the SEM may be used. 
     When the pore diameter of the filter portion  2  is 1 μm to 60 μm and the filter portion  2  has three types of the filter portions  2   a,    2   b  and  2   c  having different pore diameters, like the above example, the pore diameter of the first filter portion  2   a  may be 10 μm to 60 μm, the pore diameter of the second filter portion  2   b  may be 5 μm to 30 μm, and the pore diameter of the third filter portion  2   c  may be 1 μm to 15 μm, for example. 
     Also, in the examples of  FIGS. 11 and 12 , the filter portion  2  formed of porous ceramics has two types of filter portions  2   d  and  2   e  having different porosities. In the examples of  FIGS. 11 and 12 , a fourth filter portion  2   d  having a relatively large porosity and a fifth filter portion  2   e  having a relatively small porosity are provided. When seen in a cross sectional view perpendicular to the length direction of the flow channel  11 , the porosity of the filter portion  2  positioned at an outer side is larger than the porosity of the filter portion  2  positioned at an inner side. When seen in the cross sectional view perpendicular to the length direction of the flow channel  11 , the fourth filter portion  2   d  is arranged at the outer side, and the fifth filter portion  2   e  is arranged at the inner side. 
     In the meantime, the description “positioned at the outer side” may indicate an outer side in the vertical direction, as shown in  FIG. 11 . Also, the description “positioned at the outer side” may indicate an outer side in the width direction of a flow channel  11 , as shown in  FIG. 12 . Also, the description “positioned at the outer side” may indicate an outer side both in the vertical direction and in the width direction. 
     In the example of  FIG. 11 , the fourth filter portions  2   d  are arranged at an outer side in the vertical direction (the z-axis direction), and the fifth filter portions  2   e  are arranged at an inner side. The three rows of spaces (the flow channels  11 ) are aligned in the right and left direction of  FIG. 11  (the x-axis direction), where the six filter portions  2  are aligned in the vertical direction (the z-axis direction) in each space (the flow channel  11 ). The two upper filter portions and two lower filter portions in each space are the fourth filter portions  2   d,  and the two central filter portions in each space are the fifth filter portions  2   e.  In the example of  FIG. 12 , the fourth filter portions  2   d  are arranged at the outer sides in the right and left direction of  FIG. 12  (the x-axis direction), and the fifth filter portion  2   e  is arranged at the inner side. The three rows of spaces (the flow channels  11 ) are aligned in the right and left direction (the x-axis direction), where the four filter portions  2  are aligned in the vertical direction (the z-axis direction) in each space (the flow channel  11 ). The four filter portions positioned in each of the right and left spaces of the three spaces are the fourth filter portions  2   d,  and the four filter portions positioned in the central space are the fifth filter portions  2   e.    
     When the gas containing the particulate matters flows in the spaces (the flow channels  11 ) in the particulate matter measuring device component  100 , a flow rate of the gas flowing through a central portion of the space (an inner region in the cross sectional view perpendicular to the length direction of the flow channel  11 ) tends to be greater than a flow rate of the gas flowing through an outer peripheral portion of the space (an outer region in the cross sectional view perpendicular to the length direction of the flow channel  11 ). For this reason, the filter portion  2  arranged at the inner side traps the more particulate matters than the filter portion  2  positioned at the outer side, so that the clogging of the particulate matters occurs earlier. When the clogging of the particulate matters occurs earlier, a regeneration frequency of removing the particulate matters by heater heating increases, so that the particulate matter measuring device component  100  is also deteriorated earlier. In contrast, as described above, when the porosity of the filter portion  2  (the fourth filter portion  2   d ) positioned at the outer side in the cross sectional view perpendicular to the length direction of the flow channel  11  is greater than the porosity of the filter portion  2  (the fifth filter portion  2   e ) positioned at the inner side, the gas is more likely to flow toward the filter portion  2  (the fourth filter portion  2   d ) having the larger porosity, so that a difference of the gas flow rates depending on the positions in the cross sectional view perpendicular to the length direction of the flow channel  11  is reduced. For this reason, since only the filter portion  2  positioned at the inner side is not earlier clogged by the particulate matters, it is possible to provide the particulate matter measuring device component  100  capable of continuously trapping the particulate matters for a long time and having long lifetime. 
     In  FIGS. 11 and 12 , the porosity of each of the filter portions  2  (the fourth filter portions  2   d ) positioned at the outer side in the vertical direction and at the outer side in the right and left direction is greater than the porosity of the filter portion  2  (the fifth filter portion  2   e ) positioned at the inner side. Further, these filter portions may be combined, and the porosities of the filter portions  2  positioned at the outer sides in the vertical direction and the right and left direction and positioned at the outer periphery portion in the section may be greater than the porosities of the filter portions  2  positioned at the inner sides in the vertical direction and the right and left direction and positioned at the central portion in the section. When the base portions  1  and the filter portions  2  are alternately arranged in the right and left direction (the x-axis direction), the structure as shown in  FIG. 12  where the fourth filter portions  2   d  are arranged at the outer side in the right and left direction (the x-axis direction) and the fifth filter portion  2   e  is arranged at the inner side is preferable because it can be easily manufactured by a manufacturing method as described later. 
     As the measurement method of the porosity for comparing the porosities of the filter portions  2 , for example, a mercury intrusion technique (JIS standard R1655:2003), an image analysis of a SEM image, and the like may be exemplified. The image analysis of a SEM image can be performed by capturing a SEM image of a section of the filter portion  2  and calculating an arear ratio of pores in a range of the SEM image through the image analysis. For example, the SEM image in a view field of 1.0 mm×1.3 mm at 100-fold magnification of the SEM may be used. 
     When the porosity of the filter portion  2  is 40 to 70%, the porosities of the filter portion  2   d  having a relatively large porosity and the filter portion  2   e  having a relatively small porosity may be set to 50 to 70% and 40 to 60%, respectively. 
     In the above-described particulate matter measuring device component  100 , the flow channel  11  extends from one side surface of the base portion  1  to a side surface located opposite thereto. However, the invention is not limited thereto. For example, like an example of  FIGS. 14A to 14C , the flow channel  11  may be configured so that one end thereof opens on one side surface of the base portion  1  and the other end opens on a surface (a lower surface) located at the one end of the base portion  1 . Alternatively, the flow channel may open on two opposed side surfaces of the base portion  1  and a surface (a lower surface) located at one end of the base portion  1 . 
     Also, regarding an example of the particulate matter measuring device component  100  including the pair of base portions  1  apposed so that the main surfaces face each other, and the filter portions  2  disposed so as to divide the space between the pair of base portions  1  to form the flow channel  11 , the example of  FIG. 8  is an example where the base portions  1  and the filter portions  2  are alternately arranged in the horizontal direction (the x-axis direction). However, as shown in  FIG. 13 , the base portions  1  and the filter portions  2  may be alternately arranged in the vertical direction (the z-axis direction). At this time, the retaining portion  1   a  does not have the second base portion  1   b.  A thickness of the outermost (uppermost) base portion  1  is thick, and the corresponding base portion serves as the retaining portion  1   a.  This is similar to a configuration where the portion positioned at the outer side of the flow channel  11  of the base portion  1  and the outer wall of the flow channel  11 , which is shown in the example of  FIG. 1 , are replaced with the filter portion  2 . 
     A manufacturing method of the particulate matter measuring device component  100  having the dense base portion  1  formed of ceramics and the filter portion  2  formed of porous ceramics, which are formed integrally with each other, includes a process of preparing a plurality of first ceramic green sheets  12 , a process of preparing a plurality of second ceramic green sheets  22 , a process of forming an electrode layer  32  on the first ceramic green sheet  12 , a process of forming through-holes  112  in the second ceramic green sheets  22 , a process of laminating the first ceramic green sheets  12  having the electrode layer  32  formed thereon and the second ceramic green sheets  22  having the through-holes  112  formed therein to form a laminated body  102 , and a process of firing the laminated body  102 . 
       FIGS. 15A to 15D  are schematic views depicting a manufacturing method of a particulate matter measuring device component, in each process.  FIGS. 15A to 15D  depict manufacturing processes of the particulate matter measuring device component  100  in which three base portions  1  are prepared instead of six base portions shown in  FIG. 8  and six filter portions  2 , each of which is arranged between the pair of base portions  1 , are prepared instead of four filter portions shown in  FIG. 8 . First, as shown in  FIG. 15A , a plurality of first ceramic green sheets  12 , a plurality of second ceramic green sheets  22  and a third ceramic green sheet  12   b  are prepared. The first ceramic green sheet  12  will be sintered in the subsequent firing process and become the base portion  1 , the second ceramic green sheets  22  will be the filter portions  2 , and the third ceramic green sheet  12   b  will be the second base portion  2   b.  The base portion  1  and the second base portion  1   b  are formed of densified ceramics, whereas the filter portion  2  is formed of porous ceramics. For this reason, the second ceramic green sheet  22  will have more pores (the porosity is larger) when sintered in the subsequent firing process, as compared to the first ceramic green sheet  12  and the third ceramic green sheet  12   b.  Specifically, the second ceramic green sheet  22  has more components which become pores when sintered in the firing process, as compared to the first ceramic green sheet  12  and the third ceramic green sheet  12   b.  Specifically, more organic binder components and a pore-forming material are included. Alternatively, in order to lower the sintering performance to increase the pores, sintering aid components are less included. 
     The use of a pore-forming material is desirable from the viewpoint of easiness in adjustment of pore diameter and porosity. The pore-forming material has the form of particles that will be burnt to vanish in the subsequent firing process. Examples of the pore-forming material include acrylic resin beads (methacrylic ester copolymer beads), carbon powder, and crystalline cellulose. The pore-forming material in use preferably has a particle size which is 1 to 1.2 times the pore diameter of the filter portion  2 . As described previously, in the case of forming the filter portion  2  having pore diameters of 1 μm to 60 μm, it is possible to use a pore-forming material having an average particle size of 1 μm to 72 μm. Porosity adjustment is accomplished by adjusting the particle size and the amount of the pore-forming material. 
     In the case where the base portion  1  is formed of alumina ceramics, with respect to the first ceramic green sheet  12  and the third ceramic green sheet  12   b,  a slurry is prepared by admixing an organic binder such as acryl-based resin, an organic solvent such as toluene and acetone, and a solvent such as water in alumina powders and sintering aids (powders of SiO 2 , MgO, CaO, etc.) The slurry may be formed into a sheet shape by a film formation method such as a doctor blade method. In the example of  FIGS. 15A to 15D , thicknesses of the first ceramic green sheet  12  and the third ceramic green sheet  12   b  are different but may be the same. The first ceramic green sheet  12  and the third ceramic green sheet  12   b  have different sizes, and the third ceramic green sheet  12   b  is smaller in size than the first ceramic green sheet  12 . For the second ceramic green sheet  22 , a slurry in which the pore-forming material is added to the slurry for the first ceramic green sheet  12  is preferably prepared. The second ceramic green sheet  22  contains the pore-forming material, in addition to the material for the first ceramic green sheet  12 . The second ceramic green sheet  22  is also smaller in size than the first ceramic green sheet  12 . An aligned size of the second ceramic green sheet  22  and the third ceramic green sheet  12   b  is substantially the same as the first ceramic green sheet  12 . 
     When the filter portions  2  have the different pore diameters, it is preferably to prepare a plurality of types of the second ceramic green sheets  22  having different average particle diameters of the pore-forming materials contained by using the pore-forming materials having different average particle diameters, as the pore-forming materials added to the slurry for the second ceramic green sheets  22 , for example. When the filter portions  2  have the different porosities, it is preferable to prepare a plurality of types of the second ceramic green sheets  22  having different average particle diameters of the pore-forming material included by making amounts of the pore-forming materials which are added to the slurry for the second ceramic green sheets  22 , different. 
     Then, as shown in  FIG. 15B , an electrode layer  32  is formed on the first ceramic green sheet  12 . The electrode layer  32  will be the electrode  3  through sintering in the subsequent firing process. The electrode layer  32  is preferably formed by applying a metal paste having a metal material such as platinum or tungsten, which is a main component of the electrode  3 , as a main component, onto the first ceramic green sheet  12 . The metal paste may be prepared by adding a resin binder and a solvent to powders of the metal material and mixing the same. The metal paste is preferably applied in a wiring pattern shape of the electrode  3  by a screen printing method or otherwise. At this time, the electrode layer  32  is formed on only one surface of the first ceramic green sheet  12 . 
     Also, as shown in  FIG. 15C , the second ceramic green sheet  22  is provided with through-holes  112 . The through-hole  112  will be the flow channel  11 . The second ceramic green sheet  22  is preferably provided with the through-holes  112  by punching processing of using a metallic die or laser processing. 
     Then, as shown in  FIG. 15D , the first ceramic green sheets  12  having the electrode layers  32  formed thereon, the second ceramic green sheets  22  having the through-holes  112  formed therein and the third ceramic green sheets  12   b  are laminated to form a laminated body  102 . In the example of  FIG. 15D , the portions which become the three base portions  1  are respectively formed by laminating the two layers of the first ceramic green sheets  12 , and the portions which become the filter portions  2  are formed by laminating the two layers of the second ceramic green sheets  22 . All may be formed using one or three or more layers of the ceramic green sheets. Also, the second ceramic green sheets  22  and the third ceramic green sheets  12   b  are aligned so as to be in contact with each other in a planar direction, and the first ceramic green sheets  12  are laminated on the top and bottom thereof. A portion in which the first ceramic green sheets  12 , the second ceramic green sheets  22  and the third ceramic green sheets  12   b  are laminated on one another is a portion  12   a  that will be the retaining portion  1   a.    
     The example of  FIG. 15D  is the laminated body  102  corresponding to a case where the particulate matter measuring device component  100  having the electrodes  3  embedded in the base portion  1 , like the example of  FIG. 8 , is manufactured. Therefore, the electrode layer  32  is positioned between the two layers of the first ceramic green sheets  12 . The first ceramic green sheet  12  without the electrode layer  32  is laminated on the first ceramic green sheet  12  having the electrode layer  32  formed thereon. 
     When manufacturing the particulate matter measuring device component  100  as shown in the example of  FIG. 2 , the first ceramic green sheet  12  without the electrode layer  32  is laminated on the first ceramic green sheet  12  having the electrode layer  32  formed thereon, only a portion of the second ceramic green sheet  22  which portion will be the filter portion  2  is laminated thereon, and the first ceramic green sheet  12  having a frame shape is laminated so as to surround a periphery thereof. 
     In the above-described structure where the base portion  1  in contact with the filter portion  2  is provided as a sidewall outside (below) the filter portion  2  positioned at the bottom of the particulate matter measuring device component  100  as shown in the example of  FIG. 8 , the first ceramic green sheet  12  is preferably additionally bonded to a side surface of the laminated body  102  as shown in  FIG. 15D . 
     In order to form the laminated body  102 , the first ceramic green sheets  12  having the electrode layers  32  formed thereon and the second ceramic green sheets  22  having the through-holes  112  formed therein are preferably overlapped and pressurized and integrated by a uniaxial press machine or the like. 
     By filling the through-holes  112  with resin or the like which will be burnt to vanish in the subsequent firing process, it is possible to suppress deformation in a part of the first ceramic green sheet  12  which part lies above or below the through-hole. 
     By firing the laminated body  102 , there is obtained such a particulate matter measuring device component  100  as described hereinabove in which the ceramics-made densified base portion  1  and the porous ceramics-made filter portion  2  are formed integrally with each other. In the case where the base portion  1  and the filter portion  2  are formed of alumina ceramics, the firing temperature is set at 1500° C. to 1600° C. 
     In order to manufacture the particulate matter measuring device component  100  as shown in the example  FIG. 13 , a manufacturing method as shown in  FIGS. 16A to 16D  is preferably used. As compared to the manufacturing method of  FIGS. 15A to 15D , in the example of  FIGS. 16A to 16D , the third ceramic green sheet  12   b  which will be the second base portion  2   b  is not used, as shown in  FIG. 16A . Also, the first ceramic green sheet  12  and the second ceramic green sheet  22  have substantially the same size. 
     A process shown in  FIG. 16B  of forming the electrode layer  32  on the first ceramic green sheets  12  and a process shown in  FIG. 16C  of forming the through-holes  112  in the second ceramic green sheet  22  are respectively similar to the processes shown in  FIG. 15B  and  FIG. 15C . The process of firing the laminated body  102  is also similar. 
     In a process shown in  FIG. 16D  of forming the laminated body  102  by laminating the first ceramic green sheets  12  having the electrode layers  32  formed thereon and the second ceramic green sheets  22  having the through-holes  112  formed therein, a plurality of first ceramic green sheets  12  are additionally laminated on the uppermost first ceramic green sheet  12  having the electrode layer  32  formed thereon. A portion in which the plurality of first ceramic green sheets  12  are laminated is a portion  12   a  which will be the retaining portion  1   a.  The first ceramic green sheet  12  of the portion is preferably thicker than the first ceramic green sheet which is in contact with the second ceramic green sheet  22 . 
     In the meantime, when the outermost second ceramic green sheet  22  in  FIGS. 16A to 16D  is replaced with the first ceramic green sheet  12 , the particulate matter measuring device component  100  as shown in the example of  FIG. 2  can be manufactured. Preferably, the second ceramic green sheet  22  is slightly smaller than the first ceramic green sheet  12 , and the first ceramic green sheet  12  having a frame shape is arranged to surround the second ceramic green sheet  22 . 
     In order to form the through-conductor, before preparing the laminated body  102 , a necessary ceramic green sheet is provided with through-holes by punching processing of using a metallic die or laser processing, and a conductive paste, which is similar to the paste for forming the electrode layer  32 , is filled in the through-holes. 
     REFERENCE SIGNS LIST 
       1 : Base portion 
       1   a:  Retaining portion 
       1   b:  Second base portion 
       11 : Flow channel 
       12 : Divided flow channel 
       2 : Filter portion 
       3 : Electrode 
       4 : Sealing portion 
       100 : Particulate matter measuring device component