EXHAUST GAS PARTICULATE MATTER SENSOR

Abstract

Disclosed is an exhaust gas particulate matter (PM) sensor. According to an embodiment of the present invention, there is provided an exhaust gas particulate matter (PM) sensor that is provided on an exhaust line through which exhaust gas from a vehicle passes and is provided with an electrode formed to detect PM, the PM sensor including: a first insulating layer; a PM detection electrode placed under the first insulating layer; a temperature compensation electrode placed in parallel with the PM detection electrode; a second insulating layer placed under the PM detection electrode and the temperature compensation electrode; a heater electrode placed under the second insulating layer; and a third insulating layer placed under the heater electrode.

Claims

1. An exhaust gas particulate matter (PM) sensor for a vehicle, the sensor comprising: a first insulating layer; a temperature compensation electrode placed under the first insulating layer; a PM detection electrode placed with the temperature compensation electrode side by side on the same plane; a second insulating layer placed under the PM detection electrode and the temperature compensation electrode; a heater electrode placed under the second insulating layer; and a third insulating layer placed under the heater electrode, wherein external electrodes of the PM detection electrode and of the temperature compensation electrode and the temperature compensation electrode are not exposed to exhaust gas by the first insulating layer, and a sensing electrode of the PM detection electrode is exposed to the exhaust gas.

2. The sensor of claim 1, wherein a sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are placed with the same length side by side in a leftward-rightward direction along a longitudinal direction of the PM sensor.

3. The sensor of claim 1, wherein a sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are placed with the same width side by side in an inward-outward direction along a longitudinal direction of the PM sensor, and the sensing electrode of the PM detection electrode is placed further outward in comparison with the sensing electrode of the temperature compensation electrode.

4. The sensor of claim 2, further comprising: a semiconducting layer placed between the second insulating layer and the sensing electrodes of the PM detection electrode and the temperature compensation electrode, wherein the semiconducting layer, particulate matter, and the sensing electrodes of the PM detection electrode and the temperature compensation electrode are in order of decreasing magnitude in resistivity, and the sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are the same in area and material, and a resistance value R1 of the PM detection electrode and a resistance value R2 of the temperature compensation electrode are measured, and temperature compensation of the PM detection electrode is performed using a difference between the R1 and the R2 or a ratio between the R1 and the R2.

5. The sensor of claim 3, further comprising: a semiconducting layer placed between the second insulating layer and the sensing electrodes of the PM detection electrode and the temperature compensation electrode, wherein the semiconducting layer, particulate matter, and the sensing electrodes of the PM detection electrode and the temperature compensation electrode are in order of decreasing magnitude in resistivity, and the sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are the same in area and material, and a resistance value R1 of the PM detection electrode and a resistance value R2 of the temperature compensation electrode are measured, and temperature compensation of the PM detection electrode is performed using a difference between the R1 and the R2 or a ratio between the R1 and the R2.

6. An exhaust gas particulate matter (PM) sensor for a vehicle, the sensor comprising: a first insulating layer; a PM detection electrode placed under the first insulating layer; a second insulating layer placed under the PM detection electrode; a temperature compensation electrode placed under the second insulating layer; a third insulating layer placed under the temperature compensation electrode; a heater electrode placed under the third insulating layer; and a fourth insulating layer placed under the heater electrode, wherein external electrodes of the PM detection electrode and of the temperature compensation electrode are not exposed to exhaust gas by the first insulating layer, and only a sensing electrode of the PM detection electrode is exposed to the exhaust gas.

7. The sensor of claim 6, further comprising: a semiconducting layer placed between the sensing electrode of the PM detection electrode and the second insulating layer, and between a sensing electrode of the temperature compensation electrode and the third insulating layer, wherein the semiconducting layer, particulate matter, and the sensing electrodes of the PM detection electrode and the temperature compensation electrode are in order of decreasing magnitude in resistivity, and the sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are the same in area and material, and a resistance value R1 of the PM detection electrode and a resistance value R2 of the temperature compensation electrode are measured, and temperature compensation of the PM detection electrode is performed using a difference between the R1 and the R2 or a ratio between the R1 and the R2.

8. An exhaust gas particulate matter (PM) sensor for a vehicle, the sensor comprising: a first insulating layer; a PM detection electrode placed under the first insulating layer; a second insulating layer placed under the PM detection electrode; a heater electrode placed under the second insulating layer; a third insulating layer placed under the heater electrode; a temperature compensation electrode placed under the third insulating layer; and a fourth insulating layer placed under the temperature compensation electrode, wherein external electrodes of the PM detection electrode and of the temperature compensation electrode are not exposed to exhaust gas by the first insulating layer, and only a sensing electrode of the PM detection electrode is exposed to the exhaust gas.

9. The sensor of claim 8, further comprising: a semiconducting layer placed between the sensing electrode of the PM detection electrode and the second insulating layer, and between the third insulating layer and a sensing electrode of the temperature compensation electrode, wherein the semiconducting layer, particulate matter, and the sensing electrodes of the PM detection electrode and the temperature compensation electrode are in order of decreasing magnitude in resistivity, and the sensing electrode of the temperature compensation electrode and the sensing electrode of the PM detection electrode are the same in area and material, and a resistance value R1 of the PM detection electrode and a resistance value R2 of the temperature compensation electrode are measured, and temperature compensation of the PM detection electrode is performed using a difference between the R1 and the R2 or a ratio between the R1 and the R2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0033] FIG. 1 is a diagram illustrating a structure of a conventional exhaust gas particulate matter sensor;

[0034] FIG. 2 is a diagram illustrating a structure of an exhaust gas particulate matter sensor according to the present invention;

[0035] FIG. 3 is a diagram illustrating stages at which PM is deposited in an exhaust gas particulate matter sensor according to the present invention;

[0036] FIG. 4 is a graph illustrating change in resistance and electrical conductance for each stage at which PM is deposited according to the present invention;

[0037] FIG. 5 is a diagram illustrating a length (L.sub.O) of a sensing electrode and PM particle size (1) according to the present invention;

[0038] FIG. 6 is a diagram illustrating a shape of a sensing electrode and an external electrode that are capable of correction to a temperature of a PM sensor and deposited particulate matter according to the present invention;

[0039] FIG. 7 is a diagram illustrating an example of temperature sensing and heater regeneration structure of a PM sensor according to the present invention;

[0040] FIG. 8 is a diagram illustrating another example of temperature sensing and heater regeneration structure of a PM sensor according to the present invention;

[0041] FIG. 9 is a diagram illustrating still another example of temperature sensing and heater regeneration structure of a PM sensor according to the present invention; and

[0042] FIG. 10 is a diagram illustrating still another example of temperature sensing and heater regeneration structure of a PM sensor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Embodiments described below are provided so that those skilled in the art can easily understand the technical spirit of the present invention, and thus the present invention is not limited thereto. In addition, the matters described in the attached drawings may be different from those actually implemented by schematized drawings to easily describe embodiments of the present invention.

[0044] It will be understood that when an element is referred to as being coupled or connected to another element, it can be directly coupled or connected to the other element or intervening elements may be present therebetween.

[0045] The term connection as used herein means a direct connection or an indirect connection between a member and another member, and may refer to all physical connections such as adhesion, attachment, fastening, bonding, coupling, and the like.

[0046] Also, the expressions such as first, second, etc. are used only to distinguish between plural configurations, and do not limit the order or other specifications between configurations.

[0047] As used herein, the singular forms a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is to be understood that terms such as including, having, etc. are intended to indicate the existence of the features, numbers, steps, actions, elements, parts, or combinations thereof disclosed in the specification, and are intended to include the possibility that one or more other features, numbers, steps, actions, elements, parts, or combinations thereof may be added.

[0048] Hereinafter, an exhaust gas particulate matter sensor according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0049] FIG. 1 is a diagram illustrating a structure of a conventional exhaust gas particulate matter sensor. FIG. 2 is a diagram illustrating a structure of an exhaust gas particulate matter sensor according to the present invention.

[0050] In FIG. 1, a PM detection electrode of the conventional PM sensor is formed of a pair of interlocking interdigital electrodes (IDEs) wherein patterned electrodes on a ceramic substrate are spaced apart from each other by a predetermined distance. As the material of the interdigital electrode, platinum having resistivity of 10.sup.7 m may be used.

[0051] In FIG. 1, the PM detection electrode is composed of a sensing electrode and an external electrode. The PM detection electrode is intended to measure resistance change caused by deposition of particulate matter in the sensing electrode that is located between the external electrodes, and has a disadvantage in that the resistance change is affected not only by particulate matter generated by incomplete combustion and but also by metal particles contained in exhaust gas. That is, the exhaust gas includes fine metal particles contained in lubricating oil, and the like, which may affect resistance change. When a metal particle causes an electric current to be applied to the electrode, electrical conductance rises rapidly, resulting in the fatal impact on the function of the PM sensor measuring the resistance change.

[0052] In FIG. 2, according to the present invention, in order to reduce the influence of metal particles contained in the exhaust gas, a sensing electrode 21 that has greater resistivity (namely, low electrical conductivity (=1/p)) than that of an external electrode and particulate matter 22 is placed between external electrodes 20. As the material of the external electrode, platinum having resistivity of 10.sup.7 m may be used. As the material of the sensing electrode, SiC, which is a semiconducting material, having resistivity of 10.sup.3 m may be used.

[0053] That is, as particulate matter is deposited in the sensing electrode, the current that has been flowing through the sensing electrode flows through particulate matter having low resistivity (namely, relatively high electrical conductivity than that of the sensing electrode), so the total resistance is reduced. The resistance change at this time is measured to find out the amount of deposited particulate matter.

[0054] The present invention has a difference to the conventional one in that the distance between the sensing electrodes can be larger. Because the present invention makes it possible to measure the signals from the PM deposition between the sensing electrodes. And this difference results in lower effect of metal particle in the exhaust gas.

[0055] FIG. 3 is a diagram illustrating stages at which PM 22 is deposited in an exhaust gas particulate matter sensor according to the present invention. The initial stage is that there is no particulate matter deposited in the sensing electrode 21 located between the external electrodes 20. Stage 1 where deposition of the particulate matter starts and Stage 2 where deposition proceeds are followed by Stage 3 where particulate matter is sufficiently deposited. A characteristic for distinguishing the stages is described with change in resistance or electrical conductance shown in FIG. 4.

[0056] After the deposition of particulate matter starts, the change in total resistance is related to the amount of particulate matter deposited in the sensing electrode as well as to the size of particulate matter, which may be represented by V.sub.0/l.sup.n. The total amount (hereinafter, the total amount means volume) of the particulate matter deposited in the sensing electrode is denoted by Vo, the diameter of the deposited particulate matter is denoted by l, and a constant according to the shape of the particulate matter is denoted by n.

[0057] The change in total resistance at Stage 3 where the particulate matter is sufficiently deposited is related only to the total amount of the deposited particulate matter. Therefore, the total amount (Vo) of the deposited particulate matter may be measured from the resistance value at Stage 3, and the number of particulate matter may be calculated by offsetting VO from the resistance value at Stage 1. After Stage 3, when a predetermined amount or more of particulate matter is deposited, continuous monitoring is possible through a regeneration step.

[0058] This is represented by an equation as follows.

[0059] The resistance (R) at the sensing electrode located between the external electrodes is represented by 1/R=1/R.sub.SiC+1/R.sub.C, wherein the resistance R.sub.SiC is caused by SiC which is the semiconducting substrate and the resistance R.sub.C is caused by the particulate matter.

[0060] The total resistance (R) at Stage 1 is represented by R=.sub.SiC/A.sub.SiC(L.sub.0V.sub.0/l.sup.2)=.sub.SiCL.sub.0/A.sub.SiC.sub.SiCV.sub.0/A.sub.SiCl.sup.2, wherein .sub.SiC, A.sub.SiC, L.sub.0, V.sub.0, and l denote resistivity of the sensing electrode, the cross-sectional area of the sensing electrode, the length of the sensing electrode, the total volume of the deposited particulate matter, and the diameter of the deposited particulate matter, respectively.

[0061] Here, .sub.SiCL.sub.0/A.sub.SiC is R.sub.0, .sub.SiCV.sub.0/A.sub.SiCl.sup.2 is R.sub.PM, and R=R.sub.0+R.sub.PM is obtained.

[0062] In the meantime, V.sub.0 is V.sub.0=v.sub.0.Math.t. The total amount of the particulate matter deposited in the sensing electrode is denoted by V.sub.0, and the amount of particulate matter deposited per unit of time is denoted by v.sub.0, and time is denoted by t. When applying this, at Stage 1, R=.sub.SiC/A.sub.SiC (L.sub.0V.sub.0/l.sup.2)=.sub.SiCL.sub.0/A.sub.SiC.sub.SiCV.sub.0/A.sub.SiCl.sup.2=.sub.SiCL.sub.0/A.sub.SiC(.sub.SiCv.sub.0/A.sub.SiCl.sup.2).Math.t is a linear equation that increases linearly with respect to time t and the slope m1 is (.sub.SiCv.sub.0/A.sub.SiC l.sup.2).

[0063] The total resistance (R) at Stage 3 is dependent on the resistance (R.sub.C) caused by the particulate matter.

[0064] That is, RR.sub.C=p.sub.C L.sub.0/A.sub.C=p.sub.C L.sub.0.sup.2/V.sub.0 is obtained. The resistivity and the cross-sectional area of the deposited particulate matter are denoted by p.sub.C and A.sub.C, respectively. The length of the sensing electrode and the total volume of the deposited particulate matter are denoted by L.sub.0 and V.sub.0, respectively.

[0065] From this, electrical conductance G=V.sub.0/(p.sub.C L.sub.0.sup.2), which is the inverse of the resistance, is obtained. When applying V.sub.0=v.sub.0.Math.t, electrical conductance G=(v.sub.0/p.sub.C L.sub.0.sup.2).Math.t is obtained. That is, electrical conductance is represented by a linear equation having the slope m3=(v.sub.0/p.sub.C L.sub.0.sup.2) with respect to time.

[0066] In the meantime, the amount v.sub.0 of particulate matter deposited per unit of time is proportional to the amount (V.sub.PM) of particulate matter in the exhaust gas. From this, v.sub.0=.Math.V.sub.PM is represented, and V.sub.PM=(p.sub.C L.sub.0.sup.2/).Math.m3 is obtained.

[0067] In the meantime, at Stage 1, from m1=(p.sub.SiCv.sub.0/A.sub.SiC l.sup.2), m3=(v.sub.0/p.sub.C L.sub.0.sup.2), and l.sup.2=(p.sub.SiCv.sub.0/A.sub.SiC) m3/m1, the size of the particulate matter is determined.

[0068] In the meantime, the size 1 of particulate matter depends mainly on the type of fuel, such as gasoline or diesel, and the characteristic of the engine, such as direct injection or turbocharging, so the size I does not change much over time and is regarded as a constant (l.sub.0). From this, the amount of particulate matter at Stage 1 is determined by V.sub.PM=(A.sub.SiCl.sub.0.sup.2/p.sub.SiC ).Math.m1.

[0069] In the meantime, FIG. 4 is a diagram illustrating change in resistance and electrical conductance for each stage at which PM is deposited according to the present invention. FIG. 4 shows characteristics of Stage 1 and Stage 3. That is, Stage 1 has a characteristic that the resistance linearly decreases over time as particulate matter is deposited. Stage 3 has a characteristic that electrical conductance linearly increases over time as particulate matter is deposited. That is, the slope m1 at Stage 1 has a negative value and the slope m3 at Stage 3 has a positive value.

[0070] From the slope m3=v.sub.0/(p.sub.CL.sub.0.sup.2) of electrical conductance measured at Stage 3, is obtained.

[0071] From these values, V.sub.PM=(p.sub.C L.sub.0.sup.2/).Math.m3, which is the amount of particulate matter in the exhaust gas, is calculated. From m1=p.sub.SiC v.sub.0/(A.sub.SiC l.sup.2) measured at Stage 1, the size 1 of particulate matter, l.sup.2=(p.sub.SiC.sub.p.sub.CL.sub.0.sup.2/A.sub.SiC) m3/m1, is calculated.

[0072] FIG. 5 is a diagram illustrating a length (L.sub.O) of a sensing electrode and PM particle size (1) according to the present invention.

[0073] FIG. 6 is a diagram illustrating a shape of a sensing electrode and an external electrode that are capable of correction to a temperature of a PM sensor and deposited particulate matter according to the present invention.

[0074] Compared to FIG. 2 wherein the semiconducting substrate is used as the sensing electrode, FIG. 6 shows a concept that in addition to the external electrode with the semiconducting substrate which is used as the sensing electrode, another external electrode for temperature correction is provided with a non-conductive coating on a semiconducting substrate. FIG. 6 shows the structure of a sensing electrode-external electrode (a PM detection electrode) and semiconducting substrate 60 without temperature correction and in addition to the PM detection electrode, and also shows the structure (located at the inner bottom of the PM detection electrode in FIG. 6) of a sensing electrode-external electrode 61 (hereinafter, referred to as a temperature compensation electrode) with a non-conductive coating on a semiconducting substrate. In this specification, temperature compensation and temperature correction have substantially the same meaning. The term a temperature compensation electrode is used as the name of the electrode structure, but otherwise the term temperature correction is used.

[0075] A sensing electrode using a semiconducting substrate is described above with reference to FIGS. 2 to 5, which yields a measurement value (hereinafter, referred to as R1) without temperature correction.

[0076] A sensing electrode with a non-conductive coating, which is located between external electrodes for temperature correction yields a measurement value (hereinafter, referred to as R2) for temperature correction. The difference in resistance values caused by temperature correction is represented by R=R1R2, and the ratio of resistance values caused by temperature correction is represented by =R1/R2.

[0077] R1=R.sub.O+R.sub.T+R.sub.PM is obtained, and R2=R.sub.O+R.sub.T is obtained. The resistance before temperature change before particulate matter is deposited is denoted by R.sub.O. The resistance change caused only by temperature change is denoted by R.sub.T. The resistance change caused only by deposition of particulate matter is denoted by R.sub.PM, and is proportional to the difference between the resistivity of the semiconducting substrate and the resistivity caused by deposition of the particulate matter and to the amount of the deposited particulate matter. From this, R.sub.PM= (p.sub.SiCp.sub.C).Math.M.sub.PM is represented. The resistivity of particulate matter is negligible compared to the resistivity of a sensing electrode substrate, so R.sub.PM=.Math.p.sub.SiC.Math.M.sub.PM is represented. Here, is the proportionality constant that is equal to the ratio of the resistance change caused by deposition of particulate matter to the product of the amount of the deposited particulate matter and the difference in resistivity between the semiconducting substrate and particulate matter. When using R.sub.SiC=p.sub.SiC.Math.L.sub.0/A.sub.SiC, R.sub.PM=.Math.R.sub.SiC.Math.M.sub.PM is represented. Here, =.Math.A.sub.SiC/L.sub.0 is the proportionality constant that is equal to the ratio of the resistance change caused by deposition of particulate matter to the product of the resistance of the semiconducting substrate and the amount of the deposited particulate matter. The resistance before particulate matter is deposited is denoted by R.sub.SiC which is equal to R2. Therefore, R.sub.PM=.Math.R2.Math.M.sub.PM is represented. At Stage 1, R.sub.PM=p.sub.SiCV.sub.0/(A.sub.SiCl.sup.2) is represented. When using M.sub.PM=V.sub.0.Math..sub.PM, =1/(.sub.PM.Math.l.sup.3) is obtained. Here, density of particulate matter is denoted by .sub.PM.

[0078] From this, R=R1R2=R.sub.PM denotes the difference in resistance value caused by the deposited particulate matter, and =R1/R2 is linearly proportional to the mass of particulate matter deposited at 1+.Math.M.sub.PM.

[0079] In the meantime, SiC refers to semiconducting ceramic (SC), and SiC is an example thereof.

[0080] FIG. 7 shows a particulate matter (PM) sensor 100 that is provided on an exhaust line through which exhaust gas from a vehicle passes, the PM sensor being provided with an electrode formed to detect PM. The PM sensor 100 includes: a first insulating layer 110; a temperature compensation electrode 160 placed under the first insulating layer 110; a PM detection electrode 150 spaced apart from the temperature compensation electrode by a predetermined distance; a second insulating layer 120 placed under the PM detection electrode 150 and the temperature compensation electrode 160; a heater electrode 170 placed under the second insulating layer 120; and a third insulating layer 130 placed under the heater electrode 170.

[0081] FIG. 7 shows an example of positions of the PM detection electrode 150 without temperature correction and the temperature compensation electrode 160 for temperature correction, wherein two electrodes are spaced apart from each other by a predetermined distance along the length of the PM sensor and are positioned side by side in the leftward-rightward direction on the same plane with the same length as the PM sensor, under the first insulating layer 110. Regarding the PM detection electrode 150 and the temperature compensation electrode 160, the whole surface may be supported by the second insulating layer 120 placed below. Further, only the sensing electrodes, which are parts of the PM detection electrode 150 and the temperature compensation electrode 160 may not be directly supported by the second insulating layer 120, and the semiconducting layer 180 may be placed therebetween. The semiconducting layer 180 is a coating layer and is supported by the external electrode of the PM detection electrode 150 and of the temperature compensation electrode 160, and by the second insulating layer 120. The effect of thickness is neglected.

[0082] The first insulating layer is placed on the PM detection electrode 150 and the temperature compensation electrode 160, but does not cover the entire PM detection electrode 150 and the entire temperature compensation electrode 160. As shown in FIG. 7, the sensing electrode of the PM detection electrode 150 is not covered with the first insulating layer 110. Conversely, the entire temperature compensation electrode 160 is covered with the first insulating layer 110.

[0083] That is, except for the sensing electrode of the PM detection electrode 150, the external electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 and the temperature compensation electrode 160 may be covered with the first insulating layer 110 for support.

[0084] The temperature compensation electrode 160 is not directly exposed to exhaust gas by the first insulating layer 110, and the sensing electrode of the PM detection electrode 150 needs to be directly exposed to exhaust gas, so the first insulating layer 110 is not placed on the corresponding part.

[0085] Unlike the temperature compensation electrode 160, the first insulating layer is not placed on the sensing electrode of the PM detection electrode 150 and the sensing electrode is formed to be directly exposed to exhaust gas.

[0086] The heater electrode 170 for PM regeneration is placed under the second insulating layer 120, and the third insulating layer 130 is placed under the heater electrode 170. That is, in order to thermally remove PM deposited in the PM detection electrode 150, the heater electrode 170 is placed below the bottom of the PM detection electrode 150 with the second insulating layer 120 in between.

[0087] When deposition of PM is performed in the PM detection electrode 150, the PM detection electrode 150 needs to perform self-regeneration. Here, the heater serving as a heat source is placed below the bottom of the PM detection electrode 150. The heater and the PM detection electrode 150 are unable to be in direct contact with each other, so the insulating layer that is electrically insulated and capable of heat transfer is necessary.

[0088] In the meantime, regeneration temperature measurement is required for controlling the heater and is performed by the temperature compensation electrode 160. That is, the temperature compensation electrode 160 measures the temperature of the second insulating layer 120 for on/off control of the heater. Since the second insulating layer 120 contains a semiconducting material (for example, SiC), the relationship between the temperature and the resistance change is set in advance as a relational expression or a table. The heater voltage is controlled in such a manner as to maintain the resistance corresponding to the temperature at which PM oxidizes, so heater control is possible without a temperature sensor.

[0089] In the PM sensor 100 shown in FIG. 7, the PM detection electrode 150 and the temperature compensation electrode 160 are placed side by side in the leftward-rightward direction with respect to the longitudinal direction on the same place. In the PM sensor 200 shown in FIG. 8, the PM detection electrode 150 and the temperature compensation electrode 160 which have the same width are placed side by side in the inward-outward direction with respect to the longitudinal direction of the PM sensor on the same plane. Here, the sensing electrode of the PM detection electrode 150 is placed further outward with respect to the longitudinal direction of the PM sensor in comparison with the sensing electrode of the temperature compensation electrode 160. The sensing electrode of the temperature compensation electrode 160 is placed inward.

[0090] Similarly to the example shown in FIG. 7, in the second example shown in FIG. 8 the sensing electrodes of the PM detection electrode 150 and the temperature compensation electrode 160 are supported by the second insulating layer 120 via the semiconducting layer. That is, the semiconducting layer is provided for coating between the second insulating layer and the sensing electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160. In contrast, the external electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 are supported by the second insulating layer 120.

[0091] The heater electrode 170 is placed between the second insulating layer 120 and the third insulating layer 130 and is placed at a point where the PM detection electrode 150 is able to be heated.

[0092] In the arrangement structure shown in FIG. 7, the positions of the respective sensing electrodes of the PM detection electrode 150 and the temperature compensation electrode 160 are advantageous for extension in the longitudinal direction. In the arrangement structure shown in FIG. 8, the positions of the respective sensing electrodes of the PM detection electrode 150 and the temperature compensation electrode 160 are advantageous for extension in the traverse direction. Two types of multiple sensors may be provided in such a manner as to make the sensing electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 advantageous for extension in the longitudinal direction or the traverse direction.

[0093] The second insulating layer 120 is placed below the PM detection electrode 150 and the temperature compensation electrode 160.

[0094] The sensing electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 are not in direct contact with the second insulating layer 120 for support. The coating layer of a semiconducting material, namely, the semiconducting layer 180 is placed between the sensing electrode and the second insulating layer 120. Since the thickness of the semiconducting layer is negligible, the external electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 are in direct contact with the second insulating layer 120 for support.

[0095] The entire temperature compensation electrode 160 is not directly exposed to exhaust gas by the first insulating layer 110, and the sensing electrode of the PM detection electrode 150 needs to be directly exposed to exhaust gas, so the first insulating layer 110 is not placed on the sensing electrode of the PM detection electrode 150. Therefore, the first insulating layer 110 is shorter than the second insulating layer 120 by the length of the sensing electrode of the PM detection electrode 150 which is exposed to exhaust gas.

[0096] Similarly to the temperature compensation electrode 160, the external electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 are covered with the first insulating layer 110. That is, except for the sensing electrode of the PM detection electrode 150, the external electrodes of the PM detection electrode 150 and of the temperature compensation electrode 160 and the temperature compensation electrode 160 are covered with the first insulating layer 110.

[0097] In the meantime, when the PM detection electrode 150 and the temperature compensation electrode 160 are placed on the same plane, two electric circuits are close to each other. The fact that the PM detection electrode 150 is close to the temperature compensation electrode 160 on the same plane may be disadvantageous in an exhaust gas environment where particulate matter which is a conductive material is present.

[0098] Thus, FIG. 9 shows a structure in which the electric circuits are placed within different insulating layers.

[0099] FIG. 9 shows a particulate matter (PM) sensor 300 that is provided on an exhaust line through which exhaust gas from a vehicle passes, the PM sensor being provided with an electrode formed to detect PM. The PM sensor 400 includes: a first insulating layer 110; a PM detection electrode 150 placed under the first insulating layer 110; a second insulating layer 120 placed under the PM detection electrode 150; a temperature compensation electrode 160 placed under the second insulating layer 120; a third insulating layer 130 placed under the temperature compensation electrode 160; a heater electrode 170 placed under the third insulating layer 130; and a fourth insulating layer 140 placed under the heater electrode 170.

[0100] That is, the structure has the first insulating layer 110, the PM detection electrode 150, the second insulating layer 120, the temperature compensation electrode 160, the third insulating layer 130, the heater electrode 170, and the fourth insulating layer 140 in that order.

[0101] The sensing electrode of the PM detection electrode 150 is not covered with the first insulating layer thereon to be directly exposed to exhaust gas, and only the external electrode of the PM detection electrode 150 is covered with the first insulating layer 110 for support. Therefore, the first insulating layer 110 is shorter than the second insulating layer 120.

[0102] In FIG. 9, a first and second semiconducting layer 180-1 and 180-2 may be placed between the sensing electrode of the PM detection electrode 150 and the second insulating layer 120, and between the sensing electrode of the temperature compensation electrode 160 and the third insulating layer 130 respectively.

[0103] This is intended to more accurately measure a temperature rise that is caused by the heater electrode 170 because the temperature compensation electrode 160 is close to the heater electrode 170.

[0104] The temperature of the sensing electrode of the PM detection electrode 150 needs to be increased to 700 C. or more so that PM deposited in the sensing electrode of the PM detection electrode oxidizes. In practice, the heater needs to be heated to a higher temperature. Here, the risk of excessive temperature rise that possibly occurs may be blocked by the third insulating layer 130 and the second semiconducting layer 180-2.

[0105] FIG. 10 shows a particulate matter (PM) sensor 400 that is provided on an exhaust line through which exhaust gas from a vehicle passes, the PM sensor being provided with an electrode formed to detect PM. The PM sensor 300 includes: a first insulating layer 110; an external electrode of a PM detection electrode 150 placed under the first insulating layer 110; a second insulating layer 120 placed under the PM detection electrode 150; a heater electrode 170 placed under the second insulating layer 120; a third insulating layer 130 placed under the heater electrode 170; a temperature compensation electrode 160 placed under the third insulating layer 130; and a fourth insulating layer 140 placed under the temperature compensation electrode 160.

[0106] That is, the structure has the first insulating layer 110, the PM detection electrode 150, the second insulating layer 120, the heater electrode 170, the third insulating layer 130, the temperature compensation electrode 160, and the fourth insulating layer 140 in that order.

[0107] The second insulating layer 120 is placed under the PM detection electrode 150.

[0108] The sensing electrode of the PM detection electrode 150 may be supported via the semiconducting layer 180 without being in direct contact with the second insulating layer 120.

[0109] The temperature compensation electrode 160 is not directly exposed to exhaust gas, but the sensing electrode of the PM detection electrode 150 needs to be directly exposed to exhaust gas, so there is no first insulating layer 110 thereon.

[0110] Except the sensing electrode of the PM detection electrode 150, only the external electrode of the PM detection electrode 150 is covered with the first insulating layer 110 for support. Thus, unlike the temperature compensation electrode 160, the insulating layer is not placed on the sensing electrode of the PM detection electrode 150 and the sensing electrode is formed to be directly exposed to exhaust gas.

[0111] In FIG. 10, the semiconducting layer 180 may be placed between the sensing electrode of the PM detection electrode 150 and the second insulating layer 120, and between the third insulating layer 130 and the temperature compensation electrode 160.

[0112] Compared with the case where the PM detection electrode 150 and the temperature compensation electrode 160 are placed side by side on the same place, the number of insulating layers is increased, so electrical stability is obtained.

[0113] It is desired that the first insulating layer 110 and the fourth insulating layer 140 are provided at symmetrical points with respect to exhaust gas flow.

[0114] It will be understood by those skilled in the art that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, the above-described embodiments are the most preferred embodiments selected among various embodiments in order to help those skilled in the art to understand the present invention, and the technical idea of the present invention is not limited to the above-described embodiments. It is noted that various modifications, additions, and substitutions are possible and, equivalents thereof are also possible, without departing from the technical idea of the present invention. The scope of the present invention is characterized by the appended claims rather than the detailed description described above, and it should be construed that all alterations or modifications derived from the meaning and scope of the appended claims and the equivalents thereof fall within the scope of the present invention. It is also to be understood that all terms or words used in the specification and claims are defined on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Thus, the terms or words should not be interpreted as being limited merely to typical meanings or dictionary definitions. Further, the order of described configurations in the above-described process is not necessary to be performed in a time series, and even though the performance order of configurations and steps is changed as long as the gist of the present invention is satisfied, these processes are included in the scope of the present invention.