JP2011080780A - Particulate detection element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particulate detection element simply constituted so as to detect PM contained in gas to be measured, having no insensitive period and enhanced in reliability. <P>SOLUTION: The particulate detection element 10 is equipped with: a detection part 100 exposed to the gas to be measured and constituted by providing a pair of detection electrodes 11 and 12, which are opposed to each other at a predetermined interval, on the surface of an electric insulating heat-resistant substrate 13; and a detection means 21 for detecting electric resistor R<SB>X</SB>changed corresponding to the amount of the conductive fine particles deposited between the detection electrodes 11 and 12 of the detection part 100, and detects PM in the gas to be measured. A resistor 20 having a predetermined resistance value R<SB>FIX</SB>is provided in parallel to the electric resistor R<SB>X</SB>formed on the detection part 100 as a resistor for eliminating the insensitive period. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a particulate detection element that is used in an exhaust system of an internal combustion engine for automobiles and is suitable for detecting conductive fine particles contained in a gas to be measured.

In recent years, diesel engines and gasoline lean burn have been combined with common rail fuel injection systems, supercharger systems, oxidation catalysts, diesel particulate filters (DPFs), selective catalytic reduction (SCR) systems, exhaust gas recirculation (EGR) systems, etc. Reduction of environmentally hazardous substances such as nitrogen oxides (NOx), particulate matter (PM), unburned hydrocarbons (HC), etc., contained in combustion exhaust gas from engines and the like.
The DPF used in such a system generally has a honeycomb structure made of porous ceramics having excellent heat resistance and countless pores, and PM is contained in the pores existing in the porous partition walls. When trapped, PM accumulates, clogs the pores and the pressure loss increases, it is heated in the DPF by a burner or a heating element, or by a post injection that injects a small amount of fuel after the combustion explosion of the engine. The DPF is heated by introducing high-temperature combustion exhaust, and the PM collected in the DPF is burned and removed to be regenerated.
In order to further improve the combustion efficiency of the internal combustion engine, such a DPF regeneration timing judgment, on-board diagnosis (OBD) for detecting deterioration, breakage, etc. of the DPF, feedback of the internal combustion engine In control and the like, there is a need for detection means that can continuously detect PM contained in combustion exhaust gas with high accuracy.

  As a means for detecting PM in combustion exhaust gas, Patent Document 1 discloses that a pair of electrodes is formed on the surface of a substrate having heat resistance and electrical insulation, and a gap between the electrodes is used as a detection unit. A heating element is formed inside, and the conductive portion excluding the electrode, the detection portion, and the terminal portion forming the detection portion on the substrate is covered with a protective layer made of an airtight and electrically insulating material, and the detection portion, the protective layer, A smoke density sensor is disclosed in which the heat generation density of a heating element in the vicinity of the boundary is made higher than the heat generation density of the detection unit, and the temperature of the detection unit is heated to 400 ° C. or more and 600 ° C. or less. .

  However, in the conventional smoke concentration sensor as disclosed in Patent Document 1, the electrical resistance between the pair of electrodes that changes due to the deposition of conductive smoke is detected by an electronic circuit, but the smoke is not deposited. In this case, since the pair of electrodes is in an insulated state, the electric resistance between the pair of electrodes gradually decreases due to the deposition of smoke, and there is a dead period until the electric resistance can be detected by the electronic circuit.

  As a method for solving the problem of such a dead period, Patent Document 2 discloses, as a sensor element for a gas sensor and a method for operating the sensor element, at least two electrodes (1) and (2) exposed to an air-fuel mixture and these A gas sensor for quantifying particles in a mixed gas, particularly a sensor element for carbon, the substrate (3), the electrode (1), (2) is provided with one conductive base (4), and the electrodes (1) and (2) are electrically connected to each other by the conductive base (4). An element and a method for quantifying fine particles in a mixed gas using the sensor element are described.

  However, as disclosed in Patent Document 2, when a conductive base that electrically connects two electrodes to each other is provided, the electrical resistance of the conductive base must be accurately adjusted within a very narrow range. Is difficult. In addition, a migration phenomenon in which the electrode material diffuses into the conductive base due to long-term use may occur, the electrical resistance of the conductive base may change, and the detection accuracy may become unstable. Furthermore, since both the detection resistor and the electrical resistance of the conductive base are affected by the temperature change, it is necessary to correct the temperature of both, so that the reference is not determined and it is difficult to completely correct the temperature.

  Therefore, in view of such circumstances, the present invention is a particulate detection element that detects conductive fine particles (particulates, PM) contained in a gas to be measured with a simple configuration, and has no dead time and reliability. It is an object of the present invention to provide a particulate detecting element having a high level.

  In the first aspect of the invention, the detector is provided with a pair of detection electrodes that are exposed to the gas to be measured and is opposed to each other with a predetermined gap provided on the surface of the electrically insulating heat-resistant substrate, and is deposited between the detection electrodes of the detector A particulate detecting element for detecting conductive fine particles in a gas to be measured, wherein the resistor having a predetermined resistance value is provided in the particulate detection element. It is provided in parallel with the electric resistance formed in the detection part.

  According to the first aspect of the present invention, even when there are few conductive fine particles deposited on the detection portion and the detection resistance is high, the detection is performed by the resistor having a predetermined resistance value interposed in parallel with the detection resistance. The combined resistance of the resistor and the resistor decreases, and even a slight change in the detection resistance can be detected, so the dead period is eliminated. Therefore, the reliability as a sensor is improved. In addition, it is possible to accurately measure not only the presence or absence of conductive particles in the gas to be measured but also their abundance, so the range of applications as a sensor is expanded.

  In the second invention, the resistor provided for eliminating the dead period is placed in a thermally stable environment that is not affected by the temperature change of the gas to be measured.

  According to the present invention, since the resistor provided for eliminating the dead period is not affected by the temperature change of the gas to be measured, only the electric resistance formed by the conductive particles deposited on the detection unit can be temperature-corrected. The correction is easy, and the reliability of the particulate detection element is further improved.

Specifically, as in the third invention, the electrical resistance of the resistor provided for eliminating the dead period is set to 100Ω or more and 1MΩ or less (claim 3). By setting the electric resistance of the resistor provided for eliminating the dead period in such a range, the detection resistance is in the range of several tens MΩ to 1 kΩ depending on the amount of conductive fine particles deposited between the detection electrodes. When changed, the detection current detected by the detection means is raised to a certain value or more, and detection becomes easy, so the dead time is eliminated and a highly reliable particulate detection element can be realized.
When a resistor lower than 100Ω is interposed outside the scope of the present invention, the change in detection resistance is relatively small, the detection accuracy is reduced, and when a resistor higher than 1 MΩ is interposed, The detection current is below the detection limit of the detection means, and the dead time is not eliminated.

  More specifically, as in the fourth invention, the resistor provided for eliminating the dead period is a simple substance or a composite containing at least one of metal, metal oxide, metal compound, carbon, and carbon compound. It can be realized by the body (claim 4).

FIG. 2 is a developed perspective view showing an outline of the particulate detection element according to the first embodiment of the present invention. Sectional drawing which shows the outline | summary of the particulate detection sensor which has a particulate detection element in the 1st Embodiment of this invention. The equivalent circuit diagram which shows the example of the resistance detection means applicable to the particulate detection element in the 1st Embodiment of this invention. The expansion | deployment perspective view which shows the outline | summary of the particulate detection element in the 2nd Embodiment of this invention. The expansion | deployment perspective view which shows the outline | summary of the particulate detection element in the 3rd Embodiment of this invention. The characteristic view which shows the problem of the conventional particulate detection element. The characteristic view which shows the effect of this invention with a comparative example.

The particulate detection element 10 according to the first embodiment of the present invention is, for example, a failure of a diesel particulate filter (DPF) that collects particulate matter (PM) contained in combustion exhaust discharged from a diesel internal combustion engine. In order to perform diagnosis (OBD) and DPF regeneration control, it is used in a particulate detection sensor 1 for detecting PM in combustion exhaust gas, in particular, conductive fine particles.
Features of the particulate detection device 10 of the present invention detects the electrical resistance R _X which varies with the amount of PM deposited between the pair of detection electrodes 11 and 12 facing with a predetermined gap, the measurement gas a detects the PM in, by providing such a parallel with the detection resistor R _X a resistor 20 having a predetermined electrical resistance R _FIX as dead time eliminated resistance, electrical resistor 20 resistor _{R FIX} and the detection resistor _{R X} and the combined resistance _R SUM of _{(= R FIX · R X /} (R FIX + R X)) was low, the detection current flowing through the particulate detection device 10 when detecting the combined resistance _{R SUM} It _raises beyond the detection limit of the detection means for detecting I _SEN to eliminate the dead period.

An outline of the particulate detection element 10 and the particulate detection sensor 1 including the particulate detection element 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.
As shown in FIG. 1, the particulate detection element 10 is an electrically insulating heat-resistant substrate in which an electrically insulating heat-resistant material such as alumina is formed into a flat plate by a known method such as a doctor blade method, a press molding method, CIP, or HIP. 13, a pair of detection electrodes 11, 12 provided on the electrically insulating heat-resistant substrate 13 at a predetermined distance, and lead portions 111, 121 for electrically connecting the detection electrodes 11, 12 and external electrical resistance measuring means. and a terminal portion 112, 122, a main part of the present invention, the predetermined connected between leads 111 and 121 so as to be parallel with the detection resistor R _X formed by PM depositing between the detecting electrode between the resistance value dead time eliminated resistor 20 having R _FIX, by heating the detection portion formed by the detection electrodes 11 and 12 to a predetermined temperature, or to stabilize the detection resistor, to the detection unit A heating element 140 that generates heat by energization for heating and removing the accumulated PM, a pair of heating element lead portions 141a and 141b that connect the heating element 140 and an energization control device (not shown), and a heating element terminal portion 143a. , 143b, an electrically insulating heat-resistant substrate 15, and through-hole electrodes 142a and 142b penetrating the insulating heat-resistant substrate 15 and conducting the heating element lead portions 141a and 141b and the heating element terminal portions 143a and 143b. ing.
In order to secure the electrical insulation of the lead parts 111 and 121 from the PM deposited so as to short-circuit between the lead parts 112 and 121, an electrically insulating heat resistant material is covered so as to cover the surface of the lead parts 121 and 121. An insulating heat-resistant protective layer may be formed by using it.
As the dead time eliminating resistor 20, a resistor composed of a single substance or a complex containing at least one of metal, metal oxide, metal compound, carbon, and carbon compound is used. In the present embodiment, an example using a chip resistor that can be mounted on the surface of the electrically insulating heat-resistant substrate 13 is shown.
The dead time elimination resistor 20 is disposed on the base end side of the electrically insulating heat-resistant substrate 13 at a thermally stable position that is not easily affected by the temperature change of the gas to be measured.

With reference to FIG. 2, the particulate detection sensor 1 having the particulate detection element 10 of the present invention will be described.
The particulate detection sensor 1 is fixed to the substantially cylindrical insulator 40 that inserts and holds the particulate detection element 10 inside, and the flow path wall 60, holds the insulator 40, and includes a detection unit of the particulate detection element 10. A housing 50 that is held at a predetermined position in the measured channel 600, a cover body 30 that is provided on the distal end side of the housing 50 and protects the detection portion of the particulate detection element 10, and a proximal end side of the housing 50. Detection between the detection electrodes 11 and 12 that is connected to the terminal portions 112 and 122 of the particulate detection element 10 via the connection fittings 113 and 123 and changes according to the amount of PM collected and deposited on the detection portion 100 a pair of signal lines 114 and 124 for transmitting electrical resistance R _X to the outside of the electrical resistance detecting means, particulate sensing element 1 The heating element 140 built in 0, the heating element terminal portions 143a and 143b, and the pair of conductive wires 145a and 145b connected via the connection fittings 144a and 144b are fixed on the base end side via the sealing member 70. And a substantially cylindrical casing 80. The cover body 30 is appropriately provided with measurement gas inlet / outlet holes 310 and 311 for introducing / extracting the measurement gas containing PM to / from the detection unit 100.
In the present embodiment, an example in which a pair of electrodes are formed by opposing a plurality of comb-like detection electrodes 11 and 12 extending in a direction orthogonal to the longitudinal axis direction of the particulate detection element 10. Although shown, the shape of the pair of detection electrodes 11 and 12 is not particularly limited in the present invention, and the detection electrodes 11 and 12 are formed in a plurality of comb teeth extending in the longitudinal axis direction of the particulate detection element 10. These electrodes may be opposed to each other with a predetermined gap, or the detection electrodes 11 and 12 may be formed in a substantially spiral shape and may be opposed to each other with a predetermined gap.

Referring to FIG. 3, description will be given of a measurement principle of electrical resistance R _X which varies with PM deposited in the detection unit 100 of the particulate detection device 10 of the present invention.
The detection resistor R _X and dead time eliminated resistor 20 having a predetermined resistance value R _FIX derived from accumulated PM amount between the detection electrodes 11 and 12 to be placed on the measurement gas flow channel 800, leads The upstream side is connected to a voltage source V _DD adjusted to a predetermined detection voltage, and the dead side elimination resistor 20 and the detection resistor are connected to the downstream side. resistance detection means 21 for detecting the combined resistance _{R SUM} and R _X are provided.
The resistance detection unit 21 includes, for example, a shunt resistor 22 having a predetermined resistance value _RS, and a current flowing through the shunt resistor 22 from the potential difference (V _IN −V _REF ) at both ends of the shunt resistor 22 by the differential amplifier 23. That is, the detection current I _SEN flowing through the combined resistor R _SUM can be detected.
Since dead period resistance R _FIX rid resistor 20 is known, the value of PM amount from the detection resistor R _X can be accurately calculated from the detected change in the combined resistance R _SUM by the resistance detection means 21.
The dead time elimination resistor 20 is placed in a thermally stable environment that is not affected by the temperature change of the gas to be measured. Therefore, the temperature does not need to be corrected, but the detection resistor _RX is Since it is affected by the temperature change of the gas to be measured, it is desirable to correct the temperature according to the temperature of the gas to be measured in order to improve the detection accuracy.
Further, in the present invention, the resistance detection means 21 is not limited to this embodiment, the change in the combined resistance R _SUM of the known resistor R _FIX and PM amount from the detection resistor R _X dead time eliminated resistor 20 Any type may be used as long as it can be detected.

Here, with reference to FIG. 4, the problem of the conventional particulate detection element will be described. In the conventional particulate detection element, PM made of conductive carbon or the like contained in the gas to be measured is deposited between a pair of detection electrodes formed on the surface of the electrically insulating heat-resistant substrate with a predetermined gap therebetween. Then, a conduction path is formed between the detection electrodes by PM, and the electric resistance value between the electrodes gradually decreases. Therefore, the amount of PM is calculated by measuring this.
FIG. 4 shows changes in the electrical resistance value between the detection electrodes when the PM amount is increased at a constant speed.
However, as shown in FIG. 4, when PM is not deposited between the detection electrodes, it is in a substantially insulated state, so the electrical resistance between the detection electrodes is several tens of MΩ or more. The electric resistance value gradually decreases, but until the value becomes several MΩ or less, a detection current hardly flows and there is a dead period td in which the electric resistance value cannot be measured.
If this dead period td is long, when the particulate detection element is used for OBD as described above, it may take time to detect an abnormality, and the reliability as a sensor is lacking.

The effect of the present invention will be described with reference to FIG. FIG. 5 is a characteristic diagram showing a change in the detected current I _SEN when the amount of conductive particles in the gas to be measured is increased at a constant rate. As Example 1, the resistance of the dead-period eliminating resistor 20 is shown. shows the change in the detected current I _SEN when the value is set to 1 M.OMEGA, as example 2, illustrates the change in the detected current I _SEN when the resistance value of the dead time eliminated generating resistor 20 was set to 100 [Omega, Comparative example The change of the detection current I _SEN when the dead time elimination resistor 20 is not provided is shown.
As shown in FIG. 5, when the resistance value R _FIX dead time eliminated resistor 20 set at 1MΩ below the range of 100 [Omega, there between the detection resistor R _X to be detected is changed from a few 10MΩ to about 1MΩ However, the detection current I _SEN is shifted to 5 μA or more, which is the detection limit of the detection means 21, so that it can be easily detected, and the dead period td is eliminated.
Further, if the resistance value R _FIX dead time eliminated resistor 20 to lower than 100 [Omega, the detected current I _SEN, detecting the resistance change current change due to the R _X is relatively small, the detection accuracy is rather deteriorated If the resistance value R _FIX of the dead period eliminating resistor 20 is set higher than 1 MΩ, the detection current I _SEN becomes the detection limit or less, and thus the dead period td cannot be eliminated.

With reference to FIG. 6, the particulate detection element 10a in the 2nd Embodiment of this invention is demonstrated. In the above embodiment, the dead time eliminated resistor 20, a configuration of mounting on the electrically insulating heat substrate 13, is connected across between leads 111 and 121, parallel to the detection resistor R _X As shown in FIG. 6, the dead time elimination resistor 20 a may be provided outside the particulate element 10 as shown in FIG. 6. At this time, a resistor with a lead may be used as shown in the figure, or a chip resistor as shown in the above embodiment may be placed on the detection means 21 side.

  With reference to FIG. 7, a particulate detection element 10b according to a third embodiment of the present invention will be described. In the above embodiment, an example in which a separate fixed resistor such as a chip resistor or a lead-attached resistor is used as the dead period eliminating resistor 20, 20a has been shown. However, as shown in FIG. The insensitive period eliminating resistor 20b is formed on the surface of the conductive substrate 13 by screen printing or the like so as to cross between the lead portions 111 and 121, and the surface is covered with the electrically insulating heat-resistant protective layer 200. good.

The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.
For example, in the above-described embodiment, the particulate detection sensor mounted on an internal combustion engine such as an automobile engine has been described as an example. However, the particulate detection sensor of the present invention is not limited to being mounted on a vehicle. It can also be used for particulate detection in large-scale plants such as plants.

DESCRIPTION OF SYMBOLS 1 Particulate detection sensor 10 Particulate detection element 100 Detection part 11,12 Detection electrode 111,121 Lead part 112,122 Terminal part 113,113 Connection metal fitting 114,114 Signal line 13,15 Electrical insulation heat-resistant board 140 Heat generating body 141a , 141b Heating element lead portions 142a, 142b Through-hole electrodes 143a, 143b Heating element terminal portions 144a, 144b Connecting metal fittings 145a, 145b Conductive line td Dead period 20 Dead period eliminating resistor R _FIX Predetermined resistance value (for dead period eliminating) Resistor)
21 resistance detecting means _{R X} detecting resistor 30 cover 310 311 the measurement gas and out hole 40 insulator 50 housing 60 housing 70 sealing member 80 measured gas flow path walls 800 measurement gas channel

JP 59-197847 A German Published Application No. 102006042605

Claims (4)

A pair of detection electrodes facing each other with a predetermined gap provided on the surface of the electrically insulating heat-resistant substrate is used as a detection unit, and the electricity varies depending on the amount of conductive fine particles collected by the detection unit and deposited between the detection electrodes. In a particulate detection element that detects resistance and detects conductive fine particles in a gas to be measured, a detection unit provided with a pair of detection electrodes facing each other with a predetermined gap provided on the surface of the electrically insulating heat-resistant substrate; In the particulate detection element for detecting the conductive fine particles in the gas to be measured, comprising a detecting means for detecting an electric resistance that changes in accordance with the amount of the conductive fine particles deposited between the detection electrodes of the detection unit,
A particulate detection element, wherein a resistor having a predetermined resistance value is provided in parallel to an electric resistance formed in the detection unit.   The particulate detection element according to claim 1, wherein the resistor provided for eliminating the dead period is placed in a thermally stable environment that is not affected by a temperature change of the gas to be measured.   The particulate detection element according to claim 1 or 2, wherein an electric resistance of the resistor provided for eliminating the dead period is 100Ω or more and 1MΩ or less.   4. The resistor according to claim 1, wherein the resistor provided for eliminating the dead period is formed of a single substance or a composite containing at least one of a metal, a metal oxide, a metal compound, carbon, and a carbon compound. Particulate detection element.

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