JP2011220974A - Particulate matter detector and failure detection device for exhaust gas purification filter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particulate matter (PM) sensor allowing particulate matter detection with a single measuring circuit without requiring switching of measuring circuits between electrode regeneration and collection and detection of particulate matters (PM), and a failure detection device for a diesel particulate filter (DPF) using the particulate matter sensor.SOLUTION: The particulate matter (PM) sensor comprises: electrodes; measurement means for measuring a capacitance by applying a measurement voltage between the electrodes; particulate matter detection means for detecting a value correlated to the amount of a particulate matter (PM) based on change in the capacitance; electrode regeneration means for regenerating the electrodes; and regeneration completion determination means determining electrode regeneration completion based on the capacitance. The particulate matter detection means detects the value correlated to the amount of the particulate matter (PM) based on change in the capacitance that occurs when applying a measurement voltage at a detection frequency between the electrodes. The regeneration completion determination means determines the electrode regeneration completion based on the capacitance measured after changing the frequency of the measurement voltage that is applied between the electrodes into a regeneration frequency which is higher than the detection frequency at the time of electrode regeneration.

Description

  The present invention relates to a particulate matter detection device and a failure detection device for an exhaust purification filter using the particulate matter detection device.

  2. Description of the Related Art A technique for reducing the amount of particulate matter discharged by providing an exhaust gas purification filter for collecting particulate matter contained in exhaust gas in an exhaust pipe of an internal combustion engine is widely used. Further, a vehicle provided with an exhaust purification filter is provided with a device for detecting a failure of the exhaust purification filter. This failure detection device includes a particulate matter detection device that detects the concentration of particulate matter contained in exhaust gas downstream of the exhaust purification filter, and based on the output of the particulate matter detection device, detects failure of the exhaust purification filter. Detect.

  As the particulate matter detection device, for example, a particulate matter detection device including an electrode portion made of a porous conductive material has been proposed (see Patent Document 1). This particulate matter detection device measures the change in the electrical resistance value of the electrode due to the particulate matter being naturally collected and adhered, and based on this measurement value, the concentration of particulate matter contained in the exhaust gas Is detected. Since there is a limit to the amount of particulate matter that can be attached to the electrode portion, the particulate matter attached to the electrode portion is burned and removed by a heating means such as a heater after detection.

  For example, an electrostatic dust collection type particulate matter detection device has been proposed (see Patent Document 2). In this electrostatic dust collection type particulate matter detection device, an electrode part composed of a pair of electrode plates is provided in the exhaust pipe, and particulate matter is actively collected by applying a predetermined voltage to the detection electrode. Dust and adhere to the detection electrode. Next, the concentration of the particulate matter in the exhaust gas is detected by measuring the electrical characteristics such as the capacitance of the electrode part to which the particulate matter has adhered. Similar to the particulate matter detection device of Patent Document 1, after detection, particulate matter adhering to the electrode portion is burned and removed by a heating means such as a heater.

By the way, when the particulate matter adhering to the electrode portion is burned and removed, a means for determining whether or not the adhering particulate matter is burned and removed and the regeneration of the electrode portion is completed is required.
As such means, for example, a predetermined time required for burning and removing the adhering particulate matter is obtained by conducting an experiment in advance according to the amount of the adhering particulate matter, and whether or not the predetermined time has passed. Based on this, there is a means for determining whether or not the regeneration of the electrode unit is completed.
Further, as in Patent Document 2, there is a means for determining whether or not the regeneration of the electrode part is completed based on the capacitance of the electrode part.

JP 2006-266961 A JP 2008-139294 A

  However, the means for determining whether or not the regeneration of the electrode portion is completed based on whether or not a predetermined time set in advance has passed requires a low accuracy of determination and a longer regeneration time. As a result, power consumption due to regeneration increases and fuel consumption deteriorates, and the frequency of detection of particulate matter decreases, resulting in a decrease in the number of times the failure of the exhaust purification filter is detected.

  On the other hand, the capacitance of the particulate matter used in Patent Document 2 varies greatly depending on the temperature, and is greatly affected by external factors such as operating conditions and regeneration of the exhaust purification filter. Specifically, the capacitance of the particulate matter increases as the temperature increases. For this reason, particularly during regeneration of the electrode part, the electrode part is heated to 550 ° C. or higher, so that the capacitance of the particulate matter adhering to the electrode part is remarkably increased.

  As described above, when the electrode portion is regenerated, the capacitance of the detected particulate matter is remarkably increased, so that the measurement range of the measurement circuit is set wide. On the other hand, when collecting and detecting particulate matter, high measurement accuracy is required, and detection is performed under conditions where the temperature is relatively low, so the measurement range is set narrow. That is, the measurement range required for the measurement circuit for detecting the electrostatic capacitance is greatly different between the regeneration of the electrode portion and the dust collection / detection of the particulate matter. For this reason, the particulate matter detection device of Patent Document 2 needs to include at least two measurement circuits having different measurement ranges, resulting in an increase in cost.

  The present invention has been made in view of the above, and the object of the present invention is that there is no need to switch the measurement circuit between the regeneration of the electrode part and the dust collection / detection of the particulate matter. An object of the present invention is to provide a particulate matter detection device capable of detecting a substance and an exhaust purification filter failure determination device using the particulate matter detection device.

  In order to achieve the above object, the present invention is directed to electrode portions (for example, electrode plates 130 and 131 to be described later and collectors) to be provided in an exhaust system (for example, an exhaust pipe 4 to be described later) of an internal combustion engine (for example, an engine 1 described later). Dust portion 120), measuring means for applying a measurement voltage to the electrode portion to measure the capacitance of the electrode portion (for example, sensor control unit 17 described later), and capacitance measured by the measuring means Is based on characteristics that change due to the particulate matter adhering to the electrode part, and particulate matter detection means (for example, an ECU 5 and a sensor described later) that detects a value correlated with the amount of particulate matter contained in the exhaust gas. After the detection by the control unit 17) and the particulate matter detection means, the electrode part regeneration means (for example, regenerates the electrode part by burning and removing the particulate matter adhering to the electrode part) , Heater layers 122 and 129 and a sensor control unit 17), which will be described later, and regeneration completion determination means for determining completion of regeneration of the electrode part by the electrode part regeneration means based on the capacitance measured by the measurement means. (For example, an ECU 5, a sensor control unit 17, which will be described later, and a means related to the execution of step S64 in FIG. 11), a particulate matter detection device (for example, a PM sensor 11 and an ECU 5 which will be described later). This particulate matter detection device is a frequency changing means for changing the frequency of the alternating measurement voltage applied by the measuring means (for example, an ECU 5, a sensor control unit 17, which will be described later, and a means for executing step S61 in FIG. 11). The particulate matter detection means includes particles contained in the exhaust gas based on a change in capacitance when a measurement voltage of a detection frequency (for example, a detection frequency fa described later) is applied to the electrode portion. A value having a correlation with the amount of particulate matter is detected, and the regeneration completion judging means determines the measurement voltage applied to the electrode part by the frequency changing means when the electrode part regeneration means performs the regeneration of the electrode part. After changing the frequency to a reproduction frequency higher than the detection frequency (for example, a reproduction frequency fz described later), the capacitance measured by the measurement means Zui it, and judging the completion of the electrode portion of the reproduction by the electrode unit reproducing means.

  In the present invention, at the time of dust collection / detection of particulate matter, a measurement voltage with a detection frequency having a low frequency is applied to the electrode portion to measure the capacitance, and the exhaust gas is discharged based on the change in the measured capacitance. It was set as the structure which detects the value which has a correlation with the quantity of the particulate matter contained. In addition, at the time of regeneration of the electrode part executed after detection, the capacitance is measured by changing to a reproduction frequency higher than the detection frequency, and the completion of regeneration of the electrode part is determined based on the measured capacitance. The configuration.

  Here, when the frequency is f and the impedance is Zc, the capacitance C is represented by 1 / (2πfZc). As shown in FIG. 1, the capacitance C decreases as the frequency f increases. Has characteristics. Therefore, the change in capacitance at each frequency is theoretically as shown in FIG. 2, but in the actual particulate matter, the rising portion of the curve and the convergence position are shifted due to unspecified factors, and FIG. The frequency characteristics as shown are shown. It can be seen from FIG. 3 that the measured value of the capacitance of the particulate matter can be reduced by increasing the frequency.

Further, FIG. 4 shows the temperature characteristics of the capacitance C of the electrode portion during reproduction. As shown in FIG. 4, when the temperature of the electrode portion is increased, the change in the capacitance C is significantly greater when the particulate matter (PM) is attached than when the particulate matter (PM) is not attached. . Specifically, when the particulate matter is not attached to the electrode part, after the temperature of the electrode part reaches approximately 500 ° C., the capacitance C of the electrode part gradually increases. On the other hand, when the particulate matter adheres to the electrode portion, the capacitance C starts to increase rapidly at the temperature T ₂ (400 ° C.), and the temperature T ₁ that is the combustion temperature of the particulate matter. Increases exponentially to (550 ° C.). From FIG. 4, it can be seen that the electrostatic capacity C increases remarkably during regeneration of the electrode part to which the particulate matter has adhered, and a wider measurement range is required than during dust collection and detection.

Therefore, according to the present invention, when the electrode portion where the capacitance is remarkably increased is switched to a measurement voltage having a higher frequency than when collecting and detecting particulate matter, the measured capacitance The value of can be reduced. This makes it possible to measure the capacitance in a wider range by increasing the frequency of the measurement voltage, and complete the regeneration based on the measured capacitance without switching the measurement circuit. Can be determined. Accordingly, the particulate matter can be detected by one measurement circuit without switching the measurement circuit between the regeneration of the electrode portion and the dust collection / detection of the particulate matter, thereby reducing the cost.
Further, for example, the capacitance can be measured with higher accuracy than when the measurement range is expanded with one measurement circuit, and the completion of reproduction can be determined with higher accuracy.

In this case, the frequency changing means includes a first detection frequency (for example, a detection frequency fa described later) and a second detection frequency (for example, a detection frequency described later) higher than the first detection frequency. It is possible to switch to at least two detection frequencies of frequency fb), and the particulate matter detection means (for example, means relating to execution of the processing of FIG. 14 described later) is provided in the electrode section with the first detection frequency. Based on the change in capacitance when applying the measurement voltage, a value correlated with the amount of the particulate matter contained in the exhaust gas is detected, and the particulate matter adheres to the electrode portion to thereby detect the capacitance. Is reached from the first detection frequency to the second detection frequency by the frequency changing means, and then the particles contained in the exhaust gas are exhausted when a predetermined upper limit value (for example, a threshold value C ₃ described later) is reached. The amount of particulate matter It is preferred to continue the detection of certain values of Seki.

In the present invention, at the time of collecting and detecting particulate matter, first, the measurement voltage of the first detection frequency having a low frequency is applied to measure the capacitance, and the exhaust is performed based on the measured capacitance. In this configuration, a value having a correlation with the amount of the particulate matter contained in is detected. In addition, when the electrostatic capacity reaches a predetermined upper limit due to the particulate matter adhering to the electrode portion, the electrostatic capacity is switched to the measurement voltage of the second detection frequency higher than the first detection frequency. And the detection of a value correlated with the amount of particulate matter contained in the exhaust gas based on the measured capacitance was continued.
Thereby, when the capacitance measured by applying the measurement voltage of the first detection frequency having a low frequency reaches a predetermined upper limit value, the second detection higher than the first detection frequency. By switching to the measurement voltage at the operating frequency, the value of the measured capacitance can be reduced, and the capacitance can be measured in a wider range. For this reason, it is possible to continue detecting the change in capacitance and continuously detect a value correlated with the amount of particulate matter contained in the exhaust gas. Accordingly, since a long detection time can be secured, the detection accuracy can be improved by increasing the detection frequency of a value correlated with the amount of particulate matter. In addition, since the detection accuracy can be improved, the number of times the electrode portion is regenerated can be reduced, and the fuel consumption can be improved.
In addition, according to the present invention, since a long detection time can be ensured, measurement close to continuous measurement becomes possible, and it can be used for internal combustion engine control other than the determination of exhaust purification filter failure.

In this case, the predetermined upper limit value (for example, a threshold value C ₃ described later) is an upper limit value at which a significant change appears in the capacitance of the electrode portion due to particulate matter adhering to the electrode portion. Is preferred.

In the present invention, when the capacitance of the electrode portion measured by applying the measurement voltage of the first detection frequency reaches an upper limit value at which a significant change appears, the first detection frequency is higher than the first detection frequency. It was set as the structure switched to the measurement voltage of the frequency for 2 detection.
Thus, after measuring the capacitance to the limit at which the change in capacitance can be detected by applying the measurement voltage of the first detection frequency, the capacitance is switched to the second detection frequency. Measurement can be continued. Therefore, since the detection time can be secured longer, the detection frequency can be increased and the detection accuracy can be further improved.

Further, according to the present invention, a failure detection device (for example, an ECU 5A and a sensor control unit described later) provided in an exhaust system of the internal combustion engine and collects particulate matter contained in the exhaust (for example, a DPF 3 described later). 17). The failure detection device is detected by a particulate matter detection device (for example, a PM sensor 11 and an ECU described later) provided downstream of the exhaust purification filter and the particulate matter detection means. Failure determination means for determining failure of the exhaust purification filter based on a value (for example, PM collection rate X described later) correlated with the amount of particulate matter contained in exhaust gas (for example, ECU 5A, sensor described later) The control unit 17 and means for executing steps S734 to S736 in FIG. 16) and execution determination means for determining whether or not to perform failure determination by the failure determination means (for example, ECU 5A, sensor control unit 17 described later and 16) and a measurement voltage of the first detection frequency (for example, a detection frequency fa described later). Emission amount calculation means for calculating the emission amount of particulate matter from the internal combustion engine during the period when the electrostatic capacity was applied and applied (for example, in execution of ECU 5A described later and steps S725, S728, and S732 in FIG. 16) And the execution determination unit determines that the exhaust purification filter failure determination is to be performed when the emission amount is equal to or greater than a predetermined amount (for example, a threshold value Y ₁ described later), and the emission amount. Is less than the predetermined amount, it is determined that failure determination of the exhaust purification filter is not executed, and the particulate matter detection means (for example, means related to execution of steps S721 to S733 in FIG. 16 described later) A value correlated with the amount of particulate matter contained in the exhaust gas is detected based on a change in capacitance when the measurement voltage of the first detection frequency is applied to the electrode section. Then, when the particulate matter adheres to the electrode part, the electrostatic capacity reaches the predetermined upper limit value (for example, a threshold value C ₅ described later), and the failure determination of the exhaust purification filter is not executed by the execution determination means. Is determined, the frequency changing unit switches the first detection frequency to the second detection frequency (for example, a detection frequency fb described later), and then the particulate matter contained in the exhaust gas. The detection of a value correlated with the quantity is continued.

In this invention, when the particulate matter adheres to the electrode portion, the capacitance measured at the measurement voltage of the first detection frequency reaches the predetermined upper limit value, and the particulate matter is discharged from the internal combustion engine. When the amount is equal to or greater than the predetermined amount, the exhaust purification filter failure determination is executed. Further, when the electrostatic capacity reaches a predetermined upper limit value and the amount of particulate matter discharged from the internal combustion engine is less than a predetermined amount, the first detection frequency is not executed without executing the failure determination of the exhaust purification filter. After switching to a higher second detection frequency, detection of a value correlated with the amount of particulate matter is continued, and a failure determination is executed.
As a result, the failure determination is executed when a predetermined amount or more of particulate matter that can accurately determine the failure of the exhaust purification filter is discharged in a state where the measurement voltage of the first detection frequency is applied. High failure judgment can be made. On the other hand, failure determination is not executed when a predetermined amount of particulate matter that can be determined with high accuracy has not been discharged, thereby avoiding the risk of erroneous determination. In this case, the particulate matter contained in the exhaust gas based on the change in the capacitance measured at the measurement voltage of the second detection frequency by switching to the second detection frequency having a higher frequency. Since the detection of the value having a correlation with the amount is continued and the failure determination based on the value is executed again, the failure determination with high accuracy becomes possible.
By the way, since the measurement voltage with a low frequency is higher as the measurement accuracy, it is desirable to perform the measurement in a state where the measurement voltage of the first detection frequency having a lower frequency is applied. On the other hand, in the failure determination, high determination accuracy can be obtained by measuring the capacitance and detecting a value correlated with the amount of the particulate matter using a wide measurement range. Therefore, when the failure determination is performed by dividing the measurement voltage at the first detection frequency into a plurality of times, the accuracy of the failure determination is greatly reduced. Therefore, according to the present invention, after the measurement is performed up to the limit that can be measured under the measurement voltage of the first detection frequency, if the discharge amount of the particulate matter is small, the failure determination is not performed. Since the measurement and detection are continued after switching to the high second detection frequency and the failure determination is executed, it is possible to determine the failure with high accuracy.

  According to the present invention, there is no need to switch the measurement circuit between the regeneration of the electrode portion and the dust collection / detection of the particulate matter, and the particulate matter detection device capable of detecting the particulate matter with one measurement circuit. And the failure determination apparatus of the exhaust gas purification filter using the same can be provided.

It is a figure which shows the relationship between a frequency and an electrostatic capacitance. It is a figure which shows the electrostatic capacitance change of each frequency. It is a figure which shows the frequency characteristic of the electrostatic capacitance of a particulate matter. It is a figure which shows the temperature characteristic of the electrostatic capacitance of the electrode part at the time of reproduction | regeneration. It is a figure showing composition of an engine exhaust gas purification device to which a PM sensor concerning a 1st embodiment of the present invention is applied. It is a figure which shows schematic structure of PM sensor which concerns on the said embodiment. It is a perspective view of the sensor element which concerns on the said embodiment. It is a disassembled perspective view of the sensor element which concerns on the said embodiment. It is the figure which showed typically a mode when PM adheres and accumulates in the whole surface in the dust collection part of the sensor element which concerns on the said embodiment. It is a flowchart which shows the control procedure of PM sensor by ECU which concerns on the said embodiment. It is a flowchart which shows the procedure of the electrode part reproduction | regeneration process of PM sensor which concerns on the said embodiment. It is a figure which shows the frequency characteristic of the electrostatic capacitance of the electrode part at the time of reproduction | regeneration. It is a figure which shows the electrostatic capacitance change of the electrode part at the time of reproduction | regeneration. It is a flowchart which shows the procedure of PM detection processing of PM sensor which concerns on the said embodiment. It is a figure which shows the change of the electrostatic capacitance when frequency switching is performed. It is a flowchart which shows the procedure of PM detection processing of PM sensor which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between PM total discharge amount and an electrostatic capacitance. It is a figure which shows the relationship between PM collection rate and PM emission value.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description after the second embodiment, the same reference numerals are given to the same components as those in the first embodiment, and the description thereof is omitted.

<First Embodiment>
FIG. 5 is a schematic diagram showing a configuration of an exhaust emission control device for an internal combustion engine to which the particulate matter detection device according to the present embodiment is applied.
An internal combustion engine (hereinafter simply referred to as “engine”) 1 is a diesel engine that directly injects fuel into each cylinder, and each cylinder is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as “ECU (Electronic Control Unit)”) 5, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 5. .

  In the exhaust pipe 4 through which the exhaust of the engine 1 circulates, an exhaust purification filter (hereinafter referred to as “PM (Particulate Matter)”) that collects particulate matter mainly composed of carbon contained in the exhaust and purifies the exhaust. Hereinafter, a “DPF (Diesel Particulate Filter)”) 3 and a particulate matter detection device (hereinafter referred to as “PM sensor”) 11 for detecting PM contained in the exhaust gas are provided in this order from the upstream side. Yes.

  The DPF 3 includes a porous filter wall, and when the exhaust gas passes through the fine holes in the filter wall, PM contained in the exhaust gas is deposited on the surface of the filter wall and the fine holes in the filter wall. Collect this.

FIG. 6 is a diagram showing a schematic configuration of the PM sensor 11.
The PM sensor 11 includes a sensor element 12 provided on the downstream side of the DPF 3 in the exhaust pipe 4 and a sensor control unit 17 that is connected to the ECU 5 and controls the sensor element 12. The PM sensor 11 measures the electrostatic capacitance of the sensor element 12 to which PM contained in the exhaust gas flowing through the exhaust pipe 4 adheres as shown below, and flows through the exhaust pipe 4 based on the measured value. The PM in the exhaust is detected.

  The sensor control unit 17 includes a dust collection DC power source 13, an impedance measuring device 14, and a temperature control device 15 that controls the temperature of the sensor element 12, more specifically, the temperature of the electrode unit described later. .

FIG. 7 is a perspective view of the sensor element 12.
As shown in FIG. 7, the sensor element 12 has a vent hole through which exhaust gas containing PM passes, and the dust collecting portion 120 is formed by the vent hole. The PM contained in the exhaust is deposited on the inner wall of the dust collection unit 120.

FIG. 8 is an exploded perspective view of the sensor element 12.
As shown in FIG. 8, the sensor element 12 is configured by combining a pair of electrode plates 130 and 131 with plate-like spacers 125 </ b> A and 125 </ b> B interposed therebetween and sandwiching them between the heater layers 122 and 129 and the alumina plate 121. Is done. Thereby, the dust collecting part 120 surrounded by the electrode plates 130 and 131 and the spacers 125A and 125B is formed.

The electrode plate 130 is formed by laminating a dielectric layer 124 and a dust collecting electrode layer 123. The electrode plate 131 is formed by laminating a dielectric layer 126, a measurement electrode layer 127, and a dust collection electrode layer 128.
In addition, the electrode part of this embodiment is comprised by these electrode plates 130 and 131 and the above-mentioned dust collection part 120. FIG.

The measurement electrode layer 127 includes a pair of comb-shaped measurement electrodes 127A and 127B. Specifically, the measurement electrodes 127A and 127B include a pair of comb teeth formed at a position corresponding to the dust collection section 120 on one end of the measurement electrode layer 127, and the comb teeth extending from the comb teeth to the other end. And a pair of extending comb bodies. More specifically, the measurement electrodes 127A and 127B are arranged to face each other so that the comb tooth portion of one comb-shaped measurement electrode 127A and the comb tooth portion of the other comb-shaped measurement electrode 127B are sandwiched with each other.
The pair of comb main body portions is electrically connected to the impedance measuring instrument 14.

Here, the PM detection mechanism of the present embodiment in which the measurement electrode layer 127 includes the comb-shaped measurement electrodes 127A and 127B will be described.
FIG. 9 is a diagram schematically showing a state in which PM adheres and accumulates on the entire surface in the dust collecting portion 120 of the sensor element 12 of the present embodiment. As shown in FIG. 9, PM collected in the dust collection unit 120 is deposited on the comb teeth of the comb-shaped measurement electrodes 127A and 127B via a dielectric layer. At this time, the leakage electric field between the adjacent measurement electrodes 127A and 127B is affected by the deposited PM, and the capacitance between the measurement electrodes 127A and 127B changes. Since this change in capacitance has a correlation with the amount of adhesion of PM, PM contained in exhaust gas can be detected by measuring this change in capacitance. In the following description, the capacitance of the sensor element 12 means the capacitance of the dust collection unit 120 having a correlation with the amount of PM attached to the sensor element 12.

The dust collection electrode layers 123 and 128 include dust collection electrodes 123A and 128A made of a tungsten conductor layer. The dust collecting electrodes 123A and 128A are formed in a substantially square shape at a position corresponding to the dust collecting portion 120 on one end side of the dust collecting electrode layers 123 and 128, and the other end side of the alumina substrate from the conductor portion. A conductive wire portion extending linearly over the wire.
Further, the conducting wire portions of the dust collecting electrodes 123A and 128A are electrically connected to the dust collecting DC power source 13.
Note that the length of one side of the conductor portions of the dust collecting electrodes 123A and 128A is about 10 mm.

The heater layers 122 and 129 include heater wires 122A and 129A, and these heater wires 122A and 129A are electrically connected to the temperature control device 15 and the impedance measuring instrument 14.
The alumina plate 121 is a substantially rectangular alumina substrate and has a thickness of about 1 mm.

  The dust collection DC power supply 13 is electrically connected to the conductive wire portions of the dust collection electrodes 123A and 128A provided in the dust collection electrode layers 123 and 128. The dust collection DC power supply 13 operates based on a control signal transmitted from the ECU 5, and applies a predetermined dust collection voltage higher than a measurement voltage described later between the dust collection electrode layers 123 and 128. In the state where PM is not attached to the electrode part, a significant change in capacitance cannot be detected and measurement is impossible. However, PM is attached to some extent by applying a dust collection voltage to promote PM attachment. Thus, a state in which a significant change in capacitance can be detected can be quickly formed.

  The impedance measuring instrument 14 is electrically connected to a pair of comb main body portions of the measurement electrode layer 127. The impedance measuring device 14 operates based on the control signal transmitted from the ECU 5, detects the capacitance of the sensor element 12 under a predetermined measurement voltage and measurement cycle, and is approximately proportional to the detected capacitance. The detected signal is output to the ECU 5.

The temperature control device 15 is electrically connected to the heater wires 122A and 129A of the heater layers 122 and 129 provided in contact with the electrode plates 130 and 131, and a heater that supplies electric power to the heater layers 122 and 129. A DC power supply (not shown) is included.
The heater DC power supply operates based on a control signal transmitted from the ECU 5 and supplies a predetermined current to the heater layers 122 and 129. The heater layers 122 and 129 generate heat when current is supplied from the heater power source, and heat the electrode plates 130 and 131. Thereby, each electrode plate 130 and 131 is heated and PM adhering to the dust collection part 120 is burned and removed.
Note that the temperature of the electrode portion is calculated based on the resistance value of the heater wiring detected by the temperature control device 15.

The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter “ CPU ”). In addition, the ECU 5 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, and an output circuit that outputs control signals to the sensor control unit 17 and the fuel injection valve of the engine 1.
With the hardware configuration described above, the ECU 5 includes modules of a particulate matter detection unit, a regeneration completion determination unit, and a frequency change unit for executing the following PM sensor control process.

Next, control of the PM sensor by the ECU will be described with reference to FIGS.
FIG. 10 is a flowchart showing a control procedure of the PM sensor by the ECU. This PM sensor control process is repeatedly executed by the ECU at a predetermined cycle.

In step S1, when the frequency f of the measurement voltage applied to the electrode section is not set to the detection frequency fa that allows the high sensitivity measurement with a low frequency, switching to fa is executed. Thereafter, the process proceeds to step S2.
The detection frequency fa is set to a frequency lower than a reproduction frequency fz described later. For example, the detection frequency fa is set so as to satisfy the relational expression of fa = fz × 10 ⁻² (Hz) with respect to the reproduction frequency fz.

  In step S2, measurement of the capacitance of the electrode unit is started. Specifically, the measurement voltage of the detection frequency fa switched and set in step S1 is applied to the electrode portion, and the measurement of the capacitance is started. Thereafter, the process proceeds to step S3.

In step S3, it is determined whether or not the temperature T of the electrode portion is 100 ° C. or higher. If this determination is YES, it is determined that the condensed water generated at the start of the engine and attached to the electrode portion is in a state of volatilization, and the process proceeds to step S4. On the other hand, in the case of NO, this determination is performed again.
The temperature T of the electrode part is calculated based on the resistance value of the heater wiring detected by the temperature control device. More specifically, the temperature T of the electrode part is calculated by the ECU 5 based on the resistance values of the heater wires 122A and 129A detected by the temperature control device.

In step S4, the electrostatic capacitance C of the measured electrode portion, it is determined whether the predetermined threshold value C ₁ below. If this determination is YES, it is determined that the condensed water adhering to the electrode portion has been completely volatilized and removed, and the process proceeds to step S5. On the other hand, when this determination is NO, it is determined that the condensed water is still attached to the electrode portion, and this determination is executed again.
Note that the predetermined threshold C ₁ is equal to or lower than the temperature T ₂ shown in FIG. 4 (a temperature at which the change in the temperature characteristic of PM increases and the capacitance starts to increase rapidly, specifically 400 ° C.). It is set to the capacitance of the electrode part to which PM at a predetermined temperature is attached. Since liquid such as condensed water has high conductivity, its capacitance is significantly larger than that of PM. Therefore, it can be determined that condensed water has been completely removed if it is C ₁ or less.

In step S5, it is determined whether or not the electrode portion is regenerated. Specifically, it is determined the capacitance C of the measured electrode portion whether exceeds a predetermined threshold value C _0. If this determination is YES, it is determined that the electrode part regeneration process is necessary, and the process proceeds to the electrode part regeneration process in step S6. On the other hand, in the case of NO, it is determined that the regeneration process of the electrode part is unnecessary, and the process proceeds to the PM detection process in step S7.
The predetermined threshold value _C0 is set by conducting an experiment in advance. For example, as shown in FIG. 13 to be described later, the capacitance is set to the electrode portion where PM is not attached.

  In step S6, an electrode portion regeneration process is executed. Thereafter, the process proceeds to the PM detection process in step S7. By this step, PM adhering to the electrode portion is burned and removed. The details of the regeneration processing of this electrode part will be described later.

  In step S7, PM detection processing is executed. Thereafter, the PM sensor control process is terminated. By this step, the PM concentration in the exhaust gas and the collection rate are calculated. Details of this PM detection processing will be described later.

Next, the procedure of the electrode sensor regeneration process of the PM sensor will be described.
FIG. 11 is a flowchart showing the procedure of the electrode sensor regeneration process of the PM sensor.

In step S61, a process of switching the detection frequency fa of the measurement voltage applied to the electrode portion to the reproduction frequency fz is executed. Thereafter, the process proceeds to step S62.
The reproduction frequency fz is set to a frequency higher than the above-described detection frequency fa. For example, the reproduction frequency fz has a relational expression of fz = fa × 10 ² (Hz) with respect to the detection frequency fa. Set to meet.

Here, the detection frequency fa and the reproduction frequency fz will be described with reference to FIG.
FIG. 12 is a diagram showing the frequency characteristics of the capacitance of the electrode section during reproduction. As shown in FIG. 12, first, during dust collection during the detection process, PM is positively attached to the electrode portion by applying a dust collection voltage having a detection frequency fa to the electrode portion. The electric capacity C shows a sudden rise. Thereafter, when a measurement voltage having a detection frequency fa is applied to the electrode part, the capacitance C gradually increases and then becomes saturated as PM naturally adheres to the electrode part.
During the regeneration process, since the temperature T of the electrode part exceeds the temperature T ₂ (400 ° C.) at which the temperature characteristic change of PM begins to increase, the capacitance C increases exponentially. Then, when the temperature T of the electrode portion reaches the PM combustion temperature T _1, since the PM is burned off, the capacitance C decreases rapidly.

Thus, in the case of the detection frequency fa lower than the reproduction frequency fz, the measured capacitance value is greatly different between the detection process and the reproduction process. Therefore, in order to maintain the measurement sensitivity during the detection process, it is necessary to use the measurement circuit of the measurement range 1 during the detection process and switch to the measurement circuit of the wider measurement range 2 during the reproduction process. In contrast, in this embodiment, during the reproduction process, for example, when the temperature T of the electrode portion reaches T _2, performs switching from the detection frequency fa to reproduction frequency fz, thereby, at the time of reproduction The value of the capacitance C of the electrode part is reduced, so that it is not necessary to switch the measurement circuit during the regeneration process. Accordingly, the reproduction frequency fz is set so that the value of the measured capacitance C is within the measurement range 1, that is, the measurement range equivalent to the measurement range at the detection frequency fa. Is done.

Returning to FIG. 11, in step S62, the heater is turned on to raise the temperature of the electrode portion of the PM sensor. Thereafter, the process proceeds to step S63.
Specifically, the temperature of the electrode portion is raised to the PM combustion temperature T ₁ (550 ° C.) shown in FIG. 4 by the temperature control device.

In step S63, it determines the temperature T of the electrode portion, whether it has reached the combustion temperature T ₁ of the PM. If this determination is YES, the process proceeds to step S64, and if this determination is NO, this determination is executed again.
The temperature T of the electrode part is calculated based on the resistance value of the heater wiring detected by the temperature control device.

In step S64, the electrostatic capacitance C of the electrode portion is equal to or the predetermined threshold value C ₂ or less. If this determination is YES, it is determined that the regeneration of the electrode portion has been completed, and the routine goes to Step S65. On the other hand, in the case of NO, this determination is performed again.

Here, the predetermined threshold value C _2, will be described with reference to FIG. 13.
FIG. 13 is a diagram illustrating a change in capacitance of the electrode unit during reproduction. As shown in FIG. 13, when PM does not adhere to the electrode part, the electrostatic capacity increases as the temperature increases from the initial state of the electrostatic capacity C ₀ due to the temperature characteristics of the electrode part itself. Then, after the temperature T of the electrode portion reaches the PM combustion temperature T _1, the capacitance decreases slowly, converge at predetermined capacitance. The overshoot at the rising portion of the capacitance is considered to be caused by overshoot of the heater control, a minute amount of PM that cannot be detected, a temperature difference generated between the measurement electrode for capacitance measurement and the heater, and the like.
On the other hand, when PM adheres to the electrode portion, the capacitance increases exponentially with the temperature rise from the initial state of the capacitance C ₁ due to the temperature characteristics of the electrode portion and PM. . When the temperature T of the electrode portion reaches the PM combustion temperature T _1, since the PM is burned off, the capacitance abruptly decreases, convergence of the same capacitance and if PM was not deposited To do. The convergence value at this time is set to C _2, it is used as a criterion for the completion of the regeneration of the electrode unit.

  Returning to FIG. 11, in step S <b> 65, the heater is turned off, and the electrode portion regeneration process ends.

Next, the procedure of PM detection processing of the PM sensor will be described.
FIG. 14 is a flowchart illustrating a procedure of PM detection processing of the PM sensor.

  In step S701, when the frequency f of the measurement voltage applied to the electrode unit is not set to the detection frequency fa that allows low-frequency and high-sensitivity measurement, switching to fa is executed. Thereafter, the process proceeds to step S702.

In step S702, switching to the PM concentration map corresponding to the change in capacitance at the detection frequency fa is executed. Thereafter, the process proceeds to step S703.
Here, the concentration of PM contained in the exhaust gas is calculated by referring to a PM concentration map that is prepared in advance and stored in the ECU according to the capacitance change. As described above, since the change in capacitance varies depending on the frequency of the measurement voltage, the change in capacitance at the detection frequency fa corresponds to the change in the detection frequency fa executed in step S701. The PM concentration map is switched.

In step S703, PM dust collection is started. Thereafter, the process proceeds to step S704.
Specifically, a dust collection voltage with a detection frequency fa is applied to the electrode portion to positively collect PM contained in the exhaust gas. Dust collection starts at a predetermined timing, for example, when the vehicle speed becomes zero.

In step S704, the electrostatic capacitance C of the electrode portion is equal to or a predetermined threshold value C ₄ or higher. If this determination is YES, a significant change appears in the measured capacitance, and it is determined that PM has been collected to the extent that the PM concentration can be calculated based on the change, and the process moves to step S705. On the other hand, in the case of NO, this determination is performed again.
Predetermined threshold value C _4, by performing the experiment in advance, to the extent that appears significant change in the measured capacitance, is set to the electrostatic capacity when PM is deposited on the electrode unit.

In step S705, PM dust collection is stopped. Thereafter, the process proceeds to step S706.
Specifically, the application of the dust collection voltage of the detection frequency fa to the electrode unit is stopped, and the PM collection is stopped.

At step S706, the electrostatic capacitance C of the electrode portion is equal to or less than the predetermined threshold value C _3. If this determination is YES, it is determined that the PM sensor can detect a change in capacitance, and the process proceeds to step S707. On the other hand, in the case of NO, the PM sensor determines that the change in capacitance cannot be detected, and the process proceeds to step S708.
Predetermined threshold value C _3, by performing the experiment in advance, is set to the upper limit value appears significant change in electrostatic capacitance.

In step S707, the PM concentration in the exhaust gas is calculated. After the calculation, the process returns to step S706.
Specifically, the PM concentration is calculated by referring to a PM concentration map corresponding to a change in capacitance at the detection frequency fa.

  In step S708, it is determined whether or not the currently set measurement voltage detection frequency f has reached the reproduction frequency fz. If this determination is YES, when switching to a higher frequency is performed, the measurement range of the measurement circuit will be exceeded, so the PM detection processing is terminated without switching the frequency. On the other hand, if NO, the process moves to step S709.

  In step S709, switching to a higher detection frequency is executed. Thereafter, the process proceeds to step S710.

  In step S710, switching to the PM concentration map corresponding to the change in capacitance at the detection frequency after switching is executed. Thereafter, the process returns to step S706.

Here, switching of the detection frequency will be described with reference to FIG.
FIG. 15 is a diagram illustrating changes in capacitance when frequency switching is performed. As shown in FIG. 15, first, after applying a dust collection voltage with a low detection frequency fa to actively collect PM, and then applying a measurement voltage with the detection frequency fa, the electrode is gradually collected over time. As the PM naturally adheres to the part, the capacitance C increases. Then, when reaching the PM concentration capacitance C is set in advance in the detectable limit C _3, to perform switching to a higher frequency fb. As described above, while the capacitance decreases as the frequency increases, since the detectable limit is constant at C _3, as shown in Figure 15, the capacitance by switching of the frequency Measurement can be continued. Continued measurement at frequency fb, when the capacitance reaches a C ₃ again executes the switching to a higher frequency fc. Such frequency switching processing is repeatedly executed until the frequency f reaches the reproduction frequency fz.
As the detection frequency to be switched, for example, in addition to the detection frequency obtained by adding a predetermined value α (> 0) to the detection frequency before switching, the detection frequency before switching is multiplied by the predetermined value α. The frequency for detection obtained by doing this is mentioned.

  Note that the PM concentration calculated by the PM detection process of the present embodiment is used, for example, for DPF failure detection. Further, in the PM detection processing of the present embodiment, the capacitance can be continuously measured by switching the detection frequency, and is used, for example, for combustion control of an internal combustion engine, correction of PM deposition calculation, and the like.

According to this embodiment, the following effects are produced.
In the present embodiment, at the time of PM dust collection / detection, a measurement voltage with a low detection frequency fa is applied to the electrode portion to measure the capacitance, and the exhaust is based on the measured change in capacitance. It was set as the structure which detects the value which has a correlation with the quantity of contained PM. Further, at the time of regeneration of the electrode portion executed after detection, the capacitance is measured by changing to a reproduction frequency fz higher than the detection frequency fa, and the regeneration of the electrode portion is completed based on the measured capacitance. It was set as the structure judged.
That is, according to the present embodiment, when the electrode portion where the capacitance is remarkably increased is switched to the measurement voltage having a frequency higher than that at the time of PM dust collection / detection, the measured capacitance is reduced. The value can be reduced. This makes it possible to measure the capacitance in a wider range by increasing the frequency of the measurement voltage, and complete the regeneration based on the measured capacitance without switching the measurement circuit. Can be determined. Therefore, PM can be detected by one measurement circuit without switching the measurement circuit between the regeneration of the electrode part and the dust collection / detection of PM, thereby reducing the cost.
Further, for example, the capacitance can be measured with higher accuracy than when the measurement range is expanded with one measurement circuit, and the completion of reproduction can be determined with higher accuracy.

Further, in the present embodiment, at the time of PM dust collection / detection, first, a measurement voltage of a low frequency for detection fa is applied to measure the capacitance, and the exhaust is based on the measured capacitance. It was set as the structure which detects the value which has a correlation with the quantity of contained PM. Further, when the capacitance has reached a predetermined upper limit value C ₃ by PM from adhering to the electrode unit, the capacitance was measured by switching the high measured voltage of the detection frequency fb than detection frequency fa, Based on the measured electrostatic capacity, detection of a value correlated with the amount of PM contained in the exhaust gas is continued.
Accordingly, when the capacitance measured by applying a measurement voltage of low frequency detection frequency fa has reached a predetermined upper limit value C _3, the measurement of the high detection frequency fb than detection frequency fa By switching to the voltage, the value of the measured capacitance can be reduced, and the capacitance can be measured in a wider range. For this reason, it is possible to continuously detect the change in the capacitance, and to continuously detect a value correlated with the amount of PM contained in the exhaust gas. Accordingly, since a long detection time can be secured, the detection accuracy can be improved by increasing the detection frequency of a value correlated with the amount of PM. In addition, since the detection accuracy can be improved, the number of times the electrode portion is regenerated can be reduced, and the fuel consumption can be improved.
In addition, according to the present embodiment, since a long detection time can be secured, measurement close to continuous measurement is possible, and it can be used for engine control other than DPF failure determination.

Further, in the present embodiment, when the capacitance of the electrode portion was measured by applying a measured voltage of the detection frequency fa is, has reached the upper limit value C ₃ of significant change appears higher than the detection frequency fa It was set as the structure switched to the measurement voltage of the frequency fb for a detection.
Thus, after measuring the capacitance to the limit at which the change in capacitance can be detected by applying the measurement voltage at the detection frequency fa, switching to the detection frequency fb and continuing the measurement of the capacitance it can. Therefore, since the detection time can be secured longer, the detection frequency can be increased and the detection accuracy can be further improved.

Second Embodiment
The second embodiment differs from the first embodiment in the procedure of PM detection processing of the PM sensor. Specifically, the conditions for switching the detection frequency are different from those in the first embodiment, and the configuration of the ECU is different from that in the first embodiment.
Specifically, in the ECU 5A of the present embodiment (not shown), in addition to the configuration of the ECU 5, each module of a failure determination unit, an execution determination unit, and an emission amount calculation unit for executing the PM sensor control process shown below is Composed.
In addition, a warning light is connected to the ECU 5A of the present embodiment. The warning lamp is for indicating that the DPF is in a failure state, and is provided, for example, on a meter panel of the vehicle. The warning light is turned on based on the control signal transmitted from the ECU 5A, and thereby the driver recognizes that the DPF is in a failed state.

Hereinafter, the procedure of the PM detection process of the PM sensor according to the present embodiment will be described.
FIG. 16 is a flowchart showing a procedure of PM detection processing of the PM sensor according to the present embodiment.

  In step S721, when the frequency f of the measurement voltage applied to the electrode unit is not set to the detection frequency fa that allows the high-sensitivity measurement with a low frequency, switching to fa is executed. Thereafter, the process proceeds to step S722.

In step S722, PM dust collection is started. Thereafter, the process proceeds to step S723.
Specifically, a dust collection voltage with a detection frequency fa is applied to the electrode portion to positively collect PM contained in the exhaust gas. Dust collection starts at a predetermined timing, for example, when the vehicle speed becomes zero.

In step S723, the electrostatic capacitance C of the electrode portion is equal to or a predetermined threshold value C ₄ or higher. If this determination is YES, a significant change appears in the measured capacitance, and it is determined that PM has been collected to the extent that the PM concentration can be calculated based on the change, and the process moves to step S724. On the other hand, in the case of NO, this determination is performed again.
Predetermined threshold value C _4, by performing the experiment in advance, to the extent that appears significant change in the measured capacitance, is set to the electrostatic capacity when PM is deposited on the electrode unit.

In step S724, PM dust collection is stopped. Thereafter, the process proceeds to step S725.
Specifically, the application of the dust collection voltage of the detection frequency fa to the electrode unit is stopped, and the PM collection is stopped.

In step S725, integration of the PM amount Y discharged from the engine and flowing into the DPF is started. The integration of the PM amount Y is started after resetting to “0” when the PM amount Y is not “0”. Thereafter, the process proceeds to step S726.
The PM amount Y is calculated, for example, by searching a predetermined map corresponding to the engine speed and the fuel injection amount. Further, for example, another PM sensor can be provided in the exhaust pipe upstream of the DPF, and the PM amount Y can be calculated based on the output of this PM sensor.

In step S726, the electrostatic capacitance C of the electrode portion is equal to or a predetermined threshold value C ₅ or higher. If this determination is YES, it is determined that the PM sensor has become unable to detect a change in capacitance, and the process proceeds to step S727. On the other hand, in the case of NO, it is determined that the PM sensor is in a state in which a change in capacitance can be detected, measurement is continued, and this determination is performed again.
Predetermined threshold value C _5, by performing the experiment in advance, is set to the upper limit value appears significant change in electrostatic capacitance.

In step S727, it is determined whether or not to perform DPF failure determination. Specifically, it accumulated the PM amount Y is equal to or a predetermined threshold Y ₁ or more. When this determination is YES, it is determined that a larger amount of PM is discharged and flows into the DPF as the PM collection rate can be calculated with sufficient accuracy and the DPF failure determination can be performed with higher accuracy. Move. On the other hand, in the case of NO, it is determined that only a small amount of PM has flowed into the DPF, and it is impossible to determine the DPF failure with high accuracy, and the process proceeds to step S730.

  In step S728, since it is determined that a larger amount of PM is discharged and flows into the DPF as the accuracy of the DPF failure determination is higher in step S727, the accumulation of the PM amount Y flowing into the DPF is ended. Thereafter, the process proceeds to step S729.

In step S729, the PM collection rate X in the DPF is calculated. After the calculation, the process proceeds to step S734.
Specifically, the PM collection rate X (%) is calculated by the following formula (1). In the following formula (1), Y is an accumulated amount of PM terminated by obtaining the integration at step S728 to start the integration in step S725, _{M 1} is the integration period of the PM amount Y (i.e., the detection frequency This is the total amount of PM that has flowed out of the DPF during the period when the capacitance is measured by applying fa. This M ₁ is set based on the relationship between the total amount of PM (total amount of PM flowing out from the DPF) and the capacitance C as shown in FIG. Calculated.
[Equation 1]
X (%) = (1−M ₁ / Y) × 100 (1)

  In step S730, since it is determined in step S727 that only a small amount of PM has flowed into the DPF and it is impossible to accurately determine the DPF failure, the detection frequency fa is changed to a higher detection frequency fb. Execute the switching. Thereby, the value of the measured capacitance can be reduced, and the measurement of the capacitance can be continued. Thereafter, the process proceeds to step S731.

In step S731, the electrostatic capacitance C of the electrode portion is equal to or a predetermined threshold value C ₅ or higher. If this determination is YES, it is determined that the PM sensor has become unable to detect a change in capacitance, and the process proceeds to step S732. On the other hand, in the case of NO, it is determined that the PM sensor can detect a change in capacitance, and this determination is performed again.
Predetermined threshold value C _5, by performing the experiment in advance, is set to the upper limit value appears significant change in electrostatic capacitance.

  In step S732, the integration of the PM amount Y flowing into the DPF is terminated. Thereafter, the process proceeds to step S733.

In step S733, the PM collection rate X in the DPF is calculated. After the calculation, the process proceeds to step S734.
Specifically, the PM collection rate X (%) is calculated by the following formula (2). In Formula (2), Y is the cumulative amount of PM terminated by obtaining the integration at step S732 to start the integration in step S725, _{M 2} is the integration period of the PM amount Y (i.e., the detection frequency The total amount of PM that has flowed out of the DPF during the period in which the capacitance is measured by applying fa and the period in which the capacitance is measured by applying the detection frequency fb). This M ₂ is set based on the relationship between the total amount of PM (total amount of PM flowing out from the DPF) and the capacitance C as shown in FIG. Calculated.
[Equation 2]
X (%) = (1−M ₂ / Y) × 100 (2)

In step S734, failure determination of the DPF is executed. Specifically, step S729 or PM collection rate X calculated in step S733 it is determined whether a predetermined threshold _{X 1} or less. If this determination is NO, the process moves to step S735, where it is determined that the DPF is normal, and this PM detection process is terminated. On the other hand, in the case of YES, it moves to step S736, determines that the DPF is out of order, turns on the warning lamp, and ends this PM detection process.
The predetermined threshold value X ₁ is set by performing experiments in advance. Specifically, the predetermined threshold X _1, based on the relationship between the PM collection rate X and PM emission value as shown in FIG. 18, the PM collection rate X ₂ when PM emission value becomes a predetermined value If, PM emission value is set to a value between the PM collection rate X ₃ when a predetermined value + alpha.

According to this embodiment, in addition to the effects of the first embodiment, the following effects are further exhibited.
In the present embodiment, by PM from adhering to the electrode portion, the electrostatic capacitance measured in the measurement voltage of the detection frequency fa reaches a predetermined upper limit value C _5, and a predetermined amount emissions of PM from the engine when it is Y ₁ or more, and configured to perform a failure determination of the DPF. Further, the electrostatic capacity reaches a predetermined upper limit value C _5, and when the discharge amount of PM from the engine is less than a predetermined amount Y ₁ does not perform the failure determination of the DPF, higher than the detection frequency fa After switching to the detection frequency fb, detection of a value correlated with the amount of PM is continued, and a failure determination is executed.
Thus, in a state in which the measured voltage is applied to the detection frequency fa, for a predetermined amount Y ₁ or more of PM failure determination of the DPF can be performed accurately performs the failure determination when being discharged, a high failure determination accuracy Can do. Meanwhile, since the predetermined amount Y ₁ or more of PM failure determination can accurately be carried out does not perform failure determination when the has not been discharged, it is possible to avoid the risk of erroneous determination. Further, in this case, by switching to a higher detection frequency fb, there is a correlation with the amount of PM contained in the exhaust based on the change in capacitance measured at the measurement voltage of the detection frequency fb. Since the detection of the value is continued and the failure determination based on the value is executed again, the failure determination with high accuracy becomes possible.
By the way, since measurement voltage with a low frequency is higher as measurement accuracy, it is desirable to perform measurement in a state where a measurement voltage with a detection frequency fa having a lower frequency is applied. On the other hand, in failure determination, high determination accuracy can be obtained by measuring the capacitance and detecting a value correlated with the amount of PM using a wide measurement range. Therefore, when the failure determination is performed by dividing the measurement voltage at the detection frequency fa into a plurality of times, the accuracy of the failure determination is greatly reduced. Therefore, according to the present embodiment, after measurement is performed to the limit that can be measured under the measurement voltage of the detection frequency fa, if the PM emission amount is small, the failure determination is not performed and a higher detection is performed. Since the measurement and detection are continued after switching to the frequency fb and the failure determination is executed, the failure determination with high accuracy becomes possible.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the second embodiment, the DPF failure determination is performed based on the PM collection rate X of the DPF. However, the present invention is not limited to this. Instead of integrating the PM amount Y flowing into the DPF, the exhaust amount discharged from the engine, that is, the exhaust amount flowing into the DPF may be integrated. The displacement is calculated based on the intake amount of the engine. In this case, instead of the PM collection rate X, an average PM concentration is calculated by dividing the total amount of PM flowing out from the DPF during the exhaust amount integration period by the exhaust amount, and the DPF is calculated based on the average PM concentration. Perform failure determination.
Alternatively, the DPF failure determination may be performed directly from the PM amount flowing into the DPF and the PM amount flowing out from the DPF.

1. Engine (internal combustion engine)
11 ... PM sensor (particulate matter detection device)
12 ... Sensor element 120 ... Dust collection part (electrode part)
122, 129 ... Heater layer (electrode unit regeneration means)
130, 131 ... Electrode plate (electrode part)
17 ... Sensor control unit (measuring means, particulate matter detecting means, electrode part regenerating means, regeneration completion determining means, frequency changing means)
3 ... DPF
4 ... Exhaust pipe (exhaust system)
5 ... ECU (particulate matter detection device, regeneration completion judging means, frequency changing means)

Claims (4)

An electrode provided in the exhaust system of the internal combustion engine;
Measuring means for measuring a capacitance of the electrode unit by applying a measurement voltage to the electrode unit;
Particulate matter for detecting a value correlated with the amount of particulate matter contained in the exhaust gas based on the characteristic that the capacitance measured by the measuring means changes due to the particulate matter adhering to the electrode part Detection means;
After performing detection by the particulate matter detection means, electrode part regeneration means for regenerating the electrode part by burning and removing particulate matter adhering to the electrode part;
A regeneration completion determination unit that determines completion of regeneration of the electrode unit by the electrode unit regeneration unit based on the capacitance measured by the measurement unit, and a particulate matter detection device comprising:
Comprising frequency changing means for changing the frequency of the alternating measurement voltage applied by the measuring means;
The particulate matter detection means detects a value correlated with the amount of particulate matter contained in the exhaust based on a change in capacitance when a measurement voltage of a detection frequency is applied to the electrode part,
The regeneration completion determining means sets the frequency of the measurement voltage applied to the electrode section by the frequency changing means to a reproduction frequency higher than the detection frequency when the electrode section regeneration means performs the regeneration of the electrode section. The particulate matter detection device, wherein the completion of regeneration of the electrode unit by the electrode unit regeneration unit is determined based on the capacitance measured by the measurement unit after being changed. The frequency changing means can be switched to at least two detection frequencies, a first detection frequency and a second detection frequency higher than the first detection frequency.
The particulate matter detection means has a value correlated with the amount of particulate matter contained in the exhaust based on a change in capacitance when a measurement voltage of the first detection frequency is applied to the electrode portion. When the electrostatic capacity reaches a predetermined upper limit due to particulate matter adhering to the electrode portion, the frequency changing means changes the first detection frequency to the second detection frequency. 2. The particulate matter detection device according to claim 1, wherein after the switching, detection of a value correlated with the amount of particulate matter contained in the exhaust gas is continued.   3. The particulate matter according to claim 2, wherein the predetermined upper limit value is an upper limit value at which a significant change appears in the capacitance of the electrode portion when the particulate matter adheres to the electrode portion. Detection device. A failure detection device for an exhaust purification filter that is provided in an exhaust system of an internal combustion engine and collects particulate matter contained in exhaust,
The particulate matter detection device according to claim 2 or 3, provided downstream of the exhaust purification filter,
Failure determination means for determining failure of the exhaust purification filter based on a value correlated with the amount of particulate matter contained in the exhaust gas detected by the particulate matter detection means;
Execution determination means for determining whether or not to perform failure determination by the failure determination means;
An emission amount calculating means for calculating an emission amount of the particulate matter from the internal combustion engine during a period in which the capacitance was measured by applying a measurement voltage of the first detection frequency,
The execution determination means determines that the exhaust purification filter failure determination is performed when the exhaust amount is equal to or greater than a predetermined amount, and determines the failure determination of the exhaust purification filter when the exhaust amount is less than the predetermined amount. Decide not to run,
The particulate matter detection means has a value correlated with the amount of particulate matter contained in the exhaust based on a change in capacitance when a measurement voltage of the first detection frequency is applied to the electrode portion. When the electrostatic capacity reaches the predetermined upper limit due to the particulate matter adhering to the electrode portion and the execution determination means determines that the exhaust purification filter failure determination is not performed, Exhaust gas characterized by continuing detection of a value correlated with the amount of particulate matter contained in the exhaust gas after switching from the first detection frequency to the second detection frequency by frequency changing means. Purification filter failure determination device.

Images