JP2010275917A - Failure determination device for particulate matter detection means - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure determination device for a PM sensor, which detects PM contained in exhaust gas based on change of electrostatic capacity of a sensor electrode part disposed in an exhaust pipe. <P>SOLUTION: The failure determining device for the PM sensor including the sensor electrode part 61 disposed in the exhaust pipe 4 of an engine 1 and detecting PM contained in exhaust gas based on change of electrostatic capacity of the sensor electrode part 61 due to adhesion of PM discharged from the engine 1 on the sensor electrode part 61 is provided. The failure determination device determines a failure of the PM sensor 6 based on change of electrostatic capacity of the sensor electrode part 61 due to adhesion of condensate generated in the exhaust pipe 4 right after start of the engine 1 on the sensor electrode part 61. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a failure determination device for particulate matter detection means. More specifically, the present invention relates to a failure determination device for particulate matter detection means for detecting particulate matter contained in exhaust gas based on a change in electrical characteristics of an electrode portion provided in an exhaust passage.

  Conventionally, particulate matter detection means is provided in an exhaust pipe serving as an exhaust passage of the internal combustion engine in order to detect particulate matter discharged from the internal combustion engine. Various methods are known for the detection of particulate matter, and above all, based on changes in the electrical characteristics of the electrode portion provided in the exhaust pipe, as shown in Patent Document 1 and Patent Document 2, among others. In recent years, particulate matter detection means for detecting particulate matter has attracted particular attention since it can be detected with high accuracy even with a simple configuration.

  More specifically, in the soot detection sensor of Patent Document 1, a pair of soot detection electrodes formed of a porous conductive material is provided in the exhaust pipe, and the soot detection electrode formed by adhering soot contained in the exhaust gas is provided. Based on the change in electrical resistance, the amount of soot contained in the exhaust is detected.

  In addition, in the particulate matter detection device of Patent Document 2, by applying a predetermined voltage to the electrode portion provided in the exhaust pipe, the particulate matter contained in the exhaust is actively attached to the electrode portion, The amount of particulate matter in the exhaust gas is detected based on the change in the electrical characteristics of the electrode portion at the time.

On the other hand, Patent Literature 3 and Patent Literature 4 show a technique in which such particulate matter detection means is applied to a failure determination device for an exhaust purification filter that collects particulate matter.
More specifically, in Patent Document 3, particulate matter detection means is provided on the downstream side of the exhaust purification filter, and the malfunction of the exhaust purification filter is based on the amount of particulate matter detected by the particulate matter detection means. A failure determination apparatus for determining

  Further, Patent Document 4 includes a failure determination device that includes particulate matter detection means on the upstream side and downstream side of an exhaust purification filter, and determines a failure of the exhaust purification filter based on outputs of these two particulate matter detection means. It is shown. In this failure determination device, the ratio of the particulate matter that has passed through the exhaust purification filter out of the particulate matter that has flowed into the exhaust purification filter is calculated based on the ratio of the output values of the two particulate matter detection means. Is compared with a normal value to determine the failure of the exhaust purification filter.

JP 2006-266961 A JP 2008-139294 A JP 2007-315275 A JP 2007-132290 A

However, although the exhaust gas purification filter failure determination device disclosed in Patent Document 3 and Patent Document 4 can determine the failure of the exhaust gas purification filter when the particulate matter detection means is operating normally, If the substance detection unit fails, it may not be possible to determine whether the exhaust gas purification filter has failed, or the internal combustion engine may be controlled based on an error signal.
For this reason, in recent years, it has been desired to develop a failure determination device for determining failure of the particulate matter detection means.

  The present invention has been made in view of the above-described problems, and relates to a particulate matter detection unit that detects particulate matter contained in exhaust gas based on a change in electrical characteristics of an electrode portion provided in an exhaust passage. An object of the present invention is to provide a failure determination device for such particulate matter detection means.

  In order to achieve the above object, an invention according to claim 1 is directed to an electrode portion (for example, a sensor electrode described later) provided in an exhaust passage (for example, an exhaust pipe 4 described later) of an internal combustion engine (for example, engine 1 described later). 61), and the particulate matter discharged from the internal combustion engine detects particulate matter contained in the exhaust gas based on a change in electrical characteristics of the electrode portion due to adhesion to the electrode portion. A failure determination device (for example, ECUs 5 and 5B described later) of the particulate matter detection means (for example, PM sensor 6 described later) is provided. The failure determination device is configured such that at least one of a liquid (for example, condensed water described later) generated in the exhaust passage and a supplied liquid (for example, a reducing agent described later) adheres to the electrode portion. A failure of the particulate matter detection means is determined based on a change in electrical characteristics of the electrode portion.

The particulate matter detection means for detecting particulate matter contained in the exhaust gas based on the change in the electrical characteristics of the electrode portion is similar to the case where particulate matter is attached, even if liquid is attached, the electrical characteristics of the electrode portion Since this changes, this can be detected. According to the present invention, using this point, the particle is based on the change in the electrical characteristics of the electrode part due to at least one of the liquid generated in the exhaust passage and the supplied liquid adhering to the electrode part. The failure of the particulate matter detection means is determined.
In general, the conductivity of the liquid is high with respect to the particulate matter mainly composed of carbon discharged from the internal combustion engine, so that the electrode portion is divided between when the particulate matter adheres and when the liquid adheres. The magnitude of the change in the electrical characteristics of is different. As described above, since it is possible to distinguish between the case where the particulate matter adheres and the case where the liquid adheres, it is possible to accurately determine the failure of the particulate matter detection means.
Further, according to this failure determination device, in order to determine the failure of the particulate matter detection means based on the same logic as the detection of the particulate matter such as the change in the electrical characteristics of the electrode part, the conventional particulate matter detection means On the other hand, the failure determination device can be manufactured without significant improvement. Therefore, the cost for manufacturing the failure determination device can be reduced.

  According to a second aspect of the present invention, in the failure determination device for particulate matter detection means according to the first aspect, the liquid generated in the exhaust passage is condensed water generated in the exhaust passage when the internal combustion engine is started. It is characterized by that.

  When starting the internal combustion engine, particularly when the internal combustion engine has been stopped for a long time, the high-temperature exhaust discharged from the internal combustion engine is drastically cooled in the exhaust passage cooled by the outside air, and thus is included in the exhaust. Water is condensed and condensed water is generated. The condensed water generated in this way may flow downstream along with the flow of exhaust and may adhere to the electrode part. According to the present invention, it is possible to determine the failure of the particulate matter detection means with higher accuracy by using the condensed water that is inevitably generated when the internal combustion engine is started. In addition, according to the present invention, it is not necessary to separately provide a device for supplying the liquid, so that the cost for manufacturing the failure determination device can be suppressed.

  According to a third aspect of the present invention, in the failure determination device for the particulate matter detection means according to the second aspect, the internal combustion engine is started based on the time from when the internal combustion engine was last stopped until the current start. Condensed water determination means for determining whether or not condensed water is sometimes generated is further provided, and when it is determined that condensed water is generated when the internal combustion engine is started, a failure of the particulate matter detection means is determined. And

  According to the present invention, it is determined whether or not condensed water is generated when the internal combustion engine is started based on the time from the previous stop of the internal combustion engine to the current start, and it is determined that condensed water is generated. By determining the failure of the particulate matter detection means, the accuracy of determining the failure of the particulate matter detection means can be further improved.

  According to a fourth aspect of the present invention, in the failure determination device for particulate matter detection means according to any of the first to third aspects, the liquid supplied to the exhaust passage is provided separately from the exhaust passage. The liquid is supplied by liquid supply means (for example, an injector 8B described later).

  According to the present invention, by using the liquid supplied by the liquid supply means provided separately from the exhaust passage, the failure of the particulate matter detection means is determined not only at the time of starting the internal combustion engine as described above. Can do. Further, by using the liquid supplied by the liquid supply means, it is easier to grasp the time when the liquid was supplied as compared with the case where the liquid generated in the exhaust passage is used as described above, so that the particulate matter detection The failure of the means can be determined with higher accuracy.

  By the way, an exhaust purification device that purifies exhaust gas is known that includes a supply device that supplies liquid such as fuel or urea water into the exhaust passage. Therefore, it is preferable to use such a supply device for the exhaust gas purification device as the liquid supply means. In this case, it is not necessary to separately provide a device for supplying the liquid, so that the cost of the failure determination device can be suppressed.

  According to a fifth aspect of the present invention, in the failure determination device for the particulate matter detection means according to the fourth aspect, the liquid supply determination means for determining whether or not liquid is supplied to the exhaust passage by the liquid supply means. And a failure of the particulate matter detection means is determined when it is determined that the liquid is supplied by the liquid supply means.

  According to the present invention, it is determined whether or not liquid is supplied by the liquid supply means, and when it is determined that the liquid is supplied, it is determined that the particulate matter detection means is out of order. It is possible to further improve the determination accuracy of the failure of the detection means.

  A sixth aspect of the present invention is the failure determination apparatus for particulate matter detection means according to any one of the first to fifth aspects, wherein a part of the exhaust gas containing liquid is rectified to the electrode portion in the exhaust passage. Rectifying means (for example, rectifying plates 65A and 66A described later) is provided.

  According to the present invention, the rectifying means for rectifying a part of the exhaust gas containing the liquid to the electrode portion is provided. Thereby, since a liquid can be more efficiently adhered to an electrode part, the failure of a particulate matter detection means can be determined with higher accuracy.

  The invention according to claim 7 is the failure determination device for the particulate matter detection means according to any one of claims 1 to 6, wherein the exhaust gas purification filter collects particulate matter contained in the exhaust gas in the exhaust passage. (For example, DPF 3 described later) is provided, and the electrode portion is provided downstream of the exhaust purification filter in the exhaust passage.

  According to the present invention, the electrode portion is provided downstream of the exhaust purification filter in the exhaust passage. Thereby, the particulate matter detection means can be applied to a failure determination device for an exhaust purification filter. That is, when the collection performance of the exhaust gas purification filter is deteriorated, the particulate matter that has passed through the exhaust gas purification filter adheres to the electrode portion, so that a failure of the exhaust gas purification filter can be determined.

  By the way, when the exhaust gas purification filter is normal, the particulate matter in the exhaust gas is collected, so that the amount of the particulate matter discharged to the downstream side of the exhaust purification filter is small. Therefore, for example, when determining the failure of the particulate matter detection means based on the change in the electrical characteristics of the electrode part due to adhering particulate matter, when the exhaust purification filter is normal, the particulate matter detection means It is difficult to determine the failure. On the other hand, in the present invention, the change in the electrical characteristics of the electrode portion due to the adhesion of liquid that can pass through the exhaust purification filter or can be generated or supplied downstream of the exhaust purification filter. Based on the above, the failure of the particulate matter detection means is determined. Therefore, the failure of the particulate matter detection means can be determined regardless of the state of the exhaust purification filter.

1 is a schematic diagram showing a configuration of a PM sensor failure determination device according to a first embodiment of the present invention, an engine to which the PM sensor failure determination device is applied, and an exhaust purification system thereof. It is a figure which shows the characteristic behavior of the electrostatic capacitance of the sensor electrode part immediately after starting of an engine. It is a flowchart which shows the procedure of PM sensor failure determination processing which concerns on the said embodiment. It is a fragmentary sectional view of the exhaust pipe which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the failure determination apparatus of PM sensor which concerns on 3rd Embodiment of this invention, the engine which applied this, and its exhaust purification system. It is a flowchart which shows the procedure of PM sensor failure determination processing which concerns on the said embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description after the second embodiment, the description of the configuration common to the first embodiment is omitted.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of a particulate matter detection means failure determination device according to the present embodiment, and an internal combustion engine (hereinafter referred to as “engine”) 1 and an exhaust purification system 2 to which the failure determination device is applied. The 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 to an electronic control unit (hereinafter referred to as “ECU”) 5, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 5.

  An exhaust purification filter (hereinafter referred to as “DPF (Diesel Particulate Filter)”) 3 and a particulate matter (hereinafter referred to as “hereinafter referred to as“ particulate matter ”) mainly composed of carbon contained in the exhaust are disposed in the exhaust pipe 4 serving as an exhaust passage of the engine 1. Particulate matter detection means (hereinafter referred to as “PM sensor”) 6 for detecting PM (Particulate Matter) ”is provided in this order from the upstream side.

  The DPF 3 includes a porous filter wall having innumerable pores. When the exhaust gas passes through the filter wall, PM contained in the exhaust gas is deposited on the surface of the filter wall and the pores in the filter wall. To collect this. When PM is collected up to the limit of the DPF 3 collection capacity, that is, the accumulation limit, the pressure loss increases. Therefore, DPF regeneration processing for burning and removing PM collected in the DPF at an appropriate time is executed by the ECU 5.

  The PM sensor 6 includes a sensor electrode unit 61 provided on the downstream side of the DPF 3 in the exhaust pipe 4, and a sensor controller 62 connected to the ECU 5 and controlling the sensor electrode unit 61.

  The sensor electrode unit 61 includes a pair of electrode plates arranged in parallel to each other. A cavity to which PM in the exhaust adheres is formed between these electrode plates. As shown below, the PM sensor 6 measures the electrical characteristics of the sensor electrode unit 61 to which PM contained in the exhaust gas flowing through the exhaust pipe 4 adheres, and based on the change in the measured value, Detect PM in circulating exhaust gas.

  The sensor controller 62 includes a power supply unit 63 that applies a dust collection voltage to the electrode plate of the sensor electrode unit 61, and an impedance measuring instrument 64 that detects electrical characteristics of the sensor electrode unit 61.

  The power supply unit 63 operates based on a control signal transmitted from the ECU 5 and applies a predetermined dust collection voltage to the electrode plate of the sensor electrode unit 61. Thereby, PM contained in the exhaust gas can be positively attached in the cavity of the sensor electrode unit 61. In addition, the power source unit 63 can warm the sensor electrode unit 61 or burn the accumulated PM to regenerate the sensor electrode unit 61 by energizing a heater provided in the sensor electrode unit 61. it can.

  The impedance measuring device 64 operates based on a control signal transmitted from the ECU 5, detects the capacitance of the sensor electrode unit 61 based on an AC signal having a predetermined measurement voltage and a measurement cycle, and detects the detected capacitance. A signal substantially proportional to the value is output to the ECU 5.

  In addition to the PM sensor as described above, a warning light 51, an ignition switch 52, and the like are connected to the ECU 5.

  The warning lamp 51 is provided, for example, on a meter panel of a vehicle (not shown) and lights up based on a control signal transmitted from the ECU 5. As will be described in detail later, when it is determined that the PM sensor 6 has failed, the ECU 5 turns on the warning lamp 51. Thereby, it is possible to notify the driver that the PM sensor 6 has failed. The ignition switch 52 is provided, for example, in the driver's seat of the vehicle, and transmits a signal instructing the engine 1 to start or stop to the ECU 5.

  The ECU 5 shapes an input signal waveform from various sensors, corrects a 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 and calculation results, an output circuit that outputs control signals to the sensor controller 62, the warning lamp 51, the fuel injection valve of the engine 1, and the like. Is provided.

  Also, with the hardware configuration described above, the ECU 5 includes various modules such as a DPF failure determination unit 53 that determines DPF failure and a PM sensor failure determination unit 54 that determines PM sensor failure.

  The DPF failure determination unit 53 determines the failure of the DPF 3 based on the output from the PM sensor 6. Since the PM discharged from the engine 1 is collected by the DPF 3, the amount of PM that reaches the sensor electrode unit 61 is limited as long as the DPF 3 is normal. However, when the DPF 3 fails, the PM discharged from the engine 1 passes through the DPF 3 and adheres to the sensor electrode unit 61. Therefore, the DPF failure determination unit 53 monitors the change in the capacitance of the sensor electrode unit 61 while the engine 1 is operating, and the PM discharged from the DPF 3 due to the failure of the DPF 3 is detected by the sensor electrode unit. The failure of the DPF 3 is determined based on the change in the capacitance of the sensor electrode unit 61 due to the adhesion to the electrode 61.

  The PM sensor failure determination unit 54 determines the failure of the PM sensor 6 based on the output from the PM sensor 6, similarly to the DPF failure determination unit 53 described above. Hereinafter, the PM sensor failure determination processing by the PM sensor failure determination unit 54 will be described in detail with reference to FIGS. 2 and 3.

FIG. 2 is a diagram showing a characteristic behavior of the capacitance of the sensor electrode portion immediately after the engine is started. In FIG. 2, the solid line indicates the measured value of the capacitance of the PM sensor operating normally, and the broken line indicates the measured value of the capacitance of the failed PM sensor.
As shown in FIG. 2, the capacitance of the sensor electrode portion temporarily shows a large value immediately after the engine is started. This is because immediately after the start of the engine, high-temperature exhaust gas exhausted from the engine flows through the exhaust pipe, and the condensed water is generated by condensation of moisture contained in the exhaust gas. It is considered that water is attached to the sensor electrode part.

  In addition, since liquid such as condensed water generally has higher conductivity than PM mainly composed of carbon, the amount of change in capacitance when condensed water adheres to the sensor electrode portion is determined by PM. It is sufficiently larger than the amount of change in capacitance when adhering to the sensor electrode portion. For this reason, when condensed water adheres to a sensor electrode part, the peak as shown in FIG. 2 generate | occur | produces in the measured value of the electrostatic capacitance of a sensor electrode part.

  The PM sensor failure determination unit 54 determines the failure of the PM sensor based on the change in the capacitance of the sensor electrode unit due to the condensed water generated in the exhaust pipe when starting the engine adheres to the sensor electrode unit. . More specifically, in the PM sensor failure determination unit 54, the measured value of the capacitance of the sensor electrode unit exceeds the predetermined normal determination value within a predetermined determination period from the time of engine start as shown in FIG. In this case, it is determined that the PM sensor is normal.

FIG. 3 is a flowchart showing a procedure of PM sensor failure determination processing. This process is executed by the PM sensor failure determination unit of the ECU immediately after the ignition switch is turned on.
In step S1, a soak time that indicates the time from when the engine was last stopped until it is started this time is acquired, and the process proceeds to step S2.

  In step S2, it is determined whether or not condensed water is generated based on the acquired soak time. More specifically, it is determined whether or not condensed water is generated by determining whether or not the soak time is a predetermined value or more. If this determination is YES, that is, if the engine has been stopped for a predetermined time or longer, the exhaust pipe is in a cooled state until it becomes substantially equal to the outside air temperature, so it is considered that condensed water is generated. Therefore, the process proceeds to step S3 in order to determine the failure of the PM sensor using the condensed water. On the other hand, if this determination is NO, it is determined that the exhaust pipe has not cooled down, and failure determination of the PM sensor using condensed water cannot be performed, and this processing is immediately terminated.

In step S3, the capacitance of the sensor element is measured over a predetermined determination period, and the process proceeds to step S4.
In step S4, it is determined whether or not the measured capacitance value exceeds the normal determination value during the determination period. If this determination is YES, it means that condensed water has been detected by the PM sensor, so it is determined that the PM sensor is in a normal state, and this process is immediately terminated. On the other hand, if this determination is NO, it means that the condensed water could not be detected by the PM sensor. Therefore, it is determined that the PM sensor is in a failure state, the process proceeds to step S5, and a warning lamp is turned on. Exit.

According to this embodiment, the following effects can be obtained.
(1) According to the present embodiment, based on the change in the capacitance of the sensor electrode unit 61 due to the condensed water generated in the exhaust pipe 4 adhering to the sensor electrode unit 61, the PM sensor 6 is failed. judge. In general, since condensed water has higher conductivity than PM, it is possible to distinguish between the case where PM adheres and the case where condensed water adheres. Can do. In addition, according to this failure determination device, since a failure of the PM sensor 6 is determined based on the same logic as the detection of PM, such as a change in electrical characteristics of the sensor electrode unit 61, a significant improvement over the conventional PM sensor. The failure determination device can be manufactured without adding. Therefore, the cost for manufacturing the failure determination device can be reduced.

  (2) According to the present embodiment, by using the condensed water that is inevitably generated when the engine 1 is started in this way, it is possible to determine the failure of the PM sensor with higher accuracy. Moreover, according to this embodiment, since it is not necessary to provide the apparatus for supplying a liquid separately, the cost concerning manufacture of a failure determination apparatus can be held down.

  (3) According to the present embodiment, based on the soak time, it is determined whether or not condensed water is generated when the engine 1 is started, and a failure of the PM sensor 6 is determined when it is determined that condensed water is generated. By doing so, the determination accuracy of the failure of the PM sensor 6 can be further improved.

  (4) According to the present embodiment, the sensor electrode unit 61 is provided in the exhaust pipe 4 downstream of the DPF 3. Thereby, the PM sensor 6 can be applied to a failure determination device for the DPF 3. That is, when the collection performance of the DPF 3 is deteriorated, the PM that has passed through the DPF 3 adheres to the sensor electrode unit 61. Therefore, the failure of the DPF 3 occurs based on the change in the capacitance of the sensor electrode unit 61 due to the adhesion of this PM. Can be determined.

  By the way, when the DPF 3 is normal, PM in the exhaust gas is collected, so that the amount of PM discharged to the downstream side of the DPF 3 is small. Therefore, for example, when determining the failure of the PM sensor 6 based on the change in the capacitance of the sensor electrode unit 61 due to the adhesion of PM, the failure of the PM sensor 6 can be determined when the DPF 3 is normal. Have difficulty. On the other hand, in the present embodiment, the capacitance of the sensor electrode 61 changes due to adhesion of liquid that can pass through the DPF 3 or can be generated or supplied to the downstream side of the DPF 3. Based on this, a failure of the PM sensor 6 is determined. Therefore, the failure of the PM sensor 6 can be determined regardless of the state of the DPF 3.

[Second Embodiment]
The failure determination device for the PM sensor 6 according to the second embodiment is different from the first embodiment in the configuration in the vicinity of the sensor electrode portion 61 in the exhaust pipe 4A.
FIG. 4 is a partial cross-sectional view of the exhaust pipe 4A.

  As shown in FIG. 4, rectifying plates 65A and 66A extending from the DPF 3 to the cavity C of the sensor electrode portion 61 on the downstream side are provided in the exhaust pipe 4A. By providing such rectifying plates 65A and 66A, a part of the exhaust gas containing liquid such as condensed water is rectified toward the cavity C of the sensor electrode unit 61, and the condensed water generated in the exhaust pipe 4A is detected by the sensor. It can be attached to the electrode part 61. Further, these rectifying plates 65A and 66A also have an action of cooling the exhaust immediately after starting the engine and actively generating condensed water on the rectifying plates 65A and 66A. Can be attached to.

As described above in detail, according to the present embodiment, in addition to the effects (1) to (4) described above, the following effects can be obtained.
(5) According to the present embodiment, the rectifying plate 65A that rectifies a part of the exhaust gas including the condensed water to the cavity C of the sensor electrode unit 61 is provided. Thereby, since condensed water can be made to adhere to the sensor electrode part 61 more efficiently, the failure of the PM sensor 6 can be determined with higher accuracy.

[Third Embodiment]
The failure determination device for the PM sensor 6 according to the third embodiment is different from the first embodiment in the configuration of the exhaust purification system 2B in which the PM sensor 6 is provided.
FIG. 5 is a schematic diagram showing a configuration of a failure determination device for the PM sensor 6 according to the present embodiment, an engine 1 to which the PM sensor 6 is applied, and an exhaust purification system 2B thereof.

  As shown in FIG. 5, in addition to the DPF 3 and the PM sensor 6, the exhaust purification system 2B includes a NOx purification device 7B that purifies NOx contained in the exhaust, and an injector 8B that supplies a reducing agent to the NOx purification device 7B. Further points differ from the first embodiment.

  The NOx purification device 7B is provided in the exhaust pipe 4 on the downstream side of the sensor electrode portion 61 of the DPF 3 and the PM sensor 6. The NOx purification device 7 captures NOx in the exhaust gas, and purifies NOx in the exhaust gas by reducing the captured NOx in the presence of the reducing agent supplied from the injector 8B.

  The injector 8B is provided between the DPF 3 and the sensor electrode 61 of the PM sensor 6 in the exhaust pipe 4, and injects a liquid reducing agent stored in a tank (not shown) into the exhaust. In addition, as the reducing agent injected by the injector 8B, for example, the fuel of the engine 1 or urea water is used. The injector 8B is electrically connected to the ECU 5B, and the injection amount and injection timing of the reducing agent from the injector 8B are controlled by the ECU 5B.

  The injector drive unit 55B of the ECU 5B sequentially accumulates the amount of NOx trapped by the NOx purification device 7B, drives the injector 8B in response to the amount of NOx trapped reaching a predetermined amount, and the exhaust pipe 4 By injecting the reducing agent into the inside, the NOx trapped by the NOx purification device 7B is reduced.

  In the PM sensor failure determination unit 54B of the ECU 5B, the failure of the PM sensor 6 is detected based on the change in the capacitance of the sensor electrode unit 61 due to the reducing agent supplied from the injector 8B adhering to the sensor electrode unit 61. judge.

  FIG. 6 is a flowchart illustrating a procedure of PM sensor failure determination processing. This process is repeatedly executed at a predetermined cycle by the PM sensor failure determination unit of the ECU after the ignition is turned on.

  In step S11, it is determined whether or not the liquid is supplied by the injector, that is, whether or not the reducing agent is supplied into the exhaust pipe by the injector. If this determination is YES, the process proceeds to step S12 in order to determine the failure of the PM sensor using the reducing agent. On the other hand, if this determination is NO, it is determined that the failure determination of the PM sensor using the reducing agent cannot be performed, and this process is immediately terminated.

In step S12, the capacitance of the sensor element is measured over a predetermined determination period, and the process proceeds to step S13.
In step S13, it is determined whether or not the measured capacitance value exceeds the normal determination value during the determination period. If this determination is YES, it means that the reducing agent has been detected by the PM sensor, so it is determined that the PM sensor is in a normal state, and this process is immediately terminated. On the other hand, if this determination is NO, it means that the reducing agent could not be detected by the PM sensor. Therefore, it is determined that the PM sensor is in a failure state, the process proceeds to step S14, the warning lamp is turned on, and this processing is performed. Exit.

As described above in detail, according to the present embodiment, in addition to the effects (1) and (4) described above, the following effects can be obtained.
(6) According to the present embodiment, by using the reducing agent supplied by the injector 8B provided separately from the exhaust pipe 4, the PM sensor 6 is not limited to the failure of the engine 1 as described above. Can be determined. Also, by using the reducing agent supplied by the injector 8B, it is easier to grasp the time when the liquid is supplied compared to the case where the condensed water generated in the exhaust pipe 4 is used as described above. The failure of the sensor 6 can be determined with higher accuracy. Further, by diverting the injector 8B of the exhaust purification system 2B, it is not necessary to separately provide a device for supplying liquid, so that the cost for manufacturing the failure determination device can be suppressed.

  (7) According to this embodiment, it is determined whether or not the reducing agent is supplied by the injector 8B, and when it is determined that the reducing agent is supplied, the failure of the PM sensor 6 is determined. The accuracy of determining the failure of the PM sensor 6 can be further improved.

The present invention is not limited to the embodiment described above, and various modifications can be made.
In the third embodiment, a reducing agent such as fuel or urea water supplied by the injector 8B of the exhaust gas purification system 2B is used for determining the failure of the PM sensor. However, not only the reducing agent but also water is used. Good.

1. Engine (internal combustion engine)
2, 2B ... Exhaust gas purification system 3 ... DPF (Exhaust gas purification filter)
4, 4A ... Exhaust pipe (exhaust passage)
6 ... PM sensor (particulate matter detection means)
61 ... Sensor electrode part (electrode part)
5 ... ECU (failure determination device, condensed water determination means, liquid supply determination means)
65A, 66A ... Rectifying plate (rectifying means)
8B ... Injector (liquid supply means)

Claims (7)

An electrode portion provided in an exhaust passage of the internal combustion engine, and included in the exhaust gas based on a change in electrical characteristics of the electrode portion caused by adhering particulate matter discharged from the internal combustion engine to the electrode portion; A failure determination device for particulate matter detection means for detecting particulate matter to be detected,
A failure of the particulate matter detection means is determined based on a change in electrical characteristics of the electrode part caused by at least one of the liquid generated in the exhaust passage and the supplied liquid adhering to the electrode part. A failure determination device for particulate matter detection means.   2. The particulate matter detection unit failure determination device according to claim 1, wherein the liquid generated in the exhaust passage is condensed water generated in the exhaust passage when the internal combustion engine is started. Condensed water determination means for determining whether or not condensed water is generated at the time of starting the internal combustion engine based on the time from when the internal combustion engine was last stopped until the current start is further provided,
3. The particulate matter detection unit failure determination apparatus according to claim 2, wherein a failure of the particulate matter detection unit is determined when it is determined that condensed water is generated when the internal combustion engine is started.   The particulate matter detection means according to any one of claims 1 to 3, wherein the liquid supplied to the exhaust passage is a liquid supplied by a liquid supply means provided separately from the exhaust passage. Failure determination device. Liquid supply determining means for determining whether or not liquid is supplied to the exhaust passage by the liquid supply means;
5. The particulate matter detection unit failure determination apparatus according to claim 4, wherein a failure of the particulate matter detection unit is determined when it is determined that liquid is supplied by the liquid supply unit.   6. The particulate matter detection means failure determination device according to claim 1, wherein the exhaust passage is provided with a rectification means for rectifying a part of the exhaust gas containing the liquid to the electrode portion. . The exhaust passage is provided with an exhaust purification filter that collects particulate matter contained in the exhaust,
The failure determination device for particulate matter detection means according to any one of claims 1 to 6, wherein the electrode portion is provided on the downstream side of the exhaust purification filter in the exhaust passage.

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