JP6505578B2 - Filter failure detection device, particulate matter detection device - Google Patents

Description

  The present invention relates to a failure detection device for a filter that collects particulate matter in exhaust gas discharged from an internal combustion engine, and a particulate matter detection device that detects the amount of particulate matter in exhaust gas.

  Conventionally, there has been proposed a device for detecting the amount of particulate matter (particulate matter, PM) in exhaust gas discharged from an internal combustion engine (see, for example, Patent Document 1). Patent Document 1 discloses that the output value of an electrical resistance sensor that outputs a value corresponding to the amount of particulate matter in exhaust gas is corrected using the exhaust temperature, the temperature of the sensor, and the exhaust flow rate. There is. According to this, it is possible to detect the amount of particulate matter with high accuracy without being affected by the temperature and the exhaust flow rate.

  Here, the electrical resistance type sensor has an adherend to which particulate matter in exhaust gas adheres, and a pair of counter electrodes provided apart from each other on the adherend. Since the particulate matter (Soot) has conductivity, the resistance value between the pair of counter electrodes decreases as the amount of the particulate matter adhering to the adherend increases. The sensor outputs a value corresponding to the resistance value between the opposing electrodes, that is, a value corresponding to the amount of particulate matter adhering to the adherend.

Patent No. 5240679 gazette

  By the way, according to the results investigated by the present inventors, under the coexistence of a specific combustion supporting gas in the exhaust gas, a part of the particulate matter collected by the sensor (adhered portion) is burned and removed, It has been found that the sensor output largely changes to the value side indicating that the particulate matter mass is small. In addition, when a sensor is disposed downstream of the filter that collects particulate matter and the failure of the filter is determined based on the output value of the sensor, the sensor output changes due to the influence of the combustion supporting gas. As a result, the accuracy of the failure determination of the filter is reduced.

  The present invention has been made in view of the above problems, and it is possible to suppress the decrease in the accuracy of the failure determination of the filter due to the effect of the supporting gas, and the particulate matter under the influence of the supporting gas and the supporting gas. It is an object of the present invention to provide a particulate matter detection device capable of suppressing the decrease in the detection accuracy of the amount.

In order to solve the above-mentioned problems, according to the first aspect of the present invention, an exhaust gas is provided downstream of a filter (12) for collecting particulate matter in exhaust gas provided in an exhaust passage (23) of an internal combustion engine (20) A sensor (13) having an attached portion (52) to which the particulate matter in the inner portion adheres, and outputting a value according to the amount of the particulate matter attached to the attached portion;
Concentration acquisition means (S2, S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S3, S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas;
Correction means (S5, S76, S77) for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition means and the temperature acquired by the temperature acquisition means , S81, 17),
Failure determination means (S6 to S8, S82 to S84) for performing failure determination of the filter based on the output value corrected by the correction means;
Equipped with
The concentration acquiring means is characterized in acquiring at least one concentration of NO, NO ₂ and O ₂ .

According to the investigation results of the present inventors, particles adhered to the adherend by an amount corresponding to the concentration of the combustion supporting gas ( at least one of NO, NO ₂ and O ₂ ) and the gas temperature coexisting in the exhaust gas Substances were burned out, and it was found that the sensor output was changed. The present invention has been made based on the results of this investigation, acquires the concentration of the combustion supporting gas and the temperature of the exhaust gas, and based on the concentration and the temperature, outputs the sensor value, the amount of particulate matter To make more Thereby, the output value of the sensor can be made close to the value before the combustion by the combustion supporting gas is performed. And since failure determination of a filter is performed based on the output value after correction, failure determination can be performed in the form which suppressed the influence of the combustion by supporting gas, and the accuracy fall of failure determination can be suppressed.

The second invention is provided downstream of a filter (12) for collecting particulate matter in exhaust gas provided in an exhaust passage (23) of an internal combustion engine (20), and adheres particulate matter in exhaust gas A sensor (13) having an attached portion (52) to be caused to output, and outputting a value corresponding to the amount of particulate matter attached to the attached portion;
Estimation means (S17, S38, S58, S78, 17) for estimating the output value of the sensor in the case where the filter is a filter serving as a reference for failure determination;
Failure determination means (S22 to S24, S42 to S44, S62 to S64, S82 to S84, 17) for determining the failure of the filter based on comparison between the value estimated by the estimation means and the actual output value of the sensor When,
Concentration acquisition means (S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas,
Output value correction for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition unit and the temperature acquired by the temperature acquisition unit, and the estimation unit Correction means (S16, S18, S19, S76, S77, S81, 17) for performing either of the estimated value correction for correcting the estimated value of P.sub.2 in the direction to reduce the amount of particulate matter.
Said failure determining means, have line failure determination of the filter by using a value corrected by the correction means,
The concentration acquiring means is characterized in acquiring at least one concentration of NO, NO ₂ and O ₂ .

According to the second aspect of the invention, the output value of the sensor in the case where the filter is a reference for failure determination is estimated, and the failure determination of the filter is performed based on a comparison between the estimated value and the actual output value of the sensor. . At this time, based on the concentration of the combustion supporting gas ( at least one of NO, NO ₂ and O ₂ ) and the temperature of the exhaust gas, the output value of the sensor is corrected to increase the amount of particulate matter. Either the correction or the estimated value correction for correcting the estimated value of the sensor output in the direction of reducing the amount of particulate matter is performed. When output value correction is performed, the output value of the sensor can be made close to the value before combustion by the combustion supporting gas, and the output value and the estimated value of the sensor can be It can compare. On the other hand, when the estimated value correction is performed, the estimated value can be made close to the value after the combustion by the combustion supporting gas, and the output value of the sensor can be compared with the estimated value in the state after the combustion. Thereby, the failure determination can be performed in the form which suppressed the influence of the combustion by the combustion supporting gas, and the precision fall of failure determination can be suppressed.

The third aspect of the present invention is a particulate matter provided in an exhaust passage (23) of an internal combustion engine (20) and adhering the particulate matter in the exhaust gas to the adherend (52). A sensor (13) that outputs a value according to the amount of
Concentration acquisition means (S2, S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S3, S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas;
Correction means (S5, S76, S77) for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition means and the temperature acquired by the temperature acquisition means , S81, 17),
Equipped with
The concentration acquiring means is characterized in acquiring at least one concentration of NO, NO ₂ and O ₂ .

According to the third invention, the output value of the sensor is increased based on the concentration of the combustion supporting gas ( at least one of NO, NO ₂ and O ₂ ) and the temperature of the exhaust gas, and the direction in which the amount of particulate matter is increased. Therefore, the output value of the sensor can be made close to the value before combustion by the combustion supporting gas is performed. Therefore, it can suppress that the precision of the particulate matter mass detected by a sensor falls by the influence of the gas supporting gas.

It is a block diagram of an engine system. It is the figure which showed the structure of PM sensor typically. It is a figure which shows the mode of a pair of opposing electrodes vicinity in a sensor element, and is a figure explaining the detection principle of PM amount by PM sensor. It is the figure which showed the gas concentration and the output reduction rate of PM sensor for every kind of combustion supporting gas. _NO, indicating for each O 2, NO ₂ gas species, for the gas temperature is a diagram showing a change in the CO ₂ generation amount corresponding to the combustion amount of PM trapped in the PM sensor. It is the figure which showed the relationship data of gas temperature, NO density | concentration, and output correction value _ANO . Is a diagram showing the relationship data between the gas temperature and the NO ₂ concentration and the output correction value A _NO2. Is a diagram showing the relationship data between the gas temperature and the O ₂ concentration and the output correction value A _O2. It is the flowchart which showed the failure determination processing of DPF in 1st Embodiment. It is the figure which showed the change of the sensor output with respect to collection time, and showed the mode of the correction | amendment in 1st Embodiment. It is a figure showing change of the output of PM sensor to collection time, and showing the actual sensor output and the presumed output of PM sensor in case DPF is reference fault DPF. It is the flow chart which showed failure determination processing of DPF in a 2nd embodiment. It is the figure which showed the change of the sensor output with respect to collection time, and showed the mode of the correction | amendment in 2nd Embodiment. It is the flow chart which showed failure determination processing of DPF in a 3rd embodiment. It is the figure which showed the change of the sensor output with respect to collection time, and showed the mode of the correction | amendment in 3rd Embodiment. It is the flow chart which showed failure determination processing of DPF in a 4th embodiment. It is the figure which showed the change of the sensor output with respect to collection time, and showed the mode of the correction | amendment in 4th Embodiment. It is the flowchart which showed the failure determination processing of DPF in 5th Embodiment. It is the figure which showed the change of the sensor output with respect to collection time, and showed the mode of the correction | amendment in 5th Embodiment.

First Embodiment
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a vehicle engine system 100 to which the present invention is applied. The engine system 100 includes a multi-cylinder (four cylinders in FIG. 1) diesel engine 20 (hereinafter simply referred to as an engine) as an internal combustion engine. The engine 20 is provided with an injector 6 for injecting fuel into the cylinder 7. The engine 20 generates power for driving a vehicle by self-ignition of fuel injected from the injector 6 in the cylinder 7.

  The intake passage 10 of the engine 20 is provided with a supercharger 1, which compresses air, an intercooler 2, which cools air compressed by the supercharger 1, and a throttle valve 3, which adjusts the amount of air, from the upstream side. . The intake passage 10 is connected to an intake manifold 5 having a branch passage connected to each cylinder 7.

  An exhaust manifold 8 is connected to each of the cylinders 7 for collectively delivering the exhaust gas discharged from each of the cylinders 7 to the exhaust passage 23. The exhaust passage 23 is provided with a turbine of the turbocharger 1, and on the upstream side of the turbine, an EGR (Exhaust Gas Recirculation) passage 19 for returning a part of the exhaust gas to the intake system is connected. . The EGR passage 19 is connected to the intake passage 10 at a position between the throttle valve 3 and the air flow meter 4. The EGR passage 19 is provided with an EGR valve 9 for adjusting the amount of exhaust gas (EGR amount) to be recirculated to the intake system.

  The exhaust passage 23 is provided with an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 11 for oxidizing and removing CO, HC and the like in the exhaust gas downstream of the position where the EGR passage 19 is connected. Downstream from the oxidation catalyst 11, a diesel particulate filter (DPF) 12 corresponding to the filter of the present invention is provided. The DPF 12 is a ceramic filter having a known structure. For example, a heat-resistant ceramic such as cordierite is formed into a honeycomb structure so that a large number of cells serving as gas flow paths are alternately arranged on the inlet side or the outlet side. Sealed and configured. Exhaust gas discharged from the engine 20 flows downstream while passing through the porous partition walls of the DPF 12, and PM (particulate matter, particulate matter) contained in the exhaust gas is collected and accumulated gradually during that time.

  An electric resistance type PM sensor 13 as a sensor of the present invention for detecting the amount of PM in exhaust gas is provided downstream of the DPF 12 of the exhaust passage 23. Here, FIG. 2 is a view schematically showing the structure of the PM sensor 13. As shown in FIG. 2, the PM sensor 13 includes, for example, a metal cover 51 whose inside is hollow and a sensor element 52 disposed in the cover 51. A large number of holes 511 are formed in the cover 51, and a part of the exhaust gas flowing through the exhaust passage 23 is introduced into the cover 51 from the holes 511. Further, the cover 51 is formed with a discharge hole 512 for discharging the exhaust gas introduced into the cover 51. In addition, in FIG. 2, the discharge hole 512 has shown the example formed in the front-end | tip of the cover 51. As shown in FIG.

  The sensor element 52 is composed of an insulator substrate such as ceramics. On one surface of the sensor element 52 (insulator substrate), a pair of opposing electrodes 53 which are separated from each other and opposed to each other are provided. Here, FIG. 3 is a view for explaining the detection principle of the amount of PM by the PM sensor 13, and shows a state of PM adhesion in the vicinity of the pair of opposing electrodes 53. As shown in FIG. As shown in FIG. 3, the sensor element 52 is connected to a voltage application circuit 55 that applies a predetermined DC voltage between the pair of opposing electrodes 53. A part of the PM in the exhaust gas introduced into the cover 51 is collected (adhered) on the sensor element 52 by its own adhesiveness.

  When a voltage is applied between the opposing electrodes 53 by the voltage application circuit 55, each opposing electrode 53 is charged positively and negatively. As a result, PM passing through the vicinity of the counter electrode 53 is charged, and collection on the sensor element 52 is promoted. In the following, collection of PM on the sensor element 52 by applying a voltage between the opposing electrodes 53 is referred to as electrostatic collection.

  The output characteristic of the PM sensor 13 can be described as follows. The PM sensor 13 uses the fact that the resistance between the opposing electrodes 53 is changed by the PM collected by the sensor element 52, and the PM amount collected by the sensor element 52 ( An output corresponding to the integrated amount obtained by integrating the PM adhesion amount at each time point is generated. That is, the PM sensor 13 outputs a value according to the resistance value between the opposing electrodes 53 as the PM amount. In detail, the sensor output does not occur while the amount of PM collected on the sensor element 52 is small (strictly, an output smaller than a threshold output which can be regarded as rising of the sensor output is generated). Since the Soot component contained in PM is composed of carbon particles and has conductivity, when the amount of collected PM reaches a certain amount or more, the pair of opposite electrodes 53 conduct and the sensor output rises (threshold Output more than output occurs).

  After the rise of the sensor output, the resistance between the pair of opposing electrodes 53 decreases as the amount of collected PM increases, so the current flowing between the opposing electrodes 53, that is, the sensor output increases. The engine system 1 is provided with a detection unit 56 (see FIG. 3) for converting the current flowing between the counter electrodes 53 or the current into a voltage and detecting the voltage, and the measurement value of the detection unit 56 is a PM sensor It becomes 13 outputs. Note that, for example, a resistance value between a pair of opposing electrodes 53 may be measured as a value correlated to the current flowing between the opposing electrodes 53, and the resistance value may be used as an output of the PM sensor 13.

  In addition, the sensor element 52 is provided with a heater 54 for heating the sensor element 52. The heater 54 is used, for example, to burn off the PM collected by the sensor element 52 and regenerate the PM sensor 13. The heater 54 is provided, for example, on the surface of the sensor element 52 (insulator substrate) on which the counter electrode 53 is not provided or inside the sensor element 52. The heater 54 is made of, for example, a heating wire such as platinum (Pt). In the regeneration of the PM sensor 13, the temperature at which all the components (Soot component, SOF component, etc.) constituting the PM can be burned and removed, specifically, for example, a temperature of 600 ° C. or more (eg 700 ° C.) The heater 54 is controlled. The heater 54 is connected to the SCU 14. The sensor element 52 corresponds to the adherend in the present invention.

  Returning to the description of FIG. 1, the engine system 100 is provided with various sensors necessary for the operation of the engine 20 in addition to the PM sensor 13. Specifically, for example, an air flow meter 4 that detects the amount of air drawn into the cylinder 7, a rotation speed sensor 15 that detects the rotation speed of the engine 20 (for example, a crank angle sensor that detects a crank angle) An accelerator pedal sensor 24 for detecting an operation amount (depression amount) of an accelerator pedal for informing the vehicle side of a required torque is provided. Furthermore, an exhaust gas temperature sensor 21 for detecting the temperature of the exhaust gas is provided in the exhaust passage 23 downstream of the DPF 12. Detection signals from these sensors are input to the ECU 17.

  Further, the engine system 100 is provided with an EDU 16 (electronic drive device) that controls the injector 6. The EDU 16 drives the injector 6 so that fuel is injected under the injection conditions (injection timing, injection amount, etc.) instructed from the ECU 17.

  In addition, the engine system 100 is provided with a sensor control unit (SCU) 14. The SCU 14 has the voltage application circuit 55 and the detection unit 56 shown in FIG. 3, and controls the voltage application between the opposing electrodes 53 by the voltage application circuit 55, that is, controls the implementation of electrostatic collection or energizes the heater 54. It controls the operation of the PM sensor 13 such as control. When controlling the heater 54, the SCU 14 adjusts the current (energization amount) to be supplied to the heater 54 and the energization time. Further, the SCU 14 detects the current flowing between the counter electrodes 53 or the value correlated thereto by the detection unit 56. The SCU 14 and the ECU 17 are connected by a communication line such as CAN (Controller Area Network), and can communicate bi-directionally.

  The engine system 100 is provided with an ECU (Electronic Control Unit) 17 that controls the overall control of the engine system 100. The ECU 17 has a normal computer structure, and includes a CPU (not shown) that performs various calculations, and a memory 18 such as a ROM, a RAM, and a flash memory that stores various information. The ECU 17 detects the operating condition of the engine 20, for example, based on detection signals from the various sensors described above, calculates the optimal fuel injection amount, injection timing, injection pressure, etc. according to the operating condition, and injects fuel into the engine 20. Control. Furthermore, the ECU 17 executes a failure determination process of determining the presence or absence of a failure of the DPF 12 based on the detection value of the PM sensor 13. The details of the failure determination process will be described later. The memory 18 also stores various information such as control programs for processing executed by the ECU 17 (CPU) and related data shown in FIGS. 6 to 8 described later.

By the way, when PM is in coexistence with a specific gas, the PM burns off by the gas, and the output of the PM sensor 13 decreases. Here, FIG. 4 and FIG. 5 show that the PM sensor collects the NO, O ₂ and NO ₂ contained in the exhaust gas among the oxidizing gas (fuel supporting gas) containing oxygen atoms. The experimental results show that part of the PM that has been burned burns (oxidizes) and the output of the PM sensor decreases. FIG. 4 shows the power reduction rate of the PM sensor in the coexistence of NO, O ₂ or NO ₂ . The experimental conditions of FIG. 4 will be described. A PM sensor is installed in the environment of exhaust gas of the engine, and when the output of the PM sensor reaches a predetermined value, the PM sensor is brought to the electric furnace. After waiting for the output of the PM sensor to stabilize in a state held at 400 ° C. in an electric furnace, any one of NO, O ₂ , and NO ₂ is supplied as a combustion supporting gas, and the supply start After that, the output decrease rate of the PM sensor after a predetermined time has elapsed is confirmed. The power reduction rate is a reduction rate with respect to the output value of the PM sensor at the time of gas supply start. The concentration of the feed gas is 2000 ppm for NO, 20% for O ₂ and 500 ppm for NO ₂ . As shown in FIG. 4, the sensor output decreases in any of NO, O ₂ and NO ₂ . Also, the rate of decrease in sensor output differs depending on the gas type.

Further, FIG. 5 shows an experimental result different from FIG. 4, and CO ₂ generation corresponding to the combustion amount of PM collected by the PM sensor with respect to temperature in the coexistence of NO, O ₂ or NO ₂ It shows the change of quantity. To explain the experimental conditions of FIG. 5, the PM sensor which has collected a certain amount of PM is removed from the actual machine and brought to the electric furnace. Then, any one gas of NO, O ₂ , or NO ₂ is supplied into the electric furnace, and the temperature in the electric furnace is changed in the range of 0 ° C. to 800 ° C. at each temperature. Detect CO ₂ production. The CO ₂ generation amount, the feed gas (NO, _{O 2,} or NO ₂₎ and a CO ₂ generation amount generated by the PM is oxidized reaction, the feed gas of the PM trapped in the PM sensor It corresponds to the amount burned and removed by The concentration of the feed gas is 1% for NO, 10% for O ₂ and 1% for NO ₂ .

As shown in FIG. 5, the tendency of the change of the CO ₂ generation amount (PM combustion amount) to the temperature differs depending on the gas type. Specifically, when the feed gas is NO, the amount of CO ₂ generation decreases in the range of 0 ° C. to 400 ° C., and in the range of 400 ° C. or more, the amount of CO ₂ generation gradually as the temperature increases. It will increase.

When the supplied gas is NO _2, the amount of CO ₂ produced is small in the range of 0 ° C. to 200 ° C., and the amount of CO ₂ produced gradually increases as the temperature rises from around 200 ° C. Then, the CO ₂ production amount takes a peak value at a temperature around 400 ° C., and in a temperature range higher than that, the CO ₂ production amount gradually decreases as the temperature rises. Even at around 800 ° C., the amount of CO ₂ produced increases somewhat.

When the coexisting gas is O _2, the amount of CO ₂ generation is small in the range of 0 ° C. to 400 ° C., and the amount of CO ₂ generation rapidly increases from around 400 ° C., and CO ₂ around 650 ° C. The peak value of the amount of production is taken, and when the temperature at which the peak value is taken is exceeded, the amount of CO ₂ production decreases rapidly.

  In addition, the inventors of the present invention have confirmed that the amount of PM removed by combustion increases and the output reduction rate of the PM sensor increases as the concentration of the combustion supporting gas increases. Furthermore, even if the same type of gas, concentration, and temperature coexist, the inventor of the present invention increases the amount of PM removed by combustion as the coexistence time increases, and the output reduction rate of the PM sensor increases. Have confirmed that.

According to these experimental results, part of the PM collected by the PM sensor is burned and removed by the combustion supporting gas coexisting with PM, the output of the PM sensor decreases, and to what extent the output decreases. It can be seen that it varies with the type, concentration and temperature of the combustible gas. Based on this finding, the memory 18 of the ECU 17 stores the relationship data between the type, concentration, and temperature of the combustion supporting gas and the output correction value of the PM sensor, as shown in FIGS. Note that the related data may be stored in the memory of the SCU 14. The output correction value is a decrease in the sensor output O2 when a predetermined time has elapsed from the reference time with respect to the sensor output O1 at the reference time when the PM sensor in which PM is collected is placed in the coexistence of each combustion supporting gas It is a value corresponding to a ratio (= (O1-O2) / O1). In other words, the output correction value is the reduction ratio of the sensor output when each gas coexists at each concentration and temperature to the sensor output when each gas of NO, NO ₂ and O ₂ does not coexist Is a value corresponding to Each output correction value of FIGS. 6-8 is a value smaller than one.

6, during the NO coexist, shows the relationship data between the temperature and NO concentrations and output correction value A _NO. The decrease in the output of the PM sensor at the coexistence of the combustion supporting gas correlates with the amount by which the PM collected by the PM sensor is burned off by the combustion supporting gas. Therefore, the relationship between the output correction value A _NO and the temperature in FIG. 6 is the same as the relationship between the temperature in FIG. 5 and the CO ₂ generation amount when NO coexists. Further, at the same temperature, the output correction value _ANO is a larger value as the NO concentration is higher.

7, when NO ₂ coexist, shows the relationship data between the temperature and the NO ₂ concentration and the output correction value _{A NO2.} The relationship between the output correction value A _NO2 and the temperature in FIG. 7 is the same as the relationship between the temperature in FIG. 5 and the CO ₂ generation amount when NO ₂ coexists. Further, at the same temperature, the output correction value A _NO2 is a larger value as the NO ₂ concentration is higher.

8, the O ₂ when coexistence shows the relationship data between the temperature and the O ₂ concentration and the output correction value A _O2. The relationship between the output correction value A ₀₂ and the temperature in FIG. 8 is the same as the relationship between the temperature in FIG. 5 and the CO ₂ generation amount when O ₂ coexists. Further, at the same temperature, the output correction value A ₀₂ has a larger value as the O ₂ concentration is higher. Relational data in FIGS. 6 to 8 can be obtained by the same method as the experiment in FIGS. 4 and 5.

  Next, failure determination processing executed by the CPU of the ECU 17 will be described. FIG. 9 shows a flowchart of the failure determination process. In the process of FIG. 9, after the start of the engine 20, the drying judgment as to whether or not the exhaust pipe has been dried to the extent that the PM sensor 13 (especially the sensor element 52) does not get wet is established. 3), and the sensor regeneration for burning and removing the PM collected by the sensor element 52 is performed and then started. In the drying determination, for example, it is determined whether the temperature of the exhaust gas detected by the exhaust temperature sensor 21 is equal to or higher than a predetermined temperature (for example, 100 ° C.) at which dew condensation water disappears due to evaporation.

  When the process of FIG. 9 is started, the ECU 17 causes the SCU 14 to perform electrostatic collection of the PM sensor 13 (S1). Thereby, PM collection to the PM sensor 13 is started.

Next, the concentrations of NO, NO ₂ and O ₂ in the exhaust gas that has passed through the DPF 12 are detected (S 2). Since the composition in the exhaust gas changes depending on the operating conditions of the engine 20, the concentrations of NO, NO ₂ and O ₂ are estimated based on the operating conditions of the engine 20, for example. Specifically, under the same conditions as in the actual machine, relationship data between engine operating conditions and gas concentration downstream of the DPF are checked in advance and stored in the memory 18 for each gas type. Then, the engine operating condition of this time is acquired, and the gas concentration corresponding to the acquired operating condition is determined from the relational data. Specifically, the engine operating conditions are engine rotational speed, fuel injection conditions into the cylinder (fuel injection amount, injection timing, etc.), intake air amount, EGR rate (ratio of EGR amount to intake air amount), and the like. The engine speed is obtained by a speed sensor 15. The fuel injection condition may be a command value set by the ECU 17 based on the engine speed and the detected value of the accelerator pedal sensor 24 (engine load). Further, the amount of intake air can be obtained by the air flow meter 4. The EGR rate may be a target value set by the ECU 17 itself or the opening degree of the EGR valve 9 from the engine rotational speed, the engine load, and the like.

As shown in FIG. 1, a sensor 22 for detecting the concentration of the coexisting gas may be provided in the vicinity of the PM sensor 13 downstream of the DPF 12 and the gas concentration may be acquired from the sensor 22. As the sensor 22, in particular it can be used and NOx sensor for detecting the NOx concentration, the _{O 2} sensor for detecting the _{O 2} concentration (e.g., air-fuel ratio sensor). The concentration of some of the NO, NO ₂ and O ₂ may be estimated based on the engine operating conditions, and the concentration of the remaining gas may be obtained from a sensor. At this time, if the NOx sensor can not be detected by distinguishing between NO concentration and NO ₂ concentration is estimated from the engine operating conditions for NO concentration and NO ₂ concentration, O ₂ concentration may be obtained from the O ₂ sensor .

  Next, the temperature of the exhaust gas downstream of the DPF 12 is detected (S3). This temperature may be acquired from the exhaust temperature sensor 21 or may be estimated based on the operating conditions of the engine 20. When estimating the gas temperature from the engine operating conditions, the relationship data between the engine operating conditions (engine speed, engine load, etc.) and the gas temperature is stored in the memory 18, and the gas temperature corresponding to the current engine operating conditions is stored. Is determined from the related data. Further, the temperature of the sensor element 52 when the heating by the heater 54 is not performed becomes the same value as the temperature of the exhaust gas. Therefore, when the PM sensor 13 is provided with a temperature sensor that detects the temperature of the sensor element 52, the temperature of the exhaust gas may be estimated based on the detection value of the temperature sensor.

Next, SCU14 in by detecting the output _{E 1} of the PM sensor 13, acquires the output _{E 1} from SCU14 (S4).

Then, S2, S3 detects the gas species, based on the gas concentration and gas temperature, the sensor output E ₁ detected in S4, the correction in a direction to increase the PM amount (S5). Specifically, the output correction value A is calculated based on the gas type, the gas concentration, and the gas temperature detected in S2 and S3, and the relationship data of FIGS. 6 to 8 show the output correction values A _NO , A _NO2 and A _O2 for each gas type, but in S5, one of the output correction values A _NO , A _NO2 and A _O2 is reflected. A total correction value A is determined. For that purpose, for example, the relationship data (A = f (gas species, concentration, etc.) between the gas type, the gas concentration and the gas temperature, and the overall correction value A obtained in the memory 18 based on the relationship data of FIGS. Temperature) is stored, and a total correction value A is obtained based on the related data. The total correction value A can be, for example, a value obtained by adding the output correction values A _NO , A _NO2 , and A _O2 shown in FIGS.

Also, based on the respective relationship data in FIGS. 6 to 8, first, the output correction values A _NO , A _NO2 and A _O2 for each gas type are individually determined, and those output correction values A _NO , A _NO2 and A _O2 are _calculated . The overall correction value A may be determined by performing a predetermined operation (for example, addition).

The total correction value A determined is when NO, NO ₂ and O ₂ coexist at the concentration and temperature detected in S 2 and S 3 with respect to the sensor output when each gas of NO, NO ₂ and O ₂ does not coexist Is a value corresponding to the rate of decrease of the sensor output. Therefore, in S5, with the total correction value A, to correct the sensor output E ₁ so as to offset this reduction ratio. Specifically, E _{1 R} = (1 + A) × E ₁ is calculated, where the corrected sensor output is E _{1 R.}

  Here, FIG. 10 is a diagram showing a state of correction of S5, in which the sensor output with respect to the elapsed time (collection time) from the start of electrostatic collection is corrected (thick solid line) before correction (thin solid line) And solid lines). Further, FIG. 10 shows three different sensor outputs (1), (2), and (3) before correction and three sensor outputs after correction. As described above, by performing the correction of S5, the sensor output after the correction becomes a large value before the correction.

Then, on the basis of the sensor output _{E 1R} corrected, the failure determination of the DPF 12 (S6). Specifically, for example, it is determined whether or not the sensor output E _{1 R} after correction in the predetermined time is larger than a predetermined threshold K, for the elapsed time from the start of electrostatic collection. Also, for example, it may be determined whether the degree of change with time of sensor output _1R after output generation, that is, the slope of the sensor output line (thick solid line) after correction in FIG. 11 is larger than a predetermined threshold. .

If the sensor output _1R is larger than the threshold K (S6: YES), it is determined that the DPF 12 is not functioning normally, that is, the DPF 12 is malfunctioning (S7), assuming that the amount of PM flowing out of the DPF 12 is larger than expected. On the other hand, when the sensor output _1R is less than or equal to the threshold value K (S6: NO), it is determined that the DPF 12 is normal as the amount of PM flowing out of the DPF 12 is small (S8). In the example of FIG. 10, for example, the sensor outputs of (1) and (2) after correction are determined to be DPF failure, and the sensor output of (3) is determined to be DPF normal. After S7 and S8, the process of FIG. 9 is ended.

As described above, in the present embodiment, the sensor output is corrected in the direction of increasing the amount of PM according to the type, concentration, and temperature of the combustion supporting gas (NO, NO ₂ , O ₂ ). The output can be made close to the value before PM combustion by the coexisting gas is performed, and deterioration in detection accuracy of the PM amount due to the influence of the combustion supporting gas can be suppressed. Further, since the failure determination of the DPF is performed based on the sensor output after the correction, it is possible to suppress the decrease in the accuracy of the failure determination due to the influence of the combustion supporting gas.

Second Embodiment
Next, a second embodiment of the present invention will be described focusing on differences from the above embodiment. The configuration of the present embodiment is the same as that of FIG. The failure determination process executed by the ECU 17 is different from that of the above embodiment.

  First, the basic concept of the failure determination process of the present embodiment will be described with reference to FIG. FIG. 11 is a diagram showing a change in the output of the PM sensor 13 with respect to the time (collection time) from the start of the electrostatic collection. More specifically, the dashed-dotted line line in FIG. 11 indicates the estimated output value Ee of the PM sensor 13 when the DPF 12 is a filter (hereinafter referred to as a reference fault filter) serving as a reference for failure determination. The lines (1), (2) and (3) indicate actual output values of the PM sensor 13.

  In the present embodiment, in order to determine the failure of the DPF 12, the output value Ee of the PM sensor 13 in the case where the DPF 12 is a reference failure filter is estimated. Based on the comparison between the estimated output value Ee and the actual output value of the PM sensor 13, it is determined whether the DPF 12 has a failure. More specifically, the timing at which the estimated output value Ee reaches the predetermined threshold value K is determined as the failure determination timing, and the DPF failure is determined if the actual sensor output value at the failure determination timing is larger than the threshold K. Determine that DPF is normal. This means that if the actual sensor output value is larger than the estimated output value Ee, it is determined that the DPF failure, and if smaller than the estimated output value Ee, it is determined that the DPF is normal. In the example of FIG. 11, it is determined that DPF failure occurs when the actual output values are the lines (1) and (2), and DPF is determined normal when the line (3).

  The failure determination method described in FIG. 11 is the same as the method described in Japanese Patent No. 5115873. That is, the failure determination method of the present embodiment estimates the timing (reference timing) (corresponding to the failure determination timing in FIG. 11) in which the output of the PM sensor 13 rises when the DPF 12 is a reference failure filter. Then, it is determined that the DPF 12 is broken when the time when the output of the PM sensor 13 actually rises (actual time) is earlier than the reference time, and it is determined that the DPF 12 is normal in the latter case. means.

6 to 8 are stored in the memory 18 as in the first embodiment, but the output correction values A _NO , A _NO2 and A _O2 of this embodiment are units of sensor output The value is set to a value corresponding to the rate of decrease (degree of decrease) per time Δt seconds.

  Next, the details of the failure determination process of the present embodiment will be described. FIG. 12 shows a flowchart of failure determination processing of the present embodiment. The ECU 17 executes the process of FIG. 12 instead of the process of FIG. Similar to the process of FIG. 9, the process of FIG. 12 is started after the sensor regeneration is performed after the drying determination of the exhaust pipe is established.

When the process of FIG. 12 is started, first, an elapsed time t from the start of electrostatic collection is set to an initial value (= 0) (S11), and the SCU 14 is instructed to perform electrostatic collection (S12). ). Next, the elapsed time t is updated to a time (t = t + Δt) which has advanced by a predetermined unit time Δt seconds (S13). Next, in the same manner as S2 and S3 in FIG. 9, the concentrations of NO, NO ₂ and O ₂ in the exhaust gas having passed through the DPF 12 are detected (S14), and the temperature of the exhaust gas downstream of the DPF 12 is detected S15). The gas species, the gas concentration and the gas temperature detected here are the gas species, the gas concentration and the gas temperature at a unit time Δt based on the current time t.

Next, the environment of the detected gas type, gas concentration and gas temperature based on the gas type, gas concentration and gas temperature detected in S14 and S15, and the relationship data of FIGS. 6 to 8 stored in the memory 18 A correction value A (Δt) corresponding to the degree of decrease in output per unit time Δt of the PM sensor 13 in the lower part is calculated (S16). Here, as in the first embodiment, one total correction value A (= f (gas type, concentration, temperature)) reflecting all of the output correction values A _NO , A _NO2 and A _O2 for each gas type is _calculated . Ask. The total correction value A (Δt) can be, for example, a value obtained by adding the output correction values A _NO , A _NO2 , and A _O2 shown in FIGS.

Next, based on the operating conditions of the engine 20, the output change amounts E _{2 and Δt} per unit time Δt of the PM sensor 13 when the DPF 12 is the reference failure DPF are estimated (S17) (see also FIG. 11). Here, specifically, the reference failure DPF in the present embodiment is that the collection rate of the DPF 12 significantly decreases due to a failure, and the amount of PM passing through the DPF 12 is a self failure diagnosis (OBD: on-board-diagnostics). We say DPF, which is the amount equivalent to the regulation value. The OBD regulation value is set to a value larger than the EM regulation value (emission gas regulation value) such as EURO6. For example, when the PM amount in the EM restriction value = 4.5 mg / km in a specific traveling mode, the OBD restriction value is set to, for example, about 2.67 times the PM amount = 12.0 mg / km.

  In S17, specifically, first, based on the operating conditions of the engine 20, the amount f per unit time Δt is estimated based on the current time t of PM passing through the DPF 12 when the DPF 12 is the reference failure DPF. Do. Specifically, similarly to the method of Japanese Patent No. 5115873, the amount of PM per unit time discharged from the engine 20 based on the operating conditions of the engine 20 such as the rotation speed and load (fuel injection amount) of the engine 20 In other words, the amount of PM per unit time (the amount of inflow PM) flowing into the reference failure DPF is estimated. For example, a map of the inflow PM amount per unit time with respect to the operating conditions (rotation speed, load, etc.) of the engine 20 is stored in advance in the memory 18. Then, the inflow PM amount corresponding to the operating condition of the engine 20 at this time may be read out from the map.

  Also, the PM collection rate of the reference failure DPF is estimated. Specifically, for example, a predetermined value α is used as the PM collection rate of the reference failure DPF. Further, the PM collection rate of the DPF also changes depending on the amount of PM deposited in the DPF (PM deposition amount) and the exhaust flow rate, so the PM collection rate α according to the PM deposition amount and the exhaust flow rate You may correct it. The PM deposition amount may be estimated, for example, based on the differential pressure across the DPF 12. Further, the exhaust flow rate may be estimated based on, for example, the intake air amount detected by the air flow meter 4.

  Then, based on the estimated inflow PM amount and the PM collection rate of the reference failure DPF, the PM amount f (outflow PM amount) per unit time flowing out from the reference failure DPF is obtained.

Next, the amount of PM collected by the PM sensor 13 out of the obtained outflow PM amount f is estimated. Specifically, for example, of the PM flowing outside the PM sensor 13, how much PM penetrates into the cover 51 through the hole 511 (see FIG. 2), or how much PM out of the PM that has invaded inside the cover 51 The PM collection rate β to the PM sensor 13 is estimated in consideration of whether the sensor element 52 is attached to the sensor element 52 or the like. The PM collection rate β may use a predetermined predetermined value regardless of various conditions such as the exhaust gas flow rate, λ (excess air ratio), exhaust temperature, temperature of the sensor element 52, etc. The values corrected accordingly may be used. For example, as the exhaust gas flow rate is larger, PM is less likely to intrude into the cover 51, PM which has intruded into the cover 51 is less likely to adhere to the sensor element 52, and may easily detach from the sensor element 52 even if it adheres. Further, the smaller the λ, that is, the richer and the higher the PM concentration, the higher the proportion of PM not collected by the PM sensor 13. Therefore, for example, the PM collection rate β is estimated to be a smaller value as the exhaust gas flow rate is larger or as λ is smaller. Further, according to the temperature of the exhaust temperature and the sensor element 52, the heat swimming power which acts on the sensor element 52 is changed, PM collection efficiency β is varies. Then, the amount of PM collected by the PM sensor 13 is obtained based on the above-mentioned amount of flow-out PM f and the PM collection rate β. Since the output of the PM sensor 13 increases as the PM amount increases, the relationship between the PM amount and the output of the PM sensor 13 is checked in advance and stored in the memory 18. Then, based on this relationship and the amount of PM obtained this time, estimated values E _{2 and Δt of the} amount of change in output per unit time of the PM sensor 13 when the DPF 12 is the reference failure DPF are obtained.

Next, based on the correction value A (Δt) obtained in S16, the estimated values E2 _{and Δt} obtained in S17 are corrected in the direction to reduce the PM amount (S18). Specifically, E _{2 R, Δt} = (1−A (Δt)) × E _{2, Δt} is calculated _, assuming that the estimated value of the output change amount after correction is E _{2 R, Δt} .

Next, at the current time t, the output estimated value E _{2R, t} of the PM sensor 13 in the case where the DPF 12 is the reference failure DPF is determined (S19). Specifically, the estimated output value E _{2 R, t} is updated by adding the corrected estimated value E _{2 R, Δt} obtained in S18 this time to the estimated output value E _{2R, t} obtained in S19 of the previous time. That is, _{E2R, t} = _{E2R, t} + _{E2R,? T} are calculated.

Next, based on the output estimated values _{E2R and t} obtained in S19, it is determined whether the timing for determining the DPF failure (failure determination timing) has been reached (S20). Specifically, it is determined whether or not the output estimated value E _{2R, t} is larger than a predetermined threshold value K. The threshold value K is set to, for example, a value that can be regarded as the output of the PM sensor 13 has risen. In S20, it is synonymous with determining whether the timing at which the output of the PM sensor 13 rises in the case where the DPF 12 is a reference failure DPF has arrived.

If the failure determination timing has not been reached in S20, that is, if the output estimated value E _{2 R, t} is less than or equal to the threshold K (S20: NO), the process returns to S12. As described above, while the failure determination timing is not reached, the output change amount per unit time at each time of the PM sensor 13 is corrected based on the gas type, gas concentration and gas temperature at each time, and the output change after correction By integrating the amount over the elapsed time from the start of electrostatic collection, the output estimated value is corrected.

As a result, as shown in FIG. 13, the estimated output value E _{2 R} after correction becomes a smaller value than before correction, and as a result, the arrival of the failure determination timing becomes later than before correction.

If the failure determination timing arrives at S20, that is, if the output estimated value E _{2 R, t} exceeds the threshold K (S20: YES), the actual output E ₁ of the PM sensor 13 is acquired from the SCU 14 (S21) . As the sensor output E ₁ determines whether larger than the threshold K that is set to the same value as the threshold value K of S20 (S22). Then, when the sensor output _{E 1} is greater than the threshold value K (S22: YES), DPF12 determines that the PM trapping ability than a reference fault DPF is faulty DPF was reduced (S23). In contrast, if the sensor output _{E 1} is less than the threshold value K (S22: NO), DPF12 determines that the PM trapping ability than a reference fault DPF is a good normal DPF (S24). In the example of FIG. 13, at the failure determination timing (after correction), the sensor output is larger than the threshold K in the cases of (1) and (2), so it is determined that the DPF failure. In the case of (3), the sensor output is the threshold K Since it is smaller, it is determined that the DPF is normal. After S23 and S24, the process of FIG. 12 ends.

As described above, in this embodiment, the sensor output in the case of the reference failure DPF is estimated, and the failure determination of the DPF is performed based on the comparison between the estimated value and the actual sensor output. It can be determined with high accuracy whether it is high or low. In addition, since the estimated value of the sensor output is corrected in the direction to reduce the PM amount according to the type, concentration and temperature of the flame retardant gas (NO, NO ₂ , O ₂ ), the estimated value is It can be close to the value after PM combustion with gas, and the actual output value of the sensor can be compared with the estimated value in the state after combustion. As a result, the failure determination of the DPF can be performed in a form in which the influence of the combustion by the combustion supporting gas is suppressed, and the accuracy reduction of the failure determination can be suppressed. For example, in the example of FIG. 13, when the sensor output is (2), when carrying out the failure determination at the failure determination timing based on the estimated output value E ₂ before correction (pre-correction), the sensor output and the threshold value K is It becomes a close value, and there is a possibility that it is misjudged as normal despite the DPF failure. On the other hand, when the failure determination is performed at the failure determination timing (after correction) based on the estimated output value E _{2 R} after correction, the sensor output is clearly larger than the threshold K, so that the DPF failure can be determined with high accuracy.

  Furthermore, as correction of the estimated value of the sensor output, integration correction is performed by integrating each time correction based on concentration and temperature for each gas type at each time over the elapsed time from the start of electrostatic collection. It is possible to obtain highly accurate estimated values that reflect the gas species, gas concentration, and gas temperature at each time, and the elapsed time from the start of collection. Therefore, it is possible to further suppress the deterioration in the accuracy of the failure determination of the DPF.

Third Embodiment
Next, a third embodiment of the present invention will be described focusing on differences from the above embodiment. The configuration of the present embodiment is the same as that of FIG. The failure determination process executed by the ECU 17 is different from that of the above embodiment. In the second embodiment, the failure determination timing is corrected to a late timing as a result by correcting the estimated output value of the PM sensor, but in the present embodiment, the threshold compared with the estimated output value is corrected, As a result, the failure determination timing is corrected to a later timing.

  Further, also in the present embodiment, as in the second embodiment, the output correction value A in the relational data of FIGS. 6 to 8 stored in the memory 18 corresponds to the reduction rate per unit time Δt of sensor output. It is set to a value.

  The ECU 17 executes the processing of FIG. 14 as the failure determination processing of the DPF. The process of FIG. 14 is started after sensor regeneration is performed after the drying determination of the exhaust pipe is established as in the above embodiment. When the process of FIG. 14 is started, the same processes as the processes of S11 to S16 of FIG. 12 are executed (S31 to S36).

  Next, integrated correction value A (t) obtained by integrating correction value A (Δt) corresponding to the degree of decrease in output per unit time Δt of PM sensor 13 obtained by the processing of S36 of each time up to the current time t Is calculated (S37). Specifically, the integrated correction value A (t) is updated by adding the correction value A (Δt) obtained in the current S36 to the integrated correction value A (t) obtained in the previous S37. That is, A (t) = A (t) + A (Δt) is calculated.

Then, based on the operating conditions of the engine 20, estimates the output _{E 2} of the PM sensor 13 when DPF12 is the reference fault DPF (S38). In S17 of FIG. 12, the output change amounts E _{2 and Δt} per unit time Δt of the PM sensor 13 are estimated. Here, the output variation at each time in the same manner as S17 E _2, seeking _{Delta] t,} the output change amount E ₂ was _obtained, the integrated value obtained by integrating over the current time t from the start of the electrostatic trapping _{Delta] t,} the current It is estimated as the output E ₂ of the PM sensor 13 at time t.

Next, based on the integrated correction value A (t) obtained in S37, the threshold K (corresponding to the first threshold of the present invention) for determining the timing of the failure determination is corrected in the direction to increase the PM amount ( Corresponding to the first threshold value correction of the present invention) (S39). Specifically, K _R = (1 + A (t)) × K is calculated with the corrected threshold value as K _R.

Next, the estimated output _{E 2} obtained in S38, it is determined whether the threshold value _{K R} is greater than or not the corrected calculated in S39 (S40). Estimated output _{E 2} is the threshold value _K in the case of _R below (S40: NO), as yet not reached the failure determination timing, the flow returns to S32. As described above, while the failure determination timing is not reached, the integrated correction value A (t) gradually increases with the elapsed time, and as a result, the threshold value K _R gradually increases. Also, the estimated value of the sensor output E ₂ also gradually increases with the passage of time.

If the estimated output _{E 2} exceeds the threshold value _{K R} in S40 (S40: YES), the failure determination timing has reached, and acquires the actual output _{E 1} of the PM sensor 13 from SCU14 (S41). Next, the sensor output _{E 1} determines whether greater than a predetermined threshold value K (S42). The threshold value K is set to the same value as the threshold value K for determining the failure determination timing before the correction of S39 is performed. If the sensor output _{E 1} is greater than the threshold value K (S42: YES) determines DPF failure and (S43), in the case of less than the threshold value K (S42: NO) DPF normal and determining (S44). After S43 and S44, the process of FIG. 14 ends.

The failure determination process of the present embodiment will be described with reference to FIG. 15. The threshold value K for determining the failure determination timing is corrected to increase the PM amount based on the type, concentration, and temperature of the gas supporting gas. Then, the timing at which the estimated output value Ee exceeds the corrected threshold value K _R (fault diagnosis execution determination threshold value) is determined as a failure determination timing. Therefore, the failure determination timing can be made later than the failure determination timing when the threshold value K is not corrected. By delaying the failure determination timing, it is possible to increase the sensor output at the failure determination timing, and it is possible to suppress that the decrease in the sensor output due to the influence of the combustion supporting gas affects the failure determination of the DPF. For example, in the example of FIG. 15, when the sensor output is (2), if the failure determination is performed at the failure determination timing (before correction) based on the threshold K before correction, the sensor output and the threshold K are close to each other Therefore, there is a possibility that the DPF failure may be misjudged as normal despite being a failure. On the other hand, when carrying out the failure determination at the failure determination timing based on the threshold K _R after correction (corrected), the sensor output is greater than the obviously threshold K, it can determine DPF failure with high accuracy.

  In addition, as correction of threshold K, correction value per unit time based on concentration and temperature for each gas type at each time is integrated based on integrated correction value integrated over the elapsed time from the start of electrostatic collection. Since the correction of the threshold is performed, it is possible to reflect the gas type, the gas concentration, and the gas temperature at each time and the elapsed time from the start of collection on the corrected threshold. The failure determination timing is determined based on the corrected threshold value, and the failure determination is performed at the failure determination timing to determine the type of gas at each time, the gas concentration, and the gas temperature, and the collection start from the failure determination. And the elapsed time of Therefore, it is possible to obtain a highly accurate determination result in which the influence of the supporting gas is suppressed.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described focusing on differences from the above embodiment. The configuration of the present embodiment is the same as that of FIG. The failure determination process executed by the ECU 17 is different from that of the above embodiment.

The ECU 17 executes the process of FIG. 16 as the failure determination process of the DPF. The process of FIG. 16 is started after the sensor regeneration is performed after the drying determination of the exhaust pipe is established as in the above embodiment. Comparing the process of FIG. 16 with the process of FIG. 14, in the process of FIG. 16, the process corresponding to the process of S39 of FIG. 14 is omitted, and the process of FIG. It is different from Further, in the processing of S59, the output estimate E ₂ are compared with the threshold value K of the correction unexecuted. Further, in the processing of S62 is compared with the threshold value K _R and the corrected sensor output E _1. Other than that is the same as the processing of FIG. That is, the processes of S51 to S58 of FIG. 16 are the same as the processes of S31 to S38 of FIG. 14, the process of S60 is the same as the process of S41, and the processes of S63 and S64 are the same as the processes of S43 and S44. It is.

When the process is started in FIG. 16, similarly to the third embodiment calculates the cumulative correction value A (S51~S57), estimates the output _{E 2} of the PM sensor 13 in the case DPF12 is a reference fault DPF (S58), the estimated output value E ₂ determines whether exceeds a threshold value K (S59). If not exceeded (S59: NO), it returns to S52, and updates the cumulative correction value A and the estimated output value _{E 2 (S52~S58).}

If the estimated output value _{E 2} exceeds the threshold value K, that is, when it reaches the failure determination timing (S59: YES), then obtains the actual output _{E 1} of the PM sensor 13 from SCU14 (S60). Next, based on the integrated correction value A (t) obtained in S57, the failure determination threshold K (corresponding to the second threshold of the present invention) is corrected in a direction to reduce the PM amount (second threshold of the present invention Corresponding to the correction) (S61). Specifically, K _R = (1−A (t)) × K is calculated, where the corrected threshold is K _R.

Next, the sensor output _{E 1} to determine threshold _K or _R is larger than the corrected (S62). If the sensor output _{E 1} is greater than the threshold value _{K R} (S62: YES) determines DPF failure and (S63), in the case of less than the threshold value _{K R} (S62: NO) DPF normal and determining (S64). Thereafter, the process of FIG. 16 is ended.

In the third embodiment, while the threshold value for determining the failure determination timing (the threshold value to be compared with the estimated output value Ee) is corrected, in the present embodiment, as shown in FIG. The failure determination threshold value K is corrected to a value smaller by an amount of decrease in the output of the PM sensor due to the influence of the combustion supporting gas. As a result, it is possible to compare the sensor output with the failure determination threshold in the form of offsetting the decrease in the output, and to suppress the decrease in accuracy of the failure determination of the DPF. For example, in the example of FIG. 17, when the sensor output is (2), when the failure determination is performed with the threshold value K before correction, the sensor output and the threshold value K become close values, and the DPF failure is also caused. Regardless, there is a possibility that it may be misjudged as normal. On the other hand, when carrying out the failure determination at the threshold K _R after the correction, the sensor output is greater than the obviously threshold K _R, it can determine DPF failure with high accuracy.

Fifth Embodiment
Next, a fifth embodiment of the present invention will be described focusing on differences from the above embodiment. The configuration of the present embodiment is the same as that of FIG. The failure determination process executed by the ECU 17 is different from that of the above embodiment.

  The ECU 17 executes the process of FIG. 18 as the failure determination process of the DPF. The process of FIG. 18 is started after the sensor regeneration is performed after the drying determination of the exhaust pipe is established as in the above embodiment. Comparing the process of FIG. 18 with the process of FIG. 16, the process of FIG. 18 is different from the process of FIG. 16 in the processes of S81 and S82, and the process of FIG. 16 is otherwise (S71 to S80, S83, S84). (S51 to S60, S63, S64).

In the process of FIG. 18, when the failure determination timing has arrived (S 79: YES), the actual sensor output E ₁ is detected (S 80), and then the sensor output E ₁ is integrated correction value A (t (t Correction is performed to increase the amount of PM based on (S81). Specifically, E _{1 R} = (1 + A (t)) × E ₁ is calculated, where the corrected sensor output is E _{1 R.} Next, it is judged whether or not the sensor output E _{1 R} after correction is larger than the threshold K (S 82), and if larger (S 82: YES), it is judged as DPF failure (S 83). (S82: NO) It is determined that the DPF is normal (S84). Thereafter, the process of FIG. 18 ends.

  As described above, in the present embodiment, since the sensor output is corrected as in the first embodiment (see FIG. 19), the sensor output can be made close to the value before PM combustion by the combustion supporting gas, and before PM combustion. The sensor output and the failure determination threshold can be compared in the state of. As a result, the failure determination can be performed in the form of suppressing the influence of the PM combustion due to the combustion supporting gas, and the decrease in accuracy of the failure determination can be suppressed. FIG. 19 shows a state in which only the sensor output of (3) is corrected.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the claims. For example, in the above embodiment, correction of the sensor output etc. is carried out based on the concentrations of NO, NO ₂ and O ₂ as the combustion supporting gas, but any one or two of NO, NO ₂ and O ₂ The correction may be performed based on the gas concentration. Also by this, as compared with the case where correction is not performed, failure determination of the DPF can be performed in a form in which the influence of the gas supporting gas is suppressed, and degradation in accuracy of failure determination can be suppressed. In addition, the correction may be performed in consideration of the concentration of the combustion supporting gas (for example, sulfur oxides (SO _{2 and the} like)) other than NO, NO ₂ and O ₂ .

  Moreover, in the said embodiment, although PM sensor was used for the application of the failure detection of DPF, you may use PM sensor in applications other than failure detection. For example, a PM sensor may be disposed upstream of the DPF, and this PM sensor may be used for detecting the amount of PM discharged from the engine (the amount of PM flowing into the DPF). At this time, by correcting the sensor output according to the present invention, it is possible to detect the amount of PM before the PM combustion by the combustion supporting gas is performed with high accuracy.

  In the above embodiment, although the ECU executes the failure determination process, the SCU may execute the failure determination process, or the ECU executes a part of the process of the failure determination process. May be executed by the SCU.

  In the above embodiment, the PM sensor 13, the SCU 14 and the ECU 17 correspond to the filter failure detection device and the particulate matter detection device of the present invention. 9, FIG. 12, FIG. 14, FIG. 16, FIG. 18 execute the process of the concentration acquisition means, temperature acquisition means, correction means, failure judgment means, estimation means, timing judgment means, calculation means and integration of the present invention. It corresponds to the correction means.

12 DPF (filter)
13 PM sensor 14 SCU
17 ECU
20 engine (internal combustion engine)
23 Exhaust passage 52 Sensor element (adhered portion)

Claims (9)

An attached portion provided downstream of a filter (12) for collecting particulate matter in exhaust gas provided in an exhaust passage (23) of an internal combustion engine (20) and adhering the particulate matter in exhaust gas ( 52), and a sensor (13) for outputting a value corresponding to the amount of particulate matter attached to the attached portion;
Concentration acquisition means (S2, S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S3, S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas;
Correction means (S5, S76, S77) for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition means and the temperature acquired by the temperature acquisition means , S81, 17),
Failure determination means (S6 to S8, S82 to S84, 17) for performing failure determination of the filter based on the output value corrected by the correction means;
Equipped with
The apparatus for detecting a failure of a filter, wherein the concentration acquisition means acquires at least one concentration of NO, NO ₂ and O ₂ . An attached portion provided downstream of a filter (12) for collecting particulate matter in exhaust gas provided in an exhaust passage (23) of an internal combustion engine (20) and adhering the particulate matter in exhaust gas ( 52), and a sensor (13) for outputting a value corresponding to the amount of particulate matter attached to the attached portion;
Estimation means (S17, S38, S58, S78, 17) for estimating the output value of the sensor in the case where the filter is a filter serving as a reference for failure determination;
Failure determination means (S22 to S24, S42 to S44, S62 to S64, S82 to S84, 17) for determining the failure of the filter based on comparison between the value estimated by the estimation means and the actual output value of the sensor When,
Concentration acquisition means (S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas,
Output value correction for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition unit and the temperature acquired by the temperature acquisition unit, and the estimation unit Correction means (S16, S18, S19, S76, S77, S81, 17) for performing either of the estimated value correction for correcting the estimated value of P.sub.2 in the direction to reduce the amount of particulate matter.
Said failure determining means, have line failure determination of the filter by using a value corrected by the correction means,
The apparatus for detecting a failure of a filter, wherein the concentration acquisition means acquires at least one concentration of NO, NO ₂ and O ₂ . It comprises timing determination means (S20, S40, S59, S79, 17) for determining the timing when the estimated value of the estimation means reaches a predetermined first threshold value,
The failure determination means performs failure determination of the filter based on a comparison between an output value of the sensor at the timing determined by the timing determination means and a second threshold value having the same value as the first threshold value.
The correction means (S16, S18, S19, S36, S37, S39, S56, S57, S61, S76, S77, S81, 17) are the concentration acquired by the concentration acquisition unit and the temperature acquired by the temperature acquisition unit. Based on the output value correction, the estimated value correction, a first threshold value correction for correcting the first threshold value in a direction to increase the amount of particulate matter, and the second threshold value for particulate matter 3. The filter failure detection device according to claim 2, wherein any one of the second threshold value correction that corrects in the direction of decreasing the amount is performed. The concentration acquisition means (S14, S34, S54, S74, 17) and the temperature acquisition means (S15, S35, S55, S75, 17) acquire the concentration and the temperature at each time,
The correction means (S16, S18, S19, S36, S37, S39, S56, S57, S61, S76, S77, S81, 17) are the concentration and the temperature at each time, and the particles to the adherend portion The filter failure detection apparatus according to any one of claims 1 to 3, wherein the correction is performed in such a manner as to reflect an elapsed time from the start of the collection of the particulate matter. The correction means is
Calculation means for calculating a correction value corresponding to the change degree per unit time of the output value of the sensor due to combustion of the particulate matter by the gas supporting gas based on the concentration and the temperature for each time (S16 , S36, S56, S76, 17),
The amount of change per unit time of the correction target at each time is corrected based on the correction value, and the amount of change after the correction is integrated over the elapsed time from the start of collection to the adherend, or Integration correction means (S18, S19, S37, S39, S57, S61, S77, S81, S17, S17, S71, S81, S17) that perform integration correction that corrects the correction target value based on the integration correction value obtained by integrating the correction value over the elapsed time. The failure detection device for a filter according to claim 4 , characterized in that The concentration acquisition means specifies the type of the combustion supporting gas and acquires the concentration,
The correction means is related data of the type of the gas supporting gas, the concentration and the temperature, and the correction value corresponding to the change degree of the output value of the sensor due to the burning of the particulate matter by the gas supporting gas. The filter failure detection apparatus according to any one of claims 1 to 5, wherein the filter failure correction device performs correction based on the related data. The concentration acquisition means, and the operating conditions of the internal combustion engine has a relationship data between the concentration of combustion assisting gas, according to claim 1, wherein obtaining the concentration based on the relationship data The failure detection apparatus for a filter according to any one of the above. The filter failure detection according to any one of claims 1 to 7, wherein the concentration acquisition means acquires the concentration from a sensor (22) provided in the exhaust passage for detecting the concentration. apparatus. An attached portion (52) provided in the exhaust passage (23) of the internal combustion engine (20) to which particulate matter in the exhaust gas adheres, which corresponds to the amount of particulate matter attached to the adhered portion A sensor (13) that outputs a value,
Concentration acquisition means (S2, S14, S34, S54, S74, 17) for acquiring the concentration of the combustion supporting gas coexisting with the particulate matter in the exhaust gas;
Temperature acquisition means (S3, S15, S35, S55, S75, 17) for acquiring the temperature of the exhaust gas;
Correction means (S5, S76, S77) for correcting the output value of the sensor in the direction of increasing the amount of particulate matter based on the concentration acquired by the concentration acquisition means and the temperature acquired by the temperature acquisition means , S81, 17),
Equipped with
The particulate matter detection device according to claim 1 , wherein the concentration acquisition unit acquires the concentration of at least one of NO, NO ₂ and O ₂ .

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