JP6172466B2 - Filter failure detection device and 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 particulate matter.

  Conventionally, there has been proposed a filter failure detection device that collects particulate matter (particulate matter, PM) in exhaust gas discharged from an internal combustion engine (see, for example, Patent Document 1). In the failure detection device of Patent Literature 1, a failure of a filter is detected using an electric resistance sensor that generates an output corresponding to the amount of particulate matter in exhaust gas. The electric resistance type sensor includes an insulating element having a pair of electrodes, and is used in such a manner that a voltage is applied between the pair of electrodes. Since the particulate matter is mainly composed of a conductive soot component (soot), when a certain amount or more of particulate matter is collected in the element, the pair of electrodes become conductive. The detection value corresponding to the amount of the substance is output.

  In the failure detection device of Patent Document 1, this sensor is arranged downstream of the filter, and the presence or absence of a filter failure is determined based on the timing when the sensor output rises (conduction start timing). Specifically, the time (reference time) when the sensor output rises when the filter is a failure filter serving as a criterion for failure determination is estimated. Then, the time when the sensor output actually rises (actual time) is compared with the reference time, and when the actual time is earlier than the reference time, it is determined that the filter is faulty.

Japanese Patent No. 5115873

  By the way, in addition to the soot component, the particulate matter has a low conductivity component (low conductivity) such as an unburned fuel, an organic solvent soluble component (SOF) such as oil, or a sulfate (sulfide). Ingredients) are also included. However, what can be detected by an electric resistance type sensor is mainly a soot component having high conductivity, and a low conductivity component is difficult to detect. Therefore, since the amount detected by the sensor is a part (mainly the amount of soot components) of the particulate matter amount, it may not be possible to accurately detect a DPF failure.

  In addition, when a low-conductivity component is collected by the sensor, the low-conductivity component inhibits the conduction of the Soot component, which may reduce the detection sensitivity of the sensor. When the detection sensitivity of the sensor is lowered, a filter failure cannot be detected accurately. Further, since the SOF component of the low-conductivity component is highly sticky, the stickiness makes it difficult for the particulate matter to move on the sensor element, and the sensor detection sensitivity varies depending on the ratio of the SOF component. Particulate matter may not be successfully collected between the electrodes. This also lowers the detection sensitivity of the sensor and makes it impossible to accurately detect a filter failure.

  The present invention has been made in view of the above circumstances, and provides a filter failure detection device capable of accurately detecting a filter failure by considering the presence of a low-conductivity component when detecting a filter failure. Is an issue. It is another object of the present invention to provide a particulate matter detection device that can prevent the detection sensitivity of a sensor from varying or decreasing due to the presence of a low-conductivity component.

In order to solve the above problems, a filter failure detection device of the present invention is provided in an exhaust passage of an internal combustion engine, and a filter that collects particulate matter in exhaust gas,
An insulating element having a pair of electrodes, which is provided downstream of the filter in the exhaust passage and collects particulate matter in the exhaust gas, and is collected by the element during conduction between the pair of electrodes; A sensor that generates an output in accordance with the amount of particulate matter produced,
A failure determination means for determining the presence or absence of a failure of the filter based on a soot amount output that is an output of the sensor in a state where a soot component of the particulate matter is collected by the element;
When the failure determination means determines the presence or absence of a failure of the filter, the soot component is allowed to remain in the element, and a low conductivity component having lower conductivity than the soot component remains in the element. Collection control means for controlling to suppress this,
It is characterized by providing.

  According to the present invention, the soot component is allowed to remain in the sensor element when the collection control means determines the presence or absence of a filter failure, while the residual low conductivity component is suppressed. It is possible to prevent variation and decrease in detection sensitivity of the sensor. Therefore, it is possible to detect the filter failure more accurately than in the case where the presence or absence of the filter failure is determined in a state where the low conductivity component is allowed to remain.

Further, the filter failure detection device of the present invention is provided in the exhaust passage of the internal combustion engine, a filter for collecting particulate matter in the exhaust gas,
An insulating element having a pair of electrodes, which is provided downstream of the filter in the exhaust passage and collects particulate matter in the exhaust gas, and is collected by the element during conduction between the pair of electrodes; A sensor that generates an output in accordance with the amount of particulate matter produced,
Output estimating means for estimating the output of the sensor when the filter is a filter that is a criterion for failure determination based on the operating state of the internal combustion engine;
Comparing and determining means for determining the presence or absence of a failure of the filter based on a comparison between the threshold and the actual output of the sensor with the output estimated by the output estimating means as a threshold;
The output estimation means calculates the collected soot amount, which is the amount of the soot component of the particulate matter collected by the element, when the filter is a filter that serves as a criterion for failure determination, as an operating state of the internal combustion engine. And a soot amount estimating means for estimating the threshold based on the collected soot amount.

  According to the present invention, since the threshold value for determining the failure of the filter is estimated based on the collected soot amount, it is possible to obtain a threshold value corresponding to the amount of the soot component excluding the influence of the low conductivity component. Further, the actual sensor output is a value corresponding to the amount of the soot component having high conductivity. That is, the failure determination threshold value and the actual sensor output can be aligned with a value corresponding to the amount of the Soot component. Therefore, since the filter failure is determined by comparing these, the filter failure can be accurately detected.

A particulate matter detection device according to the present invention includes an insulating element having a pair of electrodes, which is provided in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas, and between the pair of electrodes. A sensor that generates an output in accordance with the amount of particulate matter collected by the element during conduction;
The soot component of particulate matter is allowed to be collected by the element, and the collection control is performed so as to prohibit the low conductive component having lower conductivity than the soot component from being collected by the element. Collection control means;
It is characterized by providing.

  According to the present invention, the collection control means allows the soot component to be collected in the sensor element, while the collection of the low-conductivity component is prohibited. Can be prevented.

It is a block diagram of an engine system. It is the figure which showed the structure of PM sensor typically. FIG. 4 is a diagram illustrating a state in the vicinity of a pair of electrodes in a sensor element and explaining a principle of detection of a PM amount by a PM sensor. It is a schematic diagram of the component structure of PM. It is a flowchart of a failure determination process. It is the figure which showed the time change of the various states relevant to a failure determination process. It is the figure which illustrated how the ratio of a Soot component and the ratio of a SOF component changed with respect to the change of cooling water temperature or exhaust temperature. It is the figure which showed the mode of the PM collection state in PM sensor in SOF regeneration control.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a vehicle engine system 1 to which the present invention is applied. The engine system 1 corresponds to a “filter failure detection device” of the present invention. The engine system 1 includes a diesel engine 2 (hereinafter simply referred to as an engine) as an internal combustion engine. The engine 2 is provided with an injector that injects fuel into the combustion chamber. The engine 2 generates power for driving the vehicle by the fuel injected from the injector self-igniting in the combustion chamber.

  A diesel particulate filter (DPF) 4 as a “filter” of the present invention is installed in the exhaust passage 3 of the engine 2. The DPF 4 is a ceramic filter having a known structure. For example, heat resistant ceramics such as cordierite is formed into a honeycomb structure so that a large number of cells serving as gas flow paths are staggered on the inlet side or the outlet side. Contained and configured. Exhaust gas discharged from the engine 2 flows downstream while passing through the porous partition walls of the DPF 4, and PM (particulate matter, particulate matter) contained in the exhaust gas is collected and gradually accumulated.

  An electrical resistance PM sensor 5 as a “sensor” of the present invention for detecting the amount of PM in the exhaust gas is provided downstream of the DPF 4 in the exhaust passage 3. Here, FIG. 2 is a diagram schematically showing the structure of the PM sensor 5. As shown in FIG. 2, the PM sensor 5 includes, for example, a metal cover 51 whose inside is hollow, and a sensor element 52 disposed in the cover 51. A number of holes 511 are formed in the cover 51, and a part of the exhaust gas flowing through the exhaust passage 3 can enter the cover 51 from the holes 511. Further, the cover 51 is formed with a discharge hole 512 for discharging the exhaust gas that has entered the cover 51. FIG. 2 shows an example in which the discharge hole 512 is formed at the tip of the cover 51.

  The sensor element 52 is composed of an insulating substrate. On one surface of the sensor element 52 (insulator substrate), a pair of electrodes 53 spaced apart from each other and facing each other are provided. FIG. 3 is a diagram for explaining the principle of detection of the PM amount by the PM sensor 5 and shows the state of PM adhesion in the vicinity of the pair of electrodes 53. As shown in FIG. 3, the sensor element 52 is connected to a voltage application circuit 54 that applies a predetermined DC voltage between a pair of electrodes 53 based on a command from the ECU 6 described later. Part of the PM in the exhaust gas that has entered the cover 51 is collected (attached) to the sensor element 52 due to its own adhesiveness. PM that has not been collected by the sensor element 52 is discharged from the discharge hole 512.

  Further, when a voltage is applied between the electrodes 53 by the voltage application circuit 54, each electrode 53 is charged positively and negatively, respectively. Thereby, PM passing through the vicinity of the electrode 53 is charged, and collection into the sensor element 52 is promoted. In the present embodiment, the amount of PM trapped in the sensor element 52 when no voltage is applied between the electrodes 53 is assumed to be negligibly small compared to when a voltage is applied. Hereinafter, PM collection on the sensor element 52 by applying a voltage between the electrodes 53 is referred to as “electrostatic collection”.

  The output characteristics of the PM sensor 5 will be described. The PM sensor 5 uses the fact that the resistance between the electrodes 53 is changed by the PM collected by the sensor element 52, and according to the amount of PM collected by the sensor element 52. Output. Specifically, the sensor output does not occur while the amount of PM trapped in the sensor element 52 is small (strictly, only an output smaller than a threshold output that can be regarded as the sensor output rising) is generated. Since the soot component contained in the PM is composed of carbon particles and has high conductivity, when the amount of collected PM becomes a certain amount or more, the pair of electrodes 53 conducts and the sensor output rises (threshold value) Output more than output).

  After the sensor output rises, the resistance between the pair of electrodes 53 decreases as the amount of collected PM increases, so that the current flowing between the electrodes 53, that is, the sensor output increases. The engine system 1 is provided with an ammeter 55 (see FIG. 3) that measures the current flowing between the electrodes 53, and the measured value of the ammeter 55 becomes the output of the PM sensor 5.

  As shown in FIG. 2, the sensor element 52 is provided with a heater 56 that heats the sensor element 52 in order to regenerate the PM sensor 5 by burning and removing the PM collected by the sensor element 52. . The heater 56 is provided on the surface where the electrode 53 of the sensor element 52 (insulator substrate) is not provided, for example. The heater 56 is composed of a heating wire such as platinum (Pt). In the regeneration of the PM sensor 5, it is necessary to heat the sensor element 52 so as to reach a temperature at which all the components (Soot component, SOF component, etc.) constituting the PM can be burned and removed. The SOF component burns at 200 to 300 ° C or higher, while the Soot component burns at 500 to 600 ° C or higher. Therefore, the heater 56 heats the sensor element 52 to a temperature of 500 to 600 ° C. or higher (for example, about 700 ° C.) when the PM sensor 5 is regenerated. The heater 56 corresponds to the “heating means” of the present invention.

  Returning to the description of FIG. 1, the engine system 1 is provided with various sensors necessary for the operation of the engine 2 in addition to the PM sensor 5. Specifically, for example, a rotational speed sensor 71 that detects the rotational speed of the engine 2, an accelerator pedal sensor 72 that detects an operation amount (depression amount) of an accelerator pedal for notifying the vehicle side of the torque required by the driver of the vehicle, An exhaust temperature sensor 73 for detecting the temperature of exhaust gas (exhaust temperature), an air flow meter 74 for detecting the amount of fresh air sucked into the engine 2, a water temperature sensor 75 for detecting the temperature of cooling water for cooling the engine 2, and the like. Is provided.

  The engine system 1 also includes an ECU 6 that controls the entire engine system 1. The ECU 6 has a normal computer structure, and includes a CPU (not shown) for performing various calculations and a memory 61 for storing various information. The ECU 6 detects the operating state of the engine 2 based on detection signals from the various sensors, for example, calculates the optimal fuel injection amount, injection timing, injection pressure, etc. according to the operating state, and injects fuel into the engine 2. To control.

  Further, the ECU 6 executes a failure determination process for determining whether or not the DPF 4 has failed based on the detection value of the PM sensor 5. Here, as described above in the section “Problems to be Solved by the Invention”, the failure detection of the DPF 4 using the PM sensor 5 has the following problems. FIG. 4 is a schematic diagram of the component composition of PM, but as shown in FIG. 4, PM is mainly composed of a soot component, an SOF component, and a sulfate component that constitute the soot. The SOF component is a fuel or lubricating oil discharged without being burned alone or impregnated with a Soot component. The sulfate component is a product in which the oxidation product (sulfide) of the sulfur content in the fuel dissolves in the moisture in the exhaust gas and is atomized.

  While the Soot component has high conductivity, the SOF component and the sulfate component have low conductivity. Therefore, what can be detected by the PM sensor 5 is mainly a soot component having high conductivity, and it is difficult to detect the SOF component and the sulfate component. That is, the PM amount detected by the PM sensor 5 is a part rather than all of the PM amount collected by the PM sensor 5. Further, since the SOF component and the sulfate component collected by the PM sensor 5 act in the direction of inhibiting the conduction of the soot component (conduction between the pair of electrodes 53), the detection sensitivity of the PM sensor 5 is lowered, that is, a trace amount. The amount of PM cannot be detected. Further, the SOF component makes the PM difficult to move on the sensor element 52 due to its strong adhesiveness, and prevents the PM from being aligned between the pair of electrodes 53 during electrostatic collection. This also decreases the detection sensitivity of the PM sensor 5, and the detection sensitivity varies depending on the ratio of the SOF component.

  As described above, the PM amount detected by the PM sensor 5 is a part rather than all of the collected PM amount, and the detection sensitivity of the PM sensor 5 decreases due to the presence of the SOF component and the sulfate component. Because of the variation, there is a possibility that the presence or absence of the failure of the DPF 4 cannot be accurately determined. The ratio of the soot component, the SOF component, and the sulfate component in the PM varies depending on the operating state of the engine 2, but the soot component is 60% to 100%, the SOF component is 0% to 35%, and the sulfate component is about 5%. It is. Thus, while the SOF component increases to a rate that cannot be ignored depending on the operating state, the sulfate component is a small rate that hardly affects the output of the PM sensor 5. Therefore, in the failure determination process by the ECU 6, the failure determination of the DPF 4 is performed after excluding the influence of the SOF component even among the low conductivity components having lower conductivity than the Soot component. Hereinafter, details of the failure determination process will be described. In the failure determination process described below, the PM is assumed to be composed of a soot component and an SOF component.

  FIG. 5 shows a flowchart of the failure determination process. FIG. 6 shows time changes of various states related to the failure determination processing. Specifically, from the top, the vehicle speed pattern (time elapse) in the authentication mode whether or not the vehicle satisfies the exhaust gas regulations is shown from above. The change in the output of the PM sensor 5 over time, the on / off change in electrostatic collection over time, and the on / off change of the heater 56 over time. The second stage from the top of FIG. 6 shows the output change 101 when the DPF 4 is faulty and the output change 102 when the DPF 4 is normal as changes in the output of the PM sensor 5.

  The failure determination process in FIG. 5 starts after the preparation period shown in the second row in FIG. 6 has elapsed, for example, in the authentication mode indicated by the vehicle speed pattern in the uppermost row in FIG. The preparation period includes a period of waiting until moisture in the exhaust gas decreases to prevent the PM sensor 5 from getting wet (a wet prevention period), and a period of regenerating the PM sensor 5 by the heater 56 (heater regeneration period). , And the period of waiting until the PM sensor 5 that has become high temperature due to sensor regeneration cools (sensor cooling period). In the preparation period, no voltage is applied between the electrodes 53 yet. Note that the failure determination process may be executed at any time other than during the authentication mode, and specifically, may be executed during normal travel.

  When the process of FIG. 5 starts, the ECU 6 first determines whether or not a collection permission condition that is set in advance as a condition for permitting the implementation of electrostatic collection is satisfied (S1). Specifically, the collection permission condition is an operation state of the engine 2 in which almost no SOF component is generated, that is, an operation state of the engine 2 in which the proportion of the Soot component in PM is close to 100% (non-occurrence operation state). Is set. Even if the SOF component is generated in the combustion chamber of the engine 2, it is oxidized at 200 to 300 ° C. or higher. Therefore, the collection permission condition (non-occurring operation state) is set to, for example, a predetermined temperature or higher (for example, 250 ° C. or higher) at which the SOF component is oxidized and removed. The exhaust temperature can be obtained from the exhaust temperature sensor 73.

  When the exhaust temperature is lower than the predetermined temperature (S1: No), the electrostatic collection is stopped because the collection permission condition is not satisfied (S2). That is, voltage application between the pair of electrodes 53 is turned off. As a result, PM containing the SOF component can be prevented from being collected by the PM sensor 5. In other words, it is possible to suppress the SOF component from remaining in the PM sensor 5 (sensor element 52) when determining whether or not the DPF 4 has failed in S9 to S11 described later. Further, in S2, the PM sensor 5 is regenerated by controlling the heater 56 so that the sensor element 52 is heated to a predetermined regeneration temperature (for example, 700 ° C.) after the electrostatic collection is stopped. As a result, a small amount of PM that has been collected while electrostatic collection is stopped can be removed from the sensor element 52, and the failure determination of the DPF 4 can be performed accurately in the processing after S3. After S2, the process returns to S1.

  On the other hand, when the exhaust temperature is equal to or higher than the predetermined temperature (S1: Yes), electrostatic collection is started assuming that the collection permission condition is satisfied (S3). That is, a predetermined voltage is applied between the pair of electrodes 53 by the voltage application circuit 54 (see FIG. 3). As a result, PM containing almost no SOF component, that is, PM with a proportion of the Soot component≈100% can be collected on the sensor element 52. In addition, ECU6 which performs the process of S1-S3 corresponds to the "collection control means" of this invention. The ECU 6 that executes the process of S1 corresponds to the “state determination means” of the present invention. The ECU 6 that executes the processes of S2 and S3 corresponds to the “execution control means” of the present invention.

  Next, based on the state of the engine 2, the PM amount (PM trapping amount) A collected by the PM sensor 5 when the DPF 4 is the reference failure DPF is estimated (S4). Note that the reference failure DPF in the present embodiment specifically means that the collection rate of the DPF 4 is significantly reduced due to the failure, and the amount of PM passing through the DPF 4 is regulated by self-failure diagnosis (OBD). The DPF is an amount corresponding to the value. The OBD regulation value is set to a value larger than the EM regulation value (exhaust gas regulation value) such as EURO6. For example, in a specific travel mode, when the PM amount in the EM regulation value = 4.5 mg / km, the OBD regulation value is set to, for example, about 2.67 times the PM amount = 12.0 mg / km.

  In S4, specifically, similarly to Patent Document 1, the amount of PM discharged from the engine 2 based on the state of the engine 2 such as the rotational speed and torque (fuel injection amount) of the engine 2, in other words, the reference failure The amount of PM flowing into the DPF (inflow PM amount) is estimated. The rotational speed of the engine 2 is obtained from the rotational speed sensor 71. The torque (fuel injection amount) is obtained from the detection value of the accelerator pedal sensor 72, the engine speed, and the like. A map of the inflow PM amount with respect to the state of the engine 2 (revolution, torque, etc.) is stored in advance in the memory 61 (see FIG. 1). Then, the inflow PM amount corresponding to the current state of the engine 2 may be read from the map.

  In addition, 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, since the PM collection rate of the DPF also varies depending on the amount of PM accumulated in the DPF (PM accumulation amount) and the exhaust gas flow rate, the PM collection rate depends on the PM accumulation amount and the exhaust gas flow rate. The rate α may be corrected. Note that the PM accumulation amount may be estimated based on, for example, the differential pressure across the DPF 4. Further, the exhaust gas flow rate may be estimated as the volume flow rate of the exhaust gas based on, for example, the amount of fresh air detected by the air flow meter 74 (see FIG. 1). At this time, the exhaust gas expansion corresponding to the exhaust temperature detected by the exhaust temperature sensor 73 (see FIG. 1) and the exhaust gas compression corresponding to the pressure detected by the pressure sensor (not shown) are taken into consideration. To estimate the exhaust gas flow rate.

Then, based on the estimated inflow PM amount and the PM collection rate of the reference failure DPF, the PM amount flowing out from the reference failure DPF (outflow PM amount) is obtained. Next, the PM amount collected by the PM sensor 5 in the outflow PM amount is estimated as the PM collection amount A per unit time. Specifically, for example, how much of the PM flowing outside the PM sensor 5 enters the cover 51 from the hole 511 (see FIG. 2), or how much PM of the PM that has entered the cover 51 The PM collection rate β to the PM sensor 5 is estimated in consideration of whether the sensor element 52 is attached to the sensor element 52 or the like. As the PM collection rate β, a constant predetermined value may be used regardless of various states such as the exhaust gas flow rate, λ (excess air ratio), the exhaust temperature, the temperature of the sensor element 52, and the like. A value corrected accordingly may be used. For example, the larger the exhaust gas flow rate, the more difficult it is for PM to enter the cover 51, and PM that has entered the cover 51 is less likely to adhere to the sensor element 52, and even if it adheres, it is likely to be detached from the sensor element 52. Further, the smaller λ is, that is, the richer the PM concentration becomes, the higher the ratio of PM not collected by the PM sensor 5 becomes. Therefore, for example, the PM collection rate β is estimated such that the larger the exhaust gas flow rate or the smaller λ, the smaller the value. 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. Based on the outflow PM amount and the PM collection rate β, the PM collection amount A per unit time can be obtained.

  Λ may be estimated from, for example, the operating state of the engine 2 (engine speed, fuel injection amount, etc.), or a sensor for detecting λ may be provided in the exhaust passage 3 and the detection value of that sensor may be used. good. The exhaust temperature is obtained from the exhaust temperature sensor 73. Further, the temperature of the sensor element 52 may be, for example, a temperature sensor provided in the sensor element 52 and the detection value of the temperature sensor used.

  Thus, the PM collection amount A is the exhaust gas for correcting the basic collection amount a1 determined from the basic operating state (engine speed, torque, etc.) of the engine 2 and the basic collection amount a1. (Corrected collection amount a2 (correction coefficient)) determined from the state (exhaust gas flow rate, λ, exhaust temperature, etc.).

  Next, a ratio B (hereinafter referred to as a soot ratio) occupied by the soot component in the PM amount per unit time discharged from the engine 2 is estimated (S5). Specifically, since the soot ratio B changes depending on the combustion state in the engine 2 (the operating state of the engine 2), in S5, the soot ratio B is estimated based on the current combustion state. Since the fuel injection amount and the air system control value (intake air amount, EGR amount, etc.) are determined by the rotational speed of the engine 2 and the required torque, the basic combustion state is determined. The basic combustion state varies depending on environmental conditions such as the temperature of cooling water (cooling water temperature) for cooling the engine 2 and the exhaust gas temperature.

  Therefore, in S5, for example, a basic soot ratio b1 (basic soot ratio) is first obtained based on the rotational speed of the engine 2 and the required torque. Specifically, a map of the basic soot ratio b1 with respect to the rotation speed of the engine 2 and the required torque is stored in the memory 61 in advance. And the basic soot ratio b1 corresponding to the current state of the engine 2 is read from the map. Thereafter, the basic soot ratio b1 is corrected according to environmental conditions (cooling water temperature, exhaust temperature, etc.). Specifically, for example, a coefficient b2 (correction coefficient) for correcting the basic soot ratio b1 with respect to the environmental condition is set.

  Here, FIG. 7 is a diagram for explaining an example of the concept of the correction coefficient b2 with respect to the cooling water temperature and the exhaust gas temperature. Specifically, how the soot ratio and the SOF component ratio are changed with respect to the change in the cooling water temperature or the exhaust gas temperature. It is illustrated how it changes. As the cooling water temperature and the exhaust gas temperature are higher, the combustion in the combustion chamber is effectively performed, so the amount of unburned fuel discharged from the engine 2 is reduced. Therefore, in FIG. 7, the higher the cooling water temperature or the exhaust gas temperature, the smaller the ratio of the SOF component due to unburned fuel. When the ratio of the SOF component is decreased, the soot ratio is relatively increased. Therefore, the correction coefficient b2 is set so as to increase as the cooling water temperature or the exhaust gas temperature increases, for example. Thereafter, the soot ratio B is obtained by multiplying the basic soot ratio b1 by the correction coefficient b2.

  The relationship in FIG. 7 is a simplified example for explanation, and the combustion state changes depending on conditions other than the cooling water temperature or the exhaust temperature (pressure in the combustion chamber, etc.). Even if it becomes higher, the soot ratio does not necessarily increase depending on other conditions. In S5, more accurate correction coefficient b2 can be obtained by considering as many conditions as possible among various conditions (engine speed, required torque, cooling water temperature, exhaust temperature, pressure, etc.) that affect the combustion state. As a result, a more accurate soot ratio can be obtained.

  Next, the cumulative amount C of the Soot component collected by the PM sensor 5 when the DPF 4 is the reference failure DPF (hereinafter referred to as the collected soot amount) is estimated (S6). Specifically, first, the amount of soot components per unit time collected by the PM sensor 5 at the present time is multiplied by multiplying the PM collection amount A estimated in S4 by the soot ratio B estimated in S5 (= A × B) is obtained. Next, by adding the amount of the soot component per unit time to the collected soot amount C (i−1) at the previous time obtained in the previous S6, the currently collected soot amount C is obtained. Ask.

  Next, SOF regeneration control is performed to control the heater 56 so as to heat the sensor element 52 at a temperature at which the SOF component burns but the Soot component does not burn (S7). Specifically, as described above, the SOF component burns at 200 to 300 ° C. or higher, whereas the Soot component does not burn unless it is 500 to 600 ° C. or higher. Therefore, in the SOF regeneration control, the sensor element 52 is heated at a temperature of 200 to 300 ° C. or more and less than 500 to 600 ° C. (for example, about 300 ° C., hereinafter referred to as SOF regeneration temperature). Thus, the SOF component can be excluded from the PM collected by the PM sensor 5. In other words, only the Soot component can be collected by the PM sensor 5, and the SOF component can be prevented from remaining in the PM sensor 5 (sensor element 52) when determining whether or not the DPF 4 has failed.

Further, the SOF regeneration control, at all times, when you turn on the heater 56, since the sensor element 52 is to be heated constantly SOF regeneration temperature, the frequency of acts heat swimming power away from the sensor element 52 increases, PM trapping efficiency of the PM sensor 5 is lowered by the influence of the thermal swimming power. Therefore, in the SOF regeneration control, a period 103 (see the lowermost stage in FIG. 6) for turning off the heater 56 is provided. Then, by performing electrostatic collection in the off period 103 (see the third stage in FIG. 6), PM is once collected in a form that allows the PM sensor 5 to collect SOF components. FIG. 8 shows a state of PM collection by the PM sensor 5 in the SOF regeneration control, and shows a state in the off period 103 on the left side of FIG. Thereafter, the heater 56 is turned on to provide a period 104 (see the lowermost stage in FIG. 6) for heating the sensor element 52 to the SOF regeneration temperature, and the SOF component collected by the PM sensor 5 is combusted during the heating period 104. Remove. A state in the heating period 104 is shown in the middle of FIG. Thereby, only the Soot component can be collected efficiently. In the present embodiment, electrostatic collection is stopped during the heating period 104 (see the third stage in FIG. 6), but electrostatic collection may be performed during the heating period 104 as well.

  After the heating period 104, the heater 56 is turned off, and a voltage is applied between the pair of electrodes 53, that is, electrostatic collection is performed. As a result, as shown in the right side of FIG. 8, the soot component remaining after the SOF regeneration can be aligned between the pair of electrodes 53 by electrostatic force due to electrostatic collection, and the amount of the soot component is a certain amount or more. In this case, the pair of electrodes 53 can be electrically connected.

  When the amount of the Soot component has not yet reached a certain amount at which conduction starts, the above-described off period 103 and heating period 104 are repeated again, and PM collection → SOF component combustion removal is repeated. Eventually, as shown in the bottom of FIG. 6, in the SOF regeneration control, the off period 103 and the heating period 104 are alternately repeated. In the present embodiment, the width of the off period 103 is constant during each off period 103, and the width of the heating period 104 is constant between each heating period 104. Further, the width of the off period 103 and the width of the heating period 104 may be the same or may be different. If the width of the off period 103 and the width of the heating period 104 are too long, there is a possibility that the timing (rising time) when the output of the PM sensor 5 occurs cannot be accurately grasped. That is, when the output of the PM sensor 5 is confirmed after the off period 103 and the heating period 104, there is a possibility that a considerable time has elapsed since the generation of the output. Therefore, it is preferable not to make the widths of the off period 103 and the heating period 104 too long. The ECU 6 that executes the process of S7 corresponds to “collection control means” and “heating control means” of the present invention.

  Next, it is determined whether or not the DPF failure determination timing based on the rising timing of the sensor output has been established (arrived) (S8). Specifically, the collection soot amount C estimated in S6 is a value K1 (conduction start collection amount) predetermined as the PM collection amount at which the output of the PM sensor 5 rises (conduction between the electrodes 53 starts). It is determined whether or not it is reached. Thus, in S8, it is determined whether or not the time t0 (reference time) when the output of the PM sensor 5 rises when the DPF 4 is the reference failure DPF has arrived. The second stage in FIG. 6 shows the reference time t0.

  If the collection soot amount C has not yet reached the conduction start collection amount K1 (S8: No), it is determined that the reference time t0 (determination timing) has not yet arrived, and the process returns to S4. In this case, after the collection soot amount C is updated (S4 to S6) and the SOF regeneration control is performed (S7), the updated collection soot amount C reaches the conduction start collection amount K1 again. Is determined (S8).

  When the collection soot amount C reaches the conduction start collection amount K1 (S8: Yes), it is assumed that the reference time t0 (determination timing) has arrived, and then the actual output of the PM sensor 5 (the SOF component is It is determined whether or not the excluded output (Sot amount output) has already occurred (S9). Specifically, it is determined whether the output of the PM sensor 5 is equal to or higher than a predetermined rising output value K2 (predetermined value). In S9, it means that it is determined whether the time (actual time) when the output of the actual PM sensor 5 rises is before or after the reference time t0. When the sensor output is less than the predetermined value K2 (S9: No), the sensor output has not yet risen, that is, the actual rise time (actual time) of the PM sensor 5 is later than the reference time t0. In this case, the output change of the line 102 shown in the second stage of FIG. In this case, the DPF 4 is determined to be normal because the amount of PM passing through the DPF is smaller than that of the reference failure DPF (S11).

  On the other hand, when the sensor output is equal to or greater than the predetermined value K2 (S9: Yes), the sensor output has already risen, that is, the actual time is ahead of the reference time t0. In this case, the output change of the line 101 shown in the second stage of FIG. In this case, since the amount of PM passing through the DPF is larger than that of the reference failure DPF, the DPF 4 is determined to be a failure (S10). After S10 and S11, the process of the flowchart of FIG. In addition, ECU6 which performs the process of S4-S6 and S8-S11 is equivalent to the "failure determination means" of this invention. The ECU 6 that executes the processes of S4 to S6 and S8 corresponds to the “output estimating means” of the present invention. ECU6 which performs the process of S9-S11 is equivalent to the "comparison determination means" of this invention. The ECU 6 that executes the processes of S4 to S6 corresponds to the “soot amount estimating means” of the present invention. The PM sensor 5 and the ECU 6 that executes the processes of S1 to S3 and S7 correspond to the “particulate matter detection device” of the present invention.

  As described above, according to the present embodiment, electrostatic collection is performed only when the SOF component is hardly generated by the processing of S1 to S3 in FIG. PM not included) can be collected by the PM sensor 5. Therefore, it is possible to prevent a decrease in detection sensitivity and variation of the PM sensor 5 due to the presence of the SOF component, and the PM sensor 5 can detect a very small amount of PM. As a result, it is possible to accurately determine whether or not the DPF 4 has failed.

  Further, according to the present embodiment, since the SOF regeneration control is executed in the process of S7 in FIG. 5, when electrostatic collection is started in S3, it is assumed that a small amount of SOF component is contained in the PM. Moreover, the SOF component can be excluded from the collection target of the PM sensor 5. Therefore, it is possible to further prevent the detection sensitivity of the PM sensor 5 from being lowered, and more accurately determine whether or not the DPF 4 has failed.

  In addition, according to the present embodiment, the processing of S4 to S6 and S8 in FIG. 5 sets the reference time as a threshold for determining the failure of the DPF 4 based on the collected soot amount excluding the SOF component. The rise time (actual time) of the reference time and the actual sensor output (output corresponding to the amount of the Soot component) can be made to have the same personality value. Therefore, it is possible to accurately determine whether or not the DPF 4 has failed.

  In addition, this invention is not limited to the said embodiment, A various change is possible to the limit which does not deviate from description of a claim. For example, in the above-described embodiment, in the SOF regeneration control, the heater off period and the heating period width are constant regardless of the engine operating state, but the width depends on the PM discharge state based on the engine operating state. May be changed. Specifically, for example, when the amount of PM discharged from the engine is large, the off period is lengthened and a larger amount of PM is collected by the PM sensor. Thereby, PM can be efficiently collected by the PM sensor in accordance with the state of PM emission from the engine. In addition, the SOF component can be efficiently burned and removed by changing the width of the heating period according to the amount of PM (the amount of SOF component) collected during the off period.

  Moreover, in the said embodiment, in the process of FIG. 5, the 1st characteristic based on the process of S1-S3 (I carry out electrostatic collection only when an SOF component does not generate | occur | produce) and the process based on the process of S4-S6, S8. An example in which all of the two features (the failure judgment threshold (reference time) is set based on the collected soot amount (soot ratio)) and the third feature (combustion removal of only the SOF component) based on the processing of S7 will be described. did. However, all three of these features need not be implemented, and any one or only two may be implemented. Specifically, for example, when only the first feature is performed, in the process of FIG. 5, for example, the processes of S5 to S7 are omitted, and in S8, the accumulated value of the PM collection amount A estimated in S4 is It is determined whether or not the starting collection amount K1 has been reached. That is, electrostatic collection is performed only when no SOF component is generated in the processes of S1 to S3, and thereafter, a failure determination of the DPF is performed based on the rising timing of the sensor output by the same method as in Patent Document 1. Moreover, what is necessary is just to add the process of S7 to this, also when implementing a 3rd characteristic.

  For example, when only the first feature and the second feature are implemented, the process of S7 may be omitted in the process of FIG. Further, for example, when only the second feature is performed, the processes of S1 and S2 and the process of S7 may be omitted in the process of FIG. When implementing the second feature and the third feature, the processing of S1 and S2 may be omitted in the processing of FIG. For example, when only the third feature is performed, the processing of S1 and S2 and the processing of S5 and S6 are omitted in the processing of FIG. 5, and in S8, the cumulative value of the PM collection amount A estimated in S4. However, it may be determined whether or not the conduction start collection amount K1 has been reached. In this way, even if only one or two of the three features are implemented, it is possible to accurately detect a DPF failure.

  In the above embodiment, the DPF failure is determined based on the rise time of the sensor output. However, the DPF failure is determined based on the output change (output slope) after the rise. The features of may be applied. Specifically, for example, while performing the first feature (the processing of S1 to S3) and the third feature (the processing of S7), the output change of the PM sensor when the DPF is the reference failure DPF is used as a failure determination threshold value. Then, the threshold value is compared with the actual output change, and if the actual output change is larger than the threshold value, it is determined that the DPF has failed, and if it is smaller, it is determined that the DPF is normal. Thus, by implementing the first feature and the third feature, the sensitivity of the actual output change compared with the threshold value (PM sensor detection sensitivity) can be improved, so that the DPF failure determination can be performed accurately. Furthermore, this threshold value (PM sensor output change when the DPF is the reference failure DPF) may be set based on the second feature. That is, the soot amount (collected soot amount) collected by the PM sensor is estimated based on the soot ratio (S4 to S6 in FIG. 5), and a change in the estimated collected soot amount is set as a threshold value. As a result, a failure of the DPF can be accurately detected.

  The detection of the PM amount based on the first feature and the third feature may be applied to uses other than the DPF failure determination. Specifically, for example, a PM sensor is installed upstream of the DPF, and the first feature (processing of S1 to S3) or the third is used for estimating the amount of PM flowing into the DPF based on the output of the PM sensor. The feature (the process of S7) may be applied. As a result, the detection sensitivity of the PM sensor can be improved, so that the amount of PM into which the DPF flows can be accurately estimated.

1 Engine system (filter failure detection device)
2 Diesel engine (internal combustion engine)
3 Exhaust passage 4 DPF (filter)
5 PM sensor (sensor)
52 Sensor element
53 Electrode 6 ECU

Claims (16)

A filter (4) provided in the exhaust passage (3) of the internal combustion engine (2) for collecting particulate matter in the exhaust gas;
An insulating element (52) having a pair of electrodes (53) that is provided downstream of the filter in the exhaust passage and collects particulate matter in the exhaust gas, and is connected between the pair of electrodes. A sensor (5) that generates an output depending on the amount of particulate matter sometimes collected in the element;
Failure determination means (S4 to S6, S8 to S11) for determining the presence or absence of a failure of the filter based on a soot amount output which is an output of the sensor in a state where a soot component is collected in the element. )When,
When the failure determination means determines the presence or absence of a failure of the filter, the soot component is allowed to remain in the element, and a low conductivity component having lower conductivity than the soot component remains in the element. Collection control means (S1 to S3, S7) for controlling to suppress this,
A filter failure detection apparatus (1), comprising: Heating means (56) for heating the element;
The collection control means controls the heating means to heat the element at a temperature of 200 to 300 ° C. or more and less than 500 to 600 ° C. as a temperature at which the low-conductivity component burns but the soot component does not burn. The filter failure detection device according to claim 1, further comprising heating control means (S7). Said heating control means, after the collection of the particulate matter containing Soot component and the low-conductive component in the device while the off heat to the element, heating the element at said temperature 3. The filter failure detection device according to claim 2, wherein the SOF component as the low-conductivity component is excluded from the particulate matter collected by the sensor .   The heating control means includes an off period (103) in which particulate matter containing a soot component and the low-conductivity component is collected in the element in a state where heating to the element is turned off, and the element at the temperature. The filter according to claim 3, wherein heating of the element is controlled so that a heating period (104) in which the low-conductivity component is burned and removed from the element is alternately repeated by heating the element. Failure detection device. The collection control means includes
State determination means (S1) for determining whether or not a predetermined non-occurrence operating state is established as an operating state of the internal combustion engine in which the low conductivity component is not generated;
When the state determination means determines that the non-occurrence operation state is established, a voltage is applied between the pair of electrodes to collect particulate matter on the element, while the non-occurrence operation state And a control unit (S2, S3) for stopping the application of voltage between the pair of electrodes and stopping the collection of the particulate matter to the element when it is determined that the above is not established. The filter failure detection device according to any one of claims 1 to 4. The failure determination means includes
Output estimation means (S4 to S6, S8) for estimating the output of the sensor when the filter is a filter that is a criterion for failure determination based on the operating state of the internal combustion engine;
Comparing and determining means (S9 to S11) for determining the presence or absence of a failure of the filter based on a comparison between the threshold value and the actual output of the sensor, using the output estimated by the output estimating means as a threshold value. The filter failure detection device according to any one of claims 1 to 5.   The output estimation means calculates the collected soot amount, which is the amount of the soot component of the particulate matter collected by the element, when the filter is a filter that serves as a criterion for failure determination, as an operating state of the internal combustion engine. 7. A filter failure detection apparatus according to claim 6, further comprising a soot amount estimating means (S4 to S6) for estimating the threshold based on the collected soot amount. A filter (4) provided in the exhaust passage (3) of the internal combustion engine (2) for collecting particulate matter in the exhaust gas;
An insulating element (52) having a pair of electrodes (53) that is provided downstream of the filter in the exhaust passage and collects particulate matter in the exhaust gas, and is connected between the pair of electrodes. A sensor (5) that generates an output depending on the amount of particulate matter sometimes collected in the element;
Output estimation means (S4 to S6, S8) for estimating the output of the sensor when the filter is a filter that is a criterion for failure determination based on the operating state of the internal combustion engine;
Comparing and determining means (S9 to S11) for determining the presence or absence of a failure of the filter based on a comparison between the threshold value and the actual output of the sensor, with the output estimated by the output estimating means as a threshold value;
The output estimation means calculates the collected soot amount, which is the amount of the soot component of the particulate matter collected by the element, when the filter is a filter that serves as a criterion for failure determination, as an operating state of the internal combustion engine. And a soot amount estimating means (S4 to S6) for estimating the threshold based on the collected soot amount. The output estimating means (S8) estimates, based on the collected soot amount, a reference time, which is a time when the output of the sensor rises when the filter is a filter serving as a reference for failure determination, as the threshold value,
The comparison / determination unit compares the reference time with an actual time when the output of the sensor actually rises, and determines that the filter is faulty when the actual time is earlier than the reference time. The filter failure detection device according to claim 7 or 8, wherein the filter is determined to be normal when the actual time is later than the reference time. An insulating element (52) having a pair of electrodes (53) that is provided in the exhaust passage (3) of the internal combustion engine (2) and collects particulate matter in the exhaust gas, the pair of electrodes A sensor (5) for generating an output corresponding to the amount of particulate matter collected by the element during conduction between the element and
The soot component of particulate matter is allowed to be collected by the element, and the collection control is performed so as to prohibit the low conductive component having lower conductivity than the soot component from being collected by the element. Collection control means (6);
A particulate matter detection device comprising: Heating means (56) for heating the element;
The collection control means controls the heating means to heat the element at a temperature of 200 to 300 ° C. or more and less than 500 to 600 ° C. as a temperature at which the low-conductivity component burns but the soot component does not burn. The particulate matter detection device according to claim 10, further comprising a heating control unit (S <b> 7). Said heating control means, after the collection of the particulate matter containing Soot component and the low-conductive component in the device while the off heat to the element, heating the element at said temperature The particulate matter detection device according to claim 11, wherein the SOF component as the low-conductivity component is excluded from the particulate matter collected by the sensor .   The heating control means heats the element at an off period in which particulate matter including a Soot component and the low-conductivity component is collected in the element in a state where heating to the element is turned off, and the temperature. The particulate matter detection device according to claim 12, wherein heating of the element is controlled so that a heating period for burning and removing the low-conductivity component from the element is alternately repeated. The collection control means includes
State determination means (S1) for determining whether or not a predetermined non-occurrence operating state is established as an operating state of the internal combustion engine in which the low conductivity component is not generated;
When the state determination means determines that the non-occurrence operation state is established, a voltage is applied between the pair of electrodes to collect particulate matter on the element, while the non-occurrence operation state And a control unit (S2, S3) for stopping the application of voltage between the pair of electrodes and stopping the collection of the particulate matter to the element when it is determined that the above is not established. The particulate matter detection device according to any one of claims 10 to 13.   The filter failure detection apparatus according to claim 1, wherein the low-conductivity component is an organic solvent-soluble component.   The particulate matter detection device according to claim 10, wherein the low-conductivity component is an organic solvent-soluble component.