JP6210030B2 - Particulate filter abnormality judgment device - Google Patents

Description

  The present invention relates to an abnormality determination device for a particulate filter that determines whether an abnormality (failure) has occurred in a particulate filter disposed in an exhaust passage of an internal combustion engine.

  Conventionally, a “particulate filter” that collects particulates (PM) discharged from the internal combustion engine (particularly a diesel engine) is disposed. When this filter is applied to a diesel engine, this filter is called “DPF (Diesel Particulate Filter)”.

  Such a particulate filter is generally a wall flow type filter. That is, the particulate filter collects the fine particles contained in the exhaust gas when the exhaust gas passes through the porous partition walls provided in the particulate filter. The particulate filter is a filter that causes flow path resistance. When exhaust gas passes through the particulate filter, it is the differential pressure across the particulate filter (the difference between the pressure on the inlet side and the outlet side of the filter, Hereinafter, it is also simply referred to as “front / rear differential pressure”), which is a certain value even when the amount of collected fine particles is small.

  On the other hand, when the particulate filter is damaged, the differential pressure across the front and rear becomes small. Therefore, the conventional apparatus is configured to determine whether or not an abnormality has occurred in the particulate filter using the differential pressure across the particulate filter (see, for example, Patent Document 1).

JP 2011-252423 A

  By the way, the differential pressure before and after the particulate filter has a variation for each individual particulate filter (hereinafter also referred to as “individual variation”). According to the inventor's experiment, during the period from the start of the accumulation of fine particles on an unused particulate filter until the first regeneration process of the filter (hereinafter also referred to as “filter regeneration process”) is performed. It was found that the degree of variation was significantly large. Further, when one cycle from one filter regeneration process to the next filter regeneration process is defined as one cycle, it has been found that the individual variation is reduced by executing this cycle one to several times. The reason for this is not clear, but an unused particulate filter does not have any fine particles in the surface layer portion and pore portion of the partition wall, so there is a correlation with the fact that the collection state (mode) of the fine particles is not stable. It is assumed that there is.

  More specifically, when the newly installed particulate filter is a filter that tends to deposit fine particles on the surface layer portion of the partition walls but does not easily deposit fine particles on the pore portions of the partition walls. The flow of exhaust gas is relatively difficult to block. As a result, the differential pressure before and after the exhaust gas flow rate, which is a normal particulate filter, can be considered to be relatively low. When “abnormality determination” is performed using such a differential filter for such a particulate filter, the differential pressure before and after a normal product may be approximately the same as the differential pressure before and after an abnormal product. That is, although the particulate filter is a normal product, it is determined that an abnormality has occurred by mistake.

  The present invention has been made in order to address the above-described problems, and the object thereof is an apparatus for performing the above-described “abnormality determination using the differential pressure across the front and back”, and that a normal product is an abnormal product. An object of the present invention is to provide an “abnormality determination device” for a particulate filter that is less likely to be erroneously determined.

  The “abnormality determination device” for a particulate filter disposed in an exhaust passage of an internal combustion engine according to the present invention includes a differential pressure acquisition unit, a gas flow rate acquisition unit, a filter installation signal detection unit, a counting unit, and an abnormality determination. A section.

  The differential pressure acquisition unit acquires a differential pressure across the particulate filter. The differential pressure acquisition unit may be a known differential pressure sensor that detects a differential pressure between the upstream pressure (inlet side pressure) and the downstream pressure (outlet side pressure) of the particulate filter. Alternatively, the differential pressure acquisition unit calculates the differential pressure across the particulate filter based on the output of the pressure sensor that detects the upstream pressure of the particulate filter and the output of the pressure sensor that detects the downstream pressure of the particulate filter. It may be an acquisition device.

  The gas flow rate acquisition unit acquires a passing gas flow rate (for example, a volume flow rate) that is a flow rate of gas passing through the particulate filter. The gas flow rate acquisition unit may be a device (for example, a volumetric flow meter) that directly acquires (measures) the upstream gas flow rate (inlet side flow rate) of the particulate filter. Alternatively, the gas flow rate acquisition unit acquires (estimates) the passing gas flow rate based on the intake air amount detected by an air flow meter disposed in the intake passage, the intake air temperature, the upstream temperature (inlet side temperature) of the particulate filter, and the like. ).

  The filter installation determining unit determines whether or not the particulate filter is first installed in the exhaust passage or has been replaced with a new one. For example, the installation or replacement of the particulate filter in the exhaust passage is generally performed in a state in which the vehicle battery and the vehicle electrical system are disconnected. Therefore, the filter installation determination unit determines whether or not the power supplied to the electric system of the vehicle has started to be supplied again after being cut off. When the power starts to be supplied again, the particulate filter is installed or replaced. It may also be determined that there is a possibility that Alternatively, when the particulate filter is first installed in the exhaust passage or replaced with a new one, it is operated by an operator or automatically by installation of the particulate filter in the exhaust passage. A switch ”may be provided, and the above determination may be made based on a change in the state of the switch.

  The counting unit is executed from the time when it is determined that the particulate filter is first installed in the exhaust passage or may be replaced with a new one to the next time when the same determination is made. The number of filter regenerations that is the number of regenerations of the particulate filter is counted. The counting unit may be a known counter circuit. As is well known, filter regeneration is performed in order to eliminate clogging caused by fine particles deposited on the particulate filter. Filter regeneration is performed by raising the temperature of the exhaust gas that passes through the particulate filter and burning the particulates deposited on the particulate filter.

When the abnormality determination unit is to determine whether an abnormality has occurred in the particulate filter,
(1) When the number of filter regenerations is less than a predetermined number,
Based on a comparison result between a “differential pressure correlation value correlated with the differential pressure across the particulate filter acquired when the passing gas flow rate is equal to or higher than a predetermined first flow rate” and a predetermined first threshold value. It is determined whether an abnormality has occurred in the particulate filter,
(2) When the filter regeneration number is equal to or greater than the predetermined number,
Comparison of “the differential pressure correlation value correlated with the front-rear differential pressure acquired when the passing gas flow rate is equal to or higher than a predetermined second flow rate smaller than the first flow rate” and a predetermined second threshold value Based on the result, it is determined whether or not an abnormality has occurred in the particulate filter.

  “When to determine whether or not an abnormality has occurred in the particulate filter” is when, for example, the ignition key switch of the vehicle is changed from the on position to the off position. Furthermore, a condition may be added when the abnormality determining unit has collected a sufficient number of data necessary for determining abnormality.

  Since the front-rear differential pressure increases as the passing gas flow rate increases, the front-rear differential pressure when the passing gas flow rate is equal to or higher than the predetermined first flow rate is a predetermined second flow rate where the passing gas flow rate is smaller than the first flow rate. It is larger than the differential pressure before and after. Furthermore, the differential pressure across the normal particulate filter (normal product) increases relatively rapidly as the passing gas flow rate increases, whereas the differential pressure across the abnormal particulate filter (abnormal product) It increases relatively gently (slowly) as it increases. That is, as the flow rate of the passing gas is increased, the difference between the differential pressure across the normal product and the differential pressure across the abnormal product increases.

  By the way, as described above, when the number of regenerations after the installation or replacement of the particulate filter is less than a predetermined number, the variation in the differential pressure across the particulate filter (individual variation) is large. In this case, when the passing gas flow rate is smaller than the predetermined first flow rate, the abnormality determination unit may determine that a normal particulate filter (normal product) is abnormal due to individual variation.

  Therefore, when the number of regenerations after the installation or replacement of the particulate filter is less than the predetermined number, the abnormality determination unit uses the differential pressure acquisition unit when the passing gas flow rate is equal to or higher than the relatively large first flow rate. Acquire the differential pressure across the particulate filter.

  That is, the abnormality determination unit sets a flow rate that is larger than the lower limit of the passing gas flow rate range in which the normal product and the abnormal product can be distinguished even when the individual variation of the particulate filter is large as the first flow rate. For example, in a vehicle having an EGR (Exhaust Gas Recirculation) device, the first flow rate is often realized under an operating condition in which the flow rate of the EGR gas to be refluxed is “0”.

  On the other hand, when the number of regenerations after the installation or replacement of the particulate filter is greater than or equal to a predetermined number (1 to several times), the variation in the differential pressure across the particulate filter is small.

  Therefore, the abnormality determining unit determines that the passage gas flow rate is “a predetermined second flow rate smaller than the first flow rate” when the number of regenerations after the installation or replacement of the particulate filter is equal to or greater than a predetermined number (1 to several times). When it is above, the differential pressure acquisition unit is used to acquire the differential pressure across the particulate filter. As a result, when the individual variation of the particulate filter is small, the abnormality determination unit can increase the chances of detecting the differential pressure across the front and back than when the individual variation is large.

  The device according to the present invention performs filter abnormality determination based on the comparison result between the differential pressure correlation value thus obtained and a predetermined threshold value. Therefore, the device of the present invention can execute “filter abnormality determination” that does not erroneously determine that a normal product is abnormal even if it is a particulate filter immediately after being first installed or replaced with a new one.

  The “differential pressure correlation value having a correlation with the front-rear differential pressure” may be a value that varies according to the front-rear differential pressure. For example, the differential pressure correlation value may be the front-rear differential pressure itself or the reciprocal of the front-rear differential pressure.

  In the abnormality determination device according to an aspect of the present invention, the abnormality determination unit may be configured such that the minimum value in the range of variation in the front-rear differential pressure caused by the individual difference between the normal particulate filters is abnormal. The first flow rate is configured to be within a range of the passing gas flow rate such that a relationship larger than a maximum value in a range of variation in the front-rear differential pressure caused by the difference is established.

  According to this, even when the number of filter regenerations is less than the predetermined number and the variation in front-back differential pressure is large, erroneous abnormality determination can be prevented.

In the abnormality determination device according to an aspect of the present invention, the abnormality determination unit may be configured such that when the filter regeneration number is less than the predetermined number of times, the differential pressure when the passing gas flow rate is equal to or higher than the predetermined first flow rate. A plurality of data of the differential pressure before and after which is the basic data of the correlation value are acquired, and an average value of the passing gas flow rate when the plurality of data is acquired is obtained, and the first threshold value is determined based on the obtained average value. Decide
When the number of filter regenerations is equal to or greater than the predetermined number, a plurality of front and rear differential pressure data that are basic data of the differential pressure correlation value are acquired when the passing gas flow rate is equal to or greater than the predetermined second flow rate. In addition, the second threshold value is determined based on the average value of the passage gas flow rates obtained when the plurality of data are acquired.

  In this case, the first threshold value and the second threshold value may be calculated by substituting each of the average values of the passing gas flow rates obtained as described above into a predetermined function. Alternatively, the first threshold value and the second threshold value may be obtained by referring to the average value of the passing gas flow rate obtained as described above and a lookup table that defines the relationship between these threshold values. .

  The first threshold value changes in accordance with the average value of the passing gas flow rate when the passing gas flow rate is equal to or higher than the predetermined first flow rate and when the differential pressure data is acquired. Similarly, the second threshold value changes in accordance with the average value of the passing gas flow rate when the passing gas flow rate is equal to or higher than the predetermined second flow rate and when the differential pressure data is acquired. Therefore, according to the above aspect, since the first threshold value and the second threshold value are set to appropriate values, an accurate abnormality determination can be performed.

  Other objects, other features, and attendant advantages of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

FIG. 1 is a schematic configuration diagram of an internal combustion engine to which a “particulate filter abnormality determination device” according to an embodiment of the present invention is applied. FIG. 2 (A) is a graph showing the relationship between the exhaust gas flow rate and the differential pressure across the DPF shown in FIG. 1 that has been subjected to filter regeneration processing several times. FIG. 2 is a graph showing the relationship between the exhaust gas flow rate and the differential pressure before and after the DPF shown in FIG. FIG. 3 shows the relationship between the differential pressure before and after the particulate filter at an arbitrary gas flow rate, the count value of the regeneration counter, the front and rear differential pressure stabilization flag, and the exhaust gas flow rate lower limit value at the time of abnormality determination data acquisition. It is a time chart. FIG. 4 is a flowchart showing a “differential pressure stabilization flag determination routine” executed by the CPU shown in FIG. FIG. 5 is a flowchart showing a “DPF abnormality determination routine” executed by the CPU shown in FIG.

<Embodiment>
A particulate filter abnormality determination device (hereinafter also referred to as “determination device”) according to an embodiment of the present invention will be described below with reference to the drawings.

(Constitution)
The determination device is applied to the internal combustion engine (engine) 10 shown in FIG. The engine 10 is a multi-cylinder (in this example, in-line four cylinders), four-cycle, piston reciprocating type, and diesel engine. The engine 10 includes an engine body 20, a fuel supply system 30, an intake system 40, an exhaust system 50, and an EGR system 60.

  The engine body 20 includes a body 21 including a cylinder block, a cylinder head, a crankcase, and the like. Four cylinders (combustion chambers) 22 are formed in the main body 21. A fuel injection valve (injector) 23 is disposed above each cylinder 22. The fuel injection valve 23 opens in response to an instruction from an electronic control unit 70 to be described later, and directly injects fuel into the cylinder.

  The fuel supply system 30 includes a fuel pressurization pump (supply pump) 31, a fuel delivery pipe 32, and a common rail (pressure accumulation chamber) 33. The discharge port of the fuel pressurization pump 31 is connected to the fuel delivery pipe 32. The fuel delivery pipe 32 is connected to the common rail 33. The common rail 33 is connected to the fuel injection valve 23.

  The fuel pressurizing pump 31 pumps up fuel stored in a fuel tank (not shown), pressurizes the fuel, and supplies the pressurized high-pressure fuel to the common rail 33 through the fuel delivery pipe 32.

  The intake system 40 includes an intake manifold 41, an intake pipe 42, and a compressor 43 of the supercharger TC.

  The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe 52, a diesel oxidation catalyst 53, a particulate filter 54, and a turbine 55 of a supercharger TC. Hereinafter, the diesel oxidation catalyst 53 is referred to as “DOC53”. The particulate filter 54 is referred to as “DPF 54”. DPF is an abbreviation for diesel particulate filter.

  The exhaust manifold 51 includes a branch portion connected to each cylinder and a collective portion in which the branch portions are gathered. The exhaust pipe 52 is connected to a collecting portion of the exhaust manifold 51. The exhaust manifold 51 and the exhaust pipe 52 constitute an exhaust passage. A turbine 55, a DOC 53, and a DPF 54 are disposed in the exhaust pipe 52 from the upstream side to the downstream side of the exhaust gas flow.

The DOC 53 purifies the exhaust gas by oxidizing unburned components (HC, CO, NO) in the exhaust gas using a noble metal such as platinum and palladium as a catalyst. That is, DOC 53 oxidizes HC to water and CO ₂ , CO is oxidized to CO ₂ , and NO is oxidized to NO ₂ .

  The DPF 54 collects PM (fine particles, that is, particulate matter) containing carbon soot and organic substances attached to the soot. The DPF 54 is a known wall flow type ceramic filter. More specifically, the DPF 54 includes a plurality of gas flow paths formed of heat-resistant ceramics such as “cordylite and silicon carbide” formed into a honeycomb structure. In the gas flow path, one end of the adjacent gas flow path is alternately packed. The exhaust gas that has flowed into the DPF 54 cannot pass through the filter directly by clogging, but passes through the porous partition walls constituting the plurality of gas flow paths. At that time, PM, ash, and the like in the exhaust gas are collected inside the DPF 54 (pores in the partition walls, surface layers of the partition walls, and the like).

  As PM is collected and accumulated in the DPF 54, the wall flow type DPF 54 is clogged, and the flow path resistance inside the DPF 54 increases. That is, as PM accumulates on the DPF 54, the pressure difference between the exhaust gases before and after the DPF 54 (hereinafter referred to as “front / rear differential pressure”) increases. If PM accumulates excessively on the DPF 54 and the front-rear differential pressure becomes excessively large, the performance of the DPF 54 and the fuel consumption of the engine may be deteriorated. Therefore, a so-called filter regeneration process for removing the PM accumulated on the DPF 54 when the separately estimated PM accumulation amount reaches a predetermined value or by the operation of the driver is executed according to an instruction from the electronic control unit 70 described later. .

  The filter regeneration process is performed by raising the temperature of the exhaust gas passing through the DPF 54 and burning the PM deposited on the DPF 54. The temperature of the exhaust gas passing through the DPF 54 is increased as follows. Fuel (unburned components) is supplied to the exhaust pipe 52 upstream of the DOC 53 from the engine or a fuel addition valve (not shown). The temperature of the DOC 53 rises due to the heat generated when the DOC 53 oxidizes the supplied unburned components. As a result, the temperature of the exhaust gas flowing out from the DOC 53 increases. And the exhaust gas which became high temperature flows in into DPF54, and PM deposited on DPF54 is burned. Hereinafter, the volume flow rate of the gas passing through (inflowing into) the DPF 54 is also referred to as “DPF passage gas flow rate Vdpf”.

An SCR catalyst (not shown) may be provided downstream of the DPF 54. The SCR catalyst is a “NOx selective reduction catalyst” that purifies exhaust gas by reducing NOx with ammonia (NH ₃ ). In this case, an apparatus for supplying urea for generating ammonia supplied to the SCR catalyst by hydrolysis is provided.

  The EGR system 60 includes an exhaust gas recirculation pipe 61, an EGR control valve 62, and an EGR cooler 63. The EGR system 60 is also referred to as an EGR device.

  The exhaust gas recirculation pipe 61 is an exhaust gas passage (exhaust manifold 51) that is upstream of the turbine 55 and an intake air passage (intake manifold 41) that is downstream of the throttle valve 46 so as to constitute an EGR gas passage. , Communicate. In other words, the exhaust gas (EGR gas) take-out port is provided on the upstream side of the DPF 54 in the exhaust passage. For this reason, when the amount of gas flowing into the main body 21 (all cylinders 22) is constant, the flow rate of gas flowing into the DPF 54 (volumetric flow rate; Also called “DPF gas passing gas flow rate”) increases.

  The EGR control valve 62 is disposed in the exhaust gas recirculation pipe 61. The EGR control valve 62 is recirculated from the exhaust passage to the intake passage by changing the cross-sectional area of the EGR gas passage in response to a drive signal (duty ratio signal) Decr that is an instruction from the electric control device 70. The amount of exhaust gas (EGR gas amount) can be changed. In other words, the EGR control valve 62 can control the flow rate of the gas flowing into the DPF 54 (the passing gas flow rate of the DPF 54). As the drive signal Decr increases, the opening degree of the EGR control valve 62 increases. Therefore, as the drive signal Decr decreases, the opening degree of the EGR control valve 62 decreases, and as a result, the EGR gas amount decreases while the exhaust gas flow rate V (and hence the DPF passage gas flow rate Vdpf) increases.

  The EGR cooler 63 is interposed in the exhaust gas recirculation pipe 61 and reduces the temperature of the EGR gas passing through the exhaust gas recirculation pipe 61.

  As is apparent from the above, the EGR system 60 constitutes a flow rate changing device that can change the DPF gas passage flow rate.

  The electronic control device 70 is an electronic circuit including a well-known microcomputer, and includes a CPU, ROM, RAM, backup RAM (static RAM (SRAM) or nonvolatile memory), a counter, an interface, and the like. The electronic control unit 70 is connected to sensors described below, and receives (inputs) signals from these sensors. Furthermore, the electronic control unit 70 is configured to send instruction (drive) signals to various actuators in accordance with instructions from the CPU.

  The electronic control unit 70 includes an air flow meter 71, a throttle valve opening sensor 72, an EGR control valve opening sensor 73, a front / rear differential pressure sensor 74, an exhaust gas temperature sensor 75, an exhaust gas pressure sensor 76, an atmospheric pressure sensor 77, and an accelerator pedal operation amount. The sensor 78 and the ignition key switch 79 are connected.

The air flow meter 71 measures the mass flow rate of intake air (fresh air not including EGR gas) passing through the intake passage, and outputs a signal representing the mass flow rate (hereinafter referred to as “intake air amount Ga”). . Further, the air flow meter 71 detects the temperature of the intake air and outputs a signal representing the intake air temperature THA.
The throttle valve opening sensor 72 detects the throttle valve opening and outputs a signal representing the throttle valve opening TA.

The EGR control valve opening sensor 73 detects the opening of the EGR control valve 62 and outputs a signal Vegr representing the opening.
The front-rear differential pressure sensor 74 is a pressure difference between the upstream pressure of the DPF 54 (inlet pressure, pressure between the DOC 53 and the DPF 54, i.e., upstream pressure) and downstream pressure (outlet pressure, i.e., downstream pressure). This is a well-known pressure sensor that detects a front-rear differential pressure and outputs a front-rear differential pressure ΔP.

  The exhaust gas temperature sensor 75 is disposed in the exhaust pipe 52 at a position between the DOC 53 and the DPF 54. The exhaust gas temperature sensor 75 detects the temperature of the exhaust gas that passes through the DOC 53 and flows into the DPF 54, and outputs a signal representing the exhaust gas temperature T1.

  The exhaust gas pressure sensor 76 is disposed in the exhaust pipe 52 and downstream of the DPF 54. The exhaust gas pressure sensor 76 is a well-known pressure sensor that detects the downstream pressure (exit pressure, that is, downstream pressure) of the DPF 54 and outputs a signal representing the exhaust gas pressure P2.

The atmospheric pressure sensor 77 is disposed in a case in which the electronic control unit 70 is stored. The atmospheric pressure sensor 77 is a known pressure sensor that detects atmospheric pressure and outputs a signal representing the atmospheric pressure P1.
The accelerator pedal operation amount sensor 78 detects the operation amount of the accelerator pedal AP and outputs a signal representing the accelerator pedal operation amount Accp.

  The ignition key switch 79 is a switch having an on position for starting the engine 10 and an off position for stopping.

  In this determination apparatus, the DPF passage gas flow rate Vdpf described above is defined as an exhaust gas flow rate (DPF inlet flow rate) Vf at the inlet of the DPF 54 as shown below.

In general, the exhaust gas flow rate V represents the volume (m ³ / sec) of gas per unit time. Assuming that the gas pressure is P (Pa), the absolute gas temperature is T (K), and the amount of substance per unit time of the gas is n (mol / sec), the relationship shown in the following equation is established. .

(P · V) / (n · T) = R (constant) (1)

In the formula (1), R is referred to as a gas constant (unit: J · K ⁻¹ · mol ⁻¹ ). That is, the exhaust gas flow rate V is proportional to the absolute temperature T. From the above equation, the exhaust gas flow rate V is obtained by the following equation.

V = nRT / P (2)

Therefore, the DPF inlet flow rate Vf (m ³ / sec) is expressed by the following equation using equation (2).

Vf = R · Ga (T1 + 273) / (P1 + P2 + ΔP) (3)

In equation (3), Ga is the intake air amount (g / sec) detected by the air flow meter 71, T1 is the exhaust gas temperature (° C.) detected by the exhaust gas temperature sensor 75 located upstream of the DPF 54, and P1 is the atmospheric pressure sensor. P2 is the DPF rear pressure (Pa) detected by the exhaust gas pressure sensor 76 located downstream of the DPF 54, and ΔP is the DPF front-rear differential pressure detected by the front-rear differential pressure sensor 74 ( Pa). That is, (P1 + P2 + ΔP), which is the denominator of the equation (3), represents the exhaust gas pressure at the inlet portion of the DPF 54.

(Overview of operation)
Hereinafter, an outline of the operation of the determination apparatus will be described with reference to FIGS. 2 and 3.

  FIG. 2A shows that a normal DPF 54 (normal DPF) and an abnormality occur in a DPF 54 that has been initially installed in a vehicle equipped with the engine 10 or has been replaced with a new one and has been subjected to filter regeneration several times. 4 is a graph showing “relation between exhaust gas flow rate V (DPF passage gas flow rate Vdpf) and front-to-back differential pressure ΔP of DPF 54” of the DPF 54 (abnormal DPF) being operated.

  FIG. 2B shows the “exhaust gas flow rate V and DPF 54 of normal DPF and abnormal DPF 54 for the DPF 54 after being first installed in the vehicle or replaced with a new one and before the first filter regeneration is executed. It is the graph which showed "the relationship with front-back differential pressure | voltage (DELTA) P."

  2A and 2B, a curve C1 is a curve related to normal DPF (an approximate curve for the distribution of normal DPF), a curve C1max is a curve indicating the upper limit of variation in normal DPF, and a curve C1min Is a curve showing the lower limit of the variation of normal DPF. The curve C2 is a curve related to the abnormal DPF (approximate curve for the distribution of the abnormal DPF), the curve C2max is a curve indicating the upper limit of the variation of the abnormal DPF, and the curve C2min is a curve indicating the lower limit of the variation of the abnormal DPF.

  As understood from FIGS. 2 (A) and 2 (B), the width of the variation of the front-rear differential pressure ΔP represented by the difference between the curve C2max and the curve C2min with respect to a certain “exhaust gas flow rate V” is the curve C1max. Is larger than the range of variation with respect to the “exhaust gas flow rate V”.

As understood from the curves C1 and C2 in FIGS. 2A and 2B, the front-rear differential pressure ΔP increases in a quadratic function with respect to the exhaust gas flow rate V. That is, the front-rear differential pressure ΔP and the exhaust gas flow rate V for the normal DPF have a relationship of ΔP = a · V ² , and the front-rear differential pressure ΔP ′ and the exhaust gas flow rate V ′ for the abnormal DPF are ΔP ′ = b · V 'It can be said that it has a relationship of ^two . However, a (positive constant) is larger than b (positive constant). The front-rear differential pressure ΔP ′ for the abnormal DPF can be said to be substantially proportional to the exhaust gas flow rate V ′ because the value of b is small, and can also be expressed by the equation ΔP ′ = k · V ′. . Therefore, the difference (ΔP−ΔP ′) between the front-rear differential pressure ΔP of the normal DPF and the front-rear differential pressure ΔP ′ of the abnormal DPF increases as the exhaust gas flow rate V increases.

  Therefore, as understood from “curve C1min and curve C2max” in each of FIGS. 2A and 2B, the lower limit of the variation in the front-to-back differential pressure ΔP of the normal DPF and the front-to-back differential pressure ΔP ′ of the abnormal DPF The difference from the upper limit of variation increases as the exhaust gas flow rate V increases.

  2A and 2B, a region 1 is a range in which the exhaust gas flow rate V is greater than or equal to the flow rate Va and less than the flow rate Vb (the region 1 is also referred to as a “small flow rate region”). Region 2 is in the range above flow rate Vb. The region 2 ′ is a region in which the exhaust gas flow rate V is greater than or equal to Vc larger than Vb in the region 2 (the region 2 ′ is also referred to as “large flow region”). A range that is the region 2 but not the region 2 ′ is also referred to as a “medium flow region”.

  In the example shown in FIG. 2A, regarding the normal DPF, when the exhaust gas flow rate V is in the region 2 but not in the region 2 ′ (Vb ≦ V <Vc: medium flow rate region), the point Z1 is indicated. Point data is obtained. The (exhaust gas flow rate V, the differential pressure ΔP) at the point Z1 is (V1, ΔP1). The point Z1 is data on the curve C1min.

  When the exhaust gas flow rate V is in the range of the region 2 '(V ≧ Vc, large flow rate region), data of the point indicated by the point Z2 is obtained. The (exhaust gas flow rate V, front-rear differential pressure ΔP) at the point Z2 is (V2, ΔP2). The point Z2 is data on the curve C1min.

  Regarding the abnormal DPF, when the exhaust gas flow rate V is in the range 2 but not in the range 2 ′ (Vb ≦ V <Vc, medium flow rate range), data of the point indicated by the point Y <b> 1 is obtained. The (exhaust gas flow rate V, front-rear differential pressure ΔP) at the point Y1 is (V1, ΔP3). The point Y1 is data on the curve C2max, and the exhaust gas flow rate V is the same exhaust gas flow rate V1 as the point Z1.

  When the exhaust gas flow rate V is in the range of the region 2 '(V ≧ Vc, large flow rate region), data of the point indicated by the point Y2 is obtained. The (exhaust gas flow rate V, front-rear differential pressure ΔP) at the point Y2 is (V2, ΔP4). The point Y2 is data on the curve C2max, and the exhaust gas flow rate V is the same exhaust gas flow rate V2 as the point Z2.

  As understood from FIG. 2A, the front-rear differential pressure ΔP at any exhaust gas flow rate V is smaller when an abnormality (damage) occurs in the DPF 54 than when the DPF 54 is normal. For example, the differential pressure ΔP3 before and after the point Y1 at the same exhaust gas flow rate V1 is clearly smaller than the differential pressure ΔP1 at the point Z1 at the exhaust gas flow rate V1. Further, the front-rear differential pressure ΔP4 at the point Y2 at the same exhaust gas flow rate V2 is clearly smaller than the front-rear differential pressure ΔP2 at the point Z2 at the exhaust gas flow rate V2. That is, the front-rear differential pressure ΔP on the curve C1min at a certain exhaust gas flow rate V is clearly larger than the front-rear differential pressure ΔP on the curve C2max at the exhaust gas flow rate V. However, when the exhaust gas flow rate V is a value in a region (small flow rate region) less than Va, the difference between the front-rear differential pressure ΔP on the curve C1min and the front-rear differential pressure ΔP on the curve C2max is relatively small.

  Therefore, after the filter regeneration is performed several times or more on the DPF 54, the front-rear differential pressure ΔP obtained when the exhaust gas flow rate V is equal to or higher than Vb is “exhaust gas when the front-rear differential pressure ΔP is obtained”. By determining that the DPF 54 is abnormal when it is smaller than a predetermined threshold ΔPth that changes according to the flow rate V, and determining that the DPF 54 is normal when the front-rear differential pressure ΔP is equal to or greater than the threshold ΔPth, the DPF 54 The abnormality determination can be performed with high accuracy.

  On the other hand, in the example shown in FIG. 2B, regarding the normal DPF, when the exhaust gas flow rate V is in the region 2 but not in the region 2 ′ (Vb ≦ V <Vc, medium flow region), Data of a point indicated by Z1 ′ is obtained. The (exhaust gas flow rate V, front-rear differential pressure ΔP) at the point Z1 ′ is (V1 ′, ΔP1 ′). The point Z1 'is data on the curve C1min.

  When the exhaust gas flow rate V is in the range 2 '(V≥Vc, large flow rate range), data of the point indicated by the point Z2' is obtained. The (exhaust gas flow rate V, front-rear differential pressure ΔP) at the point Z2 ′ is (V2 ′, ΔP2 ′). The point Z2 'is data on the curve C1min.

  Regarding the abnormal DPF, when the exhaust gas flow rate V is in the range 2 but not in the range 2 '(Vb≤V <Vc, medium flow rate range), the data of the point indicated by the point Y1' is obtained. The (exhaust gas flow rate V, the differential pressure ΔP) at the point Y1 ′ is (V1 ′, ΔP3 ′). The point Y1 'is data on the curve C2max, and the exhaust gas flow rate V is the same exhaust gas flow rate V1' as the point Z1 '.

  When the exhaust gas flow rate V is in the range 2 '(V≥Vc, large flow rate range), data of the point indicated by the point Y2' is obtained. The (exhaust gas flow rate V, differential pressure ΔP) at the point Y2 ′ is (V2 ′, ΔP4 ′). The point Y2 'is data on the curve C2max, and the exhaust gas flow rate V is the same exhaust gas flow rate V2' as the point Z2 '.

  As understood from FIG. 2B, even in this case (before the first filter regeneration process for the new DPF 54 is executed), the front-rear differential pressure ΔP at any exhaust gas flow rate V is abnormal (damaged). ) Is smaller than when the DPF 54 is normal. However, the variation in the differential pressure ΔP across the normal DPF in this case is large. Therefore, if the exhaust gas flow rate V is a value in the region (small flow region and medium flow region) less than Vb, the lower limit value within the variation range of the normal DPF front-rear differential pressure ΔP is the lower limit value of the abnormal DPF front-rear differential pressure ΔP. It becomes smaller than the upper limit value within the range of variation. That is, as understood from the comparison between the point Y1 ′ and the point Z1 ′, the differential pressure ΔP before and after the point on the curve C1min at a certain exhaust gas flow rate V (V <Vc) is on the curve C2max at the exhaust gas flow rate V. It becomes smaller than the differential pressure ΔP before and after the point.

  On the other hand, in the large flow rate region (V ≧ Vc), the lower limit value within the variation range of the differential pressure ΔP before and after the normal DPF is always greater than the upper limit value within the variation range of the differential pressure ΔP before and after the abnormal DPF. growing. That is, as understood from the comparison between the point Y2 ′ and the point Z2 ′, the differential pressure ΔP before and after the point on the curve C1min at a certain exhaust gas flow rate V (V ≧ Vc) is on the curve C2max at the exhaust gas flow rate V. It is larger than the point differential pressure ΔP.

  Therefore, before the first filter regeneration for the new DPF 54 is executed, the front-rear differential pressure ΔP obtained when the exhaust gas flow rate V is equal to or higher than Vc is “the exhaust gas flow rate V when the front-rear differential pressure ΔP is obtained”. It is determined that the DPF 54 is greater than or equal to a predetermined threshold value ΔPth that changes according to the threshold value, and that the DPF 54 is normal when the front-rear differential pressure ΔP is equal to or greater than the threshold value ΔPth. The determination can be performed with high accuracy.

  FIG. 3 shows the differential pressure before and after the DPF 54 at a specific gas flow rate, the count value of the regeneration counter (counting unit that counts the number of filter regeneration), and the differential pressure before and after the filter regeneration count exceeds a predetermined number. It is a figure which shows the relationship between a stability flag (Xstable flag) and the exhaust gas flow volume lower limit at the time of the data for abnormality determination acquisition.

  The horizontal axis in FIG. 3 is the engine operating time, and the time t0 is immediately after the initial installation or replacement of the DPF 54 with a new one. A curve D0 is a curve of the DPF 54 indicating a typical front-rear differential pressure ΔP. A curve D1 is a curve of the DPF 54 showing a relatively low value of the front-rear differential pressure ΔP. A curve D2 is a curve of the DPF 54 that shows a relatively high value of the front-rear differential pressure ΔP. At time t0, the differential pressure ΔP across the DPF 54 (curves D0, D1, and D2) is ΔP0. PM deposition starts at time t0, and the differential pressure ΔP increases gradually.

  Time t1 is the time at which the electronic control unit 70 estimates that the amount of PM deposited on the DPF 54 has reached the amount to be regenerated, and the first filter regeneration process is started. The electronic control unit 70 estimates the PM accumulation amount based on the engine operation time, the engine speed (NE), the engine load (KL), and the like.

  Time t2 is the time when the first filter regeneration process is completed. During filter regeneration, PM accumulated in the DPF 54 burns and the clogging of the filter is eliminated, so the front-rear differential pressure ΔP decreases from time t1 to time t2. The front-rear differential pressure ΔP2 at time t2 is higher than the initial front-rear differential pressure ΔP0. This indicates that a part of the PM clogged in the filter remains without burning.

  The DPF 54 starts to deposit PM again from time t2. Time t3 is the time when the second filter regeneration process is started. At the time t3, the magnitude of the deviation of the curves D1 and D2 from the curve D0 with respect to the typical DPF 54 is smaller than the magnitude of the deviation at the time t1. That is, as a result of the first filter regeneration process, it is shown that the variation in the front-to-back differential pressure ΔP is small.

  Time t4 is the time when the second filter regeneration process is completed. The front-rear differential pressure ΔP at time t4 is substantially equal to the front-rear differential pressure ΔP2 at time t2. That is, it is considered that a part of the above-mentioned clogged PM remains without burning even in the second filter regeneration process.

  The DPF 54 starts to deposit PM again from time t4. Time t5 is the time when the third filter regeneration process is started. At time t5, the magnitude at which the curves D1 and D2 deviate from the curve D0 with respect to the typical DPF 54 is substantially equal to the magnitude at which they deviate at time t3.

  As described above, as the number of filter regeneration processes increases, the variation in the front-to-back differential pressure ΔP decreases. Furthermore, although the amount of decrease in the range of variation in the front-to-back differential pressure ΔP due to the first filter regeneration process (the difference between the variation at time t1 and the variation at time t3) is large, The amount of decrease in the variation range (for example, the difference between the variation at time t3 and the variation at time t5) is not so large. Therefore, it is understood that if the first filter regeneration process is executed, the exhaust gas flow rate V when acquiring the front-rear differential pressure ΔP for performing the abnormality determination of the DPF 54 does not have to be so large.

  From the above, this determination apparatus determines abnormality of the DPF 54 as follows.

This determination apparatus determines whether or not the number of filter regenerations for a new DPF 54 has reached a predetermined number.
(A) When the number of filter regenerations has not reached the predetermined number.
(A-1) This determination apparatus obtains (DPF passing gas flow rate Vdpf, front-rear differential pressure ΔP) a plurality of times when the DPF passing gas flow rate Vdpf is in a large flow rate region where the “predetermined first flow rate” Vc or higher. To do.
(A-2) The determination device obtains respective average values (Vave, ΔPave) of the acquired (DPF passage gas flow rate Vdpf, front-rear differential pressure ΔP).
(A-3) This determination apparatus determines the first threshold value ΔPth1 based on the average value Vave of the acquired DPF passage gas flow rate Vdpf.
(A-4) This determination apparatus compares ΔPave, which is a “differential pressure correlation value”, with ΔPth1, which is a “predetermined first threshold value”.
(A-5) This determination apparatus determines that the DPF 54 is abnormal when the differential pressure correlation value ΔPave is smaller than a predetermined first threshold value ΔPth1. The determination apparatus determines that the DPF 54 is normal when the differential pressure correlation value ΔPave is equal to or greater than a predetermined first threshold value ΔPth1.
(B) When the number of filter regenerations reaches a predetermined number (B-1) This determination device is in a medium flow rate region and a large flow rate region where the DPF passage gas flow rate Vdpf is equal to or greater than the “predetermined second flow rate” Vb. (DPF passage gas flow rate Vdpf, front-rear differential pressure ΔP) is acquired a plurality of times.
(B-2) The determination device obtains respective average values (Vave, ΔPave) of the acquired (DPF passage gas flow rate Vdpf, front-rear differential pressure ΔP).
(B-3) This determination apparatus determines the second threshold value ΔPth2 based on the average value Vave of the acquired DPF passage gas flow rate Vdpf.
(B-4) This determination apparatus compares ΔPave, which is the “differential pressure correlation value”, with ΔPth2, which is the “predetermined second threshold value”.
(B-5) This determination apparatus determines that the DPF 54 is abnormal when the differential pressure correlation value ΔPave is smaller than a predetermined second threshold value ΔPth2. The determination apparatus determines that the DPF 54 is normal when the differential pressure correlation value ΔPave is equal to or greater than a predetermined second threshold value ΔPth2.

<Actual operation>
Next, a specific operation of the determination apparatus will be specifically described with reference to FIG. FIG. 4 shows a “differential pressure stabilization flag acquisition routine” executed by the CPU of the electronic control unit 70.

  The description will be continued assuming that the DPF 54 is first installed in a vehicle to which the present determination apparatus is applied or has just been replaced with a new one, and that the filter regeneration is not being performed.

  When the appropriate timing is reached, the CPU starts processing from step 400 in FIG. 4 and proceeds to step 405 to determine whether or not the DPF 54 is first installed in the vehicle or immediately after being replaced with a new one. According to the above assumption, the DPF 54 is just installed in the vehicle or immediately after being replaced with a new one. Therefore, the CPU makes a “Yes” determination at step 405 to proceed to step 410 to set the count value C of the reproduction counter to “0”.

  Specifically, the count value C is set as follows. As a normal operation, when the DPF 54 is first installed in the vehicle or replaced with a new one, the vehicle battery and the electronic control device 70 are electrically disconnected, and power is not supplied to the electronic control device 70. To be.

  The count value C of the reproduction number counter is held in a static RAM (SRAM) provided in the electronic control unit 70. In the SRAM, when no voltage is applied (no power is supplied), the stored data is cleared.

  Therefore, when the DPF 54 is installed in the vehicle or when the DPF 54 is replaced, power is not supplied to the SRAM, so the stored data is cleared and set to “0”. That is, it can be said that the operations of Step 405 and Step 410 are automatically performed by the operation of the SRAM.

  In addition, when the DPF 54 is first installed in the exhaust passage or is replaced with a new one, a “switch” is provided which is operated by an operator or automatically operated by installing the DPF 54 in the exhaust passage. In addition, the CPU may perform the determination in step 405 and the processing in step 410 based on the state change of the switch.

  Next, the CPU proceeds to step 415 to determine whether or not filter regeneration processing has been performed. According to the above assumption, the filter regeneration process is not executed. Therefore, the CPU makes a “No” determination at step 415 to directly proceed to step 425 to determine whether or not the filter regeneration count (count value) is equal to or greater than the filter regeneration count threshold Cth. The filter regeneration frequency threshold Cth is an arbitrary integer equal to or greater than 1 (in this example, Cth = 2).

  At this time, since the filter regeneration count is “0”, it is smaller than the filter regeneration count threshold Cth. Accordingly, the CPU makes a “No” determination at step 425 to proceed to step 435, sets the differential pressure stabilization flag Xstable to “0”, proceeds to step 495, and once ends this routine.

  Further, at an appropriate timing, the CPU starts the process from step 500 in FIG. 5 and proceeds to step 505 to determine whether or not the filter regeneration process is not being executed. At present, the filter regeneration process is not executed. Therefore, the CPU makes a “Yes” determination at step 505 to proceed to step 510 to determine whether or not the differential pressure stabilization flag Xstable is “0”. At this time, the differential pressure stabilization flag Xstable is “0”. Therefore, the CPU makes a “Yes” determination at step 510 to proceed to step 515 to determine whether or not the DPF passage gas flow rate Vdpf is greater than or equal to the flow rate threshold value Vc.

  The situation where the DPF passage gas flow rate Vdpf exceeds the flow rate threshold value Vc (in the range of the large flow rate region) is, for example, when the engine operating state is such that the amount of EGR gas recirculated by EGR becomes “0”.

  If the exhaust gas flow rate V is greater than or equal to the flow rate threshold value Vc, the CPU makes a “Yes” determination at step 515 to proceed to step 520 to update the integrated value SumΔP1 of the front-rear differential pressure ΔP (the integrated value SumΔP1 before and after the current time). Add differential pressure ΔP). At the same time, the CPU updates the integrated value SumV1 of the DPF passage gas flow rate Vdpf (adds the current DPF passage gas flow rate Vdpf to the integration value SumV1). Further, the CPU increments the value of the counter N indicating the number of accumulated data by “1”, and proceeds to step 525.

  On the other hand, when the exhaust gas flow rate V is smaller than the flow rate threshold value Vc, the CPU makes a “No” determination at step 515 to directly proceed to step 525.

  When the CPU proceeds to step 525, if the ignition key switch 79 is not immediately after being changed from the on position to the off position, the CPU makes a “No” determination at step 525 to proceed directly to step 595. The routine is temporarily terminated.

  From this point onward, the CPU repeats the process of an appropriate step from step 505 to step 520 until it determines “Yes” in step 525. Therefore, the integrated value SumΔP1 of the front-rear differential pressure ΔP, the integrated value SumV1 of the DPF passage gas flow rate Vdpf, and the value of the counter N are updated.

  On the other hand, when the time point when the CPU executes the process of step 525 is immediately after “change of the ignition key switch 79 to the OFF position”, the CPU makes a “Yes” determination at step 525 to determine step 530. Proceed to In step 530, the CPU determines whether or not the differential pressure stabilization flag Xstable is “0”.

  At this time, the differential pressure stabilization flag Xstable is “0”. Therefore, the CPU makes a “Yes” determination at step 530 to proceed to step 535. In step 535, the CPU divides the integrated value SumΔP1 of the front-rear differential pressure ΔP by “N which is the value of the counter N”. As a result, the average value of the front-rear differential pressure ΔP when the DPF passage gas flow rate Vdpf is equal to or greater than the large flow rate region is acquired as the front-rear differential pressure ΔPave. At the same time, the CPU divides the integrated value SumV1 of the DPF passage gas flow rate Vdpf by “N which is the value of the counter N” to obtain the average value of the DPF passage gas flow rate Vdpf in the period in which the average value ΔP1 of the front-rear differential pressure is obtained. Obtain as Vave.

  Further, the CPU calculates the first threshold value ΔPth1 by substituting the acquired “average value Vave of the DPF passage gas flow rate Vdpf” into the function g1 (Vave). The function g1 (Vave) is determined in advance as a function that defines a determination threshold for the average value Vave obtained based on the plurality of DPF passage gas flow rates Vdpf acquired in the large flow rate region, that is, the first threshold value ΔPth1. ing. In addition, the CPU acquires the calculated first threshold value ΔPth1 as the predetermined threshold value ΔPth.

  Next, the CPU proceeds to step 540 and determines whether or not the average value ΔPave of the front-rear differential pressure ΔP is smaller than a predetermined threshold value ΔPth (in this case, ΔPth1).

  At this time, if the differential pressure correlation value ΔPave is equal to or greater than the predetermined threshold value ΔPth, the CPU makes a “No” determination at step 540 to proceed to step 570, determines that the DPF 54 is normal, and informs the backup RAM of that fact. To remember. Thereafter, the CPU proceeds to step 550. On the other hand, if the differential pressure correlation value ΔPave is smaller than the predetermined threshold value ΔPth, the CPU makes a “Yes” determination at step 540 to proceed to step 545, determines that the DPF 54 is abnormal, and backs up to that effect. Store in RAM. Thereafter, the CPU proceeds to step 550.

  In step 550, the CPU clears the average value ΔPave of the front-rear differential pressure ΔP, the average value Vave of the DPF passage gas flow rate Vdpf, and the value N of the counter N, proceeds to step 595, and once ends this routine.

  Even during the subsequent operation of the engine 10, the CPU repeatedly executes the routine shown in FIG. In this case, the present time is not immediately after the DPF 54 is first installed in the vehicle or replaced with a new one. Therefore, the CPU makes a “No” determination at step 405 to directly proceed to step 415 to determine whether filter regeneration has been performed.

  At present, the filter regeneration process is not executed. Therefore, the CPU makes a “No” determination at step 415 to proceed directly to step 425. At this time, the count value C of the reproduction number counter remains “0”, which is smaller than the determination threshold Cth. Therefore, the CPU makes a “No” determination at step 425 to proceed to step 435, sets the differential pressure stabilization flag Xstable to “0”, proceeds to step 495, and once ends this routine.

  Next, a case immediately after the filter regeneration process is performed will be described. In the flowchart shown in FIG. 4, when the appropriate timing is reached, the CPU proceeds to step 405, determines “No”, and directly proceeds to step 415. According to the above assumption, it is immediately after the filter regeneration process is performed. Accordingly, the CPU makes a “Yes” determination at step 415 to proceed to step 420, and increments the count value C of the reproduction number counter by one (ie, the count value is changed from “0” to “1”). .

  Thereafter, the CPU proceeds to step 425. At present, the count value C is smaller than Cth (in this example, “2”). Therefore, the CPU makes a “No” determination at step 425 to proceed to step 435, sets the differential pressure stabilization flag Xstable to “0”, proceeds to step 495, and once ends this routine.

  That is, when the number of filter regeneration processes is less than the determination threshold value Cth, the CPU obtains (DPF passage gas flow rate Vdpf, front-rear differential pressure ΔP) when the exhaust gas flow rate V is in the large flow rate region (the flow rate threshold value Vc or more). To do. The CPU obtains the respective average values (Vave, ΔPave) acquired, and compares the average value ΔPave of the differential pressure ΔP with the first threshold value ΔPth (Vave) in the average value Vave of the DPF passage gas flow rate Vdpf. Abnormality judgment is performed.

  Further, a case where filter regeneration processing is performed will be described. In this case, in the flowchart shown in FIG. 4, the CPU proceeds directly from step 405 to step 420, and increments the count value C of the reproduction number counter by one (C = Cth).

  Thereafter, the CPU proceeds to step 425. At present, the count value C is Cth. Therefore, the CPU makes a “Yes” determination at step 425 to proceed to step 430, sets the differential pressure stabilization flag Xstable to “1”, proceeds to step 495, and once ends this routine.

  Thereafter, the CPU proceeds to step 505 in the flowchart shown in FIG. According to the above assumption, the filter regeneration process is not in progress. Therefore, the CPU makes a “Yes” determination at step 505 to proceed to step 510.

  According to the above assumption, the differential pressure stabilization flag Xstable is “1”. Therefore, the CPU makes a “No” determination at step 510 to proceed to step 555 to determine whether or not the DPF passage gas flow rate Vdpf is greater than or equal to the flow rate threshold value (medium flow rate region lower limit) Vb.

  The situation where the exhaust gas flow rate V exceeds the flow rate threshold value Vb (in the range of the middle flow rate region) is, for example, a sudden start from waiting for a signal when traveling in an urban area, or a normal depression operation of the accelerator pedal AP when traveling at a high speed Acceleration can be considered.

  If the exhaust gas flow rate V is greater than or equal to the flow rate threshold value Vb, the CPU makes a “Yes” determination at step 555 to proceed to step 560 to update the integrated value SumΔP2 of the front-rear differential pressure ΔP (the integrated value SumΔP2 before and after the current time). At the same time, the integrated value SumV2 of the DPF passage gas flow rate Vdpf (in this case, equal to the exhaust gas flow rate V) is updated (the current DPF passage gas flow rate Vdpf is added to the integration value SumV2). At the same time, the CPU increases the value of the counter N indicating the number of accumulated data by “1”. On the other hand, when the exhaust gas flow rate V is smaller than the flow rate threshold value Vb, the CPU makes a “No” determination at step 555 to directly proceed to step 525.

  If the CPU executes the process of step 525 immediately after “change of the ignition key switch 79 to the OFF position”, the CPU makes a “Yes” determination at step 525 to proceed to step 530. .

  At this time, the differential pressure stabilization flag Xstable is “1”. Accordingly, the CPU makes a “No” determination at step 530 to proceed to step 565. The CPU divides the integrated value SumΔP2 of the front-rear differential pressure ΔP by “the value of the counter N” to obtain the average value of the front-rear differential pressure ΔP when the DPF passage gas flow rate Vdpf is greater than or equal to the large flow rate region. Acquired as pressure ΔPave. At the same time, the CPU divides the integrated value SumV2 of the DPF passage gas flow rate Vdpf by “N which is the value of the counter N”, thereby obtaining the average value of the DPF passage gas flow rate Vdpf in the period in which the differential pressure (average value) ΔP2 is obtained. Is acquired as the exhaust gas flow rate Vave.

  Further, the CPU calculates the second threshold value ΔPth2 by substituting the acquired “average value Vave of the DPF passage gas flow rate Vdpf” into the function g2 (Vave). This function g2 (Vave) is determined in advance as a function that defines a determination threshold for the average value Vave obtained based on the plurality of DPF passage gas flow rates Vdpf acquired in the middle flow rate region, that is, the second threshold value ΔPth2. ing. In addition, the CPU acquires the calculated second threshold value ΔPth2 as the predetermined threshold value ΔPth.

  Next, the CPU proceeds to step 540 to determine whether or not the average value ΔPave of the front-rear differential pressure ΔP is smaller than a second threshold value ΔPth (in this case, ΔPth2).

  At this time, if the differential pressure correlation value ΔPave is equal to or greater than a predetermined second threshold value ΔPth, the CPU makes a “No” determination at step 540 to proceed to step 570 to determine that the DPF 54 is normal, to that effect. Is stored in the backup RAM. Thereafter, the CPU proceeds to step 595 via step 550. On the other hand, if the differential pressure correlation value ΔPave is smaller than the predetermined second threshold value ΔPth, the CPU determines “Yes” in step 540 and proceeds to step 545 to determine that the DPF 54 is abnormal. The fact is stored in the backup RAM. Thereafter, the CPU proceeds to step 595 via step 550.

As described above, this determination apparatus is an abnormality determination apparatus for the particulate filter (DPF 54) disposed in the exhaust passage (exhaust pipe 52) of the internal combustion engine,
A differential pressure acquisition unit (front / rear differential pressure sensor 74) for acquiring a differential pressure ΔP before and after the particulate filter;
A gas flow rate acquisition unit (an air flow meter 71, a front-rear differential pressure sensor 74, an exhaust gas temperature sensor 75, an exhaust gas pressure sensor 76, and a gas flow rate acquisition unit for acquiring a passing gas flow rate (DPF passing gas flow rate Vdpf) that is a flow rate of gas passing through the particulate filter. Atmospheric pressure sensor 77),
A filter installation determination unit (step 405) for determining whether or not the particulate filter is first installed in the exhaust passage or has been replaced with a new one;
The particulate filter executed from the time when it is determined that the particulate filter is initially set in the exhaust passage or may have been replaced with a new one to the time when the same determination is made next. A counting unit (reproduction count counter) (step 420) for counting the number of times of filter regeneration C that is the number of regenerations;
When it is determined whether or not an abnormality has occurred in the particulate filter (steps 525 and 530),
When the number of filter regenerations is smaller than the predetermined number (determination threshold Cth) (steps 425 and 435),
Based on a comparison result between the differential pressure correlation value ΔPave correlated with the differential pressure before and after the passage gas flow rate is equal to or higher than a predetermined first flow rate Vc and a predetermined first threshold value ΔPth (Vave). It is determined whether an abnormality has occurred in the particulate filter (step 530, step 535 and step 540),
When the filter regeneration number is equal to or greater than a predetermined number (steps 425 and 430),
A differential pressure correlation value ΔPave having a correlation with the differential pressure before and after the particulate filter acquired when the passing gas flow rate is equal to or higher than a predetermined second flow rate Vb smaller than the first flow rate and a predetermined second threshold value Based on the comparison result with ΔPth (Vave), it is determined whether or not an abnormality has occurred in the particulate filter (step 530, step 565 and step 540), and an abnormality determination unit is provided.

  Further, the abnormality determination unit determines that the minimum value C1min in the range of variation in the front-rear differential pressure caused by the individual difference of the normal particulate filter (normal DPF) is an individual difference of the abnormal particulate filter (abnormal DPF). The first flow rate Vc is set within the range of the passing gas flow rate Vdpf so that a relationship larger than the maximum value C2max in the range of the variation in the differential pressure between the front and rear is generated.

In addition, when the filter regeneration number C is smaller than the predetermined number of times (determination threshold Cth), the abnormality determining unit determines that the differential pressure correlation value ΔPave when the passing gas flow rate is equal to or higher than a predetermined first flow rate Vc. A plurality of pieces of data of the front-rear differential pressure ΔP, which are basic data, are obtained (step 520), and an average value Vave of the passing gas flow rate Vdpf when the plurality of pieces of data is obtained is obtained based on the obtained average value. Determining the first threshold value ΔPth1 (step 535);
When the filter regeneration number is equal to or greater than the predetermined number of times, a plurality of data of the front-rear differential pressure ΔP, which becomes basic data of the differential pressure correlation value ΔPave when the passing gas flow rate is equal to or higher than the predetermined second flow rate Vb, Obtaining (step 560) the second threshold value ΔPth2 is determined based on the average value Vave of the passing gas flow rate Vdpf obtained when the plurality of data are obtained (step 565). Is done.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention.

  For example, the determination device acquires data of (exhaust gas flow rate V, differential pressure ΔP before and after) when the exhaust gas flow rate V enters the “flow rate range in which data should be acquired”, but acquires the exhaust gas flow rate V data. You may perform control which increases so that it may become the flow range which should be. For example, the amount of EGR gas recirculated by the EGR device 60 may be reduced in order to increase the exhaust gas flow rate V to a predetermined flow rate region. Alternatively, the exhaust gas temperature may be raised by supplying unburned HC into the exhaust path upstream of the DPF 54.

  The determination device obtains the exhaust gas flow rate V based on the output of the air flow meter 71, the output of the differential pressure sensor 74, the exhaust gas temperature sensor 75, the exhaust gas pressure sensor 76, the atmospheric pressure sensor 77, and the like. On the other hand, the determination device may acquire the exhaust gas flow rate V by estimating the exhaust gas flow rate V based on the operating state of the engine (fuel injection amount Qfin, engine rotational speed NE) and the like. Further, the determination device may provide an exhaust gas flow rate sensor in the exhaust path and acquire the exhaust gas flow rate V based on the output of the exhaust gas flow rate sensor.

  When the exhaust gas flow rate V is within the flow rate range from which data is to be acquired, the determination device continues to acquire data to be used for abnormality determination until the ignition key switch 79 is changed from the on position to the off position. However, a limit value may be provided for the number N of acquired data.

  Furthermore, although the determination device uses the differential pressure correlation value as the front-rear differential pressure ΔP itself, the differential pressure correlation value may be a reciprocal of the front-rear differential pressure ΔP.

DESCRIPTION OF SYMBOLS 10 ... Engine, 20 ... Engine body part, 30 ... Fuel supply system, 40 ... Intake system, 51 ... Exhaust manifold, 52 ... Exhaust pipe, 53 ... DOC, 54 ... DPF, 60 ... EGR system, 71 ... Air flow meter, 73 ... EGR control valve opening sensor, 74 ... front-rear differential pressure sensor, 75 ... exhaust gas temperature sensor, 76 ... exhaust gas pressure sensor, 77 ... atmospheric pressure sensor, 79 ... ignition key switch.

Claims (3)

An abnormality determination device for a particulate filter disposed in an exhaust passage of an internal combustion engine,
A differential pressure acquisition unit that acquires a differential pressure across the particulate filter;
A gas flow rate acquisition unit for acquiring a passing gas flow rate that is a flow rate of gas passing through the particulate filter;
A filter installation determining unit that determines whether the particulate filter is first installed in the exhaust passage or has been replaced with a new one;
The particulate filter that is executed from the time when it is determined that the particulate filter is first installed in the exhaust passage or may be replaced with a new one to the next time when the determination is made. A counter for counting the number of filter regenerations, which is the number of regenerations;
When it should be determined whether an abnormality has occurred in the particulate filter,
If the filter regeneration number is less than a predetermined number,
Based on a comparison result between a differential pressure correlation value correlated to the differential pressure before and after the particulate filter acquired when the passing gas flow rate is equal to or higher than a predetermined first flow rate, and a predetermined first threshold value. Determine whether an abnormality has occurred in the curate filter,
When the filter regeneration number is equal to or greater than the predetermined number,
Based on a comparison result between the differential pressure correlation value correlated with the front-rear differential pressure acquired when the passing gas flow rate is equal to or higher than a predetermined second flow rate smaller than the first flow rate, and a predetermined second threshold value. An abnormality determination unit for determining whether an abnormality has occurred in the particulate filter;
An abnormality determination device comprising: In the abnormality determination device according to claim 1,
The abnormality determination unit has a minimum value in a range of variation in the front-rear differential pressure caused by an individual difference of the normal particulate filter within a range of variation in the front-rear differential pressure caused by an individual difference of the abnormal particulate filter. An abnormality determination device configured to set the first flow rate within a range of the passing gas flow rate such that a relationship larger than a maximum value is established. In the abnormality determination device according to claim 1 or 2,
The abnormality determination unit
When the filter regeneration number is less than the predetermined number of times, a plurality of data of the front and rear differential pressures, which become basic data of the differential pressure correlation value when the passing gas flow rate is equal to or higher than the predetermined first flow rate, are acquired. And determining the first threshold value based on the average value obtained by obtaining an average value of the flow rate of the passing gas when the plurality of data is acquired,
When the number of filter regenerations is equal to or greater than the predetermined number, a plurality of front and rear differential pressure data that are basic data of the differential pressure correlation value are acquired when the passing gas flow rate is equal to or greater than the predetermined second flow rate. And obtaining the average value of the passing gas flow rate when acquiring the plurality of data, and determining the second threshold based on the average value obtained simultaneously.
An abnormality determination device configured as described above.

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