JP2020133507A - Diagnostic device - Google Patents

Abstract

To effectively detect abnormality or normality of a filter by using a simple configuration.SOLUTION: A diagnostic device for a filter 33 capable of collecting particulate matters in exhaust gas discharged from an engine 10 includes: a casing 31 capable of accommodating the filter 33; a downstream exhaust pipe 40 bent so that a flow passage axial center X2 thereof is inclined to an axial center X1 of the casing 31 at a predetermined angle and connected to a downstream end of the casing 31; a differential pressure sensor 90 including an upstream sensor part 91 acquiring an upstream pressure value P1 on the upstream side of a portion of the casing 31 in which the filter 33 is accommodated and a downstream sensor part 92 acquiring a downstream pressure value P2 on the downstream side of the portion of the casing 31 in which the filter 33 is accommodated; and a diagnosis part 110 determining abnormality and/or normality of the filter 33 by comparing the upstream pressure value P1 and the downstream pressure value P2 acquired by the differential pressure sensor 90 with each other.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a diagnostic device, and more particularly to a diagnostic device of a particulate filter (hereinafter, filter) capable of collecting particulate matter (Particulate Matter: hereinafter, PM) in exhaust gas discharged from an internal combustion engine. ..

As an example of the exhaust purification device, one provided with a filter for collecting PM in the exhaust gas discharged from the internal combustion engine is known. The PM deposited on the filter mainly contains soot (soot) components discharged from the engine, as well as engine oil components and the like. The soot component is burned and removed by filter regeneration, but the nonflammable engine oil becomes unburned ash (ash). Therefore, it is necessary to take out the filter from the casing of the exhaust gas purification device and perform maintenance to periodically clean and remove the accumulated ash and the like.

If the filter is forgotten to be returned to the casing during maintenance, or if the filter cracks or cracks occur due to thermal runaway during filter regeneration, PM is released into the atmosphere without being normally collected. It ends up. For this reason, in-vehicle failure diagnosis (OBD: On Board Diagnosis) that detects an abnormality of the filter by a sensor is performed (see, for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2017-083288 Japanese Unexamined Patent Publication No. 2016-0378999

In the above-mentioned filter abnormality diagnosis, a so-called resistance type sensor that detects PM based on the resistance value between the electrodes that changes with the adhesion of PM may be arranged on the downstream side of the filter. However, the resistance type sensor itself is relatively expensive and may increase the cost of the entire device.

It is also conceivable to use a differential pressure sensor that detects the differential pressure before and after the filter for diagnosing an abnormality of the filter. However, in the diagnosis based on the differential pressure value of the differential pressure sensor, it may not be possible to clearly distinguish the abnormality or normality of the filter depending on the casing and the shape of the exhaust pipe on the downstream side.

An object of the present disclosure technique is to provide a diagnostic device capable of effectively detecting an abnormality or normality of a filter with a simple configuration.

The technique of the present disclosure is a diagnostic device for a filter capable of collecting particulate matter in exhaust gas discharged from an engine, a casing capable of accommodating the filter, and a flow path thereof at a downstream end of the casing. Acquires the downstream exhaust pipe connected by bending the axis so as to be inclined at a predetermined angle with respect to the axis of the casing, and the upstream pressure value on the upstream side of the portion of the casing in which the filter is housed. A differential pressure sensor including an upstream sensor unit and a downstream sensor unit that acquires a downstream pressure value on the downstream side of the portion of the casing in which the filter is housed, and the upstream pressure value acquired by the differential pressure sensor. A diagnostic apparatus comprising: a diagnostic unit for determining an abnormality or normality of the filter by comparing the downstream pressure value with the downstream pressure value.

Further, the downstream sensor unit is provided on the downstream side of the casing where the filter is housed, on the side opposite to the bending direction of the downstream exhaust pipe, and the diagnostic unit is the diagnostic unit. When the upstream pressure value is equal to or less than the downstream pressure value, it is preferable to diagnose the filter as abnormal.

Further, it is preferable that the diagnosis unit diagnoses the filter as normal when the upstream pressure value is higher than the downstream pressure value.

Further, the downstream sensor unit is provided on a portion of the casing on the bending direction side of the downstream exhaust pipe on the downstream side of the portion in which the filter is housed, and the diagnostic unit is the upstream pressure value. When the pressure difference between the downstream pressure value and the downstream pressure value is equal to or less than the predetermined first differential pressure threshold value, the filter is determined to be normal, and the pressure difference is larger than the first differential pressure threshold value. When it is equal to or more than the threshold value, it is preferable to determine that the filter is abnormal.

Further, when the pressure difference is equal to or greater than the second differential pressure threshold value, the diagnostic unit determines that the filter is abnormal if the upstream pressure value is equal to or less than a predetermined first pressure threshold value, and determines the upstream pressure value. When is equal to or higher than a predetermined second pressure threshold value higher than the first pressure threshold value, it is preferable to determine that filter regeneration is required to burn and remove particulate matter deposited on the filter.

According to the technique of the present disclosure, it is possible to effectively detect an abnormality or normality of a filter with a simple configuration.

It is a schematic overall block diagram which shows the exhaust system of the engine which concerns on this embodiment. It is a schematic whole block diagram which shows the main part of the diagnostic apparatus which concerns on 1st Embodiment. It is a schematic diagram explaining the operation mainly of the diagnostic apparatus which concerns on 1st Embodiment. It is a flowchart explaining the diagnostic process which concerns on 1st Embodiment. It is a schematic diagram explaining the operation mainly of the diagnostic apparatus which concerns on 2nd Embodiment.

Hereinafter, the diagnostic apparatus according to the present embodiment will be described with reference to the accompanying drawings. The same parts have the same reference numerals, and their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

[First Embodiment]
FIG. 1 is a schematic overall configuration diagram showing an engine exhaust system according to the present embodiment.

As shown in FIG. 1, each cylinder of the engine 10 is provided with an in-cylinder injector 11 that directly injects fuel into the cylinder. The fuel injection amount, injection timing, injection frequency, and the like of the in-cylinder injector 11 are controlled according to an instruction signal input from the electronic control unit (hereinafter, ECU) 100. The engine 10 is not limited to the 4-cylinder engine shown in the illustrated example, and may be a single-cylinder engine or a multi-cylinder engine other than the 4-cylinder engine. Further, the engine 10 is not limited to the direct injection engine, and may be a premixed engine or the like.

The engine 10 is provided with an exhaust manifold 12 that collects exhaust gas discharged from each cylinder. An upstream exhaust pipe 13 for drawing out exhaust gas is connected to the exhaust collecting portion of the exhaust manifold 12. The upstream exhaust pipe 13 is preferably provided with an exhaust pipe injector 20. Further, the exhaust aftertreatment device 30, the downstream exhaust pipe 40, and the like are connected to the upstream exhaust pipe 13 in this order.

The exhaust aftertreatment device 30 includes a casing 31 connected to the upstream exhaust pipe 13. Further, the oxidation catalyst 32 and the filter 33 are housed in the casing 31 in order from the upstream side of the exhaust gas. A differential pressure sensor 90 that acquires the front-rear differential pressure of the filter 33 is provided at the exhaust inlet portion and the exhaust outlet portion of the filter 33. The sensor value of the differential pressure sensor 90 is transmitted to the electrically connected ECU 100.

The oxidation catalyst 32 is formed by supporting a catalyst component or the like on the surface of a ceramic carrier 32A such as a cordierite honeycomb structure. When unburned fuel (HC) is supplied by the post injection of the in-cylinder injector 11 or the exhaust pipe injection of the exhaust pipe injector 20, the oxidation catalyst 32 oxidizes the unburned fuel (HC) to raise the exhaust temperature.

In the filter 33, for example, a large number of cells 33C partitioned by a partition wall 33B are provided on a porous ceramic carrier 33A along the axial direction, and the upstream end and the downstream end of these cells 33C are alternately provided by a plug 33D. It is formed by sealing the eyes. The filter 33 collects PM in the exhaust gas in the pores and the surface of the partition wall 33B, and periodically burns and removes the accumulated PM to perform filter regeneration. In the filter regeneration, unburned fuel is supplied to the oxidation catalyst 32 by post-injection of the in-cylinder injector 11 or exhaust pipe injection of the exhaust pipe injector 20, and the temperature of the exhaust gas flowing into the filter 33 is set to the PM combustion temperature (for example, PM combustion temperature). It is carried out by raising the temperature to about 600 ° C.).

The ECU 100 controls various controls such as the engine 10, and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. Further, the ECU 100 includes a filter diagnosis unit 110 (diagnosis unit of the present disclosure) as a part of the functional elements. Details of the diagnostic process by the filter diagnostic unit 110 will be described later.

FIG. 2 is a schematic overall configuration diagram showing a main part of the diagnostic apparatus according to the present embodiment.

As shown in FIG. 2, the diagnostic device includes a casing 31 forming a part of the exhaust aftertreatment device 30, a downstream exhaust pipe 40 connected to the downstream end of the casing 31, a differential pressure sensor 90, and functions of the ECU 100. It includes a filter diagnostic unit 110 as an element. The casing 31 and the downstream exhaust pipe 40 may be formed separately or integrally.

The casing 31 is formed in a substantially cylindrical shape having an inner diameter of substantially the same diameter from the upstream side to the downstream side. Inside the casing 31, a filter 33 having a substantially columnar carrier 33A is housed. Specifically, the filter 33 is placed in a predetermined portion in the casing 31 in a state where the axis of the carrier 33A (direction of the flow path of the cell 33C) is substantially parallel to the axis X1 of the casing 31, preferably not shown. It is housed and held via a mat member or the like.

That is, with the filter 33 housed in the casing 31, the exhaust gas passing through the filter 33 flows along each cell 33C of the filter 33 substantially parallel to the axis X1 of the casing 31. There is. The shape of the casing 31 may be another shape such as an elliptical cylinder or a hollow prismatic shape, depending on the shape of the carrier 33A of the filter 33.

The downstream exhaust pipe 40 is formed in a substantially cylindrical shape, and its upstream opening is connected to the downstream opening of the casing 31. The shape of the downstream exhaust pipe 40 may be another shape such as an elliptical cylinder or a hollow prismatic shape, depending on the shape of the casing 31.

In the present embodiment, the downstream exhaust pipe 40 has a casing 31 so that its flow path axis X2 is tilted at a predetermined angle θ (preferably an obtuse angle larger than 90 degrees) with respect to the casing 31 axis X1. It is bent and connected to the downstream end. That is, the flow path axis X2 of the downstream exhaust pipe 40 goes from the upstream side to the downstream side with respect to the axis X2 of the carrier 33A of the filter 33 housed in the casing 31 (or the axis X1 of the casing 31). Therefore, it is provided so as to be eccentric toward the bending direction side.

As a result, for example, as shown in FIG. 3A, when the filter 33 is housed in the casing 31, the exhaust gas E flowing in the casing 31 flows along the cell 33C of the filter 33 in the casing 31. It is rectified substantially parallel to the axis X1 (see FIG. 2), flows substantially uniformly in the casing 31, and then flows into the downstream exhaust pipe 40. That is, of the downstream side in the casing 31, the exhaust gas E is in any region of the anti-bending side (anti-eccentric side) A and the bending side (eccentric side) B on the side opposite to the bending direction of the downstream exhaust pipe 40. Will be swept away.

On the other hand, as shown in FIG. 3B, when the filter 33 is not housed in the casing 31 (or when the filter 33 is significantly damaged or the like), the exhaust gas flowing in the casing 31 E cannot obtain the rectifying effect of the filter 33. In this case, the exhaust gas E flows in the casing 31 toward the bending side (eccentric side) B, and does not flow in the region of the anti-bending side (anti-eccentric side) A to the downstream exhaust pipe 40. Will flow in.

The differential pressure sensor 90 includes an inlet sensor unit 91 that acquires an inlet pressure P1 on the exhaust inlet side of the filter 33, and an outlet sensor unit 92 that acquires an outlet pressure P2 on the exhaust outlet side of the filter 33. In the present embodiment, the outlet sensor portion 92 of the differential pressure sensor 90 corresponds to the anti-bending side (anti-eccentric side) A of the downstream exhaust pipe 40 among the downstream end portions of the casing 31 adjacent to the exhaust outlet portion of the filter 33. It is provided in the part to be used.

That is, as shown in FIG. 3A, when the filter 33 is housed in the casing 31, the exhaust gas E rectified by the cell 33C of the filter 33 flows in the vicinity of the outlet sensor unit 92. The inlet pressure P1 shows a higher value than the outlet pressure P2 (P1> P2). On the other hand, as shown in FIG. 3B, when the filter 33 is not housed in the casing 31 (or the filter 33 is significantly damaged), the exhaust is exhausted in the vicinity of the outlet sensor unit 92. Since the gas E does not flow, the inlet pressure P1 shows a value lower than or substantially the same as the outlet pressure P2 (P1 ≦ P2).

The filter diagnosis unit 110 determines whether the filter 33 is abnormal or normal based on the magnitude relationship between the inlet pressure P1 and the outlet pressure P2 of the sensor units 91 and 92 input from the differential pressure sensor 90. Specifically, if the inlet pressure P1 is higher than the outlet pressure P2 (P1> P2), as shown in FIG. 3 (A), the filter 33 is housed in the casing 31, and the filter 33 is large. It is estimated that no damage has occurred. In this case, the filter diagnosis unit 110 determines that the filter 33 is normal. On the other hand, if the inlet pressure P1 is equal to or less than the outlet pressure P2 (P1 ≦ P2), as shown in FIG. 3 (B), the filter 33 is not housed in the casing 31, or the filter 33 is severely damaged. Etc. are presumed to have occurred. In this case, the filter diagnosis unit 110 determines that the filter 33 is abnormal (forgot to insert or damage has occurred).

The determination result by the filter diagnosis unit 110 is preferably output to a display device and a speaker provided in a driver's cab (not shown). The determination result may be transmitted to the vehicle management base station or the like via an external communication device or the like (not shown).

Next, the flow of the diagnostic process according to the present embodiment will be described with reference to FIG. This routine is started, for example, by turning on the ignition switch of the engine 10.

In step S100, the inlet pressure P1 acquired by the inlet sensor unit 91 of the differential pressure sensor 90 and the outlet pressure P2 acquired by the outlet sensor unit 92 are compared. Specifically, it is determined whether or not the inlet pressure P1 is higher than the outlet pressure P2. When the inlet pressure P1 is higher than the outlet pressure P2 (Yes), this control proceeds to step S110, and determines that the filter 33 is normal. When the process proceeds from step S100 to step S110, the processes of steps S100 and S110 are repeatedly executed until the ignition switch is turned off.

On the other hand, in step S100, when the inlet pressure P1 is not higher than the outlet pressure P2 (No), in other words, if the inlet pressure P1 is equal to or less than the outlet pressure P2, this control proceeds to step S120 and the filter 33 is abnormal. Is determined.

Next, in step S130, the determination result is output to a display device and / or a speaker provided in the driver's cab (not shown), and then this control ends.

According to the diagnostic apparatus according to the first embodiment described in detail above, the downstream exhaust pipe 40 in which the flow path axis X2 is tilted with respect to the casing 31 axis X1 at the downstream end of the casing 31 accommodating the filter 33. Are connected in a bent state. That is, the flow path axis X2 of the downstream exhaust pipe 40 goes from the upstream side to the downstream side with respect to the axis X2 of the carrier 33A of the filter 33 housed in the casing 31 (or the axis X1 of the casing 31). Therefore, it is provided so as to be eccentric to the bending side B.

As a result, when the filter 33 is housed in the casing 31, the exhaust gas flows substantially uniformly in the casing 31 from the upstream side to the downstream side due to the rectifying effect of the filter 33, while in the casing 31. If the filter 33 is not accommodated in the filter 33, or if the filter 33 is severely damaged, the rectifying effect of the filter 33 cannot be obtained, so that the exhaust gas is on the anti-bending side (anti-eccentric side) A. The gas flows to the bending side (eccentric side) B without flowing into the air.

In the present embodiment, the outlet sensor portion 92 of the differential pressure sensor 90 is provided at a portion of the downstream end portion of the casing 31 corresponding to the anti-bending side (anti-eccentric side) A of the downstream exhaust pipe 40. That is, in the state where the filter 33 is housed in the casing 31, the exhaust gas rectified by the filter 33 flows in the vicinity of the outlet sensor unit 92, so that the inlet pressure P1 shows a higher value than the outlet pressure P2. When the filter 33 is not housed in the casing 31 or the filter 33 is severely damaged, the exhaust gas E does not flow into the vicinity of the outlet sensor portion 92, so that the inlet pressure P1 is increased. A value lower than or substantially equivalent to the outlet pressure P2 will be shown.

From this, if the inlet pressure P1 is higher than the outlet pressure P2 (P1> P2), the filter 33 can be easily determined to be normal, and if the inlet pressure P1 is equal to or less than the outlet pressure P2 (P1 ≦ P2). The filter 33 can be easily determined to be abnormal, and the filter 33 can be reliably diagnosed with a simple configuration. Further, since it is not necessary to provide a relatively expensive resistance type sensor on the downstream side of the filter 33, the cost of the entire device can be effectively suppressed.

[Second Embodiment]
FIG. 5 is a schematic overall configuration diagram showing the diagnostic apparatus according to the second embodiment.

In the diagnostic device according to the second embodiment, the outlet sensor portion 92 of the differential pressure sensor 90 is placed on the bent side (eccentric side) of the downstream exhaust pipe 40 among the downstream ends of the casing 31 adjacent to the exhaust outlet portion of the filter 33. It is provided in the part corresponding to B.

Specifically, as shown in FIG. 5A, when a new filter 33 or a filter 33 having a small amount of PM deposited is housed in the casing 31, the vicinity of the outlet sensor portion 92 is rectified by the filter 33. While the exhaust gas flows, as shown in FIG. 5 (B), if the filter 33 is not housed in the casing 31, or if the filter 33 is significantly damaged, the flow is unevenly distributed. The exhaust gas E is configured to flow into the vicinity of the outlet sensor unit 92. That is, the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 in the state shown in FIG. 5 (B) is larger than the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 in the state shown in FIG. 5 (A). It comes to show the differential pressure value.

When the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 is equal to or less than the predetermined first differential pressure threshold value ΔP _{_1} (ΔP ≦ ΔP _{_1} ), the filter diagnosis unit 110 according to the second embodiment normally performs the filter 33. When the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 is larger than the first differential pressure threshold ΔP _{_1 and} equal to or greater than the predetermined second differential pressure threshold ΔP _{_2} (ΔP ≧ ΔP _{_2} ), the filter 33 Is judged to be abnormal (forgot to insert or damage occurred).

As shown in FIG. 5C, when PM is deposited on the filter 33, the inlet pressure P1 acquired by the inlet sensor unit 91 of the differential pressure sensor 90 becomes higher, so that the inlet pressure P1 and the outlet are increased. The pressure difference ΔP with the pressure P2 shows a large value. Therefore, when the determination based on only the pressure difference [Delta] P, FIG. 5 is a pressure difference [Delta] P that PM is more deposited the state shown in FIG. 5 (B) becomes more than a second differential pressure threshold value [Delta] P _{_2,} filter 33 ( It is not possible to distinguish from the state shown in C), which may lead to erroneous judgment.

In order to prevent such an erroneous determination, the filter diagnosis unit 110 uses the inlet sensor unit 91 to acquire the inlet when the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 is equal to or greater than the second differential pressure threshold value ΔP _{_2.} If the pressure P1 is equal to or less than the predetermined first pressure threshold value _{P_1} , the filter 33 is determined to be abnormal. The filter diagnosis unit 110, when the pressure difference [Delta] P between the inlet pressure P1 and the outlet pressure P2 is equal to or greater than the second differential pressure threshold value [Delta] P _{_2,} inlet pressure P1 obtained by the inlet sensor 91 is a first pressure threshold value P if given a second pressure threshold P _{_2} or higher than _{- 1,} filter regeneration to burn and remove PM deposited on the filter 33 is configured to determine the required state. The first differential pressure threshold value [Delta] P _{_1,} the second differential pressure threshold value [Delta] P _{_2,} the first pressure threshold value _{P _1} and, in either the extent of the value of the second pressure threshold value _{P _2,} engine displacement and the casing 30 of the engine 10 It may be appropriately set according to various specifications such as the cross-sectional area of the flow path and the capacity of the filter 33.

According to the diagnostic apparatus according to the second embodiment described in detail above, the outlet sensor portion 92 of the differential pressure sensor 90 is located on the anti-bending side (anti-eccentric side) A of the downstream exhaust pipe 40 among the downstream end portions of the casing 31. It is provided in the part corresponding to. That is, in the state where the filter 33 is housed in the casing 31, the exhaust gas rectified by the filter 33 flows in the vicinity of the outlet sensor unit 92, while the filter 33 is not housed in the casing 31. Is configured so that the drifted exhaust gas E flows into the vicinity of the outlet sensor unit 92 when the filter 33 is severely damaged or the like.

From this, if the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 is equal to or less than the first differential pressure threshold value ΔP _{_1} (ΔP ≦ ΔP _{_1} ), the filter 33 can be easily determined to be normal, and the inlet pressure P1 can be easily determined. can and to easily determine the pressure difference [Delta] P if the second differential pressure threshold value [Delta] P _{_2} or greater than the first differential pressure threshold value _{ΔP _1 (ΔP ≧ P _2)} , the filter 33 and abnormality of the outlet pressure P2 As in the first embodiment, the filter 33 can be reliably diagnosed with a simple configuration, and the cost of the entire device can be effectively suppressed.

Further, when the pressure difference ΔP between the inlet pressure P1 and the outlet pressure P2 is equal to or greater than the second differential pressure threshold value ΔP _{_2} , if the inlet pressure P1 is equal to or less than the first pressure threshold value P _{_1} , the filter 33 is determined to be abnormal. if given a second pressure threshold P _{_2} or higher than the inlet pressure P1 is the first pressure threshold value P _{_1,} filter regeneration is configured to determine the required state. As a result, it is possible to reliably distinguish between an abnormality in the filter 33 (forgot to insert or damage) and a state in which a large amount of PM is accumulated on the filter 33, and these erroneous determinations can be effectively prevented.

It should be noted that the present disclosure is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the gist of the present disclosure.

For example, the downstream distribution / exhaust pipe 40 may be formed so as to reduce the cross-sectional area of the flow path toward the downstream side. Further, the downstream distribution / exhaust pipe 40 may be formed so as to be curved toward the downstream side. Further, the upstream sensor portion 91 of the differential pressure sensor 90 may be provided at a portion of the casing 31 on the upstream side of the oxidation catalyst 32. In any of these cases, the same action and effect as those of the above-described embodiment can be obtained.

10 Engine 30 Exhaust aftertreatment device 31 Casing 32 Oxidation catalyst 33 Filter 40 Downstream exhaust pipe 90 Differential pressure sensor 91 Upstream sensor section 92 Downstream sensor section 100 ECU
110 Filter Diagnosis Department (Diagnosis Department)

Claims (5)

A diagnostic device for filters that can collect particulate matter in the exhaust gas emitted from the engine.
A casing that can accommodate the filter and
A downstream exhaust pipe connected to the downstream end of the casing so that the center of the flow path is bent at a predetermined angle with respect to the center of the casing.
An upstream sensor unit that acquires an upstream pressure value on the upstream side of the portion of the casing in which the filter is accommodated, and a downstream sensor portion that acquires a downstream pressure value on the downstream side of the portion of the casing that accommodates the filter. The differential pressure sensor including the sensor part and
A diagnostic apparatus comprising: a diagnostic unit for determining an abnormality or normality of the filter by comparing the upstream pressure value acquired by the differential pressure sensor with the downstream pressure value. The downstream sensor unit is provided on the downstream side of the casing where the filter is housed, on the side opposite to the bending direction of the downstream exhaust pipe.
The diagnostic device according to claim 1, wherein the diagnostic unit diagnoses the filter as abnormal when the upstream pressure value is equal to or less than the downstream pressure value. The diagnostic device according to claim 1 or 2, wherein the diagnostic unit diagnoses the filter as normal when the upstream pressure value is higher than the downstream pressure value. The downstream sensor unit is provided on a portion of the casing on the bending direction side of the downstream exhaust pipe, which is located on the downstream side of the portion in which the filter is housed.
When the pressure difference between the upstream pressure value and the downstream pressure value is equal to or less than a predetermined first differential pressure threshold value, the diagnostic unit determines that the filter is normal, and the pressure difference is the first differential pressure threshold value. The diagnostic device according to claim 1, wherein the filter is determined to be abnormal when the pressure is greater than or equal to a predetermined second differential pressure threshold value. When the pressure difference is equal to or greater than the second differential pressure threshold value, the diagnostic unit determines that the filter is abnormal if the upstream pressure value is equal to or less than a predetermined first pressure threshold value, and the upstream pressure value is the said. The diagnostic apparatus according to claim 4, wherein if the pressure is equal to or higher than a predetermined second pressure threshold value higher than the first pressure threshold value, it is determined that the filter regeneration for burning and removing the particulate matter deposited on the filter is necessary.

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