JP2016070077A - Diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a failure of a particulate filter.SOLUTION: A diagnostic device of a DPF 220 provided in an exhaust passage 110 of an internal combustion engine 100 so as to capture PM in exhaust gas includes: a PM sensor 10 arranged in the exhaust passage 110 on an exhaust downstream side of the DPF 220, and having a filter member 31 including a cell for capturing a particulate substance in the exhaust gas, and at least a pair of electrode members 32 and 33 disposed so as to face each other across the cell and forming a capacitor; and a DPF failure determining section 43 for determining a failure of the DPF 220 on the basis of electrostatic capacity between the electrode members 32 and 33.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a diagnostic device, and more particularly, to a diagnostic device for a particulate filter that collects particulate matter (hereinafter referred to as PM) in exhaust gas.

  2. Description of the Related Art Conventionally, an exhaust gas purification device for an internal combustion engine is known that includes a particulate filter that collects PM in exhaust gas. If a failure such as erosion or breakage occurs in the particulate filter, the amount of PM released to the atmosphere without being collected by the particulate filter is not preferable. For this reason, there is a request for diagnosing a particulate filter failure in an on-board state.

  As a technique for diagnosing the failure of the particulate filter, for example, the PM detection value of the electrical resistance PM sensor provided on the downstream side of the particulate filter, and the outflow PM estimation when the previously acquired particulate filter is in a normal state An apparatus that detects a failure of a particulate filter by comparing the amount is proposed (for example, see Patent Document 1).

JP 2011-179467 A

  By the way, since the electric resistance type PM sensor has a simple structure in which PM is adhered to each electrode, there is a possibility that a part of the PM adhering to the electrode may be detached, particularly in an operation state in which the exhaust gas flow rate increases. There is a problem that the accuracy of detection cannot be guaranteed. In addition, since the electrical resistance value between the electrodes does not change until the electrodes are connected to each other due to the deposition of PM, there is a problem that the PM amount cannot be accurately detected during the regeneration interval period of the sensor.

  For this reason, there is a possibility that a conventional diagnostic device using an electrical resistance PM sensor cannot accurately detect a failure of the particulate filter.

  It is an object of the disclosed diagnostic device to detect a failure of a particulate filter with high accuracy.

  The disclosed diagnostic device is a particulate filter diagnostic device that is provided in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas, and the exhaust passage on the downstream side of the particulate filter. A filter member including a cell that is disposed on the filter and that collects particulate matter in the exhaust gas, and is provided with at least a pair of electrode members that are disposed opposite to each other with the cell interposed therebetween, and the pair of electrode members And a failure determination means for determining failure of the particulate filter based on the capacitance between them.

  According to the disclosed diagnostic apparatus, a failure of the particulate filter can be detected with high accuracy.

It is a schematic block diagram which shows an example of the exhaust system of the engine to which the diagnostic apparatus which concerns on 1st embodiment was applied. It is a typical fragmentary sectional view showing PM sensor of a diagnostic device concerning a first embodiment. It is a functional block diagram which shows the electronic control unit of the diagnostic apparatus which concerns on 1st embodiment. It is a figure explaining sensor regeneration of PM sensor concerning a first embodiment. (A) is a typical perspective view which shows the sensor part of PM sensor which concerns on 2nd embodiment, (B) is a typical exploded perspective view which shows the sensor part of PM sensor which concerns on 2nd embodiment. . It is a typical fragmentary sectional view showing PM sensor of a diagnostic device concerning other embodiments.

  Hereinafter, based on an accompanying drawing, a diagnostic device concerning each embodiment of the present invention is explained. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First embodiment]
FIG. 1 is a schematic configuration diagram illustrating an example of an exhaust system of a diesel engine (hereinafter simply referred to as an engine) 100 to which the diagnostic device according to the first embodiment is applied. The exhaust pipe 110 is provided with an oxidation catalyst 210, a particulate filter (hereinafter referred to as DPF) 220, and the like in order from the exhaust upstream side. The PM sensor 10 of this embodiment is provided in the exhaust pipe 110 on the downstream side of the DPF 220.

  Next, a detailed configuration of the PM sensor 10 according to the present embodiment will be described based on FIG.

  The PM sensor 10 includes a case member 11 inserted into the exhaust pipe 110, a pedestal portion 20 that attaches the case member 11 to the exhaust pipe 110, a sensor unit 30 accommodated in the case member 11, and an electronic control unit (hereinafter referred to as an electronic control unit). 40).

  The case member 11 is formed in a bottomed cylindrical shape with the bottom side (the lower end side in the illustrated example) closed. The length L in the cylinder axis direction of the case member 11 is formed to be substantially the same as the radius R of the exhaust pipe 110 so that the bottom cylindrical wall portion protrudes to the vicinity of the axial center CL of the exhaust pipe 110. ing. In the following description, the bottom side of the case member 11 is the front end side, and the side opposite to the bottom side is the base end side of the case member 11.

A plurality of inlets 12 arranged at intervals in the circumferential direction are provided in the cylindrical wall portion on the distal end side of the case member 11. In addition, a plurality of outlets 13 arranged at intervals in the circumferential direction are provided in the base end side cylindrical wall portion of the case member 11. The total opening area S ₁₂ of the inlet 12 is smaller than the total opening area S ₁₃ of the outlet _{13 (S 12 <S 13)} . That is, in the exhaust flow velocity V ₁₂ of the inlet 12 near slower than the exhaust flow velocity V ₁₃ near guide outlet 13 (V ₁₂ <V _13), the pressure P ₁₂ in the inlet 12 side pressure outlet 13 side It is higher than the _{P 13 (P 12> P 13} ). As a result, exhaust gas is smoothly taken into the case member 11 from the inlet 12, and at the same time, exhaust gas in the case member 11 is smoothly led out into the exhaust pipe 110 from the outlet 13.

  The pedestal portion 20 includes a male screw portion 21 and a nut portion 22. The male screw portion 21 is provided at the base end portion of the case member 11 and closes the base end side opening of the case member 11. The male screw portion 21 is screwed with a female screw portion of a boss portion 110 </ b> A formed in the exhaust pipe 110. The nut portion 22 is, for example, a hexagonal nut, and is fixed to the upper end portion of the male screw portion 21. The male screw portion 21 and the nut portion 22 are formed with through holes (not shown) through which conductive wires 32A, 33A described later are inserted.

  The sensor unit 30 includes a filter member 31, a plurality of pairs of electrodes 32 and 33, and an electric heater 34.

  The filter member 31 is formed, for example, by alternately plugging the upstream side and the downstream side of a plurality of cells forming a lattice-like exhaust flow path partitioned by porous ceramic partition walls. The filter member 31 is held on the inner peripheral surface of the case member 11 via a cushion member 31A in a state in which the flow path direction of the cell is substantially parallel to the axial direction of the case member 11 (vertical direction in the drawing). . The PM in the exhaust gas taken into the case member 11 from the introduction port 12 flows from the cell plugged on the downstream side into the cell plugged on the upstream side, so that the surface of the partition wall It is collected in the hole. In the following description, a cell whose downstream side is plugged is referred to as a measurement cell, and a cell whose upstream side is plugged is referred to as an electrode cell.

  The electrodes 32 and 33 are, for example, conductive metal wires, and are alternately inserted from the downstream side (non-plugged side) into the electrode cells facing each other across the measurement cell to form a capacitor. These electrodes 32 and 33 are connected to a capacitance detection circuit (not shown) built in the ECU 40 via conductive wires 32A and 33A, respectively.

  The electric heater 34 is, for example, a heating wire and constitutes the regenerating means of the present invention. The electric heater 34 generates heat by energization and heats the measurement cell, thereby performing so-called sensor regeneration that burns and removes the PM accumulated in the measurement cell. For this reason, the electric heater 34 is formed by being bent into a continuous S-shape, and straight portions parallel to each other are inserted into each measurement cell along the flow path.

  Next, details of the ECU 40 of the present embodiment will be described with reference to FIG. The ECU 40 includes a sensor regeneration control unit 41, a PM amount estimation calculation unit 42, and a DPF failure determination unit 43 as functional elements. These functional elements are described as being included in the ECU 40 that is an integral piece of hardware, but may be provided in separate hardware.

  The sensor regeneration control unit 41 is a part of the regeneration means of the present invention, and turns on the electric heater 34 according to the capacitance Cp between the electrodes 32 and 33 detected by a capacitance detection circuit (not shown). ) Perform sensor regeneration. The electrostatic capacitance Cp between the electrodes 32 and 33 is expressed by the following formula 1 where the dielectric constant ε of the medium between the electrodes 32 and 33, the area S of the electrodes 32 and 33, and the distance d between the electrodes 32 and 33 are expressed. .

  In Formula 1, the surface areas S of the electrodes 32 and 33 are constant, and when PM is collected by the filter member 31, the dielectric constant ε and the distance d change, and the capacitance Cp also changes accordingly. That is, a proportional relationship is established between the capacitance Cp between the electrodes 32 and 33 and the amount of PM deposited on the filter member 31.

As shown in FIG. 4, when the electrostatic capacity Cp between the electrodes 32 and 33 reaches a predetermined electrostatic capacity upper limit threshold _{CP_max} indicating the PM upper limit accumulation amount of the filter member 31, the sensor regeneration control unit 41 Sensor regeneration to turn ON 34 is started. This sensor regeneration is continued until the capacitance Cp falls to a predetermined capacitance lower limit threshold _{CP_min} indicating complete removal of PM.

Estimating the PM amount calculation unit 42, based on the variation amount of capacitance [Delta] Cp _n between regeneration interval T _n (next sensor reproduction start from the sensor reproduction end), estimates and calculates the total amount of PM m _{PM_sum} in the exhaust.

PM quantity m _{PM_n} to be trapped by the filter member 31 between regeneration interval T _n is obtained by Equation 2 below obtained by multiplying the first coefficient β to the variation amount of capacitance [Delta] Cp _n.

The PM amount estimation calculation unit 42 sequentially accumulates the PM amount m _{PM_n} between the regeneration intervals T _n calculated from Equation 2 based on the following Equation 3 to calculate the total PM amount m _{PM_sum in the} exhaust gas flowing into the filter member 31. Is calculated in real time as the output value of the PM sensor 10.

DPF failure judgment unit 43, a failure determination means of the present invention, the sensor views of the PM sensor 10 or based on the reproduction interval T _n, determine the fault (function failure) caused by melting or damage of DPF220 To do. Hereinafter, details of the failure determination according to the present embodiment will be described.

[Judgment based on the number of sensor regenerations]
When the PM slip amount increases due to melting or breakage of the DPF 220, the number of sensor regenerations (execution frequency) of the PM sensor 10 arranged on the downstream side also increases. In the present embodiment, the number of sensor regenerations of the PM sensor 10 acquired in advance in a normal state of the function of the DPF 220 by an experiment or the like is stored as a reference number _{N_Reg_Std} in a storage unit (not shown) of the ECU 40. The DPF failure determination unit 43 determines that a failure has occurred in the DPF ₂₂₀ when the sensor regeneration count value _{N_Reg_Count} by the sensor regeneration control unit 41 is _greater than the reference count _{N_Reg_Std} ( _{N_Reg_Count} > _{N_Reg_Std} ).

[Judgment based on playback interval]
When PM slip amount is increased by melting and damage of DPF220, regeneration interval T _n of the PM sensor 10 is reduced gradually. In the present embodiment, the storage interval (not shown) of the ECU 40 stores the regeneration interval T _n of the PM sensor 10 acquired in advance in a normal state of the function of the DPF 220 through experiments or the like as the reference interval _{T_Std} . DPF failure judgment unit 43, the reproduction interval T _n is shorter than the reference interval _{T _Std (T n <T _Std} ), it determines that the failure occurs in the DPF220.

Note that the failure determination method is not limited to the number of sensor regenerations and the regeneration interval. For example, the total PM amount m _{PM_sum} estimated by the PM amount estimation calculation unit 42 is in a normal state in which the DPF 220 acquired through an experiment or the like is normal. In this case, the DPF 220 may be determined to be faulty when the reference PM amount m _{PM_Std} flowing out downstream _becomes larger.

  Next, the effect of the diagnostic apparatus according to the present embodiment will be described.

  The electric resistance type PM sensor has a simple structure that attaches PM to each electrode, so that part of the PM may be detached from the electrode, especially in an operating state where the exhaust flow rate increases, ensuring the detection accuracy of the PM amount. There is a problem that cannot be done. In addition, since the electrical resistance value between the electrodes does not change until the electrodes are connected by PM, there is a problem that the amount of PM cannot be accurately detected during the regeneration interval period. For this reason, the conventional diagnostic apparatus using the electrical resistance PM sensor on the downstream side of the DPF 220 has a problem that a failure of the DPF 220 cannot be accurately detected.

  On the other hand, the diagnostic device of the present embodiment reliably collects PM in the exhaust gas in the filter member 31 of the PM sensor 10 even in a state where the exhaust gas flow rate is large, and has an electrode 32 with better sensitivity than the electric resistance value. The failure of the DPF 220 is determined based on the number of sensor regenerations performed based on the capacitance Cp between 33 and the regeneration interval. Therefore, according to the diagnostic device of the present embodiment, it is possible to detect a failure due to damage or melting of the DPF 220 with high accuracy.

[Second Embodiment]
Next, based on FIG. 5, the detail of the diagnostic apparatus which concerns on 2nd embodiment is demonstrated. The diagnostic device according to the second embodiment is a PM sensor 10 according to the first embodiment in which the sensor unit 30 is a stacked type. Since other components have the same structure, detailed description and illustration are omitted.

  5A is a perspective view of the sensor unit 60 according to the second embodiment, and FIG. 5B is an exploded perspective view of the sensor unit 60. The sensor unit 60 includes a plurality of filter layers 61 and a plurality of first and second electrode plates 62 and 63.

  The filter layer 61 is, for example, plugged alternately upstream and downstream of a plurality of cells that are partitioned by partition walls such as porous ceramics to form an exhaust passage, and these cells are arranged in parallel in one direction. It is formed in a rectangular parallelepiped shape. The PM contained in the exhaust gas flows into the cell C2 whose upstream side is plugged from the cell C1 whose downstream side is plugged, as indicated by a broken line arrow in FIG. 5B. Thus, it is collected on the partition wall surface and pores of the cell C1. In the following description, the cell flow path direction is the length direction of the sensor section 60 (arrow L in FIG. 5A), and the direction orthogonal to the cell flow path direction is the width direction of the sensor section 60 (FIG. 5). (A) Arrow W).

  The first and second electrode plates 62 and 63 are, for example, plate-like conductive members, and are formed so that the outer dimensions in the length direction L and the width direction W are substantially the same as those of the filter layer 61. The first and second electrode plates 62 and 63 are alternately stacked with the filter layer 61 interposed therebetween, and are connected to a capacitance detection circuit (not shown) built in the ECU 40 via conductive lines 62A and 63A, respectively. ing.

  That is, the first electrode plate 62 and the second electrode plate 63 are disposed to face each other, and the filter layer 61 is sandwiched between the electrode plates 62 and 63, so that the entire cell C1 forms a capacitor. . As described above, in the second embodiment, the entire cell C1 is made the capacitor by the flat electrode plates 62 and 63, so that the electrode surface area S can be effectively secured, and the detectable capacitance absolute It becomes possible to increase the value. Further, since the inter-electrode distance d becomes the cell pitch and is made uniform, variations in the initial capacitance can be effectively suppressed.

  When the PM accumulated in the cell C1 is burned and removed, a voltage is directly applied to the electrode plates 62 and 63, or a heater substrate (not shown) is interposed between the filter layer 61 and the electrode plates 62 and 63. Just set up.

[Others]
The present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the spirit of the present invention.

  For example, as shown in FIG. 6, in the PM sensor 10 of the first embodiment, the positions of the inlet 12 and the outlet 13 are interchanged so that the flow of exhaust gas introduced into the case member 11 is reversed. Also good. In this case, the filter member 31 may be stored in the case member 11 by being inverted.

DESCRIPTION OF SYMBOLS 10 PM sensor 11 Case member 12 Inlet port 13 Outlet port 20 Base part 21 Male screw part 22 Nut part 30 Sensor part 31 Filter member 32, 33 Electrode 34 Electric heater 40 ECU
41 Sensor regeneration control unit 42 PM amount estimation calculation unit 43 DPF failure determination unit 100 Engine 110 Exhaust pipe 220 DPF

Claims (5)

A particulate filter diagnostic device that is provided in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas,
At least a pair of filter members that are disposed in the exhaust passage downstream of the particulate filter and that collect particulate matter in the exhaust and that are opposed to each other with the cell interposed therebetween. A sensor provided with an electrode member;
And a failure determination means for determining failure of the particulate filter based on a capacitance between the pair of electrode members. The sensor further includes regeneration means for performing sensor regeneration for burning and removing particulate matter accumulated in the cells when the capacitance between the pair of electrode members reaches a predetermined upper limit threshold.
The failure determination means determines a failure of the particulate filter based on the number of times sensor regeneration is performed by the regeneration means or a regeneration interval from the end of sensor regeneration by the regeneration means to the start of the next sensor regeneration. The diagnostic apparatus according to 1. The sensor is formed in a cylindrical shape and houses the filter member in the cylinder, and exhaust gas introduced into the cylinder from one end opening is passed through the filter member and led out of the cylinder from the other end opening. The diagnostic device according to claim 1, comprising a case member. The filter member is a filter layer in which a plurality of the cells are arranged in parallel in one direction, and the pair of electrode members are flat plate-like first and second electrode plates facing each other with the filter layer interposed therebetween. 4. The diagnostic device according to any one of 3. The plurality of first electrode plates, the second electrode plates, and the filter layers, respectively, and the plurality of first and second electrode plates are alternately stacked with the plurality of filter layers sandwiched one by one. 4. The diagnostic device according to 4.

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