JP6409452B2 - Diagnostic equipment - Google Patents

Description

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

  Conventionally, an electrical resistance type PM sensor is known as a sensor for detecting PM in exhaust discharged from an internal combustion engine. An electrical resistance type PM sensor uses a pair of conductive electrodes facing each other on the surface of an insulating substrate, and the electrical resistance value changes depending on the conductive PM (mainly soot component) adhering to these electrodes. The PM amount is estimated (see, for example, Patent Document 1).

  As a diagnostic device for such an electric resistance type PM sensor, a device for detecting a failure of the PM sensor by comparing the electric resistance value between the electrodes during the sensor regeneration period with a value obtained when the sensor is normal is proposed. (For example, refer to Patent Document 2).

  In addition, as a diagnostic device for an electric resistance type PM sensor, a device that compares the regeneration times of two PM sensors with each other and determines a failure when the difference between the regeneration times of these sensors is larger than a predetermined value has been proposed. (For example, refer to Patent Document 3).

JP2012-83210A JP 2014-15914 A JP 2009-144512 A

  By the way, in the method of comparing the electrical resistance value in the sensor regeneration period and the method of comparing the regeneration times of the two sensors, the execution of diagnosis is limited to the sensor regeneration period. It may not be possible to detect functional deterioration at an early stage. Further, in the method of comparing the regeneration times of two PM sensors, there is a problem that it is impossible to determine which PM sensor has a failure.

  The disclosed diagnostic device aims to detect PM sensor failure early and with high accuracy.

  The disclosed diagnostic device includes at least a pair of electrode members that are disposed in an exhaust passage of an internal combustion engine and that include a cell that collects particulate matter in exhaust gas and that is disposed opposite to the cell so as to form a capacitor. And a second sensor for detecting an exhaust temperature provided in the exhaust passage and an estimation means for estimating an amount of particulate matter in the exhaust based on a capacitance between the pair of electrode members And an abnormality determining means for comparing the capacitance between the pair of electrode members and the sensor value of the second sensor to determine an abnormality of the first sensor.

  According to the disclosed diagnostic apparatus, a failure of the PM sensor can be detected early and 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. It is a figure which compares the electrostatic capacitance behavior between electrodes at the time of the fuel injection stop of an engine, and the sensor value behavior of an exhaust temperature sensor. (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. It is a figure explaining arrangement | positioning of PM sensor and exhaust temperature sensor of the diagnostic apparatus which concerns on other embodiment.

  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. In the exhaust pipe 110, a first exhaust temperature sensor 250, an oxidation catalyst 210, a second exhaust temperature sensor 260, a particulate filter (hereinafter referred to as DPF) 220, a NOx reduction catalyst 230, and the like are provided in order from the exhaust upstream side. It has been. The PM sensor 10 of the present embodiment is provided in the exhaust pipe 110 upstream of the oxidation catalyst 210 (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 PM sensor abnormality 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 is a means for estimating the present invention, based on the variation amount of capacitance [Delta] Cp _n between regeneration interval T _n (next sensor reproduction start from the sensor reproduction end), the total PM in the exhaust The quantity m _{PM_sum} is estimated and calculated.

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 sensor 10.

  The PM sensor abnormality determination unit 43 is an example of an abnormality determination unit of the present invention, and determines an abnormality of the PM sensor 10 based on a sensor value input from the first exhaust temperature sensor 250.

In the above formula 1, the area S of the electrodes 32 and 33 is constant, and when PM is not collected by the filter member 31, the distance d between the electrodes 32 and 33 is also constant. As a result, when the dielectric constant ε changes under the influence of temperature, the capacitance Cp also changes accordingly. That is, when PM is not discharged from the engine 100 such as when the fuel injection of the engine 100 is stopped, the capacitance Cp between the electrodes 32 and 33 and the sensor value of the first exhaust temperature sensor 250 have the same behavior (change). (See times t _{1 to} t _{2 in} FIG. 5). The PM sensor abnormality determination unit 43 calculates a deviation ΔT between the behavior of the capacitance Cp between the electrodes 32 and 33 and the behavior of the sensor value of the first exhaust temperature sensor 250 in real time when the fuel injection of the engine 100 is stopped. At the same time, when the deviation ΔT exceeds a predetermined threshold, it is determined that an abnormality has occurred in the PM sensor 10.

  When the fuel injection of engine 100 is stopped, the oxidation reaction does not occur in oxidation catalyst 210, so that sensor values of first exhaust temperature sensor 250 and second exhaust temperature sensor 260 are substantially equal. Therefore, the sensor value of the second exhaust temperature sensor 260 may be used as the sensor value to be compared with the above-described capacitance Cp.

  Further, as a functional element of the ECU 40, an exhaust temperature estimation unit for estimating the exhaust temperature from a capacitance / temperature characteristic map (not shown) showing the relationship between the capacitance Cp and the exhaust temperature created in advance is added. You may comprise so that the exhaust temperature estimated by an estimation part and the sensor value of the 1st or 2nd exhaust temperature sensor 250,260 may be compared directly.

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

  In the conventional technique for comparing the electrical resistance value in the sensor regeneration period of the electrical resistance type PM sensor with the normal value, the diagnosis cannot be performed during the regeneration interval period in which the electrical resistance value between the electrodes does not change. There is a problem that failure and functional deterioration cannot be detected early.

  On the other hand, in the diagnostic device of this embodiment, when the fuel injection of the engine 100 in which PM is not collected by the filter member 31 is stopped, the PM sensor 10 fails during both the sensor regeneration and the regeneration interval period. It is configured to be able to diagnose depressions and functional deterioration based on the temperature characteristics of the capacitance Cp. Therefore, according to the diagnostic apparatus of the present embodiment, it is possible to effectively ensure the diagnosis frequency of the PM sensor 10 and to detect an abnormality of the PM sensor 10 at an early stage and with high accuracy.

[Second Embodiment]
Next, based on FIG. 6, 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.

  6A is a perspective view of the sensor unit 60 according to the second embodiment, and FIG. 6B 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 from the cell C1 whose downstream side is plugged into the cell C2 whose upstream side is plugged, as indicated by a broken line arrow in FIG. 6B. 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. 6A), and the direction orthogonal to the cell flow path direction is the width direction of the sensor section 60 (FIG. 6). (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. 7, 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.

  Further, as shown in FIG. 8, the PM sensor 10 and the exhaust temperature sensor 270 are disposed downstream of the DPF 220, and abnormality diagnosis of the PM sensor 10 is executed when the PM trapping function of the DPF 220 is normal. You may comprise as follows. The functional diagnosis of the DPF 220 may be performed, for example, by comparing the sensor regeneration count and regeneration interval of the PM sensor 10 with a normal value acquired in advance.

  Moreover, although it demonstrated as what diagnoses abnormality of PM sensor 10 based on the sensor value of exhaust temperature sensor 260-270, abnormality of exhaust temperature sensor 260-270 was demonstrated based on the electrostatic capacitance Cp between the electrodes 32 and 33. FIG. It can also be configured to diagnose.

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 PM sensor abnormality determination unit 100 Engine 110 Exhaust pipe 210 Oxidation catalyst 220 DPF
250 First exhaust temperature sensor 260 Second exhaust temperature sensor

Claims (6)

A filter member including a cell that is disposed in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas is provided with at least a pair of electrode members that are disposed opposite to each other with the cell interposed therebetween to form a capacitor. A first sensor including estimation means for estimating the amount of particulate matter in the exhaust based on the capacitance between the electrode members;
A second sensor provided in the exhaust passage for detecting the exhaust temperature;
An abnormality determining means for comparing the capacitance between the pair of electrode members and the sensor value of the second sensor to determine an abnormality of the first sensor ;
The abnormality determination means determines an abnormality of the first sensor by comparing a capacitance between the pair of electrode members and a sensor value of the second sensor when particulate matter is not discharged from the internal combustion engine. Diagnostic device. The exhaust passage is provided with a particulate filter that collects particulate matter in the exhaust,
The first sensor and the second sensor are arranged in an exhaust passage on the upstream side of the particulate filter,
2. The abnormality determination unit determines an abnormality of the first sensor by comparing a capacitance between the pair of electrode members and a sensor value of the second sensor when fuel injection of the internal combustion engine is stopped. The diagnostic device according to 1. The first sensor further includes regeneration means for performing sensor regeneration for burning and removing the accumulated particulate matter when the amount of particulate matter collected by the filter member reaches a predetermined value,
The estimation means calculates the amount of particulate matter collected by the filter member during the sensor regeneration interval from the amount of change in capacitance between the pair of electrodes during the sensor regeneration interval, and calculates each sensor regeneration The diagnostic apparatus according to claim 1 or 2 , wherein the particulate matter amount in the exhaust gas is estimated in real time by sequentially integrating the particulate matter amount between the intervals. The first sensor is formed in a cylindrical shape and accommodates the filter member in the cylinder, and exhaust gas introduced into the cylinder from one end opening portion is passed through the filter member to be outside the cylinder from the other end opening portion. The diagnostic device according to any one of claims 1 to 3 , further comprising a case member to be derived. 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. 5. The diagnostic device according to any one of 4 . 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. 5. The diagnostic device according to 5 .

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