JP6417780B2 - Sensor - Google Patents

Description

  The present invention relates to a sensor, and more particularly to 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 gas discharged from an internal combustion engine. In general, an electrical resistance type PM sensor has a pair of conductive electrodes opposed to each other on the surface of an insulating substrate, and the electrical resistance value varies depending on the conductive PM (mainly soot component) adhering to these electrodes. This is used to estimate the PM amount (see, for example, Patent Document 1).

JP2012-83210A

  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 flow rate increases. There is a problem that cannot be guaranteed. Further, 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 amount of PM cannot be accurately estimated during the period until the electrodes are connected by PM. Furthermore, since the electrical resistance value between the electrodes does not change during the regeneration period in which PM accumulated between the electrodes is burned and removed by the electric heater, there is a problem that the amount of PM cannot be estimated during the regeneration period.

  For this reason, the electric resistance type PM sensor cannot continuously estimate the amount of PM discharged from the engine, and its use is failed downstream of the diesel particulate filter (hereinafter referred to as DPF). Are limited to those diagnosed on board.

  This invention is made | formed in view of such a point, The objective is to provide the sensor which can estimate PM amount contained in exhaust gas continuously.

  The disclosed sensor includes at least a pair of a porous filter member including a plurality of cells that collect particulate matter in exhaust gas discharged from an internal combustion engine, and a capacitor that is disposed so as to face the cell. When the particulate matter is deposited up to a predetermined amount in the cell, the regeneration means for performing regeneration of the filter by heating the cell to burn and remove the deposited particulate matter, and completion of filter regeneration by the regeneration means The regeneration interval period from the start to the next filter regeneration is to estimate the amount of particulate matter contained in the exhaust gas based on the capacitance change amount between the pair of electrode members, and the filter regeneration period by the regeneration means is Estimation means for estimating the amount of particulate matter contained in the exhaust gas based on the operating state of the internal combustion engine.

  According to the disclosed sensor, the amount of PM contained in exhaust gas can be continuously estimated.

It is a schematic block diagram which shows an example of the intake / exhaust system to which PM sensor of 1st embodiment was applied. It is a typical fragmentary sectional view showing PM sensor of a first embodiment. FIG. 5 is a timing chart illustrating filter regeneration and PM amount integration according to the first embodiment. It is a typical fragmentary sectional view showing PM sensor of a second embodiment. (A) is a schematic perspective view of a PM sensor according to the third embodiment, and (B) is a schematic exploded perspective view of the PM sensor according to the third embodiment. It is a schematic block diagram which shows an example of the exhaust system to which PM sensor of other embodiment was applied. It is a typical fragmentary sectional view showing PM sensor of other embodiments.

  Hereinafter, based on an accompanying drawing, PM sensor 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 intake and exhaust system of a diesel engine (hereinafter simply referred to as an engine) 100 to which the PM sensor 10A of the first embodiment is applied. In the intake pipe 120, an air cleaner 120, a MAF sensor 130, an intercooler 121, an intake air temperature sensor 131, an intake oxygen concentration sensor 132, a boost pressure sensor 133, and the like are provided in this order from the intake upstream side. The exhaust pipe 110 is provided with an exhaust oxygen concentration sensor 134, an air-fuel ratio sensor 135, an exhaust temperature sensor 136, an oxidation catalyst 210, a DPF 220, a NOx purification catalyst 230, and the like in order from the exhaust upstream side. The PM sensor 10 </ b> A of the present embodiment may be provided, for example, in either the exhaust pipe 110 upstream of the DPF 220 or the exhaust pipe 110 downstream of the DPF 220. In FIG. 1, reference numeral 137 denotes an engine speed sensor, reference numeral 138 denotes an accelerator opening sensor, and reference numeral 40 denotes a control unit.

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

  The PM sensor 10 </ b> A includes a case member 11 inserted into the exhaust pipe 110, a pedestal portion 20 for attaching the case member 11 to the exhaust pipe 110, a sensor unit 30 accommodated in the case member 11, and a control unit 40. I have.

  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 control unit 40 via conductive lines 32A and 33A, respectively.

  The electric heater 34 is an example of the regenerating unit of the present invention, and is formed of, for example, a heating wire. The electric heater 34 generates heat by energization and heats the measurement cell, thereby performing so-called filter regeneration for burning and removing PM accumulated in the measurement cell. For this reason, the electric heater 34 is preferably 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.

  The control unit 40 performs various controls, and includes a known CPU, ROM, RAM, input port, output port, and the like. In addition, the control unit 40 includes a filter regeneration control unit 41, a first PM amount estimation unit 42, a second PM amount estimation unit 43, and a total PM amount calculation unit 44 as functional elements. These functional elements are described as being included in the control unit 40 that is an integral piece of hardware, but may be provided in separate hardware.

  The filter regeneration control unit 41 is an example of a regeneration unit of the present invention, and turns on the electric heater 34 in accordance with the capacitance Cp between the electrodes 32 and 33 detected by a capacitance detection circuit (not shown). The filter regeneration control to be (energized) is executed. The capacitance Cp between the electrodes 32 and 33 is expressed by the following mathematical formula (1), where the dielectric constant ε of the medium between the electrodes 32 and 33, the surface area S of the electrodes 32 and 33, and the distance d between the electrodes 32 and 33 are expressed. Is done.

In the formula (1), the surface areas S of the electrodes 32 and 33 are constant, and when the dielectric constant ε and the distance d change due to PM collected in the measurement cell, 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. 3, the filter regeneration control unit 41 _turns on the electric heater 34 when the capacitance Cp of the electrodes 32 and 33 reaches a predetermined capacitance upper limit threshold C _{P_max} indicating the PM upper limit deposition amount. Start filter playback. This filter regeneration is continued until the capacitance Cp falls to a predetermined capacitance lower limit threshold C _{P_min} that indicates complete removal of PM.

The first PM amount estimation unit 42 is an example of the estimation means of the present invention, and the amount of PM collected by the filter member 31 during the regeneration interval period from the end of the filter regeneration to the start of the next filter regeneration (hereinafter, the interval period PM estimation computed based on referred to as quantity m _{PM_Int_n)} the capacitance change amount [Delta] Cp _n between the electrodes 32 and 33 (see FIG. 3). More specifically, the first 1PM amount estimation unit 42 multiplies a first coefficient β to the variation amount of capacitance [Delta] Cp _n between the electrodes 32 and 33 which are detected by the electrostatic capacitance detection circuit (not shown) to the regeneration interval duration Based on the following formula (2), the interval period PM amount m _{PM_Int_n} is sequentially calculated.

The interval period PM amount m _{PM_Int_n} calculated by the first PM amount estimating unit 42 is sequentially output to a total PM amount calculating unit 44 described later.

The second PM amount estimating unit 43 is an example of the estimating means of the present invention, and the PM amount collected by the filter member 31 during the filter regeneration execution period (hereinafter referred to as regeneration period PM amount m _{PM_Reg_n} ) of the engine 100. An estimation calculation is performed based on the operating state (see FIG. 3). More specifically, the second PM amount estimating unit 43 includes, for example, an intake flow rate, an oxygen concentration, an air-fuel ratio, an exhaust temperature, an engine speed, an accelerator opening, and the like detected by various sensors 130 to 139 as input signals. The regeneration period PM amount m _{PM_Reg_n} is sequentially calculated using the equation. The regeneration period PM amount m _{PM_Reg_n} calculated by the second PM amount estimating unit 43 is sequentially output to the total PM amount calculating unit 44 described later. The calculation of the regeneration period PM amount m _{PM_Reg_n} is not limited to the model formula, and a map (not shown) that is referred to based on the engine speed, the accelerator opening, and the like created in advance by experiments or the like may be used.

The total PM amount calculation unit 44 is an example of the estimation means of the present invention, and the interval period PM amount m _{PM_Int_n} input from the first PM amount estimation unit 42 and the regeneration period PM input from the second PM amount estimation unit 43. The total PM amount m _{PM_sum} in the exhaust gas discharged from the engine 100 is calculated in real time on the basis of the following formula (3) in which the amount m _{PM_Reg_n} is alternately and sequentially integrated.

Thus, in this embodiment, while calculating the interval PM amount m _{PM_Int_n} based on the reproduction interval period Int _{_n} sensitivity good capacitance variation [Delta] Cp _n than the electric resistance value, the filter regeneration duration Reg _{_n} is It is possible to estimate the PM amount in the exhaust gas discharged from the engine 100 in real time and with high accuracy by calculating the regeneration period PM amount m _{PM_Reg_n} based on a model formula or the like created in advance and sequentially integrating these. become.

  Next, the function and effect of the PM sensor 10A according to this embodiment will be described.

  In an electrical resistance PM sensor that estimates the amount of PM based on the electrical resistance value between the electrodes, the electrical resistance value does not change during the electrode regeneration period and the period until each electrode is connected to each other by PM. There is a problem that the amount of PM inside cannot be estimated in real time.

  In contrast, the PM sensor 10A of the present embodiment estimates the PM amount based on the capacitance change amount between the electrodes 32 and 33 having good sensitivity during the regeneration interval period, and the operating state of the engine 100 during the filter regeneration period. The PM amount in the exhaust gas is calculated by estimating the PM amount based on the above and sequentially integrating the estimated PM amount. Therefore, according to the PM sensor 10A of the present embodiment, the PM amount in the exhaust gas discharged from the engine 100 can be estimated with high accuracy and in real time.

  In addition, in the electric resistance type PM sensor that attaches PM to each electrode, for example, there is a possibility that a part of the PM may be detached from the electrode in an operation state in which the exhaust gas flow rate increases, and there is a problem that the estimation accuracy of the PM amount cannot be ensured. is there. In contrast, the PM sensor 10 </ b> A of the present embodiment is configured to reliably collect PM in the exhaust gas by the filter member 31. Therefore, according to the PM sensor 10A of the present embodiment, it is possible to effectively ensure the estimation accuracy of the PM amount even in an operation state in which the exhaust gas flow rate increases.

  Further, in the PM sensor 10A of the present embodiment, the case member 11 that houses the sensor unit 30 has its tip projecting to the vicinity of the axis center CL where the exhaust gas flow velocity is the fastest in the exhaust pipe 110. An inlet 12 that takes in exhaust gas into the case member 11 is provided in the cylindrical wall portion on the distal end side of the case member 11. In addition, a outlet port 13 having an opening area larger than that of the inlet 12 is provided in the base end side cylindrical wall portion of the case member 11. That is, according to the PM sensor 10A of the present embodiment, the introduction port 12 is disposed in the vicinity of the axial center CL of the exhaust pipe 110 having a high exhaust flow rate, and the opening area of the outlet port 13 is increased, so that the introduction port 12 and the introduction port 12 are guided. A large static pressure difference from the outlet 13 can be secured, and the flow of exhaust gas passing through the sensor unit 30 can be effectively promoted.

[Second Embodiment]
Next, based on FIG. 4, the detail of PM sensor 10B which concerns on 2nd embodiment is demonstrated. The PM sensor 10B of the second embodiment is a PM sensor 10A of the first embodiment in which the case member 11 has a double tube structure. Since other components have the same structure, detailed description thereof is omitted. Further, the conductive lines 32A and 33A and the control unit 40 are not shown.

  The case member 11 of the second embodiment includes a bottomed cylindrical inner case portion 11A and a cylindrical outer case portion 11B that surrounds a cylindrical outer peripheral surface of the inner case portion 11A.

  The inner case portion 11A is formed to have a longer axial length than the outer case portion 11B so that the tip side protrudes from the outer case portion 11B. In addition, at the bottom of the inner case portion 11A, a lead-out port 13 for leading the exhaust gas in the inner case portion 11A into the exhaust pipe 110 is provided. Furthermore, a plurality of passage openings 14 are provided in the cylindrical wall portion on the proximal end side of the inner case portion 11A and arranged at intervals in the circumferential direction. The passage port 14 allows the exhaust gas in the flow path 15 defined by the outer peripheral surface of the inner case portion 11A and the inner peripheral surface of the outer case portion 11B to pass through the inner case portion 11A.

At the downstream end of the flow path 15, an annular introduction port 12 is formed that is partitioned by the distal end side cylindrical wall portion of the inner case portion 11 </ b> A and the distal end portion of the outer case portion 11 </ b> B. The opening area S ₁₂ of the inlet ₁₂ is formed smaller than the opening area S _{13 of the} outlet 13 (S ₁₂ <S ₁₃ ).

  That is, the exhaust gas flowing through the exhaust pipe 110 hits the cylindrical wall surface of the inner case portion 11A protruding from the outer case portion 11B, and smoothly enters the flow path 15 from the inlet 12 disposed in the vicinity of the axial center CL of the exhaust pipe 110. Is taken in. Further, the exhaust gas flowing in the flow path 15 is taken into the inner case portion 11A from the passage port 14, passes through the filter member 31, and then is exhausted from the outlet port 13 disposed in the vicinity of the axial center CL of the exhaust pipe 110. 110 is smoothly led out. As described above, in the PM sensor 10B of the second embodiment, the inlet 12 and the outlet 13 are disposed in the vicinity of the axial center CL where the exhaust flow velocity is the fastest in the exhaust pipe 110, thereby passing through the filter member 31. It is possible to effectively increase the exhaust flow rate.

[Third embodiment]
Next, the details of the PM sensor according to the third embodiment will be described with reference to FIG. The PM sensor of the third embodiment is a stacked type of the sensor unit 30 of the first embodiment. 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 third 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 respectively connected to a capacitance detection circuit (not shown) built in the control unit 40 via the conductive lines 62A and 63A. It is connected.

  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 PM sensor according to the third embodiment, since the entire cell C1 is a capacitor by the flat electrode plates 62 and 63, the electrode surface area S can be effectively secured, and a detectable static It becomes possible to increase the absolute value of the capacitance. 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, a bypass pipe 190 that branches from between the oxidation catalyst 210 and the DPF 220 and joins upstream of the NOx purification catalyst 230 is connected to the exhaust pipe 110, and the sensor unit of the first embodiment. 30 or the sensor unit 60 of the third embodiment may be arranged in the bypass pipe 190.

  Further, as shown in FIG. 7, in the first embodiment (or the second embodiment), the positions of the inlet 12 and the outlet 13 are interchanged, and the flow of the exhaust gas introduced into the case member 11 is changed. The direction may be reversed. 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 (regeneration means)
40 control unit 41 filter regeneration control unit (reproducing means)
42 1st PM amount estimation part (estimation means)
43 2nd PM amount estimating section (estimating means)
44 Total PM amount calculation unit (estimating means)

Claims (4)

A porous filter member including a plurality of cells that collect particulate matter in exhaust gas discharged from an internal combustion engine;
At least a pair of electrode members that are arranged opposite to each other with the cell interposed therebetween to form a capacitor;
When particulate matter is deposited in the cell up to a predetermined amount, regeneration means for performing filter regeneration for heating and removing the deposited particulate matter by heating the cell;
The regeneration interval period from the end of filter regeneration by the regeneration means to the start of the next filter regeneration estimates the amount of particulate matter contained in the exhaust gas based on the amount of change in capacitance between the pair of electrode members, and A sensor comprising: an estimation unit that estimates an amount of particulate matter contained in exhaust gas based on an operating state of the internal combustion engine during a filter regeneration period by the regeneration unit. The estimating means includes a particulate matter amount estimated based on the variation amount of capacitance between the pair of electrode members to the reproduction interval period, the particulate matter that is estimated based on the operating state of the internal combustion engine in filter regeneration period The sensor according to claim 1, wherein the amount of particulate matter in the exhaust gas discharged from the internal combustion engine is estimated in real time by sequentially integrating the amount. The sensor according to claim 1, wherein the regeneration unit includes a heating wire that is inserted into the cell and generates heat when energized. The filter member is a filter layer in which the plurality of cells are arranged in parallel in one direction, and the pair of electrode members are flat first and second electrode plates facing each other with the filter layer in between, and the regeneration The means includes a flat heater substrate that generates heat when energized, and the heater substrate is interposed between the first electrode plate and the filter layer or between the second electrode plate and the filter layer. The sensor according to claim 1 or 2.

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