JP6458368B2 - Sensor - Google Patents

Description

  The present invention relates to a sensor, and more particularly to a PM sensor capable of detecting particulate matter (hereinafter referred to as PM) 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. In addition, there is a problem that the amount of PM cannot be accurately estimated because the electrical resistance of PM attached to the electrode changes when it is affected by the exhaust flow rate. Furthermore, the electrical resistance value between the electrodes does not change until the electrodes are connected to each other by deposition of PM. For this reason, the amount of PM discharged from the engine cannot be detected in real time, and its use is to diagnose failure on board on the downstream side of the diesel particulate filter (hereinafter referred to as DPF). There is also a problem that is limited.

  An object of the present invention is to provide a PM sensor capable of accurately estimating the amount of PM contained in exhaust gas by ensuring the electrode surface area effectively while reliably collecting PM between the electrodes. There is to do.

  In order to achieve the above object, the sensor of the present invention is opposed to a filter layer having one or more cells partitioned by a porous partition and collecting particulate matter in exhaust gas, with the filter layer interposed therebetween. A first electrode plate and a second electrode plate, and an estimation unit that estimates the amount of particulate matter based on the capacitance between the first electrode plate and the second electrode plate.

  In addition, the first electrode plate, the second electrode plate, and the plurality of filter layers each have a plurality, and the plurality of first and second electrode plates are alternately stacked with the plurality of filter layers sandwiched one by one. It may be a thing.

  And a filter regeneration unit capable of performing filter regeneration for burning and removing the accumulated particulate matter when the amount of the particulate matter collected in the filter layer reaches a predetermined value. The amount of particulate matter collected by the filter layer during the regeneration interval is calculated from the amount of change in capacitance between the exhaust gas and the exhaust gas by sequentially integrating the calculated amount of particulate matter between the regeneration intervals. The amount of the particulate matter inside may be estimated in real time.

  Further, the estimation unit may estimate an instantaneous particulate matter amount in real time based on a capacitance change amount per unit time.

  According to the sensor of the present invention, the amount of PM contained in the exhaust gas can be estimated with high accuracy by ensuring the electrode surface area while reliably collecting PM between the electrodes.

It is a schematic block diagram which shows an example of the exhaust system to which PM sensor of this embodiment was applied. (A) is a schematic perspective view of the PM sensor according to the present embodiment, and (B) is a schematic exploded perspective view of the PM sensor according to the present embodiment. It is a timing chart explaining filter regeneration concerning this embodiment. It is a figure which shows an example of the map which concerns on this embodiment. It is a typical side view which shows a part of PM sensor which concerns on this embodiment.

  Hereinafter, based on an accompanying drawing, a sensor concerning one 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.

  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 PM sensor 10 of the present embodiment is applied. The exhaust pipe 110 of the engine 100 is provided with an exhaust aftertreatment device 200 in which an oxidation catalyst 210 and a DPF 220 are arranged in order from the exhaust upstream side. The PM sensor 10 of the present embodiment has an upstream side (see reference A) from the exhaust aftertreatment device 200, a downstream side from the exhaust aftertreatment device 200 (see reference B), or a bypass passage that bypasses the exhaust aftertreatment device 200. 130 (see reference C) may be provided.

  Next, the detailed structure of the PM sensor 10 of this embodiment is demonstrated based on FIG. 2A is a perspective view of the PM sensor 10, and FIG. 2B is an exploded perspective view of the PM sensor 10. The PM sensor 10 includes a plurality of filter layers 11, a plurality of first and second electrode plates 12 and 13, and a control unit 40.

  The filter layer 11 is, for example, plugged upstream and downstream of a plurality of cells that are partitioned by partition walls such as porous ceramics to form an exhaust flow path, 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. Thus, it is collected on the partition wall surface and pores of the cell C1. In the following description, the cell channel direction is the length direction of PM sensor 10A (arrow L in FIG. 2A), and the direction orthogonal to the cell channel direction is the width direction of PM sensor 10A (FIG. 2). (A) Arrow W).

  The first and second electrode plates 12 and 13 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 11. The first and second electrode plates 12 and 13 are alternately stacked with the filter layer 11 interposed therebetween. That is, the first electrode plate 12 and the second electrode plate 13 are disposed to face each other, and the filter layer 11 is sandwiched between the electrode plates 12 and 13 so that the entire cell C1 forms a capacitor. . Reference numerals 12A and 13A in FIG. 2A denote conductive lines that connect the first electrode plate 12 and the second electrode plate 13 to a capacitance detection circuit (not shown) built in the control unit 40, respectively. Yes.

  The control unit 40 includes a filter regeneration control unit 41 and a PM amount estimation calculation unit 42 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 performs filter regeneration control that directly applies a voltage to the electrode plates 12 and 13 to burn and remove PM in the cell C1. The electrostatic capacity Cp between the electrode plates 12 and 13 is expressed by the following formula 1 as the dielectric constant ε of the medium between the electrode plates 12 and 13, the surface area S of the electrode plates 12 and 13, and the distance d between the electrode plates 12 and 13. It is represented by

In Formula 1, the surface areas S of the electrode plates 12 and 13 are constant, and when the dielectric constant ε and the distance d change due to PM collected in the cell C1, the capacitance Cp also changes accordingly. That is, a proportional relationship is established between the capacitance Cp between the electrode plates 12 and 13 and the amount of PM deposited in the cell C1. When the capacitance Cp between the electrode plates 12 and 13 reaches a predetermined capacitance upper limit threshold C _{P_max} indicating the PM upper limit deposition amount, the filter regeneration control unit 41 directly applies a voltage to each electrode plate 12 and 13. Filter regeneration is started (see times t ₁ , t ₂ and t _{3 in} FIG. 3). 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.

Estimating the PM amount calculation unit 42, based on inter regeneration interval T _n (from the fill playback end next filter regeneration start) the variation amount of capacitance [Delta] Cp _n in total PM amount m in the exhaust gas discharged from the engine 100 Estimate _{PM_sum} . PM quantity m _{PM_n} to be trapped in the cell C1 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 in the exhaust gas discharged from the engine 100. m _{PM_sum} is calculated in real time.

The instantaneous PM amount m _{PM_new} contained in the exhaust gas can also be estimated in real time from the change amount ΔCp / Δt per unit time of the capacitance Cp. In this case, as the instantaneous PM amount m _{PM_new} , a map (see FIG. 4) showing a relationship between the capacitance Cp and the PM amount m _PM obtained in advance through experiments or the like is used, and the instantaneous capacitance change amount is used in this map. It can be obtained by multiplying ΔCp / Δt. Thus, when estimating the instantaneous PM amount m _{PM_new} , the PM sensor 10 is located upstream of the exhaust aftertreatment device 200 (see reference A in FIG. 1) or the bypass passage 130 (see reference C in FIG. 1). In any case, since the instantaneous PM amount m _{PM_new} discharged from the engine 100 can be estimated in real time, engine control such as smoke limit can be effectively performed.

  Next, the effect of the PM sensor 10 according to the present embodiment will be described.

  In the electric resistance type PM sensor that estimates the amount of PM based on the electric resistance value between the electrodes, it becomes difficult to reliably attach the PM to the electrodes when the exhaust gas flow rate increases, and thus there is a problem that the estimation accuracy cannot be ensured. . In addition, there is a problem that the amount of PM cannot be accurately estimated because the electrical resistance of PM attached to the electrode changes when it is affected by the exhaust flow rate. Furthermore, since the electrical resistance value between the electrodes does not show a change until the electrodes are connected to each other by deposition of PM, there is a problem that the amount of PM cannot be estimated in real time.

On the other hand, the PM sensor 10 of the present embodiment sequentially accumulates the PM amount m _{PM_n} of each regeneration interval T _n while reliably collecting PM in the exhaust gas in the cell C1 of the filter layer 11. The total PM amount m _{PM_sum} in the exhaust gas discharged from the engine 100 is calculated in real time. Therefore, according to the PM sensor 10 of the present embodiment, the total PM amount m _{PM_sum} discharged from the engine 100 can be estimated with high accuracy and in real time. In particular, if the instantaneous PM amount m _{PM_new} is estimated from the capacitance change amount ΔCp / Δt per unit time, the PM sensor 10 is provided on the upstream side of the exhaust aftertreatment device 200 or in the bypass passage 130. This makes it possible to effectively control the engine. Further, when the PM sensor 10 is provided on the downstream side of the exhaust aftertreatment device 200, a failure of the DPF 220 can be detected on-board with high accuracy and early.

  Further, as shown in FIG. 5, the PM sensor 10 of the present embodiment sandwiches the filter layer 11 between the flat plate-like first and second electrode plates 12 and 13, and alternately laminates them, thereby the entire cell C1. Form a capacitor. As a result, the electrode surface area S can be effectively secured, and the detectable absolute value of capacitance can be increased. In addition, since the inter-electrode distance d becomes the cell pitch and becomes uniform, variations in the initial capacitance can be effectively suppressed, and the amount of PM in the exhaust gas can be estimated with high accuracy.

  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, when a heater substrate is inserted between the first electrode plate 12 and the filter layer 11 or between the second electrode plate 13 and the filter layer 11 and filter regeneration is performed, a voltage is applied to the heater substrate. It may be configured. Further, the channel cross-sectional shape of the cells C1 and C2 is not limited to the rectangular shape in the illustrated example, and may be other shapes such as a triangular shape.

DESCRIPTION OF SYMBOLS 10 PM sensor 11 Filter layer 12 1st electrode plate 13 2nd electrode plate 40 Control unit 41 Filter regeneration control part 42 PM amount estimation calculating part

Claims (3)

A filter layer having a plurality of cells partitioned by a porous partition wall and collecting particulate matter in the exhaust gas;
Flat plate-like first and second electrode plates opposed across the filter layer;
An estimation unit that estimates the amount of particulate matter based on a capacitance between the first electrode plate and the second electrode plate,
The plurality of cells are arranged in a width direction of the first and second electrode plates ,
A plurality of the first electrode plate, the second electrode plate, and the filter layer are provided and stacked, and the first and second electrode plates cover both sides of the one filter layer in the stacking direction. A sensor characterized by forming a flow path . A filter regeneration unit capable of performing filter regeneration for burning and removing the accumulated particulate matter when the amount of particulate matter collected in the filter layer reaches a predetermined value;
The estimation unit calculates the amount of particulate matter collected by the filter layer during the regeneration interval from the amount of change in capacitance between regeneration intervals, and sequentially calculates the amount of particulate matter between the regeneration intervals. The sensor according to claim 1 , wherein the amount of particulate matter in the exhaust gas is estimated in real time by integrating. The sensor according to claim 1 , wherein the estimation unit estimates an instantaneous particulate matter amount in real time based on a capacitance change amount per unit time.

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