JP2005232972A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device with a first electrode and a second electrode between which corona discharge is generated to charge treated objects in exhaust gas to be trapped by the second electrode, preventing the formation of a conduction path due to dirt on the inner face of an outer cylinder, a coating of a high voltage cable and a coating of the first electrode. <P>SOLUTION: The exhaust emission control device 1 comprises the first electrode 20 and the second electrode 30 arranged in the outer cylinder 10 through which exhaust gas G from an internal combustion engine passes, in sequence from the upstream side. Herein, high voltage is applied to the first electrode 20 to generate corona discharge which charges treated components in the exhaust gas G to be trapped by the second electrode 30. The second electrode 30 is formed in a metal honeycomb structure. A first semiconductor layer 51 covering the inner face of the outer cylinder 10 around the first electrode 20 is provided in the state of being electrically insulated form the metal honeycomb structure 30. At least in corona discharge, the polarity of potential of the first semiconductor layer 51 is the same as that of potential of the first electrode 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification device that collects and purifies particulate matter (PM) in exhaust gas such as a diesel engine using corona discharge.

  In order to remove particulate matter (particulate matter: hereinafter referred to as PM) contained in exhaust gas of a diesel engine or the like, a physical filter (hereinafter referred to as DPF) called a diesel particulate filter is generally used. ing. Usually, in this DPF, since the particle size of PM is small, it is necessary to make the filter finer, and since heat resistance is required, unglazed porous ceramic filters are often used.

  In this DPF, since the filter is blocked by the collected PM, DPF regeneration for forcibly burning and removing the collected PM is performed. As one of the DPF regeneration methods, two exhaust gas treatment paths having DPF are provided, and when the DPF provided in one path becomes clogged with the collected PM, the other DPF is switched to the other path. In addition, there is an intermittent regeneration method in which PM is continuously collected and the PM collected in one DPF is heated and removed by a heater or the like.

Also, the exhaust gas treatment path is a single system, and an oxidation catalyst is installed in the upstream (upstream side) of the DPF, and NO (nitrogen monoxide) in the exhaust gas is oxidized by this oxidation catalyst to NO ₂ (nitrogen dioxide). The exhaust gas temperature is obtained by burning the fuel supplied to the oxidation catalyst by the oxidation catalyst by the method of oxidizing the PM collected in the DPF with this NO ₂ , the post injection in the fuel injection, the direct fuel injection to the exhaust passage, or the like. A continuous regeneration method is used in which the PM collected by the DPF on the downstream side is burned and the PM is burned. There is also a method in which an oxidation catalyst is supported on the filter surface of the DPF instead of being provided in the front stage of the DPF.

  However, since these conventional DPFs use fine filters, the back pressure of the engine increases, causing problems such as deterioration of fuel consumption and engine output, and two exhaust gas processing paths. In this case, there is a problem that the apparatus becomes large and the cost becomes high. Further, even when the exhaust gas treatment path is made into one system, there is a problem that the apparatus is increased in size and cost due to the arrangement of the oxidation catalyst. Further, when adopting a method of burning PM by raising the exhaust gas temperature by fuel injection, there is a problem of deteriorating fuel consumption. And these problems are expected to become more serious with the request for further improvement of the PM purification rate in the future.

  For this reason, DPFs that collect PM using corona discharge are being developed. One of these is a cell-shaped receiving electrode in which a cell space is formed between multilayer metal foil plates on the downstream side of a discharge electrode made of one or more linear conductors in a container through which exhaust gas passes. Has been proposed (see, for example, Patent Document 1).

  Also, instead of the unglazed ceramic DPF, a metal honeycomb structure DPF excellent in heat resistance is used, and a device for charging the PM in the exhaust gas positively or negatively by corona discharge, There has been proposed a particulate matter removing device that combines and charges the metal honeycomb structure negatively or positively and captures the charged PM by an electric attractive force (see, for example, Patent Document 2).

  However, there is a problem of high voltage leakage as a major problem of the electric dust collection technology. Since the voltage used is a high voltage of several thousand volts to several tens of thousands of volts, if a high voltage current leaks through a small conductive path between the high voltage application section and the ground section, a predetermined electric field formation or corona A situation occurs in which discharge cannot be generated. The main components that form the conductive path are moisture in the exhaust gas and carbon particles called SOOT in the PM, and it is essential to prevent the formation of the conductive path due to these.

In particular, if the insulating portion such as the surface of the high voltage cable connected to the corona discharge electrode or the inner surface of the outer cylinder surrounding the corona discharge electrode is adsorbed and contaminated, the insulation will deteriorate and the conductive path will be deteriorated. It becomes easy to form.
JP 7-293227 A JP 2002-147218 A (page 7, right column, FIG. 9)

  An object of the present invention is to provide an exhaust gas purifying apparatus that charges a workpiece in exhaust gas by corona discharge between a first electrode and a second electrode and collects it by the second electrode. An object of the present invention is to provide an exhaust gas purifying device capable of preventing cable covering, dirt on an insulating portion such as an inner surface of an outer cylinder, and formation of a conductive path due to the dirt.

  An exhaust gas purifying apparatus for achieving the above object has a first electrode and a second electrode arranged in order from the upstream side in an outer cylinder through which exhaust gas of an internal combustion engine passes, and a high voltage is applied to the first electrode. The second electrode is formed of a metal honeycomb structure in an exhaust gas purifying apparatus that generates a corona discharge when applied, charges a component to be treated in the exhaust gas by the corona discharge, and collects it by the second electrode. In addition, a first semiconductor layer that covers the inner surface of the outer cylinder at the periphery of the first electrode is provided to be electrically insulated from the metal honeycomb structure, and at least the potential of the first semiconductor layer during corona discharge Is configured to have the same polarity as that of the first electrode.

  The high voltage referred to here includes not only the plus side but also the minus side. That is, it means a voltage having a high absolute voltage value. The main component to be treated in the exhaust gas is PM, but other components may be used. In short, any component that is contained in the exhaust gas and is charged by corona discharge may be used. Further, the potential of the first semiconductor layer is preferably substantially the same potential with the same polarity as the first electrode, but may be lower (the absolute value may be smaller).

  According to this configuration, although the heat resistance is excellent, the metal honeycomb structure that cannot be used as the DPF because the PM filter function is inferior and the PM filter function is inferior. By using it as a dust collecting electrode, the PM collected and deposited in the DPF can be combusted at a time, so that the DPF regeneration can be performed in a short time without worrying about melting or breakage of the DPF.

  Furthermore, according to this configuration, the first semiconductor layer is provided on the inner surface of the outer cylinder in the peripheral portion of the first electrode, and the first semiconductor layer is set to the same polarity potential as the first electrode, preferably substantially the same potential. Therefore, the PM charged by the corona discharge is strongly repelled by the first semiconductor layer having the same polarity as the first electrode, and the first semiconductor layer and the inner surface portion of the outer cylinder around the first electrode It will not adhere. Therefore, in this portion, it is possible to prevent contamination due to the adhesion of PM and formation of a conductive path due to this contamination. Further, since it is formed of a semiconductor, unlike a conductor, there is no need to worry about leakage current, discharge, spark, or the like.

  Alternatively, the first electrode and the second electrode are arranged in order from the upstream side in the outer cylinder through which the exhaust gas of the internal combustion engine passes, and a high voltage is applied to the first electrode to generate a corona discharge. In the exhaust gas purification apparatus that charges the component to be treated in the exhaust gas and collects it by the second electrode, the second electrode is formed of a metal honeycomb structure, and the high voltage connected to the first electrode A second semiconductor layer is provided on the surface of the portion of the cable in the outer tube, and at least during corona discharge, the potential of the second semiconductor layer is set to the same polarity as that of the first electrode.

  According to this configuration, the second semiconductor layer is provided on the surface of the portion in the outer tube of the high-voltage cable, and the second semiconductor layer has the same polarity as the first electrode, preferably substantially the same potential as the first electrode. Therefore, the same effect as that of the first semiconductor layer can be obtained, and the surface portion of the portion in the outer tube of the high voltage cable can prevent the contamination due to the PM and the formation of the conductive path due to the contamination.

  Alternatively, the first semiconductor layer is provided, and a second semiconductor layer is provided on the surface of the portion in the outer tube of the high-voltage cable connected to the first electrode, and at least the potential of the second semiconductor layer during corona discharge Is configured to have the same polarity as that of the first electrode. According to this configuration, the first semiconductor layer and the second semiconductor layer allow the PM to adhere to both the inner surface portion of the outer cylinder around the first electrode and the surface portion of the high voltage cable in the outer cylinder. It is possible to prevent the contamination due to and the formation of the conductive path due to the contamination.

  In the exhaust gas purifying apparatus, the first electrode is formed by arranging a plurality of pins parallel to the exhaust gas flow direction on a pin holder that extends in a direction perpendicular to the exhaust gas flow direction. And covering the entire first electrode with the third semiconductor layer except for the tip of the pin so that the potential of the third semiconductor layer is at least the same polarity as that of the first electrode during corona discharge. Constitute.

  According to this configuration, the discharge start portion of the first electrode is formed into a pin shape with a sharp tip, so that dielectric breakdown occurs between the metal honeycomb structure serving as the target electrode due to the concentration of electric lines of force due to an unequal electric field. Since corona discharge easily occurs, a uniform and stable strong electric field and corona discharge can be obtained. In addition, the third semiconductor layer, which has the same effect as the first and second semiconductor layers, prevents contamination due to PM adhesion and the formation of a conductive path due to this contamination in the entire first electrode excluding the tip of the pin. it can.

  Furthermore, in the above exhaust gas purifying device, when an insulating heat insulating layer is provided under the at least one semiconductor layer of the first to third semiconductor layers, the insulating heat insulating layer can keep the semiconductor layer warm, In the semiconductor portion, it is possible to prevent the occurrence of moisture condensation in the exhaust gas due to cooling after the engine is stopped, and to prevent the formation of a conductive path due to this condensation. Further, only a necessary portion of the surface of the insulating heat insulating layer can be made into a semiconductor to provide a semiconductor layer.

  Note that, during corona discharge, setting the first to third semiconductor layers to substantially the same potential using the same electrode as the first electrode means that each of the first to third semiconductor layers is electrically connected to a high voltage cable. This can be easily realized. It can also be easily realized by electrically connecting the first to third semiconductor layers and electrically connecting any one of the first to third semiconductor layers to a high voltage cable.

  According to the above configuration, particularly when applying the electric dust collection technology to the DPF, since the exhaust gas targeted by the DPF contains a large amount of moisture and PM, ensuring and maintaining insulation against high voltage. Although it is important, this structure can prevent dirt and dew condensation on the surface portion of the insulator and the formation of a conductive path caused by these, so that insulation can be secured, so that an appropriate electric field and corona discharge can be formed. .

  According to the exhaust gas purification apparatus of the present invention, PM charged by corona discharge is likely to adhere to the inner surface of the outer cylinder in the periphery of the first electrode, or a portion in the outer cylinder of the high voltage cable connected to the first electrode. The entire surface of the first electrode and the entire first electrode excluding the tip of the pin are covered with the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer, respectively, and at least during corona discharge, the potentials of these semiconductor layers are set. Since the potential has the same polarity as that of the first electrode, preferably the same potential, PM charged by corona discharge is strongly repelled by the semiconductor layer that has become the repelling electrode and does not adhere to these semiconductor layers. Therefore, these portions can prevent contamination due to PM adhesion and formation of conductive paths due to the contamination. Further, by forming the layer serving as the repulsive electrode with a semiconductor, unlike the case of forming with a conductor, leakage current, discharge, spark, and the like can be prevented.

  Therefore, according to this configuration, by providing a semiconductor layer in a portion where it is necessary to further reduce the contamination of the insulating portion and having a function as a full-fledged repulsive electrode, the contamination due to the adhesion of PM and the conductivity due to this contamination can be achieved. It is possible to prevent the formation of a path, and it is possible to prevent the electric field and corona discharge from being unstable and the dust collection efficiency from being lowered due to electric leakage.

  Hereinafter, an exhaust gas purifying apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the exhaust gas purification apparatus 1 includes an outer cylinder 10 that includes a corona discharge pin electrode 20 that serves as a first electrode and a metal honeycomb structure 30 that serves as a second electrode. . The corona discharge pin electrode 20 is disposed on the upstream side of the metal honeycomb structure 30 and is connected to a high voltage power supply 24 via a high voltage cable 22 and a high voltage control device 23. Further, the metal honeycomb structure 30 is grounded (grounded) via a grounding cable 31. The metal honeycomb structure 30 functions as a diesel particulate filter (DPF) that collects PM charged by corona discharge. In addition, as a heat source for regeneration of the metal honeycomb structure 30, the heater 32 is disposed on the upstream side of the metal honeycomb structure 30 via the insulating heat transfer layer 33.

  At the time of corona discharge, a DC voltage of several thousand to several tens of thousands of volts is applied to the corona discharge pin electrode 10 from the high voltage power supply 13. By applying this DC voltage, a strong electric field is generated between the corona discharge pin electrode 10 and the metal honeycomb structure 20 to generate corona discharge. Note that the electrical polarity of the corona discharge pin electrode 10 at this time is preferably negative because it is more negative than positive because the stability of corona discharge is higher.

  The outer cylinder 10 has an inlet 11 through which exhaust gas G flows in and an outlet 12 through which purified exhaust gas Gc flows out, and is formed in a cylindrical shape from a conductive material such as SUS409L or SUS410L. The inlet 11 is provided with a dispersion mechanism 11a for equalizing the flow of the exhaust gas G in the outer cylinder 10. Further, at a portion where the corona discharge pin electrode 20 and the metal honeycomb structure 30 are disposed, at least in a peripheral portion of the metal honeycomb structure 30, it is formed inside the outer tube 10 by a ceramic such as cordierite or alumina. An insulating heat insulating cylinder 13 is disposed.

  In the present invention, the inner periphery of the insulating heat insulating cylinder 13 around the corona discharge pin electrode 20, that is, the inner surface of the outer cylinder 10, is formed by a semiconductor ceramic or an ultra-thin film coating of a conductor. A first semiconductor layer 51 is provided. The first semiconductor layer 51 can be formed by installing a semiconductor cylinder on the surface of the insulating heat insulating cylinder 13 or by subjecting only the target surface of the insulating heat insulating cylinder 13 to a semiconductor. The first semiconductor layer 51 is disposed with a gap S between the first semiconductor layer 51 and the metal honeycomb structure 30 so as to be electrically insulated from the metal honeycomb structure 30.

  Further, a part of the first semiconductor layer 51 is electrically connected to the high voltage cable 22 so that the potential of the first semiconductor layer 51 is the same as that of the corona discharge pin electrode 20 during corona discharge (in this embodiment, negative). Of potential. Since this potential is for preventing the adhesion of charged PM, it is not always necessary to have the same potential as the high voltage cable 22 as long as the potential has the same polarity. The potential of the first semiconductor layer 51 may be raised to a potential between the corona discharge pin electrode 20 and the ground potential (zero) (by increasing the absolute value) at least during corona discharge by another electric circuit.

  According to this configuration, the insulating heat insulating cylinder 13 is disposed below the first semiconductor layer 51, and the insulating heat insulating cylinder 13 serves as an insulating heat insulating layer. Accordingly, the first semiconductor layer 51, the insulating heat insulating cylinder (insulating heat insulating layer) 13, and the outer cylinder 10 are disposed in the peripheral portion of the corona discharge pin electrode 20. Further, the metal honeycomb structure 30 is installed on the outer cylinder 10 via the insulating heat insulating cylinder 13. And since this insulation heat insulation cylinder 13 can electrically shield between the outer cylinder 10 and the corona discharge pin electrode 20 and the first semiconductor layer 51, the corona discharge pin electrode 20 and the metal honeycomb structure The electric field and corona discharge between the bodies 30 can be maximized.

  The high voltage cable 22 is connected to the corona discharge pin electrode 20 through the insulator 14 that penetrates the outer cylinder 10 and the insulating heat insulating cylinder 13. This high voltage cable 22 is insulated with a heat resistant insulation coating 21.

  This heat-resistant insulating covering 21 is formed in a rod shape so as to cover the high-voltage cable 22. In order to prevent moisture condensation that occurs when the engine is cooled by stopping the engine, a heat insulating function is provided to make it difficult to cool. Is preferred. Further, the position of the insulator 14 through which the high voltage cable 22 passes is a portion where the surface of the outer cylinder 20 is directed downward in order to prevent accumulation of water and SOOT which are the main causes of high voltage leakage. It is preferable that the uppermost part of the outer cylinder 20 be used.

  And in this invention, the 2nd semiconductor layer 52 formed by the semiconductor ceramic, the ultra-thin coating of a conductor, etc. is provided in the surface of this heat-resistant insulation coating body 21. As shown in FIG. That is, the second semiconductor layer 52 is provided on the surface of the portion in the outer tube 10 of the high voltage cable 22 connected to the corona discharge pin electrode (first electrode) 20. The second semiconductor layer 52 can be formed by providing a semiconductor cylinder on the surface of the heat-resistant insulating covering 21 or by converting the surface of the heat-resistant insulating covering 21 into a semiconductor. Furthermore, by electrically connecting a part of the second semiconductor layer 52 to the high voltage cable 22 or the like, the potential of the second semiconductor layer 52 is at least the same polarity as that of the corona discharge pin electrode 20 at the time of corona discharge (this embodiment). In this case, the potential is minus), preferably substantially the same as that of the corona discharge pin electrode 20. Note that, according to this configuration, the heat-resistant insulating covering 21 serving as an insulating heat insulating layer is disposed below the second semiconductor layer 52.

  In the corona discharge pin electrode 20, a large number (a plurality) of pins 21a parallel to the flow direction of the exhaust gas G are arranged on the pin holder 20a extending in the direction perpendicular to the flow direction of the exhaust gas G. Composed. That is, the corona discharge pin electrode 20 is configured as an aggregate of sharp pins 20b directed to the ground portion of the metal honeycomb structure 30 or the like serving as a discharge target.

  This structure is shown in FIGS. 2 and 3 are perspective views of the corona discharge pin electrode 20, the heat-resistant insulating covering 21 and the high voltage cable 22 from a slightly downstream side, and FIGS. 4 and 5 are views seen from the side. FIG. 2 shows a sieve net type pin holder 20a formed of a disk-like lattice plate, and FIG. 3 shows a radial pin holder 20Aa formed of struts extending radially. When these pin holders 20a and 20Aa are viewed from the side, as shown in FIG. 4, the pin holders 20a and 20Aa are linear, and the parallel pins 21a protrude from the straight portion in the flow direction of the exhaust gas G. It will be. The pin 20b is disposed at the intersection of the members on the hole net. In addition to this, the shape of the pin holder 20a is such that the flow resistance of exhaust gas such as a brush shape as shown in FIG. 6, that is, the back pressure is small, and the pin is on a surface perpendicular to the flow direction of the exhaust gas. Any device that can be arranged substantially evenly may be used.

  According to the present invention, the pin 20b is covered with the insulating heat insulating layer 20c and the third semiconductor layer 20d formed of a semiconductor ceramic or an ultra-thin coating of a conductor, except for the vicinity of the tip, and the pin holding The bodies 20a and 20Aa are similarly covered with the insulating heat insulating layer 20c and the third semiconductor layer 20d. Further, by electrically connecting a part of the third semiconductor layer 20d to the high voltage cable 22, the potential of the third semiconductor layer 20d is at least the same polarity as that of the corona discharge pin electrode 20 at the time of corona discharge (this embodiment In this case, the potential is minus), preferably substantially the same as that of the corona discharge pin electrode 20. In addition, according to this structure, the insulating heat insulation layer 20c is arrange | positioned under the 3rd semiconductor layer 20d.

  The pin holders 20a and 20Aa hold the pin 20b in a form facing the metal honeycomb structure 30, and are connected to the high voltage cable 22 passing through the insulator 14 penetrating the outer cylinder 10 and the insulating heat insulating cylinder 13. Connected. Then, a high voltage from the high voltage power supply 24 is applied to the pin 20b via the high voltage control device 23, the high voltage cable 22, and the pin holders 20a and 20Aa. When this high voltage is applied, the sharp tip of the pin 20b breaks down due to concentration of electric lines of force due to an unequal electric field with the metal honeycomb structure 30 that is the target electrode, and corona discharge occurs.

  Since the pin 20b becomes high temperature due to corona discharge, the material forming the pin 20b is required to have high heat resistance. The material of the pin 20b is most preferably platinum in view of oxidation degradation. However, when there is a problem in terms of cost, a platinum plated tungsten wire, nichrome wire, SUS436L or the like can be used. Joined to 20a, 20Aa by welding or the like.

  In addition, it is important to reduce the flow resistance of the exhaust gas G, that is, the back pressure as much as possible for the parts such as the pin holders 20a and 20Aa other than the discharge part. In FIG. However, other shapes may be used as long as low back pressure, high insulation, and uniform dispersion of the pins 20b can be realized at the same time.

  In the corona discharge pin electrode 20 of this structure, only the tip portion of the pin 20b is exposed, and the rest is covered and insulated with an insulating material, and the pin 20b is directed toward the metal honeycomb structure 30 as a discharge target. Therefore, a uniform and stable strong electric field and corona discharge can be obtained.

  Then, as shown in FIG. 5, when it is desired to positively discharge the corona discharge to the upstream side of the corona discharge pin electrode 20, the pin 20Ab is also installed on the upstream side portion of the pin holders 20a and 20Aa. That is, the pins 20b and 20Ab are arranged in both the downstream direction and the upstream direction. With this configuration, it is possible to generate an upstream corona discharge at the corona discharge pin electrode 20 to enhance the charge to the PM in the exhaust gas G, and an effective measure when the charge to the PM is insufficient. Become. Further, it is possible to prevent the PM from adhering to the inner surface of the insulating heat insulating cylinder 13 upstream from the corona discharge pin electrode 20 and to prevent the conductive path from being formed by the contamination.

  The corona discharge pin electrode 20 having this structure starts from the root of the pin 20b between the exposed portion to which a high voltage is applied at the tip of the pin 20b and the nearest ground portion such as the heater 32 or the metal honeycomb structure 30. In addition, a high-voltage insulation path can be formed through the insulator covering the surfaces of the pin holders 20a and 20Aa, the heat-resistant insulation covering body 21, and the insulation heat insulating cylinder 13.

  The first semiconductor layer 51, the second semiconductor layer 52, and the third semiconductor layer 20d provided on the surfaces of these insulators have the same polarity as that of the corona discharge pin electrode 20 that is the first electrode (in the embodiment shown in FIG. 1). Since a negative potential is applied, it functions as a repelling electrode (minus) that strongly repels PM charged to the same polarity (minus) by corona discharge. Can be prevented. Therefore, the insulation maintenance effect in these surfaces increases. Further, by providing heat insulation to the insulators 13, 21, and 20c under the semiconductor layers 51, 52, and 20d, moisture condensation generated when the engine is cooled down and leakage due to the condensed water are prevented. it can.

  Note that setting the first to third semiconductor layers 51, 52, and 20d to substantially the same potential by using the same electrode as the corona discharge pin electrode 20 causes a part of the first to third semiconductor layers 51, 52, and 20d to be respectively formed. The first to third semiconductor layers 51, 52, and 20d are electrically connected to the high-voltage cable 22 or the first to third semiconductor layers 51, 52, and 20d are electrically connected. It can be easily realized by electrically connecting any one of the above to the high voltage cable 22.

  In the electric dust collection technology, the insulating structure is maintained by these insulators 13, 21, and 20c and the structure in which the semiconductor layers 51, 52, and 20d on the surface prevent contamination by PM. Since it is a high voltage of 10,000 volts, current leaks into a small conductive path between the high voltage application part and the ground part, making it impossible to form a predetermined electric field or corona discharge, but this can be prevented. it can.

  The metal honeycomb structure 30 is a PM dust collecting portion that forms the core of the exhaust gas purification device 1, is formed of a material such as SUS304, and is grounded by the ground cable 31. An alumina washcoat carrying an oxidation catalyst is applied to the surface of the cells of the metal honeycomb structure 30.

  Further, the heater 32 is disposed in close contact with the upstream side of the exhaust gas of the metal honeycomb structure 30 via the insulating heat transfer layer 33. The heater 32 and the insulating heat transfer layer 33 are formed so as to allow ventilation, and are configured to allow the exhaust gas G to flow into the metal honeycomb structure 30 and to reduce the flow resistance as much as possible. A heater power supply 34 and a heater control device 35 are wired to the heater 32.

  The heater 32 is preferably formed of solid platinum or a platinum plating material in order to utilize the catalytic action for reducing the ignition temperature of the collected PM, but the heater power supply 34 has a sufficient capacity. Sometimes it is not necessary to form platinum with platinum when cost becomes a problem. In the state where this current is passed, the potential of the heater 32 is a potential between the potential of the metal honeycomb structure 30 and the potential of the corona discharge pin electrode 20, but is a potential close to the potential of the metal honeycomb structure 30. , So that PM can be collected.

  The insulating heat transfer layer 33 is provided in order to prevent the current supplied from the heater power source 34 from leaking to the surface of the metal honeycomb structure 30, and is formed of glass fiber, ceramic fiber, porcelain, etc. Since the exhaust gas G passes therethrough, heat transfer can be performed even by convective heat transfer, so that an appropriate gap can be substituted.

  The metal honeycomb structure 30 is provided with a movement actuator 37 controlled by the actuator control device 36, and the movement actuator 37 is driven according to the control by the actuator control device 36 so that the metal honeycomb structure 30 is predetermined. It can be moved to the position. In other words, the distance L between the corona discharge pin electrodes 20 can be adjusted.

  An engine speed Ne indicating the detected value Tg of the exhaust gas temperature sensor 41 provided at the inlet 11 of the outer cylinder 10, the operating state of the engine, etc. is sent to a control device 40 called an engine control unit (ECU) that controls the engine. The control means for the exhaust gas purifying apparatus 1 is configured by a program or the like previously input to the control device 40, the high voltage control device 23, the high voltage power supply 24, the heater control device 35, The actuator control device 36 and the like are controlled.

  Next, PM collection in the exhaust gas purification apparatus 1 having the above-described configuration will be described.

  When the engine is started and the exhaust gas G flows into the exhaust gas purification device 1 or before that, the high-voltage power supply control device 23 supplies several thousand to the corona discharge pin electrode 20 from the high-voltage power supply 24 via the high-voltage cable 22. A DC high voltage on the negative side of tens of thousands of volts from the volt is applied to form a uniform and stable strong electric field and corona discharge with the metal honeycomb structure 30.

  Exhaust gas G discharged from the engine (internal combustion engine) enters the outer cylinder 10 through the inlet 11 and passes through this corona discharge portion. At this time, the PM in the exhaust gas G is charged to the same polarity (minus) as that of the corona discharge pin electrode (first electrode) 20. Therefore, when the exhaust gas G passes through the metal honeycomb structure 30, the charged PM is charged. Are attracted to the metal honeycomb structure (second electrode) 30 which is an electrode of different polarity (plus) by the electric attractive force, and adheres to the wall surface of the cell and loses electric charge. Since the oxidation catalyst is supported on the wall surface of this cell, when the temperature of the wall surface is high, the adhering PM is oxidized by the catalytic action of the oxidation catalyst to become carbon dioxide gas. Further, when the wall surface temperature is low, it is deposited on the wall surface without being oxidized. Thereby, PM is removed from the exhaust gas G to become purified exhaust gas Gc, which flows out from the outlet 12 of the outer cylinder 10.

  In this exhaust gas purification, the corona discharge is optimally controlled. In other words, discharge becomes easier when the exhaust gas G becomes high temperature, but abnormal discharge such as spark is also likely to occur. If this abnormal discharge continues, the dust collection rate decreases, and devices such as the high-voltage power supply 24 are installed. Therefore, the corona discharge is controlled so as to increase the PM collection rate while preventing abnormal discharge according to the state of the exhaust gas.

  More specifically, what determines the state of the corona discharge is the applied voltage, the current, the distance L between the corona discharge pin electrode 20 and the metal honeycomb structure 30, and the exhaust gas temperature. On the other hand, control factors that can be controlled for corona discharge control are applied voltage, current, and distance L between electrodes. Therefore, these control factors are controlled by a program created in advance.

  Specifically, the high-voltage control device 23 monitors the current flowing through the high-voltage cable 22 and takes into account information such as the engine speed and load, the engine operating state, and other information. On / off control and control to adjust the value of the applied high voltage to a predetermined voltage. At the same time, the actuator 37 is controlled by the actuator control device 36 to move the metal honeycomb structure 30 to a predetermined inter-electrode distance Lo calculated according to the operating state of the engine. The high voltage application timing, the predetermined voltage value, and the predetermined inter-electrode distance Lo are set in advance according to the engine operating state and the like through experiments or the like, and are input to the program in the form of map data or the like. Corresponding to this data, by appropriately adjusting and controlling the high voltage application timing, voltage value, and interelectrode distance L, a stable corona discharge capable of obtaining a high dust collection rate is generated and continued. Can do.

  With this control, the applied voltage and the interelectrode distance L between the first electrode (corona discharge pin electrode) 20 and the second electrode (metal honeycomb structure) 30 can be changed according to the operating state of the engine. The PM collection can be optimized in accordance with various states of the exhaust gas G such as changing PM concentration and flow velocity.

  For example, exhaust gas such as idling or low-load low-rotation operation continues when the engine is operating at a low temperature, and the PM collected and deposited on the metal honeycomb structure 30 increases. The force of holding PM on the wall surface of the metal honeycomb structure 30 is weakened, and a phenomenon called re-scattering in which PM is diffused occurs, causing a decrease in PM dust collection rate.

  Therefore, before this re-scattering occurs, current is passed through the heater 32 to heat and catch the collected PM to start PM combustion removal. Specifically, when the preset DPF regeneration start condition is reached, a current is passed through the heater 32 for a predetermined time, and the PM deposited on the heater 32 or the PM deposited on the downstream metal honeycomb structure 30 is reduced. The heater 32 is heated to a predetermined temperature at which combustion starts, and PM is ignited by combustion by this heating. By this ignition, the combustion of PM spreads from the upstream side to the downstream side of the metal honeycomb structure 30, and when the entire PM deposited on the metal honeycomb structure 30 burns, the regeneration of the metal honeycomb structure 30 is performed. Complete.

  The heating timing of the heater 32 is generated by burning the PM by heating the heater 32 when an amount of PM that can be combusted and generate a desired amount of heat is accumulated on the heater 32, and is generated by this combustion. When heat is supplied to the downstream (rear stage) oxidation catalyst to combust and remove the downstream PM, or when combustion of PM is necessary even when an appropriate amount of PM has not accumulated on the heater 32 Then, the heater 32 is heated and the heat generated in the heater 32 is transferred to the oxidation catalyst of the downstream metal honeycomb structure 30, and the combustion of the downstream PM is started by the catalytic action of this oxidation catalyst, and the downstream side For example, PM may be removed by combustion.

  In particular, according to this configuration, the heater 32 is a portion where the electric field for electric dust collection is strong, and the dust collection rate is high, so the amount of PM collected on the heater 32 is increased, In addition to facilitating ignition, it is arranged upstream of the metal honeycomb structure 30, so that it can easily play the role of the formation of ignition of PM combustion. In this case, by making the heater 32 a part of the electrostatic precipitator electrode, accumulation of PM that can be used as a heat source for ignition of DPF regeneration is promoted. Further, when the ignition heater 32 is made of platinum or the like, PM can be easily ignited by the oxidation catalytic action of platinum or the like.

  When the DPF is regenerated, the metal honeycomb structure 30 is made of metal and has excellent heat resistance. Therefore, it is possible to perform a single combustion of PM, which cannot be performed because a ceramic filter of the prior art is damaged due to thermal stress. Become. Therefore, according to the regeneration method of the metal honeycomb structure 30, there is no need for a gentle continuous regeneration method by fuel injection or a method of intermittent regeneration by switching a filter as in the prior art. The deposited PM itself can be used as a heat source for regeneration. This eliminates the need for control of fuel injection into the exhaust pipe or multistage injection in the fuel injection, facilitates the structure and control of the apparatus, and reduces fuel consumption.

  In addition, the ignition of the PM accumulated on the upstream side spreads to the downstream side, and the PM is burned and removed at a high temperature and in a short time by a single combustion, so that the PM can be reliably burned and the regeneration time is shortened.

  According to the exhaust gas purification apparatus 1 having the above-described configuration, the PM charged by corona discharge easily adheres to the inner surface of the outer cylinder 10 around the corona discharge pin electrode 20 or the corona discharge pin electrode (first electrode) 20. The surface of the portion of the high voltage cable 22 connected to the outer cylinder 10 and the entire corona discharge pin electrode 20 excluding the tip of the pin 20b are respectively connected to the first semiconductor layer 51, the second semiconductor layer 52, and the second semiconductor layer 52. 3 The semiconductor layer 20d is covered and the potentials of these semiconductor layers 51, 52, and 20d are set to the same polarity as that of the corona discharge pin electrode 20, preferably about the same potential as that of the corona discharge pin electrode 20. The charged PM is strongly repelled by the semiconductor layers 51, 52, and 20d having the same polarity as the corona discharge pin electrode 20, and does not adhere to these semiconductor layers 51, 52, and 20d.Therefore, these portions can prevent contamination due to PM adhesion. Further, since it is formed of a semiconductor, unlike a conductor, there is no need to worry about leakage current, discharge, spark, or the like.

  Therefore, according to this configuration, by providing the semiconductor layers 51, 52, and 20d in the portions where it is necessary to further reduce the contamination of the insulating portion to provide a full-scale repulsive pole, Contamination of the cable 22 and the corona discharge pin electrode 20 can be prevented, and instability of corona discharge and reduction of dust collection efficiency due to electric leakage caused by the contamination can be prevented.

It is a figure which shows the structure of the exhaust-gas purification apparatus of embodiment which concerns on this invention. It is a perspective view which shows the structure of the corona discharge pin electrode which is a 1st electrode. It is a perspective view which shows the other structure of the corona discharge pin electrode which is a 1st electrode. It is a side view which shows the structure of the corona discharge pin electrode which is a 1st electrode. It is a side view which shows the other structure of the corona discharge pin electrode which is a 1st electrode. It is a fragmentary perspective view which shows the other structure of the corona discharge pin electrode which is a 1st electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 10 Outer cylinder 13 Insulation heat insulation cylinder (insulation heat insulation layer)
20 Corona discharge pin electrode (first electrode)
20a, 20Aa Pin holder 20b, 20Ab Pin 20c, 20Ac Insulating heat insulating layer 20d, 20Ad Third semiconductor layer 21 Heat resistant insulating covering (insulating heat insulating layer)
22 High voltage cable 30 Metal honeycomb structure (second electrode)
51 1st semiconductor layer 52 2nd semiconductor layer

Claims (5)

A first electrode and a second electrode are arranged in order from the upstream side in an outer cylinder through which exhaust gas of an internal combustion engine passes, and a high voltage is applied to the first electrode to generate corona discharge. In the exhaust gas purification apparatus that charges the component to be treated in the gas and collects it by the second electrode,
The second electrode is formed of a metal honeycomb structure, and a first semiconductor layer that covers the inner surface of the outer cylinder at the periphery of the first electrode is provided to be electrically insulated from the metal honeycomb structure, An exhaust gas purifying apparatus, wherein the potential of the first semiconductor layer is set to a potential having the same polarity as that of the first electrode at least during corona discharge. A first electrode and a second electrode are arranged in order from the upstream side in an outer cylinder through which exhaust gas of an internal combustion engine passes, and a high voltage is applied to the first electrode to generate corona discharge. In the exhaust gas purification apparatus that charges the component to be treated in the gas and collects it by the second electrode,
The second electrode is formed of a metal honeycomb structure, and a second semiconductor layer is provided on the surface of the portion in the outer cylinder of the high voltage cable connected to the first electrode, and at least during the corona discharge, the second semiconductor layer The exhaust gas purifying apparatus is characterized in that the potential of the exhaust gas is set to the same polarity as that of the first electrode.   A second semiconductor layer is provided on the surface of the portion of the high-voltage cable connected to the first electrode in the outer cylinder, and at least during corona discharge, the potential of the second semiconductor layer is set to the same polarity as that of the first electrode. The exhaust gas purifying device according to claim 1.   The first electrode is formed by arranging a plurality of pins parallel to the exhaust gas flow direction on a pin holder that extends in a direction perpendicular to the exhaust gas flow direction, and excluding the tip of the pin. The entire first electrode is covered with a third semiconductor layer, and the potential of the third semiconductor layer is set to the same polarity as that of the first electrode at least during corona discharge. The exhaust gas purifying device according to claim 1.   The exhaust gas purification device according to any one of claims 1 to 4, wherein an insulating heat insulating layer is provided below at least one of the first to third semiconductor layers.

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