JP2005232971A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for optimizing the trap of PMs while preventing abnormal discharge such as spark by generating corona discharge suitable to various conditions of exhaust gas including an exhaust gas temperature, PM concentration and a flow rate, changed depending on the operated conditions of an engine. <P>SOLUTION: The exhaust emission control device 1 comprises a first electrode 20 and a second electrode 30 arranged in an 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. In accordance with data showing the operated conditions of the engine, an electrode distance L between the first electrode 20 and the second electrode 30 is changed. <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 one system, and an oxidation catalyst is installed in the upstream (upstream side) of the DPF, and NO in the exhaust gas is oxidized to NO ₂ by this oxidation catalyst, and this NO ₂ is collected in the DPF. The fuel supplied to the oxidation catalyst by the method of oxidizing the generated PM, post-injection in fuel injection, direct fuel injection into the exhaust passage, etc. is burned by the oxidation catalyst to raise the exhaust gas temperature, and the downstream DPF A continuous regeneration method for burning the collected PM is used. 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 some cases, there is a problem that the apparatus becomes larger and the cost becomes higher. Even when the exhaust gas treatment path is made into one system, there is a problem that the apparatus is enlarged and the cost is increased due to the arrangement of the oxidation catalyst. There is a problem that fuel efficiency is deteriorated when a method of burning PM by raising the exhaust gas temperature by fuel injection is employed. 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, corona discharge easily occurs when the exhaust gas becomes high temperature, but abnormal discharge such as sparks also easily occurs.If this abnormal discharge continues, the dust collection rate decreases, and a high voltage power source is started. There is a problem that the device to be damaged. Therefore, it is necessary to control the corona discharge so as not to lower the PM collection rate while preventing abnormal discharge according to the state of the exhaust gas.

On the other hand, the present inventor determined the state of corona discharge through experiments and the like, and applied voltage, current, interelectrode distance between the first electrode (corona discharge electrode) and the second electrode (dust collection electrode), and exhaust. On the other hand, it has been found that the control factors that can be controlled for the corona discharge control in the exhaust gas purification apparatus are the applied voltage, the current, and the distance between the electrodes.
JP 7-293227 A JP 2002-147218 A (page 7, right column, FIG. 9)

  The object of the present invention is to change not only the applied voltage but also the interelectrode distance between the first electrode (corona discharge electrode) and the second electrode (dust collecting electrode) in accordance with the operating state of the engine, particularly the exhaust gas temperature. By doing so, it is possible to optimize the PM collection by generating appropriate corona discharge corresponding to various exhaust gas states such as the exhaust gas temperature, PM concentration, and flow velocity that change depending on the operating state of the engine. An object is to provide an exhaust gas purification device.

  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, the distance between the first electrode and the second electrode is changed based on the data indicating the operating state of the engine.

  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.

  According to these configurations, when purifying exhaust gas using corona discharge, the distance between the first electrode and the second electrode can be changed according to the state of the exhaust gas, thereby preventing abnormal discharge. However, by optimizing the state of corona discharge, it is possible to prevent equipment failure and a decrease in PM collection rate.

  In the exhaust gas purification apparatus, the data indicating the operating state of the engine is configured to include at least exhaust gas temperature data. Corona discharge in the exhaust gas is affected by the exhaust gas temperature, PM concentration, flow velocity, etc., but the exhaust gas temperature is particularly affected, so this exhaust gas temperature data is included in the data for controlling the distance between the electrodes. Make it.

  Further, the exhaust gas temperature data is configured to be data detected by an exhaust gas temperature sensor disposed upstream of the first electrode. The exhaust gas temperature is preferably detected directly by a temperature sensor, but it can also be estimated from the engine speed and load indicating the operating state of the engine.

  Further, the exhaust gas purification device is configured such that the higher the exhaust gas temperature, the larger the distance between the electrodes. As the exhaust gas temperature is higher, discharge becomes easier and abnormal discharge such as spark is more likely to occur. Therefore, the occurrence of abnormal discharge is avoided by increasing the distance between the electrodes.

  Further, in the above exhaust gas purifying apparatus, a movement actuator for moving the metal honeycomb structure is provided, the metal honeycomb structure is provided so as to be movable in the flow direction of the exhaust gas, and the distance between the electrodes is set. The moving actuator is controlled so as to coincide with a predetermined inter-electrode distance determined based on data indicating the operating state of the engine.

  In order to make the distance between the electrodes variable, either one or both of the first electrode and the second electrode may be configured to move. However, the moving actuator moves the metal honeycomb structure to which no high voltage is applied. With this configuration, the problem of electrical insulation is reduced and the structure can be simplified.

  The predetermined inter-electrode distance is set in advance corresponding to the operating state of the engine through experiments or the like, and is input to the program in the form of map data or the like. By appropriately adjusting and controlling the distance between the electrodes corresponding to this data, a stable corona discharge capable of obtaining a high dust collection rate can be generated and can be continued.

  According to the exhaust gas purification apparatus of the present invention, when exhaust gas purification using corona discharge is performed, not only the applied voltage but also between the first electrode and the second electrode according to the operating state of the engine, particularly the exhaust gas temperature. By changing the distance between the electrodes, the distance between the first electrode and the second electrode can be changed according to the state of the exhaust gas, so that the state of corona discharge is optimized while preventing abnormal discharge. Thus, it is possible to prevent a failure of the device and a decrease in the PM collection rate.

  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. Therefore, the metal honeycomb structure 30 is installed in the outer cylinder 10 through the insulating heat insulating cylinder 13. Since this insulation heat insulating cylinder 13 can electrically shield the outer cylinder 10 and the corona discharge pin electrode 20, the electric field and corona discharge between the corona discharge pin electrode 20 and the metal honeycomb structure 30. Can be maximized.

  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 a pin holder 20a that spreads in a plane 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.

  The pin 20b is covered with an insulator except for the vicinity of the tip, and the pin holders 20a and 20Aa are also covered with an insulator. The pin holders 20a and 20Aa hold the pins 20b in a form facing the metal honeycomb structure 30, and are connected to the high voltage cable 22 penetrating the outer tube 10 and the insulating heat insulating tube 13. The high voltage cable 22 is insulated with a heat-resistant insulation coating 21. 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 avoid the PM from adhering to the inner surface of the insulating heat insulating cylinder 13 upstream from the corona discharge pin electrode 20 and becoming dirty.

  Further, the heat-resistant insulating covering 21 is formed of a material such as enamel and is formed in a rod shape covering the high voltage cable 22, but in order to prevent condensation of moisture generated when the engine is cooled by stopping the engine, It is preferable to provide a function to make it difficult to cool. Further, the portion of the heat-resistant insulating covering 21 that penetrates the outer cylinder 10 and the insulating heat-insulating cylinder 13 has the surface of the outer cylinder 20 facing downward in order to avoid accumulation of water and SOOT that are the main causes of high voltage leakage. It is preferable to set it as the site | part which is, and it is most preferable to set it as the uppermost part of the outer cylinder 20.

  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.

  Since these insulators are easily charged, the PM charged to the same polarity (minus in the embodiment of FIG. 1) as that of the corona discharge pin electrode 20 during corona discharge, and the PM charged to the same polarity (minus) by corona discharge is charged. Since it functions also as a repelling electrode (minus) which repels, adhesion of PM can be prevented, and further, the insulation maintaining effect of these insulators is enhanced. Further, by providing these insulators with heat insulation, it is possible to prevent moisture condensation that occurs when the engine is cooled by stopping the engine and leakage due to the condensed water.

  Due to the structure that maintains these insulation properties, in the electric dust collection technology, the high voltage of several thousand volts to several tens of thousands of volts, so that current leaks into a small conductive path between the high voltage application part and the ground part. Thus, it becomes impossible to form a predetermined electric field or corona discharge, but this can be prevented.

  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.

  In the present invention, in order to move the metal honeycomb structure (second electrode) 30, a movement actuator 37 controlled by an actuator control device 36 is provided, and the movement honeycomb 37 is used to move the metal honeycomb structure. 30 is configured to be movable in the flow direction of the exhaust gas. If the metal honeycomb structure 30 to which no high voltage is applied is moved rather than the corona discharge pin electrode 20 to which a high voltage is applied, the problem of electrical insulation is reduced. , Can simplify the structure.

  The moving actuator 37 may be a pneumatic piston or a hydraulic piston that expands and contracts in the direction of the exhaust gas flow, but is formed of an AC servo motor / DC servo motor, pulse motor, or the like that enables highly accurate control. The

  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.

  Then, in accordance with control by the actuator control device 36, the movement actuator 37 is driven, and the inter-electrode distance L is determined based on data indicating the engine operating state such as the engine speed Ne, the engine load Q, and the exhaust gas temperature Tg. A predetermined inter-electrode distance Lo is set to match. That is, when purifying exhaust gas using corona discharge, the corona discharge pin electrode (first electrode) corresponds to various states of the exhaust gas G such as the exhaust gas temperature Tg, PM concentration, and flow velocity that change depending on the engine operating state. ) It is configured to be able to adjust the distance L between the electrodes 20.

  In particular, since the exhaust gas temperature Tg has a large influence on corona discharge, the data for adjusting the inter-electrode distance L includes at least the data of the exhaust gas temperature Tg. The exhaust gas temperature Tg can be estimated from the engine speed Ne, the engine load Q, and the like based on map data inputted in advance, but the corona discharge pin electrode 20 can generate a corona discharge in a better state. It is preferable that an exhaust gas temperature sensor 41 is disposed upstream of the exhaust gas temperature sensor 41 and a value detected by the exhaust gas temperature sensor 41 is used. In addition, the higher the exhaust gas temperature Tg, the easier the discharge and the more likely the occurrence of abnormal discharge such as sparks. Therefore, the higher the exhaust gas temperature Tg, the larger the predetermined inter-electrode distance Lo, thereby causing abnormalities. Avoid discharges.

  The predetermined inter-electrode distance Lo is set in advance in accordance with the operating state of the engine through experiments or the like, and is input to the program in the form of map data or the like. A stable corona discharge capable of obtaining a high dust collection rate can be generated and continued by appropriately adjusting and controlling the interelectrode distance L in correspondence with this data.

  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 these configurations, since the inter-electrode distance L between the corona discharge pin electrode (first electrode) 20 and the metal honeycomb structure (second electrode) 30 can be changed, the corona discharge is prevented while preventing abnormal discharge. By optimizing the state, it is possible to prevent equipment failure and a decrease in PM collection rate.

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 20 Corona discharge pin electrode (1st electrode)
23 High Voltage Control Device 24 High Voltage Power Supply 30 Metal Honeycomb Structure (Second Electrode)
36 Actuator control device 37 Actuator for movement 40 Control device (ECU)

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 the distance between the first electrode and the second electrode is changed based on data indicating an operating state of the engine. Exhaust gas purification device.   The exhaust gas purifying apparatus according to claim 1, wherein the data indicating the operating state of the engine includes at least exhaust gas temperature data.   The exhaust gas purification apparatus according to claim 2, wherein the exhaust gas temperature data is data detected by an exhaust gas temperature sensor disposed upstream of the first electrode.   The exhaust gas purification apparatus according to claim 2 or 3, wherein the distance between the electrodes is increased as the exhaust gas temperature is higher. Provided with a moving actuator for moving the metal honeycomb structure, the metal honeycomb structure is provided so as to be movable in the flow direction of the exhaust gas, and the distance between the electrodes is used as data indicating the operating state of the engine. The exhaust gas purifying apparatus according to any one of claims 1 to 4, wherein the moving actuator is controlled so as to coincide with a predetermined distance between electrodes determined based on the distance.

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