JP2006170021A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress electric leakage between electrodes caused by deposition of PM in an exhaust emission control device for purifying exhaust gas by the action of high voltage. <P>SOLUTION: An upstream end surface of a honeycomb structure 10 and a charging electrode 20 are spaced at a predetermined distance a. This supresses possibility of the electric leakage between the charging electrode 20 and an outer peripheral electrode 15 serving as a receiving electrode even when PM deposits on the upstream end surface of the honeycomb structure 10. The charging electrode 20 and an electric field forming electrode 25 are formed in separate bodies so that these charging electrode 20 and electric field forming electrode 25 are separately supplied with power so that power supply in accordance with purposes of the respective electrodes can be made. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that is provided in an exhaust system such as a diesel engine or a lean burn engine and captures PM (Particulate Matter) contained in the exhaust gas.

  As a technique for removing PM in exhaust gas, a DPF (Diesel Particulate Filter) using a porous honeycomb structure has been proposed (see, for example, Patent Document 1). This DPF, for example, plugs some of the openings from the upstream end face to the downstream end face of the honeycomb structure at the upstream end, and downstream the other openings. By plugging at the end on the side, the exhaust gas flowing in from the opening opening on the upstream side is filtered through the porous partition wall and discharged from the opening opening on the downstream side. PM in the exhaust gas is collected by the partition wall.

  On the other hand, an apparatus including a cylindrical counter electrode opened at the upstream end and the downstream end, and a single bar-shaped internal electrode extending through the axis of the counter electrode from the vicinity of the upstream end of the counter electrode is also proposed. (For example, refer to Patent Document 2). In this apparatus, the PM in the exhaust gas charged by the internal electrode is adsorbed to the counter electrode by the interaction between the potential and the electric field between both electrodes. Part of the adsorbed PM is burned and incinerated, and a plasma state is generated by applying a high voltage between both electrodes, and decomposition of substances such as NOx is promoted.

Japanese Patent Publication No. 6-29545 JP 2004-19534 A

  By the way, when it is considered to install a honeycomb structure having a large number of cells inside the counter electrode of the device of Patent Document 2, the PM deposited on the front end of the honeycomb structure causes the internal electrode and the counter electrode to be separated from each other. It is thought that there is a possibility that the electric leakage will occur between them and the purification performance may be lowered.

  Accordingly, an object of the present invention is to suppress the risk of electric leakage between electrodes due to PM accumulation in an exhaust gas purification apparatus that purifies exhaust gas by the action of a high voltage.

  A first aspect of the present invention includes a honeycomb structure having a large number of cells between a receiving electrode and an electric field forming electrode, and an exhaust gas is generated by an electric field formed between the receiving electrode and the electric field forming electrode. An exhaust gas purifying apparatus for adsorbing a predetermined substance in the honeycomb structure, further comprising a charging electrode for charging the predetermined substance in the exhaust gas upstream of the electric field forming electrode. The exhaust gas purifying apparatus is characterized in that the electrode for use and the end face on the upstream side of the honeycomb structure are separated from each other by a predetermined distance.

  In the first aspect of the present invention, PM in the exhaust gas is charged by the charging electrode, and is adsorbed to the honeycomb structure on the downstream side by the action of the electric field between the electric field forming electrode and the receiving electrode. Here, in the first aspect of the present invention, since the upstream end face of the honeycomb structure and the charging electrode are separated by a predetermined distance, even when PM is deposited on the upstream end face of the honeycomb structure, the charging is performed. The risk of electric leakage between the electrode for use and the receiving electrode can be suppressed.

  The second aspect of the present invention is the exhaust gas purification apparatus according to claim 1, wherein the receiving electrode is cylindrical, the honeycomb structure is disposed in a region surrounded by the receiving electrode, and the electric field forming device is provided. An exhaust gas purification apparatus, wherein an electrode is inserted through the honeycomb structure.

  In the second aspect of the present invention, the same effect as that of the first aspect of the present invention can be obtained in the configuration in which the honeycomb structure is disposed inside the cylindrical receiving electrode.

  A third aspect of the present invention is the exhaust gas purifying apparatus according to claim 1 or 2, further comprising a high-voltage power source that individually supplies power to the charging electrode and the electric field forming electrode. It is a purification device.

  In the third aspect of the present invention, power can be supplied according to the purpose of each of the charging electrode and the electric field forming electrode by supplying power separately to the charging electrode and the electric field forming electrode.

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

  FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus 1 according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a honeycomb structure 10 as a main part thereof. The exhaust gas purification apparatus 1 is provided in an exhaust system of an engine (not shown) (diesel or lean burn gasoline engine or the like).

  The exhaust gas purification apparatus 1 includes a metal case 2 and has a honeycomb structure 10 supported inside the case 2. A cylindrical outer peripheral electrode 15 as a receiving electrode is formed on the outer peripheral surface of the honeycomb structure 10. A space between the outer peripheral electrode 15 and the case 2 is sealed with an alumina mat (not shown). Instead of the configuration in which the outer peripheral electrode 15 is provided separately from the case 2 as in the present embodiment, the case 2 may have the function of the outer peripheral electrode.

  As shown in FIG. 2, the honeycomb structure 10 includes a large number of cells, that is, exhaust gas passages 12 partitioned by porous partition walls 11, all of the exhaust gas passages 12 flowing in the exhaust gas (direction A in the figure). ) In parallel. A partial opening on the upstream side of the exhaust gas passage 12 and an opening on the downstream side of the exhaust gas passage 12 where the upstream opening is opened are closed by a plug 13.

  The honeycomb structure 10 is made of a porous ceramic material, and specifically, cordierite, SiC (silicon carbide), or the like is preferably used. The porosity of the base material portion (wall portion) excluding the exhaust gas passage of the honeycomb structure 10 is 60 to 80%, and the average pore diameter is 20 to 60 μm.

The partition walls 11 of the honeycomb structure 10 are coated with a NOx storage reduction catalyst (NSR) in which, for example, Li = 3 mol / L, Pt = 5 g / L, and the coating material is Al ₂ O ₃ as a catalyst material. Has been. The coating amount of the NOx storage reduction catalyst is, for example, 300 g / L.

  In the honeycomb structure generally used, the partition wall porosity is generally 55 to 60% and the partition wall average pore diameter is 9 to 30 μm. In this embodiment, the porosity is 60 to 80% and the partition wall average Since the pore diameter is set to 20 to 60 μm, a relatively low exhaust resistance can be realized while adopting a wall flow type structure in which exhaust gas is filtered through the porous partition wall 11. In general, the loading amount of the catalyst material is about 150 g / L. In this embodiment, the loading amount of the catalyst material can be set to a relatively large value such as 100 to 400 g / L, and the loading of the catalyst material is carried out. Even in such a state, exhaust resistance can be suppressed.

  A charging electrode 20 is disposed upstream of the honeycomb structure 10 in the exhaust gas flow direction. The charging electrode 20 extends on an extension of the axial center of the honeycomb structure 10, and a front end portion of the charging electrode 20 protrudes outside the case 2. The charging electrode 20 is formed by covering a part of the surface of a rod-shaped electrode body 21 with an insulating layer 22 such as an insulator. The covering ratio by the insulating layer 22 is defined by the engine exhaust amount and the PM exhaust amount, and it is preferable that the covering ratio by the insulating layer 22 is lower as the engine exhaust amount and the PM exhaust amount are larger. A metal connection 23 is connected to the electrode body 21 outside the case 2. The charging electrode 20 and the upstream end surface of the honeycomb structure 10 are separated from each other by a predetermined distance a. This distance a is such that conduction does not occur between the charging electrode 20 and the upstream end face of the honeycomb structure 10 even when PM is accumulated to the maximum extent on the upstream end face of the honeycomb structure 10. And

  An electric field forming electrode 25 is arranged inside the honeycomb structure 10 surrounded by the outer peripheral electrode 15. The electric field forming electrode 25 extends on the axial center of the honeycomb structure 10, and its rear end protrudes to the outside of the case 2. The electric field forming electrode 25 is formed by covering a part or the entire surface of a rod-shaped electrode body 26 with an insulating layer 27 such as an insulator. A metal connection 28 is connected to the electrode body 26 outside the case 2.

  The electrode bodies 21 and 26 can be formed of chromium steel having excellent corrosion resistance (for example, 10Cr5Al), but is not limited thereto, and other conductive metals or other conductive materials having corrosion resistance. The body can be used. The insulating layers 22 and 27 are preferably made of a material having high heat resistance such as ceramics. However, in the case of an engine having a low exhaust system temperature such as a diesel engine, the insulating layers 22 and 27 are heat resistant such as acrylic resin. May be a relatively low material.

  The case 2 and the outer peripheral electrode 15 are electrically grounded. On the other hand, the metal wires 23 and 28 for supplying power to the charging electrode 20 and the electric field forming electrode 25 are respectively connected to the charging power supply unit 30a and the electric field forming power supply unit 30b of the high-voltage power supply 30, which are separately configured. Yes.

  Each of these power supply units 30a and 30b includes an inverter circuit, a transformer, a rectifying diode, a smoothing circuit, etc., and boosts a direct current from a battery (not shown) into a charging electrode 20 and an electric field forming electrode 25. Supply power. The power supply units 30a and 30b are configured to be able to supply power to the charging electrode 20 and the electric field forming electrode 25 individually (that is, with different voltages and waveforms as needed). The power supply from the high-voltage power supply 30 is, for example, an alternating pulse wave for the charging electrode 20 and a direct current for the electric field forming electrode 25, and these voltages are preferably 5 kV or more, for example, about 15 to 30 kV. However, the present invention is not limited thereto, and an arbitrary waveform and voltage such as direct current, direct current pulse, alternating current, or superposition of direct current and direct current pulse can be selected. The high voltage power supply 30 is controlled by a control output from an electronic control unit (ECU) 40.

  The ECU 40 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like (not shown). An engine water temperature sensor 41, an air flow meter 42, a crank angle sensor 43, and the like are connected to the input / output port of the ECU 40. The ECU 40 calculates respective values based on these detection signals and processes them as described below. .

  The ECU 40 follows a predetermined control program and the like, and based on signals indicating the state of the internal combustion engine from various sensors, a drive pulse signal (gate signal) for driving the inverter circuit of the high-voltage power supply 30, A voltage instruction signal for instructing an output voltage value from 30 is generated.

  When the drive pulse signal and the voltage instruction signal are given from the ECU 40, in the high voltage power source 30, the DC voltage from the DC power source is converted into an AC voltage by an inverter circuit, boosted by a transformer, and rectified by a diode as necessary. As a result, a predetermined voltage is output as described later.

  On the other hand, in the ROM of the ECU 40, correction coefficients x1f and x1r corresponding to the engine water temperature and correction coefficients x2f and x2r corresponding to the engine load are used to correct the voltage values for the charging electrode 20 and the electric field forming electrode 25. A correction coefficient map storing the values of is stored.

  As shown in FIG. 3, the correction coefficient x1f is for correcting the voltage value to the charging electrode 20, and takes a value smaller than 1 when the engine water temperature is low, and exceeds 1 as the engine water temperature increases. The value is set to increase gradually. The reason why the value of the correction coefficient x1f is set in this way is that, in general, the PM is relatively small when cold. The correction coefficient x1r is used to correct the voltage value to the electric field forming electrode 25, but is set to 1 here regardless of the engine water temperature.

  As shown in FIG. 4, the correction coefficient x2f is for correcting the voltage value to the charging electrode 20, and takes a value smaller than 1 when the engine load is low, and the value becomes 1 as the engine load increases. It is set to gradually increase beyond The correction coefficient x2r is for correcting the voltage value to the electric field forming electrode 25. The correction coefficient x2r takes a value smaller than 1 when the engine load is low, and the value gradually approaches a value near 1 as the engine water temperature increases. Is set to The engine load is calculated based on the intake air amount calculated from the detection value of the air flow meter 42 and the engine rotation speed calculated from the detection value of the crank angle sensor 43, for example. The reason why the correction coefficients x2f and x2r according to the engine load are set in this way is that the amount of supplied PM generally increases at a high load, but the PM is likely to aggregate at a high load, and the subsequent electric field formation. This is because it is considered that PM is easily adsorbed even if the electric field by the electrode 25 is small.

  The correction coefficients x1f, x1r, x2f, and x2r set in this way are reflected in the output voltages from the power supply units 30a and 30b of the high-voltage power supply 30. That is, the output voltage Vf from the charging power supply unit 30a is determined by the product of a predetermined base voltage Vfb and correction coefficients x1f and x2f. The output voltage Vr from the electric field forming power supply unit 30b is determined by the product of a predetermined base voltage Vrb and correction coefficients x1r and x2r. These calculations are executed in the ECU 40.

  In the exhaust gas purification apparatus 1 of the first embodiment configured as described above, when exhaust gas containing PM discharged from the engine is guided into the case 2 through the exhaust pipe, the exhaust gas is exhaust gas passage 12 having an upstream end opening. From the exhaust gas passage 12 of the downstream end opening to the downstream side. In this process, PM is filtered by the partition wall 11.

  On the other hand, when the high-voltage power supply 30 is turned on simultaneously with the start of the engine and a high voltage is applied between the charging electrode 20, the electric field forming electrode 25 and the outer peripheral electrode 15, PM in the exhaust gas is discharged from the charging electrode 20. Since the negative electrode is charged by the discharge and an electric field is formed between the electric field forming electrode 25 and the outer peripheral electrode 15, PM is attracted toward the honeycomb structure 10 by an electric attractive force. As a result, the movement path of the PM flowing through the partition walls 11 of the honeycomb structure 10 is deflected, and the PM is adsorbed in the pores of the partition walls 11. The adsorbed PM is promoted to burn or oxidize by the active gas generated with the application of a high voltage.

  Here, in this embodiment, since the upstream end face of the honeycomb structure 10 and the charging electrode 20 are separated by a predetermined distance a, when PM is deposited on the upstream end face of the honeycomb structure 10 In addition, the risk of electric leakage between the charging electrode 20 and the outer peripheral electrode 15 can be suppressed.

  Further, in the present embodiment, by supplying power separately to the charging electrode 20 and the electric field forming electrode 25, it is possible to perform power supply according to the respective purposes of the charging electrode 20 and the electric field forming electrode 25. .

  Further, in this embodiment, as shown in FIG. 3, the correction coefficient x1f for correcting the voltage value to the charging electrode 20 takes a value smaller than 1 when the engine water temperature is low, and the higher the engine water temperature is, the higher the engine water temperature is. Since the value is set so as to gradually increase beyond 1, it is possible to suppress power consumption during cold, which is generally considered to have a relatively small amount of PM.

  Further, in the present embodiment, as shown in FIG. 4, the correction coefficient x2f for correcting the voltage value to the charging electrode 20 is a value smaller than 1 when the engine load is low, and the higher the engine load is, the higher the engine load is. The correction coefficient x2r for setting the value to gradually increase beyond 1 and correcting the voltage value to the electric field forming electrode 25 is smaller than 1 when the engine load is low, and the engine water temperature is high. Since the value is set to gradually approach a value close to 1, it is possible to charge the PM well at high loads when the amount of supplied PM increases generally, and to form an electric field at high loads where PM tends to aggregate. Power consumption in the electrode 25 can be suppressed. However, such a control method is merely an example, and in the present invention, in addition to the engine water temperature, the intake air amount, and the engine speed as in the above-described embodiment, other parameters such as the throttle opening and the honeycomb structure 10 Various other physical quantities according to the state of the vehicle, such as the pressure loss detected by the pressure difference from the pressure sensors provided at the front and back, exhaust gas temperature, etc. can be used as input variables for control, for example these inputs In the estimation based on the variables, it is possible to perform setting such as gradually increasing the correction coefficient as the PM amount increases.

  In the above embodiment, the upstream side and the downstream side of the honeycomb structure 10 in the case 2 are bent, while the charging electrode 20 and the electric field forming electrode 25 are linear, and the power feeding path and the exhaust path are in different directions. Since the insulating layers 22 and 27 are drawn out through the case 2 by deflecting, the charging electrode 20 and the electric field forming electrode 25 cover the insulating layers 22 and 27 in the entire region in the exhaust path. It is possible to effectively suppress leakage. However, in the present invention, various modifications can be made to the shape and structure of each electrode, such as using a mesh electrode instead of the structure of each electrode 15, 20, 25 in the above embodiment.

  Further, in the above embodiment, each cell of the honeycomb structure 10 is alternately sealed, and a so-called wall flow type or filtration type device in which the exhaust gas passes through the partition wall 11 and is filtered is used. You may comprise as what is called a straight flow type apparatus which adsorb | sucks PM by an electrostatic force without plugging a body.

  Next, a second embodiment of the present invention will be described. In the first embodiment described above, the honeycomb structure 10 has a substantially cylindrical shape, and the electric field forming electrode 25 penetrates the honeycomb structure 10, but the shape of the honeycomb structure in the present invention is arbitrary, The electric field forming electrode does not need to penetrate the honeycomb structure. The second embodiment is another configuration example regarding the shape and structure of the honeycomb structure and the electric field forming electrode.

  FIG. 5 is a schematic configuration diagram of the exhaust gas purification apparatus 101 according to the second embodiment of the present invention. The exhaust gas purifying apparatus 101 includes a metal rectangular cylindrical case 102 and also has a honeycomb structure 110 supported inside the case 102.

  The honeycomb structure 110 has a substantially rectangular cross section in the flow direction of the exhaust gas. The honeycomb structure 110 includes a large number of cells, that is, exhaust gas passages partitioned by porous partition walls, and the exhaust gas passages are all parallel to the inflow direction of the exhaust gas. The honeycomb structure 110 may be of a filtration type or a so-called wall flow type in which upstream side exhaust gas passages and downstream side exhaust gas passages are alternately arranged. Alternatively, the honeycomb structure 110 may be of a so-called straight flow type that does not have such a plug.

  A charging electrode 120 is disposed upstream of the honeycomb structure 110 in the exhaust gas flow direction. The charging electrode 120 has an axial center extending toward the center of the honeycomb structure 110, and a front end portion of the charging electrode 120 protruding to the outside of the case 102. The charging electrode 120 is formed by covering a part or the entire surface of a rod-shaped electrode body 121 with an insulating layer 122 such as an insulator. The covering ratio by the insulating layer 122 is defined by the engine exhaust amount and the PM exhaust amount. It is preferable that the covering ratio by the insulating layer 22 is lower as the engine exhaust amount and the PM exhaust amount are larger. A metal connection 123 is connected to the electrode body 121 outside the case 102. The charging electrode 120 and the upstream end surface of the honeycomb structure 110 are separated from each other by a predetermined distance b. This distance b is such a distance that conduction does not occur between the charging electrode 120 and the upstream end surface of the honeycomb structure 110 even when PM is accumulated to the maximum extent on the upstream end surface of the honeycomb structure 110. And

  A planar electric field forming electrode 125 is formed on one side surface (upper surface in FIG. 5) of the honeycomb structure 110. The electric field forming electrode 125 and the case 102 are sealed with an alumina mat (not shown) or the like. A plug electrode 126 a of a power plug 126 is connected to the electric field forming electrode 125. The periphery of the plug electrode 126a is covered with an insulating layer 127, and the insulating layer 127 electrically insulates the plug electrode 126a from the case 102.

  On the opposite side of the electric field forming electrode 125 across the honeycomb structure 110, a receiving electrode 115 is disposed at a predetermined distance from the honeycomb structure 110. The receiving electrode 115 is electrically grounded.

  A charging power supply unit 30 a is connected to the charging electrode 120. An electric field forming power supply unit 30 b is connected to the power supply plug 126. The configuration of the charging power supply unit 30a, the electric field forming power supply unit 30b, and the control system for controlling them is the same as that of the first embodiment. The materials of the case 102, the honeycomb structure 110, the charging electrode 120, the plug electrode 126a, and the like are the same as those of the case 2, the honeycomb structure 10, the charging electrode 20, the electrolytic forming electrode 25, and the like in the first embodiment. It is.

  In the exhaust gas purification apparatus 101 according to the second embodiment configured as described above, when exhaust gas containing PM discharged from the engine is led into the case 102 through the exhaust pipe, the exhaust gas passes through the exhaust gas passage at the upstream end opening. The honeycomb structure 110 enters the honeycomb structure 110, passes through the porous partition walls, and is discharged downstream from the exhaust gas passage at the downstream end opening. In this process, PM is filtered by the partition wall.

  On the other hand, when the high voltage power supply 30 is turned on simultaneously with the start of the engine and a high voltage is applied between the charging electrode 120, the electric field forming electrode 125 and the receiving electrode 115, PM in the exhaust gas is discharged from the charging electrode 120. Since the negative electrode is charged by the discharge and an electric field is formed between the electric field forming electrode 125 and the receiving electrode 115, PM is attracted toward the honeycomb structure 110 by an electric attraction force. As a result, the movement path of the PM flowing through the partition walls of the honeycomb structure 110 is deflected, and the PM is adsorbed in the pores of the partition walls. The adsorbed PM is promoted to burn or oxidize by the active gas generated with the application of a high voltage.

  As described above in detail, in the second embodiment, since the upstream end face of the honeycomb structure 110 and the charging electrode 120 are separated by a predetermined distance b, the honeycomb structure is the same as in the first embodiment. Even when PM is deposited on the end face on the upstream side of the body 110, the risk of leakage between the charging electrode 120 and the receiving electrode 115 can be suppressed.

  In the present embodiment, since the honeycomb structure 110 has a substantially prismatic shape, the arrangement of the entire apparatus can be improved.

  In each of the above embodiments, the electric field forming electrodes 20 and 120 are connected to the negative electrode, and the outer peripheral electrode 15 and the receiving electrode 115 are grounded. However, in the present invention, a predetermined high voltage is applied between the two. As long as it is in the form, it may be of the opposite polarity. The applied power may be DC, AC, pulse, AC, or a combination of DC and pulse depending on the purpose. Further, the mode of voltage application is not limited to the above-described constant application, and may be performed at a desired time according to the necessity of PM collection request or combustion processing request, and such a configuration is also within the scope of the present invention. Belongs to.

It is a schematic block diagram which shows the exhaust gas purification apparatus of 1st Embodiment of this invention. It is sectional drawing which shows a honeycomb structure. It is a graph which shows the example of a setting of the value of correction coefficient x1f and x1r according to the engine water temperature in a correction coefficient map. It is a graph which shows the example of a setting of the value of correction coefficient x2f and x2r according to the engine load in a correction coefficient map. It is a schematic block diagram which shows the exhaust gas purification apparatus of 2nd Embodiment of this invention.

Explanation of symbols

1,101 Exhaust gas purification device 10,110 Honeycomb structure 15 Outer peripheral electrode (receiving electrode)
20, 120 Charging electrodes 25, 125 Electric field forming electrodes 22, 27 Insulating layer 30 High voltage power supply 30a Charging power supply section 30b Electric field forming power supply section 115 Receiving electrode

Claims (3)

A honeycomb structure having a large number of cells is provided between the receiving electrode and the electric field forming electrode, and the predetermined substance in the exhaust gas is supplied by the electric field formed between the receiving electrode and the electric field forming electrode. An exhaust gas purification device for adsorbing to a honeycomb structure,
A charging electrode for charging the predetermined substance in the exhaust gas is further provided upstream of the electric field forming electrode,
The exhaust gas purifying apparatus, wherein the charging electrode and the end face on the upstream side of the honeycomb structure are separated from each other by a predetermined distance. The exhaust gas purification device according to claim 1,
The exhaust gas purification apparatus, wherein the receiving electrode is cylindrical, the honeycomb structure is disposed in a region surrounded by the receiving electrode, and the electric field forming electrode is inserted through the honeycomb structure. The exhaust gas purifying apparatus according to claim 1 or 2,
An exhaust gas purification apparatus, further comprising a high-voltage power supply that individually supplies power to the charging electrode and the electric field forming electrode.

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