JP4725149B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter of exhaust gas.

  Particulate matter is contained in exhaust gas discharged from an internal combustion engine such as a diesel engine. For this reason, it is necessary to attach an exhaust purification device for removing the particulate matter from the exhaust gas to the exhaust passage of the internal combustion engine. The exhaust purification device is provided with a filter, and particulate matter is collected by the filter. In this filter, the collected particulate matter is subjected to a treatment such as an oxidation treatment.

  The particulate matter is composed of fine particles of various sizes, fine particles having a size of 50 nm or less (hereinafter simply referred to as “nanoparticles”), and fine particles larger than 50 nm (hereinafter simply referred to as “PM”). And can be broadly divided. The particulate matter flows into the filter together with the exhaust gas, is collected by the filter, and is oxidized.

  However, since the size of the nanoparticles is as small as 50 nm or less, the nanoparticles are easily diffused into the atmosphere and are not easily collected by the filter. The cause of the generation of nanoparticles is due to fuel atomization due to the recent increase in fuel injection pressure, combustion temperature drop due to idling (light load) state of the internal combustion engine, and vehicle deceleration state It has been considered that soluble organic matter (SOF) is agglomerated due to oil suction or the like generated due to a drop in cylinder pressure.

  In Patent Document 1, a discharge device is provided on the downstream side of a filter, nanoparticles passing through the filter are charged by discharge, and the charged nanoparticles are collected using an electrode. The quantity is reduced.

JP 2004-76669 A

  This invention is made | formed in view of the above point, and provides the exhaust gas purification apparatus of the internal combustion engine which can collect a nanoparticle with a filter.

In one aspect of the present invention, an exhaust emission control device for an internal combustion engine includes an exhaust passage that guides exhaust gas discharged from the internal combustion engine, and an adsorption capacity for particulate matter contained in the exhaust gas in the exhaust passage. A particulate supply device that supplies particulates having the following: and an operating state of the internal combustion engine, among a vehicle deceleration state, an accelerator off state, a state in which the engine rotation change amount is negative, a brake on state, and an exhaust brake on state Operating state detecting means for detecting any state as a predetermined operating state, and when the operating state detecting means detects a predetermined operating state, the particulate supply device supplies the particulates to the exhaust passage. It is characterized by.

The exhaust gas purification apparatus for an internal combustion engine is for collecting particulate matter contained in the exhaust gas of the internal combustion engine with a filter while suppressing atmospheric diffusion, and guides the exhaust gas discharged from the internal combustion engine. An exhaust passage, and a fine particle supply device that supplies the exhaust passage with fine particles capable of adsorbing particulate matter contained in the exhaust gas. Here, the particulate matter refers to so-called nanoparticles. Thereby, the nanoparticles can be adsorbed and aggregated by the fine particles supplied from the fine particle supply device, and the atmospheric diffusion of the nanoparticles can be suppressed. In addition, it is possible to improve the collection efficiency of a nano-sized nano-particle filter that has been difficult to collect. Further, when the internal combustion engine is in a predetermined operation state, the fine particle supply device is operated to supply the fine particles to the exhaust passage, thereby adsorbing nanoparticles generated by the predetermined operation state to the fine particles. Can aggregate.

  In a preferred embodiment of the present invention, the fine particles have an action of aggregating particulate matter smaller than the carbon fine particles.

  In one aspect of the exhaust gas purification apparatus for an internal combustion engine, the fine particle supply device always includes a fine particle generation device that generates the fine particles, a control valve disposed between the exhaust passage and the fine particle generation device, The fine particles are supplied to the exhaust passage by opening the control valve. As a result, it is possible to improve the responsiveness of the particulate emission to the exhaust passage with respect to the control signal.

  As a preferred embodiment, the fine particle supply device uses carbon fine particles as the fine particles.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
First, an exhaust emission control device according to a first embodiment of the present invention will be described.

  FIG. 1 shows a schematic configuration of a first embodiment in which an exhaust gas purification apparatus according to the present invention is applied to an internal combustion engine. The internal combustion engine 1 is an in-line four-cylinder diesel engine in which four cylinders 2 are arranged in a line, and an intake passage 3, an exhaust passage 4, and a turbocharger 5 that supercharges the internal combustion engine 1. I have. The intake passage 3 is provided with an air filter 13, an air flow meter 14 for measuring the intake flow rate, a compressor 5a of the turbocharger 5, and an intercooler 7 for cooling the intake air compressed by the compressor 5a. ing. The exhaust passage 4 is provided with a turbine 5b of the turbocharger 5 and an exhaust purification device 20 for reducing harmful substances in the exhaust gas. The intake passage 3 and the exhaust passage 4 are connected by an EGR passage 6 so that a part of the exhaust gas is recirculated from the exhaust passage 4 to the intake passage 3. The EGR passage 6 is provided with an EGR cooler 17 for cooling the exhaust gas to be recirculated to the intake passage 3 and an EGR valve 8 for adjusting the recirculation amount of the exhaust gas. The internal combustion engine 1 is provided with four injectors 9 corresponding to the respective cylinders 2. The four injectors 9 are connected to the common rail 10. The common rail 10 is connected to a supply pump 11 that pumps fuel from a fuel tank (not shown) and pumps the fuel to the common rail 10.

  The exhaust purification device 20 includes a NOx occlusion reduction catalyst 19, a filter 22 having a function of collecting PM in the exhaust gas of the internal combustion engine 1, a carbon particulate generator 21, an oxidation catalyst 23, an engine control unit (ECU) 24).

  The carbon particulate generator 21 is provided on the upstream side of the filter 22 and has a function of generating carbon particulates having the same size as that of PM and discharging the generated carbon particulates from the outlet 50 to the exhaust passage 4. Have.

  The carbon fine particles generated by the carbon fine particle generator 21 are supplied as an aerosol very similar to PM generated in the combustion process of the engine. Aerosol is a term indicating a state of a dispersion system in which a dispersion medium is a gas (eg, exhaust gas) and a dispersed phase is a solid (eg, carbon fine particles) or a liquid. The fine particles in the dispersed phase (solid) are likely to aggregate due to very active Brownian motion, and are generally unstable dispersions, and have the property of sedimenting due to gravity over time. By introducing such carbon fine particles into the exhaust gas passage, the nanoparticles can be aggregated. Further, by disposing the filter 22 on the downstream side of the outlet 50 of the carbon particle generator 21, the carbon fine particles adsorbed with the nanoparticles can be easily collected together with the nanoparticles by the filter 22.

  The oxidation catalyst 23 is provided on the downstream side of the filter 22, and oxidizes the PM that has passed without being processed in the filter 22. Therefore, the carbon fine particle generator 21 functions as a fine particle supply device in the present invention.

  An A / F sensor 32 that detects the air-fuel ratio of the exhaust gas is provided between the filter 22 and the oxidation catalyst 23, and a detection signal S10 of the A / F sensor 32 is input to the ECU 24. Further, the exhaust purification device 20 includes a fuel addition injector 28 that adds a reducing agent (fuel) to the exhaust passage 4 in order to reduce NOx stored by the NOx storage reduction catalyst 19. The fuel addition injector 28 is connected to the supply pump 11. The addition of fuel by the injector 28 for addition is controlled by the ECU 24 based on the input signal S10 from the A / F sensor 32 as necessary to reduce the NOx stored in the NOx storage reduction catalyst 19.

  The ECU 24 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown), and is electrically connected to the accelerator sensor 31, the brake sensor 32, the rotation speed sensor 33, and the exhaust brake sensor 34. Has been. The accelerator sensor 31 detects a detection signal S1 indicating that an accelerator pedal (not shown) is depressed, and the brake sensor 32 indicates a detection signal S2 that indicates that a brake pedal (not illustrated) is depressed. The ECU 24 supplies the ECU 24 with a detection signal S3 indicating the engine speed of the internal combustion engine 1, and the exhaust brake sensor 34 supplies a detection signal S4 indicating that the exhaust brake is activated. Based on the detection signals S1, S2, S3, and S4 from the accelerator sensor 31, the brake sensor 32, the rotation speed sensor 33, and the exhaust brake sensor 34, the ECU 24 determines that the internal combustion engine 1 is in the accelerator off state and the engine rotation change amount. Detects a negative state, a brake-on state, and an exhaust brake-on state. This is because a particularly large amount of nanoparticles tend to be generated when the operating state of the internal combustion engine 1 is in such an idle state or a vehicle deceleration state. Therefore, if the ECU 24 determines that the operation state of the internal combustion engine 1 is such an idle state or a vehicle deceleration state, the ECU 24 estimates that nanoparticles are generated in the exhaust gas, and the carbon fine particles are removed from the exhaust passage 4. Is supplied to the carbon fine particle generator 21. Therefore, the accelerator sensor 31, the brake sensor 32, the rotation speed sensor 33, and the exhaust brake sensor 34 function as the driving state detection means in the present invention.

FIG. 2 shows a cross-sectional view of the filter 22. The filter 22 is formed in a honeycomb shape having a large number of cells (through holes) 51. Each cell 51 is plugged with a plug 52 at one of the ends. The plug 52 is provided so that the cells 51 plugged at the inlet end 51in and the cells 51 plugged at the outlet end 51out are alternately arranged. A partition wall 53 is provided between the cells 51 adjacent to each other, and a large number of fine holes 54 are formed. Exhaust gas containing PM 55 and nanoparticles 56 guided to the inlet end 51 in of the filter 21 passes through the partition wall 53 and is guided to the outlet end 51 out as indicated by an arrow 61. When the exhaust gas passes through the partition wall 53, the PM 55 contained in the exhaust gas follows the path indicated by the dashed arrow 61 a by the inertia force and collides with the partition wall 53. Thus, PM55 is collected by the partition wall 53 by inertial collision. The partition wall 53 carries an oxidation catalyst material such as platinum (Pt) or cerium oxide (CeO ₂ ), and the filter 22 has a function of promoting the oxidation of PM 55 collected by the action of the oxidation catalyst material. However, since the nanoparticle 56 has a smaller mass than PM55, its inertial force is also small. Therefore, as shown by the arrow 62, the nanoparticles 56 may not be collected by the partition wall 53 but may be guided to the outlet end 51out together with the exhaust gas and eventually pass through the filter 22. Therefore, in the exhaust emission control device of the present invention, on the upstream side of the filter 22, by adsorbing nanoparticles to the carbon fine particles released from the carbon fine particle generator 21, the atmospheric diffusion of nano PM is suppressed and at the same time, together with the carbon fine particles. The nanoparticles can be collected by the filter 22.

  FIG. 3 is a cross-sectional view showing the internal structure of the carbon fine particle generator 21. The carbon fine particle generator 21 has a structure having graphite electrodes 41 a and 41 b inside a container 42. The carbon fine particle generator 21 generates a carbon fine particle Cn in the graphite electrodes 41a and 41b by applying a high voltage between the graphite electrodes 41a and 41b to generate corona discharge. The carbon fine particle generator 21 has a gas flow that leads to the exhaust passage by the carrier gas introduced from the outside. The carbon fine particles Cn generated by the graphite electrodes 41 a and 41 b are carried on the carrier gas and carried to the exhaust passage 4. Here, for example, argon (Ar) is used as the carrier gas. The magnitude of the voltage applied between the graphite electrodes 41a and 41b is controlled by a control signal S5 from the ECU 24 shown in FIG. When the control signal S5 is supplied, the carbon fine particle generator 21 applies a voltage between the graphite electrodes 41a and 41b to start generation of the carbon fine particles Cn, and the magnitude of the voltage applied according to the control signal S5. The amount of carbon fine particles Cn produced is adjusted by changing the. That is, whether or not carbon fine particles Cn are generated by the carbon fine particle generator 21 is controlled by a control signal S5 from the ECU 24.

  FIG. 4 is an enlarged view of the carbon fine particle outlet 50 discharged from the carbon fine particle generator 21. The carbon fine particles Cn produced by the carbon fine particle generator 21 are carried on the carrier gas and carried to the exhaust passage 4 and then released into the exhaust gas flowing through the exhaust passage 4. Since the carbon fine particles have a property of adsorbing nanoparticles, the nanoparticles Pa in the exhaust gas are adsorbed on the released carbon fine particles Cn. Here, the size of the carbon fine particles Cn produced by the carbon fine particle generator 21 is larger than 50 nm. On the other hand, the size of the nanoparticles Pa adsorbed to the carbon fine particles Cn is smaller than the size of the carbon fine particles, and generally has a size about one-tenth that of the carbon fine particles. Therefore, a plurality of nanoparticles Pa can be adsorbed on one carbon fine particle Cn. By doing in this way, especially the nanoparticle of 10 nm or less can be effectively aggregated with carbon fine particles.

  The carbon fine particles Cn on which the nanoparticles Pa are adsorbed flow into the downstream filter 22 together with the exhaust gas. Since the size of the carbon fine particles Cn is larger than 50 nm, it is very similar to the particle size range of PM. Therefore, the filter 22 can collect the carbon fine particles Cn similarly to PM. At this time, since the nano particles Pa are adsorbed on the carbon fine particles Cn, the filter 22 can collect the nano particles Pa together with the carbon fine particles Cn.

[Second Embodiment]
Next, an exhaust emission control device according to a second embodiment of the present invention will be described.

  FIG. 5 shows a schematic configuration of a second embodiment in which the exhaust purification device 20a according to the present invention is applied to an internal combustion engine. FIG. 6 is an enlarged view of the outlet 50a of the carbon fine particles released from the carbon fine particle generator 21. FIG. In the exhaust emission control device 20 according to the first embodiment, the carbon particulate generator 21 controls whether or not carbon particulates are generated by a control signal S5 from the ECU 24. On the other hand, in the exhaust emission control device 20a according to the second embodiment, the carbon particulate generator 21 is always operated, and the carbon particulates are always generated and released. A control valve 26 for adjusting the amount of carbon fine particles flowing into the exhaust passage 4 is provided at the outlet. When the control valve 26 is in a closed state, the carbon fine particles generated by the carbon fine particle generator 21 are retained by being stopped by the control valve 26.

  The control valve 26 is controlled by a control signal S5 from the ECU 24. As a result, when the control signal S5 instructing the release of the carbon fine particles Cn from the ECU 24 to the exhaust passage is supplied to the control valve 26, the control valve 26 is stored in the control valve 26 by opening the valve. The carbon fine particles Cn are discharged into the exhaust passage 4. Therefore, in the exhaust purification device 20a according to the second embodiment, the carbon fine particles Cn generated in advance can be immediately released into the exhaust passage 4 simply by opening the control valve 26. Therefore, as compared with the exhaust gas purification apparatus 20 according to the first embodiment, it takes less time until the carbon fine particles Cn are released to the exhaust passage. Therefore, in the exhaust emission control device 20a according to the second embodiment, it is possible to improve the responsiveness of the carbon particulate emission to the control signal S5 from the ECU 24.

[Carbon fine particle generation control treatment]
Next, the details of the carbon particulate generation control process in the exhaust purification apparatus of the present invention will be specifically described with reference to FIG. 7, taking the exhaust purification apparatus 20 according to the first embodiment as an example. The ECU 24 performs carbon fine particle generation control processing according to a program stored in a memory such as a ROM.

  FIG. 7 is a flowchart of the carbon particle generation control process according to the first embodiment. In the carbon fine particle generation control process of the present invention, nanoparticles generated when the internal combustion engine 1 is in an idle state or a vehicle deceleration state are agglomerated by adsorbing the carbon fine particles to fine particles having the same size as PM. Increase diameter.

  The ECU 24 detects the operating state of the internal combustion engine 1 based on the detection signals S1, S2, S3, S4 supplied from the accelerator sensor 31, the brake sensor 32, the rotational speed sensor 33, and the exhaust brake sensor 34, respectively (step). S101). The ECU 24 determines whether the internal combustion engine 1 is in an idle state or a vehicle deceleration state based on the detected operating state (step S102). Specifically, based on the detection signals S1, S2, S3, and S4, the ECU 24 selects one of the accelerator off state, the engine rotation change amount is negative, the brake on state, and the exhaust brake on state. When this state is detected, it is determined that the internal combustion engine 1 is in the idle state or the vehicle deceleration state. If the internal combustion engine 1 is in an idle state or a vehicle deceleration state (step S102: Yes), the ECU 24 supplies the control signal S5 for operation to the carbon particulate generator 21 (step S103). Thereby, the carbon particulate generator 21 generates carbon particulates by starting operation, and discharges the carbon particulates into the exhaust passage.

  In this way, the carbon fine particles released into the exhaust passage adsorb the nanoparticles to aggregate the nanoparticles. On the other hand, when the detected operation state of the internal combustion engine 1 is neither the idle state nor the vehicle deceleration state (step S102: No), the ECU 24 supplies the control signal S5 to the carbon particulate generator 21. If the carbon fine particle generator 21 is operating, control to stop is performed (step S104). In the case of the exhaust emission control device 20a according to the second embodiment, the release of the carbon fine particles is stopped by closing the control valve 26.

  In the case of the exhaust emission control device 20a according to the second embodiment, as shown in parentheses in FIG. 7, by opening the control valve 26 in step S103, the carbon fine particles generated in advance are released. To do. In this way, the carbon fine particles generating device 21 constantly discharges the carbon fine particles generated to the exhaust passage. Further, in step S104, the control valve 26 is not opened and the valve closed state is maintained. This prevents carbon fine particles from being discharged into the exhaust passage.

  As described above, according to the present invention, nanoparticles can be increased in size by adsorbing and aggregating with the fine particles supplied from the fine particle supply device, and at the same time suppressing atmospheric diffusion and easily using a filter. It can be collected.

It is the figure which showed embodiment which applied the exhaust gas purification apparatus of 1st Embodiment to the internal combustion engine. It is the figure which showed the filter of the exhaust gas purification device. It is the figure which showed the carbon particulate generator. It is an enlarged view of the outflow port of the carbon particulate generator in an exhaust passage. It is the figure which showed embodiment which applied the exhaust gas purification apparatus of 2nd Embodiment to the internal combustion engine. It is an enlarged view of the outflow port of the carbon particulate generator in an exhaust passage. The flowchart of the carbon particle generation | occurrence | production control processing of the exhaust gas purification apparatus of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Exhaust passage 20 Exhaust gas purification device 21 Carbon particulate generator 22 Filter 23 Oxidation catalyst 24 ECU

Claims (4)

An exhaust passage for guiding exhaust gas discharged from the internal combustion engine;
A fine particle supply device for supplying fine particles having adsorbability to the particulate matter contained in the exhaust gas to the exhaust passage;
As the operating state of the internal combustion engine, any one of a vehicle deceleration state, an accelerator off state, a state in which the engine rotation change amount is negative, a brake on state, and an exhaust brake on state is detected as a predetermined operating state. Operating state detecting means for performing ,
An exhaust gas purification apparatus for an internal combustion engine , wherein the particulate supply device supplies the particulates to the exhaust passage when the operation state detecting means detects a predetermined operation state . The fine particles, the exhaust purification system of an internal combustion engine according to claim 1, characterized in that it has an effect of agglomerating the small particulate matter than the fine particles. The fine particle supply device comprises:
A microparticle generator that constantly generates the microparticles;
A control valve disposed between the exhaust passage and the particulate generator,
By opening the control valve, the exhaust purification system of an internal combustion engine according to claim 1, characterized in that supplying the particulate in the exhaust passage. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3 , wherein the fine particle supply device uses carbon fine particles as the fine particles.

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