JP4811149B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine including a particulate filter that collects particulate matter in exhaust gas.

  Oxidation catalyst for oxidizing nanoparticles contained in the exhaust gas that passed through the particulate filter is provided after the particulate filter, and ozone is generated so that ozone can be supplied between the oxidation catalyst and the particulate filter. There is known an exhaust emission control device provided with a vacuum vessel (see Patent Document 1).

JP 2005-226473 A

  The PM regeneration process for oxidizing and removing particulate matter (PM) collected by a particulate filter (hereinafter sometimes abbreviated as “filter”) is a temperature at which PM is oxidized and removed, for example, 650 ° C. or higher. However, when the temperature of the filter is raised to such a high temperature, the adsorption energy, which is energy required for adsorbing PM on the filter surface, increases, so that it is difficult for PM to adsorb on the filter surface. There is a possibility that the PM collection rate of the filter is lowered. Therefore, at the time of PM regeneration processing, PM in exhaust gas is not sufficiently purified by the filter, and exhaust emission may be deteriorated.

  Accordingly, an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can execute a function regeneration process of a particulate filter without deteriorating exhaust emission.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided with a first filter means that is provided in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and branches from an exhaust passage downstream of the first filter means. A branch passage; a second filter means provided in the branch passage for collecting particulate matter in the exhaust; and an inflow of exhaust gas to the branch passage is blocked, and the branch passage branches from the exhaust passage. The first position where the inflow of exhaust gas into the exhaust passage downstream of the branch portion is permitted, and the inflow of exhaust gas into the exhaust passage downstream of the branch portion is blocked and the inflow of exhaust gas into the branch passage is permitted. The valve means switchable to the second position, and the first filter means during the first regeneration process for raising the temperature to a temperature at which the particulate matter collected by the first filter means is oxidized and removed. The valve means is the second Comprising an operation control means for switching the location, and ozone supply means capable of supplying ozone into the upstream of the branch passage than said second filter means, said operation control means is trapped in the second filter means When performing the second regeneration process for oxidizing and removing the particulate matter using ozone supplied from the ozone supply means, the valve means is switched to the second position, and then the second filter means is the second filter means. When the temperature is raised to the target temperature during the regeneration process, the valve means is switched to the first position and the ozone supply means is operated so that ozone is supplied into the branch passage, thereby solving the above-described problem. (Claim 1).

  According to the exhaust gas purification apparatus of the present invention, the valve means is switched to the second position during the first regeneration process, so that the exhaust gas that has passed through the first filter means is guided to the second filter means. Therefore, the PM collection rate of the first filter means is reduced by the first regeneration process, and even if particulate matter (PM) passes through the first filter means, the PM can be collected by the second filter means. Therefore, it is possible to perform the first regeneration process for oxidizing and removing PM collected by the first filter means without deteriorating the exhaust emission.

Further, according to the exhaust gas purification apparatus of the present invention, since ozone is supplied to the branch passage after the valve means is switched to the first position, the inflow of exhaust gas to the branch passage is prevented when ozone is supplied. In this case, since it is possible to suppress the ozone supplied to the branch passage from being diluted by the exhaust, the amount of ozone used for the second regeneration process can be reduced. Further, before supplying ozone, the valve means is switched to the second position and the second filter means is heated to the target temperature by exhaust, so that it is not necessary to provide a new device for raising the temperature of the second filter means. .

In one form of the exhaust emission control device of the present invention, the second filter means is configured such that when the valve means is switched to the second position, the temperature of the second filter means causes the particulate matter generated by the second filter means. You may provide in the position maintained within the predetermined temperature range suitable for collection ( Claim 2 ). By providing the second filter means at such a position, even if the valve means is switched to the second position and the second filter means is heated by the exhaust heat, it is possible to prevent a decrease in the PM collection rate of the second filter means. .

In one form of the exhaust gas purification apparatus of the present invention, an NOx storage reduction catalyst is supported on the first filter means, and the operation control means recovers S poisoning by releasing sulfur oxide from the NOx storage reduction catalyst. The valve means may be switched to the second position during processing ( Claim 3 ). In order to release sulfur oxides from the NOx storage reduction catalyst, it is necessary to raise the temperature of the NOx storage reduction catalyst to a temperature at which particulate matter is oxidized and removed. Therefore, during the S poisoning recovery process, the temperature of the first filter means on which the NOx storage reduction catalyst is carried may become high, and the PM collection rate of the first filter means may be reduced. Therefore, the valve means is switched to the second position and the exhaust gas that has passed through the first filter means is guided to the second filter means to prevent the exhaust emission from deteriorating.

In one form of the exhaust emission control device of the present invention, an NOx storage reduction catalyst may be carried on the second filter means ( claim 4 ). In this case, nitrogen oxide (NOx), sulfur oxide (SOx), etc. in the exhaust gas can be purified by the second filter means.

  As described above, according to the present invention, the valve means is switched to the second position when the first regeneration process is performed on the first filter means, so that the exhaust gas that has passed through the first filter means Guided to the second filter means. Therefore, PM that has passed through the first filter means can be collected by the second filter means. Therefore, the first regeneration process of the first filter means can be executed without deteriorating the exhaust emission.

  FIG. 1 shows an internal combustion engine in which an exhaust emission control device according to one embodiment of the present invention is incorporated. An internal combustion engine (hereinafter also referred to as an engine) 1 in FIG. 1 is a diesel engine, which is mounted on a vehicle as a driving power source, and includes a plurality of (four in FIG. 1) cylinders 2, An intake passage 3 and an exhaust passage 4 connected to the cylinder 2 are provided. The intake passage 3 is provided with a throttle valve 5 for adjusting the intake air amount, a compressor 6a of the turbocharger 6, and an intercooler 7 for cooling the intake air. In the exhaust passage 4, a turbine 6 b of the turbocharger 6 and an exhaust purification device 10 are provided. Further, as shown in FIG. 1, the exhaust passage 4 is connected to a branch passage 8 branched from the branch portion 4a. The branch portion 4a prevents the inflow of exhaust gas into the branch passage 8 and is downstream of the branch portion 4a. The first position (position A in FIG. 1) that permits the inflow of exhaust gas into the exhaust passage 4 and the inflow of exhaust gas into the exhaust passage 4 downstream of the branching portion 4a are blocked and the inflow of exhaust gas into the branch passage 8 An exhaust control valve 9 is provided as a valve means that can be switched to a second position (position B in FIG. 1) that permits this. The exhaust passage 4 and the intake passage 3 are connected by an EGR passage 20, and an EGR cooler 21 and an EGR valve 22 are provided in the EGR passage 20. The engine 1 includes an injector 30 provided in each cylinder 2, a common rail 31 that stores high-pressure fuel supplied to each injector 30, and a fuel pump 32 that supplies fuel from a fuel tank (not shown) to the common rail 31. I have.

  The exhaust purification device 10 includes a front-stage oxidation catalyst 11 provided in the exhaust passage 4 upstream of the branching portion 4a, a main particulate filter (hereinafter also abbreviated as a main filter) 12 as first filter means, A post-stage oxidation catalyst 13 provided in the exhaust passage 4 downstream of the branch portion 4a, and a sub-particulate filter (hereinafter also abbreviated as a sub filter) 14 as second filter means provided in the branch passage 8. And a fuel addition valve 15 for adding fuel (light oil) to the exhaust passage 4. The main filter 12 carries an NOx storage reduction catalyst material (hereinafter also abbreviated as NOx catalyst), and the main filter 12 also functions as an NOx storage reduction catalyst. The post-stage oxidation catalyst 13 is provided close to the engine main body 1a of the engine 1 so that the temperature of the post-stage oxidation catalyst 13 is maintained in an active temperature range where exhaust gas purification performance is exhibited by the exhaust heat. On the other hand, the sub-filter 14 has a predetermined temperature suitable for collecting PM even when the exhaust control valve 9 is switched to the second position and the exhaust flows into the branch passage 8 and is heated by the heat of the exhaust. It is provided so as to be maintained in a region (for example, 500 ° C. or less). The particulate filters 12 and 14, the pre-stage and post-stage oxidation catalysts 11 and 13, and the NOx storage reduction catalyst material may be the same as known ones used for purifying exhaust gas, and thus detailed description thereof is omitted.

  When the amount of PM trapped in each of the filters 12 and 14 increases, the exhaust gas hardly flows due to the PM. Therefore, in the engine 1, PM regeneration is periodically performed in which the filters 12 and 14 are heated to a target temperature range where PM is oxidized and removed to remove PM. Thus, by removing the PM of the filters 12 and 14 by oxidation, PM regeneration of the main filter 12 corresponds to the first regeneration process of the present invention, and PM regeneration of the sub-filter 14 corresponds to the second regeneration process of the present invention. Equivalent to. Further, if the NOx catalyst carried on the main filter 12 is sulfur poisoned by SOx in the exhaust, the exhaust purification performance is lowered. Therefore, in order to recover the exhaust purification performance of the NOx catalyst, the temperature of the main filter 12 is raised to a release temperature range (for example, 650 ° C. or more) from which the SOx is released from the NOx catalyst, and the air-fuel ratio of the exhaust near the NOx catalyst is stoichiometrically reduced. S regeneration that eliminates sulfur poisoning of the NOx catalyst by making it richer than the fuel ratio or the stoichiometric air-fuel ratio is periodically performed. In addition, NOx reduction is periodically performed in which the air-fuel ratio of the exhaust near the NOx catalyst is made richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and NOx stored in the NOx catalyst is released and reduced to nitrogen. Hereinafter, S regeneration and PM regeneration may be collectively referred to as regeneration processing. The regeneration process of the main filter 12 is performed by adding fuel from the fuel addition valve 15 to the exhaust passage 4.

  It should be noted that the NOx storage reduction catalyst material only needs to be able to hold NOx in the catalyst, and whether it is absorbed or adsorbed is not limited by the term of storage. Moreover, the aspect of SOx poisoning is not limited. Furthermore, the mode of the release of NOx and SOx is not limited.

  The engine 1 includes an ozone supply device 40 as ozone supply means. The ozone supply device 40 includes an ozone generator 41 that generates ozone, an air pump 42 that supplies air to the ozone generator 41, and ozone that is generated by the ozone generator 41 in the branch passage 8 upstream of the sub-filter 14. And an open / close valve 44 that opens and closes the ozone supply passage 43. The ozone generator 41 includes an AC power supply 45 and a plurality of electrodes 46, and is a well-known device that converts oxygen in the air supplied from the air pump 42 into ozone using means such as corona discharge.

  The operations of the exhaust control valve 9, the fuel addition valve 15 and the ozone supply device 40 are controlled by an engine control unit (ECU) 50. The ECU 50 is configured as a computer including a microprocessor and peripheral devices such as RAM and ROM necessary for its operation. The ECU 50 is a known computer unit that operates various devices such as the injectors 30 based on signals input from various sensors to control the operating state of the engine 1. As sensors connected to the ECU 50, for example, a first differential pressure sensor 51 that outputs a signal corresponding to a difference in pressure between the upstream and downstream of the upstream oxidation catalyst 11 and the main filter 12, and flows into the upstream oxidation catalyst 11. A first exhaust temperature sensor 52 that outputs a signal corresponding to the temperature of the exhaust gas to be output, a filter temperature sensor 53 that outputs a signal corresponding to the temperature of the main filter 12, and a signal corresponding to the temperature of the exhaust gas that has passed through the sub-filter And a second differential pressure sensor 55 for outputting a signal corresponding to the difference in pressure between the upstream side and the downstream side of the sub-filter 14.

As described above, it is necessary to periodically perform regeneration processing for the main filter 12 and periodically perform PM regeneration for the sub-filter 14. Therefore, the ECU 50 determines whether or not the regeneration process should be performed on the main filter 12, and if it is determined that the regeneration process should be performed, an appropriate amount of fuel necessary for performing the regeneration process is contained in the exhaust passage 4. The operation of the fuel addition valve 15 is controlled so as to be added to. For example, the ECU 50 should execute PM regeneration on the main filter 12 with reference to the output signal of the first differential pressure sensor 51 so that the differential pressure before and after the main filter 12 is maintained below a preset allowable value. If it is determined whether or not PM regeneration should be performed, fuel necessary for raising the temperature of the main filter 12 to the target temperature range (650 ° C. or higher) during PM regeneration is added to the exhaust passage 4 The fuel addition valve 15 is operated as described above. Similarly, the ECU 50 determines whether or not it is necessary to execute the S regeneration for the main filter 12. If it is determined that the S regeneration should be performed, the fuel required to execute the S regeneration is added from the fuel addition valve 15. . In addition, the ECU 50 also operates the fuel addition valve 15 when performing NOx reduction on the main filter 12. The PM regeneration for the sub filter 14 will be described later.

  FIG. 2 shows an exhaust control valve control routine that the ECU 50 repeatedly executes at a predetermined cycle during operation of the engine 1 in order to control the operation of the exhaust control valve 9. In the control routine of FIG. 2, the ECU 50 first determines in step S11 whether or not regeneration processing of the main filter 12, that is, PM regeneration or S regeneration is being performed. Whether or not the regeneration process is being performed is determined based on, for example, whether or not the fuel addition valve 15 is controlled to add fuel to the exhaust passage 4, and when the fuel addition valve 15 is controlled to add fuel. It is determined that the playback process is in progress. If it is determined that the main filter 12 is in the regeneration process, the process proceeds to step S12, and the ECU 50 determines whether or not the temperature of the main filter 12 is higher than a predetermined determination temperature. The collection of PM by the main filter 12 is performed well when the temperature of the main filter 12 is within a predetermined temperature range (for example, 500 ° C. or less), and the PM collection rate of the main filter 12 decreases when the temperature is out of this temperature range. To do. Therefore, an upper limit value (for example, 500 ° C.) of the predetermined determination temperature is set as the predetermined determination temperature. When it is determined that the temperature of the main filter 12 is higher than the predetermined determination temperature, the process proceeds to step S13, and the ECU 50 switches the exhaust control valve 9 to the second position. Thereafter, the current control routine is terminated.

  If a negative determination is made in step S11 or a negative determination is made in step S12, the process proceeds to step S14, and the ECU 50 switches the exhaust control valve 9 to the first position. Thereafter, the current control routine is terminated.

  When the exhaust control valve 9 is switched to the second position, all the exhaust that has passed through the main filter 12 is guided to the sub-filter 14. During the regeneration process, the main filter 12 is heated to a temperature higher than the determination temperature, so that the PM collection rate of the main filter 12 is decreased. Even if the PM passes through the main filter 12, the PM can be collected by the sub-filter 14. Thus, since the emission of PM to the atmosphere can be suppressed, the regeneration process of the main filter 12 can be performed without deteriorating the exhaust emission. Thus, by executing the control routine of FIG. 2 and controlling the operation of the exhaust control valve 9, the ECU 50 functions as the operation control means of the present invention.

  The exhaust control valve 9 may not be immediately switched to the first position when the regeneration process for the main filter 12 is completed. When the PM and NOx catalyst sulfur oxides collected in the main filter 12 are removed by the regeneration process, the diameter of the pores in the wall of the main filter 12 increases, so immediately after the regeneration process is finished, The PM collection rate of the main filter 12 may be reduced. Therefore, the exhaust control valve 9 may be maintained at the second position for a while until the PM collection rate of the main filter 12 is recovered. By controlling the exhaust control valve 9 in this way, exhaust emission can be improved.

  FIG. 3 shows a sub-filter PM regeneration control routine that the ECU 50 executes to perform PM regeneration of the sub-filter 14. The control routine of FIG. 3 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 3, the ECU 50 first determines in step S21 whether or not a predetermined PM regeneration condition for executing PM regeneration of the sub-filter 14 is satisfied. Whether or not the PM regeneration condition is satisfied is determined based on, for example, an output signal of the second differential pressure sensor 55, and the pressure difference between the upstream side and the downstream side of the sub filter 14 exceeds a preset allowable upper limit value. In this case, it is determined that the PM regeneration condition is satisfied. Further, it may be determined that the PM regeneration condition is satisfied when the integrated value of the time when the exhaust control valve 9 is switched to the second position and the exhaust is guided to the sub-filter 14 exceeds a preset threshold value.

  If it is determined that the PM regeneration condition of the sub-filter 14 is satisfied, the process proceeds to step S22, and the ECU 50 determines whether or not the temperature of the sub-filter 14 is lower than the lower limit temperature of the target temperature range when executing the PM regeneration of the sub-filter 14. Judge. Note that the temperature of the sub-filter 14 is acquired with reference to the output signal of the second exhaust temperature sensor 54. As will be described later, the PM regeneration of the sub-filter 14 is performed using ozone. Since ozone has a strong oxidizing power, PM can be oxidized at a lower temperature when ozone is used than when ozone is not used. For this reason, a temperature range lower than a target temperature range (for example, 650 ° C. or higher) when PM is oxidized and removed without using ozone is set in the predetermined target temperature range used in step S22. As such a temperature range, for example, 100 ° C. to 200 ° C. is set. Therefore, for example, 100 ° C. is set as the lower limit temperature of the target temperature range. When it is determined that the temperature of the sub-filter 14 is lower than the lower limit temperature of the predetermined target temperature range, the process proceeds to step S23, and the ECU 50 switches the exhaust control valve 9 to the second position. Thereafter, the current control routine is terminated. If the exhaust control valve 9 has already been switched to the second position, it is maintained at that position. By switching the exhaust control valve 9 to the second position in this way, the exhaust can be guided to the branch passage 8, so that the temperature of the sub-filter 14 can be raised by the heat of the exhaust.

  On the other hand, if it is determined that the temperature of the sub-filter 14 is equal to or higher than the lower limit temperature of the predetermined target temperature range, that is, the sub-filter 14 has been heated to the target temperature for PM regeneration using ozone, the process proceeds to step S24, and the ECU 50 controls the exhaust control. The valve 9 is switched to the first position. If it has already been switched to the first position, it is maintained at that position. In addition, since the temperature of the sub filter 14 can be lowered by switching the exhaust control valve 9 to the first position in this way and preventing the inflow of exhaust gas into the branch passage 8, the temperature of the sub filter 14 falls within the target temperature range. When the temperature is equal to or higher than the upper limit temperature, the temperature of the sub-filter 14 can be adjusted within the target temperature range by switching the exhaust control valve 9 to the first position. Therefore, it can be determined that the temperature of the sub-filter 14 is raised to the target temperature for PM regeneration using ozone even when the temperature of the sub-filter 14 is raised to the upper limit temperature of the target temperature range. In the next step S25, the ECU 50 operates the ozone supply device 40 so that ozone is supplied into the branch passage 8. The supply of ozone is performed by starting the ozone generator 41 and the air pump 42 and opening the on-off valve 44. If the ozone supply device 40 has already been operated, the operation is continued. Thereafter, the current control routine is terminated.

  When a negative determination is made in step S21, the process proceeds to step S26, where the ECU 50 switches the exhaust control valve 9 to the first position, stops the ozone supply device 40, and stops the ozone supply to the branch passage 8. The ozone supply is stopped by stopping the ozone generator 41 and the air pump 42 and closing the on-off valve 44. If the exhaust control valve 9 has already been switched to the first position and the ozone supply device 40 has stopped, that state is maintained. Thereafter, the current control routine is terminated.

  In this sub-filter regeneration control routine, when ozone is supplied to the branch passage 8 and PM regeneration of the sub-filter 14 is performed, the exhaust control valve 9 is switched to the first position to prevent the exhaust gas from flowing into the branch passage 8. Therefore, it can suppress that the ozone supplied to the branch channel | path 8 is diluted with exhaust_gas | exhaustion. Therefore, the amount of ozone used for PM regeneration of the subfilter 14 can be reduced. Further, the exhaust control valve 9 is switched to the second position, and the temperature of the sub-filter 14 is increased by exhaust heat. Therefore, the temperature of the sub-filter 14 can be increased without providing a heating means.

  This invention is not limited to each form mentioned above, It can implement with a various form. For example, the present invention is not limited to a diesel engine, and may be applied to various internal combustion engines that use gasoline or other fuels. The exhaust purification catalyst provided in the exhaust purification device is not limited to the oxidation catalyst. Various catalysts used for exhaust purification, such as a NOx storage reduction catalyst, may be provided instead of the oxidation catalyst. The main filter may be provided with a particulate filter that does not carry a catalyst. Further, the NOx storage reduction catalyst material may be supported on the sub-filter.

The figure which shows the internal combustion engine in which the exhaust gas purification apparatus which concerns on one form of this invention was integrated. The flowchart which shows the exhaust control valve control routine which ECU performs. The flowchart which shows the sub filter PM regeneration control routine which ECU performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Exhaust passage 4a Branch part 8 Branch passage 9 Exhaust control valve (valve means)
10 exhaust purification device 12 main particulate filter (first filter means)
14 Sub-particulate filter (second filter means)
40 Ozone supply device (ozone supply means)
50 Engine control unit (operation control means)

Claims (4)

A first filter means provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust; a branch passage branched from the exhaust passage downstream of the first filter means; and provided in the branch passage. Second filter means for collecting particulate matter in the exhaust, and exhaust to the exhaust passage downstream from the branch portion where the branch passage branches from the exhaust passage while the inflow of exhaust into the branch passage is blocked A valve that can be switched between a first position where the inflow of the exhaust gas is permitted and a second position where the inflow of the exhaust gas to the exhaust passage downstream of the branching portion is prevented and the inflow of the exhaust gas to the branching passage is permitted And control of switching the valve means to the second position during a first regeneration process in which the first filter means is heated to a temperature at which the particulate matter collected by the first filter means is oxidized and removed. and means, before And a ozone supply means capable of supplying ozone into the upstream of the branch passage than the second filter means,
When the operation control means performs a second regeneration process of oxidizing and removing particulate matter collected by the second filter means using ozone supplied from the ozone supply means, the valve means is After switching to the second position, when the second filter means is heated to the target temperature during the second regeneration process, the valve means is switched to the first position and ozone is supplied into the branch passage. An exhaust gas purification apparatus for an internal combustion engine, wherein the ozone supply means is operated . The second filter means maintains the temperature of the second filter means within a predetermined temperature range suitable for collection of particulate matter by the second filter means when the valve means is switched to the second position. The exhaust purification device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is provided at a position where the exhaust gas purification is performed. The NOx storage reduction catalyst is supported on the first filter means,
3. The internal combustion engine according to claim 1 , wherein the operation control unit switches the valve unit to the second position during an S poison recovery process for releasing sulfur oxide from the NOx storage reduction catalyst. Exhaust purification equipment. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 3 , wherein an NOx storage reduction catalyst is supported on the second filter means.

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