JP5478276B2 - Particulate filter regeneration method - Google Patents

Description

  The present invention relates to a method for regenerating a particulate filter.

  Particulate matter (particulate matter) discharged from diesel engines is mainly composed of carbonaceous soot and SOF (Soluble Organic Fraction) consisting of high-boiling hydrocarbon components. Furthermore, the composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. Has been performed conventionally.

  The particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the respective channels partitioned in a lattice shape are alternately sealed, and the channels are not sealed. The outlet is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow path is discharged downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust, so a catalyst regeneration type that integrally supports an oxidation catalyst. Adoption of a particulate filter is being studied.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type regeneration oxidation catalyst is separately placed in front of the particulate filter, and fuel is added to the exhaust gas upstream of the regeneration oxidation catalyst when the amount of particulate accumulation increases. Therefore, it is considered to perform forced regeneration of the particulate filter.

  That is, the fuel (HC) added upstream from the particulate filter undergoes an oxidation reaction while passing through the preceding regeneration oxidation catalyst, and the particulate filter immediately after the inflow of exhaust gas heated by the reaction heat flows. The catalyst bed temperature is raised, the particulates are burned out, and the particulate filter is regenerated.

  As a specific means for executing this kind of fuel addition, post-injection is added at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. What is necessary is just to add a fuel in gas.

  As prior art document information related to the forced regeneration of such a particulate filter, there is the following Patent Document 1 by the same applicant as the present invention.

JP 2003-193824 A

  However, when purifying exhaust gas from a diesel engine, it is not sufficient to remove particulates in the exhaust gas as described above, and it is also necessary to remove NOx (nitrogen oxide) contained in the exhaust gas. In general, a part of the exhaust gas extracted from the exhaust system is returned to the intake system by the EGR line, and the combustion of the fuel in the engine is suppressed by the exhaust gas returned to the intake system to lower the combustion temperature. EGR device (EGR: Exhaust Gas Recirculation) that reduces the generation of NOx (nitrogen oxides) is used in combination, but if exhaust gas recirculation is continued even during forced regeneration of the particulate filter, exhaust is performed by post injection. The added fuel added to the gas contaminates the EGR line while flowing through the EGR line, and the efficiency of the heat exchange part of the EGR cooler In the past, measures were taken to close the EGR valve and stop the exhaust gas recirculation during forced regeneration of the particulate filter, because there was a risk that the cooling capacity would be reduced. There was a problem that the amount of NOx emissions temporarily increased.

  Therefore, the present inventor additionally provided a fuel addition device at a position upstream of the particulate filter in the middle of the exhaust pipe, and added to the EGR line by adding fuel from the fuel addition device during forced regeneration of the particulate filter. We have come up with a method to continue the exhaust gas recirculation without directing the fuel, but if this method is used, the exhaust will be operated in a light-load operation mode such as in urban driving. The drastic decrease in temperature causes a new problem in that the particulate filter causes a reproduction failure and takes a long reproduction time.

  That is, when the exhaust gas recirculation is stopped at the time of forced regeneration of the particulate filter and fuel is added by post-injection as before, the post-injection is preceded by the combustible timing immediately after main injection. It is common to take measures to raise the temperature of the exhaust to add injection, and the thermal efficiency of the internal combustion engine decreases due to the combustion of this after-injection fuel when it is difficult to convert it to output, and the amount of heat generated by the fuel The amount of heat that is not used for the power of the engine increases and the exhaust temperature rises, but the addition of such after injection also tends to increase the amount of unburned fuel in the exhaust gas and contaminates the EGR line Therefore, when switching to fuel addition by a fuel addition device and continuing recirculation of exhaust gas, the effect of increasing the temperature of exhaust by after injection cannot be obtained. Of aplastic particulate filter it was likely to occur in the operating mode of a light load, such as a city in the running.

  For this reason, in light-load operation modes such as urban driving, countermeasures for adding fuel by post-injection as before, stopping exhaust gas recirculation, are considered. The fact that exhaust gas recirculation must be stopped at the forced regeneration of the particulate filter at the engine is not preferable from the viewpoint of suppressing the NOx emission amount, and the particulate filter in the light load operation mode is not preferable. There is a need for countermeasures that allow the exhaust gas recirculation to continue as much as possible even during forced regeneration.

  The present invention has been made in view of the above circumstances, and it is intended to suppress NOx emissions so that exhaust gas recirculation can be continued as much as possible even during forced regeneration of a particulate filter in a light load operation mode. It is an object.

  The present invention adds a fuel to exhaust gas upstream of a catalyst regeneration type particulate filter provided in the middle of an exhaust pipe with a regeneration oxidation catalyst in the front stage, and the added fuel is on the regeneration oxidation catalyst. The particulate filter in the latter stage particulate filter is combusted by the heat of reaction when the oxidation reaction is carried out in order to forcibly regenerate the particulate filter, and is in the exhaust pipe on the inlet side of the regeneration oxidation catalyst. A fuel addition means for directly injecting fuel, an EGR line for extracting a part of the exhaust gas from the exhaust system upstream of the fuel addition means and recirculating it to the intake system, and the exhaust gas in the exhaust gas at the most upstream part of the EGR line. An EGR oxidation catalyst that oxidizes unburned fuel, and when the outlet side exhaust temperature of the regeneration oxidation catalyst is higher than a first set temperature for determining the presence or absence of catalytic activity of the regeneration oxidation catalyst, While the R line is opened and the exhaust gas is recirculated, fuel is added by the fuel adding means, and the outlet side exhaust temperature of the regeneration oxidation catalyst is equal to or lower than the first set temperature and the outlet side exhaust of the EGR oxidation catalyst. When the temperature is higher than the second set temperature for determining the presence or absence of the catalytic activity of the oxidation catalyst for EGR, the post-injection is added along with the after-injection on the engine side while the EGR line is opened and the exhaust gas is recirculated. And when the outlet exhaust temperature of the regeneration oxidation catalyst is equal to or lower than the first set temperature and the outlet exhaust temperature of the EGR oxidation catalyst is equal to or lower than the second set temperature, the EGR line is closed to remove the exhaust gas. The fuel injection is performed by adding the post injection together with the after injection while stopping the recirculation.

  Thus, when the regeneration oxidation catalyst has already reached a temperature having catalytic activity, the outlet side exhaust temperature becomes higher than the first set temperature, and fuel is added by the fuel addition means. Oxidizes while passing through the regeneration oxidation catalyst, and the catalyst bed temperature of the particulate filter immediately after that rises due to the inflow of exhaust gas heated by the reaction heat, the particulates are burned out, and the particulate filter Regeneration will be achieved.

  At this time, the EGR line is opened and the exhaust gas recirculation is continued. However, a part of the exhaust gas is extracted from the exhaust system upstream of the fuel addition means and recirculated to the intake system. Therefore, there is no concern that the added fuel is guided to the EGR line, and the EGR line is prevented from being contaminated due to the adhesion of unburned fuel.

  However, with fuel addition by means of fuel addition, it is not possible to expect an increase in exhaust gas temperature due to the addition of after-injection as in post-injection. There is a risk that the regeneration oxidation catalyst will become inactive, and in such a case, the outlet side exhaust temperature of the regeneration oxidation catalyst will be lower than or equal to the first set temperature so that the fuel addition means The post-injection is switched to the post-injection on the side, and the post-injection is added together with the after-injection to add fuel.

  As a result, even in a light load operation mode such as driving in a city, the exhaust gas temperature is increased by adding after injection, the catalytic activity of the regeneration oxidation catalyst is increased, and the particulate filter causes regeneration failure. Thus, a situation where the playback time is long is avoided.

  At this time, if the outlet side exhaust temperature of the oxidation catalyst for EGR is higher than the second set temperature, the EGR line is opened and exhaust gas recirculation is continued, but the most upstream of the EGR line Since the unburned fuel content in the exhaust gas is oxidized by the EGR oxidation catalyst in the section, it is avoided that the inside of the EGR line is contaminated by the unburned fuel content.

  However, if the outlet exhaust temperature of the EGR oxidation catalyst is equal to or lower than the second set temperature, it is considered that the EGR oxidation catalyst is in an inactive state, and therefore the EGR line is blocked and the exhaust gas is recirculated. Circulation is stopped.

  Further, in the present invention, the exhaust pipe upstream of the regeneration oxidation catalyst is provided with a temperature raising oxidation catalyst, and it is determined whether or not the outlet exhaust temperature of the regeneration oxidation catalyst is higher than the first set temperature. Prior to comparing the regeneration exhaust temperature of the regeneration oxidation catalyst with a third preset temperature lower than the first set temperature, the regeneration oxidation is performed only if the regeneration exhaust catalyst exhaust temperature is equal to or lower than the third set temperature. Without proceeding to the determination of whether or not the outlet exhaust temperature of the catalyst is higher than the first set temperature, the outlet exhaust temperature of the temperature raising oxidation catalyst determines whether or not the temperature raising oxidation catalyst has catalytic activity. The process proceeds to a determination of whether or not the temperature is higher than the fourth set temperature. When the outlet side exhaust temperature of the temperature-raising oxidation catalyst is higher than the fourth set temperature, the EGR line is closed to stop the exhaust gas recirculation. Fuel is added by adding injection together with after-injection. When the outlet side exhaust gas temperature is below the fourth preset temperature, it is preferable to be performed only after injection while by closing the EGR line to stop recirculation of exhaust gas.

  In this way, the exhaust temperature will continue to be very low due to heavy traffic congestion, etc., and the bed temperature of the regeneration oxidation catalyst will drop significantly, making it impossible to perform forced regeneration of the particulate filter. In some cases, it is determined that the outlet exhaust temperature of the regeneration oxidation catalyst is equal to or lower than the third set temperature, and whether or not the outlet exhaust temperature of the regeneration oxidation catalyst is higher than the first set temperature. Without proceeding to the determination, the process proceeds to a determination as to whether or not the outlet side exhaust temperature of the temperature raising oxidation catalyst is higher than the fourth set temperature.

  When the outlet side exhaust temperature of the temperature-raising oxidation catalyst is higher than the fourth set temperature, the EGR line is closed, exhaust gas recirculation is stopped, post injection is added together with after injection, and fuel is added. In addition, the temperature of the exhaust gas is raised by the reaction heat caused by the oxidation reaction of the added fuel on the oxidation catalyst for temperature rise, and the temperature rise of the exhaust gas is also achieved by adding after injection.

  Here, since the temperature-raising oxidation catalyst is provided in the exhaust pipe upstream of the regeneration oxidation catalyst, high-temperature exhaust gas that has just been exhausted from the engine is introduced into the temperature-raising oxidation catalyst. As a result, it can be activated relatively easily even in an operating state where the exhaust temperature is low.

  The fuel addition by post injection at this time is not intended to forcibly regenerate the particulate filter, but only for the purpose of raising the exhaust gas temperature. A relatively small amount that is exhausted is sufficient.

  On the other hand, when the outlet side exhaust temperature of the temperature raising oxidation catalyst is equal to or lower than the fourth set temperature, the EGR line is closed and the exhaust gas recirculation is stopped, and only the after injection is performed to raise the temperature of the exhaust gas. It will be.

  According to the method for regenerating a particulate filter of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, even when the particulate filter is forcibly regenerated in the light load operation mode, if the EGR oxidation catalyst is in an active state, post injection is performed. In addition to after-injection, the exhaust gas recirculation can be continued while raising the exhaust gas temperature, so that a temporary increase in NOx emissions can be significantly suppressed compared to the conventional method. If it is in a sufficiently active state, switching from post-injection to fuel addition means can reliably prevent contamination of the EGR line due to unburned fuel.

  (II) According to the invention described in claim 2 of the present invention, prior to the forced regeneration of the particulate filter, when the bed temperature of the regeneration oxidation catalyst is greatly lowered due to a long-time traffic jam or the like. The temperature of the exhaust gas can be raised, and the temperature condition at which the forced regeneration can be executed by raising the bed temperature of the particulate filter can be adjusted.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the specific control procedure of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 passes through an intake pipe 5. The intake air 4 sent to the compressor 2 a of the turbocharger 2 and pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7. The diesel engine 1 is distributed to each cylinder 8 (only four cylinders are schematically shown in FIG. 1).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

  A filter case 12 is interposed in the middle of the exhaust pipe 11, and a catalyst regeneration type particulate filter 13 that integrally carries an oxidation catalyst is accommodated in the filter case 12. The flow-through type regeneration oxidation catalyst 14 is accommodated in the preceding stage of the particulate filter 13.

  In addition, an EGR line 15 connects between one end of the exhaust manifold 10 in the arrangement direction of the cylinders 8 and one end of the intake pipe 5 connected to the intake manifold 7, and is extracted from the exhaust manifold 10. A part of the exhaust gas 9 is recirculated to the intake pipe 5 through the water-cooled EGR cooler 16 and the EGR valve 17, and each cylinder is recirculated from the exhaust system to the intake system. The generation of NOx can be reduced by reducing the combustion temperature by suppressing the combustion of fuel in the fuel cell 8.

  On the other hand, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 18 that detects the accelerator opening as a load of the diesel engine 1, and a rotation sensor that detects the rotational speed at an appropriate position of the diesel engine 1. 19, the accelerator opening signal 18a and the rotation speed signal 19a from the accelerator sensor 18 and the rotation sensor 19 are input to a control device 20 constituting an engine control computer (ECU: Electronic Control Unit). It has become.

  In the control device 20, a fuel injection signal 21a for instructing the fuel injection timing and the injection amount is output to the fuel injection device 21 for injecting fuel into each cylinder 8 of the diesel engine 1. .

  Here, the fuel injection device 21 is constituted by a plurality of injectors (not shown) provided for each cylinder 8, and the solenoid valve of each injector is appropriately controlled to be opened by the fuel injection signal 21a. The injection timing and the injection amount (valve opening time) are appropriately controlled.

  The control device 20 outputs a fuel injection signal 21a for instructing normal main injection according to the current operating state based on the accelerator opening signal 18a and the rotational speed signal 19a. Accordingly, after-injection is added at a combustible timing immediately after the main injection of fuel performed near the compression top dead center (crank angle 0 °), or non-ignition later than the compression top dead center following the main injection. A fuel injection signal 21a for further adding post-injection at timing is also output.

  In the exhaust purification apparatus configured as described above, in the present embodiment, the flow-through type temperature-raising oxidation catalyst 22 is disposed in the exhaust pipe 11 upstream of the regeneration oxidation catalyst 14 (near the outlet of the turbine 2b). Immediately after the temperature raising oxidation catalyst 22, a fuel addition device 23 (fuel addition means) for directly injecting fuel into the exhaust pipe 11 on the inlet side of the regeneration oxidation catalyst 14 is provided. The fuel addition device 23 is configured to perform fuel addition in response to a fuel addition signal 23 a from the control device 20.

  Further, an EGR oxidation catalyst 24 for oxidizing the unburned fuel in the exhaust gas 9 is provided at the most upstream portion of the EGR line 15, and if the EGR oxidation catalyst 24 is in an active state, The exhaust gas 9 can be recirculated by opening the EGR valve 17 while performing post injection on the diesel engine 1 side, and the exhaust gas 9 is continuously recirculated by opening and closing the EGR valve 17. Stop is instructed by a control signal 17a from the control device 20.

  Further, immediately after each of the regeneration oxidation catalyst 14, the temperature raising oxidation catalyst 22, and the EGR oxidation catalyst 24 described above, temperature sensors 25, 26, and 27 are provided for detecting the exhaust temperature immediately after leaving each catalyst. The detection signals 25a, 26a, and 27a from the temperature sensors 25, 26, and 27 are input to the control device 20.

  In the example shown here, a selective reduction catalyst 28 capable of selectively reacting NOx with hydrocarbons even in the presence of oxygen is provided downstream of the particulate filter 13 in the filter case 12 to reduce NOx. Additional equipment is added to assist in purification.

  Thus, the forced regeneration of the particulate filter 13 in the exhaust purification apparatus having such a configuration is performed by appropriately switching the post injection on the diesel engine 1 side and the fuel addition apparatus 23 by the control device 20. 9 is performed while continuing recirculation as much as possible, and more specifically, it is performed according to the control procedure as shown in the flowchart of FIG.

  That is, first in step S1, based on the detection signal 25a from the temperature sensor 25, it is confirmed that the outlet side exhaust temperature of the regeneration oxidation catalyst 14 is higher than 200 ° C. (third set temperature), and then the process proceeds to step S2. It is then determined whether or not the outlet side exhaust temperature of the regeneration oxidation catalyst 14 is higher than 350 ° C. (first set temperature).

  Here, the determination in step S1 is so drastically that the exhaust temperature of the exhaust catalyst 14 continues to be very low due to traffic jams for a long time, and the bed temperature of the regeneration oxidation catalyst 14 cannot be forcibly regenerated. The determination in step S2 is to confirm whether or not the regeneration oxidation catalyst 14 is in an active state.

  When the determination in step S2 is “YES”, the process proceeds to step S3. In step S3, the control signal 17a for instructing the opening operation to the EGR valve 17 is output and to the fuel addition device 23. The fuel addition signal 23a is output, and the fuel addition device 23 performs control to add fuel while the EGR line 15 is opened and the exhaust gas 9 is recirculated.

  On the other hand, if the determination in step S2 is “NO”, the process proceeds to step S4. In step S4, based on the detection signal 27a from the temperature sensor 27, the outlet side exhaust gas temperature of the EGR oxidation catalyst 24 is 230. It is determined whether or not the temperature is higher than the second temperature (second set temperature), and it is confirmed whether or not the EGR oxidation catalyst 24 is in an active state.

  When the determination in step S4 is “YES”, the process proceeds to step S5. In step S5, the control signal 17a for instructing the opening operation to the EGR valve 17 is output and the fuel injection device 21 is also output. The fuel injection signal 21a for adding the post-injection to the engine and the after-injection is output, and the EGR line 15 is opened and the exhaust gas 9 is recirculated to add the post-injection with the after-injection on the diesel engine 1 side. The control to be performed is executed.

  On the other hand, if the determination in step S4 is “NO”, the process proceeds to step S6. In step S6, the control signal 17a for instructing the closing operation to the EGR valve 17 is output, and the fuel injection device 21. A fuel injection signal 21a for adding post-injection toward the engine is output, and the EGR line 15 is closed to stop the recirculation of the exhaust gas 9, and the diesel engine 1 side adds post-injection along with after-injection to produce fuel. Control to perform the addition is executed.

  However, if “NO” determination is made in the first step S1, assuming that the bed temperature of the regeneration oxidation catalyst 14 has decreased so much that the particulate filter 13 cannot be forcibly regenerated, step NO. The process proceeds to step S7 without proceeding to the determination of whether or not the outlet side exhaust temperature of the regeneration oxidation catalyst 14 in S2 is higher than 350 ° C. (first set temperature). In step S7, the detection signal from the temperature sensor 26 is detected. 26a, it is determined whether or not the outlet side exhaust temperature of the temperature raising oxidation catalyst 22 is higher than 230 ° C. (second set temperature), and whether or not the temperature raising oxidation catalyst 22 is in an active state. It is confirmed.

  When the determination in step S7 is “YES”, the process proceeds to step S8. In step S8, the control signal 17a for instructing the closing operation to the EGR valve 17 is output, and the fuel injection device 21 is also informed. The fuel injection signal 21a is added to add the post-injection to the engine along with the after-injection, and the EGR line 15 is closed to stop the recirculation of the exhaust gas 9, and the post-injection is added together with the after-injection on the diesel engine 1 side to add fuel. Control to perform is executed.

  The fuel addition by the post injection at this time is performed for the purpose of raising the temperature of the exhaust gas by the reaction heat by oxidizing the added fuel with the oxidation catalyst 22 for raising the temperature of the particulate filter 14. The addition amount may be smaller than that during forced regeneration.

  On the other hand, if the determination in step S7 is “NO”, the process proceeds to step S9. In step S9, the control signal 17a for instructing the closing operation to the EGR valve 17 is output, and the fuel injection device 21. The fuel injection signal 21a for adding only after-injection toward the engine is output, and the EGR line 15 is closed to stop the recirculation of the exhaust gas 9, and control is performed to add fuel by adding only after-injection on the diesel engine 1 side. Is executed.

  As described above, if the particulate filter 13 is forcibly regenerated in accordance with the control procedure shown in the flowchart of FIG. 2, when the regeneration oxidation catalyst 14 has already reached a temperature at which it has catalytic activity, its outlet side exhaust temperature The fuel is added by the fuel addition device 23 when it becomes higher than 350 ° C. (first set temperature), and the exhausted fuel undergoes an oxidation reaction while passing through the regeneration oxidation catalyst 14 and is heated by the reaction heat. The catalyst bed temperature of the particulate filter 13 immediately after the inflow of the gas 9 is raised, the particulates are burned out, and the particulate filter 13 is regenerated.

  At this time, the EGR line 15 is opened and the recirculation of the exhaust gas 9 is continued. However, a part of the exhaust gas 9 is extracted from the exhaust manifold 10 upstream of the fuel addition device 23 and recirculated to the intake pipe 5. Therefore, there is no concern that the added fuel is guided to the EGR line 15, and the inside of the EGR line 15 is prevented from being contaminated due to adhesion of unburned fuel.

  However, the fuel addition by the fuel addition device 23 cannot be expected to raise the exhaust gas temperature due to the addition of after-injection as in the case of post-injection. However, in this case, the outlet side exhaust temperature of the regeneration oxidation catalyst 14 becomes 350 ° C. (first set temperature) or less. Thus, the fuel injection device 23 switches to post injection on the diesel engine 1 side, and the post injection is added together with the after injection to perform fuel addition.

  As a result, even in a light load operation mode such as traveling in the city, the exhaust gas temperature is increased by the addition of after injection, the catalytic activity of the regeneration oxidation catalyst 14 is increased, and the particulate filter 13 is poorly regenerated. This will avoid a situation in which the playback time takes a long time.

  At this time, if the outlet side exhaust temperature of the EGR oxidation catalyst 24 is higher than 230 ° C. (second set temperature), the EGR line 15 is opened, and the recirculation of the exhaust gas 9 is continued. Since the unburned fuel in the exhaust gas 9 is oxidized by the EGR oxidation catalyst 24 at the most upstream part of the EGR line 15, the inside of the EGR line 15 may be contaminated by the unburned fuel. Avoided.

  However, if the outlet side exhaust temperature of the EGR oxidation catalyst 24 is 230 ° C. (second set temperature) or less, it is considered that the EGR oxidation catalyst 24 is in an inactive state, and therefore the EGR line 15 is The recirculation of the exhaust gas 9 is stopped due to the blockage.

  Particularly in the present embodiment, the operation state in which the exhaust temperature is very low continues due to a long-time traffic jam, etc., and the bed temperature of the regeneration oxidation catalyst 14 is greatly lowered, so that the particulate filter 13 is forcibly regenerated. Is determined when the outlet side exhaust temperature of the regeneration oxidation catalyst 14 is 200 ° C. (third set temperature) or less, and the outlet side exhaust temperature of the regeneration oxidation catalyst 14 is determined. To determine whether the outlet side exhaust temperature of the temperature-raising oxidation catalyst 22 is higher than 230 ° C. (fourth set temperature) without proceeding to the determination whether the temperature is higher than 350 ° C. (first set temperature). Will be migrated.

  When the outlet side exhaust temperature of the temperature-raising oxidation catalyst 22 is higher than 230 ° C. (fourth set temperature), the EGR line 15 is closed and the recirculation of the exhaust gas 9 is stopped, and post injection is added together with after injection. Then, the fuel is added, and the temperature of the exhaust gas is raised by the reaction heat generated by the oxidation reaction of the added fuel on the temperature raising oxidation catalyst 22, and the temperature of the exhaust gas is also raised by the addition of after injection. Become.

  Here, since the temperature raising oxidation catalyst 22 is provided in the exhaust pipe 11 upstream of the regeneration oxidation catalyst 14, the high-temperature exhaust gas 9 that has just been exhausted from the diesel engine 1 is used for the temperature raising. By being introduced into the oxidation catalyst 22, it is activated relatively easily even in an operation state where the exhaust temperature is low.

  The fuel addition by the post injection at this time is not intended to forcibly regenerate the particulate filter 13 but is performed only for the purpose of raising the temperature of the exhaust gas. The amount is relatively small enough to be consumed.

  On the other hand, when the outlet side exhaust temperature of the temperature-raising oxidation catalyst 22 is 230 ° C. (fourth set temperature) or lower, the EGR line 15 is closed, the recirculation of the exhaust gas 9 is stopped, and only after injection is performed. As a result, the temperature of the exhaust can be raised.

  Therefore, according to the above embodiment, even when the particulate filter 13 is forcibly regenerated in the light load operation mode, if the EGR oxidation catalyst 24 is in an active state, post injection is added together with after injection. Since the exhaust gas 9 can be continuously recirculated while raising the temperature of the exhaust gas, a temporary increase in the NOx emission amount can be significantly suppressed as compared with the prior art, and the regeneration oxidation catalyst 14 is sufficiently activated. If so, it is possible to reliably prevent the EGR line 15 from being contaminated by the unburned fuel by switching from the post injection to the fuel addition device 23.

  In particular, in the case of the present embodiment, when the bed temperature of the regeneration oxidation catalyst 14 is significantly lowered due to a long-time traffic jam or the like, the exhaust gas temperature is raised prior to the forced regeneration of the particulate filter 13. Therefore, it is possible to adjust the temperature condition in which forced regeneration can be performed by raising the bed temperature of the particulate filter 13.

  Note that the method for regenerating a particulate filter of the present invention is not limited to the above-described embodiments, and it is needless to say that various changes can be made without departing from the scope of the present invention.

1 Diesel engine (engine)
5 Intake pipe (intake system)
7 Intake manifold (intake system)
9 Exhaust gas 10 Exhaust manifold (exhaust system)
11 Exhaust pipe (exhaust system)
DESCRIPTION OF SYMBOLS 13 Particulate filter 14 Oxidation catalyst for regeneration 15 EGR line 16 EGR cooler 17 EGR valve 17a Control signal 20 Control device 21 Fuel injection device 21a Fuel injection signal 22 Oxidation catalyst for temperature rise 23 Fuel addition device (fuel addition means)
23a Fuel addition signal 24 EGR oxidation catalyst 25 Temperature sensor 25a Detection signal 26 Temperature sensor 26a Detection signal 27 Temperature sensor 27a Detection signal

Claims (2)

  Fuel was added to the exhaust gas upstream of the catalyst regeneration type particulate filter provided in the middle of the exhaust pipe equipped with a regeneration oxidation catalyst, and the added fuel oxidized on the regeneration oxidation catalyst. In this method, the collected particulate matter in the downstream particulate filter is burned by the reaction heat at the time, and the particulate filter is forcibly regenerated. Fuel is directly injected into the exhaust pipe on the inlet side of the regeneration oxidation catalyst. Fuel adding means, a part of the exhaust gas extracted from the exhaust system upstream from the fuel adding means, and recirculated to the intake system, and the unburned fuel content in the exhaust gas at the most upstream part of the EGR line An EGR oxidation catalyst that oxidizes the EGR line, and when the outlet side exhaust temperature of the regeneration oxidation catalyst is higher than a first set temperature for determining the presence or absence of the catalytic activity of the regeneration oxidation catalyst, The fuel is added by the fuel addition means while the exhaust gas is recirculated and the exhaust gas temperature of the regeneration oxidation catalyst is equal to or lower than the first set temperature, and the exhaust gas temperature of the EGR oxidation catalyst is equal to the exhaust gas temperature. When the EGR oxidation catalyst is higher than the second set temperature for determining the catalytic activity, the EGR line is opened and exhaust gas is recirculated while post-injection is added along with after-injection on the engine side to add fuel. When the outlet side exhaust temperature of the regeneration oxidation catalyst is lower than the first set temperature and the outlet side exhaust temperature of the EGR oxidation catalyst is lower than the second set temperature, the EGR line is closed to recirculate the exhaust gas. A method for regenerating a particulate filter, comprising adding post-injection together with after-injection while stopping and adding fuel.   A temperature raising oxidation catalyst is provided in the exhaust pipe upstream of the regeneration oxidation catalyst, and prior to determining whether the outlet exhaust temperature of the regeneration oxidation catalyst is higher than the first set temperature, the regeneration oxidation catalyst The outlet side exhaust temperature of the regeneration oxidation catalyst is compared only when the outlet side exhaust temperature is compared with the third set temperature lower than the first set temperature and the outlet side exhaust temperature of the regeneration oxidation catalyst is equal to or lower than the third set temperature. Without proceeding to the determination of whether or not the temperature is higher than the first set temperature, whether or not the outlet side exhaust temperature of the temperature-raising oxidation catalyst is higher than the fourth set temperature for determining the presence or absence of catalytic activity of the temperature-raising oxidation catalyst When the outlet side exhaust temperature of the temperature raising oxidation catalyst is higher than the fourth set temperature, the post-injection is added together with the after-injection while closing the EGR line and stopping the exhaust gas recirculation. The fuel is added, and the exhaust temperature on the outlet side of the oxidation catalyst for temperature rise is When it is a temperature below the particulate filter reproducing method according to claim 1, characterized in that only the abort while after injection of recirculation of exhaust gas by closing the EGR line.

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