JP2012154237A - Exhaust gas purification system and method for forced regeneration of diesel particulate filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification system and a method for forced regeneration of a DPF (diesel particulate filter) preventing the event that the temperature of the DPF rises in forced regeneration of the DPF and the melt loss, crack and the like occur in the DPF, and suppressing deterioration of fuel efficiency accompanying forced regeneration.SOLUTION: In the exhaust gas purification system 1 of an internal combustion engine obtained by arranging an oxidation catalyst 12, a turbine 13a of a turbocharger 13, the DPF 14, a urea supply device 15, and a selective reduction catalyst 16 in an exhaust gas passage 11 of the internal combustion engine 10 in this order from the upstream side, a control device of the exhaust gas purification system 1 performs control so that: in forced regeneration of the DPF 14, nitrogen monoxide generated in the internal combustion engine 10 is increased; the nitrogen monoxide is oxidized into nitrogen dioxide by the oxidation catalyst 12; soot accumulated in the DPF 14 is oxidized by the nitrogen dioxide; and nitrogen oxide generated in oxidation of the soot is reduced into nitrogen by the selective reduction catalyst 16.

Description

  The present invention relates to an exhaust gas purification system and a forced regeneration method for a diesel particulate filter that can prevent melting damage, cracks, and the like from occurring during forced regeneration of a diesel particulate filter, and can suppress deterioration in fuel consumption associated with forced regeneration. .

  An exhaust gas purification system equipped with a diesel particulate filter (DPF: Diesel Particulate Filter) to remove PM (Particulate Matter: particulate matter) in exhaust gas discharged from diesel engines Is used. This diesel particulate filter collects PM, and if the amount of PM collected increases, the exhaust pressure rises and fuel consumption deteriorates. Therefore, before the amount of PM collected reaches the limit, the diesel particulate filter It is necessary to process the PM deposited on the substrate.

One of the components of PM, SOOT (soot, soot) is an engine emission material mainly composed of carbon (C), which is said to be particularly difficult to burn, and is a method for removing SOOT by oxidation. There are known a method of burning with oxygen (O ₂ ) at a temperature of 600 ° C. or higher and a method of burning with nitrogen dioxide (NO ₂ ) at a temperature of about 300 ° C. as shown in FIGS.

FIG. 7 shows that nitrogen monoxide (NO) is oxidized with oxygen (O ₂ ) in exhaust gas by an upstream oxidation catalyst (DOC: Diesel Oxidation Catalyst) to form nitrogen dioxide (NO ₂ ). (NO ₂ ) is a downstream diesel particulate filter (DPF), which oxidizes SOOT (C) by the reaction of “C + 2NO ₂ → CO ₂ + 2NO” and returns to nitric oxide (NO). . The oxidation of SOOT (C) theoretically requires 7.66 times as much nitrogen dioxide (NO ₂ ) by weight.

FIG. 8 shows the oxidation ability of carbon (C) in relation to temperature and carbon dioxide (CO ₂ ) concentration. In the case of oxygen (O ₂ ), carbon dioxide at 400 ° C. to 600 ° C. whereas (CO ₂₎ concentration is increased, in the case of nitrogen dioxide (NO _2), it can be seen that rapid carbon dioxide (CO ₂₎ concentration at 200 ° C. to 300 ° C. has increased.

In this connection, an oxidation catalyst, DPF, urea water addition means, SCR catalyst, upstream from the upstream side to the exhaust path for the purpose of maximizing the purification efficiency of the SCR catalyst regardless of the operating status of the engine body. An exhaust gas purification device provided with an oxidation catalyst and an exhaust gas purification device that adjusts the temperature of the oxidation catalyst so that the molar ratio of NO to NO ₂ is 1: 1 have been proposed (see, for example, Patent Document 1). ).

  However, in order to oxidize and remove SOOT deposited in the diesel particulate filter by forced regeneration with nitrogen dioxide, a large amount of nitrogen dioxide is required. Therefore, a cylinder is required to discharge a large amount of nitrogen oxide (NOx). If the fuel injection timing is advanced, the exhaust temperature will decrease due to this advance angle. Further, since measures against nitrogen oxides in exhaust gas have been strengthened, the amount of nitrogen oxides in exhaust gas has decreased, and generation of a large amount of nitrogen dioxide can hardly be expected.

  Therefore, in the conventional technology, the temperature of the diesel particulate filter is raised to 600 ° C. or higher and SOOT is burned with oxygen, thereby completely burning the SOOT in the diesel particulate filter and resetting the PM calculation cumulative value. is doing.

  However, in this SOOT oxidation removal method using oxygen, since SOOT is burned at 600 ° C. or higher, when the accumulated SOOT is higher than expected, the temperature in the diesel particulate filter becomes higher than 600 ° C. In some cases, the temperature reaches a temperature at which melting or cracking occurs, and there is a problem that various measures must be taken to improve safety in order to prevent this. Further, since the temperature of the diesel particulate filter is raised to a high temperature, the fuel injection amount for increasing the exhaust gas temperature is controlled to be increased so that the fuel consumption is greatly deteriorated.

JP 2010-265862 A

  The present invention has been made in view of the above-described situation, and the purpose of the present invention is to cause the diesel particulate filter to become hot during forced regeneration of the diesel particulate filter, resulting in melting damage, cracks, etc. in the diesel particulate filter. Exhaust gas purification system and forced regeneration of diesel particulate filter that can suppress the deterioration of fuel consumption caused by forced regeneration of diesel particulate filter It is to provide a method.

  In order to achieve the above object, an exhaust gas purification system of the present invention includes an oxidation catalyst, a turbocharger turbine, a diesel particulate filter, a urea supply device, and a selector in order from an upstream side to an exhaust passage of an internal combustion engine. In an exhaust gas purification system of an internal combustion engine in which a reduction catalyst is arranged, the control device of the exhaust gas purification system increases the nitrogen monoxide generated in the internal combustion engine during forced regeneration of the diesel particulate filter, Nitrogen oxide is oxidized to nitrogen dioxide by the oxidation catalyst, SOOT accumulated in the diesel particulate filter is oxidized by the nitrogen dioxide, and nitrogen oxide generated by the oxidation of SOOT is reduced to nitrogen by the selective reduction catalyst. Configured to perform control.

  This SOOT is one of the components of PM (particulate matter) emitted from an internal combustion engine, particularly a diesel engine, and is an engine exhaust material mainly composed of carbon (C). This substance is called soot, candy, etc.

  According to this configuration, by disposing the oxidation catalyst (DOC) in front of the turbine, the distance between the exhaust manifold and the oxidation catalyst is shortened and the amount of decrease in the temperature of the exhaust gas is reduced. Thus, the temperature of the exhaust gas flowing into the oxidation catalyst can be easily increased to the activation temperature of the oxidation catalyst.

And since oxidation of SOOT with nitrogen dioxide (NO ₂ ) can be oxidized and removed at a lower temperature than oxygen (O ₂ ), the diesel particulate filter becomes hot during forced regeneration of the diesel particulate filter. It is possible to prevent melting or cracks from occurring. In addition, the amount of fuel for increasing the temperature of the diesel particulate filter can be reduced, and deterioration of fuel consumption associated with forced regeneration of the diesel particulate filter can be suppressed. In the exhaust gas purification system, a first exhaust gas temperature sensor is provided between the oxidation catalyst and the turbine, and a second exhaust gas temperature sensor is provided between the turbine and the diesel particulate filter. Is input to a control device that controls the operation of the internal combustion engine and the exhaust gas purification system, and the control device closes the EGR valve and stops EGR during the forced regeneration of the diesel particulate filter. The excess air ratio is within the range of 1.3 to 1.6 until the intake throttle is closed and the first exhaust gas temperature detected by the first exhaust gas temperature sensor becomes equal to or higher than a predetermined first determination temperature. When the exhaust gas temperature raising control is performed and the first exhaust gas temperature becomes equal to or higher than the predetermined first determination temperature, the second exhaust gas temperature is Post-cylinder fuel injection pilot injection and main injection are advanced so that the second exhaust gas temperature detected by the sensor falls within a range of a predetermined second determination temperature and a predetermined third determination temperature. In addition to performing exhaust temperature maintenance control for performing injection, in the exhaust temperature maintenance control, the NOx map for calculating the fuel injection timing is advanced from the NOx map during normal operation with the timing advanced from that during normal operation. Urea that switches to the NOx map for forced regeneration that increases the generation amount and adjusts the urea supply amount from the urea supply device in accordance with the NOx amount that is generated based on the data of the NOx map for forced regeneration If it is configured to perform the amount adjustment control, the nitrogen monoxide generated in the internal combustion engine is increased during the forced regeneration of the diesel particulate filter. Nitric oxide is oxidized to nitrogen dioxide by the oxidation catalyst, SOOT accumulated in the diesel particulate filter is oxidized by the nitrogen dioxide, and nitrogen oxide generated by the oxidation of SOOT is reduced to nitrogen by the selective reduction catalyst. Control can be easily performed.

  That is, NOx can be increased by stopping EGR, and the amount of NOx generated can be further increased by the advance angle of pilot injection and main injection. Further, the exhaust temperature can be raised by closing the intake throttle, and the temperature of the exhaust gas can be further raised by oxidizing the unburned fuel supplied by post injection with an oxidation catalyst. In addition, the post-injection is controlled to stop when the second exhaust gas temperature does not exceed the predetermined third judgment temperature, so that the exhaust gas temperature does not rise too much due to the post-injection. it can.

  Further, by switching the NOx map for calculating the fuel injection timing and controlling the urea injection amount in accordance with the NOx amount generated based on the data of the NOx map for forced regeneration, the combustion in the cylinder Thus, a large amount of NOx can be generated to oxidize and remove SOOT, and this large amount of NOx can be purified by a selective reduction catalyst with an appropriate amount of urea.

  And the forced regeneration method of the diesel particulate filter of the present invention for achieving the above-mentioned object is the following: in order from the upstream side to the exhaust passage of the internal combustion engine, the oxidation catalyst, the turbocharger turbine, the diesel particulate filter In the forced regeneration method of the diesel particulate filter in the exhaust gas purification system of the internal combustion engine in which the urea supply device and the selective reduction catalyst are arranged, the nitrogen monoxide generated in the internal combustion engine is increased during the forced regeneration of the diesel particulate filter. The nitric oxide is oxidized to nitrogen dioxide by the oxidation catalyst, the SOOT accumulated in the diesel particulate filter is oxidized by the nitrogen dioxide, and the nitrogen oxides generated by the oxidation of the SOOT are selectively reduced. Reduction to nitrogen with a catalyst. .

  According to this method, oxidation of SOOT with nitrogen dioxide rather than oxygen can be removed by oxidation at a lower temperature. Therefore, the diesel particulate filter is heated at the time of forced regeneration of the diesel particulate filter, resulting in erosion and cracks. And the like can be prevented. In addition, the fuel for increasing the temperature of the diesel particulate filter can be reduced, and deterioration of fuel consumption due to forced regeneration can be suppressed.

  In the above-described forced regeneration method of the diesel particulate filter, the EGR valve is closed to stop the EGR, the intake throttle is closed, and the first exhaust gas temperature between the oxidation catalyst and the turbine is equal to or higher than a predetermined first determination temperature. Until the excess air ratio is within the range of 1.3 to 1.6, and when the first exhaust gas temperature is equal to or higher than the predetermined first determination temperature, The pilot injection and the main injection of in-cylinder fuel injection are advanced so that the second exhaust gas temperature between the diesel particulate filters is in a range not less than a predetermined second determination temperature and not more than a predetermined third determination temperature. In this exhaust temperature maintenance control, a NOx map for calculating the fuel injection timing is displayed as NO during normal operation. The map is switched to the NOx map for forced regeneration that increases the NOx generation amount by advancing the timing from the normal operation, and corresponds to the NOx amount generated based on the data of the NOx map for forced regeneration. When the urea amount adjustment control for adjusting the urea supply amount from the urea supply device is performed, the nitrogen monoxide generated in the internal combustion engine is increased during the forced regeneration of the diesel particulate filter, and the nitric oxide is Easily controlled to oxidize to nitrogen dioxide with oxidation catalyst, oxidize SOOT accumulated in the diesel particulate filter with the nitrogen dioxide, and reduce nitrogen oxide generated by oxidation of SOOT to nitrogen with the selective reduction catalyst Can be done.

  According to the exhaust gas purification system and the diesel particulate filter forced regeneration method of the present invention, during the forced regeneration of the diesel particulate filter, nitric oxide generated in the internal combustion engine is oxidized into nitrogen dioxide by an oxidation catalyst. The SOOT accumulated in the diesel particulate filter is oxidized with nitrogen dioxide, and the nitrogen oxides generated by this oxidation are reduced to nitrogen with the selective reduction catalyst. Therefore, the diesel particulate filter becomes hot during forced regeneration of the diesel particulate filter. Therefore, it is possible to prevent melting damage and cracks from occurring. In addition, the fuel for increasing the temperature of the diesel particulate filter can be reduced, and deterioration of fuel consumption due to forced regeneration can be suppressed.

It is the figure which showed the structure of the exhaust-gas purification system of embodiment which concerns on this invention. It is the figure which showed the flow of the forced regeneration method of the diesel particulate filter of embodiment which concerns on this invention. It is a typical figure showing change of the target temperature of the 1st exhaust gas temperature. It is a typical figure showing change of the target temperature of the 2nd exhaust gas temperature. It is the figure which showed typically the mode of the advance angle of pilot injection and main injection. It is a figure which shows the relationship between predetermined 2nd determination temperature of 2nd exhaust gas temperature with respect to engine speed and load, and predetermined 3rd determination temperature. It is the figure which showed typically the mode of oxidation of nitric oxide (NO) in an oxidation catalyst, and the oxidation of SOOT (C) in a diesel particulate filter. Oxygen (O ₂₎ and oxide and temperature relationship SOOT (C) by nitrogen dioxide (NO ₂₎ is a diagram showing in carbon dioxide (CO ₂₎ concentration.

  Hereinafter, an exhaust gas purification system and a method for forcibly regenerating a diesel particulate filter according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an exhaust gas purification system 1 according to an embodiment of the present invention includes an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 12 in an exhaust passage 11 of an internal combustion engine (diesel engine) 10 in order from the upstream side. The turbocharger 13 includes a turbine 13a, a diesel particulate filter (DPF: Diesel Particulate Filter) 14, a urea supply device 15, and a selective reduction catalyst (SCR: Selective Catalytic Reduction) 16. Further, a compressor 13 b and an intake throttle 18 of the turbocharger 13 are provided in the intake passage 17, and an EGR valve 20 is provided in the EGR passage 19.

  Further, the first exhaust gas temperature sensor 21 is provided between the oxidation catalyst 12 and the turbine 13a, the second exhaust gas temperature sensor 22 is provided between the turbine 13a and the diesel particulate filter 14, and the diesel particulate filter 14 and the selective reduction catalyst 15 are provided. A third exhaust gas temperature sensor 23 is provided between each of these, and these detection signals are input to a control device (not shown) for controlling the operation of the internal combustion engine 10 and the exhaust gas purification system 1.

Then, the control device of the exhaust gas purification system increases nitrogen monoxide (NO) generated in the internal combustion engine 10 at the time of forced regeneration of the diesel particulate filter 14, and this nitrogen monoxide is converted into nitrogen dioxide by the oxidation catalyst 12. It is oxidized to (NO ₂ ), the SOOT (C) accumulated in the diesel particulate filter 14 is oxidized with this nitrogen dioxide, and the nitrogen oxide (NOx) containing nitrogen monoxide generated by the oxidation of this SOOT is selectively reduced. The catalyst 16 is configured to perform control for reduction to nitrogen (N ₂ ).

  More specifically, at the time of forced regeneration of the diesel particulate filter 14, it is configured to perform forced regeneration control including the next exhaust gas temperature increase control, exhaust temperature maintenance control, and the like.

  The EGR valve 20 is closed to stop EGR, the intake throttle 18 is closed, and the excess air ratio is maintained until the first exhaust gas temperature T1 detected by the first exhaust gas temperature sensor 21 becomes equal to or higher than a predetermined first determination temperature T1a. Exhaust gas temperature raising control is performed so that λ is in the range of 1.3 to 1.6.

  When the first exhaust gas temperature T1 becomes equal to or higher than the predetermined first determination temperature T1a, the second exhaust gas temperature T2 detected by the second exhaust gas temperature sensor 22 is equal to or higher than the predetermined second determination temperature T2a and predetermined Exhaust temperature maintenance control for performing post injection by advancing pilot injection and main injection of in-cylinder fuel injection so as to be within the range of the third determination temperature T2b or lower is performed.

  At the same time, in this exhaust temperature maintenance control, the NOx map for calculating the fuel injection timing is used for forced regeneration to increase the NOx generation amount by advancing the timing from the NOx map at the time of normal operation than at the time of normal operation. The urea amount adjustment control is performed to adjust the supply amount of urea from the urea supply device 15 in accordance with the NOx amount generated based on the data of the NOx map for forced regeneration.

  Next, the forced regeneration method of the diesel particulate filter according to the present invention will be described with reference to the flow of FIG. The flow of FIG. 2 is called and executed when it is determined that forced regeneration of the diesel particulate filter 14 is necessary in the upper flow for controlling the internal combustion engine 10 and the exhaust gas purification system 1, and the flow of FIG. When the execution of is completed, the flow returns to the upper flow, and is shown to be called repeatedly during forced regeneration.

  The time when the forced regeneration is necessary is, for example, estimating the amount of PM (particulate matter) deposited on the diesel particulate filter 14 during normal driving operation or idling operation. For example, when the PM calculation cumulative value obtained by accumulating the estimated amount exceeds a predetermined cumulative determination amount, or when the exhaust pressure value exceeds a predetermined exhaust pressure determination value.

  During normal operation in which the diesel particulate filter 14 is not forcibly regenerated, SOOT is collected by the upstream diesel particulate filter 14, and urea is supplied from the urea supply device 15 to the selective catalytic reduction catalyst 16 on the downstream side. NOx in the exhaust gas is purified. During this normal operation, the amount of urea supplied from the urea supply device 15 is adjusted in accordance with the amount of NOx generated based on the data of the NOx map during normal operation to purify NOx.

  Then, if the amount of SOOT accumulated in the diesel particulate filter 14 (PM calculation cumulative value) exceeds a certain prescribed amount (estimated prescribed amount by exhaust pressure, calculation, distance), forced regeneration is required and forced regeneration is performed. The mode is entered and the flow of FIG. 2 is called.

  When it is determined that the forced regeneration is necessary and the flow of FIG. 2 is called, the flow of FIG. 2 starts. In step S11, the EGR valve 20 is closed to increase NOx, and then the EGR is stopped. In order to raise the exhaust gas temperature, the intake throttle 18 is closed, and the exhaust gas temperature raising control for adjusting the excess air ratio λ within the range of 1.3 to 1.6 is performed for a predetermined time (the temperature check interval in step S12). For the relevant time).

  FIG. 3 schematically shows a change in the first exhaust gas temperature T1 during the forced regeneration control, and FIG. 4 schematically shows a change in the second exhaust gas temperature T2. As shown in FIG. 3, the first exhaust gas temperature T1 rises from the point A when the forced regeneration control is entered (actually there is a time delay, so the temperature rise is inclined), and a predetermined first determination temperature T1a. Exhaust temperature raising control is performed so that the above temperature is reached. The first exhaust gas temperature T1 returns to the original value at the point C when the forced regeneration control ends (actually, there is a time delay, so the temperature drop is inclined). Further, at this time, the second exhaust gas temperature T2 rises as the first exhaust gas temperature T1 rises as shown in FIGS. 4A to 4B (in fact, there is a time delay, so the temperature rise is inclined). To do).

  In the next step S12, it is determined whether or not the first exhaust gas temperature T1 detected by the first exhaust gas temperature sensor 21 is equal to or higher than a predetermined first determination temperature T1a. If not (NO), Returning to S11, if it is the above (YES), go to the next step S13. Thus, the exhaust gas temperature raising control in step S11 is performed until the first exhaust gas temperature T1 becomes equal to or higher than the predetermined first determination temperature T1a. The predetermined first determination temperature T1a is set to 200 ° C., for example, although it depends on the type of catalyst of the oxidation catalyst 12.

  In the next step S13, exhaust temperature maintenance control, urea amount adjustment control, and elapsed time counting are performed for a predetermined time (time related to the elapsed time check interval in step S14).

  In this exhaust temperature maintenance control, in order to further generate NOx, as shown in FIG. 5, pilot injection Fp and main injection Fm of in-cylinder fuel injection are advanced. At the same time, the post-injection is performed so that the second exhaust gas temperature T2 detected by the second exhaust gas temperature sensor 22 is in a range not lower than a predetermined second determination temperature T2a and not higher than a predetermined third determination temperature T2b. This post-injection is stopped when the second exhaust gas temperature T2 exceeds a predetermined third determination temperature T2b, and is controlled so that the second exhaust gas temperature T2 is equal to or lower than the predetermined third determination temperature T2b. . The predetermined second determination temperature T2a is set to 300 ° C., for example, and the predetermined third determination temperature T2b is set to 400 ° C., for example.

  Note that, in the post-injection control of the exhaust gas temperature maintenance control, the second target gas temperature T2 is set to a temperature within the range of the predetermined second determination temperature T2a and the predetermined third determination temperature T2b. You may control by feedback control etc. so that it may become T2t. The second target temperature T2t is set to 350 ° C., for example.

  As shown in FIGS. 4B to 4C, the second exhaust gas temperature T2 is in a range from the time point B when the exhaust gas temperature maintenance control is started to a predetermined second determination temperature T2a and a predetermined third determination temperature T2b. The exhaust temperature is maintained and controlled so that the temperature is within the range (actually there is a time delay, so the temperature rises incline), and returns to the original time C when this forced regeneration control ends (there is actually a time delay) The temperature drop is inclined).

  Further, in the urea amount adjustment control, the NOx map for calculating the fuel injection timing is changed from the NOx map at the time of normal operation, and the NOx for forced regeneration that increases the NOx generation amount by advancing the timing from that at the time of normal operation Switching to the map, control is performed to adjust the supply amount of urea from the urea supply device 15 in accordance with the NOx amount generated based on the data of the NOx map for forced regeneration. In counting the elapsed time, the elapsed time t is defined as the time from the point A when the first exhaust gas temperature T1 exceeds the predetermined first determination temperature T1a in step S13.

  In the next step S14, it is determined whether or not the elapsed time t is equal to or longer than the predetermined determination time ta. If not (NO), the process returns to step S13, and if it is (YES), the next step S15. go to. Thereby, the exhaust gas temperature maintenance control in step S13 is performed until the elapsed time t becomes equal to or longer than the predetermined determination time ta. The predetermined determination time ta is a value set in advance by experiments or the like, and corresponds to a time during which SOOT deposited on the diesel particulate filter 14 is oxidized and removed. By this forced regeneration termination method, the SOOT deposited on the diesel particulate filter 14 can be partitioned by combustion. In order to ensure the oxidation of SOOT, the time when the second exhaust gas temperature T2 exceeds the predetermined second determination temperature T2a may be accumulated to be the elapsed time t.

  In step S15, the forced regeneration control is finished. In the end operation of the forced regeneration control, the valve opening of the EGR valve 20 and the intake throttle 18 is returned to the valve opening of the normal operation control, the advance angle of the pilot injection and the main injection is returned, or the post injection is stopped. , PM calculation accumulated value is reset to zero. After completion of this forced regeneration control, the process returns to the upper flow. Note that the normal operation is normal driving operation or idling operation, in an operation state in which the forced regeneration control of the diesel particulate filter 14 is not performed (during non-DPF forced regeneration control), and in the selective reduction catalyst 16. This is an operation state in which forced regeneration control for sulfur poisoning is not performed (during non-SCR sulfur poisoning regeneration control).

  By disposing the oxidation catalyst 12 in front of the turbine 13a by the exhaust gas purification system 1 and the forced regeneration method of the diesel particulate filter, the distance between the exhaust manifold and the oxidation catalyst 12 is shortened, and the temperature decrease amount of the exhaust gas is reduced. Therefore, the temperature of the exhaust gas flowing into the oxidation catalyst 12 can be easily increased to the activation temperature of the oxidation catalyst 12 by closing the intake throttle 18.

  Further, by performing post injection while advancing the injection timings of pilot injection Fp and main injection Fm for in-cylinder fuel injection, a large amount of nitric oxide is generated and nitric oxide is oxidized to nitrogen dioxide by the oxidation catalyst 12. Then, a large amount of nitrogen dioxide is discharged, and the SOOT is at a relatively low temperature within a range not lower than a predetermined second determination temperature T2a and not higher than a predetermined third determination temperature T2b, for example, in a range of 300 ° C to 400 ° C. The diesel particulate filter 14 can be forcibly regenerated by being oxidized and removed. In addition, in order to remove nitrogen oxide containing a large amount of nitric oxide due to oxidation of SOOT or the like, the NOx map during normal operation is switched from the NOx map to the advanced timing, and urea injection adapted to it is performed. . That is, the nitrogen oxides are reduced and removed by the selective catalytic reduction catalyst 16 by urea adjusted to an optimum supply amount from the urea supply device 15 and the exhaust temperature.

  Therefore, since SOOT is oxidized by nitrogen dioxide rather than oxygen, it can be oxidized and removed at a lower temperature, and when the diesel particulate filter 14 is forcibly regenerated, the diesel particulate filter 14 is heated to cause melting or cracking. Can be prevented. In addition, the amount of fuel required to make the diesel particulate filter 14 high is low, and the deterioration of fuel consumption due to forced regeneration can be suppressed.

  According to the exhaust gas purification system and the forced regeneration method of the diesel particulate filter of the present invention, it is possible to prevent the diesel particulate filter from being heated at the time of forced regeneration of the diesel particulate filter to cause melting, cracking, etc. Since deterioration of fuel consumption due to forced regeneration can be suppressed, it can be used as an exhaust gas purification system for an internal combustion engine such as a diesel engine mounted on an automobile and a forced regeneration method for a diesel particulate filter.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system 10 Internal combustion engine 11 Exhaust passage 12 Oxidation catalyst (DOC)
13 Turbocharger 13a Turbine 13b Compressor 14 Diesel particulate filter (DPF)
15 Urea supply device 16 Selective reduction catalyst (SCR)
17 Intake passage 18 Intake throttle 19 EGR passage 20 EGR valve 21 First exhaust gas temperature sensor 22 Second exhaust gas temperature sensor T1 First exhaust gas temperature T1a Predetermined first determination temperature T2 Second exhaust gas temperature T2a Predetermined second Determination temperature T2b Predetermined third determination temperature

Claims (4)

  In an exhaust gas purification system for an internal combustion engine in which an oxidation catalyst, a turbocharger turbine, a diesel particulate filter, a urea supply device, and a selective reduction catalyst are arranged in this order from the upstream side in the exhaust passage of the internal combustion engine. The control device of the purification system increases nitrogen monoxide generated in the internal combustion engine during forced regeneration of the diesel particulate filter, and oxidizes the nitrogen monoxide to nitrogen dioxide with the oxidation catalyst. An exhaust gas purification system configured to oxidize SOOT accumulated in the diesel particulate filter and to control nitrogen oxides generated by the oxidation of the SOOT to nitrogen by the selective reduction catalyst. . A first exhaust gas temperature sensor is provided between the oxidation catalyst and the turbine, and a second exhaust gas temperature sensor is provided between the turbine and the diesel particulate filter. These detection signals are used for the operation of the internal combustion engine and the exhaust gas. It is configured to input to a control device that controls the gas purification system,
In the forced regeneration of the diesel particulate filter, the control device closes the EGR valve to stop EGR, closes the intake throttle, and the first exhaust gas temperature detected by the first exhaust gas temperature sensor is a predetermined value. Exhaust temperature rise control is performed so that the excess air ratio is in the range of 1.3 to 1.6, until the first determination temperature is equal to or higher than the first determination temperature, and the first exhaust gas temperature is equal to or higher than the predetermined first determination temperature. Then, pilot injection of in-cylinder fuel injection is performed so that the second exhaust gas temperature detected by the second exhaust gas temperature sensor is in a range not less than a predetermined second determination temperature and not more than a predetermined third determination temperature. And the exhaust temperature maintenance control for performing post injection by advancing the main injection, and in the exhaust temperature maintenance control, the NOx map for calculating the fuel injection timing is changed to NOx during normal operation. Switch to the NOx map for forced regeneration that increases the NOx generation amount by advancing the timing from the normal operation to correspond to the NOx amount generated based on the data of the NOx map for forced regeneration. The exhaust gas purification system according to claim 1, wherein urea amount adjustment control is performed to adjust a supply amount of urea from the urea supply device.   A diesel particulate filter in an exhaust gas purification system of an internal combustion engine in which an oxidation catalyst, a turbocharger turbine, a diesel particulate filter, a urea supply device, and a selective reduction catalyst are arranged in this order from the upstream side in the exhaust passage of the internal combustion engine. In the forced regeneration method of the above, during the forced regeneration of the diesel particulate filter, the nitrogen monoxide generated in the internal combustion engine is increased, and the nitric oxide is oxidized to nitrogen dioxide by the oxidation catalyst. A method for forcibly regenerating a diesel particulate filter, comprising oxidizing SOOT accumulated in a diesel particulate filter and reducing nitrogen oxide generated by the oxidation of the SOOT to nitrogen by the selective reduction catalyst.   During forced regeneration of the diesel particulate filter, the EGR valve is closed to stop EGR, the intake throttle is closed, and the first exhaust gas temperature between the oxidation catalyst and the turbine is equal to or higher than a predetermined first determination temperature. Until the excess air ratio is within a range of 1.3 to 1.6, and when the first exhaust gas temperature is equal to or higher than the predetermined first determination temperature, the turbine and the The pilot injection and the main injection of in-cylinder fuel injection are advanced so that the second exhaust gas temperature between the diesel particulate filters is in a range not less than a predetermined second determination temperature and not more than a predetermined third determination temperature. In this exhaust temperature maintenance control, a NOx map for calculating the fuel injection timing is displayed in the NOx map during normal operation. Switch to a NOx map for forced regeneration that increases the NOx generation amount by advancing the timing from the normal operation, and corresponds to the NOx amount generated based on the data of the NOx map for forced regeneration. 4. The method for forcibly regenerating a diesel particulate filter according to claim 3, wherein urea amount adjustment control for adjusting a supply amount of urea from the urea supply device is performed.

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