JP2004036552A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To certainly and smoothly regenerate an NOx trap catalyst. <P>SOLUTION: The NOx trap catalyst 13 and fine-grain capturing filter 14 are interposed in an exhaust passage 7 of a diesel engine 1. The NOx trap catalyst 13 traps NOx when exhaust is lean, and discharges and purifies the NOx when the exhaust is rich. When the NOx is deposited and regenerating time comes, an excess air ratio λ of the exhaust is controlled to a rich side, thereby conducting regenerating. When the regenerating time is near and catalyst temperature is low, as regenerating preparation, the excess air ratio λ of the exhaust is made to be small by intake air throttling and the like, thereby raising exhaust gas temperature. At that time, so as to make deterioration in fuel efficiency within a permissible level, the excess air ratio λ is made to be small in a range of λ≥1.3. At the time of regenerating, the catalyst temperature is raised in advance, regeneration by a rich spike is made to be certain and smooth. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine suitable mainly for a diesel engine, and particularly to an exhaust gas purifying apparatus for treating NOx and exhaust particulates.
[0002]
[Prior art]
As an exhaust gas purifying apparatus for an internal combustion engine, for example, a technique described in Japanese Patent No. 2604002 (hereinafter referred to as Conventional Technique 1) or a technique described in Japanese Patent Application Laid-Open No. 2000-192811 (hereinafter referred to as Conventional Technique 2) is used. Are known.
[0003]
The prior art 1 includes a NOx trap catalyst that traps inflowing NOx when the exhaust air-fuel ratio is lean, and releases and purifies the trapped NOx when the exhaust air-fuel ratio is rich. And the exhaust air-fuel ratio is made rich to regenerate the NOx trap catalyst, thereby purifying NOx in the exhaust gas.
[0004]
Further, the prior art 2 deals with a decrease in the function of the NOx trap catalyst due to so-called sulfur poisoning. When the SOx poisoning amount of the NOx trap catalyst exceeds a predetermined amount, the SOx poisoning in the expansion stroke is performed separately from the main injection. By performing post-injection of injecting a small amount of fuel, the exhaust air-fuel ratio is made rich to increase exhaust temperature. After that, when the temperature of the NOx trap catalyst reaches a predetermined temperature required for SOx regeneration, the exhaust air-fuel ratio is stoichiometric (theoretically). (Equivalent to the air-fuel ratio), and the SOx regeneration of the NOx trap catalyst is performed.
[0005]
[Problems to be solved by the invention]
The NOx trap catalysts used in the prior arts 1 and 2 trap NOx when the exhaust air-fuel ratio is lean. However, if the temperature of the NOx trap catalyst is lower than its activation temperature, the NOx trap rate is low. , The NOx purification rate decreases.
[0006]
Further, in the above prior art 1, when the air-fuel ratio of the exhaust gas is made rich and the temperature of the NOx trap catalyst is lower than the activation temperature, the release rate of trapped NOx is low. Again, the NOx purification rate decreases.
[0007]
On the other hand, in the above prior art 2, when SOx regeneration is required and the operation is performed in a situation where the low-speed and low-load operation occupies a high ratio, the exhaust temperature is low and the temperature of the NOx trap catalyst is low. The amount of post-injection required to raise the temperature of the trap catalyst to a predetermined temperature required for SOx regeneration is large, and therefore, the fuel consumption deteriorates greatly with SOx regeneration.
[0008]
That is, in the above-described prior arts 1 and 2, there is a problem that the NOx purification rate of the NOx trap catalyst decreases due to the temperature of the NOx trap catalyst, and the fuel efficiency deteriorates remarkably due to an increase in the amount of fuel for the regeneration operation. was there.
[0009]
[Means for Solving the Problems]
An exhaust gas purifying apparatus for an internal combustion engine according to the present invention is disposed in an exhaust passage of the internal combustion engine and oxidizes or traps exhaust components in the exhaust gas flowing into the exhaust gas purifying means, and the temperature of the exhaust gas purifying means is lower than a predetermined temperature. Sometimes, an excess air ratio control means is provided for controlling the total amount of air flowing into the cylinder to reduce the excess air ratio of the exhaust gas within an allowable level of fuel efficiency. Here, "the total amount of air flowing into the cylinder" is meant to include everything that affects the working gas, such as intake throttle, EGR, and supercharging.
[0010]
By reducing the excess air ratio of the exhaust by controlling the air amount in this manner, the exhaust temperature increases. That is, even if the fuel injection amount is not increased, the temperature of the exhaust gas purifying means can be increased without a decrease in output, and a reduction in the purification rate or trap rate of the exhaust gas purifying means can be prevented.
[0011]
The excess air ratio within the range of the fuel consumption allowable level is approximately λ ≧ 1.3, for example, as described in claim 12. Within this range, extreme deterioration in fuel efficiency is avoided.
[0012]
According to the second aspect of the present invention, the exhaust gas purifying means is disposed in an exhaust passage of the internal combustion engine and traps exhaust components in the exhaust gas flowing into the exhaust gas, and the regeneration of the exhaust gas purifying means is performed based on the amount of exhaust components trapped by the exhaust gas purifying means. And a regeneration timing determining means for determining timing. The excess air ratio control means controls the total amount of air flowing into the cylinder when the exhaust gas purification means is near the regeneration time and the temperature of the exhaust gas purification means is lower than a predetermined temperature, so that the exhaust gas The excess air ratio is controlled to a first target excess air ratio smaller than the normal target excess air ratio according to the operation state, and when the regeneration time comes, the excess air ratio of the exhaust gas is reduced to the target excess air ratio for regeneration. Control to rate.
[0013]
That is, in this case, the control for reducing the excess air ratio of the exhaust to increase the exhaust temperature is performed only when the exhaust gas purifying unit is near the regeneration time.
[0014]
【The invention's effect】
According to the present invention, since the excess air ratio of exhaust gas is reduced by controlling the amount of air when the temperature of the exhaust gas purification means is low, it is possible to raise the temperature of the exhaust gas purification means without increasing the fuel injection amount. As a result, the temperature of the exhaust gas purifying means can be increased while minimizing deterioration of fuel efficiency.
[0015]
Further, if the excess air ratio of the exhaust gas is reduced and the exhaust temperature is increased only when the exhaust gas purification means is near the regeneration time, the excess air ratio of the exhaust gas is reduced. Deterioration of drivability and deterioration of exhaust performance and fuel efficiency due to control can be minimized.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 shows the overall configuration of a diesel engine provided with an exhaust gas purification apparatus according to the present invention. This diesel engine 1 is provided with a so-called common rail type fuel injection device. Fuel pressurized to a predetermined pressure by a high-pressure fuel pump 2 is introduced into a common rail 3 and, via the common rail 3, The fuel is supplied to the fuel injection nozzle 4 of the cylinder. The opening and closing of the fuel injection nozzle 4 is controlled by a control signal from the control unit 10, and the fuel injection amount and the injection timing can be independently controlled for each cylinder.
[0018]
The diesel engine 1 includes a variable nozzle type turbocharger 6, a turbine is disposed in an exhaust passage 7, a compressor is disposed in an intake passage 8, and a compressor downstream of the intake passage 8. , An intercooler 9 is provided. The nozzle opening of the variable nozzle of the turbocharger 6 is controlled by the control unit 10, and the actual opening is detected by a sensor (not shown), and is sent to the control unit 10 as a nozzle opening signal. Has been entered.
[0019]
Further, the diesel engine 1 includes an exhaust gas recirculation device. That is, an EGR passage 11 is provided between the exhaust passage 7 and the intake passage 8, and an EGR valve 12 is interposed here. The opening of the EGR valve 12 is controlled by an EGR valve control signal output from the control unit 10.
[0020]
A NOx trap catalyst 13 carrying a noble metal as a catalyst and having an oxidizing function and a particulate trapping filter (DPF: diesel particulate filter) serving as an exhaust particulate trap are provided on the downstream side of the exhaust passage 7 as the exhaust purifying means of the present invention. 14 are interposed. Both have independent casings, and are arranged in series such that the NOx trap catalyst 13 is on the upstream side. On the outlet side of the particulate filter 14, an exhaust gas temperature sensor 15 for detecting the exhaust gas temperature and thus the temperature of these exhaust gas purifying means, and an air-fuel ratio sensor 16 for measuring the exhaust air-fuel ratio, that is, the excess air ratio of the exhaust gas, are provided. The detection signals are input to the control unit 10. Note that a temperature sensor 15 may be disposed inside the NOx trap catalyst 13 and the particulate filter 14 so as to directly detect the temperature of the filter. Alternatively, a temperature sensor 15 may be arranged upstream of the NOx trap catalyst 13 to estimate the temperatures of the NOx trap catalyst 13 and the particulate filter 14 from the temperature of the exhaust gas flowing into the NOx trap catalyst 13.
[0021]
Further, the diesel engine 1 includes a crank angle sensor 17 for detecting a crank angle serving as a basis of an engine speed, and an accelerator opening sensor 18 for detecting an accelerator opening operated by a driver. The detection signal is also input to the control unit 10.
[0022]
If necessary, an intake throttle valve (not shown) for variably controlling the amount of fresh air introduced is provided in the intake passage 8.
[0023]
When the exhaust air-fuel ratio is lean, that is, when the excess air ratio of the exhaust gas is large, the NOx trap catalyst 13 traps NOx in the inflowing exhaust gas. When the rate is small, it has the characteristic of releasing trapped NOx, and this released NOx is ₂ As can be purified. Forcibly performing the above-described temporary enrichment of the exhaust air-fuel ratio is referred to as a rich spike, and the process of releasing NOx from the NOx trap catalyst 13 by the rich spike is hereinafter referred to as NOx regeneration. It is known that the performance of the NOx trap catalyst 13 gradually decreases due to the accumulation of the sulfur component in the fuel, and it is necessary to forcibly remove the sulfur component at an appropriate time. This process is hereinafter referred to as sulfur poisoning release or SOx regeneration.
[0024]
On the other hand, the exhaust particulates discharged from the diesel engine 1 are basically trapped by the particulate capture filter 14, and are prevented from being discharged to the outside. Part of the exhaust particulates deposited on the particulate capture filter 14 is spontaneously combusted and removed in the course of changes in operating conditions. However, when the exhaust particulates have accumulated to a predetermined level, the exhaust temperature is increased. Perform forced combustion removal. This is hereinafter referred to as DPF regeneration.
[0025]
Next, a flow of control including regeneration of the exhaust gas purification device and the like will be described with reference to flowcharts shown in FIG.
[0026]
FIG. 2 is a main flowchart showing the overall flow of control. In step 1, first, the operating state of the engine is read based on the detection signals of the crank angle sensor 17 and the accelerator opening sensor 18. Next, in step 2, the amount of NOx deposited on the NOx trap catalyst 13 upstream of the particulate filter 14 is calculated. For example, as in the calculation of the NOx adsorption amount described in Japanese Patent No. 2600492, the NOx adsorption amount may be estimated from the integrated value of the engine speed, or the NOx adsorption amount may be calculated every time the vehicle travels a predetermined distance or time. A method of adding may be used.
[0027]
In step 3, the amount of sulfur component (abbreviated as S in the figure) deposited on the NOx trap catalyst 13 upstream of the particulate filter 14 is calculated. Since the method of calculating the sulfur accumulation amount is not the main part of the invention, for example, like the calculation of the NOx absorption amount described in Patent No. It will be guessed from. In the present embodiment, the NOx trap catalyst 13 is arranged upstream of the particulate matter trapping filter 14, but the reverse is not a problem. Another method is to use a NOx catalyst on the particulate filter 14.
[0028]
In step 4, the amount of exhaust particulates (abbreviated as PM in the drawing) deposited on the particulate filter 14 is detected. Since it is difficult to directly detect the amount of accumulated exhaust particulates in the particulate capture filter 14, the accumulated amount of exhaust particulates is predicted by monitoring the exhaust pressure upstream of the particulate capture filter 14. As the amount of accumulated exhaust particles increases, the exhaust pressure naturally increases. Further, the accumulated amount of exhaust particulates may be detected by combining the travel distance from the previous regeneration or the integrated value of the engine speed and the exhaust pressure.
[0029]
In Step 5, it is determined whether the particulate filter 14 is in the DPF regeneration mode, that is, in the DPF regeneration mode. In the case of the DPF regeneration mode in which the DPF regeneration is performed as described later, since the reg1 flag is set, the processing proceeds to the processing after step 101 shown in FIG.
[0030]
In step 6, it is determined whether the NOx trap catalyst 13 is in the sulfur poisoning release mode. In the sulfur poisoning release mode, since the desul flag is set as described later, the process proceeds to the processing after step 201 in FIG.
[0031]
In step 7, it is determined whether or not the rich spike mode for NOx regeneration of the NOx trap catalyst 13 is in operation. In the case of the rich spike mode, since the sp flag is set as described later, the flow proceeds to the processing after step 301 in FIG.
[0032]
In step 8, it is determined whether or not the operation is in the melting prevention mode during DPF regeneration and sulfur poisoning release. In the melting prevention mode, since the rec flag is set as described later, the process proceeds to the processing after step 401 in FIG.
[0033]
In step 9, it is determined whether a request for improving the activity of the NOx trap catalyst 13 has been issued. When there is an activity improvement request, that is, when the prep flag is 1, the process proceeds to step 501 in FIG. 7, and λ (excess air ratio of exhaust gas) control for improving the catalyst activity is performed.
[0034]
In step 10, it is determined whether the amount of the exhaust particulate accumulated on the particulate filter 14 has reached the predetermined amount PM1 and the regeneration time has come. Whether or not the predetermined amount PM1 has been reached is determined from the exhaust pressure of the particulate filter 14 under predetermined operating conditions. That is, the threshold value of the exhaust pressure is read out in accordance with the operating condition in accordance with the characteristic shown in FIG. In the drawings, Ne on the horizontal axis represents the engine speed, and Q on the vertical axis represents the fuel injection amount, that is, the load. Further, a method may be used in which the regeneration time is determined when the travel distance from the previous regeneration exceeds a predetermined distance and the exhaust pressure exceeds a threshold. If it is determined that it is the regeneration time, the DPF regeneration flag reg1 is set to 1 in step 601 in FIG. 8, and the DPF regeneration process shown in FIG. 3 is immediately executed.
[0035]
In step 11, it is determined whether the amount of sulfur deposited on the NOx trap catalyst 13 has reached the predetermined amount S1 and the regeneration time has come. When it is determined that the sulfur poisoning release is necessary because the predetermined amount S1 or more is accumulated, the sulfur poisoning release request flag desul is set to 1 in step 701 in FIG. 9 and the sulfur poisoning release processing in FIG. Immediately.
[0036]
In step 12, it is determined whether the amount of NOx adsorbed on the NOx trap catalyst 13 has reached the predetermined amount NOx2 and the regeneration time has come. When NOx is adsorbed to the predetermined amount NOx2 or more and NOx regeneration is determined to be necessary, the NOx regeneration flag sp is set to 1 in step 801 in FIG. 10 to execute NOx regeneration.
[0037]
Next, at step 13, it is determined whether or not the NOx trap catalyst 13 is approaching the regeneration time. That is, it is determined whether the amount of NOx adsorbed on the NOx trap catalyst 13 has reached the predetermined amount NOx1. This predetermined amount NOx1 is set to a value smaller than the predetermined amount NOx2 corresponding to the regeneration timing in step 12. The amount of NOx adsorbed on the NOx trap catalyst 13 can be estimated in the same manner as in step 2. Alternatively, at a point in time when a predetermined time has elapsed from the previous execution of the regeneration of the NOx trap catalyst 13, only the NOx1 may be adsorbed and it may be determined that the regeneration time is near. According to the method based on this time, it is possible to determine that the reproduction time is near with ease and sufficient accuracy. If it is determined in step 13 that the reproduction time is near, the activation improvement request flag, that is, the prep flag is set to 1 in step 901 in FIG. 11 to enter the reproduction preparation state. As described above, the process proceeds from step 9 to step 501 based on this flag.
[0038]
FIG. 3 shows the flow of the DPF regeneration process. First, in step 101, it is determined whether or not the exhaust particulates deposited on the particulate capture filter 14 have reached a temperature T2 (for example, 600 ° C.) required for combustion. If the temperature T2 has not been reached, the routine proceeds to step 102, where the excess air ratio λ of the exhaust gas is controlled to a target λ1 (this is set to approximately 1 to rich). Here, the target λ1 is controlled by the above-described intake throttle by the intake throttle valve, EGR (exhaust gas recirculation), and post injection. As a result, the exhaust temperature can be increased.
[0039]
On the other hand, if the temperature has reached the predetermined temperature T2, the process proceeds to step 103. In this step 103, since the temperature of the particulate trap filter 14 is at a temperature at which the exhaust particulates can be burned, the excess air ratio λ of the exhaust is controlled in accordance with the deposition amount considered to be deposited. Here, the target λ2 is controlled using the intake throttle or EGR. Here, the target excess air ratio λ2 is smaller than the target excess air ratio λ1, and is set as an excess air ratio that can secure an oxygen concentration necessary for burning the exhaust particulates of the particulate capture filter 14. More specifically, as shown in FIG. 18, the target excess air ratio λ2 is such that, as shown in FIG. 18, the smaller the amount of accumulated exhaust particles (PM), the larger the target excess air ratio λ2 becomes. Set by characteristics. Since the actual excess air ratio λ of the exhaust gas is detected by the air-fuel ratio sensor 16 downstream of the particulate filter 14, the intake throttle and the supercharging pressure are controlled so as to match the target value λ2. To λ2.
[0040]
Then, in step 104, it is determined whether or not the reference time tdpfreg1 has elapsed since the target excess air ratio was set to λ2. After a predetermined reference time has elapsed, the exhaust particulates deposited on the particulate capture filter 14 are reliably burned and removed.
[0041]
In step 105, the reg1 flag is set to 0 since the reproduction mode has ended. In step 106, the exhaust mode is ended, but if the excess air ratio λ of the exhaust gas is suddenly increased when the unburned residue of the exhaust particulates is present in the particulate capture filter 14, the exhaust particulates burn at once in the particulate capture filter 14. Since there is a possibility of melting, the rec flag is set to 1 to enter the melting prevention mode.
[0042]
FIG. 4 shows a process in the sulfur poisoning release mode. First, in step 201, it is determined whether or not the sulfur component (SOx) deposited on the NOx trap catalyst 13 has reached the temperature T4 required for combustion. If the temperature has not reached T4, the routine proceeds to step 209, where the excess air ratio λ of the exhaust gas is controlled to the target excess air ratio λ3 (this is set to approximately 1 to rich). Here, the target λ3 is controlled by the above-described intake throttle by the intake throttle valve, EGR (exhaust gas recirculation), and post injection. As a result, the exhaust temperature can be increased.
[0043]
On the other hand, if the temperature has reached the predetermined temperature T4, the process proceeds to step 202. Here, for example, when the Ba-based NOx trap catalyst 13 is used, in order to release sulfur poisoning, it is necessary to set the temperature to 600 ° C. or more in a rich to stoichiometric atmosphere. Set to 600 ° C.
[0044]
In step 202, since the temperature of the NOx trap catalyst 13 has reached the predetermined temperature T4, the excess air ratio λ of the exhaust gas is controlled to λ4 corresponding to the stoichiometric air-fuel ratio (stoichiometric). Specifically, the air amount is suppressed so that the target intake air amount at which λ = 1 shown in FIG. 14 is reached, and the excess air ratio λ of the exhaust reaches the target λ4. If the actual excess air ratio λ detected by the air-fuel ratio sensor 16 downstream of the particulate filter 14 deviates from the target λ4, the exhaust λ is adjusted using the intake throttle or EGR.
[0045]
In step 203, it is determined whether a predetermined time tdesul has elapsed since the target excess air ratio was set to λ4. If the predetermined time has elapsed, it is considered that sulfur has been sufficiently burned, and the process proceeds to step 204 and subsequent steps. In step 204, since the sulfur poisoning release has been completed, the operation with the target set to λ4, that is, the stoichiometric operation is released. In step 205, although the sulfur poisoning release mode has ended, if the exhaust air excess ratio λ suddenly increases when the exhaust particulates are deposited on the particulate capture filter 14 under such high temperature conditions, the particulate capture filter At 14, the rec flag is set to 1 in order to enter the erosion prevention mode since the exhaust fine particles may be burned at once and may be melted. In step 206, since the sulfur poisoning release mode has been completed, the reg4 flag is set to 0. In step 207, since sulfur poisoning has been released, the amount of sulfur accumulated in the catalyst is reset to 0. In step 208, the NOx regeneration flag sp is set to 0. This is because when the above-mentioned sulfur poisoning release is performed, NOx regeneration is simultaneously performed by exposing the catalyst to exhaust gas corresponding to λ = 1 for a long time. In other words, if a request for NOx regeneration has been issued, the sulfur poisoning is released and the NOx regeneration is also performed at the same time.
[0046]
Next, the flowchart of FIG. 5 shows the processing of the rich spike. First, in step 301, control is performed to a predetermined excess air ratio λ (the target λ is set to the rich side) for performing a rich spike. FIG. 16 shows characteristics of a target intake air amount for the rich spike operation, and the intake throttle valve, the supercharger 6, and the EGR are controlled so as to achieve the target intake air amount.
[0047]
In step 302, it is determined whether or not such a rich condition has continued for a predetermined time tspike. Then, in step 303, the rich operation is canceled and the flag sp is set to 0 to terminate the rich spike mode. In step 304, the NOx accumulation amount on the catalyst is reset to 0, and the prep flag is also released.
[0048]
The flowchart in FIG. 6 shows the processing in the erosion prevention mode. In step 401, the temperature of the particulate filter 14 is detected. Subsequently, in step 402, since the temperature of the particulate trap filter 14 is very high immediately after the regeneration or immediately after the high-load operation, the excess air in the exhaust gas is set so that the unburned or deposited exhaust particulates are burnt at once and are not damaged. The rate λ is controlled to a predetermined value, for example, λ ≦ 1.4. Specifically, the amount of air flowing into the cylinder is controlled to a target intake air amount having characteristics as shown in FIG. 15, and feedback control is performed based on the output of the air-fuel ratio sensor 16.
[0049]
In step 403, it is determined whether the temperature of the particulate filter 14 has fallen below a predetermined temperature T3. This temperature T3 corresponds to a temperature at which rapid oxidation of the exhaust particulates does not start. If the temperature T3 is lower than this temperature T3, it is possible to avoid erosion of the particulate capture filter 14 even if the oxygen concentration is equal to that of the atmosphere. Become. Accordingly, the process proceeds to step 404, where the λ control in step 402 is terminated, and in step 405, the rec flag is set to 0.
[0050]
Next, FIG. 7 shows an exhaust temperature raising process in a regeneration preparation state, which is a main part of the present invention. In step 501, it is determined whether the catalyst bed temperature of the NOx trap catalyst 13 is higher than T5, which is the activation temperature of the catalyst. In this case, the activity of the catalyst can be determined from the catalyst outlet temperature detected by the temperature sensor 15, and as shown in FIG. 17, the activity of the catalyst is determined from the operating conditions when the regeneration preparation state is entered. You can also. That is, the bed temperature is lower than the activation temperature T5 in the low speed / low load region shown in FIG. If it is determined that the temperature is lower than the temperature T5, the process proceeds to step 502, where the excess air ratio λ of the exhaust gas is controlled to the target excess air ratio λ5 in order to increase the exhaust temperature. FIG. 12 shows the relationship between the excess air ratio λ of the exhaust gas and the exhaust gas temperature and the fuel efficiency. As shown in FIG. Can be heated. Here, particularly, the fuel efficiency deterioration is small until the excess air ratio λ of the exhaust is about λ = 1.3, and is within the allowable level. As shown in the figure, when the excess air ratio λ is further reduced, the fuel efficiency sharply deteriorates. Therefore, when the temperature is lower than the temperature T5, that is, when the catalyst is not activated, the excess air ratio λ of the exhaust gas is controlled to be small within a range of λ ≧ 1.3.
[0051]
The control of the excess air ratio λ of the exhaust gas is performed by controlling the intake throttle, the EGR, and the supercharging pressure. At this time, the EGR ratio is not changed so as to minimize the specific heat of the intake gas flowing into the cylinder. By reducing the intake volume of fresh air with the intake throttle, it is possible to maintain a high exhaust gas temperature
As described above, in the above-described embodiment, when the NOx accumulation amount in the NOx trap catalyst 13 is equal to or more than the predetermined amount NOx1 close to the regeneration timing, the regeneration preparation state is established, and by controlling the excess air ratio λ of the exhaust gas, the operation conditions are improved. Regardless, the NOx trap catalyst 13 is maintained at the temperature T5 or higher. Therefore, when the rich spike mode is reached after the regeneration time is reached, NOx regeneration of the NOx trap catalyst 13 by the rich spike is performed smoothly, and it is possible to avoid deterioration in drivability due to long term enrichment. it can.
[0052]
In the above embodiment, the exhaust temperature raising control in steps 501 and 502 is performed only when the NOx regeneration is near, but may be performed when the DPF regeneration or the SOx regeneration is near. Further, regardless of whether the regeneration is near or not, the regeneration may be always performed when the catalyst is not activated.
[0053]
Further, as in the above embodiment, the exhaust temperature raising control of the present invention may be performed not only when the temperature of the NOx trap catalyst 13 is not active but also when the catalyst is active. it can. That is, the temperature required for releasing sulfur poisoning is as high as about 600 ° C. as described above, and therefore, the temperature is increased by performing post-injection. At this time, even if the temperature of the NOx trap catalyst 13 is in the active region, if the difference from the temperature required for SOx regeneration is large, the required post-injection amount becomes large, and the fuel consumption deteriorates. Therefore, even if the NOx trap catalyst 13 is active, if the regeneration time of SOx regeneration is near and the temperature of the NOx trap catalyst 13 is considerably lower than the temperature required for SOx regeneration, the exhaust temperature increase according to the present invention is performed. By performing the temperature control, the temperature of the NOx trap catalyst 13 can be raised in advance before the SOx regeneration, and deterioration of fuel efficiency due to post injection can be suppressed to a minimum.
[0054]
This can also be applied to DPF regeneration of the particulate filter 14, which requires a large temperature rise for regeneration. That is, when the regeneration time of DPF regeneration is near and the difference between the temperature of the particulate filter 14 and the temperature required for DPF regeneration (eg, 600 ° C.) is large, the exhaust temperature increase control of the present invention is performed. Before the DPF regeneration, the temperature of the particulate capture filter 14 can be raised in advance, and the deterioration of fuel efficiency due to post injection is minimized.
[0055]
For example, when the present invention is applied to the SOx regeneration of the NOx trap catalyst 13, when the regeneration time of the SOx regeneration is near and the temperature of the NOx trap catalyst 13 is lower than a predetermined temperature (an appropriate temperature lower than 600 ° C., for example, a catalyst activation temperature) Then, the excess air ratio λ of the exhaust gas is controlled to λ5 corresponding to the first target excess air ratio, and the regeneration start temperature (600 ° C.) at which the temperature of the NOx trap catalyst 13 is set to the predetermined temperature or more at the regeneration time. If it is lower, the excess air ratio λ of the exhaust gas is controlled to λ3 corresponding to the second target excess air ratio smaller than λ5, which is the above first target excess air ratio, and the temperature of the NOx trap catalyst 13 is reached at the time of regeneration. Is higher than the regeneration start temperature (600 ° C.), the excess air ratio λ of the exhaust gas can be controlled to λ4, which is the target excess air ratio for regeneration.
[0056]
Further, in the above embodiment, the NOx trap catalyst 13 itself has an oxidation catalyst function, but an oxidation catalyst may be arranged upstream of the NOx trap catalyst 13 separately from the NOx trap catalyst 13. By providing the NOx trap catalyst 13 itself or an oxidation catalyst upstream thereof, unburned HC and CO in the exhaust gas are oxidized by the oxidation catalyst, and the exhaust gas temperature can be increased.
[Brief description of the drawings]
FIG. 1 is a configuration explanatory view of an entire diesel engine provided with an exhaust gas purification device according to the present invention.
FIG. 2 is a main flowchart showing the flow of control in the embodiment.
FIG. 3 is a flowchart showing a DPF regeneration routine.
FIG. 4 is a flowchart showing a routine for releasing sulfur poisoning.
FIG. 5 is a flowchart illustrating a NOx regeneration routine.
FIG. 6 is a flowchart showing a routine for preventing erosion.
FIG. 7 is a flowchart showing a temperature raising routine for preparation for regeneration.
FIG. 8 is a flowchart showing a processing routine of a DPF regeneration flag.
FIG. 9 is a flowchart showing a processing routine for a sulfur poisoning release request flag.
FIG. 10 is a flowchart showing a processing routine of a NOx regeneration flag.
FIG. 11 is a flowchart showing a processing routine of an activity improvement request flag.
FIG. 12 is a characteristic diagram showing a relationship between an excess air ratio λ of exhaust gas, exhaust gas temperature, and fuel efficiency.
FIG. 13 is a characteristic diagram showing characteristics of an exhaust pressure threshold for DPF regeneration.
FIG. 14 is a characteristic diagram of a target intake air amount required for operation at λ = 1.
FIG. 15 is a characteristic diagram of a target intake air amount in the melting prevention mode.
FIG. 16 is a characteristic diagram of a target intake air amount during a rich spike.
FIG. 17 is a characteristic diagram showing an operation region in which exhaust temperature raising (activation assist) control is required.
FIG. 18 is a characteristic diagram showing a relationship between an exhaust particulate accumulation amount and an excess air ratio λ of exhaust during regeneration.
[Explanation of symbols]
1. Diesel engine
10 ... Control unit
13. NOx trap catalyst
14 ... Particle trapping filter
15 ... Temperature sensor
16 ... Air-fuel ratio sensor

Claims (12)

Exhaust purification means disposed in an exhaust passage of the internal combustion engine, for oxidizing purification or trapping exhaust components in the inflowing exhaust gas,
When the temperature of the exhaust gas purifying means is lower than a predetermined temperature, an excess air rate controlling means for controlling the total amount of air flowing into the cylinder to reduce the excess air rate of the exhaust gas within an allowable level of fuel efficiency. When,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: A regeneration timing determination unit configured to determine a regeneration timing of the exhaust purification unit based on an amount of the exhaust component trapped by the exhaust purification unit;
The excess air ratio control means reduces the excess air rate of exhaust gas when the regeneration time of the exhaust gas purification means is near and the temperature of the exhaust gas purification means is lower than a predetermined temperature. Item 2. An exhaust gas purification device for an internal combustion engine according to item 1. Exhaust purifying means disposed in an exhaust passage of the internal combustion engine and trapping exhaust components in the inflowing exhaust gas;
Regeneration time determination means for determining a regeneration time of the exhaust gas purification means based on an amount of exhaust components trapped by the exhaust gas purification means;
When the regeneration time of the exhaust gas purifying means is near and the temperature of the exhaust gas purifying means is lower than a predetermined temperature, by controlling the total amount of air flowing into the cylinder, the excess air ratio of the exhaust gas is changed according to the operating state. Excess air ratio control means for controlling the first excess air ratio smaller than the normal target excess air ratio and controlling the excess air ratio of the exhaust to the target excess air ratio for regeneration when the regeneration time comes. When,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: The excess air rate control means controls the excess air rate of the exhaust to the first target excess air rate when the regeneration time of the exhaust gas purification means is near and the temperature of the exhaust gas purification means is lower than a predetermined temperature. When the temperature of the exhaust gas purifying means is lower than the regeneration start temperature which is set to be equal to or higher than the predetermined temperature at the time of the regeneration, the excess air ratio of the exhaust gas is reduced to a second target air excess smaller than the first target excess air ratio. And controlling the excess air rate of the exhaust gas to the target excess air rate for regeneration when the temperature of the exhaust gas purifying means is higher than the regeneration start temperature at the regeneration time. Item 4. An exhaust gas purification device for an internal combustion engine according to item 3. 5. The exhaust gas purifier according to claim 2, wherein when the amount of the exhaust gas component trapped by the exhaust gas purifier reaches a predetermined amount, the regeneration time judging means considers that the exhaust gas purifier has a near regeneration time. An exhaust purification device for an internal combustion engine according to claim 1. The regeneration timing judging means, when a predetermined time has elapsed since the end of the regeneration of the exhaust purification means, considers that the regeneration timing of the exhaust purification means is near. Exhaust purification device for internal combustion engine. 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said predetermined temperature is an activation temperature of said exhaust gas purifying means. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the predetermined temperature is a regeneration temperature when the exhaust gas purification means needs to be regenerated. The exhaust gas purifying means traps NOx in the inflowing exhaust gas when the excess air ratio of the exhaust gas is large, and releases and purifies the trapped NOx when the excess air ratio of the exhaust gas is small. And at least one of an exhaust particulate trap for trapping particulates,
The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein the regeneration time determination means determines the regeneration time according to the amount of NOx or exhaust particulate trapped by the exhaust gas purification means. . The excess air ratio control means includes an intake throttle valve arranged in an intake passage of the internal combustion engine and capable of adjusting the amount of air flowing into the cylinder, and controlling the amount of air flowing into the cylinder by the intake throttle valve. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 9, wherein The exhaust gas purifying means includes a NOx trap catalyst that traps NOx in the inflowing exhaust gas when the excess air ratio of the exhaust gas is large, and releases and purifies the trapped NOx when the excess air ratio of the exhaust gas is small,
The exhaust gas purification apparatus according to any one of claims 1 to 10, wherein the NOx trap catalyst has an oxidation catalyst function, or a catalyst having an oxidation function is arranged upstream of the NOx trap catalyst. 2. The exhaust gas purifying apparatus according to claim 1, wherein the excess air ratio within the range of the allowable level of the fuel efficiency is approximately λ ≧ 1.3.

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