JP3870673B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for purifying exhaust gas discharged from an internal combustion engine, and more particularly, to nitrogen oxide (NO) in lean burn exhaust gas containing excessive oxygen. _x ) And particulates (exhaust particulates, particularly soot; hereinafter referred to as PM).
[0002]
[Prior art]
Diesel internal combustion engines that perform compression ignition have the advantage of low CO2 emissions, while NO. _x Reducing PM, which is in a trade-off relationship, is a major issue. Therefore, a diesel particulate filter (hereinafter referred to as DPF) that collects PM in the exhaust is disposed in the exhaust passage, and an oxidation catalyst is disposed upstream of the DPF. (Nitric oxide) is oxidized to NO ₂ (Nitrogen dioxide) is produced, and this produced highly oxidizing NO ₂ Thus, the DPF is regenerated by burning and removing the PM collected in the DPF (see JP-A-8-303227).
[0003]
[Problems to be solved by the invention]
When such a DPF, particularly a candle-type DPF made of ceramic fiber, is used as a filter-collection type DPF, generally, the amount of accumulated PM and the PM purification rate of the DPF are shown in FIG. The relationship is as shown. That is, if the amount of accumulated PM is too much or too little, the PM purification rate (PM collection efficiency) is lowered, and the desired PM purification performance cannot be obtained. In other words, the filtration and collection type filter has a characteristic that when the PM accumulation amount is accumulated to some extent, the area through which the exhaust can pass becomes smaller and the collection efficiency is improved.
[0004]
The present invention has been made by paying attention to the characteristics peculiar to such a particulate filter (particularly the filtration collection type), and is a novel internal combustion engine capable of effectively obtaining a desired PM collection performance. One object is to provide an exhaust purification device.
[0005]
[Means for Solving the Problems]
Accordingly, an invention according to claim 1 is an exhaust purification device disposed in an exhaust passage of an internal combustion engine, wherein NO in the engine exhaust is NO. ₂ An oxidation catalyst having a function of oxidizing the particulate matter, a particulate filter provided downstream of the oxidation catalyst for collecting particulates in the engine exhaust, and a deposit amount for detecting the particulate deposit amount deposited on the particulate filter In order to adjust the particulate matter deposition amount with the detection means, the particulates are NO in the particulate filter. ₂ Has combustion speed control means to control the combustion speed The combustion rate control means deposits the particulate when the particulate accumulation amount is equal to or lower than the lower limit value and the particulate purification rate changing according to the particulate deposition amount is less than the target purification rate. Perform particulate deposition operation It is characterized by that.
[0006]
That is, since the collection efficiency of the particulate filter (DPF) varies depending on the particulate (PM) deposition amount, in this invention, in order to stably obtain the desired PM collection efficiency, the PM deposition amount is directly or This is indirectly detected from the exhaust pressure at the inlet of the DPF, etc., and this PM accumulation amount is adjusted within a predetermined range.
[0007]
In particular, as in the invention according to claim 2, when the particulate filter is a filtration and collection type filter, typically, as shown in FIG. 2, the collection characteristic of the particulate filter depends on the PM accumulation amount. Change greatly. Therefore, the desired PM collection performance can be stably obtained by adjusting the PM deposition amount to a predetermined range (for example, a predetermined lower limit value ACC or more).
[0008]
Preferably, as in the invention according to claim 3, the combustion speed control means is configured to increase the particulate deposition amount when the NO flowing into the particulate filter is increased. ₂ And the ratio of particulates to NO ₂ When reducing / PM and reducing the amount of particulate deposits, the ratio NO ₂ Increase / PM.
[0009]
That is, the PM deposited on the particulate filter is the NO in the exhaust gas. ₂ Because it is possible to remove oxidation by using NO, inflowing NO ₂ If the ratio of PM to PM is greater than or equal to a predetermined value, NO ₂ PM oxidation (combustion) due to progresses, and the amount of PM deposited on the DPF decreases. Therefore, when not much PM is deposited on the DPF and the amount of deposited PM should be increased, the above ratio NO ₂ Reduce / PM. Conversely, when PM accumulates excessively on the DPF and causes excessive increase of exhaust pressure and deterioration of fuel consumption due to this, the above ratio NO ₂ / PM is increased, and PM deposited on DPF is changed to NO. ₂ Is removed by continuous combustion using an oxidizing agent. Thus, the above-mentioned ratio NO according to the PM deposition amount ₂ By controlling / PM, it is possible to stably obtain desired PM collection performance.
[0010]
The invention according to claim 4 provides the ratio NO. ₂ In order to adjust / PM, the exhaust gas temperature flowing into the oxidation catalyst is controlled.
[0011]
That is, NO → NO in the oxidation catalyst ₂ Since the oxidation activation reaction of the catalyst greatly depends on the exhaust gas temperature, the NO gas flowing into the DPF can be controlled by controlling the exhaust gas temperature at the catalyst inlet. ₂ / PM ratio can be controlled effectively. That is, by controlling the exhaust gas temperature flowing into the oxidation catalyst according to the amount of PM deposited on the DPF, it is possible to effectively obtain a desired PM collection performance.
[0012]
NO → NO with respect to the exhaust temperature at the inlet of the oxidation catalyst ₂ As shown in FIG. 9, the conversion rate typically exhibits a characteristic having a peak at a predetermined temperature T1. Therefore, the above ratio NO ₂ As shown in FIG. 10, / PM also shows a characteristic having the temperature T1 as a peak. For this reason, the predetermined temperature range T2 to T3 based on the temperature T1 is a continuous combustion formation temperature range in which PM deposition is reduced by continuous combustion. On the contrary, the range out of T2 to T3 is an operation region in which the PM deposition rate is faster than the continuous combustion rate and the PM deposition amount increases.
[0013]
Therefore, preferably, as in the invention according to claim 5, the exhaust gas flowing into the oxidation catalyst is in an operating state in which the particulate deposition amount is lower than a predetermined lower limit value and the particulate deposition amount should be increased. The temperature is the above ratio NO ₂ When / PM is higher than the maximum temperature (T1), the exhaust temperature is increased (than T3). On the other hand, as in the invention according to claim 6, the particulate deposition amount is lower than a predetermined lower limit value, and the exhaust temperature flowing into the oxidation catalyst is in an operating state in which the particulate deposition amount should be increased. , The above ratio NO ₂ When / PM is lower than the maximum temperature (T1), the exhaust temperature is lowered (than T2) by using a technique such as increasing the engine intake air amount.
[0014]
Preferably, as in the invention according to claim 9, the exhaust gas flowing into the oxidation catalyst is in an operating state in which the particulate accumulation amount is lower than a predetermined lower limit value and the particulate accumulation amount should be increased. When the temperature is higher than the temperature (T1) at which the oxidation catalyst is most activated, the exhaust temperature flowing into the oxidation catalyst is increased (over T3), while the particulate accumulation amount is lower than a predetermined lower limit value. If the exhaust gas temperature is low and the exhaust gas temperature flowing into the oxidation catalyst is lower than the temperature (T1) at which the oxidation catalyst is most activated, the flow rate will flow into the oxidation catalyst. Reduce the exhaust temperature (than T2).
[0015]
As described above, when the exhaust temperature is higher than the predetermined temperature (T1), the exhaust temperature is raised, while when the exhaust temperature is lower, the exhaust temperature is lowered. It can be quickly changed to a certain temperature range.
[0016]
According to a seventh aspect of the present invention, there is provided an exhaust gas recirculation passage for recirculating exhaust gas to a combustion chamber of an internal combustion engine, and an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage for adjusting an exhaust gas recirculation rate. The exhaust gas recirculation rate is controlled in order to adjust the accumulation amount.
[0017]
In other words, if the amount of NO discharged from the engine is controlled, NO flowing into the DPF ₂ / PM ratio can be controlled. For example, when the PM accumulation amount should be increased, NO exhausted from the engine by increasing the exhaust gas recirculation rate _x NO inflow into DPF ₂ / PM ratio should be lowered. As described above, by controlling the exhaust gas recirculation rate according to the PM accumulation amount, it is possible to obtain a desired PM collection performance.
[0018]
The invention according to claim 8 is characterized in that an exhaust gas temperature flowing into the particulate filter is controlled in order to adjust the particulate deposition amount.
[0019]
As a technique for adjusting the exhaust gas temperature flowing into the oxidation catalyst or the particulate filter in this way, for example, in the invention according to claim 10, after the main fuel is injected, the post-injection is performed to inject the sub fuel, and In the invention, the engine intake amount or the engine exhaust amount is controlled using a throttle valve. In the invention according to claim 12, a supercharger capable of adjusting the supercharging pressure by changing the supercharging efficiency is provided. The supercharging pressure by the machine is controlled.
[0020]
【The invention's effect】
As described above, according to the present invention, the particulate collection performance of the particulate filter is maintained at a high level by detecting the particulate accumulation amount and appropriately adjusting the particulate accumulation amount. be able to.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which an exhaust emission control device of the present invention is applied to an exhaust passage 5 of an in-line four-cylinder diesel internal combustion engine 1 will be described in detail with reference to the drawings.
[0022]
As shown in FIG. 1, the internal combustion engine 1 includes a so-called common rail type fuel injection device 2, and an intake manifold 3 and an exhaust manifold 4 are arranged one above the other so as to overlap each other. An exhaust catalyst (exhaust passage) 5 connected to the exhaust manifold 4 is provided with an oxidation catalyst 7 and a diesel particulate filter (DPF) 9 described later in order from the upstream side. An exhaust temperature sensor 6 for detecting the exhaust temperature flowing into the oxidation catalyst 7 is provided at the inlet of the oxidation catalyst 7, and an exhaust pressure sensor 8 for detecting the exhaust pressure (back pressure) of the DPF 9 is provided at the inlet of the DPF 9. It has been.
[0023]
Further, an exhaust gas recirculation passage 10 for recirculating a part of the exhaust gas from the exhaust pipe 5 to the intake manifold 3 is provided. For example, an electronically controlled exhaust gas recirculation control valve 11 for adjusting an exhaust gas recirculation rate is provided in the exhaust gas recirculation passage 10. Is intervening. Furthermore, a variable nozzle type turbocharger 13 is provided which preloads the intake air in the intake pipe 12 using exhaust gas. The turbocharger 13 can adjust the supercharging pressure by changing the supercharging efficiency, and a water-cooled or air-cooled intercooler 14 is provided on the downstream side of the turbocharger 13. .
[0024]
The control unit (engine control unit) 15 is a known computer system that includes a memory, a CPU, and the like for storing and executing various arithmetic processes, and in addition to the sensors 6 and 8 described above, an engine that detects the engine speed Ne. Various sensors for detecting the engine operating state such as the rotational speed sensor 16 and the accelerator opening sensor 17 for detecting the accelerator opening L are connected, and various engine controls are performed based on detection signals from these sensors. Do. That is, the control unit 15 calculates the fuel injection timing and the injection amount based on the accelerator opening L, the engine speed Ne, and the like, and controls the drive of the fuel injection device 2 based on the calculation results. The exhaust gas recirculation control valve 11 and the turbocharger 13 are driven and controlled in accordance with the operating state to control the exhaust gas recirculation rate (EGR rate) and the supercharging pressure.
[0025]
The oxidation catalyst 7 is equipped with a reducing component (HC) adsorption catalyst, which oxidizes NO in the engine exhaust to produce NO. ₂ And at the same time has the ability to adsorb HC. Specifically, for example, activated alumina in which a noble metal component is supported on a monolithic carrier made of cordierite, and zeolite as an HC adsorption catalyst having an action of adsorbing and desorbing HC in the exhaust by changing the temperature of the catalyst or exhaust The ingredients are mixed and coated. Each may be coated in layers.
[0026]
Pt, Pd, etc. are known as the above-mentioned noble metal components, and ZSM-5, β, USY, and mordenite types are known as the zeolite components, and these are preferably used alone or in combination. Pt supports zeolite (for example, ZSM-5) with relatively weak HC adsorption power as a zeolite component, and HC is desorbed at a temperature at which the oxidation activity of the oxidation catalyst becomes strong, and is not oxidized and burned by the catalyst. It is desirable to do so. This is to prevent a decrease in HC concentration fluctuation accompanying oxidative combustion of HC.
[0027]
With such a configuration, HC, which is an unburned component in the exhaust, is adsorbed at a low exhaust temperature, so that the reduction rate of HC at a low exhaust temperature is improved. In addition, when the temperature rises, HC and CO, which are unburned components in the exhaust, can be oxidized and purified with high efficiency, and the NO component is oxidized to NO. ₂ Generate ingredients.
[0028]
The DPF 9 collects the PM in the exhaust, and the collected PM is NO in the exhaust. ₂ Is a filter for collecting and treating PM to be reacted with a hollow cylinder having a closed end and a depth filtration type filter. Specifically, it is composed of a core member having a bottomed cylindrical shape with a large number of holes in the peripheral surface portion, and an outer layer portion formed by winding a number of layers of ceramic fibers around the core member. The bottom end is closed so that the end is on the downstream side, and the exhaust is introduced from the other open end of the core member. Accordingly, the exhaust gas flows from the inner layer portion to the outer layer portion in the radial direction outer peripheral side, and PM in the exhaust gas is collected by the ceramic fiber. The DPF 9 is not limited to this type, and a conventionally known knit fiber, ceramic foam type, or a combination thereof may be used.
[0029]
The characteristics of the ceramic fiber used in the DPF 9 will be described. One characteristic of the ceramic fiber is that the surface area of the fiber used per unit volume is very large (about 10,000 cm 2 / cc). This is overwhelmingly larger than the surface area per unit volume (about 20-30 cm 2 / cc) of a cordierite monolith support used for a general catalyst support, for example, a large surface area can be obtained with a small volume. Therefore, it is a suitable material for catalysis.
[0030]
FIG. 5 is a flowchart showing the flow of control according to the first embodiment of the present invention. This routine is repeatedly executed by the control unit 15 at predetermined intervals, for example.
[0031]
First, in S (step) 1, the engine operating state is read. Specifically, the engine speed Ne is read from the engine speed sensor 16, and the accelerator opening degree L is read from the accelerator opening sensor 17. In S2, the fuel injection amount Q is calculated based on the engine speed Ne, the accelerator opening L, and the like.
[0032]
In S3, the amount of PM deposited on the DPF 9 is detected. Since it is difficult to directly detect the PM accumulation amount on the DPF 9, in this embodiment, the PM accumulation amount is predicted by monitoring the exhaust pressure at the inlet of the DPF 9 by the exhaust pressure sensor 8. Instead, the exhaust pressure value may be predicted based on the intake air amount. The exhaust pressure varies depending on factors other than the PM accumulation amount. For example, the exhaust pressure increases as the exhaust gas amount increases. 6 and 7 are maps for estimating the PM accumulation amount. As shown in FIG. 6, the exhaust pressure corresponding to the upper limit value ACC2 and the lower limit value ACC1 of the PM accumulation amount depends on the engine speed Ne and the fuel injection amount Q. Will change accordingly.
[0033]
In S4, the forced regeneration operation state flag reg. Determine if 1 is standing. When the forced regeneration flag is 1, the process proceeds to S15 and the forced regeneration operation described later is continued. In S5, the PM accumulation operation state flag reg. Determine whether 2 is standing. When the PM accumulation operation state flag is 1, the process proceeds to S10, and the PM accumulation operation described later is continued.
[0034]
In S6, it is determined whether the amount of PM deposited on the DPF 9 is less than a predetermined upper limit ACC2. Actually, the exhaust pressure upper limit value corresponding to the upper limit value ACC2 is calculated by referring to the map shown in FIG. 6 based on the current engine speed Ne and the fuel injection amount Q, and the current exhaust pressure value Pf is calculated. It is determined whether it is less than the exhaust pressure upper limit.
[0035]
When it is determined that the PM accumulation amount is less than the upper limit value ACC2, the process proceeds to S7, and it is determined whether the PM accumulation amount of the DPF 9 is larger than a predetermined lower limit value ACC1. Actually, the exhaust pressure lower limit value corresponding to the lower limit value ACC1 is determined by referring to the map shown in FIG. 7 based on the current engine speed Ne and the fuel injection amount Q, and the current exhaust pressure value Pf is determined as follows. It is determined whether the exhaust pressure lower limit is exceeded.
[0036]
Here, when the DPF that captures the fine particles is a depth filtration method as in the present embodiment, the PM purification rate changes according to the amount of PM deposited on the DPF, as shown in FIG. In general, the PM purification rate tends to increase as the amount of accumulated PM increases. That is, in order to obtain the target PM purification rate, the PM accumulation amount needs to exceed the lower limit value ACC1.
[0037]
When it is determined that the PM accumulation amount of the DPF 9 does not exceed the predetermined lower limit ACC1, the process proceeds to S8, and the PM accumulation operation for actively depositing PM on the DPF 9 is started. In order to deposit PM actively, the PM deposited on the DPF is NO with respect to the deposition rate of the PM on the DPF. ₂ What is necessary is just to slow down the continuous combustion rate which reacts with and burns (purifies).
[0038]
FIG. 3 shows the characteristics when the catalyst inlet temperature is 450 ° C., and the pressure ratio dP in the figure represents the ratio between the pressure loss of the DPF immediately after the start of evaluation and the pressure loss after elapse of a predetermined time. . When this pressure ratio dP is larger than 1, it means that the amount of PM deposited is larger than the amount of PM to be purified, and the operation state (PM deposition operation state) increases. As shown in FIG. 3, when the catalyst inlet temperature is 450 ° C., NO at the DPF inlet ₂ If the ratio of / PM is less than a predetermined value (8 in this example), the deposition rate of PM on the DPF is NO. ₂ As a result, the amount of PM deposited on the DPF increases. Conversely, NO ₂ If the ratio of / PM is greater than 8, it is more NO than the rate of PM deposition on the DPF. ₂ The combustion speed of PM due to this increases, and the amount of PM deposition decreases.
[0039]
Above ratio NO ₂ / PM is related to the EGR rate as shown in FIG. In other words, the higher the EGR rate, the more NO ₂ The ratio of / PM is reduced. Therefore, in order to perform the PM deposition operation, the exhaust gas recirculation control valve 11 is driven and controlled so that the EGR rate is set to NO. ₂ A predetermined value T at which the ratio of / PM is 8 _EGR Should be larger.
[0040]
More specifically, in the normal operation state, the EGR rate is set such that the continuous combustion speed in the DPF is higher than the PM deposition speed. However, when it is desired to deposit PM on the DPF, the normal operation is performed. NO flow into the DPF by setting the EGR rate higher than the conditions ₂ And reducing the PM continuous combustion rate. Conversely, if the EGR rate is made lower than normal operating conditions, PM deposited on the DPF can be further easily purified.
[0041]
In S9, a flag reg. Indicating that the PM accumulation operation is continuing. 2 is 1. In S10, it is determined whether the operation time for performing PM deposition is longer than a predetermined time t1. When the PM deposition operation time has passed the predetermined time t1, the process proceeds to S11, and the PM deposition operation is terminated. Specifically, the EGR rate setting is returned to the normal setting state. In S12, reg. The 2 flag is returned to 0 and this routine is terminated.
[0042]
When it is determined in S6 that the PM accumulation amount is the upper limit value ACC2 or more, that is, when it is determined that PM of the predetermined amount ACC2 or more accumulates in the DPF 9 and the exhaust pressure increase cannot be avoided by continuous combustion, Proceeding to S13, the forced regeneration operation for forcibly regenerating the DPF 9 is started. Specifically, the exhaust temperature flowing into the oxidation catalyst 7 and the DPF 9 is raised to about 600 ° C., which is the self-combustion temperature of PM.
[0043]
As a method for adjusting the exhaust temperature in this way, post injection for injecting secondary fuel after main fuel injection, controlling the engine intake amount or engine exhaust amount using a throttle valve, turbocharging, etc. In addition to controlling the supercharging pressure by the machine 13, a burner is provided at the inlet of the oxidation catalyst 7 and the DPF 9, and the use of such a burner adds an HC component such as fuel.
[0044]
In S14, the forced regeneration flag reg1 is set to 1 to indicate that the forced regeneration operation is being continued. In S15, it is determined whether the operation time of the forced regeneration operation has passed the predetermined time t3. When the predetermined time t3 has elapsed, the process proceeds to S16, where the forced regeneration operation is terminated and the regeneration flag reg1 is set to 0 in S17, and this routine is terminated.
[0045]
FIG. 8 is a flowchart showing the flow of control according to the second embodiment of the present invention.
[0046]
First, in S21, the engine operating state is read. Specifically, the engine speed Ne is read from the engine speed sensor 16, and the accelerator opening degree L is read from the accelerator opening sensor 17. In S22, the fuel injection amount Q is calculated based on the engine speed Ne, the accelerator opening L, and the like.
[0047]
In S23, the amount of PM deposited on the DPF 9 is detected. Here, as in the first embodiment, the PM accumulation amount is indirectly detected based on the exhaust pressure at the inlet of the DPF 9 detected by the exhaust pressure sensor 8. The exhaust pressure value may be estimated based on the intake air amount. The exhaust pressure varies depending on factors other than the PM accumulation amount. For example, the exhaust pressure increases as the exhaust gas amount increases. That is, as shown in FIGS. 6 and 7, the exhaust pressure corresponding to the upper limit value ACC2 and the lower limit value ACC1 of the PM accumulation amount changes according to the engine speed Ne and the fuel injection amount Q.
[0048]
In S24, the forced regeneration operation state flag reg. Determine if 1 is standing. When the forced regeneration flag is 1, the process proceeds to S43, and the forced regeneration operation described later is continued. In S25, the first PM deposition operation state flag reg. Determine whether 2 is standing. When the first PM accumulation operation state flag is 1, the process proceeds to S33, and the first PM accumulation operation described later is continued. In S26, the second PM deposition operation state flag reg. Determine if 3 is standing. When the second PM accumulation operation state flag is 1, the process proceeds to S38, and the second PM accumulation operation described later is continued.
[0049]
In S27, it is determined whether the amount of PM deposited on the DPF 9 is less than a predetermined upper limit ACC2. Actually, the exhaust pressure upper limit value corresponding to the upper limit value ACC2 is calculated by referring to the map shown in FIG. 6 based on the current engine speed Ne and the fuel injection amount Q, and the current exhaust pressure value Pf is calculated. It is determined whether it is less than the exhaust pressure upper limit.
[0050]
When it is determined that the PM accumulation amount is less than the upper limit value ACC2, the process proceeds to S28, and it is determined whether the PM accumulation amount of the DPF 9 is larger than the predetermined lower limit value ACC1. Actually, the exhaust pressure lower limit value corresponding to the lower limit value ACC1 is determined by referring to the map shown in FIG. 7 based on the current engine speed Ne and the fuel injection amount Q, and the current exhaust pressure value Pf is determined as follows. It is determined whether the exhaust pressure lower limit is exceeded.
[0051]
Here, when the DPF that captures the fine particles is a depth filtration method as in the present embodiment, the PM purification rate changes according to the amount of PM deposited on the DPF, as shown in FIG. In general, the PM purification rate tends to increase as the amount of accumulated PM increases. That is, in order to obtain the target PM purification rate, the PM accumulation amount needs to exceed the lower limit value ACC1.
[0052]
When it is determined that the PM accumulation amount of the DPF 9 does not exceed the predetermined lower limit ACC1, the process proceeds to S29, and it is determined whether or not the operation condition is to deposit PM on the DPF. Specifically, it is determined whether the inlet temperature of the oxidation catalyst 7 detected by the exhaust temperature sensor 6 is within the range from T2 to T3.
[0053]
This point will be described in detail. As shown in FIG. 9, NO → NO with respect to the inlet temperature of the oxidation catalyst 7. ₂ The conversion ratio of the above shows a characteristic having a peak at a predetermined temperature T1, and the ratio NO to the inlet temperature is ₂ As shown in FIG. 10, / PM also shows a characteristic having a peak at a predetermined temperature T1. As in the case of the first embodiment, the ratio NO ₂ Assuming that the PM accumulation amount decreases when / PM is equal to or greater than a predetermined value (here, 8), the range of T2 to T3 with T1 as a reference is shown in FIG. It becomes the continuous combustion formation temperature range in which the amount decreases. Conversely, the region outside T2 to T3 is a PM deposition operation region in which the PM deposition rate is higher than the continuous combustion rate and the PM deposition amount of the DPF increases.
[0054]
Therefore, when the catalyst inlet temperature (exhaust temperature) is in the temperature range T2 to T3, the process proceeds to S30, and the exhaust temperature is adjusted so as to be out of the temperature range T2 to T3. That is, in S30, the exhaust temperature is changed from NO to NO. ₂ When it is determined that the conversion rate to is higher than the exhaust gas temperature T1 at which it reaches a peak, that is, in the region of T1 to T3, the process proceeds to S31 and the first PM deposition operation is started. Specifically, after the main fuel injection is completed, that is, after the compression top dead center (ATDC), the sub-injection is performed in the range of 60 to 150 °, thereby raising the exhaust temperature above T3. However, if the exhaust temperature rises excessively (for example, 550 ° C. to 600 ° C. or more), the purification of the DPF 9 is promoted by PM self-ignition, and PM hardly accumulates. To the extent.
[0055]
As another method for raising the exhaust temperature, the engine intake amount or the engine exhaust amount is controlled using a throttle valve, or the supercharging pressure by the turbocharger 13 is controlled (the working gas amount is reduced). In addition, a burner may be provided at the inlet of the oxidation catalyst 7 or the DPF 9, or an HC component such as fuel may be added together with the use of such a burner.
[0056]
In subsequent S32, the flag reg2 is set to 1 to indicate that the first PM deposition operation is continuing. When the operation time of the first PM deposition operation has passed the predetermined time t1, the process proceeds from S33 to S34, and the first PM deposition operation due to the exhaust temperature rise is terminated. Specifically, the post injection is terminated. In step S35, the flag reg2 is returned to 0, and this routine is terminated.
[0057]
On the other hand, when it is determined in S30 that the exhaust temperature is equal to or lower than T1, the process proceeds to S36 and the second PM deposition operation is started. Specifically, the exhaust temperature is lowered below T2. In this embodiment, the exhaust gas temperature is made lower than T2 by supercharging pressure control (intake air amount increase). That is, by closing the variable nozzle (not shown) of the turbocharger 13 disposed upstream of the oxidation catalyst 7 from the normal state, the supercharging pressure is raised and the exhaust temperature is lowered.
[0058]
Next, in S37, the flag reg3 is set to 1 to indicate that the second PM deposition operation due to the decrease in exhaust temperature is continuing. When it is determined that the second PM deposition operation has passed the predetermined time t1, the process proceeds from S38 to S39, and the second PM deposition operation due to a decrease in exhaust temperature is terminated. That is, the nozzle of the turbocharger 13 is returned to the opening degree by normal control. In S40, the flag reg3 is returned to 0, and this routine is terminated.
[0059]
In S27 described above, when it is determined that the PM accumulation amount of the DPF 9 is equal to or greater than the upper limit value ACC2, that is, PM is excessively accumulated, and it is determined that the exhaust pressure increase cannot be avoided by continuous combustion, the process proceeds to S41 and is forcedly performed. The forced regeneration operation for regenerating the DPF 9 is started. Specifically, the exhaust temperature is raised to about 600 ° C., which is the self-combustion temperature of PM, by the above-described intake / exhaust throttle, control of the EGR rate, post injection, and the like. Alternatively, the exhaust temperature may be increased by providing a burner or adding HC as described above.
[0060]
In subsequent S42, the forced regeneration flag reg1 is set to 1 to indicate that the forced regeneration operation is continuing. When this forced regeneration operation elapses for a predetermined time t3, the process proceeds from S43 to S44, and the forced regeneration operation is terminated. Specifically, the exhaust temperature rise to the PM self-combustion temperature is terminated. In S45, the regeneration flag reg1 is returned to 0, and this routine is terminated.
[0061]
According to the first and second embodiments as described above, the PM accumulation amount is detected, and the PM accumulation amount is adjusted to a predetermined range, specifically, the range from the lower limit value ACC1 to the upper limit value ACC2. In addition, the PM collection performance in the DPF 9 can be maintained at a high level.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the relationship between the amount of accumulated PM and the PM purification rate of the DPF.
FIG. 3 NO flowing into the DPF ₂ FIG. 6 is a characteristic diagram showing the relationship between the ratio of PM to PM and the pressure ratio dP of DPF.
FIG. 4 shows an EGR rate and NO flowing into the DPF. ₂ The characteristic view which shows the relationship between the ratio of PM and PM.
FIG. 5 is a flowchart showing a control flow according to the first embodiment of the present invention.
FIG. 6 is a map for estimating exhaust pressure corresponding to the upper limit value ACC2 of the PM accumulation amount.
FIG. 7 is a map for estimating exhaust pressure corresponding to the lower limit ACC1 of the PM accumulation amount.
FIG. 8 is a flowchart showing a control flow according to the second embodiment of the present invention.
FIG. 9: oxidation catalyst inlet temperature and NO → NO ₂ The characteristic view which shows the relationship with the conversion rate.
FIG. 10 shows the oxidation catalyst inlet temperature and NO flowing into the DPF. ₂ The characteristic view which shows the relationship between the ratio of PM and PM.
[Explanation of symbols]
5. Exhaust pipe (exhaust passage)
7 ... Oxidation catalyst
9 ... DPF (diesel particulate filter)
8 ... Exhaust pressure sensor (accumulation amount detection means)
10 ... Exhaust gas recirculation passage
11 ... Exhaust gas recirculation control valve
13 ... Turbocharger
15 ... Control unit

Claims (12)

An exhaust purification device disposed in an exhaust passage of an internal combustion engine,
An oxidation catalyst having a function of oxidizing NO in the engine exhaust to NO ₂ ;
A particulate filter provided downstream of the oxidation catalyst for collecting particulates in the engine exhaust;
A deposition amount detecting means for detecting a particulate deposition amount deposited on the particulate filter;
To adjust the particulate matter deposit amount, possess a burn rate control means for controlling the combustion rate of particulate matter in the particulate filter is burned with NO _2, and,
This combustion speed control means is configured to deposit the particulates when the particulate accumulation amount is equal to or lower than the lower limit value and the particulate purification rate changing according to the particulate deposition amount is less than the target purification rate. An exhaust gas purification apparatus for an internal combustion engine characterized by performing a deposition operation . 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the particulate filter is a filtration and collection type filter. The combustion speed control means reduces the ratio NO ₂ / PM of NO ₂ and particulate flowing into the particulate filter when increasing the particulate deposition amount, and reduces the ratio when reducing the particulate deposition amount. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein NO ₂ / PM is increased. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein an exhaust gas temperature flowing into the oxidation catalyst is controlled in order to adjust the ratio NO ₂ / PM. The particulate matter deposition amount is lower than a predetermined lower limit value, and the exhaust temperature flowing into the oxidation catalyst is the temperature at which the ratio NO ₂ / PM is maximum in an operating state in which the particulate deposition amount is to be increased. 5. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the exhaust gas temperature is raised when the temperature is higher than that of the internal combustion engine. The particulate matter deposition amount is lower than a predetermined lower limit value, and the exhaust temperature flowing into the oxidation catalyst is the temperature at which the ratio NO ₂ / PM is maximum in an operating state in which the particulate deposition amount is to be increased. The exhaust gas purification apparatus for an internal combustion engine according to claim 4 or 5, wherein the exhaust gas temperature is lowered when the temperature is lower than the lower limit. An exhaust gas recirculation passage for recirculating exhaust gas to the combustion chamber of the internal combustion engine, and an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage for adjusting the exhaust gas recirculation rate,
The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas recirculation rate is controlled in order to adjust the particulate accumulation amount. 8. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein an exhaust gas temperature flowing into the particulate filter is controlled in order to adjust the particulate accumulation amount. The particulate accumulation amount is lower than a predetermined lower limit, and the exhaust temperature flowing into the oxidation catalyst is higher than the temperature at which the oxidation catalyst is most activated in an operating state where the particulate accumulation amount is to be increased. If it is high, while increasing the exhaust temperature flowing into the oxidation catalyst,
The particulate accumulation amount is lower than a predetermined lower limit, and the exhaust temperature flowing into the oxidation catalyst is higher than the temperature at which the oxidation catalyst is most activated in an operating state where the particulate accumulation amount is to be increased. 9. The exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein when the temperature is low, the temperature of the exhaust gas flowing into the oxidation catalyst is lowered. The post-injection for injecting the auxiliary fuel after the main fuel injection is performed to adjust the temperature of the exhaust gas flowing into the oxidation catalyst or the particulate filter. Exhaust gas purification device for internal combustion engine. 11. The engine intake amount or the engine exhaust amount is controlled by using a throttle valve in order to adjust the exhaust temperature flowing into the oxidation catalyst or the particulate filter. An exhaust purification device for an internal combustion engine as described. Equipped with a supercharger that can adjust the supercharging pressure by changing the supercharging efficiency,
12. The internal combustion engine according to claim 4, wherein a supercharging pressure by the supercharger is controlled in order to adjust an exhaust gas temperature flowing into the oxidation catalyst or the particulate filter. Exhaust purification equipment.

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