JP2002213229A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform reliable and rapid regeneration of a particulate filter in an exhaust gas passage. SOLUTION: A particulate accumulation amount of the particulate filter is detected (S3) and when the accumulation amount exceeds a given value, it is decided (S5) that it reaches a regeneration timing. At the regeneration timing, during a time in which the temperature of a particulate filter exceeds a given temperature T2 at which combustion of particulate collected thereby is propagated, rich operation is effected to lower oxygen concentration in exhaust gas (S6), and the temperature of the particulate filter is increased through post injection (S7). After the temperature of the particulate exceeds the given temperature T2, switching to lean operation is effected to increase oxygen concentration in exhaust gas (S12), and this treatment burns the particulate at a stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to a technique for regenerating a particulate filter (hereinafter referred to as a particulate filter) for trapping particulates (hereinafter referred to as particulates) in exhaust gas. .

[0002]

2. Description of the Related Art When oxygen concentration of exhaust gas flowing into an exhaust passage is high (in a lean operation), NOx (nitrogen oxide) in the exhaust gas is absorbed, and when oxygen concentration is low (in a rich operation).
Japanese Patent No. 2722987 is known as an exhaust gas purifying apparatus for an internal combustion engine in which a NOx absorbent for reducing and purifying NOx absorbed in the exhaust gas and a particulate filter for collecting particulates in exhaust gas are arranged.

[0003] In this conventional technique, a reducing agent is supplied in a rich operation (closing an intake throttle valve) to absorb NO in a NOx absorbent.
x is reduced and purified, and thereafter, a reducing agent is supplied in a lean operation (opening of the intake throttle valve) to burn and remove the particulates collected by the particulate filter. Thus, the heat generated during NOx purification can be used for burning and removing the particulates, so that when performing the burning and removing of the particulates, it is possible to reduce the need for performing a heating process using an electric heater or a burner.

[0004] The NOx absorbent contains S in the flowing exhaust gas.
If Ox (sulfur oxide) is present, this SOx will also be absorbed. When the SOx absorption amount of the NOx absorbent increases (SOx poisoning), the capacity for absorbing NOx decreases and the NOx purification efficiency decreases, so it is necessary to release SOx poisoning at regular intervals. is there. As an exhaust gas purifying apparatus for an internal combustion engine that releases SOx poisoning, for example, Japanese Patent No.
No. 727906 is known.

[0005]

By the way, when the temperature of the particulate filter is set to 650 ° C. or more and oxygen is supplied to the particulate filter at a stretch, the particulate collected by the particulate filter burns vigorously by combustion propagation. Therefore, a maximum combustion speed can be obtained. When the burning of the particulates by the combustion propagation starts, if the oxygen amount is sufficient, then 650 ° C.
Combustion due to combustion propagation is maintained until all of the trapped particulates are removed even when the following occurs.

However, if oxygen is present in the particulate filter before the temperature of the particulate filter reaches 650 ° C. or higher, the particulates start burning due to an oxidation reaction, and the particulate density in the particulate filter decreases. Therefore, 650
Even if the temperature rises to more than ℃, combustion propagation hardly occurs (combustion becomes harder to propagate as the particulate density becomes lower than when it is high), and the combustion rate becomes higher than when 650 ° C. or more and oxygen is supplied at once. Slows down.

Therefore, the above prior art (Japanese Patent No. 27229)
No. 87), the configuration in which heat generated by performing NOx purification is used for burning out particulates cannot increase the burning speed of the particulates to the maximum. Specifically, NOx can be purified at a relatively low temperature (NOx purification starts at 250 ° C.).
When the Ox purification is completed and the operation is switched from the rich operation to the lean operation, the temperature of the particulate filter becomes 650 ° C.
Never exceed. Then, even if the reducing agent (fuel) is supplied and the temperature is continuously increased after switching to the lean operation, 650 is required.
Before the temperature reaches ° C, an oxidation reaction of the particulates occurs to lower the concentration of the collected particulates, so that the collected particulates cannot be vigorously burned and removed.

As a result, the time required for regeneration of the particulate filter is prolonged, so that fuel efficiency is deteriorated in order to maintain rich operation, and unburned particulates are generated. There is a problem that the fuel efficiency is deteriorated and the fuel consumption during normal operation is deteriorated. An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can reliably and promptly regenerate a particulate filter in view of such a conventional problem.

[0009]

According to the present invention, there is provided a particulate filter disposed in an exhaust passage of an internal combustion engine for trapping particulates in exhaust gas flowing into the internal combustion engine. Regeneration time judgment means for judging regeneration time, filter heating means capable of increasing the temperature of the particulate filter, oxygen concentration control means capable of controlling the oxygen concentration in exhaust gas, and regeneration time of the particulate filter, Until the temperature of the particulate filter exceeds a predetermined temperature, the oxygen concentration in the exhaust gas is lowered by the oxygen concentration control means, and the temperature of the particulate filter is raised by the filter temperature raising means. After the temperature exceeds a predetermined temperature, the oxygen concentration in the exhaust gas is controlled by the oxygen concentration control means. And filter regeneration control means for increasing,
The configuration is provided with.

According to a second aspect of the present invention, in the first aspect of the present invention, the predetermined temperature is set to a temperature at which the particulates collected by the particulate filter propagate and propagate. According to a third aspect of the present invention, in the first or second aspect of the present invention, the filter regeneration control means includes a step of regenerating the particulate filter during the regeneration of the particulate filter until the temperature of the particulate filter exceeds a predetermined temperature. The concentration control means sets the oxygen concentration in the exhaust gas to an oxygen concentration at which the amount of oxygen that the particulate matter trapped by the particulate filter burns and propagates cannot be secured, and the filter temperature raising means raises the temperature of the particulate filter. After the temperature of the particulate filter exceeds a predetermined temperature, the oxygen concentration in the exhaust gas is set by the oxygen concentration control means to the oxygen concentration at which the particulates collected by the particulate filter burn and propagate. And

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, NOx in the exhaust gas is trapped when the oxygen concentration of the inflowing exhaust gas is high. When a NOx trap catalyst for reducing and purifying trapped NOx is provided, the filter temperature raising means also raises the temperature of the NOx trap catalyst to a temperature at which SOx deposited on the NOx trap catalyst can be desorbed. It is characterized by being.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the filter regeneration control means controls the NOx even if the temperature of the particulate filter exceeds a predetermined temperature.
The oxygen concentration in the exhaust gas is kept low until the desorption of SOx from the trap catalyst is completed. According to a sixth aspect of the present invention, in the first to fifth aspects, a catalyst having a three-way function is disposed in the exhaust passage. In this case, by providing the NOx trap catalyst with an oxidation function, the catalyst may be used as a catalyst having a three-way function.

According to a seventh aspect of the present invention, in the sixth aspect of the invention, when the oxygen concentration is reduced, the excess air ratio is set to 1 or less (14.7 or less in the air-fuel ratio). According to an eighth aspect of the present invention, in the first to seventh aspects of the present invention, the filter temperature increasing means performs additional injection (post-injection) of the fuel into the combustion chamber after the main injection of the fuel and after the expansion stroke to thereby increase the exhaust gas. It is characterized by means for raising the temperature.

According to a ninth aspect of the present invention, in the first to eighth aspects, the oxygen concentration control means is an intake throttle valve.

[0015]

According to the first aspect of the present invention, during the regeneration time of the particulate filter, until the temperature of the particulate filter exceeds a predetermined temperature, the temperature is raised while the oxygen concentration in the exhaust gas is low. In this way, the particulate matter trapped in the particulate filter is suppressed from starting combustion, and when the temperature of the particulate filter exceeds a predetermined temperature, the oxygen concentration in the exhaust gas is increased, thereby causing the combustion to propagate. The particulates trapped in the particulate filter can be burned at a stretch, and the particulate filter can be regenerated at a high burning rate.

According to the second aspect of the present invention, the above effect can be ensured by setting the predetermined temperature to a temperature at which the particulates collected by the particulate filter propagate and propagate. . According to the third aspect of the invention, until the temperature of the particulate filter exceeds a predetermined temperature, it is not possible to secure a sufficient amount of oxygen for the particulates collected by the particulate filter to burn and propagate in the exhaust gas. When the temperature of the particulate filter exceeds a predetermined temperature, the above-mentioned effect is ensured by ensuring that the amount of oxygen that the particulates collected by the particulate filter can propagate and burn in the exhaust gas can be secured. In particular, it is possible to secure an amount of oxygen that does not exhaust even if all of the collected particulates start burning at a stretch, and to prevent misfiring due to lack of oxygen.

According to the fourth aspect of the present invention, when a NOx trap catalyst is provided, S
By raising the temperature to a temperature sufficient for Ox to be desorbed, the particulates collected by the particulate filter can be burned vigorously by combustion propagation, and the SOx poisoning of the NOx trap catalyst is also released. Can be.

According to the fifth aspect of the present invention, even when the temperature of the particulate filter exceeds a predetermined temperature at the time of regeneration of the particulate filter, the temperature of the NOx trap catalyst becomes a temperature at which SOx can be desorbed. By maintaining the oxygen concentration in the exhaust gas low until a predetermined period (for example, a predetermined time) elapses, SOx poisoning of the NOx trap catalyst can be reliably released in this period.

According to the invention of claim 6, in the exhaust passage,
By arranging a catalyst having a three-way function, it is possible to purify HC and CO generated by the rich operation for lowering the oxygen concentration in the exhaust gas and the post-injection for raising the temperature. According to the invention of claim 7, when reducing the oxygen concentration in the exhaust gas,
By setting the excess air ratio to 1 or less (stoichiometric), the three-way function of the catalyst works effectively, and it is possible to suppress the deterioration of the emission during the rich operation.

According to the eighth aspect of the present invention, the temperature of the particulate filter is increased by post-injection, so that the filter can be implemented without adding hardware. According to the ninth aspect of the present invention, the oxygen concentration control is easily realized by realizing the control of the intake throttle valve.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of an internal combustion engine (here, a diesel engine) showing an embodiment of the present invention. In the diesel engine 1, air taken in from an intake pipe 2 is supplied to a variable nozzle type turbocharger 3.
After being supercharged by an intake compressor, cooled by an intercooler 4 and passed through an intake throttle valve 5, a collector 6
And flows into the combustion chamber of each cylinder. The fuel is pressurized by a high-pressure fuel pump 7, sent to a common rail 8, and directly injected from a fuel injection valve 9 of each cylinder into a combustion chamber. The air that has flowed into the combustion chamber and the injected fuel burn here by compression ignition, and the exhaust flows out to the exhaust passage 10.

A part of the exhaust flowing into the exhaust passage 10 is E
The EGR control valve 1 is used as the GR gas by the EGR pipe 11.
It is returned to the intake side via 2. The remainder of the exhaust passes through and drives the exhaust turbine of the variable nozzle turbocharger 3. Here, a NOx trap catalyst 13 is disposed downstream of the exhaust turbine in the exhaust passage 10 for purifying the exhaust gas.
Is arranged.

The NOx trap catalyst 13 traps (adsorbs or absorbs) NOx in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and reduces and purifies the trapped NOx when the oxygen concentration is low. In the present embodiment, a ternary function is provided by further supporting a noble metal to have an oxidation function for HC and CO. This NOx trap catalyst 13 also traps SOx when SOx is present in the exhaust gas flowing into the NOx trap catalyst 13. NOx
If the trapping amount of SOx trapped by the trap catalyst 13 increases (SOx poisoning), the capacity for trapping NOx decreases and the NOx purification efficiency decreases, so it is necessary to release SOx poisoning at regular intervals. There is.

The particulate filter 14 collects particulates in the exhaust gas flowing into the filter. An increase in the amount of particulates collected (accumulated) by the particulate filter 14, that is, an increase in the amount of accumulated particulates increases exhaust resistance and deteriorates fuel efficiency. It is necessary to regenerate the particulate filter 14 by burning and removing the curate.

In this embodiment, the NOx trap catalyst 13 is arranged upstream of the particulate filter 14, but if only the basic object of the present invention is achieved, the arrangement is reversed. Or both may be integrated. To control the engine 1, signals are input to the control unit 20 from a rotation speed sensor 21 for detecting an engine rotation speed Ne, an accelerator opening sensor 22 for detecting an accelerator opening APO, and the like.

In the present embodiment, the exhaust passage 10
An exhaust pressure sensor 23 is provided between the NOx trap catalyst 13 and the particulate filter 14, and an exhaust temperature sensor 24 is provided downstream of the particulate filter 14, and these signals are also sent to the control unit 20. Has been entered. Control unit 2
Numeral 0 outputs a fuel injection command signal for controlling the fuel injection timing to the fuel injection valve 9 and the injection amount, an opening command signal to the intake throttle valve 5 and the like based on these input signals.

In particular, according to the present invention, it is determined whether or not the particulate filter 14 needs to be regenerated, and a predetermined regenerating process is performed in the case of the regenerating time. Such particulate filter regeneration control will be described in detail below. Will be described. FIG. 2 is a flowchart of the particulate filter regeneration control executed by the control unit 20.

In S1, first, the operating state of the engine (engine speed Ne and accelerator opening APO) is read from the rotation speed sensor 21 and the accelerator opening sensor 22. S2
Then, from a map (not shown) using the engine speed Ne and the accelerator opening APO as parameters, the fuel injection amount Q
(For main injection) is calculated. In S3, the particulate accumulation amount (abbreviated as PM accumulation amount in the flow) of the particulate filter 14 is detected in order to determine the regeneration time of the particulate filter 14. Since it is difficult to directly detect the amount of particulate matter accumulated in the particulate filter 14, here, if the amount of particulate matter accumulated in the particulate filter 14 increases, the exhaust pressure upstream of the particulate filter 14 naturally rises. Thus, the exhaust pressure sensor 23 detects the exhaust pressure on the upstream side of the particulate filter 14 (back pressure of the particulate filter 14).

In S4, the particulate filter 14
It is determined whether or not the reproduction request flag has already been set (= 1). When the reproduction request flag = 0, the process proceeds to S5, and when the reproduction request flag = 1, the process proceeds to S9. S5
Then, it is determined whether or not the particulate accumulation amount of the particulate filter 14 (abbreviated as PM accumulation amount in the flow) exceeds a predetermined value. Particulate filter 14
Is indirectly detected by the exhaust pressure on the upstream side of the particulate filter 14,
It is determined whether the exhaust pressure on the upstream side of the particulate filter 14 has exceeded a predetermined threshold value (back pressure threshold value) ACC1. The back pressure threshold ACC1 used here is set from the map shown in FIG. 3, that is, a map using the engine speed Ne and the fuel injection amount Q as parameters.

That is, the exhaust pressure in the current operation state (Ne, Q) is equal to the back pressure threshold AC in the corresponding operation state in FIG.
If it does not exceed C1, it is determined that it is not the regeneration time yet, and the routine returns. However, the exhaust pressure in the current operation state (Ne, Q) is equal to the back pressure threshold AC in the corresponding operation state in FIG.
If it exceeds C1, the particulate filter 1
It is determined that the particulates are excessively accumulated in No. 4, that is, the particulate accumulation amount exceeds the predetermined value and the regeneration time has been reached, and the forced regeneration mode after S6 is entered.

In S6, first, in order to reduce the oxygen concentration in the exhaust gas, the rich operation is started by controlling the opening of the intake throttle valve 5 to adjust the amount of intake air. At the time of such a rich operation, the target intake air amount is obtained from the map shown in FIG. 4, that is, the map in which the target intake air amount for the rich operation is determined using the engine speed Ne and the fuel injection amount Q as parameters. The opening degree of the intake throttle valve 5 is adjusted so as to have that value.

At S7, post injection is started to increase the exhaust gas temperature. That is, post injection, which is an additional fuel injection in the expansion stroke or the exhaust stroke, after the main injection of fuel in the compression stroke is started. When performing post-injection, the map shown in FIG.
e and the fuel injection amount Q for main injection are used as parameters to obtain a target post injection amount from a map that determines a target post injection amount for heating up to a target exhaust temperature at which the particulate filter 14 can be regenerated. The fuel is injected at a predetermined post injection timing.

Here, as shown in FIG. 6, the temperature of the particulate filter 14 is increased by post-injection in a state where the oxygen concentration is very low (rich operation), and the temperature of the particulate filter 14 is reduced. If oxygen (lean exhaust gas) capable of combustion propagation is supplied after the temperature is raised to a predetermined temperature T2 at which combustion propagation is possible, the deposited particulates can be burned at a stretch, and the particulates can be burned at a high burning speed. The reproduction time can be shortened because the curated filter can be reproduced.

However, as shown in FIG. 7, when the temperature is increased in a lean state containing a large amount of oxygen, partial oxidation starts before reaching a temperature at which combustion propagation occurs, and when the temperature reaches T2, the combustion propagation starts. , The accumulated particulates do not burn at once. Therefore, even if the temperature is raised for the same time, the present invention can efficiently and efficiently regenerate in a shorter time.

The post-injection itself is described in JP-A-9-53.
442 (page 4). If post-injection is performed with an O2 sensor arranged before and after the catalyst and the air-fuel ratio is fed back, the exhaust gas during temperature rise is three-way treated by the noble metal of the catalyst, and the emission is improved. That is, the oxidation function of the NOx trap catalyst 13 can purify HC and CO discharged by post-injection.

At S8, the reproduction request flag is set to "1". When the reproduction request flag is set to 1, in the next and subsequent routines, the process proceeds to S9 and subsequent steps in the determination at S4. In S9,
It is determined whether the exhaust gas temperature has exceeded a predetermined temperature T1. This is to determine whether or not the temperature of the NOx trap catalyst 13 has reached a temperature sufficient for SOx poisoning release (SOx desorption temperature). Here, the predetermined temperature T1 is for determining the temperature of the NOx trap catalyst 13, and is usually 550 to 650 ° C. in the rich operation. However, since the predetermined temperature T1 is determined based on the exhaust gas temperature on the downstream side of the particulate filter 14,
The setting is made in consideration of the difference from the temperature of the NOx trap catalyst 13. However, the catalyst temperature may be estimated from the operating state and its history.

The routine returns until the exhaust gas temperature exceeds the predetermined temperature T1, and proceeds to S10 when the exhaust gas temperature exceeds the predetermined temperature T1. S1
In the case of 0, in order to determine whether or not SOx poisoning has been completely released, it is determined whether or not the elapsed time after the exhaust gas temperature has reached the predetermined temperature T1 has exceeded the predetermined time t1. This is because if the rich operation continues for t1 or more, the deposited SOx is also desorbed into the exhaust gas. Note that the predetermined time t1 here is:
The SOx trap amount of the NOx trap catalyst 13 upstream of the particulate filter 14 may be calculated and set based on this. The SOx trap amount can be estimated from the integrated value of the engine speed.

Return until the predetermined time t1 has elapsed,
After the elapse of the predetermined time t1, the process proceeds to S11. In S11, it is determined whether or not the exhaust gas temperature has exceeded a predetermined temperature T2. This is to determine whether or not the temperature of the particulate filter 14 has reached a temperature at which combustion propagation of particulates can be expected under lean operation. The predetermined temperature T2 here
Is for determining the temperature of the particulate filter 14. For example, when there is no catalytic reaction, the temperature is about 650 ° C. However, since the determination is made based on the exhaust gas temperature on the downstream side of the particulate filter 14, the difference is taken into consideration. To set. However, the temperature of the particulate filter 14 may be estimated from the operating state and its history.

The routine returns until the exhaust temperature exceeds the predetermined temperature T2, and proceeds to S12 when the exhaust temperature exceeds the predetermined temperature T2. S1
In 2, the rich operation is canceled because combustion propagation can be expected. That is, in order to increase the oxygen concentration in the exhaust gas, the intake throttle valve 5 is almost fully opened, and the operation is switched to the lean operation.

At S13, post injection is stopped. S1
In 4, since the reproduction operation has been completed, the reproduction request flag is reset to 0, and this routine ends. here,
Steps S3 and S5 correspond to the reproduction timing determination means.
The portion 14 corresponds to a filter regeneration control means using an oxygen concentration control means (intake throttle valve 5) and a filter temperature raising means (post injection).

As described above, the period from the time when the exhaust gas temperature exceeds the predetermined temperature T1 sufficient for SOx deposited on the NOx trap catalyst 13 to desorb until the predetermined time t1 elapses,
By maintaining the rich operation even when the exhaust gas temperature exceeds the predetermined temperature T2, the SOx poisoning of the NOx trap catalyst 13 can be reliably released, the predetermined time t1 has elapsed, and the exhaust gas temperature has reached the predetermined temperature. When the time exceeds T2, by switching to the lean operation, sufficient oxygen is supplied to the particulate filter 14, so that the accumulated particulates can be burned at a stretch, and the particulate filter 14 can be burned at a high combustion speed. Can be reproduced.

[Brief description of the drawings]

FIG. 1 is a system diagram of an internal combustion engine showing an embodiment of the present invention.

FIG. 2 is a flowchart of particulate filter regeneration control.

FIG. 3 is a map of a back pressure threshold value for judging regeneration timing.

FIG. 4 is a map of a target intake air amount for a rich operation.

FIG. 5 is a map of a target post injection amount for temperature rise.

FIG. 6 is a diagram showing particulate combustion in rich → lean

FIG. 7 is a diagram showing particulate combustion in lean.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Intake pipe 5 Intake throttle valve 7 High pressure fuel pump 9 Fuel injection valve 10 Exhaust passage 13 NOx trap catalyst 14 Particulate filter 20 Control unit 21 Speed sensor 22 Accelerator opening sensor 23 Exhaust pressure sensor 24 Exhaust temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/08 F01N 3/08 AG 3/20 3/20 E 3/24 3/24 EU 3 / 28 301 3/28 301C F02D 9/02 F02D 9/02 R 351 351M 41/04 360 41/04 360A 380 380M 41/38 41/38 41/38 B F-term (reference) 3G065 AA01 AA03 AA04 CA12 DA04 GA06 GA08 GA10 GA18 GA46 JA04 JA09 JA11 KA02 3G090 AA01 BA01 CA00 CA01 CB00 DA03 DA10 DA12 DA18 DA20 EA02 EA04 EA07 3G091 AA02 AA10 AA11 AA18 AB03 AB06 AB09 AB13 BA00 BA11 BA14 BA15 BA19 CB02 CB03 HA07 FB07 HA11 EB07 HA11 JA24 JA25 LA01 LB11 MA01 MA11 MA18 MA27 NA06 NA08 NC02 ND02 NE13 NE14 NE15 NE23 PA11Z PB03A PB03Z PB05Z PB06A PD02Z PD11Z PD14Z PE01Z PF03Z 4D058 JA01 JB02 JB22 MA41 MA51 SA08 UA01

Claims (9)

[Claims] 1. A particulate collection filter disposed in an exhaust passage of an internal combustion engine for trapping particulates in flowing exhaust gas, a regeneration timing determining means for determining a regeneration timing of the particulate collection filter, and the particulates Filter temperature raising means capable of raising the temperature of the collection filter; oxygen concentration control means capable of controlling the oxygen concentration in the exhaust gas; and, at the time of regeneration of the particle collection filter, the temperature of the particle collection filter becomes a predetermined temperature. Until it exceeds, the oxygen concentration in the exhaust gas is lowered by the oxygen concentration control means, and the temperature of the fine particle collection filter is raised by the filter temperature raising means, and the temperature of the fine particle collection filter exceeds a predetermined temperature. And a filter regeneration control means for increasing the oxygen concentration in the exhaust gas by the oxygen concentration control means. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the predetermined temperature is set to a temperature at which the particulates collected by the particulate collection filter burn and propagate. 3. The filter regeneration control means, wherein during the regeneration time of the particulate collection filter, the oxygen concentration control means controls the oxygen concentration in the exhaust gas until the temperature of the particulate collection filter exceeds a predetermined temperature. Is set to an oxygen concentration at which the amount of oxygen in which the fine particles trapped by the fine particle collecting filter burns and propagates cannot be secured, and the temperature of the fine particle collecting filter is raised by the filter temperature raising means, and the temperature of the fine particle collecting filter is increased. After the temperature exceeds a predetermined temperature, the oxygen concentration control means sets the oxygen concentration in the exhaust gas to the oxygen concentration at which the fine particles trapped by the fine particle trapping filter burn and propagate. Item 3. An exhaust gas purification device for an internal combustion engine according to Item 2. 4. An NOx trap catalyst disposed in an exhaust passage for trapping NOx in exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and reducing and purifying the trapped NOx when the oxygen concentration is low. In this case, the filter temperature raising means also raises the temperature of the NOx trap catalyst to a temperature at which SOx deposited on the NOx trap catalyst can be desorbed. The exhaust gas purification apparatus for an internal combustion engine according to any one of the above. 5. The filter regeneration control means according to claim 1, wherein said NOx filter is provided even when the temperature of said particulate trapping filter exceeds a predetermined temperature.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the oxygen concentration in the exhaust gas is kept low until the desorption of SOx from the trap catalyst is completed. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a catalyst having a three-way function is disposed in the exhaust passage. 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 6, wherein when the oxygen concentration is reduced, the excess air ratio is set to 1 or less. 8. The apparatus according to claim 1, wherein the filter temperature raising means is means for increasing the exhaust gas temperature by additionally injecting fuel into the combustion chamber after the main injection of fuel and after the expansion stroke. An exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 7 to 7. 9. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said oxygen concentration control means is an intake throttle valve.