JP2003322016A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of realizing excellent NOx purification efficiency even under low-temperature exhaust gas conditions. <P>SOLUTION: This exhaust emission control device comprises an oxygen storage means 4 having an oxygen storage component on the upstream side of an exhaust gas passage of an internal combustion engine, and an NOx trap catalyst 5 on the downstream side of it. The oxygen storage means 4 is disposed at such a position that heat due to oxygen quantity emitted when the oxygen storage component is rich in air-fuel ratio of exhaust gas is sufficient to heat the NOx trap catalyst 5 to be activated. Between the oxygen storage means 4 and the NOx trap catalyst 5, an oxygen concentration detecting means 6, and an air-fuel ratio detecting means 7 are disposed. A three-way catalyst 3 is installed on the upstream side of the oxygen storage means 4. <P>COPYRIGHT: (C)2004,JPO

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 device, and more particularly, to an exhaust gas purifying device that realizes excellent NOx (nitrogen oxide) purifying efficiency even under low-temperature exhaust gas conditions. Regarding

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 2000-154713 discloses a first half of a carrier of an NOx trap catalyst (upstream part)
And carries an O ₂ storage component that absorbs oxygen (O ₂ ) in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and releases the O ₂ that is absorbed when the air-fuel ratio of the exhaust gas is rich,
O ₂ released when the exhaust gas air-fuel ratio is rich reacts with H ₂ and CO components in the exhaust gas to raise the temperature of the NOx trap catalyst, increase the activity of the NOx trap catalyst, and reduce NOx. An exhaust gas purification device for an internal combustion engine is disclosed in which the NOx purification capability of a trap catalyst is improved. In this exhaust emission control device, O is added to the upper layer of the NOx trap catalyst.
A three-way catalyst supporting two storage components or an O2 storage component is arranged in the first half portion adjacent to the NOx trap catalyst.

[0003]

However, in such a conventional exhaust gas purification apparatus, when the O2 storage component is carried in the upper layer of the NOx trap catalyst, the HC flowing into the exhaust gas when the air-fuel ratio of the exhaust gas is rich. , CO, and H ₂ react preferentially with O ₂ released from the O ₂ storage component, and the amount of reducing agent that purifies NOx released from the NOx trap catalyst at the same air-fuel ratio is insufficient. , Unpurified NO
There is a problem that x is released into the atmosphere. On the other hand, when the three-way catalyst carrying the O2 storage component is arranged in the first half portion adjacent to the NOx trap catalyst, the reducing agent flowing in when the exhaust gas air-fuel ratio is rich is purified by the three-way catalyst arranged in the first half portion. There is a problem that the amount of reducing agent for purifying NOx released from the NOx trap catalyst is insufficient, and unpurified NOx is released into the atmosphere. Further, in order to solve the above-mentioned problems, it is conceivable to further increase the air-fuel ratio, but such excessive enrichment causes a problem that fuel consumption increases and fuel efficiency deteriorates. .

Further, the combustion effect is similar to that of a diesel engine.
In an internal combustion engine with a high exhaust gas temperature but a low exhaust gas temperature,
Is, for example, the inlet temperature of the NOx trap catalyst is 200 ° C.
When the exhaust gas air-fuel ratio is rich,
O released from O2 storage components _TwoSince the concentration will decrease,
HC (hydrocarbon), CO and H_TwoFor combustion with reducing agents such as
The amount of heat generated is reduced and transferred to the NOx trap catalyst.
The heat (temperature) generated becomes low, and the desired NOx trap
It is said that the activity of the medium cannot be obtained and the NOx purification capacity does not improve.
There is also a problem.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an exhaust gas which realizes an excellent NOx purification efficiency even under a low temperature exhaust gas condition. It is to provide a gas purifier.

[0006]

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the above-mentioned problems can be solved by arranging the oxygen storage means at a predetermined position in the exhaust gas passage. The invention was completed.

That is, in the exhaust gas purifying apparatus of the present invention, the oxygen storage means and the N are sequentially arranged in the exhaust gas passage of the internal combustion engine from the upstream side.
It is an exhaust gas purification device in which an Ox trap catalyst is arranged. Further, in this exhaust gas purifying apparatus, the installation position of the oxygen storage means is such that in the exhaust gas passage, the amount of oxygen released when the oxygen storage component is rich in the exhaust gas air-fuel ratio and the amount of reducing agent when the exhaust gas air-fuel ratio is rich. The heat caused by NOx
It is located at a position sufficient to activate the trap catalyst by raising its temperature.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying apparatus of the present invention will be described in detail below. As described above, the exhaust gas purifying apparatus of the present invention is an exhaust gas purifying apparatus in which the oxygen storage unit having an oxygen storage component is located upstream of the exhaust gas passage of the internal combustion engine and the NOx trap catalyst is located downstream thereof. . Further, in the oxygen storage means, the heat due to the catalytic reaction released when the oxygen storage component is rich in the exhaust gas air-fuel ratio is
The Ox trap catalyst is arranged at a position sufficient to heat it and activate it.

Here, in the internal combustion engine to which the exhaust gas purifying apparatus of the present invention is applied, the air-fuel ratio of the exhaust gas fluctuates between rich and lean, and the catalyst is activated when it comes into contact with the NOx trap catalyst. An internal combustion engine that may be operated to emit exhaust gas at a temperature that is too low to
The most specific example is a diesel engine in which a NOx trap catalyst is arranged in a so-called underfloor position. As described above, the “low temperature exhaust gas” means exhaust gas at a temperature that is not sufficient to activate the NOx trap catalyst, and typically has a temperature of 200 ° C. when contacting the NOx purification catalyst. The following exhaust gas corresponds, but in this case, the exhaust gas temperature is usually 300 ° C. or lower immediately after the exhaust manifold.

In the exhaust gas purifying apparatus of the present invention, O ₂ and H released when the oxygen storage means is rich in the exhaust gas air-fuel ratio.
C, CO, and a reducing agent such as H ₂ are burned on the NOx trap catalyst or in the vicinity thereof, and the heat generated thereby is used to reach the activation temperature of the NOx trap catalyst to obtain a good N
It realizes the Ox purification rate. Therefore, the oxygen storage means needs to be in a state capable of releasing O ₂ , and the oxygen storage component does not sufficiently release O ₂ at a low temperature of about 200 ° C., so that this component is heated to 300 ° C. or higher. It is preferably arranged at the passage position. Typically, the oxygen storage means may be arranged immediately after the exhaust manifold and / or upstream of the front tube (so-called pre-position).

Further, in the exhaust gas purifying apparatus of the present invention, it is possible to add an exhaust gas purifying catalyst such as a three-way catalyst upstream of the oxygen storage means.
The Ox trap catalyst can prevent unpurified HC, CO, etc. from flowing out. Further, in the exhaust gas purifying apparatus of the present invention, it is possible to add an exhaust gas purifying catalyst such as a three-way catalyst in parallel to the oxygen storage means, whereby excess reducing agents such as HC and CO can be added. At the same time as being able to purify, HC and C necessary for purifying the trapped NOx
It is possible to supply a reducing agent such as O and H ₂ from the exhaust passage side in which the oxygen storage means is arranged, and to better prevent release of unpurified NOx when the exhaust gas air-fuel ratio is rich. You can In the exhaust gas purifying device of the present invention, it is not necessary to provide a bypass or a switching valve between the three-way catalyst and / or oxygen storage means and the NOx trap catalyst, and this purifying device is easy to design. It also contributes to cost reduction.

Furthermore, in the exhaust gas purifying apparatus of the present invention, between the oxygen storage means and the NOx trap catalyst,
Oxygen concentration detection means and air-fuel ratio detection means may be added,
NO depending on the oxygen concentration detected by this oxygen concentration detecting means
By controlling the air-fuel ratio of the exhaust gas flowing into the x-trap catalyst to realize more efficient NOx purification,
The fuel economy of the internal combustion engine can also be improved.

As described above, the exhaust gas purifying apparatus of the present invention uses O ₂ and HC, C released from the oxygen storage component.
Although the combustion reaction with a reducing agent such as O and H ₂ is used, the exhaust gas when O 2 is released has H ₂ concentration and H ₂
A particularly good effect is exhibited when the ratio (hydrogen concentration / total reducing agent concentration) <0.3 with the total reducing agent concentration of C, CO, H _{2 and the} like is satisfied. The reason for this is that hydrogen in the reducing agent reacts rapidly with oxygen and generates steam to be consumed, which cannot sufficiently contribute to purification of NOx, but CO and HC
Can contribute to both the NOx purification and the combustion reaction on the NOx trap catalyst. Therefore, it is more convenient for the exhaust gas purifying apparatus of the present invention that the hydrogen concentration in the total reducing agent is lower.

Hereinafter, the exhaust gas purifying apparatus of the present invention will be described in more detail with reference to some drawings by some embodiments.

(Embodiment 1) FIG. 1 is a schematic configuration diagram showing an embodiment of an exhaust gas purifying apparatus of the present invention. In the present embodiment, the present invention is applied to a diesel engine for an automobile that performs lean combustion. Is shown. In FIG. 1, the engine 1
Is a 4-cylinder diesel engine, not shown,
Engines such as a fuel injection valve that directly injects fuel into a cylinder, an air flow meter that detects the amount of intake air that flows into the engine 1, a rotation speed sensor that detects engine rotation, and a means that detects the amount of depression of the accelerator pedal of the driver Means for detecting signals associated with combustion of the.

Reference numeral 2 represents a control device (electronic control circuit; ECM) of the engine 1. The control device 2 appropriately controls the combustion state of the engine, that is, the fuel injection timing and the fuel injection amount, based on the signal sent from the signal detection means related to the combustion state of the engine provided in the engine 1, and exhaust gas empty The operation is performed so that the fuel ratio is lean to rich. In the exhaust passage into which the exhaust gas from the engine 1 flows, the three-way catalyst 3, which is an example of the exhaust gas purifying catalyst, is provided in the uppermost stream, and O
2 storage means 4, NOx trap catalyst 5 is arranged at the last stage. In this embodiment, no means for supplying O ₂ from the outside, a means for increasing the temperature of the catalyst by applying electric energy from the outside, and the like are provided at all.

As described above, the three-way catalyst 3 located in the uppermost stream of the exhaust passage is arranged immediately after the exhaust manifold of the engine 1, and the O2 storage means 4 is arranged at the subsequent stage. The three-way catalyst 3 may be any three-way catalyst that is generally used in automobiles, such as Pt, Pd and R.
A catalyst in which at least one kind of noble metal such as h is supported on a base material such as activated alumina can be used.

Further, O ₂ storage component contained in the O2 storage means 4 is generally O ₂ rich atmosphere, i.e. exhaust gas air-fuel ratio stored the O ₂ in the exhaust gas flowing at the time of lean,
O ₂ when the reducing atmosphere, that is, the exhaust gas air-fuel ratio is rich
Any material can be used as long as it has a function of releasing methane, and oxides such as cerium and praseodymium are used. In addition,
It is preferable to use a material in which cerium and zirconium are solid-dissolved in order to improve the heat resistance of the O2 storage component because the O2 storage component is arranged upstream of the exhaust passage.

Further, as the NOx trap catalyst 5 arranged at the last stage of the exhaust passage as described above, for example, P
A catalyst (integral structure type catalyst) applied to a cordierite-based monolith carrier by mixing and pulverizing a powder of at least one of noble metals such as t, Pd, and Rh supported on a base material such as activated alumina, for example, potassium (K), sodium (N
a), alkali metals such as lithium (Li) and cesium (Cs), barium (Ba), calcium (Ca)
And at least one of alkaline earth metals such as strontium (Sr) and rare earths such as lanthanum (La), cerium (Ce) and yttrium (Y).

The NOx trap catalyst uses the NOx flowing into the exhaust passage when the exhaust gas air-fuel ratio is lean to form nitrate ions (NO ₃ ⁻ ) on the catalytic noble metal. It is trapped in the NOx trap catalyst by combining with Ba oxide and / or Ba carbonate carried as the NOx trapping agent. Then, when the exhaust gas air-fuel ratio is rich, NO ₃ on the precious metal of the NOx trap catalyst ^- to decrease, NO is trapped in the catalyst ₃ ^- is released in the form of NO _2, the exhaust on the catalyst precious metal NO ₂ is reduced and purified by reacting with a reducing agent such as HC, CO and H 2 contained in the gas.

In the present embodiment, as shown in FIG.
A means 6 for detecting the O ₂ concentration is provided in the intermediate portion between the storage means 4 and the NOx trap catalyst 5, and a means 7 for detecting the exhaust gas air-fuel ratio flowing into the NOx trap catalyst 5 is provided. O2 concentration detector 6 detects the O ₂ concentration of the air-fuel ratio is discharged from the O2 storage means 4 when the rich. In the present embodiment, based on the detected O ₂ concentration and the NOx supply amount estimated by the control device 2 according to the engine speed of the engine 1, the fuel injection amount, the air-fuel ratio, the accelerator opening degree, the intake air amount, and the like. Based on the estimated NOx trap amount, the amount of reducing agent required to raise the temperature of the NOx trap catalyst 5 and the amount of reducing agent required to desorb and purify NOx with respect to the NOx trap amount are determined, The exhaust gas air-fuel ratio formed by 1 is set to the air-fuel ratio for supplying a desired amount of reducing agent. Then, the state of purification by the NOx trap catalyst 5 is detected by the air-fuel ratio detecting means 7 arranged downstream of the NOx trap catalyst, and the rich state can be continued or ended as appropriate according to the value of the air-fuel ratio. Even when the exhaust gas air-fuel ratio is made rich, a small amount of O ₂ is contained in the exhaust gas flowing from the engine 1 into the exhaust passage, so that it flows into the NOx trap catalyst at the NOx trap catalyst inlet. A means for detecting the air-fuel ratio of the exhaust gas is provided, the set air-fuel ratio is corrected, and the exhaust gas air-fuel ratio flowing from the engine 1 into the exhaust passage can be determined.

The exhaust gas air-fuel ratio setting process for desorbing and purifying NOx trapped in the NOx trap catalyst in the exhaust gas purifying apparatus of this embodiment will be described in detail below. FIG. 2 shows a flowchart of the exhaust gas air-fuel ratio setting processing control in the present embodiment. In FIG. 2, it is determined from the operating conditions of the engine 1 shown in FIG. 1 whether the exhaust gas air-fuel ratio flowing into the exhaust passage is lean (step 1). If the exhaust gas air-fuel ratio is lean, the process flow shown in FIG. 2 is continued, and if it is an air-fuel ratio other than lean, the process ends.

Next, at step 2, the NOx amount (ΣNOx) flowing into the NOx trap catalyst 5 shown in FIG.
Is added. The NOx amount flowing into the NOx trap catalyst when the exhaust gas air-fuel ratio is lean is stored in advance in the control device 2 in a map format according to the operating conditions of the engine 1,
The NOx amount flowing into the NOx trap catalyst 5 always integrates the NOx amount flowing into the exhaust passage under the operating condition of the engine 1, and under the next operating condition, the NOx under the operating condition is incremented with respect to the integrated value.

Then, in step 3, it is judged if the integrated value (ΣNOx) of the NOx amount flowing into the NOx trap catalyst 5 exceeds a certain threshold value (SNOx). In the present embodiment, a certain threshold value (SNOx) represents the limit amount of NOx that can be trapped in the NOx trap catalyst 5. However, this threshold value can be appropriately selected, and an appropriate ratio such as 80% of the trap limit amount can also be adopted. In step 3, ΣNOx is SNOx
When it does not exceed NOx, the NOx trap catalyst 5 is
It is determined that the trappable limit has not been reached, and the process returns to step 2 to trap NOx. On the contrary, ΣNOx
When SNOx exceeds SNOx, the process proceeds to step 4, N
The Ox purification flag FNOxp is set to 1.

In step 4, after setting FNOxp = 1, in the engine 1, the exhaust gas air-fuel ratio RAF flowing into the exhaust passage is trapped in the NOx trap catalyst 5 by ΣNO.
Air-fuel ratio RAF that supplies a reducing agent that reduces NOx equivalent to x
The enrichment process is executed so that the value becomes 1. In step 5, when RAF = RAF1, O2 storage component 4
The amount of O ₂ released from is detected using the O ₂ concentration detecting means 6. The amount of reducing agent required for the oxidation reaction with respect to the released O ₂ concentration is estimated in the control circuit 2, the exhaust gas air-fuel ratio RAF formed by the engine 1 is corrected, and RAF = RAF1
+ RAFos To estimate the amount of reducing agent required for the oxidation reaction with respect to the released O ₂ concentration, the combustion reaction of O ₂ and CO represented by the following equation is used. 2CO + O2 → 2CO2 + Q ... The above reaction is an exothermic reaction, and combustion heat Q is generated. Since this reaction occurs on the NOx trap catalyst, the internal temperature of the NOx trap catalyst 5 increases by the heat quantity Q generated by combustion. Therefore, the combustion heat with respect to the O ₂ concentration detected by the O ₂ concentration detecting means is estimated from the above reaction, the exhaust gas air-fuel ratio for supplying CO corresponding to this is set as RAFos, formed in the engine 1, and the exhaust gas is formed. The exhaust gas air-fuel ratio RAF flowing into the passage is RA to the air-fuel ratio setting RAF1 to which the reducing agent used for NOx purification should be supplied.
It becomes a value obtained by adding Fos, and the rich degree becomes slightly deeper.

Then, in step 6, it is judged whether or not the NOx trap catalyst purifies NOx based on the air-fuel ratio (TR) of the NOx trap catalyst downstream. TR
Is smaller than a specified value (TR0) (TR
<TR0), the enrichment process is terminated, and the process proceeds to step 7. On the contrary, when TR> TR0, the enrichment process is continued. As described above, performing the rich process without controlling the air-fuel ratio at the time of richness by the air-fuel ratio in the downstream of the NOx trap catalyst causes the surplus of the internal temperature rise of the NOx trap catalyst 5 due to the combustion of CO and the purification of NOx. The reducing agent is supplied, and the unpurified reducing agent is released into the atmosphere, which is not preferable from the viewpoint of exhaust gas purification. Step 6
After the enrichment process is completed in step FNOxp in step 7.
= 0 and ΣNOx = 0, the air-fuel ratio setting is completed. By performing the above control flow in the exhaust gas purification device of FIG. 1, it becomes possible to exert the NOx purification capacity even at a low temperature such as a NOx trap catalyst temperature of 200 ° C. or lower.

(Embodiment 2) FIG. 3 is a schematic diagram showing another embodiment of the exhaust gas purifying apparatus of the present invention. Note that the substantially same members as those in the case of the exhaust gas purifying apparatus shown in FIG. 1 are designated by the same reference numerals. In the present embodiment, the engine 1 is a 4-cylinder diesel engine, and the engines # 1 to # 4 are used.
The cylinders are divided into two cylinder groups whose compression ignition timings are not continuous with each other. The compression ignition sequence of the engine 1 is 1-
3-4-2, the cylinder groups # 1 and # 4, and
The cylinder groups 2 and # 3 are formed. The exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to the exhaust passage for each cylinder group. In FIG. 3, 8a is an exhaust manifold for connecting exhaust ports of a cylinder group consisting of # 1 and # 4 cylinders to an individual exhaust passage 9a, and 8b.
Is an exhaust manifold that connects the exhaust ports of a cylinder group consisting of # 2 and # 3 cylinders to the individual exhaust passage 9b.

In this embodiment, the three-way catalyst 4 is connected to the exhaust manifold 8a, and the O2 storage component 3 is connected to the exhaust manifold 8b. A means 6 for detecting the O ₂ concentration in the exhaust passage is arranged on the individual exhaust passage 9b. Further, the individual exhaust passages 9 a and 9 b join together in the wake of the three-way catalyst 4 and the O 2 storage component 3 and are connected to the common exhaust passage 10. The NOx trap catalyst 5 is connected to the common exhaust passage 10.

The present embodiment is characterized in that the O2 storage component 3 is arranged in parallel with the three-way catalyst 4 in the form of divided cylinder groups. When an internal combustion engine having excellent combustion efficiency such as a diesel engine is used, the combustion temperature in the engine is low, so that the internal combustion engine according to the present embodiment is more likely to be installed than a position separated from the engine 1 as shown in FIG. By arranging it at a position closer to the engine, it becomes easier to secure the temperature of the O2 storage component. Further, in the present embodiment, the reducing agent discharged from the cylinder group in which the O 2 storage component 4 is arranged does not pass through the three-way catalyst 4 but directly flows into the NOx trap catalyst 5. Therefore, when making the exhaust gas air-fuel ratio rich,
The degree of enrichment can be made shallower than that of the configuration shown in FIG. 1, and as a result, the fuel consumption in the engine 1 can be reduced and the deterioration of fuel efficiency due to the enrichment processing can be reduced. In the present embodiment, since the reducing gas (CO, HC) flowing into the O2 storage component is extremely small in amount purified by the O2 storage component, the amount of CO flowing into the NOx trap catalyst 5 is large. The heat generation amount due to the combustion reaction can be increased, and the NOx trap catalyst 5 can be activated more quickly.

Although the present invention has been described in detail above with reference to some embodiments, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the gist of the present invention. For example, the application target of the present invention is not limited to the diesel engine, and it goes without saying that the present invention can also be applied to a so-called lean burn engine.

[0031]

As described above, according to the present invention, the oxygen storage means is arranged at a predetermined position in the exhaust gas passage, so that the NOx purification efficiency is excellent even under low temperature exhaust gas conditions. It is possible to provide an exhaust gas purification device that realizes the above.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an exhaust gas purification device of the present invention.

FIG. 2 is a flowchart showing air-fuel ratio enrichment processing control in the exhaust gas purification device of the present invention.

FIG. 3 is a schematic configuration diagram showing another embodiment of the exhaust gas purification device of the present invention.

[Explanation of symbols]

1 engine (diesel engine) 2 controller 3 O2 storage means 4 three-way catalyst 5 NOx trap catalyst 6 O2 concentration detection means 7 Exhaust gas air-fuel ratio detection means 8a Individual exhaust manifold a 8b Individual exhaust manifold b 9a Individual exhaust passage a 9b Individual exhaust passage b 10 common exhaust passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 F01N 3/28 301C F term (reference) 3G091 AA02 AA18 AB03 AB06 BA14 CA26 CB02 DA02 DB10 DC03 EA33 EA34 FB02 GA06 GB02W GB03W GB05W GB10Y HA03 HA08 HA19 HA20 HA36 HA37 HB02

Claims (7)

[Claims] 1. An exhaust gas purifying apparatus comprising an oxygen storage means having an oxygen storage component on the upstream side of an exhaust gas passage of an internal combustion engine, and an NOx trap catalyst on the downstream side thereof, the exhaust gas from the internal combustion engine Gas has a rich air-fuel ratio
There are times when the temperature fluctuates in the lean state and the NOx trap catalyst cannot be activated, and there is a low temperature state where the oxygen storage means releases the amount of oxygen and the exhaust gas air-fuel ratio rich when the oxygen storage component is exhaust gas air-fuel ratio rich. An exhaust gas purifying apparatus, characterized in that heat caused by the amount of reducing agent at the time is arranged at a position sufficient to raise the temperature and activate the NOx trap catalyst. 2. The exhaust gas purifying apparatus according to claim 1, wherein the oxygen storage means is arranged in the exhaust gas passage at a position where the oxygen storage component is heated to 300 ° C. or higher. . 3. The exhaust gas purifying apparatus according to claim 1, wherein the oxygen storage means is arranged immediately after the exhaust manifold and / or upstream of the front tube. 4. An exhaust gas purifying catalyst is added to the upstream side of the oxygen storage means.
The exhaust gas purification device according to any one of paragraphs 1. 5. An exhaust gas purifying catalyst is added in parallel to the oxygen storage means.
3. The exhaust gas purification device according to any one of item 3. 6. The oxygen concentration detecting means and the air-fuel ratio detecting means are additionally provided between the oxygen storage means and the NOx trap catalyst, and the NOx is detected according to the oxygen concentration detected by the oxygen concentration detecting means. The exhaust gas purifying apparatus according to any one of claims 1 to 5, wherein the air-fuel ratio of the exhaust gas flowing into the trap catalyst is controlled. 7. The reducing agent in the exhaust gas when oxygen is released from the oxygen releasing means is hydrogen concentration / total reducing agent concentration <
7. The relationship of 0.3 is satisfied, which is characterized in that
The exhaust gas purification device according to any one of paragraphs 1.