JP3514200B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxide (NO) from exhaust gas discharged from an internal combustion engine capable of lean combustion.
x) is related to an exhaust gas purification device.

[0002]

2. Description of the Related Art There is an NOx storage reduction catalyst as an exhaust gas purification apparatus for purifying NOx from exhaust gas discharged from an internal combustion engine capable of lean combustion. This NOx storage reduction catalyst (hereinafter sometimes abbreviated as NOx catalyst) absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean (that is, in an oxygen excess atmosphere), and the oxygen concentration of the inflowing exhaust gas is It is a catalyst that releases NOx absorbed and reduces it to N ₂ when it decreases.

When this NOx storage reduction catalyst is arranged in the exhaust passage of an internal combustion engine, nitrogen oxides (NOx) can be absorbed from the exhaust gas with a lean air-fuel ratio, but the NOx absorption capacity of the NOx catalyst is also limited. Therefore, when the NOx absorption amount reaches a predetermined amount, a reducing gas having a low oxygen concentration (for example, an exhaust gas having a stoichiometric air-fuel ratio or a rich air-fuel ratio) is passed through the NOx catalyst to desorb the absorbed NOx. It is necessary to restore the NOx absorption capacity by reducing it to ₂ (hereinafter, this processing is referred to as NOx releasing processing).

Therefore, as an exhaust gas purification system using a NOx storage reduction catalyst, as disclosed in Japanese Patent Application Laid-Open No. 62-106826, the exhaust passage is branched in the middle of the exhaust gas.
Book exhaust passages, and storage reduction type N in each exhaust passage
An exhaust gas in which an Ox catalyst is arranged and exhaust gas is passed through one NOx catalyst to absorb NOx in the exhaust gas, while reducing gas is passed through the other NOx catalyst to perform NOx release processing of the NOx catalyst. Purification systems are being developed.

In the exhaust gas purification device disclosed in the above publication,
In order to be able to process the NOx catalysts in parallel as described above, the exhaust gas is diverted to the branch portion of the exhaust passage.
An exhaust switching valve for switching between flowing to the x-catalyst is provided, and a reducing gas supply port is provided in each exhaust passage between this exhaust switching valve and each NOx catalyst so that reducing gas can be supplied to each NOx catalyst, and further reduction is performed. A reducing gas switching means for selectively switching which reducing gas supply port the gas is introduced is provided.

[0006]

However, in the above-mentioned conventional exhaust gas purification device, two reducing gas supply ports are required, and therefore, there are also two reducing gas passages for introducing the reducing gas into each reducing gas supply port. In addition, since the reducing gas switching means and its control are required, the apparatus becomes complicated and the cost is increased. In particular, in the case of an exhaust emission control device mounted on a vehicle, the mounting space is small, and thus the complication of the device becomes a major obstacle.

The present invention has been made in view of the above-mentioned problems of the prior art, and the problem to be solved by the present invention is to simplify the apparatus by using a single reducing agent supply port. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine, which can reduce costs.

[0008]

The present invention adopts the following means in order to solve the above problems. (1) The present invention relates to (a) an exhaust passage of an internal combustion engine capable of lean combustion, which is branched into a plurality of parallel exhaust passages;
(B) NO is provided when the air-fuel ratio of the inflowing exhaust gas is lean, which is arranged in each of the plurality of branched exhaust passages.
a storage-reduction type NOx catalyst that absorbs x and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas is low, and reduces it to N _2;
Exhaust path switching means for selectively introducing into the catalyst, and (d) the storage reduction type NO in which exhaust gas does not flow.
In an exhaust gas purification apparatus for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent to the catalyst, the reducing agent supply port of the reducing agent supply means has the exhaust path switching means for storing and reducing exhaust gas. It is characterized in that it is located in a flow path connected to a storage reduction type NOx catalyst in which exhaust gas does not flow regardless of whether it is introduced into the type NOx catalyst.

In this exhaust gas purification apparatus for an internal combustion engine, it is selected by the exhaust path switching means which of the storage reduction type NOx catalysts the exhaust gas should flow through, and the selected storage reduction type NOx catalyst is selected.
By flowing the exhaust gas through the x catalyst, NOx in the exhaust gas is absorbed by the NOx storage reduction catalyst. In the meantime, the reducing agent is supplied from the reducing agent supply device to the NOx storage reduction catalyst in which exhaust gas is not flowing, so that the NOx absorbed in the NOx storage reduction catalyst is desorbed, and N ₂ is absorbed.
To the N, and thereby the N of the storage reduction type NOx catalyst is reduced.
Restores Ox absorption capacity. That is, the NOx removal process in the exhaust gas and the NOx absorption capacity recovery process of the NOx storage reduction catalyst can be simultaneously executed in parallel. In this exhaust gas purification device, only one reducing agent supply means and one reducing agent supply port are required, so that the device can be simplified and the cost can be reduced.

In the exhaust gas purifying apparatus for an internal combustion engine described in (1) above, when the temperature of the NOx storage reduction catalyst or the exhaust gas temperature is below a predetermined temperature, the exhaust path switching means all of the occlusions. The reduction type NOx catalyst may be operated so as to flow the exhaust gas. By doing so, a mixed gas of the lean air-fuel ratio exhaust gas and the reducing agent can be supplied to all the NOx storage reduction catalysts, and as a result, the reducing agent is oxidized in the NOx storage reduction catalysts. It is possible to raise the temperature of the NOx storage reduction catalyst.

In the exhaust gas purifying apparatus for an internal combustion engine described in (1) above, an ignition means can be provided upstream of the NOx storage reduction catalyst. In this way, the reducing agent supplied to the NOx storage reduction catalyst in which exhaust gas does not flow can be ignited by the ignition means upstream of the NOx storage reduction catalyst, and as a result, the heat of combustion of the reducing agent is reduced. Can be used to heat and raise the temperature of the NOx storage reduction catalyst. Therefore, it is necessary to quickly raise the catalyst bed temperature of the NOx storage reduction catalyst to the temperature required for NOx absorption, or to raise the catalyst bed temperature of the NOx catalyst quickly to the temperature required for NOx release / reduction. You can

(2) Further, according to the present invention, when the air-fuel ratio of the exhaust gas flowing into the exhaust passage of the internal combustion engine capable of lean burn is lean and the oxygen concentration of the exhaust gas flowing in is low, the NOx is absorbed. An exhaust gas purification apparatus for an internal combustion engine, which is provided with an occlusion reduction type NOx catalyst that releases absorbed NOx and reduces it to N ₂ , and includes a reducing agent supply means for supplying a reducing agent to an exhaust passage upstream of the occlusion reduction type NOx catalyst. In the above, the exhaust passage is provided with an upstream exhaust passage connected to an internal combustion engine, and a first branch that is branched from the upstream exhaust passage into two.
A downstream exhaust passage and a second downstream exhaust passage, the first and second downstream exhaust passages are provided with the NOx storage reduction catalyst, and the upstream exhaust passage of the exhaust passage and the first and second exhaust passages. 2 An exhaust path switching valve is provided in a branch portion with the downstream exhaust passage, and the exhaust path switching valve includes (a) a first port connected to the upstream exhaust passage and the first downstream exhaust passage. A housing having a second port connected thereto and a third port connected to the second downstream exhaust passage,
(B) A first position, which is rotatably supported in the housing, connects the first port and the second port, and shuts off the third port from these ports;
A valve body that connects the port and the third port and that can switch to a second position that blocks the second port from these ports; and (c) when the valve body is provided in the housing and the valve body is in the first position. A reducing agent supply unit that is cut off from the first port and communicates with the third port, and that is cut off from the first port and communicates with the second port when positioned at the second position. The reducing agent is supplied from the reducing agent supply means to the reducing agent supply unit of the switching valve.

In this exhaust gas purification apparatus for an internal combustion engine, when the valve body of the exhaust path switching valve is located at the first position, the exhaust gas flows into the first downstream side exhaust passage and does not flow into the second downstream side exhaust passage, and the exhaust gas is exhausted. NOx in the gas is absorbed by the NOx storage reduction catalyst provided in the first downstream exhaust passage. And
When the reducing agent is supplied to the reducing agent supply unit while the valve body is located at the first position as described above, the reducing agent flows into the second downstream side exhaust passage, and is stored in the second downstream side exhaust passage. NOx absorbed in the reduced NOx catalyst is desorbed,
The NOx absorption capacity of the storage-reduction type NOx catalyst is restored by being reduced to N ₂ . That is, NOx in the exhaust gas
The removal process and the NOx absorption capacity recovery process of the NOx storage reduction catalyst can be simultaneously executed in parallel.

Further, when the valve body of the exhaust path switching valve is positioned at the second position, the exhaust gas flows into the second downstream exhaust passage and does not flow into the first downstream exhaust passage, and NOx in the exhaust gas is exhausted.
Is absorbed by the NOx storage reduction catalyst provided in the second downstream exhaust passage. Then, when the reducing agent is supplied to the reducing agent supply unit while the valve body is positioned at the second position in this way, the reducing agent flows into the first downstream side exhaust passage and is provided in the first downstream side exhaust passage. The NOx absorbed by the storage reduction type NOx catalyst is desorbed and reduced to N ₂ , whereby the NOx absorption capacity of the storage reduction type NOx catalyst is restored. That is, the NOx removal process in the exhaust gas and the NOx absorption capacity recovery process of the NOx storage reduction catalyst can be simultaneously executed in parallel. In this exhaust gas purification device, only one reducing agent supply means and one reducing agent supply unit are required, so that the device can be simplified and the cost can be reduced.

In the exhaust gas purifying apparatus for an internal combustion engine as described in (2) above, the exhaust path switching valve is in the third position in which the first port, the second port, the third port and the reducing agent supply section are in communication at the same time. The valve body can be held. By doing so, it becomes possible to supply the mixed gas of the lean air-fuel ratio exhaust gas and the reducing agent to both the first downstream exhaust passage and the second downstream exhaust passage, and as a result, the storage reduction type By oxidizing the reducing agent in the NOx catalyst, it is possible to raise the temperature of the storage reduction type NOx catalyst.

In the exhaust gas purifying apparatus for an internal combustion engine according to (2), between the exhaust path switching means and the NOx storage reduction catalyst in the first downstream exhaust passage, and the exhaust path switching means. Ignition means may be provided between the second downstream exhaust passage and the NOx storage reduction catalyst.

In this case, the ignition means belonging to the first or second downstream side exhaust passage to be closed by the exhaust path switching means closes the circulation of the exhaust gas to the downstream side exhaust passage. Therefore, the exhaust path switching means can be operated after switching the exhaust path.

In order to supply a reducing agent to the NOx storage reduction catalyst to release NOx from the NOx storage reduction catalyst and reduce it to N ₂ , the NOx storage reduction catalyst must be heated to a predetermined temperature or higher. Therefore, when the NOx storage / reduction type NOx catalyst to be NOx released / reduced does not reach the predetermined temperature, it is preferable to heat the storage / reduction type NOx catalyst to raise the temperature. When NOx is released from the NOx storage reduction catalyst and is reduced, the exhaust gas is closed to the NOx catalyst. At that time, the exhaust path switching means controls the exhaust gas flow to the NOx storage reduction catalyst. After closing the flow, when the ignition means of the downstream side exhaust passage accommodating the storage reduction type NOx catalyst is operated, the reducing agent can be burned upstream of the storage reduction type NOx catalyst, and the combustion heat is generated. By utilizing this, the temperature of the storage reduction type NOx catalyst can be raised.

Further, in the exhaust gas purification device for an internal combustion engine as described in (2) above, between the exhaust path switching means and the storage reduction type NOx catalyst in the first downstream exhaust passage, and the exhaust path switching means. And an NOx storage reduction catalyst in the second downstream side exhaust passage, the first or second downstream side exhaust passage through which the exhaust gas flow switching means should start the flow of the exhaust gas when an ignition means is provided. The ignition means belonging to can be made to operate before the exhaust path switching means switches the exhaust path in order to flow the exhaust gas to the downstream side exhaust passage.

In order for the NOx in the exhaust gas to be absorbed by the NOx storage reduction catalyst, it is necessary to raise the temperature of the NOx storage reduction catalyst to a predetermined temperature or higher. Therefore, when the NOx in the exhaust gas is absorbed by flowing the exhaust gas through the NOx storage reduction catalyst, if the NOx storage reduction catalyst does not reach the predetermined temperature, the NOx storage reduction catalyst is heated. It is preferable to raise the temperature. When starting the flow of the exhaust gas to the storage reduction type NOx catalyst, the exhaust path switching means allows the flow of the exhaust gas to the storage reduction type NOx catalyst, but at that time, by the exhaust path switching means Before allowing the exhaust gas to flow to the NOx storage reduction catalyst, that is, the exhaust path switching means switches the exhaust path so as to flow the exhaust gas to the downstream exhaust passage in which the NOx storage reduction catalyst is accommodated. If the ignition means of the downstream side exhaust passage is activated before, the reducing agent can be burned upstream of the NOx storage reduction catalyst, and the heat of combustion is used to raise the temperature of the NOx storage reduction catalyst. can do.

In the exhaust gas purification apparatus for an internal combustion engine according to the above (1) and (2), examples of the lean burn internal combustion engine include a diesel engine and a lean burn gasoline engine.

In the exhaust gas purification apparatus for an internal combustion engine as described in (1) and (2) above, LPG (liquefied natural gas), CNG (natural gas), gasoline, gas obtained by vaporizing light oil, or the like is further used as a reducing agent. A gas obtained by heating and decomposing gas, a combustion gas discharged from a combustion heater, or the like can be used. Here, the combustion heater is a device that burns fuel in a combustion chamber provided separately from an internal combustion engine as a power source to obtain thermal energy for the purpose of promoting warm-up and improving the performance of a vehicle interior heating device. is there.

In the exhaust gas purification apparatus for an internal combustion engine as described in (1) and (2) above, the NOx storage reduction catalyst uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, and cesium are supported on the carrier. At least one selected from alkali metals such as Cs, barium Ba, alkaline earths such as calcium Ca, lanthanum La, rare earths such as yttrium Y, and a noble metal such as platinum Pt are supported. It can be illustrated.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings of FIGS. Each of the following embodiments is a mode in which the present invention is applied to a diesel engine as an internal combustion engine.

[First Embodiment] First, a first embodiment of an exhaust purification system for an internal combustion engine according to the present invention will be described with reference to the drawings of FIGS. 1 to 4. FIG. 1 is a diagram showing a schematic configuration of an exhaust emission control device for a diesel engine as an internal combustion engine. In this figure, the engine 1 has four in-line cylinders, and intake air is supplied to each cylinder via an intake pipe 2 and an intake manifold 3.

The fuel (light oil) in the fuel tank 4 is sucked up by the fuel supply pump 5 whose discharge pressure can be controlled and supplied to the common rail 6. The engine control electronic control unit (ECU) 50 controls the operation of the fuel supply pump 5 so that the fuel pressure in the common rail 6 becomes a predetermined pressure value according to the operating state of the engine 1.

Further, the engine 1 is provided with a fuel injection valve 7 for injecting the fuel supplied from the common rail 6 into each cylinder, and the opening timing and opening period of the fuel injection valve 7 are the engine 1 It is controlled by the ECU 50 according to the operating state of the.

Fuel is injected into the combustion chamber of each cylinder from the corresponding fuel injection valve 7 in the vicinity of the compression top dead center in each cylinder, and the exhaust gas generated by combustion at a lean air-fuel ratio is exhausted via the exhaust manifold 8. It is discharged to the pipe 9.

The exhaust pipe 9 is connected to an S trap 20 containing an SOx absorbent 21 therein, and the S trap 20 is connected to a three-way valve (exhaust passage switching means, exhaust passage switching valve) 30 via the exhaust pipe 10. Has been done. In this embodiment, the exhaust pipes 9 and 10 form an upstream exhaust passage.

The SOx absorbent 21 absorbs SOx when the air-fuel ratio of the exhaust gas is lean, and can be composed of a three-way catalyst, a storage reduction type NOx catalyst, a selective reduction type NOx catalyst or the like.

The housing 31 of the three-way valve 30 has a rugby ball shape and has three ports 31a, 31b and 31c. The first port 31a is provided on the upstream end side of the housing 31, and the exhaust pipe 1 is connected to the first port 31a.
0s are connected. Second port 31b and third port 3
1c is arranged on the downstream side of the first port 31a and spaced apart from each other, and exhaust pipes 11 and 12 are connected to the second port 31b and the third port 31c, respectively.

Storage-reduction type NOx catalysts (hereinafter abbreviated as NOx catalysts) 61 and 62 are housed in the exhaust pipes 11 and 12, respectively, and the exhaust pipes 11 and 12 are located downstream of the NOx catalysts 61 and 62. Joined 13 NOx
The catalysts 61 and 62 will be described in detail later. In addition, in this embodiment, the exhaust pipe 11 constitutes a first downstream side exhaust passage, and the exhaust pipe 12 constitutes a second downstream side exhaust passage.

A valve element 32 is mounted inside the housing 31 so as to be rotatable around a support shaft 33 as a rotation center.
The support shaft 33 is arranged so as to be displaced downstream from the center of the housing 31, and when the valve body 32 is rotated around the support shaft 33 as a rotation center, the entire peripheral edge of the valve body 32 is located in the housing 31. It is designed to slide on the inner surface.

A reducing agent supply chamber (reducing agent supply section) 34 which bulges outward is provided on the downstream end side of the housing 31, and a valve for the housing 31 is provided only in the reducing agent supply chamber 34. The sliding state of the body 32 is released.

The valve body 32, as shown in FIG.
The downstream side edge of the valve element 3 slightly deviates from the reducing agent supply chamber 34
A position where the entire peripheral edge of 2 is in sliding contact with the inner surface of the housing 31 (positions indicated by thick solid lines and thick broken lines in FIG. 2)
The rotation range (operating range) is set so as to rotate within the range. The valve body 32 is rotationally driven by the valve drive device 35, and the stop position of the valve body 32 is controlled by the ECU 50.

When the valve body 32 is positioned as shown by the thick solid line in FIG. 2 (in the following description, "valve body 32
Is located at the first position "), the first port 31a and the second port 31b communicate with each other, and the exhaust pipe 10
And the exhaust pipe 11 communicate with each other. At the same time, the third port 31c is connected to the first port 31a and the second port 31b.
And is connected to the reducing agent supply chamber 34.

Further, when the valve element 32 is positioned as shown by the thick broken line in FIG. 2 (hereinafter, "when the valve element 32 is positioned at the second position"), the first port 31a and the third port 31a are connected. The port 31c communicates with each other, and the exhaust pipe 10 and the exhaust pipe 12 communicate with each other. At the same time, the second port 31b is blocked from the first port 31a and the third port 31c and communicates with the reducing agent supply chamber 34.

Therefore, the three-way valve 30 controls the exhaust gas to N
It can be said to be an exhaust path switching means for selectively switching which of the Ox catalysts 61 and 62 is to be introduced. Further, the reducing agent supply chamber 34 is a part of the flow path connected to the NOx catalyst in which the exhaust gas does not flow, regardless of whether the three-way valve 30 introduces the exhaust gas into the NOx catalyst 61 or 62. it can.

Further, as shown by the thin broken line in FIG. 2, when the valve body 32 is positioned so that the downstream side edge of the valve body 32 fits in the center of the reducing agent supply chamber 34 (in the following description, "valve body" will be referred to as "valve body"). "When 32 is in the third position")
The first port 31a, the second port 31b, the third port 31c, and the reducing agent supply chamber 34 are all in communication with each other, and as a result, the exhaust pipe 10 and the rich gas supply nozzle 40 described later are connected to the exhaust pipes 11 and 12. Connect to both.

The housing 31 is provided with a rich gas supply nozzle (reducing agent supply port) 40 facing the reducing agent supply chamber 34, and the rich gas supply nozzle 40 is supplied from a rich gas supply device (reducing agent supply means) 41. The rich gas (reducing agent) is released into the reducing agent supply chamber 34. This rich gas is used as the storage reduction type NOx catalyst 6 as described later.
It is supplied to 1, 62 as a reducing agent and used for releasing and reducing NOx. The operation of the rich gas supply device 41 is controlled by the ECU 50.

The rich gas is a gas obtained by vaporizing LPG (liquefied natural gas), CNG (natural gas), gasoline, or light oil, a gas obtained by heating these gases to decompose them, or is discharged from a combustion heater. Combustion gas or the like can be used. Here, the combustion heater is a device that burns fuel in a combustion chamber provided separately from an internal combustion engine as a power source to obtain thermal energy for the purpose of promoting warm-up and improving the performance of a vehicle interior heating device. is there.

The exhaust pipe 13 is provided with an output signal corresponding to the temperature of the exhaust gas at a position near the exhaust pipes 11 and 12 by the ECU 5
An exhaust temperature sensor 16 that outputs 0 is attached.
The ECU 50 is composed of a digital computer, and ROM (read only memory), RAM (random access memory), CPU which are mutually connected by a bidirectional bus.
A central processor unit, an input port, and an output port are provided, and basic control such as fuel injection amount control of the engine 1 is performed. In this embodiment, operation control of the valve body 32 of the three-way valve 30 is performed. There is.

For these controls, an input signal from the accelerator opening sensor 14 is input to the input port of the ECU 50,
An input signal from the crank angle sensor 15 is input. The accelerator opening sensor 14 outputs an output voltage proportional to the accelerator opening to the ECU 50, and the ECU 50 calculates the engine load based on the output signal of the accelerator opening sensor 14. The crank angle sensor 15 outputs an output pulse to the ECU 50 every time the crankshaft rotates by a certain angle, and the EC
U50 calculates the engine speed based on this output pulse. The engine operating state is determined by the engine load and the engine speed.

Next, regarding the NOx catalysts 61 and 62 housed in the exhaust pipes 11 and 12, that is, the NOx storage reduction type
The catalyst will be described. The NOx catalyst (storage-reduction type NOx catalyst) uses, for example, alumina as a carrier, and on this carrier, for example, potassium metal such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earth metal such as barium Ba, and calcium Ca. , At least one selected from rare earths such as lanthanum La and yttrium Y,
A noble metal such as platinum Pt is supported.

This NOx catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is lean, and the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or becomes rich to the exhaust gas. N absorbed when the oxygen concentration of
Emit Ox. Here, the exhaust air-fuel ratio means the ratio of air and fuel (reducing agent) supplied into the exhaust passage upstream of the engine intake passage and the NOx catalyst.

Therefore, when the fuel, reducing agent or air is not supplied into the exhaust passage upstream of the NOx catalyst, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber.

Although the mechanism of NOx absorption / release action of the NOx catalyst is not clear in some parts, it is considered to be performed by the mechanism shown in FIG. This mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on the carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

First, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration of the inflowing exhaust gas greatly increases. Therefore, as shown in FIG. 3 (A), oxygen O ₂ becomes O ₂ ⁻ or O ^{2 −.} It adheres to the surface of platinum Pt in the form of. Next, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

Next, the produced NO ₂ is absorbed on the NOx catalyst while being oxidized on platinum Pt and is combined with barium oxide (BaO) to form NO _{3 in} the form of nitrate ion NO ₃ ^−.
x Diffuses in the catalyst. In this way, NOx is absorbed in the NOx catalyst.

As long as the oxygen concentration of the inflowing exhaust gas is high, platinum P
As long as NO ₂ is produced on the surface of t and the NOx absorbing ability of the NOx catalyst is not saturated, NO ₂ is absorbed in the NOx catalyst to produce nitrate ion NO ₃ ⁻ .

On the other hand, when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or becomes rich and the oxygen concentration of the inflowing exhaust gas decreases, the amount of NO ₂ produced decreases and the reaction proceeds in the opposite direction (NO ₃ ^- → NO ₂ ), the nitrate ion NO ₃ ⁻ in the NOx catalyst is released from the NOx catalyst in the form of NO ₂ or NO.

On the other hand, when reducing components such as HC and CO are present in the inflowing exhaust gas, these components react with oxygen O ₂ ⁻ or O ^{2 −} on platinum Pt to be oxidized, and oxygen in the exhaust gas is removed. It consumes and reduces the oxygen concentration of the exhaust gas. In addition, the N concentration released from the NOx catalyst due to the decrease in the oxygen concentration of the exhaust gas
O ₂ or NO, as shown in FIG.
It reacts with O and is reduced to N ₂ .

[0053] That is, HC in the inflowing exhaust gas, CO, first oxygen O ₂ on the platinum Pt ^- or O ^2- immediately be reacted with oxidized, then the platinum Pt on the oxygen O ₂ ^- or O ^2- If HC and CO still remain after the consumption of
NOx discharged from the NOx catalyst and NOx discharged from the engine are reduced to N ₂ by C and CO.

In this way, NO ₂ is formed on the surface of platinum Pt.
Alternatively, when NO is no longer present, NO ₂ or NO is released one after another from the NOx catalyst and is further reduced to N ₂ . Therefore, if the air-fuel ratio of the inflowing exhaust gas is made stoichiometric or rich, the NOx absorbed by the NOx catalyst will be released within a short time.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx catalyst, and when the exhaust air-fuel ratio is made stoichiometric or rich, NOx is released from the NOx catalyst within a short time and reduced to N ₂ . To be done. Therefore, it is possible to prevent the emission of NOx into the atmosphere.

By the way, in the case of a diesel engine,
Since combustion is performed in a much leaner range than stoichiometric (theoretical air-fuel ratio, A / F = 13 to 14), the air-fuel ratio of exhaust gas flowing into the NOx catalyst is very lean in a normal engine operating state, NOx in the exhaust gas is absorbed by the NOx catalyst, and the amount of NOx released from the NOx catalyst is extremely small.

In the case of a gasoline engine, the air-fuel ratio of the exhaust gas is made stoichiometric or rich by making the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber stoichiometric or rich. Lower NOx
NOx absorbed by the catalyst can be released, but in the case of diesel engine, if the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is set to the stoichiometric air-fuel ratio or rich, soot will be generated during combustion. There is a problem and we cannot hire.

Therefore, in a diesel engine, N
Before the NOx absorption capacity of the Ox catalyst is saturated, it is necessary to supply the reducing agent directly to the NOx catalyst separately from the air-fuel mixture for combustion at a predetermined timing to release NOx.

Therefore, in this embodiment, a rich gas containing a reducing agent is supplied to the exhaust passages upstream of the NOx catalysts 61 and 62 so that NOx is released from the NOx catalyst and reduced.

Next, the operation of the exhaust purification system in the present embodiment will be described. In this embodiment, E
The CU 50 operates the rich gas supply device 41 at the same time when the engine 1 is started, and constantly supplies the rich gas from the rich gas supply nozzle 40 to the reducing agent supply chamber 34 of the three-way valve 30.

As described above, since the engine 1 is a diesel engine, the exhaust air-fuel ratio is lean and the oxygen concentration is high under normal operating conditions. This exhaust gas is SOx absorbent 2
When it flows to 1, the SOx in the exhaust gas is absorbed by the SOx absorbent 21, so the exhaust gas from which SOx has been removed flows out of the SOx absorbent 21, passes through the three-way valve 30, and the downstream NOx.
It flows into the catalysts 61 and 62. Therefore, the NOx catalyst 6
1,62 SOx poisoning is prevented.

The NOx catalysts 61 and 62 have a catalyst bed temperature T
Is a predetermined temperature (hereinafter, this temperature is called a catalyst activation temperature) T
If it does not reach 0, the NOx purification rate becomes extremely low. Therefore, in this exhaust emission control device, the NOx catalyst 6 is used as when starting the engine 1 at a low temperature.
When the catalyst bed temperature T of 1, 62 does not reach the catalyst activation temperature T0, the valve body 32 of the three-way valve 30 is held in the third position shown by the thin broken line in FIG. Connect to both 12. By doing so, the exhaust gas having a high lean air-fuel ratio, which is discharged from the engine, and the rich gas, which is supplied from the rich gas supply nozzle 40 and has a high reducing agent concentration, flow in both exhaust pipes 11 and 12. As a result, both NO
In the x catalysts 61 and 62, the reducing agent contained in the rich gas is oxidized and the NOx catalysts 61 and 62 are heated. In this embodiment, the catalyst bed temperature of the NOx catalysts 61 and 62 is the NOx catalyst 6 detected by the exhaust temperature sensor 16.
The exhaust gas temperature at the outlets of 1, 62 is substituted.

When the catalyst bed temperature T of the NOx catalysts 61 and 62 is equal to or higher than the catalyst activation temperature T0, the valve body 32 of the three-way valve 30 is shown in the first position shown by a thick solid line in FIG. 2 or by a thick broken line in FIG. Positioned at any of the second positions, the exhaust gas is caused to flow through one of the NOx catalysts 61 and 62, the NOx catalyst absorbs NOx in the exhaust gas, and the other NOx catalyst is caused to flow rich gas. The NOx absorbed by the NOx catalyst is released, and is reduced to N ₂ for purification.

More specifically, for example, the valve body 3 of the three-way valve 30.
When 2 is set to the first position, in the three-way valve 30, the first port 31a and the second port 31b communicate with each other, and the third port 31c and the reducing agent supply chamber 34 communicate with each other.
As a result, the exhaust pipe 10 and the exhaust pipe 11 communicate with each other, and the exhaust pipe 12
Is cut off, the exhaust gas of the lean air-fuel ratio flowing from the exhaust pipe 10 into the housing 31 flows to the exhaust pipe 11,
NOx in the exhaust gas is absorbed by the NOx catalyst 61 of the exhaust pipe 11, and the exhaust gas from which NOx has been removed flows out to the exhaust pipe 13. At the same time, the rich gas supplied to the reducing agent supply chamber 34 flows to the exhaust pipe 12 and flows to the NOx catalyst 62, so that the NOx absorbed in the NOx catalyst 62 is released and reduced to N ₂ for purification. The purified gas flows out to the exhaust pipe 13.

On the other hand, when the valve body 32 of the three-way valve 30 is positioned at the second position, the three-way valve 30 has the first port 31a.
And the third port 31c communicate with each other, and the second port 3
1b communicates with the reducing agent supply chamber 34. As a result, since the exhaust pipe 10 and the exhaust pipe 12 communicate with each other and the exhaust pipe 11 is cut off, the lean air-fuel ratio exhaust gas flowing from the exhaust pipe 10 into the housing 31 flows into the exhaust pipe 12 and N in the exhaust gas is exhausted.
Ox is absorbed by the NOx catalyst 62 of the exhaust pipe 12, and the exhaust gas from which NOx has been removed flows into the exhaust pipe 13. At the same time, the rich gas supplied to the reducing agent supply chamber 34 flows through the exhaust pipe 11 and the NOx catalyst 61, so that the NOx catalyst 6 is discharged.
The NOx absorbed in 1 is released and is reduced to N ₂ for purification, and the purified gas flows out to the exhaust pipe 13.

Next, with reference to FIG. 4, a switching process execution routine for the three-way valve 30 in this embodiment will be described.
A flow chart including each step constituting this routine is stored in the ROM of the ECU 50, and all the processing in each step of the flow chart is performed by the CP of the ECU 50.
Performed by U.

<Step 101> First, the ECU 50
The catalyst bed temperature T of the NOx catalysts 61 and 62 is the catalyst activation temperature T0.
It is determined whether or not the above.

<Step 102> When a negative determination is made in Step 101, the ECU 50 proceeds to Step 102, holds the valve element 32 of the three-way valve 30 in the third position,
Both the NOx catalyst 61, the mixed gas of the exhaust gas and the rich gas,
Then, the temperature of the NOx catalysts 61 and 62 is raised. The temperature raising process in step 102 is step 1
The process continues until a positive determination is made at 01.

<Step 103> When the affirmative determination is made in Step 101, the ECU 50 proceeds to Step 103 and determines whether or not the valve body 32 of the three-way valve 30 is located at the first position.

If the negative determination is made in step 101 the last time this routine was executed, the three-way valve 30
Since the valve body 32 of is located in the third position, EC
U50 makes a negative determination in step 103, and returns to step 10
In step 6, it is determined whether the valve element 32 of the three-way valve 30 is in the second position. In this step 106, a negative determination is made and the process proceeds to step 108 where the valve element 32 of the three-way valve 30 is switched to the first position, and after switching. The counting of the elapsed time from is started and this routine is once ended.

By positioning the valve body 32 at the first position, the exhaust gas flows through the exhaust pipe 11 and the NOx catalyst 61, and NOx in the exhaust gas is absorbed by the NOx catalyst 61, so that N
The exhaust gas from which Ox has been removed flows out to the exhaust pipe 13. Further, the rich gas supplied from the rich gas supply nozzle 40 flows into the exhaust pipe 12 and the NOx catalyst 62, and the NOx catalyst 62
The NOx absorbed in the exhaust gas is released, is reduced to N ₂ and flows out to the exhaust pipe 13.

<Step 104> When the affirmative determination is made in step 103, the ECU 50 proceeds to step 104 and determines whether or not the elapsed time after switching the valve body 32 to the first position has passed the NOx releasing time. . Here, the NOx release time is the flow time of the rich gas necessary to release almost all the NOx absorbed in the NOx catalyst 62, and the NOx release time is set to a predetermined time by conducting an experiment in advance, and Is stored in the ROM of the ECU 50. When the elapsed time does not exceed the NOx releasing time, the valve element 32 of the three-way valve 30 is continuously held at the first position.

<Step 105> When the affirmative determination is made in Step 104, the ECU 50 proceeds to Step 105, switches the valve body 32 of the three-way valve 30 to the second position, and starts counting the elapsed time after the switching. This routine is once ended.

By positioning the valve body 32 at the second position, the exhaust gas flows into the exhaust pipe 12 and the NOx catalyst 62, and NOx in the exhaust gas is absorbed by the NOx catalyst 62, so that N
The exhaust gas from which Ox has been removed flows out to the exhaust pipe 13. Further, the rich gas supplied from the rich gas supply nozzle 40 flows into the exhaust pipe 11 and the NOx catalyst 61, and the NOx catalyst 61
The NOx absorbed in the exhaust gas is released, is reduced to N ₂ and flows out to the exhaust pipe 13.

<Step 106> When the determination in step 103 is negative, the ECU 50 proceeds to step 106 and determines whether the valve element 32 of the three-way valve 30 is located at the second position. Here, when the affirmative determination is made in step 101 when this routine is executed last time, since the valve body 32 of the three-way valve 30 is located at the second position, the ECU 50 makes an affirmative determination in step 106, Proceed to 107.

<Step 107> In step 107, the ECU 50 determines whether or not the elapsed time after switching the valve element 32 to the second position has passed the NOx releasing time. Here, the NOx release time is the flow time of the rich gas required to release almost all the NOx absorbed by the NOx catalyst 61, and the NOx of the NOx catalyst 62 is N.
It is the same as the Ox release time. When the elapsed time does not exceed the NOx release time, the valve body 32 of the three-way valve 30 is set to the second position.
Continue to hold in position.

<Step 108> When the affirmative determination is made in Step 107, the ECU 50 proceeds to Step 108, switches the valve element 32 of the three-way valve 30 to the first position, starts counting the elapsed time after the switching, This routine ends.

As described above, in the exhaust gas purification device of this embodiment, only one switching valve 30, one rich gas supply device 41, and one rich gas supply nozzle 40 are sufficient. Therefore, the device can be simplified. Therefore, the cost can be reduced. Further, the control of the three-way valve 30 and the rich gas supply device 41 is also simplified.

In the above-described embodiment, the rich gas supply device 41 is always operated, and the NOx releasing process of one NOx catalyst is completed, and at the same time, the position of the valve body 32 of the three-way valve 30 is switched to change the NOx catalyst of the other. Although it is controlled to execute the NOx releasing process, the position switching timing of the valve body 32 is not limited to this. For example, even if the NOx releasing process of one NOx catalyst is completed, the three-way valve 30
Without switching the position of the valve body 32, the one NOx catalyst is kept in the standby state and the exhaust gas is continuously flown to the other NOx catalyst, and the NOx absorbed by the other NOx catalyst.
When the ECU 50 determines that the amount has reached a predetermined amount, the position of the valve body 32 of the three-way valve 30 is switched to set the other N
The present invention can be realized by controlling the Ox catalyst so that the NOx releasing process is executed. In that case, one of the N
At the same time when the NOx release processing of the Ox catalyst is completed (that is, N
It is preferable that the rich gas supply device 41 is stopped to stop the supply of the rich gas, and the rich gas supply device 41 is operated simultaneously with the switching of the position of the valve body 32 so that the rich gas is supplied so as to supply the rich gas.

[Second Embodiment] Next, a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings of FIGS. 5 and 6. The difference between the exhaust emission control device of the second embodiment and that of the first embodiment will be described below.

In the exhaust emission control system of the second embodiment, N
The Ox catalysts 61 and 62 are housed on the downstream end side of the exhaust pipes 11 and 12, and the NOx catalyst 6 is placed in the exhaust pipes 11 and 12.
Ignition plugs (ignition means) 42, 43 are attached to the sites spaced apart by a predetermined distance from 1, 1, 62 upstream. The operation of the spark plugs 42 and 43 is controlled by the ECU 50.

Further, the exhaust pipes 11 and 12 have spark plugs 4
Fire extinguishing body 4 at a part that is separated from 2, 43 upstream by a predetermined dimension.
4 and 45 are attached, and extinguishers 44 and 45 and N
Between the Ox catalysts 61 and 62 are heating chambers 46 and 47, respectively. The extinguishers 44 and 45 are for preventing a flame generated in the heating chambers 46 and 47 from flashing back into the three-way valve 30 from the heating chambers 46 and 47 as described later.

Since the other structure is the same as that of the first embodiment, the same reference numerals are given to the same aspect parts and the description thereof will be omitted. Incidentally, in the second embodiment,
The rich gas supply device 41 is always operated, and one of the NOx
Simultaneously with the end of the NOx releasing process of the catalyst, the position of the valve element 32 of the three-way valve 30 is switched to control the NOx releasing process of the other NOx catalyst.

The exhaust purification system of the second embodiment has the following actions in addition to the actions of the exhaust purification system of the first embodiment described above. As mentioned above, N
If the catalyst bed temperature of the Ox catalysts 61 and 62 does not reach the catalyst activation temperature, the NOx purification rate becomes extremely low. In other words, when the catalyst bed temperature of the NOx catalysts 61 and 62 is lower than the catalyst activation temperature, the NOx absorption capacity and the NOx release / reduction capacity become extremely low.

Therefore, when executing the NOx releasing process for the NOx catalysts 61, 62, it is desirable that the NOx catalysts 61, 62 have reached the catalyst activation temperature from the start of the NOx releasing process.

However, depending on the engine operating state before the exhaust gas path switching by the three-way valve 30, the catalyst bed temperature of the NOx catalyst to be subjected to the NOx releasing processing at the time of the path switching (that is, the starting point of the NOx releasing processing) is In some cases, the catalyst activation temperature has not been reached.

Therefore, in this second embodiment, in such a case, not only the rich gas is supplied to the reducing agent supply chamber 34, but also the NOx catalyst (61 or 62) which is the target of the NOx releasing process is accommodated. By operating the spark plug (42 or 43) attached to the exhaust pipe (11 or 12) being operated, the rich gas supplied to the exhaust pipe is ignited, and the flame is introduced into the heating chamber (46 or 47). To heat the upstream space of the NOx catalyst and the exhaust pipe wall, and to heat these heats to the NOx catalyst to quickly raise the catalyst bed temperature of the NOx catalyst to the catalyst activation temperature necessary for the NOx releasing process. I chose When the catalyst bed temperature of the NOx catalyst reaches the catalyst activation temperature required for the NOx releasing process, the operation of the spark plug is stopped and N
The supply of rich gas for heating the Ox catalyst is terminated, and thereafter, supply of rich gas for NOx release / reduction is performed.

For example, when the valve body 32 of the three-way valve 30 is switched from the first position to the second position and the NOx releasing process is executed for the NOx catalyst 61, N
When the catalyst bed temperature of the Ox catalyst 61 has not reached the catalyst activation temperature required for NOx release processing, E is set immediately after the path switching (the position switching) by the three-way valve 30.
The CU 50 operates the spark plug 42. Then, the rich gas supplied to the reducing agent supply chamber 34 flows into the exhaust pipe 11,
It passes through the extinguishing body 44 and enters the heating chamber 46, where the spark plug 4
It is ignited by 2. Since the exhaust gas is almost prevented from flowing into the exhaust pipe 11 by the valve element 32, a flame can be easily formed.

This flame heats the upstream space of the NOx catalyst 61 and the pipe wall of the exhaust pipe 11, and the NOx catalyst 61 receives these heats and rises in temperature. Then, when the catalyst bed temperature of the NOx catalyst 61 reaches the catalyst activation temperature required for the NOx release processing, the ECU 50 stops the operation of the spark plug 42 and NO
The supply of the rich gas for heating the x-catalyst 61 is terminated, and thereafter, the rich gas for releasing and reducing NOx is supplied. It should be noted that the size of the heating chamber 46 and the ignition plug 42 and the NOx are prevented so that the NOx catalyst 61 is not directly exposed to the flame.
The distance from the catalyst 61 is set.

According to the exhaust gas purification apparatus of the second embodiment which executes the heating process for the NOx catalyst as described above, the NOx releasing process for the NOx catalyst can be performed very efficiently.

[Third Embodiment] Next, a third embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described. The configuration of the exhaust emission control device of the third embodiment is exactly the same as that of the second embodiment described above. The exhaust gas purifying apparatus of the third embodiment is greatly different from that of the second embodiment in the heating timing for the NOx catalysts 61 and 62. Hereinafter, this difference will be described.

In the exhaust purification system of the third embodiment, even if the NOx releasing process of one NOx catalyst is completed, the position switching of the valve element 32 of the three-way valve 30 is not executed immediately and the NOx catalyst of the one NOx catalyst is not executed. And the other N
Exhaust gas continues to flow through the Ox catalyst, and when the ECU 50 determines that the NOx amount absorbed by the other NOx catalyst has reached a predetermined amount, the position of the valve body 32 of the three-way valve 30 is switched to the other NOx catalyst. Shall be controlled to execute the NOx releasing process for

Further, in the third embodiment, at the same time when the NOx releasing process of one NOx catalyst is completed (that is,
Rich gas supply device 41 (after NOx release time elapses)
Is stopped to stop the supply of the rich gas, and at the same time as the position of the valve element 32 is switched, the rich gas supply device 41 is operated to supply the rich gas for the NOx release process.

When controlled in this way, exhaust gas does not flow to the NOx catalyst that is in a standby state after the SOx release process is completed, so the catalyst bed temperature of the NOx catalyst is expected to gradually decrease. . Therefore, when the standby state is released and exhaust gas should flow through the NOx catalyst, the catalyst bed temperature of the NOx catalyst may be lower than the catalyst activation temperature required for NOx absorption.

Therefore, in the exhaust gas purifying apparatus of the third embodiment, in such a case, the valve element 3 of the three-way valve 30 is used.
Before switching the second position, the rich gas supply device 41
Is activated, and NO in the standby state is passed through the reducing agent supply chamber 34.
x The rich gas supplied to the exhaust pipe is ignited by supplying the rich gas to the exhaust pipe (11 or 12) corresponding to the catalyst and operating the spark plug (42 or 43) provided in the exhaust pipe. , A flame is generated in the heating chamber (46 or 47) to heat the NOx catalyst upstream space and the exhaust pipe wall, and the heat is received by the NOx catalyst, and the catalyst bed temperature of the NOx catalyst is required for NOx absorption. The temperature was quickly raised to the catalyst activation temperature. And
When the catalyst bed temperature of the NOx catalyst reaches the catalyst activation temperature required for NOx absorption, the operation of the spark plug is stopped and the supply of rich gas for heating the NOx catalyst is terminated.

After the heating of the NOx catalyst is completed, the position of the valve body 32 of the three-way valve 30 is switched, and the rich gas supply device 41 is operated to supply the rich gas to the reducing agent supply chamber 34. Said NO
Exhaust gas is passed through the x catalyst and NO of the other NOx catalyst
x Discharge process is executed.

More specifically, for example, now, the valve element 32 of the three-way valve 30 is in the second position, the exhaust gas is passed through the NOx catalyst 62 to absorb the NOx, and the NOx catalyst 61 is used. Has already completed the NOx release processing and is in a standby state.

When the ECU 50 determines that the NOx amount absorbed by the NOx catalyst 62 has reached the predetermined amount, before switching the valve body 32 of the three-way valve 30 from the second position to the first position, It is determined whether or not the catalyst bed temperature of the NOx catalyst 61 has reached the catalyst activation temperature required for NOx absorption.

When the catalyst bed temperature of the NOx catalyst 61 has reached the catalyst activation temperature required for NOx absorption, the ECU 50
Immediately switches the valve element 32 of the three-way valve 30 from the second position to the first position and operates the rich gas supply device 41 to supply the rich gas to the NOx catalyst 62 via the reducing agent supply chamber 34. As a result, the exhaust gas flows into the exhaust pipe 11, and NOx in the exhaust gas is absorbed by the NOx catalyst 61. At the same time, N due to rich gas
The NOx releasing process of the Ox catalyst 62 will be executed.

On the other hand, when the catalyst bed temperature of the NOx catalyst 61 has not reached the catalyst activation temperature required for NOx absorption, the ECU 50 controls the valve body 32 of the three-way valve 30 from the second position to the first position. Before switching to, the rich gas supply device 41 is operated to supply the rich gas to the reducing agent supply chamber 34, and the spark plug 42 is operated.
Then, the rich gas supplied to the reducing agent supply chamber 34 flows into the exhaust pipe 11, passes through the extinguishing body 44 and enters the heating chamber 46, where it is ignited by the ignition plug 42, and a flame is generated. Since the exhaust gas is almost prevented from flowing into the exhaust pipe 11 by the valve body 32, a flame can be easily formed. This flame heats the space upstream of the NOx catalyst 61 and the wall of the exhaust pipe 11, and the NOx catalyst 61 receives these heats and rises in temperature.

The catalyst bed temperature of the NOx catalyst 61 is N
When the catalyst activation temperature required for Ox absorption is reached, the ECU
Reference numeral 50 stops the operation of the rich gas supply device 41 and the spark plug 42, and stops the heating of the NOx catalyst 61.

Immediately after that, the ECU 50 switches the valve body 32 of the three-way valve 30 from the second position to the first position and operates the rich gas supply device 41 to supply the rich gas to the NOx catalyst via the reducing agent supply chamber 34. Supply to 62. As a result, the exhaust gas flows into the exhaust pipe 11, and NOx in the exhaust gas is absorbed by the NOx catalyst 61. At the same time, the NOx releasing process of the NOx catalyst 62 with the rich gas is executed.

According to the exhaust gas purification apparatus of the third embodiment which executes the heat treatment for the NOx catalyst as described above, the N-fluid gas immediately after the exhaust gas path is switched by the three-way valve 30.
The Ox purification rate can be improved.

Incidentally, the above-mentioned second embodiment and third embodiment
Also in the exhaust emission control device of the embodiment of the present invention, the NOx catalyst 6 is used when the engine 1 is started at a low temperature.
When the catalyst bed temperature of Nos. 1 and 62 has not reached the catalyst activation temperature, the valve body 32 of the three-way valve 30 is held in the third position shown by the thin broken line in FIG.
1 and 12 are communicated with each other, the rich gas supply device 41 is operated to supply the rich gas to the reducing agent supply chamber 34, and the exhaust gas having a high lean air-fuel ratio of oxygen and exhausted from the engine and supplied from the rich gas supply device 41. The mixed gas with the rich gas having a high reducing agent concentration is supplied to both exhaust pipes 11 and 12.
And the spark plugs 42 and 43 are actuated to ignite the mixed gas to generate flames in both heating chambers 46 and 47, and the flames cause an upstream space of both NOx catalysts 61 and 62 and exhaust pipes 11 and 12 to flow. The pipe wall of the
Both NOx catalysts 61 and 62 are caused to receive heat by the Ox catalysts 61 and 62.
It is also possible to quickly raise the catalyst bed temperature to the catalyst activation temperature.

In this case, NOx may be released from the NOx catalysts 61 and 62 during heating of the NOx catalysts 61 and 62. Therefore, in order to reduce and purify the released NOx, the exhaust gas having a lean air-fuel ratio is used. It is preferable to control the rich degree of the rich gas and the flow rate of the rich gas so that the air-fuel ratio of the mixed gas with the rich gas supplied from the rich gas supply device 41 becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio.

Further, in the exhaust gas purification devices of the first, second and third embodiments, the base materials of the NOx catalysts 61 and 62 are wall flow type and the PM (particulate) in the exhaust gas is also simultaneously. It can also be made removable.

[0107]

According to the exhaust purification system for an internal combustion engine of the present invention, NOx in the exhaust gas by the NOx storage reduction catalyst.
The removal process of NOx and the NOx absorption capacity recovery process of the NOx storage reduction catalyst can be simultaneously executed in parallel.
The excellent effect that the apparatus can be simplified and the cost can be reduced is achieved.

Further, when an ignition device is provided upstream of the NOx storage reduction catalyst, the NOx storage reduction catalyst is provided as necessary.
The temperature of the catalyst can be raised, and the NOx purification capacity of the exhaust purification system can be improved.

[Brief description of drawings]

1 is a first embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
It is a schematic block diagram in the embodiment of.

FIG. 2 is an enlarged cross-sectional view of a three-way valve used in the first embodiment.

FIG. 3 is a diagram for explaining the NOx absorption / release / reduction action of the NOx storage reduction catalyst.

FIG. 4 is an example of a switching process execution routine for the three-way valve in the above embodiment.

FIG. 5 is a second exhaust purification system for an internal combustion engine according to the present invention.
It is a schematic block diagram in the embodiment of.

FIG. 6 is a configuration diagram showing an enlarged main part in the second embodiment.

[Explanation of symbols]

1 Diesel engine (internal combustion engine) 7 Fuel injection valve 9 Exhaust pipe (upstream exhaust passage) 10 Exhaust pipe (upstream exhaust passage) 11 Exhaust pipe (first downstream exhaust passage) 12 Exhaust pipe (second downstream exhaust passage) 16 Exhaust temperature sensor 30 3-way valve (exhaust path switching valve, exhaust path switching means) 31 housing 31a 1st port 31b 2nd port 31c 3rd port 32 valve 34 Reductant supply room (reducing agent supply unit) 40 Rich gas supply nozzle (reductant supply port) 41 Rich gas supply device (reducing agent supply means) 42,43 Spark plug (ignition means) 46,47 heating chamber 50 ECU 61,62 NOx catalyst (NOx catalyst of occlusion reduction type)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/28 F01N 3/28 301H 7/08 7/08 B F02D 9/04 F02D 9/04 E (58) Fields investigated (58) Int.Cl. ⁷ , DB name) F01N 3/08-3/36 F01N 7/08 F02D 9/04

Claims (8)

(57) [Claims] 1. An exhaust passage of an internal combustion engine capable of lean combustion, the exhaust passage being branched into a plurality of parallel lines.
(B) NO is provided when the air-fuel ratio of the inflowing exhaust gas is lean, which is arranged in each of the plurality of branched exhaust passages.
a storage-reduction type NOx catalyst that absorbs x and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas is low, and reduces it to N _2;
Exhaust path switching means for selectively introducing into the catalyst, and (d) the storage reduction type NO in which exhaust gas does not flow.
In an exhaust gas purification apparatus for an internal combustion engine, comprising: a reducing agent supply means for supplying a reducing agent to the catalyst, the reducing agent supply port of the reducing agent supply means has the exhaust path switching means for storing and reducing exhaust gas. An exhaust gas purification apparatus for an internal combustion engine, characterized in that it is located in a flow path connected to an occlusion reduction type NOx catalyst in which exhaust gas does not flow, regardless of whether or not it is introduced into the type NOx catalyst. 2. When the temperature of the NOx storage reduction catalyst or the temperature of the exhaust gas is equal to or lower than a predetermined temperature, the exhaust path switching means operates so as to flow the exhaust gas to all the NOx storage reduction catalysts. The exhaust emission control device for an internal combustion engine according to claim 1. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising an ignition device upstream of the NOx storage reduction catalyst. 4. An exhaust passage of an internal combustion engine capable of lean burn,
A storage-reduction type NOx catalyst that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas is low and reduces it to N ₂ is provided. In an exhaust gas purification apparatus for an internal combustion engine, which comprises a reducing agent supply means for supplying a reducing agent to an exhaust passage upstream of a NOx catalyst, the exhaust passage includes an upstream exhaust passage connected to the internal combustion engine and the upstream exhaust gas. A first downstream side exhaust passage and a second downstream side exhaust passage, which are branched in two from the passage and arranged in parallel; and the first and second downstream side exhaust passages are provided with the NOx storage reduction catalyst, respectively. An exhaust path switching valve is provided at a branch portion between the upstream exhaust path and the first and second downstream exhaust paths of the exhaust path, and the exhaust path switching valve is connected to the upstream exhaust path. 1 port and the first
A housing having a second port connected to the downstream side exhaust passage and a third port connected to the second downstream side exhaust passage; and a housing rotatably supported in the housing, the first port and the second port. A first position in which the ports are communicated with each other and a third port is blocked from these ports; and a communication between the first port and the third port and a second position from these ports
A valve body that is switchable to a second position that shuts off the port, and that is provided in the housing, shuts off from the first port when the valve body is located at the first position, and communicates with the third port; A reducing agent supply section that is cut off from the first port and communicates with the second port when positioned in the second position, and the reducing agent is supplied from the reducing agent supply means to the reducing agent supply section of the exhaust path switching valve. An exhaust gas purification device for an internal combustion engine, which is supplied. 5. The exhaust path switching valve is capable of holding the valve element in a third position in which the first port, the second port, the third port and the reducing agent supply section are in communication at the same time. Item 4. An exhaust gas purification device for an internal combustion engine according to item 4. 6. Between the exhaust path switching means and the NOx storage reduction catalyst of the first downstream exhaust passage, and between the exhaust path switching means and the NOx storage reduction catalyst of the second downstream exhaust passage. 5. An exhaust emission control device for an internal combustion engine according to claim 4, characterized in that an ignition means is provided between the two. 7. The ignition means belonging to the first or second downstream side exhaust passage whose exhaust gas flow is to be closed by the exhaust path switching means is arranged to close the exhaust gas flow to the downstream side exhaust passage. 7. The exhaust emission control device for an internal combustion engine according to claim 6, wherein the exhaust path switching means is operated after switching the exhaust path. 8. The ignition means belonging to the first or second downstream side exhaust passage, which should start the flow of the exhaust gas by the exhaust path switching means, switches the exhaust path to flow the exhaust gas into the downstream side exhaust passage. 7. The exhaust emission control device for an internal combustion engine according to claim 6, wherein the means is activated before switching the exhaust path.