JP2007046515A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively separate and purify components stored in a NOx storage-reduction catalyst by suitably supplying a reducing agent from a reducing agent supply device to the NOx storage-reduction catalyst. <P>SOLUTION: An exhaust emission control device of an internal combustion engine comprises an oxidation catalyst 20 disposed in an engine exhaust passage, the NOx storage-reduction catalyst 23 disposed on the exhaust downstream side, the reducing agent supply device 25 for supplying the reducing agent only to the NOx storage-reduction catalyst, and separates NOx from the NOx storage-reduction catalyst by a NOx separation treatment for making an air-fuel ratio of exhaust gas discharged from an engine body 1 almost a theoretical air-fuel ratio or rich when a NOx storage amount to the NOx storage-reduction catalyst is larger than a limit storage amount. The exhaust emission control device is constructed to supply the reducing agent from the reducing agent supply device to the NOx storage-reduction catalyst during the NOx separation treatment only while a predetermined supply time elapses from start of the NOx separation treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

The exhaust gas discharged from the internal combustion engine main body contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ), in order to remove these harmful components. Further, the internal combustion engine is provided with an exhaust purification catalyst. _The NO _X storage reduction catalyst can be cited as one of such exhaust gas purification catalyst, the air-fuel ratio of the NO _X storage reduction catalyst the exhaust gas flowing into the NO _X occluding and reducing catalyst (hereinafter referred to as "inflow exhaust gas") when is lean (i.e., when the oxygen concentration in the inflowing exhaust gas is high) to occlude NO _X in the inflowing exhaust gas. On the other hand, when the air-fuel ratio of the inflowing exhaust gas is substantially stoichiometric or rich (that is, when the oxygen concentration in the inflowing exhaust gas is low), the stored NO _x is desorbed. The desorbed NO _x is reduced and purified by a reducing agent (hydrocarbon (HC) or carbon monoxide (CO)) in the exhaust gas. Such an NO _x storage reduction catalyst makes it possible to remove NO _x in the exhaust gas even when the air-fuel ratio of the exhaust gas is lean.

However, the storage capacity of the NO _X storage reduction catalyst is limited, and the NO _X storage reduction catalyst cannot store more NO _X than a certain amount. In particular, when a gasoline direct injection and lean-burn engine mainly performs stratified combustion as an internal combustion engine, NO _X is absorbed in the lean and is _the NO _X storage reduction catalyst when the air-fuel ratio in most of the exhaust gas is increased On the other hand. Therefore, in the internal combustion engine provided with _the NO _X storage reduction catalyst performs rich spike to approximately the stoichiometric air-fuel ratio or rich air-fuel ratio temporarily inflowing exhaust gas, the NO _X which is stored in _the NO _X storage reduction catalyst Desorption / purification.

By the way, a reducing agent is required to reduce NO _X desorbed from the NO _X storage reduction catalyst. As described above, when NO _x is desorbed, the air-fuel ratio of the exhaust gas is almost stoichiometric or rich, so HC and CO exist in the exhaust gas. It can also be used as a reducing agent. On the other hand, when compared as a reducing agent, since higher in the reduction ability of hydrogen (H ₂₎ than the HC and CO reduction capabilities, the use of hydrogen from _the NO _X storage reduction catalyst the NO _X effectively as a reducing agent de Can be released and reduced.

Therefore, in the exhaust gas purification device described in Patent Document 1, when NO _X is to be desorbed from the NO _X storage reduction catalyst, the air-fuel ratio of the inflowing exhaust gas is substantially made to the stoichiometric air fuel ratio by the rich spike, and NO _X storage is performed. By supplying hydrogen to the reduction catalyst, NO _x is effectively desorbed and reduced. In particular, in the above exhaust purification apparatus, hydrogen is supplied to the NO _x storage reduction catalyst after a predetermined period has elapsed since the start of the rich spike, thereby reducing the consumption of hydrogen.

JP 2002-180824 A JP 2002-235594 A JP 2001-254640 A Japanese Patent Laid-Open No. 5-106430

By the way, at the time of execution of rich spike, there is a case where a part of NO _x desorbed from the NO _x storage reduction catalyst at the beginning of the rich spike starts out from the NO _x storage reduction catalyst without being reduced. On the other hand, after a certain amount of time has elapsed since the start of the rich spike, the above-described outflow does not occur so much. On the other hand, although the supplying hydrogen at the exhaust purification apparatus when the predetermined period has elapsed since the start of the rich spike to the NO _X occluding and reducing catalyst described in Patent Document 1, by supplying hydrogen after a predetermined period of time also it can not be prevented exudation of the NO _X from _the NO _X storage reduction catalyst as described above, effectively purifying the NO _X hydrogen from _the NO _X storage reduction catalyst despite the supply as a reducing agent I can't. Therefore, in order to effectively desorption and purification of NO _X that is occluded in the NO _X occluding and reducing catalyst, it is necessary to supply the appropriate reducing agent from the reducing agent supply device to _the NO _X storage reduction catalyst.

Further, the NO _X occluding and reducing catalyst is SO _X also occluding well NO _{X, the} NO _X storage ability of the NO _X occluding and reducing catalyst decreases with increasing SO _X storage amount. Therefore, in order to ensure the NO _X storage capacity, SO _X stored in the NO _X storage reduction catalyst must be desorbed, and at this time, it is necessary to supply a reducing agent. In order to effectively desorb SO _X stored in the NO _X storage reduction catalyst even in SO _X desorption, a reducing agent is appropriately supplied from the reducing agent supply device to the NO _X storage reduction catalyst. There is a need.

Therefore, an object of the present invention is to effectively desorb the components stored in the NO _X storage reduction catalyst by appropriately supplying the reducing agent to the NO _X storage reduction catalyst from the reducing agent supply device. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can be purified.

In order to solve the above problems, in the first aspect of the invention, the upstream side exhaust purification catalyst disposed in the engine exhaust passage, and the downstream side exhaust disposed in the engine exhaust passage downstream of the upstream side exhaust purification catalyst. A purification agent and a reducing agent supply device that supplies a reducing agent only to the downstream side exhaust purification catalyst. The downstream side exhaust purification catalyst removes NO _x in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. the NO _X when the air-fuel ratio of the inflowing exhaust gas is occluded when almost the stoichiometric air-fuel ratio or rich is desorbed with occluded, NO _X storage amount to the downstream exhaust purifying catalyst when greater than the limit storage amount in the exhaust purification system of an internal combustion engine desorbing the NO _X from the downstream exhaust purifying catalyst by NO _X desorption process for substantially stoichiometric air-fuel ratio or a rich air-fuel ratio of the exhaust gas discharged from the engine body, the NO _X And to supply the reducing agent from the reducing agent supply device only during the period from NO _X desorption process start until a predetermined supply time has passed downstream exhaust purifying catalyst during the release process.
If you run NO _X desorption process, it is possible to appropriately purify the NO _X with the exception of the initial of the NO _X desorption process, in the initial of the NO _X desorption process NO _X from the downstream exhaust purifying catalyst It exudes. According to the first aspect of the present invention, NO _X seepage can be suppressed by supplying the reducing agent from the reducing agent supply device to the downstream side exhaust purification catalyst at the initial stage of the NO _X desorption process.
The "predetermined feed time", the time exudation phenomena may occur, i.e. NO _X desorption process after the start, corresponding to the time NO _X can flow out from _the NO _X storage reduction catalyst to be supplied to the reducing agent Means time to do.

According to a second invention, in the first invention, the amount of reducing agent supplied from the reducing agent supply device to the downstream side exhaust purification catalyst from the start of the NO _x desorption treatment until a predetermined supply time elapses. It is determined according to _the NO _X storage amount in the NO _X desorption process at the start.
If you do not supply the reducing agent from the reducing agent supply device, the amount of the NO _X leaking from _the NO _X storage reduction catalyst when executing the NO _X desorption process in accordance with _the NO _X storage amount in the NO _X desorption process at the start Different. In the second invention, since the supply amount of the reducing agent is determined according to the NO _X storage amount, it is possible to supply the reducing agent in accordance with the exudation amount of the NO _X from _the NO _X storage reduction catalyst.

  In 3rd invention, in the 1st or 2nd invention, the said reducing agent supply apparatus is a hydrogen supply apparatus which supplies hydrogen as a reducing agent.

In order to solve the above-mentioned problems, in a fourth aspect of the invention, an exhaust purification catalyst disposed in the engine exhaust passage and a hydrogen supply device that supplies hydrogen to the exhaust purification catalyst are provided. when the air-fuel ratio is at a temperature of approximately stoichiometric air-fuel ratio or rich is a by the exhaust gas purification catalyst air-fuel ratio of the inflowing exhaust gas while absorbing the SO _X in the inflowing exhaust gas is higher SO _X desorption temperature at the time of lean gases When the stored SO _X is desorbed and the SO _X storage amount in the exhaust purification catalyst is larger than the limit storage amount, the air-fuel ratio of the exhaust gas exhausted from the engine body is almost the stoichiometric air-fuel ratio or rich. in the exhaust purification system of temperature SO _X internal combustion engine desorbing SO _X from the exhaust purification catalyst by performing the SO _X desorption process of raising the temperature to above the desorption temperature of the exhaust gas purifying catalyst as well as, SO _X desorption From the start of processing After a certain waiting time had elapsed, hydrogen was supplied from the hydrogen supply device to the exhaust purification catalyst while performing the SO _X desorption process.
In the SO _X desorption treatment, there is a region where SO _X is difficult to desorb from the NO _X storage reduction catalyst. The SO _X occluded in such a region takes time to desorb, and tends to remain without being desorbed in the later stage of the SO _X desorption process. According to the fourth aspect, since the hydrogen high reducing ability later in the SO _X desorption process is supplied, it is possible to SO _X also rapidly eliminated which is stored in such region.
The predetermined waiting time means, for example, the time from the start of the SO _X desorption process to the hydrogen supply start time, and the “hydrogen supply start time” means, for example, the SO _X storage amount of the NO _X storage reduction catalyst is the limit storage amount. It means a time when the stored amount becomes less than a predetermined amount or a time when the SO _X outflow rate from the NO _X storage reduction catalyst becomes a predetermined outflow rate or less.

According to a fifth aspect, in the fourth aspect, the apparatus further comprises a SO _x concentration detecting device for detecting the concentration of SO _{x in} the exhaust gas downstream of the exhaust purification catalyst, and the SO _x concentration detecting device. Based on the detected SO _X concentration, the hydrogen supply amount from the hydrogen supply device was controlled.

  According to a sixth invention, in any one of the third to fifth inventions, further comprising a hydrogen concentration detection device for detecting a hydrogen concentration in the exhaust gas upstream of the hydrogen supply device, the hydrogen concentration The supply amount of hydrogen from the hydrogen supply device was controlled based on the hydrogen concentration detected by the detection device.

According to the first to third invention, NO _X in the initial stage of the desorption process by supplying the reducing agent to the downstream exhaust purifying catalyst from a reducing agent supply device, NO _X occluding and reducing catalyst stored in the NO _X Thus, the components stored in the NO _X storage reduction catalyst can be effectively desorbed and purified.

According to a sixth aspect of, SO _X by supplying hydrogen from the hydrogen supply device to the NO _X occluding and reducing catalyst at the later stage of desorption process, SO SO _X is occluded in the desorbed difficult area _X Also, the components occluded in the NO _x storage reduction catalyst can be effectively desorbed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a case where the exhaust emission control device according to the first embodiment of the present invention is applied to an in-cylinder injection type spark ignition internal combustion engine. The present invention can also be applied to other spark ignition internal combustion engines and compression self-ignition internal combustion engines.

  As shown in FIG. 1, in the present embodiment, the engine body 1 includes a cylinder block 2, a piston 3 that reciprocates within the cylinder block 2, and a cylinder head 4 fixed on the cylinder block 2. . A combustion chamber 5 is formed between the piston 3 and the cylinder head 4. In the cylinder head 4, an intake valve 6, an intake port 7, an exhaust valve 8, and an exhaust port 9 are arranged for each cylinder. Further, as shown in FIG. 1, a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is disposed around the inner wall surface of the cylinder head 4. Further, a cavity 12 extending from the lower side of the fuel injection valve 11 to the lower side of the spark plug 10 is formed on the top surface of the piston 3.

The intake port 7 of each cylinder is connected to a surge tank 14 via an intake branch pipe 13, and the surge tank 14 is connected to an air cleaner 16 via an intake pipe 15. A throttle valve 18 driven by a step motor 17 is disposed in the intake pipe 15. On the other hand, the exhaust port 9 of each cylinder is connected via an exhaust branch pipe 19 to a catalytic converter 21 containing an upstream side exhaust purification catalyst (for example, a three-way catalyst) 20. The catalytic converter 21 is connected via an exhaust pipe 22 to a catalytic converter 24 incorporating a downstream side exhaust purification device (NO _x storage reduction catalyst) 23, and this catalytic converter 24 communicates with the atmosphere via a muffler (not shown). Is done.

  The internal combustion engine of the present embodiment includes a fuel reforming system (reformer system) 25 that can generate a reformed gas by reforming an air-fuel mixture of hydrocarbon fuel such as gasoline and air. Therefore, the engine main body 1 is operated using both or either of the reformed gas generated by the fuel reforming system 25 and the fuel supplied by the fuel injection valve 11. The fuel reforming system 25 is disposed at one end of the reforming system main body 26, a reforming system main body 26 formed in a cylindrical shape, a reforming catalyst 27 built in the reforming system main body 26, and the reforming system main body 26. And a reforming fuel injection valve 28. As the reforming catalyst 27, for example, a catalyst in which rhodium is supported on zirconia is used. The reforming fuel injection valve 28 is connected to a fuel tank (not shown), and in this embodiment, the same fuel as the fuel supplied to the fuel injection valve 11 is injected.

The one end of the reforming system body 26 is connected to a reforming intake pipe 29, and the reforming intake pipe 29 is connected to the intake pipe 15 on the intake upstream side of the throttle valve 18. The other end of the reforming system body 26 is connected to an intake side reformed gas supply pipe 30 and an exhaust side reformed gas supply pipe 31, and the intake side reformed gas supply pipe 30 is connected to each intake branch pipe 13. The exhaust side reformed gas supply pipe 31 is connected to the exhaust pipe 22 or the catalytic converter 24 on the exhaust downstream side of the three-way catalyst 20 and on the exhaust upstream side of the NO _x storage reduction catalyst 23. A flow rate adjustment valve 32 is connected to the reforming intake pipe 29, and a reformed gas storage tank 33 and a reformed gas pump 34 are connected to the exhaust-side reformed gas supply pipe 31.

In the fuel reforming system 25 configured as described above, air is supplied to the reforming system main body 26 via the reforming intake pipe 29 when the flow rate adjustment valve 32 is opened. Then, fuel mixture is generated by performing fuel injection from the reforming fuel injection valve 28 with the supply of air, and the mixture is passed through the reforming catalyst 27, so that the hydrocarbon system is used in the reforming catalyst 27. The fuel and air are reacted to produce a reformed gas containing H ₂ and CO. The generated reformed gas is supplied to the intake branch pipe 13 via the intake side reformed gas supply pipe 31 and stored in the reformed gas storage tank 33 via the exhaust side reformed gas supply pipe 31. . The reformed gas stored in the reformed gas storage tank 33 is supplied to the NO _x storage reduction catalyst 23 by driving the reformed gas pump 34. Since the reformed gas contains H ₂ as described above, the following description assumes that H ₂ is generated by the fuel reforming system 25 and supplies H ₂ to the NO _x storage reduction catalyst 23. To do.

  The electronic control unit (ECU) 41 comprises a digital computer, and is connected to each other via a bidirectional bus 42, a RAM (random access memory) 43, a ROM (read only memory) 44, a CPU (microprocessor) 45, an input. A port 46 and an output port 47 are provided.

An air flow meter 50 for detecting the flow rate of air (intake gas) passing through the intake pipe 15 is disposed in the intake pipe 15 on the intake upstream side of the throttle valve 18, and reforming intake air on the upstream side of the flow rate adjustment valve 32. An air flow meter 51 for detecting the flow rate of air passing through the reforming intake pipe 29 is disposed in the pipe 29. The exhaust branch pipe 19 includes an air-fuel ratio of exhaust gas passing through the exhaust branch pipe 19 (the exhaust gas upstream of the NO _x storage reduction catalyst 23, the combustion chamber 5 and the air and fuel supplied to the intake passage) An air-fuel ratio sensor 52 for detecting the concentration of H _{2 in} the exhaust gas passing through the exhaust pipe 22 in the exhaust pipe 22 upstream of the NO _x storage reduction catalyst 23. An H ₂ sensor 53 is arranged. Further, NO _X occluding and reducing SO _X for the exhaust pipe of the exhaust gas downstream side for detecting the concentration of SO _X in the temperature sensor 54 and in such exhaust gases for detecting the temperature of the exhaust gas passing through the exhaust pipe of the catalyst 23 A sensor 55 is disposed, and the NO _x storage reduction catalyst 23 has a difference for detecting the differential pressure between the exhaust gas pressure upstream of the NO _x storage reduction catalyst 23 and the exhaust gas pressure downstream of the exhaust. A pressure sensor 56 is disposed. Further, a load sensor 58 that generates an output voltage proportional to the amount of depression of the accelerator pedal 57 is connected to the accelerator pedal 57. The output signals of these sensors 50 to 58 are input to the input port 46 via the corresponding AD converters 48 respectively. Further, a crank angle sensor 59 is connected to the input port 46, and the CPU 35 calculates the engine speed based on the output pulse of the crank angle sensor 59.

  On the other hand, the output port 47 is connected to the spark plug 10, the fuel injection valve 11, and the step motor 17 via the corresponding drive circuit 49, and these are controlled based on the output from the ECU 41.

The NO _x storage reduction catalyst 23 used as the downstream side exhaust purification catalyst in the present embodiment is when the air-fuel ratio of the exhaust gas flowing into the NO _x storage reduction catalyst 23 (hereinafter referred to as “inflow exhaust gas”) is lean. That is, when the oxygen concentration in the inflowing exhaust gas is high, NO _x in the inflowing exhaust gas is occluded, and when the air-fuel ratio of the inflowing exhaust gas is almost stoichiometric or rich, that is, the oxygen concentration in the inflowing exhaust gas is low time, desorbing the NO _X that is occluded. The desorbed NO _x reacts with a reducing agent (for example, unburned HC) contained in the inflowing exhaust gas to be purified.

There is a limit to the NO _X storage capacity of the NO _X storage reduction catalyst 23, and it is not possible to store more than a certain amount of NO _X. Therefore, when the air-fuel ratio of the exhaust gas continues engine operating condition is a lean, _the NO _X storage _the NO _X storage amount to the reducing catalyst 23 exceeds the above predetermined amount, NO _X is NO then the inflow exhaust gas _{The X} occlusion reduction catalyst 23 is not occluded and flows out downstream of the exhaust. Therefore, in many internal combustion engine equipped with _the NO _X storage reduction catalyst 23, de the NO _X from _the NO _X storage reduction catalyst 23 when _the NO _X storage amount to _the NO _X storage reduction catalyst 23 has exceeded the limit storage amount The NO _x desorption process is performed to release and reduce.

In the NO _X desorption process, the air-fuel ratio of the exhaust gas is controlled so that the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 23 becomes substantially the stoichiometric air-fuel ratio or rich. In the present embodiment, the air-fuel ratio of the exhaust gas discharged from the engine body 1 is controlled so as to be substantially the stoichiometric air-fuel ratio or rich. As such control, for example, fuel injection is performed from the fuel injection valve 11 during the intake stroke or the compression stroke so that the air-fuel ratio of the exhaust gas filled in the combustion chamber 5 becomes substantially stoichiometric or rich, or For example, fuel injection may be performed from the fuel injection valve 11 so that the air-fuel ratio of the exhaust gas in the combustion chamber 5 after combustion becomes substantially stoichiometric or rich.

Thus, by performing NO _X desorption process, together with the NO _X concentration of oxygen has been occluded in the NO _X occluding and reducing catalyst by reduction in the inflowing exhaust gas is accounted de tied up from _the NO _X storage reduction catalyst removal The separated NO _x is reduced and purified by HC and CO contained in the inflowing exhaust gas. Then, NO _X desorption process When _the NO _X storage amount NO _X is being desorbed from _the NO _X storage reduction catalyst 23 becomes substantially zero by NO _X desorption process is made to completion.

  It is to be noted that a fuel addition device capable of adding fuel to the exhaust gas passing through the exhaust pipe 22 is provided, and by adding the fuel from the fuel addition device, the air-fuel ratio of the exhaust gas is substantially the stoichiometric air-fuel ratio or You may make it rich.

2, NO _X concentration in the exhaust gas flowing out from _the NO _X storage reduction in the exhaust gas flowing into the catalyst 23 NO _X concentration (dashed line) and _the NO _X storage reduction catalyst 23 in the case of performing the NO _X desorption process It is the figure which showed (solid line). In the figure, in addition to the NO _x concentration in the exhaust gas, the air-fuel ratio of the exhaust gas discharged from the engine body 1 is shown, and the period during which the air-fuel ratio is switched from lean to rich is indicated as NO _x desorption. This is the period during which processing is performed. Therefore, in the example shown in FIG. 2, the NO _x desorption process is performed at intervals of about 1 minute.

As shown in FIG. 2, when the NO _x desorption process is started and the air-fuel ratio of the exhaust gas discharged from the engine body 1 is made rich (or almost the stoichiometric air-fuel ratio), it flows out from the NO _x storage reduction catalyst 23. The NO _x concentration in the exhaust gas (hereinafter referred to as “outflow exhaust gas”) temporarily increases and then decreases.

Figure 3 is a desorption amount of the NO _X from _the NO _X storage reduction catalyst 23 during one cycle of execution of the NO _X desorption process, the amount of reducing agent in the inflowing exhaust gas, NO _X concentration in the exhaust gas flowing FIG. Similar to FIG. 2, FIG. 3 shows the air-fuel ratio of the outflow exhaust gas, and the period during which the air-fuel ratio is rich is the period during which the NO _x desorption process is performed. In the example shown in FIG. 3, NO _X desorption process once is performed about 0.5 seconds to 3 seconds.

As shown in FIG. 3, when the NO _x desorption process is started, the air-fuel ratio of the exhaust gas exhausted from the engine body 1 is made rich, so that the oxygen concentration of the exhaust gas is reduced, and thus the inflow The oxygen concentration in the exhaust gas is reduced. Therefore, elimination of the NO _X is started from immediately _the NO _X storage reduction catalyst 23 when the NO _X desorption process is started.

On the other hand, the amount of reducing agent in the inflowing exhaust gas does not increase immediately after the start of the NO _x desorption process, and starts to increase after a certain amount of time has passed. In the initial stage of the NO _x desorption process, the reducing agent contained in the exhaust gas discharged from the engine body 1 is consumed in the three-way catalyst 20 disposed on the exhaust upstream side of the NO _x storage reduction catalyst 23. Because. That is, in the three-way catalyst, oxygen or the like is adsorbed on the three-way catalyst 20 while the exhaust gas flowing into the three-way catalyst 20 is lean, and flows into the three-way catalyst 20 at the initial stage of the NO _x desorption process. The reducing agent (HC or CO) in the exhaust gas reacts with oxygen adsorbed on the three-way catalyst 20. Therefore, at the initial stage of the NO _x desorption process, the reducing agent contained in the exhaust gas discharged from the engine body 1 is consumed in the three-way catalyst 20, and in the exhaust gas flowing into the NO _x storage reduction catalyst 23. It is hardly included.

Therefore, at the initial stage of the NO _x desorption treatment, there is a period in which the reducing agent is not contained in the inflowing exhaust gas even though the oxygen concentration in the inflowing exhaust gas is low. During this period, the NO _x storage reduction NO _X is desorbed from the catalyst 23, but NO _X is not reduced, and therefore flows out of the NO _X storage reduction catalyst 23 (see FIG. 3). This phenomenon is referred to as “exudation” of NO _X hereinafter. Called).

Further, after a certain amount of time has elapsed after the start of the NO _x desorption process, the reducing agent begins to flow into the NO _x storage reduction catalyst 23 when the reducing agent is no longer consumed in the three-way catalyst 20. However, oxygen or the like even in the NO _X occluding and reducing catalyst 23 has the adsorption, to react with oxygen to which they adsorbed before reacting with desorbed NO _X, thus reducing agents to the NO _X occluding and reducing catalyst 23 but it does not contribute to the reduction of nO _X is to soon be started to flow. This state is shown by a broken line in FIG. Broken line in FIG. 3 shows the amount of contributing reducing agent for the reduction of NO _X. This also becomes a factor of exudation occurs of the NO _X from _the NO _X storage reduction catalyst in the early of the NO _X desorption process.

Therefore, in the present embodiment, after the start of the NO _x desorption process, the reformed fuel generated by the fuel reforming system, particularly H ₂ , is supplied to the NO _x storage reduction catalyst 23 during a period in which the seepage phenomenon may occur. Yes.

Specifically, the reformed gas pump 34 is driven simultaneously with the start of the NO _x desorption process to supply H ₂ stored in the reformed gas storage tank 33 to the NO _x storage reduction catalyst 23. Then, after a predetermined supply period has elapsed since the start of the NO _X desorption process, the drive of the reformed gas pump 34 is stopped, and the supply of H _{2 to} the NO _X storage reduction catalyst 23 is terminated. Thus, even when no reducing agent is present in the exhaust gas flowing into the NO _x storage reduction catalyst 23 via the three-way catalyst 20, NO _x can be reliably reduced and purified by the reformed fuel.

Here, the predetermined supply period is, for example, a period during which a seepage phenomenon may occur, that is, a certain amount from the NO _X storage reduction catalyst 23 unless a reducing agent such as reformed gas is supplied after the start of the NO _X desorption process. It means a period corresponding to a period during which an amount of NO _x can flow out (period T in FIG. 3).

Further, as shown in FIG. 4, there is a constant relationship between the NO _X exudation amount in the initial of the NO _X storage amount and NO _X desorption process in NO _X desorption process at the start, _the NO _X storage NO _X exudation amount if the amount is increased also increases. Therefore, in this embodiment, it is calculated in advance by experimentally or calculated the relationship between _the NO _X storage amount and NO _X exudation amount, is stored in ROM44 of ECU41 as a map. Then, based on _the NO _X storage amount to _the NO _X storage reduction catalyst 23 in the NO _X desorption process at the start, and to calculate the amount of H ₂ to be fed into the predetermined supply period. In particular, in the present embodiment, the NO _X desorption process is performed when the NO _X storage amount exceeds the limit storage amount as described above, but the limit storage amount depends on the deterioration of the NO _X storage reduction catalyst 23 or the like. Since it changes, the supply amount of H ₂ also changes with the change.

Incidentally, _the NO _X storage and reduction catalyst 23 desorbing NO _X from, as a method for reducing the H ₂ produced by the fuel reformer system 25 without desorbing NO _X by the NO _X desorption process _the NO _X storage It is also conceivable to only supply to the reduction catalyst. However, in order to desorb and reduce NO _x from the NO _x storage reduction catalyst only with H ₂ , a large amount of H ₂ is required. Therefore, the fuel reforming ability of the fuel reforming system 25 must be made high. In addition, the capacity of the reformed gas storage tank 33 must be increased. For this reason, it is necessary to enlarge the fuel reforming system 24 and the reformed gas storage tank 33, and the mountability of these devices on a vehicle deteriorates.

Further, when generating H ₂ , it is necessary to raise the temperature of the reforming catalyst 27 to a considerably high temperature. Therefore, a certain amount of energy is required to generate H ₂ . In particular, in order to increase the fuel reforming capability, it is necessary to increase the reforming catalyst 27, and the energy required to raise the temperature of such a large reforming catalyst 27 also increases. Accordingly, by supplying the H ₂ generated by the fuel reforming system 25 to the NO _X storage reduction catalyst 23 while executing the NO _X desorption process as in the present embodiment, the NO _X storage reduction catalyst 23 reduces NO _X. By performing desorption / reduction, NO _x can be desorbed / reduced while ensuring the mountability of the fuel reforming system 25 or the like on a vehicle and maintaining a reduction in energy consumption.

In the above embodiment, it is assumed that H ₂ is mainly used as the reducing agent supplied to the NO _X storage reduction catalyst 23 in the initial stage of the NO _X desorption process. However, such a reducing agent is not H ₂ , Any reducing agent may be used. Thus, for example, HC or CO can be used as such a reducing agent. However, since the reducing ability of H ₂ is very high, it is most preferable to use H ₂ as such a reducing agent.

FIG. 5 is a flowchart of a control routine for control related to NO _x desorption processing in the exhaust purification system of the first embodiment of the present invention. Each control routine is performed by interruption at regular time intervals.

First, in step 101, it is determined whether or not the H ₂ supply flag XH2 is zero. H ₂ feed flag XH2 is a flag indicating whether the whether when supplied with H ₂ in the NO _X occluding and reducing catalyst 23, is not performed 1, H ₂ supply when performing with H ₂ supply Sometimes 0. If it is determined in step 101 that H ₂ is not supplied (XH2 = 0), the process proceeds to step 102. In step 102, it is determined whether or not the NO _X desorption flag XRS is zero. NO _X desorption flag XRS is a flag indicating whether the whether when running NO _X desorption process, executes the 1, NO _X desorption process when running NO _X desorption process 0 when not. If it is determined in step 102 that the NO _x desorption process is not being executed (XRS = 0), the process proceeds to step 103.

In step 103, it is determined whether or not the NO _X storage amount QNOX to the NO _X storage reduction catalyst 23 exceeds the limit storage amount QNOXL. _The NO _X storage amount QNOX to _the NO _X storage reduction catalyst 23 is calculated based on the differential pressure of the NO _X occluding and reducing catalyst 23 for example, which is detected by the differential pressure sensor 56. When it is determined that the NO _X storage amount QNOX does not exceed the limit storage amount QNOXL (QNOX ≦ QNOXL), the control routine is ended. On the other hand, if it is determined at step 103 that the NO _X storage amount QNOX exceeds the limit storage amount QNOXL (QNOX> QNOXL), the routine proceeds to step 104. In step 104, the amount of the NO _X which is expected to oozes when trying to desorption and reduction of NO _X from _the NO _X storage reduction catalyst 23 by NO _X desorption process only (hereinafter "estimated seepage amount" Is calculated from the deterioration of the NO _x storage reduction catalyst 23 and the limit storage amount QNOXL based on the map as shown in FIG. Next, at step 105, the time when H ₂ should be supplied to the NO _X storage reduction catalyst 23 by a map or the like based on the estimated exudation amount estimated at step 104 (hereinafter referred to as “target supply time”) TS and H _An amount QS to be supplied (hereinafter referred to as “target supply amount”) QS is calculated.

Next, in step 106 and step 107, the NO _x desorption process and the supply of H ₂ are started. Here, the supply amount of H ₂ per unit time is, for example, a value obtained by dividing the target supply amount QS by the target supply time TS. In step 108, the H ₂ supply flag XH ₂ and the NO _X desorption flag XRS are set to 1, and the control routine is ended.

In the control routine of the next cycle, it is determined in step 101 that H ₂ is being supplied (XH2 = 1), and the process proceeds to step 109. In step 109, it is determined whether or not the target supply time TS has elapsed since the start of the supply of H _{2. If} it is determined that the target supply time TS has not elapsed, the control routine is terminated and the supply of H ₂ is completed. Will continue. On the other hand, if it is determined in step 109 that the target supply time TS has elapsed, the process proceeds to step 110. In step 110, the supply of H ₂ is terminated, and then in step 111, the H ₂ supply flag XH2 is set to zero.

In the control routine of the next cycle in which the supply of H ₂ is thus terminated, it is determined in step 101 that the supply of H ₂ is not being performed (XH2 = 0), and NO _X desorption processing is performed in step 102. It is determined that it is being executed (XRS = 1), and the process proceeds to step 112. In step 112, it is determined whether or not an end condition for the NO _x desorption process is satisfied. Here, the case where the termination condition of the NO _X desorption process is satisfied, for example, like the case where _the NO _X storage reduction catalyst 23 NO _X that was stored in the occupied almost all desorbed and the like. If it is determined in step 112 that the termination condition for the NO _x desorption process is not satisfied, the control routine is terminated. On the other hand, if it is determined that the termination condition for the NO _x desorption process is satisfied, the routine proceeds to step 113. In step 113, the NO _x desorption process is terminated, and then in step 114, the NO _x desorption flag XRS is set to zero.

Next, an exhaust emission control device according to a second embodiment of the present invention will be described.
The above-described NO _X storage reduction catalyst 23 can store not only NO _X in the inflowing exhaust gas but also SO _X. That is, the NO _X storage reduction catalyst 23 stores SO _X in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is approximately the stoichiometric air-fuel ratio or rich so that the NO _X storage is performed. When the temperature of the reduction catalyst 23 is equal to or higher than the SO _X desorption temperature, the stored SO _X is desorbed.

In _the NO _X storage reduction catalyst 23, NO if SO _X storage amount of _X occluding and reducing catalyst 23 is increased, absorbing possible amount of NO _X is decreased, _the NO _X storage ability is lowered. Therefore, in order to maintain _the NO _X storage ability of the NO _X occluding and reducing catalyst 23, it is necessary to reduce maintain SO _X storage amount of the NO _X occluding and reducing catalyst 23. However, when the engine operating state in which the air-fuel ratio of the exhaust gas is lean continues, the SO _X storage amount of the NO _X storage reduction catalyst 23 also increases. Therefore, the exhaust gas purifying apparatus of the present embodiment, when the SO _X storage amount of the NO _X occluding and reducing catalyst 23 exceeds a predetermined limit amount of occlusion, NO _X occluding reduction temperature of the catalyst 23 SO _X desorption temperature higher The SO _X desorption process is performed to bring the air-fuel ratio of the inflowing exhaust gas to substantially the stoichiometric air-fuel ratio or rich while maintaining the temperature at a high level. In this case the air-fuel ratio of the exhaust gas is also exhausted from the engine body 1 to the approximate theoretical air-fuel ratio or rich air-fuel ratio of the inflowing exhaust gas as in the NO _X desorption process is substantially the stoichiometric air-fuel ratio or rich The With such SO _X desorption process, _the NO _X storage reduction SO _X storage amount is substantially zero next to the catalyst 23 SO _X that was stored in the provided desorbed _the NO _X storage reduction catalyst 23, _the NO _X storage reduction catalyst 23 of _the NO _X storage capacity is made to recovery.

Meanwhile, from the state, but _the NO _X storage agent to the NO _X occluding and reducing catalyst 23 is supported, state SO _X in the NO _X absorbent is occluded is the NO _X is stored in the NO _X absorbent Is also stable. Therefore, SO _X stored in the NO _X storage reduction catalyst 23 is less likely to be desorbed than NO _X , and the above-described NO _X desorption process is completed in about 0.5 to 3 seconds, whereas SO _X desorption is completed. Even if the separation treatment is performed for about 30 minutes, it may not be completely desorbed. As another reason time-consuming the SO _X to desorb, SO _X, which from the upstream end desorbed of the NO _X occluding and reducing catalyst 23 is again occluded downstream thereof, are occluded by repeating this It can be mentioned that the SO _x gradually moves to the downstream side and is finally discharged from the NO _x storage reduction catalyst 23.

FIG. 6 is a graph showing the transition of the SO _X desorption amount from the NO _X storage reduction catalyst 23 after the start of the SO _X desorption process. The solid line in the figure shows the transition of SO _X desorption amount when executing the SO _X desorption process while performing supply of H ₂ present invention to be described later, whereas the broken line in the figure such H ₂ It shows the transition of the SO _X desorption amount when running without SO _X desorption process to perform the supply of.

As can be seen from FIG. 6, the SO _X desorption process is started by raising the temperature of the NO _X storage reduction catalyst 23 to the SO _X desorption temperature or higher and making the air-fuel ratio of the inflowing exhaust gas substantially the stoichiometric air-fuel ratio or rich. As a result, the SO _X outflow amount increases rapidly and then gradually decreases. As described above, the SO _X outflow amount gradually decreases because of the temperature distribution in each region of the NO _X storage reduction catalyst 23 or from the place where NO _X is stored to the noble metal (such as platinum). This is considered to be because there is a place where SO _x is easily desorbed from the NO _x storage-reduction catalyst 23 and a place where it is difficult to desorb, and SO _x stored in a place where it is difficult to desorb tends to remain. That is, even after some time from the start of SO _X desorption process, SO _X which is stored in desorbed difficult place hardly desorbed reducing capability in order to rapidly desorb such SO _X Therefore, it is necessary to supply a high reducing agent to the NO _x storage reduction catalyst 23.

From such a point of view, as the reducing agent supplied to the NO _x storage reduction catalyst 23 during the SO _x desorption process, the reducing ability is used rather than using HC or CO contained in the exhaust gas discharged from the engine body 1. It is preferable to use high H ₂ . On the other hand, if only H ₂ is used as the reducing agent during the SO _X desorption treatment as described above, the fuel reforming system 24 and the reformed gas storage tank 33 need to be enlarged and the reforming catalyst 33 is used. As a result, the energy required to raise the temperature increases.

Therefore, in the present embodiment, H ₂ is not supplied to the NO _X storage reduction catalyst 23 in the first half of the SO _X desorption process, and H ₂ is supplied only in the _{second half} . Thus, in the previous period of SO _X desorption process, can also cause relatively quickly desorb SO _X by HC and CO in the exhaust gas discharged from the engine body 1, in late S regeneration, NO by supplying of H ₂ in the _X occluding and reducing catalyst 23, so that desorption, to flow out quickly sO _X even later in the sO _X desorption process, as shown by the solid line in FIG. This makes it possible to rapidly desorb SO _x while minimizing the supply amount of H ₂ .

The “late stage” of the SO _X desorption process means that a predetermined waiting time has elapsed, that is, after the H ₂ supply start time, and the “H ₂ supply start time” means the SO _{X of the} NO _X storage reduction catalyst 23. It means a time when the occlusion amount becomes equal to or less than a predetermined occlusion amount (hereinafter referred to as “supply start occlusion amount”) smaller than the above limit occlusion amount. The H ₂ supply start timing is determined on the basis of the elapsed time from the start of the SO _X desorption process, the output of the SO _X sensor 55 as described later, and the like.

Further, in this embodiment, it has a SO _X sensor 55 on the exhaust downstream side of the NO _X occluding and reducing catalyst 23 as described above, SO _X desorption process ends timing, H ₂ supply start timing, etc. of the SO _X Control is performed according to the output of the sensor 55. Specifically, the concentration of SO _{X in} the exhaust gas flowing out from the NO _X storage reduction catalyst 23 detected by the SO _X sensor 55 during S regeneration is a predetermined concentration (the SO _X storage amount is the supply start storage amount). In some cases, the concentration of SO _X correspondingly (hereinafter referred to as “H ₂ supply start concentration”) starts to supply H ₂ to the NO _X storage reduction catalyst 23 when CSOX ₁ or less. When the detected concentration of SO _x becomes almost zero, the SO _x desorption process is terminated.

FIG. 7 is a flowchart of a control routine of control related to SO _X desorption processing in the exhaust purification system of the second embodiment of the present invention. Each control routine is performed by interruption at regular time intervals.

First, in step 151, it is determined whether or not the H ₂ supply flag XHS is zero. The H ₂ supply flag XHS is a flag similar to the H ₂ supply flag XH2 used for the control of FIG. If it is determined in step 151 that H ₂ is not supplied (XHS = 0), the process proceeds to step 152. In step 152, it is determined whether or not the SO _X desorption flag XS is zero. SO _X desorption flag XS is a flag indicating whether or not when running SO _X desorption process, 0 when the 1, not running when running SO _X desorption process It is said. If it is determined in step 152 that the SO _X desorption process has not been executed, the process proceeds to step 153.

In step 153, it is determined whether or not the SO _X storage amount QSOX to the NO _X storage reduction catalyst 23 exceeds the limit storage amount QSOXL. Here, the SO _X storage amount in the NO _X storage reduction catalyst 23 is obtained by, for example, multiplying the total amount of fuel supplied after executing the previous SO _X desorption process by the sulfur component content per unit mass of the fuel. Is calculated by When it is determined that the SO _X storage amount QSOX is equal to or less than the limit storage amount QSOXL (QSOX ≦ QSOXL), the control routine is terminated. On the other hand, if it is determined in step 153 that the SO _X storage amount QSOX exceeds the limit storage amount QSOXL (QSOX> QSOXL), the routine proceeds to step 154. In step 154, the SO _X desorption process is started. In the SO _X desorption process, the NO _X storage reduction catalyst 23 is first heated up to the SO _X desorption temperature, and then the air-fuel ratio of the exhaust gas discharged from the engine body 1 is substantially stoichiometric or rich. The In step 155, the SO _X desorption flag XS is set to 1, and the control routine is ended.

In the control routine of the next cycle, it is determined in step 152 that the SO _X desorption process is being performed (XS = 1), and the process proceeds to step 156. In step 156, it is determined whether or not the SO _X concentration CSOX detected by the SO _X sensor 55 is equal to or lower than the H ₂ supply start concentration CSOX _{1. If} it is determined that the SO ₂ concentration CSOX ₁ is higher than the H ₂ supply start concentration CSOX _1. The control routine is terminated. On the other hand, if it is determined in step 156 that the SO _X concentration CSOX is equal to or lower than the H ₂ supply start concentration CSOX ₁ , the process proceeds to step 157. In step 157, the supply of H ₂ to the NO _x storage reduction catalyst 23 is started. Next, at step 158, the H ₂ supply flag XHS is set to 1, and the control routine is ended.

Thus, in the control routine of the next cycle in which the supply of H ₂ is started, it is determined in step 151 that the supply of H ₂ is being performed (XHS = 1), and the process proceeds to step 159. In step 159, it is determined whether or not the SO _X concentration CSOX detected by the SO _X sensor 55 is substantially zero, that is, whether or not all the SO _X stored in the NO _X storage reduction catalyst 23 has been desorbed. When the determination is made and the SO _X concentration CSOX is not near zero, the control routine is terminated. On the other hand, if it is determined at step 159 that the SO _X concentration CSOX detected by the SO _X sensor 55 is substantially zero, the routine proceeds to step 160. In step 160, the supply of H ₂ is terminated, and then in step 161, the SO _x desorption process is terminated. Thereafter, in step 162, the SO _X desorption flag XS and the H ₂ supply flag XHS are set to 0, and the control routine is ended.

By the way, when SO _{X is} to be desorbed by supplying H ₂ , sulfur dioxide (H ₂ S) may be generated in the NO _X storage reduction catalyst 23. This H ₂ S should be released little by little because it emits a bad odor when released in a large amount in the atmosphere in a short time. Such generation of H ₂ S varies depending on the air-fuel ratio of the inflowing exhaust gas as shown in FIG. 8, and H ₂ S is more easily generated as the richness of the inflowing exhaust gas is higher. On the other hand, if the concentration of H ₂ flowing into the NO _x storage reduction catalyst 23 is low, the SO _x desorption rate may decrease. Therefore, the concentration of H _{2 in} the exhaust gas flowing into the NO _x storage reduction catalyst 23 should be maintained within a certain range.

Here, a small amount of H ₂ is also contained in the exhaust gas of the internal combustion engine. Therefore, the fuel when it is supplied with H ₂ in the NO _X occluding and reducing catalyst 23 from the reforming system 25, _the NO _X storage reduction total inflow of H ₂ the catalyst 23 is H ₂ in the exhaust gas from the engine body 1 Inflow amount and the supply amount of the supply H ₂ from the fuel reforming system 25 are totaled. Therefore, when the inflow of H ₂ supplied from the fuel reforming system 25 constant inflow of H ₂ flowing to the NO _X occluding and reducing catalyst 23 varies depending on the concentration of H ₂ in the exhaust gas End up.

Therefore, in the present embodiment, based on the output of the H ₂ sensor 53 disposed in the exhaust upstream of the NO _X occluding and reducing catalyst 23, and H ₂ feed to _the NO _X storage reduction catalyst 23 from the fuel reformer system 25 We are going to adjust. Specifically, when the H ₂ concentration in the exhaust gas detected by the H ₂ sensor is low, the amount of H ₂ supplied from the fuel reforming system 25 to the NO _x storage reduction catalyst 23 is assumed to be large. If the H ₂ concentration in the exhaust gas detected by the H ₂ sensor is high, the amount of H ₂ supplied from the fuel reforming system 25 to the NO _X storage reduction catalyst 23 is reduced, and the NO _X storage reduction catalyst It is assumed that the concentration of H ₂ flowing into 23 is maintained almost constant. Thereby, the generation amount of H ₂ S can be kept low while maintaining the SO _x desorption efficiency high.

Note that adjusting the amount of H ₂ supplied from the fuel reforming system 25 to the NO _x storage reduction catalyst 23 based on the output of the H ₂ sensor 53 in this way can also be used in the first embodiment described above. .

It is a figure which shows the whole internal combustion engine in which the exhaust gas purification apparatus of this invention is used. And NO _X desorption process is a diagram showing the relationship between the concentration of NO _X exhaust gas flowing out from the exhaust gas and _the NO _X storage reduction catalyst flows into _the NO _X storage reduction catalyst. A desorption amount of the NO _X from _the NO _X storage reduction catalyst during one cycle of execution of the NO _X desorption process, the amount of reducing agent in the inflowing exhaust gas, the NO _X outflow from _the NO _X storage reduction catalyst It is a figure which shows transition. It is a diagram showing the relationship between the NO _X exudation amount in the initial stage of the NO _X storage amount and NO _X desorption process in NO _X desorption process at the start. It is a flowchart of a control routine of the control related to NO _X desorption process. After starting the SO _X desorption process is a diagram showing a change in the SO _X outflow from _the NO _X storage reduction catalyst. 7 is a flowchart of a control routine for control related to SO _X desorption processing. It is a diagram showing the relationship between the concentration of H ₂ S which flows from the air-fuel ratio and _the NO _X storage reduction catalyst of the inflowing exhaust gas.

Explanation of symbols

1 engine body 10 spark plug 11 fuel injection valve 18 throttle valve 20 oxidation catalyst 23 NO _X occluding and reducing catalyst 25 fuel reforming system 27 reforming catalyst 28 for reforming fuel injection valve 41 ECU
52 Air-fuel ratio sensor 53 H ₂ sensor 55 SO _X sensor

Claims (6)

A reducing agent is disposed only on the upstream side exhaust purification catalyst disposed in the engine exhaust passage, the downstream side exhaust purification catalyst disposed in the engine exhaust passage downstream of the upstream side exhaust purification catalyst, and the downstream side exhaust purification catalyst. The downstream exhaust purification catalyst stores NO _x in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is substantially the stoichiometric air-fuel ratio. Alternatively, when the engine is rich, the stored NO _x is desorbed, and when the NO _x occlusion amount in the downstream side exhaust purification catalyst is larger than the limit occlusion amount, the air-fuel ratio of the exhaust gas discharged from the engine body is substantially reduced. In an exhaust gas purification device for an internal combustion engine that desorbs NO _X from a downstream side exhaust purification catalyst by NO _X desorption treatment to make the theoretical air-fuel ratio or rich,
In the NO _X in the desorption process was to supply the reducing agent to the downstream exhaust purifying catalyst from the only reducing agent supply device during the NO _X desorption process start until a predetermined supply time has elapsed, the internal combustion engine Exhaust purification equipment. The amount of reducing agent supplied from the reducing agent supply device to the downstream side exhaust purification catalyst from the start of the NO _X desorption process to the passage of a predetermined supply time is determined by the NO _X at the start of the NO _X desorption process. The exhaust emission control device for an internal combustion engine according to claim 1, which is determined according to the amount of occlusion.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the reducing agent supply device is a hydrogen supply device that supplies hydrogen as a reducing agent. An exhaust purification catalyst disposed in the engine exhaust passage, and a hydrogen supply device for supplying hydrogen to the exhaust purification catalyst, wherein the exhaust purification catalyst is SO 2 in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. _When the air-fuel ratio of the inflowing exhaust gas is substantially the stoichiometric air-fuel ratio or rich and the temperature of the exhaust purification catalyst is equal to or higher than the SO _X desorption temperature, the stored SO _X is desorbed and the exhaust purification is performed. When the SO _X storage amount to the catalyst is larger than the limit storage amount, the air-fuel ratio of the exhaust gas discharged from the engine body is made substantially stoichiometric or rich, and the temperature of the exhaust purification catalyst is set to the SO _X desorption temperature. In an exhaust gas purification apparatus for an internal combustion engine that performs SO _X desorption treatment to raise the temperature to the above to desorb SO _X from the exhaust purification catalyst,
After a predetermined wait time has elapsed from the SO _X desorption process start was hydrogen from the hydrogen supply device while performing the SO _X desorption process is supplied to the exhaust purification catalyst, exhaust gas purification system of an internal combustion engine. The exhaust gas purification than the catalyst comprises a SO _X concentration detecting device for detecting the concentration of SO _X in the exhaust gas in the exhaust downstream Furthermore, the hydrogen supply device based on the SO _X concentration detected by the SO _X concentration detecting device The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the supply amount of hydrogen from the engine is controlled.   A hydrogen concentration detection device that detects the hydrogen concentration in the exhaust gas upstream of the hydrogen supply device is further provided, and hydrogen is supplied from the hydrogen supply device based on the hydrogen concentration detected by the hydrogen concentration detection device. The exhaust emission control device for an internal combustion engine according to any one of claims 3 to 5, wherein the amount is controlled.

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