JP2008208739A - Exhaust purification device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately release NO<SB>x</SB>from each of a plurality of NO<SB>x</SB>storing catalysts. <P>SOLUTION: The plurality of NO<SB>x</SB>storing catalysts 11, 12 are arranged in series in an engine exhaust passage, reducing agent feed valves 14, 15 for supplying a reducing agent to the NO<SB>x</SB>storing catalysts 11, 12 are individually provided for the NO<SB>x</SB>storing catalysts 11, 12. When NO<SB>x</SB>should be released from the NO<SB>x</SB>storing catalysts 11, 12, the upstream-most NO<SB>x</SB>storing catalyst 11 is fed with the reducing agent required for consuming the oxygen contained in the exhaust gas in addition to the reducing agent required for reducing the NO<SB>x</SB>stored in the upstream-most NO<SB>x</SB>storing catalyst 11 from the first reducing agent feed valve 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

A lean NO _x catalyst capable of reducing NO _x contained in the exhaust gas in the presence of hydrocarbons, ie HC, is arranged in series in the engine exhaust passage and HC is supplied to each lean NO _x catalyst. internal combustion engine so as HC provided supply device individually for each lean NO _X catalyst, supplying HC required to reduce the NO _X in the lean NO _X catalyst from the HC supply device respectively corresponding to the It is known (see Patent Document 1). In this internal combustion engine, NO _x is satisfactorily reduced in each lean NO _x catalyst.
JP 10-54223 A

A pair of _the NO _X storage, however the air-fuel ratio of the exhaust gas flowing at the time of lean that releases NO _X air-fuel ratio of the exhaust gas which is occluded becomes the stoichiometric air-fuel ratio or rich for occluding NO _X contained in the exhaust gas inflow supplying the reducing agent necessary for reducing the NO _X that is occluded in the same manner as described above for an internal combustion engine for each the NO _X storing catalyst to each _the NO _X storage catalyst in the case of arranging the catalyst in the engine exhaust passage Even in this case, it is not possible to obtain a good NO _x reduction action in each NO _x storage catalyst.

That is, when a pair of NO _x storage catalysts are arranged in the engine exhaust passage, there is an appropriate reducing agent supply method corresponding to the NO _x storage catalyst.
An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that optimally supplies a reducing agent when a plurality of NO _x storage catalysts are arranged in an engine exhaust passage.

That is, according to the present invention, when the air-fuel ratio of the inflowing exhaust gas is lean, NO _X contained in the exhaust gas is occluded, and when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich, the occluded NO _x is stored. provided individually reducing agent feeder for feeding the respective reducing agent in each _the NO _X storage catalyst as well as arranged in series a plurality of the NO _X storage catalyst to release the engine exhaust passage for each _the NO _X storage catalyst, NO _When NO _X should be released from the _X storage catalyst, oxygen contained in the exhaust gas is consumed, so that the most upstream NO _X storage catalyst is stored in the most upstream NO _X storage catalyst with respect to the most upstream NO _X storage catalyst. It has a number of reducing agents than the reducing agent required for reducing the NO _X which are to be supplied from the corresponding reducing agent supply device.

The NO _X that is occluded in the NO _X storage catalyst can be appropriately reduced.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to a plurality of NO _X storage catalysts 11, 12 arranged in series. In other words, the exhaust outlet of the turbine 7b is connected to the inlet of the most upstream the NO _X storing catalyst 11 positioned on the most upstream side, the most upstream NO _X exit adsorption catalyst 11 via the exhaust pipe 13 furthest upstream the NO _X storing catalyst 11 Is connected to the inlet of the downstream NO _x storage catalyst 12 located downstream of the catalyst. In the embodiment shown in FIG. 1, only one downstream NO _x storage catalyst 12 is arranged, but a plurality of downstream NO _x catalysts 12 may be arranged in series.

As shown in FIG. 1, a first reducing agent supply valve 14 for supplying a reducing agent made of hydrocarbons to the most upstream NO _X storage reduction catalyst 11 is disposed in the exhaust manifold 5, and downstream NO _X storage reduction. A second reducing agent supply valve 14 for supplying a reducing agent made of hydrocarbons to the catalyst 12 is disposed in the exhaust pipe 13. That is, the reducing agent supply device is provided separately for each the NO _X storing catalyst 11, 12 having a reducing agent feed valve 14, 15 for supplying the respective reducing agent in each the NO _X storing catalyst 11 and 12.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 16, and an electronically controlled EGR control valve 17 is disposed in the EGR passage 16. A cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 20 through a fuel supply pipe 19. Fuel is supplied into the common rail 20 from an electronically controlled variable discharge amount fuel pump 21, and the fuel supplied into the common rail 20 is supplied to the fuel injection valve 3 through each fuel supply pipe 19.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random accelerator memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36 It comprises. The most upstream the NO _X storing catalyst 11 the temperature sensor 22 for detecting the temperature of the most upstream the NO _X storing catalyst 11 is attached, the output signal of the output signal and the temperature sensor 22 in the intake air amount detector 8 are each corresponding The signal is input to the input port 35 via the AD converter 37. A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. . Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the reducing agent supply valves 14 and 15, the EGR control valve 17, and the fuel pump 21 through corresponding drive circuits 38.

First, the NO _X storage catalysts 11 and 12 shown in FIG. 1 will be described. These NO _X storage catalysts 11 and 12 are supported on a monolith support or pellet support having a three-dimensional network structure. A cross section of a surface portion of a catalyst carrier 45 made of alumina is schematically shown. As shown in FIG. 2, a noble metal catalyst 46 is dispersed and supported on the surface of the catalyst carrier 45, and a layer of NO _x absorbent 47 is formed on the surface of the catalyst carrier 45.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 46, and the constituents of the NO _x absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, calcium Ca. At least one selected from alkaline earths such as these, lanthanum La, and rare earths such as yttrium Y is used.

When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passages upstream of the NO _x storage catalysts 11 and 12 is referred to as the air-fuel ratio of the exhaust gas, the NO _x absorbent 47 is air-fuel ratio of the exhaust gas is absorbed NO _X when the lean, the oxygen concentration in the exhaust gas performs the absorbing and releasing action of the NO _X that releases NO _X absorbed and reduced.

That is, the case where barium Ba is used as a component constituting the NO _x absorbent 47 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, it is contained in the exhaust gas. As shown in FIG. 2, NO is oxidized on platinum Pt 46 to become NO ₂ , and then absorbed into the NO _X absorbent 47 and combined with barium oxide BaO, and in the form of nitrate ions NO ₃ ⁻ , the NO _X absorbent. It diffuses into 47. In this way, NO _x is absorbed in the NO _x absorbent 47. Exhaust oxygen concentration in the gas is NO ₂ with high long as the surface of the platinum Pt46 are generated, _the NO _X absorbent 47 of the NO _X absorbing capacity so long as NO ₂ not to saturate is absorbed in the NO _X absorbent 47 nitrate ions NO ₃ ^- is generated.

On the other hand, if the air-fuel ratio of the exhaust gas is made rich or the stoichiometric air-fuel ratio by supplying the reducing agent from the reducing agent supply valves 14 and 15, the oxygen concentration in the exhaust gas decreases, so that the reaction is reversed (NO ₃ ^- → proceeds to NO _2), thus to _the NO _X absorbent in the 47 nitrate ions NO ₃ and ^- is released from _the NO _X absorbent 47 in the shape of NO _2. Next, the released NO _x is reduced by unburned HC and CO contained in the exhaust gas.

Thus, when the air-fuel ratio of the exhaust gas is lean, that is, when combustion is performed under the lean air-fuel ratio, NO _X in the exhaust gas is absorbed into the NO _X absorbent 47. However becomes saturated is NO _X absorbing capacity of the NO _X absorbent 47 during the combustion of the fuel under a lean air-fuel ratio is continued, no longer able to absorb NO _X by _the NO _X absorbent 47 and thus End up. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by supplying the reducing agent from the reducing agent supply valves 14 and 15 before the absorption capacity of the NO _x absorbent 47 is saturated, thereby NO. NO _X is released from the _X absorbent 47.

Incidentally, SO _X in the exhaust gas, that is, contains SO _2, this SO ₂ flows into the NO _X storing catalyst 11 This SO ₂ is the is oxidized SO ₃ in the platinum Pt 46. Next, this SO ₃ is absorbed into the NO _x absorbent 47 and bonded to the barium oxide BaO, while diffusing into the NO _x absorbent 47 in the form of sulfate ions SO ₄ ²⁻ to form a stable sulfate BaSO ₄ . To do. However, since the NO _x absorbent 47 has a strong basicity, this sulfate BaSO ₄ is stable and difficult to decompose. If the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO ₄ is not decomposed and remains as it is. Remain. Thus will be sulfates BaSO ₄ increases as time in the NO _X absorbent 47 has elapsed, that the amount of NO _{X the} NO _X absorbent 47 can absorb as thus to time has elapsed is reduced Become. That is, the NO _x storage catalysts 11 and 12 are deteriorated.

Then the _the NO _X storage catalytic action of the respective the NO _X storing catalyst 11 and 12 with reference to FIG. 3, the NO _X release and reduction action from the the NO _X storing catalyst 11 and 12.
In FIG. 3 ShigumaNOX1 shows the occluded amount of NO _X occluded in the most upstream the NO _X storing catalyst 11, ΣNOX2 shows the occluded amount of NO _X occluded in the downstream the NO _X storing catalyst 12. These occluded amount of NO _X ΣNOX1, ΣNOX2 is calculated from the NO _X amount exhausted from the engine per unit time. In FIG. 3, ΣSOX1 indicates the stored SO _X amount stored in the most upstream NO _X storage catalyst 11, and the stored SO _X amount ΣSOX1 is also calculated from the SO _X amount discharged per unit time from the engine.

First, a method for calculating the occluded NO _x amount will be described with reference to FIG. Note that the routine for calculating the amount of occluded NO _{x and the} like shown in FIG. 4 is executed by interruption every predetermined time.
Discharge amount of NO _X NOXA exhausted from the engine per unit time is calculated first, at step 50 and reference to FIG. The discharge amount of NO _X NOXA is stored in advance in the ROM32 in the form of a map shown in FIG. 5 (A) as a function of the required torque TQ and engine speed N. Then discharge SO _X amount SOXA is calculated to be exhausted from the engine per unit time in step 51. The exhaust SO _X amount SOXA is also stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N in the form of a map as shown in FIG.

Most of the SO _X discharged from the engine is stored in the most upstream NO _X storage catalyst 11. Accordingly SO _X amount SOXA calculated from FIG. 5 (B) to the occluded SO _X amount ΣSOX1 occluded in the most upstream the NO _X storing catalyst 11 at step 52 is added.

Then _the NO _X storage speed of the most upstream the NO _X storing catalyst 11 in step 53, i.e. the most upstream the NO _X storing catalyst 11 per unit time absorbing possible amount of NO _X QNOX is calculated. The more storage amount of NO _X ΣNOX1 increases, and as the storage SO _X amount ΣSOX1 since many becomes higher NO _X is less likely to be occluded in the most upstream the NO _X storing catalyst 11 storable amount of NO _X QNOX occluding amount of NO _X ΣNOX1 increases It decreases, and decreases as the stored SO _X amount ΣSOX1 increases. Further, the storable NO _x amount QNOX decreases as the exhaust gas flow rate increases, that is, as the intake air amount increases, and further changes according to the temperature of the most upstream NO _x storage catalyst 11. The stored NO _X amount QNOX is stored in advance in the ROM 32 as a function of the stored NO _X amount ΣNOX1, the stored SO _X amount ΣSOX1, the intake air amount, and the temperature of the most upstream NO _X storage catalyst 11, and this stored relationship is stored. From this, the storable NO _x amount QNOX is calculated.

Then discharge amount of NO _X NOXA from the engine at step 54 whether or not greater than storable amount of NO _X QNOX is determined. If NOXA> Qnox Qnox only because it is not occluded at this time are occluded amount of NO _X NOX1 to be stored per unit time in the uppermost upstream the NO _X storing catalyst 11 is Qnox proceeds to Step 55. Next, the routine proceeds to step 57. In contrast, when it is determined in step 54 that NOXA ≦ QNOX, all the exhausted NO _X amount NOXA is stored in the most upstream NO _X storage catalyst 11, so at this time the routine proceeds to step 56 where the exhausted NO _X amount NOXA is. The stored NO _X amount is NOX1. Next, the routine proceeds to step 57.

In step 57 occluded amount of NO _X NOX1 the occluded amount of NO _X ΣNOX1 occluded in the most upstream the NO _X storing catalyst 11 is added. Then occluded amount of NO _X NOX2 be stored per unit time downstream the NO _X storing catalyst 12 is calculated by subtracting the occluded amount of NO _X NOX1 from step 58 discharge amount of NO _X NOXA. Then occluded amount of NO _X NOX2 is added to the occluded amount of NO _X ΣNOX2 occluded in the downstream the NO _X storing catalyst 12 in step 59. Such occlusion amount of NO _X ΣNOX2 being occluded is calculated and the occluded amount of NO _X ΣNOX1 and downstream the NO _X storing catalyst 12 is occluded in the most upstream the NO _X storing catalyst 11 on.

Returning to FIG. 3 again, in the embodiment according to the present invention, the stored NO _X amount ΣNOX1 stored in the most upstream NO _X storage catalyst 11 reaches the allowable value NX1 or is stored in the downstream NO _X storage catalyst 12. NO _X releasing action from the the NO _X storing catalyst 11 is carried out when the occluded amount of NO _X ΣNOX2 there are reaches the allowable value NX2. Incidentally, NO _X emission action lines from the the NO _X storing catalyst 11 by adsorption amount of NO _X ΣNOX1 occluded in the most upstream the NO _X storing catalyst 11 reaches the allowable value NX1 In the example shown in FIG. 3 Shows the case.

As shown in FIG. 3, when ΣNOX1 reaches NX1, the reducing agent is supplied from the first reducing agent supply valve 14 as shown by the reducing agent supply 1, and thereby flows into the most upstream NO _X storage catalyst 11. The air-fuel ratio (A / F) 1 of the exhaust gas is temporarily switched from lean to rich. In this case NO _X that is occluded from the most upstream the NO _X storing catalyst 11 is released and reduced.

By the way, when NO _X should be released from the most upstream NO _X storage catalyst 11 in this way, oxygen contained in the exhaust gas is consumed, so that the most upstream NO _X storage catalyst 11 is changed to the most upstream NO _X storage catalyst 11. many reducing agents than the reducing agent required for reducing the NO _X being occluded is supplied from the first reducing agent feed valve 14. That is, the theoretical air-fuel ratio of the exhaust gas to say macroscopically when the air-fuel ratio of the exhaust gas flowing into the most upstream the NO _X storing catalyst 11 so as to release the NO _X from the most upstream the NO _X storing catalyst 11 from lean to rich Necessary to reduce the air-fuel ratio from the stoichiometric air-fuel ratio to rich, and the amount of reducing agent required to reduce the air-fuel ratio, that is, to consume oxygen contained in the exhaust gas. that the amount of reducing agent required to reduce to release NO _X occluded in the innermost upstream the NO _X storing catalyst 11 is supplied.

That is, it is necessary to consume the oxygen contained in the exhaust gas flowing into the most upstream the NO _X storing catalyst 11 First to emit NO _X from the most upstream the NO _X storing catalyst 11. Therefore to reduce the NO _X occluded in the most upstream the NO _X storing catalyst 11 to the most upstream the NO _X storing catalyst 11 when, as described above in the present invention from the most upstream the NO _X storing catalyst 11 should be released NO _X In addition to the necessary reducing agent, the reducing agent necessary for consuming oxygen contained in the exhaust gas is supplied from the first reducing agent supply valve 14.

Next, when the exhaust gas flow portion in which the air-fuel ratio has become rich due to the supply of the reducing agent from the first reducing agent supply valve 14 reaches the reducing agent injection region of the second reducing agent supply valve 15, the reducing agent supply 2 As shown, the reducing agent is supplied from the second reducing agent supply valve 15, and the exhaust gas flow portion containing the reducing agent supplied from the second reducing agent supply valve 15 is in the downstream side NO _X storage catalyst 12. Flow into.

Oxygen in the exhaust gas in this exhaust gas flow portion has already been consumed by the reducing agent supplied from the first reducing agent supply valve 14, so that the downstream side NO _X storage catalyst 12 passes from the second reducing agent supply valve 15. It is sufficient to supply an amount of reducing agent necessary for releasing and reducing NO _X stored in the catalyst. Accordingly the present invention Taking the case where a plurality of downstream the NO _X storing catalyst 12 downstream of the most upstream the NO _X storing catalyst 11 is disposed as an example, should be released NO _X from the downstream side the NO _X storing catalyst 12 sometimes reducing agent required for reducing the NO _X occluded in the respective downstream the NO _X storing catalyst 12 is supplied from the second reducing agent supply valve 15 to respectively correspond.

  In the embodiment according to the present invention, as described above, the reducing agent is supplied from the second reducing agent supply valve 15 to the exhaust gas flow portion in which the air-fuel ratio has decreased due to the supply of the reducing agent from the first reducing agent supply valve 14. As shown in FIG. 3, the reducing agent supply timing from the second reducing agent supply valve 15 is delayed by Δt time as shown in FIG. 3 with respect to the reducing agent supply timing from the first reducing agent supply valve 14. . The reducing agent supply delay time Δt becomes shorter as the flow rate of the exhaust gas increases, that is, as the intake air amount increases. This reducing agent supply delay time Δt is stored in advance in the ROM 32 as a function of the intake air amount.

As shown in FIG. 3, the SO _X amount ΣSOX 1 stored in the most upstream NO _X storage catalyst 11 gradually increases with time. That is, the most upstream NO _x storage catalyst 11 gradually deteriorates with time. FIG. 6 shows a change in the supply ratio of the reducing agent that changes in accordance with the degree of deterioration of the most upstream NO _x storage catalyst 11 in the same operation state. In FIG. 6, Q 0 indicates the amount of reducing agent necessary for consuming oxygen in the exhaust gas flowing into the most upstream NO _X storage catalyst 11, and Q 1 is stored in the most upstream NO _X storage catalyst 11. and NO _X represents the amount of reducing agent required to reduce by releasing, Q2 is of the reducing agent required to reduce by releasing NO _X occluded in the downstream the NO _X storing catalyst 12 Indicates the amount.

Each numerical value in FIG. 6 represents the amount Q0, Q1, Q2 of each reducing agent when the total amount of reducing agent supplied is 100. 1, no. 2No. 3 shows the cases where the degree of deterioration of the most upstream NO _x storage catalyst 11 is different. No. 1 with the lowest degree of deterioration of the most upstream NO _x storage catalyst 11. 1, Q0 is 80, Q1 is 15, Q2 is 5, Q0 + Q1 is supplied from the first reducing agent supply valve 14, and Q2 is supplied from the second reducing agent supply valve 15. .

On the other hand, since the amount of NO _X deterioration of most upstream the NO _X storing catalyst 11 are inserted in the uppermost stream the NO _X storing catalyst 11 when traveling decreases No. As shown in FIG. 2, Q1 is 5 and Q2 is 15. That, _the amount of NO _X occluded in the downstream the NO _X storing catalyst 12 than _the amount of NO _X occluded in the most upstream the NO _X storing catalyst 11 increases. In addition, this No. In the case of 2, Q0 is No. The same as the case of 1.

On the other hand, the amount of NO _X deterioration of most upstream the NO _X storing catalyst 11 are inserted in the most upstream the NO _X storing catalyst 11 progresses further becomes zero No. As shown in FIG. 3, Q1 becomes 0 and Q2 becomes 15. That is, all the NO _X contained in the exhaust gas is stored in the downstream NO _X storage catalyst 13. In addition, this No. In the case of 3, Q0 is No. 1, no. This is the same as the case of 2.

That is, when the inside of the most upstream NO _x storage catalyst 11 is deteriorated and filled with the stored SO _x , the basicity of the layer of the NO _x absorbent 47 is weakened and the oxidation performance by the platinum 46 is enhanced. Therefore, in order to consume oxygen contained in the exhaust gas satisfactorily by the reducing agent supplied by utilizing the enhanced oxidation performance, No. Even in the case of 3, Q0 is supplied from the first reducing agent supply valve 14.

As described above, in the embodiment according to the present invention, the degree of deterioration of the most upstream NO _X storage catalyst 11 is estimated from the stored SO _X amount ΣSOX1, and the most upstream NO _X storage catalyst 11 and the downstream side are determined according to the estimated degree of deterioration. the amount of reducing agent reducing agent supplied from the supply valve 14, 15 respectively corresponding to the NO _X storing catalyst 12 is adjusted. In this case, the amount of reducing agent supplied from the second reducing agent supply valve to the downstream side NO _X storage catalyst 12 increases as the degree of deterioration of the most upstream NO _X storage catalyst 11 increases.

Next, the reducing agent supply control routine will be described with reference to FIG.
Referring to FIG. 7, first, at step 60, it is judged if the stored NO _X amount ΣNOX1 stored in the most upstream NO _X storage catalyst 11 exceeds the allowable value NX1. When ΣNOX1> NX1, the routine jumps to step 62, and when ΣNOX1 ≦ NX1, the routine proceeds to step 61. In step 61, it is determined whether or not the stored NO _X amount ΣNOX2 stored in the downstream NO _X storage catalyst 12 exceeds the allowable value NX2. When ΣNOX2> NX2, the process proceeds to step 62, and when ΣNOX2 ≦ NX2, the processing cycle is completed. That is, when the stored NO _X amount ΣNOX1 stored in the most upstream NO _X storage catalyst 11 exceeds the allowable value NX1, or the stored NO _X amount ΣNOX2 stored in the downstream NO _X storage catalyst 12 is the allowable value NX2. When the value is exceeded, the routine proceeds to step 62.

At step 62 reducing agent amount Q1 required to reduced to release NO _X being occluded based on the calculated value of the occluded amount of NO _X ΣNOX1 occluded in the most upstream the NO _X storing catalyst 11 is calculated. Reducing agent amount Q2 is calculated required to reduced to release NO _X that is occluded by then based on the calculated value of the occluded amount of NO _X ΣNOX2 occluded in the downstream the NO _X storing catalyst 12 in step 63 . Then the excess of oxygen from the intake air amount in step 64 and the fuel injection quantity, i.e. the reducing agent quantity Q0 required to consume the oxygen in the exhaust gas flowing into the most upstream the NO _X storing catalyst 11 is calculated. Next, at step 65, the reducing agent supply delay time Δt is calculated.

  Next, at step 66, the sum of Q 0 and Q 1 is supplied from the first reducing agent supply valve 14. Next, at step 67, the process waits until the reducing agent supply delay time Δt elapses. When the reducing agent supply delay time Δt elapses, the routine proceeds to step 68 where Q2 is supplied from the second reducing agent supply valve 15. Next, at step 69, ΣNOX1 and ΣNOX2 are cleared.

1 is an overall view of a compression ignition type internal combustion engine. 2 is a cross-sectional view of a surface portion of a catalyst carrier of an NO _X storage catalyst. It is a time chart which shows supply control of a reducing agent. It is a flowchart for calculating the amount of occluded NO _x and the like. It is a diagram showing a map such as occluded amount of NO _X NOXA. It is a figure which shows the amount of each reducing agent. It is a flowchart for performing supply control of a reducing agent.

Explanation of symbols

4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 11 Uppermost stream NO _x storage catalyst 12 Downstream NO _x storage catalyst 14 First reducing agent supply valve 15 Second reducing agent supply valve

Claims (5)

A plurality of NO _X storage catalysts that store NO _X contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and release the stored NO _X when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich the provided a reducing agent supply device for supplying the respective reducing agent with each _the NO _X storage catalyst arranged in series in the engine exhaust passage separately for each _the NO _X storage catalyst, release the NO _X from the NO _X storing catalyst for the time to put the to consume oxygen contained in the exhaust gas, for reducing the NO _X occluded in the outermost upstream _the NO _X storage catalyst with respect to the most upstream _the NO _X storage catalyst located at the most upstream side An exhaust gas purification apparatus for an internal combustion engine that supplies more reducing agent than the necessary reducing agent from a corresponding reducing agent supply device. Exhaust gas in addition to the reducing agent required for reducing the NO _X occluded in the outermost upstream _the NO _X storage catalyst with respect to the most upstream _the NO _X storage catalyst when the the NO _X storing catalyst should release the NO _X oxygen is supplied from the corresponding reducing agent supply device reducing agent required to consume the, outermost upstream _the NO _X storage each downstream NO for each downstream _the NO _X storage catalyst located downstream of the catalyst contained in the an exhaust purification system of an internal combustion engine according to claim 1 which is adapted to supply the reducing agent supply device in which a reducing agent respectively corresponding required for reducing the NO _X which is stored in _X storage catalyst. The degree of deterioration of the most upstream NO _x storage catalyst is estimated, and each downstream NOx located downstream of the most upstream NO _x storage catalyst and the most upstream NO _x storage catalyst according to the estimated degree of deterioration. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of the reducing agent supplied from the reducing agent supply device corresponding to each of the _X storage catalysts is adjusted. 4. The internal combustion engine according to claim 3, wherein the amount of the reducing agent supplied from the corresponding reducing agent supply device to the downstream NO _X storage catalyst increases as the degree of deterioration of the most upstream NO _X storage catalyst increases. Exhaust purification device. Reduction of downstream _the NO _X storage catalyst as a reducing agent to be supplied to the downstream side _the NO _X storage catalyst in the exhaust gas stream portion the air-fuel ratio is decreased by reducing agent supplied to the most upstream _the NO _X storage catalyst is supplied An exhaust purification system of an internal combustion engine according to claim 1, the supply timing of the agent is slow to live the supply timing of the reducing agent to the most upstream _the NO _X storage catalyst.

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