JP5746008B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

HC in exhaust gas, CO, and to purify NO _X, it is known to place a three-way catalytic converter in the engine exhaust system. However, a noble metal catalyst such as platinum generally used in a three-way catalyst device is expensive, and it has been proposed to use a base metal catalyst instead of the noble metal catalyst (see Patent Document 1).

However, in the three-way catalyst device, when the base metal catalyst is used instead of the noble metal catalyst, or when a part of the noble metal catalyst is replaced with the base metal catalyst, the NO _x reduction performance as the NO _x reduction catalyst device decreases. the combustion air-fuel ratio in the slightly more rich stoichiometric air-fuel ratio, it is considered possible to facilitate the reduction of NO _X by increasing the concentration of the reducing substance such as HC and CO in the exhaust gas.

JP2011-125862A

As described above, in the exhaust purification system for an internal combustion engine having a reducing capability is low NO _X reduction catalyst device of the NO _X carries a base metal catalyst, the combustion air-fuel ratio to satisfactorily reduce NO _X than the stoichiometric air-fuel ratio If it is made rich, fuel consumption will be greatly degraded.

Accordingly, the present invention purposes, in the exhaust purification system for an internal combustion engine having a reducing capability is low NO _X reduction catalyst device of the NO _X carries a base metal catalyst, the fuel consumption for the reduction of the NO _X in the exhaust gas It is to improve the deterioration.

An exhaust purification system of an internal combustion engine according to claim 1 according to the present invention comprises a first NO _X reduction catalyst device carrying the disposed in an exhaust passage base metal catalyst, the first NO _X reduction catalyst device of the exhaust passage bypass for bypassing the second NO _X reduction catalyst device, a hydrocarbon-absorbing device disposed upstream of the first NO _X reduction catalyst device, the hydrocarbon-absorbing device having the ammonia storage capacity which is disposed downstream comprising a passage, when the air-fuel ratio of the exhaust gas flowing into the first NO _X reduction catalyst device is richer than the stoichiometric air-fuel ratio, and reducing the NO _X in the exhaust gas by the first NO _X reduction catalyst device and generates ammonia Te, when occludes the generated the ammonia into the second NO _X reduction catalyst device, the air-fuel ratio of the exhaust gas flowing into the first NO _X reduction catalyst device is lean is In the exhaust purification system of an internal combustion engine reduction using the ammonia to NO _X occluded in said NO _X reducing catalyst device in the exhaust gas by the second NO _X reduction catalyst device, the rich combustion air-fuel ratio of an internal combustion engine The exhaust gas is discharged from the lean passage and the hydrocarbon so that the hydrocarbon stored in the hydrocarbon storage device is discharged immediately before the combustion air-fuel ratio of the internal combustion engine is made rich from the lean. Which of the storage devices is allowed to pass and the combustion air-fuel ratio of the internal combustion engine are controlled.

  An internal combustion engine exhaust gas purification apparatus according to claim 2 of the present invention is the internal combustion engine exhaust gas purification apparatus according to claim 1, wherein the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio. If the exhaust gas temperature is lower than the set temperature, the exhaust gas passes through the hydrocarbon storage device. If the exhaust gas temperature is equal to or higher than the set temperature, the exhaust gas passes through the bypass passage. When the fuel ratio is made leaner than the stoichiometric air-fuel ratio, the exhaust gas is allowed to pass through the bypass passage. When the combustion air-fuel ratio of the internal combustion engine is made rich from the lean to the rich, the exhaust gas temperature is less than the set temperature. If the exhaust gas passes through the bypass passage, the combustion air-fuel ratio of the internal combustion engine is made rich, and if the exhaust gas temperature is equal to or higher than the set temperature, the exhaust gas The exhaust gas is allowed to pass through the hydrocarbon storage device, and when the air-fuel ratio of the exhaust gas flowing out from the hydrocarbon storage device becomes leaner than the stoichiometric air-fuel ratio, the combustion air-fuel ratio of the internal combustion engine is made rich. Which of the bypass passage and the hydrocarbon storage device passes the gas and the combustion air-fuel ratio of the internal combustion engine are controlled.

An internal combustion engine exhaust gas purification apparatus according to a third aspect of the present invention is the internal combustion engine exhaust gas purification apparatus according to the first or second aspect, wherein the exhaust passage is disposed downstream of the second NO _x reduction catalyst device. an oxidation catalyst device, which is a secondary air supply device for supplying secondary air between the second NO _X reduction catalyst device of the exhaust passage and the oxidation catalyst device, the second NO _X in the exhaust passage comprising a first NO _X sensor disposed between the reduction catalyst device and the oxidation catalyst device, and a second NO _X sensor that is disposed on the downstream side of the oxidation catalyst device of the exhaust passage, the internal combustion engine the combustion air-fuel ratio by supplying the secondary air by the secondary air supply system as well as to the rich, the when the NO _X is detected by the second NO _X sensor, NO _X is detected by at least a first NO _X sensor Combustion of the internal combustion engine until Characterized by the ratio to the lean.

According to the exhaust purification system of an internal combustion engine according to claim 1 according to the present invention, a first NO _X reduction catalyst device carrying the disposed in an exhaust passage base metal catalyst, the first NO _X reduction catalyst device in the exhaust passage A second NO _x reduction catalyst device having ammonia storage capacity disposed on the downstream side, a hydrocarbon storage device disposed on the upstream side of the first NO _x reduction catalyst device, and a bypass passage that bypasses the hydrocarbon storage device; When the air-fuel ratio of the exhaust gas flowing into the first NO _x reduction catalyst device is richer than the stoichiometric air-fuel ratio, the NO _x in the exhaust gas is reduced by the first NO _x reduction catalyst device even if the reduction capacity is low. can be reduced, ammonia is generated from a portion of the NO _X. The ammonia thus produced is occluded in the second NO _x reduction catalyst device. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the first NO _x reduction catalyst device is leaner than the stoichiometric air-fuel ratio, the second NO _x reduction catalyst device converts the NO _x in the exhaust gas into the second NO _x reduction catalyst device. Reduction is performed using the stored ammonia. Thus, even when the air-fuel ratio of the exhaust gas flowing into the first NO _x reduction catalyst device is leaner than the stoichiometric air-fuel ratio, the NO _x in the exhaust gas can be reduced well. Thereby, the deterioration of fuel consumption can be improved as compared with the case where the combustion air-fuel ratio is always made richer than the stoichiometric air-fuel ratio in order to reduce NO _{x in} the internal combustion engine.

Further, a hydrocarbon storage device is disposed upstream of the first NO _x reduction catalyst device, and when the combustion air-fuel ratio of the internal combustion engine is made rich, the hydrocarbons stored in the hydrocarbon storage device are internal combustion. Whether the exhaust gas is allowed to pass through the bypass passage or the hydrocarbon storage device and the combustion air-fuel ratio of the internal combustion engine are controlled so that they are released immediately before the combustion air-fuel ratio of the engine is made rich from lean. ing. Thereby, even if can not be reduced of the NO _X to use occluding ammonia by combustion air-fuel ratio of the internal combustion engine the second NO _X reduction catalyst device is lean, while the hydrocarbons are released, the first NO _X reduction in the catalytic device of the NO _X reduction is possible, in order to be able to shorten the period for the combustion air-fuel ratio of an internal combustion engine to a rich, deterioration of fuel consumption can be further improved.

  According to the exhaust gas purification apparatus for an internal combustion engine according to claim 2 of the present invention, in the exhaust gas purification apparatus for the internal combustion engine according to claim 1, the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio. When the exhaust gas temperature is lower than the set temperature, the hydrocarbon in the exhaust gas is stored in the hydrocarbon storage device so that the exhaust gas passes through the hydrocarbon storage device. However, if the exhaust gas temperature is equal to or higher than the set temperature, if the exhaust gas passes through the hydrocarbon storage device, the stored hydrocarbon is released, so that the exhaust gas passes through the bypass passage. When the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio, since the exhaust gas contains almost no hydrocarbon, the exhaust gas is allowed to pass through the bypass passage.

When the combustion air-fuel ratio of the internal combustion engine is made lean to rich, if the exhaust gas temperature is lower than the set temperature, hydrocarbons cannot be released from the hydrocarbon storage device, so that the exhaust gas passes through the bypass passage and The combustion air-fuel ratio of the engine is made rich, but if the exhaust gas temperature is equal to or higher than the set temperature, the exhaust gas passes through the hydrocarbon storage device, and the stored hydrocarbon is released from the hydrocarbon storage device. NO was _X fuel ratio of the exhaust gas flowing to the reducing catalyst device richer than the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the hydrocarbon-absorbing device has become leaner than the stoichiometric air-fuel ratio storage hydrocarbons is almost released Sometimes the combustion air-fuel ratio of the internal combustion engine is made rich. In this way, by controlling which of the bypass passage and the hydrocarbon storage device the exhaust gas passes through and the combustion air-fuel ratio of the internal combustion engine, it is possible to store the hydrocarbons well in the hydrocarbon storage device. In addition, the first NO _x reduction catalyst can effectively release the occluded hydrocarbons from the hydrocarbon occlusion device, and when the internal combustion engine is lean before the combustion air-fuel ratio is made richer than the stoichiometric air-fuel ratio. It is possible to reduce NO _x by making the air-fuel ratio of the exhaust gas flowing into the device richer than the stoichiometric air-fuel ratio, and to further improve the deterioration of fuel consumption by shortening the period during which the combustion air-fuel ratio of the internal combustion engine is rich. it can.

Further, according to the exhaust purification system of an internal combustion engine according to claim 3 of the present invention, in the exhaust purification system of an internal combustion engine according to claim 1 or 2, downstream of the second NO _X reduction catalyst device in the exhaust passage An oxidation catalyst device disposed in the exhaust passage, a secondary air supply device for supplying secondary air between the second NO _x reduction catalyst device in the exhaust passage and the oxidation catalyst device, and a second NO _x reduction catalyst device in the exhaust passage and the first NO _X sensor disposed between the oxidation catalyst device, comprises a second NO _X sensor arranged downstream of the oxidation catalyst device in the exhaust passage, the combustion air-fuel ratio of an internal combustion engine to a rich At the same time, the secondary air is supplied by the secondary air supply device. Thus, even at low reducing ability of the NO _X in the first NO _X reduction catalyst device can be reduced satisfactorily NO _X in the first NO _X reduction catalyst device, flows from the first NO _X reduction catalyst device HC and CO can be oxidized using oxygen in the secondary air in the downstream oxidation catalyst device.

Ammonia produced by the reduction of the NO _X in the first NO _X reduction catalyst device is occluded in the second NO _X reduction catalyst device having a first NO _X reducing ammonia storage capacity which is disposed downstream of the catalytic converter, When ammonia storage capacity of the second NO _X reduction catalyst device is saturated ammonia flows out from the second NO _X reduction catalyst device flows into the second NO _X reduction oxidation catalyst device disposed downstream of the catalytic converter two use of oxygen in the next air is oxidized, NO _X is produced. Accordingly, when NO _X is detected by the second NO _X sensor, the second NO _X reduction catalyst device stores a saturated amount of ammonia, and the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio. To.

As a result, NO _x in the exhaust gas is not reduced in the first NO _x reduction catalyst device, but is well reduced by the ammonia stored in the second NO _x reduction catalyst device and hardly released into the atmosphere. . When all of the occluded ammonia is used for the reduction of the NO _X in the second NO _X reduction catalyst device, NO _X by the first NO _X sensor NO _X from the second NO _X reduction catalyst device flows out is detected The At least until this time, the combustion air-fuel ratio of the internal combustion engine is made lean. Thereafter, in order in the second NO _X reduction catalyst device can not be reduced to NO _X, the first NO _X reduction catalyst using the hydrocarbons released the combustion air-fuel ratio from a hydrocarbon storage device while lean or reducing the NO _X by the device, or, so that the reduction of NO _X by the first NO _X reduction catalyst device combustion air-fuel ratio rich. Thus, the deterioration of fuel consumption can be improved as compared with a case where the combustion air-fuel ratio is always made richer than the stoichiometric air-fuel ratio in the internal combustion engine.

1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a flowchart which shows control of the exhaust gas purification apparatus of FIG.

  FIG. 1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. The internal combustion engine 10 is, for example, an in-cylinder injection spark ignition four-cylinder internal combustion engine. A hydrocarbon storage device 40 is disposed in the exhaust passage 30 on the downstream side of the exhaust manifold 20 of the internal combustion engine 10. The hydrocarbon storage device 40 is, for example, one in which, for example, zeolite or the like is supported as a hydrocarbon storage material on a substrate having a honeycomb structure. When the exhaust gas temperature is lower than a set temperature (for example, 300 ° C.), the hydrocarbon storage device 40 stores the hydrocarbon in the exhaust gas well, and when the exhaust gas temperature becomes equal to or higher than the set temperature, the stored hydrocarbon Are to be released.

  A bypass passage 32 that bypasses the hydrocarbon storage device 40 is connected to the exhaust passage 30 via a switching valve 31 provided on the upstream side of the hydrocarbon storage device 40, and the switching valve 31 is set to the first position. As a result, the exhaust gas does not pass through the bypass passage 32 as indicated by the solid arrow, but passes through the hydrocarbon storage device 40. By setting the switching valve 31 to the second position, the exhaust gas is indicated by the dotted arrow. As shown, it does not pass through the hydrocarbon storage device 40 but passes through the bypass passage 32.

A first NO _x reduction catalyst device 50 is disposed downstream of the joining position 33 of the bypass passage 32 of the exhaust passage 30 (that is, downstream of the hydrocarbon storage device 40). The first NO _x reduction catalyst device 50 is not an expensive noble metal catalyst such as platinum Pt, but a base metal catalyst such as copper Cu, iron Fe, silver Ag, or gold Au on alumina or ceria on a substrate having a honeycomb structure, for example. Etc. as a carrier. In addition, the first NO _x reduction catalyst device 50 is configured to reduce the amount of expensive noble metal catalyst used by replacing a part of the noble metal catalyst of a general three-way catalyst device with a base metal catalyst. Can do.

Further, on the downstream side of the first NO _x reduction catalyst device 50 in the exhaust passage 30, for example, zirconia ZrO ₂ subjected to super strong acid treatment is supported on a substrate having a honeycomb structure, or copper Cu or iron Fe is added to the zeolite ZSM5. Alternatively, a second NO _x reduction catalyst device 60 formed by supporting SAPO as a carrier and having an ammonia storage function is disposed. The second NO _x reduction catalyst device 60 can reduce NO _x using ammonia stored as a reducing agent even when the air-fuel ratio of the exhaust gas is lean. Further, on the downstream side of the second NO _X reduction catalyst device 60 in the exhaust passage 30, for example, on a substrate of a honeycomb structure, the oxidation catalyst device 70 carrying a base metal catalyst (or a noble metal catalyst) is disposed.

A secondary air supply device 80 for supplying secondary air is disposed between the second NO _x reduction catalyst device 60 and the oxidation catalyst device 70 in the exhaust passage 30. A first NO _x sensor 91 is disposed between the second NO _x reduction catalyst device 60 and the oxidation catalyst device 70 in the exhaust passage 30, and the first NO _x sensor 91 is disposed downstream of the oxidation catalyst device 70 in the exhaust passage 30. two NO _X sensor 92 is arranged. The first NO _X sensor 91 and the second NO _X sensor 92 can detect the NO _X concentration in the exhaust gas.

The first NO _X reduction catalyst device 50 described above, as compared to the general three-way catalytic converter which carries a noble metal catalyst, for reduction performance decreases, sufficient reduction of NO _X in the exhaust gas of the stoichiometric air-fuel ratio can not be clean, in order to sufficiently reduce the NO _X is not so combustion air-fuel ratio to the stoichiometric air-fuel ratio slightly more rich (e.g. air-fuel ratio 14) increase the concentration of reducing substances in the exhaust gas I must. However, if the combustion air-fuel ratio is always made richer than the stoichiometric air-fuel ratio, fuel consumption will deteriorate.

  In order to improve this problem, the exhaust emission control device is controlled by an electronic control device (not shown) according to the flowchart shown in FIG. This flowchart is started when the engine is started. First, in step 101, it is determined whether or not the flag F is 1. Since the flag F is reset to 0 when the engine is stopped, the determination in step 101 is initially denied and the process proceeds to step 102.

  In step 102, the combustion air-fuel ratio of the internal combustion engine is made slightly richer (for example, air-fuel ratio 14) than the stoichiometric air-fuel ratio. In order to enable such control of the combustion air-fuel ratio, a first air-fuel ratio sensor 34 capable of detecting the air-fuel ratio of the exhaust gas is disposed upstream of the switching valve 31 in the exhaust passage 30. Next, in step 103, the secondary air is supplied from the secondary air supply device 80 to the upstream side of the oxidation catalyst device 70. Next, in step 104, it is determined whether or not the exhaust gas temperature T is equal to or higher than a set temperature T ′ (for example, 300 ° C.).

  The exhaust gas temperature T may be measured by a temperature sensor (not shown) immediately upstream of the switching valve 31, but a map or the like is used based on the current engine operating state (engine load and engine speed). It may be estimated. When the determination at step 104 is negative, the switching valve 31 is set to the first position at step 105, and when the determination at step 104 is positive, the switching valve 31 is set to the second position at step 106.

When the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, the amount of NO _x produced is small compared to when the lean air-fuel ratio is made leaner than the stoichiometric air-fuel ratio, and the switching valve 31 is set to any position. However, the air-fuel ratio of the exhaust gas flowing into the first NO _x reduction catalyst device 50 becomes richer than the stoichiometric air-fuel ratio, and the NO _x in the exhaust gas is also reduced in the first NO _x reduction catalyst device 50 having a low reduction performance. The reduction action becomes active and is reduced well using HC and CO contained in the exhaust gas. At this time, ammonia is generated from a part of _{NO X (CO + H 2 O} → H 2 + CO 2, 2NO + 2CO + 3H 2 → 2NH 3 + 2CO 2). The ammonia thus generated is occluded in the second NO _x reduction catalyst device 60.

Further, when the combustion air-fuel ratio of the internal combustion engine is richer than the stoichiometric air-fuel ratio, the concentrations of HC and CO in the exhaust gas become high, and some HC and CO are in the first NO _x reduction catalyst device 50. The first NO _x reduction catalyst device 50 flows out without being used for the reduction of NO _x and without being oxidized. The HC and CO flowing out in this way pass through the second NO _x reduction catalyst device 60 and flow into the oxidation catalyst device 70, and use oxygen contained in the secondary air supplied from the secondary air supply device 80. Therefore, since it is oxidized in the oxidation catalyst device 70, it is hardly released into the atmosphere.

  When the exhaust gas temperature T is lower than the set temperature T ′, the hydrocarbon storage device 40 sets the switching valve 31 to the first position in step 105 in order to store the hydrocarbons in the exhaust gas satisfactorily. Thus, exhaust gas richer than the stoichiometric air-fuel ratio is allowed to pass through the hydrocarbon storage device 40, and a part of the hydrocarbons in the exhaust gas is stored in the hydrocarbon storage device 40. On the other hand, if the exhaust gas temperature T is equal to or higher than the set temperature T ′, when the exhaust gas is allowed to pass through the hydrocarbon storage device 40, the stored hydrocarbon is released. By setting 31 to the second position, the exhaust gas passes through the bypass passage 32. Thus, when the combustion air-fuel ratio of the internal combustion engine is richer than the stoichiometric air-fuel ratio, if the exhaust gas temperature T is lower than the set temperature T ′, the hydrocarbon storage device 40 stores hydrocarbons.

Next, at step 107, it is determined by the second NO _X sensor 92 whether NO _X is contained in the exhaust gas flowing out from the oxidation catalyst device 70. Initially, the exhaust gas flowing out from the oxidation catalyst device 70 contains almost no NO _x , and the determination at step 107 is denied and the routine proceeds to step 109.

In step 109, it is determined whether or not NO _x is contained in the exhaust gas flowing out from the second NO _x reduction catalyst device 60 by the first NO _x sensor 91. Initially, the exhaust gas flowing out from the second NO _x reduction catalyst device 60 contains almost no NO _x , the determination at step 109 is denied, and the routine returns directly to step 101.

  Although details will be described later, if the determination in step 109 is affirmed, it is determined in step 110 whether or not the exhaust gas temperature T is equal to or higher than the set temperature T ′. In 111, the switching valve 31 is set to the second position, and in step 114, the flag F is reset to zero.

  On the other hand, when the determination in step 110 is affirmative, the switching valve 31 is set to the first position in step 112, and then, in step 113, whether or not the air-fuel ratio of the exhaust gas flowing out from the hydrocarbon storage device 40 is lean. When this determination is affirmed, the flag F is reset to 0 in step 114.

As described above, when the combustion air-fuel ratio of the internal combustion engine continues to be richer than the stoichiometric air-fuel ratio, ammonia generated in the first NO _x reduction catalyst device 50 continues to be stored in the second NO _x reduction catalyst device 60, finally, ammonia storage amount of the second NO _X reduction catalyst device 60 reaches the upper limit value, so that the ammonia from the second NO _X reduction catalyst device 60 flows out. The ammonia flowing out in this way flows into the oxidation catalyst device 70 and is oxidized in the oxidation catalyst device 70 using oxygen contained in the secondary air supplied from the secondary air supply device 80 to generate NO _x ( 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O).

Thereby, in order for the second NO _X sensor 92 to detect NO _X , the determination in step 107 is affirmed, and the flag F is set to 1 in step 108. In this case, still combustion air-fuel ratio to be richer than the stoichiometric air-fuel ratio, the exhaust gas flowing out from the second NO _X reduction catalyst device 60 NO _X is not included almost step 109 Judgment is never affirmed.

When the flag F is set to 1, the determination in step 101 is affirmed. In step 115, the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio (for example, air-fuel ratio 15), and in step 116, the secondary air supply device. The supply of secondary air from 70 is stopped (in order to simplify the control, the supply of secondary air may always be performed). Thus, the combustion air-fuel ratio of the internal combustion engine is lean of the stoichiometric air-fuel ratio, to the air-fuel ratio of the exhaust gas flowing into the first NO _X reduction catalyst device 50 becomes leaner than the stoichiometric air-fuel ratio, a first NO _X in the reduction catalytic device 50, the reducing action becomes inactive, it is impossible to satisfactorily reduce NO _X in the exhaust gas, the exhaust gas containing NO _X flows into the second NO _X reduction catalyst device 60 .

In the second NO _X reduction catalyst device 60, the air-fuel ratio of the exhaust gas is a lean, NO _X in the exhaust gas is satisfactorily reduced ammonia occluded in the second NO _X reducing catalyst device 60 as a reducing agent (6NO + 4NH ₃ → 5N ₂ + 6H ₂ O). Thus, almost no NO _x is released into the atmosphere. At this time, ammonia does not flow out from the second NO _x reduction catalyst device 60 as it is, and the determination in step 107 is denied, but the flag F remains 1. Further, since NO _X in the exhaust gas is reduced in the second NO _X reduction catalyst device 60, the determination in step 109 is also denied.

Thus, the combustion air-fuel ratio of the internal combustion engine continues to be lean of the stoichiometric air-fuel ratio, ammonia occluded in the second NO _X reduction catalyst device 60 continues to be used for the reduction of NO _X, finally, the second NO _X reduction The ammonia storage amount of the catalyst device 60 becomes zero or very small, and NO _x in the exhaust gas cannot be reduced.

As a result, even if the second NO _X sensor 92 detects NO _X in the exhaust gas flowing out from the oxidation catalyst device 60 and sets the flag F to 1 in step 107, the first NO _X sensor 91 does not change the second NO _X reduction catalyst. In order to detect NO _x in the exhaust gas flowing out from the device 60, the determination in step 109 is affirmed and the flag F is reset to 0 in step 114.

  Here, when the determination in step 109 is affirmed, if the exhaust gas temperature T is lower than the set temperature T ′, the determination in step 110 is denied, and in step 111, the switching valve 31 is set to the second position. Since the flag F is reset to 0 in step 114 so that the exhaust gas passes through the bypass passage 32, the determination in step 101 is negative, and in step 102, the combustion air-fuel ratio of the internal combustion engine is calculated again. The air / fuel ratio is made slightly richer (for example, air / fuel ratio 14). Next, in step 103, the secondary air is supplied from the secondary air supply device 80 to the upstream side of the oxidation catalyst device 70.

However, if the determination in step 109 is affirmative and the exhaust gas temperature T is equal to or higher than the set temperature T ′, the determination in step 110 is affirmed, and in step 112, the switching valve 31 is set to the first position and the exhaust gas. Pass through the hydrocarbon storage device 40. Thus, while the combustion air-fuel ratio of the internal combustion engine is richer than the stoichiometric air-fuel ratio, the hydrocarbons stored in the hydrocarbon storage device 40 when the exhaust gas temperature T is lower than the set temperature T ′ are converted into the high-temperature exhaust gas. Even if the combustion air-fuel ratio of the internal combustion engine is not made richer than the stoichiometric air-fuel ratio, the exhaust gas air-fuel ratio can be made richer than the stoichiometric air-fuel ratio, and the downstream side first NO _x reduction catalyst device At 50, NO _x in the exhaust gas can be reduced satisfactorily. In this way, the period during which the combustion air-fuel ratio of the internal combustion engine is richer than the stoichiometric air-fuel ratio can be shortened.

93 is a second air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas flowing out from the hydrocarbon storage device 40. The flag F is not reset to 0 until the output of the second air-fuel ratio sensor 93 becomes lean. It is like that. Also by the release of hydrocarbons from the hydrocarbon-absorbing device 40, if a leaner than the air-fuel ratio is the stoichiometric air-fuel ratio of the exhaust gas, to satisfactorily reduce NO _X in the exhaust gas in the first NO _X reduction catalyst device 50 In this case, the determination at step 113 is affirmed, and the flag F is reset to 0 at step 114. As a result, the determination in step 101 is denied, and in step 102, the combustion air-fuel ratio of the internal combustion engine is made slightly richer than the stoichiometric air-fuel ratio (for example, air-fuel ratio 14). Next, in step 103, the secondary air is supplied from the secondary air supply device 80 to the upstream side of the oxidation catalyst device 70.

In this way, the combustion air-fuel ratio of the internal combustion engine is made rich and lean alternately, but as described above, almost no NO _x can be released into the atmosphere, and the combustion air-fuel ratio in the internal combustion engine is always reduced. Deterioration of fuel consumption can be improved as compared with the case where the air-fuel ratio is made richer than the theoretical air-fuel ratio. Further, by using a hydrocarbon storage device 40, when still being lean in immediately before the rich combustion air-fuel ratio of the internal combustion engine from lean to the stoichiometric air-fuel ratio, flows into the first NO _X reduction catalyst device 50 The air-fuel ratio of the exhaust gas to be made can be made richer than the stoichiometric air-fuel ratio, and the deterioration of fuel consumption can be further improved by shortening the period during which the combustion air-fuel ratio of the internal combustion engine is rich.

10 internal combustion engine 30 exhaust passage 31 switching valve 32 bypass passage 34 first air-fuel ratio sensor 40 hydrocarbon storage device 50 first NO _X reduction catalyst device 60 second NO _X reduction catalyst device 70 oxidation catalyst device 80 a secondary air supply device 91 First NO _X sensor 92 Second NO _X sensor 93 Second air-fuel ratio sensor

Claims (2)

Second NO _X reduction catalyst having a first NO _X reduction catalyst device carrying the placed base metal catalyst in the exhaust passage, the first NO _X reducing ammonia storage capacity which is disposed downstream of the catalytic converter of the exhaust passage An apparatus, a hydrocarbon storage device disposed upstream of the first NO _X reduction catalyst device, and a bypass passage that bypasses the hydrocarbon storage device, and flows into the first NO _X reduction catalyst device When the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, the first NO _x reduction catalyst device reduces the NO _x in the exhaust gas to generate ammonia, and the generated ammonia is converted into the second NO _When the air-fuel ratio of the exhaust gas stored in the _X reduction catalyst device and flowing into the first NO _X reduction catalyst device is lean, the second NO _X reduction catalyst device reduces the NO _X in the exhaust gas. In an exhaust gas purification apparatus for an internal combustion engine that uses the ammonia stored in the NO _x reduction catalyst device to reduce, the carbonization stored in the hydrocarbon storage device when the combustion air-fuel ratio of the internal combustion engine is made rich. Whether the exhaust gas passes through the bypass passage or the hydrocarbon storage device so that hydrogen is released immediately before the combustion air-fuel ratio of the internal combustion engine is made rich from the lean, the combustion air-fuel ratio of the internal combustion engine, and two between but is controlled, and the oxidation catalyst device disposed downstream of the second NO _X reduction catalyst device of the exhaust passage, and the second NO _X reduction catalyst device of the exhaust passage and the oxidation catalyst device a secondary air supply device for supplying the following air, a first NO _X sensor disposed between the second NO _X reduction catalyst device of the exhaust passage and the oxidation catalyst device, the oxidation of the exhaust passage ; And a second NO _X sensor arranged downstream of the catalytic converter, by supplying secondary air by the secondary air supply system as well as the combustion air-fuel ratio of an internal combustion engine in the rich, the second NO _X when the NO _X is detected by the sensor, an exhaust purifying apparatus for an internal combustion engine, characterized in that to the lean combustion air-fuel ratio of the internal combustion engine until the NO _X is detected by at least a first NO _X sensor.   When the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, if the exhaust gas temperature is lower than the set temperature, the exhaust gas passes through the hydrocarbon storage device, and the exhaust gas temperature is equal to or higher than the set temperature. If so, the exhaust gas passes through the bypass passage, and when the combustion air-fuel ratio of the internal combustion engine is leaner than the stoichiometric air-fuel ratio, the exhaust gas passes through the bypass passage, and the combustion air-fuel ratio of the internal combustion engine From the lean to the rich, if the exhaust gas temperature is lower than the set temperature, the exhaust gas passes through the bypass passage so that the combustion air-fuel ratio of the internal combustion engine is rich, and the exhaust gas temperature is the set temperature. If so, the exhaust gas passes through the hydrocarbon storage device, and the air-fuel ratio of the exhaust gas flowing out of the hydrocarbon storage device is equal to the stoichiometric air-fuel ratio. Whether the exhaust gas passes through the bypass passage or the hydrocarbon occlusion device and the combustion air-fuel ratio of the internal combustion engine are controlled so that the combustion air-fuel ratio of the internal combustion engine becomes rich when lean. The exhaust emission control device for an internal combustion engine according to claim 1.

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