JP2013122179A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve deterioration in fuel consumption for NOreduction in exhaust gas, in an exhaust emission control device for an internal combustion engine provided with a NOreduction catalyst device carrying a base metal catalyst and having low NOreduction performance.SOLUTION: An exhaust emission control device for an internal combustion engine includes: a first NOreduction catalyst device 40 carrying a base metal catalyst disposed at an exhaust passage 30; a second NOreduction catalyst device 50 disposed at the exhaust passage at a downstream side of the first NOreduction catalyst device and having ammonia storage capability; and a first NOsensor 80 disposed at the exhaust passage at a downstream side of the second NOreduction catalyst device. After a combustion air-fuel ratio of the internal combustion engine is made richer than a theoretical air-fuel ratio, the combustion air-fuel ratio of the internal combustion engine is made leaner than the theoretical air-fuel ratio. When the combustion air-fuel ratio of the internal combustion engine is made leaner than the theoretical air-fuel ratio, if NOis detected by the first NOsensor, the combustion air-fuel ratio of the internal combustion engine is made richer than the theoretical air-fuel ratio.

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, this way the three-way catalytic converter, or use a base metal catalyst instead of the noble metal catalyst, or, when a portion of a noble metal catalyst or replace the base metal catalyst, reduction performance of the NO _X is reduced as NO _X reducing catalyst device for the, the combustion air-fuel ratio in the slightly richer than the 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 A second NO _x reduction catalyst device having ammonia storage capacity arranged on the downstream side, and a first NO _x sensor arranged on the exhaust passage downstream of the second NO _x reduction catalyst device; When the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio after the combustion air-fuel ratio of the engine is made richer than the stoichiometric air-fuel ratio, and when the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio, the first when the NO _X is detected by the NO _X sensor is characterized in that the richer than the stoichiometric air-fuel ratio combustion air-fuel ratio of the internal combustion engine.

An exhaust purification system of an internal combustion engine according to claim 2 of the present invention, in the exhaust purification system of an internal combustion engine according to claim 1, an oxidation catalyst disposed downstream of the first NO _X sensor of the exhaust passage A secondary air supply device for supplying secondary air between the second NO _x reduction catalyst device and the oxidation catalyst device in the exhaust passage, and a downstream side of the oxidation catalyst device in the exhaust passage ; and a second NO _X sensors, when the combustion air-fuel ratio of at least the internal combustion engine is made rich than the stoichiometric air-fuel ratio, said secondary air supply device supplies the secondary air, the second NO _X sensor by the time the NO _X is detected, characterized in that the lean of the stoichiometric air-fuel ratio of the combustion air-fuel ratio of an internal combustion engine.

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 comprising a second NO _X reduction catalyst device having arranged ammonia storage capacity downstream, and a first NO _X sensor arranged downstream of the second NO _X reduction catalyst device in the exhaust passage, the internal combustion engine by combustion air-fuel ratio is made rich than the stoichiometric air-fuel ratio, by NO _X reducing ability is low first NO _X reduction catalyst device includes a NO _X in the exhaust gas in the exhaust gas of a rich air-fuel ratio HC And CO can be used to reduce well.

Ammonia is produced by reduction of the NO _X in the first NO _X reduction catalyst device, thus ammonia produced, the second NO _X reduction having a first NO _X reducing ammonia storage capacity which is disposed downstream of the catalytic converter Occluded in the catalyst device. Accordingly, even if the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio after the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, NO _X in the exhaust gas is reduced in the second NO _X reduction catalyst device. Reduced well using occluded ammonia. In this way, compared with the case where the combustion air-fuel ratio of the internal combustion engine is always made richer than the stoichiometric air-fuel ratio, it is possible to improve the deterioration of fuel consumption due to the reduction of NO _{x in} the exhaust gas.

In case it is leaner than the stoichiometric air-fuel ratio combustion air-fuel ratio of the internal combustion engine, if it is impossible to sufficiently reduce the NO _X in the exhaust gas by ammonia which is stored in the second NO _X reduction catalyst device, an exhaust passage The first NO _x sensor disposed downstream of the second NO _x reduction catalyst device detects NO _x , and at this time, the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, was of the NO _X to be reduced by the first NO _X reduction catalyst device, the ammonia generated in this case occludes the second NO _X reduction catalyst device, then leaner than the combustion air-fuel ratio is the stoichiometric air-fuel ratio of an internal combustion engine In preparation for the reduction of NO _x by the second NO _x reduction catalyst device.

Further, according to the exhaust purification system of an internal combustion engine according to claim 2 according to the present invention, in the exhaust purification system of an internal combustion engine according to claim 1, arranged downstream of the first NO _X sensor of the exhaust passage the oxidation catalyst device, which is disposed downstream of the oxidation catalyst device for a secondary air supply device and an exhaust passage for supplying secondary air between the second NO _X reduction catalyst device in the exhaust passage and the oxidation catalyst device comprising a two NO _X sensor, when the combustion air-fuel ratio of at least the internal combustion engine is made rich than the stoichiometric air-fuel ratio, the secondary air supply apparatus is arranged to supply secondary air, whereby the internal combustion engine When the combustion air-fuel ratio is made richer than the stoichiometric air-fuel ratio, HC and CO that pass through the first and second NO _x reduction catalyst devices are used, and oxygen in the secondary air is used in the downstream oxidation catalyst device. Can be oxidized.

In addition, when the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, the ammonia storage capacity is saturated in the second NO _X reduction catalyst device that stores ammonia generated in the first NO _X reduction catalyst device. then, the ammonia flows out from the second NO _X reduction catalyst device is oxidized using a second NO _X reduction of oxygen flows into the arranged oxidation catalyst device on the downstream side secondary air in the catalytic converter, NO _X is generated. 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. It is supposed to be.

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 first NO _x reduction catalyst 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 first NO _x reduction catalyst device 40 is not an expensive noble metal catalyst such as platinum Pt such as a general three-way catalyst device, but a copper Cu, iron Fe, silver Ag, or gold on a substrate having a honeycomb structure. A base metal catalyst such as Au is supported on alumina or ceria as a carrier. Further, the first NO _x reduction catalyst device 40 may be one in which the amount of expensive noble metal catalyst used is reduced by replacing a part of the noble metal catalyst of a general three-way catalyst device with a base metal catalyst.

Further, a second NO _X reduction catalyst device 50 is disposed downstream of the first NO _X reduction catalyst device 40 in the exhaust passage 30. The second NO _X reduction catalyst device 50, on the substrate of the honeycomb structure, for example, or zirconia ZrO ₂ was super acid treatment, copper Cu, or iron Fe is obtained by carrying zeolite ZSM5 or SAPO as the carrier, ammonia storage function have. Thereby, the second NO _x reduction catalyst device 50 can reduce NO _x using ammonia stored as a reducing agent even when the air-fuel ratio of the exhaust gas is lean. Further, an oxidation catalyst device 60 that supports a base metal catalyst (or a noble metal catalyst) is disposed downstream of the second NO _x reduction catalyst device 50 in the exhaust passage 30.

A secondary air supply device 70 for supplying secondary air is disposed between the second NO _x reduction catalyst device 50 and the oxidation catalyst device 60 in the exhaust passage 30. A first NO _x sensor 80 is disposed between the second NO _x reduction catalyst device 50 and the oxidation catalyst device 60 in the exhaust passage 30, and the first NO _x sensor 80 is disposed downstream of the oxidation catalyst device 60 in the exhaust passage 30. two NO _X sensor 90 is arranged. The first NO _x sensor 80 and the second NO _x sensor 90 can detect the NO _x concentration in the exhaust gas. An air-fuel ratio sensor 100 that detects the air-fuel ratio of the exhaust gas is disposed upstream of the first NO _x reduction catalyst device 40 in the exhaust passage 30 in order to control the combustion air-fuel ratio of the internal combustion engine.

The first NO _X reduction catalyst device 40 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 It cannot be purified, and the combustion air-fuel ratio must be slightly richer than the stoichiometric air-fuel ratio (for example, air-fuel ratio 14) to increase the concentration of the reducing substance in the exhaust gas so that NO _x can be sufficiently reduced. 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. Next, in step 103, secondary air is supplied from the secondary air supply device 70 to the upstream side of the oxidation catalyst device 60.

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 smaller than when the combustion air-fuel ratio of the internal combustion engine is leaner than the stoichiometric air-fuel ratio, and the internal combustion engine NO _X in the exhaust gas discharged from, even in a low reduction performance first NO _X reduction catalyst device 40 is well reduced 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 50.

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 40. The first NO _x reduction catalyst device 40 flows out without being used for NO _x reduction and without being oxidized. The HC and CO flowing out in this way pass through the second NO _x reduction catalyst device 50 and flow into the oxidation catalyst device 60, and use oxygen contained in the secondary air supplied from the secondary air supply device 70. Therefore, since it is oxidized in the oxidation catalyst device 60, it is hardly released into the atmosphere.

Next, at step 104, it is determined by the second NO _X sensor 90 whether NO _X is contained in the exhaust gas flowing out from the oxidation catalyst device 60. Initially, the exhaust gas flowing out from the oxidation catalyst device 60 contains almost no NO _x , and the determination at step 104 is denied and the routine proceeds to step 106.

In step 106, it is determined whether or not NO _x is contained in the exhaust gas flowing out from the second NO _x reduction catalyst device 50 by the first NO _x sensor 80. Initially, the exhaust gas flowing out from the second NO _x reduction catalyst device 50 contains almost no NO _x , the determination at step 106 is negative, and the routine returns directly to step 101.

Thus, if the combustion air-fuel ratio of the internal combustion engine continues to be richer than the stoichiometric air-fuel ratio, ammonia produced in the first NO _x reduction catalyst device 40 continues to be occluded in the second NO _x reduction catalyst device 50, and finally the first It reached a two NO _X reduction upper limit ammonia storage amount of the catalyst device 50, so that the ammonia from the second NO _X reduction catalyst device 50 flows out. At this time, even if the combustion air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the second NO _x reduction catalyst device 50 can satisfactorily reduce NO _{x in} the exhaust gas. The ammonia flowing out of the second NO _x reduction catalyst device 50 flows into the oxidation catalyst device 60 and is oxidized in the oxidation catalyst device 60 using oxygen contained in the secondary air supplied from the secondary air supply device 70. To produce NO _x (4NH ₃ + 5O ₂ → 4NO + 6H ₂ O).

Thereby, in order for the second NO _X sensor 90 to detect NO _X , the determination in step 104 is affirmed, and the flag F is set to 1 in step 105. At this time, since the combustion air-fuel ratio is still richer than the stoichiometric air-fuel ratio, the exhaust gas flowing out from the second NO _x reduction catalyst device 50 contains almost no NO _x , and in step 106 Judgment is never affirmed.

When the flag F is set to 1, the determination in step 101 is affirmed, and in step 108, 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 109, 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, the first NO _X reduction catalyst device 40 is not able to satisfactorily reduce NO _X in the exhaust gas, exhaust gas containing the NO _X The gas flows into the second NO _x reduction catalyst device 50.

In the second NO _X reduction catalyst device 50, although the air-fuel ratio of the exhaust gas is lean, NO _X is satisfactorily reduced ammonia that is occluded in the second NO _X reducing catalyst device 50 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 50 as it is, and the determination in step 104 is negative, but the flag F remains at 1. Further, since NO _x in the exhaust gas is reduced by the second NO _x reduction catalyst device 50, the determination in step 106 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 50 continues to be used for the reduction of NO _X, finally, the second NO _X reduction The ammonia storage amount of the catalyst device 50 becomes zero or very small, and NO _x in the exhaust gas cannot be sufficiently reduced.

As a result, even if the second NO _X sensor 90 detects NO _X in the exhaust gas flowing out from the oxidation catalyst device 60 and sets the flag F to 1 in Step 105, the first NO _X sensor 80 does not stop the second NO _X reduction catalyst. In order to detect NO _x in the exhaust gas flowing out from the apparatus 50, the determination in step 106 is affirmed, and the flag F is reset to 0 in step 107.

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, secondary air is supplied from the secondary air supply device 70 to the upstream side of the oxidation catalyst device 60. 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 is always reduced in the internal combustion engine. Compared with the case where the stoichiometric air-fuel ratio is made richer, it is possible to improve the deterioration of fuel consumption due to the reduction of NO _{x in} the exhaust gas.

Further, when, for example, a zeolite-based material is used for the second NO _x reduction catalyst device 50, not only the ammonia storage capacity but also the hydrocarbon HC storage capacity can be provided. Thereby, when the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, the second NO _x reduction catalyst device 50 not only produces the first NO _x reduction catalyst device 40 but also the first NO _x reduction catalyst device 40. HC flowing out from the NO _x reduction catalyst device 40 can also be occluded. As a result, when the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio, NO _X in the exhaust gas can be reduced by the stored HC in addition to the stored ammonia, and the combustion air-fuel ratio of the internal combustion engine can be reduced. The fuel consumption can be further improved by lengthening the period during which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio.

10 internal combustion engine 30 exhaust passage 40 first NO _X reduction catalyst device 50 second NO _X reduction catalyst device 60 oxidation catalyst device 70 a secondary air supply device 80 first NO _X sensor 90 second NO _X 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 internal combustion engine after the combustion air-fuel ratio of the internal combustion engine is made richer than the stoichiometric air-fuel ratio, and a first NO _x sensor disposed downstream of the second NO _x reduction catalyst device in the exhaust passage combustion air-fuel ratio is lean than the stoichiometric air-fuel ratio, combustion air-fuel ratio of the internal combustion engine when the NO _X is detected by the first NO _X sensor when the combustion air-fuel ratio of the internal combustion engine is lean than the stoichiometric air-fuel ratio of An exhaust purification device for an internal combustion engine, characterized in that the air-fuel ratio is made richer than the stoichiometric air-fuel ratio. Two said supplying an oxidation catalyst device disposed downstream of the first NO _X sensor in the exhaust passage, the secondary air between the second NO _X reduction catalyst device of the exhaust passage and the oxidation catalyst device A secondary NO _x sensor disposed downstream of the oxidation catalyst device in the exhaust passage, and at least when the combustion air-fuel ratio of the internal combustion engine is richer than the stoichiometric air-fuel ratio, The secondary air supply device supplies secondary air, and when NO _x is detected by the second NO _x sensor, the combustion air-fuel ratio of the internal combustion engine is made leaner than the stoichiometric air-fuel ratio. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.

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