JP6817864B2 - Exhaust gas purification device - Google Patents

Description

The present invention relates to an exhaust gas purifying device that purifies the exhaust gas exhausted from the engine.

In order to improve fuel efficiency, engines capable of lean combustion have been developed in which fuel is burned at a leaner air-fuel ratio than the theoretical air-fuel ratio (stoichi). When lean combustion is performed, nitrogen oxides (NOx) are more likely to be generated as compared with the case where combustion is performed at the stoichiometric air-fuel ratio. Therefore, a NOx storage reduction catalyst (LNT: Lean NOx Trap) is provided in the exhaust passage of the engine capable of executing the lean combustion to remove NOx from the exhaust gas (for example, Patent Document 1).

The NOx storage reduction catalyst removes NOx from the exhaust gas by storing NOx during lean combustion. Then, by performing rich combustion (rich spike) in which the fuel is burned at an air-fuel ratio richer than that of stoichiometric at a predetermined timing, NOx stored in the NOx occlusion reduction catalyst is desorbed and NOx is produced in the NOx occlusion reduction catalyst. Reduce.

Japanese Patent Application Laid-Open No. 4-265415

In the engine capable of performing the lean combustion, the development of a technique capable of further improving the fuel efficiency while reducing the NOx emission amount is desired.

An object of the present invention is to provide an exhaust gas purification device capable of further improving fuel efficiency while reducing NOx emissions.

In order to solve the above problems, the exhaust gas purification device of the present invention comprises a ternary catalyst provided in the upstream exhaust gas passage through which the exhaust gas exhausted from the engine passes, and the ternary catalyst in the upstream exhaust gas passage. A plurality of NOx storage reduction catalysts provided in each of the plurality of downstream exhaust passages branched from the downstream side of the engine and different distances from the engine, and the temperatures of the NOx storage reduction catalysts. And, based on the air-fuel ratio of the engine , the switching unit is provided with a switching unit for switching the flow of the exhaust gas to the downstream exhaust gas path of any one of the plurality of downstream exhaust gas paths, and the switching unit is empty. When the fuel ratio is lean and the temperature of the first NOx storage reduction catalyst is within the storage temperature range, the exhaust gas passes through the downstream exhaust passage provided with the first NOx storage reduction catalyst. In the case where the air-fuel ratio is lean, the temperature of the first NOx storage reduction catalyst exceeds the upper limit of the storage temperature range, and the distance from the engine is larger than that of the first NOx storage reduction catalyst. If the temperature of the distant second said NOx storage reduction catalyst is within the storage temperature range, Ru passed through the exhaust gas to the downstream exhaust passage, wherein the second NOx storage reduction catalyst is provided.

Further, when the air-fuel ratio is lean and the temperature of the second NOx storage reduction catalyst exceeds the upper limit of the storage temperature range, the switching unit is provided with the first NOx storage reduction catalyst. Exhaust gas may be passed through the downstream exhaust passage provided and the downstream exhaust passage provided with the second NOx storage reduction catalyst .

Further, a cooling unit for cooling the NOx storage reduction catalyst may be provided.

Further, the downstream exhaust passage is provided with a bypass path that is branched from the upstream side of the NOx storage reduction catalyst and reconnected to the downstream side of the NOx storage reduction catalyst, and the switching unit allows the flow of the exhaust gas to flow. You may switch to any one of the plurality of downstream exhaust passages and the bypass passage.

According to the present invention, it is possible to further improve fuel efficiency while reducing NOx emissions.

It is the schematic which shows the structure of the engine system of 1st Embodiment. It is a figure explaining the relationship between the temperature of a NOx occlusion reduction catalyst, and the occlusion and reduction of NOx. It is a figure explaining the setting of the air-fuel ratio by the air-fuel ratio control unit, and the switching condition by a switching control unit. It is a flowchart explaining the flow of the air-fuel ratio setting process and the switching process of 1st Embodiment. It is the schematic which shows the structure of the engine system of 2nd Embodiment.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, other specific numerical values, and the like shown in the embodiment are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to omit duplicate description, and elements not directly related to the present invention are not shown. To do.

(First Embodiment)
FIG. 1 is a schematic view showing the configuration of the engine system 100 of the first embodiment. In FIG. 1, the signal flow is indicated by a broken line arrow. As shown in FIG. 1, the engine system 100 is provided with an ECU (Engine Control Unit) 110 which is a microcomputer including a central processing unit (CPU), a ROM in which programs and the like are stored, and a RAM as a work area. , The entire engine 120 is controlled by the ECU 110. However, in the following, the configurations and processes related to the present embodiment will be described in detail, and the configurations and processes unrelated to the present embodiment will be omitted. Further, here, the gasoline engine will be described as an example of the engine 120.

An exhaust manifold is communicated with the exhaust port of the engine 120, and an upstream exhaust passage 130 is communicated with the gathering portion of the exhaust manifold.

The engine system 100 is provided with an exhaust gas purifying device 200 that purifies the exhaust gas exhausted from the engine 120. Hereinafter, the specific configuration of the exhaust gas purification device 200 will be described in detail.

(Exhaust gas purification device 200)
The exhaust gas purification device 200 includes a three-way catalyst (TWC: Three-Way Catalyst) 210, downstream exhaust passages 220A and 220B, a NOx storage reduction catalyst (LNT: Lean NOx Trap) 230A and 230B, and a switching unit 240. , A cooling unit 250 and the like. The ECU 110 also functions as an air-fuel ratio control unit 310 and a switching control unit 320 that constitute the exhaust gas purification device 200.

A three-way catalyst 210 is provided in the upstream exhaust passage 130. The three-way catalyst 210 is composed of, for example, a carrier carrying platinum (Pt), palladium (Pd), and rhodium (Rh), and is exhaust gas discharged from the engine 120 when the engine 120 is performing stoichiometric combustion. Purifies (oxidizes and reduces) hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the gas.

The downstream end of the upstream exhaust passage 130 is branched into a downstream exhaust passage 220A and a downstream exhaust passage 220B.

A NOx storage reduction catalyst 230A is provided in the downstream exhaust passage 220A. A NOx storage reduction catalyst 230B is provided in the downstream exhaust passage 220B. The NOx storage reduction catalyst 230A is arranged at a position closer to the engine 120 than the NOx storage reduction catalyst 230B. That is, the exhaust gas flow path formed between the engine 120 and the NOx storage reduction catalyst 230A is shorter than the exhaust gas flow path formed between the engine 120 and the NOx storage reduction catalyst 230B. Therefore, when the exhaust gas having the same temperature is exhausted from the engine 120, the temperature of the NOx storage reduction catalyst 230B is lower than that of the NOx storage reduction catalyst 230A.

The NOx occlusion reduction catalysts 230A and 230B are composed of carriers carrying, for example, platinum (Pt), palladium (Pd), rhodium (Rh), barium (Ba), and potassium (K), and the engine 120 performs lean combustion. If so, store NOx once. Further, the NOx storage reduction catalysts 230A and 230B purify (reduce) the stored NOx when the engine 120 is performing rich combustion. Further, the NOx storage reduction catalysts 230A and 230B also function as a three-way catalyst when the engine 120 is performing stoichiometric combustion, and in addition to reducing NOx, purify (oxidize) HC and CO.

FIG. 2 is a diagram for explaining the relationship between the temperatures of the NOx storage reduction catalysts 230A and 230B and the storage and reduction of NOx. As shown in FIG. 2, the NOx storage reduction catalysts 230A and 230B occlude NOx if the air-fuel ratio is lean in a predetermined temperature range. The temperature range in which the NOx storage reduction catalysts 230A and 230B can store NOx is referred to as a storage temperature range. Therefore, if the NOx storage reduction catalysts 230A and 230B exceed the upper limit value Kmax of the storage temperature range, it becomes difficult to store NOx.

On the other hand, the NOx storage reduction catalysts 230A and 230B purify NOx if the temperature is at least a predetermined minimum temperature Rmin and the air-fuel ratio is rich even if the upper limit value Kmax of the storage temperature range is exceeded. Further, if the NOx storage reduction catalysts 230A and 230B have a predetermined minimum temperature Rmin or more and the air-fuel ratio is stoichiometric, they also function as a three-way catalyst and purify HC and CO in addition to NOx. Here, the minimum temperature Rmin exceeds the lower limit value Kmin of the storage temperature range and is less than the upper limit value Kmax of the storage temperature range. The NOx storage reduction catalysts 230A and 230B can reduce NOx and oxidatively reduce HC, CO, and NOx as long as the minimum temperature is Rmin or higher. However, the NOx storage reduction catalysts 230A and 230B are deteriorated by heat when the upper limit value Kmax of the storage temperature range is exceeded and the predetermined maximum temperature Rmax is exceeded. Therefore, in the present embodiment, the ECU 110 controls the NOx storage reduction catalysts 230A and 230B so that the maximum temperature is Rmax or less. Hereinafter, the range of the minimum temperature Rmin or more and the maximum temperature Rmax or less is referred to as a deterioration suppression range.

Returning to FIG. 1, the switching unit 240 includes a valve provided at a branching point between the downstream exhaust passage 220A and the downstream exhaust passage 220B. The switching unit 240 switches the flow of the exhaust gas that has passed through the upstream exhaust passage 130 to the downstream exhaust passage 220A or the downstream exhaust passage 220B in accordance with the control by the switching control unit 320 described later.

The cooling unit 250 cools the NOx storage reduction catalysts 230A and 230B according to the control by the switching control unit 320. The cooling unit 250 includes a pump 252, a refrigerant supply pipe 254, 256, and a refrigerant switching unit 258. The pump 252 supplies the refrigerant (for example, water or outside air) to the refrigerant supply pipes 254 and 256. One end of the refrigerant supply pipe 254 was connected to the pump 252, and the other end was connected to the upstream side (between the switching unit 240 and the NOx storage reduction catalyst 230A) of the NOx storage reduction catalyst 230A in the downstream exhaust passage 220A. It is a pipe. The refrigerant supply pipe 256 is a pipe branched from the refrigerant supply pipe 254 and connected to the upstream side (between the switching unit 240 and the NOx storage reduction catalyst 230B) of the NOx storage reduction catalyst 230B in the downstream exhaust passage 220B. The refrigerant switching unit 258 is composed of a valve provided at a branching point between the refrigerant supply pipe 254 and the refrigerant supply pipe 256. The refrigerant switching unit 258 switches the supply destination of the refrigerant supplied by the pump 252 to the refrigerant supply pipe 254 or the refrigerant supply pipe 256.

The air-fuel ratio control unit 310 controls the air-fuel ratio of the engine 120 by adjusting the amount of fuel injected into the engine 120. The air-fuel ratio control unit 310 controls the air-fuel ratio according to the engine load (engine speed). The air-fuel ratio control unit 310 sets the air-fuel ratio to one of stoichiometric, lean, and rich. It should be noted that the air-fuel ratio control unit 310 is set to be rich for a short period of time in order to reduce the NOx stored in the NOx storage reduction catalyst 230A or the NOx storage reduction catalyst 230B regardless of the engine load. When set to, it is distinguished from the case where it is set rich according to the engine load.

The switching control unit 320 controls the switching unit 240, the pump 252, and the refrigerant switching unit 258 based on the temperatures of the NOx storage reduction catalysts 230A and 230B and the air-fuel ratio set by the air-fuel ratio control unit 310.

FIG. 3 is a diagram for explaining the setting of the air-fuel ratio by the air-fuel ratio control unit 310 and the switching conditions by the switching control unit 320. As shown in FIG. 3, the air-fuel ratio control unit 310 sets the air-fuel ratio to lean when the engine load is less than the first threshold value. The switching control unit 320 first acquires the temperature of the NOx storage reduction catalyst 230A when it is set to lean. The exhaust gas purification device 200 is provided with a temperature sensor (not shown) for measuring the temperature of the NOx storage reduction catalyst 230A and the NOx storage reduction catalyst 230B, and the switching control unit 320 measures the temperature sensor. Get the value.

Then, if the temperature of the NOx storage reduction catalyst 230A is within the storage temperature range, the switching control unit 320 controls the switching unit 240 to guide the flow of the exhaust gas to the downstream exhaust passage 220A. On the other hand, when the temperature of the NOx storage reduction catalyst 230A exceeds the upper limit value Kmax of the storage temperature range, the switching control unit 320 acquires the temperature of the NOx storage reduction catalyst 230B. Then, if the temperature of the NOx storage reduction catalyst 230B is within the storage temperature range, the switching control unit 320 controls the switching unit 240 to guide the flow of the exhaust gas to the downstream exhaust passage 220B.

As described above, when the exhaust gas having a low temperature such that the temperature of the NOx storage reduction catalyst 230A is within the storage temperature range is exhausted, that is, when the engine load is relatively low below the first threshold value, the exhaust gas Let the downstream exhaust passage 220A be the flow path.

On the other hand, as described above, since the NOx storage reduction catalyst 230B is farther from the engine 120 than the NOx storage reduction catalyst 230A, the temperature of the exhaust gas that reaches is relatively low. Therefore, when the high temperature exhaust gas in which the temperature of the NOx storage reduction catalyst 230A exceeds the upper limit value Kmax of the storage temperature range is exhausted, that is, when the engine load is relatively high below the first threshold value. However, the temperature of the NOx storage reduction catalyst 230B may be maintained within the storage temperature range. In this case, the switching control unit 320 can store NOx in the NOx storage reduction catalyst 230B while executing lean combustion by setting the flow path of the exhaust gas to the downstream side exhaust path 220B.

Therefore, the range of engine load capable of performing lean combustion can be expanded as compared with the conventional exhaust gas purification device provided with only the NOx storage reduction catalyst 230A. This makes it possible to improve fuel efficiency. Further, since it is possible to avoid a situation in which a high temperature exhaust gas in which the temperature of the NOx storage reduction catalyst 230A exceeds the upper limit value Kmax of the storage temperature range flows into the NOx storage reduction catalyst 230A, the NOx storage reduction catalyst 230A can be avoided. It is possible to suppress the deterioration of.

Further, when the engine load becomes higher and the temperature of the NOx storage reduction catalyst 230B exceeds the upper limit value Kmax of the storage temperature range, the switching control unit 320 controls the switching unit 240 to control the flow of the exhaust gas to the downstream side. The exhaust passage 220A and the downstream exhaust passage 220B are alternately guided. When the temperature of the NOx storage reduction catalyst 230A reaches the upper limit value Kmax of the storage temperature range, the switching control unit 320 switches the flow of the exhaust gas to the downstream exhaust passage 220B, and the temperature of the NOx storage reduction catalyst 230B is within the storage temperature range. When the upper limit value Kmax is reached, the flow of the exhaust gas is switched to the downstream exhaust passage 220A.

Further, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage where the exhaust gas does not flow. The switching control unit 320 supplies an amount of refrigerant that cools the temperatures of the NOx storage reduction catalysts 230A and 230B to within the storage temperature range (upper limit value Kmax or less). As a result, by pre-cooling the unused NOx storage reduction catalysts 230A and 230B, the temperature of the NOx storage reduction catalysts 230A and 230B will exceed the upper limit value Kmax of the storage temperature range the next time they are used. The situation can be avoided. Therefore, it is possible to suppress the deterioration of the NOx storage reduction catalysts 230A and 230B while storing NOx in the NOx storage reduction catalysts 230A and 230B.

In the air-fuel ratio control unit 310, the engine load is less than the first threshold value, and the temperatures of the NOx storage reduction catalysts 230A and 230B are within the deterioration suppression range (specifically, the minimum temperature Rmin or more of the deterioration suppression range is within the storage temperature range. If the upper limit value is Kmax or less), the rich spike is set at predetermined intervals. This makes it possible to reduce (purify) NOx stored in the NOx storage reduction catalysts 230A and 230B.

Then, when the engine load becomes too high to be carried by lean combustion and becomes equal to or higher than the first threshold value, the air-fuel ratio control unit 310 sets the air-fuel ratio to stoichiometric value. As a result, the NOx storage reduction catalysts 230A and 230B can purify HC, CO, and NOx contained in the exhaust gas. In this case, it is estimated that the temperatures of the NOx storage reduction catalysts 230A and 230B both exceed the upper limit value Kmax of the storage temperature range. Therefore, the switching control unit 320 controls the switching unit 240 to alternately guide the flow of the exhaust gas to the downstream exhaust passage 220A and the downstream exhaust passage 220B. As a result, deterioration of the NOx storage reduction catalysts 230A and 230B due to the heat of the exhaust gas can be suppressed.

When the temperature of the NOx storage reduction catalyst 230A reaches the maximum temperature Rmax of the deterioration suppression range, the switching control unit 320 switches the flow of the exhaust gas to the downstream exhaust passage 220B, and the temperature of the NOx storage reduction catalyst 230B is within the deterioration suppression range. When the maximum temperature Rmax is reached, the flow of the exhaust gas is switched to the downstream exhaust passage 220A.

Further, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage where the exhaust gas does not flow. The switching control unit 320 supplies an amount of refrigerant that cools the temperatures of the NOx storage reduction catalysts 230A and 230B to within the deterioration suppression range (maximum temperature Rmax or less). As a result, deterioration of the NOx storage reduction catalysts 230A and 230B can be suppressed.

Further, when the engine load becomes equal to or higher than the second threshold value larger than the first threshold value, the air-fuel ratio control unit 310 sets the air-fuel ratio rich. As a result, NOx contained in the exhaust gas can be purified by the NOx storage reduction catalysts 230A and 230B. In this case, it is estimated that the temperatures of the NOx storage reduction catalysts 230A and 230B both exceed the upper limit value Kmax of the storage temperature range. Therefore, the switching control unit 320 controls the switching unit 240 to alternately guide the flow of the exhaust gas to the downstream exhaust passage 220A and the downstream exhaust passage 220B. As a result, deterioration of the NOx storage reduction catalysts 230A and 230B due to the heat of the exhaust gas can be suppressed.

When the temperature of the NOx storage reduction catalyst 230A reaches the maximum temperature Rmax of the deterioration suppression range, the switching control unit 320 switches the flow of the exhaust gas to the downstream exhaust passage 220B, and the temperature of the NOx storage reduction catalyst 230B is within the deterioration suppression range. When the maximum temperature Rmax is reached, the flow of the exhaust gas is switched to the downstream exhaust passage 220A.

Further, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage where the exhaust gas does not flow. The switching control unit 320 supplies an amount of refrigerant that cools the temperatures of the NOx storage reduction catalysts 230A and 230B to within the deterioration suppression range (maximum temperature Rmax or less). As a result, deterioration of the NOx storage reduction catalysts 230A and 230B can be suppressed.

(Air-fuel ratio setting process and switching process)
Subsequently, the air-fuel ratio setting process by the air-fuel ratio control unit 310 and the switching process by the switching control unit 320 will be described. FIG. 4 is a flowchart illustrating the flow of the air-fuel ratio setting process and the switching process of the first embodiment. The air-fuel ratio setting process and the switching process are executed as interrupt processes at predetermined time intervals.

(Step S110)
The air-fuel ratio control unit 310 determines whether or not the engine load is less than the first threshold value. As a result, if it is determined that the engine load is less than the first threshold value, the process is transferred to step S112, and if it is determined that the engine load is not less than the first threshold value, the process is transferred to step S120.

(Step S112)
The air-fuel ratio control unit 310 adjusts the amount of fuel injected into the engine 120 and sets the air-fuel ratio of the engine 120 to lean.

(Step S114)
The switching control unit 320 determines whether or not the temperature of the NOx storage reduction catalyst 230A is less than the upper limit value Kmax of the storage temperature range. As a result, when it is determined that the temperature of the NOx storage reduction catalyst 230A is less than the upper limit value Kmax of the storage temperature range, the process is moved to step S116, and when it is determined that the temperature is not less than the upper limit value Kmax of the storage temperature range. The process is transferred to step S118.

(Step S116)
The switching control unit 320 controls the switching unit 240 to switch the flow of the exhaust gas to the downstream exhaust passage 220A, and ends the process. Further, if the temperature of the NOx storage reduction catalyst 230B exceeds the upper limit value Kmax of the storage temperature range, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage 220B. To do.

(Step S118)
The switching control unit 320 controls the switching unit 240 to switch the flow of the exhaust gas to the downstream exhaust passage 220B, and ends the process. Further, if the temperature of the NOx storage reduction catalyst 230A exceeds the upper limit value Kmax of the storage temperature range, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage 220A. To do.

(Step S120)
The air-fuel ratio control unit 310 determines whether or not the engine load is less than the second threshold value. As a result, if it is determined that the engine load is less than the second threshold value, the process is transferred to step S122, and if it is determined that the engine load is not less than the second threshold value, the process is transferred to step S124.

(Step S122)
The air-fuel ratio control unit 310 adjusts the amount of fuel injected into the engine 120, sets the air-fuel ratio of the engine 120 to stoichiometric, and shifts the process to step S126.

(Step S124)
The air-fuel ratio control unit 310 adjusts the amount of fuel injected into the engine 120, sets the air-fuel ratio of the engine 120 to be rich, and shifts the process to step S126.

(Step S126)
The switching control unit 320 determines whether or not the temperature of the NOx storage reduction catalyst 230A is less than the maximum temperature Rmax in the deterioration suppression range. As a result, when it is determined that the temperature of the NOx storage reduction catalyst 230A is less than the maximum temperature Rmax in the deterioration suppression range, the process is moved to step S128, and when it is determined that the temperature is not less than the maximum temperature Rmax in the deterioration suppression range, The process is transferred to step S130.

(Step S128)
The switching control unit 320 controls the switching unit 240 to switch the flow of the exhaust gas to the downstream exhaust passage 220A, and ends the process. Further, if the temperature of the NOx storage reduction catalyst 230B exceeds the maximum temperature Rmax in the deterioration suppression range, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage 220B. To do.

(Step S130)
The switching control unit 320 controls the switching unit 240 to switch the flow of the exhaust gas to the downstream exhaust passage 220B, and ends the process. Further, if the temperature of the NOx storage reduction catalyst 230A exceeds the maximum temperature Rmax in the deterioration suppression range, the switching control unit 320 controls the pump 252 and the refrigerant switching unit 258 to supply the refrigerant to the downstream exhaust passage 220A. To do.

As described above, the exhaust gas purification device 200 of the present embodiment expands the range of the engine load capable of performing lean combustion as compared with the conventional exhaust gas purification device provided only with the NOx storage reduction catalyst 230A. be able to. This makes it possible to improve fuel efficiency.

(Second Embodiment)
FIG. 5 is a schematic view showing the configuration of the engine system 400 of the second embodiment. In FIG. 5, the signal flow is indicated by a broken line arrow. Further, the components substantially the same as those of the engine system 100 described above are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 5, the engine system 400 includes an ECU 410, an engine 120, an upstream exhaust passage 130, and an exhaust gas purification device 500. Further, the exhaust gas purification device 500 includes a three-way catalyst 210, downstream exhaust passages 220A and 220B, NOx storage reduction catalysts 230A and 230B, a cooling unit 250, a bypass passage 510, and a switching unit 540. Consists of. The ECU 410 also functions as an air-fuel ratio control unit 310 and a switching control unit 420 that constitute the exhaust gas purification device 500.

The bypass path 510 is a pipe that is branched from a branching point (upstream side of the NOx storage reduction catalyst 230A) of the downstream side exhaust passage 220A and the downstream side exhaust passage 220B and reconnected to the downstream side of the NOx storage reduction catalyst 230A. That is, the bypass path 510 is a pipe that bypasses the NOx storage reduction catalyst 230A.

The switching unit 540 is composed of a valve provided at a branching point between the downstream exhaust passage 220A, the downstream exhaust passage 220B, and the bypass passage 510. In response to the control by the switching control unit 420, the switching unit 540 transfers the flow of the exhaust gas passing through the upstream exhaust path 130 to either the downstream exhaust path 220A, the downstream exhaust path 220B, or the bypass path 510. Switch.

The switching control unit 420 controls the switching unit 540 based on the temperatures of the NOx storage reduction catalysts 230A and 230B and the air-fuel ratio set by the air-fuel ratio control unit 310.

Specifically, when the air-fuel ratio is set to lean, the switching control unit 420 performs the same control as the switching control unit 320 of the first embodiment.

On the other hand, the switching control unit 420 controls the switching unit 540 to control the flow of exhaust gas when the engine load is equal to or higher than the first threshold value and the air-fuel ratio is set to stoichiometric or rich by the air-fuel ratio control unit 310. Is alternately guided to the downstream exhaust passage 220A and the downstream exhaust passage 220B, or alternately to the downstream exhaust passage 220B and the bypass passage 510.

The switching control unit 420 alternately guides the downstream exhaust passage 220A and the downstream exhaust passage 220B based on the performance of the three-way catalyst 210 and the temperature of the exhaust gas, or connects with the downstream exhaust passage 220B. It is determined whether or not the bypass path 510 is alternately guided.

When the switching control unit 420 alternately guides the downstream exhaust passage 220A and the downstream exhaust passage 220B, when the temperature of the NOx storage reduction catalyst 230A reaches the maximum temperature Rmax in the deterioration suppression range, the exhaust gas flow is downstream. The exhaust gas flow is switched to the downstream exhaust gas 220A when the temperature of the NOx storage reduction catalyst 230B reaches the maximum temperature Rmax in the deterioration suppression range.

When the switching control unit 420 alternately guides the downstream exhaust path 220B and the bypass path 510, when the temperature of the NOx storage reduction catalyst 230B reaches the maximum temperature Rmax in the deterioration suppression range, the exhaust gas flow is transferred to the bypass path 510. When the temperature of the NOx storage reduction catalyst 230B is cooled to within the deterioration suppression range, the flow of the exhaust gas is switched to the downstream exhaust passage 220B.

By providing the bypass path 510, the exhaust gas purification device 500 of the second embodiment can further suppress deterioration of the NOx storage reduction catalysts 230A and 230B.

Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. Will be done.

In the first embodiment, the configuration in which the ECU 110 functions as the air-fuel ratio control unit 310 and the switching control unit 320 has been described as an example. Further, in the second embodiment, the configuration in which the ECU 410 functions as the air-fuel ratio control unit 310 and the switching control unit 420 has been described as an example. However, the air-fuel ratio control unit 310 and the switching control unit 320 may be configured separately from the ECU 110. Further, the air-fuel ratio control unit 310 and the switching control unit 420 may be configured separately from the ECU 410.

Further, in the first embodiment, the configuration in which the engine system 100 includes a NOx storage reduction catalyst 230A and a temperature sensor for measuring the temperature of the NOx storage reduction catalyst 230B has been described as an example. However, a temperature sensor that measures the temperature of the NOx storage reduction catalyst 230A and the NOx storage reduction catalyst 230B is not essential. When the NOx storage reduction catalyst 230A and the temperature sensor for measuring the temperature of the NOx storage reduction catalyst 230B are not provided, the engine load, the temperature of the NOx storage reduction catalyst 230A, and the temperature of the NOx storage reduction catalyst 230B are associated with each other. The map may be stored in advance, and the switching control unit 320 may acquire the temperature by referring to the map. Further, when a temperature sensor for measuring the temperature of the exhaust gas passing through the collecting portion of the exhaust manifold is provided, the temperature of the exhaust gas, the temperature of the NOx storage reduction catalyst 230A, and the temperature of the NOx storage reduction catalyst 230B are measured. The associated map may be stored in advance, and the switching control unit 320 may acquire the temperature by referring to the map.

Further, in the above embodiment, the configuration in which the three-way catalyst 210 is provided in the upstream exhaust passage 130 has been described as an example. However, instead of the three-way catalyst 210, a NOx storage reduction catalyst may be provided in the upstream exhaust passage 130.

Further, the air-fuel ratio control unit 310 may set the air-fuel ratio to stoichiometric when the engine load is less than the first threshold value at the time of cold start or the like. In this case, the switching control units 320 and 420 may switch the flow of the exhaust gas to any of the downstream exhaust passage 220A, the downstream exhaust passage 220B, and the bypass passage 510.

Further, in the above embodiment, the exhaust gas purification devices 200 and 500 provided with two downstream exhaust passages have been described as an example. However, the number of downstream exhaust passages may be plural, and the number of downstream exhaust passages may be, for example, three or more. Further, the NOx storage reduction catalyst may be provided in each of the plurality of downstream exhaust passages, and the distances from the engine 120 may be different from each other.

The present invention can be used for an exhaust gas purifying device that purifies the exhaust gas exhausted from the engine.

200, 500 Exhaust gas purification device 210 Three-way catalyst 220A, 220B Downstream exhaust passage 230A, 230B NOx storage reduction catalyst 240, 540 Switching unit 510 Bypass path

Claims (4)

A three-way catalyst provided in the upstream exhaust path through which the exhaust gas exhausted from the engine passes,
A plurality of downstream exhaust passages branched from the downstream of the three-way catalyst in the upstream exhaust passage,
A plurality of NOx storage reduction catalysts provided in each of the plurality of downstream exhaust passages and having different distances from the engine,
A switching unit that switches the flow of the exhaust gas to the downstream exhaust passage of any one of the plurality of downstream exhaust passages based on the temperature of the NOx storage reduction catalyst and the air-fuel ratio of the engine .
Equipped with a,
The switching unit is
When the air-fuel ratio is lean and the temperature of the first NOx storage reduction catalyst is within the storage temperature range, the exhaust gas is exhaust gas in the downstream exhaust passage provided with the first NOx storage reduction catalyst. Let it pass,
When the air-fuel ratio is lean, the temperature of the first NOx storage reduction catalyst exceeds the upper limit of the storage temperature range, and the distance from the engine is farther than that of the first NOx storage reduction catalyst. If the temperature of the NOx storage-reduction catalyst 2 is within the storage temperature range, the second NOx storage reduction catalyst the exhaust gas purifying apparatus Ru passed through the exhaust gas to the downstream exhaust passage provided. The switching unit is provided with the first NOx storage reduction catalyst when the air-fuel ratio is lean and the temperature of the second NOx storage reduction catalyst exceeds the upper limit of the storage temperature range. the downstream exhaust passage, and an exhaust gas purifying apparatus according to claim 1, wherein the second NOx storage reduction catalyst is Ru passes the exhaust gas to the downstream exhaust passage provided. The exhaust gas purification device according to claim 1 or 2, further comprising a cooling unit for cooling the NOx storage reduction catalyst. A bypass path is provided which is branched from the upstream side of the NOx storage reduction catalyst in the downstream exhaust passage and reconnected to the downstream side of the NOx storage reduction catalyst.
The exhaust gas purification device according to any one of claims 1 to 3, wherein the switching unit switches the flow of the exhaust gas to any one of the plurality of downstream exhaust passages and the bypass passage.

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