Exhaust purifier

Abstract

To improve fuel economy.SOLUTION: An exhaust emission control device includes: a first exhaust pipe connected to an engine; a first housing connected to a downstream side of the first exhaust pipe and storing a three-way catalyst; a second exhaust pipe connected to a downstream side of the first housing; and a second housing connected to a downstream side of the second exhaust pipe and storing a nitrogen oxide storage catalyst. The three-way catalyst has a first region and a second region having OSC capacity lower than that of the first region, and the first region is arranged on a center axis of a gas flow sent from the first exhaust pipe into the first housing.SELECTED DRAWING: Figure 5

Description

Technical Field

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[0001] The present invention relates to an exhaust gas purification device.

Background Art

[0002] In an exhaust gas purification device that purifies exhaust gas discharged from an engine, various catalysts are used to purify harmful components in the exhaust gas. As such a catalyst, there is a nitrogen oxide storage catalyst that can store nitrogen oxides (hereinafter also referred to as NOx) in the exhaust gas. The NOx storage ability, which is the ability to store NOx in the nitrogen oxide storage catalyst, decreases as the NOx storage amount, which is the amount of NOx stored in the nitrogen oxide storage catalyst, increases. Therefore, for example, as disclosed in Patent Document 1, a process called NOx purge is performed to temporarily make the air-fuel ratio of the exhaust gas rich. By the NOx purge, the NOx stored in the nitrogen oxide storage catalyst is reduced and purified, and the NOx storage ability of the nitrogen oxide storage catalyst is restored.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an exhaust gas flow path communicating with the engine, a three-way catalyst may be provided upstream of the nitrogen oxide storage catalyst. The three-way catalyst has an OSC ability, which is the ability to store oxygen. Therefore, when the NOx purge is performed, when the rich exhaust gas passes through the three-way catalyst, a part of the components for purifying NOx among the components in the exhaust gas reacts with the oxygen stored in the three-way catalyst. As a result, the fuel consumed for purifying NOx increases, and the fuel consumption deteriorates.

[0005] Therefore, the present invention aims to provide an exhaust gas purification device capable of improving fuel efficiency. [Means for solving the problem]

[0006] To solve the above problems, an exhaust gas purification device according to one embodiment of the present invention is The first exhaust pipe connected to the engine, A first housing connected to the downstream side of the first exhaust pipe and housing a three-way catalytic converter, A second exhaust pipe connected to the downstream side of the first housing, A second housing connected to the downstream side of the second exhaust pipe and containing a nitrogen oxide storage catalyst, Equipped with, The three-way catalyst has a first region and a second region having lower OSC activity than the first region. The first region is positioned on the central axis of the gas flow sent from the first exhaust pipe into the first housing. 、 The first housing is, A cylindrical portion housing the three-way catalyst, The first exhaust pipe and the cylindrical section are connected, and the first enlarged diameter section expands in diameter as it progresses from the upstream side to the downstream side, The second exhaust pipe and the cylindrical section are connected, and the second enlarged diameter section expands in diameter as it proceeds from the downstream side to the upstream side, It has, The degree of expansion of the first expanded portion is smaller than the degree of expansion of the second expanded portion. . [Effects of the Invention]

[0007] According to the present invention, it is possible to improve fuel efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the general configuration of the intake and exhaust system of a vehicle according to an embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing an example of the functional configuration of a control device according to an embodiment of the present invention. [Figure 3] Figure 3 is a flowchart showing an example of the processing flow performed by a control device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing how exhaust gas passes through the three-way catalyst during normal operation in the exhaust gas purification device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing how exhaust gas passes through the three-way catalyst during NOx purge in the exhaust gas purification device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of the distribution of the OSC ability in the three-way catalyst according to an embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram showing how exhaust gas passes through the three-way catalyst during normal operation in the exhaust gas purification device according to a modified example. [Figure 8] FIG. 8 is a schematic diagram showing how exhaust gas passes through the three-way catalyst during NOx purge in the exhaust gas purification device according to a modified example.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The specific dimensions, materials, numerical values, etc. shown in such embodiments 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 functions and configurations are denoted by the same reference numerals to omit redundant explanations, and elements not directly related to the present invention are not shown.

[0010] <Overview of the Intake and Exhaust System of the Vehicle> Referring to FIGS. 1 to 3, an overview of the intake and exhaust system 2 of the vehicle 1 according to an embodiment of the present invention will be described. The exhaust gas purification device 3 according to an embodiment of the present invention is provided in the intake and exhaust system 2 of the vehicle 1.

[0011] FIG. 1 is a schematic diagram showing a schematic configuration of the intake and exhaust system 2 of the vehicle 1. As shown in FIG. 1, the intake and exhaust system 2 includes an engine 10, an intake passage 20, and an exhaust passage 30.

[0012] The engine 10 is, for example, a spark ignition internal combustion engine. The engine 10 has one or more cylinders 11. In FIG. 1, only one cylinder 11 out of the plurality of cylinders 11 provided in the engine 10 is shown for ease of understanding. A piston 12 is slidably provided in the cylinder 11. A combustion chamber 13 is formed inside the cylinder 11. The combustion chamber 13 is partitioned by the inner surface of the cylinder 11 and the crown surface of the piston 12. The cylinder 11 is provided with a spark plug 14 facing the combustion chamber 13. Further, the cylinder 11 is provided with a fuel injection valve 15 that injects fuel toward the combustion chamber 13. An air-fuel mixture containing air and fuel is formed in the combustion chamber 13. The air-fuel mixture is ignited by the spark plug 14 and burns. Thereby, the piston 12 in each cylinder 11 performs a linear reciprocating motion, and power is transmitted to the crankshaft connected to each piston 12.

[0013] Note that the fuel injection valve 15 is not limited to a type that directly injects fuel into the combustion chamber 13. For example, the fuel injection valve 15 may be provided in the intake passage 20 and inject fuel into the intake passage 20. In this case, the fuel is inhaled into the combustion chamber 13 together with the intake air.

[0014] Each combustion chamber 13 of the engine 10 communicates with the intake passage 20 via an intake port and communicates with the exhaust passage 30 via an exhaust port. Each cylinder 11 is provided with an intake valve 16 that can open and close the intake port and an exhaust valve 17 that can open and close the exhaust port. By driving the intake valve 16 and the exhaust valve 17, supply of intake air to the combustion chamber 13 and discharge of exhaust gas from the combustion chamber 13 are performed.

[0015] The intake passage 20 is connected to the engine 10 and is a passage through which air supplied to the combustion chamber 13 of the engine 10 flows. An intake port (not shown) is provided at the upstream end of the intake passage 20 for taking in outside air from outside the vehicle 1. An air filter 21 is provided downstream of the intake port in the intake passage 20. The air filter 21 removes foreign matter contained in the air flowing through the intake passage 20. A throttle valve 22 is provided downstream of the air filter 21 in the intake passage 20. The throttle valve 22 adjusts the flow rate of intake air sent to the engine 10 through the intake passage 20. The flow rate of intake air sent to the engine 10 changes according to the opening of the throttle valve 22.

[0016] A surge tank 23 is provided downstream of the throttle valve 22 in the intake passage 20. The surge tank 23 temporarily stores the intake air sent to the engine 10. Downstream of the surge tank 23 in the intake passage 20, an intake manifold (not shown) is provided. The intake manifold branches out toward each cylinder 11 of the engine 10 and connects to the intake port of each cylinder 11.

[0017] In the intake passage 20, outside air is drawn in from the intake port. The drawn-in air passes through the air filter 21, then sequentially through the throttle valve 22 and surge tank 23 before being sent to the engine 10.

[0018] An airflow meter 24 is provided in the intake passage 20. The airflow meter 24 detects the intake air volume, which is the flow rate of air drawn into and circulating through the intake passage 20. The airflow meter 24 is installed, for example, between the air filter 21 and the throttle valve 22.

[0019] The exhaust passage 30 is connected to the engine 10 and is a passage through which exhaust gas discharged from the combustion chamber 13 of the engine 10 flows. An exhaust port (not shown) is provided at the downstream end of the exhaust passage 30, through which the exhaust gas is discharged to the outside of the vehicle 1. An exhaust manifold (not shown) is provided in the exhaust passage 30. The exhaust manifold branches out toward each cylinder 11 of the engine 10 and is connected to the exhaust port of each cylinder 11.

[0020] A three-way catalytic converter 31 is provided downstream of the exhaust manifold in the exhaust passage 30. The three-way catalytic converter 31 oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and reduces NOx in the exhaust gas, thereby purifying these harmful components into harmless water vapor (H2O), carbon dioxide (CO2), and nitrogen (N2). The three-way catalytic converter 31 has an OSC (Oxygen Storage) capacity, which is the ability to store oxygen. The OSC capacity is realized by components such as ceria (CeO2) contained in the three-way catalytic converter 31.

[0021] A nitrogen oxide storage catalyst 32 is provided downstream of the three-way catalyst 31 in the exhaust flow path 30. The nitrogen oxide storage catalyst 32 is a catalyst capable of absorbing NOx from the exhaust gas.

[0022] The exhaust gas emitted from the engine 10 passes sequentially through the three-way catalytic converter 31 and the nitrogen oxide storage catalyst 32 before being released to the outside of the vehicle 1 through the exhaust port. When the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage catalyst 32 is a lean air-fuel ratio, which is a higher air-fuel ratio than the stoichiometric air-fuel ratio, NOx that has passed through the three-way catalytic converter 31 without being purified can be absorbed by the nitrogen oxide storage catalyst 32.

[0023] The exhaust flow path 30 is equipped with an upstream NOx concentration sensor 33 and a downstream NOx concentration sensor 34. The upstream NOx concentration sensor 33 is installed between the three-way catalyst 31 and the nitrogen oxide storage catalyst 32 and detects the concentration of NOx in the exhaust gas flowing into the nitrogen oxide storage catalyst 32. The downstream NOx concentration sensor 34 is installed downstream of the nitrogen oxide storage catalyst 32 in the exhaust flow path 30 and detects the concentration of NOx in the exhaust gas flowing out from the nitrogen oxide storage catalyst 32.

[0024] The exhaust gas purification device 3 includes the three-way catalyst 31, nitrogen oxide storage catalyst 32, upstream NOx concentration sensor 33, and downstream NOx concentration sensor 34 as described above. The exhaust gas purification device 3 also includes a first exhaust pipe 41, a second exhaust pipe 42, a third exhaust pipe 43, a first housing 51, and a second housing 52 as components forming the exhaust gas flow path 30.

[0025] The first exhaust pipe 41 is connected to the engine 10. Specifically, the first exhaust pipe 41 is connected to the exhaust port of the engine 10 via the exhaust manifold. The first housing 51 is connected to the downstream side of the first exhaust pipe 41. In other words, the downstream end of the first exhaust pipe 41 and the upstream end of the first housing 51 are connected to each other. The first housing 51 houses the three-way catalytic converter 31.

[0026] The second exhaust pipe 42 is connected to the downstream side of the first housing 51. In other words, the downstream end of the first housing 51 and the upstream end of the second exhaust pipe 42 are connected to each other. An upstream NOx concentration sensor 33 is provided in the second exhaust pipe 42. The second housing 52 is connected to the downstream side of the second exhaust pipe 42. In other words, the downstream end of the second exhaust pipe 42 and the upstream end of the second housing 52 are connected to each other. The second housing 52 houses the nitrogen oxide storage catalyst 32.

[0027] The third exhaust pipe 43 is connected to the downstream side of the second housing 52. In other words, the downstream end of the second housing 52 and the upstream end of the third exhaust pipe 43 are connected to each other. A downstream NOx concentration sensor 34 is provided in the third exhaust pipe 43. The third exhaust pipe 43 is connected to the exhaust port of the exhaust passage 30.

[0028] The exhaust gas purification device 3 includes a control device 60. The control device 60 has one or more processors 61 and one or more memories 62 connected to the processors 61. The processors 61 include, for example, a CPU (Central Processing Unit). The memories 62 include, for example, ROM (Read Only Memory) and RAM (Random Access Memory). ROM is a memory element that stores programs and arithmetic parameters used by the CPU. RAM is a memory element that temporarily stores data such as variables and parameters used in processing executed by the CPU.

[0029] The control device 60 communicates with each device provided in the intake and exhaust system 2 (for example, the spark plug 14, fuel injector 15, throttle valve 22, airflow meter 24, upstream NOx concentration sensor 33, and downstream NOx concentration sensor 34). Communication between the control device 60 and each device is achieved, for example, using CAN (Controller Area Network) communication.

[0030] Figure 2 is a block diagram showing an example of the functional configuration of the control device 60. For example, as shown in Figure 2, the control device 60 has an acquisition unit 60a and a control unit 60b. Various processes, including those described below, performed by the acquisition unit 60a or the control unit 60b can be executed by the processor 61. In detail, various processes are executed by the processor 61 executing a program stored in the memory 62.

[0031] The acquisition unit 60a acquires various types of information used in the processing performed by the control unit 60b and outputs them to the control unit 60b. For example, the acquisition unit 60a acquires information from the airflow meter 24, the upstream NOx concentration sensor 33, and the downstream NOx concentration sensor 34.

[0032] The control unit 60b controls the operation of each device in the intake and exhaust system 2. Specifically, the control unit 60b controls the operation of the engine 10. For example, the control unit 60b controls the ignition timing of the spark plug 14. Also, for example, the control unit 60b controls the fuel injection timing and fuel injection amount in the fuel injection by the fuel injector 15. Also, for example, the control unit 60b controls the opening degree of the throttle valve 22.

[0033] Here, the control unit 60b can control the air-fuel ratio of the exhaust gas discharged from the engine 10 by controlling the fuel injection amount, etc. Specifically, the control unit 60b can perform NOx purging, which temporarily enriches the air-fuel ratio of the exhaust gas in order to reduce NOx absorbed by the nitrogen oxide storage catalyst 32.

[0034] The functions of the control device 60 according to this embodiment may be divided among multiple devices, or multiple functions may be implemented by a single device. If the functions of the control device 60 are divided among multiple devices, these multiple devices may be connected to each other via a communication bus such as CAN.

[0035] Figure 3 is a flowchart showing an example of the processing flow performed by the control device 60. The control flow shown in Figure 3 is repeated, for example, at a predetermined time interval.

[0036] When the control flow shown in Figure 3 is initiated, first, in step S101, the control unit 60b calculates the NOx storage amount, which is the amount of NOx absorbed by the nitrogen oxide storage catalyst 32.

[0037] In step S101, for example, the control unit 60b calculates the increase in NOx storage per unit time based on the detection results of the airflow meter 24, the upstream NOx concentration sensor 33, and the downstream NOx concentration sensor 34. Specifically, the control unit 60b can calculate the amount of NOx flowing into the nitrogen oxide storage catalyst 32 per unit time based on the intake air volume and the concentration of NOx in the exhaust gas flowing into the nitrogen oxide storage catalyst 32. The control unit 60b can also calculate the amount of NOx flowing out of the nitrogen oxide storage catalyst 32 per unit time based on the intake air volume and the concentration of NOx in the exhaust gas flowing out of the nitrogen oxide storage catalyst 32. The control unit 60b can then calculate the difference between the amount of NOx flowing into the nitrogen oxide storage catalyst 32 per unit time and the amount of NOx flowing out of the nitrogen oxide storage catalyst 32 per unit time as the increase in NOx storage per unit time. The control unit 60b can calculate the amount of NOx absorbed by accumulating the increase in the amount of NOx absorbed per unit time calculated in this way.

[0038] Following step S101, in step S102, the control unit 60b determines whether the NOx storage amount is greater than a threshold. The threshold in step S102 is set to a value that allows for the determination of whether the NOx storage capacity of the nitrogen oxide storage catalyst 32 has decreased to the extent that it is necessary to restore its NOx storage capacity. If the NOx storage amount is greater than the threshold, it corresponds to the case where it is necessary to restore the NOx storage capacity of the nitrogen oxide storage catalyst 32.

[0039] If it is determined that the NOx storage amount is greater than the threshold (YES in step S102), the process proceeds to step S103, where the control unit 60b performs NOx purging, and the control flow shown in Figure 3 ends. On the other hand, if it is not determined that the NOx storage amount is greater than the threshold (NO in step S102), the control flow shown in Figure 3 ends.

[0040] The above describes an example where there is one nitrogen oxide storage catalyst 32. However, there may be two or more nitrogen oxide storage catalysts 32. In this case, multiple nitrogen oxide storage catalysts 32 are arranged in series downstream of the three-way catalyst 31 in the exhaust flow path 30, and the exhaust gas discharged from the three-way catalyst 31 passes through each of the nitrogen oxide storage catalysts 32 in sequence.

[0041] <Details of the exhaust purification system> With reference to Figures 4 to 6, the details of the exhaust gas purification device 3 according to an embodiment of the present invention will be described.

[0042] As described above, in the exhaust gas purification device 3, NOx purging is performed to restore the NOx storage capacity of the nitrogen oxide storage catalyst 32. When NOx purging is performed, as the enriched exhaust gas passes through the three-way catalyst 31, some of the components in the exhaust gas that purify NOx react with the oxygen stored in the three-way catalyst 31. This can lead to an increase in the amount of fuel consumed to purify NOx, potentially worsening fuel efficiency. Therefore, in this embodiment, the three-way catalyst 31 is designed to suppress the increase in fuel used for NOx purging and improve fuel efficiency. The configuration of the three-way catalyst 31 and its surroundings will be described in detail below with reference to Figures 4 to 6.

[0043] Figure 4 is a schematic diagram showing how exhaust gas passes through the three-way catalytic converter 31 in the exhaust gas purification device 3 under normal conditions. In Figure 4 and Figures 5, 7, and 8 described later, the flow of exhaust gas is indicated by arrows. Under normal conditions, NOx purging is not being performed. The exhaust gas flow rate changes according to the air-fuel ratio of the air-fuel mixture in the engine 10. The torque of the engine 10 is basically determined by the amount of fuel supplied to the engine 10. Therefore, if the torque of the engine 10 is constant, the higher the air-fuel ratio, the greater the exhaust gas flow rate. Under normal conditions, the air-fuel ratio is equal to or higher than the stoichiometric air-fuel ratio. On the other hand, during NOx purging, the air-fuel ratio becomes lower than the stoichiometric air-fuel ratio. Therefore, the exhaust gas flow rate under normal conditions (for example, during lean combustion with a high air-fuel ratio) is greater than the exhaust gas flow rate during NOx purging with a low air-fuel ratio.

[0044] As shown in Figure 4, the first housing 51 that houses the three-way catalyst 31 has a cylindrical portion 51a, a first enlarged diameter portion 51b, and a second enlarged diameter portion 51c.

[0045] The cylindrical portion 51a houses the three-way catalyst 31. The three-way catalyst 31 has a cylindrical shape. In the example in Figure 4, the central axis of the three-way catalyst 31 extends in the left-right direction. The cylindrical portion 51a has a cylindrical shape. In the example in Figure 4, the central axis of the cylindrical portion 51a extends in the left-right direction. The inner diameter of the cylindrical portion 51a is larger than the outer diameter of the three-way catalyst 31. The axial length of the cylindrical portion 51a is longer than the axial length of the three-way catalyst 31. The cylindrical portion 51a is arranged coaxially with the three-way catalyst 31. The upstream end of the cylindrical portion 51a (left side in the example in Figure 4) is located upstream of the upstream end of the three-way catalyst 31. The downstream end of the cylindrical portion 51a (right side in the example in Figure 4) is located downstream of the downstream end of the three-way catalyst 31. In other words, the outer circumferential surface of the three-way catalyst 31 faces the inner circumferential surface of the cylindrical portion 51a over its entire surface.

[0046] The first enlarged diameter section 51b connects the first exhaust pipe 41 and the cylindrical section 51a, and its diameter increases as it progresses from the upstream side to the downstream side. In the example shown in Figure 4, the first exhaust pipe 41 is arranged coaxially with the cylindrical section 51a. The first enlarged diameter section 51b has a frustoconical shape.

[0047] The second enlarged diameter section 51c connects the second exhaust pipe 42 and the cylindrical section 51a, and its diameter increases as it progresses from the downstream side to the upstream side. In the example shown in Figure 4, the second exhaust pipe 42 is arranged coaxially with the cylindrical section 51a. The second enlarged diameter section 51c has a frustoconical shape.

[0048] The three-way catalyst 31 has a first region 31a and a second region 31b, each with different OSC (Optical Stem Cell) activity. In Figure 4, the first region 31a is shown by a dashed line. The OSC activity of the second region 31b is lower than that of the first region 31a. Specifically, in the second region 31b, the concentration of components such as ceria required to achieve OSC activity is lower compared to the first region 31a.

[0049] In the example shown in Figure 4, the first region 31a is located coaxially with the central axis of the three-way catalyst 31. The first region 31a is located radially inward of the three-way catalyst 31. The first region 31a has a cylindrical shape. The first region 31a extends from the upstream end to the downstream end of the three-way catalyst 31. The second region 31b is the region of the three-way catalyst 31 excluding the first region 31a. The second region 31b is located radially outward of the three-way catalyst 31. The second region 31b has a cylindrical shape.

[0050] The first region 31a is positioned on the central axis 70 of the gas flow (specifically, the exhaust gas flow) sent from the first exhaust pipe 41 into the first housing 51. The exhaust gas flow sent from the first exhaust pipe 41 into the first housing 51 actually expands radially outward at the outlet of the downstream end of the first exhaust pipe 41. The central axis 70 passes through the center of the distribution of exhaust gas sent from the first exhaust pipe 41 into the first housing 51. In other words, the central axis 70 is the axis indicating the main flow direction of the exhaust gas sent from the first exhaust pipe 41 into the first housing 51. The central axis 70 coincides, for example, with the central axis of the first exhaust pipe 41. Therefore, the first region 31a is positioned on the extension line of the first exhaust pipe 41. The extension line of the first exhaust pipe 41 is a line that extends along the extension direction of the first exhaust pipe 41, and is, for example, the extension line of the central axis of the first exhaust pipe 41.

[0051] As shown by the arrows in Figure 4, under normal conditions where the exhaust gas flow rate is higher than during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 basically flows along the central axis 70 within the first housing 51. Therefore, in the three-way catalyst 31, the exhaust gas basically passes only through the first region 31a and not through the second region 31b. The second exhaust pipe 42 is aligned with the axial direction of the three-way catalyst 31 relative to the first region 31a. Therefore, the exhaust gas that has passed through the first region 31a is smoothly sent to the second exhaust pipe 42.

[0052] Figure 5 is a schematic diagram showing how exhaust gas passes through the three-way catalytic converter 31 during NOx purging in the exhaust gas purification device 3. As described above, the flow rate of exhaust gas during NOx purging is smaller than the flow rate of exhaust gas under normal conditions. Therefore, as indicated by the arrows in Figure 5, during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 expands radially outward within the first diameter-expanding section 51b and proceeds downstream. Thus, in the three-way catalytic converter 31, the exhaust gas passes not only through the first region 31a but also through the second region 31b. Therefore, in the three-way catalytic converter 31, the region through which the exhaust gas flows is distributed between the first region 31a and the second region 31b. After passing through the first region 31a and the second region 31b, the exhaust gas passes through the second diameter-expanding section 51c and is then sent to the second exhaust pipe 42.

[0053] As explained above, in the exhaust gas purification device 3, the three-way catalyst 31 has a first region 31a and a second region 31b having lower OSC capacity than the first region 31a. The first region 31a is positioned on the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51. As a result, under normal conditions, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 can pass through the first region 31a of the three-way catalyst 31, thereby allowing the OSC capacity of the three-way catalyst 31 to be properly exercised. On the other hand, during NOx purging, a portion of the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 can pass through the second region 31b, thereby suppressing the reaction of components in the exhaust gas that purify NOx with oxygen stored in the three-way catalyst 31. Therefore, the increase in fuel used for NOx purging can be suppressed, and fuel efficiency can be improved.

[0054] Here, in the example shown in Figures 4 and 5, in the first housing 51, the degree of expansion of the first enlarged portion 51b is greater than the degree of expansion of the second enlarged portion 51c. small The degree of diameter expansion refers to the degree of expansion of the inner diameter when advanced by a unit length in the axial direction. An example of the degree of diameter expansion is the size of the taper. In the example in Figures 4 and 5, the taper of the first diameter expansion section 51b is greater than the taper of the second diameter expansion section 51c. small This ensures that, during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 is properly expanded radially outward within the first diameter-expanding section 51b and sent to the second region 31b of the three-way catalyst 31.

[0055] Figure 6 shows an example of the distribution of OSC activity in the three-way catalyst 31. Specifically, Figure 6 shows the radial distribution of OSC activity in the three-way catalyst 31. The vertical axis in Figure 6 represents the radial position of the three-way catalyst 31, and the horizontal axis represents the OSC activity. In Figure 6, the horizontal axis coincides with the central axis of the three-way catalyst 31. In the example in Figure 6, the OSC activity of the three-way catalyst 31 is maximum on the central axis of the three-way catalyst 31. The OSC activity of the three-way catalyst 31 gradually decreases as you move radially outward from the central axis of the three-way catalyst 31. The first region 31a corresponds to the region where the OSC activity is higher than the reference OSC activity. On the other hand, the second region 31b corresponds to the region where the OSC activity is below the reference OSC activity.

[0056] In the exhaust gas purification device 3, the central axis of the three-way catalyst 31 coincides with the central axis 70 (see Figures 4 and 5) of the gas flow sent from the first exhaust pipe 41 into the first housing 51. Therefore, in the example of Figure 6, the OSC (Optical Surge Control) capacity of the three-way catalyst 31 is distributed such that it decreases as it moves away from the central axis 70. This appropriately increases the OSC capacity of the first region 31a, which is located on the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51, and decreases the OSC capacity of the second region 31b. Furthermore, the flow rate of the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 is distributed such that it decreases as it moves away from the central axis 70. Therefore, by distributing the OSC capacity of the three-way catalyst 31 in a way that decreases as it moves away from the central axis 70, similar to the distribution of the exhaust gas flow rate within the first housing 51, the OSC capacity of the three-way catalyst 31 can be more appropriately utilized under normal conditions.

[0057] In the above, Figure 6 illustrates an example of the distribution of OSC activity in the three-way catalyst 31. However, the distribution of OSC activity in the three-way catalyst 31 is not limited to the example in Figure 6. For example, the OSC activity in the three-way catalyst 31 may change in a stepwise manner in the radial direction. Also, for example, there may be a region in the three-way catalyst 31 where the OSC activity increases as you move away from the central axis 70. Furthermore, for example, in the first region 31a, the OSC activity may be constant regardless of the radial position. Also, for example, in the second region 31b, the OSC activity may be constant regardless of the radial position.

[0058] <Effects of exhaust gas purification devices> The effects of the exhaust gas purification device 3 according to an embodiment of the present invention will be described below.

[0059] In the exhaust gas purification device 3 according to this embodiment, the three-way catalyst 31 has a first region 31a and a second region 31b having lower OSC capacity than the first region 31a. The first region 31a is positioned on the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51. As a result, under normal conditions, exhaust gas can pass through the first region 31a of the three-way catalyst 31, allowing the OSC capacity of the three-way catalyst 31 to be properly exercised. On the other hand, during NOx purging, a portion of the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 can pass through the second region 31b, thereby suppressing the reaction of components in the exhaust gas that purify NOx with oxygen stored in the three-way catalyst 31. Therefore, the increase in fuel used for NOx purging can be suppressed, and fuel efficiency can be improved.

[0060] Furthermore, in the exhaust gas purification device 3 according to this embodiment, it is preferable that the first region 31a is positioned on the extension of the first exhaust pipe 41. This appropriately ensures that under normal conditions, the exhaust gas passes through the first region 31a of the three-way catalyst 31, and during NOx purging, a portion of the exhaust gas passing through the three-way catalyst 31 passes through the second region 31b. Thus, it is possible to appropriately suppress the increase in fuel used for NOx purging.

[0061] Furthermore, in the exhaust gas purification device 3 according to this embodiment, it is preferable that the OSC capacity of the three-way catalyst 31 is distributed such that it decreases as it moves away from the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51. This appropriately increases the OSC capacity of the first region 31a located on the central axis 70 and decreases the OSC capacity of the second region 31b. Thus, it appropriately suppresses the increase in fuel used for NOx purging. In addition, by distributing the OSC capacity of the three-way catalyst 31 such that it decreases as it moves away from the central axis 70, similar to the distribution of the exhaust gas flow rate within the first housing 51, the OSC capacity of the three-way catalyst 31 can be more appropriately exhibited under normal conditions.

[0062] Furthermore, in the exhaust gas purification device 3 according to this embodiment, the first housing has a cylindrical portion 51a that houses the three-way catalyst 31, a first expanding portion 51b that connects the first exhaust pipe 41 and the cylindrical portion 51a and expands in diameter as it proceeds from the upstream side to the downstream side, and a second expanding portion 51c that connects the second exhaust pipe 42 and the cylindrical portion 51a and expands in diameter as it proceeds from the downstream side to the upstream side, and the degree of expansion of the first expanding portion 51b is greater than the degree of expansion of the second expanding portion 51c. small This is preferable. As a result, during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 is properly expanded radially outward within the first diameter expansion section 51b and sent to the second region 31b of the three-way catalyst 31. Therefore, the increase in fuel used for NOx purging is properly suppressed.

[0063] <Variation> Referring to Figures 7 and 8, a modified exhaust gas purification device 3A will be described. In exhaust gas purification device 3A, the configuration of the three-way catalyst 31 and its surroundings differs from that of the exhaust gas purification device 3 described above. The configuration of the three-way catalyst 31 and its surroundings in exhaust gas purification device 3A will be described below.

[0064] Figure 7 is a schematic diagram showing how exhaust gas passes through the three-way catalyst 31 under normal conditions in the exhaust gas purification device 3A. As shown in Figure 7, the first housing 51 that houses the three-way catalyst 31 has a cylindrical portion 51a, a first enlarged diameter portion 51b, and a second enlarged diameter portion 51c, similar to the exhaust gas purification device 3 described above. The first exhaust pipe 41 and the cylindrical portion 51a are connected via the first enlarged diameter portion 51b. The second exhaust pipe 42 and the cylindrical portion 51a are connected via the second enlarged diameter portion 51c.

[0065] In exhaust gas purification device 3A, unlike exhaust gas purification device 3 described above, the first exhaust pipe 41 is inclined with respect to the central axis of the cylindrical section 51a. The second exhaust pipe 42 is parallel to the cylindrical section 51a, but is not arranged coaxially with the cylindrical section 51a. Specifically, in the example in Figure 7, the central axis of the first exhaust pipe 41 (i.e., the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51) is inclined upward in Figure 7 as it proceeds downstream (hereinafter simply referred to as "upper"). The central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51 passes through the upper part of the three-way catalyst 31. Therefore, as shown in Figure 7, in exhaust gas purification device 3A, the first region 31a is located in the upper part of the three-way catalyst 31. In Figure 7, the first region 31a is shown by a dashed line. On the other hand, the second region 31b is located in the lower part of the three-way catalyst 31.

[0066] As shown by the arrows in Figure 7, under normal conditions where the exhaust gas flow rate is higher than during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 basically flows along the central axis 70 within the first housing 51. Therefore, in the three-way catalyst 31, the exhaust gas basically passes only through the first region 31a and not through the second region 31b. The central axis of the second exhaust pipe 42 is located above the central axis of the cylindrical portion 51a, and the second exhaust pipe 42 is aligned with the axial direction of the three-way catalyst 31 relative to the first region 31a. Therefore, the exhaust gas that has passed through the first region 31a is smoothly sent to the second exhaust pipe 42.

[0067] Figure 8 is a schematic diagram showing how exhaust gas passes through the three-way catalytic converter 31 during NOx purging in the exhaust gas purification device 3A. As indicated by the arrows in Figure 8, during NOx purging, the exhaust gas sent from the first exhaust pipe 41 into the first housing 51 expands radially outward within the first diameter-expanding section 51b and proceeds downstream. Therefore, in the three-way catalytic converter 31, the exhaust gas passes not only through the first region 31a but also through the second region 31b. Thus, in the three-way catalytic converter 31, the region through which the exhaust gas flows is distributed between the first region 31a and the second region 31b. After passing through the first region 31a and the second region 31b, the exhaust gas passes through the second diameter-expanding section 51c and is then sent to the second exhaust pipe 42.

[0068] As explained above, in the exhaust gas purification device 3A, similar to the exhaust gas purification device 3 described above, the three-way catalyst 31 has a first region 31a and a second region 31b having lower OSC capacity than the first region 31a. The first region 31a is positioned on the central axis 70 of the gas flow sent from the first exhaust pipe 41 into the first housing 51. Therefore, similar to the exhaust gas purification device 3 described above, the increase in fuel used for NOx purging can be suppressed, thereby improving fuel efficiency.

[0069] As described above, the relative positions of the first exhaust pipe 41 and the second exhaust pipe 42 with respect to the first housing 51 are not particularly limited. Furthermore, the assumed orientation of the first exhaust pipe 41 and the second exhaust pipe 42 with respect to the first housing 51 is not particularly limited.

[0070] Preferred embodiments of the present invention have been described above with reference to the attached drawings. However, it goes without saying that the present invention is not limited to the embodiments described above, and that various modifications or alterations within the scope of the claims also fall within the technical scope of the present invention.

[0071] For example, the processes described using flowcharts in this specification do not necessarily have to be performed in the order shown in the flowcharts. Additional processing steps may be adopted, and some processing steps may be omitted. [Explanation of Symbols]

[0072] 1 vehicle 2. Intake and Exhaust System 3. Exhaust purifying device 3A Exhaust Purification System 10 Engines 11 cylinders 12 pistons 13 Combustion chamber 14 Spark plugs 15 Fuel Injector 16 Intake valves 17 Exhaust valve 20 Intake passage 21 Air filter 22 Throttle valve 23 Surge Tank 24 Airflow Meter 30 Exhaust passage 31 Three-way catalyst 31a 1st area 31b 2nd area 32 Nitrogen oxide storage catalysts 33 Upstream NOx concentration sensor 34 Downstream NOx concentration sensor 41. First exhaust pipe 42. Second exhaust pipe 43. Third exhaust pipe 51 Housing 1 51a Cylindrical section 51b 1st enlarged diameter section 51c 2nd enlarged diameter section 52 Second Housing 60 Control device 60a Acquisition section 60b Control Unit 61 processors 62 memory 70 center axis

Claims

1. The first exhaust pipe connected to the engine, A first housing connected to the downstream side of the first exhaust pipe and housing a three-way catalytic converter, A second exhaust pipe connected to the downstream side of the first housing, A second housing connected to the downstream side of the second exhaust pipe and housing a nitrogen oxide storage catalyst, Equipped with, The three-way catalyst has a first region and a second region having lower OSC activity than the first region. The first region is positioned on the central axis of the gas flow sent from the first exhaust pipe into the first housing, The first housing is, A cylindrical portion housing the three-way catalyst, The first exhaust pipe and the cylindrical section are connected, and the first enlarged diameter section expands in diameter as it progresses from the upstream side to the downstream side, The second exhaust pipe and the cylindrical section are connected, and the second enlarged diameter section expands in diameter as it proceeds from the downstream side to the upstream side, It has, The degree of expansion of the first expanded portion is smaller than the degree of expansion of the second expanded portion. Exhaust gas purification device.

2. The first region is located on the extension of the first exhaust pipe, The exhaust gas purification device according to claim 1.

3. The OSC activity of the three-way catalyst is distributed such that it decreases as it moves away from the central axis. The exhaust gas purification device according to claim 1 or 2.

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