Exhaust emission control device

Abstract

To suppress phosphorus poisoning of a reduction catalyst while purifying exhaust gas.SOLUTION: An exhaust emission control device according to one embodiment includes: a first reduction catalyst; a second reduction catalyst provided in an exhaust passage downstream of the first reduction catalyst; a bypass passage branched from the exhaust passage on the upstream side of the first reduction catalyst and merged with the exhaust passage between the first reduction catalyst and the second reduction catalyst; a bypass valve for switching a path of exhaust gas between a first path passing through the first reduction catalyst and a second path passing through the bypass passage; and a control device. The control device controls the bypass valve so that exhaust gas passes through the first path when a temperature of the second reduction catalyst is higher than a second reference temperature that is higher than a first reference temperature and an NOx concentration is higher than a reference NOx concentration, and controls the bypass valve so that exhaust gas passes through the second path when a temperature of the second reduction catalyst is higher than the second reference temperature and the NOx concentration is lower than the reference NOx concentration.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an exhaust purification device. [Background technology]

[0002] There is known an exhaust purification device that purifies exhaust gas discharged from an internal combustion engine. For example, Patent Document 1 describes an exhaust aftertreatment system including a first SCR catalyst, an oxidation catalyst provided downstream of the first SCR catalyst, a particulate filter provided downstream of the oxidation catalyst, a second SCR catalyst provided downstream of the particulate filter, a first injector that supplies gaseous ammonia to the first SCR catalyst, and a second injector that supplies urea to the second SCR catalyst. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2015-507118 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, exhaust gas contains phosphorus compounds derived from engine oil, etc. The phosphorus compounds contained in exhaust gas adhere to catalysts and inhibit the activity of the catalyst. This phenomenon is called phosphorus poisoning. In the above-mentioned exhaust purification device, the first SCR catalyst is constantly exposed to exhaust gas, so the first SCR catalyst is easily affected by phosphorus poisoning and loses activity.

[0005] Therefore, an object of the present disclosure is to suppress phosphorus poisoning of a reduction catalyst while purifying exhaust gas. [Means for solving the problem]

[0006] An exhaust purification device according to one embodiment includes: a first reduction catalyst provided in an exhaust passage of an internal combustion engine and reducing nitrogen oxides (NOx) contained in exhaust gas from the internal combustion engine; a second reduction catalyst provided in the exhaust passage downstream of the first reduction catalyst and reducing NOx contained in the exhaust gas; a first reducing agent addition device that adds a reducing agent to the exhaust gas upstream of the first reduction catalyst; a second reducing agent addition device that adds a reducing agent to the exhaust gas at a position between the first reduction catalyst and the second reduction catalyst; a bypass passage that branches off from the exhaust passage upstream of the first reduction catalyst and joins the exhaust passage between the first reduction catalyst and the second reduction catalyst; a bypass valve that switches the path of the exhaust gas between a first path that passes through the first reduction catalyst and a second path that passes through the bypass passage; a temperature sensor that measures a temperature of the second reduction catalyst; a NOx sensor that measures a NOx concentration in the exhaust gas downstream of the second reduction catalyst; and a control device. The control device controls the bypass valve to cause the exhaust gas to pass through the first path when the temperature of the second reduction catalyst is lower than a first reference temperature, or when the temperature of the second reduction catalyst is higher than a second reference temperature that is higher than the first reference temperature and the NOx concentration is higher than a reference NOx concentration, and controls the bypass valve to cause the exhaust gas to pass through the second path when the temperature of the second reduction catalyst is higher than the second reference temperature and the NOx concentration is lower than the reference NOx concentration.

[0007] In this embodiment, when the temperature of the second reduction catalyst is higher than the second reference temperature and the NOx concentration is higher than the reference NOx concentration, the exhaust gas is supplied to the first reduction catalyst, so that the exhaust gas is effectively purified. On the other hand, when the temperature of the second reduction catalyst is higher than the second reference temperature and the NOx concentration is lower than the reference NOx concentration, the exhaust gas is supplied to the second reduction catalyst, bypassing the first reduction catalyst, so that the phosphorus poisoning of the reduction catalyst can be suppressed while purifying the exhaust gas.

[0008] In one embodiment, the control device may control the bypass valve so that the exhaust gas passes through the first path when the temperature of the second reduction catalyst is equal to or higher than the first reference temperature and equal to or lower than the second reference temperature, the NOx concentration is lower than the reference NOx concentration, and the temperature of the second reduction catalyst is on a downward trend, and control the bypass valve so that the exhaust gas passes through the second path when the temperature of the second reduction catalyst is equal to or higher than the first reference temperature and equal to or lower than the second reference temperature, the NOx concentration is lower than the reference NOx concentration, and the temperature of the second reduction catalyst is on an upward trend. When the temperature of the second reduction catalyst 14 is on a downward trend, it is predicted that the activity of the second reduction catalyst will decrease in the future and the NOx removal ability will decrease. Therefore, when the temperature of the second reduction catalyst is on a downward trend, the control device supplies the exhaust gas to the first reduction catalyst to improve the NOx removal ability. On the other hand, when the temperature of the second reduction catalyst is on an upward trend, it is predicted that the second reduction catalyst will be activated in the future and the NOx removal ability will improve. Therefore, when the temperature of the second reduction catalyst is on the rise, the control device supplies exhaust gas to the second reduction catalyst, bypassing the first reduction catalyst, thereby suppressing phosphorus poisoning of the first reduction catalyst.

[0009] In one embodiment, the exhaust passage and the bypass passage may form a double pipe structure, and the bypass passage may be provided so as to surround the outside of the first reduction catalyst. By making the bypass passage a double pipe structure that surrounds the outside of the first reduction catalyst, the exhaust gas can flow while bypassing the first reduction catalyst. Effect of the Invention

[0010] According to various aspects of the present invention, it is possible to suppress phosphorus poisoning of the reduction catalyst while purifying exhaust gas. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of an exhaust gas purification device according to an embodiment. [Diagram 2] FIG. 4 is a diagram showing a route of exhaust gas determined based on the temperature and NOx concentration of a second reduction catalyst. [Diagram 3] 3 is a flowchart showing the operation of the exhaust purification device. [Figure 4] FIG. 4 is a schematic configuration diagram of an exhaust gas purification device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Various embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations of the same or corresponding parts will be omitted. In the following description, the terms "upstream" and "downstream" are based on the flow direction of exhaust gas.

[0013] 1 is a schematic configuration diagram of an exhaust purification device according to one embodiment. The exhaust purification device 10 is mounted on a vehicle having an engine (internal combustion engine) 1, and purifies exhaust gas G discharged from the engine 1. The vehicle is, for example, a large vehicle such as a truck, a bus, or a trailer.

[0014] The engine 1 is, for example, a diesel engine. The engine 1 includes a plurality of cylinders 50a. An intake manifold 52 that supplies air to the cylinders 50a and an exhaust manifold 53 that discharges exhaust gas G from the cylinders 50a are connected to the cylinders 50a.

[0015] An intake passage 54 is connected to the intake manifold 52. A compressor 55 and an intercooler 56 are provided in this order from the upstream side of the intake air in the intake passage 54. An introduction pipe 57 into which the intake air flows is connected to the compressor 55. An air cleaner 58 is provided in the introduction pipe 57.

[0016] The exhaust passage 2 is connected to the exhaust manifold 53 via a turbine 59. The turbine 59 is connected to the compressor 55 via a connecting shaft. The turbine 59 is rotated by the flow of exhaust gas G discharged from the exhaust manifold 53 of the engine 1. The compressor 55 rotates with the rotation of the turbine 59, takes in air (intake air) from an intake pipe 57, and sends the compressed air to the intake passage 54. That is, the compressor 55 and the turbine 59 constitute a turbocharger. The air introduced into the intake passage 54 is introduced into the multiple cylinders 50a through the intake manifold 52. The air introduced into the multiple cylinders 50a is compressed in each cylinder 50a.

[0017] Further, a plurality of injectors 64 are provided in proximity to the plurality of cylinders 50a of the engine 1. A fuel supply passage 63 is connected to the plurality of injectors 64. A fuel pump 62 is connected to the fuel supply passage 63. The fuel pump 62 pressure-feeds fuel, such as diesel, stored in a fuel tank 61 through the fuel supply passage 63 to the plurality of injectors 64. The plurality of injectors 64 inject the fuel supplied from the fuel tank 61 into each of the plurality of cylinders 50a.

[0018] Fuel from the injector 64 is injected into the compressed air and combusted in each cylinder 50a, causing a piston disposed in each cylinder 50a to reciprocate within the cylinder 50a. The reciprocating motion of the piston drives the engine 1. Exhaust gas G generated by the operation of the engine 1 is discharged into the exhaust passage 2 via the exhaust manifold 53. An exhaust purification device 10 that purifies the exhaust gas G is provided in the exhaust passage 2.

[0019] 1, the exhaust purification device 10 includes a first reduction catalyst 11, an oxidation catalyst 12, a filter 13, a second reduction catalyst 14, an ammonia reduction device 15, a first reducing agent addition device 16, a second reducing agent addition device 17, a temperature sensor 18, and a NOx sensor 19. The first reduction catalyst 11, the oxidation catalyst 12, the filter 13, the second reduction catalyst 14, and the ammonia reduction device 15 are accommodated in the exhaust passage 2 in this order from the upstream side of the exhaust passage 2 (the engine 1 side).

[0020] The first reduction catalyst 11 reduces nitrogen oxides (NOx) to nitrogen and water using a reducing agent. The first reduction catalyst 11 is a catalyst containing a metal such as copper, iron, or vanadium, and is supported on a ceramic carrier. The activity of the first reduction catalyst 11 depends on the temperature of the exhaust gas G. For example, the first reduction catalyst 11 is activated in a high temperature range of 180°C or higher, and the reduction efficiency of NOx is improved.

[0021] The oxidation catalyst 12 is provided downstream of the first reduction catalyst 11 in the exhaust passage 2. The oxidation catalyst 12 is a precious metal such as platinum or palladium, or a metal oxide, and is supported on a support made of, for example, ceramics. The oxidation catalyst 12 oxidizes and purifies toxic components contained in the exhaust gas G, such as hydrocarbons (HC) and carbon monoxide (CO).

[0022] The filter 13 is provided downstream of the oxidation catalyst 12 in the exhaust passage 2. The filter 13 is, for example, a DPF (Diesel Particulate Filter), and collects particulate matter in the exhaust gas G.

[0023] The second reduction catalyst 14 is provided downstream of the filter 13 in the exhaust passage 2, and reduces nitrogen oxides (NOx) to nitrogen and water using a reducing agent. The second reduction catalyst 14 is a catalyst containing a metal such as copper, iron, or vanadium, and is supported on a ceramic carrier. The activity of the second reduction catalyst 14 depends on the temperature of the exhaust gas G. For example, the second reduction catalyst 14 is activated in a high temperature range of 180°C or more, and the reduction efficiency of NOx is improved.

[0024] The ammonia reduction device 15 is provided downstream of the second reduction catalyst 14 in the exhaust passage 2. The ammonia reduction device 15 oxidizes and renders harmless the excess reducing agent (ammonia) that has passed (slips) through the second reduction catalyst 14 without reacting with NOx.

[0025] The first reducing agent addition device 16 adds a reducing agent to the exhaust gas G in the exhaust passage 2 upstream of the first reduction catalyst 11. The reducing agent includes a precursor of the reducing agent. For example, the first reducing agent addition device 16 injects urea water into the exhaust passage 2 from an injector provided between the engine 1 and the first reduction catalyst 11. The urea water injected into the exhaust passage 2 is decomposed by the heat of the exhaust gas G flowing through the exhaust passage 2, and becomes ammonia. This ammonia reacts with NOx on the first reduction catalyst 11 to reduce the NOx. The amount of urea water supplied from the first reducing agent addition device 16 is controlled by a control device 30 described later.

[0026] Similarly, the second reducing agent addition device 17 supplies a reducing agent into the exhaust passage 2 upstream of the second reduction catalyst 14. For example, the second reducing agent addition device 17 injects urea water into the exhaust passage 2 from an injector provided between the filter 13 and the second reduction catalyst 14. The urea water injected into the exhaust passage 2 is decomposed by the heat of the exhaust gas G flowing through the exhaust passage 2, and becomes ammonia. The ammonia reacts with NOx on the second reduction catalyst 14 to reduce the NOx. The amount of urea water supplied from the second reducing agent addition device 17 is controlled by a control device 30, which will be described later.

[0027] The temperature sensor 18 measures the temperature of the second reduction catalyst 14. The temperature sensor 18 may measure the temperature of a carrier that supports the second reduction catalyst 14 and use the measured value as the temperature of the second reduction catalyst 14, or may measure the temperature of the exhaust gas G flowing through the second reduction catalyst 14 and use the measured value as the temperature of the second reduction catalyst 14. The temperature sensor 18 outputs information indicating the temperature of the second reduction catalyst 14 to the control device 30.

[0028] The NOx sensor 19 measures the NOx concentration of the exhaust gas G downstream of the second reduction catalyst 14. For example, as shown in Fig. 1, the NOx sensor 19 is provided at the outlet of the exhaust passage 2 (downstream of the ammonia reduction device 15). The NOx sensor 19 outputs information indicating the measured NOx concentration of the exhaust gas G to the control device 30.

[0029] The exhaust purification device 10 further includes a bypass passage 21, a bypass valve 22, and a control device 30. The bypass passage 21 has one end connected to the exhaust passage 2 between the engine 1 and the first reduction catalyst 11, and the other end connected to the exhaust passage 2 between the first reduction catalyst 11 and the oxidation catalyst 12. In other words, the bypass passage 21 branches off from the exhaust passage 2 upstream of the first reduction catalyst 11 and merges with the exhaust passage 2 between the first reduction catalyst 11 and the second reduction catalyst 14. The bypass passage 21 provides a route for exhaust gas G to bypass the first reduction catalyst 11.

[0030] The bypass valve 22 is, for example, a three-way valve, and has a first port 22a, a second port 22b, and a third port 22c. The first port 22a of the bypass valve 22 is connected to the engine 1 via the exhaust passage 2. The second port 22b is connected to the first reduction catalyst 11 via the exhaust passage 2. The third port 22c is connected to one end of the bypass passage 21. Note that the bypass valve 22 only needs to have one inlet and two outlets, and may be configured by one or two two-way valves.

[0031] The bypass valve 22 switches the path of the exhaust gas G between a first path L1 passing through the first reduction catalyst 11 and a second path L2 passing through the bypass passage 21. For example, when the first port 22a and the second port 22b of the bypass valve 22 are connected to each other, the exhaust gas G discharged from the engine 1 is sent to the second reduction catalyst 14 through the first reduction catalyst 11, the oxidation catalyst 12, and the filter 13 (the first path L1 in FIG. 1). On the other hand, when the first port 22a of the bypass valve 22 is connected to the third port 22c, the exhaust gas G discharged from the engine 1 bypasses the first reduction catalyst 11 and is sent to the second reduction catalyst 14 through the oxidation catalyst 12 and the filter 13 (the second path L2 in FIG. 1).

[0032] The control device 30 controls the overall operation of the exhaust purification device 10. The control device 30 is an electronic control unit having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a CAN (Controller Area Network) communication circuit, etc. The control device 30 realizes various functions by, for example, loading a program stored in the ROM into the RAM and executing the program loaded into the RAM by the CPU.

[0033] The control device 30 is communicatively connected to the first reducing agent addition device 16, the second reducing agent addition device 17, the temperature sensor 18, the NOx sensor 19, and the bypass valve 22. For example, the control device 30 controls the amount of reducing agent added to the exhaust gas G from the first reducing agent addition device 16 and the second reducing agent addition device 17 based on the output of the engine 1, the temperature of the second reduction catalyst 14, and the like.

[0034] In addition, the control device 30 acquires information indicating the temperature T of the second reduction catalyst 14 measured by the temperature sensor 18 and information indicating the NOx concentration measured by the NOx sensor 19, and controls the operation of the bypass valve 22 based on the temperature T and NOx concentration C of the second reduction catalyst 14. Fig. 2 shows a path of the exhaust gas G determined based on the temperature T and NOx concentration C of the second reduction catalyst 14.

[0035] As shown in FIG. 2, when the temperature T of the second reduction catalyst 14 is lower than the first reference temperature T1, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the first path L1. The first reference temperature T1 is, for example, 180° C. When the temperature of the second reduction catalyst 14 is lower than the first reference temperature T1, the urea water supplied from the second reducing agent addition device 17 is not completely thermally decomposed, and the NOx removal ability of the second reduction catalyst 14 decreases. In contrast, since the first reduction catalyst 11 is disposed upstream of the second reduction catalyst 14 (close to the engine 1), the temperature of the first reduction catalyst 11 is higher than the temperature T of the second reduction catalyst 14, and NOx can be removed. Therefore, when the temperature T of the second reduction catalyst 14 is lower than the first reference temperature T1, the control device 30 causes the exhaust gas G to flow through the first path L1 and removes NOx in the exhaust gas G using the first reduction catalyst 11.

[0036] When the temperature T of the second reduction catalyst 14 is higher than a second reference temperature T2 that is higher than the first reference temperature T1 and the NOx concentration C is higher than a reference NOx concentration Cr, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the first path L1. The second reference temperature is, for example, 200°C.

[0037] When the temperature T of the second reduction catalyst 14 is lower than the second reference temperature T2, the second reduction catalyst 14 is activated, but the NOx concentration C being higher than the reference NOx concentration Cr means that the NOx removal capability of the second reduction catalyst 14 is insufficient. Therefore, when the temperature T of the second reduction catalyst 14 is higher than the second reference temperature T2 and the NOx concentration C is higher than the reference NOx concentration Cr, the control device 30 causes the exhaust gas G to flow through the first path L1 and removes the NOx in the exhaust gas G using both the first reduction catalyst 11 and the second reduction catalyst 14.

[0038] When the temperature T of the second reduction catalyst 14 is higher than a second reference temperature T2 and the NOx concentration C is lower than the reference NOx concentration Cr, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the second path L2.

[0039] Generally, the exhaust gas G contains phosphorus compounds derived from engine oil and the like. The phosphorus compounds may adhere to the first reduction catalyst 11 and inhibit the activity of the first reduction catalyst 11. This phenomenon is called phosphorus poisoning. When the temperature T of the second reduction catalyst 14 is higher than the second reference temperature T2 and the NOx concentration C is lower than the reference NOx concentration Cr, it is determined that the NOx removal ability of the second reduction catalyst 14 is sufficient. In this case, the control device 30 causes the exhaust gas G to flow through the second path L2 that bypasses the first reduction catalyst 11. This blocks the inflow of the exhaust gas G to the first reduction catalyst 11, and the phosphorus poisoning of the first reduction catalyst 11 can be suppressed. On the other hand, the NOx in the exhaust gas G is removed by the second reduction catalyst 14.

[0040] Furthermore, when the temperature of the second reduction catalyst 14 is equal to or higher than the first reference temperature and equal to or lower than the second reference temperature, and the NOx concentration C is higher than the reference NOx concentration Cr, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the first path L1. On the other hand, when the temperature of the second reduction catalyst 14 is equal to or higher than the first reference temperature and equal to or lower than the second reference temperature, and the NOx concentration C is lower than the reference NOx concentration Cr, the control device 30 determines the path of the exhaust gas G according to the trend of the temperature T of the second reduction catalyst 14. Note that the trend of the temperature T of the second reduction catalyst 14 (whether it is increasing or decreasing) is determined based on the history of the measured values ​​of the temperature T of the second reduction catalyst 14 by the temperature sensor 18.

[0041] For example, when the temperature T of the second reduction catalyst 14 is equal to or higher than the first reference temperature T1 and equal to or lower than the second reference temperature T2, the NOx concentration C is lower than the reference NOx concentration Cr, and the temperature T of the second reduction catalyst 14 is on a downward trend, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the first path L1. When the temperature T of the second reduction catalyst 14 is on a downward trend, it is predicted that the activity of the second reduction catalyst 14 will decrease in the future, and the NOx removal ability will decrease. Therefore, when the temperature T of the second reduction catalyst 14 is on a downward trend, the control device 30 supplies the exhaust gas G to the first reduction catalyst 11 to suppress the decrease in the NOx removal ability.

[0042] On the other hand, when the temperature T of the second reduction catalyst is equal to or higher than the first reference temperature T1 and equal to or lower than the second reference temperature T2, the NOx concentration C is lower than the reference NOx concentration Cr, and the temperature T of the second reduction catalyst 14 is on the rise, the control device 30 controls the bypass valve 22 so that the exhaust gas G passes through the second path L2. When the temperature of the second reduction catalyst 14 is on the rise, it is predicted that the second reduction catalyst 14 will be activated in the future and the NOx removal ability will be improved. Therefore, when the temperature T of the second reduction catalyst 14 is on the rise, the exhaust gas G is caused to flow bypassing the first reduction catalyst 11, thereby suppressing phosphorus poisoning of the first reduction catalyst.

[0043] Next, the operation of the exhaust gas purification device 10 according to one embodiment will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the operation of the exhaust gas purification device 10.

[0044] 3, first, the temperature T of the second reduction catalyst 14 is measured by the temperature sensor 18 (step ST1). Next, the control device 30 judges whether or not the temperature T of the second reduction catalyst 14 is lower than a first reference temperature T1 (step ST2). When it is judged that the temperature T of the second reduction catalyst 14 is lower than the first reference temperature T1, the control device 30 determines the path of the exhaust gas G to be the first path L1, and controls the bypass valve 22 so that the exhaust gas G passes through the first reduction catalyst 11 (step ST3).

[0045] On the other hand, when it is determined that the temperature T of the second reduction catalyst 14 is equal to or higher than the first reference temperature T1, the control device 30 determines whether or not the temperature T of the second reduction catalyst 14 is higher than a second reference temperature T2 (step ST4). When it is determined that the temperature T of the second reduction catalyst 14 is higher than the second reference temperature T2, the NOx sensor 19 measures the NOx concentration C of the exhaust gas G downstream of the second reduction catalyst 14 (step ST5).

[0046] Next, the control device 30 judges whether or not the NOx concentration C of the exhaust gas G measured by the NOx sensor 19 is lower than the reference NOx concentration Cr (step ST6). If the NOx concentration C is lower than the reference NOx concentration Cr, that is, if the NOx concentration C complies with the NOx regulation value, the control device 30 determines the route of the exhaust gas G to be the second route L2, and controls the bypass valve 22 so that the exhaust gas G bypasses the first reduction catalyst 11 (step ST7). On the other hand, if the NOx concentration C is higher than the reference NOx concentration Cr, that is, if the NOx concentration C does not complies with the NOx regulation value, the control device 30 determines the route of the exhaust gas G to be the first route L1, and controls the bypass valve 22 so that the exhaust gas G passes through the first reduction catalyst 11 (step ST8).

[0047] When the temperature T of the second reduction catalyst 14 is equal to or higher than the first reference temperature T1 and equal to or lower than the second reference temperature T2, the control device 30 acquires the trend of the temperature T of the second reduction catalyst 14 (step ST9). For example, the control device 30 determines whether the temperature T of the second reduction catalyst 14 is tending to decrease or increase from past changes in the temperature T of the second reduction catalyst 14.

[0048] Next, the control device 30 determines whether or not the temperature T of the second reduction catalyst 14 is tending to decrease (step ST10), and if it is determined that the temperature T of the second reduction catalyst 14 is tending to decrease, it determines the route of the exhaust gas G to be the first route L1, and controls the bypass valve 22 so that the exhaust gas G passes through the first reduction catalyst 11 (step ST11).

[0049] On the other hand, when it is determined that the temperature T of the second reduction catalyst 14 has an increasing tendency, the NOx sensor 19 measures the NOx concentration C of the exhaust gas G downstream of the second reduction catalyst 14 (step ST12). Next, the control device 30 determines whether the NOx concentration C measured by the NOx sensor 19 is lower than the reference NOx concentration Cr (step ST13).

[0050] When the NOx concentration C is lower than the reference NOx concentration Cr, i.e., when the NOx concentration C complies with the NOx regulation value, the control device 30 determines the route of the exhaust gas G to be the second route L2, and controls the bypass valve 22 so that the exhaust gas G bypasses the first reduction catalyst 11 (step ST14). On the other hand, when the NOx concentration C is higher than the reference NOx concentration Cr, i.e., when the NOx concentration C does not complies with the NOx regulation value, the control device 30 determines the route of the exhaust gas G to be the first route L1, and controls the bypass valve 22 so that the exhaust gas G passes through the first reduction catalyst 11 (step ST15).

[0051] As described above, in the exhaust purification device 10 according to one embodiment, when the temperature T of the second reduction catalyst 14 is higher than the second reference temperature T2 and the NOx concentration C is higher than the reference NOx concentration Cr, the exhaust gas G is supplied to the first reduction catalyst 11, and the exhaust gas is effectively purified. On the other hand, when the temperature T of the second reduction catalyst 14 is higher than the second reference temperature T2 and the NOx concentration C is lower than the reference NOx concentration Cr, the exhaust gas G is supplied to the second reduction catalyst 14, bypassing the first reduction catalyst 11, and therefore phosphorus poisoning of the first reduction catalyst 11 can be suppressed while purifying the exhaust gas G.

[0052] Although exhaust gas purification devices according to various embodiments have been described above, the present invention is not limited to the above-described embodiments and various modifications can be made without departing from the spirit and scope of the invention.

[0053] For example, the bypass passage 21 does not have to be an independent pipe, and may be provided so as to surround the exhaust passage 2 outside the first reduction catalyst 11 so that the exhaust passage 2 and the bypass passage 21 form a double pipe structure, as shown in Fig. 4. Even when this configuration is adopted, it is possible to suppress phosphorus poisoning of the first reduction catalyst 11 while purifying the exhaust gas G.

[0054] In addition, the bypass passage 21 may branch off from the exhaust passage 2 upstream of the first reduction catalyst 11 and merge into the exhaust passage 2 between the first reduction catalyst 11 and the second reduction catalyst 14. For example, the bypass passage 21 may merge into the exhaust passage 2 between the oxidation catalyst 12 and the filter 13, or between the filter 13 and the second reduction catalyst 14.

[0055] Furthermore, the exhaust purification device 10 does not necessarily have to include the oxidation catalyst 12 and the filter 13. The various embodiments described above can be arbitrarily combined within a range that does not cause any contradiction. [Explanation of symbols]

[0056] 1...engine (internal combustion engine), 2...exhaust passage, 10...exhaust purification device, 11...first reduction catalyst, 14...second reduction catalyst, 16...first reducing agent addition device, 17...second reducing agent addition device, 18...temperature sensor, 19...NOx sensor, 21...bypass passage, 22...bypass valve, 30...control device, C...NOx concentration, Cr...reference NOx concentration, G...exhaust gas, L1...first path, L2...second path.

Claims

1. a first reduction catalyst provided in an exhaust passage of an internal combustion engine and configured to reduce nitrogen oxides (NOx) contained in exhaust gas from the internal combustion engine; a second reduction catalyst provided in the exhaust passage downstream of the first reduction catalyst and configured to reduce NOx contained in the exhaust gas; a first reducing agent addition device that adds a reducing agent to the exhaust gas upstream of the first reduction catalyst; a second reducing agent addition device that adds a reducing agent to the exhaust gas at a position between the first reduction catalyst and the second reduction catalyst; a bypass passage that branches off from the exhaust passage upstream of the first reduction catalyst and merges with the exhaust passage between the first reduction catalyst and the second reduction catalyst; a bypass valve that switches a path of the exhaust gas between a first path that passes through the first reduction catalyst and a second path that passes through the bypass passage; A temperature sensor for measuring a temperature of the second reduction catalyst; a NOx sensor that measures a NOx concentration of the exhaust gas downstream of the second reduction catalyst; A control device; Equipped with The control device includes: When a temperature of the second reduction catalyst is lower than a first reference temperature, or when the temperature of the second reduction catalyst is higher than a second reference temperature that is higher than the first reference temperature and the NOx concentration is higher than a reference NOx concentration, the bypass valve is controlled so that the exhaust gas passes through the first path; When the temperature of the second reduction catalyst is higher than the second reference temperature and the NOx concentration is lower than the reference NOx concentration, the bypass valve is controlled so that the exhaust gas passes through the second path. Exhaust purification device.

2. The control device includes: When the temperature of the second reduction catalyst is equal to or higher than a first reference temperature and equal to or lower than the second reference temperature, the NOx concentration is lower than the reference NOx concentration, and the temperature of the second reduction catalyst is tending to decrease, the bypass valve is controlled so that the exhaust gas passes through the first path; When the temperature of the second reduction catalyst is equal to or higher than a first reference temperature and equal to or lower than the second reference temperature, the NOx concentration is lower than the reference NOx concentration, and the temperature of the second reduction catalyst is on an upward trend, the bypass valve is controlled so that the exhaust gas passes through the second path. The exhaust gas purification device according to claim 1 .

3. 3. The exhaust purification device according to claim 1, wherein the exhaust passage and the bypass passage form a double pipe structure, and the bypass passage is provided so as to surround the exhaust passage outside the first reduction catalyst.

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